Polymerization of carboxylic ester functionalized norbornenes catalyzed by (η3‐allyl)palladium complexes bearing N‐heterocyclic carbene ligands

An in situ generated cationic allylpalladium complex bearing N‐heterocyclic carbene (NHC) ligands, derived from the reaction of [(η³‐C₃H₅)Pd(NHC)Cl] with AgX (X = BF₄ or SbF₆), is an active catalyst for the addition polymerization of norbornene and norbornene derivatives [5‐norbornene‐2‐carboxylic acid methyl ester ( b ) and 5‐norbornene‐2‐carboxylic acid n‐butyl ester ( c )] with an ester group containing a large portion of endo‐isomers. The catalytic activities, polymer yields, molecular weights, and molecular weight distributions of polynorbornenes were investigated under various reaction conditions: the catalytic activity was highly dependent on the counteranion, the reaction solvent, and the reaction temperature. For b , as the portion of an endo‐isomer increased, the activity of 13 (SbF) was much higher than those of 14 and 15 , and for c (exo/endo = 95:5), the maximum turn over number (TON) was observed with 15 (SbF). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 3042–3052, 2007     

Solvent‐Free Ring‐Opening Metathesis Polymerization of Norbornene over Silica‐Supported Tungsten–Oxo Perhydrocarbyl Catalysts

Ring opening metathesis polymerization (ROMP) of bicyclo[2.2.1]hept‐2‐ene (norbornene) is carried out over silica‐supported catalysts based on tungsten complexes bearing an oxo ligand ( 1 : [(SiO)W(O)(CH₂SiMe₃)₃, 2 : [(SiO)W(O)(CHCMe₂Ph)(dAdPO)], dAdPO  2,6 diadamantyl‐4‐methylphenoxide, 3 : [(SiO)₂W(O)(CH₂SiMe₃)₂]). The evaluation of the catalytic activities of the aforementioned materials in ROMP indicates that at low reaction time (0.5 min), the highest polymer yield is obtained with catalyst 2 . However, for longer reaction time (>2 min), complex 3 , a model of the industrial catalyst, exhibits a better monomer conversion. The polymers obtained are characterized. Moreover, these catalysts are shown to be rather preferentially selective to give the cis polynorbornene (>65%), characterized by high melting points (≈300 °C). The experimental values of the average molecular weight (M_n) of polynorbornenes are found to be close to the theoretical ones for the polymers prepared using catalyst 2 and higher for those originated from catalyst 3 .

     

Hydrogenation of norbornene catalyzed by magnesium oxide-supported polyalumazane–platinum complexes

A magnesium oxide-supported polyalumazane–platinum complex was synthesized and characterized by X-ray photoelectron spectroscopy (XPS) and its performance toward the hydrogenation of norbornene. XPS data indicated that a large amount of platinum existed in a zero-valent state. The catalyst showed high performance for the hydrogenation of norbornene. Its performance depended on the type of the support, the platinum loading and the reaction temperature. With 0.1544 mmol/g platinum loading at 25°C, the hydrogenation of norbornene to norbornane was completed within 2 min. Also, the turnover number of the catalyst reached 11,000 within 280 min.     

Strained Diphosphines Built upon a Calix[4]arene Skeleton. Synthesis of a Highly Active Norbornene Polymerization Catalyst

Summary: The complexes cis‐P,P′‐(η⁵‐cylopentadienyl)‐{5,17‐dibromo‐11,23‐bis(diphenylphosphino)‐25,26,27,28‐tetrapropoxy‐calix[4]arene}nickel(II ) tetrafluoroborate ( 1 ) and dibromo‐{5,17‐dibromo‐11,23‐bis(diphenylphosphino)‐25,26,27,28‐tetrapropoxycalix[4]arene}nickel(II ) ( 2 ), both of which contain a constrained chelating diphosphine, were evaluated for the polymerization of norbornene. Combined with methylaluminoxane, they result in remarkably active systems for the production of high‐molar‐mass vinyl‐type polynorbornene. Turnover frequencies of up to 7.5 × 10⁵ mol(NBE) · mol(Ni)⁻¹ · h⁻¹ are observed. A plausible explanation for their high performances relies on a periodic P–Ni–P bite angle enlargement that temporarily increases the steric hindrance about the catalytic centre, which in turn favours the insertion steps.

Molecular structure of 2 .     

Glass Transition Temperature and Chain Flexibility of Ethylene‐Norbornene Copolymers from Molecular Dynamics Simulations

Summary: Model chains of ethylene‐norbornene copolymers were built up using the results of ¹³C NMR spectral analysis of copolymer samples synthesized with metallocene‐based catalysts. Our models statistically reproduce the microstructure, composition, and tacticity of the copolymer chains of experimental samples. They were used to test if MD simulations are suitable to investigate the relationships between microstructure and macroscopic properties. In particular, MD simulations were applied to calculate the glass transition temperature and to study the chain flexibility by the analysis of ACF of specific virtual bonds. Plots of specific volume versus temperature computed for models of four copolymer samples having different microstructures and norbornene contents yield T_g values in good agreement with experiments. Moreover, comparison of the ACFs provides some qualitative indications about the relationship between chain stereochemistry and T_g.

ACF functions of the virtual bonds with microstructures NENE (bottom) and ENNE (top).     

Copolymerization of carbon monoxide and norbornene derivatives with ester groups by palladium catalyst

In this article we will discuss the synthesis of the new copolymers of norbornene derivatives with an ester group and carbon monoxide, using Pd(CH₃CN)₄(BF₄)₂ as a catalyst and 2,2′-bipyridine as a ligand in nitromethane/methanol at 60°C. Elementary analysis, infrared spectra, and NMR spectra indicated that copolymers contain ketone, ester, and bicyclic structures. Methanol functions as the coinitiator and chain transfer agent in copolymerization. A decrease in the molar ratio of [CH₃OH]/[Pd] caused an increase in molecular weight and a decrease in yield of the copolymer. The number-average molecular weight of copolymers (M _n) ranged from 3800 to 5300, and the glass transition temperature (T_g) ranged from −32 to 117°C. Thermal analysis revealed that both T and T exceeded 180 and 230°C, respectively. Linear long-chain substituents such as n-C₁₁H₂₃C(O) O CH₂ drastically reduced T_g to a value of −32°C. In general, copolymers having a longer linear side-chain substituents of ester on norbornene have a more desirable solubility. Moreover, X-ray diffraction demonstrated that the degree of crystallinity decreases with an increasing length of side chain substituents. © 1998 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 36: 1785–1790, 1998     

Monodentate aminophosphine nickel(II)‐ and palladium(II)‐catalyzed ethylene oligomerization and norbornene polymerization

Nickel(II) and palladium(II) complexes of monodentate aminophosphine ligands were prepared and characterized. In ethylene oligomerization and subsequent Friedel–Crafts alkylation of toluene, the Ni(II) complexes Ni‐1 and Ni‐2 were activated with aluminium co‐catalysts and generated tandem catalysts with high activities (up to 1.1 × 10⁶ g (mol Ni)^?1 h^?1) which are comparable with those of previously reported bidentate Ni(II) catalysts. The Pd(II) precatalyst Pd‐1 showed high activities (up to 2.0 × 10⁵ g (mol Pd)^?1 h^?1) in the polymerization of norbornene.     

Phosphine (oxide)‐(thio) phenolate palladium complexes: Synthesis,characterization and (co)polymerization of norbornene

A series of palladium complexes ( 2a–2g ) ( 2a : [6‐^tBu‐2‐PPh₂‐C₆H₃O]PdMe(Py); 2b : [6‐C₆F₅–2‐PPh₂‐C₆H₃O]PdMe(Py); 2c : [6‐^tBu‐2‐PPh^tBu‐C₆H₃O]PdMe(Py); 2d : [2‐PPh^tBu‐C₆H₄O] PdMe(Py); 2e : [6‐SiMe₃–2‐PPh₂‐C₆H₃O]PdMe(Py); 2f : [2‐^tBu‐6‐(Ph₂P=O)‐C₆H₃O]PdMe(Py); 2g : [6‐SiMe₃–2‐(Ph₂P=O)‐C₆H₃S]PdMe(Py)) bearing phosphine (oxide)‐(thio) phenolate ligand have been efficiently synthesized and characterized. The solid‐state structures of complexes 2d , 2f and 2g have been further confirmed by single‐crystal X‐ray diffraction, which revealed a square‐planar geometry of palladium center. In the presence of B(C₆F₅)₃, these complexes can be used as catalysts to polymerize norbornene (NB) with relatively high yields, producing vinyl‐addition polymers. Interestingly, 2a /B(C₆F₅)₃ system catalyzed the polymerization of NB in living polymerization manner at high temperature (polydispersity index 1.07, M_n up to 1.5 × 10⁴). The co‐polymerization of NB and polar monomers was also studied using catalysts 2a and 2f . All the obtained co‐polymers could dissolve in common solvent.     

Silyl‐Terminated Ethylene‐co‐Norbornene Copolymers by Organotitanium‐Based Catalysts

Ethylene (E) and norbornene (N) were copolymerized in the presence of PhSiH₃ as chain‐transfer agent with [Ti(η⁵:η¹‐C₅Me₄SiMe₂NBu^t)(η¹‐Me)₂] precatalyst combined with [Ph₃C][B(C₆F₅)₄]. The silane was introduced at chain‐ends of E‐co‐N copolymers with concomitant reinitiation of the growing polymer chain. The concentrations of the silane and polymer molecular weight are inversely correlated. The characteristic signals of  SiH₂Ph chain‐ends were observed by ¹H NMR. The Si heteroatom is predominantly adjacent to ethylene units in E‐co‐N copolymers with high N content.