PHOTOCHEMICAL ACTIVATION OF METALLOPORPHYRIN CARBENE COMPLEXES

While the photochemistry of simple metalloporphyrin complexes has been explored to some extent, the photoactivation of multiple-bonded axial ligands coordinated to metalloporphyrins has not been previously exam ined. We report here the photochemistry of several iron porphyrin carb ene and vinylidene complexes. Irradiation of these complexes with visi ble light cleaves the iron-carbon double bond and produces a four coor dinate iron(II) porphyrin and a free carbene, which can be trapped in high yield with a variety of alkenes. This photochemistry is unique am ong organo transition metal complexes of carbenes or alkylidenes. For these metalloporphyrin carbene complexes, the presence of the porphyri n ring alters the photoreactivity of the metal-carbon bond. This is pr obably due to the mixing between the pi orbitals of the porphyrin ri ng and the iron-carbon orbitals, which is also responsible for the hyp so-type spectrum (i.e. blue-shifted) seen in these complexes. Hypso sp ectra are a common trait in other photodissociative porphyrin complexe s, most notably CO complexes.