Dihapto-coordinated amide, ester, and aldehyde complexes and their role in decarbonylation

The pi-basic metal fragment {TpW(NO)(PMe3)} forms thermally stable eta2 complexes with acetaldehyde, acetone, ethyl acetate, methyl formate, and N,N-dimethylformamide (where Tp = hydridotris(pyrazolyl)borate). The related system {TpMo(NO)(MeIm)} (Melm = 1-methylimidazole) also forms stable eta(2) 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)(eta(2)-DMF) and TpW-(NO)(PMe3)(eta(2)-DMF) are rare examples of eta(2) amide complexes, demonstrating the exceptional strength of these group 6 pi bases.