New Alkyl−Cobalt(III) Complexes Containing Chiral Centers in the Chelating System

The complex mer-[CoIII(L1Npy)2]+ (1‘) where the L1Npy- is the tridentate 3-[(2-pyridyl)methylimino]butan-2-one oximate
ligand, gives alkyl−cobalt derivatives after reduction with NaBH4/Pd2+ to the CoI and alkylation. The formation of
the cobalt−carbon bond is accompanied by the reduction to the amino form of one or both imino ligands (depending
on the experimental conditions) initially present in 1‘. In one series of experiments, complexes of the type fac-[RCoIII(L1Npy)(H-L1NHpy)]+ (R = Me, i-Pr, CH2Cl, CH2Br, CH2CF3, and Bz) were obtained, in which only one of the
two ligands was reduced to the amino form (H-L1NHpy). The saturation of one azomethine group causes the
products to assume a fac configuration and induces the formation of one asymmetric carbon and one asymmetric
nitrogen center in the chelating system. When an excess of reducing agent is used, both azomethine groups may
be saturated, causing the introduction of one pair of chiral carbons and one pair of chiral nitrogens. Two isomers
of the methyl derivative [MeCoIII(L1NHpy)(H-L1NHpy)]+ were isolated. The X-ray analysis reveals that these isomers
differ from one another in configuration of the C and N chiral centers. Possible reaction mechanisms leading to
these different types of complexes are proposed.