Synthesis, characterization and crystal structure of triphenylphosphine copper(I) methylpyruvate thiosemicarbazones

This paper reports the synthesis of a series of methylpyruvate thiosemicarbazone derivatives containing, on the terminal nitrogen, substituents of different nature and size and namely, ethyl, phenyl and methylphenyl. These ligands were reacted with bis(triphenylphosphine)copper(I) nitrate and acetate to produce the respective complexes: [Cu(PPh3)2(Et-Hmpt)]2(NO3)2 (1), [Cu(PPh3)2(Ph-Hmpt)]NO3 (2), [Cu(PPh3)2(MePh-Hmpt)]NO3 (3), [Cu2(O2CCH3)(Et-pt)(PPh3)2] H2O (4), [Cu(Ph-mpt)(PPh3)] (5) and [Cu2(MePh-mpt)2(PPh3)2] (6). All of them were characterized by elemental analysis, IR, 1H NMR, EPR spectroscopy and, for compounds 1, 2, 4, and 6, by X-ray crystallography. The characterization revealed that the coordinating behaviour of the ligands is influenced by a series of factors, predominant among which is the hard soft nature of the atoms involved in the interactions with the metal centre. The complexes obtained from the nitrate copper(I) salt are formed by cationic molecules with a nitrate as a counterion, while those derived from the acetate salt present deprotonated ligands and a few unexpected features. In particular, one of the compounds (4) is a mixed valence dinuclear complex with an acetate oxygen and the thiosemicarbazone sulfur acting as bridging between the two Cu(I) and Cu(II) ions. Another one (6) presents instead a Cu(I)–Cu(I) sulfur bridged binuclear cluster.