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

Article abstract of DOI:10.1021/ic990970r

Depending on experimental conditions and the nature of the hydrazine, the reactions of ReCl₃P₃ [P = PPh(OEt)₂] with RNHNH₂ (R = H, CH₃, (t)Bu) 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 P1 with a = 15.396(5) A, b = 16.986(5) A, c = 11.560(5) A, 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) A, b = 23.367(5) A, c = 12.863(3) A, 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) A, b = 20.101(5) A, c = 19.918(5) A, 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 Bronsted 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.