High-pressure spectroscopic studies of reactions of the clusters [Rh4(CO)12–x{P(OPh)3}x](x= 1–4) with carbon monoxide or syngas

Abstract

The fragmentation and recombination reactions of the clusters [Rh₄(CO)_12–xL_x][L = P(OPh)₃, x= 1–4] under applied pressure of CO or CO–H₂(1:1) gases have been studied by multinuclear NMR spectroscopy using a high-pressure, high-resolution cell and by high-pressure, IR spectroscopy. Fragmentation to mixtures of dinuclear species [Rh₂(CO)_{8 –x}L_x](x= 0–2) is observed. The proportions of the variously substituted dimers in the fragmented mixture depends both on the cluster originally present in the solution and on the rhodium concentration. The dimers undergo a fluxional process analogous to that found in [Co₂(CO)₈]. Recombination on depressurisation can occur either to predominantly the original Rh₄ derivative or to mixtures in which several Rh₄ species are present in comparable amounts depending on the rhodium to phosphorus ratio. No evidence has been obtained for the formation of hydride species [RhH(CO)_4–xL_x](x= 0 or 1).