Oxidative addition of 8-bromo-9-ethyl-1,N6-ethenoadenine to d10 metals

Abstract

The 8-bromoadenine derivative 8-bromo-9-ethyl-1,N6-ethenoadenine 3 was prepared from adenine in three steps. Treatment of 8-bromo-9-ethyl-1,N6-ethenoadenine 3 with the zero-valent metal precursors [M0(PPh3)4] (M = Pd, Pt) in the presence of NH4BF4 as proton source gave exclusively the compounds trans-[4]BF4 and trans-[5]BF4. The obtained complexes bear a modified C8-bound adenine derivative with a protonated endocyclic nitrogen atom N7. A stepwise reaction sequence consisting of an initial oxidative addition of the C8–Br bond of 3 to [Pt0(PPh3)4] followed by treatment with HBF4·Et2O as proton source led to the dinuclear complex [6]2+ after a reaction time of several days. This complex features two adenine-derived NHC ligands coordinating to two PtII ions in a µ-κC8:κN7 bridging fashion. Protonation of the NHC ligands occurred at the nitrogen atom N6 instead of N7 of the purine scaffold. The molecular structures of the three complexes were determined by X-ray diffraction studies.