Chemical and photochemical properties of a ruthenium nitrosyl complex with the N-monosubstituted cyclam 1-(3-Propylammonium)-1,4,8,11-tetraazacyclotetradecane

Abstract

The amine-functionalized trans-[Ru(NO)Cl(1-pramcyH)](PF6)3 complex (1-pramcyH = 1-(3-propylammonium)-1,4,8,11-tetraazacyclotetradecane) was synthesized from trans-[RuCl(tfms) (1-pramcyH)](tfms)2 (tfms = trifluoromethanesulfonate) in acidic aqueous solution in the presence of nitric oxide (NO). The complex was characterized by elemental, spectroscopic (UV-Vis, IR, 1H and 13C NMR) and electrochemical analyses. Two pKa values (7.0 and 8.2) were estimated for trans-[Ru(NO)Cl(1-pramcyH)](PF6)3 and were assigned to one of the cyclam nitrogen protons and to the protonated aminopropyl group. Reduction of trans-[Ru(NO)Cl(1-pramcyH)]3+ results in rapid loss of chloride followed by slower loss of NO, while irradiation of the complex in aqueous deaerated conditions suggests photochemical labilization of NO. The quantum yields for NO photoaquation decrease as the irradiation wavelength increases, being noticeable only at λirr < 370 nm, and increase as pH increases. The behavior of trans-[Ru(NO)Cl(1-pramcyH)]3+, which contains an aminopropyl substituted cyclam, parallels that reported for the analogous complex with the unsubstituted ligand, but differs from that described for the complex in which carboxypropyl is the substituent.