Enhanced Reactivities toward Amines by Introducing an Imine Arm to the Pincer Ligand: Direct Coupling of Two Amines To Form an Imine Without Oxidant

Abstract

Dehydrogenative homocoupling of primary alcohols to form esters and coupling of amines to form imines was accomplished using a class of novel pincer ruthenium complexes. The reactivities of the ruthenium pincer complexes for the direct coupling of amines to form imines were enhanced by introducing an imine arm to the pincer ligand. Selective oxidation of benzylamines to imines was achieved using aniline derivatives as the substrate and solvent.

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

“…Various benzyl amine substrates were explored with the formation of imines in good to excellent yields. Moreover, the cross-coupling of benzyl amines and anilines could also be achieved [72] (Table 5 Based on these experimental results, a mechanism was proposed (Scheme 29). The dearomatized Ru complex dehydrogenates the primary amine to form the intermediate IV and the benzaldimine.…”

“…The desired crude product could be employed for metal complex synthesis without further purification [72] (Scheme 6). Scheme 7.…”

“…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.…”

“…Ru12, Ru13 and Ru15, exhibited good to excellent reactivities for the dehydrogenative homo-coupling of primary alcohols (Table 4). Several linear aliphatic alcohols and benzyl alcohol could be converted into the corresponding esters effectively with catalyst Ru15 [72]. After the dehydrogenative coupling of primary alcohols to esters was achieved in high yields at 110-160 °C, the extension of this system to alcohols with lower boiling points was also investigated, such as ethanol and 1-propanol.…”

Tunable regioselectivity in 1,3-butadiene polymerization by using 2,6-bis(dimethyl-2-oxazolin-2-yl)pyridine incorporated transition metal (Cr, Fe and Co) catalysts

“…We have been establishing pyridine based compounds as ligand family for transition metal catalyzed organic transformations [42][43][44] and olefin polymerizations [45]. The modification of substituents at proper positions of ligand may conveniently be altered to allow for the fine-tuning of both the steric and electronic properties of ligand, which in turn mediate metal induced catalytic performances.…”