A New Organocobalt Complex Containing a Co−N−C Three Membered Ring

Treatment of R = −CH2X (X = halogen) derivatives of the type [RCoIII(LNH-py)(HLNH-py)]+, where HLNH-py = 2-(2-pyridyl-ethyl)amino-3-butanone oxime and LNH-py its conjugated base with diluted NaOH, afforded
a new complex containing a three-membered ring by a pathway involving the intramolecular nucleophilic addition
of an equatorial nitrogen donor to the axial carbon. The X-ray analysis reveals a highly distorted structure. The
C−Co−N angle is acute (42.8°) with the distortion of the coordination sphere concentrated in the Co−C axial
and Co−N bonds, which move away from the pseudo-octahedral positions in the CH2X parent complex to form
the C−N bond of the metallocycle. Kinetic studies of the formation of this novel complex starting from [(XCH2CoIII(LNH-py)(HLNH-py)]+ (X = Cl,Br,I) showed that the metallocycle formation rates increase in the order Cl
< Br < I. Kinetic data are consistent with a mechanism involving an intermediate species resulting from the
deprotonation of an amine equatorial nitrogen in a rapid preequilibrium, followed by the slow step of the ring
closure.