Hydrogen Activation with Ru-PN³P Pincer Complexes for the Conversion of C₁ Feedstocks

Abstract

The hydrogenation of C 1 feedstocks (CO and CO 2 ) has been investigated using ruthenium complexes [RuHCl(CO)-(PN 3 P)] as the catalyst. PN 3 P pincer ligands containing amines in the linker between the central pyridine donor and the phosphorus donors with bulky substituents (tert-butyl (1) or TMPhos (2)) are required to obtain mononuclear single-site catalysts that can be activated by the addition of KO t Bu to generate stable fivecoordinate complexes [RuH(CO)(PN 3 P−H)], whereby the pincer ligand has been deprotonated. Activation of hydrogen takes place via heterolytic cleavage to generate [RuH 2 (CO)(PN 3 P)], but in the presence of CO, coordination of CO occurs preferentially to give [RuH(CO) 2 (PN 3 P−H)]. This complex can be protonated to give the cationic complex [RuH(CO) 2 (PN 3 P)] + , but it is unable to activate H 2 heterolytically. In the case of the less coordinating CO 2 , both ruthenium complexes 1 and 2 are highly efficient as CO 2 hydrogenation catalysts in the presence of a base (DBU), which in the case of the TMPhos ligand results in a TON of 30,000 for the formation of formate.