Recently, the neutral κ2-(N,O)-salicylaldiminato Ni(II) complexes (see Chart 1) are reported as the most promising candidate for the synthesis of highly branched low molecular wight polyethylene that are of industrial interest. The microstructure of the polymer is showed to be strongly dependent on the catalyst structure and, in particular, on the size and on the nature of the ligand substituents.1 In order to clarify the role of the substituents, the mechanism of the linear propagation reaction as well as the termination and the branches formation reaction were studied theoretically by density functional theory calculations.2 The results showed that the linear propagation and termination/branches formation mechanisms overlap until the ethylene coordination occurs with the monomer in the position trans and the chain in the position cis to the oxygen ligand, respectively. After that, the reaction can proceed toward the new insertion (linear propagation) or toward a de-coordination of the monomer. The de-coordination is the key step for the following a) B-H elimination and 2,1 re-insertion of the unsaturated chain end (branches pathway) or b) chain transfer reaction. Interestingly, in the de-coordination transition state, the ethylene is replaced by a η2 coordination of the aromatic ring of the ligand. Since the strength of the interaction between the Ni and the aromatic ring strongly depends on the steric and electronic effects of the remote substituents of the ligand, by tuning these effects the structure of the polyethylene can be regulate, in agreement with the experimental results. 1Wiedemann T.; Voit G.; Tchernook A.; Roesle P.; Göttker-Schnetmann I.; Mecking S. J. Am. Chem. Soc. 2014, 136, pp 2078-2085 2 Falivene L.; Cavallo L.; Caporaso L submitted

Hyperbranched ethylene oligomers by κ2-(N,O)-salicylaldiminato Ni(II) complexes: DFT investigation of role of remote substituents

251st National Meeting (2016)

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