Photocatalytic Oxidation of Bromide to Bromine

Inorg Chem. 2017 Jan 17;56(2):693-696. doi: 10.1021/acs.inorgchem.6b01652. Epub 2016 Sep 7.

Abstract

Three consecutive bimolecular reactions are employed to photocatalyze bromide oxidation to bromine. The system consists of a ruthenium(II) complex, [Ru(deeb)2(dmbpy)]2+ (deeb = 4,4'-diethylester-2,2'-bipyridine; dmbpy = 4,4'-dimethyl-2,2'-bipyridine), 4-bromobenzenediazonium tetrafluoroborate (ArN2BF4), and Br-. Varying reagent concentrations allowed us to optimize the sequence of reactions for product formation. The electronically excited ruthenium complex (*Ru) reacts first with ArN2BF4 to produce a ruthenium(III) (RuIII) intermediate, triggering a subsequent reaction with Br-. Transient absorption measured at 486 and 380 nm provides insight into the time-dependent concentrations of *Ru, RuIII, and Br2•-. Without interference of back-electron transfer, the rate constant for an equal concentration bimolecular reaction of Br2•- was determined to be 5 × 109 M-1 s-1. The final products, bromine and tribromide, were spectroscopically characterized, and the turnover number (TON) was 230.