Dehydroalkylative Activation of CNN- and PNN-Pincer Ruthenium Catalysts for Ester Hydrogenation
Dehydroalkylative Activation of CNN- and PNN-Pincer Ruthenium Catalysts for Ester Hydrogenation
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DOI：
10.1021/jacs.9b09326
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发表时间：
2019-10-30
影响因子：
15
通讯作者：
Chianese, Anthony R.
中科院分区：
文献类型：
--
作者：
He, Tianyi;Buttner, John C.;Chianese, Anthony R.
带有二乙基或二异丙氨基侧基的CNN-和PNN-钳形配体的钌-钳配合物，此前已被报道为酯加氢的活性预催化剂，在三环己基膦存在下加热时发生脱氢烷基化，释放乙烷或丙烷，得到含有新生的五配位钌(0)配合物。 亚胺官能团。乙烷或丙烷在催化酯加氢条件下也会释放，时程研究表明这种释放伴随着催化的开始。新型 PNN-钳钌 (0)-亚胺络合物是一种在室温下用于酯加氢的高活性催化剂，无需添加碱即可产生高达 15 500 次的转化。该络合物在室温下与两当量的氢发生可逆反应，得到二氢化钌(II)络合物，其中亚胺官能团已被氢化，得到质子胺侧基。这些观察结果对于酯氢化和相关转化中催化中间体的识别具有潜在广泛的影响。
Ruthenium-pincer complexes bearing CNN- and PNN-pincer ligands with diethyl- or diisopropylamino side groups, which have previously been reported to be active precatalysts for ester hydrogenation, undergo dehydroalkylation on heating in the presence of tricyclohexylphosphine to release ethane or propane, giving five-coordinate ruthenium(0) complexes containing a nascent imine functional group. Ethane or propane is also released under the conditions of catalytic ester hydrogenation, and time-course studies show that this release is concomitant with the onset of catalysis. A new PNN-pincer ruthenium(0)-imine complex is a highly active catalyst for ester hydrogenation at room temperature, giving up to 15 500 turnovers with no added base. This complex was shown to react reversibly at room temperature with two equivalents of hydrogen to give a ruthenium(II)-dihydride complex, where the imine functionality has been hydrogenated to give a protic amine side group. These observations have potentially broad implications for the identities of catalytic intermediates in ester hydrogenation and related transformations.