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Issue 12, 2013
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Computational study of the double C–Cl bond activation of dichloromethane and phosphine alkylation at [CoCl(PR3)3]

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Abstract

Density functional theory calculations have been employed to model the double C–Cl bond activation of CH2Cl2 at [CoCl(PR3)3] to give [CoCl3(CH2PR3)(PR3)2]. Calculations incorporating dichloromethane solution (PCM approach) on a [CoCl(PMe3)3] model system showed the two C–Cl cleavage steps to involve different mechanisms. The first C–Cl cleavage step occurs on the triplet surface and proceeds via Cl abstraction with a barrier of 19.1 kcal mol−1. Radical recombination would then give singlet mer,trans-[CoCl2(CH2Cl)(PMe3)3] with an overall free energy change of +1.8 kcal mol−1. Alternative C–Cl activation processes based on nucleophilic attack by the Co centre at dichloromethane with loss of Cl have significantly higher barriers. The second C–Cl cleavage occurs via nucleophilic attack of PMe3 at the CH2Cl ligand with formation of a new P–C bond and displacement of Cl. This may either occur in an intermolecular fashion (after prior PMe3 dissociation) or intramolecularly. Both processes have similar barriers of ca. 12 kcal mol−1. The comproportionation of [CoCl3(CH2PMe3)(PMe3)2] with [CoCl(PMe3)3] to give [CoCl2(CH2PMe3)(PMe3)], [CoCl2(PMe3)2] and 2 PMe3 is computed to be strongly exergonic, consistent with the observation of this process in analogous experimental systems.

Graphical abstract: Computational study of the double C–Cl bond activation of dichloromethane and phosphine alkylation at [CoCl(PR3)3]

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Publication details

The article was received on 27 Sep 2012, accepted on 19 Nov 2012 and first published on 18 Dec 2012


Article type: Paper
DOI: 10.1039/C2DT32272B
Citation: Dalton Trans., 2013,42, 4208-4217
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    Computational study of the double C–Cl bond activation of dichloromethane and phosphine alkylation at [CoCl(PR3)3]

    A. G. Algarra, P. Braunstein and S. A. Macgregor, Dalton Trans., 2013, 42, 4208
    DOI: 10.1039/C2DT32272B

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