Framework expansion versus edge opening in a 50-electron phosphido-bridged triruthenium cluster. A case study

Abstract

The electron rich cluster Ru[sub 3]([mu][sub 3]-[eta][sup 2]-P(C[sub 6]H[sub 5])(C[sub 5]H[sub 4]N))([mu]-P(C[sub 6]H[sub 5])[sub 2])[sub 3](CO)[sub 6] (9) is prepared by incorporation of diphenylphosphido groups into the ligand shell of triruthenium complexes that already contain a face-bridging phosphido-pyridyl ligand. The two precursors are (i) the known acyl complex Ru[sub 3]([mu]-C(O)(C[sub 6]H[sub 5]))([mu][sub 3]-[eta][sup 2]-P(C[sub 6]H[sub 5])(C[sub 5]H[sub 4]N))(CO)[sub 9] (1), which reacts with 3 equiv of diphenylphosphine in refluxing methylcyclohexane to produce 9 in 75% yield, and (ii) the complex Ru[sub 3]([mu][sub 3]-[eta][sup 2]-P(C[sub 6]H[sub 5])(C[sub 5]H[sub 4]N))([mu]-P(C[sub 6]H[sub 5])[sub 2])(CO)[sub 6]([mu]-CO)[sub 2] (4), which also leads to 9 via reaction with 2 equiv of diphenylphosphine (yield 75%). The structure of compound 9 has been determined by X-ray diffraction. The structure consists of a triangular array of ruthenium atoms capped by a phenylpyridylphosphido ligand as referred to the antecedent species. Each Ru-Ru edge is supported by a diphenylphosphido group occupying equatorial coordination sites. The environment of each Ru atom is completed by two terminal carbonyl ligands. Even though this trinuclear species contains 50 cluster valence electrons, the three Ru-Ru bond distances are equivalent within experimental error. An electrochemical study carried out in CH[sub 2]Cl[sub 2] reveals that the compound undergoesmore » two well-defined reversible one-electron oxidations at E[sub 1/2] = 0.16 V and E[sub 1/2] = 0.53 V, respectively (vs Ag/AgCl, KCl 0.1 M, H[sub 2]O). The unusual closed geometry of 9 is rationalized in terms of molecular orbital calculations of extended Hueckel type and compared with that of the isostructural 48-e closed complex 4 and the isoelectronic 50-e open cluster Ru[sub 2]([mu][sub 3]-[eta][sup 2]-P(C[sub 6]H[sub 5])(C[sub 5]H[sub 4])([mu]-P(C[sub 6]H[sub 5])[sub 2]))(CO)[sub 9] (5). 32 refs., 6 figs., 6 tabs.« less