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Dinuclear ruthenium sawhorse-type complexes containing bridging ligands with ferrocenyl substituents in endo/endo, endo/exo and exo/exo orientations
The dinuclear Ru complexes Ru2(CO)4(OOCC5H4FeC5H5)2L2 (L = py: 1, L = PPh3: 2) were synthesized from Ru3(CO)12, ferrocene carboxylic acid and pyridine or PPh3, resp. The single-crystal x-ray structure anal. reveals for 1 and 2 a Ru2(CO)4 sawhorse backbone with the two ferrocenyl substituents of the two carboxylato bridges being endo/exo with respect to each other in the solid state. With the new pyridine deriv. NC5H4OOCC5H4FeC5H5-4 (4-ferrocenoyloxypyridine) (3) as axial ligand, the complex Ru2(CO)4(OOCC5H4FeC5H5)2(NC5H4OOCC5H4FeC5H5-4)2 (4) was obtained, the single crystal x-ray structure anal. showing an exo/exo orientation of the two carboxylato bridges in the solid state. The endo/endo orientation is found in the solid-state structure of Ru2(CO)4(HNOCC5H4FeC5H5)2(PPh3)2 (5), the two OCNH bridges being transoid with respect to each other; this complex is accessible from Ru3(CO)12, ferrocenamide and PPh3. [on SciFinder(R)]
Water-Soluble Arene Ruthenium Complexes Containing a trans-1,2-Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous Solution
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 %.
Dinuclear manganese complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo bridges
The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L-Me2) with MnCl2 • 4H2O in acetonitrile gives, in the presence of sodium formate, hydrogen peroxide, triethylamine and KPF6, the dinuclear Mn(III)–Mn(IV) complex cation [(L-Me2)2Mn2 (O) 2 (OOCH)]2+ (1) which crystallises as the hexafluorophosphate salt.The analogous reaction with sodium benzoate, however, yields the dinuclear Mn(III)–Mn(III) complex cation [(L-Me2)2Mn2 (O)(OOCC6H5)2]2+ (2), isolated also as the hexafluorophosphate salt.In the case of sodium acetate, both cations, the Mn(III)–Mn(IV) complex [(L-Me2)2Mn2 (O) 2 (OOCCH3)]2+ (3) and the known Mn(III)–Mn(III) complex [(L-Me2)2Mn2 (O)(OOCCH3)2]2+ (4) are available, depending upon the molar ratio.The single-crystal X-ray structure analyses show for the green crystals of [1][PF6]1.5 [Cl]0.5 • 1.5 H2O and [3][PF6]2 • (CH3)2CO, a Mn–Mn distance of 2.620(2) and 2.628(4) Å, respectively, while for the red-violet crystal of [4][PF6]2, a Mn–Mn distance of 3.1416(8) Å is observed.All four compounds show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water and in acetonitrile to give acetone in the presence of oxalic or ascorbic acid as co-catalysts.
endo and exo Coordination of Indanol: Synthesis, Isolation and Structural Characterisation of [H3Ru3 (endo-Indanol)(C6Me6)2(O)]+ and [H3Ru3 (exo-Indanol)(C6Me6)2 (O)]+ as Their Tetrafluoroborate Salts
The reaction of 2,3,4,7-tetrahydro-1H-inden-2-ol with ruthenium chloride hydrate in refluxing ethanol yields the chloro-bridged dinuclear complex [RuCl2(indanol)]2 (1). The mononuclear complex [Ru(indanol)(H2O)3]2+ (2), formed in situ from 1 in aqueous solution, reacts with the dinuclear complex [H3Ru2(C6Me6)2]+ to give a trinuclear arene-ruthenium cluster as a mixture of two isomers, the cations [H3Ru3(endo-indanol)(C6Me6)2(O)]+ (3a) and [H3Ru3(exo-indanol)(C6Me6)2(O)]+ (3b), in a 1:1 ratio. The hydroxy function of the indanol ligand is oriented towards the μ3-oxo cap of 3a, whereas the OH group is bent away from the metal skeleton of 3b. These two isomers, which can easily be separated by silica-gel chromatography, were isolated and characterised as their tetrafluoroborate salts. The single-crystal X-ray structure analysis of [3a][BF4] shows a strong intramolecular hydrogen bond between the μ3-oxo ligand and the hydroxyl function, which even persists in acetone solution, as demonstrated by NMR spectroscopy. On the other hand, the hydroxy function of 3b was found to be free in the solid state as well as in solution, as shown by an X-ray crystal structure analysis and by NMR spectroscopy. The catalytic activities of the water-soluble trinuclear cations 3a and 3b for the hydrogenation of benzene to give cyclohexane under biphasic conditions are considerably different, the exo isomer 3b being more active than the endo isomer 3a.
Dinuclear iron, ruthenium and cobalt complexes containing 1,4-dimethyl-1,4,7-triazacyclononane ligands as well as carboxylato and oxo or hydroxo bridges
The reaction of 1,4-dimethyl-1,4,7-triazacyclononane (L–Me2) with FeSO4 • 7H2O in aqueous ethanol gives, in the presence of sodium carboxylates, hydrogen peroxide, sodium hydroxide and KPF6, the dinuclear Fe(III)–Fe(III) complex cations [(L–Me2)2Fe2(O)(OOCR) 2]2+ (R = H: 1, R = CH3: 2, R = C6H5: 3), which crystallise as the hexafluorophosphate salts. The corresponding reaction with RuCl3 • nH2O does not work, however, the analogous Ru(III)–Ru(III) complex [(L–Me2)2Ru2 (O)(OOCCH3)2]2+ (5) can be synthesised by reacting Ru(dmso)4Cl2 with L–Me2, HCl and air in refluxing ethanol, followed by addition of sodium acetate, the mononuclear intermediate (L–Me2)RuCl3 • H2O (4) being also isolated and characterised. The reaction of L–Me2, sodium acetate, hydrogen peroxide and triethylamine with CoCl2 • 6H2O in acetonitrile yields, however, the hydroxo-bridged Co(III)–Co(III) complex [(L–Me2)2Co2 (OH)(OOCCH3)2]3+ (6). The molecular structures of 2, 5 and 6, solved by single-crystal X-ray structure analyses of the hexafluorophosphate salts, reveal for the orange crystals of [2][PF6]2 a Fe–Fe distance of 3.104(1) Å, for the purple crystals of [5][PF6]2 a Ru–Ru distance of 3.230(1) Å, and for the violet crystals of [6][PF6]3 • (CH3)2CO a Co–Co distance of 3.358(1) Å. All six complexes show catalytic activity for the oxidation of isopropanol with hydrogen peroxide in water to give acetone in the presence of ascorbic acid as co-catalyst.