Topic
Norbornene
About: Norbornene is a research topic. Over the lifetime, 5628 publications have been published within this topic receiving 104495 citations. The topic is also known as: norbornylene & norcamphene.
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TL;DR: Kinetic studies provide the empirical rate law, rate = k(obs)[Pt][sulfonamide], and are consistent with a mechanism in which attack of a sulfonamide on the Pt-coordinated olefin is the rate-determining step.
Abstract: Electrophilic Pt(II) complexes catalyze efficient hydroaminations of olefins by sulfonamides and weakly basic anilines. Catalysts include the structurally characterized complex (COD)Pt(OTf)2 (1) and the known dimer [PtCl2(C2H4)]2, activated by AgBF4. Experiments with substituted anilines establish an empirical pKa cutoff (conjugate acid pKa < 1) for the participation of nitrogen-containing substrates in this catalysis. Arylsulfonamides (conjugate acid pKa approximately -6) with various para substituents hydroaminate olefins such as cyclohexene in yields greater than 95% at 90 degrees C. Hydroamination of propylene by p-toluenesulfonamide proceeds with Markovnikov selectivity, suggesting a mechanism that involves olefin activation at Pt. With norbornene and p-toluenesulfonamide as the substrates and 1 as the catalyst, intermediate [(COD)Pt(norbornene)2][OTf]2 (3) was identified and characterized by 19F and 195Pt NMR spectroscopies and mass spectrometry. Kinetic studies provide the empirical rate law, rate = k(obs)[Pt][sulfonamide], and are consistent with a mechanism in which attack of a sulfonamide on the Pt-coordinated olefin is the rate-determining step.
151 citations
TL;DR: In this article, the authors compared the performance of two catalysts, iPr[FluCp]ZrCl2/MAO and Me2Si[Ind]2-ZrCL2/MEO, with the same number of α-olefins.
Abstract: The stereorigid ansa-metallocene catalysts [2,4-cyclopentadien-1-ylidene(isopropylidene)-fluoren-9-ylidene]zirconium dichloride/methylaluminoxane (iPr[FluCp]ZrCl2/MAO) and [(dimethylsilylene)bis(η5-inden-1-ylidene)]zirconium dichloride/methylaluminoxane (Me2Si[Ind]2-ZrCl2/MAO) are different in respect to the symmetry and, therefore, to the behaviour of the stereospecifity, in the size of the angle between the planes of the π-ligand systems and in the homopolymerization behaviour of ethylene and propene. The present paper concerns itself with comparing the investigations of the ethylene/α-olefin and the ethylene/cycloolefin copolymerization with both catalyst systems. The main kinetic result for both catalysts is that the α-olefins show an accelerating effect on the ethylene polymerization rate during the copolymerization whereas norbornene shows exclusively a rate-decreasing effect. The acceleration effect can be explained by an increase in the concentration of active centres and/or an increase of the rate constant of the ethylene insertion. The analysis of the microstructures of the formed copolymers by the use of statistical models demonstrates that in copolymers with a high content of α-olefins, the experimental trial distributions can only be described satisfactorily with second-order Markovian statistics. That means that in this case the last two monomers have influence on the insertion of the subsequent monomer. A further main result of all investigated copolymerizations is that the r-parameters for the α-olefin insertion are more favourable for the system iPr[FluCp]ZrCl2/MAO than for the system Me2Si[Ind]2ZrCl2/MAO; the reason for this is the different size in the coordination gap aperture of the π-ligands. Furthermore, the r-parameters show only a small dependence on the chain length of the α-olefin. Finally, it is remarkable that the stereospecifity (syndiotactic or isotactic α-olefin blocks) remains intact in the copolymers.
149 citations
TL;DR: Both the identification of a monoprotected 3-amino-2-hydroxypyridine/pyridone-type ligand and the use of a modified norbornene as a mediator are crucial for the realization of these two unprecedented meta-C-H transformations.
Abstract: Using a modified norbornene (methyl bicyclo[2.2.1]hept-2-ene-2-carboxylate) as a transient mediator, meta-C–H amination and meta-C–H alkynylation of aniline and phenol substrates have been developed for the first time. Both the identification of a monoprotected 3-amino-2-hydroxypyridine/pyridone-type ligand and the use of a modified norbornene as a mediator are crucial for the realization of these two unprecedented meta-C–H transformations. A variety of substrates are compatible with both meta-C–H amination and meta-C–H alkynylation. Amination and alkynylation of heterocyclic substrates including indole, indoline, and indazole afford the desired products in moderate to high yields.
149 citations
TL;DR: In this article, the norbornene/ethene copolymerization was investigated by using two C petertoddS-symmetric catalysts with methylaluminoxane (MAO) as cocatalyst.
Abstract: The norbornene/ethene copolymerization was investigated by using two C
S-symmetric ([Me2C(Fluo)(Cp)]ZrCl2
III, [Ph2C(Fluo)(Cp)]ZrCl2
IB) and two C
2-symmetric ([Me2Si(Ind)2]ZrCl2
I, [Ph2Si(Ind)2]ZrCl2
II) catalysts with methylaluminoxane (MAO) as cocatalyst. This investigation focussed not only on the different polymerization behavior, like catalyst activity, but also considers the material properties of the synthesized copolymers. It was found, that the C
S-symimetric catalysts are very well suitable to yield amorphous copolymers with glass transition temperatures above 180°C and molecular weights >100.000 g/mol. These copolymers could be used as potential starting materials for optical discs and fibers.
148 citations
TL;DR: A modular system based on the bioorthogonal cycloaddition reaction between 3-(4-benzylamino)-1,2,4,5-tetrazine and the strained dienophile norbornene will allow for both greater versatility and more facile cross-comparisons in the development of antibody-based radiopharmaceuticals.
148 citations