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. Photocatalytic 2‐iodoethanol (IEO) reductive coupling to 1,4‐butanediol (BDO) over semiconductors is kinetically slow and shows low selectivity because of the negative reduction potential of IEO and competitive side reactions of the βHE radical intermediate. A molecular Ni catalyst rapidly extracts electrons from TiO2 and thereby promotes photocatalytic reduction of IEO selectively.