Arene Ruthenium Complexes as Versatile Catalysts in Water in both Transfer Hydrogenation of Ketones and Oxidation of Alcohols. Selective Deuterium Labeling of rac-1-Phenylethanol

Abstract

The preparation of three series of arene Ru(II) half-sandwich compounds with the functional ligand 4,4′-dimethoxy-2,2′-bipyridine (dmobpy) is described. The new cationic derivatives have the general formula [(η6-arene)RuCl(κ2-N,N-dmobpy)]X (arene = benzene, X = Cl– ([1]Cl), BF4 – ([1][BF 4 ]), TsO– ([1]TsO), PF6 – ([1][PF 6 ]); arene = p-cymene (p-cym), X = Cl– ([2]Cl), BF4 – ([2][BF 4 ]), TsO– ([2]TsO), PF6 – ([2][PF 6 ]); arene = 2-phenoxy-1-ethanol (phoxet), X = Cl– ([3]Cl), BF4 – ([3][BF 4 ]), TsO– ([3]TsO), PF6 – ([3][PF 6 ])). The structures of [1]Cl, [1]TsO, [2]TsO, [2][BF 4 ], and [2][PF 6 ] were determined by X-ray crystallography. All of the complexes except the PF6 – salts were water-soluble, and they behaved as active catalysts in two different processes: the transfer hydrogenation of water-soluble and -insoluble ketones to the corresponding alcohols, using HCOONa as the hydrogen source at pH 4, and the oxidation of rac-1-phenylethanol to acetophenone with tBuOOH at pH 7, both in aqueous solution. For the transfer hydrogenation with p-cymene complexes the aqua, formato, and hydride species were detected by means of 1H NMR experiments in D2O. It was found that the cationic hydrido complex was [(η6-p-cymene)RuD(dmobpy)]+. The reversible and pH-dependent formation of the hydroxo derivative was also observed. When the catalytic transfer hydrogenation was performed in D2O, the 1-phenylethanol obtained was selectively deuterated at the benzylic carbon. Mechanistic proposals are also included.

Ruthenium(II) η6-arene complexes containing a dinucleating ligand based on 1,8-naphthyridine

“…These parameters are typical for the coordination of a nitrogen donor and an h 6 -arene to a ruthenium(II) ion. The Ru(1)eCl(1) and Ru(2)eCl (2) bond lengths and coordination angles are similar to those reported for related arene Ru(II) complexes with bipyridine ligands [21,41,42]. The chelating bis-pyridinyl ligand has a bite angle of 82.6(1) for Ru(1) and 83.0(1) for Ru (2), deviating from 90 due to the geometrical constraint.…”

The Golden Age of Transfer Hydrogenation

“…The ruthenium−arene complexes containing 4,4′-dimethoxy-2,2′-bipyridine (74) showed catalytic activity in the reduction of water-soluble and -insoluble ketones with the use of HCOONa as the hydrogen donor at pH 4. 353 The introduction of OH groups in the bipyridine moiety largely enhanced water solubility of the ruthenium catalyst. In addition, the hydrogen bond of the OH groups eventually induced metal−ligand bifunctional catalysis resulting in excellent performance in TH of ketones in aqueous media.…”

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

“…Among bases K 2 CO 3 was 25 found most suitable. Among other aryl bromides the activated ones gave good conversion when SMC was carried out 45 for 1-2 h in the presence of 1, however the reaction time increased with 2 for coupling of the same substrate (Table 1, Entries 3-6). In Table 1 optimum mol% of catalyst required, reaction time, % isolated yield and % conversion estimated at the end of reaction with 1 H NMR are reported.…”

“…The scope of substrates for the catalytic TH with 3 and 4 85 was studied and results are given in Tables 5. 33a 10 Using HCOONa as a hydrogen source at pH 4 in water, [Ru(η 6 -20 arene)(dmobpy)Cl] + (dmobpy = 4,4′-dimethoxy-2,2′-bipyridine) 45 shows better catalytic efficiency than 3 and 4. The conversion of acetophenone is ~ 99% with 4 and 70% with 3 (Table 5, Entry 4).…”

“…33a 10 Using HCOONa as a hydrogen source at pH 4 in water, [Ru(η 6 -20 arene)(dmobpy)Cl] + (dmobpy = 4,4′-dimethoxy-2,2′-bipyridine) 45 shows better catalytic efficiency than 3 and 4. 50 High electron donating ability of Se and S makes metal center electron rich which probably promotes the formation of metal- 45 hydride species during the catalysis. The catalytic TH efficiency of RuCl 2 (TPPMS) 2 ] (TPPMS = 4-(diphenylphosphino)benzenesulfonic acid) 48 in aqueous medium is comparable to those of 3 and 4.…”