Polymerization of Norbornene and Methyl Acrylate by a Bimetallic Palladium(II) Allyl Complex

The sequential reaction of {(allyl)Pd(μ-Cl)}2 (2) with AgPF6 and PCy3 in CH2Cl2 generates a mixture (1-in situ) of [{(allyl)Pd(PCy3)}2(μ-Cl)][PF6] (1), 2, [(allyl)Pd(PCy3)2][PF6] (3), and (allyl)PdCl(PCy3) (4), which evolves to form pure 1 after 20 h at 23 °C. Complex 1 reacts with PCy3 to generate 3 and 4 and undergoes facile exchange of Pd units with 4. Both 1 and 1-in situ polymerize mixtures of norbornene (NB) and methyl acrylate (MA) to a mixture of poly(NB) and poly(MA) via competing NB insertion polymerization and MA radical polymerization

Polymerization of Norbornene and Methyl Acrylate by a Bimetallic Palladium(II) Allyl Complex

The sequential reaction of {(allyl)Pd(μ-Cl)}2 (2) with AgPF6 and PCy3 in CH2Cl2 generates a mixture (1-in situ) of [{(allyl)Pd(PCy3)}2(μ-Cl)][PF6] (1), 2, [(allyl)Pd(PCy3)2][PF6] (3), and (allyl)PdCl(PCy3) (4), which evolves to form pure 1 after 20 h at 23 °C. Complex 1 reacts with PCy3 to generate 3 and 4 and undergoes facile exchange of Pd units with 4. Both 1 and 1-in situ polymerize mixtures of norbornene (NB) and methyl acrylate (MA) to a mixture of poly(NB) and poly(MA) via competing NB insertion polymerization and MA radical polymerization

Inhibitory Role of Carbon Monoxide in Palladium(II)-Catalyzed Nonalternating Ethene/Carbon Monoxide Copolymerizations and the Synthesis of Polyethene-<i>block</i>-poly(ethene-<i>alt</i>-carbon monoxide)

We report the first well-defined palladium-based system for the living homopolymerization of ethene, as well as the living copolymerization of ethene with carbon monoxide. We demonstrate this by the synthesis of polyethene-block-poly(ethene-alt-carbon monoxide). In addition, it has been possible to monitor chain growth by sequential insertions of carbon monoxide and ethene into palladium−carbon bonds. The mechanistic studies have also allowed us to pinpoint the hitherto not well-understood reason for the general failure to obtain alkene/carbon monoxide copolymers with low carbon monoxide content

Inhibitory Role of Carbon Monoxide in Palladium(II)-Catalyzed Nonalternating Ethene/Carbon Monoxide Copolymerizations and the Synthesis of Polyethene-<i>block</i>-poly(ethene-<i>alt</i>-carbon monoxide)

We report the first well-defined palladium-based system for the living homopolymerization of ethene, as well as the living copolymerization of ethene with carbon monoxide. We demonstrate this by the synthesis of polyethene-block-poly(ethene-alt-carbon monoxide). In addition, it has been possible to monitor chain growth by sequential insertions of carbon monoxide and ethene into palladium−carbon bonds. The mechanistic studies have also allowed us to pinpoint the hitherto not well-understood reason for the general failure to obtain alkene/carbon monoxide copolymers with low carbon monoxide content

Inhibitory Role of Carbon Monoxide in Palladium(II)-Catalyzed Nonalternating Ethene/Carbon Monoxide Copolymerizations and the Synthesis of Polyethene-<i>block</i>-poly(ethene-<i>alt</i>-carbon monoxide)

We report the first well-defined palladium-based system for the living homopolymerization of ethene, as well as the living copolymerization of ethene with carbon monoxide. We demonstrate this by the synthesis of polyethene-block-poly(ethene-alt-carbon monoxide). In addition, it has been possible to monitor chain growth by sequential insertions of carbon monoxide and ethene into palladium−carbon bonds. The mechanistic studies have also allowed us to pinpoint the hitherto not well-understood reason for the general failure to obtain alkene/carbon monoxide copolymers with low carbon monoxide content

Kinetic and Mechanistic Aspects of Ethylene and Acrylates Catalytic Copolymerization in Solution and in Emulsion

Ethylene was copolymerized with acrylates in solution and in emulsion using sulfonated arylphosphine Pd-based catalysts. The copolymerization of C2H4 and methyl acrylate in toluene was slowed by the σ-coordination of the acrylate on Pd. The substitution of pyridine by itself was shown to proceed via an associative mechanism with activation parameters ΔH‡ = 16.8 kJ/mol and ΔS‡ = −98 J mol−1 K−1 whereas the activation parameters for the substitution of pyridine by methyl acrylate were found to be ΔH‡ = 18.1 kJ/mol and ΔS‡ = −87 J mol−1 K−1. Using these Pd-based catalysts in an emulsion polymerization process, latexes of copolymers of ethylene with various acrylates having particle diameters ∼200 nm were obtained for the first time. Their solid contents did not exceed 5% because of the low activity of the catalyst resulting from the coordination of water and from the slow decomposition of the active site by water

Addition Polymerization of Norbornene-Type Monomers. High Activity Cationic Allyl Palladium Catalysts

A family of high activity catalysts for the vinyl addition polymerization of norbornene-type monomers based on cationic η-allylpalladium complexes coordinated by phosphine ligands has been discovered. The palladium complex [(η3-allyl)Pd(tricyclohexylphosphine)(ether)][B(3,5-(CF3)2C6H3)4] (2) was found to copolymerize 5-butylnorbornene and 5-triethoxysilylnorbornene (95:5 molar ratio) with truly high activity and is capable of producing more than a metric ton of copolymer per mole Pd per hour. Multicomponent catalyst systems based on the addition of salts of weakly coordinating anions (e.g., Na[B(3,5-(CF3)2C6H3)4] or Li[B(C6F5)4]·2.5Et2O) to (η3-allyl)Pd(X)(PR3) (X = chloride, acetate, nitrate, trifluoroacetate, and triflate) in the presence of norbornene-type monomers were developed. NMR tube experiments confirm that Na[B(3,5-(CF3)2C6H3)4] abstracts the Cl ligand from the palladium complex forming the cationic complex in situ. Control experiments confirmed that a high activity polymerization system requires a palladium cation containing an allyl ligand, a neutral, two-electron-donor phosphine ligand, and a weakly coordinating counterion. Those complexes where X contained electron-withdrawing groups such as trifluoroacetate or triflate were found to be the most active catalyst precursors. η3-Allylpalladium catalyst precursors with larger cone angle phosphine ligands yield lower molecular weight polymers. The poly(norbornene) molecular weights can be further tuned by addition of α-olefin chain transfer agents to the reaction mixture. The catalyst systems were also found to polymerize norbornene-type monomers in aqueous media to high conversion at very low catalyst loadings. The effect of molecular weight on thermomechanical properties was explored

Synthesis, Solution Dynamics, and X-ray Crystal Structure of Bis(2,4,6-tris(trifluoromethyl)- phenyl)(1,2-dimethoxyethane)nickel

Reaction of dichloro(1,2-dimethoxyethane)nickel with 2 equiv of (tris(2,4,6-trifluoromethyl)phenyl)lithium, generated in situ, produced bis(2,4,6-tris(trifluoromethyl)phenyl)(1,2-dimethoxyethane)nickel. Significant nickel−fluorine interactions are revealed both in the solid state (X-ray crystal structure data) and in solution (variable-temperature 19F NMR spectral data)

Addition Polymerization of Norbornene-Type Monomers Using Neutral Nickel Complexes Containing Fluorinated Aryl Ligands

The strong Lewis acid B(C6F5)3 was found to activate complexes of nickel toward the polymerization of norbornene-type monomers. The active species in this reaction is created by the transfer of C6F5 from boron to nickel. As a result, a class of neutral, single-component nickel complexes was developed containing two electron-withdrawing aryl ligands that polymerize norbornene and norbornenes with functional pendant groups. Active complexes include Ni(C6F5)2(PPh2CH2C(O)Ph), (η6-toluene)Ni(C6F5)2, and Ni(2,4,6-tris(trifluoromethyl)phenyl)2(1,2-dimethoxyethane). In the case of (η6-toluene)Ni(C6F5)2, isolation and characterization of low molecular weight norbornene polymers, using ethylene, indicated that each polymer chain contained a C6F5 headgroup. This points to the initiation step as being the insertion of norbornene into the Ni−C6F5 bond. The polymer microstructure as revealed by 1H and 13C NMR spectrometry is entirely different from that produced using the cationic nickel catalyst, [(η-crotyl)Ni(1,4-COD)]PF6. This difference in microstructure led to improved mechanical properties for 80:20 copolymers of norbornene and 5-triethoxysilylnorbornene