Cyclobutadiene–metal complexes. XI. Tetramethylcyclobutadienecobalt(I) complexes

The ligand-transfer reaction of tetramethylcyclobutadienenickel chloride dimer with dicobalt octacarbonyl gave tetramethylcyclobutadienedicobalt hexacarbonyl [Me4C4Co(CO)2Co(CO)4] and nickel tetracarbonyl. Triphenylphosphine replaced one carbonyl in Me4C4Co(CO)2·Co(CO)4 to give Me4C4Co(CO)2·Co(CO)3PPh3. Both Me4C4Co(CO)2·Co(CO)4 and Me4C4Co(CO)2·Co(CO)3PPh3 underwent cleavage with iodine at low temperatures to give tetramethylcyclobutadienecobalt dicarbonyl iodide (Me4C4Co(CO)2I); this was also obtained in quantitative yield from [Me4C4NiI2]2 and Co2(CO)8. One carbonyl in Me4C4Co(CO)2I was replaced on reaction with triphenylphosphine, giving Me4C4Co(CO)(PPh3)I. Me4C4Co(Co)2I reacted with both sodium cyclopentadienide and [C5H5Fe(CO)2]2 to give (π-cyclopentadienyl)-(π-tetramethylcyclobutadiene) cobalt.