Chang Mu-Chieh, Jesse Kate A, Filatov Alexander S, Anderson John S
Department of Chemistry , The University of Chicago , Chicago , Illinois 60637 , USA . Email:
Chem Sci. 2018 Nov 6;10(5):1360-1367. doi: 10.1039/c8sc03719a. eCollection 2019 Feb 7.
A T-shaped Ni(ii) complex [DHPy]Ni has been prepared and characterized. EPR spectra and DFT calculations of this complex suggest that the electronic structure is best described as a high-spin Ni(ii) center antiferromagnetically coupled with a ligand-based radical. This complex reacts with water at room temperature to generate the dimeric complex [DHPy]Ni(μ-OH)Ni[DHPyH] which has been thoroughly characterized by SXRD, NMR, IR and deuterium-labeling experiments. Addition of simple ligands such as phosphines or pyridine displaces water and demonstrates the reversibility of water activation in this system. The water activation step has been examined by kinetic studies and DFT calculations which suggest an unusual homolytic reaction a bimetallic mechanism. The Δ , Δ and KIE ( / ) of the reaction are 5.5 kcal mol, -23.8 cal mol K, and 2.4(1), respectively. In addition to the reversibility of water addition, this system is capable of activating water towards net O-atom transfer to substrates such as aromatic C-H bonds and phosphines. This reactivity is facilitated by the ability of the dihydrazonopyrrole ligand to accept H-atoms and illustrates the utility of metal ligand cooperation in activating O-H bonds with high bond dissociation energies.
已制备并表征了一种T形镍（II）配合物[DHPy]Ni。该配合物的电子顺磁共振光谱（EPR）和密度泛函理论（DFT）计算表明，其电子结构最好描述为一个高自旋镍（II）中心与一个基于配体的自由基反铁磁耦合。该配合物在室温下与水反应生成二聚体配合物[DHPy]Ni(μ-OH)Ni[DHPyH]，已通过同步辐射X射线衍射（SXRD）、核磁共振（NMR）、红外光谱（IR）和氘标记实验对其进行了全面表征。添加膦或吡啶等简单配体会取代水，证明了该体系中水活化的可逆性。通过动力学研究和DFT计算对水活化步骤进行了研究，结果表明这是一种不寻常的均裂反应——双金属机理。该反应的Δ 、Δ 和动力学同位素效应（KIE， / ）分别为5.5 kcal mol、-23.8 cal mol K和2.4(1)。除了加水的可逆性外，该体系还能够使水向底物（如芳香族C-H键和膦）进行净氧原子转移活化。二肼基吡咯配体接受氢原子的能力促进了这种反应活性，说明了金属-配体协同作用在活化具有高键解离能的O-H键方面的效用。
