The crystal and molecular structure of the title compound has been examined by single crystal X-ray diffraction. The crystals are monoclinic with a = 28.045(10), b = 8.766(3), c = 12.376(5) Å, β = 91.14(3)°. The space group is C2/c and there are eight molecules per unit cell. A total of 5053 independent reflections, of which 2860 were observed, were examined on a Syntex [Formula: see text] diffractometer. The structure was refined by full matrix least squares to an R2 value of 0.0449. The ligands form a very rough octahedron around the rhenium atom with Re—Cl(1), 2.441(3); Re—Cl(2), 2.366(3), Re—O(1), 1.684(7); Re—O(2), 1.896(6); Re—N(1), 2.144(7); Re—N(2), 2.132(7) Å. The pyridine rings are a dominant factor in determining the details of the molecular structure.

Studies of the rhenium-oxygen bond. 11. ' The crystal and molecular structure of p-oxobis(cis-dichloro-cis-di(pyridine)-trans-oxorhenium(V)), 0Re(C5H,N)2C120Re(C5H,N)2C1,0 Chem. 56, 179 (1978). The crystal structure of ~-oxobis(cis-dichloro-cis-di(pyridine)-trn~is-oxorhenium(V)), 0Re(C5H5N),CI,~O~Re(CSHSN)ZC120 has been studied by single crystal X-ray methods.The crystals were orthorhombic with lattice parameters n = 15.367(2), b = 10.283(2), c = 16.685(2) A. The space group was Pna2, and there were four formula weights per unit cell. A total of 3339 reflections, of which 2990 were observed, were examined, and the structure refined by full matrix least squares (treating the pyridine rings as groups) to an R, value of 0.0449.The dimer had a roughly rectilinear 0-Re-0-Re-0 backbone with pairs of chlorine atoms and pyridine molecules arranged cis in each half of the dimer. The two halves of the dimer were arranged such that the pairs of cis atoms in one half were rotated about the Re (1) [Traduit par le journal]

Oxidative addition of acetyl chloride to the compound [RhCI(PPh,),] leads to the formation of two acetyl-and one methyl-rhodium species, all isomeric, before reductive elimination of methyl chloride occurs to give [ RhCI(C0) -(PPh,),].The structures of all the compounds have been determined using i.r. and both l H and 31P n.rn.r. spectroscopy. The effects of changing the nature of the acid halide and the tertiary phosphine have been determined as have thermodynamic parameters for the ' carbonyl-insertion ' reactions involved. The X-ray crystal structure of the compound [RhCI,(COCH,CH,Ph) (PPh,),] demonstrates essentially a square pyramid with trans-basal chlorides, trans-basal phosphines, and an apical acyl group.REVERSIBLE ' insertion ' of carbon monoxide into is generally accepted that the mechanism involves a (carbonylation of) a metal-carbon CT bond to form an 1,2 migration of the alkyl group between a co-ordinated acylmetal compound is a very well known reaction in carbonyl group and a cis co-ordination site on the metal organotransition-metal chemistry, and is undoubtedly a [equation (l)]. This mechanism is consistent with a key step in hydroformylation-type syntheses.lY2 The group, have therefore been studied in great detail, and it reaction and it-reverse, decarbonylation of an acylmetal A. Wojcickip oyganometazzic 1973J 11, 87.

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