Direct catalytic conversion of ethanol to hydrocarbon blend-stock can increase biofuels use in current vehicles beyond the ethanol blend-wall of 10–15%. Literature reports describe quantitative conversion of ethanol over zeolite catalysts but high C2 hydrocarbon formation renders this approach unsuitable for commercialization. Furthermore, the prior mechanistic studies suggested that ethanol conversion involves endothermic dehydration step. Here, we report the complete conversion of ethanol to hydrocarbons over InV-ZSM-5 without added hydrogen and which produces lower C2 (<13%) as compared to that over H-ZSM-5. Experiments with C2H5OD and in situ DRIFT suggest that most of the products come from the hydrocarbon pool type mechanism and dehydration step is not necessary. Thus, our method of direct conversion of ethanol offers a pathway to produce suitable hydrocarbon blend-stock that may be blended at a refinery to produce fuels such as gasoline, diesel, JP-8 and jet fuel, or produce commodity chemicals such as BTX.

A monomeric Mn(II) complex has been prepared with the facially-coordinating Tp(Ph2) ligand, (Tp(Ph2) = hydrotris(3,5-diphenylpyrazol-1-yl)borate). The X-ray crystal structure shows three coordinating solvent molecules resulting in a six-coordinate complex with Mn-ligand bond lengths that are consistent with a high-spin Mn(II) ion. Treatment of this Mn(II) complex with excess KO2 at room temperature resulted in the formation of a Mn(III)-O2 complex that is stable for several days at ambient conditions, allowing for the determination of the X-ray crystal structure of this intermediate. The electronic structure of this peroxomanganese(III) adduct was examined by using electronic absorption, electron paramagnetic resonance (EPR), low-temperature magnetic circular dichroism (MCD), and variable-temperature variable-field (VTVH) MCD spectroscopies. Density functional theory (DFT), time-dependent (TD)-DFT, and multireference ab initio CASSCF/NEVPT2 calculations were used to assign the electronic transitions and further investigate the electronic structure of the peroxomanganese(III) species. The lowest ligand-field transition in the electronic absorption spectrum of the Mn(III)-O2 complex exhibits a blue shift in energy compared to other previously characterized peroxomanganese(III) complexes that results from a large axial bond elongation, reducing the metal-ligand covalency and stabilizing the σ-antibonding Mn dz(2) MO that is the donor MO for this transition.

We report the generation and characterization of two peroxomanganese(III) complexes supported by the L7py24-Cl and L7iso-q2 ligands {L7py24-Cl = 1,4-bis[(4-chloro-2-pyridyl)methyl]-1,4-diazepane and L7iso-q2 = 1,4-bis[(2-isoquinolinyl)methyl]-1,4-diazepane} and describe X-ray structures of corresponding manganese(II) compounds. Ground and excited state properties of these peroxomanganese(III) complexes, as well as previously reported [MnIII(O2)(L7py24-Me)]+ and [MnIII(O2)(L7q2)]+ species {L7py24-Me = 1,4-bis[(4-methyl-2-pyridyl)methyl]-1,4-diazepane and L7q2 = 1,4-bis[(2-quinolinyl)methyl]-1,4-diazepane} were probed using low-temperature electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD spectroscopy. These data sets afford electronic transition energies and estimates of ground-state zero-field splitting parameters, which permit a detailed comparison of electronic structure. These data support the proposal that all complexes share a similar geometry, consisting of a side-on peroxomanganese(III) moiety coordinated by the tetradentate ligand in a trans fashion. However, differences in d-d transition energies offer conclusive evidence that, among this series of complexes, it is the location, and thus the steric influence, of the pyridine substituent that modulates the electronic and geometric structure of the MnIII-O2 unit. Within this series, perturbations in electronic properties of the supporting ligand have little impact on d-d transition energies. Models of peroxomanganese(III) complexes developed using density functional theory (DFT) computations support this proposal, and time-dependent DFT computations qualitatively reproduce the experimental trend in d-d transition energies.

A series of new heterobimetallic zeolites has been synthesized by incorporating a secondary metal cation M (Sc3+, Fe3+, In3+, and La3+) in Cuexchanged ZSM-5, zeolite-beta, and SSZ-13 zeolites under carefully controlled experimental conditions. Characterization by diffuse-reflectance ultraviolet-visible spectroscopy (UV-vis), X-ray powder diffraction (XRD), extended X-ray absorption fine structure spectroscopy (EXAFS), and electron paramagnetic resonance spectroscopy (EPR) does not permit conclusive structural determ nation but supports the proposal that M3+ is hosted in zeolite structures in the vicinity of Cu(II), resulting in high NOx conversion activity at 150 degrees C. Among various zeolites reported here, CuFe-SSZ-13 offers the best NOx conversion activity in the 150-650 degrees C range and is hydrothermally stable when tested under accelerated aging conditions. Mechanistic studies employing stopped-flow diffuse reflectance FT-IR spectroscopy (DRIFTS) suggest that the high concentration of NO+ generated by heterobimetallic zeolites is probably responsible for their superior low-temperature NOx activity.

The ground and excited state properties of [Mn(OMe)3(Me3TACN)]+ (Me3TACN=1,4,7-trimethyl-1,4,7-triazacyclononane), which features a mononuclear MnIV center, were investigated using electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field (VTVH) MCD spectroscopies. Due to small zero-field splittings (ZFSs), MnIV centers are difficult to study using X-band electron paramagnetic resonance (EPR) spectroscopy. In this work, VTVH MCD spectroscopy was explored as an alternative method. [Mn(OMe)3(Me3TACN)]+ served as a test complex, because accurate ZFS parameters are available from high-field, high-frequency EPR (HF-EPR) data [33]. Using an E/D of 0, as determined from X-band EPR data, the VTVH MCD data collected for [Mn(OMe)3(Me3TACN)]+ yield an axial ground-state ZFS parameter (D) of similar accuracy, but lower precision, than that obtained from HF-EPR spectroscopy (D=+0.2(1) and +0.250(5)cm−1 from VTVH MCD and HF-EPR data, respectively). Thus, when combined with X-band EPR spectroscopy, the VTVH MCD method can serve as an alternative to HF-EPR spectroscopy even for systems with small ZFSs. In addition, analysis of electronic absorption and MCD spectral data collected for [Mn(OMe)3(Me3TACN)]+ permit the extraction of excited state parameters 10Dq and B (∼18490 and 595cm−1, respectively), which are comparable to those of other MnIV complexes.

Three peroxomanganese(III) complexes [Mn(III)(O(2))(mL(5)(2))](+), [Mn(III)(O(2))(imL(5)(2))](+), and [Mn(III)(O(2))(N4py)](+) supported by pentadentate ligands (mL(5)(2) = N-methyl-N,N',N'-tris(2-pyridylmethyl)ethane-1,2-diamine, imL(5)(2) = N-methyl-N,N',N'-tris((1-methyl-4-imidazolyl)methyl)ethane-1,2-diamine, and N4py = N,N-bis(2-pyridylmethyl)-N-bis(2-pyridyl)methylamine) were generated by treating Mn(II) precursors with H(2)O(2) or KO(2). Electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD data demonstrate that these complexes have very similar electronic transition energies and ground-state zero-field splitting parameters, indicative of nearly identical coordination geometries. Because of uncertainty in peroxo (side-on η(2) versus end-on η(1)) and ligand (pentadentate versus tetradentate) binding modes, density functional theory (DFT) computations were used to distinguish between three possible structures: pentadentate ligand binding with (i) a side-on peroxo and (ii) an end-on peroxo, and (iii) tetradentate ligand binding with a side-on peroxo. Regardless of the supporting ligand, isomers with a side-on peroxo and the supporting ligand bound in a tetradentate fashion were identified as most stable by >20 kcal/mol. Spectroscopic parameters computed by time-dependent (TD) DFT and multireference SORCI methods provided validation of these isomers on the basis of experimental data. Hexacoordination is thus strongly preferred for peroxomanganese(III) adducts, and dissociation of a pyridine (mL(5)(2) and N4py) or imidazole (imL(5)(2)) arm is thermodynamically favored. In contrast, DFT computations for models of [Fe(III)(O(2))(mL(5)(2))](+) demonstrate that pyridine dissociation is not favorable; instead a seven-coordinate ferric center is preferred. These different results are attributed to the electronic configurations of the metal centers (high spin d(5) and d(4) for Fe(III) and Mn(III), respectively), which results in population of a metal-peroxo σ-antibonding molecular orbital and, consequently, longer M-O(peroxo) bonds for peroxoiron(III) species.

Peroxomanganese(iii) adducts have been postulated as important intermediates in manganese-containing enzymes and small molecule oxidation catalysts. Synthetic peroxomanganese(iii) complexes are known to be nucleophilic and facilitate aldehyde deformylation, offering a convenient way to compare relative reactivities of complexes supported by different ligands. In this work, tetradentate dipyridyldiazacycloalkane ligands with systematically perturbed steric and electronic properties were used to generate a series of manganese(ii) and peroxomanganese(iii) complexes. X-Ray crystal structures of five manganese(ii) complexes all show the ligands bound to give trans complexes. Treatment of these Mn(II) precursors with H(2)O(2) and Et(3)N in MeCN at -40 °C results in the formation of peroxomanganese(iii) complexes that differ only in the identity of the pyridine ring substituent and/or the number of carbons in the diazacycloalkane backbone. To determine the effects of small ligand perturbations on the reactivity of the peroxo group, the more thermally stable peroxomanganese(iii) complexes were reacted with cyclohexanecarboxaldehyde. For these complexes, the rate of deformylation does not correlate with the expected nucleophilicity of the peroxomanganese(iii) unit, as the inclusion of methyl substituents on the pyridines affords slower deformylation rates. It is proposed that adding methyl-substituents to the pyridines, or increasing the number of carbons on the diazacycloalkane, sterically hinders nucleophilic attack of the peroxo ligand on the carbonyl carbon of the aldehyde.

The electronic structures of the bis(hydroxo)manganese(IV) and oxohydroxomanganese(IV) complexes [Mn(IV)(OH)(2)(Me(2)EBC)](2+) and [Mn(IV)(O)(OH)(Me(2)EBC)](+) were probed using electronic absorption, magnetic circular dichroism (MCD), and variable-temperature, variable-field MCD spectroscopies. The d-d transitions of [Mn(IV)(OH)(2)(Me(2)EBC)](2+) were assigned using a group theory analysis coupled with the results of time-dependent density functional theory computations. These assignments permit the development of an experimentally validated description for the pi and sigma interactions in this complex. A similar analysis performed for [Mn(IV)(O)(OH)(Me(2)EBC)](+) reveals that there is a significant increase in the ligand character in the Mn pi* orbitals for the Mn(IV)=O complex relative to the bis(hydroxo)manganese(IV) complex, whereas the compositions of the Mn sigma* orbitals are less affected. Because of the steric features of the Me(2)EBC ligand, we propose that H-atom transfer by these reagents proceeds via the sigma* orbitals, which, because of their similar compositions among these two compounds, leads to modest rate enhancements for the Mn(IV)=O versus Mn(IV)OH species.

A set of four [Mn(II)(L(7)py(2)(R))](2+) complexes, supported by the tetradentate 1,4-bis(2-pyridylmethyl)-1,4-diazepane ligand and derivatives with pyridine substituents in the 5 (R = Br) and 6 positions (R = Me and MeO), are reported. X-ray crystal structures of these complexes all show the L(7)py(2)(R) ligands bound to give a trans complex. Treatment of these Mn(II) precursors with either H(2)O(2)/Et(3)N or KO(2) in MeCN at -40 degrees C results in the formation of peroxomanganese complexes [Mn(III)(O(2))(L(7)py(2)(R))](+) differing only in the identity of the pyridine ring substituent. The electronic structures of two of these complexes, [Mn(III)(O(2))(L(7)py(2)(H))](+) and [Mn(III)(O(2))(L(7)py(2)(Me))](+), were examined in detail using electronic absorption, low-temperature magnetic circular dichroism (MCD) and variable-temperature variable-field (VTVH) MCD spectroscopies to determine ground-state zero-field splitting (ZFS) parameters and electronic transition energies, intensities, and polarizations. DFT and TD-DFT computations were used to validate the structures of [Mn(III)(O(2))(L(7)py(2)(H))](+) and [Mn(III)(O(2))(L(7)py(2)(Me))](+), further corroborating their assignment as peroxomanganese(III) species. While these complexes exhibit similar ZFS parameters, their low-temperature MCD spectra reveal significant shifts in electronic transition energies that are correlated to differences in Mn-O(2) interactions among these complexes. Taken together, these results indicate that, while the [Mn(III)(O(2))(L(7)py(2)(H))](+) complex exhibits symmetric Mn-O(peroxo) bond lengths, consistent with a side-on bound peroxo ligand, the peroxo ligand of the [Mn(III)(O(2))(L(7)py(2)(Me))](+) complex is bound in a more end-on fashion, with asymmetric Mn-O(peroxo) distances. This difference in binding mode is rationalized in terms of the greater electron-donating abilities of the methyl-appended pyridines and suggests a simple way to modulate Mn(III)-O(2) bonding through ligand perturbations.