Porphyrin-containing metallacycles built upon formation of N-heterocyclic carbene-metal bonds

A porphyrin-based metallacycle, namely [Au₂(1)₂](PF 6 ) 2 , was synthesized using zinc(II) porphyrin 1 bearing two peripheral N-heterocyclic carbene (NHC) ligands on the meso positions 5 and 15. The dimeric complex was formed through coordination-driven assembly with Ag(I), followed by transmetallation with Au(I). The two porphyrins adopt a cofacial yet flexible arrangement, and spectroscopic studies revealed solvent-dependent behaviour. DFT calculations showed that the metallacycle can expand to accommodate 1,4-diazabicyclo[2.2.2]octane (DABCO). Proton NMR experiments confirmed the encapsulation of DABCO with rapid exchange compared to the related porphyrin-based metallacage constructed from a zinc(II) porphyrin bearing four peripheral NHC ligands on the meso positions 5, 10, 15 and 20.