One-Electron Transfer Processes in the Reaction of Indium(I) Halides with Substituted o-Quinones

Indium(I) halides (InX; X = Cl, Br, I) react with 3,5-di-tert-butyl-o-quinone (TBQ) in toluene/tmen solution to give the corresponding semiquinone-indium(III) derivatives (TBSQ)InX₂-tmen (tmen = N,N,N′,N′-tetramethylethanediamine). Related species have been prepared by the reaction between Na⁺TBSQ⁻and InX₃, and the presence of the semiquinone has been confirmed by X-ray crystallography in the case of (TBSQ)InBr₂·2CH₃C₅H₄N·0.5(N,N-dimethylformamide), which is monoclinic, with a = 31.479 (8) Å,b = 10.941 (4) Å, c = 21.962 (8) Å, β = 125.06 (2)°, V= 6191.5 (3) ų, Z = 8, and space group C2/c; R = 0.0529 and T = 21 °C. This molecule has a distorted-octahedral InO₂N₂Br₂kernel, and the C-O distances with the ligand confirm the presence of the semiquinone. The reaction of InX and TBQ in toluene/pyridine gives species analyzing as (TBSQ°)InX-2py (X = Cl, Br), identified as dimeric indium(II) derivatives. These systems have also been investigated by electron spin resonance spectroscopy. The reaction mechanism proposed involves an initial one-electron transfer process, followed by dimerization and rearrangement reactions, and is in good agreement with both preparative and spectroscopic work. Studies with InX and phen-anthrene-9,10-quinone give less detailed but similar results.