One-pot synthesis of cobalt complexes with 2,6-bis(arylimino)phenoxyl/phenthioxyl ligands and catalysis on isoprene polymerization

Several cobalt complexes supported by 2,6-bis(arylimino)phenoxyl/phenthioxyl ligands kappa(2)(N,X)-(Ar)[NXN]CoCl(THF) (1a, X = O, Ar = 2,6-Me2C6H3; 1b, X = O, Ar = 2,6-(Pr2C6H3)-Pr-i; 2a, X = S, Ar = 2,6-Me2C6H3; 2b, X = S, Ar = 2,6-(Pr2C6H3)-Pr-i) were synthesized by direct oxygen(sulfur) insertion into the C-Co bond of the mixed-valence cobalt complexes {kappa(2)(C,N),eta(6-Ar)[NCN]Co-kappa(N)-CoCl(mu-Cl)}(2). Crystallization of 1b in the presence of water gave the hydrolysis product 1b '. Treatment of (Ar)[NCN]Li with dioxygen followed by the addition of CoCl2 afforded the heteroatomic complexes {kappa(2)(N,O)-(Ar)[NON]Co(mu-Cl)(2)Li}(2) (3a, Ar = 2,6-Me2C6H3; 3b, Ar = 2,6-(Pr2C6H3)-Pr-i) or kappa(2)(N,O)-(Ar)[NON]Co2Cl2(mu-Cl)(2)Li(THF)(2) (4a, Ar = 2,6-Me2C6H3; 4b, Ar = 2,6-(Pr2C6H3)-Pr-i) depending on the amount of CoCl2 used. The Co(iii)/Li heterometallic complex 3b ' with imino-phenoxyl-amino ligands was formed probably via a redox reaction of 3b. The reactions of (Ar)[NCN]Li with elemental sulfur and CoCl2 gave kappa(2)(N,S)-(Ar)[NSN]Co2Cl2(mu-Cl)(2)Li(THF)(2) (5a, Ar = 2,6-Me2C6H3; 5b, Ar = 2,6-(Pr2C6H3)-Pr-i) respectively. These complexes were well characterized by FT-IR and elemental analyses, and the molecular structures of 1b ', 3b ', 4a, and 4b were confirmed by X-ray crystallography. Upon activation with Al2Et3Cl3 in toluene, these complexes showed high activities in isoprene polymerization affording cis-1,4 enriched polymers with a moderate molecular weight (0.85-4.72 x 10(4) Da).