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- ItemLewis acid behavior of MoF5 and MoOF4: syntheses and characterization of MoF5(NCCH3), MoF5(NC5H5)n, and MoOF4(NC5H5)n (n- 1, 2)(ACS Publications, 2021) Bykowski, Janelle; Turnbull, Douglas; Hahn, Nolan; Boeré, René T.; Wetmore, Stacey D.; Gerken, MichaelThe Lewis acid–base adducts MoF5(NC5H5)n and MoOF4(NC5H5)n (n = 1, 2) were synthesized from the reactions of MoF5 and MoOF4 with C5H5N and structurally characterized by X-ray crystallography. Whereas the crystal structures of MoF5(NC5H5)2 and MoOF4(NC5H5)2 are isomorphous containing pentagonal-bipyramidal molecules, the fluorido-bridged, heptacoordinate [MoF5(NC5H5)]2 dimer differs starkly from monomeric, hexacoordinate MoOF4(NC5H5). For the weaker Lewis base CH3CN, only the 1:1 adduct, MoF5(NCCH3), could be isolated. All adducts were characterized by Raman spectroscopy in conjunction with vibrational frequency calculations. Multinuclear NMR spectroscopy revealed an unprecedented isomerism of MoOF4(NC5H5)2 in solution, with the pyridyl ligands occupying adjacent or nonadjacent positions in the equatorial plane of the pentagonal bipyramid. Paramagnetic MoF5(NC5H5)2 was characterized by electron paramagnetic resonance (EPR) spectroscopy as a dispersion in solid adamantane as well as in a diamagnetic host lattice of MoOF4(NC5H5)2; EPR parameters were computed using ZORA with the BPW91 functional using relativistic all-electron wave functions for Mo and simulated using EasySpin. Density functional theory calculations (B3LYP) and natural bond orbital analyses were conducted to elucidate the distinctive bonding and structural properties of all adducts reported herein and explore fundamental differences observed in the Lewis acid behavior of MoF5 and MoOF4.
- ItemSyntheses and characterization of W(NC6F5)F5– and W2(NC6F5)2F9– salts and computational studies of the W(NR)F5– (R = H, F, CH3, CF3, C6H5, C6F5) and W2(NC6F5)2F9– anions(American Chemical Society, 2017) Turnbull, Douglas; Wetmore, Stacey D.; Gerken, MichaelConvenient preparative routes to fluorido[(pentafluorophenyl)imido]tungstate(VI) salts have been developed. The reaction of WF6·NC5H5 or [N(CH3)4][WF7] with C6F5NH2 results in quantitative formation of the C5H5NH+ or N(CH3)4+ salt of the W(NC6F5)F5– anion, respectively. The dissolution of [C5H5NH][W(NC6F5)F5] in anhydrous HF results in the formation of [C5H5NH][W2(NC6F5)2F9]. These salts have been comprehensively characterized in the solid state by X-ray crystallography and Raman spectroscopy and in solution by 19F and 1H NMR spectroscopy. The crystal structures of the W(NC6F5)F5– salts reveal conformational differences in the anions, and the 19F NMR spectra of these salts in CH3CN reveal coupling of the axial fluorido ligand to the 14N nucleus of the imido ligand. In addition, density functional theory (DFT-B3LYP) calculations have been performed on a series of W(NR)F5– anions (R = H, F, CH3, CF3, C6H5, C6F5) and the W2(NC6F5)2F9– anion, including gas-phase geometry optimizations, vibrational frequencies, molecular orbitals, and natural bond orbital (NBO) analyses.
- ItemSyntheses, characterisation, and computational studies of tungsten hexafluoride adducts with pyridine and its derivatives(Elsevier, 2018) Turnbull, Douglas; Kostiuk, Nathan; Wetmore, Stacey D.; Gerken, MichaelThe reactions of WF6 with pyridine, 4-methylpyridine, 4-(dimethylamino)pyridine, and 4,4′-bipyridine (4,4′-bipy) in CH2Cl2 afford the Lewis-acid-base adducts WF6(4-NC5H4R) (R = H, CH3, N(CH3)2) and F6W(4,4′-bipy)WF6 as solids in quantitative yields. These adducts have been characterised in the solid state by Raman spectroscopy at ambient temperature and, in the cases of the mononuclear adducts, by X-ray crystallography at −173 °C. Furthermore, density-functional-theory (DFT-B3LYP) studies have been conducted to aid in predicting the structure of F6W(4,4′-bipy)WF6, assigning the vibrational frequencies of the adducts, and comparing their electronic properties.
- ItemSyntheses, characterization, and computational study of AsF5 adducts with ketones(Elsevier, 2019) Stuart, Daniel; Wetmore, Stacey D.; Gerken, MichaelLewis acid-base adducts between AsF5 and the ketones, acetone, cyclopentanone, and adamantanone, were synthesized from SO2 and CH2Cl2 solutions. These adducts, which contain O---As pnictogen bonding interactions, were found to be stable in solutions at room temperature. Raman and NMR spectroscopy of the solid adducts showed a characteristic decrease in the C=O stretching frequency, as well as dramatic deshielding of the 13C resonance of the carbonyl group upon adduct formation. Fluorine-19 NMR spectroscopy showed the two fluorine environments of the O–AsF5 moiety. Optimization of the gas-phase geometry using DFT calculations yielded geometries with essentially planar CC=OAs moieties. NBO analyses of the adducts and the free ketones show the polarization of the C=O bond upon adduct formation. The lowering of the LUMO energies upon adduct formation is more dramatic than what was found for protonation of ketones and reflects the substantially enhanced electrophilicity of the adducted ketones.
- ItemSynthesis, characterization, and Lewis acid behavior of [W(NC6F5)F4]x and computational study of W(NR)F4 (R = H, F, CH3, CF3, C6H5, C6F5), W(NC6F5)F4(NCCH3), and W(NC6F5)F4(NC5H5)n (n = 1, 2)(American Chemical Society, 2019) Turnbull, Douglas; Wetmore, Stacey D.; Gerken, MichaelAmorphous [W(NC6F5)F4]x has been synthesized by the reaction of [C5H5NH][W(NC6F5)F5] with AsF5 in CH2Cl2. The reaction of [W(NC6F5)F4]x with CH3CN yields monomeric W(NC6F5)F4(NCCH3), whereas reaction with a sub-2-fold excess of C5H5N in CH3CN results in quantitative conversion to W(NC6F5)F4(NC5H5). Meanwhile, the reaction of W(NC6F5)F4(NCCH3) with a large excess of C5H5N results in the precipitation of W(NC6F5)F4(NC5H5)2. These compounds have been characterized in the solid state by Raman spectroscopy and in solution by multinuclear NMR spectroscopy. The crystal structures of W(NC6F5)F4(NCCH3) and W(NC6F5)F4(NC5H5), as well as improved structures of WOF4(NC5H5)n (n = 1, 2), have been obtained at low temperatures. Furthermore, density functional theory (DFT-B3LYP) calculations have been conducted on the W(NR)F4 (R = H, F, CH3, CF3, C6H5, C6F5) series as well as W(NC6F5)F4(NCCH3) and W(NC6F5)F4(NC5H5)n (n = 1, 2), providing optimized gas-phase geometries, vibrational frequencies, molecular orbitals, fluoride-ion affinities, and natural bond orbital (NBO) analyses.
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