Format

Send to

Choose Destination
See comment in PubMed Commons below
J Am Chem Soc. 2011 Jun 8;133(22):8518-21. doi: 10.1021/ja203434c. Epub 2011 May 17.

Experimental evidence for cobalt(III)-carbene radicals: key intermediates in cobalt(II)-based metalloradical cyclopropanation.

Author information

1
Department of Chemistry, University of South Florida, Tampa, Florida 33620-5250, USA.

Abstract

New and conclusive evidence has been obtained for the existence of cobalt(III)-carbene radicals that have been previously proposed as the key intermediates in the underlying mechanism of metalloradical cyclopropanation by cobalt(II) complexes of porphyrins. In the absence of olefin substrates, reaction of [Co(TPP)] with ethyl styryldiazoacetate was found to generate the corresponding cobalt(III)-vinylcarbene radical that subsequently dimerizes via its γ-radical allylic resonance form to afford a dinuclear cobalt(III) porphyrin complex. X-ray structural analysis reveals a highly compact dimeric structure wherein the two metalloporphyrin units are arranged in a face-to-face fashion through a tetrasubstituted 1,5-hexadiene C(6)-bridge between the two Co(III) centers. The γ-radical allylic resonance form of the cobalt(III)-vinylcarbene radical intermediate could be effectively trapped by TEMPO via C-O bond formation to give a mononuclear cobalt(III) complex instead of the dimeric product. The allylic radical nature and related reactivity profile of the cobalt(III)-carbene radical, including its inability to abstract hydrogen atoms from toluene solvent, were established by DFT calculations.

PMID:
21563829
DOI:
10.1021/ja203434c
PubMed Commons home

PubMed Commons

0 comments
How to join PubMed Commons

    Supplemental Content

    Full text links

    Icon for American Chemical Society
    Loading ...
    Support Center