Terdentate RuX(CNN)(PP) (X = Cl, H, OR) Complexes: Synthesis, Properties, and Catalytic Activity in Fast Transfer Hydrogenation
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- 作者：Walter Baratta ; Marco Bosco ; Giorgio Chelucci ; Alessandro Del Zotto ; Katia Siega ; Micaela Toniutti ; Ennio Zangrando ; Pierluigi Rigo
- 刊名：Organometallics
- 出版年：2006
- 出版时间：September 11, 2006
- 年：2006
- 卷：25
- 期：19
- 页码：4611 - 4620
- 全文大小：152K
- 年卷期：v.25,no.19(September 11, 2006)
- ISSN：1520-6041
文摘
Terdentate ruthenium(II) complexes of general formula RuX(CNN)(dppb) (X = chloride, hydride,alkoxide; dppb = Ph2P(CH2)4PPh2), where CNN is a deprotonated 2-aminomethyl-6-arylpyridine ligand,have been prepared. The orthometalated derivative RuCl(b)(dppb) (1) has been obtained by reaction ofRuCl2(PPh3)(dppb) with N,N-dimethyl-2-aminomethyl-6-(4-methylphenyl)pyridine (Hb) in 2-propanoland in the presence of triethylamine by elimination of PPh3 and HCl. Similarly, RuCl(a)(dppb) (2) andthe chiral analogue RuCl(c)(dppb) (3), containing primary amine ligands, have been isolated startingfrom 2-aminomethyl-6-(4-methylphenyl)pyridine (Ha) and (R)-2,2-dimethyl-1-(6-phenylpyridin-2-yl)propylamine (Hc), respectively. The synthesis of the functionalized pyridines Ha-Hc is here described,whereas the crystal structure of 3 has been determined through an X-ray diffraction experiment. Treatmentof 1-3 with sodium or potassium isopropoxide gives the corresponding hydrides RuH(b)(dppb) (4),RuH(a)(dppb) (5), and RuH(c)(dppb) (6) from the ruthenium isopropoxide complexes, via a 
-Helimination process. Studies in solution show that the isopropoxides bearing a NH donor group are inequilibrium with the corresponding hydrides (5 and 6). Reaction of 5 with benzophenone leads to thealkoxide Ru(OCHPh2)(a)(dppb) (7), which has been proven to interact with benzhydrol in C6D6, leadingto the adduct 7·(HOCHPh2), the alkoxide ligand, and the alcohol being in rapid exchange. Complexes 2and 3 display a remarkable high catalytic activity for the transfer hydrogenation of ketones to alcohol in2-propanol using a very small amount of catalyst. With the chiral complex 3 (0.005 mol %) methyl-arylketones can be quickly reduced (TOF ranging from 5.4 × 105 to 1.4 × 106 h-1) with an enatiomericexcess up to 88%.
-Helimination process. Studies in solution show that the isopropoxides bearing a NH donor group are inequilibrium with the corresponding hydrides (5 and 6). Reaction of 5 with benzophenone leads to thealkoxide Ru(OCHPh2)(a)(dppb) (7), which has been proven to interact with benzhydrol in C6D6, leadingto the adduct 7·(HOCHPh2), the alkoxide ligand, and the alcohol being in rapid exchange. Complexes 2and 3 display a remarkable high catalytic activity for the transfer hydrogenation of ketones to alcohol in2-propanol using a very small amount of catalyst. With the chiral complex 3 (0.005 mol %) methyl-arylketones can be quickly reduced (TOF ranging from 5.4 × 105 to 1.4 × 106 h-1) with an enatiomericexcess up to 88%.