The cationic iron η 2 -(α,ω-diene) complexes of the type, [(η 5 -C 5 H 5 )Fe(CO) 2 {η 2 -(α,ω-diene)}]PF 6 , (diene=1,3-butadiene; 1,4-pentadiene; 1,5-hexadiene; and 1,7-octadiene) were prepared by the reaction of η 1 -alkenyl compounds of the type [(η 5 -C 5 H 5 )Fe(CO) 2 (η 1 -alkenyl)] with the so-called trityl salt, (Ph 3 CPF 6 ). The reactions of the η 2 -diene complexes with a number of nucleophiles give a range of products resulting from nucleophillic addition to the coordinated diene and/or displacement of the diene. The reaction with triethylamine results in deprotonation leading to the formation of [(η 5 -C 5 H 5 )Fe(CO) 2 (η 1 -allyl)] complexes.