A New Member of the Growing Family of Interconvertible {RuNO}6,7,8 Species. Redox and Acid-Base Characterization of [Ru((CH2py)2Me[9]aneN3)(NO)]n+

Abstract

The preparation and characterization of a new ruthenium nitrosyl based on the pentadentate ligand (CH2py)2Me[9]aneN3 (1-methyl-4,7-bis(pyridin-2-ylmethyl)-1,4,7-triazacyclononane) is reported. The octahedral species contains a {RuNO}6 fragment and can be isolated in the solid state as a PF6− salt. In acetonitrile, this platform allows exploring the reduction processes in 1-electron steps from {RuNO}6 to {RuNO}8, with associated E° values of 0.421 V and −0.628 V (vs. Ag/AgCl, 3 M NaCl), respectively. The {RuNO}7 species is paramagnetic, its EPR spectrum in vitrified acetonitrile at 90 K is consistent with an S= (Formula presented.) center with g=(2.0095, 1.9992, 1.8785) coupled to a 14N nucleus, with A=(6.9, 30.24, 1.85)×10−4 cm−1. In acidified aqueous solution, the first reduction process at 0.101 V leads to the formation of {RuNO}7, as in aprotic medium (acetonitrile). However, the incorporation of a second electron is coupled to a protonation process of the nitroxyl group, generating a coordinated azanone (HNO) compound with pKa(HNO)=11.0. Spectroscopic information obtained via spectroelectrochemistry and electronic structure calculations assist in the rationalization of results. Overall, this new compound enhances the library of nitrosylated Ru species with combined redox, acid-base, and spectroscopic characterization in water and confirms experimental correlations found in related species.