Facile activation of hydrogen by unsaturated platinum–osmium carbonyl cluster complexes

Abstract

The electronically unsaturated cluster complex Os 3Pt 2(CO) 10(PBu t 3) 2 ( 10) was obtained from the reaction of Os 3(CO) 10(NCMe) 2 with Pt(PBu t 3) 2. Three side products: PtOs 3(CO) 10(PBu t 2)CMe 2CH 2(μ-H) ( 13), Os 3(CO) 10(PBu t 3) 2 ( 14) and Pt 2Os 3(CO) 10(PBu t 3)(PBu t 2)CMe 2CH 2(μ-H) ( 15) were also obtained from this reaction. The three osmium atoms in 10 lie in the equatorial plane of a trigonal bipyramid. The platinum atoms occupy the apical positions. When heated, compound 10 was converted to 15 by metallation of one of the methyl groups of one of the PBu t 3 ligands at the platinum atom to which it is coordinated. The platinum atom then shifted to an edge of the Os 3 triangle by cleaving one of its Pt–Os bonds. Compound 13 also contains a metallated PBu t 3 ligand attached to the platinum atom of the tetrahedral PtOs 3 cluster. Compound 10 reacts with hydrogen at 0 °C to yield the di- and tetra-hydrido compounds Os 3Pt 2(CO) 10(PBu t 3) 2(μ-H) 2 ( 11) and Os 3Pt 2(CO) 10(PBu t 3) 2(μ-H) 4 ( 12) with the hydrido ligands bridging Os–Pt and Os–Os bonds. With each addition of hydrogen, one of the platinum atoms in the cluster was shifted to an edge of the Os 3triangle. When solutions of 12 at 25 °C were purged with nitrogen, hydrogen was eliminated and the compounds 10 and 11 were regenerated. The electronic structures of 10 and 11 were also investigated by Fenske–Hall molecular orbital theory. When compound 10 was exposed to hydrogen for 2.5 h, compound 12 was formed together with the new tetranuclear metal cluster complexes PtOs 3(CO) 10(PBu t 3)(μ-H) 2 ( 16), PtOs 3(CO) 9(PBu t 3)(μ-H) 4 ( 17) and PtOs 3(CO) 8(PBu t 3) 2(μ-H) 4 ( 18). Compounds 16– 18 contain tetrahedrally shaped clusters of four metal atoms with bridging hydrido ligands. All new compounds were characterized structurally by single-crystal X-ray diffraction methods.