Carbene-Complexes and Mechanisms

In order to clarify the mechanism of cyclopropanation, several carbene-complexes of ruthenium have been isolated by reaction with diazocompounds. In the case of Pybox, the corresponding ruthenium-carbene complexes 38 were isolated and characterized using either NMR or X-ray analysis [32]. Similar ruthenium-carbene complexes, such as porphyrin-ruthenium carbene complex 39 [33] and pyridine-diimine-ruthenium complex 40 [34] were isolated and characterized (Chart 7.6). 

The catalytic activity of ruthenium complexes for the cyclopropanation of olefins and diazoacetates has been well investigated and, depending on the ligands utilized, the complexes have a high potential to produce high yields, stereoselectivities and enantioselectivities that are almost comparable to those of rhodium or copper catalysts [35], Moreover, related carbene complexes of ruthenium have been isolated in order to clarify the mechanism of cyclopropanation [32-34], It is likely that further improvements in these reactions will lead to the development of industrial processes utilizing cyclopropanation. 

Horihata, N. Kondo, K. Itoh, Organome-talUcs 1989, 8, 846 H. Nishiyama, M. Kondo, 

Tsuchiya, F. Takezawa, H. Nishiyama, Tetrahedron Asymm. 2003, 14, 855 S. Iwasa, 

Takezawa, Y. Tuchiya, H. Nishiyama, Chem. Commun. 2001, 59 S. Iwasa, 

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