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

Abstract

AbstractAlthough 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 [LHZnII(OH2)]2(ClO4)2 (1H‐Aq, where LH=tridentate N,N,O‐donor monoanionic ligand) is illustrated to react with tBuONO 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 [LHZnII(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 [LHZnII(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.