π-Bonded dithiolene complexes: Synthesis, molecular structures, electrochemical behavior, and density functional theory calculations

摘要

The synthesis and X-ray molecular structure of the first metal-stabilized o-dithiobenzoquinone [Cp*Ir-o-(η4-C6H 4S2)] (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(C6H 4S2)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(C 6H4S2)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.