Modeling Reactivity of Nitrite and Nitrous Acid at a Phenolate Bridged Dizinc(II) Site: Insights into NO Signaling at Zinc.

Abstract

Although nitrite-to-NO transformation at various transition metals including Fe and Cu are relatively well explored, examples of such a reaction at the redox-inactive zinc(II) site are limited. The present report aims to gain insights into the reactivity of nitrite anions, nitrous acid (HONO), and organonitrite (RONO) at a dizinc(II) site. A phenolate-bridged dizinc(II)-aqua complex [LH ZnII (OH2 )]2 (ClO4 )2 (1H -Aq, where LH =tridentate N,N,O-donor monoanionic ligand) is illustrated to react with t BuONO to provide a metastable arene-nitrosonium charge-transfer complex 2H . UV-vis, FTIR, multinuclear NMR, and elemental analyses suggests the presence of a 2 : 1 arene-nitrosonium moiety. Furthermore, the reactivity of a structurally characterized zinc(II)-nitrite complex [LH ZnII (ONO)]2 (1H -ONO) with a proton-source demonstrates HONO reactivity at the dizinc(II) site. Reactivity of both RONO (R=alkyl/H) at the phenolate-bridged dizinc(II) site provides NO+ charge-transfer complex 2H . Subsequently, the reactions of 2H with exogenous reductants (such as ferrocene, thiol, phenol, and catechol) have been illustrated to generate NO. In addition, NO yielding reactivity of [LH ZnII (ONO)]2 (1H -ONO) in the presence of the above-mentioned reductants have been compared with the reactions of complex 2H . Thus, this report sheds light on the transformations of NO2 - /RONO (R=alkyl/H) to NO/NO+ at the redox-inactive zinc(II) coordination motif.