The preparation and reactions of ω-bromoacylmanganese pentacarbonyls

Abstract

. J. Chem. 68, 502 (1990).The reaction of o-bromoacyl chlorides Br-CH2-(CH2),-COCI and Mn(CO)5-is reported. In the case of n = 0, one obtains ketene, Mn(CO)5Br, 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 w-bromoacylmanganese complexes. On mild heating, the n = 1 complex produces only ethylene and Mn(CO)5Br. 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 o-bromoalkyl complex is produced initially on heating, but further heating again produces mainly the I-alkene. However, the n = 2 complex also produces appreciable amounts of cyclopropane. On a Ctudit les reactions des chlorures de o-bromoacyles (Br-CH2-(CH2),-COC1) avec le Mn(CO)5-. Dans le cas ob n = 0, on obtient du cttkne, du Mn(CO),Br et de I'ion chlorure. Par opposition, le compost chlort correspondant fournit le complexe chloroacyl mangankse connu. Lorsque n = 1, 2 ou 3, on peut isoler les complexes o-bromoacylmangankse correspondants. Lorsqu'on le chauffe ltgkrement, le complexe dans lequel n = 1 ne conduit qu'h d'tthylkne et de Mn(CO)5Br. Les complexes dans lesquels n = 2 ou 3 sont aussi relativement labiles; lorsqu'on les soumet a un chauffage, en solution dans le THF, le produit organique majeur est le 1-alckne. En solution dans le chloroforme, il y a formation des complexes o-bromoalkyles correspondants; mais, si l'on continue le chauffage, il y a principalement formation du 1-alckne. Toutefois, le complexe dans lequel n = 2 conduit a la formation d'une quantitt apprtciable de cyclopropane.Mots elks : bromoacylmangankse pentacarbonyl, pentacarbonyl manganate, tthylkne, cyclopropane.[Traduit par la revue]Acylrnanganese pentacarbonyls 1 are a very well-known class of organometallic compounds (I). The readily lose carbon monoxide to form the alkyl complex 2 and the mechanism of this reversible reaction has been elegantly determined by labelling studies (2) and supported by later theoretical calculation^ (3).A great many derivatives of 1 are known, but there has been no systematic study of cases where R = -(CH2),--CH2Br, 3, although most of the corresponding chloro compounds have been prepared. The fact that the first member of this series (n = 0) reacted in a totally different way compared to the chloro analog makes the extension to the bromo analogs non-trivial. Our interest was mainly in the fate of the organic part of these complexes when they were subjected to thermolysis, i.e., unsaturated (16eP) organometallics often add oxidatively to a C-Br bond. It was planned to study acyl system 3 where n was varied from 0 to 3. The usual route for preparing such complexes is to react the corresponding acyl halide with Mn(CO)5-salts. This reaction is in fact a very general ketene synthesis, which has been described in other publications (4). The reaction of Mn(CO)5-with acyl chlorides to give acylmanganese orga...