Synthesis, Structures, and Olefin Polymerization Characteristics of Group 4 Catalysts [Zr{(OAr)₂py}Cl₂(D)] (D = O-Donors, Cl[HPR₃]) Supported by Tridentate Pyridine-2,6-bis(aryloxide) Ligands

Abstract

The Zr(IV) complexes [Zr(L1)X2(D)] [H2L1 = 2,6-di(3-tert-butyl-5-methylphen-2-ol)pyridine; X = Cl, D = thf (1), OEt2 (2), acetophenone (3), benzophenone (4), 2-acetonaphthone (5), Cl[HPR3] {R = Me (6), Et (7); R3 = Me2Ph (8)}; X = CH2Ph (9)] have been synthesized, and the crystal structures of 3, 4, and 7 have been determined. These catalysts, assisted by the robustness and chelating strength of the pyridine-bis(phenolate) moiety, exhibit excellent activities for ethylene polymerization in conjunction with MAO. Studies to assess the impact of the donor group during the catalytic process suggest that the same active species is generated by 1−8/MAO and the donor group does not play an active role. Even higher activities are observed for the 1/iBu3Al/Ph3CB(C6F5)4 system in ethylene polymerization and propylene copolymerization reactions (36 590 and 15 700 g of polymer (mmol of catalyst)-1 h-1, respectively), with the latter displaying good C3 incorporation (25.4 mol % C3). Insight into the catalytic behavior of the 1/MAO system has been derived from GPC and NMR characterization of the polymers prepared under different reaction conditions. 1H and 13C NMR end-group analyses reveal resonances for saturated methyl chain-end groups only and undetectable or negligible levels of unsaturated vinyl chain ends. This indicates that for the polymerization chain-transfer mechanism, the conventional β-H transfer reactions to the metal/monomer are insignificant and the unusual chain transfer to Al pathway is vastly dominant.

Highly Thermally Stable Eight-Coordinate Dichloride Zirconium Complexes Supported by Tridentate [ONN] Ligands: Syntheses, Characterization, and Ethylene Polymerization Behavior

“…The Cl1–Zr1–Cl2 angle is 91.83(5)°, indicating that the two chlorides are located in positions cis to each other, which is favorable for ethylene polymerization. The average Zr–ligand bond distances (Zr–O = 2.054(5) Å, Zr–N(imine) = 2.372(5) Å, Zr–N(pyridyl) = 2.508(4) Å, Zr–Cl = 2.5384(5) Å) are comparable to those observed in six-coordinate zirconium complexes which contain phenoxy-imine ligands or pyridyl derivatives. − ,− In addition, in complex C2 , the imine CN bond has a distinctive double-bond character (N1–C7 = 1.265(6) Å, N3–C37 = 1.280(5) Å).…”

Neutral and Cationic N-Heterocyclic Carbene Zirconium and Hafnium Benzyl Complexes: Highly Regioselective Oligomerization of 1-Hexene with a Preference for Trimer Formation

“…Titanium complexes supported by tridentate thio bis(phenolate) ligands coordinating in a fac fashion efficiently catalyze the syndiotactic polymerization of styrene . More recently, various tridentate bis(phenolate) ligand platforms with a central heteroatom L donor were shown to coordinate in a mer fashion to group 4 metal centers, with the resulting complexes being highly active in ethylene polymerization and/or displaying a reasonable activity in propene polymerization and 1-hexene oligomerization . Though factors governing polymerization/oligomerization parameters in these tridentate ligand supported systems are rather complicated, the robustness and stability of the metal chelate in such fairly electron-deficient five-coordinate metal species certainly play a crucial role both in avoiding ligand-involving side reactions and favoring the generation of viable/stable group 4 alkyl cations, the actual polymerization catalysts …”

Olefin Polymerization Reactivity of Group 4 Post‐Metallocene Catalysts Bearing a Four‐Membered C(sp3)‐Donor Chelate Ring

“…The catalytic efficiency of 1 /[Ph 3 C][B(C 6 F 5 ) 4 ] (up to 12.3 kg mmol −1 h −1 ) at 1 atmosphere of ethylene pressure is noticeably higher than the [O,N,C(σ‐aryl)] relatives,, and approaches those reported for the Zr‐[O,N,O] (2,6‐bis(aryloxo)pyridine) system . As anticipated, the diminished bite angle conferred by the four‐membered N,C(sp 3 )‐donor chelate may offer enhanced accessibility for monomers and facilitate chain migration processes.…”

“…The catalytic efficiency of 1/[Ph 3 C][B(C 6 F 5 ) 4 ] (up to 12.3 kg mmol À 1 h À 1 ) at 1 atmosphere of ethylene pressure is noticeably higher than the [O,N,C(σ-aryl)] relatives [5,11,13] and approaches those reported for the Zr-[O,N,O] (2,6-bis(aryloxo) pyridine) system. [45] As anticipated, the diminished bite angle conferred by the four-membered N,C(sp 3 )-donor chelate may offer enhanced accessibility for monomers and facilitate chain migration processes. DFT calculations have provided some insights into the polymerization process: (1) although the initial ethylene assimilation step in pathway a is accessible for 1[B(C 6 F 5 ) 4 ], a kinetic preference is indicated for conventional propagation (pathway b); however, the similar results for 2 + , 3 + , and 6 + (with [B(C 6 F 5 ) 4 ] À ) may not be reconciled with their apparent multisite behavior [see below], (2) both the ethyleneassimilated and conventional propagation pathways are competitive for 4 + and 5 + (with [B(C 6 F 5 ) 4 ] À ), (3) the purportedly facile ethylene assimilation into the TiÀ C(sp 3 ) bond of the fourmembered chelate (resulting in release of ring strain; pathway a) is clearly exothermic, but the resultant six-membered species (INT2a) is stable and relatively inactive; indeed, the resultant substantial increase in the bite angle [e. g. for 1[B (C 6 F 5 ) 4 ]: 146 to 230°(for before and after assimilation)] would hinder subsequent ethylene insertion and lead to higher activation barriers.…”