Characterization of an Fe≡N-NH2 Intermediate Relevant to Catalytic N2 Reduction to NH3.
Characterization of an Fe≡N-NH2 Intermediate Relevant to Catalytic N2 Reduction to NH3.
复制标题
DOI：
10.1021/jacs.5b03432
复制
发表时间：
2015-06-24
影响因子：
15
通讯作者：
Peters JC
中科院分区：
文献类型：
--
作者：
Anderson JS;Cutsail GE 3rd;Rittle J;Connor BA;Gunderson WA;Zhang L;Hoffman BM;Peters JC
某些过渡金属介导N2还原为NH3的能力在生物和无机化学界引起了广泛的兴趣。早期过渡金属如Mo和W容易结合N2并在一个或多个N原子处介导其质子化，以提供可表征的M（NxHy）物质，并进而挤出NH3。相比之下，Fe-N2物质直接质子化为Fe（NxHy）产物，其特征在于一直是难以捉摸的。在此我们发现，在低温下加入酸到[（TPB）Fe（N2）][Na（1/2-冠-4）]中会产生新的S = 1/2 Fe物种。EPR，ENDOR，Mössbauer和EXAFS分析，加上DFT研究，明确指定这种新的物种为[（TPB）Fe NH-NH 2]+，一种双质子化的酰肼（2-）络合物，具有Fe-到-N三键。这种不稳定的物种提供了强有力的证据，铁介导的氮还原[（TPB）Fe（N2）][Na（12-冠-4）]的第一步可以进行沿着的远端或“查特型”的途径。还提供了关于后续催化步骤是否可能涉及N-N键的早期或晚期裂解的简要讨论，如分别在限制远端或交替机制中发现的。
The ability of certain transition metals to mediate the reduction of N2 to NH3 has attracted broad interest in the biological and inorganic chemistry communities. Early transition metals such as Mo and W readily bind N2 and mediate its protonation at one or more N atoms to furnish M(NxHy) species that can be characterized and, in turn, extrude NH3. By contrast, the direct protonation of Fe-N2 species to Fe(NxHy) products that can be characterized has been elusive. Herein we show that addition of acid at low temperature to [(TPB)Fe(N2)][Na(12-crown-4)] results in a new S = 1/2 Fe species. EPR, ENDOR, Mössbauer, and EXAFS analysis, coupled with a DFT study, unequivocally assign this new species as [(TPB)Fe≡N-NH2]+, a doubly protonated hydrazido(2-) complex featuring an Fe-to-N triple bond. This unstable species offers strong evidence that the first steps in Fe-mediated nitrogen reduction by [(TPB)Fe(N2)][Na(12-crown-4)] can proceed along a distal or `Chatt-type' pathway. A brief discussion of whether subsequent catalytic steps may involve early or late stage cleavage of the N-N bond, as would be found in limiting distal or alternating mechanisms, respectively, is also provided.