Reactivity Studies of a Stable N-Heterocyclic Silylene with Triphenylsilanol and Pentafluorophenol

Reactivity Studies of a Stable N‑Heterocyclic Silylene withTriphenylsilanol and PentafluorophenolRamachandran Azhakar, Rajendra S. Ghadwal,* Herbert W. Roesky,* Markus Granitzka,and Dietmar Stalke*

Institut fur Anorganische Chemie der Universitat Gottingen, Tammannstrasse 4, 37077 Gottingen, Germany

*S Supporting Information

ABSTRACT: The reaction of the stable N-heterocyclic silylene [CH{(CCH2)(CMe)(2,6-iPr2C6H3N)2}Si] (1) with triphenylsilanol and pentafluor-ophenol in a 1:2 molar ratio resulted in quantitative yields of thepentacoordinate silicon-containing compounds [CH{(CMe)2(2,6-iPr2C6H3N)2}Si(H){OSiPh3}2] (2) and [CH{(CMe)2(2,6-iPr2C6H3N)2}Si-(H){OC6F5}2] (3), respectively. Compounds 2 and 3 were formed by O−Hbond activation of triphenylsilanol and pentafluorophenol. They werecharacterized by elemental analysis, NMR spectroscopy, and EI-MSspectrometry. In their solid-state structures the silicon atom is tetracoordinatein 2, whereas it is pentacoordinate in 3.

■ INTRODUCTION

Silylenes are highly reactive chemical compounds possessing adivalent silicon atom.1 In 1994, West et al. reported on the firstisolable N-heterocyclic silylene (NHSi).2 After that report,many stable N-heterocyclic silylenes (NHSi's)1b−d,3 have beendocumented. They are considered to be the silicon analogues ofN-heterocyclic carbenes (NHC's). The chemical reactivity ofNHSi's is quite comparable with that of the NHC's, where thelatter led to a variety of applications in chemistry.4,5 Silyleneshave two nonbonding electrons in the HOMO and an empty porbital as the LUMO which feature both nucleophilic as well aselectrophilic reactive sites at the same silicon center. In linewith these properties, silylenes possess an ambiphilic characterand behave as Lewis acids as well as Lewis bases.6 Due to this,there has been widespread research activity carried out withsilylenes. In the last two decades many remarkable reactivitystudies of stable NHSi's toward various substrates have beenreported, such as insertion (C−H,7 N−H,8 O−H,9 S−H,8a P−P,10 N−Si,11 C−X (X = Cl, Br, I),12 Si−Cl,12 etc.),addition,8c,13a−h metal complexes,14 and Lewis acids.15 Wehave reported the N−H bond activation of ammonia8b andhydrazines,8c C−H as well as C−F bond activation offluoroarenes,16 regiospecific C−H activation of ylide,13g anddouble N−H bond activation of N,N′ bis-substituted hydrazinecompounds13h by utilizing the stable NHSi [CH{(CCH2)(CMe)(2,6-iPr2C6H3N)2}Si] (1).3c Up to now therehave been no reports on investigations of NHSi's toward silanoland phenolic compounds. We were curious to know thereactivity between these two compounds with NHSi's.Treatment of 1 with triphenylsilanol resulted in O−H bondactivation leading to [CH{(CMe)2(2,6-iPr2C6H3N)2}Si(H)-{OSiPh3}2] (2) possessing a pentacoordinate silicon atom. Inorder to compare the reactivity pattern of Si(O−H) with thatof C(O−H), we treated 1 with pentafluorophenol. The

reactivity is similar to that of silanol involving O−H bondactivation leading to the pentacoordinate silicon compound[CH{(CMe)2(2,6-iPr2C6H3N)2}Si(H){OC6F5}2] (3).

■ RESULTS AND DISCUSSIONCompounds 2 and 3 were obtained in good yield when 1 wastreated with triphenylsilanol and pentafluorophenol in a 1:2molar ratio, respectively (Scheme 1). Compounds 2 and 3 werefully characterized by NMR spectroscopy, EI-MS, andelemental analysis. Furthermore, the molecular structures of 2and 3 were unequivocally confirmed by single-crystal X-raystructural analyses.The reaction of 1 with triphenylsilanol in toluene at room

temperature proceeds rapidly, yielding product 2 (Scheme 1).The formation of 2 involves two O−H bond activations withthe formation of two oxygen−silicon bonds and one hydro-gen−silicon bond, and the other hydrogen atom is involved inC−H bond formation at the backbone of the β-diketiminatoligand. Compound 2 is soluble in common organic solvents.Further, it is stable both in the solid state as well as in solutionfor a long time without any decomposition under an inert-gasatmosphere. The 29Si NMR spectrum of 2 resonates at δ−82.94 and −18.17. The δ −82.94 resonance corresponds tothe pentacoordinate β-diketiminato supported silicon atom,which is shifted upfield in comparison to that of 1 (δ 88.4ppm). Moreover, the resonance is shifted upfield in comparisonwith those of the tetracoordinate silicon species which weresynthesized from 1.13f However, the resonance is in agreementwith those of other species obtained from 1 containingpentacoordinate silicon and other pentacoordinate siliconspecies.13h−j The 29Si NMR resonance at δ −18.17 corresponds

Received: May 30, 2012Published: July 24, 2012

Article

pubs.acs.org/Organometallics

© 2012 American Chemical Society 5506 dx.doi.org/10.1021/om300476q | Organometallics 2012, 31, 5506−5510

to −OSiPh3, which can be compared with that of HOSiPh3 (δ−12.20 in CDCl3).

17a In the 1H NMR spectrum, the resonancefor the γ-CH proton of compound 2 is observed at δ 4.88 andfor the Si−H proton at δ 5.29 (by an HSQC experiment). Theprotons of NCCH3 resonate at δ 1.67 (for six hydrogen atoms),and correspondingly the absence of a NCCH2 proton signalindicates the protonation of the methylene group at the ligandbackbone of 1. The IR spectrum of 2 shows a Si−H stretchingabsorption at 2192 cm−1.17b In addition, 2 exhibits its molecularion peak in its mass spectrum at m/z 997 [M+].The formation of the O−H bond activated product 2 was

unambiguously established by single-crystal X-ray structuralanalysis. Compound 2 crystallizes in the triclinic space groupP1, and the molecular structure is shown in Figure 1. In thecrystal structure, the silicon atom is tetracoordinate and featuresa distorted-tetrahedral geometry. We surmise that thetetracoordinate silicon in the solid state is due to the presence

of the bulky −OSiPh3 moiety attached to the silicon center.The coordination environment of the silicon atom features onenitrogen atom from the β-diketiminato ligand, two oxygenatoms, and a hydrogen atom. The two Si−O bond lengths(Si1−O1 = 1.6041(10) Å and Si1−O2 = 1.6070(10) Å) arenearly similar. The Si1−N1 bond length is 1.7283(11) Å.18 Theposition of the silicon-bound hydrogen atom was taken fromthe Fourier difference map and refined freely. The Si−Hdistance of 1.359(15) Å is comparable with the literaturevalues.13h

Similar to the case for triphenylsilanol, the reaction ofpentafluorophenol with 1 resulted in compound 3 withpentacoordinate silicon, with two O−H bond activationscomparable to that of 2. Compound 3 is soluble in all commonorganic solvents. It is stable in both the solid and the solutionstate under an inert atmosphere. The 29Si NMR spectrum ofcompound 3 shows a upfield resonance at δ −106.15. In the 1HNMR spectrum the resonance for the γ-CH proton ofcompound 3 is observed at δ 5.16 and for the Si−H protonat δ 5.04 (corroborated by a 1H−29Si HSQC experiment). Thevariance in the 29Si and 1H NMR chemical shifts of 2(−OSiPh3) and 3 (−OC6F5) is due to the influence of thedifferent sizes of the substituents attached to the siliconcenter.13h The proton resonance of NCCH3 is observed at δ1.54. The 19F NMR spectrum of compound 3 shows threesignals (δ −157.73 (d), −165.94 (t), and −168.07 (t)), whichcorrespond to the o-, m-, and p-fluorine atoms. The Si−Hstretching absorption for compound 3 appears at 2145 cm−1 inits IR spectrum. Compound 3 exhibits its molecular ion peak inits EI-MS at m/z 812 [M+].The formation of 3 was further confirmed by single-crystal X-

ray structural analysis. Compound 3 crystallizes in themonoclinic space group P21/n, and the molecular structure isshown in Figure 2. The silicon atom is coordinated in adistorted-trigonal-bipyramidal geometry, made up of twonitrogen atoms, two oxygen atoms, and a hydrogen atom.The two nitrogen atoms attached to the silicon atom originatefrom the chelating β-diketiminato ligand. The structural indexτ, which defines the extent of deviation from a trigonal-bipyramidal to square-pyramidal geometry (τ = 1 for a perfecttrigonal bipyramid; τ = 0 for a perfect square-based pyramid19),is 0.74, indicating a distorted-trigonal-bipyramidal geometry.

Scheme 1. Synthesis of Compounds 2 and 3

Figure 1. Molecular structure of 2. Anisotropic displacementparameters are depicted at the 50% probability level. Hydrogenatoms other than Si−H are omitted for clarity. Selected bond lengths(Å) and bond angles (deg): N1−Si1 = 1.7283(11), O2−Si1 =1.6070(10), O1−Si1 = 1.6041(10), H1−Si1 = 1.359(15); N1−Si1−O2 = 110.89(5), N1−Si1−O1 = 108.63(5), O2−Si1−O1 = 109.89(5).

Organometallics Article

dx.doi.org/10.1021/om300476q | Organometallics 2012, 31, 5506−55105507

There are two types of Si−N and Si−O bonds present in 1: oneis shorter (N1−Si1 = 1.8093(11) Å; Si1−O1 = 1.6866(9) Å)and the other is longer (N2−Si1 = 1.9277(10) Å; Si1−O2 =1.7631(9) Å), which is due to the presence of a nitrogen and anoxygen atom present in the axial and equatorial positions.There is an appreciable change in the N−Si−N bite angle of 3(92.77(4)°), in comparison with that of 1 (99.317(54)°).3c

This change is attributed to the protonation of the backbone ofthe ligand. As for 2, the position of the silicon-bound hydrogenatom was taken from the Fourier difference map and refinedfreely. The Si−H distance of 1.361(15) Å is nearly similar tothat of 2.

■ CONCLUSIONWe report for the first time the reactivity of silanol and phenolwith a stable N-heterocyclic silylene. The reactivity of 1 withtriphenylsilanol involves O−H bond activation, leading to[CH{(CMe)2(2,6-iPr2C6H3N)2}Si(H){OSiPh3}2] (2). Simi-larly, the reaction of 1 with pentafluorophenol also leads toO−H bond activation, resulting in [CH{(CMe)2(2,6-iPr2C6H3N)2}Si(H){OC6F5}2] (3). The silicon atom istetracoordinate in 2 while it is pentacoordinate in 3 in theirsolid-state structures.

■ EXPERIMENTAL SECTIONAll manipulations were carried out under an atmosphere of dinitrogenusing standard Schlenk techniques and in a dinitrogen-filled glovebox.Solvents were purified by an MBRAUN MB SPS-800 solventpurification system. All chemicals were purchased from Aldrich andused without further purification. Compound 1 was prepared asreported in the literature.3c 1H, 19F, and 29Si NMR spectra wererecorded with a Bruker Avance DRX 300 or a Bruker Avance DRX 500spectrometer, using C6D6 as solvent. Chemical shifts δ are givenrelative to SiMe4. IR spectra were recorded on a Bio-Rad Digilab FTS7

spectrometer in the range 4000−400 cm−1 as Nujol mulls. EI-MSspectra were obtained using a Finnigan MAT 8230 instrument.Elemental analyses were performed by the Institut fur AnorganischeChemie, Universitat Gottingen.

Synthesis of 2. Toluene (60 mL) was added to a Schlenk flask(100 mL) containing 1 (0.43 g, 0.97 mmol) and triphenylsilanol (0.54g, 1.95 mmol). The reaction mixture was stirred at room temperaturefor 12 h. The solution was filtered, and the solvent was reduced invacuo to about 20 mL and stored at 0 °C in a freezer overnight toobtain single crystals of 2. (0.82 g, 85%). Anal. Calcd forC65H72N2O2Si3 (997.54): C, 78.26; H, 7.28; N, 2.81. Found: C,78.10; H, 7.16; N, 2.63. 1H NMR (500 MHz, C6D6, 25 °C): δ 1.15 (d,12H, J = 7 Hz, 4 × CH(CH3)2), 1.21 (d, 12H, J = 7 Hz, 4 ×CH(CH3)2), 1.67 (s, 6H, 2 × NCCH3), 3.26−3.34 (m, 4H, 4 ×CH(CH3)2), 4.88 (s, 1H, γ-CH), 5.29 (s, 1H, SiH), 7.01−7.05 (m,ArH), 7.11−7.17 (m, ArH), 7.54−7.59 (m, ArH) ppm. 29Si{1H} NMR(99.36 MHz, C6D6, 25 °C): δ −18.17 (s, SiPh3), −82.94 (s, SiH) ppm.FT-IR (Nujol, cm−1): ν 2192 (s) (SiH). EI-MS: m/z 997 (M+).

Synthesis of 3. n-Hexane (60 mL) was added to a Schlenk flask(100 mL) containing 1 (0.35 g, 0.79 mmol) and pentafluorophenol(0.30 g, 1.63 mmol). The reaction mixture was stirred at roomtemperature for 12 h. The solution was filtered, and the solvent wasreduced in vacuo to 20 mL and stored in a freezer at −32 °C for 1week to obtain colorless single crystals of 3. (0.53 g, 83%). Anal. Calcdfor C41H42F10N2O2Si (812.29): C, 60.58; H, 5.21; N, 3.45. Found: C,60.37; H, 5.16; N, 3.34. 1H NMR (300 MHz, C6D6, 25 °C): δ 1.06 (d,12H, J = 7 Hz, 4 × CH(CH3)2), 1.20 (d, 12H, J = 7 Hz, 4 ×CH(CH3)2), 1.54 (s, 6H, 2 × NCCH3), 3.15−3.27 (m, 4H, 4 ×CH(CH3)2), 5.04 (br, 1H, SiH), 5.16 (s, 1H, γ-CH), 7.02−7.13 (m,ArH), ppm. 19F NMR (282.40 MHz, C6D6, 25 °C): δ −157.73 (d, 2H,J = 21 Hz, o-F), −165.94 (t, 2H, J = 21 Hz, m-F), −168.07 (t, 1H, J =21 Hz, p-F) ppm. 29Si{1H} NMR (59.36 MHz, C6D6, 25 °C): δ−106.15 ppm. FT-IR (Nujol, cm−1): ν 2145 (s) (SiH). EI-MS: m/z812 (M+).

Crystal Structure Determination. Suitable single crystals of 2and 3 were selected from the liquor in the Schlenk flask and coveredwith perfluorinated polyether oil on a microscope slide, which wascooled with a nitrogen gas flow using an X-Temp2 apparatus.20 Anappropriate crystal was selected using a polarizing microscope,mounted on the tip of a MITEGEN MicroMount, fixed to agoniometer head, and shock-cooled by the crystal cooling device. Thedata for 2 and 3 were collected at 100(2) K20 on a Bruker D8 three-circle diffractometer equipped with a SMART APEX II CCD detectorand Bruker TXS-Mo rotating anode with mirror optics. The data wereintegrated with SAINT,21 and a semiempirical absorption correctionwith SADABS22 was applied. The structures were solved by directmethods (SHELXS-97)23a and refined by full-matrix least-squaresmethods against F2 (SHELXL-97)23b,c within the SHELXLE GUI.23d

All non-hydrogen atoms were refined with anisotropic displacementparameters. The hydrogen atoms were refined isotropically oncalculated positions using a riding model with their Uiso valuesconstrained to 1.5Ueq of their pivot atoms for terminal sp3 carbonatoms and 1.2Ueq for all other carbon atoms if not mentionedotherwise in the text (Si1−H1). The disorder of the C6F5 group wasrefined using bond length restraints and anisotropic displacementparameter restraints.

■ ASSOCIATED CONTENT

*S Supporting InformationCIF files and a table giving crystal data and details of thestructure solution and refinement for 2 (CCDC-870572) and 3(CCDC-870573). This material is available free of charge viathe Internet at http://pubs.acs.org.

Figure 2. Molecular structure of 3. Anisotropic displacementparameters are depicted at the 50% probability level. Hydrogenatoms other than Si−H and the positional disorder of one of the C6F5groups are omitted for clarity. Selected bond lengths (Å) and bondangles (deg): N1−Si1 = 1.8093(11), N2−Si1 = 1.9277(10), O2−Si1 =1.7631(9), O1−Si1 = 1.6866(9), H1−Si1 = 1.361(15); N1−Si1−N2 =92.77(4), N1−Si1−O2 = 92.52(4), N2−Si1−O2 = 174.60(4), N1−Si1−O1 = 108.35(4), O2−Si1−O1 = 92.55(4).

Organometallics Article

dx.doi.org/10.1021/om300476q | Organometallics 2012, 31, 5506−55105508

■ AUTHOR INFORMATIONCorresponding Author*E-mail: hroesky@gwdg.de (H.W.R.); rghadwal@uni-goettingen.de (R.S.G.); dstalke@chemie.uni-goettingen.de(D.S.).NotesThe authors declare no competing financial interest.

■ ACKNOWLEDGMENTSWe thank the Deutsche Forschungsgemeinschaft (DFG) forsupporting this work. R.A. is grateful to the Alexander vonHumboldt Stiftung for a research fellowship. M.G. and D.S.acknowledge the DFG Priority Programm 1178 and the DanishNational Research Foundation (DNRF) funded Center forMaterials Crystallography (CMC) for support.

■ REFERENCES(1) (a) Gaspar, P. P.; West, R. In The Chemistry of Organic SiliconCompounds, 2nd ed.; Rappoport, Z., Apeloig, Y., Eds.; Wiley: NewYork, 1999; Vol. 2, Part 3, pp 2463−2568. (b) Haaf, M.; Schmedake,T. A.; West, R. Acc. Chem. Res. 2000, 33, 704−714. (c) Gehrhus, B.;Lappert, M. F. J. Organomet. Chem. 2001, 617−618, 209−223. (d) Sen,S. S.; Khan, S.; Samuel, P. P.; Roesky, H. W. Chem. Sci. 2012, 3, 659−682. (e) Yao, S.; Xiong, Y.; Driess, M. Organometallics 2011, 30,1748−1767. (f) Asay, M.; Jones, C.; Driess, M. Chem. Rev. 2011, 111,354−396.(2) Denk, M.; Lennon, R.; Hayashi, R.; West, R.; Belyakov, A. V.;Verne, H. P.; Haaland, A.; Wagner, M.; Metzler, N. J. Am. Chem. Soc.1994, 116, 2691−2692.(3) (a) So, C.-W.; Roesky, H. W.; Magull, J.; Oswald, R. B. Angew.Chem. 2006, 118, 4052−4054; Angew. Chem., Int. Ed. 2006, 45, 3948−3950. (b) Sen, S. S.; Roesky, H. W.; Stern, D.; Henn, J.; Stalke, D. J.Am. Chem. Soc. 2010, 132, 1123−1126. (c) Driess, M.; Yao, S.; Brym,M.; van Wullen, C.; Lentz, D. J. Am. Chem. Soc. 2006, 128, 9628−9629. (d) Kong, L.; Zhang, J.; Song, H.; Cui, C. Dalton Trans. 2009,5444−5446. (e) Sen, S. S.; Hey, J.; Herbst-Irmer, R.; Roesky, H. W.;Stalke, D. J. Am. Chem. Soc. 2011, 133, 12311−12316. (f) Yamaguchi,T.; Sekiguchi, A.; Driess, M. J. Am. Chem. Soc. 2010, 132, 14061−14063. (g) Azhakar, R.; Ghadwal, R. S.; Roesky, H. W.; Wolf, H.;Stalke, D. Chem. Commun. 2012, 48, 4561−4563. (h) Azhakar, R.;Ghadwal, R. S.; Roesky, H. W.; Wolf, H.; Stalke, D. Organometallics2012, 31, 4588−4592.(4) (a) Nolan, S. P. In N-Heterocyclic Carbenes in Synthesis; Wiley-VCH: Weinheim, Germany, 2006. (b) Glorius, F. In N-HeterocyclicCarbenes in Transition Metal Catalysis; Springer-Verlag: Berlin, 2007.(c) Clavier, H.; Nolan, S. P. Annu. Rep. Prog. Chem., Sect. B: Org. Chem.2007, 103, 193−222. (d) Weskamp, T.; Bohm, V. P. W.; Herrmann,W. A. J. Organomet. Chem. 2000, 600, 12−22. (e) Jafarpour, L.; Nolan,S. P. Adv. Organomet. Chem. 2000, 46, 181−222. (f) Solorio-Alvardo,C. R.; Wang, Y.; Echavarren, A. M. J. Am. Chem. Soc. 2011, 133,11952−11955. (g) Fustier, M.; Goff, F. L.; Floch, P. L.; Mezailles, N. J.Am. Chem. Soc. 2010, 132, 13108−13110. (h) Boyd, P. D. W.; Wright,J.; Zafar, M. N. Inorg. Chem. 2011, 50, 10522−10524. (i) Hess, J. L.;Hsieh, C.-H.; Reibenspies, J. H.; Darensbourg, M. Y. Inorg. Chem.2011, 50, 8541−8552. (j) Phillips, E. M.; Riedrich, M.; Scheidt, K. A. J.Am. Chem. Soc. 2010, 132, 13179−13181. (k) Mathew, J.; Suresh, C.H. Inorg. Chem. 2010, 49, 4665−4669. (l) Jana, A.; Azhakar, R.;Tavcar, G.; Roesky, H. W.; Objartel, I.; Stalke, D. Eur. J. Inorg. Chem.2011, 3686−3689. (m) Kronig, S.; Theuergarten, E.; Holschumacher,D.; Bannenberg, T.; Daniliuc, C. G.; Jones, P. G.; Tamm, M. Inorg.Chem. 2011, 50, 7344−7359. (n) Martin, D.; Melaimi, M.;Soleilhavoup, M.; Bertrand, G. Organometallics 2011, 30, 5304−5313.(5) (a) Yang, C.-H.; Beltran, J.; Lemaur, V.; Cornil, J.; Hartmann, D.;Sarfert, W.; Frohlich, R.; Bizzari, C.; De Cola, L. Inorg. Chem. 2010, 49,9891−9901. (b) Mills, D. P.; Soutar, L.; Lewis, W.; Blake, A. J.; Liddle,S. T. J. Am. Chem. Soc. 2010, 132, 14379−14381. (c) Park, H.-J.; Kim,K. H.; Choi, S. Y.; Kim, H.-M.; Lee, W. I.; Kang, Y. K.; Chung, Y. K.

Inorg. Chem. 2010, 49, 7340−7352. (d) Crees, R. S.; Cole, M. L.;Hanton, L. R.; Sumby, C. J. Inorg. Chem. 2010, 49, 1712−1719.(e) Chuprakov, S.; Malik, J. A.; Zibinsky, M.; Fokin, V. V. J. Am. Chem.Soc. 2011, 133, 10352−10355. (f) Dzik, W. I.; Zhang, P.; de Bruin, B.Inorg. Chem. 2011, 50, 9896−9903. (g) Dash, C.; Shaikh, M. M.;Butcher, R. J.; Ghosh, P. Inorg. Chem. 2010, 49, 4972−4983. (h) Fu,C.-F.; Lee, C.-C.; Liu, Y.-H.; Peng, S.-M.; Warsink, S.; Elsevier, C. J.;Chen, J.-T.; Liu, S.-T. Inorg. Chem. 2010, 49, 3011−3018. (i) Hsieh,C.-H.; Darensbourg, M. Y. J. Am. Chem. Soc. 2010, 132, 14118−14125.(j) Huang, F.; Lu, G.; Zhao, L.; Wang, Z.-X. J. Am. Chem. Soc. 2010,132, 12388−12396. (k) Zhang, W.-Q.; Whitwood, A. C.; Fairlamb, I. J.S.; Lynam, J. M. Inorg. Chem. 2010, 49, 8941−8952. (l) Naeem, S.;Delaude, L.; White, A. J. P.; Wilton-Ely, J. D. E. T. Inorg. Chem. 2010,49, 1784−1793. (m) Goedecke, C.; Leibold, M.; Siemeling, U.;Frenking, G. J. Am. Chem. Soc. 2011, 133, 3557−3569. (n) Wang, Y.;Robinson, G. H. Inorg. Chem. 2011, 50, 12326−12337.(6) (a) Li, R.-E.; Sheu, J.-H.; Su, M.-D. Inorg. Chem. 2007, 46, 9245−9253. (b) Bharatam, P. V.; Moudgil, R.; Kaur, D. Inorg. Chem. 2003,42, 4743−4749. (c) Bharatam, P. V.; Moudgil, R.; Kaur, D.Organometallics 2002, 21, 3683−3690. (d) Percival, P. W.;Brodovitch, J.-C.; Mozafari, M.; Mitra, A.; West, R.; Ghadwal, R. S.;Azhakar, R.; Roesky, H. W. Chem. Eur. J. 2011, 17, 11970−11973.(e) Inoue, S.; Epping, J. D.; Irran, E.; Driess, M. J. Am. Chem. Soc.2011, 133, 8514−8517. (f) Inoue, S.; Wang, W.; Prasang, C.; Asay, M.;Irran, E.; Driess, M. J. Am. Chem. Soc. 2011, 133, 2868−2871.(g) Azhakar, R.; Roesky, H. W.; Ghadwal, R. S.; Holstein, J. J.;Dittrich, B. Dalton Trans. 2012, DOI: 10.1039/C2DT31326J.(7) Yao, S.; van Wullen, C.; Sun, X.-Y.; Driess, M. Angew. Chem.2008, 120, 3294−3297; Angew. Chem., Int. Ed. 2008, 47, 3250−3253.(8) (a) Meltzer, A.; Inoue, S.; Prasang, C.; Driess, M. J. Am. Chem.Soc. 2010, 132, 3038−3046. (b) Jana, A.; Schulzke, C.; Roesky, H. W.J. Am. Chem. Soc. 2009, 131, 4600−4601. (c) Jana, A.; Schulzke, C.;Roesky, H. W.; Samuel, P. P. Organometallics 2009, 28, 6574−6577.(9) (a) Yao, S.; Brym, M.; van Wullen, C.; Driess, M. Angew. Chem.2007, 119, 4237−4240; Angew. Chem., Int. Ed. 2007, 46, 4159−4162.(b) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Heinicke, J.; Boese,R.; Blaser, D. J. Organomet. Chem. 1996, 521, 211−220. (c) Haaf, M.;Schmiedl, A.; Schmedake, T. A.; Powell, D. R.; Millevolte, A. J.; Denk,M.; West, R. J. Am. Chem. Soc. 1998, 120, 12714−12719.(10) Xiong, Y.; Yao, S.; Brym, M.; Driess, M. Angew. Chem. 2007,119, 4595−4597; Angew. Chem., Int. Ed. 2007, 46, 4511−4513.(11) (a) Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F.; Slootweg, J.C. Chem. Commun. 2000, 1427−1428. (b) Antolini, F.; Gehrhus, B.;Hitchcock, P. B.; Lappert, M. F.; Slootweg, J. C. Dalton Trans. 2004,3288−3294.(12) Xiong, Y.; Yao, S.; Driess, M. Organometallics 2009, 28, 1927−1933.(13) (a) Xiong, Y.; Yao, S.; Driess, M. Chem. Eur. J. 2009, 15, 5545−5551. (b) Xiong, Y.; Yao, S.; Driess, M. Organometallics 2010, 29,987−990. (c) Ghadwal, R. S.; Azhakar, R.; Roesky, H. W.; Propper, K.;Dittrich, B.; Klein, S.; Frenking, G. J. Am. Chem. Soc. 2011, 133,17552−17555. (d) Gehrhus, B.; Hitchcock, P. B. Organometallics2004, 23, 2848−2849. (e) Azhakar, R.; Ghadwal, R. S.; Roesky, H. W.;Hey, J.; Stalke, D. Organometallics 2011, 30, 3853−3858. (f) Azhakar,R.; Sarish, S. P.; Tavcar, G.; Roesky, H. W.; Hey, J.; Stalke, D.; Koley,D. Inorg. Chem. 2011, 50, 3028−3036. (g) Azhakar, R.; Sarish, S. P.;Roesky, H. W.; Hey, J.; Stalke, D. Organometallics 2011, 30, 2897−2900. (h) Azhakar, R.; Ghadwal, R. S.; Roesky, H. W.; Hey, J.; Stalke,D. Dalton Trans. 2012, 41, 1529−1533. (i) Kobelt, C.; Burschka, C.;Bertermann, R.; Guerra, C. F.; Bickelhaupt, F. M.; Tacke, R. DaltonTrans. 2012, 41, 2148−2162. (j) Kawashima, T. J. Organomet. Chem.2000, 611, 256−263.(14) (a) Li, J.; Merkel, S.; Henn, J.; Meindl, K.; Doring, A.; Roesky,H. W.; Ghadwal, R. S.; Stalke, D. Inorg. Chem. 2010, 49, 775−777.(b) Azhakar, R.; Sarish, S. P.; Roesky, H. W.; Hey, J.; Stalke, D. Inorg.Chem. 2011, 50, 5039−5043. (c) Tavcar, G.; Sen, S. S.; Azhakar, R.;Thorn, A.; Roesky, H. W. Inorg. Chem. 2010, 49, 10199−10202.(d) Ghadwal, R. S.; Azhakar, R.; Propper, K.; Holstein, J. J.; Dittrich,B.; Roesky, H. W. Inorg. Chem. 2011, 50, 8502−8508. (e) Azhakar, R.;

Organometallics Article

dx.doi.org/10.1021/om300476q | Organometallics 2012, 31, 5506−55105509

Ghadwal, R. S.; Roesky, H. W.; Wolf, H.; Stalke, D. J. Am. Chem. Soc.2012, 134, 2423−2428. (f) Azhakar, R.; Ghadwal, R. S.; Roesky, H.W.; Hey, J.; Stalke, D. Chem. Asian J. 2012, 7, 528−533.(g) Schmedake, T. A.; Haaf, M.; Paradise, B. J.; Millevolte, A. J.;Powell, D.; West, R. J. Organomet. Chem. 2001, 636, 17−25.(15) (a) Azhakar, R.; Tavcar, G.; Roesky, H. W.; Hey, J.; Stalke, D.Eur. J. Inorg. Chem. 2011, 475−477. (b) Jana, A.; Azhakar, R.; Sarish, S.P.; Samuel, P. P.; Roesky, H. W.; Schulzke, C.; Koley, D. Eur. J. Inorg.Chem. 2011, 5006−5013.(16) Jana, A.; Samuel, P. P.; Tavcar, G.; Roesky, H. W.; Schulzke, C.J. Am. Chem. Soc. 2010, 132, 10164−10170.(17) (a) Coan, P. S.; Hubert-Pfalzgraf, L. G.; Caulton, K. G. Inorg.Chem. 1992, 31, 1262−1267. (b) Chen, W.; Shimada, S.; Tanaka, M.Science 2002, 295, 308−310.(18) (a) Kocher, N.; Henn, J.; Gostevskii, B.; Kost, D.; Kalikhman, I.;Engels, B.; Stalke, D. J. Am. Chem. Soc. 2004, 126, 5563−5568.(b) Chandrasekhar, V.; Boomishankar, R.; Azhakar, R.; Gopal, K.;Steiner, A.; Zacchini, S. Eur. J. Inorg. Chem. 2005, 1880−1885.(19) (a) Addison, A. W.; Rao, T. N.; Reedijk, J.; van Rijn, J.;Verschoor, G. C. J. Chem. Soc., Dalton Trans. 1984, 1349−1356.(b) Chandrasekhar, V.; Azhakar, R.; Senapati, T.; Thilagar, P.; Ghosh,S.; Verma, S.; Boomishankar, R.; Steiner, A.; Kogerler, P. Dalton Trans.2008, 1150−1160.(20) (a) Stalke, D. Chem. Soc. Rev. 1998, 27, 171−178. (b) Kottke,T.; Stalke, D. J. Appl. Crystallogr. 1993, 26, 615−619. (c) Kottke, T.;Lagow, R. J.; Stalke, D. J. Appl. Crystallogr. 1996, 29, 465−468.(21) SAINT V7.68A in Bruker APEX, version 2011.9; Bruker AXS Inst.Inc., Madison, WI, 2008.(22) Sheldrick, G. M. SADABS 2008/2; Universitat Gottingen,Gottingen, Germany, 2008.(23) (a) Sheldrick, G. M. Acta Crystallogr., Sect. A 1990, 46, 467−473.(b) Sheldrick, G. M. Acta Crystallogr., Sect. A 2008, 64, 112−122.(c) Muller, P.; Herbst-Irmer, R.; Spek, A. L.; Schneider, T. R.; Sawaya,M. R. In Crystal Structure Refinement-A Crystallographer’s Guide toSHELXL; Muller, P., Ed.; Oxford University Press: Oxford, U.K.,2006; IUCr Texts on Crystallography Vol. 8. (d) Hubschle, C. B.;Sheldrick, G. M.; Dittrich, B. J. Appl. Crystallogr. 2011, 44, 1281−1284.

Organometallics Article

dx.doi.org/10.1021/om300476q | Organometallics 2012, 31, 5506−55105510