Regime Switch in the Dual-Catalyzed Coupling of Alkyl Silicates with Aryl Bromides.

Abstract

Metallaphotoredox catalyzed cross-coupling of an arylbromide (Ar-Br) with an alkyl bis-catecholato silicate (R-Si⊖) has been analyzed in depth using a continuum of analytical techniques (EPR, fluorine NMR, electrochemistry, photophysics) and modeling (micro-kinetics and DFT calculations). These studies converged on the impact of four control parameters consisting in the initial concentrations of the iridium photocatalyst ([Ir]0), nickel precatalyst ([Ni]0) and silicate ([R-Si⊖]0) as well as light intensity I0 for an efficient reaction between Ar-Br and R-Si⊖. More precisely, two regimes were found to be possibly at play. The first one relies on an equimolar consumption of Ar-Br with R-Si⊖ smoothly leading to Ar-R, with no side-product from R-Si⊖ and a second one in which R-Si⊖ is simultaneously coupled to Ar-Br and degraded to R-H. This integrative approach could serve as a case study for the investigation of other metallaphotoredox catalysis manifolds of synthetic significance.