P-31{H-1} NMR studies of the preparation of dichlorotris(2,4,6-tribromophenoxy)phosphorane, trichlorobis(2,4,6-tribromophenoxy)phosphorane and tetrachloro(2,4,6-tribromophenoxy)phosphorane, and their nonoxidative chlorination reactions with dimethyl phosphonate

Dichlorotris(2,4,6-tribromophenoxy)phosphorane can serve as a nonoxidative chlorinating agent for the conversion of secondary phosphites into chloroph osphites. However, the route reported for the synthesis of this material on ly gives a 22% yield, and the product contains significant impurities. To b etter understand the reasons for this poor yield, detailed P-31{H-1} NMR st udies of the reactions of phosphorus pentachloride with one, two and three equivalents of 2,4,6-tribromophenol have been carried out. These studies de monstrate that mixtures of the phosphoranes in which one, two and three of the chlorides are substituted by 2,4,6-tribromophenoxy groups are obtained even when a 3:1 ratio of the phenol to PCl5 is used, Studies of the reactio ns of these mixtures with dimethyl phosphonate indicate that all three phos phoranes are equally capable of transforming dimethyl phosphonate into dime thyl chlorophosphonite in quantitative yield. The more highly substituted p hosphoranes are very sensitive to water and difficult to handle suggesting that the monosubstituted phosphorane is the reagent of choice. To demonstra te the synthetic utility of this nonoxidative chlorination reaction, W(CO)( 5){P(OMe)(2)Cl} has been prepared in a one pot reaction involving the nonox idative chlorination of dimethyl phosphonate with the monosubstituted phosp horane followed by the reaction of the dimethyl chlorophosphonite with W(CO )(5)(MeCN).