Preparation of a series of Ru(ii) complexes with N-heterocyclic carbeneligands for the catalytic transfer hydrogenation of aromatic ketones

Abstract

The reaction of [RuCl(2)(p-cymene](2) with Ag-N-heterocyclic carbene (NHC) complexes yields a series of [(p-cymene)Ru(NHC)] complexes (2a-f). All synthesised compounds were characterized by elemental analysis, NMR spectroscopy and the molecular structure of 2a was determined by X-ray crystallography. All complexes have been tested as catalysts for the transfer hydrogenation of aromatic ketones, showing excellent activity in this reaction.

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

“…It is observed that NaOH and KOH show good conversions when compared to Cs 2 CO 3 , K 2 CO 3 , t ‐BuOK and NaOAc in the hydrogenation reactions. As in previous studies, the best results are obtained with KOH . In the absence of a base no transfer hydrogenation of ketones is observed.…”

“…The reduction of acetophenone to 1‐phenylethanol was initially used as a model reaction with in situ prepared Ru(II) systems with 1a , 1b , 1c , 1d , 1e , 1f as catalysts in the transfer hydrogenation. In order to ensure complete formation of the active catalyst, a 2‐propanol solution of 1 mol% [RuCl 2 ( p ‐cymene)] 2 and 2 mol% 1a is stirred in the presence of 2 mmol of KOH at room temperature for 0.5 h. According to the literature during the formation of Ru–carbene complexes with [RuCl 2 ( p ‐cymene)] 2 , one carbene molecule bonds to the Ru center . Then acetophenone (1.00 mmol) is added and the reaction performed at 80°C for 1 h. When a lower catalyst molar ratio is used, conversion decreases (Table , entries 10 and 11).…”

“…We have previously reported imidazolidine, benzimidazole‐2‐ylidene–ruthenium(II) complexes and an in situ formed tetrahydropyrimidine–ruthenium(II) system which exhibit high activity . In order to find more efficient ruthenium catalysts we have prepared a series of new 1,3‐dialkyl‐3,4,5,6‐tetrahydropyrimidinium salts, 1a , 1b , 1c , 1d , 1e , 1f (Scheme ), and we now report the use of the in situ generated catalytic system composed of [RuCl 2 ( p ‐cymene)] 2 as ruthenium source, 1a , 1b , 1c , 1d , 1e , 1f as carbene precursors and KOH as a base for the transfer hydrogenation of aryl ketones in 2‐propanol for 1 h. All synthesized compounds were characterized using 1 H NMR, 13 C NMR and IR spectroscopy and elemental analysis, the results of which support the proposed structures.…”

Synthesis of palladium complexes derived from imidazolidin‐2‐ylidene ligands and used for catalytic amination reactions

“…Imidazolinium salts were prepared according to the literature . The palladium complexes were prepared by means of the Ag–carbene transfer method developed by Wang and Lin .…”

‘Click’ generated 1,2,3-triazole based organosulfur/selenium ligands and their Pd(ii) and Ru(ii) complexes: their synthesis, structure and catalytic applications

“…Activity of both 3 and 4 is highest for benzaldehyde (isolated yield up to ~99%, Table 5, Entry 1). The optimum loading of [(p-cymene)Ru(NHC)] 46 as a TH catalyst in 2propanol is reported higher than those of 3 and 4, but with a short reaction time ≤1 h. The optimum loading of Ru(II) 25 complexes of 1,3,5-triaza-7-phosphaadamantane (PTA) for biphasic TH in aqueous medium 47 is reported higher than those of 3 and 4. The complex 4 is efficient for catalytic TH of furfuraldehyde, 4-chlorobenzaldehyde and 4-90 bromobenzaldehyde but activity of 3 is lower ( and H-source their conversions were good ( 44 is 1 mol%, higher than those of present complexes.…”