Photocatalytic Oxidation of Bromide to Bromine

Three consecutive bimolecular reactions are employed to photocatalyze bromide-oxidation to bromine. The system consists of a ruthenium(II) complex, [Ro(claeb)(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) (Ru-III)-intermediate, triggering a subsequent reaction with Br-. transient absorption measured at 486 and 380 nm provides insight into the time-dependent concentrations of *Ru, Ru-III, and,Br-2(center dot-). Without interference of back electron transfer, the rate constant for an-equal concentration bimolecular reaction of Br-2(center dot-) was determined to be 5 X 10(9) M-1 S-1 The final products, bromine and tribrcimide, were spectroscopically characterized, and; the turnover,number-(TON) was 230.