Abstract
The formally Co(O) complex LCo(N-2) (L = 2,6-bis(2,6-dimethylphenyliminoethyl)pyridine) can be prepared via either Na/Hg reduction of LCoCl2 or hydrogenolysis of LCoCH2SiMe3. In the latter reaction, LCoH could be trapped by reaction with N=CC6H4-4-Cl to give LCoN=CHC6H4-4-Cl. LCo(N-2) reacts with many alkyl and aryl halides RX, including aryl chlorides, to give a mixture of LCoR and LCoX in a halogen atom abstraction mechanism. Inter-mediacy of free alkyl and aryl radicals is confirmed by the ring-opening of cyclopropylmethyl to crotyl, and the rearrangement of 2,4,6-(Bu3C6H2)-Bu-t to 3,5-(Bu2C5H3CMe2CH2)-Bu-t, before binding to Co. The organocobalt species generated in this way react further with activated halides R'X (alkyl iodides; allyl and benzyl halides) to give cross-coupling products RR' in what is most likely again a halogen abstraction mechanism. DFT studies support the proposed radical pathways for both steps. MeI couples smoothly with LCoCH2SiMe3 to give LCoI and CH3CH2SiMe3, but the analogous reaction of (BuI)-Bu-t leads in part to radical attack at the 3 and 4 positions of the pyridine ring to form (Bu-t(2)-L)CoI and (Bu-t(2)-L)CoI2.