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Chemistry of the Unsaturated Cluster Compound >; X-Ray Crystal Structures of >, >, and > (Two Isomers)

DOI: 10.1039/DT9850000177

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 177 - 190 (1985)

Update date:2022-08-11

Topics:

Authors:

Farrugia, Louis J.Farrugia, Louis J.

Green, MichaelGreen, Michael

Hankey, David R.Hankey, David R.

Murray, MartinMurray, Martin

Orpen, A. GuyOrpen, A. Guy

Stone, F. Gordon A.Stone, F. Gordon A.

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Article abstract of DOI:10.1039/DT9850000177

Reactions of the unsaturated cluster compound > with hydrogen and with diazomethane have been investigated, and the structures of the products determined by X-ray diffraction.The structure of the previously prepared carbon monoxide adduct P(cyclo-C6H11)3>> has also been established.The latter species, which is formed in a readily reversed reaction, has a 'butterfly' arrangement of the metal atoms with the platinum atom at a wing-tip position.One hydrido-ligand bridges the Os-Os vector of the body of the butterfly, and the other an Os-Pt edge.The latter is cis to the P(cyclo-C6H11)3 group on the platinum, which also carries a CO ligand.The osmium atom at the other wing-tip is ligated by four CO groups, and the remaining two Os are each terminally bonded to three carbonyls.The hydrogen adduct > is also formed reversibly but in contrast with the product from carbon monoxide has a closo-tetrahedral metal core.The hydrido-ligands occupy edge-bridging sites on the cluster framework, with two bridging Os-Pt vectors and two bridging Os-Os vectors.Thus the M4 tetrahedron has D2d symmetry with two short unbridged edges and four longer bridged edges.Diazomethane readily adds to > to give the complex > which exists as an equilibrium mixture of two isomeric forms (orange-yellow and red crystals).Both species have a closo distorted tetrahedral geometry for the metal atoms, with the methylene group bridging an Os-Os edge cisoid to the P(cyclo-C6H11)3 ligand on the platinum in the orange-yellow form and transoid to the phosphine group in the red isomer.The relative positions of the hydrido-ligands also differ.In the orange-yellow form they bridge the remaining two Os-Os edges, while although not located directly in the red isomer, being assigned on potential-energy grounds, they bridge an Os-Os edge and the Os-Pt edge cis to the P(cyclo-C6H11)3 ligand.N.m.r. studies reveal that the two isomers maintain these solid-state structures in solution.The mechanism of formation of the two isomers is discussed in the context of the orange-yellow form being the kinetically controlled product, which after several days in solution establishes a 1:4 equilibrium with the red form.

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