Sequential H/D Exchanges Resulting from Rollover-Cyclometallation during Photoirradiation of Rhodium(III) Complex in Methanol-d.

We present the photoreaction of newly prepared bis(6,6'-dimethyl-2,2'-bipyridine)(oxalato)rhodium(III) ([Rh(N N)(ox)]) in CDOD. Photoirradiation of this complex causes the dissociation of ox, followed by the formation of the unprecedented Rh(III) complex with Rh-H and Rh-C σ bonds, [Rh(N N)(C N)(H)(CDOD)] (C N=[6,6'-dimethyl-2,2'-bipyridine]-3-yl-κC,κN). This hydride formation and cyclometallation spontaneously proceed owing to the conflict between the steric hindrance arising from the methyl groups of N N and the driving force for the structural change due to [Rh(N N)] formation. Although [Rh(N N)(C N)(H)(CDOD)] is initially converted to [Rh(N N)] by photoirradiation, it is immediately regenerated by the rollover cyclometallation of the [Rh(N N)] complex. [Rh(N N)(C N)(H)(CDOD)] undergoes H/D exchange for the H atoms in the Rh-H bond and at the 3, 3'-positions of the N N ligand during the photoirradiation. DFT calculations predict with reasonable certainty the spontaneous structural change of [Rh(N N)] to [Rh(N N)(C N)(H)(CDOD)] and the subsequent photodriven Rh-C bond rupture leading to the formation of [Rh(N N)] accompanied by H/D exchange reactions.