Asymmetric by Design: Heteroleptic Coordination Compounds with Redox-Active Dithiolene and 1,2,4,5-Tetrakis(isopropylthio)benzene Ligands.

The 1,2,4,5-tetrakis(alkylthio)benzenes are redox-active organosulfur molecules that support oxidation to a stable radical cation. Their utility as ligands for the assembly of multimetal complexes with tailored functionality/property is unexamined. Here, 1,2,4,5-tetrakis(isopropylthio)benzene (tptbz, ) is shown to bind PdCl at either one end, leaving the other open, or at both ends to form centrosymmetric [ClPd(tptbz)PdCl], . Ligand metathesis between Na[(N≡C)CS] (Namnt) and [ClM(tptbz)] (M = Pd, ; M = Pt, ) yields [(mnt)M(tptbz)] (M = Pd, ; M = Pt, ), but an alternative route involving transmetalation with [(mnt)SnMe] delivers substantially greater yield. The mixed dithiolene-dithioether compound [(PhCS)Pt(tptbz)] () is formed by a similar transmetalation protocol using [(PhCS)SnBu]. Compounds , , and are the first such heteroleptic complexes prepared by deliberate synthesis. The cyclic voltammetry of reveals anodic waves at +0.14 and +0.97 V vs Fc/Fc, which are attributed to successive dithiolene oxidation processes. While oxidized at +0.73 V as a free ligand, the redox-active MO of tptbz is pushed to a higher potential upon coordination to Pt and is inaccessible. Calculations of the structures of [] and of [((Cl-3,5-CH)CS)Pt(tptbz)] show that, in the latter, the dithiolene MOs are drawn down in energy into proximity with the tptbz MOs.