FULVALENYL MONOIRON AND DIIRON COMPLEXES - PHOTOLYTIC AND ELECTRON-TRANSFER-INDUCED SUBSTITUTION OF THE BENZENE LIGANDS BY PHOSPHINES AND CO IN THE DIIRON FULVALENYL DIBENZENE COMPLEXES [FE(2)FV(C6H6)(2)](2+ 0) - GENERATION OF THE AVERAGE-VALENCE SPECIES [FE(2)FVL(6)](3+) (L EQUALS PHOSPHINE)/

The bi-sandwich complex [Fe(2)Fv(C6H6)(2)](2+)(PF6-)(2) (1(2+); Fv = m u(2)-eta(5):eta(5)-fulvalenyl, unless noted otherwise) synthesized fro m biferrocene, was photolyzed with visible light in acetonitrile in th e presence of 1,2-bis(diphenylphosphino)ethane (dppe) or bis(diphenylp hosphino)methane (dppm) at -15 degrees C to give [Fe(2)Fv(dppe)(2)(NCM e)(2)](2+)(PF6-)(2) (2a(2+)) or [Fe(2)Fv(dppm)(2)(NCMe)(2)](2+)(PF6-)( 2) (2b(2+)). The complexes 2a(2+) and 2b(2+) reacted in refluxing 1,2- dichloroethane with CO to give [Fe(2)Fv(dppe)(2)(CO)(2)](2+)(PF6-)(2) (3a(2+)) and [Fe(2)Fv(dppm)(2)(CO)(2)](2+)(PF6-)(2) (3b(2+)), and 2a(2 +) reacted similarly with PMe3 to give [Fe(2)Fv(dppe)(2)(PMe3)](2+)(PF 6-)(2) (4(2+)). The dir;educed 38-electron (38e) complex 1 reacted at -15 degrees C with 1 atm of CO to give [Fe-2(mu(2)-eta(4):eta(4)-Fv)(C O)(6)] (7) and with PMe3 to give [Fe(2)Fv(PMe3)(4)] (9). When Na+PF6- was present in stoichiometric amounts in THF, these reactions followed a different course and Na+PF6--induced electron transfer (disproporti onation) by irreversibly dislocating ion pairs: the reaction of 1 with 1 atm of CO gave [Fe(eta(5)-Fv)(eta(6)-C6H6), Na+PF6-] (5), and that with PMe3 gave [Fe(2)Fv(PMe3)(6)](2+)(PF6-)(2) (8(2+)) and the known c omplex [Fe(PMe3)(4)] (10). The cyclic voltammograms (CV) of 2a(2+) and 2b(2+) contain irreversible oxidation and reduction waves, but the CV s of 3a(2+) and 3b(2+) showed two close reversible monoelectronic redu ction waves (no oxidation wave). The CVs of the hexaphosphine complexe s indicated partially or fully irreversible reduction waves, respectiv ely, but two reversible waves at +0.71 and +0.95 V for 4(2+) and +0.70 and +1.08 V for 8(2+) (vs SCE, Pt, DMF, 0.1 M n-Bu4NBF4 -30 degrees C ). The bielectronic reduction of 2a(2+) and the bielectronic oxidation of 4(2+) and 8(2+) using redox reagents led to decomposition, but the monoelectronic oxidation of 4(2+) and 8(2+) using (p-Br-C6H4)(3)N+SbC l6- in CH2Cl2 gave the stable mixed-valence trications 4(3+) and 8(3+) , for which the Mossbauer spectra showed delocalized average valency o n the Mossbauer time scale. These studies have opened the route to a v ariety of mono- and diiron fulvalenyl organometallic compounds, confir ming the great importance of the presence of Na+PF6-. This salt can ch ange reaction pathways and, in particular, induce electron-transfer re actions, underlining the extraordinary electronic flexibility of the f ulvalenyl Ligand and its ability to transfer the electron flow between two metal centers.