THERMAL RACEMIZATION OF CHIRAL ALKYL COBALT COMPLEXES AND ESTIMATION OF Co–C BOND DISSOCIATION ENERGY

Abstract

Measurement of the thermal racemization rates of alkyl cobalt complexes having chirality only at the carbon coordinated directly to cobalt enabled estimation of the activation parameters of the Co–C bond homolysis and the bond dissociation energies. The effects of substituents of the alkyl moiety and axial bases on the Co–C bond dissociation energy are discussed.

Dynamic motion and various reaction paths of cobaloxime complexes in crystalline-state photoreaction

“…ESR spectra obtained after the crystal was exposed to X-rays revealed that the Co-C bond was cleaved homolytically to produce the ce radical and the Co(II) complex [17][18][19]. The Co-C bond dissociation energy for cobaloxime complexes was estimated to be 117-122 kJ mol À1 [20]. The racemization rate of the complex crystal by X-rays was far Figure 7.…”

Catalytic hydrogen atom transfer to alkenes: a roadmap for metal hydrides and radicals

“…Measuring the optical rotation of enantioenriched (alkyl)bis(dimethylglyoximato)cobalt(III) at a constant temperature over time led to a rst-order rate of racemization of the organocobalt. 136 The identity of the axial pyridine base had a small effect on the racemization rate, while the presence of an electron-withdrawing group on the a-carbon led to slower racemization, likely by increasing the bond dissociation energy of the organocobalt complex. Another study monitored the racemization of an acyl-rhodium(III) alkyl complex over time, establishing a rst order rate of racemization (k rac ¼ 6.4 Â 10 À6 ).…”

Bimetallic catalysis. A new method for the activation of chloroarenes toward palladium-catalyzed coupling with olefins

“…For example, bromobenzene undergoes palladium-catalyzed coupling with ethyl acrylate to give ethyl cinnamate in 78% yield2 but performing the reaction with chlorobenzene lowers the yield to 4%.3 456Only in the presence of styrene or stoichiometric amounts of preformed 1 (X = Cl) has successful coupling of olefins with chlorobenzene been observed. 4,5 Chloroarenes substituted with electron-withdrawing groups undergo olefin coupling but rarely in yields above 30%. An indirect method based on palladium-catalyzed CO extrusion from aroyl halides has been reported.…”