Synthesis and characterization of chromium complexes 2-Me₄CpC₆H₄CH₂(R)NHCrCl₂ and their catalytic properties in ethylene homo- and co-polymerization

Abstract

New half-metallocene chromium complexes with a coordinated secondary amine side-arm were synthesized and studied as catalysts for olefin polymerization.

Controlling Polyethylene Molecular Weights and Distributions Using Chromium Complexes Supported by SNN-Tridentate Ligands

“…Therefore, the development of tunable catalytic systems that could produce different polyethylenes is highly desirable but challenging. , One of the industrially most relevant catalyst is the chromium-based Phillips catalyst (CrO x /SiO 2 ). − Discovered in 1951 by Hogan and Banks at Phillips Petroleum, this heterogeneous catalyst allows the manufacture of one-third of the high-density polyethylene (HDPE) commercialized, which is the most widely used polymer . Although the Phillips catalyst has been studied for over 70 years by both academic and industrial scientists, the nature of the initiation process, the coordination environment and the oxidation state of the metal in the active species, and the catalytic mechanism remain a hot and sometimes controversial topic. − Furthermore, much effort has been dedicated to the development of well-defined homogeneous Cr-based catalysts, ,− that are more amenable to detailed spectroscopic and structural studies than heterogeneous catalysts. In particular, multidentate ligands containing N, O, S, and/or P donor atoms have allowed a better control of the metal coordination sphere and a fine-tuning of its stereochemical features toward improved catalytic properties .…”

Replacement of the Common Chromium Source CrCl3(thf)3 with Well-Defined [CrCl2(μ-Cl)(thf)2]2

“…The catalyst [iPrN{P(C 6 H 4 -p-Si(nBu) 3 ) 2 } 2 CrCl 2 ] + [B(C 6 F 5 ) 4 ] − , prepared according to Scheme 1 using CrCl 3 (thf) 3 , which was prepared via the evacuation step, provided extremely high activity (~5000 kg/g-Cr/h). In contrast, the catalyst prepared using either the commercial source of CrCl 3 (thf) 3 or the one prepared according to the reported method without the evacuation step did not exhibit such a high activity (~3000 kg/g-Cr/h), and there was some amount of methylcyclohexane-insoluble fraction when ligand iPrN{P(C 6 H 4 -p-Si(nBu) 3 ) 2 } 2 was reacted with [(CH 3 CN) 4 CrCl 2 ] + [B(C 6 F 5 ) 4 ] − . The insoluble fraction was negligible when CrCl 3 (thf) 3 , which was prepared via the evacuation step, was used as the starting material.…”

“…The bond distances between Cr and terminal-Cl (2.277 and 2.289 Å) were shorter than that between Cr and bridge-Cl (2.362 Å) as well as the Cr-Cl distances (3.299, 3.318, and 3.352 Å) observed for mer-CrCl3(thf)3, whose structure has been previously revealed using a single crystal obtained was isolated by precipitation in CH 3 CN at −30 • C, the precipitate was not composed of good-quality crystals; thus, X-ray crystallography could not be used for characterization. We crosschecked the tentatively assigned structure of [(CH 3 CN) 4 CrCl 2 ] + [B(C 6 F 5 ) 4 ] − by counting the number of CH 3 CN molecules per each Cr atom through the analysis of integration values in the 1 H-NMR spectra recorded using THF-d 8 with 9-methylanthracene as an internal standard. For the product obtained using CrCl 3 (thf) 3 prepared via the evacuation step, the number of CH 3 CN per Cr was in good agreement with the expected value of 4 (4.1, 3.8, or 4.0).…”

“…CrCl 3 (thf) 3 has been widely used as a starting material for the synthesis of organometallic and coordination compounds of Cr [1][2][3][4][5][6][7][8][9][10]. Its preparation method was reported 60 years ago; anhydrous CrCl 3 , which is insoluble in organic solvents as well as in water, was extracted with THF by the aid of Zn dust using Soxhlet apparatus [11][12][13].…”

A tridentate phenoxy-phosphine (POP) divalent chromium complex and its reactivities in olefin polymerization

“…This represents a rare example of limited Cr catalysts which are known to copolymerize α-olefins with ethylene. 47,[75][76][77][78] End group analysis by 1 H NMR shows the presence of various olefinic end groups (vinyl, vinylidene, and 1,2-disubstituted olefinic) (Fig. S20-S23 †).…”