Mechanoredox

Mechanoredox catalysis, or mechanoredox, is a mode of chemical catalysis in which mechanical energy is converted into redox equivalents by piezoelectric materials to drive single-electron transfer reactions. It sits within the broader field of mechanochemistry and is typically implemented in ball milling or grinding setups, where mechanical force polarizes piezoelectric catalysts and generates surface charges that participate in redox cycles. This approach can enable radical transformations without external electrical power, photoredox catalysts, or traditional chemical oxidants or reductants.

Mechanism and scope are centered on piezoelectric materials that respond to mechanical stress by producing electron–hole pairs. The generated electrons can reduce substrates such as organic halides to radical species, while the holes can oxidize donor species; subsequent reactions with coupling partners propagate the catalytic cycle. The specific pathways depend on the substrates, catalysts, and additives used, but the general outcome is the generation and control of radical intermediates under mechanical activation rather than light or electricity.

Common materials include piezoelectric ceramics such as barium titanate (BaTiO3), zinc oxide (ZnO), and related ferroelectric compounds. Mechanoredox has been applied to reactions including dehalogenative reductions and various bond-forming processes that proceed through radical intermediates, such as C–N, C–O, and C–C functionalizations, often in solvent-minimized or solvent-free conditions.

Advantages of mechanoredox include elimination of external electrical input and potential alignment with green chemistry goals. Limitations involve scope and reproducibility, energy efficiency, and challenges in scaling up ball-milling processes. Ongoing research explores substrate diversity, catalyst design, and combinations with other activation modes to broaden applicability.