Novel κ2-Nim,S- and κ4-C,Nim,(μ-S),(μ-S)-coordination of di-2-thienyl ketone thiosemicarbazone (dtktsc). Hydrogen evolution and catalytic properties of palladacyclic [Pd(κ4-C,Nim,(μ-S),(μ-S)-dtktsc-2H)

Abstract

The reaction between di-2-thienyl ketone thiosemicarbazone, dtktsc, (1) and Zn(OAc)2·2H2O in ethanol produced [Zn(κ2-Nim,S-dtktsc-H)2] (2). When PdCl2(CH3CN)2 was used in place Zn(OAc)2·2H2O novel [Pd(κ4-C,Nim,(μ-S),(μ-S)-dtktsc-2H)]4 (3) was isolated. These reactions are in contrast with those reported for the synthesis of [Zn(κ3-Npy,Nim,S-dpktsc-H)2] and [PdCl(κ3-Npy,Nim,S),PdCl2(κ2-Npy,Nam)-dpktsc-H)] • CH3CN when di-2-pyridyl ketone thiosemicarbazone (dpktsc) was used in place of 1. The identities of 2 and 3 were established from results of their elemental compositions, spectroscopic and electrochemical properties. The κ2-Nim,S-coordination of the imide deprotonated dtktsc (dtktsc-H)– to the Zn(II) ion was established from 13C and 1H NMR measurements. X-ray structural analysis on a single crystal of 3 • dmf confirmed the κ4-Nim,C,(μ-S),(μ-S)-coordination of amide deprotonated and thienyl metallated dtktsc (dtktsc-2H)2- to the Pd(II) ion. In acidic or basic media 2 suffers dissociation, while 3 is stable under similar conditions. Electrochemical measurements on dmf solutions of 2 and 3, along with electrochemical reactions of dtktsc with Zn(OAc)2·2H2O and PdCl2(CH3CN)2 revealed facile coordination of dtktsc to the metal ions. The palladacyclic 3 shows good electro-catalytic behavior toward proton reduction and moderate catalytic activity toward CC cross-coupling reactions.