Synthesis of bis(N-arylcarboximidoylchloride)pyridine cobalt(ii) complexes and their catalytic behavior for 1,3-butadiene polymerization

Abstract

A new family of bis(N-arylcarboximidoylchloride)pyridine cobalt(II) complexes with the general formula [2,6-(ArN=CCl)2C5H3N]CoCl2 (Ar = 2,4,6-Me3C6H2, 4a; 2,6-(i)Pr2C6H3, 4b; 2,6-Me2C6H3, 4c; C6H5, 4d; 4-Cl-2,6-Me2C6H2, 4e) and a typical Brookhart-Gibson-type reference complex [2,6-(2,4,6-Me3C6H2N=CMe)2C5H3N]CoCl2 (5a) were synthesized and characterized. Determined by X-ray crystallographic analysis, complexes 4a, 4c-e, and 5a adopted a trigonal bipyramidal configuration, and 4b adopted a distorted square pyramidal geometry. In combination with ethylaluminum sesquichloride (EASC), all the complexes were highly active towards 1,3-butadiene polymerization, affording polybutadiene with predominant cis-1,4 content (up to 96%). 4a with chlorine atoms at the imine groups exhibited higher catalytic activity than did 5a, indicating that the incorporation of chlorine atoms into the ligand improves the activity. The activity of the complexes in 1,3-butadiene polymerization was in the order of 4a > 4c ∼ 4e ∼ 4b > 4d, which is consistent with the trend of spatial opening degree around the metal center in the complexes as revealed by crystallographic data. Screening polymerization conditions proved that EASC was the most efficient among the cocatalysts examined.

Cobalt and nickel complexes supported by 2,6-bis(imidate)pyridyl ligands: Synthesis, characterization, and 1,3-butadiene polymerization studies

“…Interestingly, the introduction of strong electron-withdrawing substituents led to an increase of polymer yield (1d vs 1b) which might be owing to the enhanced electropositivity of the cobalt centre caused by the electron-withdrawing effect of trifluoroethoxy group. Similar results were observed in other Co(II)-based complexes36,37 . The incorporation of phenoxy substituent to the imine-carbon (1e) resulted in a slight decrease in polymer yield compared to the complexes with alkoxy groups (1a-1c).…”

“…We recently reported that Co(II) complexes bearing bis(imino)pyridine 33 and α-diimine 34 ligands exhibited high catalytic activity and cis-1,4-selectivity for 1,3-butadiene polymerization, and quite interestingly, the addition of phosphines to these systems not only enhanced the catalytic activity but also switched the selectivity from cis-1,4-to 1,2-manner. 35 In these our previous reports, it was found that, for Gibson-type catalysts, the substituents on the C=N carbon position showed a large influence on the catalytic behaviors of the corresponding Co(II) complexes 36 . Furthermore, besides us, the effect of substituents at C=N carbon position on the catalytic behaviors of 1,3-diene polymerization were rarely investigated 37 and 2c were further characterized by single-crystal X-ray diffraction analysis, the selected bond distances and angles are summarized in Table 1.…”

The behaviour of β-triketimine cobalt complexes in the polymerization of isoprene

“…Advantage of electron-withdrawing substituents has been seen before in polymerization of butadiene by cobalt catalysts 43 and can be rationalised here as being due to a more electrophilic metal demanding more electron-density from the co-ordinated isoprene thus facilitating its attack by polymeryl chain-end. 1-3) were less active than those with single alkyls or uoro-substituents (4-7).…”

Nickel(ii) complexes chelated by 2,6-pyridinedicarboxamide: syntheses, characterization, and ethylene oligomerization

“…1 Using the above procedure, N,N′-bis(2,6-fluorophenyl)-2,6pyridinedicarboxamide was prepared in 78.5% yield (3.05 g, 7.85 mmol). 1 N,N′-phenyl-2,6-pyridinedicarboxamide (L3), 24 N,N′-bis(2,6dimethylphenyl)-2,6-pyridinedicarboxamide (L4), 25 N,N′bis(2,6-diethylphenyl)-2,6-pyridinedicarboxamide (L5) 26 and N,N′-bis(2,6-diisopropylphenyl)-2,6-pyridinedicarboxamide (L6) 27 were prepared using the above procedure and confirmed by NMR in according with the literature reports.…”