Targeting polyethylene waxes: 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridylnickel halides and their use as catalysts for ethylene polymerization

Abstract

A series of 9-(2-cycloalkylphenylimino)-5,6,7,8-tetrahydrocycloheptapyridine derivatives (L1-L3) was synthesized, and reacted with nickel halides to form their corresponding nickel complexes (bromide: Ni1-Ni3; chloride: Ni4-Ni6). All organic compounds and nickel complexes were well characterized. The structure of a representative complex Ni1 was determined by a single crystal X-ray study, revealing a distorted trigonal bipyramidal geometry at the nickel centre. Upon activation with either modified methylaluminoxane (MMAO) or diethylaluminium chloride (Et 2 AlCl), all nickel complexes showed high activities toward ethylene polymerization. The obtained polymers were confirmed to be polyethylene waxes with low molecular weights (in the range of 1.83 to 6.78 kg mol À1 ) and narrow polydispersity (PDI:1.38-1.78); moreover, the obtained polyethylenes were highly branched ones. These polyethylene waxes have potential application as functional adducts of lubricants or pour-point depressants.

Recent Progress in Ethylene Polymerization Catalyzed by Ni and Pd Catalysts

“…Inspired by iminopyridine ligands, ligands containing cyclic imine components (e.g., Figure ) have recently been widely studied in terms of backbone geometry and ring tension but just in the case of Ni catalysts , , . This series of catalysts exhibited moderate activities below 10 7 g of PE (mol of Ni) –1 h –1 .…”

“…Interestingly, there are cases in which particular sizes of the substituents on the N ‐aryl ligand are needed in order to obtain high activities ,. [36c] It is possible that the unique structures of these catalysts facilitate chain propagation to some extent.…”

“…An α‐diamine catalyst with a distorted chelate ring shows that the correct size of the substituent around the metal can generate a polymer with high molecular weight whereas bulky groups may block equatorial coordination sites A similar result with an N–N chelating catalyst was found by Sun's group. [36c] Certainly, there are still cases in which a bulky substituent on the backbone has a minor effect on molecular weight for N–N chelating catalysts. [30c]…”

“…Intriguingly, some catalysts afford PE with very similar molecular weights at varied reaction times. [27n], [36b] This may become a new method for controlling the molecular weight of polymer. Some catalytic systems, however, show that the coexistence of more than one type of active species can result in polymers with broad or bimodal[36c] distributions of molecular weight, which are influenced by the electronic or steric[36c] environments of the active species.…”

Recent advances in Ni-mediated ethylene chain growth: Nimine-donor ligand effects on catalytic activity, thermal stability and oligo-/polymer structure

“…< Figure 22> The impact of strain within the fused cycloalkyl ring of the N,N-ligand framework has been thoroughly investigated and shown to affect the catalytic performance of the nickel pre-catalyst [107][108][109][110][111]. For example, the nickel complexes, 42, chelated by a 9-aryliminocycloheptapyridine N^N ligand have been synthesized and assessed for their ability to promote ethylene enchainment (Fig.…”