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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.
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