Enhancing Ethylene Polymerization of NNN-Cobalt(II) Precatalysts Adorned with a Fluoro-substituent

Abstract

Unsymmetrical 2-(1-(2,4-dibenzhydryl-6-fluorophenylimino)ethyl)-6-(1-alkylphenyl-imino)ethyl)pyridine compounds (Ar = 2,6-Me 2 C 6 H 3 in L1 ; 2,6-Et 2 C 6 H 3 in L2 ; 2,6- i Pr 2 C 6 H 3 in L3 ; 2,4,6-Me 3 C 6 H 2 in L4 ; 2,6-Et 2 -4-Me-C 6 H 2 in L5 ) were prepared and characterized. The treatment of CoCl 2 with the compounds L1 – L5 afforded the corresponding cobalt complexes Co1 – Co5 in excellent yields. The molecular structures of Co3 and Co4 were determined by single-crystal X-ray diffraction, revealing the distorted-square-pyramidal geometry with three nitrogen atoms and two chlorine atoms around the cobalt center. Compared with previous bis(imino)pyridylcobalt analogues, all of the cobalt precatalysts displayed exceptionally higher activities toward ethylene polymerization with 1.32 × 10 7 g (PE) mol –1 (Co) h –1 at 60 °C in the presence of a co-catalyst MAO or MMAO. These cobalt catalysts produced highly linear polyethylene (PE) waxes with vinyl end groups and low molecular weight ( M w up to 8.23 kg mol –1 ) along with a relatively lower melting point (all-round T m s < 128 °C). The narrow dispersity of resultant polyethylenes indicated the single-site active species of the catalytic system.

Cobalt Catalysts Bearingortho‐(4,4′‐Dichlorobenzhydryl) Substituents and Their Use in Generating Narrowly Dispersed Polyethylene of High Linearity

“…All complexes provided satisfactory microanalytical data that were in full support of compositions based on ( N,N,N′ )CoCl 2 . In the FT‐IR spectra of Co1 − Co6 , absorption bands seen at between 1616 and 1621 cm −1 can be assigned to coordinated imine groups [50–55] . By comparison in the free ligands L1 − L6 , the corresponding v (C=N) bands were observed at higher wavenumber (typically between 1630 and 1640 cm −1 ).…”

“…In the FT-IR spectra of Co1À Co6, absorption bands seen at between 1616 and 1621 cm À 1 can be assigned to coordinated imine groups. [50][51][52][53][54][55] By comparison in the free ligands L1À L6, the corresponding v (C=N) bands were observed at higher wavenumber (typically between 1630 and 1640 cm À 1 ).…”

Exploring fluoride effects in sterically enhanced cobalt ethylene polymerisation catalysts; a combined experimental and DFT study

“…A-G, Chart 1). 5,14,15,[23][24][25][26][27][28][29] For example, for symmetrical A, bearing benzhydryl groups at the 2-and 6-positions, both the iron and cobalt species were inactive for ethylene polymerisation. It was proposed that the huge steric hindrance imparted on both sides of the metal hinders the coordination of ethylene, which makes the polymer chain difficult to propagate.…”

From tetramerization to oligomerization/polymerization of ethylene by dinuclear pyridyl‐imine Co‐ and Ni‐based catalysts

“…[4][5][6] On the other way, there are many reports on late transition metal (LTM) complexes as an interesting class of catalysts due to feasibly preparation and modification, capability of production of a wide range of polyethylene/oligoethylene, intriguing and unusual behavior (e.g., chain-walking olefin polymerization). 1,[7][8][9][10][11][12][13][14][15][16][17][18][19][20][21] Multinuclear LTM catalysts along with their mononuclear analogs are widely used for preparation of ethylene homopolymers/copolymers and oligomers. [22][23][24] In the most cases, not only higher catalytic activity has been observed but also metal-metal cooperative effect in terms of greater selectivity in products has been reported.…”

“…These structures are massively various and belonged to different generation of catalyst systems 4–6 . On the other way, there are many reports on late transition metal (LTM) complexes as an interesting class of catalysts due to feasibly preparation and modification, capability of production of a wide range of polyethylene/oligoethylene, intriguing and unusual behavior (e.g., chain‐walking olefin polymerization) 1,7–21 …”