Modular Synthesis of Ru(II)–Ir(III) Complexes Bridged by a Ditopic Carbanionic NHC Ligand: Influence of Heterodinuclear Architecture on Tandem Catalysis

High Resolution Image Download MS PowerPoint Slide The development of polymetallic complexes incorporating N-heterocyclic carbene (NHC) ligands is a promising strategy for achieving enhanced performance that may arise from the presence of multiple metal centers in chemical transformations and/or physicochemical properties. However, quantifying cooperativity in these systems remains a significant challenge. We report a modular synthetic strategy to obtain Ru(II)–Ir(III) heterodinuclear complexes bridged by a bis-bidentate ditopic carbanionic NHC (dc-NHC) ligand (L 2 ). Our synthetic methodology allowed selective metal coordination at the C2 and C4 imidazolium positions. A series of homo- and heterodinuclear complexes were synthesized, fully characterized, and evaluated as catalysts in tandem α-alkylation/transfer hydrogenation of ketones with alcohols under mild, neat, and base-limited conditions. Notably, the heterodinuclear complexes [Ru-L 2 -Ir]PF 6 and [Ir-L 2 -Ru]PF 6 exhibited the highest catalytic activity for tandem products, compared to the corresponding monometallic Ru(II) and Ir(III) analogues under the same metal percentage loadings. Additionally, a possible contribution of the heterodinuclear arrangement was examined by kinetic experiments ( E a ), which indicate lowered activation barriers for [Ru-L 2 -Ir]PF 6 .