Mixed-metal cluster chemistry. 2.¹ site-selective substitution of CpWIr₃(CO)₁₁ by phosphines: X-ray crystal structures of CpWIr₃(μ-CO)₃(CO)₇(PPh₃), CpWIr₃(μ-CO)₃(CO)₆(PPh₃) ₂, and CpWIr₃(μ-CO)₃(CO)₇(PMe₃)

Abstract

Reactions of CpWIr3(CO)11 (1) with stoichiometric amounts of phosphines afford site-selective products CpWIr3(μ-CO)3(CO)8-x(L)x (L = PPh3, x = 1 (2), 2 (3), or 3 (4); L = PMe3, x = 1 (5), 2 (6), or 3 (7)) in fair to excellent yields (38-63%). These products exhibit ligand fluxionality in solution, resolvable at low temperature into the constituent interconverting isomers. The structures of three of the species, namely 2a, 3a, and 5a, have been determined by X-ray diffraction studies. The single-crystal X-ray studies reveal that ligand substitution induces a rearrangement in the cluster coordination sphere from the all-terminal carbonyl ligand geometry of CpWIr3(CO)11 to one in which the three edges of a WIr2 face of the tetrahedral core contain bridging carbonyls (2a, 3a) or one in which the three edges of the triiridium face are bridged by carbonyl ligands (5a). The triphenylphosphine 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 this face. The trimethylphosphine ligand in 5a is located in an axial site with respect to the basal carbonyl-bridged triiridium plane. Information from the crystallographically-verified isomers, the ligand substitution pattern in the related tetrairidium system, and chemical shifts of signals in the 31P NMR spectra has been used to suggest coordination geometries for the isomeric forms of the complexes above and for other reported derivatives.