The photochemistry of polyhaloarenes XIII. The photohydrodehalogenation of 3,4-dibromobiphenyl

Article abstract of DOI:10.1016/0040-4020(96)00407-3

Irradiation of 3,4-dibromobiphenyl (BpBr₂) in acetonitrile resulted in the formation of 4-bromobiphenyl (BpBr) and 3- bromobiphenyl (3-BpBr) in a ratio of 7.6 ± 0.1 up to 22% conversion of starting material. The dependence of the reciprocal of the quantum yield (1/Φ) upon 1/BpBr₂ is linear. Reduction of BpBr₂ with lithium di-tert-butylbiphenylide generates a 3.6:1.0 ratio of BpBr to 3-BpBr, while photohydrodebromination of BpBr₂ in the presence of triethylamine produces a similar ratio of 1.8:1.0. Product determining radical stability was assessed by radical debromination of BpBr₂ using Ph₃SnH in THF, which resulted in a BpBr:3-BpBr ratio of 1.5:1.0 AMI calculations on the product determining radicals provide the basis for rationalization of products via excimer and radical anion intermediates.