Hydrogenation of Esters Catalyzed by Ruthenium PN³-Pincer Complexes Containing an Aminophosphine Arm

Abstract

Hydrogenation of esters under mild conditions was achieved using air-stable ruthenium PN 3 -pincer complexes containing an aminophosphine arm. High efficiency was achieved even in the presence of water. DFT studies suggest a bimolecular proton shuttle mechanism which allows H 2 to be activated by the relatively stable catalyst with a reasonably low transition state barrier.

C–H and H–H bond activation via ligand dearomatization/rearomatization of a PN3P-rhodium(i) complex

“…28 Intriguingly, the transition state (6TS) located for the direct interconversion between these isomers was 51.4 kcal/mol, implying a more complicated mechanism for the hydrogen activation process. While we have demonstrated that in the analogous Ru system, two water molecules were required for the H 2 activation, 47 we do not consider it reasonable under this reaction condition. In summarize, we have demonstrated that complex (PN 3 P)Rh I Cl (2) is capable of activating benzene and H 2 effectively at room temperature upon treatment of a suitable base.…”

A new class of PN3-pincer ligands for metal–ligand cooperative catalysis

“…Upon the treatment of 6-bromo-2,2'-bipyridine under a high pressure of NH 3 in the M a n u s c r i p t presence of a Cu 2 O catalyst, the amino product could be obtained. The phosphine group was introduced by the same procedure described above [74] ( Scheme 8).…”

“…Most importantly, this was the first time that a unique dearomatization process of the central pyridine ring was drmonstarted. Employing the same strategy, other PN 3 -pincer complexes were synthesized successfully [72][73][74]. Scheme 21.…”

“…Milstein and coworkers have shown that MRu2 catalyzed the hydrogenation of non-activated esters to corresponding alcohols under relatively mild and neutral conditions. The PN 3 -Ru complexes were examined for the hydrogenation of esters [74] (Table 6). The symmetrical PN 3 ruthenium complex Ru7 showed poor reactivities, but the unsymmetrical PN 3 -Ru complexes, Ru8-Ru11 exhibited good reactivities with the formation of the desired alcohols in comparable yields (Table 6, entries 2-5).…”

“…Selected data for the hydrogenation reaction of unactivated esters. a [74] A c c e p t e d M a n u s c r i p t…”