Aldehyde End-Capped Degradable Polyethylenes From Hydrogen-Controlled Ethylene/CO Copolymerization.

To access degradable polyolefin plastic, non-alternating copolymerization of ethylene (E) and carbon monoxide (CO) for producing polyethylene (PE) with in-chain ketones is particularly appealing; however, it still presents significant challenges such as molecular weight modulation (hydrogen response) and chain endgroup control (functional terminal). In this study, we achieved hydrogen-controlled E/CO non-alternating copolymerization using late transition metal catalysts. This process results in linear PEs containing the desired non-alternating in-chain keto groups (1.

Accessing Functionalized Ultra-High Molecular Weight Poly(α-olefin)s via Hafnium-Mediated Highly Isospecific Copolymerization.

Inspired by the favorable impact of heteroatom-containing groups in phenoxy-imine titanium and late transition metal catalysts, a series of novel pyridylamido hafnium catalysts bearing ─OMe (Cat-OMe), ─CF (Cat-CF), and ─CF (Cat-CF) substituents are designed and synthesized. Together with the established hafnium catalysts Cat-H and Cat-iPr by Dow/Symyx, these catalysts are applied in the polymerization of α-olefins, including 1-hexene, 1-octene, and 4M1P, as well as in the copolymerization of these α-olefins with a specifically designed polar monomer. The enhancement of polymer molecular weight derived from catalyst modification and the incorporation of polar monomers is discussed in detail.

Aqueous Coordination-Insertion Copolymerization for Producing High Molecular Weight Polar Polyolefins.

Hydrocarbons, when used as the medium for transition metal catalyzed organic reactions and olefin (co-)polymerization, are ubiquitous. Environmentally friendly water is highly attractive and long-sought, but is greatly challenging as coordination-insertion copolymerization reaction medium of olefin and polar monomers. Unfavorable interactions from both water and polar monomer usually lead to either catalyst deactivation or the formation of low-molecular-weight polymers.

Photodegradable polar-functionalized polyethylenes.

The degradation of plastics has attracted much attention from the global community. Polyethylenes (PEs), as the most abundant synthetic plastics, are most frequently studied. PE is non-degradable and non-polar because of the sole presence of the pure hydrocarbon components.

Cyclic Olefin Terpolymers with High Refractive Index and High Optical Transparency.

Cyclic olefin copolymer (COC) is one of the most promising optical materials; however, the brittle COC suffers from issues including a low refractive index. In this contribution, by the introduction of high refractive index comonomers including phenoxy substituted α-olefin (COAr), -tolylthio substituted α-olefin (CSAr) and carbazolyl substituted α-olefins (CNAr, CNAr, and CNAr), the zirconocene mediated terpolymerization of ethylene (E) and tetracyclododecene (TCD) produces the preferred E-TCD-CNAr ( = 2, 3, and 4) cyclic olefin terpolymers (COT) with tunable compositions (TCD: 11.5- 35.

Polar-Functionalized Polyethylenes Enabled by Palladium-Catalyzed Copolymerization of Ethylene and Butadiene/Bio-Based Alcohol-Derived Monomers.

Polar-functionalized polyolefins are high-value materials with improved properties. However, their feedstocks generally come from non-renewable fossil products; thus, it requires the development of renewable bio-based monomers to produce functionalized polyolefins. In this contribution, via the Pd-catalyzed telomerization of 1,3-butadiene and three types of bio-based alcohols (furfuryl alcohol, tetrahydrofurfuryl alcohol, and solketal), 2,7-octadienyl ether monomers including , and were synthesized and characterized, respectively.

Unsymmetrical Strategy on α-Diimine Nickel and Palladium Mediated Ethylene (Co)Polymerizations.

Among various catalyst design strategies used in the α-diimine nickel(II) and palladium(II) catalyst systems, the unsymmetrical strategy is an effective and widely utilized method. In this contribution, unsymmetrical nickel and palladium α-diimine catalysts ( and ) derived from the dibenzobarrelene backbone were constructed via the combination of pentiptycenyl and diisopropylphenyl substituents, and investigated toward ethylene (co)polymerization. Both of these catalysts were capable of polymerizing ethylene in a broad temperature range of 0-120 °C, in which could maintain activity in the level of 10 g mol h even at 120 °C.

Suppression of Chain Transfer at High Temperature in Catalytic Olefin Polymerization.

Living polymerization by suppressing chain transfer is a very useful method for achieving precise molecular weight and structure control. However, the suppression of chain transfer at high temperatures is extremely challenging in any catalytic polymerization. This has been a severe limitation for catalytic olefin polymerization, which is one of the most important chemical reactions.

Selective branch formation in ethylene polymerization to access precise ethylene-propylene copolymers.

Polyolefins with branches produced by ethylene alone via chain walking are highly desired in industry. Selective branch formation from uncontrolled chain walking is a long-standing challenge to generate exclusively branched polyolefins, however. Here we report such desirable microstructures in ethylene polymerization by using sterically constrained α-diimine nickel(II)/palladium(II) catalysts at 30 °C-90 °C that fall into industrial conditions.

Fluorinated α-Diimine Nickel Mediated Ethylene (Co)Polymerization.

Fluorine substituents in transition metal catalysts are of great importance in olefin polymerization catalysis; however, the comprehensive effect of fluorine substituents is elusive in seminal late transition metal α-diimine catalytic system. In this contribution, fluorine substituents at various positions (ortho-, meta-, and para-F) and with different numbers (F ; n=0, 1, 2, 3, 5) were installed into the well-defined N-terphenyl amine and thus were studied for the first time in the nickel α-diimine promoted ethylene polymerization and copolymerization with polar monomers. The position of the fluorine substituent was particularly crucial in these polymerization reactions in terms of catalytic activity, polymer molecular weight, branching density, and incorporation of polar monomer, and thus a picture on the fluorine effect was given.

Efficient Suppression of Chain Transfer and Branching via C -Type Shielding in a Neutral Nickel(II) Catalyst.

An effective shielding of both apical positions of a neutral Ni active site is achieved by dibenzosuberyl groups, both attached via the same donors' N-aryl group in a C -type arrangement. The key aniline building block is accessible in a single step from commercially available dibenzosuberol. This shielding approach suppresses chain transfer and branch formation to such an extent that ultrahigh molecular weight polyethylenes (5×10  g mol ) are accessible, with a strictly linear microstructure (<0.

Ultrahigh Branching of Main-Chain-Functionalized Polyethylenes by Inverted Insertion Selectivity.

Branched polyolefin microstructures resulting from so-called "chain walking" are a fascinating feature of late transition metal catalysts; however, to date it has not been demonstrated how desirable branched polyolefin microstructures can be generated thereby. We demonstrate how highly branched polyethylenes with methyl branches (220 Me/1000 C) exclusively and very high molecular weights (ca. 10  g mol ), reaching the branch density and microstructure of commercial ethylene-propylene elastomers, can be generated from ethylene alone.

Systematic studies on dibenzhydryl and pentiptycenyl substituted pyridine-imine nickel(ii) mediated ethylene polymerization.

As the analogues of classical α-diimine nickel catalysts, pyridine-imine nickel catalysts are of great interest for olefin polymerization to produce low molecular weight and branched polyethylenes. In this contribution, pyridine-imine nickel complexes Ni1-Ni4 bearing dibenzhydryl- and pentiptycenyl-N-aryl substituents and H- and Me-imine backbones were synthesized and systematically studied for ethylene polymerization. X-ray diffraction studies revealed that Ni1, Ni2 and Ni4 adopted a monoligated/binuclear structure, while Ni3 was found to adopt a monoligated/mononuclear structure, which differed from the bisligated/mononuclear mode reported previously.

Influence of initiating groups on phosphino-phenolate nickel catalyzed ethylene (co)polymerization.

In transition-metal catalyst structures, both the ligand structure and the initiating group are crucial components for olefin polymerization. Compared to numerous studies on tuning the electronic and steric effects of ligands, there is no report on the comprehensive investigation of initiating groups. In this contribution, five different initiating groups including "NiMe", "NiPh", "Ni(allyl)", "Ni(COD)", and "Ni(acac)/AlEt2Cl" were designed and installed into sterically bulky phosphino-phenolate nickel complexes Ni1-Ni5, respectively, which were further tested for ethylene (co)polymerization.

Formation of borata-alkene/iminium zwitterions by ynamine hydroboration.

The ynamine TMP-C[triple bond, length as m-dash]C-CH3 adds HB(C6F5)2 to give the unsaturated C2-bridged N/B FLP 5. Compound 5 shows the structural data indicating a marked participation of the zwitterionic mesomeric borata-alkene/iminium form. It splits dihydrogen at r.

Zirconocene mediated acetylboron chemistry.

The methyl zirconocene complex Cp*2Zr(Me)OMes reacts with H3C-B(C6F5)2 and CO to give the respective acetyl(methyl)borate Zr complex. Cp*2Zr(H)OMes reacts with H3C-B(C6F5)2 and CO to give the respective acetyl(hydrido)borate Zr product, admixed with a minor amount of the formyl(methyl)borate Zr complex isomer. Prolonged exposure to CO under close to ambient conditions results in the uptake of another CO equivalent to yield the corresponding borata-β-lactone zirconocene product.

A hydroboration route to geminal P/B frustrated Lewis pairs with a bulky secondary phosphane component and their reaction with carbon dioxide.

The secondary aryl-P(H) phosphanyl substituted tert-butylacetylenes 7a,b (aryl: Mes or Mes*) undergo hydroboration with [HB(CF)] to give the geminal vinylidene-bridged P/B Lewis pairs 8a,b. The treatment of 8a,b with benzonitrile, N-sulfinylaniline, and phenyl isothiocyanate, respectively, gives the addition products 12a,b, 13a,b, and 14 with proton transfer from the phosphorus to the more basic nitrogen site. The reaction of the FLPs 8a,b with carbon dioxide yields a doubly boron bonded addition product.

CO-Reduction Chemistry: Reaction of a CO-Derived Formylhydridoborate with Carbon Monoxide, with Carbon Dioxide, and with Dihydrogen.

Treatment of the bulky metallocene hydride Cp*Zr(H)OMes (Cp* = pentamethylcyclopentadienyl, Mes = mesityl) with Piers' borane [HB(CF)] and carbon monoxide (CO) gave the formylhydridoborate complex [Zr]-O═CH-BH(CF) ([Zr] = Cp*Zr-OMes). From the dynamic NMR behavior, its endergonic equilibration with the [Zr]-O-CH-B(CF) isomer was deduced, which showed typical reactions of an oxygen/boron frustrated Lewis pair. It was trapped with CO to give an O-[Zr] bonded borata-β-lactone.

Direct Synthesis of Telechelic Polyethylene by Selective Insertion Polymerization.

A single-step route to telechelic polyethylene (PE) is enabled by selective insertion polymerization. Pd -catalyzed copolymerization of ethylene and 2-vinylfuran (VF) generates α,ω-di-furan telechelic polyethylene. Orthogonally reactive exclusively in-chain anhydride groups are formed by terpolymerization with carbic anhydride.

Direct Synthesis of Imidazolium-Functional Polyethylene by Insertion Copolymerization.

Cationic imidazolium-functionalized polyethylene is accessible by insertion copolymerization of ethylene and allyl imidazolium tetrafluoroborate (AIm-BF4 ) with phosphinesulfonato palladium(II) catalyst precursors. Imidazolium-substituted repeat units are incorporated into the main chain and the initiating saturated chain end of the linear polymers, rather than the terminating unsaturated chain end. The counterion of the allyl imidazolium monomer is decisive, with the chloride analogue (AIm-Cl) no polymerization is observed.

Insertion Homo- and Copolymerization of Diallyl Ether.

The previously unresolved issue of polymerization of allyl monomers CH2 CHCH2 X is overcome by a palladium-catalyzed insertion polymerization of diallyl ether as a monomer. An enhanced 2,1-insertion of diallyl ether as compared to mono-allyl ether retards the formation of an unreactive five-membered cyclic O-chelate (after 1,2-insertion) that otherwise hinders further polymerization, and also enhances incorporation in ethylene polymers (20.4 mol %).

Suppression of chain transfer in catalytic acrylate polymerization via rapid and selective secondary insertion.

In catalytic copolymerization, undesired chain transfer after incorporation of a polar vinyl monomer is a fundamental problem. We show an approach to overcome this problem by a fast consecutive insertion. The second double bond of acrylic anhydride rapidly inserts intramolecularly to regio- and stereoselectively form a cyclic repeat unit and a primary alkyl favorable for chain growth (>96%).

Insights into functional-group-tolerant polymerization catalysis with phosphine-sulfonamide palladium(II) complexes.

Two series of cationic palladium(II) methyl complexes {[(2-MeOC6 H4 )2 PC6 H4 SO2 NHC6 H3 (2,6-R(1) ,R(2) )]PdMe}2 [A]2 ((X) 1(+) -A: R(1) =R(2) =H: (H) 1(+) -A; R(1) =R(2) =CH(CH3 )2 : (DIPP) 1(+) -A; R(1) =H, R(2) =CF3 : (CF3) 1(+) -A; A=BF4 or SbF6 ) and neutral palladium(II) methyl complexes {[(2-MeOC6 H4 )2 PC6 H4 SO2 NC6 H3 (2,6-R(1) ,R(2) )]PdMe(L)} ((X) 1-acetone: L=acetone; (X) 1-dmso: L=dimethyl sulfoxide; (X) 1-pyr: L=pyridine) chelated by a phosphine-sulfonamide were synthesized and fully characterized. Stoichiometric insertion of methyl acrylate (MA) into all complexes revealed that a 2,1 regiochemistry dominates in the first insertion of MA. Subsequently, for the cationic complexes (X) 1(+) -A, β-H elimination from the 2,1-insertion product (X) 2(+) -AMA-2,1 is overwhelmingly favored over a second MA insertion to yield two major products (X) 4(+) -AMA-1,2 and (X) 5(+) -AMA .

Intramolecular C-H bond activation induced by a scandium terminal imido complex.

A CpPN-based scandium terminal imido complex was isolated, which could induce the intramolecular C-H bond activation of a phenyl group even at room temperature.