Reactivity studies of η2-acyl complexes of molybdenum. kinetics of η2-acyl to η2-iminoacyl isomerization in their reactions with isocyanides

Abstract

Treatment of the dihaptoacyls [Mo{η²-C(O)R}L(CO)(PMe₃)₂] with carbon monoxide afforded the dicarbonyl derivatives [Mo{η²-C(O)R}L(CO)₂(PMe₃)][L = H₂B(pz)₂ or H₂B(dmpz)₂; pz = pyrazolyl, dmpz = 3,5-dimethylpyrazolyl; R = Me, CH₂SiMe₃ or CH₂CMe₃]. The analogous reactions with isocyanides, CNR′, yielded two types of products, namely the acyl-isocyanides [Mo{η²-C(O)R}L(CO)(CNR′)(PMe₃)] or the η²-iminoacyls [Mo{η²-C(NR′)R}L(CO)₂(PMe₃)](R′= CNC₆H₃Me-2,6, CNC₆H₄OMe-p, CNCH₂Ph or CNC₆H₁₁) depending upon the nature of the bis(pyrazolyl)borate ligand and the R group. Kinetic studies of the transformation [Mo{η²-C(O)CH₂SiMe₃}{H₂B(dmpz)₂}CO(CNR′)(PMe₃)]→[Mo{η²-C(NR′)CH₂-SiMe₃}{H₂B(dmpz)₂}(CO)₂(PMe₃)](R′= 2,6-Me₂C₆H₃) show first-order behaviour and are consistent with a mechanism involving deinsertion of CO to give a seven-co-ordinate alkyl intermediate in the rate-determining step.