Dinuclear Benzene Linker Bis(pyrazolyl)amine Cobalt(II) Complexes and their Application as Selective Ethylene Dimerization Catalysts

Reactions of synthons N , N′ ‐(1,4‐phenylenebis(methylene))bis(2‐(1 H ‐pyrazol‐1‐yl)ethan‐1‐amine) ( L1) , N , N ′‐(1,4‐phenylenebis(methylene))bis(2‐(3,5‐dimethyl‐1 H ‐pyrazol‐1‐yl)ethan‐1‐amine) ( L2) , N , N ′‐(1,4‐phenylenebis(methylene))bis(2‐(3,5‐di‐ tert ‐butyl‐1 H ‐pyrazol‐1‐yl)ethan‐1‐amine) ( L3) , and N , N ′‐(1,3‐phenylenebis(methylene))bis(2‐(3,5‐dimethyl‐1 H ‐pyrazol‐1‐yl)ethan‐1‐amine) ( L4) with CoCl 2 produce the dinuclear cobalt(II) complexes [Co 2 ( L1 )Cl 4 ] ( Co1 ), [Co 2 ( L2 )Cl 4 ] ( Co2 ), [Co 2 ( L3 )Cl 4 ] ( Co3 ), and [Co 2 ( L4 )Cl 4 ] ( Co4 ), respectively. These new complexes are characterized using fourier transform‐infra red and ultra‐violet (UV)–Visible spectroscopies, elemental analysis, and single crystal X‐ray crystallography diffraction for complexes Co2 and Co3 . The molecular structures of Co2 and Co3 confirm the formation of the dinuclear cobalt species. Activation of the precatalysts Co1 – Co4 with either EtAlCl 2 or Me 3 Al, affords active (up to 5.26 × 10 5 g·mol −1 Co h −1 ) and selective ethylene dimerization (>98%) catalysts. The steric parameters of the coordinated ligands, as dictated by the substituents on the pyrazolyl ring, largely controll both the activity and regioselectivity of the resultant catalysts.