Homoleptic platinum(II) and palladium(II) complexes of 1,5,9-trithiacyclododecane: the crystal structures of [Pt(12S3) 2](PF 6) 2 · 2CH 3NO 2 and [Pd(12S3) 2](BF 4) 2 · 0.5H 2O

Abstract

The synthesis, spectroscopy, electrochemistry, and crystal structures of two new mononuclear homoleptic Pt(II) and Pd(II) complexes with the crown trithioether 1,5,9-trithiacyclododecane (12S3) are reported. In contrast to behavior with analogous smaller ring trithiacrowns, both metal complexes exhibit exodentate axial sulfur donors, a consequence of the preferred conformation of the 12S3 ligand. The lack of two axial metal–sulfur interactions correlates with the observed electronic spectroscopy and oxidative electrochemistry displayed by the complexes and contrasts with properties exhibited by complexes containing smaller polythioether macrocycles. The two complexes have electronic spectra dominated by charge transfer, not d–d bands and show no M 2+/M 3+ couples. Both complexes show a fluxional 12S3 ligand in solution due to a 1,5-metallotropic shift, an uncommon observation of this particular type of intramolecular ligand exchange. The 195Pt NMR chemical shift of −4201 ppm for [Pt(12S3) 2] 2+ is consistent with an alternating positioning of the four sulfur lone pairs on the coordinated thioethers. Although 12S3 is poorly pre-organized for facial complexation, its flexibility to position a sulfur in an exodentate fashion enables it to form stable complexes with d 8 metal ions such as Pt(II) and Pd(II).