Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes

The chlorido-bridged dimeric complex [Rh-2(mu-Cl)(2)(trop(2)NH)(2)] [trop(2)NH = bis(benzo[a,d]cycloheptenyl)amine] or the acetonitrile complexes [Rh(trop(2)NH)(MeCN)(2)](+) (CF3SO3-) and [IrCl(MeCN)(trop(2)NH)] 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 1,8-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=C-trop units is in an equatorial position. The cationic amino complexes [M(trop(2)NH)(R,R-phen)](+) are sufficiently acidic (pK(a) in dmso: 18.2-19.0) to be quantitatively deprotonated by one equivalent of KOtBu to give neutral amido complexes [M(trop(2)N)(R,R-phen)] (M = Rh, Ir). These can be easily oxidized to give aminyl radical complexes [M(trop(2)N(center dot))(R,R-phen)](+)A(-), which for M = Rh can be isolated as green crystals. The iridium complex [Ir(trop(2)N(center dot))(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(trop(2)N center dot)(phen)](+): g(1,2,3) = 2.084(2), 2.049(2), 2.027(2); vertical bar A(iso)vertical bar = 45.4 (N1), 10.4 (N2), 3.1 (N3) 27.0 (Rh) MHz; [Ir(trop(2)N(center dot))(phen)](+): g(1,2,3) = 2.140(2), 2.107(2), 2.015(2); vertical bar A(iso)vertical bar = 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 trop(2)N ligand. In reactions with stannanes (R3SnH) and thiols (RSH), H-atom transfer to the trop(2)N nitrogen atom is observed, [M(trop(2)N(center dot))(phen)](+) + EH -> [M(trop(2)NH)(phen)](+) + 1/2HE-EH. ((C) Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)