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

Abstract

The title compound 1,3-di-tert-butylimidazol-2-ylidene·SO 2 (2) was obtained from the respective stable carbene 1 and SO 2 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

N‐Heterocyclic Olefin–Carbon Dioxide and –Sulfur Dioxide Adducts: Structures and Interesting Reactivity Patterns

“…Only in a propynesulfinate ligand coordinated to tin through one of the oxygen atoms is a similar bond length (1.862 Å) observed . The C2−S1 bond in NHC–SO 2 22 has a length of 1.859(1) Å, which is significantly shorter than the C−S distance in a cyclic diaminocarbene–SO 2 adduct (2.030(2) Å) . It is, however, in perfect agreement with the C−S bond length in thiourea S , S ‐dioxide (1.859(1) Å) .…”

“…The question arises as to whether NHO 7 forms a similar adduct with the Lewis acid SO 2 and whether a NHO–SO 2 adduct will show similar reactivity patterns to its CO 2 counterpart, for example, if treated with methanol. According to literature reports, aromatic NHCs such as 16 do not form stable adducts with SO 2 . Previous reports of an adamantyl‐substituted aromatic NHC–SO 2 adduct in the form of a planar sulfene have been doubted .…”

Recent Developments in the Chemistry of Thiourea Oxides

“…This CS bond is one of the longest carbon–sulfur bonds known in chemistry;43 a longer CS bond was reported for the TDO derivative N,N ′‐dimethylthiourea dioxide (1.880 Å44) and the 1,3‐di‐ tert ‐butylimidazolidin‐2‐ylidene . SO 2 (2.030 Å) 45. The CS bond lengthening is likely due to the antibonding interaction between the filled π‐orbitals in the CN 2 central unit and the sulfur lone pair 44…”

Quantitative Description of Structural Effects on the Stability of Gold(I) Carbenes

“…To weaken this bond, an SO 2 moiety was introduced to give a carbonSO 2 imidazolium configuration comparable to that of the neutral and stable gold alkyl complex A 15. The SO 2 imidazolylidene moiety acts as a leaving group, which further dissociates to give gaseous SO 2 and imidazolylidene 16. The imidazolium function is desirable as it, not only provides the charge for gas‐phase detection of the complex, but, in solution, its basic properties can be advantageous for a catalytic reaction during which catalytic amounts of base is required.…”