Synthesis and Structures of Homoleptic Methyl- and Phenylthiomethylaluminium Complexes [Al(CH2SR)3](R = Me, Ph)

Abstract

Sulfur-substituted methylmercury compounds [Hg(CH2SR)2](1a, R = Me; 1b, R = Ph) react with aluminium amalgam in refluxing toluene with transmetallation to give homoleptic tris(thiomethyl)aluminium complexes [Al(CH2SR)3](2a, R = Me; 2b, R = Ph) (degree of conversion: >80%, isolated yields: 2a 63%, 2b 41%). Their identities were confirmed by NMR spectros-copy (1H, 13C) and X-ray crystal structure analyses. In crystals of compound 2a the aluminium atoms possess a trigonal-bipyramidal arrangement with the coordination polyhedron defined by three carbon and two sulfur atoms. Two of the three CH2SMe ligands are bridging ligands (μ-η2; 1kC:2kS), the third one is terminal bound (η1; kC). The structure is polymeric. Crystals are threaded by helical chains built up of six-membered Al2C2S2 rings. Crystals of 2b are built up of centrosymmetrical dimers with six-membered Al2C2S2 rings having bridging CH2SPh ligands (μ-η2; 1kC:2kS). On each Al atom two terminal (η1; kC)CH2SPh ligands are bound. They exhibit quite different Al-C-S angles (116.7(4) and 106.5(3)?). Similar values (114.32115.7? and 109.52109.9?) were found in ab initio calculations of model compounds [{Al(CH2SR)3}2](3a, R=H; 3b, R=Me; 3c, R=CH=CH2). A conformational energy diagram for rotation of one of the terminal CH2SH ligand in the parent compound 3a around the Al-C bond is discussed in terms of repulsive interactions of lone electron pairs of sulfur atoms.