Synthetic Methodologies and Structures of Metal-[C60]Fullerene Complexes

Journal of Cluster Science, Vol. 9. No. 4, 1998

Review

INTRODUCTION

Since the report on the first structurally characterized complex of C60,[(n2-C60)(OsO4)(4-tBuC5H4N)2], an osmate ester with C-O-Os bonds[1], and the crystal structure of the first organometallic complex offullerene [Pt(n2-C60)(PPh3)2] -C4H8O [2], numerous other fullerene com-plexes of transition metals have been synthesized and characterized. Muchof the work in fullerene chemistry has been performed on [60] fullerene, themost abundant representative of fullerene family. Synthetic methodologiesnow allow for macroscopic quantities of C60 to be prepared, and a largenumber of C60 derivatives with interesting magnetic, electronic and opticalproperties have been studied [3]. Addition reactions on C60 occur promi-nently at the 6:6 ring junctions, and the presence of 30 such junctions ina C60 molecule leads to the possibility of forming a wide variety of adducts.Although a majority of the complexes of C60 have metal atoms bound inn2-fashion, in recent times there has also been substantial development inmetal-C60 ^-complex chemistry. There is some interest in developingmethods to obtain complexes where the fullerene interacts with ligands.

' Chemistry Department, Indian Institute of Technology, Powai, Bombay 400 076, India.2 To whom all correspondence should be addressed.

Synthetic Methodologies and Structures ofMetal-[C60]Fullerene Complexes

Pradeep Mathur,1,2 Ipe J. Mavunkal,1 and Shubhangi B. Umbarkar1

Received April 28. 1998

A review of the chemistry of transition metal-[C60] fullerene complexes ispresented. The main focus is directed toward the different methodologies forobtaining both metal bound and ligand bound complexes of C60, and thedifferent types of structures which have been so far identified for metal-C60

complexes.

KEY WORDS: Fullerene; transition-metal; complex; synthesis; structure.

393

1040-7278/98/1200-0393$15.00/0 © 1998 Plenum Publishing Corporation

394 Mathur, Mavunkal, and Umbarkar

Scheme 1. Reaction of (n5-C5H5)2Zr(H)Cl with C60.

Motivation for preparing the ligand-bound fullerenes arises from theirenhanced kinetic stability [4] and possibilities for decomplexation ofmodified fullerenes [5].

In this article, we summarize the developments made in synthesis ofcomplexes of C60 with metals of Groups 4-10, along with their structuralfeatures. The discussion on complexes of metals of each group is given inseparate section.

Group 4 (Ti, Zr, Hf)

Among the Group 4 metals, only zirconium is reported to complex toC60. Reaction of (n5-C5H5)2Zr(H)Cl with C60 in benzene at room tem-perature, followed by hydrolysis using HC1, leads to hydrogenation of C60

to yield C60H2. It is proposed that the reaction proceeds through an inter-mediate, [(n5-C5H5)2ZrCl]nC60Hn (1), which on acid hydrolysis givesC60H2n. 1H NMR spectrum of the reaction mixture, before hydrolysis, isconsistent with the intermediate 1 (Scheme 1) [6].

Group 5 (V, Nb, Ta)

In Group 5 also, only one metal is so far reported to form a complexwith C60. Treatment of equimolar amounts of (n5-C5H5)2TaH3 and C60

in benzene solvent yields {(n5-C5H5)2(H)Ta(n2-C60)} (2) (Fig. 1) in over

Fig. 1. Structure of [(n5-C5H5)2(H)Ta(n2-C6 0)] (8).

Scheme 2. Reaction of Cr11(TPP) with C60.

90% yield after 12 hr. Identity of 2 has been ascertained on the basis of IRand solid state 13C NMR spectroscopy [7].

Group 6 (Cr, Mo, W)

Anaerobic treatment of a THF solution of Cr11(TPP), (TPP = tetra-phenylporphinato) with C60 in toluene, in 1:1 molar ratio, givesCrIII(TPP) + C60 .- (3). Its identification is based on uv-vis spectral studies,and its molecular formulation, Cr(TPP)(C60)(THF)3 has been confirmedby elemental analysis. Shift in the uv-vis band for C60 from 329 to 331 nmis observed, consistent with conversion of C60 to C60 , and a shift inporphyrin Soret band from 421 to 451 nm is observed, diagnostic of Cr(II)to Cr(III) oxidation. Dissolution of product in toluene completely reversesthe redox reaction. Addition of a few drops of THF to the toluene solutionpromotes the electron transfer again (Scheme 2) [8].

Nefedova and co-workers [9] have reported the formation of a chro-mium derivative of C60 in which C60 is attached to Cr through an organicfragment. Chromium-tricarbonylation of benzophenone hydrazone yieldeda mono-^-complex from which a diazomethane complex [N2-C(Ph)-(v6-C6H5)Cr(CO)3] was obtained. Treatment of the diazomethane com-plex, [N2-C(Ph)-(n6-C6H5)Cr(CO)3] with an equimolar amount of C60

yielded C60[C(Ph)-(n6-C6H5)Cr(CO)3] (4) (Scheme 3). Characterization

Scheme 3. Formation of C60[C(Ph)-(n6-C6H5)Cr(CO),] (4).

Synthetic Methodologies and Structures of Metal-[C60]Fullerene Complexes 395


Fig. 2. Representation of isomers of C60[C(Ph)-(n6-C6H5)Cr(CO)3] (4).

of 4 is based on IR, uv-vis and 1H NMR spectroscopy and mass spec-trometry. 1H NMR spectrum of 4 indicates that it exists as a mixture oftwo isomers (Fig. 2).

Room temperature reaction of the dihydrides, [(n5-C5H4R)2MoH2](R = H, Bun) with 1 equivalent of C60 yields [(n5-C5H4R)2Mo(C60)](R = H, 5; R = Bun, 6) (Scheme 4), both of which have been characterizedby 1H and 13C NMR spectroscopy [7].

Jin and co-workers [10] have reported that when C60 was treatedwith [M(CO)4(phen)] and dbm (M=Mo, W; phen= 1,10-phenan-throline; dbm = dibutyl maleate) under thermolytic reaction conditions,[M(n2-C60)(CO)2(phen)(dbm)].2C6H6.C5H12, (M=Mo (7), W (8))were obtained. Characterization of 7 and 8 is based on IR, uv-vis, 1H and13C NMR spectroscopy and single crystal X-ray diffraction analysis (Fig. 3).

Shapley and co-workers have reported the synthesis of C60 derivativesof molybdenum and tungsten, C60[M(CO)3(diphos)] (9a: M=Mo, 9b:M = W) (diphos=l,2-bis(diphenylphosphino)ethane) and C60[W(CO)3

(diphos)]2 (10) (formation of C60[Mo(CO)3(diphos)]2 is not reported)by photolytic reaction of 1:1 mixture of M(CO)4(diphos) and C60 in1,2-dichlorobenzene followed by chromatographic separation of the twoproducts. The compounds have been characterized by IR, 1H and

Scheme 4. Reaction of [(n5-C5H4R)2MoH2] (R= H, Bu11) with C60.

Synthetic Methodologies and Structures of Metal-[C60Fullerene Complexes 397

Fig. 3. Molecular structure of [W(n2-C60)(CO)2(phen)(dbm)] ·2C6H6·C5H1 2 (8) (repro-duced with permission from the Royal Society of Chemistry (1997). J. Chem. Soc., DaltonTrans. 3585).

31P NMR, and uv-vis spectroscopy as well as by FAB mass spectrometry.Molecular structures of 9a and 9b have been determined by single crystalX-ray diffraction analysis (Fig. 4). Distorted octahedral geometries areobserved for the metal centers in both cases, with the dppe and olefinligands in a mer configuration. There are significant secondary interactionsbetween the fullerene moiety and the phenyl groups of the diphosphineligands [11]. Compounds 9 and 10 are found to be very stable towardsdisplacement of C60 ligand; heating at 110°C in pyridine for overnight doesnot show any reaction. This exceptional stability has been attributed to theoctahedrally coordinated metal centers which preclude associative displace-ment reactions.

Fig. 4. Molecular structure of [(n2-C60)W(CO)3(l,2-diphenylphosphinoethane)] (9b)(reproduced with permission from The Electrochem. Soc. Inc. (1994). The Electrochem. Soc.Proc. Ser. 94, 1255).


Group 7 (Mn, Tc, Re)

There is no example reported of Mn directly attached to C60. A Mncluster attached to Si( 111 )-7 X 7 terminated by C60 monolayer has recentlybeen reported [12].

Flash photolysis or continuous sun-lamp irradiation of a benzenesolution containing Re2(CO)10 with C60 in benzene is reported to formC60{Re(CO)5}2 (11) (Fig. 5). Compound 11 is also obtained from thethermal reaction of C60 with a rhenium pentacarbonyl radical source,(n3-Ph3C)Re(CO)4 in presence of CO. Formation of 11 has been detectedby IR spectroscopic studies of the reaction mixture. It is suggested that twoRe(CO)5 units add on to one of the six membered rings of C60 in the 1, 4positions. Compound 11 is unstable and readily decomposes to Re2(CO)10

and C60 at room temperature [13].

Group 8 (Fe, Ru, Os)

The monoadduct derivatives, [M(CO)4(n2-C60)] (M = Fe, (12);M = Ru, (13)) are reported to form from the reaction of C60 with Fe2(CO)9

and Ru(CO)5, respectively, in benzene solvent at room temperature(Scheme 5). They have been characterized by IR and 13C NMR spectros-copy. Both are only moderately stable, with the binding of ruthenium tofullerene being stronger than that of iron [7, 14].

Treatment of l,2-(3,5-cyclohexadieno)buckminsterfullerene with tri-iron dodecacarbonyl in refluxing benzene is reported to yield [n4-l,2-(3,5-cyclohexadieno)buckminsterfullerene]iron tricarbonyl (14) (Scheme 6).

Fig. 5. Structure of C60{Re(CO)5}2 (11) (reproduced with permission from the AmericanChemical Society (1993). J. Am. Chem. Soc. 115, 6705).


Scheme 5. Formation of [M(CO)4(n2-C60)] M = Fe, (12); M = Ru, (13).

Compound 14 has been characterized by IR, 1H and 13C NMR spectros-copy, and structurally characterized by X-ray diffraction analysis (Fig. 6).Its molecular structure shows one apical carbonyl group on the iron atomto be in close proximity to the C60 surface. The contact distances are in therange of 3.23-3.49 A which are well within the range of Van der Waals dis-tances. It also shows a significant steric compression between the Fe(CO)3

and C60 moieties [15].Rauchfuss and co-workers [5] have reported the photoaddition

of Fe2S2(CO)6 to C60 (Scheme 7). Multiple addition products,C60[Fe2S2(CO)6]n, n = l-6, are obtained in these reactions and can beseparated by HPLC techniques. They have been characterized by IR,13C NMR and uv-vis spectroscopy, and mass spectrometry. Single crystalX-ray analysis of the monoadduct, C60Fe2S2(CO)6 (15) shows that the S-Sbond of the Fe2 reagent is cleaved to give a dithiolate with idealized C2v

symmetry (Fig. 7). On treatment of C60 with Fe2S2(CO)5(PPh3) underphotolytic conditions the multiple addition products C60[Fe2S2(CO)5

(PPh3)], n = 1 (16), 2 (17) are obtained (Scheme 8).

Scheme 6. Formation of [n4-l,2-(3,5-cyclohexadieno)buckminsterfullerene]iron tricarbonyl (14).


Fig. 6. Molecular structure of [n4-l,2-(3,5-cyclohexadieno)buckminsterfullerene]iron tricar-bonyl (14) (reproduced with permission from the American Chemical Society (1996).Organometallics 15, 4340).

Fig. 7. Molecular structure of C60Fe2S2(CO)6 (15) (reproduced with permission from theAmerican Chemical Society (1996). Inorg. Chem. 35, 7140).

Scheme 7. Reaction of (CO)6Fe2S2 with C60.

Scheme 8. Reaction of (CO)5(PPh3)Fe2S2 with C60.


Fig. 8. Molecular structure of Cp*2Ru2(u-Cl)(u-H)(C60) (18) (reproduced with permissionfrom the American Chemical Society (1995). Organometallics 14, 4454).

The redox properties of the C60/Fe2S2(CO)6 adducts have beenstudied by cyclic voltametry. Neither Fe2S2(CO)6 nor Fe2S2(CO)5(PPh3)is electroactive, whereas four reductions are observed for C60Fe2S2(CO)6

at -450, -831, -1281, and -1782 mV vs Ag/AgCl. In comparison toC60, the first couple is shifted cathodically by about 25 mV.

Reaction of an equimolar mixture of [Cp*Ru(u-H)2]2 and[Cp*RuCl2]2 with C60 yields Cp*2Ru2(u-Cl)(u-H)(C60) (18), whereasreaction of [Cp*RuCl2]2 with C60 gives Cp*2Ru2(u-Cl)2(C60) (19). Struc-tures of both the compounds have been established crystallographically(Figs. 8 and 9 respectively) [16].

Fig. 9. Molecular structure of Cp*2Ru2(u-Cl)2(C6 0) (19) (reproduced with permission fromthe American Chemical Society (1995). Organometallics 14, 4454).


A cationic complex, [{Cp*Ru(CH3CN)2}3C60]3+ (X-)3 (20), isformed by the reaction of excess of Cp*Ru(CH3CN)3 + X- with C60. Thisreaction is consistent with C60 behaving more like an electron poor than anelectron rich alkene [2].

The synthesis and structural characterization of a hexahapto C60

complex in which C60 displays arene like coordination to the open faceof triruthenium cluster has been reported by Shapley and co-workers[17]. Thermolytic reaction of C60 with Ru3(CO)12 in hexane yieldedRu3(CO)9(u3-n2 ,n2 ,n2-C6 0) (21) (Fig. 10) in which a Ru3 triangle is posi-tioned centrally over a ring of six carbons in the fullerene framework andthe two planes are essentially parallel. IR spectroscopic features and struc-tural features observed in the single crystal X-ray diffraction analysis ofcompound 21 are similar to that observed for Ru3(CO)9(u3-n2,n2,n2-C6H6).

The first X-ray crystallographic analysis of the carbon framework ofC60 was achieved by derivatising the fullerene using OsO4, thus providingthe first definite proof of the C60 structure [1]. The stoichiometry of thereaction was controlled by varying the ligands on the OsO4 unit of thederivatised C60. Following the strategy adopted for the osmylation ofpolycyclic aromatic hydrocarbons, Hawkins and co-workers successfullysynthesized (C60)OsO4(4-t-BuC5H4N)2 (22) (Scheme 9) and grew singlecrystals suitable for the X-ray diffraction analysis (Fig. 11).

Addition of triosmium unit to C60 is found to be sensitive to the reac-tion conditions used. A toluene solution of Os3(CO)11(NCMe) reacts with

Fig. 10. Molecular structure of Ru3(CO)9 (u3-n2, n2, n2-C60) (21) (reproduced with permis-sion from the American Chemical Society (1996). J. Am. Chem. Soc. 118, 9192).


Scheme 9. Formation of (C6 0)OsO4(4-t-BuC5H4N)2 (22) .

C60 at 80°C to give Os3(CO)11(n2-C60) (23). It is suggested that the singletriosmium unit is attached to C60 through an n2-fashion. In a similarmanner, Os3(CO)10(NCMe)2 also reacts with C60 to give two isomers ofOs3(CO)10(NCMe)(n2-C60), (24(i) and 24(ii)). These two compounds areshown to be interconvertible by carbonylation or decarbonylation.Phosphine substituted triosmium complexes, Os3(CO)10)(PPh3)(n2-C60)(25) and Os3(CO)9(PPh3)2(n2-C60) (26) have been obtained from thereaction of Os3(CO)11(PPh3) and Os3(CO),10(PPh3)2, respectively, withMe3NO and MeCN in CH2Cl2 followed by treatment with C60 in tolueneat room temperature. Compound 24 reacts with PPh3 to yield compounds25 and 26 upon decarbonylation with Me3NO. Compounds 23-26 havebeen primarily characterized by IR, and 1H, 13C, and 31P NMR spec-troscopy, and by mass spectrometry (Fig. 12). Although double addition ofthe triosmium units to the C60 core is also observed in the same reactions,these products are much less stable than the single addition products and

Fig. 11. Structure of (C6 0)OsO4(4-t-BuC5H4N)2 (22).


Fig. 12. Products obtained from reactions of Os3(CO)12_x(L)x, L = NCMe, PPh3; x= 1, 2with C60.

readily convert to the latter. On dropwise addition of a chlorobenzene solu-tion containing equimolar quantities of Os3(CO)11(L) (L = NCMe, PMe3)and Me3NO to a refluxing chlorobenzene solution of C60, formation ofOs3(CO)8L(u3,n2,n2,n2-C60) (L = NCMe (27), PMe3 (28)) occurs. Com-pounds 27 and 28 (Fig. 12) have been characterized by IR and 1H, 13C,and 31P NMR spectroscopy and by mass spectrometry [18, 19].

Group 9 (Co, Rh, Ir)

A series of C60-rhodium complexes [Rh(acac)(L)2(n2-C60)], (L = py(29), 4-Mepy (30), 3,5-Me2py (31)) have been prepared by the reaction of[Rh(acac)(C2H4)2] with C60 followed by treatment with pyridine or itsderivatives (Scheme 10). The molecular structure of 31 is reported (Fig. 13)[20].


Although seemingly straightforward, the synthesis of some metal-fullerene derivatives is dependent on nature of solvent used. This is shownby the reaction of [Rh(PPh3)3(CO)H] with C60 in dichloromethane toform [Rh(PPh3)2(CO)(n2-C60)H] (32) in 75% yield [21]. Compound 32has been characterized by IR and 1H and 31P NMR spectroscopy. Its struc-ture has also been established crystallographically (Fig. 14). A muchimproved yield ( > 95 %) of compound 32 is obtained when the reaction is

Fig. 13. Molecular structure of [Rh(acac)(3,5-Me2py)2(n2-C60)] (31) (reproduced with per-mission from the Chemical Society of Japan (1994). Chem. Leu. 801).

Scheme 10. Complexation of [Rh(acac)(C2H4)] and [Rh(PPh3)3(CO)H] with C60.


Fig. 14. Molecular structure of [Rh(PPh 3 ) 2 (CO)(n 2 -C 6 0 )H] (32).The hydride ligand wasnot located directly by crystallographic methods, but its position has been inferred to be theapparently vacant site opposite to carbonyl ligand (reproduced with permission from theAmerican Chemical Society (1993). Inorg. Chem. 32, 3577).

performed in toluene solvent (Scheme 10). It has been shown to catalyzethe hydroformylation of ethene and propene [7].

The compounds, Ir(CO)Cl(PR3)2 are excellent reagents in thederivatization of the fullerenes. Various adducts of C60 are synthesized bychanging the R group in the phosphine ligand, as well as the phosphineitself (Scheme 11), with an important feature of these reactions beingthe reversibility of addition. For example, the reaction betweenIr(CO)Cl(PPh3)2 and C60 in benzene forms (n2-C60)Ir(CO)Cl(PPh3)2

(33), which has been characterized by IR spectroscopy and single crystalX-ray diffraction analysis (Fig. 15) [22]. Reaction of Ir(CO)Cl(bobPPh2)2

Scheme 11. Reaction of C60 with [ I rCl(CO)( P P h 2 R ) 2 ] ; R = Ph. C 6 H 5 C H 2 O C 6 H 4 C H 2

3,5-bis( benzyloxy(benzyl, 3,5-bis( 3,5-bis(benzyloxy)oxy)benzyl.


Fig. 15. Molecular structure of [(n2-C60)Ir(CO)Cl(PPh3)2] (33) (reproduced with permis-sion from the American Chemical Society (1991). Inorg. Chem. 30, 3980).

(bob = C6H5CH2OC6H4CH2) with C60 yields a complex (n2-C60)Ir-(CO)Cl(bob PPh2)2 (34) (Fig. 16) in which two arms of phosphine ligandof one molecule reach out to cradle the C60 portion of an adjacentmolecule. This interaction continues on to the next molecule, and aninfinite chain results [23].

Fig. 16. Molecular structure of [n 2 -C 6 0 ) I r (CO)Cl{ (C 6 H 5 CH 2 OC 6 H 4 CH 2 )PPh 2 } 2 ] (34)(reproduced with permission from the American Chemical Society (1992) . J. Am. Chem. Soc.114, 5455).


Scheme 12. Reaction of C60 with [IrCl(CO)(PPh2R)2]; R = 3,5-bis(benzyloxy(benzyl, 3,5-bis( 3,5-bis(benzyloxy)oxy (benzyl.

Formation of the monoadducts, trans-Ir(CO)Cl(PPh2(G-l))2(C60)(35) and trans-Ir(CO)Cl(PPh2(G-2))2(C60) (36), [G-l =3,5-bis(ben-zyloxy)benzyl and G-2 = 3,5-bis((3,5-,bis(benzyloxy)oxy)benzyl] is observedfrom the reaction of C60 with trans-Ir(CO)Cl(PPh2R)2; R = G-1, G-2, inchlorobenzene (Scheme 12). Thermodynamic data and IR and 31P{1H}NMR spectral line width analysis indicate reversible binding in chloroben-zene [24].

In order to obtain suitable single crystals of fullerene oxides for X-raydiffraction studies, Balch and co-workers studied the reaction betweenC60O and Vaska type iridium complexes. While reaction of C60O withIr(CO)Cl(PPh3)2 resulted in partial deoxygenation of fullerene epoxide, its

Fig. 17. Molecular structure of (n2-C6lO)Ir(CO)Cl(AsPh3)2.4.82C6H6.0.18CHCl3 (37)(reproduced with permission from the American Chemical Society (1996). Inorg. Chem. 35,458).


Scheme 13. Reaction of C60 with [IrCl(CO)(P R2R')2]; R, R' = Me, Et, Ph.

Fig. 18. Molecular structures of [n2-C60IrCl(CO)(PR2R)2]; R = Me, R' = Ph (38) R,R' = Me, (39); Et, (40) (reproduced with permission from the American Chemical Society(1992). J. Am. Chem. Soc. 114, 10984 and the American Chemical Society (1994). Inorg. Chem.33, 5238).


Scheme 14. Reaction of C60 with Ir(CO)(C,H7).

reaction with Ir(CO)Cl(AsPh3)2 produced crystalline (n2-C6 0O)Ir(CO)Cl(AsPh3)2.4.82C6H6 .0.18CHC13 (37). The structure of 37 shows that theiridium complex is bound to a 6:6 ring junction of the fullerene with fourpartially occupied sites for epoxide oxygen atom (Fig. 17) [25].

Double adduct compounds, [(C60){Ir(CO)Cl(PR2R')2}2] (R = Me,R' = Ph; (38) [26] R, R'= Me; (39) R, R'= Et (40) [27] have alsobeen reported (Scheme 13), and the structures of these compounds havebeen elucidated crystallographically (Fig. 18). An indenyl derivative,(C60)Ir(C9H7)(CO) (41) has been prepared according to Scheme 14, andit has been characterized by IR and 1H NMR spectroscopy [28].

A multimetallic addition product, C60{Ir2CL2(l,5-cod)2}2, (42) inwhich two units of Ir2Cl2(l,5-cod)2 bind to opposite ends of a C60

framework, giving a C60 point group symmetry for a molecule, has beensynthesized by treating C60 with Ir2Cl2(l,5-cod)2 in 1:1 molar ratio atroom temperature [29], and its structure established crystallographically(Fig. 19).

Fig. 19. Molecular structure of [(C60){ Ir2Cl2( l,5-cod)2} ] (42) (reproduced with permissionfrom the American Chemical Society (1993). J. Am. Chem. Soc. 115, 4901).

Group 10 (Ni, Pd, Pt)

The ammoniate [Ni(NH3)6]C60 ·6NH3 (43) has been prepared viacation exchange in liquid ammonia, and its structure has been determinedcrystallographically [30]. Reaction of [Ni(C5Me5)2] with C60 in CS2

formed [Ni(C5Me5)2 + ][C6 0 -]-CS2 (44) [31]. Its structure, establishedcrystallographically, shows a C60 anion which is slightly distorted from Th

symmetry. The [Ni(C5Me5)2] + is found directly over a pentagonal ring ofthe C60- anion, with the closest C5Me5 ring staggered relative to the C60 -

ring.The only bis fullerene Ni complex to have been reported is the ionic

Ni(C60)2 + (45), observed in the gas phase by FT mass spectrometry [32].Room temperature reaction of equimolar quantities of M(PEt3)4 and

C60 yields monoadducts, [(n2-C60)M(PEt3)2] M = Ni (46), Pd (47), Pt(48) (Scheme 15).

A multiple adduct, (n2-C60){M(PEt3)2}6 (M = Ni (49), Pd (50), Pt(51)) has been obtained from the reaction of excess M(PEt3)4 with C60

(Scheme 16). Single crystal X-ray diffraction analysis of 51 shows sixn2-interactions [33, 34].

Equimolar quantities of Pd(PPh3)4 and C60 react at room temperatureto produce (n2-C60)Pd(PPh3)2 (52). Compound 52 has been spectroscopi-cally and structurally characterized by 31P NMR spectroscopy, elementalanalysis, absorption spectrometry and single crystal X-ray diffractionanalysis (Fig. 20) [35].

Similarly, in the room temperature reaction of [(C6H5)3P]2Pt(n2-C2H4)] with C60 in toluene, the coordinated ethylene is displaced by C60

to yield the Pt-C60 complex, [(C6H5)3P]2Pt(n2-C60)] (53). Its structurehas been established crystallographicaly (Fig. 21) [2],

A C60-supported Pd catalyst has been prepared by reaction of C60

with Pd(OAc)2(PPh3)2 in toluene, followed by H2 treatment to give thecomplex C60[Pd(OAc)2(PPh3)]3 (54), It has been characterized by FTIR,

Synthetic Methodologies and Structures of Metal-[C60] Fullerene Complexes 411

Scheme 15. Reaction of C60 with (PEt3)4M; M = Ni, Pd, Pt.

Scheme 16. Reaction of C60 with excess of (PEt3) 4M; M = Ni, Pd, Pt.

412

mass spectrometry, thermogravimetry, powder X-ray diffraction, transmis-sion electron microscopy and X-ray photoelectron spectroscopy, and isreported to promote hydrogenation of diphenylacetylene, phenylacetylene,cyclohexene and hex-1-ene to give 100% conversion to respectivehydrogenated products [36].

Organopalladium or platinum complexes, (n2-C60)M(CNR)2 (M = Pd(55), Pt (56), R = tBu, 2,6-Me2C6H3, 2,4,6-Me3C6H2, cyclohexyl) havebeen synthesized from C60Mn (M = Pd, Pt, n = ca. 1) and the correspond-ing isonitriles (Scheme 17). Compounds 56a-d have been characterized byIR and 1H and 13C NMR spectroscopy. The Pt complexes (56a-c) reactwith additional isonitrile to form (n2-C60)Pt(CNR)4 (57a-c), where Ptbinds to C60 through CNR ligand (Scheme 18) [37].

Reaction of [60] fullerene with [Pt(cod)2] results in facile displace-ment of the cod ligand to form insoluble PtC60. When the THF suspensionof PtC60 is treated with bidentate diphosphine L-L = Ph2P(CH2)nPPh2

(« = 2, 3), a cleavage of the C-Pt bond occurs and [Pt(n2-C60)(L-L)](L-L = dppe (58), dppp (59)) are formed (Scheme 19). Both have beencharacterized by IR and 1H, 13C and 31P-{1H} NMR spectroscopy, andelectron-impact mass spectrometry [38].

Fig. 21. Structure of [(n2-C60)Pt(PPh3)2] (55).

Mathur, Mavunkal, and Umbarkar

Fig. 20. Molecular structure of [(n2-C60)Pd(PPh3)2] (50) (reproduced with permissionfrom the American Chemical Society (1993). Organometallics 12, 991).


Scheme 17. Reaction of C60 Mn, M = Pd, Pt; n = ca 1 with isonitrile.

Scheme 18. Formation of (n2-C6 0) Pt(CNR)4 .

Scheme 19. Formation of [ ( n 2 - C 6 0 ) P t ( L - L ) ] ; L-L = dppe (56), dppp (57).

414

Reaction of trans-[Pt(H)2(PCy3)2] with C60 at room temperatureaffords [Pt(PCy3)2 (n2-C60)] (60) in nearly quantitative yield (Scheme 20).The most probable reaction pattern suggested is the insertion of a fullerene6,6 junction onto a Pt-H bond yielding a n1 alkyl derivative which, afterhydrogen extrusion, gives 60 [39].

CONCLUSIONS

The above survey clearly shows that a large number of complexes ofC60 with transition metals are now available. Continued efforts by research-ers in this area will no doubt yield additional approaches for obtainingmore new metal bound and ligand bound complexes. Also, it is anticipatedthat in view of the good NLO responses shown by C60 [40] and recentlyby some metal carbonyl compounds containing bridging ligands derivedfrom elements of Groups 15 and 16 [41], complexation of C60 with suchmixed transition metal, nonmetal moieties might produce compounds withenhanced NLO activities and other interesting physical properties.

REFERENCES

1. J. M. Hawkins, A. Mayer, T. A. Lewis, S. Loren, and F. J. Hollander (1991). Science 252,312.

2. P. J. Fagan, J. C. Calabrese, and B. Malone (1991). Science 252, 1160.3. (a) A. Hirsch, The Chemistry of Fullerenes (Thieme, Stuttgart, 1994); (b) J. R. Bowser

(1994). Adv. Organomet. Chem. 36, 57; (c) A. L. Balch, in R. Taylor (ed.), The Chemistryof Fullerenes, Advanced Series in Fullerenes, Vol 4 (World Scientific Publishing,Singapore, 1995), p 200; (d) A. H. H. Stephens and M. L. H. Green (1997). Adv. Inorg.Chem. 44, 1.

4. S. Yamage, M. Yanagawa, and E. Nakamura (1994). J. Chem. Soc., Chem. Commun. 2093.5. M. D. Westmeyer, T. B. Rauchfuss, and A. K. Verma (1996). Inorg. Chem. 35, 7140.6. S. Bellenweng, R. Gleiter, and W. Kratschmer (1993). Tel. Lett. 34, 3737.7. R. E. Douthwaite, M. L. H. Green, A. H. H. Stephens, and J. F. C. Turner (1993).

J. Chem. Soc., Chem. Commun. 1522.8. A. Penicaud, J. Hsu, and C. A. Reed (1991). J. Am. Chem. Soc. 113, 6698.9. M. N. Netedova and V. I. Sokolov (1995). Russian Chemical Bulletin 44, 761.

Mathur, Mavunkal, and Umbarkar

Scheme 20. Reaction of C60 with [trans-Pt(H)2(PCy3)2].

10. K. Tang, S. Zheng, X. Jin, H. Zeng, Z. Gu, X. Zhou, and Y. Tang (1997). J. Chem. Soc.Dalton Trans. 3585.

11. (a) J. R. Shapley, Y. Du, H.-F. Hsu, and J. J. Way, in K. M. Radish and R. S. Ruoff(eds.),The Electrochemical Society Proceedings Series, Vol. 94 (Pennington, New Jersey, 1994),p. 1255; (b| H.-F. Hsu, Y. Du, T. E. Albright-Schmitt, S. R. Wilson, and J. R. Shapley(1998). Organometallics 17, 1756.

12. M. D. Upward, P. Moriarty, P. H. Beton, S. H. Baker, C. Binns, and K. Edmonds (1997).Appl Phys. Lett. 70, 2114.

13. S. Zang, T. L. Brown, Y. Du, and J. R. Shapley (1993). J. Am. Chem. Soc. 115, 6705.14. M. Rasinkangas, T. T. Pakkanen, and T. A. Pakkanen (1994). J. Organomet. Chem. 476,

C6.15. M.-J. Arce, A. L. Viado, S. 1. Khan, and Y. Rubin (1996). Organometallics 15, 4340.16. I. J. Mavunkal, Y. Chi, S.-M. Peng, and G.-H. Lee (1995). Organometallics 14, 4454.17. H.-F. Hsu and J. R. Shapley (1996). J. Am. Chem. Soc. 118, 9192.18. J. T. Park, J.-J. Cho, and H. Song (1995) J. Chem. Soc., Chem. Commun. 15.19. J. T. Park, H. Song, J.-J. Cho, M.-K. Chung, J.-H. Lee, and I.-H. Suh (1997). Organome-

tallics 17, 227.20. Y. Ishii, H. Hoshi, Y. Hamada, and M. Hidai (1994). Chem. Lett. 801.21. A. L. Balch, J. W. Lee, B. C. Noll, and M. M. Olmstead (1993). Inorg. Chem. 32, 3577.22. A. L. Balch, V. J. Catalano, and J. W. Lee (1991). Inorg. Chem. 30, 3980.23. A. L. Balch, V. J. Catalano, J. W. Lee, and M. M. Olmstead (1992). J. Am. Chem. Soc.

114, 5455.24. V. J. Catalano and N. Parodi (1997). Inorg. Chem. 36, 537.25. A, L. Balch, D. A. Costa, B. C. Noll, and M. M. Olmstead (1996). Inorg. Chem. 35, 458.26. A. L. Balch, J. W. Lee, B. C. Noll, and M. M. Olmstead (1992). J. Am. Chem. Soc. 114,

10984.27. A. L. Balch, J. W. Lee, B. C. Noll, and M. M. Olmstead (1994). Inorg. Chem. 33, 5238.28. R. S. Koefod, M. F. Hudgens, and J. R. Shapley (1991). J. Am. Chem. Soc. 113, 8957.29. M. Rasinkangas, T. T. Pakkanen, T. A. Pakkanen, M. Ahlgren, and J. Rouvinen (1993).

J. Am. Chem. Soc. 115, 4901.30. K. Himmel and M. Jansen (1998). J. Chem. Soc., Chem. Commun. 1205.31. W. C. Wan, X. Liu, G. M. Sweeney, and W. E. Broderick (1995). J. Am. Chem. Soc. 117,

9580.32. Y. Huang and B. S. Freiser (1991). J. Am. Chem. Soc. 113, 8186.33. P. J. Fagan, J. C. Calabrese, and B. J. Malone (1991). J. Am. Chem. Soc. 113, 9408.34. P. J. Fagan, J. C. Calabrese, and B. J. Malone (1992). Acc. Chem. Res. 25, 134.35. V. V. Bashilov, P. V. Petrovski, V. I. Sokolov, S. V. Lindeman, I. A. Guzey, and Y. T.

Struchkov (1993). Organometallics 12, 991.36. R. Yu, Q. Liu, K.-L. Tan, G.-Q. Xu, S. C. Ng, H. S. O. Chan, and T. S. A. Hor (1997).

J. Chem. Soc., Faraday Trans. 2207.37. H. Nagashima, M. Nakazawa, T. Furukawa, and K. Itoh (1996). Chem. Lett. 405.38. M. van Wijnkoop, M. F. Meidine, A. G. Avent, A. D. Darwish, H. W. Kroto, R. Taylor,

and D. R. M. Walton (1997). J. Chem. Soc.. Dalton Trans. 675.39. L. Pandolfo and M. Maggini (1997). J. Organomet. Chem. 540, 61.40. (a) S. Couris, E. Koudoumas. A. A. Ruth , and S. Leach (1995) . J. Phys. B 28, 4537:

(b) C. Li, R. Wang, Y. Song, and Y. Wang (1994). J. Opt. Soc. Am. B 11, 1356.41. (a) S. Banerjee, G. R. Kumar, P. Mathur, and P. Sekar (1997) . J. Chem. Soc., Chem. Com-

mini. 299; (b) P. Mathur, S. Ghose, M. M. Hossain. C. V. V. Satyanarayana. S. Banerjee.G. R. Kumar. P. B. Hitchcock, and J. F. Nixon (1997). Organometallics 16, 3815.


Documents

Synthetic Methodologies and Structures of Metal-[C60]Fullerene Complexes