Differences in the CO photolability of cis- and trans-[RuCl2(azpy)(CO)2] complexes: Effect of metal-to-ligand back-bonding

Reaction of [RuCl2(CO)3]2 with 2-phenylazopyridine (azpy) in methanolic solution affords cis-[RuCl2(azpy)(CO)2] (1) and trans-[RuCl2(azpy)(CO)2] (2) depending on the temperature of the reaction mixture. In both complexes, the two CO ligands are cis to each other. Competition in π backbonding labilizes CO trans to the azo-N (N3) in 2 and increases the rate of CO photorelease of 2 (the trans isomer) compared to 1 (the cis isomer).