Dihapto-Coordinated Amide, Ester, and Aldehyde Complexes and Their Role in Decarbonylation

The π-basic metal fragment {TpW(NO)(PMe3)} forms thermally stable η2 complexes with
acetaldehyde, acetone, ethyl acetate, methyl formate, and N,N-dimethylformamide (where
Tp = hydridotris(pyrazolyl)borate). The related system {TpMo(NO)(MeIm)} (MeIm =
1-methylimidazole) also forms stable η2 complexes with acetone, methyl formate, and N,N-dimethylformamide. When the tungsten fragment is combined with a carboxylic acid,
oxidative addition yields a seven-coordinate hydride complex. These results are compared
to those observed for analogous Re and Os systems. TpMo(NO)(MeIm)(η2-DMF) and TpW(NO)(PMe3)(η2-DMF) are rare examples of η2 amide complexes, demonstrating the exceptional
strength of these group 6 π bases.