Meso-tetracinnamylporphyrin: Synthesis,characterization and the catalytic activity of its Mn(III) complex in olefin epoxidation with tetra-n-butylammonium hydrogen monopersulfate

Meso-tetracinnamylporphyrin (H₂tcp) has been synthesized and characterized by UV–Vis, ¹H NMR and IR spectroscopies. Protonation of H₂tcp with HCl is accompanied by a blue shift (77 cm⁻¹) of the Q(0,0) band, probably indicating a decrease in the efficiency of the π-electron donation from the meso-substituents to the a_2u orbital in comparison with the corresponding dication of meso-tetraphenylporphyrin (H₂tpp). The unusual NH signal multiplicity observed in ¹H NMR spectrum of H₂tcp shows evidence of a long distance coupling between the vinyl protons and NH ones. This long range coupling can occur between the remote centers using the a_2u orbital as a connector. Mntcp(OAc) shows higher catalytic activity (ca. 1.2-fold higher) than Mntpp(OAc) in olefin epoxidation with tetra-n-butylammonium hydrogen monopersulfate (TBAO). The low ratio (∼1.5) of cis- to trans-stilbene oxide, in competitive oxidation of cis- and trans-stilbene with TBAO, strongly suggests the involvement a common high-valent manganese oxo complex as the reactive intermediate responsible for oxygen atom transfer.