Sequential H/D Exchanges Resulting from Rollover‐Cyclometallation during Photoirradiation of Rhodium(III) Complex in Methanol‐d4.

We present the photoreaction of newly prepared bis(6,6'‐dimethyl‐2,2'‐bipyridine)(oxalato)rhodium(III) ([Rh(N N)2(ox)]+) in CD3OD. 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)(CD3OD)]+ (C N=[6,6'‐dimethyl‐2,2'‐bipyridine]‐3‐yl‐κC3,κN1'). 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)2]+ formation. Although [Rh(N N)(C N)(H)(CD3OD)]+ is initially converted to [Rh(N N)2]+ by photoirradiation, it is immediately regenerated by the rollover cyclometallation of the [Rh(N N)2]+ complex. [Rh(N N)(C N)(H)(CD3OD)]+ 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)2]+ to [Rh(N N)(C N)(H)(CD3OD)]+ and the subsequent photodriven Rh−C bond rupture leading to the formation of [Rh(N N)2]+ accompanied by H/D exchange reactions. [ABSTRACT FROM AUTHOR]