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

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 ≥250 °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 (μ‐OCH 3 ) 2 ](OTf) 2 has been determined by single crystal X‐ray crystallography (Space group P $\bar 1$ ( a =8.2532(17); b =12.858(3); c =14.363(3) Å; α =64.38(3); β =77.26(3); γ = 87.12(3)°, R =4.36 %).