Ligand substitutions in Ru–Pt clusters: isolation of compounds with unusual geometries

Abstract

Ligand substitution reactions of the COD (1,5-cyclooctadiene) ligand for CO or phosphines in the clusters [Ru₅C(CO)₁₄Pt(COD)] (1) and [Ru₆C(CO)₁₆Pt(COD)] (2) were investigated. Reactions with carbon monoxide gave selectively [Ru₅CPt(CO)₁₆] (3) from 1, but led to loss of either a ruthenium or the Pt(COD) unit from the Ru₆Pt cluster (2). Substitution of the COD ligand by PPh₃ in 1 gave [Ru₅C(CO)₁₄Pt(PPh₃)₂] (8) selectively, while with dppm the main product of the reaction was [Ru₅C(CO)₁₄Pt(μ-dppm)] (10). On the other hand, the reactions involving [Ru₆C(CO)₁₆Pt(COD)] (2) and phosphines led mainly to extrusion of the Pt(COD) fragment and formation of Ru-only derivatives. More precisely, with triphenylphosphine, the two clusters [Ru₆C(CO)₁₆PPh₃] (16) and [Ru₆C(CO)₁₅(PPh₃)₂] (18) were obtained from 2, while with dppm, the compounds [Ru₆C(CO)₁₅(dppm)] (15) and [Ru₆C(CO)₁₃(dppm)₂] (19) were formed. In the latter case, two additional products of increased nuclearity were isolated: [Ru₆C(CO)₁₅Pt₂(dppm)] (20) and [Ru₆C(CO)₁₆Pt₃(dppm)₂] (21). All the compounds described were characterised by spectroscopic methods and the structures of the new species were determined by X-ray crystallography.