Organometallics 1995,14, 3901-3919
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Mixed-Ring and Indenyl Analogues of Molybdenocene and Tungstenocene:' Preparation and Characterization Jose R. Ascenso,' Cristina G. de Azevedo,' Isabel S. GonCalves, Eberhardt Herdtweck,t Domitflia S. Moreno, Miguel Pessanha, and Carlos C. Rom8o* Instituto de Tecnologia Quimica e Biologica and Instituto Superior Tkcnico, R. da Quinta Grande 6, 2780 Oeiras, Portugal Received February 13, 1995@
A stepwise route to derivatives of the molybdenocene, CpzMo, and analogue mixed-ring CpCp'Mo (Cp' = CpMe, Cp*, Ind) fragments is described. Treatment of CpMo(y3-C3H5)(C0)2with HBFgOEt2 and C5H6 forms [CpMo(y4-C5H6)(C0)21[BF41,which reacts with Ph3CBF4 to give [CpzMo(C0)2][BF412 and decarbonylates to [Cp2MoH(CO)I[BF41. These complexes are a convenient new entry into molybdenocene chemistry allowing ready access to other derivatives of the types [Cp2MoL2I2+,[Cp2MoXLl+,CpzMoXz, and CpzMo(C0). Use of CbH5Me instead of cyclopentadiene allows the preparation of several mixed-ring, differentially substituted analogues of molybdenocene complexes, namely, [Cp(CpMe)MoCl(CO)l[BF41,[Cpand [Cp(CpMe)Mo(NCMe)2l[BF412. (CpMe)Mo(C0>2l[BF412,[Cp(CpMe)Mo(NCMe)(CO)I[BF412, Similar transformations of IndMo(y3-C3H&CO)2, through [IndMo(y4-C5H6)(CO)21[BF41, produce the indenyl substituted mixed-ring analogues of molybdenocene, [IndCpMo(CO)2l[BF4I2 and [IndCpMoH(CO)][BFJ Substitution reactions of these complexes produce [IndCpMo(NCMe)(CO)l[BF~l2,[IndCpMo(NCMe)21[BF&, [IndCpMoC1(CO)1[BF41,[IndCpMoI(C0)][BF4],[IndCpMoCl(NCMe)][BF41,IndCpMoCl2, IndCpMoH2, and IndCpMo(SPh)z. The fluorenyl complex FluMo(y3-C3H5)(C0)2does not lead to a parallel chemistry. [Cp*Mo(y4C&l6)(C0)2][BF41 reacts with Ph3CBF4 to give [Cp*CpMo(C0)21[BF412and decarbonylates slowly to [Cp*CpMoH(CO)][BF4],but [Cp*Mo(y4-Cp*H)(CO)21[BF41is inert with respect to both reaction pathways. Prolonged photolysis of [Cp*CpMo(C0)21[BF412 gives [Cp*CpMo(NCMe)(CO)][BF& and [Cp*CpMo(NCMe)21[BF4]2. Deprotonation of [IndMo(y4-C5H6)(CO)21[BF4],[CpW(y4-C5Hs)(C0)21[BF41,and [CpMo(y4-C5Hs)(C0)2][BF41with NEt3 gives the ringslipped complexes CpMo(y3-Ind)(CO)2, CpW(y3-Cp)(C0)2,and CpMo(y3-Cp)(C0)2,respectively. Oxidation of CpMo(y3-Ind)(CO)2gives the dication [IndCpMo(CO)2l[BF412. Deprotonation of [CpM(y4-Cp*H)(CO)21[BF4]occurs at one of the CH3 substituents in a terminal position of (M = Mo, W). The the diene t o give the allylic complexes [CpM{y3-C5(CH3)4H(CH2)}(C0)21 CpMo(y3-Ind)(CO)2,and [CpMoX-ray crystal structures of [IndCpMo(NCMe)(CO)l[BF4]2, { y3-C5(CH3)4H(CH2)}(CO)2] are presented. The latter is present in a n enantiomerically pure R form in the analyzed crystals. Introduction Since the discovery of CpzMHz (M = Mo, W), one of the earliest characterized transition metal hydrides,l the chemistry of molybdenocene and tungstenocene derivatives produced a number of examples of key complexes and reaction steps in organometallic chemistry. Among these reactions, acetylene insertion into the Mo-H bond,2 a-hydride e l i m i n a t i ~ nand , ~ intermolecular C-H a ~ t i v a t i o nare , ~ the most important and pioneered their respective fields. The remarkable thermodynamic and kinetic stability of the CpzM fragment ' Present address: Centro de Quimica Estrutural, Instituto Superior Tecnico, 1096 Lisboa Codex, Portugal. = Present address: Anorganisch-chemisches Institut, Technische Universitat Miinchen, Lichtenbergstrasse 4,D-85747 Garching, Germany. @Abstractpublished in Advance ACS Abstracts, July 15, 1995. (1)Green, M. L. H.; McCleverty, J. A.; Pratt, L.; Wilkinson, G. J . Chem. SOC.1961,4854. (2) Nakamura, A.; Otsuka, S. J . Molecular Catalysis 1976,1, 285 and references therein. (3)(a) Cooper, N. J.; Green, M. L. H. J . Chem. SOC.,Dalton Trans. 1979, 1121. (b) Bullock, R.M.; Headford, C. E. L.; Kegley, S. E.; Norton, J . R. J . A m . Chem. Soc., 1985,107, 727.
created the basis for reliable and extensive thermochemical studies on M-L bonds, including the important M-H and M-C bonds.5 Adding this stability to the fact that, with few exceptions, all the Cp2M derivatives are 18-electron complexes seems to explain the absence of catalytic insertion chemistry in these systems. In fact, compounds such as [CPZMR(CZH~)]+ (R = H, CH3) are typically quoted among the few stable cis-hydridoalkenes (or alkyl-alkenes) known.6 One way of changing this reactivity picture is by replacement of the Cp ligands by isoelectronic y5-dienyl congeners, heretofore referred to "Cp'". In fact, the energy of the frontier orbitals will be changed and, in the case of y5-dienyl ligands prone to undergo ringslippage to a y3-enyl coordination, new kinetically (4) (a) Green, M.L. H.; Knowles, P. J. J . Chem. SOC.A 1971,1508. (b)Giannotti, C.; Green, M. L. H. J. Chem. SOC., Chem Commun. 1972, 1114. (c) Cooper, N. J.; Green, M. L. H.; Mahtab, R. J. Chem. SOC., Dalton Trans. 1979,1557. (5) SimBes. J. A. M.: Dias. A. R. Polvhedron 1988.7. 1531. (6)Benfield, F. W. S.; Cooper, N. J.;Green, M. L. H. J . Organomet. Chem. 1974,76, 49.
0276-733319512314-3901$09.00/0 0 1995 American Chemical Society
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accessible pathways for substitution and other reactions Scheme 1 may be opened. Indeed, the existence of such ringCP* slippage activation in photolyzed Cp2W derivatives has been postulated by Green as a way of explaining some of the reactivity observed in the C-H activation reacoc I The geometrical rearrangetions of tung~tenocene.~ ment of a bent to a parallel metallocene structure was proposed by Otsuka in order to account for the results of acetylene insertion reactions into CpzMoHz bonds.2 Of course, Cp replacement by Cp’ might favor some of these transformations and help tune the reactivity of HAH analogue Cp’zM fragments. CP‘ In contrast to the case of group 4 metallocenes, in iii) - C O hv which the reactivity of the W salts allows the simple Cp’ = Cp. h d M=Mo CP introduction of Cp’ substituents and even the easy M=Mo,W H preparation of a variety of symmetrical and unsym[CpIndM(C0)21[BF412(M = Mo, W). This method is metrical ansa-metallocenes from LiCp’ reagent^,^ the based on the transformations of the diene complexes situation is more complex in group 6 metallocenes. In [CplM(y4-diene)(CO)21+ depicted in Scheme 1. fact, a similar preparation of Cp2WC12 from WCl4(DME) In this work we complete our previous report on the and NaCp was recently reported,* but it is doubtful that molybdenocene analogues [CpIndMoLP l5 and present this method may be extended to the direct preparation the extension of this route to the preparation of other of other Cp’2MwX2 complexes, especially in the case of mixed-ring formal analogues of molybdenocene and the more reducing Cp’ anions. However, the presence of general formula [Cp’Cp’’ML#+. tungstenocene of phosphine ligands capable of stabilizing lower oxidation states allowed the preparation of the molybdeResults and Discussion nocene analogue precursor (~~-Ind)(v~-Ind)Mo(dppe)~ 1. Preparation of the [Cp’Mo(q4-diene)(CO)21+ and the actual metallocene analogues (v5-2,4-Me2C5H&Complexes. The family of the title complexes has M(PR3)1° (M = Mo, W; R = Me, Et) from W ( P R & played an important role in diene activatiodfunctioncomplexes and the dienyl anions. Cp”2WC12 was obalization and is well-known in the cases where Cp’ = tained in 11%yield after a long and difficult sequence Cp, Ind, or Cp*.17 The general preparation involves of steps,ll and cocondensation of Mo vapor with CsMes NCMe displacement from [Cp’Mo(C0)2(NCMe)zl+,which, led t o Cp”2M0Me2.l~A similar metal vapor synthesis in turn, is made from [Cp’Mo(CO)& (Cp’ = Cp, Ind)17a,b starting with indene (IndH) gave a mixture of Ind2or Cp*Mo(C0)3Me.17’ In the case of the Cp and Ind MoH2, IndMoH(v6-IndH),and Mo(y6-IndH)2(Ind = v5derivatives, our approach uses the protonation of the C9H7).13 allyl ligand in the Cp’Mo(v3-allyl)precursors, a rather A method of preparing differentially substituted general method for the opening of two adjacent coorditungstenocene complexes was elegantly developed by nation positions.18 The method is particularly suitable Cooper following earlier scattered reports on nucleophilic addition a t the Cp rings of Cp2MX2 ~omp1exes.l~ for the [CpMo(CO)zl+derivatives since the corresponding allyl precursor, CpMo(v3-C3H5)(C0)2(l),is conveIn spite of the interest of many of these species as chiral niently available from Mo(v3-C3H5)C1(C0)2(NCMe)2, complexes, their reactivity remains essentially unC5H6, and NEt3 in almost quantitative yield, as dechanged since only slight modifications of the electronic scribed for its W analogue.16 structure and energy of these Cp(CsH4R)W2complexes The protonation of CpMo(v3-C3Hs)(CO)2with HBF4. are expected to occur relative t o the parent Cp2W2. Et20 in CH2C12 to give a red solution of [CpMo(q2-C3H6)We have previously reported a stepwise preparation (C0)2(FBF3)1(2) has been studied by Cutler and coof molybden~cene’~and tungstenocene16 complexes workers, who also showed that 2 reacts with several which is easily extendable to mixed-ring analogues, e.g., donors, L, to give [CpMo(C0)2L2l[BF41 (L = PPh3, dppe).l9 (7)Llinas, G. H.; Day, R. 0.; Rausch, M. D.; Chien, J. C. W. Organometallics 1993, 12, 1283 and references therein. We found that, according t o eq 1, addition of dienes (8) Persson, C.; Andersson, C. Organometallics 1993, 12, 2370. to a solution of 2 leads to the rapid formation of the (9) Poli, R.; Mattamana, S. P.; Falvello, L. R. Gazz. Chim. Ital. 1992,
-
I
122,315. (10)(a) Stahl, L.; Hutchinson, J. P.; Wilson, D. R.; Ernst, R. D. J . Am. Chem. SOC.1985, 1 0 7 , 5016. (b) Ernst, R. D. Chem. Rev. 1988, 88, 1255. (11) For the preparation of Cp*MXz (M = hlo, W) see: Cloke, F. G. N.; Day, J. P.; Green; J. C.; Morley, C. P.; Swain, A. C. J . Chem. SOC. Dalton Trans. 1991, 789 and references therein. (12) Green, J . C.; Green, M. L. H.; Morley, C. P. J. Organomet. Chem. 1982.233. C4. (13)VanDam, E. M.; Brent, W. N.; Silvon, M. P.; Skell, P. S. J . Am. Chem. SOC.1975,97,465 (14) (a) McNally, J. P.; Glueck, D. Cooper, N. J. J . Am. Chem. SOC. 1988, 110, 4838. (b) McNally, J. P.; Cooper, N. J. J . Am. Chem. SOC. 1989,111,4500. ( c ) Forschner, T. C.; Cooper, N. J. J. A m . Chem. SOC. 1989, 111, 7420. (15) Ascenso, J . R.; de Azevedo, C. G.; Gonqalves, I. S.; Herdtweck, E.; Moreno, D. S.; Romlo, C. C.; Ziihlke, J . Organometallics 1994,13, -~
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(16) Goncalves, I. S.; Romlo, C. C. J . Organomet. Chem. 1995,486, 155.
(17)(a) Faller, J. W.; Murray, H. H.; White, D. L.; Chao, K. H. Organometallics 1983, 2, 400. (b) Pearson, A. J.; Khan, Md. N. I.; Clardy, J. C.; Cun-heng, H. J . A m . Chem. SOC.1985, 107, 2748. ( c ) Green, M.; Greenfield, S.; Kersting, M. J . Chem. SOC.,Chem. Commun. 1985, 18. (d) Green, M.; Greenfield, S.; Kersting, M.; Orpen, A. G.; Rodrigues, R. A. J . Chem. SOC.,Chem. Commun. 1987, 97. (e) Baxter, J. S.; Green, M.; Lee, T. V. J . Chem. Soc., Chem. Commun. 1989,1595. (0 Pearson, A. J . Adu. Met. Org. Chem. 1989, 1, 1. (g) Pearson, A. J.; Mallik, S.; Mortezaei, R.; Perry, W. D.; Shively, R. J.; Youngs, W. J. J . A m . Chem. SOC.1990,112,8034. (h)Norris, D. J.; Corrigan, J . F.; Sun, Y.; Taylor, N. J.; Collins, S. Can. J . Chem. 1993,71,1029. (i) Benyunes, S. A,; Binelli, A.; Green, M.; Grimshire, M. J. J . Chem. SOC.,Dalton Trans. 1991, 895. (i)King, R. B.; Bisnette, M. B. Inorg. Chem. 1965, 4 , 475. (k) Bottrill, M.; Green, M. J . Chem. Soc., Dalton Trans. 1977, 2365. (18)Schrock, R. R.; Johnson, B. F. G.; Lewis, J. J. Chem. Soc., Dalton Trans. 1974, 951. (19) Markham, J.; Menard, K.; Cutler, A. Inorg. Chem. 1985, 2 4 , 1581.
Mixed-Ring and Indenyl Analogues of Mo-and WCp2
Organometallics, Vol. 14, No. 8, 1995 3903
Chart 1. Diene Complexes of the Type [Cp'Mo(q*=diene)(CO)~llBF~I [CpMo(y4-diene)(C0)2]BF4 (1)
3a-g [CpM0(~~-diene)(CO)2l[BF41 cations 3a-g presented in Chart 1. Of these, 3e,17a 3f,20 and 3g21 have been reported in the literature. Both conjugated and nonconjugated dienes coordinate readily to the [CpMo(C0)2]+fragment generated from 2, and the product yields obtained largely exceed those reported for the similar reaction in diethyl ether for the cases of 3e and 3g. However, the reaction is not entirely general since CsPhsH and pentaphenylcyclopentadienone (C5Ph4O) do not react with 2 whereas dimethylfulvene reacts sluggishly to g v e still unidentified products. Diene isomerization occurred in the formation of [CpMo(q4-CH~CHCHCHMe)(CO)~l[BF41 (SD, which was prepared by treatment of 2 with the nonconjugated 1,4-pentadiene. A variable temperature lH NMR (VT 'H NMR) study of 3f showed it t o be unambiguously identical to the piperylene complex described by Faller and Rosan.20 Variable temperature lH NMR shows that all complexes 3 are fluxional. The spectra obtained at room temperature are, in all cases, average spectra of the two conformers generated by the orientation of the coordinated diene relative to the Cp ring, as sketched in 4 (ex0 conformation) and 5 (endo conformation).
)LRl
R2
4 ex0
5 endo
Detailed studies of this type of processes have been reported for similar complexes, like the butadiene that show derivatives [CpMo(y4-C4H4R2)(C0)21[BF41, that rotation around the Mo-diene axis is able to perform the observed interconversion of the conformers and that the endo conformation is thermodynamically preferred.20 Lowering the temperature freezes this rotation, and the corresponding NMR spectra below ca. -50 "C show the presence of the two conformers in solutions of the new complexes 3a,c. [CpMo(y4-C5Ph4H2)(CO)21[BF4](3d)shows an average spectrum a t room temperature, but no VT NMR studies were undertaken. At -80 "C one isomer of 3a becomes slightly predominant, 52%, over the other, and, in agreement with the observations made for other [CpMo(y4diene)(CO)~][BF41 complexes,20we assign the endo conformation to the former isomer. In the case of 3c three conformers are observed. The two more abundant and interconvertible ones are assigned, on the basis of steric arguments, to the ex0 and endo conformers with the (20)Faller, J. W.; Rosan, A. M. J.Am. Chem. SOC.1977, 99,4858. (21)Kryvikh, V. V.; Gusev, 0. V.; Rybinskaya, M . I . J. Organomet. Chem. 1989,362, 351.
Dienes
I
bridgehead CH3 group on the external face of the C5Me5H ring as for 4 and 5, R I = CH3, RZ= H. They show the average bridgehead CH3 doublet at 6 0.79 ppm. The third and minor isomer of 3c (
