Photocatalytic 2-Iodoethanol Coupling to Produce 1,4-Butanediol Mediated by TiO₂ and a Catalytic Nickel Complex

Photocatalytic 2-iodoethanol (IEO) coupling provides 1,4-butanediol (BDO) of particular interest to produce degradable polyesters. However, the reduction potential of IEO is too negative (-1.9 vs NHE) to be satisfied by most of the semiconductors, and the kinetics of transferring one electron for IEO coupling is slow. Here we design a catalytic Ni complex, which works synergistically with TiO₂ , realizing reductive coupling of IEO powered by photo-energy. Coordinating by terpyridine stabilizes Ni²⁺ from being photo-deposited to TiO₂ , thereby retaining the steric configuration beneficial for IEO coupling. The Ni complex can rapidly extract electrons from TiO₂ , generating a low-valent Ni capable of reducing IEO. The photocatalytic IEO coupling thus provides BDO in 72 % selectivity. By a stepwise procedure, BDO is obtained with 70 % selectivity from ethylene glycol. This work put forward a strategy for the photocatalytic reduction of molecules requiring strong negative potential.