Fast formation of methyl radical from methylaquocobaloxime as studied by time-resolved optical and ESR techniques

A closer look at photochemical reactions of transition-metal compounds by time-resolved EPR

“…As noted previously, an early application of TREPR in the study of the photochemistry of transition-metal complexes concemed the [(CH3)(H20)Co(dmg)2 ] (II-H20 ) complex [14]. Photoexcitation of solutions of this complex in water or 2-propanol generates CH~ radicals that give rise to an emissive four-line TREPR spectrum with an intensity pattem that closely matches the binomial distribution.…”

“…Previous investigations dealing with methyl radical formation by photoinduced cleavage of a Co-CH 3 bond demonstrated that TREPR can be applied in this field of research and revealed some interesting novel CIDEP effects [14,15]. Also, a series of FTEPR studies have been carried out on the bond homolysis reactions of the transition-metal complexes [Re(R)(CO)3(dmb)], [Ru(I)(R)(CO)2(iPr-DAB)], [Ru(CH3)(SnPh3)(CO)z(iPr-DAB)] and [Pt(CH3)4(iPr-DAB)] [16][17][18][19][20].…”

“…Monomolecular reactions, such as the photoinduced bond homolysis reactions with which this review is concerned, can occur on a subnanosecond time scale so that kf > /'1-l. In that case, strong TM CIDEP can be generated [14]. However, ir is important to note that the generation of spin polarization in triplet-state molecules requires that the lifetime of the t¡ lets exceeds the inverse of the electron spin Larmor frequency, COo ~ [30].…”

“…An early example is the application of cw TREPR in the study of methyl radical formation by photoinduced homolysis of the Co-CH 3 bond in a bis(dimethylglyoximato)cobalt complex (methylcobaloxime, [(CH3)(H20)Co(dmg)2]) [14]. The four-line spectrum due to the CH; radical formed by photolysis of this complex in water and 2-propanol was found to be in emission with retative line intensities close to the binomial 1:3:3:1 ratio.…”

“…2b), has been a subject of a number of EPR studies [14,63,64]. The interest in these compounds stems in part from the structural similarity to the cobalamins (I).…”