A Monolithium Monohydrogen Porphyrin

Porphyrins and their metal complexes play essential roles in biological and industrial processes, functioning as key components in catalysis, photodynamic therapy, and organic (opto-)electronic materials. Despite their significance, the intermediate states involved in metal incorporation into porphyrins remain poorly understood and are rarely observed as stable compounds. Here, we report the solvent-free synthesis of the first neutral alkali metal monohydrogen porphyrin, which was selectively obtained by reaction of lithium vapor with thin films of tetraphenylporphyrin (H₂TPP) under ultrahigh vacuum (UHV) conditions. The resulting monolithium monohydrogen tetraphenylporphyrin (LiHTPP) exhibits remarkable thermal stability and can be sublimated under UHV at 485 K without disproportionation, enabling its isolation. LiHTPP reacts with additional lithium to form dilithium tetraphenylporphyrin (Li₂TPP), as confirmed through product analysis and reaction monitoring via photoelectron spectroscopy and mass spectrometry. Complementary theoretical simulations provide deeper insight into the chemical structure of this non-planar complex and the energetics of its formation. This study advances the understanding of monohydrogen metalloporphyrins and their role in metalation pathways, introducing a novel synthetic route for stable intermediates. The study also underscores the potential of monohydrogen metalloporphyrins for developing catalysts and electronic materials with tunable properties.