Dicopper complexes templated by dinucleating, pacman dipyrrin ligand scaffolds (dmx, dmx: dimethylxanthine-bridged, cofacial bis-dipyrrin) were synthesized by deprotonation/metalation with mesitylcopper (CuMes; Mes: mesityl) or by transmetalation with cuprous precursors from the corresponding deprotonated ligand. Neutral imide complexes (dmx)Cu(μ-NAr) (R: Mes, Bu; Ar: 4-MeOCH, 3,5-(FC)CH) were synthesized by treatment of the corresponding dicuprous complexes with aryl azides. While one-electron reduction of (dmx)Cu(μ-N(CHOMe)) with potassium graphite initiates an intramolecular, benzylic C-H amination at room temperature, chemical reduction of (dmx)Cu(μ-NAr) leads to isolable [(dmx)Cu(μ-NAr)] product salts.
View Article and Find Full Text PDFMetalation of the deprotonated dipyrrin (L)Li with NiCl(py) afforded the divalent Ni product (L)NiCl(py) () (L: 1,9-di(1-adamantyl)-5-perfluorophenyldipyrrin; py: pyridine). To generate a reactive synthon on which to explore oxidative group transfer, we used potassium graphite to reduce , affording the monovalent Ni synthon (L)Ni(py) () and concomitant production of a stoichiometric equivalent of KCl and pyridine. Slow addition of mesityl- or 1-adamantylazide in benzene to afforded the oxidized Ni complexes (L)Ni(NMes) () and (L)Ni(NAd) (), respectively.
View Article and Find Full Text PDFSeventeen Cu complexes with formal oxidation states ranging from Cu to Cu are investigated through the use of multiedge X-ray absorption spectroscopy (XAS) and density functional theory (DFT) calculations. Analysis reveals that the metal-ligand bonding in high-valent, formally Cu species is extremely covalent, resulting in Cu K-edge and L-edge spectra whose features have energies that complicate physical oxidation state assignment. Covalency analysis of the Cu L-edge data reveals that all formally Cu species have significantly diminished Cu d-character in their lowest unoccupied molecular orbitals (LUMOs).
View Article and Find Full Text PDFNitrogen K-edge X-ray absorption spectra (XAS) were obtained for 19 transition metal complexes bearing bipyridine, ethylenediamine, ammine, and nitride ligands. Time-dependent density functional theory (TDDFT) and DFT/restricted open configuration interaction singles (DFT/ROCIS) calculations were found to predict relative N K-edge XAS peak energies with good fidelity to experiment. The average difference (|Δ|) between experimental and linear corrected calculated energies were found to be 0.
View Article and Find Full Text PDFReaction of the tricopper(I)-dinitrogen tris(β-diketiminate) cyclophane, Cu(N)L, with O-atom-transfer reagents or elemental Se affords the oxido-bridged tricopper complex Cu(μ-O)L (2) or the corresponding Cu(μ-Se)L (4), respectively. For 2 and 4, incorporation of the bridging chalcogen donor was supported by electrospray ionization mass spectrometry and K-edge X-ray absorption spectroscopy (XAS) data. Cu L-edge X-ray absorption data quantify 49.
View Article and Find Full Text PDFCoordination of redox-active ligands to metals is a compelling strategy for making reduced complexes more accessible. In this work, we explore the use of redox-active formazanate ligands in low-coordinate iron chemistry. Reduction of an iron(II) precursor occurs at milder potentials than analogous non-redox-active β-diketiminate complexes, and the reduced three-coordinate formazanate-iron compound is characterized in detail.
View Article and Find Full Text PDFReduction of previously reported iminyl radical (L)FeCl(N(CH-p-Bu)) (2) with potassium graphite furnished the corresponding high-spin (S = /) imido (L)Fe(N(CH-p-Bu)) (3) (L = 5-mesityl-1,9-(2,4,6-PhCH)dipyrrin). Oxidation of the three-coordinate imido (L)Fe(NAd) (5) with chlorotriphenylmethane afforded (L)FeCl(NAd) (6) with concomitant expulsion of PhC(CH)CPh. The respective aryl/alkyl imido/iminyl pairs (3, 2; 5, 6) have been characterized by EPR, zero-field Fe Mössbauer, magnetometry, single crystal X-ray diffraction, XAS, and EXAFS for 6.
View Article and Find Full Text PDFCopper/aminoxyl species are proposed as key intermediates in aerobic alcohol oxidation. Several possible electronic structural descriptions of these species are possible, and the present study probes this issue by examining four crystallographically characterized Cu/aminoxyl halide complexes by Cu K-edge, Cu L-edge, and Cl K-edge X-ray absorption spectroscopy. The mixing coefficients between Cu, aminoxyl, and halide orbitals are determined via these techniques with support from density functional theory.
View Article and Find Full Text PDFThe contested electronic structure of [Cu(CF3)4](1-) is investigated with UV/visible/near IR spectroscopy, Cu K-edge X-ray absorption spectroscopy, and 1s2p resonant inelastic X-ray scattering. These data, supported by density functional theory, multiplet theory, and multireference calculations, support a ground state electronic configuration in which the lowest unoccupied orbital is of predominantly trifluoromethyl character. The consensus 3d(10) configuration features an inverted ligand field in which all five metal-localized molecular orbitals are located at lower energy relative to the trifluoromethyl-centered σ orbitals.
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