Recycling of Waste Silicon Wafers for Semihydrogenation of Alkynes

The semihydrogenation of alkynes to alkenes without relying on scarce metal resources and high-pressure hydrogen is a valuable strategy from both environmental and safety perspectives. This study explores the use of silicon powder recovered from end-of-life photovoltaic panels in the semihydrogenation of terminal/internal alkynes without transition metals/hydrogen. A catalytic amount of fluoride salt and a proton source, such as acetic acid, was used for the reaction, generating 30 examples of terminal and internal alkenes with high yield and selectivity with many intact functional groups, including formyl groups and nitriles. Notably, silicon powder derived from discarded solar panels exhibited reactivity comparable to that of high-purity silicon. A combination of in situ Fourier transform infrared (FT-IR), electron spin resonance (ESR), photoluminescence spectroscopy (PLS), and X-ray photoelectron spectroscopy (XPS) measurements, along with control reaction experiments, suggested that the formation of reactive Si–H species on the silicon surface facilitated hydrosilylation with an alkyne. This is the first study that reports on alkyne semihydrogenation using silicon powder as a reducing agent and introduces a synthetic approach distinct from existing methods.