Preparations, structures, and electrochemical studies of aryldiazene complexes of rhenium: Syntheses of the first heterobinuclear and heterotrinuclear derivatives with bis(diazene) or bis(diazenido) bridging ligands

The mono- and binuclear aryldiazene complexes [Re(C6H5N=NH)(Co)(5-n)P-n]BY4 (1-5) and [{Re(CO)(5-n)P-n}(2)(mu-HN=NAr-ArN=NH)](BY4)(2) (6-12) [P = P(OE t)(3), PPh(OEt)(2), PPh2OEt; n = 1-4; Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-(2-CH3)C 6H3-C6H3(2-CH3), 4,4'-C6H4-CH2-C6H4; Y = F, Ph) were prepared by reacting t he hydride species ReH(CO)(5-n)P-n with the appropriate mono- and bis(aryld iazonium) cations. These compounds, as well as other prepared compounds, we re characterized spectroscopically (IR; H-1, P-31, C-13, and N-15 NMR data) , and 1a was also characterized by an X-ray crystal structure determination . [Re(C6H5N=NH)(CO){P(OEt)(3)}(4)]BPh4 (1a) crystallizes in space group P ( 1) over bar with a = 15.380(5) Angstrom, b = 13.037(5) Angstrom, c = 16.649 (5) Angstrom, alpha = 90.33(5)degrees, beta = 91.2(1)degrees, gamma = 89.71 (9)degrees, and Z = 2. The "diazene-diazonium" complexes [M(CO)(3)P-2(HN=NA r-ArN=N)](BF4)(2) (13-15, 17) [M = Re, Mn; P = PPh2OEt, PPh2OMe, PPh3; Ar-A r = 4,4'-C6H4-C6H4, 4,4'-C6H4-CH2-C6H4] and [Re(CO)(4)(PPh2OEt)(4,4'-HN=NC6 H4-C6H4N=N](BF4)(2) (16b) were synthesized by allowing the hydrides MH(CO)( 3)P-2 or ReH(CO)(4)P to react with equimolar amounts of bis(aryldiazonium) cations under appropriate conditions. Reactions of diazene-diazonium comple xes 13-17 with the metal hydrides M2H(2)P(4)' and M2'H(CO)(5-n)P-n("), affo rded the heterobinuclear bis(aryldiazene) derivatives [M1(CO)(3)P-2(mu-HN=N Ar-ArN=NH)M2HP(4)'](BPh4)(2) (ReFe, ReRu, ReOs, MnRu, MnOs) and [M1(C0)(3)P -2(mu-HN=NAr-ArN=NH)M2'-(CO)(5-n)P-n(")](BPh4)(2) (ReMn, MnRe) [M1 = Re, Mn ; M2 = Fe, Ru, Os; M2' = Mn, Re; P = PPh2OEt, PPh2OMe; P', P " = P(OEt)(3), PPh(OEt)(2); Ar-Ar = 4,4'-C6H4-C6H4, 4,4'-C6H4-CH2-C6H4; n = 1, 2],The het erotrinuclear complexes [ReCCO)(3)(PPh2OEt)(2)(mu-4,4'-HN=NC6H4-C6H4N=NH)M{ P(OEt)(3)}(4)(mu-4,4'-HN=NC6H4-C6H4N=NH)Mn(CO)(3)(PPh2OEt)(2)](BPh4)(4) (M = Ru, Os) (ReRuMn, ReOsMn) were obtained by reacting the heterobinuclear co mplexes ReRu and ReOs with the appropriate diazene-diazonium cations. The heterobinuclear complex with a bis(aryldiazenido) bridging ligand [Mn(C O)(2)(PPh2OEt)(2)(mu-4,4'-N2C6H4-C6H4N2)Fe{P(OEt)(3)}(4)]BPh4 (MnFe) was pr epared by deprotonating the bis(aryldiazene) compound [Mn(CO)(3)(PPh2OEt)(2 )(mu-4,4'-HN=NC6H4-C6H4N=NH)Fe(4-CH3C6H4CN){P(OEt)(3)}(4)](BPh4)(3). Finall y, the binuclear compound [Re(CO)(3)(PPh2OEt)(2)(mu-4,4'-HN=NC6H4-C6H4N2)Fe (CO)(2){P(OPh)(3)}(2)](BPh4)(2) (ReFe) containing a diazene-diazenido bridg ing ligand was prepared by reacting [Re(CO)(3)(PPh2OEt)(2)(4,4'-HN=NC6H4-C6 H4N=N](+) with the FeH2(CO)(2){P(OPh)(3)}(2) hydride derivative. The electr ochemical reduction of mono- and binuclear aryldiazene complexes of both rh enium (1-12) and the manganese, as well as heterobinuclear ReRu and MnRu co mplexes, was studied by means of cyclic voltammetry and digital simulation techniques. The electrochemical oxidation of the mono- and binuclear aryldi azenido compounds Mn(C6H5N2)(CO)(2)P-2 and {Mn(CO)(2)P-2}(2)(mu-4,4'-N2C6H4 -C6H4N2) (P = PPh2OEt) was also examined. Electrochemical data show that, f or binuclear compounds, the diazene bridging unit allows delocalization of electrons between the two different redox centers of the same molecule, whe reas the two metal centers behave independently in the presence of the diaz enido bridging unit.