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-nPn]BY4 (1−5) and [{Re(CO)5-nPn}2(μ-HNNAr−ArNNH)](BY4)2 (6−12) [P = P(OEt)3, PPh(OEt)2, PPh2OEt; n = 1−4; Ar−Ar = 4,4‘-C6H4−C6H4, 4,4‘-(2-CH3)C6H3−C6H3(2-CH3), 4,4‘-C6H4−CH2−C6H4; Y = F, Ph) were prepared by reacting the hydride
species ReH(CO)5-nPn with the appropriate mono- and bis(aryldiazonium) cations. These compounds, as well as
other prepared compounds, were characterized spectroscopically (IR; 1H, 31P, 13C, and 15N 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 P1̄ with a = 15.380(5) Å, b = 13.037(5) Å, c = 16.649(5) Å, α = 90.33(5)°, β =
91.2(1)°, γ = 89.71(9)°, and Z = 2. The “diazene−diazonium” complexes [M(CO)3P2(HNNAr−ArN⋮N)](BF4)2 (13−15, 17) [M = Re, Mn; P = PPh2OEt, PPh2OMe, PPh3; Ar−Ar = 4,4‘-C6H4−C6H4, 4,4‘-C6H4−CH2−C6H4] and [Re(CO)4(PPh2OEt)(4,4‘-HNNC6H4−C6H4N⋮N)](BF4)2 (16b) were synthesized by allowing
the hydrides MH(CO)3P2 or ReH(CO)4P to react with equimolar amounts of bis(aryldiazonium) cations under
appropriate conditions. Reactions of diazene−diazonium complexes 13−17 with the metal hydrides M2H2P‘4
and M2‘H(CO)5-nP‘ ‘n afforded the heterobinuclear bis(aryldiazene) derivatives [M1(CO)3P2(μ-HNNAr−ArNNH)M2HP‘4](BPh4)2 (ReFe, ReRu, ReOs, MnRu, MnOs) and [M1(CO)3P2(μ-HNNAr−ArNNH)M2‘(CO)5-nP‘ ‘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 heterotrinuclear
complexes [Re(CO)3(PPh2OEt)2(μ-4,4‘-HNNC6H4−C6H4NNH)M{P(OEt)3}4(μ-4,4‘-HNNC6H4−C6H4NNH)Mn(CO)3(PPh2OEt)2](BPh4)4 (M = Ru, Os) (ReRuMn, ReOsMn) were obtained by reacting the heterobinuclear complexes ReRu and ReOs with the appropriate diazene−diazonium cations. The heterobinuclear complex
with a bis(aryldiazenido) bridging ligand [Mn(CO)2(PPh2OEt)2(μ-4,4‘-N2C6H4−C6H4N2)Fe{P(OEt)3}4]BPh4 (MnFe)
was prepared by deprotonating the bis(aryldiazene) compound [Mn(CO)3(PPh2OEt)2(μ-4,4‘-HNNC6H4−C6H4NNH)Fe(4-CH3C6H4CN){P(OEt)3}4](BPh4)3. Finally, the binuclear compound [Re(CO)3(PPh2OEt)2(μ-4,4‘-HNNC6H4−C6H4N2)Fe(CO)2{P(OPh)3}2](BPh4)2 (ReFe) containing a diazene−diazenido bridging ligand was prepared
by reacting [Re(CO)3(PPh2OEt)2(4,4‘-HNNC6H4−C6H4N⋮N)]+ with the FeH2(CO)2{P(OPh)3}2 hydride derivative. The electrochemical reduction of mono- and binuclear aryldiazene complexes of both rhenium (1−12) and
the manganese, as well as heterobinuclear ReRu and MnRu complexes, was studied by means of cyclic
voltammetry and digital simulation techniques. The electrochemical oxidation of the mono- and binuclear
aryldiazenido compounds Mn(C6H5N2)(CO)2P2 and {Mn(CO)2P2}2(μ-4,4‘-N2C6H4−C6H4N2) (P = PPh2OEt) was
also examined. Electrochemical data show that, for binuclear compounds, the diazene bridging unit allows
delocalization of electrons between the two different redox centers of the same molecule, whereas the two metal
centers behave independently in the presence of the diazenido bridging unit.