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.嘌呤核碱基（purine nucleobases）是一类优异的金属离子配体，通常通过利用其骨架中的氮给体原子与金属形成配位维尔纳型键（coordinative Werner-type bonds）。我们在此报道，8-氯咖啡因（8-chlorocaffeine）与8-溴-9-甲基腺嘌呤（8-bromo-9-methyladenine）等嘌呤类化合物，可与[Pt(PPh3)4]发生反应，反应经由C8-卤键向金属中心发生氧化加成（oxidative addition）的路径进行。所得二价铂（PtII）配合物具有一个以C8位为结合位点的亚烷基配体（ylidene ligand）；对该亚烷基配体在N7或N9原子处进行质子化，可得到一类配合物，其配体为源自嘌呤碱基、带有NMe与NH取代模式的质子型氮杂环卡宾（protic N-heterocyclic carbene）。