Cleavage of tert-Butyl Groups from the Tri-tert-butylphosphine Ligand in Osmium−Platinum Carbonyl Cluster Complexes

Two products, Pt 2 Os 3 (CO) 10 (PBu t 3 )(PBu t 2 CMe 2 CH 2 )(µ-H) ( 1 ) and Pt 2 Os 3 (CO) 9 (PBu t 3 )(µ-PBu t 2 )(µ-H)(µ 3 -CCMe 2 ) ( 2 ), were obtained from the reaction of Os 3 (CO) 12 with Pt(PBu t 3 ) 2 at 97 °C. Compound 2 is new and consists of a square-pyramidal cluster of five metal atoms with a bridging PBu t 2 ligand, a bridging hydrido ligand, and a triply bridging dimethylvinylidene ligand C═CMe 2 formed by transformations of a tri- tert -butylphosphine ligand. Compound 1 was transformed into 2 at 125 °C, and compound 2 was transformed into two new compounds, PtOs 3 (CO) 7 (PBu t 3 )(µ-PBu t 2 )(µ 4 -CHCMeCH) ( 3 ) and Pt 4 Os 3 (CO) 12 (µ-PBu t 2 ) 2 ( 4 ), at 174 °C. Compound 3 contains a bridging PBu t 2 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 PtOs 3 (CO) 8 (PBu t 3 )(µ-PBu t 2 )(µ 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.