Synthesis and Structure of the Hexaethylcyclohexaarsoxane Complexes [ { M(CO)3} 2{cyclo-(C2H5AsO)6}], M = Cr, Mo, W

Abstract

The hexaethylcyclohexaarsoxane complexes [{M(CO)3}2{cyclo-(C2H5AsO)6}], M = Cr, Mo, W, 2-4 have been prepared by the reaction of (C2H5AsO)n with the respective metal hexacarbonyl in toluene and characterized by their IR and NMR spectroscopic data. For 2 the molecular structure was established by X-ray structural analysis. The 12 atoms of the As6O6 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 approximately S6 symmetry is displayed by the Cr2As6O6 core. Average values of respectively 116.3 and 98.9° are observed for the As–O–As and O–As–O angles in the hexadentate ligand. The ΕΙ-MS and 1H NMR data for (C2H5AsO)n suggest that this alkylcycloarsoxane is present in solution as a mixture of species including trimers and tetramers so that a metal assisted ring expansion is required for the formation of 2-4.