Mixed-metal cluster chemistry 15: some bidentate phosphine chemistry of tungsten-iridium clusters

Reactions of [Cp2W2Ir2(CO)(10)] (4) with equimolar amounts of the bidentate phosphines bis(diphenylphosphino)methane (dppm) and 1,2-bis(diphenylphosph ino)ethane (dppe) afford the substitution products [Cp2W2Ir2(mu-Co)(3)(mu-L )(CO)(5)] [L = dppm (5), dppe (6)] in excellent yields (76% and 80%, respec tively). The clusters 5 and 6 are fluxional in solution, with the interconv erting isomers of 6 resolvable at low temperatures. Variable-temperature P- 31- and C-13-NMR for 5 and 6 enable structural assignment of the isomers. C -13-NMR exchange spectroscopy (EXSY) spectra reveal that the fluxional proc ess observed with 5, and which interconverts the isomers of 6, involves a ' waggling' of the CpW(CO)(2) group over the W2Ir faces or complete tripodal rotation at the apical CpW(CO)(2). Reaction of [CpWIr3(CO)(11)] (1) with an equimolar amount of the bidentate phosphine 1,2-bis(diphenylphosphino)benz ene (pdpp) affords the substitution product [CpWIr3(mu-CO)(3)(mu-pdpp)(CO)( 6)] (7) in reasonable yield (62%). Spectroscopic data suggest 7 adopts one configuration in solution, in contrast to the two configurations observed w ith [CpWIr3(mu-CO)(3)(mu-L)(CO)(6)] [L = dppe (2), dppm (3)], a result ascr ibed to the inflexible diphosphine backbone. (C) 1999 Elsevier Science S.A. All rights reserved.