Reductive C–O Silylation by Rhodium/Lanthanum Cooperative Catalysis

In the realm of synthetic organic chemistry, a transformation enabling access to high-value-added compounds from readily available starting materials is the most ideal. Cross-electrophile coupling (XEC) reactions, the coupling of two different electrophiles, are of great importance in terms of the variety and availability of electrophiles compared with common nucleophiles. Among various electrophiles, phenols and aryl ethers can be particularly useful aryl electrophiles owing to their low toxicity, robustness, and availability. However, XEC of phenols and aryl ethers remains elusive because it is generally challenging to distinguish between two electrophiles and selectively obtain cross-coupling products under harsh reaction conditions that are often required for the activation of the less reactive C–O bonds. Meanwhile, chlorosilanes are easily available and serve as silicon electrophiles to access the most known organosilicon compounds through coupling with organic nucleophiles. Considering the utility of organosilicon compounds as organic materials and building blocks for organic synthesis, the XEC of phenols and chlorosilanes can be a highly practical and useful transformation but has never been viable. Here we describe the XEC of phenol and alcohol derivatives with chlorosilanes by cooperative rhodium and lanthanum catalysis. This reaction allows a range of anisole derivatives as well as benzylic ethers, phenols, benzylic alcohols, allylic ethers, and allylic alcohols to be transformed into various organosilicon compounds in a single step. Mechanistic studies including kinetics, stoichiometric organometallic reactions, XAS, and theoretical calculations suggest a heterobimetallic complex bearing a Rh–Mg and/or Rh–La bond as a key catalytically active species. This method can be applied to the development of novel silicon- containing organic materials and drugs containing silicon as a carbon isostere. On the other hand, the XEC of phenol derivatives enables the use of biomass-derived resources as an alternative to petroleum to produce useful compounds in a sustainable manner.