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)]4

The reaction between di-2-thienyl ketone thiosemicarbazone, dtktsc, (1) and Zn(OAc)(2)center dot 2H(2)O in ethanol produced [Zn(kappa(2)-N-im,S-dtktsc-H)(2)] (2). When PdCl2(CH3CN)(2) was used in place Zn(OAc)(2)center dot 2H(2)O novel [Pd(kappa(4)-C,N-im, (mu-S),(mu-S)-dtktsc-2H)](4) (3) was isolated. These reactions are in contrast with those reported for the synthesis of [Zn(kappa(3)-N-py,N-im,S-dpktsc-H)(2)] and [PdCl(kappa(3)-N-py,N-im,S),PdCl2(kappa(2)-N-py,N-am)-dpktsc-H)] center dot 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 kappa(2)-N-im,S-coordination of the imide deprotonated dtktsc (dtktsc-H)- to the Zn(II) ion was established from C-13 and H-1 NMR measurements. X-ray structural analysis on a single crystal of 3 center dot dmf confirmed the kappa(4)-N-im,C,(mu-S),(mu-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)center dot 2H(2)O and PdCl2(CH3CN)(2) revealed facile co-ordination of dtktsc to the metal ions. The palladacyclic 3 shows good electro-catalytic behavior toward proton reduction and moderate catalytic activity toward C-C cross-coupling reactions.