The influence of substituents (R) at the C 2 carbon on bonding properties of thiosemicarbazones {RC 2(H) [dbnd]N 3-N 2H–C 1( [dbnd]S)–N 1H 2} in palladium(II) complexes

Abstract

Reactions of the trans-PdCl 2(PPh 3) 2 precursor with furan-2-carbaldehyde thiosemicarbazone (Hftsc) and thiophene-2-carbaldehyde thiosemicarbazone (Httsc), in 1:1 molar ratios in the presence of Et 3N base, removed one Cl and one PPh 3 group from the Pd II center, and yielded the complexes [Pd(η 2- N 3, S-ftsc)(PPh 3)Cl] ( 1) and [Pd(η 2- N 3, S-ttsc)(PPh 3)Cl] ( 2), respectively. However, when a 1:2 molar ratio (M:L) was used, both Cl and PPh 3 ligands were removed, yielding the complexes trans-[Pd(η 2- N 3, S-ftsc) 2] ( 3) and trans-[Pd(η 2- N 3, 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 N 3, S-chelating ligands in complexes 1– 4. In contrast, pyrrole-2-carbaldehyde thiosemicarbazone (H 2ptsc) and salicylaldehyde thiosemicarbazone (H 2stsc) invariably formed the complexes [Pd(η 3- N 4, N 3, S-ptsc)(PPh 3)] ( 5) and [Pd(η 3–O, N 3, S-stsc)(PPh 3)] ( 6), respectively, and the ligands acted as binegative tridentate donors (N 4, N 3, S, 5; O, N 3, S, 6).