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Keywords:

  • Cyclic voltammetry;
  • Iridium;
  • Organometallic compounds;
  • Phosphanes;
  • Reaction mechanisms;
  • Rhodium

Abstract

The chlorido-bridged dimeric complex [Rh2(μ-Cl)2(trop2NH)2] [trop2NH = bis(benzo[a,d]cycloheptenyl)amine] or the acetonitrile complexes [Rh(trop2NH)(MeCN)2]+ (CF3SO3) and [IrCl(MeCN)(trop2NH)] are well-suited precursor complexes for phenanthroline-type complexes [M(trop2NH)(R,R-phen)]+A (M = Rh, Ir; R = H, Me, Ph substituents in the 4,7- or 5,6-positions of the phen ligand, A = CF3SO3, PF6). These complexes contain 18-valence-electron configured metal centers in a trigonal–bipyramidal coordination sphere with the amino (NH) group in an axial position and each of the olefinic C=Ctrop units is in an equatorial position. The cationic amino complexes [M(trop2NH)(R,R-phen)]+ are sufficiently acidic (pKa in dmso: 18.2–19.0) to be quantitatively deprotonated by one equivalent of KOtBu to give neutral amido complexes [M(trop2N)(R,R-phen)] (M = Rh, Ir). These can be easily oxidized to give aminyl radical complexes [M(trop2N·)(R,R-phen)]+A, which for M = Rh can be isolated as green crystals. The iridium complex [Ir(trop2N·)(phen)]+ is unstable. High-resolution pulse EPR spectroscopy was used to gain insight into the electronic structure of the aminyl radical complexes. Remarkably, the rhodium and iridium complexes have a very similar electronic structure, as revealed by their EPR parameters {[Rh(trop2N·)(phen)]+: g1,2,3 = 2.084(2), 2.049(2), 2.027(2); |Aiso| = 45.4 (N1), 10.4 (N2), 3.1 (N3) 27.0 (Rh) MHz; [Ir(trop2N·)(phen)]+: g1,2,3 = 2.140(2), 2.107(2), 2.015(2); |Aiso| = 47 (N1), 7.9 (N2), 3.5 (N3), 26.8 (Ir) MHz} and these show that about 60 % of the spin population is localized on the nitrogen center (N1) of the trop2N ligand. In reactions with stannanes (R3SnH) and thiols (RSH), H-atom transfer to the trop2N nitrogen atom is observed, [M(trop2N·)(phen)]+ + EH [RIGHTWARDS ARROW] [M(trop2NH)(phen)]+ + 1/2HE–EH.(© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)