Monomeric and Trimeric Manganese(III) Complexes of 2-Hydroxy-5,10,15,20-tetraphenylporphyrin. Synthesis and Characterization.

Abstract

The hydrolysis of the monomeric five-coordinate (2-BzO-TPP)Mn(III)Cl complex has been investigated.(1) Evidence for the formation of the cyclic trimeric complex [(2-O-TPP)Mn(III)](3) is presented. The (1)H NMR spectroscopic evidence indicates that the trimeric manganese(III) complex has a head-to-tail cyclic trimeric structure with the pyrrolic alkoxide groups forming bridges from one macrocycle to the manganese(III) ion in the adjacent macrocycle PMn-O-PMn-O-PMn-O. The three manganese(III) porphyrin subunits are not equivalent. The characteristic upfield shift of the 3-H pyrrole resonance (-111.5 ppm at 291 K) was determined and considered as the diagnostic feature for the high-spin d(4) manganese(III)-pyrrole alkoxide coordination. The strong upfield shift of the 3-H resonance has been accounted for by the donation of the electron density from the filled orbital of the 2-O atom on the half-occupied d(z)()()2 orbital of the external manganese(III) ion. The other pyrrole resonances produce the complex multiplet at the typical -5 to -40 ppm region. The (1)H NMR spectra of the series of monomeric 2-substituted manganese(III) 5,10,15,20-tetraphenylporphyrin complexes (2-X-TPP)Mn(III)Cl have been obtained and analyzed. The pattern of the assigned seven pyrrole resonances reflects the asymmetry imposed by 2-substitution and has been used as a (1)H NMR spectroscopic probe to map the spin density distribution. The electronic effect is strongly localized at the beta-substituted pyrrole. The upfield shift of the 3-H resonance increases in the order (2-NO(2)-TPP)Mn(III)Cl < (2-BzO-TPP)Mn(III)Cl < (2-OCH(3)-TPP)Mn(III)Cl < (2-OH-TPP)Mn(III)Cl < (2-NH(2)-TPP)Mn(III)Cl < [(2-O-TPP)Mn(III)(OH)](-) following the increasing electron-donating properties of the beta-substituent.