THE REDOX BEHAVIOR OF THE CLUSTER ANION [FE4N(CO)(12)](-) - ELECTRON-TRANSFER CHAIN CATALYTIC SUBSTITUTION-REACTIONS - CRYSTAL-STRUCTURE OF[FE4N(CO)(11)(PPH(3))](-)

The electrochemical investigation of the redox properties of the monoa nion [Fe4N(CO)(12)](-) points out its ability to undergo sequentially two one-electron reductions. The first step leads to the quite stable dianion [Fe4N(CO)(12)](2-); the EPR results indicate that in frozen so lution an equilibrium exists between two different molecular geometrie s of such a dianion. The second electron addition produces the relativ ely short-lived trianion [Fe4N(CO)(12)](3-). In the presence of monode ntate phosphines, the redox change [Fe4N(CO)(12)](-/2-) triggers the e lectrocatalytic substitution of one CO group to afford the substituted monoanions [Fe4N(CO)(11)(PR(3))](-). As a matter of fact, sub-stoichi ometric amounts of Ph(2)CO(.-) produce [Fe4N(CO)(11)(PPh(3))](-), the crystal structure of which has been solved. Crystal data for [N(PPh(3) )(2)][Fe4N(CO)(11)(PPh(3))]: triclinic, space group P (1) over bar (No . 2), a = 11.009(6), b = 17.285(4), c = 17.380(2) Angstrom, alpha = 10 3.11(3), beta = 91.18(2), gamma = 105.26(3)degrees, Z = 2, D-c = 1.444 g cm(-3), Mo K alpha: radiation (lambda = 0.71073 Angstrom), mu(Mo K alpha) = 10.5 cm(-1), R = 0.048 (R(w), = 0.054) for 5010 independent r eflections having I>3 sigma(I). Preliminary evidence is given that in the presence of bidentate phosphines one CO ligand substitution occurs at room temperature, whereas two CO groups are replaced at higher tem peratures.