A systematic study of stereochemical effects in homologous poly(alkenamer)s: Dewar benzene versus norbornene

Two diastereomeric derivatives of norbornene, dimethyl (1R,2R,3S,4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate and dimethyl (1R,2S,3S,4S)-bicyclo[2.2.1]hept-5-ene-2,3-dicarboxylate, were synthesized and polymerized using ring-opening metathesis polymerization (ROMP). For comparative purposes, diastereomeric derivatives of Dewar benzene, dimethyl (1R,2S,3R,4S)-bicyclo[2.2.0]hex-5-ene-2,3-dicarboxylate and dimethyl (1R,2S,3S,4S)-bicyclo[2.2.0]hex-5-ene-2,3-dicarboxylate, were also synthesized and polymerized using ROMP. The polymerization reactions proceeded in a controlled manner as evidenced in part by linear relationships between the monomer-to-catalyst feed ratios and the molecular weights of the polymer products. Chain extension experiments were also conducted which facilitated the formation of block copolymers. Although the poly(norbornene) derivatives exhibited glass transition temperatures that were dependent on their monomer stereochemistry (cis: 115°C vs. trans: 125°C), more pronounced differences were observed upon analysis of the polymers derived from Dewar benzene (cis: 70°C vs. trans: 95°C). Likewise, microphase separation was observed in block copolymers that were prepared using the diastereomeric monomers derived from Dewar benzene but not in block copolymers of the norbornene-based diastereomers. The differential thermal properties were attributed to the relative monomer sizes as reducing the distances between the polymer backbones and the pendant stereocenters appeared to enhance the thermal effects.     

Addition polymerization of norbornene using bis(β‐ketoamino)nickel(II)/tris(pentafluorophenyl)borane catalytic systems

Norbornene polymerizations proceeded in toluene with bis(β‐ketoamino)nickel(II) {Ni[CH₃C(O)CHC(NR)CH₃]₂ [R = phenyl ( 1 ) or naphthyl ( 2 )]} complexes as the catalyst precursors and the organo‐Lewis compound tris(pentafluorophenyl)borane [B(C₆F₅)₃] as a unique cocatalyst. The polymerization conditions, such as the cocatalyst/catalyst ratio (B/Ni), catalyst concentration, monomer/catalyst ratio (norbornene/Ni), polymerization temperature, and polymerization time, were studied in detail. Both bis(β‐ketoamino)nickel(II)/B(C₆F₅)₃ catalytic systems showed noticeably high conversions and activities. The polymerization activities were up to 3.64 × 10⁷ g of polymer/mol of Ni h for complex 1 /(B(C₆F₅)₃ and 3.80 × 10⁷ g of polymer/mol of Ni h for complex 2 /B(C₆F₅)₃, and very high conversions of 90–95% were maintained; both polymerizations provided high‐molecular‐weight polynorbornenes with molecular weight distributions (weight‐average molecular weight/number‐average molecular weight) of 2.5–3.0. The achieved polynorbornenes were confirmed to be vinyl‐addition and atactic polymers through the analysis of Fourier transform infrared, ¹H NMR, and ¹³C NMR spectra, and the thermogravimetric analysis results showed that the polynorbornenes exhibited good thermal stability (decomposition temperature > 410 °C). © 2007 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 45: 4733–4743, 2007     

Palladium-catalyzed three-component coupling reaction of organic halides, norbornadiene and terminal alkynes

A three-component coupling reaction of organic halides, including aryl halides, methyl iodine, alkenyl iodine and bromoalkynes, with norbornadiene and terminal alkynes catalyzed by a palladium complex and a phase transfer agent in the presence of aqueous NaOH gave 5,6-disubstituted norbornene derivatives in good yields.     

Nickel and cobalt complexes bearing β‐ketoamine ligands: syntheses,structures and catalytic behavior for norbornene polymerization

Late transition metal (nickel, cobalt) complexes (1, 2) with β‐ketoamine ligand (L) based on the pyrazolone derivative are synthesized by condensing 1‐phenyl‐3‐methyl‐4‐benzoyl‐5‐pyrazolone with p‐fluoroaniline, and then treating the β‐ketoamine (L) produced with the respective metal halide. The bis(β‐ketoamine)metal complexes can act as catalyst precursors for norbornene polymerization with activation by methylaluminoxane. The effects of the central metal variation in the complex on catalyst activities and polymer microstructure are described. Copyright © 2005 John Wiley & Sons, Ltd.     

Interaction of diazoalkanes with unsaturated compounds

The stereochemistry of cyclopropanation of norbornenes with diazomethane in the presence of Cu, Pd, and Rh compounds has been studied. Stereoselectivity of the cyclopropanation depends on the nature of the transition metal and does not depend on its valent state or ligand environment. The reaction proceeds predominantly asexo-cycloaddition of the methylene fragment. The greatest amount ofendo-isomer (up to 47 %) is formed in cyclopropanation of norbornadiene andexo-tricyclo[3.2.1.0^2,4]oct-6-ene in the presence of Cu and Rh compounds.For part 11 see ref. 1.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 4, pp. 733–735, April, 1993.     

降冰片烯桥联双酰胺化合物的合成与表征

在干燥非质子性溶剂中,以3,6-桥-亚甲基-1,2,3,6-四氢邻苯二甲酰氯与N-(3-氨基丙基)眯唑和1-氨基-4-甲基哌嗪为原料,合成了两种降冰片烯桥联双酰胺化合物,并考察了反应温度、溶剂及缚酸剂对酰氯氨解反应的影响,目标化合物结构经核磁共振氢谱、核磁共振碳谱、红外光谱及元素分析进行表征确证.     

C–C bridged Ni(II) complexes bearing β‐keto‐9‐fluorenyliminato ligands prepared by different in situ bonding mechanisms and their use in catalytic (co)polymerization of norbornene and styrene

Two C–C bridged Ni(II) complexes bearing β‐keto‐9‐fluorenyliminato ligands with electron‐withdrawing groups (─CF₃), Ni{PhC(O)CHC[N(9‐fluorenyl)]CF₂}₂ (Ni 1 ) and Ni{CF₃C(O)CHC[N(9‐fluorenyl)]Ph}₂ (Ni 2 ), were synthesized by metal coordination reaction and different in situ bonding mechanisms. The C–C bridged bonds of Ni 1 were formed by in situ intramolecular trifluoromethyl and 9‐fluorenyl carbon–carbon cross‐coupling reaction and those of Ni 2 were formed by in situ intramolecular 9‐fluorenyl carbon–carbon radical coupling reaction mechanism. The obtained complexes were characterized using ¹H NMR spectroscopy and elemental analyses. The crystal and molecular structures of Ni 1 and Ni 2 with C–C bridged configuration were determined using X‐ray diffraction. Ni 1 and Ni 2 were used as catalysts for norbornene (NB) polymerization after activation with B(C₆F₅)₃ and the catalytic activities reached 10⁶ g_polymer mol_Ni^?1 h^?1. The copolymerization of NB and styrene catalyzed by the Ni 1 /B(C₆F₅)₃ system showed high activity (10⁵ g_polymer mol_Ni^?1 h^?1) and the catalytic activities decreased with increasing feed content of styrene. All vinyl‐type copolymers exhibited high molecular weight (10⁴ g mol^?1), narrow molecular weight distribution (M_w/M_n = 1.71–2.80), high styrene insertion ratios (11.13–50.81%) and high thermal stability (T_d > 380°C) and could be made into thin films with high transparency in the visible region (400–800 nm).     

Addition copolymerization of norbornene lactone catalyzed by Pd complexes

The addition copolymerization of norbornene (NB) with functionalized monomers can lead to the modification of physical properties of poly(NB). Herein, the synthesis of new copolymer of NB with exo-norbornene lactone (exo-NBL) is reported. The copolymerization proceeded by four Pd catalytic systems, and of these, Pd(allyl)IDippCl/AgSbF₆ (IDipp = 1,3-bis[2,6-diisopropylphenyl]imidazolin-2-ylidene)) was the most effective for the incorporation of exo-NBL. Specifically, the copolymerization with exo-NBL/NB feed ratio of 50/50 at r.t. by 0.1 mol% of the Pd catalyst produced poly(NB-co-exo-NBL) with M_n of 87,000, and M_w/M_n of 1.2 in 40% yield, incorporating exo-NBL of 18 mol%. The time–conversion plots and ¹H diffusion ordered spectroscopy (DOSY) NMR analysis of the copolymer suggest that it has a random sequence. In contrast, no copolymer was formed from endo-NBL. This is because of steric hindrance of the endo-lactone moiety by considering the (co)polymerization of endo-5-norbornene-2-carboxylic acid methyl ester (endo-NBCO₂Me). The incorporation of exo-NBL improves the solubility of poly(NB-co-exo-NBL) in several chlorinated solvents and gives high thermal stability with 10% weight loss at a temperature of more than 400°C. Two amorphous halos corresponding to intra- and interchain distances were observed in the WAXD patterns, allowing to calculate d-spacing values, which are higher than that of poly(NB).     

Reaction of 2-azabicyclo[2.2.1]heptenes with nitrile oxides

The reaction of 2-azanorbornene derivatives with nitrile oxides (generated in situ by dehydrohalogenation of N-hydroxyimoyl halides) affords two regioisomers with the exo-arrangement of the isoxazoline ring.