Reactivity of Hydrides FeH₂(CO)₂P₂ (P = Phosphites) with Aryldiazonium Cations: Preparation, Characterization, X-ray Crystal Structure, and Electrochemical Studies of Mono- and Binuclear Aryldiazenido Complexes

Mono- and binuclear aryldiazenido complexes [Fe(ArN2)(CO)2P2]BPh4 (1−4) and [{Fe(CO)2P2}2(μ-N2Ar−ArN2)](BPh4)2 (5−8) [P = P(OEt)3, PPh(OEt)2, PPh2OEt, P(OPh)3; Ar = C6H5, 2-CH3C6H4, 4-CH3C6H4; Ar−Ar = 4,4‘-C6H4−C6H4, 4,4‘-(2-CH3)C6H3−C6H3(2-CH3), 4,4‘-C6H4−CH2−C6H4] were prepared by allowing hydride species FeH2(CO)2P2 to react with an excess of mono- (ArN2)(BF4) or bis-aryldiazonium (N2Ar−ArN2)(BF4)2 salts, respectively, at low temperature. A reaction path involving a hydride−aryldiazene intermediate [FeH(ArNNH)(CO)2P2]+, which, through the loss of H2, affords the final aryldiazenido complexes 1−8, is proposed. The compounds were characterized by 1H and 31P{1H} NMR spectroscopy (including 15N isotopic substitution) and X-ray crystal structure determination. The complex [Fe(CO)2{P(OEt)3}2{μ-4,4‘-N2(2-CH3)C6H3−C6H3(2-CH3)N2}](BPh4)2 (5b) crystallizes in the space group P1̄ with a = 15.008(4) Å, b = 17.094(5) Å, c = 10.553(3) Å, α = 99.56(1)°, β = 102.80(1)°, γ = 65.30(1)°, and Z = 1. The structure is centrosymmetric and consists of binuclear cations with the two iron atoms in a quite regular trigonal bipyramidal environment, with the two CO in the equatorial and the two phosphites in the apical position, respectively. Aryldiazenido complexes 1−8 react with strong acids HX (X = Cl, CF3SO3, CF3CO2) to give the corresponding aryldiazene derivatives, according to the equilibrium [Fe(ArN2)(CO)2P2]+ + HX ⇌ [FeX(ArNNH)(CO)2P2]+. Electrochemical studies of both mono- (1−4) and binuclear (5−8) compounds were undertaken, and a mechanism for oxidation and reduction processes is proposed.