The preparation and reactions of ω-bromoacylmanganese pentacarbonyls

The reaction of ω-bromoacyl chlorides Br—CH 2 —(CH 2 ) n —COCl and Mn(CO) 5 − is reported. In the case of n = 0, one obtains ketene, Mn(CO) 5 Br, and chloride ion. In contrast, the corresponding chloro compound gives the known chloroacyl manganese complex. With n = 1, 2, or 3, one can isolate the corresponding ω-bromoacylmanganese complexes. On mild heating, the n = 1 complex produces only ethylene and Mn(CO) 5 Br. The n = 2 and 3 complexes are also relatively labile on heating in THF solution and produce the 1-alkene as the major organic product. In chloroform solution, the corresponding ω-bromoalkyl complex is produced initially on heating, but further heating again produces mainly the 1-alkene. However, the n = 2 complex also produces appreciable amounts of cyclopropane. Keywords: bromoacylmanganese pentacarbonyl, pentacarbonyl manganate, ethylene, cyclopropane.