Pentacarbonylmanganese Halides

The pentacarbonylmanganese halides have been known for some time1 2 but are still the subject of intense interest. Numerous vibrational analyses h- ve been carried out,3 as well as synthetic and kinetic studies of carbonyl substitution reactions.4 Halide substitution, which requires elevated temperatures,5 leads to charged species. Diazocyclopentadienes insert into the manganese-halogen bond.6 

The best method for preparation of pentacarbonylchloromanganese is the reaction of chlorine with dimanganese decacarbonyl in carbon tetrachloride solution. Earlier versions of this procedure2 often give low yields however, the present version is reliable and produces a good yield. 

The action of CC14 alone on Mn2(CO)10 also gives MnCl(CO)s,7 but the reaction is too slow to be of synthetic utility. Recent reports8 suggest that photolysis enhances both the rate and yield of this reaction. 

A commonly used preparation of MnBr(CO)s is the reaction of Mn2(CO)10 with Br2 in CC14.2 9 However, the product is frequently contaminated with MnCl(CO)s owing to reaction of the decacarbonyl with the solvent.7 A substantial increase in the yield and purity of this compound can be achieved by the use of CS2 as the reaction solvent, as in the procedure given here. 

The iodo analogue has been prepared by thermal1 7 and photochemical8 reactions of Mn2(CO)10 with I2. The former method, which is simple to perform, is described in Section D. The reaction of MnH(CO)s and I2 also has been reported to give MnI(CO)s.10 Another procedure utilizes the nucleophilic character of the anion Mn(CO)s. This reaction, which forms the basis of the procedure in Section C, was mentioned briefly some years ago,11 but no experimental detail was provided. Advantages of the method are speed, high yield, and absence of product contamination by unreacted Mn2(CO)10. 

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Pentacarbonylmanganese Halides 159 TABLE I. IR Spectra in Carbonyl Stretching Region... 

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