1998 Volume 71 Issue 11 Pages 2527-2537
The but-3-en-1-yl group bonded to the cobalt atom in some cobaloxime complexes is isomerized to the but-2-en-1-yl group in the solid state on exposure to a xenon lamp. In order to make clear the relationship between the reaction rate and the crystal structure, six complexes with different axial base ligands were prepared; piperidine, 1, 1-vinylimidazole, 2, pyrrolidine, 3, 1-methylimidazole, 4, 4-t-butylpyridine, 5, and triphenylphosphine, 6. The crystal structures were determined by X-ray analyses and the reaction rates were estimated from the change of the 1H NMR spectra observed in several intermediate stages. One of the photo products, which has 1-vinylimidazole as an axial base ligand, 7, was prepared separately and its crystal structure was also analyzed. A pair of the but-3-en-1-yl groups are in contact with each other around an inversion center in the crystal structures of 2, 5, and 6, whereas the but- 3-en-1-yl groups in 1, 3, and 4 are isolated from the other but-3-en-1-yl groups of the neighboring molecules in their crystal structures. The reaction rates of the former complexes are significantly greater than those of the latter complexes, except 2. This suggests that the cooperative motion of the but-3-en-1-yl groups plays an important role in the process of the isomerization. A pair of the but-3-en-1-yl groups around an inversion center in 2 are too closely packed for the isomerization to occur even if the cooperative motion is taken into account.
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