Theoretical Investigation of the Reaction of O(D) with Formamide.

Carbamic acid (HNCOOH) is a small organic molecule that is terrestrially unstable in condensed phases under ambient conditions but could survive in the low densities and temperatures of the interstellar medium. In this work, the reaction of formamide (HNCOH) and electronically excited oxygen atoms in the D state, namely, O(D), has been investigated computationally to determine the feasibility of carbamic acid production. Geometries for carbamic acid and other potential reaction products have been calculated, as well as all pertinent transition states.

Polar Heterobenzylic C(sp)-H Chlorination Pathway Enabling Efficient Diversification of Aromatic Nitrogen Heterocycles.

Site-selective radical reactions of benzylic C-H bonds are now highly effective methods for C(sp-H) functionalization and cross-coupling. The existing methods, however, are often ineffective with heterobenzylic C-H bonds in alkyl-substituted pyridines and related aromatic heterocycles that are prominently featured in pharmaceuticals and agrochemicals. Here, we report new synthetic methods that leverage polar, rather than radical, reaction pathways to enable the selective heterobenzylic C-H chlorination of 2- and 4-alkyl-substituted pyridines and other heterocycles.

Practical and General Alcohol Deoxygenation Protocol.

Herein, we describe a practical protocol for the removal of alcohol functional groups through reductive cleavage of their benzoate ester analogs. This transformation requires a strong single electron transfer (SET) reductant and a means to accelerate slow fragmentation following substrate reduction. To accomplish this, we developed a photocatalytic system that generates a potent reductant from formate salts alongside Brønsted or Lewis acids that promote fragmentation of the reduced intermediate.

Electrochemical Strategy for Hydrazine Synthesis: Development and Overpotential Analysis of Methods for Oxidative N-N Coupling of an Ammonia Surrogate.

Hydrazine is an important industrial chemical and fuel that has attracted considerable attention for use in liquid fuel cells. Ideally, hydrazine could be prepared via direct oxidative coupling of ammonia, but thermodynamic and kinetic factors limit the viability of this approach. The present study evaluates three different electrochemical strategies for the oxidative homocoupling of benzophenone imine, a readily accessible ammonia surrogate.

Enantioselective photochemistry through Lewis acid-catalyzed triplet energy transfer.

Relatively few catalytic systems are able to control the stereochemistry of electronically excited organic intermediates. Here we report the discovery that a chiral Lewis acid complex can catalyze triplet energy transfer from an electronically excited photosensitizer. We applied this strategy to asymmetric [2 + 2] photocycloadditions of 2'-hydroxychalcones, using tris(bipyridyl) ruthenium(II) as a sensitizer.

Single-Molecule Investigation of Initiation Dynamics of an Organometallic Catalyst.

The action of molecular catalysts comprises multiple microscopic kinetic steps whose nature is of central importance in determining catalyst activity and selectivity. Single-molecule microscopy enables the direct examination of these steps, including elucidation of molecule-to-molecule variability. Such molecular diversity is particularly important for the behavior of molecular catalysts supported at surfaces.

Spin-Selective Generation of Triplet Nitrenes: Olefin Aziridination through Visible-Light Photosensitization of Azidoformates.

Azidoformates are interesting potential nitrene precursors, but their direct photochemical activation can result in competitive formation of aziridination and allylic amination products. Herein, we show that visible-light-activated transition-metal complexes can be triplet sensitizers that selectively produce aziridines through the spin-selective photogeneration of triplet nitrenes from azidoformates. This approach enables the aziridination of a wide range of alkenes and the formal oxyamination of enol ethers using the alkene as the limiting reagent.

Mechanistic studies of copper(I)-catalyzed 1,3-halogen migration.

An ongoing challenge in modern catalysis is to identify and understand new modes of reactivity promoted by earth-abundant and inexpensive first-row transition metals. Herein, we report a mechanistic study of an unusual copper(I)-catalyzed 1,3-migration of 2-bromostyrenes that reincorporates the bromine activating group into the final product with concomitant borylation of the aryl halide bond. A combination of experimental and computational studies indicated this reaction does not involve any oxidation state changes at copper; rather, migration occurs through a series of formal sigmatropic shifts.

Efficient and Accurate Methods for the Geometry Optimization of Water Clusters: Application of Analytic Gradients for the Two-Body:Many-Body QM:QM Fragmentation Method to (H2O)n, n = 3-10.

The structures of more than 70 low-lying water clusters ranging in size from (H2O)3 to (H2O)10 have been fully optimized with several different quantum mechanical electronic structure methods, including second-order Møller-Plesset perturbation theory (MP2) in conjunction with correlation consistent triple-ζ basis sets (aug-cc-pVTZ for O and cc-pVTZ for H, abbreviated haTZ). Optimized structures obtained with less demanding computational procedures were compared to the MP2/haTZ ones using both MP2/haTZ single point energies and the root-mean-square (RMS) deviations of unweighted Cartesian coordinates. Based on these criteria, B3LYP/6-31+G(d,2p) substantially outperforms both HF/haTZ and MP2/6-31G*.

Development of a 3-body:many-body integrated fragmentation method for weakly bound clusters and application to water clusters (H2O)(n = 3-10, 16, 17).

A 3-body:many-body integrated quantum mechanical (QM) fragmentation method for non-covalent clusters is introduced within the ONIOM formalism. The technique captures all 1-, 2-, and 3-body interactions with a high-level electronic structure method, while a less demanding low-level method is employed to recover 4-body and higher-order interactions. When systematically applied to 40 low-lying (H(2)O)(n) isomers ranging in size from n = 3 to 10, the CCSD(T):MP2 3-body:many-body fragmentation scheme deviates from the full CCSD(T) interaction energy by no more than 0.

CCSD(T) complete basis set limit relative energies for low-lying water hexamer structures.

MP2 and CCSD(T) complete basis set (CBS) limit relative electronic energies (DeltaE(e)) have been determined for eight low-lying structures of the water hexamer by combining explicitly correlated MP2-R12 computations with higher-order correlation corrections from CCSD(T) calculations. Higher-order correlation effects are quite substantial and increase DeltaE(e) by at least +0.19 kcal mol(-1) and as much as +0.

Probing the effects of heterogeneity on delocalized pi...pi interaction energies.

Dimers composed of benzene (Bz), 1,3,5-triazine (Tz), cyanogen (Cy) and diacetylene (Di) are used to examine the effects of heterogeneity at the molecular level and at the cluster level on pi...