Photolysis of (Eta-5-C5h5)fe(co)2(butadienyl) Complexes - Synthesis and Electrocyclic Ring-Closure of (Eta-5-C5h5)fe(pentadienoyl) Complexes to Hydroxyferrocenes
by Dawson, David Patton; Yongskulrote, Warunee; Bramlett, Joseph Morris; Wright, Jeffery B.; Durham, Bill; Allison, Neil T.
A study of the synthesis and photolysis of seven (eta5-C5H5)Fe(CO)2(eta1-1,3-butadienyl) complexes is reported. Photolysis of these complexes leads to the formation of the rarely accessible class of substituted hydroxyferrocenes in very high yields. Low-temperature experiments aimed at elucidating the mechanism of this conversion indicate that loss of a terminal carbonyl from (eta5-C5H5)Fe(CO)2(eta1-1,3-butadienyl) complexes is the only photochemical reaction and that (eta5-C5H5)Fe(eta5-pentadienoyl) complexes are intermediates. Spectroscopic data for two kinetically unstable pentadienoyl intermediates are presented. Pentadienoyl ligands undergo electrocyclic ring closure followed by keto-enol tautomerization to give the hydroxycyclopentadienyl ligands. Acid catalyzes this ring-closure reaction with the rate of closure being linearly dependent on the concentration of acid. Ring strain and electronic effects also influence the rate of formation of substituted bicyclic hydroxyferrocenes.
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