Mapping the Reactivity of Dicobalt Bridging Nitrides in Constrained Geometries
Mapping the Reactivity of Dicobalt Bridging Nitrides in Constrained Geometries
复制标题
绘制受限几何结构中二钴桥接氮化物的反应性
DOI：
10.1021/acs.inorgchem.0c03774
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发表时间：
2021
影响因子：
4.6
通讯作者：
Tomson, Neil C.
中科院分区：
文献类型：
--
作者：
Spentzos, Ariana Z.;Tomson, Neil C.
后过渡金属的低核氮化物是罕见的活性分子物种，几乎没有实验先例。双钴桥氮化物的第一个推定实例，[（nPDI_2）Co_2（μ-N）（PMe_3）_2][OTf]_3（n[Co 2N]3+; PDI =吡啶基二亚胺; n= 2或3，代表连接PDI亚氨基的脂肪族链的长度），最近被报道，并显示经历一系列分子内反应途径，包括N-H键形成、C-H键插入和在桥接氮化物处的P = N键形成。反应的具体模式随反应的相态和用于支持瞬态物种的大环的大小而改变。目前的贡献提供了一个计算调查到这些氮化物的几何和电子结构以及控制其反应选择性的因素。化合物n [Co 2N]3+显示基于μ-N的最低未占分子轨道（LUMO），其与低价亲电子氮化物一致。LUMO的特定取向诱导环尺寸依赖的立体电子效应，从而导致实验观察到的产物选择性。值得注意的是，氮化物还通过高能量的基于μ-N的孤对电子在μ-N处表现出一定程度的亲核性。这种两亲性的字符似乎是一个直接的结果，由折叠配体的几何形状ofn[Co 2N]3+施加的约束环境。当与实验结果相结合时，这些数据得出这样的结论：折叠配体异构体是反应物种，并且大环配体施加的约束几何形状在控制反应结果方面发挥着重要作用。
Low-nuclearity nitrides of the late transition metals are rare and reactive molecular species, with little experimental precedent. The first putative examples of dicobalt bridging nitrides, [(nPDI2)Co2(μ-N)(PMe3)2][OTf]3(n[Co2N]3+; PDI = pyridyldiimine;n= 2 or 3, representing the length of the aliphatic chain linking PDI imino groups), were reported recently and shown to undergo a range of intramolecular reaction pathways, including N–H bond formation, C–H bond insertion, and P═N bond formation at the bridging nitride. The specific mode of reactivity changed with the phase of the reaction and the size of the macrocycle used to support the transient species. The present contribution offers a computational investigation into both the geometric and electronic structures of these nitrides as well as the factors governing their reaction selectivity. The compoundsn[Co2N]3+exhibit μ-N-based lowest unoccupied molecular orbitals (LUMOs) that are consistent with subvalent, electrophilic nitrides. The specific orientations of the LUMOs induce ring-size-dependent stereoelectronic effects, thereby causing the product selectivity observed experimentally. Notably, the nitrides also exhibit a degree of nucleophilicity at μ-N by way of a high-energy, μ-N-based lone pair. This ambiphilic character appears to be a direct result of the constrained environment imposed by the folded-ligand geometries ofn[Co2N]3+. When combined with the experimental findings, these data led to the conclusion that the folded-ligand isomers are the reactive species and that the constrained geometry imposed by the macrocyclic ligand plays an important role in controlling the reaction outcome.