Catalyst Evolution in Ruthenium-Catalyzed Coupling of Amines and Alcohols
Catalyst Evolution in Ruthenium-Catalyzed Coupling of Amines and Alcohols
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DOI：
10.1021/acscatal.9b03679
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发表时间：
2020-01-03
期刊：
影响因子：
12.9
通讯作者：
Williams, Travis J.
中科院分区：
文献类型：
--
作者：
Cherepakhin, Valeriy;Williams, Travis J.
我们描述了胺和醇的钌基偶联的机制、范围和催化剂演变，该偶联来自[（eta（6）-伞花烃）RuCl（（PyCH 2 PBu 2）-Bu-t）]OTf（1）预催化剂。该方法通过氢借用机制选择性地产生仲胺，并成功地应用于几种杂环甲醇底物。在反应条件下，预催化剂1通过一系列催化中间体演变：[（eta（6）-伞花烃）RuH（（PyCH2PBu2）-Bu-t）]OTf（3），[Ru3H2Cl2（CO）（（PyCH 2 PBu 2）-Bu-t）（2）{mu-（C5 H3 N）（CH 2 PBu 2）-Bu-t}]OTf（4）和[Ru 2 HCl（CO）（2）的非对映体对（（PyCH 2 PBu 2）-Bu-t）（2）（mu-（O2 CPr）-Pr-n）]X（trans-5，X = Cl; cis-6，X = OTf）。通过单晶X射线衍射确定了化合物4和6的结构。催化活性的研究表明，4是催化剂的休眠（但活着）形式，而5和6是最终的死形式。电化学研究表明，4具有氧化还原活性，在CH_2Cl_2溶液中，在E_1/2 = 0.442V（vsFc（+）/Fc）处发生电化学可逆的单电子氧化.我们讨论了3-6形成的因素和选择性钌羰基化的作用，这是必不可少的，使生成的活性催化剂。我们还将这些发现与脂肪醇胺化条件的确定联系起来，这在我们理解催化剂复杂的形态行为之前一直困扰着我们。
We describe the mechanism, scope, and catalyst evolution for our ruthenium-based coupling of amines and alcohols, which proceeds from a [(eta(6)-cymene)RuCl((PyCH2PBu2)-Bu-t)]OTf (1) precatalyst. The method selectively produces secondary amines through a hydrogen borrowing mechanism and is successfully applied to several heterocyclic carbinol substrates. Under the reaction conditions, precatalyst 1 evolves through a series of catalytic intermediates: [(eta(6)-cymene)RuH((PyCH2PBu2)-Bu-t)]OTf (3), [Ru3H2Cl2(CO)((PyCH2PBu2)-Bu-t)(2){mu-(C5H3N)(CH2PBu2)-Bu-t}]OTf (4), and a diastereomeric pair of [Ru2HCl(CO)(2)((PyCH2PBu2)-Bu-t)(2)(mu-(O2CPr)-Pr-n)]X (trans-5, X = Cl; cis-6, X = OTf). The structures of 4 and 6 were established by single-crystal X-ray diffraction. A study of catalytic activity shows that 4 is a dormant (but alive) form of the catalyst, whereas 5 and 6 are the ultimate dead forms. Electrochemical studies show that 4 is redox active and undergoes electrochemically reversible one-electron oxidation at E-1/2 = 0.442 V (vs Fc(+)/Fc) in CH2Cl2 solution. We discuss the factors that govern the formation of 3-6 and the role of selective ruthenium carbonylation, which is essential for enabling generation of the active catalyst. We also connect these discoveries to the identification of conditions for amination of aliphatic alcohols, which eluded us until we understood the catalyst's complex speciation behavior.