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, 1 ) is shown to bind PdCl 2 at either one end, leaving the other open, or at both ends to form centrosymmetric [Cl 2 Pd(tptbz)PdCl 2 ], 4 . Ligand metathesis between Na 2 [(N≡C) 2 C 2 S 2 ] (Na 2 mnt) and [Cl 2 M(tptbz)] (M = Pd, 2 ; M = Pt, 3 ) yields [(mnt)M(tptbz)] (M = Pd, 5 ; M = Pt, 6 ), but an alternative route involving transmetalation with [(mnt)SnMe 2 ] delivers substantially greater yield. The mixed dithiolene-dithioether compound [(Ph 2 C 2 S 2 )Pt(tptbz)] ( 8 ) is formed by a similar transmetalation protocol using [(Ph 2 C 2 S 2 )Sn n Bu 2 ]. Compounds 5 , 6 , and 8 are the first such heteroleptic complexes prepared by deliberate synthesis. The cyclic voltammetry of 8 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 2+ and is inaccessible. Calculations of the structures of [ 8 ] + and of [((Cl 2 -3,5-C 6 H 3 ) 2 C 2 S 2 )Pt(tptbz)] + show that, in the latter, the dithiolene MOs are drawn down in energy into proximity with the tptbz MOs.