Bis(arylimino)pyridyl cobalt catalysts for copolymerization of buta-1,3-diene with ethene

A series of cobalt (II), iron (II) and iron (III) bis(arylimino)pyridyl complexes [2,6-(ArN = CMe)(2) C5H3N]CoCl2, where Ar is 2,4,6-Me(3)C(6)H(2; )2,6-Me2C6H3; 2,6-iPr(2)C(6)H(3) and 2-tBuC(6)H(4),; [2,6-(ArN= CCl)(2)C5H3N]CoCl2, where Ar is 2,4,6-Me3C6H2 and 2,6-iPr(2)C(6)H(3), and [2,6-(ArN= CMe)(2)C5H3N]FeCl2, where Ar is 2,4,6-Me3C6H2; [2,6-ArN = CMe)(2)C5H3N]FeCl (3), where Ar is 2,4,6-Me3C6H2 was prepared and, after activation with an alkylaluminium cocatalysts (Al2Et3Cl3 or methylaluminoxane), investigated for ethene and butadiene homopolymerization and their copolymerization. Only the cobalt complexes resulted in the effective creation of butadiene-ethene copolymers. According to the cocatalyst preference, two sets of butadiene-ethene copolymers were prepared. Ethene rich (60-85%) crystalline copolymers were obtained using methylaluminoxane and butadiene rich (70-90%) amorphous copolymers using Al2Et3Cl3. Mechanism of cobalt complexes activation was investigated in-situ by UV-VIS spectroscopy. To our best knowledge, this is the first time that bis(arylimino)pyridyl cobalt complexes have been shown to copolymerize butadiene with ethene. The copolymerization activated by Al2Et3Cl3 is cis-1,4-selective and provides elastomeric material.