CHEMOSELECTIVE HOMOGENEOUS HYDROGENATION OF PHENYLACETYLENE USING THIOSEMICARBAZONE AND THIOBENZOYLHYDRAZONE PALLADIUM(II) COMPLEXES AS CATALYSTS

A series of monometallic palladium(II) complexes with thiosemicarbazon es and thiobenzoylhydrazones has been synthesized and characterised by spectroscopic methods. The crystal structures of chloro(phenyl 2-pyri dyl ketone thiosemicarbazonato)palladium(II) 1a and chloro(phenyl 2-py ridyl ketone thiobenzoylhydrazonato)palladium(II) 2 were also determin ed. The catalytic activity of the complexes in the homogeneous hydroge nation of phenylacetylene was tested with particular regard to the che moselectivity from a triple to a double bond. Using chlorocomplexes a high chemoselectivity was always observed. Results of a kinetic study of the hydrogenation of phenylacetylene in the presence of chloro(meth yl 2-pyridyl ketone thiosemicarbazonato)palladium(II) 3 as catalyst pr ovided suggestions for the elucidation of the catalytic cycle of the r eaction.