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Water-Soluble Arene Ruthenium Complexes Containing a <i>trans</i>-1,2-Diaminocyclohexane Ligand as Enantioselective Transfer Hydrogenation Catalysts in Aqueous Solution
Auteur(s)
Canivet, Jérôme
Labat, Gael
Date de parution
2005
In
European Journal of Inorganic Chemistry, 2005/22/4493 - 4500
Résumé
The cationic chloro complexes [(arene)Ru(H<sub>2</sub>N∩NH<sub>2</sub>)Cl]<sup>+</sup> (<b>1</b>: arene = C<sub>6</sub>H<sub>6</sub>; <b>2</b>: arene = <i>p</i>-MeC<sub>6</sub>H<sub>4</sub><i>i</i>Pr; <b>3</b>: arene = C<sub>6</sub>Me<sub>6</sub>) have been synthesised from the corresponding arene ruthenium dichloride dimers and enantiopure (<i>R,R</i> or <i>S,S</i>) <i>trans</i>-1,2-diaminocyclohexane (H<sub>2</sub>N∩NH<sub>2</sub>) and isolated as the chloride salts. The compounds are all water-soluble and, in the case of the hexamethylbenzene derivative <b>3</b>, the aqua complex formed upon hydrolysis [(C<sub>6</sub>Me<sub>6</sub>)Ru(H<sub>2</sub>N∩NH<sub>2</sub>)OH<sub>2</sub>]<sup>2+</sup> (<b>4</b>) could be isolated as the tetrafluoroborate salt. The molecular structures of <b>3</b> and <b>4</b> have been determined by single-crystal X-ray diffraction analyses of [(C<sub>6</sub>Me<sub>6</sub>)Ru(H<sub>2</sub>N∩NH<sub>2</sub>)Cl]Cl and [(C<sub>6</sub>Me<sub>6</sub>)Ru(H<sub>2</sub>N∩NH<sub>2</sub>)OH<sub>2</sub>][BF<sub>4</sub>]<sub>2</sub>. Treatment of [Ru<sub>2</sub> (arene) <sub>2</sub>Cl<sub>4</sub>] with the monotosylated <i>trans</i>-1,2-diaminocyclohexane derivative (TsHN∩NH<sub>2</sub>) does not yield the expected cationic complexes, analogous to <b>1<b>-</b>3</b> but the neutral deprotonated complexes [(arene)Ru(TsN∩NH<sub>2</sub>)Cl] (<b>5</b>: arene = C<sub>6</sub>H<sub>6</sub>; <b>6</b>: arene = <i>p</i>-MeC<sub>6</sub>H<sub>4</sub><i>i</i>Pr; <b>7</b>: arene = C<sub>6</sub>Me<sub>6</sub>; <b>8</b>: arene = C<sub>6</sub>H<sub>5</sub>COOMe). Hydrolysis of the chloro complex <b>7</b> in aqueous solution gave, upon precipitation of silver chloride, the corresponding monocationic aqua complex [(C<sub>6</sub>Me<sub>6</sub>)Ru(TsHN∩NH<sub>2</sub>)(OH<sub>2</sub>)]<sup>+</sup> (<b>9</b>) which was isolated and characterised as its tetrafluoroborate salt. The enantiopure complexes <b>1</b>-<b>9</b> 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 <b>7</b>, giving a catalytic turnover frequency of 43 h<sup>-1</sup> and an enantiomeric excess of 93 %.
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journal article
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