Synthesis and Structure of the Hexaethylcyclohexaarsoxane Complexes

The hexaethylcyclohexaarsoxane complexes [{M(CO)3}2{c>’c/o-(C2H 5A sO)6}], M = Cr, Mo, W, 2 4 have been prepared by the reaction o f (C2H 5AsO)n with the respective metal hexacarbonyl in toluene and characterized by their IR and NM R spectroscopic data. For 2 the molec­ ular structure was established by X-ray structural analysis. The 12 atoms o f the As60 6 ring form a flattened cuboctahedron in which the 6 oxygen atoms lie in the central equatorial plane. Cr(CO)3 groups are coordinated facially by the upper and lower three arsenic atoms. An ap­ proximately S6 symmetry is displayed by the Cr2As60 6 core. Average values o f respectively 116.3 and 98.9° are observed for the A s O A s and O A s O angles in the hexadentate li­ gand. The E l-M S and 'H NM R data for (C2H 5AsO)„ suggest that this alkylcycloarsoxane is present in solution as a mixture o f species including trimers and tetramers so that a metal as­ sisted ring expansion is required for the formation o f 2 -4 .