M C. White. Chem 153 LM Polvmerization-306- Week of november 18. 2002 Brookhart's cationic Ni(ll) polymerization catalyst The rate of a displacement of the olefin (leading to chain termination and oligomeric products as in the SHOP process)is retarded in these systems by the steric bulk of the ligand which blocks the axial positions above and below the plane of the Ni complex(see Mechanism, Pg 46, 47) MAO branched polyethylene(PE) toluene.25°C Mw=410.000 Brookhart JACS 1995(117)6414 activity= 1.53 x 10 TO/h; mol Ni, 1.8g PE Excellent review: Brookhart Chem. Rev. 2000(100)1169 methyls(branches)1000C catalyst activation CH=I+ CH3AI(MAO) CH3+ CH3AI(MAO) propagation Linear high M, Letc. high Mw Low Mw polymersM.C. White, Chem 153 LM Polymerization -306- Week of November 18, 2002 Brookhart’s cationic Ni(II) polymerization catalyst (1 atm) toluene, 25oC Mw = 410,000 activity = 1.53 x 105 TO/h· mol Ni, 1.8 g PE 71 methyls (branches)/1000 C branched polyethylene (PE) m n N N NiII Br Br MAO Brookhart JACS 1995 (117) 6414. Excellent review: Brookhart Chem. Rev. 2000 (100) 1169. The rate of associative displacement of the olefin (leading to chain termination and oligomeric products as in the SHOP process) is retarded in these systems by the steric bulk of the ligand which blocks the axial positions above and below the plane of the Ni complex (see Mechanism, pg 46,47). NiII N Br N Br NiII N N NiII N CH3 N NiII N N NiII N N MAO CH3Al(MAO) H NiII N N H NiII N N CH3 NiII N N H H NiII N N NiII N N H NiII N N H NiII N N H CH3Al(MAO) see EM Polymerization, pg 300 n n n m n catalyst activation insertion propagation Linear high Mw polymers β-hydride elimination re-insertion w/opposite regioselectivity propagation Branched high Mw polymers n termination associative displacement etc... etc... Low Mw polymers m n Low Mw polymers branching propagation Proposed catalytic cycle: