Report

Direct Spectroscopic Characterization of a Transitory Dirhodium Donor-Acceptor Carbene Complex

Science  18 Oct 2013:
Vol. 342, Issue 6156, pp. 351-354
DOI: 10.1126/science.1243200

You are currently viewing the abstract.

View Full Text

Catching a Carbene >>

Divalent carbon fragments, or carbenes, vary widely in their stability, depending on their substituents. Some, such as N-heterocyclic carbenes, are independently isolatable. Others can be isolated in coordination complexes with metals. Kornecki et al. (p. 351, published online 12 September) synthesized a carbene coordinated to a rhodium dimer representative of an elusive class of short-lived intermediates long postulated to underlie a series of cyclopropanation and C-H insertion reactions.

Abstract

A multitude of organic transformations catalyzed by dirhodium(II) (Rh2) complexes are thought to proceed via the intermediacy of highly reactive, electrophilic carbenoid intermediates that have eluded direct observation. Herein, we report the generation of a metastable Rh2-carbenoid intermediate supported by a donor-acceptor carbene fragment. This intermediate is stable for a period of ~20 hours in chloroform solution at 0°C, allowing for an exploration of its physical and chemical properties. The Rh=C bond, characterized by vibrational and nuclear magnetic resonance spectroscopy, extended x-ray absorption fine structure analysis, and quantum-chemical calculations, has weak σ and π components. This intermediate performs stoichiometric cyclopropanation and C–H functionalization reactions to give products that are identical to those obtained from analogous Rh2 catalysis.

View Full Text