| In this work four kinds of ligand-functionalized ionic liquids (ILs), including P-containing ligand-functionalized ILs, N-containing ligand-functionalized ILs and P,N-hydrid ligand-functionalized ILs (Fig.l) have been synthesized. After the complexation of RUCl3·3H2O with the P-containing ligand-functionalized ILs and the subsequent ion-exchange, two kinds of Ru-complex-functionalized ILs could be obtained as shown in Fig.2. Then the catalytic performances of the Ru catalysts for aerobic oxidation and hydrogenation with the aid of the synthesized ligand-functionalized ILs were investigated through two methods. One was based on the catalytic system composed of hydrated ruthenium (Ⅲ) chloride (RuCl3.3H2O) and the ligand-functionalized ILs. Another method was based on the obtained Ru-complex-functionalized ILs complex. It was found that for the aerobic oxidation of alcohols, RuCl3·3H2O assisted by the functionalized ILs could catalyze oxidation of various alcohols to aldehydes and ketones with high selectivity without the presence of co-oxidants. The catalytic performance of the RuCl3·3H2O was greatly influenced by the solvents and ligands. The N-containing ligand functionalized IL with weaker ligation to Ru center exhibited better activity and much higher selectivity. Whereas, the N,P-hybrid ligand functionalized IL with bidentate chelating ability to Ru center showed relatively low activity. However, the recyclability of RuCl3·3H2O in such functionalized IL compositions was unavailable. The in situ 31P NMR spectroscopy study indicated that the oxidative degradation of the ligand itself was responsible for the deactivation of the Ru catalyst.As for the synthesized novel phosphine-ligated Ru-complex-functionalized IL of [RuCl4(DPPBMIM)2]PF6 with highly symmetrical octahedral geometry, it exhibited good catalytic performance for the hydrogenation and the transfer hydrogenation of aldehydes and ketones, which could be recycled several times without significant loss of activity due to possessing the typical IL nature. And the resultant complex of [RuCl4(DPPBMIM)2]H2PW12O40 via the anion-exchange reaction was also proved to be the efficient and recyclable catalyst for the aerobic oxidation of benzylic alcohols. It was found that, although the contribution of phosphotungstate ([H2PW12O40]-) itself to the aerobic oxidation was negligible, the presence of [H2PW12O40]- as the counter-anion could enhance the stability of [RuCl4(DPPBMIM)2]+ cation against oxidative degradation, leading to the improved catalytic performance. |
