BINUCLEAR IRON AND RUTHENIUM COMPLEXES WITH BIS(DIAZENE) OR BIS(DIAZENIDO) BRIDGING LIGANDS - SYNTHESIS, CHARACTERIZATION, X-RAY CRYSTAL-STRUCTURE, AND ELECTROCHEMICAL STUDIES

Binuclear complexes [(MHP(4))(2)(mu-HN=NAr-ArN=NH)](BPh(4))(2) [M = Fe , Ru; P = P(OMe)(3), P(OEt)(3), PPh(OEt)(2); Ar-Ar = 4,4'-C6H4-C6H4, 4 ,4'-(2-CH3)C6H3-C6H3(2-CH3), 4,4'-C6H4-CH2-C6H4] were prepared by allo wing hydride species MH(2)P(4) to react with bis(diazonium) salts (N2A r-ArN2)(BF4)(2) in a 2:1 ratio at low temperature. The compounds were characterized by H-1 and P-31{H-1} NMR spectroscopy (including N-15 is otopic substitution) and an X-ray crystal structure determination. The complex -4,4'-HN=N(2-CH3)C6H3-C6H3(2-CH3)N=NH}](BPh(4))(2) crystalliz es in the space group P (1) over bar with a 16.105(5), b = 17.551(6), c = 11.539(3) Angstrom; alpha = 96.41(2), beta = 84.49(2), gamma = 97. 97(2)degrees; and Z = 2 The structure is centrosymmetric and consists of binuclear cations with the two iron atoms in an octahedral environm ent having the hydride and the diazene ligands in mutually cis positio ns. The [(MHP(4))(2)(mu-HN=NAr-ArN=NH)](2+) cations reacted with mono( diazonium) (RN(2))BF4 salts to give the binuclear bis(diazene) derivat ives [{M(RN=NH)P-4}(2)(mu-HN=NAr-ArN=NH)](BPh(4))(4) (R = C6H5, 4-CH3C 6H4, 4-CH3OC6H4). Binuclear bis(diazenido) complexes [(MP(4))(2)(mu-N2 Ar-ArN2)](BPh(4))2 [M = Fe, Ru; P P(OEt)(3); Ar-Ar = 4,4'-C6H4-C6H4, 4 ,4'-C6H4-CH2-C6H4] were also prepared by deprotonation with triethylam ine of the diazene-nitrile {4-CH3C6H4CN)P-4}(2)(mu-HN=NAr-ArN=NH)](BPh (4))(4) derivatives. Characterization of all the complexes by infrared and H-1 and P-31 NMR spectroscopy is discussed. Cyclic voltammetry of the binuclear [(MHP(4))(2)(mu-HN=NAr-ArN=NH)](2+) and of the related mononuclear [MH(RN=NH)P-4](+) derivatives was also investigated. Elect rochemical reduction of binuclear compounds, where conjugation between the metal centers is possible, proceeds via two well-separated one-el ectron reduction steps whereas, when conjugation is hindered, the two consecutive reductions tend to merge into a onestep reduction process.