Synthesis, characterization, and crystal structure analysis of the first terdentate [C,N,S] thiosemicarbazone complex with a six-membered palladacycle:: Influence of steric effects on ring size

The reaction of the thiosemicarbazone ligands 1-(COMe)-3-[C(H)=NN(H)C(=S)NHR]C8H5N, (R = H a, Me b, Et c) with potassium tetrachloropalladate in an ethanol/water mixture led to the new tetranuclear palladium(II) compounds [Pd{1-(COMe)-3-[C(H)=NN=C(S)NHR]C8H4N-k(3)C(5),N,S}](4), (R = H 1a, Me 1b, Et 1c) which contain six-membered metallacycles. The thiosemicarbazone ligands in these complexes are terdentate through the C, N, and S atoms and are deprotonated at the NH group. The Pd-S bond formed is sufficiently strong to undergo reactions with nucleophiles without bond cleavage. Reaction of 1a and 1b with 1,2-bis(diphenylphosphanyl)ethane (dppe) gave the dinuclear species [{Pd[1-(COMe)-3-{C(H)=NN=C(S)NHR}C8H4N]}(2)(mu-Ph2P(CH2)(2)- PPh2)] (R = H 2a, Me 2b). The molecular structure of complex 1b has been determined by X-ray diffraction analysis.