A new photoisomerization process of the 4-cyanobutyl group in a cobaloxime complex crystal observed by neutron diffraction

Abstract

The 4-cyanobutyl group of (4-cyanobutyl)[3,4-lutidine](dimethylglyoximato) [O-(diphenylboryl)dimethylglyoximato] cobalt(III) was isomerized to the 1-cyanobutyl group with retention of the single-crystal form, although the corresponding cobaloxime complex without diphenylboryl in the equatorial ligands did not show such a photoisomerization. The trans-cis-cis conformation of the 4-cyanobutyl group caused by the steric repulsion from the diphenylboryl group is favorable to the crystalline-state reaction. In order to elucidate the detailed isomerization mechanism, two hydrogen atoms of the 4-cyanobutyl group were replaced with the deuterium atoms such as -CH2CH 2CH2CD2CN. After the photoisomerization, the crystal structure with deuterated 4-cyanobutyl group was analyzed by neutron diffraction. Only one of the two deuterium atoms of the 4-cyanobutyl group was transferred to the C1 atom such as -CD(CN)CH2CH 2CDH2. This result made clear that the photo-produced cyanobutyl radical turned upside down after homolytic cleavage of the Co-C bond, and then the Co(II) atom and the radical made a bond to form the 1-cyanobutyl group. © 2006 The Chemical Society of Japan.