Synthesis and 1H NMR spectroscopic properties of substituted (η4-tetraarylcyclobutadiene)(η5-cyclopentadienyl)cobalt metallocenes

The reaction of diarylacetylenes with CoCl(PPh3)3 and sodium cyclopentadienylide or sodium carbomethoxycyclopentadienylide gave (η4-tetra-arylcyclobutadiene)(η5-cyclopentadienyl)cobalt and (η4-tetra-arylcyclobutadiene)(η5-carbomethoxycyclopentadienyl)cobalt, respectively, where aryl = para-XC6H4 (X = CF3, F, MeO). The reaction was unsuccessful for the synthesis of (η4-tetra(para-methoxyphenyl)cyclobutadiene)(η5-cyclopentadienyl)cobalt, which was synthesised instead from dicarbonyl(η5-cyclopentadienyl)cobalt. In all of the examples starting with CoCl(PPh3)3 an intermediate (η5-cyclopentadienyl)- or (η5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complex was isolated, and two examples were characterised by X-ray crystallography. Heating the (η5-cyclopentadienyl)- or (η5-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraarylcobaltacyclopentadiene complexes resulted in clean conversion to the corresponding metallocenes. The influence of the para-aryl substituents on the 1H NMR of the cyclopentadienyl moiety is tabulated, together with the influence of a range of R substituents in (η4-tetraphenylcyclobutadiene)(η5-RC5H4)cobalt (R = CO2Me, CH2OH, Me, CHO, CCH, CO2H, CN, CONHR1, 2-oxazolinyl, NH2, NHAc, HgCl, Br, I, SiMe3, SnMe3, Ph).