Synthesis and Characterization of a Carbene·SO2 Adduct − New Insights into the Structure and Bonding of Thiourea S,S‐Dioxides

The title compound 1,3‐di‐tert‐butylimidazol‐2‐ylidene·SO2 (2) was obtained from the respective stable carbene 1 and SO2 in quantitative yield and investigated by single crystal X‐ray crystallography and NMR spectroscopy. Quantum chemical calculations show that thiourea‐S,S‐dioxides like 2 are Lewis acid‐base adducts of the respective diamino carbenes with SO2 (CS bond energies < 20 kcal·mol−1). They possess long CS bonds and a pyramidal sulfur atom and are thus structurally distinct from sulfur ylides or sulfenes. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2003)