Synthesis, reactivity and structural studies of (η5-methylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt and its derivatives

(η5-methylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt (1) and its derivatives, [(1-acetyl-2-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene)cobalt (2) [(1-acetyl-3-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene)cobalt (3) [(1-carbomethoxy-2-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene)cobalt (4) and [(1-carbomethoxy-3-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene) cobalt (5) have been prepared in yields varying from 11% to 28% by introducing the substituents on the cyclopentadienyl ring of methylcyclopentadienyl sodium and then reacting with diphenylacetylene and CoCl(PPh3)3. The carboxylic acids [(1-carboxy-2-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene)cobalt (6), [(1-carboxy-3-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene)cobalt (7) have been prepared after ester hydrolysis of compounds 4 and 5 using KOH/ethanol. [(1-dimethylaminomethyl-3-methyl)η5-cyclopentadienyl](η4-tetraphenylcyclobutadiene) cobalt (8), was prepared selectively by direct substitution on the cyclopentadienyl ring of (η5-methylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt in 65% yield. The 1,2-isomer was formed only in traces in this reaction. Reactivity of (η5-methylcyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt and its carbomethoxy derivative have been compared with (η5-cyclopentadienyl)(η4-tetraphenylcyclobutadiene)cobalt. All new compounds were characterized by 1H and 13C NMR, FT-IR, mass spectra and CHN analysis. Compounds 2, 4, 6 and 8 have also been structurally characterized by single crystal X-ray structural analysis.