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 backelectron 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.
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