Polymerization of 1,3‐dienes and styrene catalyzed by cationic allyl Ni(II) complexes

Polymerizations of 1,3‐dienes using in situ generated catalyst [(2‐methallyl)Ni][B(Ar F ) 4 ], 6 , (Ar F = 3,5‐bis(trifluoromethyl)phenyl) as well as [(2‐methallyl)Ni(mes)][B(Ar F ) 4 ], 14 , (mes = mesitylene) are reported. Highly sensitive complex 6 polymerizes butadiene (BD) at –30 °C to yield polybutadiene with a M n of ca. 10 K and 94% cis ‐1,4‐enchainment while less reactive isoprene (IP) was polymerized at 23 °C to yield polyisoprene with M n ca. 7 K. Complex 6 was also shown to polymerize a functionalized diene, 2,3‐bis(4‐trifluoroethoxy‐4‐oxobutyl)‐1,3‐BD, to polymer with M n = 113 K. The stable and readily isolated arene complex 14 initiates BD and IP polymerizations at somewhat higher temperatures relative to 6 and delivers polymers with higher molecular weights. Complex [(allyl)Ni(mes)][B(Ar F ) 4 ], 13 , catalyzes polymerization of styrene to yield polystyrene with high conversion, M n 's = ca. 6 K and MWD = 2. The π‐benzyl complex [(η 3 ‐1‐methylbenzyl)Ni(mes)] [B(Ar F ) 4 ], 19 , was detected as an intermediate following chain transfer by in situ NMR studies.