Luo Hang, Yang Yupeng, Fu Yukang, Yu Fangnian, Gao Lei, Ma Yunpeng, Li Yang, Wu Kaifeng, Lin Luqing
School of Chemistry, Dalian University of Technology, Dalian, Liaoning, 116024, China.
State Key Laboratory of Molecular Reaction Dynamics and Collaborative Innovation Center of Chemistry for Energy Materials (iChEM), Dalian Institute of Chemical Physics, Chinese Academy of Sciences Dalian, Dalian, Liaoning, 116023, China.
Nat Commun. 2024 Jul 5;15(1):5647. doi: 10.1038/s41467-024-50082-w.
Direct reduction of unactivated alkyl halides for C(sp3)-N couplings under mild conditions presents a significant challenge in organic synthesis due to their low reduction potential. Herein, we introduce an in situ formed pyridyl-carbene-ligated copper (I) catalyst that is capable of abstracting halide atom and generating alkyl radicals for general C(sp3)-N couplings under visible light. Control experiments confirmed that the mono-pyridyl-carbene-ligated copper complex is the active species responsible for catalysis. Mechanistic investigations using transient absorption spectroscopy across multiple decades of timescales revealed ultrafast intersystem crossing (260 ps) of the photoexcited copper (I) complexes into their long-lived triplet excited states (>2 μs). The non-Stern-Volmer quenching dynamics of the triplets by unactivated alkyl halides suggests an association between copper (I) complexes and alkyl halides, thereby facilitating the abstraction of halide atoms via inner-sphere single electron transfer (SET), rather than outer-sphere SET, for the formation of alkyl radicals for subsequent cross couplings.
在温和条件下直接还原未活化的卤代烃以实现C(sp3)-N偶联，由于其还原电位较低，在有机合成中是一项重大挑战。在此，我们介绍一种原位形成的吡啶基卡宾配位的铜（I）催化剂，它能够夺取卤原子并在可见光下产生烷基自由基用于一般的C(sp3)-N偶联。对照实验证实，单吡啶基卡宾配位的铜配合物是负责催化的活性物种。使用跨多个时间尺度的瞬态吸收光谱进行的机理研究表明，光激发的铜（I）配合物能超快地系间窜越（260皮秒）到其长寿命三重态激发态（>2微秒）。未活化的卤代烃对三重态的非斯特恩-沃尔默猝灭动力学表明铜（I）配合物与卤代烃之间存在缔合，从而促进通过内球单电子转移（SET）而非外球SET夺取卤原子，以形成烷基自由基用于后续的交叉偶联。
