Osmium carbene fragment

Further insight into the mechanism of osmium(ll) porphyrin-catalyzed cyclopropanation of alkenes by diazoalkanes was reported by Woo and coworkers [169]. A mono-carbene complex, (TTP)0s(CHC02Et), has been isolated but is not the catalytically active species. An electron-withdrawing Hg-and trans to the carbene activates the carbon fragment towards transfer to an olefin. Substrate reactivity profiles and labeling studies are consistent with a trans-osmiimi(II) bis-carbene species as the active catalyst [169]. 

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