Gayen Sourav, Assanar Faneesha, Shyamal Sampad, Dorairaj Dorothy Priyanka, Ghosh Sundargopal
Department of Chemistry, Indian Institute of Technology Madras Chennai 600036 India
Chem Sci. 2024 Sep 12;15(38):15913-24. doi: 10.1039/d4sc05092d.
In an effort to investigate small molecule activation by heavier transition metal (TM) based κ-,-chelated species, we have synthesised a series of bis-κ-1,3-,-chelated complexes of osmium, [Os(PPh)(κ-,-L/L)], 2a-b, and [Os(PPh)(L/L)(κ-,-L/L)], 3a-b (2a and 3a: L[double bond, length as m-dash] = CHNS; 2b and 3b: L = CHNS), from the thermolysis of [Os(PPh)Cl], 1, with a potassium salt of heterocyclic ligands L and L. The former complexes are diamagnetic in nature, while the EPR spectra, XPS study and density functional theory (DFT) calculations have substantiated the paramagnetic behaviour of 3a-b with a significant spin contribution from non-innocent ligands. These species were engaged in B-H activation of boranes utilizing the combined effect of hemilability and metal-ligand cooperativity (MLC), where 2a-b upon treatment with BH·SMe yielded Os(σ-borate)hydride complexes, [Os(PPh)(H){κ-,,'-BH(L/L)}], 4a-b (4a: L = CHNS; 4b: L = CHNS). The formation of 4a-b was emphasized on the basis of possible dual B-H activation that involved a few concerted steps, , (i) cleavage of one hemilabile Os-N bond and cooperative B-H bond activation, (ii) cleavage of another hemilabile Os-N bond and formation of a B-N bond and (iii) activation of another B-H bond. In stark contrast, the paramagnetic bis-κ-1,3-,-chelated species 3a-b manifested diverse activation patterns in the light of the different electronic nature of non-innocent ligands. While the reaction of 3b with borane generated dihydridoborate species, [Os(PPh)(κ-,-L)(κ-,,'-BH(OH)CHNS)], 5, complex 3a led to the formation of an Os(σ-borate) complex, [Os(PPh)(κ-,-L)(κ-,,'-BHL )], -6. As the σ-borate entity shows a tendency to adapt to different spatial arrangements around the metal center, we have established a modified synthetic strategy to isolate the isomer of 6 that involved the reaction of [Os(PPh)Cl], 1, with NaBHL . In a similar fashion, the treatment of [Os(PPh)Cl], 1, with NaBHL yielded [Os(PPh)(κ-,-L)(κ-,,'-BHL )], -7. The kinetic and thermodynamic stability of these isomeric species were investigated on the basis of extensive density functional theory (DFT) calculations. Theoretical calculations also provided insightful information on the electronic nature of the species, generated from B-H activations of boranes.
为了研究基于较重过渡金属（TM）的κ-，-螯合物对小分子的活化作用，我们通过[Os(PPh)Cl]（1）与杂环配体L和L的钾盐进行热解反应，合成了一系列锇的双κ-1,3-，-螯合配合物，即[Os(PPh)(κ-，-L/L)]（2a - b）和[Os(PPh)(L/L)(κ-，-L/L)]（3a - b）（2a和3a中L = CHNS；2b和3b中L = CHNS）。前一类配合物本质上是抗磁性的，而电子顺磁共振（EPR）光谱、X射线光电子能谱（XPS）研究以及密度泛函理论（DFT）计算证实了3a - b的顺磁性行为，且非无辜配体有显著的自旋贡献。这些物种利用半不稳定和金属 - 配体协同作用（MLC）的综合效应参与硼烷的B - H活化反应，其中2a - b与BH·SMe反应生成氢化锇（σ - 硼酸盐）配合物[Os(PPh)(H){κ-，，'-BH(L/L)}]（4a - b）（4a中L = CHNS；4b中L = CHNS）。基于可能涉及几个协同步骤的双B - H活化反应强调了4a - b的形成，即（i）一个半不稳定的Os - N键断裂和协同的B - H键活化，（ii）另一个半不稳定的Os - N键断裂和B - N键形成，以及（iii）另一个B - H键活化。与之形成鲜明对比的是，顺磁性的双κ-1,3-，-螯合物种3a - b由于非无辜配体不同的电子性质表现出多样的活化模式。虽然3b与硼烷反应生成二氢硼酸盐物种[Os(PPh)(κ-，-L)(κ-，，'-BH(OH)CHNS)]（5），但配合物3a导致形成一个锇（σ - 硼酸盐）配合物[Os(PPh)(κ-，-L)(κ-，，'-BHL )]（-6）。由于σ - 硼酸盐实体倾向于适应金属中心周围不同的空间排列，我们建立了一种改进的合成策略来分离6的异构体，该策略涉及[Os(PPh)Cl]（1）与NaBHL 的反应。以类似的方式，[Os(PPh)Cl]（1）与NaBHL 反应生成[Os(PPh)(κ-，-L)(κ-，，'-BHL )]（-7）。基于广泛的密度泛函理论（DFT）计算研究了这些异构体物种的动力学和热力学稳定性。理论计算还提供了关于硼烷B - H活化生成的物种电子性质的有见地的信息。
