Photoaquation of methylated cis-dichlorobis(1,10-phenanthroline)rhodium(III)chloride compounds by direct population of a photoactive triplet excited state

Photoaquation in compounds II and III by direct excitation into a photoactive triplet excited state is reported. The location of the singlet to triplet transition in compound III is estimated by a combination of the action spectrum for photoaquation in the region between 520 and 600 nm and the phosphorescence spectrum at 77 K. The significant increment of the reactivity (10-fold) of the triplet states in II and III as compared to that in I is explained in terms of increasing sigma-donation from the phen ligands stabilizing the pentacoordinated rhodium intermediate formed by chloride expulsion.