A simple, one‐step mechanochemical procedure for immobilisation of homogeneous metathesis catalysts in metal–organic frameworks was developed. Grinding MIL‐101‐NH2(Al) with a Hoveyda–Grubbs second‐generation catalyst resulted in a heterogeneous catalyst that is active for metathesis and one of the most stable immobilised metathesis catalysts. During the mechanochemical immobilisation the MIL‐101‐NH2(Al) structure was partially converted to MIL‐53‐NH2(Al). The Hoveyda–Grubbs catalyst entrapped in MIL‐101‐NH2(Al) is responsible for the observed catalytic activity. The developed synthetic procedure was also successful for the immobilisation of a Zhan catalyst. 相似文献
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 (Mn) 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 .
A ring‐opening metathesis polymerization‐ (ROMP‐) based monolith was synthesized using a Grubbs' first generation catalyst. The living termini were used for surface grafting of norborn‐5‐ene‐2‐ylmethyl hexafluoroglutarate. The free carboxylic acid groups of the graft polymer were converted into the corresponding silver salt and reacted with the Grubbs–Hoveyda catalyst [RuCl2(CH (2‐iPrO )C6H4)(IMesH2)] (IMesH2 = 1,3‐bis(2,4,6‐trimethylphenyl)‐4,5‐dihydroimidazol‐2‐ylidene) to yield a stable heterogeneous version of this catalyst for use in ring‐closing metathesis (RCM) under continuous flow conditions.
The monolith‐supported Grubbs–Hoveyda catalyst. 相似文献
Improvement of the activity, stability, and chemoselectivity of alkyne‐metathesis catalysts is necessary before this promising methodology can become a routine method to construct C≡C triple bonds. Herein, we show that grafting of the known molecular catalyst [MesC≡Mo(OtBuF6)3] ( 1 , Mes=2,4,6‐trimethylphenyl, OtBuF6=hexafluoro‐tert‐butoxy) onto partially dehydroxylated silica gave a well‐defined silica‐supported active alkyne‐metathesis catalyst [(≡SiO)Mo(≡CMes)(OtBuF6)2] ( 1 /SiO2‐700). Both 1 and 1 /SiO2‐700 showed very high activity, selectivity, and stability in the self‐metathesis of a variety of carefully purified alkynes, even at parts‐per‐million catalyst loadings. Remarkably, the lower turnover frequencies observed for 1 /SiO2‐700 by comparison to 1 do not prevent the achievement of high turnover numbers. We attribute the lower reactivity of 1 /SiO2‐700 to the rigidity of the surface Mo species owing to the strong interaction of the metal site with the silica surface. 相似文献
When ethene alone was contacted with silica supported cobalt catalyst (Co/SiO2), ethene homologation took place with considerable activity. Moreover, the propene metathesis reaction was suppressed ca. 1/6 fold as much as in the case using MoOX/SiO2 catalyst. The possibility of selective homologation with a lower activity for metathesis was suggested for the cobalt-based
catalyst system. 相似文献
A dicationic ruthenium–alkylidene complex [Ru(dmf)3(IMesH2)(?CH‐2‐(2‐PrO)‐C6H4)][(BF4)2] ( 1 ; IMesH2=1,3‐dimesitylimidazolin‐2‐ylidene) has been prepared and used in continuous metathesis reactions by exploiting supported ionic‐liquid phase (SILP) technology. For these purposes, ring‐opening metathesis polymerization (ROMP)‐derived monoliths were prepared from norborn‐2‐ene, tris(norborn‐5‐ene‐2‐ylmethyloxy)methylsilane, and [RuCl2(PCy3)2(CHPh)] (Cy=cyclohexyl) in the presence of 2‐propanol and toluene and surface grafted with norborn‐5‐en‐2‐ylmethyl‐N,N,N‐trimethylammonium tetrafluoroborate ([NBE‐CH2‐NMe3][BF4]). Subsequent immobilization of the ionic liquid (IL), 1‐butyl‐2,3‐dimethylimidazolium tetrafluoroborate ([BDMIM][BF4]), containing ionic catalyst 1 created the SILP catalyst. The use of a second liquid transport phase, which contained the substrate and was immiscible with the IL, allowed continuous metathesis reactions to be realized. High turnover numbers (TONs) of up to 3700 obtained in organic solvents for the ring‐closing metathesis (RCM) of, for example, N,N‐diallyltrifluoroacetamide, diethyl diallylmalonate, diethyl di(methallyl)malonate, tert‐butyl‐N,N‐diallylcarbamate, N,N‐diallylacetamide, diphenyldiallylsilane, and 1,7‐octadiene, as well as in the self‐metathesis of methyl oleate, could be further increased by using biphasic conditions with [BDMIM][BF4]/heptane. Under continuous SILP conditions, TONs up to 900 were observed. Due to the ionic character of the initiator, catalyst leaching into the transport phase was very low (<0.1 %). Finally, the IL can, together with decomposed catalyst, be removed from the monolithic support by flushing with methanol. Upon reloading with [BDMIM][BF4]/ 1 , the recycled support material again qualified for utilization in continuous metathesis reactions. 相似文献
A straightforward pyrrole synthesis from diallylamines is developed by using a tandem catalyst system leading to ring-closing metathesis with the second generation Grubbs’ catalyst (10%) followed by dehydrogenation in the presence of RuCl3 × H2O (2%). 相似文献
Two new ruthenium complexes bearing a bidentate (κ2O,C)‐isopropoxy–indenylidene ligand and a PPh3 ( 9 ) or PCy3 ( 10 , Cy=cyclohexyl) ligand have been synthesized and fully characterized by 1H and 13C NMR spectroscopy and X‐ray crystallography. Complex 10 displays a very high thermal stability with a half life of six days at 110 °C in [D8]toluene. Complex 10 was evaluated in various ring‐closing metathesis reactions and ring‐opening metathesis polymerization of dicyclopentadiene, in which it showed a latent behavior with low activity at room temperature and high activity upon thermal activation. 相似文献
Conversion–time data were recorded for various ring‐closing metathesis (RCM) reactions that lead to five‐ or six‐membered cyclic olefins by using different precatalysts of the Hoveyda type. Slowly activated precatalysts were found to produce more RCM product than rapidly activated complexes, but this comes at the price of slower product formation. A kinetic model for the analysis of the conversion–time data was derived, which is based on the conversion of the precatalyst (Pcat) into the active species (Acat), with the rate constant kact, followed by two parallel reactions: 1) the catalytic reaction, which utilizes Acat to convert reactants into products, with the rate kcat, and 2) the conversion of Acat into the inactive species (Dcat), with the rate kdec. The calculations employ two experimental parameters: the concentration of the substrate (c(S)) at a given time and the rate of substrate conversion (?dc(S)/dt). This provides a direct measure of the concentration of Acat and enables the calculation of the pseudo‐first‐order rate constants kact, kcat, and kdec and of kS (for the RCM conversion of the respective substrate by Acat). Most of the RCM reactions studied with different precatalysts are characterized by fast kcat rates and by the kdec value being greater than the kact value, which leads to quasistationarity for Acat. The active species formed during the activation step was shown to be the same, regardless of the nature of different Pcats. The decomposition of Acat occurs along two parallel pathways, a unimolecular (or pseudo‐first‐order) reaction and a bimolecular reaction involving two ruthenium complexes. Electron‐deficient precatalysts display higher rates of catalyst deactivation than their electron‐rich relatives. Slowly initiating Pcats act as a reservoir, by generating small stationary concentrations of Acat. Based on this, it can be understood why the use of different precatalysts results in different substrate conversions in olefin metathesis reactions. 相似文献
Exploiting catalytic carbonyl–olefin metathesis is an ongoing challenge in organic synthesis. Reported herein is an FeCl3‐catalyzed ring‐closing carbonyl–olefin metathesis. The protocol allows access to a range of carbo‐/heterocyclic alkenes with good efficiency and excellent trans diastereoselectivity. The methodology presents one of the rare examples of catalytic ring‐closing carbonyl–olefin metathesis. This process is proposed to take place by FeCl3‐catalyzed oxetane formation followed by retro‐ring‐opening to deliver metathesis products. 相似文献