Boron trihalide adducts of dimethyl sulphide. A nuclear magnetic resonance study of exchange reactions and mixed boron trihalide adducts

Abstract

Rapid donor-acceptor bond-breaking and halogen-redistribution reactions occur in solutions of dimethyl sulphide–boron trihalide adducts. Relative rates of donor–acceptor bond breaking are in the order BF₃ > BF₂Cl > BFCl₂ > BCl₃ > BBr₃ > BI₃ for these adducts. Halogen redistribution gives large amounts of the non-fluorine-containing mixed boron trihalide adducts, including the ternary-halogen adduct Me₂S,BClBrI. However fluorine is incompatible with the heavier halogens in these adducts. Only small amounts of Me₂S,BF₂Cl and Me₂S,BFCl₂ are present at equilibrium, and mixed F,Br- and F,I-containing adducts could not be detected. This behaviour contrasts with that of the analogous Me₂O adducts. Possible explanations are discussed.