MIXED-METAL CLUSTER CHEMISTRY VII - SOME PHOSPHINE AND ALKYNE CHEMISTRY OF CP2MO2IR2(CO)(10) - X-RAY CRYSTAL-STRUCTURES OF CP2MO2IR2(MU-CO)(3)(CO)(6)(PME3) AND CP2MO2IR2(MU(4)-ETA(2)-HC2PH)(MU-CO)(4)(CO)(4)

Reactions of Cp2Mo2Ir2(CO)(10) (1) with stoichiometric amounts of phos phines 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 excell ent yields (36-78%), shown by low temperature P-31 NMR to consist of m ixtures of interconverting isomers. An X-ray structural study of Cp2Mo 2Ir2(mu-CO)(3)(CO)(6)(PMe3) (7a), one isomer of 7, revealed that the P Me3 ligand occupies the electronically-preferred axial site (with resp ect to the plane of the bridging carbonyls). Geometries of all other i somers of 5-8 have been postulated from a combination of NMR data and results from the analogous Cp2W2Ir2(CO)(10) system. Reactions of 1 wit h 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 inserte d into the Mo-Mo bond of 1, to afford clusters with a pseudooctahedral core geometry. Qualitative analysis of reaction rates for the synthes es of 9-14 revealed the trends acetylene > terminal alkyne > internal alkyne and 4-nitrophenylacetylene > phenylacetylene, assigned to a com bination of electronic and steric effects. (C) 1997 Elsevier Science S .A.