Conversion of primary alcohol to ester in presence of Ruthenium(II)-PNP pincer complex and comparison with isoelectronic (PNP)Os and (PNP)Rh+ complexes: A computational study

Abstract

Mechanistic pathway of (PNP)Ru {PNP = bis[(2-dimethylphosphino)-ethyl]amine} mediated synthesis of an ester (2-methoxyethyl-2-methoxyacetate) from two equivalent of a primary alcohol (3-oxabutanol) is investigated using density functional theory. A ten-stage catalytic cycle is proposed. The key steps of this process is broadly described as the oxidation of first equivalent of primary alcohol into aldehyde with the elimination of H2 molecule, coupling of the aldehyde with second equivalent of alcohol to form an ester followed by the regeneration of the pincer catalyst with the liberation of second H2 molecule. Two isoelectronic pincer complexes (PNP)Os and (PNP)Rh+ are also considered to shed light on the variation of the energetics. Prior to H2 elimination, a η2-bonded metal-dihydride complex is obtained for (PNP)Ru and (PNP)Rh+, whereas pure Os-H bonds are observed in case of (PNP)Os. Theoretical catalytic efficiency and TOF values infer that (PNP)Ru is the best amongst the three pincer complexes considered here.