Homoleptic platinum(II) and palladium(II) complexes of 1,5,9-trithiacyclododecane:: the crystal structures of [Pt(12S3)2](PF6)2 • 2CH3NO2 and [Pd(12S3)2](BF4)2 • 0.5H2O

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 M2-/M3- 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 Pt-195 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 preorganized 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). (C) 2003 Elsevier B.V. All rights reserved.