Spectrophotometric study of 2,3,12,13-tetrabromo-5,10,15,20-tetraphenylporphyrin in the system 1,8-diazabicyclo[5.4.0]undec-7-ene-acetonitrile at 298 K. Deprotonation of the pyrrole rings and complex formation with Zn(OAc)2

Acid–base equilibria and coordination chemistry of the 5,10,15,20-tetraalkyl-porphyrins: implications for metalloporphyrin synthesis

“…where, n is the reaction order with salt, which is 0.5 for Cu(OAc) 2 in acetic acid, 45 and 1 for Zn(OAc) 2 in acetonitrile. 21 Activation energy E a for the studied temperature range was calculated with Arrhenius equation (eqn (6)):…”

“…The rst reaction is the generally accepted way to obtain the metalloporphyrins and has been studied in detail repeatedly, 2,6,17,18 while the macrocycle complexation with ionic mechanism was expected to be somewhat exotic and being far from the practical interest. However, our recent studies have demonstrated that the efficient metal chelation takes place also with doubly protonated forms of several porphyrin derivatives, 15,[19][20][21] we have revealed that the rate of the porphyrin complexation with Zn 2+ ions dramatically increases upon the addition to the solution of the deprotonating agent such as 1,8-diazabicyclo-[5,4,0]-undec-7-en (DBU), acting as "proton sponge" and ultimately leading to the full deprotonation of the porphyrin macrocycle core. Our ndings are in line with few early communications on the ionic mechanism of complexation, where the possibility to obtain the metalloporphyrins has been reported for the core H-bonded and monodeprotonated porphyrins.…”

“…[25][26][27][28][29][30][31] The reported to date conventional optical (spectrophotometric and luminescent) methods of the metal ion detection with porphyrin sensors approach to the detection limit of 1 Â 10 À9 mol L À1 . 31 Increased complexation rate for ionic mechanism allows to extend the detection limit at least down to 5 Â 10 À11 O 1 Â 10 À10 mol L À1 (according to difference in the porphyrin to metal salt ratio required for the metal ion chelating 15,21 ). In this communication we report on the results of the studies of the acid-base equilibria and the complexation with Cu(OAc) 2 and Zn(OAc) 2 salts for two mesoalkyl-substituted porphyrins.…”