New alkyl-cobalt(III) complexes with tridentate amino-oxime ligands: Synthesis, structure, and reactivity

The oxidative addition of alkyl halides to the Co-I species generated by th e reduction of [Co-III(LNHpy) (HLNHpy)](ClO4)(2) (1), where HLNHpy is the t ridentate 2-(2-pyridyl-ethyl)amino-3-butanone oxime ligand and LNHpy is its conjugate base, led to the formation of a new class of organocobalt comple xes of general formula [RCoIII(LNHpy) (HLNHpy)](ClO4) [R = Me (2a), Et (2b) , CH2CF3 (2c), nBu (2d), and CH2Cl (2e)]. All the complexes were characteri sed by H-1 and C-13 NMR spectroscopy. The X-ray structures of 2a, 2b and 2e provide evidence for a pseudo-octahedral configuration, where HLNHpy and L NHpy act as bi- and tridentate ligands, respectively. The axial geometry in 2a is closer to that found in methylcobalamin than that reported for other models, suggesting steric and electronic cis influences of the equatorial ligands close to those of the corrin nucleus. The solution properties and t he reactivity show strong analogies with those of the previously known Vita min Bit models.