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

Metallaphotoredox catalyzed cross-coupling of an arylbromide (Ar-Br) with an alkyl bis(catecholato)silicate (R-Si & OMINUS;) 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 & OMINUS;]0) as well as light intensity I0 for an efficient reaction between Ar-Br and R-Si & OMINUS;. 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 & OMINUS; smoothly leading to Ar-R, with no side-product from R-Si & OMINUS; and a second one in which R-Si & OMINUS; 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. Metallophotoredox catalyzed coupling of an aryl bromide with an alkyl bis(catecholato)silicate can lead to the formation of large quantity of side products when subjected to high intensity/high frequency irradiation. Two regimes were found to be possible; the ability to switch from the quantitative coupling to the simultaneous coupling and degradation of the silicate was observed.image