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Issue 41, 2013
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Impact of reducing agent, temperature, and substrate topology on diastereoselectivity of the intermolecular coupling reactions, or how “free” are cobalt-complexed propargyl radicals?

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Abstract

Applicability of the term “free radical” to organometallic radicals was studied by using the stereoselectivity of radical C–C bond formation as a diagnostic tool. Based on diastereoselectivity data, it was concluded that the reduction of π-bonded, Co2(CO)6-complexed propargyl cations with heterogeneous reducing agents (Zn, Mg) generates “free radicals”, while homogeneous reductants (Cp2Co, Na–Ph2CO) produce “sequestered radicals”, presumably associated with reductant-derived oxidized species. The latter are comparable in molecular volume to the requisite radical species, thus restricting the motion and conformational freedoms of converging, transition metal-complexed propargyl radicals. Diastereoselectivity of intermolecular reactions is determined to be much less sensitive toward temperature variation (Δde = 6–22%) than in intramolecular radical cyclizations (Δde = 106%).

Graphical abstract: Impact of reducing agent, temperature, and substrate topology on diastereoselectivity of the intermolecular coupling reactions, or how “free” are cobalt-complexed propargyl radicals?

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Publication details

The article was received on 06 Jun 2013, accepted on 30 Jul 2013 and first published on 01 Aug 2013


Article type: Paper
DOI: 10.1039/C3DT51502H
Citation: Dalton Trans., 2013,42, 14801-14812
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    Impact of reducing agent, temperature, and substrate topology on diastereoselectivity of the intermolecular coupling reactions, or how “free” are cobalt-complexed propargyl radicals?

    G. G. Melikyan, L. Carlson, N. Sahakyan, A. Floruti and M. Garrison, Dalton Trans., 2013, 42, 14801
    DOI: 10.1039/C3DT51502H

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