Systematic Synthesis of Substituted Phosphido-bridged Osmium Clusters

The labilised clusters [Os3(CO)11–nLn(NCMe)][n= 1, L = PMe3 or CNBut; n= 2, L = P(OMe)3] have been prepared. The reaction of [Os3(CO)11 –nLn(NCMe)] or [Os3(CO)10{P(OMe)3}(NCMe)] with either [Os3(CO)11(PH3)] or [Os3(µ-H)(CO)10(µ-PH2)] led to the formation of the phosphide-bridged clusters [Os6(µ-H)(CO)21{P(OMe)3}(µ-PH2)], [Os6(µ-H)(CO)21(PMe3)(µ-PH2)], [Os6(µ-H)(CO)21(CNBut)(µ-PH2)], [Os6(µ-H)(CO)20{P(OMe)3}2(µ-PH 2)] and the corresponding phosphinidene-bridged clusters [Os6(µ-H)2-(CO)21 –nLn(µ3-PH)][n= 1, L = CNBut; n= 2, L = P(OMe)3] in good yield. The Os6 clusters have been fully characterised on the basis of their spectroscopic data and the molecular structures of three have been established by single-crystal X-ray analysis. The structures of [Os6(µ-H)(CO)20{P(OMe)3}2(µ-PH 2)] and [Os6(µ-H)2(CO)19{P(OMe)3}2(µ3-PH)] differ from those of previously studied hexanuclear phosphide- and phosphinidene-bridged clusters; this difference is attributed to the steric influence of the relatively bulky phosphite ligands. Proton and phosphorus NMR spectroscopy indicate that both these clusters exist in two isomeric forms in solution.