A Conspicuous Deprotonation in Complexes of Diphenyllead(IV) with Ligands Containing Both Semicarbazone and Thiosemicarbazone Chains

Abstract

In the search for new chelating agents for organolead(IV) ions, 2,6‐diacetylpyridine was sequentially condensed with semicarbazide and 4‐methylthiosemicarbazide to give H2L1. According to an X‐ray study, this molecule is nearly planar with the semicarbazone (SC) and the thiosemicarbazone (TSC) chains in “open‐arm” and “closed‐arm” orientations, respectively. Similar condensation of 2,3‐butanedione with semicarbazide and 4‐methylthiosemicarbazide or with 4‐phenylsemicarbazide and 4‐phenylthiosemicarbazide afforded H2L2 and H2L3, respectively. The reactions of H2Lx with diphenyllead(IV) diacetate in methanol gave the complexes [PbPh2(HL1)](OAc)0.75Cl0.25·2.375H2O, [PbPh2(OAc)(HL2)]·MeOH and [PbPh2(H0.5L3)(MeOH)](OAc)0.5. When the latter was recrystallised from dmso, the new derivative [PbPh2(L3)(dmso)]·2dmso was isolated. The X‐ray study of the H2L1 complex showed that the ligand, with the TSC chain deprotonated and the SC chain not deprotonated, binds the organometallic moiety through the N3, N4, N5, O1 and S atoms to afford a previously unknown [PbC2N3OS] kernel. In the H2L2 and H2L3 complexes the coordination for the diphenyllead(IV) moiety is the same, with the ligand N,N,S,O‐bound, but these complexes differ in the protonation status of the SC chain. In [PbPh2(OAc)(HL2)]·MeOH the chain is not deprotonated, and in [PbPh2(L3)(dmso)]·2dmso it is deprotonated. Conspicuously, in [PbPh2(H0.5L3)(MeOH)](OAc)0.5 the SC “arm” is formally only “half” deprotonated according to the X‐ray study and analysis of the occupation factors in the lattice. From a more “chemical” point of view, this complex can be depicted as containing both (HL3)– and (L3)2– ligands in a 1:1 ratio. This partial deprotonation of the SC chain is supported both by a bond length analysis and by 1H NMR spectroscopy.