Ferrocene-Based N-Heterocyclic Carbenes with Functionalised Benzyl Substituents

We describe herein N-heterocyclic carbenes (NHCs) with a 1,1'-ferrocenylene backbone that contain substituents at the nitrogen atoms relevant for applications in the area of metallopharmaceuticals, namely benzyl units functionalised with dimethylamino and methoxy groups at the para position. These carbenes are too unstable for isolation. They were generated from the corresponding formamidinium tetrafluoroborates by deprotonation and efficiently trapped in situ. Trapping with elemental selenium afforded the corre-sponding selenourea derivatives, the Se-77 NMR chemical shifts of which are in accord with the comparatively high electrophilicity typical of expanded-ring NHCs. Coordinative trapping with [{Rh(mu-Cl)(cod)}(2)] (cod = cycloocta-1,5-diene) furnished air-stable complexes of the type [ RhCl(cod)(NHC)], the benzyl CH2 groups of which are engaged in pronounced anagostic C-H center dot center dot center dot Rh interactions, both in solution and in the solid state.