The mechanism of the formation and the nature of microheterogeneous catalys
ts for hydrogenation are discussed using acetylacetonate complexes of palla
dium with phosphine ligands as an example. Polynuclear palladium complexes
with phosphide and phosphinidene ligands are obtained, and their role in th
e formation of hydrogenation catalysts is found. As distinct from phosphide
complexes, amide complexes of palladium are unstable in a hydrogen atmosph
ere and undergo reduction to form highly dispersed palladium black.