Synthesis and characterization of β-triketimine cobalt complexes and their behaviour in the polymerization of 1,3-butadieneCCDC 1013347-1013349. For crystallographic data in CIF or other electronic format. see DOI: 10.1039/c4dt02196g

Three β-triketimine ligands, (L 1 : [CH{CMeN(2,4,6-Me 3 -C 6 H 2 )} 2 C(CMe 3 N(2-MeO-C 6 H 4 )], L 2 : [CH{CMeN(2,4-Me 2 -C 6 H 3 )} 2 C(CMe 3 N(2-MeO-C 6 H 4 )] and L 3 : [CH{CMeN(2-Me-C 6 H 4 )} 2 C(CMe 3 N(2-MeO-C 6 H 4 )]), were synthesized and then characterized by 1 H and 13 C{ 1 H} NMR spectroscopy, elemental analysis and electrospray (ES) MS. β-triketimine cobalt( ii ) complexes were then prepared by the interaction of cobalt( ii ) bromide with L 1-3 in the presence of NaBArF (BArF = [{3,5-(CF 3 ) 2 -C 6 H 3 } 4 B] − ). Five-coordinate dimeric bromide-bridged species [(LCoμ-Br) 2 ][BArF] 2 were obtained. The geometry of the complexes was found by single-crystal X-ray diffraction to be slightly distorted square-pyramidal. The polymerization of 1,3-butadiene catalysed by these complexes upon activation with methylaluminoxane (MAO) in chlorobenzene yielded high cis -1,4-polybutadiene (>97% cis ). The effect of steric and electronic properties of the ligands on the performance of the catalytic system was investigated: it was found that ligands with fewer methyl substituents gave more active catalytic systems. It was also found that increasing MAO: Co ratio resulted in higher activity. Stereoselectivity of all catalysts slightly decreased at higher temperature, whereas activities were maximised at 20 °C, where very high values of activity were recorded. Cobalt II ions ligated by fac -κ 3 -β-triketimine ligands form bromide-bridged square-based pyramidal dimers which upon activation with MAO and fed with a constant supply of butadiene produce high- cis -1,4-polybutadiene with activities and molecular weights surpassing all previously seen for this metal.