Zirconium Complexes of a Rigid, Dianionic Pincer Ligand: Alkyl Cations, Arene Coordination, and Ethylene Polymerization

Reaction of 4,5-bis­(2,4,6-triisopropylanilino)-2,7-di-tert-butyl-9,9-dimethylxanthene (H2XN2) with [Zr­(NMe2)4], followed by crystallization from O­(SiMe3)2, yielded [(XN2)­Zr­(NMe2)2]·{O­(SiMe3)2}0.5 (1·{O­(SiMe3)2}0.5). The zirconium dimethyl complex [(XN2)­ZrMe2] (2) was subsequently accessed (a) by treatment of 1·(O­(SiMe3)2)0.5 with excess AlMe3 or (b) via reaction of 1·(O­(SiMe3)2)0.5 with excess Me3SiCl, affording [(XN2)­ZrCl2] (3) followed by reaction of 3 with 2 equiv of MeLi. Reaction of [(XN2)­ZrMe2] (2) with one equiv of B­(C6F5)3 or [CPh3]­[B­(C6F5)4] yielded cationic [(XN2)­ZrMe]­[MeB­(C6F5)3] (4) and [(XN2)­ZrMe­(arene)]­[B­(C6F5)4] {arene = η6-benzene (5a), η6-toluene (5b), or bromobenzene (5c)}, respectively. Both 4 and 5b are active for ethylene polymerization under 1 atm of ethylene at 24 and 80°C in toluene with activities ranging from 23.5–883 kg mol–1 atm–1 h–1, yielding polymers with weight-average molecular weights (Mw) of 70,800–88,100 g mol–1 and polydispersities (Mw/Mn) of 3.94–4.67.