In situ 1H-PHIP-NMR studies of the stereoselective hydrogenation of alkynes to ( E)-alkenes catalyzed by a homogeneous [Cp*Ru]+ catalyst
作者:Dana Schleyer、Heiko G. Niessen、Joachim Bargon
DOI:10.1039/b007201j
日期:——
The hydrogenation of internal alkynes using a [Cp*Ru(alkene)]+ complex leads to the formation of (E)-alkenes. This ruthenium complex represents one of the few homogeneous catalysts that trans-hydrogenate internal alkynes directly and stereoselectively. We have studied its stereoselectivity by in situ PHIP-NMR spectroscopy (PHIP = para-hydrogen
induced polarization). With this method the initially formed products can be identified and characterized even at very low concentrations and low conversions. Furthermore, their subsequent fate can be evaluated with high sensitivity and with time resolution. Different alkyne substrates were used to demonstrate the universal applicability of this catalyst. The catalyst is not active in combination with terminal alkynes, however, possibly due to the formation of a rather stable vinylidene complex. A mechanism
proceeding ia a binuclear complex is proposed to explain the formation of the (E)-alkenes.
使用[Cp*Ru(烯烃)]+复合物对内炔进行氢化反应,生成(E)-烯烃。这种钌复合物是少数能够直接且选择性地进行反式氢化内炔的均相催化剂之一。我们通过原位PHIP-NMR光谱学(PHIP=邻氢诱导极化)研究了其选择性。利用这种方法,即便在极低的浓度和转化率下,初始生成的产物也能被识别和表征。此外,其后续变化可以高灵敏度和时间分辨率进行评估。采用不同的炔烃底物来展示这种催化剂的广泛适用性。然而,该催化剂在与端炔结合时并不活跃,可能是因为生成了相对稳定的亚乙烯基复合物。为了解释(E)-烯烃的生成,我们提出了一种通过双核复合物的反应机理。