Thiosalicylanilide complexes of nickel(II), palladium(II) and platinum(II)

Abstract

Reactions of the complexes cis-[PtCl2(PPh3)2], [PtCl2(dppf)] {dppf = Fe(C5H4PPh2)2}, [PdCl2(PPh3)2], [PdCl2(dppe)] (dppe = Ph2PCH2CH2PPh2) and [NiCl2(dppe)] with thiosalicylanilide (HSC6H4CONHPh, H2-1a) and its substituted derivatives H2-1b to H2-1d (where H2-1b = p-Cl-HSC6H4CONHPh, H2-1c = p-CH3-HSC6H4CONHPh, and H2-1d = m-OCH3-HSC6H4CONHPh) gave a series of square-planar MS2P2-type complexes. The complexes were characterised by ESI MS, 1H and 31P{1H} NMR, FTIR, and microelemental analyses, and in some cases by single crystal X-ray crystallography. The predominant coordination mode is through bonding of deprotonated thiol group of two ligands. However, the tendency to form complexes with a single, chelating S,N- and S,O-donor ligand was observed by 31P{1H} NMR in some reactions. In addition, cis/trans isomerisation was observed in some complexes by 31P{1H} NMR and confirmed by X-ray structure determinations on trans-[Pt(H-1b)2(PPh3)2] and trans-[Pd(H-1b)2(PPh3)2]. A comparison of the energetics of the reaction systems involving [Pt(1b)(PPh3)2]/[Pt(H-1b)2(PPh3)2], [Pt(1d)(PPh3)2]/[Pt(H-1d)2(PPh3)2] and [Pd(1b)(dppe)]/[Pd(H-1b)2(dppe)] using Density Functional Theory (DFT) revealed that the MS2P2 systems [Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2] and [Pd(H-1b)2(dppe)] have lower Gibbs free energies than the S,N-chelate systems [Pt(1b)(PPh3)2], [Pt(1d)(PPh3)2] and [Pd(1b)(dppe)], and are thermodynamically favoured. Intermolecular interactions quantified and visualized on Hirshfeld surfaces for trans-[Pt(H-1b)2(PPh3)2], [Pt(H-1d)2(PPh3)2].H2O, and [Pd(H-1a)2(dppe)] revealed the dominant contribution of H···H contacts to crystal packing.