Acid‐, Water‐ and High‐Temperature‐Stable Ruthenium Complexes for the Total Catalytic Deoxygenation of Glycerol to Propane

Abstract

The ruthenium aqua complexes [Ru(H(2)O)(2)(bipy)(2)](OTf)(2), [cis-Ru(6,6'-Cl(2)-bipy)(2)(OH(2))(2)](OTf)(2), [Ru(H(2)O)(2)(phen)(2)](OTf)(2), [Ru(H(2)O)(3)(2,2':6',2''-terpy)](OTf)(2) and [Ru(H(2)O)(3)(Phterpy)](OTf)(2) (bipy = 2,2'-bipyridine; OTf(-) = triflate; phen = phenanthroline; terpy = terpyridine; Phterpy = 4'-phenyl-2,2':6',2''-terpyridine) are water- and acid-stable catalysts for the hydrogenation of aldehydes and ketones in sulfolane solution. In the presence of HOS(O)(2)CF(3) (triflic acid) as a dehydration co-catalyst they directly convert 1,2-hexanediol to n-hexanol and hexane. The terpyridine complexes are stable and active as catalysts at temperatures > or = 250 degrees C and in either aqueous sulfolane solution or pure water convert glycerol into n-propanol and ultimately propane as the final reaction product in up to quantitative yield. For the terpy complexes the active catalyst is postulated to be a carbonyl species [(4'-R-2,2':6',2''-terpy)Ru(CO)(H(2)O)(2)](OTf)(2) (R = H, Ph) formed by the decarbonylation of aldehydes (hexanal for 1,2-hexanediol and 3-hydroxypropanal for glycerol) generated in the reaction mixture through acid-catalyzed dehydration. The structure of the dimeric complex [{(4'-phenyl-2,2':6',2''-terpy)Ru(CO)}(2)(mu-OCH(3))(2)](OTf)(2) has been determined by single crystal X-ray crystallography (Space group P1 (a = 8.2532(17); b = 12.858(3); c = 14.363(3) A; alpha = 64.38(3); beta = 77.26(3); gamma = 87.12(3) degrees, R = 4.36 %).