Lee Belding

Lee Belding

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30
Publications
2,754
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1,007
Citations
Citations since 2016
16 Research Items
837 Citations
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200
2016201720182019202020212022050100150200

Publications

Publications (30)
Article
This paper describes a surface analysis technique that uses the "EGaIn junction" to measure tunneling current densities (J(V), amps/cm2) through self-assembled monolayers (SAMs) terminated in a chelating group and incorporating different transition metal ions. Comparisons of J(V) measurements between bare chelating groups and chelates are used to c...
Article
This paper demonstrates that the molecular conformation (in addition to the composition and structure) of molecules making up self-assembled monolayers (SAMs) influences the rates of charge tunneling (CT) through them, in molecular junctions of the form AuTS/S(CH2)2CONR1R2//Ga2O3/EGaIn, where R1 and R2 are alkyl chains of different length. The leng...
Article
This paper addresses the mechanism for rectification in molecular tunneling junctions based on alkanethiolates terminated by a bipyridine group complexed with a metal ion, that is, having the structure AuTS-S(CH2)11BIPY-MCl2 (where M = Co or Cu) with a eutectic indium-gallium alloy top contact (EGaIn, 75.5% Ga 24.5% In). Here, AuTS-S(CH2)11BIPY is...
Article
This paper describes the relationship between molecular structure, and the rectification of tunneling current, in tunneling junctions based on self-assembled monolayers (SAMs). Simple molecular dipoles (from amide, urea, and thiourea groups) were introduced into junctions with the structure AgTS/S(CH2)nR(CH2)mCH3//Ga2O3/EGaIn. Here, R is an n-alkyl...
Article
This work describes the autocatalytic copper-catalyzed azide-alkyne cycloaddition (CuAAC) reaction between tripropargylamine and 2-azidoethanol, in the presence of Cu(II) salts. The product of this reaction, tris-(hydroxyethyltriazolylmethyl)amine (N(C3N3)3), accelerates the cycloaddition reaction (and thus its own production) by two mechanisms: i)...
Article
Aziridine aldehyde-driven macrocyclization of peptides is a powerful tool for the construction of biologically active macrocycles. While this process has been used to generate diverse collections of cyclic molecules, its mechanistic underpinnings have remained unclear. To enable progress in this area we have carried out a mechanistic study, which s...
Article
Full-text available
The synthesis of cyclopropenium-substituted amino compounds and analysis of their photophysical properties is described. Systematic structural modifications of these derivatives lead to measurable and predictable changes in molar extinction coefficients, quantum yields, and Stokes shifts. Using time-dependent density functional theory (TD-DFT) calc...
Article
Almost all pneumatic and hydraulic actuators useful for mesoscale functions rely on hard valves for control. This article describes a soft, elastomeric valve that contains a bistable membrane, which acts as a mechanical “switch” to control air flow. A structural instability—often called “snap-through”—enables rapid transition between two stable sta...
Article
This article describes a new principle for designing soft or ‘semisoft’ pneumatic actuators: SLiT (for SLit-in-Tube) actuators. Inflating an elastomeric balloon, when enclosed by an external shell (a material with higher Young's modulus) containing slits of different directions and lengths, produces a variety of motions, including bending, twisting...
Article
Aziridine aldehyde-driven macrocyclization of peptides is a powerful tool for the construction of biologically active macrocycles. While this process has been used to generate diverse collections of cyclic molecules, its mechanistic underpinnings have remained unclear. To enable progress in this area we have carried out a mechanistic study, which s...
Article
Stepwise reduction of the diiminopyridine (dimpyr) complex, dimpyrZnCl2, by KC8 leads to molecular zinc compounds dimpyrZnCl (2) and dimpyrZnCl(DMAP) (3, DMAP = 4-dimethylaminopyridine), which were characterized by X-ray diffraction and EPR spectroscopy. Compound 2 shows an unusual nearly square planar geometry of the zinc atom equally ligated by t...
Article
Bis(diisopropylamino)cyclopropenimine-substituted bis-protonated proton sponge (BDC) is a useful phase-transfer catalyst for the alkylation of compound (I) with a range of alkyl halides.
Article
The use of a bis(diisopropylamino)cyclopropenimine substituted bis-protonated proton sponge as a bifunctional phase transfer catalyst is reported. Experimental studies and DFT calculations suggest it operates simultaneously as a hydrogen bond donor and a phase transfer catalyst, facilitating the movement of charged intermediates from the interface...
Article
Herein we report the synthesis and theoretical investigation of a non-symmetric bis(diisopropylamino)cyclopropenimine (DAC) functionalized proton sponge derivative, coined the 'Janus' sponge. The reported sponge was isolated as a monoprotonated salt, though no intramolecular hydrogen bond was observed. Homodesmotic equations supported the absence o...
Article
The mechanism of the HQuin-BAM (1) catalyzed aza-Henry reaction between nitromethane and N-Boc-phenylaldimine was studied using density functional theory (DFT). Deprotonation of nitromethane by the catalyst was revealed to be the rate-limiting step, and C···C bond formation was found to be enantio-determining. The catalyst, in addition to acting as...
Article
A multicomponent reaction between an aziridine aldehyde dimer, isocyanide, and l-proline to afford a chiral piperazinone was studied to gain insight into the stereodetermining and rate-limiting steps of the reaction. The stereochemistry of the reaction was found to be determined by isocyanide addition, while the rate-limiting step was found to devi...
Article
We have prepared two new diastereoisomeric 2-aza-5-phosphabicyclo[2.2.1]heptanes from naturally occurring trans-4-hydroxy-l-proline in six chemical operations. These syntheses are concise and highly efficient, with straightforward purification. When we used these chiral phosphines as catalysts for reactions of γ-substituted allenoates with imines,...
Article
Reduction of the cationic Ge(II) complex [dimpyrGeCl][GeCl3 ] (dimpyr=2,6-(ArN=CMe)2 NC5 H3, Ar=2,6-iPr2 C6 H3 ) with potassium graphite in benzene affords an air sensitive, dark green compound of Ge(0) , [dimpyrGe], which is stabilized by a bis(imino)pyridine platform. This compound is the first example of a complex of a zero-valent Group 14 eleme...
Article
We report herein the synthesis and characterization of a new proton sponge derivative, 1,8-bis(bis(diisopropylamino)cyclopropeniminyl)naphthalene 4 (DACN), as well as its bis-protonated counterpart 6. A crystal structure of 6 is presented, along with variable temperature (1) H NMR data on the BF4 (-) salt (6⋅BF4 ). DFT calculations were performed t...
Article
The origin of enantioselectivity in the [Cu(R,R)-Ph-box](OTf)2-catalyzed intramolecular aminooxygenation of N-sulfonyl-2-allylanilines and 4-pentenylsulfonamides to afford chiral indolines and pyrrolidines, respectively, was investigated using Density Functional Theory (DFT) calculations. The pyrrolidine-forming transition state model for the major...
Article
Diastereoselective induction of planar chirality in ferrocenes often employs chiral sulfur-, carbon- or phosphorus-based directing groups. The origin of stereoselectivity in these reactions may be classified as (a) cyclopentadiene (Cp) ring-controlled or (b) base-controlled. These two categories are represented by auxiliaries that typically have st...
Article
The reaction of fused ring aziridines, 3-oxa-1-azabicyclo[3.1.0]hexan-2-ones, with amine nucleophiles can provide either an aminomethyl oxazolidinone or an aziridinyl urea. The amine, reaction solvent, and aziridine substitution have been examined with the aid of computational studies to identify reaction conditions that provide a single product. P...
Article
The DielsAlder reaction can reliably provide the expected endo-product in the presence of secondary orbital overlap. It can be considerably more difficult to access a single enantiomer of the exo-product. In this paper, a D-chiro-inositol derivative is used as a chiral tether to facilitate the regio-, diastereo-, and enatioselective cycloaddition b...
Article
Alkene difunctionalization reactions are important in organic synthesis. We have recently shown that copper(II) complexes can promote and catalyze intramolecular alkene aminooxygenation, carboamination, and diamination reactions. In this contribution, we report a combined experimental and theoretical examination of the mechanism of the copper(II)-p...
Article
Full-text available
A variety of ortho,ortho'-disubstituted hydrobenzoin derivatives are readily accessible through a directed ortho,ortho'-dimetalation strategy in which the alcohol functions in hydrobenzoin are deprotonated by n-BuLi and the resulting lithium benzyl alkoxides serve as directed metalation groups. The optimization and scope of this reaction are discus...
Article
We report in full detail our studies on the catalytic, asymmetric α-fluorination of acid chlorides, a practical method that produces an array of α-fluorocarboxylic acid derivatives in which improved yield and virtually complete enantioselectivity are controlled through electrophilic fluorination of a ketene enolate intermediate. We discovered, for...

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