CO 2 Hydrogenation Catalyzed by a Ruthenium Protic N-Heterocyclic Carbene Complex

We describe the hydrogenation of CO 2 to formate catalyzed by a Ru(II) bis(protic N-heterocyclic carbene, p-NHC) phosphine complex [Ru(bpy)(MeCN)(P Ph (p-NHC) 2 )](PF 6 ) 2 ( 1 ). Under catalytic conditions (20 μmol catalyst, 20 bar CO 2, 60 bar H 2, 5 mL THF, 140 °C, 16 h), the activity of 1 is limited only by the amount of K 3 PO 4 present in the reaction, yielding a nearly 1:1 ratio of turnover number (TON) to equivalents of K 3 PO 4 (relative to 1 ), with the highest TON = 8040. Additionally, analysis of the reaction solution post-run reveals the catalyst intact with no free ligand observed. Stoichiometric studies, including examination of unique carbamate and hydride complexes as relevant intermediates, were carried out to probe the operative mechanism and understand the importance of metal–ligand cooperativity in this system.