Ethylene polymerization using beta-diketimine complexes of zirconium

Ethylene polymerizations were conducted using beta-diketimine complexes of Zr [LZrX3 (1) and L2ZrX2 (2) with L = MeC(NAr)CHC(NAr)Me and X = Cl, R (R = Me, Bn)] as well as Cp(L)ZrX2 (3) in the presence of MAO. Complexes 1 poss ess low polymerization activities (ca. 10(5) g PE/(mol Zr h)) and provide P Es with a trimodal, molecular weight distribution. Both 2 and 3 behave as s ingle-site catalysts under these conditions, with the activity of the latte r being considerably higher than the former (ca. 10(6)-10(7) vs 10(5) g PE/ (mol Zr h)). Induction periods of 10-20 min at 70 degrees C were observed i n polymerizations involving 3 (Ar = Ph, X = Cl, Me) when activated by MAO. The use of [Ph3C][B(C6F5)(4)] and 3b (Ar = Ph, X = Me) in the presence of s mall amounts of MAO (ca. 100:1 Al:Zr) led to rapid monomer uptake and an in crease in catalytic activity by about a factor of 4. Lower activities were observed in the presence of Me3Al or (Bu3Al)-Bu-i. Little or no polymerizat ion activity was observed when excess 3b was used as a scrubbing agent (in the presence of [Ph3C][B(C6F5)(4)]), and rapid loss of activity was observe d when excess 3b was added to a catalyst system already producing PE. Compl ex 3b reacts with [Ph3C][B(C6F5)(4)] in chlorobenzene-d(5) solution at 25 d egrees C to provide [Cp(L)ZrMe][B(C6F5)(4)] (4) Complex 4 is transformed on heating in chlorobenzene to a dicationic (mu-Cl)(2) complex [(Cp(L)ZrCl)(2 )][B(C6F5)(4)](2) (5), which was characterized by X-ray crystallography. Co mplex 4 forms dinuclear complexes with 3b or Me3Al in solution at room temp erature. These complexes, [Cp(L)Zr(mu-Me)(2)AlMe2][B(C6F5)(4)] (3) or [(Cp( L)ZrMe)(2)-(mu-Me)][B(C6F5)(4)] (7), are fluxional in solution; at lower te mperature, the solution NMR spectra are consistent with the structures show n. Complex 3b is a potent inhibitor of ethylene polymerization by 4, formin g 7, which is resistant to dissociation. The presence of AlMe3 (or MAO) app ears to reversibly displace 3b from 7, allowing the reaction of 3b with [Ph 3C][B(C6F5)(4)] to proceed to completion.