Jenny V. Lockard

Privileged Phosphine-Based Metal–Organic Frameworks for Broad-Scope Asymmetric Catalysis

A robust and porous Zr metal-organic framework (MOF) based on a BINAP-derived dicarboxylate linker, BINAP-MOF, was synthesized and post-synthetically metalated with Ru and Rh complexes to afford highly enantioselective catalysts for important organic transformations. The Rh-functionalized MOF is not only highly enantioselective (up to >99% ee) but also 3 times as active as the homogeneous control. XAFS studies revealed that the Ru-functionalized MOF contains Ru-BINAP precatalysts with the same coordination environment as the homogeneous Ru complex. The post-synthetically metalated BINAP-MOFs provide a versatile family of single-site solid catalysts for catalyzing a broad scope of asymmetric organic transformations, including addition of aryl and alkyl groups to α,β-unsaturated ketones and hydrogenation of substituted alkene and carbonyl compounds.

Tuning Aryl, Hydrazine Radical Cation Electronic Interactions Using Substitutent Effects

Absorption spectra for 2,3-diaryl-2,3-diazabicyclo[2.2.2]octane radical cations (2(X)(*+)) and for their monoaryl analogues 2-tert-butyl-3-aryl-2,3-diazabicyclo[2.2.2]octane radical cations (1(X)(*+)) having para chloro, bromo, iodo, cyano, phenyl, and nitro substituents are reported and compared with those for the previously reported 1- and 2(H)(*+) and 1- and 2(OMe)(*+). The calculated geometries and optical absorption spectra for 2(Cl)(*+) demonstrate that p-C6H4Cl lies between p-C6H4OMe and C6H5 in its ability to stabilize the lowest energy optical transition of the radical cation, which involves electron donation from the aryl groups toward the pi*(NN)(+)-centered singly occupied molecular orbital of 2(X)(*+). Resonance Raman spectral determination of the reorganization energy for their lowest energy transitions (lambda(v)(sym)) increase in the same order, having values of 1420, 5300, and 6000 cm(-1) for X = H, Cl, and OMe, respectively. A neighboring orbital analysis using Koopmans-based calculations of relative orbital energies indicates that the diabatic aryl pi-centered molecular orbital that interacts with the dinitrogen pi system lies closest in energy to the bonding pi(NN)-centered orbital and has an electronic coupling with it of about 9200 +/- 600 cm(-1), which does not vary regularly with electron donating power of the X substituent.

SERS on mesostructured thin films with silver nanoparticles

Mesostructured 2d-hexagonal sol-gel films were prepared by dip-coating method. Their structures were detected by X-ray diffraction. Silver nanoparticles reduced from Ag+ ion (silver nitrate) to Ag0 were deposited into the channels of the structure produced by the neutral surfactant Brij58. Surface enhanced raman spectroscopy technique was used to characterize the films. Spectra of films without metallic particles were compared to those with silver nanoparticles; the earliest exhibit an increased intensity on the 885, 955, 1061, 1129, 1230,1429, 1521, and 1796 cm-1 bands. This enhancement due to SERS is the result of the surface plasmon excitation inside the silver particles causing a reactivation of the Raman scattering from the molecules on the surface colloids. Photoconductivity studies were performed on mesostructured films with silver colloids. φl0 and φµτ parameters are bigger than those from photorefractive crystals KnbO3:Fe3+. The photovoltaic effect increases with AgNO3 concentration. Mesostructured film without silver colloids shows a small photovoltaic parameter.