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

Article abstract of DOI:10.1021/ic980430e

Mono- and binuclear aryldiazenido complexes [Fe(ArN₂)(CO)₂P₂]BPh₄ (1-4) and [{Fe(CO)₂P₂}₂(μ-N₂Ar-ArN ₂)](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-C₆H ₃(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′-N ₂(2-CH₃)C₆H₃-C₆H ₃(2-CH₃)N₂}](BPh₄)₂ (5b) crystallizes in the space group P1^- with a = 15.008(4) A?, b = 17.094(5) A?, c = 10.553(3) A?, 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.