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

AbstractThe 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= 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.