Enhancing Precatalyst Performance and Robustness through Aromaticity: Insights from Iridaheteroaromatics.

ABSTRACT

Despite the inherent stability-enhancing benefits of dπ-pπ conjugation-induced aromaticity, metallaaromatic catalysts remain underutilized in this context, despite their reactivity with organic functionalities in stoichiometric reactions. We present a strategy for synthesizing a diverse range of iridaheteroaromatics, (L^L)IrIII(Cp*)I, including iridapyridylidene-indole, iridapyridene-indole, and iridaimidazole, via in situ deprotonation/metalation reactions utilizing [Cp*IrCl2]2 and the respective ligands. These catalysts exhibit enhanced σ-donor and π-acceptor properties, intrinsic σ-π continuum attributes, and versatile binding sites, contributing to stability through enhanced dπ-pπ conjugation-induced aromaticity. Spectroscopic data, X-ray crystallographic data, and density functional theory calculations confirm their aromaticity. These iridaheteroaromatics exhibit formidable catalytic ability across a spectrum of transformations under industrially viable conditions, notably excelling in highly selective cross alkylation and ß-alkylation of alcohols and an eco-friendly avenue for quinolone synthesis, achieving remarkably high turnover frequencies (TOFs). Additionally, this method extends to the self-condensation of bioalcohols like ethanol, n-butanol, and n-hexanol in water, replicating conditions frequently encountered in primary fermentation solutions. These iridaheteroaromatics exhibit strong catalytic activity with fast reaction rates, high TOFs, broad substrate compatibility, and remarkable selectivity, displaying their potential as robust catalysts in large-scale applications and emphasizing their practical significance beyond their structural and theoretical importance.