Kinetic isotope effect evidence for the concerted transfer of hydride and proton from hydroxycyclopentadienyl ruthenium hydride in solvents of different polarities and hydrogen bonding ability
Kinetic isotope effect evidence for the concerted transfer of hydride and proton from hydroxycyclopentadienyl ruthenium hydride in solvents of different polarities and hydrogen bonding ability
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DOI：
10.1139/v05-140
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发表时间：
2005-09-01
期刊：
影响因子：
--
通讯作者：
Johnson, JB
中科院分区：
文献类型：
--
作者：
Casey, CP;Johnson, JB
Shvo 的氢化羟基环戊二烯基钌 (4) 的甲苯基类似物可有效地将氢化物和质子转移至苯甲醛或苯乙酮以产生全醇。这种还原反应可以在甲苯、二氯甲烷和 THF 中进行。0 摄氏度时，甲苯和二氯甲烷中苯甲醛的还原反应比 THF 中的还原反应快约 300 倍。0 摄氏度时，在每种溶剂中，苯乙酮的还原反应比苯甲醛的还原反应慢 75 至 150 倍。尽管速率存在差异，但机理研究为每种溶剂中酸性氢和氢氢的类似协同转移提供了证据。向 THF 中添加水导致速率进一步降低，同时 OH/D 动力学同位素效应增强，RuH/D 动力学同位素效应减弱。向甲苯或二氯甲烷中添加过量的醇会导致还原速率显着延迟。在 THF 和醇存在下的较慢速率归因于通过氢键稳定氢化钌 4 的基态以及在羰基还原之前断裂这些键所需的额外能量。
The tolyl analogue of Shvo's hydroxycyclopentadienyl ruthenium hydride (4) efficiently transfers a hydride and proton to benzaldehyde or acetophenone to produce all alcohol. This reduction call be performed in toluene, methylene chloride, and THF Reduction of benzaldehyde in toluene and methylene chloride occurs approximately 300 times faster than in THF at 0 degrees C. Reduction of acetophenone occurs between 75 and 150 times slower than benzaldellyde at 0 degrees C in each respective solvent. Despite the differences in rate, mechanistic Studies have provided evidence for a similar concerted transfer of acidic and hydridic hydrogens in each solvent. Addition of water to THF led to further rate decrease Coupled with an increase in the OH/D kinetic isotope effect and a decrease in the RuH/D kinetic isotope effect. Addition of excess alcohol to toluene or methylene chloride results in the significant retardation of the rate of reduction. The slower rate in THF and in the presence of alcohol is attributed to the stabilization of the ground state of ruthenium hydride 4 by hydrogen bonding and the additional energy required to break these bonds prior to carbonyl reduction.