Experimental and Computational Studies of High-Valent Nickel and Palladium Complexes
Experimental and Computational Studies of High-Valent Nickel and Palladium Complexes
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DOI：
10.1021/acs.organomet.7b00613
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发表时间：
2017-11-27
期刊：
影响因子：
2.8
通讯作者：
Sanford, Melanie S.
中科院分区：
文献类型：
--
作者：
Camasso, Nicole M.;Canty, Allan J.;Sanford, Melanie S.
本文详细比较了以硼酸三吡唑酯和环新叶醇为配体的高价镍和钯模型配合物的有机金属化学。通过电化学和化学氧化的M-II前体的M-III和M-IV氧化态与每种金属的可及性进行了研究。这些研究表明，Ni-II前体容易经历单电子和双电子氧化，以产生稳定的Ni-III和Ni-IV产物。相反，在所研究的条件下，Pd-II类似物仅经历两个电子的氧化反应形成Pd-IV。分离的Ni-IV和Pd-IV络合物的反应性研究表明，两者都参与C（sp（3））-杂原子偶联反应，并且Ni-IV处的反应比Pd-IV处的反应快约2个数量级。实验和计算机制的研究暗示这些过程的外层S（N）2型途径。对于大多数亲核试剂（例如，酚盐、乙酸盐、噻吩盐），C（sp（3））-杂原子偶联反应产生TpM（II）（σ-芳基）产物。然而，用叠氮化物作为亲核试剂，初始C（sp（3））-N-3偶联的Ni-II产物经历随后的C（sp（2））-N插入反应。计算牵连在这个过程中的阴离子Ni-III-nitrene中间体，并表明，该物种的Pd类似物是一个高得多的能量物种。总的来说，结合实验和计算的研究表明显着的相似性，在化学的Ni-IV和Pd-IV，但增强作用的Ni-III，使反应性，这是不同的钯。
This article describes a detailed comparison of the organometallic chemistry of high-valent nickel and palladium model complexes supported by tris(pyrazolyl)borate and cycloneophyl ligands. The accessibility of the M-III and M-IV oxidation states with each metal is investigated through electrochemical and chemical oxidation of the M-II precursors. These studies show that the Ni-II precursor readily undergoes both one- and two-electron oxidations to generate stable Ni-III and Ni-IV products. In contrast, under the conditions examined, the Pd-II analogue undergoes exclusively two-electron-oxidation reactions to form Pd-IV. Reactivity studies of isolated Ni-IV and Pd-IV complexes show that both participate in C(sp(3))-heteroatom coupling reactions and that the reactions at Ni-IV are approximately 2 orders of magnitude faster than those at Pd-IV. Experimental and computational mechanistic studies implicate outer-sphere S(N)2-type pathways for these processes. With most nucleophiles (e.g., phenoxide, acetate, thiophenoxide), the C(sp(3))-heteroatom coupling reaction yields a TpM(II)(sigma-aryl) product. However, with azide as the nucleophile, the Ni-II product of initial C(sp(3))-N-3 coupling undergoes a subsequent C(sp(2))-N insertion reaction. Computations implicate an anionic Ni-III-nitrene intermediate in this process and show that the Pd analogue of this species is a much higher energy species. Overall, the combined experimental and computational studies demonstrate remarkable similarities in the chemistry of Ni-IV and Pd-IV but an enhanced role for Ni-III in enabling reactivity which is distinct from that of palladium.