Purine-based carbenes at rhodium and iridium

Purine-based carbenes can be attached to catalysis-related metals like rhodium and iridium through the standard method of in situ deprotonation of the respective azolium salts. Thus, 1,3,7,9-tetramethylxanthinium tetrafluoroborate is obtained by the reaction of trimethyloxonium tetrafluoroborate and caffeine. The salt and 7,9-dimethylhypoxanthinium iodide were used as a consecutive precursor to form rhodium (I) and iridium (I) carbene complexes of the type [M(L)(LCarbene)2]I and M(L)(LCarbene)(I) (M = Rh, Ir, LCarbene = 1,3,7,9-tetramethylxanthine-8-ylidene, 7,9-dimethylhypoxanthine-8-ylidene, L = η4-1,5-COD, CO) (COD = 1,5-cyclooctadiene). All compounds were characterized by 1H NMR, 13C NMR, mass spectrometry and/or elemental analysis.