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.