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Organosulphur-Transition-metal Chemistry. Part 7. Sulphur Inversion in Dimolybdenum Complexes: Crystal and Molecular Structure of t)3(η-C7H7)>

DOI: 10.1039/DT9810002235

Source and publish data:

Journal of the Chemical Society, Dalton Transactions p. 2235 - 2244 (1981)

Update date:2022-08-04

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Authors:

Benson, Ian B.Benson, Ian B.

Knox, Selby A. R.Knox, Selby A. R.

Naish, Pamela J.Naish, Pamela J.

Welch, Alan J.Welch, Alan J.

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Article abstract of DOI:10.1039/DT9810002235

Thiolato-bridged dimolybdenum complexes are formed by treating with RSH (R=Me, Et, Pri, or But) in the presence of NEt3.Infrared and variable-temperature n.m.r. spectroscopy reveal that the complexes exist as two isomers, arising from different relative orientations of the R groups on bridging sulphur. at ambient temperatures and above, these isomers interconvert rapidly, attributed to a low-energy sulphur inversion process, such that complete averaging of R group environments is achieved on the n.m.r. time scale.Interconverting isomers are also present for the monosubstituted derivatives t)3(η-C7H7)> , but for these only a limited averaging is observed, generating a time-averaged mirror plane of molecular symmetry.This results from the presence of a phosphorus ligand trans to one bridging sulphur and of CO trans to the other two, shown in an X-ray diffraction study of t)3(η-C7H7)>.Crystals are monoclinic, space group P21/n, with four molecules in unit cell of dimensions a=10.186(7), b=15.677(7), c=19.821(15) Angstroem, and β=96.31(5) deg.The structure has been solved by conventional techniques and refined by least to R 0.046 for 5149 diffractometer-measured reflection intensities.Three bridging SBut groups display an asymmetric stereochemistry about a Mo-Mo bond <2.9460(15) Angstroem>, rationalised on the basis of intramolecular terminal ligand-bridging ligand contacts.One molybdenum is η7 co-ordinated to a cycloheptatrienyl ring while the other carries the two CO groups and a P(OMe)3 ligand.Metal-sulphur distances range over 2.411(2)-2.549(2) Angstroem and Mo-P is 2.445(2) Angstroem.Free energies of activation for sulphur inversion as low as 46 kJmol-1 have been derived from coalescence temperatures for several complexes.

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