Isolation of a Cu-H Monomer Enabled by Remote Steric Substitution of a N-Heterocyclic Carbene Ligand: Stoichiometric Insertion and Catalytic Hydroboration of Internal Alkenes
Isolation of a Cu-H Monomer Enabled by Remote Steric Substitution of a N-Heterocyclic Carbene Ligand: Stoichiometric Insertion and Catalytic Hydroboration of Internal Alkenes
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DOI：
10.1021/jacs.2c05376
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发表时间：
2022-07-19
影响因子：
15
通讯作者：
Tran, Ba L.
中科院分区：
文献类型：
--
作者：
Carroll, Timothy G.;Ryan, David E.;Tran, Ba L.
瞬时Cu-H单体在Cu-H催化中的底物插入机制中一直被调用。它们的作用，从铜-氢聚集体已大多推断，因为配体稳定这些单体中间体的系统研究仍然有限。在过去的十年中，新的空间要求高的N-杂环卡宾（NHC）配体导致了可分离的Cu-H二聚体，在某些情况下，Cu-H单体在溶液中的光谱表征。我们报告了一个NHC配体，IPr*R，含有帕拉R基团的CHPh 2和CPh 3的配体周边的Cu-H单体的分离插入的内部烯烃。这种反应性还没有报道（NHC）CuH配合物，尽管它们在Cu-H催化的加氢官能化的共同应用。从CHPh 2到CPh 3的变化影响Cu-H单体的相对浓度、烯烃插入速率和三取代内烯烃的反应。具体地，对于R = CPh 3，分离单体（IPr* CPh 3）CuH并提供> 95%的单体（10 mM，在C6 D 6中）。相比之下，对于R = CHPh 2，基于H-1、C-13和H-1-C-13 HMBC NMR光谱，[（IPr * CHPh 2）CuH]（2）的溶液在25 ℃下为80%二聚体和20%（IPr* CHPh 2）CuH单体。环戊烯插入到Cu-H配合物中形成相应的Cu-环戊基配合物的定量H-1 NMR动力学研究表明，插入速率和Cu-H单体的浓度具有很强的依赖性。只有（IPr* CPh 3）CuH，它具有高的单体浓度，进行区域选择性插入的三取代的内烯烃，1-甲基环戊烯，得到（IPr* CPh 3）铜（2-甲基环戊基），这已被晶体学表征。我们还证明了（IPr* CPh 3）CuH催化环戊烯和甲基环戊烯与频哪醇硼烷的硼氢化反应。
Transient Cu-H monomers have long been invoked in the mechanisms of substrate insertion in Cu-H catalysis. Their role from Cu-H aggregates has been mostly inferred since ligands to stabilize these monomeric intermediates for systematic studies remain limited. Within the last decade, new sterically demanding N-heterocyclic carbene (NHC) ligands have led to isolable Cu-H dimers and, in some cases, spectroscopic characterization of Cu-H monomers in solution. We report an NHC ligand, IPr*R, containing para R groups of CHPh2 and CPh3 on the ligand periphery for the isolation of a Cu-H monomer for insertion of internal alkenes. This reactivity has not been reported for (NHC)CuH complexes despite their common application in Cu-H-catalyzed hydrofunctionalization. Changing from CHPh2 to CPh3 impacts the relative concentration of Cu-H monomers, rate of alkene insertion, and reaction of a trisubstituted internal alkene. Specifically, for R = CPh3, monomeric (IPr*CPh3)CuH was isolated and provided > 95% monomer (10 mM in C6D6). In contrast, for R = CHPh2, solutions of [(IPr*CHPh2)CuH](2) are 80% dimer and 20% (IPr*CHPh2)CuH monomer at 25 degrees C based on H-1, C-13, and H-1-C-13 HMBC NMR spectroscopy. Quantitative H-1 NMR kinetic studies on cyclopentene insertion into Cu-H complexes to form the corresponding Cu-cyclopentyl complexes demonstrate a strong dependence on the rate of insertion and concentration of the Cu-H monomer. Only (IPr*CPh3)CuH, which has a high monomer concentration, underwent regioselective insertion of a trisubstituted internal alkene, 1-methylcyclopentene, to give (IPr*CPh3)Cu(2-methylcyclopentyl), which has been crystallographically characterized. We also demonstrated that (IPr*CPh3)CuH catalyzes the hydroboration of cyclopentene and methylcyclopentene with pinacolborane.