Organometallics
Organometallics
5 years ago

(α-Diimine)nickel Complexes That Contain Menthyl Substituents: Synthesis, Conformational Behavior, and Olefin Polymerization Catalysis

(α-Diimine)nickel Complexes That Contain Menthyl Substituents: Synthesis, Conformational Behavior, and Olefin Polymerization Catalysis
Richard F. Jordan, Feng Zhai
We describe the synthesis and coordination chemistry of the (1R,2S,5R)-menthyl-substituted N,N′-diaryl-α-diimine ligands N,N′-(2-Men-4-Me-Ph)2-BIAN (L1, Men = menthyl, BIAN = bis(imino)acenaphthene) and N,N′-(2-Men-4,6-Me2-Ph)2-BIAN (L2), the conformational properties of these ligands and their metal complexes, and the ethylene and 1-hexene polymerization behavior of the corresponding (α-diimine)Ni complexes. Free ligands L1 and L2 and square-planar (L1)PdCl2 and (L1,2)Ni(acac)+ complexes exhibit a preference for the syn conformation, in which the two menthyl units are located on the same side of the N═CC═N plane, while tetrahedral (L1,2)MX2 (MX2 = ZnCl2, NiBr2) complexes exhibit a preference for the anti conformation, in which the menthyl units are located on opposite sides of the N═CC═N plane. Both the anti and the syn conformers of [(L2)Ni(acac)][B(C6F5)4] can be activated by Et2AlCl to generate highly active ethylene polymerization catalysts (activity (2.5–6.6) × 106 g of PE/((mol of Ni) h) at 15 psi of C2H4, room temperature). The polyethylene produced by the syn conformer (syn/anti = 91/9) has a higher molecular weight (2×) and a higher branch density (3×) in comparison to that produced by the anti conformer. The polyhexene produced by the syn conformer (syn/anti = 91/9) contains a higher level of chain straightening (syn 50%, anti 41%) and a higher percentage of Me versus Bu branches (syn 24/26, anti 6/53) in comparison to that produced by the anti isomer. These results are indicative of a greater preference for 2,1-insertion and for chain walking (versus growth) following 1,2-insertion for the syn conformer.

Publisher URL: http://dx.doi.org/10.1021/acs.organomet.7b00283

DOI: 10.1021/acs.organomet.7b00283

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