Electron ionization mass spectrometry of aryl- and fluoroalkyl-substituted palladium(II) β-diketonates and monothio-β-diketonates

Positive ion electron ionization mass spectra are presented for palladium(II) β-diketonates and monothio-β-diketonates of the general form Pd II [RC(X)CHC(O)R′] 2 , where R = phenyl, 4-methoxyphenyl, 2-thienyl, or 2-naphthyl; R′ = trifluoromethyl, pentafluoroethyl, or n-heptafluoropropyl; and X = O or S. The mass spectral behavior is in sharp contrast to that of metals of the first transition series. The spectra of the β-diketonates are dominated by metal-containing ions that arise by migration of the R group from the ligand (L) to palladium, but there is no evidence for fluorine-to-metal transfer. These findings are consistent with HSAB theory. The strong tendency of palladium to form bonds with unsaturated carbon also leads to remarkably abundant metal-containing ions that arise by losses of CO or aryloxy radicals from [PdRL] +* ions. In contrast, in decompositions of ions in the spectra of the monothio-β-diketonates, migration of the R group is suppressed; competition for palladium dπ electrons by the sulfur donor makes palladium a poorer aryl group acceptor.