Rhodium Complexes Bearing 1,10-Phenanthroline Analogue Bis-NHC Ligands Are Active Catalysts for Transfer Hydrogenation of Ketones

Abstract

Synthesis of a new example of the pyridazine annelated bis(N-heterocyclic carbene) ligand 3b (vegi) bearing benzyl substituents is reported, as well as the synthesis of its cationic Rh(cod) complex 5b. The mechanism of formation of the [Rh(cod)(vegi)] + complexes was investigated, showing a stepwise deprotonation of the imidazolium moieties via the mono-carbene imidazolium Rh(cod)Cl species 4. The [Rh-(cod)(vegi)] + complexes 5a,b show catalytic activity in the transfer hydrogenation of even sterically hindered ketones.

Hydrogen Transfer Reactions of Carbonyls, Alkynes, and Alkenes with Noble Metals in the Presence of Alcohols/Ethers and Amines as Hydrogen Donors

“…Similarly, as was observed previously for the ruthenium counterparts, depending on the ketone substrate, moderate to high conversions and excellent ee (%) (enantiomeric excess) values were determined (Scheme 4) [42]. A pyridazine-annelated bis(NHC) ligand with benzyl substituents was reported, as well as its corresponding Rh complex (Scheme 6, equation A) [44]. The mechanism of the formation of the A pyridazine-annelated bis(NHC) ligand with benzyl substituents was reported, as well as its corresponding Rh complex (Scheme 6, equation A) [44].…”

“…A pyridazine-annelated bis(NHC) ligand with benzyl substituents was reported, as well as its corresponding Rh complex (Scheme 6, equation A) [44]. The mechanism of the formation of the A pyridazine-annelated bis(NHC) ligand with benzyl substituents was reported, as well as its corresponding Rh complex (Scheme 6, equation A) [44]. The mechanism of the formation of the cationic rhodium complex were investigated, a stepwise deprotonation of the imidazolium moieties via a mono-carbene imidazolium species was observed.…”

“…A pyridazine-annelated bis(NHC) ligand with benzyl substituents was reported, as well as its corresponding Rh complex (Scheme 6, equation A) [44]. The mechanism of the formation of the Scheme 5.…”

“…Reactions with pyridazine annelated bis(NHC) ligand (A), with dicarbene tzNHC-NHC derivatives (B), chiral oxazolidine-fused NHC ligands (C). (RT = room temperature).A pyridazine-annelated bis(NHC) ligand with benzyl substituents was reported, as well as its corresponding Rh complex (Scheme 6, equation A) [44]. The mechanism of the formation of the Scheme 5.…”

Catalytic activity of Ru/tetrahydropyrimidinium salts system for transfer hydrogenation reactions

“…The first application of an NHC-Ru complex for the transfer hydrogenation reaction was reported by Grubbs and co-workers in 2001. [12] In NHC chemistry transfer hydrogenation has been described for ruthenium, [13][14][15][16][17] rhodium, [18][19][20][21][22] iridium, [18][19][20][23][24][25][26] osmium, [27] nickel [28] and palladium [29] pre-catalysts for the reduction of carbonyl, imine and nitro functionalities.…”