Catalytic Conversion of Alcohols into Carboxylic Acid Salts in Water: Scope, Recycling, and Mechanistic Insights

Abstract

The catalytic conversion of alcohols into carboxylic acid salts in water was performed in the presence of ruthenium complexes supported by aliphatic PNP pincer ligands preformed or formed in situ. High activity toward a wide substrate scope was achieved with turnover number values of up to 4000. The air-stable catalytic system can be recycled by using toluene as a catalyst-immobilizing phase; the activity is maintained after five consecutive runs. Finally, mechanistic studies allowed some fundamental aspects related to water activation to be unveiled and to the mechanism postulated.

Oxidative Transformations of Biosourced Alcohols Catalyzed by Earth‐Abundant Transition Metals

“…As observed above, 1,4‐dioxane has a harmful effect on the catalytic performance as only 69 % of butyric acid was obtained (Table , Entry 10). The monohydride bromo complex Fe ‐ 3 shows a similar catalytic activity (Table , Entry 11) to Fe ‐ 4 , which suggests that both compounds generated similar catalytically active species under reaction conditions as observed already for Ru analogues . The influence of substituent groups on the P atom of the PNP ligand was also investigated.…”

“…Previously, Fe ‐ 2 was shown to be catalytically inactive for the hydrogenation of esters under basic conditions . This is in contrast with the related Ru pincer complex [Ru(Cl)(μ‐Cl){( i Pr 2 PC 2 H 4 ) 2 NH}] 2 that catalyzes this reaction under basic conditions . This is most probably because of the easier formation of catalytically active hydrido carbonyl species under reaction conditions (i.e., in the presence of alcohol and base) in the case of Ru compared to Fe …”

“…reported a Ru‐based pincer [Ru(PNN)] complex that was remarkably active even under acceptorless conditions . We recently demonstrated that pincer P H NP Ru complexes catalyze this reaction efficiently at a low catalyst loading (0.1 mol %) . In addition, the related metal‐catalyzed MeOH decomposition to hydrogen and CO 2 via a formic acid salt intermediate has been studied extensively by different groups .…”

Acceptorless dehydrogenative coupling of alcohols catalysed by ruthenium PNP complexes: Influence of catalyst structure and of hydrogen mass transfer

“…The sp 2 hybridation of the N atom is evidenced by the sum of angles (354.82°). Bond lengths and angles are comparable to the trimethylphosphine coordinated analogue [RuH(L)(L a )] (L = CO, PMe 3 ) [32,33]. Presumably, spontaneous release of H 2 from (non-isolated) 3d affords compound 4.…”

“…at room temperature or at 80°C in C 6 D 6 did not give rise neither to the formation of any new complex nor to alcohol-derived reaction products. Interestingly, this complex was successfully used in primary alcohol oxidation into the corresponding acid, though with a significantly lesser activity than derivatives featuring less bulky substituents on the phosphorous centers, which tends to indicate that too high steric protection is detrimental to the catalytic activity [26,33]. Finally, in order to compare our results with those of other commercially available ruthenium catalysts active in the absence of a base, we probed Milstein's catalyst's (13), C12-N1-Ru1 = 123.24(11).…”