Neutral ¦Ç⁶-arene ruthenium complexes with monodentate P-donor ligands: Activation in the transfer hydrogenation reaction

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• 作者：Arnald Grabulosa ; Alberto Mannu ; Elisabetta Alberico ; Stefania Denurra ; Serafino Gladiali ; Guillermo Muller
• 关键词：Ruthenium arene complexes ; Transfer hydrogenation ; Acetophenone reduction ; Induction period
• 刊名：Journal of Molecular Catalysis A: Chemical
• 出版年：2012
• 出版时间：November, 2012
• 年：2012
• 卷：363-364
• 期：Complete
• 页码：49-57
• 全文大小：584 K

文摘

Five Ru(II) neutral complexes C of the type [RuCl₂(¦Ç⁶-arene)(P)] (P = monodentate phosphorus ligand) have been prepared: C1 (arene = p-cymene, P = PPh₃); C2 (arene = p-cymene, P = (R)-Monophos); C3 (arene = p-cymene, P = (S)-Ph-Binepine); C4 (arene = benzene, P = PPh₃); and C5 (arene = benzene, P = (S)-Ph-Binepine). These complexes have been screened as catalytic precursors in the transfer hydrogenation of acetophenone with 2-propanol. Under optimised conditions at 82 ¡ãC complexes C1 and C4 provide full conversion in less than 20 min at a [Ru]:substrate ratio of 1:200. With the chiral complexes C2 and C3 good TOF values have been reached but with low enantioselectivities. The activation of the catalytic precursor has been studied. Based on NMR evidence, a mechanism in which the catalytically active species is a Ru monohydride complex arising from the reaction of the catalyst precursor C with 2-propanol in the presence of a base is suggested. The reaction shows different sensitivity towards excess of phosphine: whereas excess of PPh₃ slows down the reaction severely, excess of (S)-Ph-Binepine does not cause such a sharp effect. An excess of chloride ion affects the activation of the precursor C.