Remote meta-selective C–H bromination of arenes using a recyclable Ru-based aminopropyl bifunctional PMO with robust imidazolium bridges

Abstract

This systematic study delves into the synthesis and characterization of robust bi-functional aminopropyl-tagged periodic mesoporous organosilica with a high loading of small imidazolium bridges in its framework (PrNH₂@R-PMO-IL, ∼2 mmol g⁻¹ of IL). The materials proved to be a reliable and enduring support for the immobilization of Ru species, demonstrating strong performance and excellent selectivity in the meta-bromination of various derivatives of 2-phenylpyridine compounds and other heterocycles, showcasing its effectiveness and robust nature. The synthesized materials were thoroughly characterized to determine their structural properties, such as pore size distribution, loading of organic groups, and surface area, using various analytical techniques. The research aims to improve the catalytic activity of supported ruthenium species in meta-selective bromination reactions through a systematic approach that emphasizes the synergistic effects of the mesoporous structure, concentration of imidazolium incorporated, and aminopropyl functionalization for enhancing the catalytic performance of the supported Ru species in these reactions. Our findings indicate that the developed catalyst system exhibits promise as a recyclable catalyst for meta-C–H activation, offering the potential for multiple reaction cycles and reduced waste production. This study highlights the enhanced catalytic performance and versatility of Ru@PrNH₂@R-PMO-IL in comparison with previously documented homogeneous and heterogeneous catalyst systems, even when using lower loading levels. This is particularly evident in meta-C–H bromination of challenging substrates, such as 1-phenylpyrazole for the first time under the described catalytic chemical reaction.