Cleavage of tert-butyl groups from the tri-tert-butylphosphine ligand in osmium-platinum carbonyl cluster complexes

Two products, Pt2Os3(CO)(10)(PBU3t)((PBU2CMe2CH2)-C-t)(mu-H) (1) and Pt2Os3(CO)(9)(PBU3t)(mu-PBU2t)(mu-H)(mu(3)-CCMe2) (2), were obtained from the reaction of Os-3(CO)(12) with Pt(PBU3t)(2) at 97 degrees C. Compound 2 is new and consists of a square-pyramidal cluster of five metal atoms with a bridging PBU2t ligand, a bridging hydrido ligand, and a triply bridging dimethylvinylidene ligand C=CMe2 formed by transformations of a tri-tert-butylphosphine ligand. Compound I was transformed into 2 at 125, degrees C, and compound 2 was transformed nto two new compounds, PtOs3(CO)(7)(PBU3t)(mu-PBU2t)(mu(4)-CHCMeCH) (3) and Pt4Os3(CO)(12)(mu-PBU2t)(2) (4), at 174 degrees C. Compound 3 contains a bridging PBUt2 ligand and a quadruply bridging CHCMeCH ligand in a butterfly cluster of four metal atoms. Compound 4 contains four platinum atoms and three osmium atoms. The metal atoms are arranged in the form of a doubly capped square pyramid with the four platinum atoms in the square base. Two triangles of the square pyramid are capped by OS(CO)3 groups. The molecule also contains two bridging di-tert-butylphosphido ligands on opposite sides of the Pt-4 square base. Compound 3 is electron-deficient by the amount of four electrons, and it reacts reversibly with CO to form the new compound PtOs3(CO)(8)(PBU3t)(mu-PBU2t)(mu(4)-CHCMeCH) (5) by the addition of one CO ligand to the platinum atom. The electronic structures of 3-5 were investigated by Fenske-Hall molecular orbital calculations.