Insertion Polymerization of Divinyl Formal

Copolymerization of ethylene and divinyl formal by [{κ²-<i>P</i>,<i>O-</i>(2-MeOC₆H₄)₂PC₆H₄SO₃}­PdMe­(dmso)] (<b>1)</b> by a coordination–insertion mechanism affords highly linear polyethylenes with a high (12.5 mol %) incorporation of divinyl formal. This significantly exceeds the thus far relatively low incorporation (6.9 mol %) and activity with vinyl ether monomer in insertion polymerization. The resulting ethylene–divinyl formal copolymers exclusively (>98%) contain five-membered (<i>trans</i>-1,3-dioxolane) and six-membered (<i>cis</i>-/<i>trans</i>-1,3-dioxane) cyclic acetal units in the main chain, and also in the initiating ends of this functionalized polyethylene. Comprehensive NMR analysis of the microstructure of these copolymers revealed that under pressure reactor conditions consecutive 2,1–1,2-insertion of divinyl formal into a Pd–H bond is preferred, but consecutive 1,2–1,2-insertion of divinyl formal into more bulky Pd–alkyls (growing polymer chain) is favored. Moreover, homopolymerization of divinyl formal yielded a non-cross-linking poly­(divinyl formal) with degrees of polymerization of DP_n ≈ 26

Short-Chain Branched Polar-Functionalized Linear Polyethylene via “Tandem Catalysis”

Cationic Pd^II complex <b>1</b> chelated by an <i>N</i>-fixed phosphine sultam has been synthesized and structurally characterized. Exposure of <b>1</b> to ethylene resulted in the formation of short-chain olefins (1-butene: 2-butene: 1-hexene: 1-octene = 86:7:6:1) with a high catalytic activity of 10⁵ mol_E mol_Pd^–1 h^–1. By combination of <b>1</b> and one of the well-known phosphinesulfonato Pd^II catalyst precursors <b>2</b>–<b>5</b>, linear polyethylenes containing methyl, ethyl, and <i>n</i>-butyl branches of up to 100 per 1000 C were generated from the polymerization of ethylene alone in a “tandem catalysis” one-pot approach. In further exploitation of this concept, linear polyethylenes with both various short-chain branches and a choice of different polar functional groups incorporated into the main chain were obtained for the first time from the copolymerization of ethylene and polar vinyl monomers (methyl acrylate, <i>N</i>-isopropylacrylamide, methyl vinyl sulfone, acrylonitrile, ethyl vinyl ether, vinyl acetate, and allyl bromide). All these apolar and polar branches are incorporated into the linear polyethylene backbones to varying degrees, while the type of initiating and terminating chain ends of the resulting polyethylenes depends significantly on the nature of polar vinyl monomer

Short-Chain Branched Polar-Functionalized Linear Polyethylene via “Tandem Catalysis”

Cationic Pd^II complex <b>1</b> chelated by an <i>N</i>-fixed phosphine sultam has been synthesized and structurally characterized. Exposure of <b>1</b> to ethylene resulted in the formation of short-chain olefins (1-butene: 2-butene: 1-hexene: 1-octene = 86:7:6:1) with a high catalytic activity of 10⁵ mol_E mol_Pd^–1 h^–1. By combination of <b>1</b> and one of the well-known phosphinesulfonato Pd^II catalyst precursors <b>2</b>–<b>5</b>, linear polyethylenes containing methyl, ethyl, and <i>n</i>-butyl branches of up to 100 per 1000 C were generated from the polymerization of ethylene alone in a “tandem catalysis” one-pot approach. In further exploitation of this concept, linear polyethylenes with both various short-chain branches and a choice of different polar functional groups incorporated into the main chain were obtained for the first time from the copolymerization of ethylene and polar vinyl monomers (methyl acrylate, <i>N</i>-isopropylacrylamide, methyl vinyl sulfone, acrylonitrile, ethyl vinyl ether, vinyl acetate, and allyl bromide). All these apolar and polar branches are incorporated into the linear polyethylene backbones to varying degrees, while the type of initiating and terminating chain ends of the resulting polyethylenes depends significantly on the nature of polar vinyl monomer

Heterocycle-Substituted Phosphinesulfonato Palladium(II) Complexes for Insertion Copolymerization of Methyl Acrylate

A family of heterocycle-substituted binuclear phosphinesulfonato Pd­(II) complexes {[R₂<i>P</i>(C₆H₄SO₂<i>O</i>)]­PdMeClLi­(dmso)}₂ (<b>1a</b>–<b>d-LiCl-dmso</b>: <b>1a-LiCl-dmso</b>, R = 2-furyl; <b>1b-LiCl-dmso</b>, R = 2-thienyl; <b>1c-LiCl-dmso</b>, R = 2-(<i>N</i>-methyl)­pyrrolyl; <b>1d-LiCl-dmso</b>, R = 2-benzofuryl) was synthesized, and the solid-state structures of <b>1a–c-LiCl-dmso</b> were determined, which revealed various modes of bridging between the two metal fragments. <b>1a</b>–<b>d-LiCl-dmso</b> further generated either the mononuclear Pd­(II) complexes {[κ²<i>P</i>,<i>O</i>-R₂<i>P</i>(C₆H₄SO₂<i>O</i>)]­PdMe­(pyr)} (<b>1a</b>–<b>d-pyr</b>) by addition of pyridine or the more labile mononuclear Pd­(II) complex {[κ²<i>P</i>,<i>O</i>-(2-thienyl)₂<i>P</i>(C₆H₄SO₂<i>O</i>)]­PdMe­(dmso)} (<b>1b-dmso</b>) by chloride abstraction with AgBF₄. Stoichiometric methyl acrylate (MA) insertion experiments indicated that, in comparison with the other three substituents, the thienyl-substituted Pd­(II) complexes undergo faster insertion of MA in a primary 2,1-fashion, and <b>1b-dmso</b> possesses the fastest insertion rate due to the relative weakly coordinating dmso molecule. All palladium complexes were employed in ethylene polymerization, affording highly linear polyethylene with relatively low molecular weights (<i>M</i>_n = (0.5–7.4) × 10³). In addition, under these pressure reactor conditions, the thienyl motif displays the highest activity (order: <b>1b-dmso</b> > <b>1b-pyr</b> > <b>1a-pyr</b> > <b>1d-pyr</b> > <b>1c-pyr</b> ≫ <b>1a</b>–<b>d-LiCl-dmso</b>). Copolymerization reactions of ethylene and MA further revealed that MA incorporation in the obtained linear copolymers depends moderately on the heterocyclic substituents

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%). This results in significantly enhanced copolymer molecular weights vs monofunctional acrylate monomers

Frustrated Lewis Pair vs Metal–Carbon σ‑Bond Insertion Chemistry at an <i>o</i>‑Phenylene-Bridged Cp₂Zr⁺/PPh₂ System

Methyl anion abstraction from (<i>o</i>-diphenylphosphino)­phenyl­(methyl)­zirconocene by trityl tetrakis­(pentafluorophenyl)­borate gives the <i>o</i>-phenylene-bridged Zr⁺/P system <b>10</b>. It behaves toward a variety of reagents as a typical Zr⁺/P frustrated Lewis pair (FLP). It undergoes cooperative 1,4-addition reactions to some chalcone derivatives and adds in a 1,2-fashion to a variety of organic carbonyls and to several heterocumulenes. The reactive Zr–C σ bond of the FLP <b>10</b> remains intact in these reactions. Complex <b>10</b> splits dihydrogen, but subsequently the Zr–C σ bond is protonolytically cleaved in this case. Only a few special reagents, among them carbon monoxide, undergo the usual insertion reaction into the Zr–C­(aryl) σ-bond of the Zr⁺/P system <b>10</b>

Frustrated Lewis Pair vs Metal–Carbon σ‑Bond Insertion Chemistry at an <i>o</i>‑Phenylene-Bridged Cp₂Zr⁺/PPh₂ System

Methyl anion abstraction from (<i>o</i>-diphenylphosphino)­phenyl­(methyl)­zirconocene by trityl tetrakis­(pentafluorophenyl)­borate gives the <i>o</i>-phenylene-bridged Zr⁺/P system <b>10</b>. It behaves toward a variety of reagents as a typical Zr⁺/P frustrated Lewis pair (FLP). It undergoes cooperative 1,4-addition reactions to some chalcone derivatives and adds in a 1,2-fashion to a variety of organic carbonyls and to several heterocumulenes. The reactive Zr–C σ bond of the FLP <b>10</b> remains intact in these reactions. Complex <b>10</b> splits dihydrogen, but subsequently the Zr–C σ bond is protonolytically cleaved in this case. Only a few special reagents, among them carbon monoxide, undergo the usual insertion reaction into the Zr–C­(aryl) σ-bond of the Zr⁺/P system <b>10</b>

Rare-Earth-Metal Complexes Bearing Phosphazene Ancillary Ligands: Structures and Catalysis toward Highly Trans-1,4-Selective (Co)Polymerizations of Conjugated Dienes

The bis-arylated phosphazene compounds [HN­(PPh₂NAr)₂] (Ar = phenyl (HL¹), 2,6-dimethylphenyl (HL²), 2,6-diisopropylphenyl (HL³)) and the imidodiphosphinate compound HN­(PPh₂O)₂ (HL⁴) have been prepared via the Staudinger reaction. Treatment of the neutral compounds HL¹, HL², and HL³ with Ln­(CH₂SiMe₃)₃(THF)₂ (Ln = Sc, Y, Lu) generated the solvent-free bis­(alkyl) complexes L¹Ln­(CH₂SiMe₃)₂ (Ln = Sc (<b>1a</b>), Y (<b>1b</b>), Lu (<b>1c</b>)), L²Sc­(CH₂SiMe₃)₂ (<b>2a</b>), L³Y­(CH₂SiMe₃)₂ (<b>3b</b>), and L³Lu­(CH₂SiMe₃)₂ (<b>3c</b>), respectively. The reaction between HL⁴ and Y­(CH₂SiMe₃)₃(THF)₂ gave the rare zwitterionic complex <b>4b</b>. Lithiation of the ligand HL¹ by <i>n</i>BuLi followed by a metathesis reaction with Nd­(BH₄)₃(THF)₃ afforded the corresponding complex L¹Nd­(BH₄)₂(THF)₂ (<b>5</b>). Complexes <b>1</b> upon incorporation of [Ph₃C]­[B­(C₆F₅)₄] and Al<i>i</i>Bu₃ led to ternary systems that initiated isoprene polymerization with high activities, among which complex <b>1a</b> was the first example of a scandium catalytic precursor providing trans-1,4-selectivity (90.0%), while the lutetium analogue <b>1c</b> had medium trans-1,4-selectivity (54.3%) and the yttrium complex <b>1b</b> exhibited high cis-1,4-selectivity (76.3%). The ternary system based on the zwitterion <b>4b</b> displayed the highest activity for the isoprene polymerization among these complexes and gave cis-1,4-regularity-enriched polyisoprene (70.6%). Highly stereospecific homopolymerizations of isoprene (trans-1,4-content: 97.0%) and butadiene (trans-1,4-content: 94.0%) were achieved by using the borohydrido complex <b>5</b> upon the activation of dibutylmagnesium. The copolymerization of isoprene and butadiene with <b>1a</b>/[Ph₃C]­[B­(C₆F₅)₄/Al<i>i</i>Bu₃] gave randomly arranged trans-1,4-regulated polybutadiene and polyisoprene sequences. The kinetics study displayed competitive polymerization rates of <i>r</i>_BD = 2.89 and <i>r</i>_IP = 0.41. The thermal behaviors of the (co)­polymers were investigated

Phosphine–Borane Frustrated Lewis Pairs Derived from a 1,1′-Disubstituted Ferrocene Scaffold: Synthesis and Hydrogenation Catalysis

(Dimesitylphosphino)­ferrocene (FcPMes₂) (<b>1</b>) reacted with HB­(C₆F₅)₂ (2 equiv) by disproportionation to give adduct FcPMes₂·H₂B­(C₆F₅) (<b>4</b>) plus B­(C₆F₅)₃, whereas 1-(dimesitylphosphino)-1′-vinylferrocene (<b>2</b>) was cleanly hydroborated with HB­(C₆F₅)₂ to afford [Fe­(η⁵-C₅H₄PMes₂)­(η⁵-C₅H₄CH₂CH₂B­(C₆F₅)₂)] (<b>7</b>). Compound <b>7</b> adopted an open non-interacting P/B frustrated Lewis pair (FLP) structure in the crystal state as well as in a solution. This frustrated Lewis pair heterolytically cleaved dihydrogen under mild conditions to give the respective zwitterionic [P]­H⁺/[B]­H^– phosphonium/hydroborate product, [Fe­(η⁵-C₅H₄PHMes₂)­{η⁵-C₅H₄CH₂CH₂BH­(C₆F₅)₂}] (<b>8</b>), which served as a catalyst for the hydrogenation of the electron-rich π-systems (imine, enamine) as well as the electron-deficient carbon–carbon double and triple bonds in some enones and an ynone under more forcing conditions (50 bar H₂ pressure, 50 °C)

Yttrium Hydride Complex Bearing CpPN/Amidinate Heteroleptic Ligands: Synthesis, Structure, and Reactivity

The reaction of the yttrium dialkyls (C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)₂(thf) (<b>1</b>) with an excess of <i>N</i>,<i>N′</i>-diisopropylcarbodiimide gave the yttrium monoalkyl complex (C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­(CH₂SiMe₃)­[^<i>i</i>PrNC­(CH₂SiMe₃)–N^<i>i</i>Pr] (<b>2</b>). <b>2</b> subsequently reacted with 1 equiv of PhSiH₃ to generate the CpPN/amidinate heteroleptic yttrium hydride {(C₅H₄–PPh₂N–C₆H₃^<i>i</i>Pr₂)­Y­[^<i>i</i>PrNC­(CH₂SiMe₃)–N^<i>i</i>Pr]­(μ-H)}₂ (<b>3</b>). Hydride <b>3</b> showed good reactivity toward various substrates containing unsaturated C–C, C–N, and N–N bonds, such as azobenzene, <i>p</i>-tolyacetylene, 1,4-bis­(trimethylsilyl)-1,3-butanediyne, <i>N</i>,<i>N′</i>-diisopropylcarbodiimide, and 4-dimethylaminopyridine, affording the yttrium hydrazide complex <b>4</b> with a rare η²-Cp bonding mode, yttrium terminal alkynyl complex <b>5</b>, yttrium η³-propargyl complex <b>6</b>, yttrium amidinate complex <b>7</b>, and yttrium 2-hydro-4-dimethylaminopyridyl product <b>8</b>, respectively