A novel photoinduced reduction system of low-valent samarium species: reduction of organic halides and chalcogenides, and its application to carbonylation with carbon monoxide

Visible light irradiation is found to enhance the reducing ability of samarium diiodide (SmI2) dramatically. Organic halides (RCl, RBr, RI) and chalcogenides (RSPh, RSePh, RTePh) are smoothly reduced to the corresponding hydrocarbons by using this SmI2–hv system. The photoactivation can be also applied to ytterbium diiodide (YbI2) successfully. When the reduction of alkyl chlorides (RCl) by using the SmI2–hv system is conducted under the pressure of carbon monoxide, unsymmetric ketones (RC(O)CH2R) are obtained as carbonylating products. A mechanistic pathway may involve the formation of acylsamarium species (RC(O)SmI2), which undergo dimerization, followed by reduction with SmI2, leading to the unsymmetric ketones.