Hydrogenation cyclopentadiene, selective

The obtained catalysts showed similar activity in cyclopentadiene hydrogenation. The selectivity data in cyclopentadiene hydrogenation are given in Table I. The selectivity of consecutive reaction was determined as a rate ratio of cyclopentene/cyclopentane formation. On the contrary, the chitosan modification influenced essentially the selectivity of the catalyst on it basis. 

The solvent effect on the diastereofacial selectivity in the reactions between cyclopentadiene and (lR,2S,5R)-mentyl acrylate is dominated by the hydrogen bond donor characteristics of the solvent... 

The chiral catalyst 142 achieves selectivities through a double effect of intramolecular hydrogen binding interaction and attractive tt-tt donor-acceptor interactions in the transition state by a hydroxy aromatic group [88]. The exceptional results of some Diels-Alder reactions of cyclopentadiene with substituted acroleins catalyzed by (R)-142 are reported in Table 4.21. High enantio- and exo selectivity were always obtained. The coordination of a proton to the 2-hydroxyphenyl group with an oxygen of the adjacent B-0 bond in the nonhelical transition state should play an important role both in the exo-endo approach and in the si-re face differentiation of dienophile. 

Conjugated dienes (such as 1,3-cyclohexadiene, cyclopentadiene, 2,4-hexadienoic-sorbic-acid) and polyenes can be selectively hydrogenated to monoenes unactivated alkenes are totally unreactive [20]. Unfortunately, the possibilities for modification of the catalyst by ligand alteration or by the use of additives are very limited [50, 51]. 

Recently, silica supported nickel-boron catalyst was tested in the hydrogenation of cyclopentadiene and was found to be selective in giving cyclopentene47. 

Raney-nickel was found to be selective in the hydrogenation of cyclopentadiene and cyclohexadiene and of their methyl and ethyl derivatives at 0-40 °C and 2-5 bar pressure137,138. The skeletal nickel proved to be selective in the semihydrogenation of conjugated polyenic compounds (equation 52)139. 

Cyclopentadiene adducts (mono-, tetra- and hexa-adducts) of were stabilized against retro-reaction by selective hydrogenation and bromination of the pendant groups [21]. Utilization of Adam s catalyst and dilute bromine solutions exclusively leads to an addition to the cyclopentene double bonds, because itself is inert towards these reagents. The increased stability of the reduced cycloadducts can be demonstrated by mass spectrometry [21]. 

Cyclopentene is produced in excellent yield by the selective hydrogenation of cyclopentadiene. Both Raney nickel in cold ethanol solution74 and Cu/A1203 aerogel in the gas phase75 are selective catalysts. The cyclopentene is converted to cyclopentane at a rate much lower than that of diene transformation to cyclopentene. Other catalytic processes for the hydrogenation of cyclopentadiene yield cyclopentane as the principal product. 

Colloidal palladium or platinum supported on chelate resin beads were employed for the stereoselective hydrogenation of olefins 86). Colloidal palladium supported on iminodiacetic acid type chelate resin beads was prepared by refluxing the palladium chloride and the chelate resin beads in methanol-water. Using the resin-supported colloidal palladium as a catalyst, cyclopentadiene is hydrogenated to cyclopentene with 97.1% selectivity at 100 % conversion of cyclopentadiene under 1 atm of hydrogen in methanol at 30 °C. Finely dispersed metal particles ranging from 1 to 6 nm in diameter are the active species in the catalyst. 

Compared to cyclopentadiene, 1,3-cyclooctadiene appears to be more selectively hydrogenated to cyclooctene, since hydrogenation of the cyclooctene produced may be depressed almost completely over selective palladium catalysts such as Pd-PVP-MeOH/NaOH74 and PAA- or CO-poisoned palladium.75 The maximum yields of cy-cloalkene obtained were higher with 1,3-cyclooctadiene than with cyclopentadiene or with 1,4- and 1,5-cyclooctadiene, as seen from the results in Table 3.13. The yields of cyclooctene were lower with a commercial 5% Pd-C or unpoisoned palladium. Over these unpoisoned catalysts the cyclooctene formed was further hydrogenated to cyclooctane, although in slower rates than the cyclooctadiene. 

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