Synthesis of Ruthenium(II) Complexes Containing Tridentate Triamine (′N ͡N ͡N′) and Bidentate Diamine Ligands (N ͡N′): as Catalysts for Transfer Hydrogenation of Ketones

Abstract

Pyridine-based tridentate triamine compounds ( 0 N kNkN 0 ) are very attractive ligands for coordination chemistry, and their transition-metal (TM) complexes have been successfully applied in homogeneous catalysis. 1À28 Although examples of the related Ru complexes are scarce, such complexes recently gained attention due to their use in catalysis and in other chemical applications. 29À48 For example, d N k N k N d -containing neutral Ru(II) complexes of the general formula [RuCl 2 ( d N k N k N d )L] (L = monodentate ligands such as CH 3 CN, PPh 3 , and CO) are effective catalysts for the transfer hydrogenation (TH) of ketones. 29,32 During the preparation of this paper, a report on unsymmetrical and asymmetrical [RuCl( 0 N k N k N 00 )(PPh 3 ) 2 ]Cl complexes which showed excellent TH activity has appeared. 49 On the other hand, Ru(II) complexes bearing chelating amine ligands such as N-sulfonated 1,2-diamines have been successfully used in the TH of acetophenone by Noyori and others. 50À63 However, in spite of these developments, there is still demand for stable and easily handled complexes prepared from cheap starting materials which make them preferred catalyst precursors. In comparison with the extensive chemistry of sulfonated 1,2-diamines, little research has been performed on pyridylsulfonamide compounds of the type C 5 H 4 NCH 2 NHSO 2 Ar, which are versatile bidentate ligands due to their ease of synthesis and variability of Ar groups. 64À68 Neutral sulfonamide ligands are expected to be poor ligands. Thus, the pyridyl-2-alkylsulfonamides generally coordinate to the metal center through the pyridyl nitrogen atom and the deprotonated nitrogen of the sulfonamide group. 69 However, Soltani et al. have recently shown that cationic Ir complexes containing neutral sulfonamide ligands are active catalysts for the TH of acetophenone derivatives in water. 70 More recently, Baratte and co-workers have shown that Ru(II) complexes containing nonsulfonated (2-aminomethyl)-pyridine ligands display excellent catalytic activity in the TH of ketones. 71 With the aim of contributing to the understanding of how geometric and electronic factors imposed by a combination of mixed tri-and bidentate ligands influence the catalyst performance, herein a series of novel Ru(II) complexes (1À10) were characterized and employed as catalysts for the TH of ketones.

Half-sandwich Ru(η6-C6H6) complexes with chiral aroylthioureas for enhanced asymmetric transfer hydrogenation of ketones – experimental and theoretical studies

“…54 Ruthenacycles obtained by cyclometalation of [(η 6benzene)RuCl 2 ] 2 with enantiopure aromatic primary amines showed 86% conversion and 54% ee and with secondary amines 99% conversion and 80% ee was reported. Conversions and ee up to 99 % were obtained (Table 1, entries [19][20][21][22][23][24]. Conversions and ee up to 99 % were obtained (Table 1, entries [19][20][21][22][23][24].…”

“…12 Ru(II) arene derivatives with chiral ligands have been screened for various catalytic reactions, the asymmetric transfer hydrogenation (ATH) of ketones being one of them. 15 Ru-catalyzed transfer hydrogenation of ketones [16][17][18][19][20][21][22][23][24][25][26][27][28][29] is found to be efficient and has been thoroughly explored by Noyori and co-workers. In ATH reactions, the reactivity of arenes follows the order benzene > p-cymene, mesitylene > hexamethyl benzene, which clearly indicates that the less sterically challenging and less electron-rich arene display the higher performance.…”

Heteroleptic ruthenium(II) complexes of 2-(2-pyridyl)benzimidazoles: A study of catalytic efficiency towards transfer hydrogenation of acetophenone

“…Since that day, many studies show that catalytic efficiencies of complexes are directly affected by ligand properties. For this purpose, Ru(II) complexes including N-donor ligands have aimed to identify the best catalyst for CTH of carbonyl compounds [20][21][22][23]. Although there are many attempts with poly-pyridyl ligands, the catalytic studies of Ru(II) complexes bearing pyridyl-benzimidazoles was not found for CTH.…”

Human carbonic anhydrase II as host protein for the creation of artificial metalloenzymes: the asymmetric transfer hydrogenation of imines

“…A recent report by Çetinkaya suggests that the transfer hydrogenase activity of d 6 -pianostool complexes with a sulfonamide-bearing 2-picolylamine is superior to that of the corresponding the 2-picolylamine-containing catalyst. 35 We thus set out to synthesize and evaluate the activity of [ These results highlight the critical inuence of the second coordination sphere interactions on the catalytic performance of pianostool complexes with a well dened rst coordination sphere.…”