Mixed-metal cluster chemistry VII:: some phosphine and alkyne chemistry of Cp2Mo2Ir2(CO)10;: X-ray crystal structures of Cp2Mo2Ir2(μ-CO)3(CO)6(PMe3) and Cp2Mo2Ir2(μ4-η2-HC2Ph)(μ-CO)4(CO)4

Reactions of Cp2Mo2Ir2(CO)(10) (1) with stoichiometric amounts of phosphines afforded the substitution products Cp2Mo2Ir2(CO)(10-x)L-x (L = PPh3, x = 1 (5), 2 (6); L = PMe3, x = 1 (7), 2 (8)), in fair to excellent yields (36-78%), shown by low temperature P-31 NMR to consist of mixtures of interconverting isomers. An X-ray structural study of Cp2Mo2Ir2(mu-CO)(3)(CO)(6)(PMe3) (7a), one isomer of 7, revealed that the PMe3 ligand occupies the electronically-preferred axial site (with respect to the plane of the bridging carbonyls). Geometries of all other isomers of 5-8 have been postulated from a combination of NMR data and results from the analogous Cp2W2Ir2(CO)(10) system. Reactions of 1 with a range of alkynes afforded Cp2Mo2Ir2(mu(4)-eta(2)-RC2R')(CO)(8) (R = R' = Ph (9), H (14); R = H, R' = Ph (10), 4-C6H4NO2 (11), 4,4'-C6H4C=CC6H4NO2 (12), CH2Br (13)) in fair to good yields (34-80%). An X-ray structural study of 10 revealed that the alkynes have formally inserted into the Mo-Mo bond of 1, to afford clusters with a pseudooctahedral core geometry. Qualitative analysis of reaction rates for the syntheses of 9-14 revealed the trends acetylene > terminal alkyne > internal alkyne and 4-nitrophenylacetylene > phenylacetylene, assigned to a combination of electronic and steric effects. (C) 1997 Elsevier Science S.A.