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

Abstract

Mono- and binuclear aryldiazenido complexes [Fe(ArN(2))(CO)(2)P(2)]BPh(4) (1-4) and [{Fe(CO)(2)P(2)}(2)(&mgr;-N(2)Ar-ArN(2))](BPh(4))(2) (5-8) [P = P(OEt)(3), PPh(OEt)(2), PPh(2)OEt, P(OPh)(3); Ar = C(6)H(5), 2-CH(3)C(6)H(4), 4-CH(3)C(6)H(4); Ar-Ar = 4,4'-C(6)H(4)-C(6)H(4), 4,4'-(2-CH(3))C(6)H(3)-C(6)H(3)(2-CH(3)), 4,4'-C(6)H(4)-CH(2)-C(6)H(4)] were prepared by allowing hydride species FeH(2)(CO)(2)P(2) to react with an excess of mono- (ArN(2))(BF(4)) or bis-aryldiazonium (N(2)Ar-ArN(2))(BF(4))(2) salts, respectively, at low temperature. A reaction path involving a hydride-aryldiazene intermediate [FeH(ArN=NH)(CO)(2)P(2)](+), which, through the loss of H(2), affords the final aryldiazenido complexes 1-8, is proposed. The compounds were characterized by (1)H and (31)P{(1)H} NMR spectroscopy (including (15)N isotopic substitution) and X-ray crystal structure determination. The complex [Fe(CO)(2){P(OEt)(3)}(2){&mgr;-4,4'-N(2)(2-CH(3))C(6)H(3)-C(6)H(3)(2-CH(3))N(2)}](BPh(4))(2) (5b) crystallizes in the space group P&onemacr; with a = 15.008(4) Å, b = 17.094(5) Å, c = 10.553(3) Å, alpha = 99.56(1) degrees, beta = 102.80(1) degrees, gamma = 65.30(1) degrees, 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, CF(3)SO(3), CF(3)CO(2)) to give the corresponding aryldiazene derivatives, according to the equilibrium [Fe(ArN(2))(CO)(2)P(2)](+) + HX right harpoon over left harpoon [FeX(ArN=NH)(CO)(2)P(2)](+). Electrochemical studies of both mono- (1-4) and binuclear (5-8) compounds were undertaken, and a mechanism for oxidation and reduction processes is proposed.

Electrochemical Methods for Assessing Kinetic Factors in the Reduction of CO2 to Formate: Implications for Improving Electrocatalyst Design

“…Albertin and co-workers have measured k s for two oxidation and two reduction events of [{Fe­(CO) 2 [P­(OEt) 3 ] 2 } 2 {μ-4,4-N 2 C 6 H 4 -C 6 H 4 N 2 }]­(BPh 4 ) 2 , and these were very slow: between 1.2 × 10 –5 and 5 × 10 –6 cm s –1 . Ferrocene (Fc/Fc + ) has a k s of 0.25 cm s –1 and is considered fast .…”

“…14 Albertin and co-workers have measured k s for two oxidation and two reduction events of [{Fe(CO) 2 [P(OEt) 3 ] 2 } 2 {μ-4,4-N 2 C 6 H 4 -C 6 H 4 N 2 }](BPh 4 ) 2 , and these were very slow: between 1.2 × 10 −5 and 5 × 10 −6 cm s −1 . 15 Ferrocene (Fc/Fc + ) has a k s of 0.25 cm s −1 and is considered fast. 16 For various organometallic complexes, Co III/II couples are reported with k s values of 0.003−0.051 cm s −1 , Co II/I couples with k s values of 0.012−0.11 cm s −1 , and a Co I/0 couple with k s values of 0.12 cm s −1 .…”

Diazo Complexes of Rhenium: Preparations and Crystal Structures of the Bis(dinitrogen), [Re(N2)2{PPh(OEt)2}4][BPh4] and Methyldiazenido [ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] Derivatives

“…Aryldiazenido complexes are reported to react with Brønsted acids to give the corresponding aryldiazene derivatives, − and we therefore tested this type of reaction using HCl, CF 3 SO 3 H, and CF 3 COOH, for both the methyldiazenido complexes 1 and 8 and the aryldiazenido complexes 4 − 7 derivatives. Results show that only bis(aryldiazenido) complexes 5 and 6 react with strong acids to give new derivatives of the type 10 , which, in the case of the reaction with HCl, was isolated in the solid state and characterized (Scheme 5).…”

“…As part of our contribution − to this field, we report here the syntheses, crystal structures and reactivity studies both of the first bis(dinitrogen) complexes of rhenium and of other diazo derivatives, including a rare example of a methyldiazenido complex.…”

Triggering N2 uptake via redox-induced expulsion of coordinated NH3 and N2 silylation at trigonal bipyramidal iron

“…Diazenido 10 is structurally distinct by virtue of having a diazenido ligand occupying an axial position of a TBP geometry. For the few 5-coordinate iron diazenido complexes that have been structurally characterized, the diazenido ligand occupies an equatorial site xxxviii,xxxix,xl,xli…”