Spectroscopic Studies of the Complexes of Acrylonitrile and Acetonitrile with the Carbonyls of Chromium, Molybdenum, and Tungsten

Infrared and proton magnetic resonance spectroscopic studies of acrylonitrile complexes of the carbonyls of Cr, Mo, and W are used to assign the geometrical isomerism and manner of attachment of the ligand in these derivatives. Similar studies are also reported for the acetonitrile derivatives, from which the acrylonitrile complexes have been obtained. Evidence is presented for attachment of acrylonitrile through the nitrogen lone-pair in (CH2CHCN)M( C0)s ( M = W) and (CHzCHCN)*M(C0)a (M = Cr, Mo, and W), which are among the first well characterized examples of this type of bonding for this ligand (heretofore assumed to attach to transition metals principally through the olefinic carbon-carbon bond). The trisubstituted complexes (CH?CHCN),M( CO)3 ( M = Mo and W) appear to have the CZ, (trans) geometry, even though they were prepared by displacement of the ligand from C3" ( c i s ) acetonitrile complexes. The acrylonitrile is attached through the olefinic carbon-carbon bond in these derivatives.