Testing the polynuclear hypothesis: multielectron reduction of small molecules by triiron reaction sites.
Testing the polynuclear hypothesis: multielectron reduction of small molecules by triiron reaction sites.
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DOI：
10.1021/ja405057n
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发表时间：
2013-08-21
影响因子：
15
通讯作者：
Betley TA
中科院分区：
文献类型：
--
作者：
Powers TM;Betley TA
高自旋三核铁配合物（tbsL）Fe 3（thf）（[tbsL]6− = [1，3，5-C6 H9（NPh-o-NSitBuMe 2）3]6−）（S = 6）促进NxHy型底物的2和4 e −还原，产生亚氨基和氮化物产物。肼或苯肼与（tbsL）Fe 3（thf）反应，分别产生三铁µ3-亚氨基簇合物（tbsL）Fe 3（µ3-NH）和氨或苯胺。（tbsL）Fe 3（µ3-NH）具有与先前报道的[（tbsL）Fe 3（µ3-N）] NBu 4相似的零场57 Fe穆斯堡尔谱，并且可以通过用四苯基硼酸镥盐质子化阴离子三铁氮化物直接合成。用双（三甲基甲硅烷基）氨基锂将三铁母体亚氨基（tbsL）Fe 3（µ3-NH）去质子化，导致用THF溶剂化的Li阳离子[（tbsL）Fe 3（µ3-N）]Li（thf）3封端的三铁氮化物络合物的再生。锂封端的氮化物在结构上类似于具有四丁基铵抗衡阳离子的伪C3对称的三铁氮化物，是严格C3对称的，其特征在于Fe-Fe 2.4802（5）μ m、Fe-N（氮化物）1.877（2）μ m和N（氮化物）-Li 1.990（6）μ m的核内距离。用（tbsL）Fe 3（thf）对1，2-二苯基肼进行类似的2 e −还原，得到（tbsL）Fe 3（µ3-NPh）和苯胺。（tbsL）Fe 3（µ3-NPh）的固态结构与本工作中合成的系列µ3-氮基和-亚胺基三铁配合物相似，平均Fe-Nimido和Fe-Fe键长分别为1.941（6）和2.530（1）。在（tbsL）Fe 3（thf）存在下，偶氮苯的还原N=N键断裂也实现，产生三铁双酰亚胺络合物（tbsL）Fe 3（µ3-NPh）（µ2-NPh），其已被结构表征。配体的氧化还原参与已经被排除，因此，电荷平衡表明双酰亚胺簇已经经历了基于4 e −金属的氧化，产生了（FeIV）（FeIII）2制剂。本文所示的一系列三铁簇合物的循环伏安图表明，高达（FeIV）（FeIII）2（在[（tbsL）Fe 3（μ3-N）] NBu 4的情况下）的氧化态是电化学可接近的。这些结果突出了高自旋多核反应位点协同介导小分子活化的功效。
High-spin trinuclear iron complex (tbsL)Fe3(thf) ([tbsL]6− = [1,3,5- C6H9(NPh-o-NSitBuMe2)3]6−) (S = 6) facilitates 2 and 4e− reduction of NxHy type substrates to yield imido and nitrido products. Reaction of hydrazine or phenylhydrazine with (tbsL)Fe3(thf) yields triiron µ3-imido cluster (tbsL)Fe3(µ3-NH) and ammonia or aniline, respectively. (tbsL)Fe3(µ3-NH) has a similar zero-field 57Fe Mössbauer spectrum compared to previously reported [(tbsL)Fe3(µ3-N)]NBu4, and can be directly synthesized by protonation of the anionic triiron nitrido with lutidinium tetraphenylborate. Deprotonation of the triiron parent imido (tbsL)Fe3(µ3-NH) with lithium bis(trimethylsilyl)amide results in regeneration of the triiron nitrido complex capped with a thf-solvated Li cation [(tbsL)Fe3(µ3-N)]Li(thf)3. The lithium capped nitrido, structurally similar to the pseudo C3-symmetric triiron nitride with a tetrabutylammonium counter cation, is rigorously C3-symmetric featuring intracore distances of Fe–Fe 2.4802(5) Å, Fe–N(nitride) 1.877(2) Å, and N(nitride)–Li 1.990(6) Å. A similar 2e− reduction of 1,2-diphenylhydrazine by (tbsL)Fe3(thf) affords (tbsL)Fe3(µ3-NPh) and aniline. The solid state structure of (tbsL)Fe3(µ3-NPh) is similar to the series of µ3-nitrido and -imido triiron complexes synthesized in this work with average Fe–Nimido and Fe–Fe bond lengths of 1.941(6) Å and 2.530(1) Å, respectively. Reductive N=N bond cleavage of azobenzene is also achieved in the presence of (tbsL)Fe3(thf) to yield triiron bisimido complex (tbsL)Fe3(µ3-NPh)(µ2-NPh), which has been structurally characterized. Ligand redox participation has been ruled out and, therefore, charge balance indicates that the bisimido cluster has undergone a 4e− metal based oxidation resulting in an (FeIV)(FeIII)2 formulation. Cyclic voltammograms of the series of triiron clusters presented herein demonstrate that oxidation states up to (FeIV)(FeIII)2 (in the case of [(tbsL)Fe3(µ3-N)]NBu4) are electrochemically accessible. These results highlight the efficacy of high-spin, polynuclear reaction sites to cooperatively mediate small molecule activation.
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