Theophylline-derived N-heterocyclic carbenes and their metal complexes

In this project, a series of N-heterocyclic carbene (NHC) precursors was synthesized, starting from theophylline as the base structure. Novel alkylating agents, such as dialkyl sulfates and alkyl sulfonates, were utilized to alkylate NHC precursors, leading to the successful synthesis of xanthinium salts with halide and PF₆- counterions. The structures of all synthesized compounds were thoroughly analyzed using NMR spectroscopy and mass spectrometry techniques. Given the extensive applications of metal-NHC complexes, particularly silver-NHC complexes in medicinal chemistry, the study proceeded to prepare Ag(NHC) complexes. These were further utilized to synthesize gold, rhodium, and palladium complexes via transmetalation or weak base reaction pathways. All synthesized metal-NHC complexes were comprehensively characterized by NMR spectroscopy, Electrospray Ionization mass spectrometry (ESI-MS), and, in selected cases, singlecrystal X-ray diffraction to confirm their structural integrity. Moreover, we optimized certain synthetic protocols, such as preparing [NHCH]I and [Au(NHC)2]PF₆. While these reactions were traditionally carried out under harsh conditions (60–80 °C), we successfully conducted them at room temperature, demonstrating a significant improvement in reaction efficiency and conditions. Finally, two novel silver-NHC complexes were synthesized, incorporating sulfur and tosylate in their structure, which imparts an additional nucleophilic center. These precursors show promising potential for future exploration in the synthesis of silver and other metal-NHC complexes, opening avenues for further investigations and applications in coordination chemistry.