金属氧化还原双催化惰性C—H键芳基化和烷基化的理论探究

Theoretical study on the inert C—H arylation and alkylation by metallaphotoredox catalysis

包括有机氧化还原和过渡金属催化循环的金属氧化还原催化已发展成为活化惰性C—H键制备C—C和C-杂原子键的有力手段。使用密度泛函理论方法,详细探究三重激发态二芳基酮和镍络合物双催化实现四氢呋喃(THF)与芳基溴化物和烷基溴化物之间的sp^(3) C—H芳基化和烷基化的反应机理。研究表明整个反应包含THF自由基的产生、镍催化下产物的形成和镍催化剂再生3个过程。计算发现,THF自由基由三重态酮抽取THF中的氢原子生成;镍催化循环中的活性催化剂不是实验使用的原始催化剂,而是与实验体系中添加的配体进行交换后形成的镍催化剂;碳酸钠在镍催化剂再生中起重要作用。类似的反应机理对于烷基化反应同样适用。

Metallaphotoredox,including organic photoredox and transition metal catalysis,has emerged as a forceful method to realize the inert C—H bond functionalization to construct C—C or C—heteroatom bonds.In this research,the detailed mechanisms for sp^(3) C—H arylation and alkylation of tetrahydrofuran(THF)with aryl halide and alkyl halide catalyzed by the triplet excited diaryl ketone and nickel complex have been investigated using density functional theory calculations.The calculations indicate that the whole reaction includes three reaction processes:the formation of THFradical,generation of the product catalyzed by nickel catalysts(nickel catalysis),and regeneration of the Ni catalyst.The THFradical could be produced by the triplet ketone extracting the H atom of THF.For the nickel catalysis,NiL(L=5,5′-dimethyl-2,2′-bipyridine),not Niacac,plays an important role in the arylated reaction.In addition,the Na2CO3 species should be indispensable to the regeneration of NiL.Moreover,the similar results have been obtained for the sp3 C—H alkylation catalyzed by NiL′(L′=4,4′-diterbutyl-2,2′-bipyridine).