A Versatile Methodology for the Regioselective C⁸‑Metalation of Purine Bases

Purine nucleo­bases are excellent ligands for metal ions, forming normally coordinative Werner-type bonds by utilizing the N donor atoms of the nucleo­base skeleton. Here we show that purines such as 8-chloro­caffeine and 8-bromo-9-methyl­adenine react with [Pt­(PPh3)4] under oxidative addition of the C8–halogen bond to the metal center. The resulting PtII complexes feature a C8-bound ylidene ligand. Protonation of the ylidene at the N7/9-atom yields complexes bearing a protic N-heterocyclic carbene ligand derived from the purine base with an NMe,NH-substitution pattern.