Half-hydrogenation of alkynes

Half-hydrogenations of alkynes are usually accomplished over poisoned Pd catalysts, but other catalysts also may also be used.13 Unpoisoned Pd sometimes does not give high stereoselectivity.14 One of the most mentioned Pd cat-... 

The mechanism of half-hydrogenation of alkynes is not fully understood, but some details are recognized. For example, it has long been recognized that alkynes adsorb more strongly than alkenes. During the half-hydrogenation of... 

FIGURE 2.2 Mechanism of half-hydrogenation of alkynes showing two possible adsorption sites. 

Hydrogenation using Raney nickel is carried out under mild conditions and gives cis alkenes from internal alkynes in yields ranging from 50 to 100% [356, 357, 358, 359, 360]. Half hydrogenation of alkynes was also achieved over nickel prepared by reduction of nickel acetate with sodium borohydride (P-2 nickel, nickel boride) [349,361,362] or by reduction with sodium hydride [49], or by reduction of nickel bromide with potassium-graphite [363]. Other catalysts are palladium on charcoal [364], on barium sulfate [365, 366], on... 

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