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 PdII center, and yielded the complexes [Pd(η2-N3,S-ftsc)(PPh3)Cl] (1) and [Pd(η2-N3,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(η2-N3,S-ftsc)2] (3) and trans-[Pd(η2-N3,S-ttsc)2] (4). Complexes 1–4 have been characterized with the help of analytical data, spectroscopic techniques (IR, 1H and 31P NMR) and single crystal X-ray crystallography. The thiosemicarbazone ligands behave as uninegative N3,S-chelating ligands in complexes 1–4. In contrast, pyrrole-2-carbaldehyde thiosemicarbazone (H2ptsc) and salicylaldehyde thiosemicarbazone (H2stsc) invariably formed the complexes [Pd(η3-N4,N3,S-ptsc)(PPh3)] (5) and [Pd(η3–O, N3,S-stsc)(PPh3)] (6), respectively, and the ligands acted as binegative tridentate donors (N4, N3, S, 5; O, N3, S, 6).

Reactions of the 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 PdII center, and yielded the complexes, [Pd(η2-N3,S-ftsc)(PPh3)Cl] (1) and [Pd(η2-N3,S-ttsc)(PPh3)Cl] (2), respectively, However, when a 1:2 molar ratio (M:L) was used, both the Cl and PPh3 ligands were removed, yielding complexes, [Pd(η2-N3,S-ftsc)2] (3) and [Pd(η2-N3,S-ttsc)2] (4). In contrast, reactions with pyrrole-2-carbaldehyde thiosemicarbazone, (H2ptsc) and salicylaldehyde thiosemicarbazone, (H2stsc) in 1:1 or 1:2 molar ratios have invariably formed the complexes [Pd(η3-N4,N3,S-ptsc)(PPh3)] (5) and [Pd(η3–O,N3,S-stsc)(PPh3)] (6), respectively.Figure optionsDownload as PowerPoint slide