π‑Bonded Dithiolene Complexes: Synthesis, Molecular Structures, Electrochemical Behavior, and Density Functional Theory Calculations

The synthesis and X-ray molecular structure of the first metal-stabilized o-dithiobenzoquinone [Cp*Ir-o-(η⁴-C₆H₄S₂)] (2) are described. The presence of the metal stabilizes this elusive intermediate by π coordination and increases the nucleophilic character of the sulfur atoms. Indeed, the π-bonded dithiolene complex 2 was found to react with the organometallic solvated species [Cp*M­(acetone)₃]­[OTf]₂ (M = Rh, Ir) to give a unique class of binuclear dithiolene compounds [Cp*Ir­(C₆H₄S₂)­MCp*]­[OTf]₂ [M = Rh (3), Ir (4)] in which the elusive dithiolene η-C₆H₄S₂ acts as a bridging ligand toward the two Cp*M moieties. The electrochemical behavior of all complexes was investigated and provided us with valuable information about their redox properties. Density functional theory (DFT) calculations on the π-bonded dithiobenzoquinone ligand and related bimetallic systems show that the presence of Cp*M at the arene system of the dithiolene ligand increases the stability compared to the known monomeric species [Cp*Ir-o-(C₆H₄S₂-κ²-S,S)] and enables these complexes Cp*Ir­(C₆H₄S₂)­MCp*]­[OTf]₂ (3 and 4) to act as electron reservoirs. Time-dependent DFT calculations also predict the qualitative trends in the experimental UV–vis spectra and indicate that the strongest transitions arise from ligand–metal charge transfer involving primarily the HOMO–1 and LUMO. All of these compounds were fully characterized and identified by single-crystal X-ray crystallography. These results illustrate the first examples describing the coordination chemistry of the elusive o-dithiobenzoquinone to yield bimetallic complexes with an o-benzodithiolene ligand. These compounds might have important applications in the area of molecular materials.