Construction of Highly Active Ruthenium(II) NNN Complex Catalysts Bearing a Pyridyl-Supported Pyrazolyl-Imidazolyl Ligand for Transfer Hydrogenation of Ketones
摘要:
A family of hemilabile ruthenium(II) NNN complexes bearing a unsymmetrical 2-(benzoimidazol-2-yl)-6-(pyrazol-l-yl)pyridine ligand has been synthesized and exhibited good to excellent catalytic activity in transfer hydrogenation of ketones in refluxing 2-propanol, reaching final TOFs up to 7.2 x 10(5) h(-1) with 0.05 mol % loading. The gamma-NH effect of the benzoimidazol-2-yl moiety in the ligand and coordination modes of the metal center in a Ru(II) NNN complex has great influence on the catalytic activity of the complex catalyst in transfer hydrogenation of ketones. It has been demonstrated that one of the structural prerequisites for an active Ru(II) complex catalyst is the coordinatively unsaturated environment around the metal center in the complex or the precatalyst, and the catalytic activity of a complex catalyst can be enhanced by making its metal center cationic. This paper presents a methodology to construct new types of efficient Ru(II) complex catalysts for transfer hydrogenation of ketones.
合成并结构表征了带有π接头支撑的双(吡唑基-咪唑基-吡啶)配体的双核钌(II)-NNN钳形配合物,它们在回流异丙醇中显示出优异的催化酮转移氢化的催化活性,达到TOF值高达到1.3×10 6 h -1。与相应的单核Ru(II)-NNN钳形络合物相比,双金属络合物可以以低至0.03 mol%Ru的浓度使用,并在酮的转移加氢反应中表现出显着增强的催化活性。二钌的高催化活性(II)络合物归因于两个配位的Ru(II)金属中心通过π接头具有出色的稳定性和可能的协同作用。本合成方法学已经建立了可应用的策略来构建高活性的双金属NNN钳形复合催化剂。
合成并结构表征了带有π接头支撑的双(吡唑基-咪唑基-吡啶)配体的双核钌(II)-NNN钳形配合物,它们在回流异丙醇中显示出优异的催化酮转移氢化的催化活性,达到TOF值高达到1.3×10 6 h -1。与相应的单核Ru(II)-NNN钳形络合物相比,双金属络合物可以以低至0.03 mol%Ru的浓度使用,并在酮的转移加氢反应中表现出显着增强的催化活性。二钌的高催化活性(II)络合物归因于两个配位的Ru(II)金属中心通过π接头具有出色的稳定性和可能的协同作用。本合成方法学已经建立了可应用的策略来构建高活性的双金属NNN钳形复合催化剂。