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Allylic C–H bond activation and functionalization mediated bytris(oxazolinyl)borato rhodium(I) and iridium(I) compounds

Hung-An Ho, Tristan S. Gray, Benjamin Baird, Arkady Ellern and Aaron D. Sadow*

Received 14th February 2011, Accepted 31st March 2011DOI: 10.1039/c1dt10249d

Allylic C–H bond oxidative addition reactions, mediated by tris(oxazolinyl)borato rhodium(I) andiridium(I) species, provide the first step in a hydrocarbon functionalization sequence. The bondactivation products ToMMH(h3-C8H13) (M = Rh (1), Ir (2)), ToMMH(h3-C3H5) (M = Rh (3), Ir (4)), andToMRhH(h3-C3H4Ph) (5) (ToM = tris(4,4-dimethyl-2-oxazolinyl)phenylborate) are synthesized byreaction of Tl[ToM] and the corresponding metal olefin chloride dimers. Characterization of these group9 allyl hydride complexes includes 1H-15N heteronuclear correlation NMR experiments that revealthrough-metal magnetization transfer between metal hydride and the trans-coordinated oxazolinenitrogen. Furthermore, the oxazoline 15N NMR chemical shifts are affected by the trans ligand, withthe resonances for the group trans to hydride typically downfield of those trans to h3-allyl andtosylamide. These group 9 oxazolinylborate compounds have been studied to develop approaches forallylic functionalization. However, this possibility is generally limited by the tendency of the allylhydride compounds to undergo olefin reductive elimination. Reductive elimination products are formedupon addition of ligands such as CO and CNtBu. Also, ToMRhH(h3-C8H13) and acetic acid react to giveToMRhH(k2-O2CMe) (8) and cyclooctene. In contrast, treatment of ToMRhH(h3-C3H5) with TsN3

(Ts = SO2C6H4Me) gives the complex ToMRh(h3-C3H5)NHTs (10). Interestingly, the reaction ofToMRhH(h3-C8H13) and TsN3 yields ToMRh(NHTs)(H)OH2 (11) and 1,3-cyclooctadiene viab-hydride elimination and Rh–H bond amination. Ligand-induced reductive elimination ofToMRh(h3-C3H5)NHTs provides HN(CH2CH CH2)Ts; these steps combine to give a propeneC–H activation/functionalization sequence.

Introduction

Selective transformations of metal-carbon bonds are centralcomponents of many catalytic conversions, including hydrocarbonfunctionalizations. However, metal hydrocarbyl species derivedfrom C–H bond activation steps are not always easily trans-formed into desired functionalized products. For example, theorganometallic compounds (L2X)MR(H)L¢ (L2X = Cp* = h5-C5Me5 , Tp* = (tris(3,5-dimethylpyrazolyl)hydridoborate); M =Rh, Ir; L = CO, PMe3), obtained from C–H bond oxidativeaddition under mild photochemical conditions, undergo C–Hreductive elimination without functionalization.1 A few of thesecompounds undergo functionalization of the hydrocarbyl moiety,including bromination after transmetalation to mercury,1b oxida-tive bromination,1d and an olefin insertion.1g This limitation, fortu-nately, has not hindered the development of a range of catalytic hy-drocarbon functionalization reactions that may or may not utilizeC–H bond oxidative addition,2 including borylation,3 oxidation,4

dehydrogenation,5 and hydroarylation.6 Still, sequences of C–Hbond activation and hydrocarbyl elaboration are often difficult to

Department of Chemistry and U.S. DOE Ames Laboratory, Iowa StateUniversity, Ames, IA 50011, USA. E-mail: sadow@iastate.edu

study outside of catalytic conversions. Investigations of these twosteps in stoichiometric systems, en route to catalysis, is importantfor understanding steric and electronic effects on selectivity andreactivity that may also lead to new transformations.

In particular, facile late transition-metal-mediated allylic C–H bond oxidative additions could complement recent ad-vances in palladium-, molybdenum-, and copper-catalyzed allylicoxidations.7,8 The electrophilic-type C–H bond activations in thesecatalyses are mechanistically distinct from the classic two-electronoxidative additions of low valent group 9 compounds, particularlyCp*IrH2(PMe3),1a,b Cp*RhL2,1c,9 and Tp*RhL2,1f,10 where theancillary ligands’ fac-coordinating and electron-donating prop-erties significantly influence the metal center’s reactivity. Theselow valent metal centers also mediate stoichiometric oxidativeadditions of allylic C–H bonds. A classic example involvesreaction of IrCl(N2)(PPh3)2 and allylbenzene which provides theIr(III) allyl hydride.11 Fac-coordinating ancillary ligands werelater shown to facilitate allylic C–H bond activations. Forexample, reaction of K[Tp] (Tp = tris(pyrazolyl)hydridoborate)and 0.5 equiv. of [Ir(m-Cl)(h2-C8H14)2]2 affords the iridium allylhydride TpIrH(h3-C8H13) along with the byproducts C8H12 andKCl.12 This transformation is highly sensitive to the reactionconditions, as the interaction of Na[Tp] and 0.5 equiv. of

6500 | Dalton Trans., 2011, 40, 6500–6514 This journal is © The Royal Society of Chemistry 2011

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[Ir(m-Cl)(h2-C8H14)2]2 results in vinylic C–H bond activationyielding TpIrH(s-C8H13)(h2-C8H14).13 In a later report, the lattercompound is converted into the former upon thermolysis.14

Although KTp* and [Ir(m-Cl)(h2-C8H14)2]2 gives a mixture offive or more products, in the presence of 2-butene the allylic C–H bond oxidative addition species anti-exo-Tp*IrH(h3-C4H6) isformed.14 Iridium(III) allyl hydrides are also formed in relatedmetalations of electron-rich Li[BP3] (BP3 = PhB(CH2PPh2)3).15

In addition to the thermal allylic C–H bond oxidative ad-ditions, photolysis of Tp*Rh(CNCH2

tBu)(PhN C NCH2tBu)

in liquid propylene generates the allylic C–H bond activationproduct Tp*RhH(h1-CH2CH CH2)(CNCHtBu).16 Irradiationof Cp*Rh(CH2 CHMe)2 yields Cp*Rh(h3-C3H5)H.17

Thus, an allylic C–H bond functionalization scheme mightinvolve a p-allyl Rh(III) or Ir(III) species as a reactive intermediate.While this appears reasonable based on known rhodium- andiridium-catalyzed allylic substitution chemistry,18,19 examples ofnucleophilic attack upon p-allyl compounds obtained from C–H bond activation are uncommon. In fact, reductive eliminationof olefin from (L2X)MH(h3-C3H4R) (L2X = Cp*, Tp*, BP3) is adominant reaction pathway, as is the case for the s-hydrocarbylcompounds. The elimination reactions provide access to highlyreactive, low valent, coordinatively unsaturated late metal com-plexes, but limit the functionalization of the allyl moiety.17,20 Wesought to utilize this mild C–H bond oxidative addition reaction asan alternative to electrophilic allylic functionalization (eqn (1)).21

(1)

We have been investigating the chemistry of tridentate,monoanionic tris(oxazolinyl)borates (ToR = ToM, tris(4,4-dimethyl-2-oxazolinyl)phenylborate; ToR = ToP, tris(4S-isopropyl-2-oxazolinyl)phenylborate;])22 as easily-accessed chiral analogs23

of the tris(pyrazolyl)borate ligand class and to develop C–H bondoxidative addition chemistry. However, we initially encountereddifficulties in our attempts to develop oxidative addition reactionsof ToRML2 (M = Ir, Rh; L2 = h4-C8H12, (CO)2) and strongelectrophiles (such as HOTf, MeOTf, and MeI) in which oxazoline-based additions occur preferentially to metal-centered oxidation.24

Weaker electrophiles (HCCl3, C3H5Br) undergo oxidative ad-dition to ToMRh(CO)2 and ToPRh(CO)2 under thermal condi-tions, showing that, despite competitive ligand-based reactivity,tris(oxazolinyl)borate ligands can provide reactive metal centers.24c

Given the isoelectronic relationship of ToR and Tp (and thus Cp)ligands and because nCO bands of ToMM(CO)2 and ToPM(CO)2

(M = Rh, Ir) suggest that the tris(oxazolinyl)borate ligands areslightly more electron donating than tris(pyrazolyl)borates togroup 9 metal centers, C–H bond oxidative addition should beaccessible with tris(oxazolinyl)borate rhodium(I) and iridium(I)centers. Moreover, allylic bond activation might be facile fromcarbonyl-free metal centers.

Here, we report the synthesis of rhodium and iridium allylhydride compounds formed by oxidative addition of allylic C–H bonds. Several compounds were crystallographically charac-terized, and solution phase NMR spectroscopy including 1H-15N HMBC (Heteronuclear Multiple Bond Correlation) andNOESY experiments revealed the configuration of the allyl

group (endo/exo) and its cis/trans disposition to coordinatedoxazoline ligands. In 1H-15N HMBC experiments, correlationsbetween the M-H and the trans-disposed oxazoline nitrogen (i.e.,through-metal 1H-15N magnetization transfer) further define thecoordination sphere and configuration of the metal center. Wehave investigated reactions of these allyl hydride compounds todevelop hydrocarbon functionalization strategies. These attemptsto transform the metal allyl hydrides have uncovered an interestingRh–H bond amination reaction that provides allylic aminationproducts after C–N bond reductive elimination.

Results

Synthesis and characterization of rhodium and iridium allylhydrides supported by ToM

Our initial attempts to prepare ToRMH(h3-C8H13) were based onreports of allylic C–H bond oxidative addition that accompanieda salt metathesis reaction of [Ir(m-Cl)(h2-C8H14)2]2 with K[Tp] orLi[BP3].12,15 Unfortunately, reactions of Li[ToM] or Li[ToP] and[M(m-Cl)(h2-C8H14)2]2 (M = Rh, Ir) give complex mixtures inbenzene, THF, methylene chloride and acetonitrile at 60 ◦C, andfar upfield resonances that might be attributed to metal hydridecomplexes were observed to have very low intensities. Only startingmaterials are observed after 24 h at ambient temperature. AllylicC–H bond activation may be sensitive to counterions present in thereaction,14 so the reaction of K[ToM] and [Ir(m-Cl)(h2-C8H14)2] wastested. Although these two reagents react at room temperature(unlike Li[ToM]), we were unable to isolate or characterize theproducts.

Tl[ToM] is an effective transfer agent for the preparation ofToMRh(CO)2, where Li[ToM] affords a mixture of products.24c

In contrast to the experiments with Li[ToM] and K[ToM], 1.4equiv. of Tl[ToM] and [Rh(m-Cl)(h2-C8H14)2]2 react on millimolarscale in benzene-d6 to provide a single soluble ToM-containingproduct and 1 equiv. of cyclooctene at room temperature. Thereaction scale may be increased to 1.8 millimoles, and althougha slight excess of [Rh(m-Cl)(h2-C8H14)2]2 is required for productisolation, the reaction proceeds to completion after 5 h at roomtemperature in benzene providing adequate quantities of productfor the studies described below. Analytically pure ToMRhH(h3-C8H13) (1) is isolated by pentane extraction (3 ¥ 25 mL) from theevaporated reaction residue in 71% yield (eqn (2)).

(2)

The NMR properties of 1 are described in detail, giventhe conflicting results associated with TpIrH(h3-C8H13) andTpIrH(C8H13)(h2-C8H14).12,13,14 The 1H NMR spectrum of 1 con-tained a diagnostic doublet at -24.3 ppm (1 H, 1JRhH = 11.6 Hz)that was assigned as a rhodium hydride. The pattern of 1H NMRresonances for the ToM ligand indicates that 1 is Cs-symmetric,such that the ring methylene resonances were observed as a singlet(3.33 ppm, 2 H) and two diastereotopic coupled doublets (3.74and 3.60 ppm, 2 H each, 2JHH = 8.4 Hz). Three singlets at 1.17,

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1.12 and 0.82 ppm were assigned to the oxazoline methyl groups.Additionally, a triplet at 5.16 ppm (1 H) and a doublet of doubletsat 3.95 ppm (2 H) were detected. These signals are characteristicof a p-allyl ligand and rule out vinylic C–H bond activation or anh1-allyl structure. No 2JRhH coupling was observed for the allylicproton resonances, but the 3JHH (8.0 Hz) for the p-allylic protonswas consistent with syn-disposed hydrogen resulting from the allylgroup’s anti-anti conformation, as required for the cyclic ligand.Crosspeaks in a NOESY experiment were detected between themethyls on the oxazoline trans to the rhodium hydride and boththe central allyl (Hcentral) and the syn-allyl hydrogen (Hsyn). Fromthese observations, we assigned the complex’s conformation asexo as shown in eqn (2) and Fig. 1. We were unable to observe acrosspeak between the central p-allyl hydrogen and the rhodiumhydride in a NOESY experiment, which suggests the exo structuralassignment.

Fig. 1 Fisher projection of k3-ToMRhH(exo-h3-C8H13) (1) showing nOesbetween allylic CHs and methyl groups on the oxazoline trans to therhodium hydride.

1H-15N HMBC experiments provide 15N chemical shift dataand support structural assignments of tris(oxazolinyl)boratecompounds.24 The chemical shifts of the two 15N NMR resonances,detected at -164.2 and -173.4 ppm, indicate that the oxazolinenitrogen are coordinated to the rhodium center and ToM isbonded as a tridentate ligand. The former signal was assignedto the oxazoline nitrogen trans to the hydride based on through-bond, through-rhodium coupling between the nitrogen and therhodium hydride. Additionally, the oxazoline trans to the rhodiumhydride coincided with the sv-mirror plane, and the 1H-15N HMBCcontained the expected crosspeak between that nitrogen signal andthe singlet methylene resonance. The resonance at -173.4 ppm wasassigned to the nitrogen on the oxazoline groups trans to the p-allylligand off the mirror plane.

h3-Coordination of the p-allyl ligand is further supportedby rhodium-carbon coupling observed in the 13C{1H} NMRspectrum. The resonances at 93.9 ppm (1JRhC = 6.0 Hz, Ccentral)and 52.15 (1JRhC = 11.4 Hz) were assigned to the h3-C8H13

group. Correlations between these resonances and the allylic1H NMR signals were detected in a 1H-13C HMQC experimentand confirmed the assignments. Finally, a characteristic nRhH

absorption in the IR spectrum of 1 appeared at 2158 cm-1. Thesedata support the formulation of 1 as ToMRhH(exo-h3-C8H13).

The corresponding reaction of [Ir(m-Cl)(h2-C8H14)2]2 andTl[ToM] in benzene provides the iridium(III) analog ToMIrH(h3-C8H13) (2) in good yield (78%). As in the rhodium system, reactions

of Li[ToM] and K[ToM] afford complex mixtures of products.The structure of the iridium and rhodium h3-C8H13 compoundsare closely related as indicated by NMR spectroscopy. Thus,the 1H NMR resonances for the ToM ligand were consistentwith a Cs-symmetric complex, a resonance characteristic of aniridium hydride was detected at -28.5 ppm, allylic resonanceswere observed in the 1H NMR spectrum as a singlet at 4.79 ppm(2 H) and a doublet of doublets at 3.98 ppm (4 H), and theexpected crosspeaks were detected in a 1H-15N HMBC experiment.As in 1, the 15N NMR resonance of the oxazoline nitrogen at-182.6 ppm, assigned as trans to the iridium hydride by symmetry,exhibited through-bond coupling to the hydride (through theiridium center). No correlations to the iridium hydride wereobserved for the 15N NMR resonance at -190.6 ppm that isassigned to the oxazolines trans to the allyl ligand.

Several ToMMH(h3-C3H4R) (M = Rh, Ir; R = H, Ph) compoundsare prepared through related reactions. These compounds eachhave distinguishing structural, stereochemical, and reactivity fea-tures that will be highlighted in the following discussion. The par-ent allyl complex ToMRhH(h3-C3H5) (3) is synthesized by reactionof Tl[ToM] and in situ-generated [Rh(m-Cl)(h2-C3H6)2]2. Progressof a micromolar-scale reaction in benzene-d6 was monitored by 1HNMR spectroscopy; only one conformer (assigned as exo below)formed after 1 h with complete conversion of Tl[ToM], but after2 h the exo:endo ratio was 4 : 1 (eqn (3)). Neither reaction timesup to 2 d nor heating at 80 ◦C for 2 h alter this ratio. In contrast,a 7 : 1 mixture of endo and exo Tp*RhMe(h3-C3H5) was reportedto isomerize quantitatively to the endo conformer at 60 ◦C.25

(3)

Exo-3 and endo-3 were identified by the 1H NMR chemicalshifts of the rhodium hydride at -22.7 and -23.2 ppm aswell as the typical p-allyl resonances. A key crosspeak in theNOESY spectrum between the rhodium hydride resonance at-22.7 ppm and the p-allyl C-2 methine proton at 5.1 ppm allowedassignment of that isomer as endo-3 (eqn (3)). Additionally,crosspeaks were observed between the allylic syn-CHs and the twodiastereotopic oxazoline methyl groups in a NOESY. In contrast,the exo conformer exhibited nOes between the anti-CHs and thetwo diastereotopic oxazolinyl methyl groups. The 3JHH couplingconstant between the hydrogen on the central carbon and synhydrogens of both endo and exo isomers was 7.2 Hz whereas the3JHH coupling to anti hydrogens was 11.2 and 11.6 Hz for endo andexo isomers, respectively, further supporting our assignments.

As in the ToMMH(h3-C8H13) compounds, the pattern for ToM

resonances in both endo and exo isomers indicated the overallCs symmetry. The Rh–H and the oxazoline coordinated trans tothe hydride are located on the mirror plane, and their 1H NMRresonances are assigned based on symmetry. The 15N NMR signalsin a 1H-15N HMBC experiment at -165.6 and -164.8 ppm forexo and endo isomers, respectively, were corroborated by through-bond correlations to the rhodium hydride. Further characteriza-tion included the two nRhH bands in the IR spectrum at 2090and 2080 cm-1 and single crystal X-ray diffraction. An X-rayquality crystal was obtained in concentrated toluene at -30 ◦C,

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Fig. 2 ORTEP diagrams of (a) endo-ToMRhH(C3H5) (endo-3) and (b) exo-ToMRhH(C3H5) (exo-3) drawn at 50% probability. A toluene molecule andhydrogen atoms on the ToM ligand are not depicted. The two isomers co-crystallize, but their relative orientation has been altered above to more clearlyillustrate the rhodium centers’ coordination geometry, and this figure does not represent their relative positions in the unit cell. Selected bond distances(A) for endo-3: Rh1–H1r, 1.67(6); Rh1–N1, 2.107(3); Rh1–N2, 2.109(3); Rh1–N3, 2.298(3); Rh1–C22, 2.160(5); Rh1–C23, 2.099(6), Rh1–C24, 2.139(5).Selected bond distances (A) for exo-3: Rh2–N4, 2.128(3); Rh2–N5, 2.223(3), Rh2–N6, 2.141(3); Rh2–C46, 2.147(7); Rh2–C47, 2.035(8); Rh2–C48,2.096(7).

and the unit cell contains both endo and exo isomers as well asa toluene molecule. The p-allyl groups in both the endo and exoisomers were refined with restraints, resulting in uncertainty in theC–C–C angles of 135.8(9) and 135(1)◦, respectively. The rhodiumhydride in the exo isomer was not located although the hydride onthe endo isomer was located objectively and refined isotropically.Despite these problems, the two isomers are readily distinguishedas shown in Fig. 2.

The Rh–N bonds trans to hydride Rh1–N3 (endo: 2.298(3) A)and Rh2–N5 (exo: 2.223(3) A) are longer than the two Rh–Nbonds trans to the allyl ligand (endo: Rh1–N1, 2.107(3); Rh1–N2,2.109(3); exo: Rh2–N4, 2.128(3); Rh2–N6, 2.141(3) A). The Rh–Ndistances trans to the allyl ligand in the exo conformer are slightlylonger than the Rh–N distances in the endo conformer.

An alternative preparation of 3 is accomplished by treatment ofisolated 1 with propene in benzene-d6. As in the in situ synthesis,only the exo conformer is formed after 1 h but a mixture of bothconformers is obtained after several hours.

The parent iridium allyl hydride ToMIrH(h3-C3H5) (4) is pre-pared by reaction of Tl[ToM] and in situ-generated [Ir(m-Cl)(h2-C3H5)2]2 (eqn (4)). Only the endo isomer is formed in the iridiumsystem. A crosspeak between the IrH and the central hydrogenon the p-allyl ligand in a NOESY experiment facilitated thisassignment.

(4)

ToMRhH(h3-C3H4Ph) (5) is synthesized by addition of Tl[ToM]to in situ generated [Rh(m-Cl)(h2-C3H4Ph)2]2 (eqn (5)). Only oneisomer was detected in the reaction mixture (four are possible,with syn and anti dispositions of the phenyl group with respect to

the central CH, and exo and endo orientations of the phenylallylligand).

(5)

The four p-allyl protons (h3-C3H4Ph) were assigned usinga COSY experiment that contained correlations between thecentral p-allyl proton resonance (5.62 ppm) and the terminalsyn and anti CH2 (3.22 and 2.84 ppm, respectively) and CHPhsignals (3.98 ppm). The syn and anti 3JHH were 9.6 and 11.2 Hz,respectively, where the former coupling constant is unusually high.The 3JHH between the central allylic CH and the benzylic CHwas 10.4 Hz. A correlation between the RhH and the centralallylic hydrogen was observed in a NOESY experiment, andthese data suggest that the molecule adopts an endo-syn-C3H4Phconformation.11 1JRhC coupling observed in the 13C{1H} NMRspectrum also supports the p-allyl-bonding description, as thecentral carbon (90.06 ppm, 1JRhC = 3.5 Hz), terminal p-allyl carbon(36.54 ppm, 1JRhC = 12.25 Hz), and the benzylic p-allyl carbon(54.52 ppm, 1JRhC = 10.5 Hz) doublet resonances indicate rhodium-carbon bonding.

Unlike the sv-symmetric h3-C3H5 and h3-C8H13 ligands, thedissymmetrical h3-C3H4Ph imparts C1 symmetry to 5, and thiswas manifested in six oxazoline methyl signals in the 1H NMRspectrum. Thus, the three oxazoline rings are inequivalent, andthree signals were observed (-168.2, -172.1 and -179.9 ppm) inthe 1H–15N HMBC spectrum. The latter resonance was assignedas trans to the hydride based on a crosspeak between thatnitrogen and the rhodium hydride. The two former resonanceswere assigned as oxazolines cis to the hydride.

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X-Ray quality crystals were obtained from a concentratedtoluene solution cooled to -30 ◦C, and a single crystal diffractionstudy confirmed the structure and configuration of endo-syn-h3-5 (Fig. 3). The rhodium-nitrogen distances range from 2.10 to2.28 A, and the Rh1–N2 distance (trans to hydride) is the longest.The distance from the rhodium center to the phenyl–substitutedallylic carbon (Rh1–C23, 2.195(4) A) is longer than the distance tothe terminal allylic carbon (Rh1–C30, 2.148(4) A) by 0.047(8) A.The carbon-carbon distances in the allylic ligand, (C22–C23,1.416(5) and C22–C30, 1.406(5) A) are, however, equivalent.

Fig. 3 ORTEP diagram of endo-ToMRhH(h3-C3H4Ph) (5) drawn at50% probability. Hydrogens and a disordered toluene molecule areomitted for clarity. The rhodium hydride was not located. Selected bonddistances (A): Rh1–N1, 2.101(3); Rh1–N2, 2.280(3); Rh1–N3, 2.132(3);Rh1–C22, 2.113(4); Rh1–C23, 2.195(4), Rh1–C30, 2.148(4). Selectedangles (◦): N1–Rh1–N2, 87.5(1); N1–Rh1–N3, 84.1(1); N2–Rh1–N3,84.9(1); C23–C22–C30, 120.6(4).

Reactions of ToMMH(g3-allyl) (1–5; M = Rh, Ir) toward C–E bondformation

Our attempts to transform the allyl moiety began with reactionswith nucleophilic reagents, including alcohols and alkoxides,amines and amides, and 1,3-dicarbonyl reagents and their enolates.However, the observed products are consistent with C–H reductiveelimination rather than C–O, C–N, or C–C bond formation. Forexample, addition of neopentyl alcohol to a benzene-d6 solutionof 1 results in formation of a black precipitate and cycloocteneafter 1 h at 60 ◦C. The same products are obtained when 1 or 2 aretreated with tert-butylamine at 80 ◦C in benzene-d6 after 4 h and24 h respectively.

In the presence of ligands such as CO or CNtBu that couldpotentially react by insertion, 1 or 2 form cyclooctene or propeneand ToMRhL2 (L = CO (6), CNtBu (7); eqn (6)) at roomtemperature. For the bis(isocyanide) 7, two signals were observedin a 1H-15N HMBC experiment at -159.6 and -201.1 ppm forthe rhodium-coordinated nitrogen in the oxazoline and isonitrilegroups, respectively. A correlation between the tert-butyl protonsand the isocyanide nitrogen distinguished the two 15N NMRsignals. As in ToMRh(CO)2,24c the room temperature 1H NMRspectrum of ToMRh(CNtBu)2 contained equivalent oxazolinegroups, whereas the solid state structure revealed a bidentateToM-rhodium interaction (Fig. 4). Additionally, the solution-

Fig. 4 ORTEP diagram of ToMRh(CNtBu)2 (7) drawn at 50% probability.Hydrogen atoms are omitted for clarity. Selected bond distances (A):Rh1–N1, 2.094(4); Rh1–N2, 2.087(4); Rh1–C22, 1.881(6); Rh1–C27,1.884(7). Selected bond angles (◦): N1–Rh1–C22, 174.9(2); N2–Rh1–C27,178.4(2); N1–Rh1–N2, 85.2(2); C22–Rh1–C27, 84.8(2).

phase IR spectrum (CH2Cl2) showed two oxazoline nCN bands;an absorption at 1614 cm-1 was assigned to a pendent, non-coordinated oxazoline group. However, four isocyanide nCN bandsat 2208, 2147, 2103, 2068 cm-1 indicated that at least two isomersare present in solution.26 Surprisingly, the iridium analogs 2 or 4and CO afford free olefin and black precipitate even though theexpected product, ToMIr(CO)2, is isolable from the reaction of COand ToMIr(h4-C8H12).24b

(6)

Transformation of compounds 1–5 into cationic species (byhydride abstraction) might increase the electrophilicity of theallyl moiety for further reactivity while impeding olefin reductiveelimination (i.e., C–H bond formation is not possible from[ToMRh(h3-C3H5)]+). Additionally, intermediates in many metal-catalyzed allylic substitution reactions are cationic complexes.Therefore we attempted to prepare cationic [ToMM(h3-C3H4R)]+

by abstracting a hydride from 1–5. These reactions do not provideisolable species. For example, reaction of 3 and B(C6F5)3 inbenzene-d6 at 60 ◦C or methylene chloride-d2 at 40 ◦C overnightaffords a mixture of unidentified products. No free olefin wasdetected in these reaction mixtures. Interestingly, treatment ofendo-4 with B(C6F5)3 at 80 ◦C in benzene-d6 for 2 days gives amixture of endo-4 and exo-4 (1 : 4 ratio).

Protonolysis and reductive elimination occurs upon treatmentof allyl hydride compounds 1–5 with Brønsted acids. For example,

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1 and acetic acid react in benzene to give ToMRhH(k2-OAc) (8) andcyclooctene. Reaction with acetic acid-d1 provides a mixture of 8and ToMRhD(k2-OAc) (8-d1) in a 3 : 1 ratio.27 In those experiments,8-d1 and cyclooctene-d1 were detected in the 2H NMR spectrumof the reaction mixture. Analytically pure product is obtained byextraction of the reaction mixture with pentane, and crystallizationin toluene at -30 ◦C provides X-ray quality crystals (an ORTEPdiagram is shown in Fig. 5).

Fig. 5 ORTEP diagram of ToMRhH(k2-O2CMe) (8) drawn at 50%probability. The hydrogen atom bonded to rhodium was found objectivelyon the difference Fourier map and is shown. The other hydrogen atoms anddisordered solvent molecules are not included. Selected bond distances(A): Rh1–H1r, 1.7(1); Rh1–N1, 2.20(1); Rh1–N2, 1.97(1); Rh1–N3,2.01(1); Rh1–O4, 2.069(9); Rh1–O5, 2.092(9). Selected bond angles(◦): N1–Rh1–H1r, 177(4); N1–Rh1–N2, 87.7(4); N1–Rh1–N3, 85.8(4);N2–Rh1–N3, 85.2(5); N2–Rh1–O4, 167.7(4); N3–Rh1–O5, 168.6(4);O4–R1–O5, 61.8(4).

The 1H NMR spectrum of 8 contained signals from a Cs-symmetric ToM ligand and characteristic hydride at -13.2 ppm(1JRhH = 11.6 Hz), and this latter resonance was correlated tothe trans oxazoline nitrogen (-154.3 ppm) in a 1H-15N HMBCexperiment. The 15N NMR signals for the oxazolines trans toacetate appeared at -221.0 ppm. The same product, 8, is formedas a minor species upon reaction of phenylallyl hydride 5 andacetic anhydride in benzene-d6 at 80 ◦C overnight. However,allylbenzene is the major organic product, and 8 is the onlyidentifiable rhodium-containing species.

Reaction of 5 and N-bromosuccinimide (NBS) results insubstitution of the hydride for a bromide ligand givingToMRhBr(h3-C3H4Ph) (9; eqn (7)). Compound 9 is the onlyallyl-containing species observed. For comparison, the treatmentof Cp*Rh(R)(H)PMe3 with bromoform followed by Br2 pro-vides RBr products,1d and Tp*Rh(H)(C6H13)CO was convertedto Tp*Rh(Cl)(C6H13)CO by reaction with CCl4.1f Additionally,cationic diimine palladium(II) and platinum(II) h3-indenyl com-pounds, obtained from electrophilic allylic C–H bond activation,react with Br2 to provide indenylbromide.21

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The 1H NMR spectrum of C1 symmetric 9 contained six uniqueoxazoline methyl resonances and three 15N signals (-217.6, -191.1and -181.5 ppm); the upfield resonance was assigned to theoxazoline nitrogen trans to the bromide. The p-allyl group iscoordinated in an endo-syn conformation, and this assignmentis based on 1H NMR chemical shifts, coupling constants, andNOESY experiments as described in detail for ToMRhH(h3-C3H4Ph) above. Thus, the p-allyl configuration is the same forthe starting material and product in eqn (7).

Treatment of a mixture of endo-3 and exo-3 with 1 equiv.of TsN3 (Ts = SO2C6H4Me) in benzene at room temperaturefor 24 h affords exo-ToMRh(NHTs)(h3-C3H5) (10) in good yield(82%) as shown in eqn (8). The product 10 corresponds to aformal insertion of a tosylnitrene into the Rh–H bond, andbubbles are formed during the reaction. Signals corresponding topropene were not detected in 1H NMR spectra of the reactionmixture. The 1H NMR spectrum of 10 contained resonancesassigned to the ToM ligand, a h3-C3H5 group bisected by a mirrorplane, and a tosyl group. The distinctive hydride resonancesof endo-3 and exo-3 were absent in the 1H NMR spectrum ofisolated 10.

(8)

Notably, compound 10 exists as only one isomer althoughthe starting material is a mixture. The oxazoline 15N chemicalshifts (-177.6 and -225.4 ppm) were measured with a 1H-15N HMBC experiment. The former signal was assigned to thenitrogen in the oxazoline rings coordinated trans to the allylgroup, based on magnetization transfer between nitrogen and thediastereotopic oxazoline methylene signals. The oxazolines transto the allyl moiety are related by, but do not contain, a sv planeand thus, the 15N NMR assignments are based on symmetry.Hydride compounds 1–4 are assigned in the same manner, butin those cases the assignments are corroborated by through-bondcoupling between the Rh–H and the trans oxazoline nitrogen. Theremaining upfield resonance in 10 corresponds to the oxazolinetrans to the amide group.

X-Ray quality single crystals are obtained by vapor diffusion ofpentane into a toluene solution at -30 ◦C. The constitution andconnectivity of 10 was thus confirmed by X-ray crystallography,which also revealed exo-h3-allyl group coordination (Fig. 6). Thereis no interaction between the oxygen atoms of the SO2C6H4Megroup and the rhodium center. Also, the Rh–Noxazoline distances arewithin ~0.02 A for the three oxazolines (Rh-N1, 2.140(3); Rh1–N2, 2.119(3); Rh1–N3, 2.121(3) A) where the oxazoline nitrogen(N2) trans (∠N2–Rh1–N4 = 163.0(1)◦) to the amido ligand hasthe shortest Rh–N distance.

Excitingly, the reaction of 10 and CO at 65 ◦C results inC–N bond reductive elimination and CO coordination to giveToMRh(CO)2 (6, 81% yield) and allyl(tosyl)amine (eqn (9)). Theorganic product, identified by GC-MS and 1H NMR spectroscopy,is formed in 29% yield. A number of other unidentified organicproducts are also present in the reaction mixture.

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Fig. 6 ORTEP diagram of exo-ToMRh(NHTs)(h3-C3H5) (10) drawnat 50% probability. Hydrogen atoms are not included to highlight theheavy atom positions. Selected bond distances (A): Rh1–N1, 2.140(2);Rh1–N2, 2.119(3); Rh1–N3, 2.121(3); Rh1–N4, 2.085(3); Rh1–C22,2.181(3); Rh1–C23, 2.145(3); Rh1–C24, 2.181(3). Selected bond angles(◦): N1–Rh1–N4, 83.8(1); N2–Rh1–N4, 163.0(1); N3–Rh1–N4, 84.4(1);Rh1–N4–S1, 138.5(2).

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Given the interesting reaction of 3 and TsN3, we investigated thereactions of TsN3 with the other metal allyl hydride compounds.The interaction of 1 and TsN3 results in the elimination of1,3-cyclooctadiene and formation of a C1-symmetric ToMRh-containing product. The reaction occurs in benzene at roomtemperature and is accompanied by significantly more vigorousN2 evolution than in the corresponding reaction of 3 and TsN3.The 1H NMR spectrum of the product contained six singletscorresponding to three inequivalent oxazoline groups in the ToM

ligand, as well as signals from a tosyl group and a rhodiumhydride (-15.75 ppm;1JRhH = 9.2 Hz). Ultimately the productToMRhH(NHTs)(OH2) (11, eqn (10)) was identified by X-raycrystallography (Fig. 7).

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A related transformation was reported in the thermol-ysis of {BP3}IrH(h3-C8H13) in the presence of PMePh2

which gave {BP3}IrH2(PMePh2) and 1,3-cyclooctadiene.20a Both{BP3}IrH(h3-C8H13) and ToMRhH(h3-C8H13) typically react byolefin elimination at room temperature (e.g., with CO), so theapparent b-elimination pathway is somewhat surprising. Further-more, 1 does not eliminate 1,3-cyclooctadiene in the absence ofTsN3. Thus, ToMRhH(h3-C3H4Ph) appeared to be a promisingcompound to react with TsN3, as b-elimination is not possible.Unfortunately, neither ToMRhH(h3-C3H4Ph), ToMIrH(h3-C3H5),

Fig. 7 ORTEP diagram of ToMRh(NHTs)(H)OH2 (11). The hydrogenatoms shown are the H1r (rhodium hydride) and H4n (amide hydrogen),and the rest are not represented for clarity. The aryl groups were drawn asball-and-stick to more clearly illustrate the rhodium center’s coordinationgeometry and the connectivity of the complex. Selected bond distances(A): Rh1–H1r, 1.88(7); Rh1–N1, 2.234(6); Rh1–N2, 2.016(7); Rh1–N3,2.064(7); Rh1–N4, 2.088(6); Rh1–O6, 2.101(6). Selected bond angles(A): N1–Rh1–H1r, 173(2); N2–Rh1–O6, 179.2(3); N3–Rh1–N4, 176.9(3);Rh1–N4–S1, 131.5(4).

nor ToMIr(h3-C8H13) afford tractable products upon treatmentwith TsN3.

Discussion

Allylic C–H bond activation and rhodium hydride amination

The tris(oxazolinyl)borate ligand itself is important as a spectatorin the C–H bond activation step, as the reaction of Tl[ToP](ToP = tris(4S-isopropyl-2-oxazolinyl)phenylborate) and [Rh(m-Cl)(h2-C8H14)2]2 provides TlCl and an unstable, hydride-free{ToPRh}-species that was not isolable. Two equivalents of non-coordinated cyclooctene are formed, and the product containsthree inequivalent oxazoline groups (suggesting a non-fluxionalsix-coordinate Rh(III) compound; eqn (11)). The absence of adetectable hydride in the product and the loss of cyclooctene argueagainst ToPRh-mediated allylic C–H bond activation, although theidentity of the product is not yet established due to its transientnature.

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This change in reactivity between C3v-symmetric ToM and C3-symmetric ToP is unexpected, as the two ligands are isoelectronicand have similar steric properties. For comparison, KTp andKTp* also react with dissimilar pathways, such that [Ir(m-Cl)(h2-C8H14)2]2 and KTp* give several products,14 whereas the KTpreaction provides TpIrH(h3-C8H13).12 The change in reactivitybetween KTp* and KTp can be explained by the greater coneangle of the former ligand (or its greater electron-donatingproperties).28 The similar electronic and steric properties of ToM

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and ToP preclude such a rationalization in the current system.24c

However, a distinction between the compounds may be foundin the ground state structures: ToPIr(CO)2 appears to contain atridentate tris(oxazolinyl)borate ligand in the solid state,24a whileToMIr(CO)2 and ToMRh(CO)2 are coordinated in a bidentate modein the solid state.24b,c Thus, the ancillary ligand may control theground state structure of the Rh(I) species that mediates C–Hbond oxidative addition. We are currently preparing new chiraloxazolinylborate rhodium(I) compounds to better assess the roleof the ancillary ligand in these types of thermal allylic C–H bondactivations.

It is also interesting to consider the effect of the counterionin these steps. For example, reactions of both [Ir(m-Cl)(h2-C8H14)2]2 and [Rh(m-Cl)(h2-C8H14)2]2 require Tl[ToM] for selectiveancillary ligand metalation, and neither Li[ToM] nor K[ToM]provide ToMMH(h3-C8H13) compounds. Metalation/C–H bondoxidative addition sequences in reactions of Na[Tp] and K[Tp]with [Ir(m-Cl)(h2-C8H14)2]2 also show counterion dependence, withK[Tp] providing TpIrH(h3-C8H13) in THF,12 and Na[Tp] givingthe vinyl C–H activated product TpIrH(s-C8H13)(h2-C8H14) indichloromethane.13 Additionally, the latter compound is convertedto the former by heating at 80–100 ◦C in cyclohexane.14 Althoughcounterions and solvent may influence allylic vs. vinylic C–H bondactivations, the Na+, K+, or Tl+ ions are not required for this stepas shown by the reaction of isolated rhodium cyclooctenyl 1 andpropene that provides the parent allyl 3. In contrast, ToMIrH(h3-C8H13) and propene do not react up to 80 ◦C, highlighting a changein reactivity between rhodium and iridium.

The distinction between rhodium and iridium is furtherhighlighted by exo to endo isomerization of ToMMH(h3-C3H5).The propenyl oxazolinylborato iridium(III) compound is inert.Isomerization of the kinetically favored endo-ToMIrH(h3-C3H5)to the thermodynamic mixture of conformers requires treatmentwith the Lewis acid B(C6F5)3. In contrast, the kinetic products ofpropene C–H bond activation is exo-3, and isomerization to thethermodynamically favored mixture of endo and exo conformersoccurs over 2 h.

The isomerization and conversions of the rhodium allyl hydride,in comparison to the inert iridium complexes, may explain thereactivity of 1 and 3 (versus 2 and 4) with tosylazide. In linewith the isomerization trend, no interaction between TsN3 andToMIrH(h3-C8H13) or ToMIrH(h3-C3H5) was detected, whereas richchemistry was observed in reactions of the rhodium analogs.In the reactions of 1 and 3 with TsN3, C–H bond reductiveelimination is not favored, contrasting the common reactionpathway for these compounds with Brønsted acids, p-acid ligandssuch as CO and CNtBu, and weak s-donors including tert-butanol and tert-butylamine. In this context, we considered thepossible pathways for the formation of the tosylamido ligand fromtosylazide and rhodium hydride that might preclude C–H bondreductive elimination.

Additionally, the formation of rhodium tosylamido ligands issomewhat unexpected because there are no previous reports toour knowledge of organoazide mediated amination of rhodium-hydrogen bonds.29 Related reactions of group 9 metal alkylcompounds and azides give secondary amides (i.e., the formalinsertion of nitrene into Co–Me and Ir–Me bonds).30 Additionally,organoazides and late metal-hydrogen bonds (e.g., Pt, Re) reactto give N2 and metal amidos.31 These reactions are generally

postulated to involve 1,1-insertion of the organoazide to give k2-triazenide species, followed by 1,3-hydrogen migration and N2

extrusion.32 This pathway is distinct from dirhodium-catalyzedC–H amination, which is proposed to involve a rhodium nitrene;in that chemistry, rhodium hydride species are not involved.33

A recent report documented the formation of an iridium(III)tosyl(aryl)amide from an iridium aryl, and this was proposed toinvolve an iridium(V) nitrene species.30b Additionally, a nitrenecompound was recently suggested as an intermediate in theformation of a palladium amido from a palladium alkyl anda tosyliminoiodinane.34 In our system, formation of a coordi-nated nitrene would invoke a pentavalent rhodium intermediateand follow a sequence that might involve Na-coordination oftosylazide, N2 elimination to give ToMRh(NTs)H(h1-C3H5), andintramolecular nitrene insertion (Scheme 1, A). The final two stepsof this sequence could be more rapid than C–H bond reductiveelimination, and this mechanism provides a rationalization foramide formation occurring more rapidly than olefin elimination,but invokes a highly reactive Rh imido species.

An alternative pathway (Scheme 1, B) might involve an eighteenelectron rhodium triazenide intermediate that does not requirehigh valent rhodium. However, this intermediate is precededby a terminally-coordinated azide species such as ToMRhH(h1-C3H5)(NgNNTs). One might expect rapid C–H bond reductiveelimination for this intermediate, as is observed in treatment of 1or 3 with the ligands CO or CNtBu. All three of these reagentscould react by 1,1-insertion, but instead CO and CNtBu promotereductive elimination. These contradictions are rationalized bymechanisms involving reversible insertion of TsN3, CO, andCNtBu into Rh–H, and only the azide insertion product is irre-versibly trapped by 1,3-coordination, 1,3-hydrogen migration andN2 elimination. Additional support for the triazenide mechanismis based on the previous reports (described above) of isolable k2-triazenide ligands forming by insertion of organoazide, as wellas the current limitation of this nitrene insertion chemistry totosylazide. Both mechanisms, importantly, involve interaction ofTsN3 and a rhodium species, as TsN3 does not afford free nitrenespontaneously.

An open coordination site is needed for azide activation; this sitecould be accessed either by oxazoline dissociation to form a {k2-ToM}RhH(h3-allyl) intermediate or via an h3-s-allyl isomerizationthrough the {k3-ToM}RhH(s-allyl) species. The initial interactionsof TsN3 and ToMRhH(h3-C8H13) are proposed to involve the latterbecause b-hydrogen elimination to give 1,3-cyclooctadiene and{k3-ToM}RhH(NHTs)(OH2) is more likely to occur from a s-allylintermediate (Scheme 2). The bulkier cyclooctenyl allyl 1 and TsN3

react more rapidly than the parent allyl 3, and the relative reactionrates provide further support for a dissociative pathway involvingthe allyl group. Finally, b-hydrogen elimination was also reportedfor a reaction of {BP3}IrH(h3-C8H13), where phosphine armdissociation is less likely than oxazoline arm dissociation in thepresent system. b-Elimination in our system requires interactionof the two reactants (i.e., tosylazide coordination), as 1 doesnot spontaneous form 1,3-cyclooctadiene even upon thermolysis(which gives cyclooctene). The sequence of steps following theinitial interaction of tosylazide and 1 likely involves b-eliminationsubsequent to tosylamide formation, again because CO inducesC–H bond reductive elimination rather than 1,3-cyclooctadieneelimination.

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Scheme 1 Possible mechanisms for the reaction of ToMRhH(h3-C3H5) (3) and tosylazide that gives a rhodium tosylamide. Pathway A invokes coordinationof the more nucleophilic Na of the organoazide, followed by N2 elimination to give a highly reactive rhodium nitrene. Pathway B involves end-on tosylazidecoordination, 1,1-insertion, 1,3-hydrogen migration, and nitrogen elimination.

Scheme 2 Proposed mechanism for divergent pathways in reactions of 1 and 3 with tosylazide.

15N NMR chemical shifts of tris(oxazolinyl)borate M(III) (M = Rh,Ir) compounds

31P NMR spectroscopy is routine for structural assignments ofcoordination complexes, and 31P NMR chemical shift data arewidely reported.35 In contrast, the low natural abundance and lowgyromagnetic ratio of the 15N nucleus has limited direct detectionmethods in 15N NMR spectroscopy for the characterization ofcoordination complexes. Indirect 15N NMR detection methodscan bypass this problem and provide chemical shift data, and 2Dheteronuclear correlation spectroscopy is also very powerful for as-signing structure. A few recent studies have highlighted the powerof 15N NMR measurements (at natural abundance) using het-eronuclear correlation methods, including identification of the co-ordination modes of tris(pyrazolyl)borate rhodium compounds.26

15N NMR chemical shifts have been reported for a series of latemetal compounds with pyridine-type ligands,36 cyclometalatedimidazoles,37 and metal-coordinated oxazolines.22,24,38,39,40 We havealso observed through-metal 1H-15N correlations in ToMMgMe,ToMAlMe2, as well as in ToMRhCl(CHCl2)CO that demonstratethat both oxazoline and alkyl ligands are bonded to the samemetal center.24c,39 The through-metal correlations described abovefor compounds 1–5 provide information into the metal center’sconfiguration.

15N NMR chemical shifts trends could also be useful forstructural assignments, and the series of ToMRhXX¢L compoundsreported here show general trends in 15N NMR shifts that relateto the transoid ligand. In Table 1, we compare 15N NMR chemicalshift values relative to the trans ligand and M-N distances for thecompounds reported in the current contribution.

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Table 1 15N NMR chemical shift data and M-N distances for oxazoline nitrogen in ToMMXX¢L compounds

Compound 15N trans to hydrideM–N distancetrans to H (A) 15N trans to allyl

M–N distancetrans to allyl

15N trans to aheteroatomic ligand

ToMRhH(h3-C8H13) (1) -164.2 n.a.a -173.4 n.a.a n.a.c

endo-ToMRhH(h3-C3H5) (endo-3) -165.6 2.298(3) -173.8 2.107(3) 2.109(3) n.a.c

exo-ToMRhH(h3-C3H5) (exo-3) -164.8 2.223(3) -173.1 2.141(3) 2.128(3) n.a.c

ToMRhH(h3-C3H4Ph) (5) -179.9 2.280(3) -168.2, -172.1 2.101(3) 2.132(3) n.a.c

ToMRhBr(h3-C3H4Ph) (9) n.a.b n.a.a ,b -191.1, -181.5 n.a.a -217.6 (Br)ToMRh(NHTs)(h3-C3H5) (10) n.a.b n.a.b -177.6 2.140(2) 2.121(3) -225.4 (NHTs)ToMRhH(NHTs)OH2 (11) -154.1 2.234(6) n.a.d n.a.d -228.6 (NHTs) -205.8 (OH2)ToMRhH(k2-O2CMe) (8) -154.3 2.20(1) n.a.d n.a.d -221.0 (OAc)ToMIrH(h3-C8H13) (2) -182.6 n.a. -190.6 n.a.a n.a.c

ToMIrH(h3-C3H5) (4) -184.9 n.a. -189.5 n.a.a n.a.c

a An X-ray crystal structure was not obtained. b The compound does not contain a metal hydride. c The compound does not contain a heteroatomicligand. d The compound does not contain an allyl group.

The 15N chemical shift of the oxazoline trans to the strong-field hydride ligand is farthest downfield for compounds 1–4. Thechemical shifts for rhodium complexes are ca. 20 ppm fartherupfield than the corresponding iridium congener. Additionally, the15N chemical shift of the oxazoline trans to hydride for the C8H13

complexes is systematically 1–2 ppm downfield in comparisonto the shift for the C3H5 complexes. However, the 15N NMRchemical shift of the hydride in ToMRhH(h3-C3H4Ph) is not thefarthest downfield in that compound, and it is approximately15 ppm upfield with respect to the other rhodium allyl com-pounds. The oxazoline trans to the tosylamide has the farthestupfield 15N NMR chemical shift, and those trans to weak-fieldbromide, water, and acetate ligands also have upfield chemicalshifts.

The hydride ligands have the strongest trans influence, asshown in Table 1 by their long Rh–N distances. However, 15NNMR chemical shifts of the oxazolines do not track with theapparent trans influence of hydride, allyl, and amido ligands. Forexample, although the Rh–Noxazoline distances trans to hydride aresignificantly longer than Rh–Noxazoline distances trans to h3-allylligands, the chemical shifts range for these two ligands are similar.Additionally, while the 15N NMR chemical shifts of the oxazolinetrans to tosylamide are 35 ppm upfield of those trans to allyl,the Rh–Noxazoline distances are similar for groups trans to allyl andamide ligands.

Conclusion

We have shown that a tris(oxazolinyl)borate ligand is a suitableancillary for rhodium(I)- and iridium(I)-mediated allylic C–Hbond oxidative addition for cyclooctene, propene and allylbenzenesubstrates under thermal (non-photolytic) conditions. Thermalallylic C–H bond activations with iridium(I) tris(pyrazolyl)borateand tris(phosphino)borate compounds had been previouslybeen described,12,13,14,15 but examples of rhodium(I)-mediatedallylic C–H bond activation were limited to photochemicalactivations.16,17

Our attempts to develop methods for functionalization ofthe allyl hydrides have uncovered the first example of (formal)nitrene insertion into rhodium-hydrogen bonds. The mecha-nism for this insertion may involve either rhodium nitrene or

rhodium triazenide intermediates; we are currently investigat-ing reactions of other organoazides with tris(oxazolinyl)boratorhodium compounds to better understand the mechanismand identify intermediates in the formation of rhodiumamides.

C–N bond formation via reductive elimination from arhodium(III) allyl amide is facilitated by carbon monoxide. Themechanism for C–N bond formation does not necessarily requirean allylic group (as in iridium-catalyzed allylation chemistry) asthe hydrocarbyl moiety is bonded in a s-only fashion prior toelimination. Thus, the sequence described here may potentiallybe applied to the functionalization of non-allylic hydrocarbonsubstrates. This sequence, (a) C–H bond oxidative addition, (b)azide-mediated amination, and (c) C–N bond reductive elimi-nation simply requires an accessible coordination site followingthe C–H bond activation step. While this open coordinationsite is provided by isomerization of ToMRhH(h3-C3H5) to thes-allyl form, dissociation of a hemilabile ancillary ligand couldalso provide such an open site. In that case, re-coordination ofthe hemilabile ligand might also mediate reductive eliminationand facilitate catalysis. We are currently considering such designfeatures for the development of new processes.

Experimental

General procedures

All reactions were carried out under an inert atmosphere usingstandard Schlenk techniques or in a glovebox. All solventswere dried and degassed unless otherwise indicated. All reagentswere purchased from Sigma–Aldrich and used without furtherpurification. Tl[ToM],24c [Rh(m-Cl)(h2-C8H14)2]2,41a [Ir(m-Cl)(h2-C8H14)2]2,41b and TsN3

41c were prepared according to reportedprocedures. All NMR spectra were obtained at room temperatureusing Bruker DRX-400 and Avance II-700 spectrometers. 15NNMR chemical shifts were determined by 1H-15N HMBC exper-iments recorded on an Avance II-700 spectrometer; the chemicalshift values are reported relative to CH3NO2. 11B NMR spectrachemical shifts are reported relative to BF3·Et2O. GC-MS datawere obtained on an Agilent 7890 A GC system containing anHP-5MS capillary column and an Agilent 5975C mass selective

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detector. Elemental analyses were obtained at the Iowa StateChemical Instrumentation Facility using a Perkin–Elmer 2400Series II CHN/S. Single crystal X-ray analysis was carried outon a Bruker APEX2 CCD Diffractometer.

ToMRhH(g3-C8H13) (1). Benzene (50 mL) was added to asolid mixture of Tl[ToM] (0.187 g, 0.319 mmol) and [Rh(m-Cl)(h2-C8H14)2]2 (0.160 g, 0.223 mmol) giving a suspension. The resultingmixture was stirred at room temperature for 5 h and then filtered.The solvent was removed from the filtrate under reduced pressure.The resulting residue was extracted with pentane (3 ¥ 25 mL),and the extractions were combined and evaporated to dryness togive analytically pure ToMRh(h3-C8H13) (1, 0.134 g, 0.225 mmol,70.6%) as a brown solid in good yield. 1H NMR (benzene-d6,400 MHz): d 8.45 (d, 2 H, 3JHH = 7.6 Hz, ortho-C6H5), 7.58 (t,2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H, 3JHH = 7.2 Hz,para-C6H5), 5.16 (t, 1 H, CH(CH)2(CH2)5, 3J HH = 8.0 Hz), 3.95(dd, 2 H, 3JHH = 16.4 Hz, 3JHH = 8.0 Hz, CH(CH)2(CH2)5), 3.74(d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O), 3.60 (d, 2 H, 2JHH =8.4 Hz, CNCMe2CH2O), 3.33 (s, 2 H, CNCMe2CH2O),2.51 (m, 2 H, (CH)3CH2(CH2)3CH2), 2.21 (m, 1 H,(CH)3(CH2)2CH2(CH2)2), 1.74 (m, 2 H, (CH)3CH2(CH2)3CH2),1.50 (m, 1 H, (CH)3(CH2)2CH2(CH2)2), 1.45 (m, 4 H,(CH)3CH2CH2CH2CH2CH2), 1.17 (s, 6 H, CNCMe2CH2O), 1.12(s, 6 H, CNCMe2CH2O), 0.82 (s, 6 H, CNCMe2CH2O), -24.27(d, 1 H, 1JRhH = 11.6 Hz, RhH). 13C{1H} NMR (benzene-d6,175 MHz): d 136.81 (ortho-C6H5), 126.93 (meta-C6H5), 125.75(para-C6H5), 93.93 (d, 1JRhC = 6.0 Hz, CH(CH)2(CH2)5), 81.96(CNCMe2CH2O), 80.93 (CNCMe2CH2O), 68.41 (CNCMe2-CH2O), 67.92 (CNCMe2CH2O), 52.15 (d, 1JRhC = 11.4 Hz,CH(CH)2(CH2)5), 38.41 ((CH)3CH2(CH2)3CH2), 29.52((CH)3CH2CH2CH2CH2CH2), 29.49 ((CH)3CH2CH2CH2-CH2CH2), 28.82 (CNCMe2CH2O), 28.57 (CNCMe2CH2O), 28.33(CNCMe2CH2O). 11B NMR (benzene-d6, 128 MHz): d -18.7. 15NNMR (benzene-d6, 71 MHz): d -164.2 (trans to RhH), -173.4(cis to RhH). IR (KBr, cm-1): n 3076 (w), 3040 (w), 2959 (m),2927 (m), 2843 (m), 2158 (m, nRhH), 1598 (s, nCN), 1462 (m), 1383(m), 1363 (m), 1275 (m), 1195 (m), 1156 (m), 996 (m), 972 (m),933 (w). Anal. Calcd. for C29H43BRhN3O3: C, 58.50; H, 7.28; N,7.06. Found: C, 58.85; H, 7.48; N, 7.10. Mp: 132–135 ◦C, dec.

ToMIrH(g3-C8H13) (2). A 100 mL Schlenk flask wascharged with Tl[ToM] (0.24 g, 0.41 mmol), [Ir(m-Cl)(h2-C8H14)2]2

(0.19 g, 0.21 mmol) and benzene (50 mL). The mixture wasstirred for one day and then was filtered. The filtrate wasevaporated, and the resulting yellow solid was washed withpentane (10 mL). The filtrate was dried in vacuo to yield 2as a light brown solid (0.22 g, 0.32 mmol, 78%). 1H NMR(benzene-d6, 400 MHz): d 8.42 (d, 2 H, 3JHH = 7.2 Hz, ortho-C6H5), 7.58 (t, 2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H,3JHH = 7.2 Hz, para-C6H5), 4.79 (t, 1 H, CH(CH)2(CH2)5, 3JHH = 8.0 Hz), 3.98 (dd, 2 H, 3JHH = 17.0 Hz, 3JHH = 8.0 Hz,CH(CH)2(CH2)5), 3.77 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.61 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O), 3.32 (s, 2 H,CNCMe2CH2O), 2.60 (m, 2 H, (CH)3CH2(CH2)3CH2),2.37 (m, 1 H, (CH)3(CH2)2CH2(CH2)2), 1.72 (m, 2 H,(CH)3CH2(CH2)3CH2), 1.61 (m, 1 H, (CH)3(CH2)2CH2(CH2)2),1.45 (m, 4 H, (CH)3CH2CH2CH2CH2CH2), 1.17 (s, 6 H,CNCMe2CH2O), 1.08 (s, 6 H, CNCMe2CH2O), 0.80 (s, 6 H,CNCMe2CH2O), -28.54 (s, 1 H, IrH). 13C{1H} NMR (benzene-

d6, 175 MHz): d 136.66 (ortho-C6H5), 127.06 (meta-C6H5), 125.98(para-C6H5), 83.20 (CH(CH)2(CH2)5), 81.49 (CNCMe2CH2O),81.18 (CNCMe2CH2O), 69.46 (CNCMe2CH2O), 69.07(CNCMe2CH2O), 39.47 (CH(CH)2(CH2)5), 33.62 ((CH)2-CH2(CH2)3CH2), 30.77 ((CH)3CH2CH2CH2CH2CH2), 30.55((CH)3CH2CH2CH2CH2CH2), 28.55 (CNCMe2CH2O), 28.50(CNCMe2CH2O), 28.23 (CNCMe2CH2O). 11B NMR (benzene-d6,128 MHz): d -17.7. 15N NMR (benzene-d6, 71 MHz): d -182.6(trans to IrH), -190.6 (cis to IrH). IR (KBr, cm-1): n 2962 (s),2925 (s, sh), 2253 (m, nIrH), 1589 (s, nCN), 1463 (w), 1355 (w), 1282(m), 1262 (m), 1200 (m), 1158 (m), 1094 (w), 966 (m), 801 (m),705 (m). Anal. Calcd. for C29H43BIrN3O3: C, 50.87; H, 6.33; N,6.14 Found: C, 50.88 H, 6.80 N, 6.38. Mp: 158 ◦C, dec.

ToMRhH(g3-C3H5) (3). Propene was bubbled through a solu-tion of [Rh(m-Cl)(h2-C8H14)2]2 (0.500 g, 0.697 mmol) in benzene(100 mL) for 10 min to form [Rh(m-Cl)(h2-C3H6)2]2. Tl[ToM](0.56 g, 0.96 mmol) was added as a solid to the [Rh(m-Cl)(h2-C3H6)2]2 solution at room temperature, and the resulting mixturewas stirred for 1 h. The solution was then filtered, and the volatilematerials in the filtrate were evaporated to dryness. The resultingresidue was extracted with pentane (3 ¥ 50 mL) and stored at-35 ◦C overnight. The solids were then collected as an analyticallypure, light-brown, flaky powder (0.39 g, 76%). This powder wasthen recrystallized from toluene at -30 ◦C to obtain X-ray qualitycrystals of co-crystallized exo-3 and endo-3. IR (KBr, cm-1): n3075 (m), 3035 (m), 2967 (m), 2927 (m), 2899 (m), 2090 (s, nRhH),2080 (s, nRhH), 1598 (s, nCN), 1567 (m, nCN), 1460 (m), 1382 (m),1365 (m), 1351 (m), 1275 (m), 1197 (m), 1155 (m), 1021 (w), 992(m), 975 (m), 902 (m), 703 (m). Anal. Calcd. for C24H35BRhN3O3:C, 54.67; H, 6.69; N, 7.97. Found: C, 54.71; H, 6.37; N, 7.71.Mp: 204–206 ◦C, dec. Although the two conformers are notindependently isolated, the NMR spectroscopic data for each isprovided separately to facilitate interpretation. exo-3: 1H NMR(benzene-d6, 400 MHz): d 8.46 (d, 2 H, 3JHH = 7.6 Hz, ortho-C6H5),7.58 (t, 2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H, 3JHH = 7.6 Hz,para-C6H5), 4.91 (m, 1 H, CH(CH2)2), 3.66 (d, 2 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.61 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.34 (s, 2 H, CNCMe2CH2O), 2.91 (d, 2 H, 3JHH = 7.2 Hz, syn-CH(CH2)2), 2.28 (d, 2 H, 3JHH = 11.6 Hz, anti-CH(CH2)2), 1.05(s, 6 H, CNCMe2CH2O), 1.02 (s, 6 H, CNCMe2CH2O), 0.79 (s,6 H, CNCMe2CH2O), -23.20 (d, 1 H, 1JRhH = 10.0 Hz, RhH).13C{1H} NMR (benzene-d6, 175 MHz): d 136.71 (ortho-C6H5),126.97 (meta-C6H5), 125.78 (para-C6H5), 93.41 (d, 1JRhC = 7.0 Hz,CH(CH2)2), 81.82 (CNCMe2CH2O), 80.53 (CNCMe2CH2O),69.00 (CNCMe2CH2O), 67.74 (CNCMe2CH2O), 32.99 (d,1JRhC = 10.5 Hz, CH(CH2)2), 28.72 (CNCMe2CH2O), 28.38(CNCMe2CH2O), 28.11 (CNCMe2CH2O). 11B NMR (benzene-d6, 128 MHz): d -18.4. 15N NMR (benzene-d6, 71 MHz): d -165.6(trans to RhH), -173.1 (cis to RhH). endo-3: 1H NMR (benzene-d6, 400 MHz): d 8.56 (d, 2 H, 3JHH = 6.8 Hz, ortho-C6H5), 7.63(t, 2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.41 (t, 1 H, 3JHH = 7.2 Hz,para-C6H5), 5.10 (m, 1 H, CH(CH2), 3.64 (d, 2 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.47 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.29 (s, 2 H, CNCMe2CH2O), 3.01 (d, 2 H, 3JHH = 7.2 Hz, syn-CH(CH2)2), 2.51 (d, 2 H, 3JHH = 11.2 Hz, anti-CH(CH2)2), 0.94(s, 6 H, CNCMe2CH2O), 0.79 (s, 6 H, CNCMe2CH2O), 0.76(s, 6 H, CNCMe2CH2O), -22.74 (s, br, 1 H, RhH). 13C{1H}NMR (benzene-d6, 175 MHz): d 136.77 (ortho-C6H5), 127.05

6510 | Dalton Trans., 2011, 40, 6500–6514 This journal is © The Royal Society of Chemistry 2011

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(meta-C6H5), 125.81 (para-C6H5), 88.28 (d, 1JRhC = 7.0 Hz,CH(CH2)2), 80.11 (CNCMe2CH2O), 79.97 (CNCMe2CH2O),69.53 (CNCMe2CH2O), 67.36 (CNCMe2CH2O), 37.46 (d,1JRhC = 10.5 Hz, CH(CH2)2), 28.38 (CNCMe2CH2O), 27.85(CNCMe2CH2O), 27.63 (CNCMe2CH2O). 11B NMR (benzene-d6, 128 MHz): d -17.7. 15N NMR (benzene-d6, 71 MHz): d -164.8(trans to RhH), -173.8 (cis to RhH).

ToMIrH(g3-C3H5) (4). In a 100 mL Schlenk flask, propenewas bubbled through a solution of [Ir(m-Cl)(h2-C8H14)2]2 (0.100 g,0.112 mmol) in benzene (30 mL) for 10 min. Tl[ToM] (0.125 g,0.213 mmol) was added to the solution at room temperature andstirred overnight. The solution was then filtered and evaporatedto dryness. The residue was washed with pentane (10 mL) anddried in vacuo to yield the product as a yellow-brown solid(0.096 g, 0.16 mmol, 73%). 1H NMR (benzene-d6, 400 MHz):d 8.43 (d, 2 H, 3JHH = 7.2 Hz, ortho-C6H5), 7.58 (t, 2 H,3JHH = 7.6 Hz, meta-C6H5), 7.38 (t, 1 H, 3JHH = 7.6 Hz, para-C6H5), 4.28 (m, 1 H, CH(CH2)2), 3.68 (d, 2 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.62 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.33 (s, 2 H, CNCMe2CH2O), 3.07 (d, 2 H, 3JHH = 6.8 Hz,syn-CH(CH2)2), 2.43 (d, 2 H, 3JHH = 10.0 Hz, anti-CH(CH2)2),1.05 (s, 6 H, CNCMe2CH2O), 1.02 (s, 6 H, CNCMe2CH2O),0.76 (s, 6 H, CNCMe2CH2O), -27.64 (s, 1 H, IrH). 13C{1H}NMR (benzene-d6, 175 MHz): d 136.58 (ortho-C6H5), 127.13(meta-C6H5), 126.05 (para-C6H5), 82.89 (CNCMe2CH2O), 80.76(CNCMe2CH2O), 79.13 (CH(CH2)2), 70.17 (CNCMe2CH2O),69.04 (CNCMe2CH2O), 28.44 (CNCMe2CH2O), 28.37(CNCMe2CH2O), 28.26 (CNCMe2CH2O), 16.53 (CH(CH2)2). 11BNMR (benzene-d6, 128 MHz): d -17.4. 15N NMR (benzene-d6,71 MHz): d -184.9 (trans to IrH), -189.5 (cis to IrH). IR(KBr, cm-1): n 3040 (w), 2963 (m), 2926 (m), 2212 (m, nIrH),1658.5 (w), 1595 (s, nCN), 1461 (w), 1383 (w), 1357 (w), 1282(s), 1263 (m), 1198 (m), 1160 (w), 1095 (w), 966 (w), 803 (s),655 (s), 603 (m). Anal. Calcd. for C24H35BIrN3O3: C, 46.75; H,5.72 N, 6.82. Found: C, 46.23; H, 6.22; N, 6.38. Mp: 144 ◦C,dec.

ToMRhH(g3-C3H4Ph) (5). Allylbenzene (0.59 mL) and [Rh(m-Cl)(h2-C8H14)2]2 (0.159 g, 0.22 mmol) were allowed to react inbenzene (10 mL) for 30 min to generate [Rh(m-Cl)(h2-C3H5Ph)2]2.Tl[ToM] (0.26 g, 0.44 mmol) was then added, and the resultingmixture was stirred overnight. The solids were removed byfiltration and the filtrate was evaporated to dryness. The residuewas washed with pentane (2 ¥ 2 mL) and the resulting solidwas dissolved in toluene (10 mL). The toluene solution wasconcentrated to 0.5 mL and the solid was collected as a greenpowder (0.160 g, 0.265 mmol, 59.8%). 1H NMR (benzene-d6,400 MHz): d 8.51 (d, 2 H, 3JHH = 7.6 Hz, ortho-C6H5), 7.60 (t,2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.44 (d, 2 H, 3JHH = 7.6 Hz,ortho-CH2CHCHPh), 7.39 (t, 1 H, 3JHH = 7.6 Hz, para-C6H5), 7.11(t, 2 H, 3JHH = 7.2 Hz, meta-CH2CHCHPh), 7.09 (t, 1 H, 3JHH =7.2 Hz, para-CH2CHCHPh), 5.62 (m, 1 H, CH2CHCHPh),3.98 (d, 1 H, 3JHH = 10.4 Hz, CH2CHCHPh), 3.64 (d, 1 H,2JHH = 8.4 Hz, CNCMe2CH2O), 3.48 (dd, 2 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.40 (dd, 2 H, 2JHH = 8.0 Hz, CNCMe2CH2O),3.22 (d, 1 H, 3JHH = 9.6 Hz, syn-CH2CHCHPh), 3.20 (d, 1 H,2JHH = 8.4 Hz, CNCMe2CH2O), 2.84 (d, 1 H, 3JHH = 11.2 Hz,anti-CH2CHCHPh), 1.02 (s, 3 H, CNCMe2CH2O), 0.91 (s,3 H, CNCMe2CH2O), 0.83 (s, 3 H, CNCMe2CH2O), 0.76

(s, 3 H, CNCMe2CH2O), 0.72 (s, 3 H, CNCMe2CH2O), 0.39(s, 3 H, CNCMe2CH2O), -22.48 (s, br, 1 H, RhH). 13C{1H}NMR (benzene-d6, 175 MHz): d 145.57 (ipso-CH2CHCHPh),136.74 (ortho-C6H5), 129.43 (meta-CH2CHCHPh), 129.21(ortho-CH2CHCHPh), 127.09 (meta-C6H5), 125.86 (para-C6H5), 125.54 (para-CH2CHCHPh), 90.06 (d, 1JRhC = 3.5 Hz,CH2CHCHPh), 81.39 (CNCMe2CH2O), 79.89 (CNCMe2CH2O),79.38 (CNCMe2CH2O), 69.91 (CNCMe2CH2O), 68.06(CNCMe2CH2O), 67.56 (CNCMe2CH2O), 54.52 (d, 1JRhC =10.5 Hz, CH2CHCHPh), 36.54 (d, 1JRhC = 12.25 Hz,CH2CHCHPh), 28.52 (CNCMe2CH2O), 27.91 (CNCMe2CH2O),27.59 (CNCMe2CH2O), 27.48 (CNCMe2CH2O), 27.03(CNCMe2CH2O), 26.89 (CNCMe2CH2O). 11B NMR (benzene-d6,128 MHz): d -19.7. 15N NMR (benzene-d6, 71 MHz): d -168.17(cis to RhH), -172.10 (cis to RhH), -179.94 (trans to RhH). IR(KBr, cm-1): n 3041 (m), 2967 (m), 2927 (m), 2882 (m), 2081(m, nRhH), 1590 (s, nCN), 1462 (w), 1366 (m), 1351 (m), 1276 (m),1198 (m), 1177 (m), 1153 (m), 1022 (w), 999 (m), 970 (m). Anal.Calcd. for C30H39BRhN3O3: C, 59.72; H, 6.52; N, 6.96. Found: C,60.18; H, 6.11; N, 6.88. Mp: 191–192 ◦C, dec.

ToMRh(CNtBu)2 (7). CNtBu (51 mL, 0.46 mmol) was added toa benzene solution of ToMRhH(h3-C8H13) (0.138 g, 0.232 mmol).The resulting solution was stirred for 2 h, and then the volatilematerials were evaporated under reduced pressure. The residue wasthen washed with ether to give a yellow solid (0.100 g, 0.153 mmol,66.2%). 1H NMR (benzene-d6, 400 MHz): d 8.42 (d, 2 H, 3JHH =7.2 Hz, ortho-C6H5), 7.48 (t, 2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.25(t, 1 H, 3JHH = 7.2 Hz, para-C6H5), 3.71 (s, 6 H, CNCMe2CH2O),1.35 (s, 18 H, CNCMe2CH2O), 0.97 (s, 18 H, CNCMe3). 13C{1H}NMR (benzene-d6, 175 MHz): d 135.47 (ortho-C6H5), 128.50 (d,1JRhC = 63.5 Hz, RhCNCMe3), 127.35 (meta-C6H5), 125.37 (para-C6H5), 79.00 (CNCMe2CH2O), 68.33 (CNCMe2CH2O), 55.98(CNCMe3), 30.76 (CNCMe2CH2O), 28.70 (CNCMe3). 11B NMR(benzene-d6, 128 MHz): d -18.0. 15N NMR (benzene-d6, 71 MHz):d -159.6 (CNCMe2CH2O), -201.1 (CNCMe3). IR (CH2Cl2, cm-1):n 2962 (m), 2924 (m), 2892 (m), 2865 (w), 2208 (w, nC N), 2147(s, nC N), 2103 (s, nC N), 2068 (s, nC N), 1614 (m, nC N), 1585 (s,nC N), 1460 (m), 1431 (w), 1368 (m), 1352 (m), 1274 (m), 1196 (m),1173 (w), 1162 (w), 1119 (w), 1036 (w), 966 (m). Anal. Calcd. forC31H47BN5O3Rh: C, 57.15; H, 7.27; N, 10.75 Found: C, 57.00; H,6.94; N, 10.32. Mp: 216–219 ◦C dec.

ToMRhH(j2-O2CMe) (8). Acetic acid (0.021 g, 0.346 mmol)and ToMRhH(h3-C8H13) (0.103 g, 0.173 mmol) were allowed toreact in benzene (10 mL) at room temperature for 10 min. Theresulting mixture was then evaporated to dryness. The residuewas extracted with pentane (15 mL), dried under vacuum,and crystallized in toluene at -35 ◦C to give a brown solid(0.043 g, 0.076 mmol, 44.0%). 1H NMR (benzene-d6, 400 MHz):d 8.40 (d, 2 H, 3JHH = 7.2 Hz, ortho-C6H5), 7.57 (t, 2 H, 3JHH =7.6 Hz, meta-C6H5), 7.38 (t, 1 H, 3JHH = 7.2 Hz, para-C6H5),3.78 (s, 2 H, CNCMe2CH2O), 3.52 (d, 2 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.47 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O),1.59 (s, 3 H, O2CMe), 1.25 (s, 6 H, CNCMe2CH2O), 1.17 (s, 6 H,CNCMe2CH2O), 1.11 (s, 6 H, CNCMe2CH2O), -13.23 (d, 1 H,1JRhH = 11.6 Hz, RhH). 13C{1H} NMR (benzene-d6, 175 MHz): d190.29 (O2CMe), 136.31 (ortho-C6H5), 127.36 (meta-C6H5), 126.38(para-C6H5), 82.22 (CNCMe2CH2O), 80.33 (CNCMe2CH2O),68.42 (CNCMe2CH2O), 67.03 (CNCMe2CH2O), 28.38

This journal is © The Royal Society of Chemistry 2011 Dalton Trans., 2011, 40, 6500–6514 | 6511

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(CNCMe2CH2O), 27.66 (CNCMe2CH2O), 23.91 (O2CMe).11B NMR (benzene-d6, 128 MHz): d -18.2. 15N NMR(benzene-d6, 71 MHz): d -154.3 (trans to RhH), -221.0 (cisto RhH). IR (KBr, cm-1): n 2963 (m), 2927 (m), 2076 (m, nRhH),1597 (s, nCN), 1470 (s, nCOO), 1387 (w), 1367 (m), 1284 (m), 1263(m), 1202 (m), 1162 (m), 1026 (w), 999 (w), 968 (m). Anal.Calcd. for C23H33BRhN3O5: C, 50.66; H, 6.10; N, 7.71. Found: C,51.05; H, 6.23; N, 7.50. Mp 115–118 ◦C, dec.

ToMRhBr(g3-C3H4Ph) (9). A benzene solution of ToMRhH(h3-C3H4Ph) (0.104 g, 0.172 mmol) and NBS (0.031 g, 0.174 mmol)was stirred at room temperature overnight. The resulting solutionwas evaporated to dryness and washed with pentane (2 mL)and ether (4 ¥ 1.5 mL). The residue was dried under vacuumto give a brown solid (0.049 g, 0.072 mmol, 42%). 1H NMR(methylene chloride-d2, 700 MHz): d 7.91 (d, 2 H, 3JHH = 6.3 Hz,ortho-CH2CHCHPh), 7.79 (d, 2 H, 3JHH = 7.0 Hz, ortho-C6H5),7.39 (t, 1 H, 3JHH = 7.0 Hz, para-CH2CHCHPh), 7.33 (t,2 H, 3JHH = 7.7 Hz, meta-CH2CHCHPh), 7.21 (t, 2 H, 3JHH =7.0 Hz, meta-C6H5), 7.14 (t, 1 H, 3JHH = 7.0 Hz, para-C6H5),6.54 (m, 1 H, CH2CHCHPh), 5.43 (d, 1 H, 3JHH = 13.3 Hz,CH2CHCHPh), 4.45 (d, 1 H, 3JHH = 8.4 Hz, syn-CH2CHCHPh),4.14 (d, 1 H, 3JHH = 11.9 Hz, anti-CH2CHCHPh), 4.11 (d, 1 H,2JHH = 7.7 Hz, CNCMe2CH2O), 3.98 (d, 1 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.96 (d, 1 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.92 (d, 1 H, 2JHH = 7.7 Hz, CNCMe2CH2O), 3.77 (d, 1 H,2JHH = 7.7 Hz, CNCMe2CH2O), 3.70 (d, 1 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 1.52 (s, 3 H, CNCMe2CH2O), 1.40 (s,3 H, CNCMe2CH2O), 1.31 (s, 3 H, CNCMe2CH2O), 1.18 (s,3 H, CNCMe2CH2O), 0.98 (s, 3 H, CNCMe2CH2O), 0.75 (s,3 H, CNCMe2CH2O). 13C{1H} NMR (methylene chloride-d2,175 MHz): d 141.77 (ipso-CH2CHCHPh), 135.85 (ortho-C6H5),129.38 (meta-CH2CHCHPh), 128.61 (ortho-CH2CHCHPh),127.04 (para-CH2CHCHPh), 126.59 (meta-C6H5), 125.67(para-C6H5), 112.29 (CH2CHCHPh), 81.40 (CNCMe2CH2O),80.74 (CNCMe2CH2O), 80.56 (CNCMe2CH2O), 72.26(CNCMe2CH2O), 72.12 (CNCMe2CH2O), 70.22 (CNCMe2-CH2O), 64.71 (CH2CHCHPh), 37.34 (d, 1JRhC = 12.25 Hz,CH2CHCHPh), 28.18 (CNCMe2CH2O), 27.86 (CNCMe2CH2O),27.81 (CNCMe2CH2O), 27.45 (CNCMe2CH2O), 26.75(CNCMe2CH2O), 26.21 (CNCMe2CH2O). 11B NMR (methylenechloride-d2, 128 MHz): d -18.2. 15N NMR (methylene chloride-d2, 71 MHz): d -181.5 (cis to RhBr), -191.1 (cis to RhBr),-217.6 (trans to RhBr). IR (KBr, cm-1): n 3039 (w), 2975 (w),2883 (w), 1590 (s, nCN), 1466 (w), 1387 (w), 1368 (w), 1286 (m),1245 (w), 1202 (m), 1028 (w), 1001 (w), 973 (m). Anal. Calcd.for C30H38BRhN3O3Br: C, 52.81; H, 5.61; N, 6.16; Found: C,52.86; H, 5.48; N, 5.90. Mp: 215–218 ◦C, dec.

exo-ToMRh(NHTs)(g3-C3H5) (10). ToMRhH(h3-C3H5)H(0.101 g, 0.192 mmol) was added to a solution of TsN3 (38 mg,0.19 mmol) in benzene (10 ml). The resulting solution was stirredfor 24 h. The benzene solvent was evaporated in vacuo, and theresidue was dissolved in a minimal amount of toluene and cooledto -30 ◦C for crystallization. Orange needles were collectedby filtration at -30 ◦C, giving analytically pure ToMRh(h3-C3H5)NHTs (10) in good yield (0.109 g, 0.157 mmol, 81.7%). 1HNMR (benzene-d6, 400 MHz): d 8.26 (d, 2 H, 3JHH = 7.2 Hz,ortho-C6H5), 7.86 (d, 2 H, 3JHH = 8.4 Hz, ortho-C6H4Me), 7.54 (t,2 H, 3JHH = 7.6 Hz, meta-C6H5), 7.36 (t, 1 H, 3JHH = 7.2 Hz, para-

C6H5), 6.87 (d, 2 H, 3JHH = 8.0 Hz, meta-C6H4Me), 5.60 (m, 1 H,CH(CH2)2), 5.17 (d, 2 H, 3JHH = 12.4 Hz, anti-CH(CH2)2), 4.19(d, 2 H, 3JHH = 8.8 Hz, syn-CH(CH2s)2), 3.58 (d, 2 H, 2JHH = 8.0,CNCMe2CH2O), 3.39 (d, 2 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.03 (s, 2 H, CNCMe2CH2O), 1.97 (s, 3 H, C6H4Me), 1.40 (s,6 H, CNCMe2CH2O), 0.92 (s, 6 H, CNCMe2CH2O), 0.37 (s,6 H, CNCMe2CH2O). 13C{1H} NMR (benzene-d6, 175 MHz):d 147.44 (ipso-C6H4Me), 140.17 (para-C6H4Me), 136.40 (ortho-C6H5), 129.34 (meta-C6H4Me), 127.18 (meta-C6H5), 126.71(ortho-C6H4Me), 126.32 (para-C6H5), 103.09 (d, 1JRhC = 5.3 Hz,CH(CH2)2), 82.78 (CNCMe2CH2O), 80.63 (CNCMe2CH2O),70.07 (CNCMe2CH2O), 69.08 (CNCMe2CH2O), 47.49 (d,1JRhC = 10.5 Hz, CH(CH2)2), 28.31 (CNCMe2CH2O), 27.58(CNCMe2CH2O), 27.51 (CNCMe2CH2O), 21.45 (C6H4Me).11B NMR (benzene-d6, 128 MHz): d -18.3. 15N{1H} NMR(benzene-d6, 71 MHz): d -177.59 (cis to RhNHTs), -255.43 (transto RhNHTs). IR (KBr, cm-1): n 3341 (m, nNH), 3000 (m), 2970(m), 2928 (m), 2885 (m), 1591 (s, nCN), 1462 (m), 1370 (m), 1287(s, nSO2), 1262 (m), 1203 (s, nSO2), 1158 (m), 1134 (s, nSO2), 1088(s), 998 (m), 965 (s, nSO2). Anal. Calcd. for C31H42BN4O5RhS: C,53.46; H, 6.08; N, 8.04. Found: C, 53.90; H, 6.38; N, 7.85. Mp:200–202 ◦C, dec.

ToMRh(NHTs)(H)OH2 (11). ToMRhH(h3-C8H13) (0.166 g,0.279 mmol) was added to a solution of TsN3 (0.055 g, 0.279 mmol)in 10 mL of benzene. The resulting mixture was stirred at roomtemperature for 3 h. All volatiles were evaporated, and the residuewas washed with pentane (2 ¥ 2 mL) to give a brown solid (0.126 g,0.187 mmol, 67.0%). 1H NMR (benzene-d6, 400 MHz): d 8.39(d, 2 H, 3JHH = 6.8 Hz, ortho-C6H5), 8.19 (d, 2 H, 3JHH = 8.0 Hz,ortho-C6H4Me), 7.56 (t, 2 H, 3JHH = 7.2 Hz, meta-C6H5), 7.37(t, 1 H, 3JHH = 7.6 Hz, para-C6H5), 6.88 (d, 2 H, 3JHH = 8.0 Hz,meta-C6H4Me), 3.79 (d, 1 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.73 (d, 1 H, 2JHH = 8.4 Hz, CNCMe2CH2O), 3.58 (d, 1 H,2JHH = 8.4 Hz, CNCMe2CH2O), 3.47 (d, 1 H, 2JHH = 8.4 Hz,CNCMe2CH2O), 3.38 (d, 1 H, 2JHH = 8.4 Hz, CNCMe2CH2O),3.30 (d, 1 H, 2JHH = 8.8 Hz, CNCMe2CH2O), 2.32 (s, 1 H, NHTs),1.92 (s, 3 H, C6H4Me), 1.63 (s, 3 H, CNCMe2CH2O), 1.61 (s,3 H, CNCMe2CH2O), 1.08 (s, 3 H, CNCMe2CH2O), 1.06 (s, 3 H,CNCMe2CH2O), 0.89 (s, 3 H, CNCMe2CH2O), 0.71 (s, 3 H,CNCMe2CH2O), -15.75 (d, 1 H, 1JRhH = 9.2 Hz, RhH). 13C{1H}NMR (benzene-d6, 175 MHz): d 142.41 (ipso-C6H4Me), 142.31(para-C6H4Me), 136.38 (ortho-C6H5), 129.78 (meta-C6H4Me),127.30 (meta-C6H5), 126.37 (ortho-C6H4Me), 126.31 (para-C6H5), 82.25 (CNCMe2CH2O), 80.70 (CNCMe2CH2O), 79.70(CNCMe2CH2O), 69.48 (CNCMe2CH2O), 67.14 (CNCMe2-CH2O), 66.98 (CNCMe2CH2O), 28.93 (CNCMe2CH2O),28.79 (CNCMe2CH2O), 27.77 (CNCMe2CH2O), 27.57(CNCMe2CH2O), 27.53 (CNCMe2CH2O), 27.29 (CNCMe2-CH2O), 21.51 (C6H4Me). 11B NMR (benzene-d6, 128 MHz): d-18.2. 15N{1H} NMR (benzene-d6, 71 MHz): d -154.1 (transto RhH), -205.8 (trans to OH2), -228.6 (trans to NHTs). IR(KBr, cm-1): n 3379 (br, nOH), 3300 (w, nNH), 3042 (w), 2964 (m),2927 (m), 2889 (m), 2067 (m, nRhH), 1594 (s, nCN), 1495 (w), 1462(m), 1433 (w), 1388 (w), 1367 (m), 1357 (m), 1289 (s, nSO2), 1267(s, nSO2), 1205 (s, nSO2), 1160 (m), 1126 (w), 1090 (m), 1028 (w),991 (m), 969 (s, nSO), 881 (w). Anal. Calcd. for C28H40BN4O6RhS:C, 49.86; H, 5.98; N, 8.31 Found: C, 49.91; H, 6.01; N, 8.30. Mp:184–186 ◦C, dec.

6512 | Dalton Trans., 2011, 40, 6500–6514 This journal is © The Royal Society of Chemistry 2011

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Acknowledgements

We thank Dr D. Bruce Fulton for assistance with 15N NMRmeasurements. This research was supported by the U.S. De-partment of Energy, Office of Basic Energy Sciences, Divisionof Chemical Sciences, Geosciences, and Biosciences through theAmes Laboratory. Tristan S. Gray was supported by the US. DOEOffice of Science, Office of Workforce Development for Teachersand Scientists through the Summer Undergraduate LaboratoryInternship Program at the Ames Laboratory. The Ames Labora-tory is operated for the U.S. Department of Energy by Iowa StateUniversity under Contract No. DE-AC02-07CH11358. AaronD. Sadow is an Alfred P. Sloan Fellow.

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6514 | Dalton Trans., 2011, 40, 6500–6514 This journal is © The Royal Society of Chemistry 2011

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