Photolytic cleavage of Co–C bond: A mechanistic study for the formation of solvent coordinated cobalt(II) complex

•Primary photochemical behaviours of Alkyl(pyridine)cobaloxime complexes were studied.•New acetonitrile coordinated cobalt(II) complex was obtained by flash photolysis studies.•Photochemical behaviours were studied in microsecond and nanosecond time scale.•More information about CT photochemistry of cobaloxime complexes from ns to s time scale.•It provides interesting facts to understand the metabolic pathways of vitamin B12 model system.

Alkyl(pyridine)cobaloxime complexes (where, alkyl groups are methyl, ethyl, etc.) were synthesized and characterized by various spectral techniques. Their primary photochemical behaviours were studied by continuous photolysis and laser flash photolysis in both acetonitrile and methanol under oxygen saturated and argon saturated conditions. The transient absorption spectra were recorded at various time scales like 0.2 μs, 1 μs and 10 μs after laser flash, which show absorption maximum at 470 nm in methanol because of homolytic cleavage of Co–C for all these complexes. The kinetic analysis of the transient species for all these complexes shows first order kinetics. Laser flash photolysis studies in acetonitrile, the formation of cobalt(II) species was confirmed by transient band observed around 440 nm and also by ESR spectral analysis. The transient band observed around 340 nm is assigned to the formation of new acetonitrile coordinated cobalt(II) complex by the reaction between the intermediate cobalt(II) species and the solvent molecule in microsecond time scale. The present investigations provide more information on the charge transfer photochemistry of cobaloxime complexes from nanosecond to second time scale.

Graphical abstractTransient absorption studies of visible light induced cleavage of Co–C bond of cobaloxime complexes and formation of solvent coordinated cobalt(II) metal complex formed by the reaction of cobalt(II) intermediate species and solvent.Figure optionsDownload full-size imageDownload as PowerPoint slide