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It is also active for the hydrosilylation of alkenes. [16] In the presence of strong base and hydrogen, Wilkinson's catalyst forms reactive Rh(I) species with superior catalytic activities on the hydrogenation of internal alkynes and functionalized tri-substituted alkenes. [17]
Mechanism for the hydrogenation of a terminal alkene using Wilkinson's catalyst. Homogeneous catalysts are also used in asymmetric synthesis by the hydrogenation of prochiral substrates. An early demonstration of this approach was the Rh-catalyzed hydrogenation of enamides as precursors to the drug L-DOPA. [10]
Crabtree's catalyst is an organoiridium compound with the formula [C 8 H 12 IrP(C 6 H 11) 3 C 5 H 5 N]PF 6.It is a homogeneous catalyst for hydrogenation and hydrogen-transfer reactions, developed by Robert H. Crabtree.
Idealized mechanism for metal-catalysed hydrosilylation of an alkene. Hydrosilylation of alkenes represents a commercially important method for preparing organosilicon compounds. The process is mechanistically similar to the hydrogenation of alkenes. In fact, similar catalysts are sometimes employed for the two catalytic processes.
Alkyne hydrogenation is stereospecific, occurring via syn addition to give the cis-alkene. [4] For example the hydrogenation of acetylenedicarboxylic acid using Lindlar catalyst gives maleic acid rather than fumaric acid. An example of commercial use is the organic synthesis of vitamin A which involves an alkyne reduction with the Lindlar catalyst.
In the dissociative mechanism, proposed by Männig and Nöth, [4] and supported by Evans and Fu [5] the coordination is accompanied by the loss of one triphenylphosphine ligand. In the associative mechanism (see below), proposed by Burgess et al., [ 6 ] the alkene binds trans to the chloride without dissociation of a triphenylphosphine ligand.
Reduction of nitriles in the synthesis of phenethylamine with Raney nickel catalyst and hydrogen in ammonia: [25] Nitrile hydrogenation; The cracking, isomerisation, and reformation of hydrocarbons to form appropriate and useful blends of petrol. In automobiles, catalytic converters are used to catalyze three main reactions:
Hérisson and Chauvin first proposed the widely accepted mechanism of transition metal alkene metathesis. [12] The direct [2+2] cycloaddition of two alkenes is formally symmetry forbidden and thus has a high activation energy. The Chauvin mechanism involves the [2+2] cycloaddition of an alkene double bond to a transition metal alkylidene to ...