Reactivity and ligand exchange in triplatinum clusters

Article abstract of DOI:10.1021/om00129a011

The phosphine ligands, L, in the triplatinum clusters Pt₃(CO)₃L₃ have been found to undergo a facile ligand substitution reaction with 3 equiv of L′ to give Pt₃(CO)₃L′₃ where L = P-t-Bu₃ and L′ = P-t-Bu₂Ph, L = P-t-Bu₂Ph and L′ = P-t-BuPh₂, PCy₃, and P-i-Pr₃, and L = PCy₃ and L′ = P-i-Pr₃. The substitution occurs by an associative mechanism with the Pt₃ triangle remaining intact during the process. Mixtures of Pt₃(CO)₃(P-t-Bu₂Ph)₃, 1, and either Pt₃(¹³CO)₃(P-t-Bu₂Ph)₃ or Pt₃(CO)₃(PCy₃)₃, 2, scramble both phosphine and carbonyl ligands in a much slower reaction (approximately 1 h at 25 °C whereas L′ substitution occurs in about 25 s). Reactions of the cluster 1 with CS₂, OCS, and SO₂ also have been examined. In all cases, fragmentation of the trimer occurs to give dimeric products. The reaction of 1 and CS₂ results in formation of either Pt₂(μ-CS₂)₂(P-t-Bu₂Ph) ₂, or Pt₂(μ-S)(CO)₂(P-t-Bu₂Ph)₂, 4, depending on reaction conditions, whereas 4 is obtained from the reaction of 1 with OCS. Treatment of 1 with SO₂ at 25 °C gives Pt₂(μ-SO₂)-(CO)₂(P-t-Bu₂Ph) ₂, 5, which on prolonged standing in solution at 25 °C converts to the triplatinum cluster Pt₃(CO)₂(SO₂) (P-t-Bu₂>Ph)₃, 6. ³¹P NMR spectroscopy reveals that the initial reaction gives mixtures of 5, 6, and Pt₃(SO₂)₂(CO)(P-t-Bu₂Ph) ₃.