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: A reaction mechanism involving an electron transfer from the excited triplet state of Ru(II)TMP(CO) to hexachloroplatinate(IV) and subsequent formation of OH(-)-coordinated Ru(III) species, leading to an oxo-ruthenium complex as the key intermediate of the photochemical epoxidation, was postulated.
Abstract: Visible light irradiation of a reaction mixture of carbonyl-coordinated tetra(2,4,6-trimethyl)phenylporphyrinatoruthenium(II) (RuIITMP(CO)) as a photosensitizer, hexachloroplatinate(IV) as an electron acceptor, and an alkene in alkaline aqueous acetonitrile induces selective epoxidation of the alkene with high quantum yield (Φ = 0.6, selectivity = 94.4% for cyclohexene and Φ = 0.4, selectivity = 99.7% for norbornene) under degassed conditions. The oxygen atom of the epoxide was confirmed to come from a water molecule by an experiment with H218O. cis-Stilbene was converted into its epoxide, cis-stilbeneoxide, without forming trans-stilbeneoxide. trans-Stilbene, however, did not exhibit any reactivity. Under neutral conditions, an efficient buildup of the cation radical of RuIITMP(CO) was observed at the early stage of the photoreaction, while an addition of hydroxide ion caused a rapid reaction with the cation radical to promote the reaction with reversion to the starting RuIITMP(CO). A possible involvemen...
95 citations
TL;DR: In this paper, the authors showed that small changes in the ligand structure could have great effects on the polymerization activity of Dihalogenometal(II) complexes with bidentate phosphane ligands.
Abstract: Dihalogenometal(II) complexes with bidentate phosphane ligands of the general type [M{Ph2P(CH2)nPPh2}X2] with n
= 2 to 5, X = Cl or Br and M = Co, Ni or Pd have been utilized as catalysts for the vinyl/addition polymerization of norbornene. These complexes can be activated with the Lewis-acids methylalumoxane (MAO) or tris(pentafluorophenyl)borane, B(C6F5)3 in combination with triethylaluminium (AlEt3). The nickel(II) and palladium(II) complexes show very high polymerization activities up to 107 gpolymer molmetal−1 h−1. Yet, the complexes Pd(dppe)Cl2
(5, 1.9 × 107 gpolymer molPd−1 h−1) and Pd(dppp)Cl2
(6, 3.0 × 103 gpolymer molPd−1 h−1) demonstrated that small changes in the ligand structure could have great effects on the polymerization activity [dppe = 1,2-bis(diphenylphosphino)ethane, Ph2P(CH2)2PPh2; dppp = 1,3-bis(diphenylphosphino)propane, Ph2P(CH2)3PPh2]. The activation process of the pre-catalysts 5 and 6 in combination with B(C6F5)3/AlEt3 was followed by multinuclear (1H, 19F, and 31P) NMR investigations and by reaction with B(C6F5)3 and Ag[closo-1-CB11H12]. The reaction of B(C6F5)3 and AlEt3 leads to an aryl/alkyl group exchange resulting in the formation of AlEt3 − n(C6F5)n and B(C6F5)3 − nEtn with Al(C6F5)3 and BEt3 as main products for an about equimolar ratio. AlEt3 − n(C6F5)n will then react with the pre-catalysts and abstract the chloride atoms to form [M{Ph2P(CH2)nPPh2}]2+ as the active species for the polymerization. The higher polymerization activity of 5/B(C6F5)3/AlEt3 compared to 6/B(C6F5)3/AlEt3 can be explained by a ligand redistribution reaction of unstable [PdII(dppe)]2+ to give inactive and isolable [PdII(dppe)2]2+ and highly active, “naked” Pd2+ cations together with the lower coordinating ability of the anionic adduct [Cl–Al(C6F5)3]− in comparison to [Cl–B(C6F5)3]−. The Lewis-acid Al(C6F5)3 is much more activating than B(C6F5)3. The [Pd(dppe)2]2+ cation from the ligand redistribution was isolated in the (X-ray) structurally elucidated compounds [PdII(dppe)2][ClB(C6F5)3]2·4CH2Cl2 and [PdII(dppe)2][CB11H11Cl]2·3CH2Cl2. The stable [Pd(dppp)]2+ cation from 6 could be crystallized as [PdII(dppp)(CB11H12)][CB11H12]
(CB11H12
= mono-anionic carborane [closo-1-CB11H12]−).
94 citations
TL;DR: In this article, the combination of N-heterocyclic carbenes and coordinatively labile ligands (phosphanes or chloro-bridged transition metals) on the ruthenium center proves not only successful regarding catalytic performance but also promising with respect to polymer properties.
94 citations
TL;DR: The effect of substituent on the palladium(II)-catalyzed addition polymerization of functionalized norbornene derivatives was examined in this article, where it was shown that endo-substituted norbornenes are polymerized more slowly than their corresponding exo isomers.
93 citations
TL;DR: The obtained polymeric manganese and cobalt complexes were successfully used as supported catalysts for the asymmetric epoxidation of olefins and the hydrolytic kinetic resolution of epoxides, providing further proof that catalyst density and site isolation are key toward highly active and selective supported salen catalysts.
Abstract: We report a modular approach toward polymer-supported, metalated, salen catalysts. This strategy is based on the synthesis of monofunctionalized Mn- and Co-salen complexes attached to a norbornene monomer via a stable phenylene-acetylene linker. The resulting functionalized monomers can be polymerized in a controlled fashion using ring-opening metathesis polymerization. This polymerization method allows for the synthesis of copolymers, resulting in an unprecedented control over the catalyst density and catalytic-site isolation. The obtained polymeric manganese and cobalt complexes were successfully used as supported catalysts for the asymmetric epoxidation of olefins and the hydrolytic kinetic resolution of epoxides. All polymeric catalysts showed outstanding catalytic activities and selectivities comparable to the original catalysts reported by Jacobsen. Moreover, the copolymer-supported catalysts are more active and selective than their homopolymer analogues, providing further proof that catalyst density and site isolation are key toward highly active and selective supported salen catalysts.
93 citations