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Bimetallic cyclometallated palladium(II) complexes readily react with silver perchlorate and tertiary diphosphines to give dipalladium compounds with terdentate [C,N,S] thiosemicarbazones, and with bridging and chelating [P,P] ligands, of the type [Pd(Ph2PCH2PPh2-P,P){Pd[4-MeOC6H3C(Me)NNC(S)NHMe](Ph2PCH2PPh2)-P,S}] [ClO4]2, 1a. The crystal structures of complexes [PdCl2{Pd[2-MeOC6H3C(Me)NNC(S)NHMe](Ph2PC(CH2)2PPh2)-P,S}] and [Pd(Ph2PCH2PPh2-P,P){Pd[3-MeOC6H3C(Me)NNC(S)NHMe](Ph2PC(CH2)2P-Ph2)-P,S}]-[ClO4]2, 6 and 4a, respectively, are the first reported examples of palladacycles with the diphosphine Ph2PC(CH2)2PPh2, bis(diphenylphosphine)cyclopropane (dcpc), in the bridging mode. The short-bite diphosphines produce strained four-membered rings at the metal; the structures for 1a and 4a show the P–C–P carbon atom puckered away from the metal coordination plane.

The reaction of the tetranuclear halide-bridged complexes 1−2(a−d) with Ph2PCH2PPh2 (dppm) or Ph2PC( CH2)PPh2 (vdpp) in 1:2 molar ratio and NH4PF6 afforded the novel tetarnuclear palladacycles 3−6 (a, c, d) as 1:2 electrolytes with bridging diphosphine and halogen ligands. The structure of 4a has been determined by X-ray diffraction analysis, and represents the first example of a tetranuclear palladacycle with bridging dppm and halogen ligands. Reaction of 1−2(a−d) with (Ph2PCH2CH2)2PPh (triphos) in 1:2 molar ratio gave 7(a−d) bearing two pentacoordinated palladium atoms. The structure of 7a, as determined by X-ray diffraction analysis, shows the distorted square pyramidal geometry around the metal centers. Treatment of 1−2(a−d) with dppm, vdpp or Ph2PN(Me)PPh2 (dppma) in 1:4 molar ratio gave the dinuclear palladacycles 8−10(a−d) with a chelating diphosphine ligand at each metal center; further treatment of 9(a−c) with the nucleophiles pyrrolidine, piperidine, morpholine or 4-methyl-piperidine gave the Michael addition derivatives 11−12(a−c), 13b, 13c and 14c, promoted by the withdrawing effect of the palladacycle which activates the C CH2 double bond.

The reaction of 1-(2,5-dimethylbenzylidene)-3-ethylthiosemicarbazone and palladium acetate in acetic acid yields a trinuclear cyclometallated palladium(II) compound. Each thiosemicarbazone ligand is tridentate with the metal bonded to the carbon atom from the 2-methyl group, to the azomethine nitrogen and to the sulfur atom, which bridges to an adjacent palladium center. The crystal structure confirms the presence of a non-planar hexagonal metallated ring plus a central six-membered palladium–sulfur core within the trimer, which also displays a rather deep intramolecular cavity.

Treatment of the thiosemicarbazones 4-FC6H4C(Me) NN(H)C( S)NHR, (R = Me, a; Ph, b) and 2-ClC6H4C(Me) NN(H)C( S)NHR (R = Ph, c) with lithium tetrachloropalladate(II) in methanol or palladium(II) acetate in acetic acid gave the tetranuclear cyclometallated complex [Pd{4-FC6H3C(Me) NN C(S)NHR}]4 (1a, 1b) and [Pd{2-ClC6H3C(Me) NN C(S)NHPh}]4 (1c). Reaction of these tetramers with the diphosphines dppe, t-dppe, dppp or dppb in a 1:2 molar ratio gave the dinuclear cyclometallated complexes [(Pd{4-FC6H3C(Me) NN C(S)NHR})2(μ-Ph2P(CH2)nPPh2)], (n = 2, 2a, 2b; 3, 4a, 4b; 4, 5a, 5b), [(Pd{4-FC6H3C(Me) NN C(S)NHPh})2(μ-Ph2PCH CHPPh2)], (3a, 3b) and [(Pd{2-ClC6H3C(Me) NN C(S)NHR})2(μ-Ph2P(CH2)nPPh2)], (n = 2, 2c, 2d; 3, 4c, 4d; 4, 5c, 5d), [(Pd{2-ClC6H3C(Me) NN C(S)NHPh})2(μ-PPh2CH CHPPh2)], (3c, 3d). The X-ray crystal structure of the ligand b and the complexes 3c, 4a and 4d were determined. The structures of complexes 4a and 4d show that the different disposition of the chain cyclometallated of the thiosemicarbazones (in the same orientation or in the opposite one) is due to the different H bonds produced.