Back donation, intramolecular electron transfer and N–O bond scission targeting nitrogen oxyanion reduction: how can a metal complex assist?
Back donation, intramolecular electron transfer and N–O bond scission targeting nitrogen oxyanion reduction: how can a metal complex assist?
复制标题
针对氮氧阴离子还原的回馈、分子内电子转移和 N-O 键断裂：金属配合物如何提供帮助？
DOI：
10.1039/d0dt03430d
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发表时间：
2021
影响因子：
4
通讯作者：
Caulton, Kenneth G.
中科院分区：
文献类型：
--
作者：
Beagan, Daniel M.;Cabelof, Alyssa C.;Caulton, Kenneth G.
密度泛函理论探索研究了一系列辅助配位配体伴随氮氧阴离子的目标是促进对不同氮氧化态的反馈捐赠。一套Ru和Rh金属配合物的评价揭示了最小的回捐赠的κ1-氮氧阴离子配体，即使在一个电子还原。这揭示了还原的一些令人惊讶的结果，包括在吡啶和氮氧阴离子解离的氧化还原活性。因此，考虑了双齿硝酸盐，其中辅助配体实施使M-NOx轨道重叠最大化的几何形状。这种策略是成功的，并在几种情况下导致完全电子转移，形成金字塔自由基NO32−配体。辅助配体对硝酸盐还原程度的影响是通过比较强有力的o-供体三卡宾硼酸盐（TCB）和温和的供体三吡唑硼酸盐（Tp）来探讨的。这表明，在较温和的Tp供体的情况下，仅在添加刘易斯碱时看到硝酸盐还原。中性和阴离子（TCB）Ru（κ2-NO3）在末端和内部氧的质子化揭示了还原物种的放能N-O键断裂，其中一个电子来自Ru，产生RuIII氢氧化物产物。H+与Na+亲电试剂的比较显示出朝向N-O键断裂的较弱进展。最后，对（TCB）Fe（κ2-NO3）和[（TCB）Fe（κ2-NO3）]-的计算表明，即使在地球丰富的3d金属中，电子转移到硝酸盐也是可能的。
A density functional theory exploration studies a range of ancillary coordinated ligands accompanying nitrogen oxyanions with the goal of promoting back donation towards varied nitrogen oxidation states. Evaluation of a suite of Ru and Rh metal complexes reveals minimum back donation to the κ1-nitrogen oxyanion ligand, even upon one-electron reduction. This reveals some surprising consequences of reduction, including redox activity at pyridine and nitrogen oxyanion dissociation. Bidentate nitrate was therefore considered, where ancillary ligands enforce geometries that maximize M–NOx orbital overlap. This strategy is successful and leads to full electron transfer in several cases to form a pyramidal radical NO32− ligand. The impact of ancillary ligand on degree of nitrate reduction is probed by comparing the powerful o-donor tris-carbene borate (TCB) to a milder donor, tris-pyrazolyl borate (Tp). This reveals that with the milder Tp donor, nitrate reduction is only seen upon addition of a Lewis base. Protonation of neutral and anionic (TCB)Ru(κ2-NO3) at both terminal and internal oxygens reveals exergonic N–O bond cleavage for the reduced species, with one electron coming from Ru, yielding a RuIII hydroxide product. Comparison of H+ to Na+ electrophile shows weaker progress towards N–O bond scission. Finally, calculations on (TCB)Fe(κ2-NO3) and [(TCB)Fe(κ2-NO3)]– show that electron transfer to nitrate is possible even with an earth abundant 3d metal.