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Issue 6, 2012
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Theoretical study of Pd(0)-catalyzed carbohalogenation of alkenes: mechanism and origins of reactivities and selectivities in alkyl halide reductive elimination from Pd(ii) species

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Abstract

The mechanism of Pd(0)-catalyzed carbohalogenation of alkenes has been investigated with density functional theory. The catalytic cycle involves oxidative addition of the aryl halide, alkene insertion, and a novel C(sp3)–I reductive elimination. The C(sp3)–I reductive elimination leads to a weakly bonded Pd–product complex, which undergoes ligand exchange via a dissociative mechanism to regenerate the catalyst. In the rate-determining reductive elimination step, bromides and chlorides have higher barriers than iodides, because the stronger Pd–Br and Pd–Cl bonds are being cleaved in these transition states. Bulky ligands, such as P(t-Bu)3 and Q-Phos, facilitate the C(sp3)–I reductive elimination by preventing the formation of tetracoordinated intermediates. The mechanism of the competing β-hydrogen elimination pathway was also investigated. For reactions involving a syn-β-hydrogen atom in the alkyl Pd(II) iodide intermediate, β-hydrogen elimination is much more favorable, leading to Heck-type side products. Blocking β-elimination by the choice of substrates is the main reason why this example of carboiodination works.

Graphical abstract: Theoretical study of Pd(0)-catalyzed carbohalogenation of alkenes: mechanism and origins of reactivities and selectivities in alkyl halide reductive elimination from Pd(ii) species

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Publication details

The article was received on 24 Jan 2012, accepted on 22 Feb 2012 and first published on 22 Feb 2012


Article type: Edge Article
DOI: 10.1039/C2SC20103H
Chem. Sci., 2012,3, 1987-1995

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    Theoretical study of Pd(0)-catalyzed carbohalogenation of alkenes: mechanism and origins of reactivities and selectivities in alkyl halide reductive elimination from Pd(II) species

    Y. Lan, P. Liu, S. G. Newman, M. Lautens and K. N. Houk, Chem. Sci., 2012, 3, 1987
    DOI: 10.1039/C2SC20103H

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