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Mechanism of Cobalt-Catalyzed Direct Aminocarbonylation of Unactivated Alkyl Electrophiles: Outer-Sphere Amine Substitution To Form Amide Bond
ACS Catalysis ( IF 12.9 ) Pub Date : 2020-01-07 , DOI: 10.1021/acscatal.9b04736
Jiandong Guo 1, 2 , Hai D. Pham 3 , Yan-Bo Wu 4 , Dongju Zhang 2 , Xiaotai Wang 1, 3
Affiliation  

Experimentalists have recently achieved the first chemoselective aminocarbonylation of unactivated alkyl electrophiles, using the common cobalt reagent Co2(CO)8 as a catalyst. Here, we present a detailed density functional theory (DFT) mechanistic study on this remarkable reaction. Induced by the Lewis base morpholine (or MOR, the amine substrate), Co2(CO)8 disproportionates to [Co(CO)3(MOR)2]+ and [Co(CO)4]. The active catalyst [Co(CO)4] undergoes an SN2 reaction with the alkyl tosylate substrate to form an alkylcobalt(I) carbonyl intermediate with an inverted configuration at the α-carbon. The alkylcobalt(I) carbonyl complex favors CO migratory insertion over β-hydride elimination. The resulting acylcobalt(I) carbonyl intermediate, along with the MOR and CO substrates, could introduce several pathways for the amide C–N bond formation. The inner-sphere pathways involving Co(I)-bound MOR are ruled out. The outer-sphere pathway in which MOR attacks the Co(I)-bound acyl leads to the amide product and the regenerated [Co(CO)4]. The SN2 process is the rate-determining step with the largest energy span (ΔG = 22.8 kcal/mol). The side reaction of double CO insertion faces a higher selectivity-determining energy barrier and hence is less favorable. This DFT work provides deep mechanistic insights into the Co2(CO)8-promoted chemoselective aminocarbonylation of unactivated alkyl electrophiles, thereby having implications for organocobalt catalysis and transition-metal-catalyzed amide C–N bond-forming reactions.

中文翻译:

未活化的烷基亲电试剂的钴催化直接氨基羰基化反应机理:外层胺取代形成酰胺键

最近,实验人员使用普通的钴试剂Co 2(CO)8作为催化剂,实现了未活化烷基亲电试剂的首次化学选择性氨基羰基化反应。在这里,我们对这种非凡的反应进行了详细的密度泛函理论(DFT)机理研究。由路易斯碱吗啉(或MOR,胺底物)诱导,Co 2(CO)8歧化为[Co(CO)3(MOR)2 ] +和[Co(CO)4 ] -。活性催化剂[Co(CO)4 ] -经受S N2与甲苯磺酸烷基酯底物反应形成在α-碳上具有反向构型的烷基钴(I)羰基中间体。烷基钴(I)羰基配合物比β-氢化物消除更有利于CO迁移插入。所产生的酰基钴(I)羰基中间体以及MOR和CO底物可能为酰胺C–N键的形成引入了几种途径。排除涉及Co(I)结合MOR的内球途径。MOR在其中攻击Co(I)结合的酰基的外球途径导致酰胺产物和再生的[Co(CO)4 ] -。在S Ñ 2个过程是速率决定步骤具有最大能量跨度(Δ ģ = 22.8 kcal / mol)。两次CO插入的副反应面临更高的决定选择性的能垒,因此不利。DFT的这项工作为未活化的烷基亲电体的Co 2(CO)8促进的化学选择性氨基羰基化提供了深刻的机理见解,从而对有机钴催化和过渡金属催化的酰胺C–N键形成反应产生了影响。
更新日期:2020-01-07
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