Rhodium and Iridium Amino, Amido, and Aminyl Radical Complexes

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 → [M(trop2NH)(phen)]+ + 1/2HE–EH.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008) Trigonal bipyramidal bis(olefin) amido 18‐electron complexes of RhI or IrI are easily oxidized (E°1/2 ≈ –0.55 V vs. Fc+/Fc) to give aminyl radical complexes. High‐resolution pulse EPR spectroscopy was used to demonstrate that both the RhI and IrI aminyl complexes have remarkably similar electronic structures (60 % of the spin density at the N center, 30 % at the metal).