Chemistry of the metal carbonyls. Part 76. Platinum–osmium carbonyl complexes derived from decacarbonyldi-µ-hydrido-triosmium; X-ray crystal structure of [Os3Pt(µ-H)2(CO)10{P(cyclo-C6H11)3}]

Abstract

Reactions between [OS₃(µ-H)₂(CO)₁₀] and the compounds [Pt(C₂H₄)₂(PR₃)][PR₃= P(cyclo-C₆H₁₁)₃, PPh₃, or PBu^t₂Me] afford tetranculear metal complexes [Os₃Pt(µ-H)₂(CO)₁₀(PR₃)]. Examination of the variable-temperature ¹H n.m.r. spectra of these ‘58-electron’ clusters reveals dynamic behaviour with site exchange of the two hydrido-ligands, the energy barrier for this process for the PBu^t₂Me derivative being ca. 58 kJ mol^–1. In order to establish the molecular structure of these complexes a single-crystal X-ray diffraction study was made on the compound containing the P(cyclo-C₆H₁₁)₃ ligand. Crystals are monoclinic, space group P2₁/c, Z= 4, in a unit cell of dimensions a= 11.822(4), b= 16.584(5), c= 17.763(9)Å, and β= 108.10(4)°. The structure has been refined to R 0.035 (R′ 0.038) for 5 737 reflections to 2θ < 60°(Mo-K_α, X-radiation) collected at 200 K. The metal atoms adopt a slightly asymmetric tetrahedral structure [Os–Os 2.777(1), 2.741(1), and 2.789(1)Å; Os–Pt 2.791(1), 2.832(1), and 2.863(1)Å]. The platinum atom is bonded to a CO group and to the P(cyclo-C₆H₁₁)₃ ligand, and each osmium is attached to three CO groups. The hydrido-ligands bridge the longer of the Os–Os and Os–Pt bonds, as deduced from observation of residual electron densities, from widening of certain Pt–Os–CO and Os–Os–CO angles, from staggered conformations of two of the Os(CO)₃ groups with respect to the two longer edges of the tetrahedron, and from calculation of potential energy minima.