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| Content Provider | World Health Organization (WHO)-Global Index Medicus |
|---|---|
| Author | Sawaki, Takuya Ishizuka, Tomoya Miyazaki, Soushi Kawano, Masaki Yoshizawa, Kazunari Fukuzumi, Shunichi Kojima, Takahiko Shiota, Yoshihito |
| Description | Author Affiliation: Ishizuka T ( Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba, Tsukuba, Ibaraki, Japan.) |
| Abstract | The pterin-coordinated ruthenium complex, $[Ru^{II}(dmdmp)(tpa)]^{+}$ (1) (Hdmdmp=N,N-dimethyl-6,7-dimethylpterin, tpa=tris(2-pyridylmethyl)amine), undergoes photochromic isomerization efficiently. The isomeric complex (2) was fully characterized to reveal an apparent 180° pseudorotation of the pterin ligand. Photoirradiation to the solution of 1 in acetone with incident light at 460 nm resulted in dissociation of one pyridylmethyl arm of the tpa ligand from the $Ru^{II}$ center to give an intermediate complex, $[Ru(dmdmp)(tpa)(acetone)]^{2+}$ (I), accompanied by structural change and the coordination of a solvent molecule to occupy the vacant site. The quantum yield (ϕ) of this photoreaction was determined to be 0.87 %. The subsequent thermal process from intermediate I affords an isomeric complex 2, as a result of the rotation of the $dmdmp^{2−}$ ligand and the recoordination of the pyridyl group through structural change. The thermal process obeyed first-order kinetics, and the rate constant at 298 K was determined to be $5.83×10^{−5} s^{−1}.$ The activation parameters were determined to be $ΔH^{≠}=81.8 kJ mol^{−1}$ and $ΔS^{≠}=−49.8 J mol^{−1} K^{−1}.$ The negative $ΔS^{≠}$ value indicates that this reaction involves a seven-coordinate complex in the transition state (i.e., an interchange associative mechanism). The most unique point of this reaction is that the recoordination of the photodissociated pyridylmethyl group occurs only from the direction to give isomer 2, without going back to starting complex 1, and thus the reaction proceeds with 100 % conversion efficiency. Upon heating a solution of 2 in acetonitrile, isomer 2 turned back into starting complex 1. The backward reaction is highly dependent on the solvent: isomer 2 is quite stable and hard to return to 1 in acetone; however, 2 was converted to 1 smoothly by heating in acetonitrile. The activation parameters for the first-order process in acetonitrile were determined to be $ΔH^{≠}=59.2 kJ mol^{−1}$ and $ΔS^{≠}=−147.4 kJ mol^{−1} K^{−1}.$ The largely negative $ΔS^{≠}$ value suggests the involvement of a seven-coordinate species with the strongly coordinated acetonitrile molecule in the transition state. Thus, the strength of the coordination of the solvent molecule to the $Ru^{II}$ center is a determinant factor in the photoisomerization of the $Ru^{II}–pterin$ complex. |
| ISSN | 09476539 |
| e-ISSN | 15213765 |
| Journal | Chemistry - A European Journal |
| Issue Number | 24 |
| Volume Number | 17 |
| Language | English |
| Publisher | Wiley-VCH;ChemPubSoc Europe |
| Publisher Date | 2011-06-06 |
| Publisher Place | Germany |
| Access Restriction | Open |
| Subject Keyword | Coordination Complexes Chemistry Pterins Ruthenium Isomerism Kinetics Ligands Molecular Structure Research Support, Non-U.S. Gov't |
| Content Type | Text |
| Resource Type | Article |
| Subject | Organic Chemistry Catalysis |
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