Solution Dynamics of Redox Noninnocent Nitrosoarene Ligands: Mapping the Electronic Criteria for the Formation of Persistent Metal-Coordinated Nitroxide Radicals
Solution Dynamics of Redox Noninnocent Nitrosoarene Ligands: Mapping the Electronic Criteria for the Formation of Persistent Metal-Coordinated Nitroxide Radicals
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DOI：
10.1021/acs.inorgchem.5b01252
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发表时间：
2015-07-20
影响因子：
4.6
通讯作者：
Figueroa, Joshua S.
中科院分区：
文献类型：
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作者：
Barnett, Brandon R.;Labios, Liezel A.;Figueroa, Joshua S.
金属配位C-亚硝基化合物的氧化还原无毒已建立在固态表征技术的基础上，但这类金属配位自由基溶液相性质的研究相对较少。本文报道了双亚硝基二自由基络合物TRAN-Pd(kappa(1)-N-PhNO)(2)(CNArDipp2)(2)的液相性质和动力学。这种络合物，最好的描述是含有单一还原的苯基氮氧自由基配体，被证明在。形成金属氮杂环丙烷Pd(ETA(2)-N，O-，PhNO)(CNArDipp2)(2)，因此在溶液中不是持久性物种。在溶液中，反式-Pd(kappa(1)-N-PhNO)(2)(CNArDipp2)(2)、Pd(ETA(2)-N，O-PhNO)(CNArDipp2)(2)与游离亚硝基苯之间建立了平衡，其中金属氮杂环丙烷占主导地位。通过添加过量的亚硝基苯来扰乱这一平衡的努力表明，反式Pd(kappa(1)-N-PhNO)(2)(CNArDipp2)的形成与Pd(ETA(2)-N，O-PhNO)(CNArDipp2)(2)的插入型化学竞争，因此不是产生动力学持久的双氮氧自由基络合物的可行策略。探索了亚硝芳烃骨架的电子修饰作为一种生成持久的反式Pd(kappa(1)-N-Arno)(2)(CNArDipp2)(2)络合物的方法。虽然大多数取代方案都不能显著地干扰相应的反式Pd(kappa(1)-N-Arno)(2)(CNArDipp2)(2)配合物中亚硝基配体的动力学稳定性，但利用对甲酰基或对氰基亚硝苯生成的双氮氧双自由基络合物在溶液中表现出动力学持久性。这种持久性的原因是由于对甲酰基和对氰基芳基能够减弱相应亚硝基芳烃的反式效应，更重要的是，使自旋密度远离芳基氮氧化物NO单元。本文提出的结果强调了金属配位氮氧化物自由基的内在不稳定性，并提出了一种在溶液中动力学稳定这些物种的一般合成策略。
The redox-noninnocence of metal-coordinated C-organo nitrosoarenes has been established on the basis of solid-state characterization techniques, but the solution-phase properties of this class of metal-coordinated radicals have been relatively underexplored. In this report, the solution-phase properties and dynamics of the bis-nitrosobenzene diradical complex trans-Pd(kappa(1)-N-PhNO)(2)(CNArDipp2)(2) are presented. This complex, which is best described as containing singly reduced phenylnitroxide radical ligands, is shown to undergo facile nitrosobenzene dissociation in. solution to form the metalloxaziridine Pd(eta(2)-N,O-,PhNO)(CNArDipp2)(2) and thus is not a persistent species in solution. An equilibrium between trans-Pd(kappa(1)-N-PhNO)(2)(CNArDipp2)(2), Pd(eta(2)-N,O-PhNO)(CNArDipp2)(2), and free nitrosobenzene is established in solution, with the metalloxaziridine being predominantly favored. Efforts to perturb this equilibrium by the addition of excess nitrosobenzene reveal that the formation of trans-Pd(kappa(1)-N-PhNO)(2)(CNArDipp2)(2) is in competition with insertion-type chemistry of Pd(eta(2)-N,O-PhNO)(CNArDipp2)(2) and is therefore not a viable strategy for the production of a kinetically persistent bis-nitroxide radical complex. Electronic modification of the nitrosoarene framework was explored as a means to generate a persistent trans-Pd(kappa(1)-N-ArNO)(2)(CNArDipp2)(2) complex. While most substitution schemes failed to significantly perturb the kinetic lability of the nitrosoarene ligands in the corresponding trans-Pd(kappa(1)-N-ArNO)(2)(CNArDipp2)(2) complexes, utilization of para-formyl or para-cyano nitrosobenzene produced bis-nitroxide diradical complexes that display kinetic persistence in solution. The origin of this persistence is rationalized by the ability of para-formyl-and para-cyano-aryl groups to both attenuate the trans effect of the corresponding nitrosoarene and, more importantly, delocalize spin density away from the aryl-nitroxide NO unit. The results presented here highlight the inherent instability of metal-coordinated nitroxide radicals and suggest a general synthetic strategy for kinetically stabilizing these species in solution.