关于[(PhTt(tBu))2Ni2(μ-O)2]的光谱和计算研究：双μ-氧代(Ni3+)2菱形核心的性质
Spectroscopic and computational studies on [(PhTt(tBu))2Ni2(mu-O)2]: nature of the bis-mu-oxo (Ni3+)2 diamond core.
作者信息
Schenker Ralph, Mandimutsira Beaven S, Riordan Charles G, Brunold Thomas C
机构信息
Department of Chemistry, University of Wisconsin-Madison, Madison, Wisconsin 53706, USA.
出版信息
J Am Chem Soc. 2002 Nov 20;124(46):13842-55. doi: 10.1021/ja027049k.
Spectroscopic and density functional theory (DFT) electronic structure computational studies on a binuclear bis-mu-oxo bridged (Ni(3+))(2) complex, [(PhTt(t(Bu))(2)Ni(2)(mu-O)(2)] (1), where (PhTt(t(Bu)) represents phenyl-tris((tert-butylthio)methyl)borate, are presented and discussed. These studies afford a detailed description of the Ni(2)O(2) core electronic structure in bis-mu-oxo (Ni(3+))(2) dimers and provide insight into the possible role of the (PhTt(t(Bu)) thioether ligand in the formation of 1 from a Ni(1+) precursor by O(2) activation. From a normal coordinate analysis of resonance Raman data, a value of k(Ni)(-)(O) = 2.64 mdyn/A is obtained for the Ni-O stretch force constant for 1. This value is smaller than k(Cu)(-)(O) = 2.82-2.90 mdyn/A obtained for bis-mu-oxo (Cu(3+))(2) dimers possessing nitrogen donor ligands, indicating a reduced metal-oxo bond strength in 1. Electronic absorption and magnetic circular dichroism spectroscopic techniques permit identification of several O-->Ni and S-->Ni charge transfer (CT) transitions that are assigned on the basis of DFT calculations. The dominant O-->Ni CT transition of 1 occurs at 17 700 cm(-)(1), red-shifted by approximately 7000 cm(-)(1) relative to the corresponding transition in bis-mu-oxo (Ni(3+))(2) dimers with nitrogen donor ligands. This red-shift along with the relatively low value of k(Ni)(-)(O) are due primarily to the presence of the thioether ligands in 1 that greatly affect the compositions of the Ni(2)O(2) core MOs. This unique property of the thioether ligand likely contributes to the reactivity of the Ni center in the precursor [(PhTt(t(Bu))Ni(1+)CO] toward O(2). DFT computations reveal that conversion of a hypothetical side-on peroxo (Ni(2+))(2) dimer, [(PhTt(t(Bu))(2)Ni(2)(mu-eta(2):eta(2)-O(2))], to the bis-mu-oxo (Ni(3+))(2) dimer 1 is energetically favorable by 32 kcal/mol and occurs without a significant activation energy barrier (DeltaH++) = 2 kcal/mol).
本文介绍并讨论了对双核双μ-氧桥联（Ni(3+)）₂配合物[(PhTt(t(Bu))₂Ni₂(μ-O)₂]（1）的光谱和密度泛函理论（DFT）电子结构计算研究，其中(PhTt(t(Bu))代表苯基-三（（叔丁基硫基）甲基）硼酸酯。这些研究详细描述了双μ-氧（Ni(3+)）₂二聚体中Ni₂O₂核心的电子结构，并深入了解了(PhTt(t(Bu))硫醚配体在通过O₂活化由Ni(1+)前体形成1的过程中可能发挥的作用。通过对共振拉曼数据的正规坐标分析，得到1的Ni-O伸缩力常数k(Ni)(-)(O)=2.64 mdyn/A。该值小于具有氮供体配体的双μ-氧（Cu(3+)）₂二聚体所得到的k(Cu)(-)(O)=2.82 - 2.90 mdyn/A，表明1中金属-氧键强度降低。电子吸收和磁圆二色光谱技术允许识别基于DFT计算所归属的几个O→Ni和S→Ni电荷转移（CT）跃迁。1的主要O→Ni CT跃迁发生在17700 cm⁻¹处，相对于具有氮供体配体的双μ-氧（Ni(3+)）₂二聚体中的相应跃迁红移了约7000 cm⁻¹。这种红移以及相对较低的值k(Ni)(-)(O)主要归因于1中硫醚配体的存在，其极大地影响了Ni₂O₂核心分子轨道的组成。硫醚配体的这种独特性质可能有助于前体[(PhTt(t(Bu))Ni(1+)CO]中Ni中心对O₂的反应性。DFT计算表明，假设的侧基过氧（Ni(2+)）₂二聚体[(PhTt(t(Bu))₂Ni₂(μ-η²:η²-O₂)]转化为双μ-氧（Ni(3+)）₂二聚体1在能量上有利32 kcal/mol，并且在没有显著活化能垒（ΔH++ = 2 kcal/mol）的情况下发生。
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