Preparation of Pincer Hafnium Complexes for Olefin Polymerization

Abstract

Pincer-type [Cnaphthyl, Npyridine, Namido]HfMe2 complex is a flagship among the post-metallocene catalysts. In this work, various pincer-type Hf-complexes were prepared for olefin polymerization. Pincer-type [Namido, Npyridine, Namido]HfMe2 complexes were prepared by reacting in situ generated HfMe4 with the corresponding ligand precursors, and the structure of a complex bearing 2,6-Et2C6H3Namido moieties was confirmed by X-ray crystallography. When the ligand precursors of [(CH3)R2Si-C5H3N-C(H)PhN(H)Ar (R = Me or Ph, Ar = 2,6-diisopropylphenyl) were treated with in situ generated HfMe4, pincer-type [Csilylmethyl, Npyridine, Namido]HfMe2 complexes were afforded by formation of Hf-CH2Si bond. Pincer-type [Cnaphthyl, Sthiophene, Namido]HfMe2 complex, where the pyridine moiety in the flagship catalyst was replaced with a thiophene unit, was not generated when the corresponding ligand precursor was treated with HfMe4. Instead, the [Sthiophene, Namido]HfMe3-type complex was obtained with no formation of the Hf-Cnaphthyl bond. A series of pincer-type [Cnaphthyl, Npyridine, Nalkylamido]HfMe2 complexes was prepared where the arylamido moiety in the flagship catalyst was replaced with alkylamido moieties (alkyl = iPr, cyclohexyl, tBu, adamantyl). Structures of the complexes bearing isopropylamido and adamantylamido moieties were confirmed by X-ray crystallography. Most of the complexes cleanly generated the desired ion-pair complexes when treated with an equivalent amount of [(C18H37)2N(H)Me]+[B(C6F5)4]−, which showed negligible activity in olefin polymerization. Some complexes bearing bulky substituents showed moderate activities, even though the desired ion-pair complexes were not cleanly afforded.

Preparation of High-Purity Ammonium Tetrakis(pentafluorophenyl)borate for the Activation of Olefin Polymerization Catalysts

“…With the species [ 5 -Ti(CH 2 N(C 18 H 37 ) 2 )] + [B(C 6 F 5 ) 4 ] − , the four NCH 2 protons, the four methyl groups attached to cyclopentadienyl ligand, and the two methyl groups attached to Si are separately observed at 3.29, 2.93, 2.77, 2.51, 2.20, 2.08, 1.88, 1.83, 0.75, and 0.58 ppm with intensity ratios of roughly 1:1:1:1:3:3:3:3:3:3, respectively, along with Ti-CH 2 signals at 0.45 and −0.71 ppm with intensity ratios of roughly 1 and 1, respectively. The same type of complex, [Cp 2 Zr(CH 2 N(C 18 H 37 ) 2 )] + [B(C 6 F 5 ) 4 ] − , was reported for the activation reaction of Cp 2 ZrMe 2 [ 46 , 47 , 48 ], and a similar transformation of [ L -M(Me)] + [B(C 6 F 5 ) 4 ] − -type complexes to other species (via the σ-bond metathesis reaction with formation of other M-C bonds and generation of CH 4 ) has also been reported for other metallocene and post-metallocene complexes [ 31 , 49 , 50 , 51 ]. Action of [Me(C 18 H 37 ) 2 N-H] + [B(C 6 F 5 ) 4 ] − to Hf-based metallocene (e.g., 3 - and 4 -HfMe 2 ), half-metallocene (e.g., 6 -HfMe 2 ), and post-metallocene (e.g., pyridylamido-HfMe 2 ) complexes usually afforded stable [ L -Hf(Me)(NMe(C 18 H 37 ) 2 )] + [B(C 6 F 5 ) 4 ] − type ion pair complexes [ 37 ].…”

Polystyrene Chain Growth Initiated from Dialkylzinc for Synthesis of Polyolefin-Polystyrene Block Copolymers

“…(Polyolefinyl) 2 Zn was prepared via coordinative chain transfer copolymerizations (CCTcoPs) performed using a pyridylamidohafnium catalyst (1 in Scheme 1) in methylcyclohexane at high temperatures of 90-110 • C by feeding ethylene/propylene mixed gases. Catalyst 1 is the best in performing CCTcoPs [22,33,[41][42][43]. It undergoes fast alkyl exchange with Zn sites to generate PO chains with a narrow molecular weight distribution [21,44].…”

Preparation of Pyridylamido Hafnium Complexes for Coordinative Chain Transfer Polymerization

“…In other catalysis [performed with Pd complexes constructed via N-heterocyclic carbene (NHC) ligands], the influence of substituents at the 2,6-position in aryl-N moieties is substantial, and derivatization of the NHC ligand has been carried out by replacing common 2,6-diisopropylphenyl-N parts with 2,6-di(3-pentyl)phenyl-N and 2,6-di(3-heptyl)phenyl-N moieties [30,31]. Much research has also been performed on I [32][33][34][35][36][37][38], and the synthesis of its analogs with the aim to improve the catalytic performance deserves attention [7,29,[39][40][41][42]. Subtle change in the ligand framework sometimes results in dramatic improvement in the polymerization performance and, hence, modification of the substituents has been a main research theme in the development of postmetallocecenes [43][44][45][46][47][48][49].…”

“…With the expectation to find a long-lived catalyst through blockage of such a deactivation process, a series of derivatives was prepared in this work by replacement of the 2,6-diisopropylphenylamido part in I with various arylamido 2,6-R 2 C 6 H 3 N-moieties (R = cycloheptyl, cyclohexyl, cyclopentyl, 3-pentyl, ethyl, or Ph). Previously, it has been observed that such a σ-bond metathesis reaction can be blocked by replacing the 2,6-diisopropylphenylamido part with a 2,6-diethylphenylamido moiety in related pincer Hf complexes [29]. In other catalysis [performed with Pd complexes constructed via N-heterocyclic carbene (NHC) ligands], the influence of substituents at the 2,6-position in aryl-N moieties is substantial, and derivatization of the NHC ligand has been carried out by replacing common 2,6-diisopropylphenyl-N parts with 2,6-di(3-pentyl)phenyl-N and 2,6-di(3-heptyl)phenyl-N moieties [30,31].…”