Density functional investigation of reactive intermediates derived from alkyne-Co2(CO)6 complexes.

By applying the hybrid density functional method B3LYP and a flexible all-electron basis set, structures and energies of reactive intermediates derived from the 1-butyne complex of Co2(CO), (1) were calculated. In particular, the geometry, electronic distribution, and configurational stability of the cationic, radical, and anionic Co2(CO)6-complexed propargylic species were studied. The calculations revealed that the configurational barrier, that is, the racemization barrier for the antarafacial migration of the CHCH3 group, is low (7.6 kcalmol(-1)) for the radical and is similar to the experimental value for the corresponding cation (ca. 10 kcalmol(-1)). However, a high racemization barrier (23.7 kcalmol(-1)) for the anionic intermediate suggests the possibility of stereospecific reactions involving Co2(CO)6-complexed propargylic anions.