Synthesis and H-1 NMR spectroscopic properties of substituted (eta(4)-tetraarylcyclobutadiene)(eta(5)-cyclopentadienyl)cobalt metallocenes

The reaction of diarylacetylenes with CoCl(PPh(3))(3) and sodium cyclopentadienylide or sodium carbomethoxycyclopentadienylide gave (eta(4)-tetra-arylcyclobutadiene)(eta(5)-cyclopentadienyl) cobalt and (eta(4)-tetraarylcyclobutadiene)(eta(5)-carbomethoxycyclopentadienyl) cobalt, respectively, where aryl = para-XC(6)H(4) (X = CF(3), F, MeO). The reaction was unsuccessful for the synthesis of (eta(4)-tetra(para-methoxyphenyl) cyclobutadiene)(eta(5)-cyclopentadienyl) cobalt, which was synthesised instead from dicarbonyl( eta(5)-cyclopentadienyl) cobalt. In all of the examples starting with CoCl(PPh(3))(3) an intermediate (eta(5)-cyclopentadienyl)- or (eta(5)-carbomethoxycyclopentadienyl)(triphenylphosphine)-2,3,4,5-tetraa rylcobaltacyclopentadiene complex was isolated, and two examples were characterised by X-ray crystallography. Heating the (eta(5)-cyclopentadienyl)- or (eta(5)-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 (1)H NMR of the cyclopentadienyl moiety is tabulated, together with the influence of a range of R substituents in (eta 4-tetraphenylcyclobutadiene)( eta(5)-RC(5)H(4)) cobalt (R = CO(2)Me, CH(2)OH, Me, CHO, CCH, CO(2)H, CN, CONHR(1), 2-oxazolinyl, NH(2), NHAc, HgCl, Br, I, SiMe(3), SnMe(3), Ph). (C) 2008 Elsevier B.V. All rights reserved.