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

Area of Science:

• Inorganic Chemistry
• Photochemistry
• Organometallic Chemistry

Background:

• Rhodium(III) complexes with bipyridine ligands are widely studied for their photochemical properties.
• Understanding ligand dissociation and rearrangement in metal complexes is crucial for developing new catalytic systems.
• The role of steric hindrance in dictating reaction pathways in coordination complexes is an active area of research.

Purpose of the Study:

• To investigate the photoreaction of bis(6,6 -dimethyl-2,2 -bipyridine)(oxalato)rhodium(III) ([Rh(N N)2(ox)]+).
• To elucidate the formation of novel rhodium(III) complexes with Rh-H and Rh-C sigma bonds.
• To understand the mechanism of hydride formation, cyclometallation, and subsequent photoreactions, including H/D exchange.

Main Methods:

• Synthesis and characterization of the [Rh(N N)2(ox)]+ complex.
• Photoirradiation experiments in CD3OD.
• Spectroscopic analysis to identify reaction intermediates and products.
• Density Functional Theory (DFT) calculations to model reaction pathways and energetics.

Main Results:

• Photoirradiation induced oxalato ligand dissociation, followed by spontaneous hydride formation and cyclometallation to yield [Rh(N N)(C N)(H)(CD3OD)]+.
• The complex [Rh(N N)(C N)(H)(CD3OD)]+ underwent photodriven Rh-C bond rupture, regenerating [Rh(N N)2]+.
• Significant H/D exchange was observed at the Rh-H bond and the 3,3 -positions of the N N ligand during photoirradiation.
• DFT calculations supported the proposed mechanism for spontaneous structural change and photodriven bond rupture.

Conclusions:

• The study presents an unprecedented photoreaction pathway for a rhodium(III) complex, leading to the formation of Rh-H and Rh-C sigma bonds.
• Steric hindrance from the methyl groups on the bipyridine ligand plays a critical role in driving the observed structural transformation.
• The dynamic photoreaction involves a reversible cycle of cyclometallation and ligand dissociation, coupled with H/D exchange, offering insights into the reactivity of rhodium complexes.