The reaction of thiosemicarbazones 4-MeC 6 H 4 C(Me)᎐ ᎐ NN(H)C(᎐ ᎐ S)NH 2 a, C 6 H 5 C(Et)᎐ ᎐ NN(H)C(᎐ ᎐ S)NH 2 b and 4-MeC 6 H 4 C(Me)᎐ ᎐ NN(H)C(᎐ ᎐ S)NHMe c with K 2 [PdCl 4 ] led to tetranuclear palladiumthe 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 Pd 4 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 1,1Ј-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 C᎐ ᎐ S 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 7aЈ and 7bЈ, respectively, as impurities, where the bidentate phosphine ligand bridges two metallated units. The crystal structure of one such compound, 7bЈ, with a bridging bis(diphenylphosphino)methane ligand, is also described.

The palladium(II) compound [Pd{3,4-(MeO)2C6H2C(H)NCy}{(Ph2PCH2CH2)2PPh-P,P,P}][PF6] was synthesized and characterized by elemental analysis (C, H, N) and by 1H and 31P{1H} NMR spectroscopy in CDCl3 and 31P{1H} solid-state NMR spectroscopy. The molecular structure was determined by X-ray crystallography, showing it to be the first pentacoordinated cyclometalated palladium(II) complex.

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Reaction of the Schiff base ligand 1, 3, 3 C 6 H 2 C(H)dNCH 2 ] 2 C 6 H 4 (1) with palladium(II) acetate in toluene gave the doubly cyclometalated complex [1,3, 3 C 6 HC(H)dNCH 2 ](µ-O 2 CMe)} 2 C 6 H 4 ] (2), in which the two palladium atoms are intramolecularly bonded by acetato bridging ligands. The crystal structure of 2 is given. Reaction of the Schiff base ligand 1,4-[2,3,4-(MeO) 3 C 6 H 2 C(H)dNCH 2 ] 2 C 6 H 4 ( 6) with palladium(II) acetate under similar reaction conditions yielded the cyclometalated complex [1,3, Reaction of 2 and 7 with aqueous sodium chloride gave the chloro-bridged complexes [1,3, 8), respectively, after a metathesis reaction. Treatment of complex 2 with Ph 2 P(CH 2 ) 3 PPh 2 (dppp) in a 1:1 molar ratio gave the dinuclear cyclometalated complex [1,3, 3 C 6 HC(H)dNCH 2 ](OAc)} 2 C 6 H 4 (µ-Ph 2 P(CH 2 ) 3 PPh 2 )] (4), in which the metal atoms are bonded by the diphosphine ligand. Treatment of the chloro-bridged complex 3 with dppp in a 1:2 molar ratio gave the dinuclear cyclometalated complex [1,3, 3 C 6 HC(H)dNCH 2 ](Cl)} 2 C 6 H 4 (µ-Ph 2 P(CH 2 ) 3 PPh 2 )] ( 5), with the palladium atoms intramolecularly bridged by the diphosphine. The complex showed a fluxional behavior in solution, with the cyclometalated moieties adopting a cis/trans arrangement. Reaction of the chloro-bridged complex 8 with dppp in a 1:2 molar ratio yielded the mixture of complexes [1,3, 3 C 6 HC(H)dNCH 2 ](Cl)} 2 C 6 H 4 (µ-Ph 2 P(CH 2 ) 3 PPh 2 )] ( 9) and [1,3, 3 C 6 HC(H)dNCH 2 ](Cl)} 2 C 6 H 4 (µ-Ph 2 P(CH 2 ) 3 PPh 2 )] 2 (10), of which only 9 was isolated pure. Compound 9 showed a structure and solution behavior similar to those of 5; however, the structure of 10 was not unambiguously established. The crystal structure of 9 is also reported.