| Summary: | 碩士 === 國立嘉義大學 === 應用化學系研究所 === 104 === 1. Abstract
The mechanisms of the photo-isomerization reactions are investigated theoretically at the M06-2X/Def2-SVPD level of theory, using the five coordinated M(CO)4(CS) (M = Cr, Mo, and W) complexes as model systems. This work demonstrates the first examination of the photochemical mechanisms of such complexes. This study provides the first theoretical evidence for the mechanisms of such photorearrangements of the five coordinated metal complexes. The model investigation indicates that the preferred reaction route for the photorearrangement reactions is as follows: reactant Franck-Condon region minimum (triplet)transition state (triplet) triplet/singlet intersystem crossing photoproduct. The theoretical findings also reveal that no radicals exist during such photo-isomerization reactions and that the energy differences between the crucial points are quite small, which demonstrates that the CS group rotates easily to form the different conformations, after the M(CO)4(CS) molecules have been photo-irradiated. These photochemical mechanisms are consistent with the available experimental observations.
2. Abstract
The potential energy surfaces that correspond to the photochemical isomerization reactions and the thermal reversal reactions of FvFe2(CO)4, FvRu2(CO)4, and FvOs2(CO)4 (Fv = bi(cyclopentadienylidene)) are studied using the M06-2X/Def2-SVPD method. The theoretical findings indicate that that the photoisomerization reactions of these reactants all undertake the same reaction path, as follows: reactant (S0) Franck-Condon region intermediate (T1) transition state-1 (T1) intersystem crossing (T1/S0) intermediate-cis (S0) transition state-1 (S0) intermediate-trans (S0) transition state-2 (S0) 4-membered ring product. However, the thermal reversal reaction is predicted to proceed as follows: 4-membered ring product transition state-2 (S0) intermediate-trans (S0) transition state-1 (S0) intermediate-cis (S0) reactant (S0). These theoretical findings demonstrate that the atomic radius of the group 8 element (Fe, Ru, and Os), as well as the M-C bond strength are crucial in determining the reactivity of the photoisomerization and the thermal reversal reactions.
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