Reactions of co-ordinated ligands. Part 30. The transformation of methylenecyclopropanes into cationic η4-trimethylenemethanemolybdenum complexes, reactions with nucleophilic reagents, and the molecular structure of [Mo{η4-C(CH2)3}(CO) 2(η-C5Me5)][BF4]

Stephen R. Allen, Stephen G. Barnes, Michael Green, Grainne Moran, Lynda Trollope, Nicholas W. Murrall, Alan J. Welch, Dima M. Sharaiha

Research output: Contribution to journalArticle

Abstract

Reaction of [Mo2(CO)6(η-C5Me5)2] with methylenecyclopropane and AgBF4 in CH2Cl2 affords the cationic trimethylenemethane complex [Mo{η4C(CH2)3}(CO)2(η-C 5Me5)][BF4]. Methylenecyclopropane and 2,2-dimethylmethylenecyclopropane react with Mo(NCMe)2(CO)2(η-C5H5)][BF 4] to give [Mo{η4-C(CH2)3}(CO) 2(η-C5H5)][BF4] and [Mo{η4-C(CH2)2CMe2}(CO) 2(η-C5H5)][BF4] respectively. A single-crystal X-ray diffraction study of [Mo{η4-C(CH2)3}(CO) 2(η-C5Me5)][BF4] confirmed that ring opening of methylenecyclopropane had occurred. The complex crystallises in the centrosymmetric orthorhombic space group Pbca with a = 12.822(2), b = 12.311 (3), c = 22.660(4) Å, and Z = 8 ion pairs. The structure has been solved by conventional methods and refined by full-matrix least squares to R = 0.0674 for 2 747 observed reflections at 268 ± 1 K. In the cation the trimethylenemethane ligand adopts an orientation that is syn with respect to the OC-Mo-CO angle. It is pyramidal with the CH2 groups bent towards the molybdenum atom by an average of 12.4°. There is intramolecular congestion involving the C5Me5 and C(CH2)3 ligands that may contribute towards the observed asymmetric bonding of the former to the metal atom. Extended Hückel molecular-orbital calculations suggest, that the observed syn stereochemistry is electronically preferred, and that the barrier to rotation of the η4-C(CH2)3 ligand relative to a Mo(CO)2(η-C5H5)+ fragment is high. The stereochemistry of the ring-opening reaction is disrotatory-out as exemplified by the conversion of cis-and trans-2,3-dimethylmethylenecyclopropane into syn,syn-dimethyl and syn,anti-dimethyl-trimethylene-methane complexes. The reaction of these cationic η4-trimethylenemethane complexes with the nucleophiles BH4-, OH-, CuMe2-, and SPh- affords η3-allylic complexes derived from attack on the peripheral carbons.

Original languageEnglish
Pages (from-to)1157-1169
Number of pages13
JournalJournal of the Chemical Society, Dalton Transactions
Issue number6
DOIs
Publication statusPublished - 1984

ASJC Scopus subject areas

  • Chemistry(all)

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