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.

A highly effective and green procedure for the formation of α-alkylated ketones has been disclosed via the reaction of primary alcohols with secondary alcohols and ketones by using [IrCl(COD)(NHC)] complexes as a catalyst. Various α-alkylated ketones were obtained in high yields from the alkylation of alcohol with alcohol and ketone with alcohol through a borrowing hydrogen reaction by using 0.05-0.5 mol % iridium(I) and a catalytic amount of KOH (5-10 mol %) as the base under air atmosphere and within very short reaction times.

Iridium­(I) complexes having an imidazol-2-ylidene ligand with benzylic wingtips efficiently catalyzed the β-alkylation of secondary alcohols with primary alcohols and acceptorless dehydrogenative cyclization of 2-aminobenzyl alcohol with ketones through a borrowing hydrogen pathway. The β-alkylated alcohols, including cholesterol derivatives, and substituted quinolines were obtained in good yields by using a minute amount of the catalyst with a catalytic amount of NaOH or KOH under the air atmosphere, liberating water (and H2 in the case of quinoline synthesis) as the sole byproduct. Notably, this system demonstrated turnover numbers of 940 000 (for β-alkylation of secondary alcohols with primary alcohols by using down to 0.0001 mol % = 1 ppm of the catalyst) and 9200 (acceptorless dehydrogenative cyclization of 2-aminobenzyl alcohol with ketones).

Under borrowing hydrogen conditions, NHC− iridium(I) catalyzed the direct or one-pot sequential synthesis of α,α-disubstituted ketones via the alkylation of secondary alcohols with primary alcohols is reported. Notably, the present approach provides a new method for the facile synthesis of α,α-disubstituted ketones and featured with several characteristics, including a broad substrate scope, using easy-to-handle alcohols as starting materials, and performing the reactions under aerobic conditions. Moreover, the selective one-pot formation of β,β-disubstituted alcohols was achieved by the addition of an external hydrogen source to the reaction mixture.

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A series of piano‐stool Ru (II) complexes (Ru1–7) bearing ethylenediamine with aryl and aliphatic groups were prepared and fully characterized by 1H, 13C, 19F and 31P NMR spectroscopy, FT‐IR and elemental analysis. The crystal structures of Ru2–4 and Ru7 were determined by X‐ray crystallography. They were successfully applied to the alpha(α)‐alkylation of aliphatic and aromatic ketones with alcohols via the borrowing hydrogen strategy in mild reaction conditions within a short time. The catalytic system has a broad substrate scope, which allows the synthesis of alpha alkylated ketones with excellent yields. The electronic and steric effects of complexes on catalytic activity were analysed. The influence of the carbon chain length of the ligand on the alpha‐alkylation reaction of ketones was also investigated. The catalytic cycle was also examined by 1H‐NMR spectroscopy in d8‐toluene.

A new method for converting terminal epoxides and primary alcohols into α-alkylated ketones under borrowing hydrogen conditions is reported. The procedure involves a one-pot epoxide ring opening and alkylation via primary alcohols in the presence of an N-heterocyclic carbene iridium­(I) catalyst, under aerobic conditions, with water as the side product.

The synthesis and characterization of seven new Ir III complexes containing o-phenoxide or o-naphthoxide chelated N-heterocyclic carbene ligands is reported herein. The crystal structures of six of the complexes have been determined. These complexes efficiently catalyze the transfer hydrogenative reductive amination (RA) of carbonyls and amines in water. Amongst the complexes tested, the introduction of o-naphthoxide on a nitrogen atom of imidazole based NHC ligand greatly increased the catalytic activity. The catalytic system has a broad substrate scope, which allows the synthesis of a variety of amines in excellent yields and with high turnover numbers up to 490 (for ketones) and 14800 (for aldehydes). The mechanism of aqueous RA reaction with an o-aryloxide chelated NHC-Ir III catalyst has been investigated by NMR spectroscopy and kinetic measurements. These studies suggest that the transfer hydrogenation (TH) is turnover-limited by the hydride formation step. As a result of the 1 H NMR studies, the higher catalytic activity of onaphthoxide chelated catalyst (3 g) over o-phenoxide chelated one (3 b) can be attributed partly due to the faster formation of an iridium hydride, the key intermediate in the RA reactions.