Three redox states of metalloniotrosyls in aqueous solutions

BARI, S.E.; L.D. SLEP; J. A. OLABE

ADVANCES IN INORGANIC CHEMISTRY

ELSEVIER ACADEMIC PRESS INC

Lugar: Burlington, MA, Estados Unidos; Año: 2015 vol. 67 p. 87 - 144

0898-8838

AbstractThis contribution deals with the structure and reactivity of bound nitrosyl in transition-metal centers (group 8: Fe, Ru, Os). The focus is set on pseudooctahedral nitrosyl-complexes with coordination number 5 and 6, containing ancillary coligands of both heme- and non-heme type. The discussion is organized in terms of Enemark and Feltham?s classification, selecting complexes within the {MNO]n framework (n = 6, 7 and 8). The examples have been chosen for a best description of the electronic structures in terms of modern structural, spectroscopical and computational methodologies. The selected {MNO]6,7,8 species reflect the occurrence of three redox states of bound nitrosyl: NO+, NO and NO− for n = 6,7 and 8, respectively. The analysis is centered on the members of a series of complexes for which the three redox states have been characterized on the same platform, viz., [Fe(CN)5(NO)]2,3,4− and [Ru(Me3[9]aneN3)(bpy)(NO)]3,2,1+, in aqueous solutions. The influence of the donor-acceptor character of the coligands is specifically addressed with emphasis on the ligand trans- to nitrosyl, showing that the latter group may exert a delabilizing influence (as NO+), as well as a labilizing one (NO− >> NO) on the trans-ligand. On the other hand, typical electrophilic reactivity patterns (toward different nucleophiles) are analyzed for M-NO+, and nucleophilic reactivity (with O2) is described for the reduced species, M-NO and M-(NO−). In the latter case, protonation is described by characterizing the bound HNO species. Important differences are highlighted in the chemistry of bound NO− and HNO, revealing the strong and mild reductant abilities of these species, respectively. The chemistry is analyzed in terms of the biological relevance to the behavior of nitrite-, NO-reductases and other NO-related enzymes.Keywords: nitrosyl ? nitroxyl ? nitrosyl hydride ? NO-complexes ? azanone