SYNTHESIS AND CHARACTERIZATION OF THE ASYMMETRIC COMPLEXES CP-ASTERISK-W(NO)(R)(R’) [R, R’ = ALKYL, ARYL] AND REGIOSELECTIVE INSERTIONS OF CO INTO THEIR W-C SIGMA-BONDS

{Treatment of Cp*W(NO)(Cl)2 (CP* = eta5-C5Me5) with 0.5 equiv of a R2Mg.X(dioxane) reagent (R = CH2CMe3, CH2SiMe3, Ph, o-tolyl) results in the formation of the alkyl and aryl chloro complexes Cp*W(NO)(R)(CI), which have been isolated and fully characterized. Metathesis of these complexes with 0.5 equiv of another R’2Mg.x (dioxane) reagent (R’ = CH2CMe3, CH2SiMe3, Me, Ph, o-tolyl) affords a series of 16-electron, mixed alkyl and aryl complexes,; Cp*W-(NO)(R)(R’), having all ten combinations of R not-equal R’. These complexes have been characterized by conventional spectroscopic methods. The competitive reactivity of the different tungsten-carbon sigma bonds in these species toward CO insertion has been investigated. Each complex reacts with 1 equiv of CO under ambient conditions to produce the corresponding eta2-acyl complex presumably via an initial carbonyl adduct. An X-ray diffraction analysis of Cp*W(NO)(Ph)-eta2-C{O}CH2CMe3) has been performed to confirm the existence of the eta2-acyl linkage in one of these complexes: space group P2(1)/n