Halogen cleavage of carbon-cobalt bonds. Demonstration of inversion at carbon

Stereochemistry and mechanism of the photochemical and thermal insertion of oxygen into the carbon-cobalt bond of alkyl(pyridine)cobaloximes

“…20 It was shown that the starting 2-butyl(pyridine)cobaloxime was optically active by bromodemetallation, a process known to occur with inversion of configuration at the asymmetric carbon. 19 The full sequence of reactions is shown in Scheme I. It was reported previously10 that the oxygen insertion reaction proceeded stereospecifically with optically active 2hydroxy-1 -phenethyl(pyridine)cobaloxime.…”

“…All cobaloximes were synthesized according to standard procedures.40 Optically active 2-butyl(pyridine)cobaloxime was made according to a previously described method. 19 The optically active 2-hydroxy-1 -phenethyl(pyridine)cobaloxime, cyclopentylmethyl-(pyridine)cobaloxime, and 5-hexenyl(pyridine)cobaloxime were obtained as described below. Bromodemetallation of optically active 2-butyl(pyridine)cobaloxime was carried out according to a previously published procedure.…”

“…Bromodemetallation of optically active 2-butyl(pyridine)cobaloxime was carried out according to a previously published procedure. 19 All other materials used were commercially available. Optical rotations were measured on either a Bendix 143-A (Faraday effect) polarimeter with a 1-cm cell or a Zeiss photoelectric polarimeter with a 10-cm cell.…”

Kinetics and mechanism of the reactions of organochromium complexes with mercury(II) and methylmercury(II) ions

“…0.5-1 half-life, and the pseudo-first-order rate constant, Zc0bsd, is computed as In (slopej/r. A = -D-Dexp(kr)] + A+r exp(kr) (9)…”

Alkyl group versus hydrogen atom transfer from metal alkyls to macrocyclic rhodium complexes

“…1 In several careful mechanistic studies of such alkyl abstraction reactions from transition metal complexes to various acceptors, the reaction has been shown to take place by back-side attack at the alpha carbon leading to inversion of configuration at alpha carbon. [9][10][11][12][13] Predictably, steric effects play a major role and become quite dramatic when both of the reactants are penta-or hexacoordinated transition metal complexes, and access to alpha carbon is severely limited, 1,[13][14][15] although in one instance an unusually small rate variation has been reported for alkyl group exchange between organocobalt(III) porphyrins and cobalt(II) complexes. 13 In-depth studies of such reactions often involve cobalt, but known examples include a number of other metals including chromium, rhodium, platinum, nickel, palladium and others.…”