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首页> 外文期刊>Dalton transactions: An international journal of inorganic chemistry >On the unprecedented level of dinitrogen activation in the calix[4]arene complex of Nb(iii)
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On the unprecedented level of dinitrogen activation in the calix[4]arene complex of Nb(iii)

机译：Nb（iii）杯[4]芳烃配合物中二氮活化的空前水平

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摘要

The calix[4]arene niobium(iii) complex ([L]Nb-NN-Nb[L] where [L] = p-tert-butylcalix[4]arene), reported to bind N_2 in a μ_2-linear dimeric capacity and to activate the N_2 triple bond to 1.39 ?, corresponding to the longest N_2 bond known in the end-on coordination mode, was subjected to a computational investigation involving both density functional and wavefunction based methods to establish the basis for the unprecedented level of activation. Replacement of the calix[4]arene ligand with hydroxide or methoxide ligands reveals that the organic backbone structure of the calix[4]arene ligand exerts negligible electronic influence over the metal centre, serving only to geometrically constrain the coordinating phenoxide groups. A fragment bonding analysis shows that metal-to-dinitrogen π~* backbonding is the principal Nb-N interaction, providing a strong electronic basis for analogy with other well-characterised three- and four-coordinate complexes which bind N2 end-on. While the calculated structure of the metallacalix[4]arene unit is reproduced with high accuracy, as is also the Nb-Nb separation, the calculated equilibrium geometry of the complex under a variety of conditions consistently indicates against a 1.39 ? activation of the N_2 bond. Instead, the calculated N-N distances fall within the range 1.26-1.30 ?, a result concordant with closely related three- and four-coordinate μ_2- N_2 complexes as well as predictions derived from trends in N-N stretching frequency for a number of crystallographically characterized linear N_2 activators. A number of potential causes for this bond length discrepancy are explored.
机译：杯[4]芳烃铌（iii）络合物（[L] Nb-NN-Nb [L]，其中[L] =对叔丁基杯[4]芳烃），据报道以μ_2-线性二聚体能力结合N_2然后将N_2三键激活至1.39？（对应于末端配位模式中已知的最长N_2键），进行了涉及密度泛函和波函数的方法的计算研究，从而为前所未有的激活水平奠定了基础。用氢氧化物或甲醇盐配体取代杯[4]芳烃配体表明杯[4]芳烃配体的有机主链结构对金属中心的电子影响可忽略不计，仅用于几何上约束配位的酚盐基团。片段键合分析表明，金属与二氮π〜*的反向键合是主要的Nb-N相互作用，为与其他特征明​​确的端接N2的三坐标和四坐标配合物的类比提供了强大的电子基础。尽管金属lacalix [4]芳烃单元的计算结构得到了高精度的再现，Nb-Nb分离也得到了很高的精确度，但在各种条件下，该络合物的平衡几何构型始终显示出1.39？ N_2键的活化。取而代之的是，所计算的NN距离落在1.26-1.30？的范围内，该结果与紧密相关的三坐标和四坐标μ_2-N_2配合物以及根据晶体学表征的线性N_2的NN拉伸频率趋势得出的预测相一致。激活剂。探索了这种键长差异的许多潜在原因。

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