Electrochemical Studies of the Cycloaddition Activity of Bismuth(III) Acetylides Towards Organic Azides Under Copper(I)-Catalyzed Conditions.

Antonina L Nazarova,Valery V Fokin,Sri R Narayan,Billal Zayat

doi:10.3389/fchem.2022.830237

Abstract

Time-dependent monitoring of the reactive intermediates provides valuable information about the mechanism of a synthetic transformation. However, the process frequently involves intermediates with short lifetimes that significantly challenge the accessibility of the desired kinetic data. We report in situ cyclic voltammetry (CV) and nuclear magnetic resonance (NMR) spectroscopy studies of the cycloaddition reaction of organobismuth(III) compounds with organic azides under the copper(I)-catalyzed conditions. A series of bismuth(III) acetylides carrying diphenyl sulfone scaffolds have been synthesized to study the underlying electronic and steric effects of the tethered moieties capable of transannular oxygen O···Bi interactions and para-functionality of the parent phenylacetylene backbones. While belonging to the family of copper-catalyzed azide-alkyne cycloaddition reactions, the reaction yielding 5-bismuth(III)-triazolide is the sole example of a complex catalytic transformation that features activity of bismuth(III) acetylides towards organic azides under copper(I)-catalyzed conditions. Stepwise continuous monitoring of the copper(I)/copper(0) redox activity of the copper(I) catalyst by cyclic voltammetry provided novel insights into the complex catalytic cycle of the bismuth(III)-triazolide formation. From CV-derived kinetic data, reaction rate parameters of the bismuth(III) acetylides coordination to the copper(I) catalyst (KA) and equilibrium concentration of the copper species [cat]eq. are compared with the overall 5-bismuth(III)-triazolide formation rate constant kobs obtained by 1H-NMR kinetic analysis.

Highlights

With an increased interest in the area of novel, non-toxic, and biocompatible nanomaterials, bismuth (Bi)-doped systems have become important in the area of near-infrared (NIR)-emitters and drugdelivery materials (Laguta and Razdobreev, 2018; Liu et al, 2018; Szostak et al, 2019; Orellana-Tavra et al, 2020)
By altering the electron-withdrawing nature of the sulfone moiety and the ability of the oxygen atom to intramolecularly coordinate to the bismuth center, we studied a variety of sulfonetype ligands that influence the bismuth(III) acetylides activity under copper(I)-catalyzed conditions (Figure 1)
While these substrates have not been used for the in situ kinetic studies, they were used for comparisons of the solid-state structures

Summary

Introduction

With an increased interest in the area of novel, non-toxic, and biocompatible nanomaterials, bismuth (Bi)-doped systems have become important in the area of near-infrared (NIR)-emitters and drugdelivery materials (Laguta and Razdobreev, 2018; Liu et al, 2018; Szostak et al, 2019; Orellana-Tavra et al, 2020). The coordination with electron donors such as sulfur (S) and nitrogen (N) was reported to increase the thermal, air, and hydrolytic stability of bismuth in the oxidation states of (III) and (V), creating new opportunities for its applications (Raţ et al, 2013; Toma et al, 2016; Toma et al, 2017). We report a mechanistic study of the reactivity of para-phenyl substituted bismuth(III) acetylides in the copper(I)-catalyzed cycloaddition reactions with organic azides (Worrell et al, 2013a). By altering the electron-withdrawing nature of the sulfone moiety and the ability of the oxygen atom to intramolecularly coordinate to the bismuth center, we studied a variety of sulfonetype ligands that influence the bismuth(III) acetylides activity under copper(I)-catalyzed conditions (Figure 1)

Methods

Results

Conclusion