Formation, characterization, and structural studies of novel thiosemicarbazone palladium(II) complexes. Crystal structures of [{Pd[C6H4C(Et)NNC(S)NH2]}4], [Pd{C6H4C(Et)NN C(S)NH2}(PMePh2)] and [{Pd[C6H4C(Et)NNC(S)NH2]}2(µ-Ph2PCH2PPh2)]

Abstract

The reaction of thiosemicarbazones 4-MeC₆H₄C(Me)NN(H)C(S)NH₂ a, C₆H₅C(Et)NN(H)C(S)NH₂ b and 4-MeC₆H₄C(Me)NN(H)C(S)NHMe c with K₂[PdCl₄] led to tetranuclear palladium(II) compounds, [{Pd[4-MeC₆H₃C(Me)NNC(S)NH₂]}₄], 1a, [{Pd[C₆H₄C(Et)NNC(S)NH₂]}₄] 1b, and [{Pd[4-MeC₆H₃C(Me) NNC(S)NHMe]}₄] 1c; the ligands are tridentate through the [C, N, S] atoms and they are deprotonated at the NH group. The Pd–S_chelating bond is sufficiently strong for the complexes to undergo reactions with nucleophiles without bond cleavage. The molecular structure of 1b has been determined by single-crystal diffraction, confirming the formation of the tetranuclear moieties. Hydrogen bonding N· · ·H and S· · ·H links Pd₄ clusters into strands in the solid state. Reaction of 1a and 1b with phosphines gave mono- and di-nuclear species, 2a, 2b, 3b and 5a, 5b, respectively. Treatment with 1,1′-bis(diphenylphosphino)ferrocene led to trimetallic compounds 6a and 6b. The molecular structure of 3b has been determined by X-ray crystallography; dimer units are present through N· · ·H hydrogen bonds. The reaction of 2b with hydrochloric acid resulted in a 1∶1 electrolyte, 4b, with NH and CS groups. Alternatively, treatment of 1a, 1b and 1c with strong chelating phosphines produced mononuclear compounds with only cleavage of the Pd–S_bridging bonds, 7a, 7b, 7c and 8c with the diphosphine monodentate; 7a and 7b were obtained with the dinuclear species 7a′ and 7b′, respectively, as impurities, where the bidentate phosphine ligand bridges two metallated units. The crystal structure of one such compound, 7b′, with a bridging bis(diphenylphosphino)methane ligand, is also described.