Tungsten(IV) alkyls and .eta.2-acyls. Carbonyl insertion and ligand substitution reactions of the tungsten dication CpW(CO)2(NCMe)2Me2+ and related complexes

The tungsten(IV) dication CpW(CO){sub 2}(NCMe){sub 2}Me{sup 2+}, obtained from the 2-electron oxidation of CpW-(CO){sub 3}Me, serves as the precursor to a number of tungsten(IV) complexes via a series of CO insertion and substitution reactions. In acetonitrile, the dication undergoes smooth CO insertion ({Delta}H* = 89.5 {sup +}{sub -} 2.5 kJ/mol, {Delta}S* = -43.9 {sup +}{sub -} 8.4J/(K{lg_bullet}mol), k(20{degrees}C) = 3.3 x 10{sup -6} 8{sup -1}) and substitution to give the {eta}{sup 2}-acetyl complex CpW(NCMe){sub 3}({eta}{sup 2}-COMe){sup 2+}. The oxidation of CpW(CO){sub 3}Et provides CpW(CO)(NCMe){sub 2}({eta}{sup 2}-COEt){sup 2+} via the intermediacy of CpW(CO){sub 2}(NCMe){sub 2}Et{sup 2+}. CpW(CO)(NCMe){sub 2}({eta}-COEt){sup 2+} in turn undergoes CO substitution to yield CpW(CO){sub 3}(NCMe)Me{sup 2+}. Analogous CO insertion reactions were not observed for the compounds CpW(CO){sub 3}(NCMe)Me{sup 2+} and CpW(CO){sub 3}(NCMe)Et{sup 2+}. 21 refs., 3 figs., 3 tabs.