Regioselective N- and C‑Metalation of Neutral 2‑Halogenobenzimidazole Derivatives
journal contributionposted on 2019-10-30, 12:36 authored by Rajorshi Das, Jonas Blumenberg, Constantin G. Daniliuc, David Schnieders, Johannes Neugebauer, Ying-Feng Han, F. Ekkehardt Hahn
Neutral 2-chlorobenzimidazole (1) and its derivatives 8-chlorotheophylline (2) and 8-bromotheophylline (3) undergo at low temperature in THF an N–H polar oxidative addition reaction with Ni0 to give exclusively the nickel(II) hydrido complexes trans-–trans- featuring an N-metalated five-membered azolato heterocycle. In spite of the reactive C–halogen bond, no C-metalation was observed in any of these reactions. At 45 °C, however, 2-chlorobenzimidazole (1) reacts in toluene/hexane in a polar oxidative addition of the C2–Cl bond to Ni0 to yield a mixture of the complexes trans- and trans- both bearing a C-metalated benzimidazolato ligand. The related complex trans- bearing a C-metalated azolato ligand is formed in the oxidative addition of 2-chlorocaffeine, featuring one alkylated ring nitrogen atom within the diaminoheterocycle to Ni0.