Diruthenium(ii)–NNN pincer complex catalysts for transfer hydrogenation of ketones

Abstract

Dinuclear ruthenium(ii)-NNN pincer complexes bearing a π linker-supported bis(pyrazolyl-imidazolyl-pyridine) ligand were synthesized and structurally characterized, and they exhibited excellent catalytic activity for the transfer hydrogenation of ketones in refluxing isopropanol, reaching TOF values up to 1.3 × 10 h. Compared with the corresponding mononuclear Ru(ii)-NNN pincer complexes, the bimetallic complexes could be applied at concentrations as low as 0.03 mol% Ru and demonstrated remarkably enhanced catalytic activity in the transfer hydrogenation reactions of ketones. The high catalytic activity of the diruthenium(ii) complexes is attributed to the excellent stability and possible cooperativity of the two coordinated Ru(ii) metal centers through the π linker. The present synthetic methodology has established an applicable strategy to construct highly active bimetallic NNN pincer complex catalysts.

Ditopic Hexadentate Ligands with a Central Dihydrobenzo‐diimidazole Unit Forming a [2x2] Zn4 Grid Complex

“…[8][9][10][11][12] In this context, a number of bimetallic complex catalysts have been reported, e. g., in asymmetric allylic alkylation, [13] water oxidation, [14][15][16][17][18] epoxidation, [19] and transfer hydrogenation of ketones. [20] The probably most adaptable and established ligands for this purpose are derivatives of 2,2':6',2"-terpyridine (terpy) type containing, inter alia, pyrazole, tetrazole, and imidazole subunits. [21][22][23][24][25][26][27][28][29] Whereas a number of ligands with tridentate chelates and tautomeric subunits have been described previously, [25,30,31,32,33] we are not aware of any examples that describe the presence of different tauto-conformers and the parallel formation of isomeric reaction products upon coordination to transition metal ions.…”

Fast Transfer Hydrogenation(TH) in Aerobic Condition and Oxidation of Alcohols with N‐Methylmorpholine‐N‐oxide Catalyzed by Ru(II) Ligated with Chalcogenated Pyridines and PPh3

“…Bond angles (°): N(2) À Ru(1) À Cl(1) 170.32 (13) (9); Ru(1) À Cl(2) 2.4695 (10); Ru(1) À P(1) 2.2967 (9). Bond angles (°): (12); N(2) À Ru(1) À Se(1) 84.26 (9); Cl(1) À Ru(1) À P(1) 91.43 3; Cl(1) À Ru(1) À Cl(2) 87.43 (3). 9; Cl(2) À Ru(1) À P(1) 100.00 (9).…”

“…Some examples of ruthenium catalysts which complete TH in short time are as follows. Yu and co-workers [3] reported completion of TH in 1 min with 0.03 mol% loading of bimetallic Ru(II)-NNN pincer complex as a catalyst. ] reported 99% conversion in 0.5 min when 0.005 mol% of Ru(II)-NNC complexes were used as catalysts.…”

Ru(II)‐PBTNNXN complex bearing functional 2‐(pyridin‐2‐yl)benzo[d]thiazole ligand catalyzed α‐alkylation of nitriles with alcohols

“…It can dramatically promote the catalytic activity applied in borrowing hydrogen catalysis using ligands containing functional groups such as NH and OH. Among them, NNN ligands bearing NH coordinated with Ru metal could be potential chelating ligands due to their synthetic accessibility and excellent air‐ and moisture‐stability compared to phosphine ligands.…”