Meso-tetracinnamylporphyrin: Synthesis, characterization and the catalytic activity of its Mn(III) complex in olefin epoxidation with tetra-n-butylammonium hydrogen monopersulfate
摘要:
Meso-tetracinnamylporphyrin (H(2)tcp) has been synthesized and characterized by UV-Vis, (1)H NMR and IR spectroscopies. Protonation of H(2)tcp 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 pi-electron donation from the meso-substituents to the a(2u) orbital in comparison with the corresponding dication of meso-tetraphenylporphyrin (H(2)tpp). The unusual NH signal multiplicity observed in (1)H NMR spectrum of H(2)tcp 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 (similar to 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. (C) 2010 Elsevier Ltd. All rights reserved.