Theoretical study on mechanism of the photochemical ligand substitution of fac-[ReI(bpy)(CO)3(PR3)]+ complex

Abstract

The mechanism of the CO ligand dissociation of fac-[Re^I(bpy)(CO)₃P(OMe)₃]⁺ has theoretically been investigated, as the dominant process of the photochemical ligand substitution (PLS) reactions of fac-[Re^I(bpy)(CO)₃PR₃]⁺, by using the (TD-)DFT method. The PLS reactivity can be determined by the topology of the T₁ potential energy surface because the photoexcited complex is able to decay into the T₁ state by internal conversions (through conical intersections) and intersystem crossings (via crossing seams) with sufficiently low energy barriers. The T₁ state has a character of the metal-to-ligand charge-transfer (³MLCT) around the Franck–Condon region, and it changes to the metal-centered (³MC) state as the Re–CO bond is elongated and bent. The equatorial CO ligand has a much higher energy barrier to leave than that of the axial CO, so that the axial CO ligand selectively dissociates in the PLS reaction. The single-component artificial force induced reaction (SC-AFIR) search reveals the CO dissociation pathway in photostable fac-[Re^I(bpy)(CO)₃Cl]; however, the dissociation barrier on the T₁ state is substantially higher than that in fac-[Re^I(bpy)(CO)₃PR₃]⁺ and the minimum-energy seams of crossings (MESXs) are located before and below the barrier. The MESXs have also been searched in fac-[Re^I(bpy)(CO)₃PR₃]⁺ and no MESXs were found before and below the barrier.