Very Large Cooperative Effects in Heterobimetallic Titanium-Chromium Catalysts for Ethylene Polymerization/Copolymerization

Abstract

The heterobimetallic complexes, (η(5)-indenyl)[1-Me2Si((t)BuN)TiCl2]-3-CnH2n-[N,N-bis(2-(ethylthio)ethyl)amine]CrCl3 (n = 0, Ti-C0-Cr(SNS); n = 2, Ti-C2-Cr(SNS); n = 6, Ti-C6-Cr(SNS)), (η(5)-indenyl)[1-Me2Si((t)BuN)TiCl2]-3-C2H4-[N,N-bis((o-OMe-C6H4)2P)amine]CrCl3 (Ti-C2-Cr(PNP)), and (η(5)-indenyl)[1-Me2Si((t)BuN)TiCl2]-3-C2H4-[N,N-bis((diethylamine)ethyl)-amine]CrCl3 (Ti-C2-Cr(NNN)), are synthesized, fully characterized, and employed as olefin polymerization catalysts. With ethylene as the feed and MAO as cocatalyst/activator, SNS-based complexes Ti-C0-Cr(SNS), Ti-C2-Cr(SNS), and Ti-C6-Cr(SNS) afford linear low-density polyethylenes (LLDPEs) with exclusive n-butyl branches (6.8-25.8 branches/1000 C), while under identical polymerization conditions Ti-C2-Cr(PNP) and Ti-C2-Cr(NNN) produce polyethylenes with heterogeneous branching (C2, C4, and C≥6) or negligible branching, respectively. Under identical ethylene polymerization conditions, Ti-C0-Cr(SNS) produces polyethylenes with higher activity (4.5× and 6.1×, respectively), Mn (1.3× and 1.8×, respectively), and branch density (1.4× and 3.8×, respectively), than Ti-C2-Cr(SNS) and Ti-C6-Cr(SNS). Versus a CGC(Et)Ti + SNSCr tandem catalyst, Ti-C0-Cr(SNS) yields polyethylene with somewhat lower activity, but with 22.6× higher Mn and 4.0× greater branching density under identical conditions. In ethylene +1-pentene competition experiments, Ti-C0-Cr(SNS) yields 5.5% n-propyl branches and 94.5% n-butyl branches at [1-pentene] = 0.1 M, and the estimated effective local concentration of 1-hexene is ∼8.6 M. In contrast, the tandem CGC(Et)Ti + SNSCr system yields 91.0% n-propyl branches under identical reaction conditions. The homopolymerization and 1-pentene competition results argue that close Ti···Cr spatial proximity together with weak C-H···Ti and C-H···S interactions significantly influence relative 1-hexene enchainment and chain transfer rates, supported by DFT computation, and that such effects are conversion insensitive but cocatalyst and solvent sensitive.

Syntheses, structures, and properties of Co(II)/Zn(II) mixed-ligand coordination polymers based on 4-[(3,5-dinitrobenzoyl)amino]benzoic acid and 1,4-bis(1-imidazolyl) benzene

“…We have successfully synthesized two coordination supramolecular complexes, namely, [Co(dnbab) 2 (bimb)](H 2 O) 4 (1) and [Zn (dnbab) 2 (bimb)](H 2 O) 5 (2), using an amide-linked carboxylic ligand and a bidentate N-donor ligands under solvothermal conditions. Complexes 1 and 2 are isostructures and each displays a 1D zigzag chain.…”

“…Supramolecular self-assemblies [1] are eliciting considerable attention from researchers, not only because of their tremendous potential applications in gas storage [2], ion-exchange [3], luminescence [4], catalysis [5], magnetism [6] and electrochemistry [7], but also because of their intriguing variety of architecture and topologies [8]. In general, coordination supramolecular complexes can be assembled through two major chemical processes, namely, coordination chemistry and supramolecular chemistry [9], which are characterized as fundamental interactions at the molecular level.…”

Polymerization of ethylene using a series of binuclear and a mononuclear Ni (II)‐based catalysts

“…Albeit mechanisms of these types of catalysts are still in ambiguous due to complexity of theirs function through the polymerization; however, there is two main supposed structure include cooperation and independent effect of active centers. Distance between the active centers and the presence of weakly basic substituents are two important factors that can control the cooperative effect of metal centers in olefin homo‐ and copolymerization of polar monomers, especially . According to the literatures, multinuclear catalysts have shown various results in comparison to correspond mononuclear catalysts such as both lower and higher catalyst activity, bimodal to wide range molecular weights distribution, isotacticity, and microstructures …”

Investigation of Bimetallic Nickel Catalysts in Catalyst‐Transfer Polymerization of π‐Conjugated Polymers

“…[23] Discussion on the critical factors that enable controlled polymerizations in CTP has been thoroughly detailed in reviews. [24][25][26] Interestingly, one area that has not been relatively explored at all in CTP, and may be useful, is multimetallic cooperative catalysis.Multimetallic cooperative catalysts have been employed to improve the quality of olefin [27][28][29] and epoxide [30] polymers (Figure 1). In these studies, the geometry of the bimetallic catalysts and the proximity of the metal centers were suggested to have critical influence on catalytic rates, branching, chain transfer, and control over molecular weight and dispersity.…”