Azolium-2-dithiocarboxylate cAAC ^Me -CS ₂ : A Coordinatively Flexible, Redox-Active Ligand in Transition Metal Chemistry

The reactivity of the cyclic (alkyl)(amino)carbene (cAAC^Me)-stabilized CS₂ adduct, the azolium-2-dithiocarboxylate cAAC^Me-CS₂ (<b>1</b>), toward selected transition metal reagents is reported. Mono- or polynuclear (cluster) complexes [(Fe(CO)₃(cAAC^Me-CS₂)] (<b>2</b>), [{CrCp(cAAC^Me-CS₂)}₂] (<b>3</b>), [Cr₃(cAAC^Me-CS₂)₄(CO)₃] (<b>4</b>), [Re(cAAC^Me-CS₂)₃][Re₂(CO)₆(μ²-Cl)₃] (<b>5</b>), and [Ni₂Br₂(cAAC^Me-CS₂)₂(cAAC^Me-CS₃)][NiBr₃] (<b>6</b>) were prepared and characterized. Solid state structural analysis, cyclic voltammetry, and spectroscopy revealed that the coordinated ligands <b>1</b> adopt multiple formal redox states in these complexes, ranging from 0 to -2. The cAAC^Me-CS₂ (<b>1</b>) ligands were observed in a range of different terminal or bridging bonding modes, which feature metal coordination either exclusively <i>via</i> the sulfur atoms (κ<i>S</i>, κ<i>S</i>'; μ²-κ²<i>S</i>, κ²<i>S</i>'; μ³-κ²<i>S</i>, κ²<i>S</i>') or, for <b>4</b>, in addition, <i>via</i> the carbon atom of the CS₂ group (μ²-κ²<i>S</i>, κ²<i>S</i>', κ<i>C</i>). Furthermore, oxidative reaction conditions involving <b>1</b> led to C-S bond cleavage, which resulted in cyclic activation products (cAAC^Me)₂(C₂S₃) (<b>7</b>) and [(cAAC^Me)₂(C₂S₃)][Br₃] (<b>8</b>), as well as the cAAC^Me-CS₃ ligand in <b>6</b>. These findings provide evidence for the ligand systems' unique adaptability and versatility in coordination modes as well as ligand redox states, proving carbene-CS₂ adducts to be most promising candidates for future endeavors into transition metal redox or cluster chemistry.