Bian Jian-Hong, Tong Wen-Yan, Pitsch Chloe E, Wu Yan-Bo, Wang Xiaotai
Key Laboratory of Materials for Energy Conversion and Storage of Shanxi Province and Institute of Molecular Science, Shanxi University, Taiyuan 030006, P. R. China.
Department of Chemistry, University of Colorado Denver, Campus Box 194, P. O. Box 173364, Denver, Colorado 80217-3364, USA.
Dalton Trans. 2021 Feb 23;50(7):2654-2662. doi: 10.1039/d0dt04121a.
We present a detailed DFT mechanistic study on the first Ni-catalyzed direct carbonyl-Heck coupling of aryl triflates and aldehydes to afford ketones. The precatalyst Ni(COD)2 is activated with the phosphine (phos) ligand, followed by coordination of the substrate PhOTf, to form [Ni(phos)(PhOTf)] for intramolecular PhOTf to Ni(0) oxidative addition. The ensuing phenyl-Ni(ii) triflate complex substitutes benzaldehyde for triflate by an interchange mechanism, leaving the triflate anion in the second coordination sphere held by Coulomb attraction. The Ni(ii) complex cation undergoes benzaldehyde C[double bond, length as m-dash]O insertion into the Ni-Ph bond, followed by β-hydride elimination, to produce Ni(ii)-bound benzophenone, which is released by interchange with triflate. The resulting neutral Ni(ii) hydride complex leads to regeneration of the active catalyst following base-mediated deprotonation/reduction. The benzaldehyde C[double bond, length as m-dash]O insertion is the rate-determining step. The triflate anion, while remaining in the second sphere, engages in electrostatic interactions with the first sphere, thereby stabilizing the intermediate/transition state and enabling the desired reactivity. This is the first time that such second-sphere interaction and its impact on cross-coupling reactivity has been elucidated. The new insights gained from this study can help better understand and improve Heck-type reactions.
我们对首例镍催化芳基三氟甲磺酸酯与醛直接羰基-Heck偶联生成酮的反应进行了详细的密度泛函理论（DFT）机理研究。预催化剂Ni(COD)₂ 与膦（phos）配体活化，随后底物PhOTf配位，形成[Ni(phos)(PhOTf)]，用于分子内PhOTf对Ni(0)的氧化加成。随后生成的苯基-Ni(ii)三氟甲磺酸酯配合物通过交换机理用苯甲醛取代三氟甲磺酸根，使三氟甲磺酸根阴离子通过库仑吸引力保留在第二配位层。Ni(ii)配合物阳离子使苯甲醛的C=O插入到Ni-Ph键中，随后进行β-氢消除，生成与Ni(ii)结合的二苯甲酮，其通过与三氟甲磺酸根交换而释放。生成的中性Ni(ii)氢化物配合物在碱介导的去质子化/还原后导致活性催化剂再生。苯甲醛的C=O插入是决速步骤。三氟甲磺酸根阴离子虽然保留在第二配位层，但与第一配位层发生静电相互作用，从而稳定中间体/过渡态并实现所需的反应活性。这是首次阐明这种第二配位层相互作用及其对交叉偶联反应活性的影响。本研究获得的新见解有助于更好地理解和改进Heck型反应。
