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

Abstract

The synthesis, spectroscopic and structural characterization, and olefin polymerization behavior of a family of pyridine‐2‐phenolate‐6‐arylmethine [O,N,CH(Ar)] Group 4 catalysts bearing a four‐membered N,C(sp3)‐donor metallacycle are described. The racemic [O,N,CH(Ar)] complexes adopt C1 symmetry, as confirmed by NMR spectroscopy and X‐ray crystallography. Advanced NMR experiments have been conducted to probe for possible C−H⋅⋅⋅F−C interactions within fluorinated derivatives. Use of a bis‐pyridyl ligand (Ar=py) resulted in the formation of C2v‐symmetric [O,NCHN] complexes containing a six‐membered partially delocalized N,N‐donor chelate. All complexes have been evaluated as ethylene polymerization catalysts. Notably, the Ti derivatives in conjunction with [Ph3C][B(C6F5)4]/iBu3Al display excellent catalytic efficiencies (TOF over 4×105 h−1 [atm C2H4]−1) at 22 °C, and are considerably more active than previously reported Ti−[O,N,C(σ‐aryl)] relatives. DFT calculations have been performed to gain insights into catalytic behavior. These studies indicate that although the ethylene assimilation process (comprising initial ethylene insertion into the Ti−C(methine) bond of the four‐membered chelate) is accessible, there exists a kinetic preference for normal chain propagation for some catalysts. The DFT results for the Ti−[O,N,CH(Ar)] (Ar=Ph) catalyst are consistent with the narrow molecular weight distributions of the polymers produced (Mw/Mn down to 2.2), suggesting close to single‐site character.

Preparation of Pincer Hafnium Complexes for Olefin Polymerization

“…By performing anionic polymerization of styrene in a one-pot reaction after CCTP with I , it is also possible to synthesize polyolefin-polystyrene block copolymers [23,24,25]. In this context, many studies have been performed to detail I and to improve the catalytic performance by modifying the skeleton of I [26,27,28,29,30,31,32,33,34,35]. With an aim to develop upgraded catalyst for I , we prepared various pincer-type Hf-complexes.…”

Group 4 Post-Metallocenes Supported by [OCH2N,C(σ-aryl)] Auxiliaries Bearing a Seven-Membered Metallacycle: Synthesis, Characterization, and Catalysts for Olefin Polymerization

“…Attention is drawn to the conformation of the benzyl moieties, which typically extend outward and away from the tridentate ligand in related group 4 postmetallocene complexes (as is the case for the Ti derivatives herein, according to ROESY experiments). 4,14,22,34 Here, the severely distorted "quasi-meridional" coordination evident in 8 causes the η 2 -coordinated benzyl group (C34−C40) to "wrap" around the σ-aryl unit (without π-stacking) so that the Zr−benzyl linkages and the alignment of the benzyl moieties are virtually perpendicular (torsional angle between C27−C28 and C34−C35 = 95.8°). Consequently, the shortest distance between the CH 2 (benzyl) and shown in Figure S4 for 2).…”

“…8,9 Our initial studies 10,11 revealed that Ti-[O,N,C] catalysts can produce polyolefins with high M w /M n values suggestive of multisite behavior, which was subsequently ascribed to facile olefin insertion into the Ti− C(σ-aryl) bond to afford supplementary "olefin-assimilated" active species, 12 and efforts have been undertaken to modify and ameliorate polymerization characteristics. 13,14 The corresponding 2-arylamido [N,N,C]-Hf catalysts were developed by Symyx and Dow through the use of highthroughput screening, 15,16 and the analogous olefin insertion into the M−C(σ-aryl) bond of these 17,18 and related 19,20 Zr derivatives to generate olefin-assimilated (or "monomerinserted") active sites have been reported. Inspired by this unusual insertion reaction, Coates et al designed pyridylamido 21 and phenolate-amine 22 ligands bearing a pendant vinyl moiety, 23 which undergo metalation with group 4 alkyl species to afford C(sp 3 )-chelating catalysts that mediate the living isoselective polymerization of α-olefins.…”

“…We recently reported a family of pyridine-2-phenolate-6-arylmethine [O,N,CH-(Ar)]-Ti catalysts featuring a four-membered N,C-donor chelate ring, which produce polyethylene (in conjunction with [Ph 3 C][B(C 6 F 5 ) 4 ]) with excellent efficiencies and narrow molecular weight distributions (M w /M n down to 2.2). 14 The present study concerns the expansion of the [O,N] metallacyle in [O,N,C] catalysts to a seven-membered chelate ring, and its effects upon polymerization behavior. Such…”

Preparation of Half- and Post-Metallocene Hafnium Complexes with Tetrahydroquinoline and Tetrahydrophenanthroline Frameworks for Olefin Polymerization

“…It was also demonstrated that the CCTP involving III , could be switched to anionic styrene polymerization to prepare polyolefin-polystyrene block copolymers [11,20,21,22]. In this context, many thorough studies have been performed to detail III , and to improve the catalytic activity by modifying its ligand skeleton [23,24,25,26,27,28,29,30,31,32]. To develop an upgraded catalyst relative to III , we prepared various Hf complexes.…”