Hydrogen Activation with Ru-PNP Pincer Complexes for the Conversion of C Feedstocks.

The hydrogenation of C feedstocks (CO and CO) has been investigated using ruthenium complexes [RuHCl(CO)(PNP)] as the catalyst. PNP pincer ligands containing amines in the linker between the central pyridine donor and the phosphorus donors with bulky substituents (-butyl () or TMPhos ()) are required to obtain mononuclear single-site catalysts that can be activated by the addition of KOBu to generate stable five-coordinate complexes [RuH(CO)(PNP-H)], whereby the pincer ligand has been deprotonated. Activation of hydrogen takes place via heterolytic cleavage to generate [RuH(CO)(PNP)], but in the presence of CO, coordination of CO occurs preferentially to give [RuH(CO)(PNP-H)]. This complex can be protonated to give the cationic complex [RuH(CO)(PNP)], but it is unable to activate H heterolytically. In the case of the less coordinating CO, both ruthenium complexes and are highly efficient as CO 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.