Triazenide-bridged rhodium–palladium complexes: [I2Rh(µ-p-MeC6H4NNNC6H4Me-p)2Pd(η3-C3H5)]−, a stable paramagnetic [RhPd]4+ species with a localised Rh(ii) centre

Abstract

Deprotonation of mixtures of the triazene complexes [RhCl(CO)₂(p-MeC₆H₄NNNHC₆H₄Me-p)] and [PdCl(η³-C₃H₅)(p-MeC₆H₄NNNHC₆H₄Me-p)] or [PdCl₂(PPh₃)(p-MeC₆H₄NNNHC₆H₄Me-p)] with NEt₃ gives the structurally characterised heterobinuclear triazenide-bridged species [(OC)₂Rh(µ-p-MeC₆H₄NNNC₆H₄Me-p)₂PdLL′] {LL′ = η³-C₃H₅1 or Cl(PPh₃) 2} which, in the presence of Me₃NO, react with [NBuⁿ₄]I, [NBuⁿ₄]Br, [PPN]Cl or [NBuⁿ₄]NCS to give [(OC)XRh(µ-p-MeC₆H₄NNNC₆H₄Me-p)₂PdCl(PPh₃)]⁻ (X = I 3⁻, Br 4⁻, Cl 5⁻ or NCS 6⁻) and [NBuⁿ₄][(OC)XRh(µ-p-MeC₆H₄NNNC₆H₄Me-p)₂Pd(η³-C₃H₅)], (X = I 7⁻ or Br 8⁻). The allyl complexes 7⁻ and 8⁻ undergo one-electron oxidation to the corresponding unstable neutral complexes 7 and 8 but, in the presence of the appropriate halide, oxidative substitution results in the stable paramagnetic complexes [NBuⁿ₄][X₂Rh(µ-p-MeC₆H₄NNNC₆H₄Me-p)₂Pd(η³-C₃H₅)], (X = I 9⁻ or Br 10⁻). X-Ray structural (9⁻), DFT and EPR spectroscopic studies are consistent with the unpaired electron of 9⁻ and 10⁻ localised primarily on the Rh(II) centre of the [RhPd]⁴⁺ core, which is susceptible to oxygen coordination at low temperature to give Rh(III)-bound superoxide.