Sarkar Aniruddha, Das Soumadip, Mondal Prasenjit, Maiti Biswajit, Sen Gupta Sayam
Department of Chemical Sciences, Indian Institute of Science Education and Research (IISER) Kolkata, Mohanpur 741246, India.
Department of Chemistry, Indian Institute of Technology Tirupati (IIT Tirupati), Tirupati, AP 517619, India.
Inorg Chem. 2023 Dec 11;62(49):20439-20449. doi: 10.1021/acs.inorgchem.3c03465. Epub 2023 Nov 24.
High-valent metal-fluoride complexes are currently being explored for concerted proton-electron transfer (CPET) reactions, the driving force being the high bond dissociation energy of H-F (BDE = 135 kcal/mol) that is formed after the reaction. Ni(III)-fluoride-based complexes on the pyridine dicarboxamide pincer ligand framework have been utilized for CPET reactions toward phenols and hydrocarbons. We have replaced the central pyridine ligand with an N-heterocyclic carbene carbene to probe its effect in both stabilizing the high-valent Ni(III) state and its ability to initiate CPET reactions. We report a monomeric carbene-diamide-based Ni(II)-fluoride pincer complex that was characterized through H/F NMR, mass spectrometry, UV-vis, and X-ray crystallography analysis. Although carbenes and deprotonated carboxamides in the Ni(II)-fluoride complex are expected to stabilize the Ni(III) state upon oxidation, the Ni(III)/Ni(II) redox process occurred at very high potential (0.87 V vs Fc/Fc, dichloromethane) and was irreversible. Structural studies indicate significant distortion in the imidazolium "NCN" carbene plane of Ni(II)-fluoride caused by the formation of six-membered metallacycles. The high-valent Ni-fluoride analogue was synthesized by the addition of 1.0 equiv CTAN (ceric tetrabutylammonium nitrate) in dichloromethane at -20 °C which was characterized by UV-vis, mass spectrometry, and EPR spectroscopy. Density functional theory studies indicate that the Ni-carbene bond elongated, while the Ni-F bond shortened upon oxidation to the Ni(III) species. The high-valent Ni(III)-fluoride was found to react with the substituted phenols. Analysis of the and linear free energy relationship correlates well with the CPET nature of the reaction. Preliminary analysis indicates that the CPET is asynchronous and is primarily driven by the of the Ni(III)-fluoride complex.
目前正在探索高价金属氟化物配合物用于协同质子 - 电子转移（CPET）反应，其驱动力是反应后形成的H - F的高键解离能（BDE = 135 kcal/mol）。基于吡啶二羧酸酰胺钳形配体框架的镍（III）氟化物配合物已被用于对酚类和烃类的CPET反应。我们用N - 杂环卡宾取代了中心吡啶配体，以探究其在稳定高价镍（III）态及其引发CPET反应能力方面的作用。我们报道了一种基于卡宾 - 二酰胺的单体镍（II）氟化物钳形配合物，通过H/F NMR、质谱、紫外 - 可见光谱和X射线晶体学分析对其进行了表征。尽管预计镍（II）氟化物配合物中的卡宾和去质子化羧酰胺在氧化时会稳定镍（III）态，但镍（III）/镍（II）氧化还原过程在非常高的电位下发生（相对于Fc/Fc为0.87 V，二氯甲烷）且是不可逆的。结构研究表明，镍（II）氟化物的咪唑鎓“NCN”卡宾平面因形成六元金属环而发生显著扭曲。通过在 - 20°C的二氯甲烷中加入1.0当量的CTAN（硝酸铈四丁铵）合成了高价镍氟化物类似物，通过紫外 - 可见光谱、质谱和电子顺磁共振光谱对其进行了表征。密度泛函理论研究表明，氧化为镍（III）物种时，镍 - 卡宾键伸长，而镍 - 氟键缩短。发现高价镍（III）氟化物与取代酚发生反应。对反应的 和线性自由能关系的分析与反应的CPET性质良好相关。初步分析表明，CPET是异步的，主要由镍（III）氟化物配合物的 驱动。
