Department of Chemistry and Biomolecular Sciences and Centre for Catalysis Research and Innovation, University of Ottawa, Ottawa, Ontario K1N 6N5, Canada.
Inorg Chem. 2022 Dec 12;61(49):19998-20007. doi: 10.1021/acs.inorgchem.2c03273. Epub 2022 Dec 1.
One of the key steps in many metal complex-catalyzed hydroboration reactions is B-H bond activation, which results in metal hydride formation. Anionic ligands that include multiple lone pairs of electrons, in cooperation with a metal center, have notable potential in redox-neutral B-H bond activation through metal-ligand cooperation. Herein, using an easily prepared NNN ligand (L), a series of divalent NiX(NNN) complexes were synthesized, with X = bromide (), phenoxide (), thiophenoxide (), 2,5-dimethylpyrrolide (), diphenylphosphide (), and phenyl (). The complexes were characterized using H and C NMR spectroscopy, mass spectrometry, and X-ray crystallography and employed as precatalysts for nitrile dihydroboration. Superior activity of the phenoxy derivative () [vs thiophenoxy () or phenyl ()] suggests that B-H bond activation occurs at the Ni-X (vs ligand Ni-N) bond. Furthermore, stoichiometric treatment of with a nitrile showed no reaction, whereas stoichiometric reactions of with pinacolborane (HBpin) gave the same Ni-H complex for , , and . Considering that only , , and successfully catalyzed nitrile dihydroboration, we suggest that the catalytic cycle involves a conventional inner sphere pathway initiated by substrate insertion into Ni-H.
在许多金属配合物催化的硼氢化反应中，关键步骤之一是 B-H 键活化，这导致金属氢化物的形成。阴离子配体包含多个孤对电子，与金属中心协同作用，通过金属-配体协同作用，在氧化还原中性的 B-H 键活化中具有显著的潜力。在此，使用一种易于制备的 NNN 配体（L），合成了一系列二价 NiX(NNN)配合物，其中 X = 溴化物（）、苯氧基（）、噻吩氧基（）、2,5-二甲基吡咯烷（）、二苯基膦（）和苯基（）。使用 H 和 C NMR 光谱、质谱和 X 射线晶体学对配合物进行了表征，并将其用作腈的双氢硼化预催化剂。苯氧基衍生物（）的优异活性[对噻吩氧基（）或苯基（）]表明 B-H 键活化发生在 Ni-X（相对于配体 Ni-N）键上。此外，与腈的化学计量处理没有反应，而与频哪醇硼烷（HBpin）的化学计量反应为 、 、和 得到相同的 Ni-H 配合物。考虑到只有 、 、和 成功地催化了腈的双氢硼化，我们认为催化循环涉及由底物插入 Ni-H 引发的常规内球途径。
