Synthesis and characterization of chromium complexes 2-Me 4 CpC 6 H 4 CH 2 (R)NHCrCl 2 and their catalytic properties in ethylene homo- and co-polymerization

Tingting Song, Xin Tao, Xiaobo Tong, Ning Liu, Wei Gao, Xiaoyue Mu, Ying Mu

Research output: Contribution to journalArticlepeer-review

Abstract

A series of new half-sandwich secondary amine-coordinated dichlorochromium complexes chelated by 2-(tetramethylcyclopentadienyl)benzylamine ligands, 2-Me 4 CpC 6 H 4 CH 2 (R)NHCrCl 2 [R = i Pr (1), Cy (2), Ph (3), 4-MePh (4), 2,6-Me 2 Ph (5), 2,6-Et 2 Ph (6)], have been synthesized from the reactions of CrCl 3 (THF) 3 with the dilithium salts of the corresponding ligands in THF, followed by the addition of 1/2 eq. of H 2 O to the reaction mixtures. The isolated yields of the chromium complexes were found to increase with the increase in the amount of H 2 O introduced and reach the highest values (66-76%) when 1/2 eq. of H 2 O is added. Attempts to isolate the 2-(tetramethylcyclopentadienyl)benzylamidochromium complexes, 2-Me 4 CpC 6 H 4 CH 2 (R)NCrCl, were not successful. The new dichlorochromium complexes were characterized by IR, 1 H NMR, EPR, and UV/Vis spectroscopy and elemental analyses, and the molecular structures of complexes 1, 5 and 6 were determined by X-ray crystallography. The X-ray crystallographic analysis reveals that these chromium complexes possess a three-legged piano-stool geometry with the amine N atom in a mitered six-membered chelating ring and the two chloride atoms as the legs. Upon activation with AlR 3 and Ph 3 CB(C 6 F 5 ) 4 , complexes 1-6 exhibit reasonable catalytic activity for ethylene polymerization and copolymerization with 1-hexene, producing polyethylenes with moderate to high molecular weights and poly(ethylene-co-1-hexene)s with moderate comonomer incorporation which are typical linear low-density polyethylenes (LLDPE). Complex 4 was found to show higher catalytic activity for ethylene homo- and co-polymerization than other complexes under similar conditions, while complex 3 produced poly(ethylene-co-1-hexene)s with the highest comonomer incorporation.

Original languageEnglish
Pages (from-to)4912-4920
Number of pages9
JournalDalton Transactions
Volume48
Issue number15
DOIs
Publication statusPublished - 2019
Externally publishedYes

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