Mixed-metal cluster chemistry -: Part 20.: Syntheses, crystal structures and electrochemical studies of W2Ir2(μ-L)(CO)8(η5-C5H4Me)2 (L = dppe, dppf)

The 60-electron tetrahedral clusters W2Ir2(mu-L)(CO)(8)(eta(5)-C5H4Me)(2) [L = dppe (2), dppf (3)] have been prepared from reaction between W2Ir2(CO)(10)(eta(5)-C5H4Me)(2) (1) and the corresponding diphosphine in 52 and 66% yields. respectively. A structural study of 2 reveals that three edges of a WIr2 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+). (C) 2002 Published by Elsevier Science B.V.