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Mononuclear [Ir{ArNC(NR2)NAr}(C8H14)2] complexes (where R = Me or Et; Ar = Ph or 4-MeC6H4; and C8H14 = cis-cyclooctene) were synthesized from the neutral N,N-dialkyl-N′,N′′-diarylguanidines via deprotonation and transmetalation. As confirmed by single-crystal structure determination, the guanidinato(1−) ligands coordinate the low-valent d8 IrI center in an N,N′-chelating binding mode, and the C–N distances of the CN3 core suggest that these ligands function as stronger donors than related monoanionic, bidentate nitrogen-based ligands. In the reaction of the complexes with O2, new [Ir{ArNC(NR2)NAr}]3 complexes were identified among the products, suggesting a new route for their synthesis. Tris(guanidinato) complexes of IrIII, [Ir{ArNC(NR2)NAr}3] (R = Me or Et; Ar = Ph or 4-MeC6H4), were synthesized and, as revealed by electrochemical measurements, can be oxidized reversibly at unusually low potentials. These potentials are even lower than those of other IrIII complexes with very electron-rich, trianonic ligand sets as, for example, in cyclometalated tris(2-pyridylphenyl), corrolato and tris(dithiocarbamato) complexes. Chemical oxidation by [FeCp2]PF6 afforded isolable, paramagnetic IrIV compounds, [Ir{ArNC(NR2)NAr}3]PF6, which were characterized by elemental analysis, mass spectrometry, electronic absorption and EPR spectroscopy and X-ray crystallography. The reactivity of these IrIV complexes toward mild inorganic and organic reductants and substrates with O–H bonds was investigated.
Similar tris(guanidinato) complexes of RhIII, [Rh{ArNC(NR2)NAr}3] (R = Me or Et; Ar = Ph, 4-MeC6H4 or 4-MeOC6H4), were synthesized. These complexes also were oxidized reversibly at low potentials, as compared to the corresponding tris(amidinato) and tris(triazenido) complexes. Chemical oxidation by [FeCp2]PF6 afforded thermally unstable, paramagnetic RhIV compounds, [Rh{ArNC(NR2)NAr}3]PF6, which were characterized by mass spectrometry and electronic absorption spectroscopy. Furthermore, two FeII complexes of tetradentate tripodal ligands, [Fe(L1)(OTf)2] and [Fe(L2)(OTf)2]; where L1 = N,N-bis(2-benzimidazolylmethyl)-N-(2-pyridylmethyl) amine and L2 = N,N-bis[(1-methylbenzimidazol-2-yl)methyl]-N-[(pyridin-2-yl)methyl] amine; were synthesized and characterized. The 1H NMR spectra for [Fe(L1)(NCMe)2](OTf)2 and [Fe(L2)(NCMe)2](OTf)2 in CD3CN solution at ambient temperature exhibit paramagnetically shifted peaks typical of high-spin FeII complexes, while variable-temperature 1H NMR spectroscopy showed that the Fe center in [Fe(L1)(NCMe)2](OTf)2 is in a spin equilibrium and that in [Fe(L2)(NCMe)2](OTf)2 in the high-spin state (at 25 °C). Highly reactive oxoiron(IV) complexes were obtained by reaction of the FeII complexes with an excess of m-CPBA at –40 °C.