Organosulphur-Transition-metal Chemistry. Part 7. Sulphur Inversion in Dimolybdenum Complexes: Crystal and Molecular Structure of [Mo2(CO)2{P(OMe)3}(μ-SBut)3(η-C7H7)]

Ian B. Benson, Selby A. R. Knox, Pamela J. Naish, Alan J. Welch

Research output: Contribution to journalArticle

Abstract

Thiolato-bridged dimolybdenum complexes [Mo2(CO)3(μ-SR)3(η-C7H 7)] are formed by treating [MoI(CO)2(η-C7H7)] 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. Intercoverting isomers are also present for the monosubstituted derivatives [Mo2(CO)2(PR′3)(μ-SBu t)3(η-C7H7)] [R′3 = P(OMe)3, PMePh2, PMe2Ph, or PMe3], 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 [Mo2(CO)2{P(OMe)3}(μ-SBut) 3(η-C7H7)]. Crystals are monoclinic, space group P21/n, with four molecules in a unit cell of dimensions a = 10.186(7), b = 15.677(7), c = 19.821(15) Å, and β = 96.31 (5)°. The structure has been solved by conventional techniques and refined by least squares to R 0.046 for 5 149 diffractometer-measured reflection intensities. Three bridging SBut groups display an asymmetric stereochemistry about a Mo-Mo bond [2.9460(15) Å], 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) Å and Mo-P is 2.445(2) Å. Free energies of activation for sulphur inversion as low as 46kJ mol-1 have been derived from coalescence temperatures for several complexes.

Original languageEnglish
Pages (from-to)2235-2244
Number of pages10
JournalJournal of the Chemical Society, Dalton Transactions
Issue number11
DOIs
Publication statusPublished - 1981

ASJC Scopus subject areas

  • Chemistry(all)

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