The interaction of imidazole with a [Cu(acac)] complex was studied using electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), hyperfine sublevel correlation spectroscopy (HYSCORE), and density functional theory (DFT). At low Im ratios (Cu:Im 1:10), a 5-coordinate [Cu(acac)Im] monoadduct is formed in frozen solution with the spin Hamiltonian parameters g = 2.063, g = 2.063, g = 2.307, A = 26, A = 15, and A = 472 MHz with Im coordinating along the axial direction. At higher Im concentrations (Cu:Im 1:50), a 6-coordinate [Cu(acac)Im] bis-adduct is formed with the spin Hamiltonian parameters g = 2.059, g = 2.059, g = 2.288, A = 30, A = 30, and A = 498 MHz with a poorly resolved N superhyperfine pattern. The isotropic EPR spectra revealed a distribution of species ([Cu(acac)], [Cu(acac)Im], and [Cu(acac)Im]) at Cu:Im ratios of 1:0, 1:10, and 1:50. The superhyperfine pattern originates from two strongly coordinating N imino nitrogens of the Im ring. Angular selective N ENDOR analysis revealed theA tensor of [34.8, 43.5, 34.0] MHz, with eqQ/h = 2.2 MHz and η = 0.2 for N. The hyperfine and quadrupole values for the remote N amine nitrogens (from HYSCORE) were found to be [1.5, 1.4, 2.5] MHz with eqQ/h = 1.4 MHz and η = 0.9. H ENDOR also revealed three sets ofA tensors corresponding to the nearly equivalent H/H protons in addition to the H and H protons of the Im ring. The spin Hamiltonian parameters for the geometry optimized structures of [Cu(acac)Im], including cis-mixed plane, trans-axial, and trans-equatorial, were calculated. The best agreement between theory and experiment indicated the preferred coordination is trans-equatorial [Cu(acac)Im]. A number of other Im derivatives were also investigated. 4(5)-methyl-imidazole forms a [Cu(acac)(Im-3)] trans-equatorial adduct, whereas the bulkier 2-methyl-imidazole (Im-2) and benzimidazole (Im-4) form the [Cu(acac)(Im-2,4)] monoadduct only. Our data therefore show that subtle changes in the substrate structure lead to controllable changes in coordination behavior, which could in turn lead to rational design of complexes for use in catalysis, imaging, and medicine.

Partial oxidative upgrading of C -C alkanes over Cu/ZSM-5 catalysts prepared by chemical vapour impregnation (CVI) has been studied. The undoped ZSM-5 support is itself able to catalyse selective oxidations, for example, methane to methanol, using mild reaction conditions and the green oxidant H O . Addition of Cu suppresses secondary oxidation reactions, affording methanol selectivities of up to 97 %. Characterisation studies attribute this ability to population of specific Cu sites below the level of total exchange (Cu/Al<0.5). These species also show activity for radical-based methane oxidation, with productivities exceeding those of the parent zeolite supports. When tested for ethane and propane oxidation reactions, comparable trends are observed.

Herein, we report a simplified method for the synthesis of Triphos homologs HCC(CHX)(CHY) (X = SPh, Y = PPh, n = 0-3). The multidentate compounds were tested for their potential to coordinate metals such as Ni, Fe, and Mo under the same experimental conditions. Cyclic voltammetry, spectroelectrochemical IR investigations as well as DFT calculations were used to examine the electronic alterations in a series of [{HCC(CHX)(CHY)}Mo(CO)] complexes and to evaluate their potential to open coordination sites or to release CO upon oxidation or in the presence of different solvents. In addition, we demonstrate that the catalytic hydrosilylation of N,N-dimethylbenzamide to N,N-dimethylbenzylamine is influenced by the applied tripodal ligand. Our investigations show the high potential of such manipulations to selectively alter the dynamics of the binding properties of Triphos-metal complexes and their reactivity.

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