Mixed-metal cluster chemistry: Part 20. Syntheses, crystal structures and electrochemical studies of W 2Ir 2(μ-L)(CO) 8(η 5-C 5H 4Me) 2 (L=dppe, dppf)

Abstract

The 60-electron tetrahedral clusters W 2Ir 2(μ-L)(CO) 8(η 5-C 5H 4Me) 2 [L=dppe ( 2), dppf ( 3)] have been prepared from reaction between W 2Ir 2(CO) 10(η 5-C 5H 4Me) 2 ( 1) and the corresponding diphosphine in 52 and 66% yields, respectively. A structural study of 2 reveals that three edges of a WIr 2 face are spanned by bridging carbonyls, that the iridium-ligated diphosphine coordinates diaxially and that the tungsten-bound methylcyclopentadienyls coordinate axially and apically with respect to the plane of bridging carbonyls. A structural study of 3 reveals that the dppf ligand bridges an IrIr bond which is also spanned by a bridging carbonyl; tungsten-ligated methylcyclopentadienyl ligands and terminal carbonyls result in electronic asymmetry (17e and 19e iridium atoms) in the electron-precise cluster. Both clusters show two reversible one-electron oxidation processes and an irreversible two-electron reduction; the dppf-containing cluster 3 has a further, irreversible, one-electron oxidation process. UV–vis-NIR spectroelectrochemical studies of the 2→ 2 +→ 2 2+ progression reveal the appearance of a low-energy transition on oxidation to 2 + which persists on further oxidation to 2 2+.