PHOTOCHEMICAL HEAD-TO-HEAD (R = H) VS HEAD-TO-TAIL DIMERIZATION (R = PH) OF IRON ACETYLIDE COMPLEXES (ETA-5-C5ME5)FE(CO)2-CC-R LEADING TO A DIMETALLACYCLOPENTENONE AND A MU-VINYLIDENE COMPLEX

Irradiation of a benzene solution of iron acetylides Fp*-C=C-R (R = H, Ph) results in dimerization of the R-C=C ligand to give dinuclear complexes with completely different structures, i.e. a dimetallacyclopentenone Cp22*Fe2(CO)(mu-CO)[mu-eta1:eta3-C(C=CH)=CHC(=O)] (R = H) and a mu-vinylidene complex Cp2*Fe2(CO)2(mu-CO)[mu-C=C(Ph)C=C-Ph)] (R = Ph), depending on the substituent (R). The formation of the products has been interpreted in terms of head-to-head (R = H) and head-to-tail coupling (R = Ph) of the alkynyl ligands within the coordination sphere of the Cp*Fe(CO) fragment.