Secondary Coordination Effect on Monobipyridyl Ru(II) Catalysts in Photochemical CO Reduction: Effective Proton Shuttle of Pendant Brønsted Acid/Base Sites (OH and N(CH)) and Its Mechanistic Investigation.

While the incorporation of pendant Brønsted acid/base sites in the secondary coordination sphere is a promising and effective strategy to increase the catalytic performance and product selectivity in organometallic catalysis for CO reduction, the control of product selectivity still faces a great challenge. Herein, we report two new (Cl)-[Ru(6-X-bpy)(CO)Cl] complexes functionalized with a saturated ethylene-linked functional group (bpy = 2,2'-bipyridine; X = -(CH)-OH or -(CH)-N(CH)) at the (6)-position of bpy ligand, which are named and , respectively. In the series of photolysis experiments, compared to nontethered case, the asymmetric attachment of tethering ligand to the bpy ligand led to less efficient but more selective formate production with inactivation of CO-to-CO conversion route during photoreaction.

A Hybrid Ru(II)/TiO Catalyst for Steadfast Photocatalytic CO to CO/Formate Conversion Following a Molecular Catalytic Route.

Herein, we employed a molecular Ru(II) catalyst immobilized onto TiO particulates of (4,4'-Y-bpy)Ru(CO)Cl (; Y = CHPO(OH)), as a hybrid catalyst system to secure the efficient and steady catalytic activity of a molecular bipyridyl Ru(II)-complex-based photocatalytic system for CO reduction. From a series of operando FTIR spectrochemical analyses, it was found that the TiO-fixed molecular Ru(II) complex leads to efficient stabilization of the key monomeric intermediate, Ru-hydride (LRu(H)(CO)Cl), and suppresses the formation of polymeric Ru(II) complex (-(L(CO)Ru-Ru(CO)L)-), which is a major deactivation product produced during photoreaction via the Ru-Ru dimeric route. Active promotion of the monomeric catalytic route in a hetero-binary system (IrPS + TiO/) that uses TiO-bound Ru(II) complex as reduction catalyst led to highly increased activity as well as durability of photocatalytic behavior with respect to the homogeneous catalysis of free Ru(II) catalyst (IrPS + Ru(II) catalyst).