Mixed arsenic-sulfur metallacyclic complexes. Synthesis and structures of (eta(5)-Cp)(2)M(-SCH3AsSCH3AsS-) (M = Ti, Zr, Hf) and (eta(5)-Cp*)(2)Zr(-SCH3AsS-)

The sodium-reduced form of the mixed trimer and tetramer of cyclo-methylarsathiane, cyclo-(CH3AsS)(3,4) (I), in THF reacts at room temperature with the metallocene dichlorides of group 4 elements to give the metallacycle complexes (eta(5)-Cp)(2)M(-SCH3AsSCH3AsS-) (M Ti (2) Zr (3) Hf (4)) and (eta(5)-Cp*)(2)Zr(-SCH3AsS-) (5). All four complexes were crystallographically characterized. The structures of 2-4 are isomorphous, consisting of a cyclohexane-like six-membered MS(3)AS(2) ring in a chair conformation with two eta(5)-Cp rings on the metal atoms in pseudo-equatorial and -axial positions and the methyl groups on arsenic in equatorial positions. These complexes have the same molecular structure as the all-sulfur metallacycles Cp2MS5 (M = Ti, Zr, Hf). Complex 5, containing Cp* groups forms a four-membered metallacycle similar to Cp*2TiS3. However, the related titanocene all-sulfur analogue possesses a puckered ''butterfly'' ring, while the ring in 5 is nearly planar and similar to the all-arsenic complexes Cp2M(RAs)(3)(M = Ti, Zr). The methyl group on the arsenic atom on 5 is above the plane of the ring, causing an inequivalency of the Cp* groups.