| hydrocyanation ： ウィキペディア英語版|
Hydrocyanation is, most fundamentally, the process whereby H+ and –CN ions are added to a molecular substrate. Usually the substrate is an alkene and the product is a nitrile. When –CN is a ligand in a transition metal complex, its basicity makes it difficult to dislodge, so, in this respect, hydrocyanation is remarkable. Since cyanide is both a good σ–donor and π–acceptor its presence accelerates the rate of substitution of ligands ''trans'' from itself, the ''trans'' effect.1 A key step in hydrocyanation is the oxidative addition of hydrogen cyanide to low–valent metal complexes.〔Cotton, F. A.; Wilkinson, G.; Murillo, C. A.; Bochmann, M. ''Advanced Inorganic Chemistry''; John Wiley & Sons: New York, 1999; pp. 244-6, 440, 1247-9.〕 In hydrocyanation of unsaturated carbonyls addition over the alkene competes with addition over the carbonyl group.
==Stoichiometry and mechanism==
Industrially, hydrocyanation is commonly performed on alkenes catalyzed by nickel complexes of phosphite (P(OR)3) ligands. A general reaction is shown:〔Piet W.N.M. van Leeuwen "Homogeneous Catalysis: Understanding the Art", 2004, Wiley-VCH, Weinheim. ISBN 1-4020-2000-7〕
:RCH=CH2 + HCN → RCH2-CH2-CN
The reaction proceeds via the oxidative addition of HCN to Ni(0) to give a hydridonickel(II) cyanide complex, abbreviated Ni(H)(CN)L2. Subsequent binding of the alkene gives the intermediate Ni(H)(CN)L(alkene), which then undergoes migratory insertion to give an alkylnickel(II) cyanide Ni(R)(CN)L2. The cycle is completed by the reductive elimination of the nitrile.
Lewis acids, such as B(C6H5)3, can increase hydrocyanation rates and allow for lower operating temperatures. Triphenylboron may derive this ability induce reductive elimination of the nitrile product.〔 Rates can also be amplified with electron–withdrawing groups (NO2, CF3, CN, C(=O)OR, C(=O)R) on the phosphite ligands, because they stabilize Ni(0).〔
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