PHOTOLYSIS OF (ETA-5-C5H5)FE(CO)2(BUTADIENYL) COMPLEXES - SYNTHESIS AND ELECTROCYCLIC RING-CLOSURE OF (ETA-5-C5H5)FE(PENTADIENOYL) COMPLEXES TO HYDROXYFERROCENES

A study of the synthesis and photolysis of seven (eta5-C5H5)Fe(CO)2(et a1-1,3-butadienyl) complexes is reported. Photolysis of these complexe s leads to the formation of the rarely accessible class of substituted hydroxyferrocenes in very high yields. Low-temperature experiments ai med at elucidating the mechanism of this conversion indicate that loss of a terminal carbonyl from (eta5-C5H5)Fe(CO)2(eta1-1,3-butadienyl) c omplexes is the only photochemical reaction and that (eta5-C5H5)Fe(eta 5-pentadienoyl) complexes are intermediates. Spectroscopic data for tw o kinetically unstable pentadienoyl intermediates are presented. Penta dienoyl ligands undergo electrocyclic ring closure followed by keto-en ol tautomerization to give the hydroxycyclopentadienyl ligands. Acid c atalyzes this ring-closure reaction with the rate of closure being lin early dependent on the concentration of acid. Ring strain and electron ic effects also influence the rate of formation of substituted bicycli c hydroxyferrocenes.