EPR spectroscopic study of Ni(I) species in the catalyst system for ethylene polymerization based on α-diimine Ni(II) complex activated by MMAO

Publication date: Available online 16 November 2018Source: Journal of Organometallic ChemistryAuthor(s): Igor E. Soshnikov, Nina V. Semikolenova, Konstantin P. Bryliakov, Artem A. Antonov, Wen-Hua Sun, Evgenii P. TalsiAbstractUsing EPR spectroscopy, nickel(I) species formed in the catalyst system 1/MMAO for ethylene polymerization has been investigated (1 = LNiBr2, L = 1,4-bis-2,4,6-dimethylphenyl-2,3-dimethyl-1,4-diazabuta-1,3-dien). It has been shown that diamagnetic cationic complex [LNiII-tBu]+[MeMMAO]– (2) persists in system 1/MMAO at low temperatures, but rapidly decays at 25 °C to give new EPR active species 3 (major product) and 4 (minor product). Species 3 is a nickel(I) complex with the proposed structure [LNiI(S)]+[MeMMAO]– (S = solvent), whereas 4 is L(•−)AlMe2 species. Upon the addition of ethylene, complex 3 partially reversibly converts into the adduct [LNiI(C2H4)]+[MeMMAO]– (5). After ethylene consumption, species 3 restores its original concentration.Graphical abstractIn the present work we have shown that reduction of nickel(II) centers to the monovalent state does not lead to the polymerization catalyst deactivation. The Ni(I) complex [LNiI(S)]+[MeMMAO]–, formed in the system LNiBr2/MMAO, is not an ultimate catalyst deactivation product but probably acts as a resting state of the catalyst.

Source: Journal of Organometallic Chemistry - November 17, 2018 Category: Chemistry Source Type: research