Pericyclic organometallic reactions. The reactions of (cht)Fe(CO)₂L (L=CO, P(OPh)₃, PPh₃) and (carbomethoxy)maleic anhydride revisited

Kinetic studies of the reaction of (cht)Fe(CO)₂L (L=CO, P(OPh)₃, PPh₃) and (carbomethoxy)maleic anhydride reveal, contrary to our previous report, that the reactions proceed by a tandem 3+2-cycloaddition-[2,2]-sigmahaptotropic rearrangement, to give the corresponding η²,η²-Diels-Alder adducts as main products, in equilibrium with the primary η¹,η³-σ,π-allylic kinetic isomers. The labile primary isomers were characterized by ¹H-, ¹³C- and ³¹P-NMR spectra. Substitution of carbonyl by phosphorus ligands increased the rates of both cycloadditions and rearrangements in the order PPh₃>P(OPh)₃>CO.