ELECTROCHEMICAL INVESTIGATION OF THE ELECTRON-POOR PRECISE (N=5 6) COMPLEXES [FE2(CO)N(MU-PR2)(MU-PR'2)] (N=5, R=R'=BU(T) N=6, R=R'=PH, R=BU(T), R'=PH R=BU(T) R'=CY) - EPR STUDY OF THE RADICAL-ANION [FE2(MU-PBUT2)2(CO)5]/

The redox behavior of the bis(phosphido)-bridged diiron carbonyl compl exes [Fe2(CO)n(mu-PR2)(mu-PR'2)] (n = 5, R=R'=Bu(t); n=6, R=R'=Ph; R=B u(t), R'=Ph; R=Bu(t), R'=Cy) has been studied electrochemically at a p latinum electrode in THF (0.1 M in Bu4N[PF6]). The electron-poor compl ex (n=5, R=R'=Bu(t)) shows two well-defined reduction steps at - 1.34 and - 2.35 V assigned to the formation of the radical anion [Fe2(CO)5( mu-PBu(t)2)].-and the dianion [Fe2(CO)5(mu-PBu(t)2)2]2-. The uninegati ve radical ion has been further investigated by EPR spectroscopy. The fluid as well as the rigid solution spectra indicate that the two phos phido bridges are linking the two iron centers in the same manner and that the unpaired electron is metal centered. The electron-precise com plexes (n = 6) are reduced at approximately the same potentials (- 1.7 4 to - 1.91 V) in two closely spaced one-electron steps. Molecular con figurational changes accompany these reductions and make both processe s, reduction and re-oxidation, quite slow.