1790 Organometallics 1989, 8, 1790-1799 The difference in Ti-C(v7) and Ti-C($) separations results in the Ti atom also fractionally disordered about the center of inversion. zyxwvutsrqpon As a result, the Ti-C(v7) distances are shorter as expected. Due to the proximity of the disordered carbon atoms, refinement of the rings was very poor. No hydrogen atoms were included. Final position parameters for zyxwvutsr 5 are given in Table IV. Several diffuse peaks near a center of inversion were observed in a difference Fourier map for 6. Analysis of these positions revealed a toluene molecule in four different positions (two related by the center of inversion). One position zyxwvutsrq [C(41)] was common to both unique orientations and was given an occupancy of 0.5. Another position [C(50)] corresponded to an aryl carbon atom on one side of the inversion center and a methyl group on the other side and was also given an occupancy of 0.5. The remaining ten carbon atoms were given occupancies of 0.25. Due to the proximity of the carbon atom positions, the refinement was poor. In the final cycles, each group of six ring atoms was idealized and only the isotropic thermal parameters were allowed to refine. The hydrogen atoms (except for those associated with the toluene molecule) were included in calculated positions 0.95 A from the bonded carbon atom and allowed to ride on that atom with zyx B fived at 5.5 A’. Final positional parameters for 6 are given in Table V. Acknowledgment. We are grateful to Fina Oil and Chemical Co., Sekisui Chemical Co., and the donors to the Petroleum Research Fund, administered by the American Chemical Society, for support of this research program. We also wish to thank Prof. Helmut Alt and Mr. Daniel Mallin for assistance in obtaining the mass and NMR spectra. The National Science Foundation Chemical In- strumentation Program provided funds used to purchase the diffractometer (N.I.U.). Supplementary Material Available: Full tables of bond distances and angles, H atom coordinates, thermal parameters, and least-squares results (11 pages); listings of structure factors (9 pages). Ordering information is given on any current masthead page. zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHG Protonation of Nickel-Molybdenum and Nickel-Tungsten Alkyne Complexes with Trifluoroacetic Acid Affording p-q’,q2-Alkenyl Species: X-ray Structure of NiW (C0)2(p-q 1 2 zyxwvutsr ,q -( E)-C(Me) =CHMe) (q5-C,H,) ($-C,H,Me)- (C02CF3) Michael J. Chetcuti,” John C. Gordon, and Kelly A. Green Department of Chemistry, University of Notre Dame, Notre Dame, Indiana 46556 Phillip E. Fanwick and David Morgenstern Department of Chemistry, Purdue University, West Lafayette, Indiana 47907 Received January 72, 7989 Protonation of the heterodinuclear bridging alkyne complexes zyxwv NiM(C0)z(lr-~2,~2-RC~R’)(~5-C5H5)(~5- C5H4Me) (M = Mo, RCzR’ = MeCzMe; M = W, RCzR’ = HCzH, MeCzMe, n-PrCzH, PhC2H) with tri- fluoroacetic acid affords the neutral alkenyl complexes NiM(CO)Z(p-v1,vz-(E)-CR=CHR’)(q5-C5H5)(v5- C5H4Me)(COzCF3), in which the alkenyl ligand is a-bonded to the group 6 metal and .Ir-bonded to the nickel atom. In some cases, the alkenyl complexes are in equilibrium with the alkyne species: the position of the equilibrium depends on the particular complex and on the solvent. Proton addition is regio- and stereospecific: isomers obtained result from Markovnikov addition to the alkyne. The nickel-tungsten isomer containing the alkenyl ligand y-v1,v2-C(Ph)=CHz, resulting from Markovnikov addition, can be thermally isomerized to the anti-Markovnikov isomer NiW(CO)z(pv1,~z-(E)-CH=CHPh)(~5-C5H5)(v5- C5H4Me)(COzCF3). Deuteration of the nickel-tungsten ethyne, 1-pentyne, or phenylacetylene complexes with trifluoroacetic acid-d,, afforded (Z)-alkenyl-d, species. However, the 2-butenylnickel-molybdenum complex exists as an equilibrium mixture of E and zyxwvuts 2 isomers, and the complex NiW(CO)z(~-~1,~2-(Z)-C- (Ph)=CHD)(v5-C5H5)(v5-CgH4Me)(CO2CF3) eventually afforded a mixture of Z and E isomers when allowed to stand in solution. The complexes have been characterized by ‘H and 13C NMR and IR spectroscopy and elemental analysis. An X-ray diffraction study was carried out on 2a, NiW(CO),(r-v1,v2-(E)-C- (Me)=CHMe)(v5-C5H5)(v5-C5H4Me)(CO2CF3). Crystals of 2a (C, Hl9F3NiO4W) belong to the monoclinic space group F’2,/n (No. 14) with a = 8.3710 (7) A, b = 27.609 (5) 1, c = 9.045 (1) A, (3 = 109.210 (7)O, and 2 = 4. Introduction Mechanistic details of these reactions have been reported.2 The protonation of these alkyne complexes was of interest in order to establish whether this would be a viable route to mixed-meta1 alkenyl Protonation of homodinuclear bridging alkyne com- Plexes to afford y-v’,v2-alkenyl species has been observed for dimolybdenum c~mplexes,~,~ and an uncommon in- we have been investigating the chemistry of the group 10 cyc~openta~ieny~-carbonyl complexes N~M- (C0)4(a5-C5H5)(q5-C5H4Me) with reactive hydrocarbon ligands. The mixed-metal species react with alkynes af- fording the bridging alkyne complexes NiM(CO)z(lr- az,az-~~2~’)(v5-~5~5.)(v5-~5~4~e) (M = M~, ~ 1 . i - (1) Chetcuti, M. J.; Eigenbrot, C.; Green, K. A. Organometallics 1987, (2) Chetcuti, M. J.; Green, K. A. Organometallics 1988, 7, 2450-2457. (3) Gerlach, R. F.; Duffy, D. N.; Curtis, M. D. Organometallics 1983, 6, 2298-2306. 2, 1172-1178. 0276-7333/89/2308-1790$01.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0 1989 American Chemical Society