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

(eta(5)-methylcyclopentadienyl)(eta(4)-tetraphenylcyclobutadiene) cobalt (1) and its derivatives, [(1-acetyl-2-methyl) eta(5)-cyclopentadienyl](eta(4)-tetraphenylcyclobutadiene) cobalt (2) [(1-acetyl-3-methyl)eta(5)-cyclopentadienyl]( eta(4)-tetraphenylcyclobutadiene) cobalt (3) [(1-carbomethoxy-2-methyl)eta 5-cyclopentadienyl](eta(4)-tetraphenylcyclobutadiene) cobalt ( 4) and [(1-carbomethoxy-3-methyl)eta(5)-cyclopentadienyl] (eta(4)-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)eta(5)-cyclopentadienyl](eta(4)-tetraphenylcyclobutadiene) cobalt (6), [(1-carboxy-3-methyl)eta(5)-cyclopentadienyl](eta(4)-tetraphenylcyclobutadiene) cobalt (7) have been prepared after ester hydrolysis of compounds 4 and 5 using KOH/ethanol. [(1-dimethylaminomethyl-3-methyl)eta(5)-cyclopentadienyl](eta(4)-tetraphenylcyclobutadiene) cobalt (8), was prepared selectively by direct substitution on the cyclopentadienyl ring of (eta(5)-methylcyclopentadienyl)( eta(4)-tetraphenylcyclobutadiene) cobalt in 65% yield. The 1,2-isomer was formed only in traces in this reaction. Reactivity of (eta(5)-methylcyclopentadienyl)(eta(4)-tetraphenylcyclobutadiene) cobalt and its carbomethoxy derivative have been compared with (eta(5)-cyclopentadienyl)(eta(4)-tetraphenylcyclobutadiene) cobalt. All new compounds were characterized by H-1 and C-13 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. (C) 2008 Elsevier B. V. All rights reserved.