Zhang Zheng-Feng, Su Ming-Der
Department of Applied Chemistry, National Chiayi University Chiayi 60004 Taiwan
Department of Medicinal and Applied Chemistry, Kaohsiung Medical University Kaohsiung 80708 Taiwan.
RSC Adv. 2019 Jan 21;9(5):2626-2640. doi: 10.1039/c8ra07669c. eCollection 2019 Jan 18.
The mechanisms for the photochemical CO-dissociation and the oxidative addition reactions are studied theoretically using three model systems: M(CO) (M = Fe, Ru, and Os) and the CASSCF/Def2-SVP (fourteen-electron/ten-orbital active space) and MP2-CAS/Def2-SVP//CASSCF/Def2-SVP methods. The structures of the intersystem crossings and the conical intersections, which play a decisive role in these CO photo-extrusion reactions, are determined. The intermediates and the transition structures in either the singlet or triplet states are also computed, in order to explain the reaction routes. These model studies suggest that after the irradiation of Fe(CO) with UV light, it quickly loses one CO molecule to generate a 16-electron iron tetracarbonyl, in either the singlet or the triplet states. It is found that the triplet Fe(CO) plays a vital role in the formation of the final oxidative addition product, Fe(CO)(H)(SiMe), but the singlet Fe(CO) plays a relatively minor role in the formation of the final product. However, its vacant coordination site interacts weakly with solvent molecules ((Me)SiH) to yield the alkyl-solvated iron complexes, which are detectable experimentally. The theoretical observations show that Ru(CO) and Os(CO) have similar photochemical and thermal potential energy profiles. In particular, this study demonstrates that the oxidative addition yield for Fe is much greater than those for its Ru and Os counterparts, under the same chemical conditions.
利用三个模型体系，即M(CO)（M = Fe、Ru和Os）以及CASSCF/Def2-SVP（十四电子/十轨道活性空间）和MP2-CAS/Def2-SVP//CASSCF/Def2-SVP方法，从理论上研究了光化学CO解离和氧化加成反应的机理。确定了在这些CO光挤出反应中起决定性作用的系间窜越和锥形交叉的结构。还计算了单重态或三重态下的中间体和过渡结构，以解释反应路径。这些模型研究表明，用紫外光照射Fe(CO)后，它会迅速失去一个CO分子，生成单重态或三重态的16电子四羰基铁。研究发现，三重态Fe(CO)在最终氧化加成产物Fe(CO)(H)(SiMe)的形成中起着至关重要的作用，但单重态Fe(CO)在最终产物的形成中作用相对较小。然而，其空的配位位点与溶剂分子((Me)SiH)弱相互作用，生成可通过实验检测到的烷基溶剂化铁配合物。理论观察表明，Ru(CO)和Os(CO)具有相似的光化学和热势能曲线。特别是，本研究表明，在相同化学条件下，Fe的氧化加成产率远高于其Ru和Os同类物。
