Pentacarbonyls, alkylmanganese

RMn(CO)5.3 Alkylmanganese pentacarbonyl complexes are obtained by reaction of alkyl halides with NaMn(CO),. Under pressures of 2-10 kbar, these complexes undergo an insertion reaction with alkenes to give usually a single manganacycle in which the electron-withdrawing group of the alkene is attached to the same carbon atom as the metal. Demetallation is accomplished by photolysis... 

The rearrangement is reminiscent of the well-known carbonyl insertion in the alkylmanganese pentacarbonyl system (51) ... 

Metal-Carbon Compounds. The existence of the insertion reaction and, in fact, the first convincing example of it, was reported by Coffield and co-workers in 1957. They showed that alkylmanganese pentacarbonyls would absorb carbon monoxide, sometimes reversibly, to form acylmanganese pentacarbonyls (16). They further showed in 1959 (17), by means of C14 labeled CO, that with methyl-manganese pentacarbonyl, a coordinated carbon monoxide inserted rather than the incoming carbon monoxide. 

As expected, coordinating molecules other than CO can react and result in the shift of a coordinated CO to an acyl CO. Cyclohexylamine, for example, reacts with alkylmanganese pentacarbonyls to produce acylmanganese tetracarbonyl cyclohexylamine complexes (59). 

Finally, (trialkylsilyl)manganese pentacarbonyl complexes (TMS-Mn(CO)5) react with oxiranes in a regioselective manner to furnish functionalized alkylmanganese pentacarbonyl complexes, which have been converted to spiroketal lactones or cyclopentenone derivatives <88JOC4892>. 

The one example where the simple insertion product is a stable product is the carbon monoxide insertion reaction. The addition of carbon monoxide to alkylcobalt tetracarbonyls to form acylcobalt tetracarbonyls has already been discussed above because of its basic importance in alkylcobalt and acylcobalt carbonyl chemistry. The mechanism of this insertion is thought to involve a 1 2 shift of the alkyl group from cobalt to carbon followed by reaction of the intermediate acylcobalt tricarbonyl with another external carbon monoxide. Although there is no conclusive evidence for or against this mechanism in the carbonylation of cobalt compounds, there is evidence for it in the related carbonylation of alkylmanganese pentacarbonyls (2, 24). 

Alkylmanganese pentacarbonyl derivatives, besides reacting with carbon monoxide to form acylmanganese pentacarbonyl derivatives, may react similarly with other electron pair-donating ligands to form substituted acylmanganese carbonyl derivatives... 

Some alkylcobalt tetracarbonyl derivatives of general formula RCo(CO)4 have been obtained. These pentacoordinate derivatives are much less stable than the corresponding hexacoordinate alkylmanganese pentacarbonyl derivatives RMn(CO)5. Treatment of Na[Co(CO)4] with a deficiency of methyl iodide under carefully controlled conditions gives a 2 to 4% yield of the very unstable CH3Co(CO)4, a volatile material which decomposes above — 35° C (55). Similar unstable ethyl and benzyl RCo(CO)4 derivatives have been obtained by treatment of Na[Co(CO)4] with [(C2H5)30][Bp4] and benzyl bromide, respectively (231). 

---