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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

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posted on 2000-07-01, 00:00 authored by Gabriele Albertin, Stefano Antoniutti, Alessia Bacchi, Emilio Bordignon, Francesca Miani, Giancarlo Pelizzi
Depending on experimental conditions and the nature of the hydrazine, the reactions of ReCl3P3 [P = PPh(OEt)2] with RNHNH2 (R = H, CH3, tBu) afford the bis(dinitrogen) [Re(N2)2P4]+ (2+), dinitrogen ReClN2P4 (3), and methyldiazenido [ReCl(CH3N2)(CH3NHNH2)P3]+ (1+) derivatives. In contrast, reactions of ReCl3P3 [P = PPh(OEt)2, PPh2OEt] with arylhydrazines ArNHNH2 (Ar = Ph, p-tolyl) give the aryldiazenido cations [ReCl(ArN2)(ArNHNH2)P3]+ (4+) and [ReCl(ArN2)P4]+ (7+) and the bis(aryldiazenido) cations [Re(ArN2)2P3]+ (5+, 6+). These complexes were characterized spectroscopically (IR; 1H and 31P NMR), and the BPh4 complexes 1, 2, and 7 were characterized crystallographically. The methyldiazenido derivative [ReCl(CH3N2)(CH3NHNH2){PPh(OEt)2}3][BPh4] (1) crystallizes in space group P1̄ with a = 15.396(5) Å, b = 16.986(5) Å, c = 11.560(5) Å, α = 93.96(5)°, β = 93.99(5)°, γ = 93.09(5)°, and Z = 2 and contains a singly bent CH3N2, group bonded to an octahedral central metal. One methylhydrazine ligand, one Cl- trans to the CH3N2, and three PPh(OEt)2 ligands complete the coordination. The complex [Re(N2)2{PPh(OEt)2}4][BPh4] (2) crystallizes in space group Pbaa with a = 23.008(5) Å, b = 23.367(5) Å, c = 12.863(3) Å, and Z = 4. The structure displays octahedral coordination with two end-on N2 ligands in mutually trans positions. [ReCl(PhN2){PPh(OEt)2}4][BPh4] (7) crystallizes in space group P21/n with a = 19.613(5) Å, b = 20.101(5) Å, c = 19.918(5) Å, β = 115.12(2)°, and Z = 4. The structure shows a singly bent phenyldiazenido group trans to the Cl- ligand in an octahedral environment. The dinitrogen complex ReClN2P4 (3) reacts with CF3SO3CH3 to give the unstable methyldiazenido derivative [ReCl(CH3N2)P4][BPh4]. Reaction of the methylhydrazine complex [ReCl(CH3N2)(CH3NHNH2)P3][BPh4] (1) with Pb(OAc)4 at −30 °C results in selective oxidation of the hydrazine, affording the corresponding methyldiazene derivative [ReCl(CH3NNH)(CH3N2)P3][BPh4] (8). In contrast, treatment with Pb(OAc)4 of the related arylhydrazines [ReCl(ArN2)(ArNHNH2)P3][BPh4] (4) [P = PPh(OEt)2] gives the bis(aryldiazenido) complexes [Re(ArN2)2P3][BPh4] (5). Possible protonation reactions of Brønsted acids HX with all diazenides, 1, 4, 5, 6, and 8, were investigated and found to proceed only in the cases of the bis(aryldiazenido) complexes 5 and 6, affording, with HCl, the octahedral [ReCl(ArNNH)(ArN2)P3][BPh4] or [ReCl{Ar(H)NN}(ArN2)P3][BPh4] (10) (Ar = Ph; P = PPh2OEt) derivative.