The influence of substituents (R) at the C2 carbon on bonding properties of thiosemicarbazones {RC2(H)=N3-N2H-C1(=S)-N1H2} in palladium(II) complexes

Reactions of the trans-PdCl2(PPh3)(2) precursor with furan-2-carbaldehyde thiosemicarbazone (Hftsc) and thiophene-2-carbaldehyde thiosemicarbazone (Httsc), in 1:1 molar ratios in the presence of Et3N base, removed one Cl and one PPh3 group from the Pd-II center, and yielded the complexes [Pd(eta(2)-N-3,S-ftsc)(PPh3)Cl] (1) and [Pd(eta(2)-N-3,S-ttsc)(PPh3)Cl] (2), respectively. However, when a 1:2 molar ratio (M:L) was used, both Cl and PPh3 ligands were removed, yielding the complexes trans-[Pd(eta(2)-N-3,S-ftSC)(2)] (3) and trans-[Pd(eta(2)-N-3,S-ttSC)(2)] (4). Complexes 1-4 have been characterized with the help of analytical data, spectroscopic techniques (IR, H-1 and (31)p NMR) and single crystal X-ray crystallography. The thiosemicarbazone ligands behave as uninegative N-3,S-chelating ligands in complexes 1-4. In contrast, pyrrole-2-carbaldehyde thiosemicarbazone (H(2)Ptsc) and salicylaldehyde thiosemicarbazone (H(2)StSC) invariably formed the complexes [Pd(eta(3)-N-4,N-3,S-ptsc)(PPh3)] (5) and [Pd(eta(3)-O, N-3,S-stsc)(PPh3)] (6), respectively, and the ligands acted as bineg-ative tridentate donors (N-4, N-3, S, 5; O, N-3, S, 6). (C) 2007 Elsevier Ltd. All rights reserved.