Benzylic oligothioethers as ditopic ligands for Group 6 transition metal carbonyls

The co-ordination preferences of a family of novel thioethers based on (alk ylsulfanylmethyl)benzene were examined. The alkyl chain length and the numb er and position of the thioether substituents were varied. The ligands were synthesized by coupling the alkanethiol to the appropriate benzyl bromide or via the reaction of benzyl mercaptans with bromoethane; Cs2CO3-DMF was e mployed as the base-solvent mixture. The molecular structure of hexakis(pro pylsulfanylmethyl)benzene (L3) and 1,2,4,5-tetrakis(propylsulfanylmethyl)be nzene (L4) were obtained at room temperature. Both have a crystallographic centre of symmetry. In L3 the S-propyl substituents ("legs") alternate "a(b ove)" and "b(elow)" the plane of the benzene ring, whereas in L4 the "legs" adopt an abba pattern. Several co-ordination modes of the ligands were obs erved. Bismetallated tetracarbonyl complexes where the ligand bridges two m onometal Group 6 carbonyl fragments (M(CO)(4)) were generated on reaction o f [W(CO)(4)(MeCN)(2)] or [Mo(CO)(3)(MeCN)(3)] with the ligands L1 and L2. T he molecular structures of the resulting complexes [{Mo(CO)(4)}(2)L] (L=L1 or L2 which are the pentyl analogues of L3 and L4 respectively) show that t he conformations of the ligands change radically to accommodate the octahed ral geometry about the metal centres. In all cases the metal atoms are chel ated by "legs" positioned ortho to each other. Changing the stoichiometry o f the reactions does not significantly influence the products.