Mono- and tetranuclear cyclopalladated complexes with N′-(9-anthracenylidene)benzothiohydrazide: Syntheses, structures and catalytic applications

Abstract

Reaction of PdCl2, LiCl, N′-(9-anthracenylidene)benzothiohydrazide (H2L, 2 Hs represent the thioamide NH proton and the 9-anthracenylidene peri proton) and NaOAc·3H2O in 1:2:1:1 mole ratio in methanol produced [Pd4(L)4] (1) in 75% yield. Treatment of 1 with PPh3 (1:4.5 mole ratio) in acetone provided [Pd(L)(PPh3)] (2) in 72% yield. The molecular formulas of the diamagnetic and non-electrolytic 1 and 2 were established by elemental analyses. Molecular structures of 1 and 2 were determined by single crystal X-ray diffraction studies. In the tetranuclear 1, the palladium(II) centers are in distorted square-planar CNS2 coordination environments created by four (L)2−, each of which acts as 5,6-membered fused chelate rings forming thioamidate-S, azomethine-N and 9-anthracenylidene peri-C donor to one metal center and uses the thioamidate-S atom to bridge a second metal center. In the mononuclear 2, (L)2− and PPh3 assemble a distorted square-planar CNSP coordination environment around the palladium(II) center. Spectroscopic (IR, NMR and UV-Vis) measurements were also used to characterize 1 and 2. The catalytic properties of both complexes in the oxidative phenylacetylene homocoupling reaction were examined.