Hydrocyanation catalysts, palladium complexes

Because of its low acidity, hydrogen cyanide seldom adds to nonactivated multiple bonds. Catalytic processes, however, may be applied to achieve such additions. Metal catalysts, mainly nickel and palladium complexes, and [Co(CO)4]2 are used to catalyze the addition of HCN to alkenes known as hydrocyanation.l67 l74 Most studies usually apply nickel triarylphosphites with a Lewis acid promoter. The mechanism involves the insertion of the alkene into the Ni—H bond of a hydrido nickel cyanide complex to form a cr-alkylnickel complex173-176 (Scheme 6.3). The addition of DCN to deuterium-labeled compound 17 was shown to take place... 

The polymer of methyl methacrylate (MMA) is known as Perspex. It is a clear transparent glasslike material with high hardness, resistance to fracture, and chemical stability. The conventional route, as shown by reaction 4.10, involves the reaction between acetone and hydrocyanic acid, followed by sequential hydrolysis, dehydration, and esterification. This process generates large quantities of solid wastes. An alternative route based on a homogeneous palladium catalyst has recently been developed by Shell. In this process a palladium complex catalyzes the reaction between propyne (methyl acetylene), methanol, and carbon monoxide. This is shown by reaction 4.11. The desired product is formed with a regioselectivity that could be as high as 99.95%. 

Olefin hydrocyanation using palladium catalysts has been less well studied than with nickel. Nevertheless, zerovalent complexes of palladium, particulrly triarylphosphite complexes, hydrocyanate a wide range of olefins in useful yields (see Table 1). Early work reported the merit of excess phosphorus ligand to promote the reaction, and further paralleling the observations with nickel, Lewis acids have been used to improve catalytic activity. However, addition of ZnClj fails to improve nitrile product yield . Asymmetric induction in hydrocyanation results in optical yields of 30% in the synthesis of exo-2-cyanonorbomane using the chiral ligand DIOP, and studies on the stereochemistry of HCN and DCN addition to terminal alkenes and a substituted cyclohexene with the same catalyst have been reported. ... 

These results coupled with the greater success of nickel and palladium catalysts may explain the long interval preceding the next report on cobalt catalysts . Cobalt(I) complexes (see Table 1) are, however, effective hydrocyanation catalysts, not only in hydro-cyanating olefins such as 4-pentenenitrile, but also are effective for isomerizing 2-methyl-... 

Ditertiary phosphines such as (86), (92), and (98) (100) (Scheme 6) have found important uses as ligands for metal-catalyzed transformations, including e.g., palladium-catalyzed Grignard cross couplings,194,205 rhodium-catalyzed Michael additions,2 hydrocyanations,206 copolymerizations,20 and palladium-catalyzed animations.208 Rhodium complexes of (86) are catalysts for the carbonylation of methanol.188 More recently the ligand bite angle of ditertiary phosphines such as (100) has been shown to influence catalytic activity/selectivity in several important catalytic processes.209-213... 

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