Quantum chemical study of butane metathesis on mixed aluminum and cobalt chloride complexes
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Activated complexes and routes of the model catalytic butane metathesis in the presence of mixed complexes of aluminum and cobalt chlorides were calculated by the quantum chemical DFT/PBE/TZ2p method. The earlier predicted bimetallic alkyl clusters containing Co-Co dimeric bonds are key intermediates leading to the formation of both isomerization products and products of alkane metathesis (pentane and propane molecules in the case of butane). The sequence of mutual rearrangements of the polynuclear complexes provides a possibility of cleavage and formation of C-C bonds in alkanes and metal-carbon bond formation. The full model of the catalytic cycle was constructed for the maximum multiplicity (7) of the catalytic system, and individual key regions related to C-C bond cleavage and formation were calculated with a lowered multiplicity (5 and 3). The obtained energy barriers of individual stages of the cyclic catalytic process of butane metathesis are not higher than 33 kcal mol−1 for multiplicity 7 and are lower by ∼15 kcal mol−1 for a lower multiplicity.
Key wordsquantum chemical calculations DFT/PBE/TZ2p method alkane metathesis bimetallic alkyl complexes cobalt-cobalt bond aluminum chloride cobalt chloride butane transition states
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