Preparations of sulfido-tricobalt clusters containing pyridyl type ligands: insertion of carbon monoxide into cobaltcarbon bond

The reaction of 2-mercaptopyridine with 1.5 M equivalent of Co2(CO)8 in THF at 25 °C for 1 h gave a sulfido-tricobalt cluster (μ3-S)Co3(CO)7(μ-C,NC5H4N) (1). Further reaction of 1 with diphenyl-2-pyridylphosphine (PPh2py) under mild reaction condition afforded a PPh2py bridged complex (μ3-S)Co3(CO)5[(μ-C(O),NC5H4N(CO))(μ-P,NPPh2py)] (3). The X-ray structure analysis of 3 revealed that a carbonylation process occurred at the CoC(pyridyl) bond of 1. Carbonylation of 1 at the same position also took place under 1 atm of carbon monoxide at room temperature and formed (μ3-S)Co3(CO)7[(μ-C(O),NC5H4N(CO))] (4). Similar results were obtained in the reaction of 2-quinolinethiol with 1.5 M equivalent of Co2(CO)8. A sulfido-tricobalt cluster (μ3-S)Co3(CO)7(μ-C,NC9H6N) (5) and tris-quinolinethiolate chelated cobalt complex [Co(μ-S,NSC9H6N)3] (6) were obtained. In contrast to 1, carbonylation did not occur in 5 at 1 atm of carbon monoxide even at 60 °C for prolonged reaction hours. However, treatment of 5 with PPh2py yielded a PPh2py coordinated (μ3-S)Co3(CO)6[(μ-C,NC9H6N)(PPh2py)] (7) as the major product, which is accompanied with a small amount of PPh2py bridged (μ3-S)Co3(CO)5[(μ-C(O),NC9H6N(CO))(μ-P,NPPh2py)] (8). Carbonylation did occur at the CoC(quinolinyl) bond of 5, even though less efficient than that of 1, while reacted with a PPh2py ligand. The same reaction pattern was observed for the reaction of 2-mercapto-nicotinic acid methyl ester with 1.5 M equivalent of Co2(CO)8; a sulfido-tricobalt cluster (μ3-S)Co3(CO)7(μ-C,NC5H3NC(O)OCH3) (9) was obtained as the major product. The crystal structures of all eight new complexes have been determined.