The Doerrer Group synthesizes and studies heterobimetallic lantern (or paddlewheel) complexes with different combinations of Pt(II) and a 3d metal center, with different S^O-donor backbone bidendate ligands for selective coordination to the metal centers. Recently, S^N-donor backbone ligands were explored, but yielded an unexpected structure. Previously, [Pt(S^O)2]2- species were prepared in situ, and a second metal center was added to form the lantern complex. With thiobenzamide instead of thioacetate, a stable deep green product precipitated out of water and acetone directly after the addition of Pt(II). Crystal structures of four different thiobenzamide derivatives revealed that the ligand reacted with itself to form a new S^N^S ligand, with a 4:2 S:N heteroatom ratio, contrary to the expected 4:4 ratio. To the best of our knowledge, this ligand is unprecedented. Two of these new thione-thiolate chelate ligands coordinate the Pt(II) center in a square planar arrangement. Condensations of O-containing amides are well-studied, but any S-amide condensation is much less explored. A goal is to understand the intra- and inter-molecular driving forces at play in the formation of this new ligand. Unexpected rotation of the phenyl rings out of the plane formed by the four S atoms, and the ortho-C to heteroatom distances suggest intramolecular stabilization due to internal CH…N hydrogen-bonding. This intramolecular dynamic may be stronger than the potential inter-molecular stabilization from pi-stacking of delocalized electron clouds of the phenyl rings, if they were coplanar with the chelate rings. DFT calculations are underway to better understand the electron distribution over this delocalized system with unusual structural characteristics. At the moment, four Pt(ctaPhX)2 complexes have been made with X = 4-H, 4-Me, 4-F, 4-Cl on the four phenyls of the chelate rings, and characterized by UV-vis and 1H NMR spectroscopy, as well as elemental analysis. The Pt-Pt distances in the crystal packing range from 3.8 to 5.0 A, above the accepted threshold for metallophilic interactions. Interestingly, cyclic voltammetry experiments on three of these variations in air- and O2-free conditions under N2 revealed four cleanly defined redox events. Possible assignments of these features will be discussed in detail.

New ligand condensed from two identical thioamides into a S^N^S thione-thiolate chelate: Pt(II) complexes and electrochemistry

2019 Spring National Meeting

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