Water‐Soluble Arene Ruthenium Complexes Containing a trans‐1,2‐Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous Solution

Abstract

The cationic chloro complexes [(arene)Ru(H2N∩NH2)Cl]+ (1: arene = C6H6; 2: arene = p‐MeC6H4iPr; 3: arene = C6Me6) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (R,R or S,S) trans‐1,2‐diaminocyclohexane (H2N∩NH2) and isolated as the chloride salts. The compounds are all water‐soluble and, in the case of the hexamethylbenzene derivative 3, the aqua complex formed upon hydrolysis [(C6Me6)Ru(H2N∩NH2)OH2]2+ (4) could be isolated as the tetrafluoroborate salt. The molecular structures of 3 and 4 have been determined by single‐crystal X‐ray diffraction analyses of [(C6Me6)Ru(H2N∩NH2)Cl]Cl and [(C6Me6)Ru(H2N∩NH2)OH2][BF4]2. Treatment of [Ru2(arene)2Cl4] with the monotosylated trans‐1,2‐diaminocyclohexane derivative (TsHN∩NH2) does not yield the expected cationic complexes, analogous to 1–3 but the neutral deprotonated complexes [(arene)Ru(TsN∩NH2)Cl] (5: arene = C6H6; 6: arene = p‐MeC6H4iPr; 7: arene = C6Me6; 8: arene = C6H5COOMe). Hydrolysis of the chloro complex 7 in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C6Me6)Ru(TsHN∩NH2)(OH2)]+ (9) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes 1–9 have been employed as catalysts for the transfer hydrogenation of acetophenone in aqueous solution using sodium formate and water as a hydrogen source. The best results were obtained (60 °C) with 7, giving a catalytic turnover frequency of 43 h–1 and an enantiomeric excess of 93 %. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2005)

Arene ruthenium oxinato complexes: Synthesis, molecular structure and catalytic activity for the hydrogenation of carbon dioxide in aqueous solution

“…The spectroscopic (MS, In contrast to arene ruthenium chloro complexes containing chelating N,N-ligands, which hydrolyze in water to give the corresponding cationic aqua complexes [11,12,39] The para-cymene chloro complex 5 crystallizes in the monoclinic centrosymmetric space group P2 1 /n. The asymmetric unit comprises only one molecule, the molecular structure of which is depicted in Fig.…”

“…A new impetus came into this field in 1988, when Ludi, Merbach, Bürgi and co-workers showed that arene ruthenium aqua complexes previously observed by NMR spectroscopy [2] can be isolated under certain conditions; the characterization of the cation [(g 6 -C 6 H 6 )Ru(H 2 O) 3 ] 2+ by singlecrystal X-ray structure analysis of the sulfate salt can be considered as a breakthrough [6]. In the 1990s we found that the chloride or tetrafluoroborate salts of cationic arene ruthenium complexes are well soluble in water, the arene ruthenium bond being robust toward hydrolysis [7][8][9], which resulted in a rapid development of arene ruthenium chemistry in aqueous solution [10], especially as far as water-soluble catalysts for transfer hydrogenation reactions in aqueous solution are concerned [11][12][13][14][15][16][17][18][19][20][21]. The hydrogenation of carbon dioxide to give formic acid in aqueous solution is an attractive approach to the use of carbon dioxide as an economical and ecological C 1 source [22].…”

“…Based on our work on water-soluble organometallic complexes containing chelating ligands for catalytic transfer hydrogenation reactions using sodium formate and water as hydrogen source [11][12], we intended to develop a complementary catalyst for the hydrogenation of CO 2 to give HCOO À , which can be coupled to the NADHregenerating (g 5 -C 5 Me 5 )Rh(ortho-phenanthroline) catalyst for the chemoenzymatic enantioselective reduction of ketones (Scheme 1), catalyst using formate as a hydrogen source to give carbon dioxide [13]. We decided to synthesize and to test (g 6 -arene)Ru(oxinato) complexes for this purpose.…”

Water‐Soluble Phenanthroline Complexes of Rhodium, Iridium and Ruthenium for the Regeneration of NADH in the Enzymatic Reduction of Ketones

“…[1] The transition-metal-based enantioselective hydrogenation or transfer hydrogenation of ketones in organic solvents [2][3][4][5][6][7][8][9][10] as well as in aqueous solutions [11][12][13][14][15][16][17][18][19][20][21] is one of the most commonly used synthetic approaches. Biotransformations of organic substrates by various enzymes have also found widespread applications, particularly because of their capability to efficiently perform enantioselective transformations.…”

Metallo‐Organic Domino Reactions: CH versus CC Bond Breaking

“…(1)]. [7][8][9][10][11] In attempts to prepare helical dinuclear ruthenium(II) benzene complexes as a part of our on-going project on helical metal complexes, [12][13][14][15] we reacted [Ru-A C H T U N G T R E N N U N G (C 6 H 6 )Cl 2 ] 2 with the helical tetradentate N-donor ligands RL (R is H or Me). The X-ray crystal structure of the ligand HL has been reported earlier by us.…”