Systematic synthesis of substituted hexanuclear phosphide- and phosphinidene-bridged osmium clusters

Abstract

The labilised clusters [Os₃(CO)_11–nL_n(NCMe)][n= 1, L = PMe₃ or CNBu^t; n= 2, L = P(OMe)₃] have been prepared. The reaction of [Os₃(CO)_{11 –n}L_n(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(CNBu^t)(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 –n}L_n(µ₃-PH)][n= 1, L = CNBu^t; 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.