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Reactions of CpWIr 3 (CO) 11 (1) with stoichiometric amounts of phosphines afford siteselective products CpWIr 3 (µ-CO) 3 (CO) 8-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 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 CpWIr 3 (CO) 11 to one in which the three edges of a WIr 2 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 WIr 2 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 crystallographicallyverified isomers, the ligand substitution pattern in the related tetrairidium system, and chemical shifts of signals in the 31 P NMR spectra has been used to suggest coordination geometries for the isomeric forms of the complexes above and for other reported derivatives.

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