双钽二氮配合物：H2 分子与“端桥接”[Ta(IV)]2(μ-η(1):η(1)-N2)和双(μ-硝化物)[Ta(V)]2(μ-N)2 配合物的反应。

Ditantalum dinitrogen complex: reaction of H2 molecule with "end-on-bridged" [Ta(IV)]2(μ-η(1):η(1)-N2) and Bis(μ-nitrido) [Ta(V)]2(μ-N)2 complexes.

机构信息

State Key Laboratory of Chemical Resource Engineering, Institute of Materia Medica, College of Science, Beijing University of Chemical Technology, Beijing 100029, PR China.

出版信息

Inorg Chem. 2011 Oct 3;50(19):9481-90. doi: 10.1021/ic201159z. Epub 2011 Aug 30.

DOI:10.1021/ic201159z

PMID:21894917

Abstract

To elucidate (i) the physicochemical properties of the {(η(5)-C(5)Me(5))Ta(IV)C(Me)N(i-Pr)}(2)(μ-η(1):η(1)-N(2)), I, Ta(IV)(μ-η(1):η(1)-N(2)), and {(η(5)-C(5)Me(5))Ta(V)C(Me)N(i-Pr)}(2)(μ-N)(2), II, Ta(V)(μ-N)(2), complexes; (ii) the mechanism of the I → II isomerization; and (iii) the reaction mechanism of these complexes with an H(2) molecule, we launched density functional (B3LYP) studies of model systems 1, 2, and 3 where the C(5)Me(5) and (i-Pr)C(Me)N(i-Pr) ligands of I (or II) were replaced by C(5)H(5) and HC(NCH(3))(2), respectively. These calculations show that the lower-lying electronic states of 1, Ta(IV)(μ-η(1):η(1)-N(2)), are nearly degenerate open-shell singlet and triplet states with two unpaired electrons located on the Ta centers. This finding is in reasonable agreement with experiments [J. Am Chem. Soc. 2007, 129, 9284-9285] showing easy accessibility of paramagnetic and diamagnetic states of I. The ground electronic state of the bis(μ-nitrido) complex 2, Ta(V)(μ-N)(2), is a closed-shell singlet state in agreement with the experimentally reported diamagnetic feature of II. The 1-to-2 rearrangement is a multistep and highly exothermic process. It occurs with a maximum of 28.7 kcal/mol free energy barrier required for the (μ-η(1):η(1)-N(2)) → (μ-η(2):η(2)-N(2)) transformation step. Reaction of 1 with H(2) leading to the 1,4-addition product 3 proceeds with a maximum of 24.2 kcal/mol free energy barrier associated by the (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) isomerization step. The overall reaction 1 + H(2) → 3 is exothermic by 20.0 kcal/mol. Thus, the addition of H(2) to 1 is kinetically and thermodynamically feasible and proceeds via the rate-determining (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) isomerization step. The bis(μ-nitrido) complex 2, Ta(V)(μ-N)(2), does not react with H(2) because of the large energy barrier (49.5 kcal/mol) and high endothermicity of the reaction. This conclusion is also in excellent agreement with the experimental observation [J. Am Chem. Soc. 2007, 129, 9284-9285].

摘要

为了阐明 (i) {(η(5)-C(5)Me(5))Ta(IV)C(Me)N(i-Pr)}(2)(μ-η(1):η(1)-N(2)), I, Ta(IV)(μ-η(1):η(1)-N(2)) 和 {(η(5)-C(5)Me(5))Ta(V)C(Me)N(i-Pr)}(2)(μ-N)(2), II, Ta(V)(μ-N)(2) 配合物的物理化学性质；(ii) I → II 异构体异构化的机制；以及 (iii) 这些配合物与 H(2) 分子的反应机制，我们对模型系统 1、2 和 3 进行了密度泛函 (B3LYP) 研究，其中 I（或 II）的 C(5)Me(5) 和 (i-Pr)C(Me)N(i-Pr) 配体分别被 C(5)H(5) 和 HC(NCH(3))(2) 取代。这些计算表明，1、Ta(IV)(μ-η(1):η(1)-N(2)) 的较低电子态是几乎简并的开壳层单重态和三重态，两个未配对电子位于 Ta 中心。这一发现与实验结果[J. Am. Chem. Soc. 2007, 129, 9284-9285]相吻合，实验表明 I 很容易进入顺磁态和抗磁态。双(μ-亚硝基)配合物 2、Ta(V)(μ-N)(2) 的基态是一个闭壳层单重态，这与实验报道的 II 的抗磁性特征一致。1 到 2 的重排是一个多步的、高度放热的过程。它以最大 28.7 kcal/mol 的自由能垒进行，这是 (μ-η(1):η(1)-N(2)) → (μ-η(2):η(2)-N(2)) 转化步骤所需的。1 与 H(2) 反应生成 1,4-加成产物 3，最大自由能垒为 24.2 kcal/mol，这与 (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) 异构化步骤有关。总体反应 1 + H(2) → 3 是放热的，释放 20.0 kcal/mol 的能量。因此，H(2) 与 1 的加成在动力学和热力学上都是可行的，并且通过速率决定步骤 (μ-η(1):η(1)-N(2)) → (μ-η(2):η(1)-N(2)) 进行。双(μ-亚硝基)配合物 2、Ta(V)(μ-N)(2) 不会与 H(2) 反应，因为反应的能垒（49.5 kcal/mol）很大，吸热性很强。这一结论也与实验观察结果[J. Am. Chem. Soc. 2007, 129, 9284-9285]非常吻合。