MIXED-METAL CLUSTER CHEMISTRY .2. SITE-SELECTIVE SUBSTITUTION OF CPWIR(3)(CO)(11) BY PHOSPHINES - X-RAY CRYSTAL-STRUCTURES OF CPWIR(3)(MU-CO)(3)(CO)(7)(PPH(3)), CPWIR(3)(MU-CO)(3)(CO)(6)(PPH(3))(2), AND CPWIR(3)(MU-CO)(3)(CO)(7)(PME(3))

Reactions of CpWIr(3)(CO)(11) (1) with stoichiometric amounts of phosp hines afford site-selective products CpWlr(3)(mu-CO)(3)(CO)(3-x)(L)(x) (L = PPh(3), x = 1 (2), 2 (3), or 3 (4); L = PMe(3), x = 1 (5), 2 (6) , or 3 (7)) in fair to excellent yields (38-63%). These products exhib it ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. The structures of three of t he species, namely 2a, 3a, and 5a, have been determined by X-ray diffr action studies. The single-crystal X-ray studies reveal that ligand su bstitution induces a rearrangement in the cluster coordination sphere from the all-terminal carbonyl ligand geometry of CpWIr(3)(CO)(11) to one in which the three edges of a WIr2 face of the tetrahedral core co ntain bridging carbonyls (2a, 3a) or one in which the three edges of t he triiridium face are bridged by carbonyl ligands (5a). The triphenyl phosphine in 2a ligates radially to the carbonyl-bridged WIr2 face; a similar site for one of the phosphines is found in 3a, with the second triphenylphosphine coordinated in an axial position with respect to t his face. The trimethylphosphine ligand in 5a is located in an axial s ite with respect to the basal carbonyl-bridged triiridium plane. Infor mation from the crystallographically-verified isomers, the ligand subs titution pattern in the related tetrairidium system, and chemical shif ts of signals in the P-31 NMR spectra has been used to suggest coordin ation geometries for the isomeric forms of the complexes above and for other reported derivatives.