Publications by authors named "Kelly M Wiggins"

10 Publications

  • Page 1 of 1

Retraction: Homonuclear bond activation using a stable ,'-diamidocarbene.

Chem Sci 2015 Jun 21;6(6):3634. Epub 2015 Apr 21.

Department of Chemistry and Biochemistry , The University of Texas at Austin , 1 University Station A1590 , Austin , 78712 , TX , USA . Email:

[This retracts the article DOI: 10.1039/C2SC20639K.].
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http://dx.doi.org/10.1039/c5sc90019kDOI Listing
http://www.ncbi.nlm.nih.gov/pmc/articles/PMC6063287PMC
June 2015

Molecular catch bonds and the anti-Hammond effect in polymer mechanochemistry.

J Am Chem Soc 2013 Aug 19;135(34):12722-9. Epub 2013 Aug 19.

Department of Chemistry and Biochemistry, University of Texas at Austin, Austin, Texas 78712, USA.

While the field of polymer mechanochemistry has traditionally focused on the use of mechanical forces to accelerate chemical processes, theoretical considerations predict an underexplored alternative: the suppression of reactivity through mechanical perturbation. Here, we use electronic structure calculations to analyze the mechanical reactivity of six mechanophores, or chemical functionalities that respond to mechanical stress in a controlled manner. Our computational results indicate that appropriately directed tensile forces could attenuate (as opposed to facilitate) mechanochemical phenomena. Accompanying experimental studies supported the theoretical predictions and demonstrated that relatively simple computational models may be used to design new classes of mechanically responsive materials. In addition, our computational studies and theoretical considerations revealed the prevalence of the anti-Hammond (as opposed to Hammond) effect (i.e., the increased structural dissimilarity between the reactant and transition state upon lowering of the reaction barrier) in the mechanical activation of polyatomic molecules.
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http://dx.doi.org/10.1021/ja4051108DOI Listing
August 2013

Squeezing new life out of polymers.

Angew Chem Int Ed Engl 2013 Apr 25;52(14):3806-8. Epub 2013 Feb 25.

University of Texas at Austin, Department of Chemistry and Biochemistry, 1 University Station, A1590, Austin, TX 78712, USA.

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http://dx.doi.org/10.1002/anie.201210025DOI Listing
April 2013

Methods for activating and characterizing mechanically responsive polymers.

Chem Soc Rev 2013 Sep 7;42(17):7130-47. Epub 2013 Feb 7.

Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, TX 78712, USA.

Mechanically responsive polymers harness mechanical energy to facilitate unique chemical transformations and bestow materials with force sensing (e.g., mechanochromism) or self-healing capabilities. A variety of solution- and solid-state techniques, covering a spectrum of forces and strain rates, can be used to activate mechanically responsive polymers. Moreover, many of these methods have been combined with optical spectroscopy or chemical labeling techniques to characterize the products formed via mechanical activation of appropriate precursors in situ. In this tutorial review, we discuss the methods and techniques that have been used to supply mechanical force to macromolecular systems, and highlight the advantages and challenges associated with each.
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http://dx.doi.org/10.1039/c3cs35493hDOI Listing
September 2013

A mechanochemical approach to deracemization.

Angew Chem Int Ed Engl 2012 Feb 4;51(7):1640-3. Epub 2012 Jan 4.

Department of Chemistry & Biochemistry, The University of Texas at Austin, 1 University Station, A1590, Austin, TX 78712, USA.

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http://dx.doi.org/10.1002/anie.201107937DOI Listing
February 2012

Unclicking the click: mechanically facilitated 1,3-dipolar cycloreversions.

Science 2011 09;333(6049):1606-9

Department of Chemistry and Biochemistry, The University of Texas at Austin, 1 University Station A1590, Austin, TX 78712, USA.

The specific targeting of covalent bonds in a local, anisotropic fashion using mechanical methods offers useful opportunities to direct chemical reactivity down otherwise prohibitive pathways. Here, we report that embedding the highly inert 1,2,3-triazole moiety (which is often prepared using the canonical "click" coupling of azides and alkynes) within a poly(methyl acrylate) chain renders it susceptible to ultrasound-induced cycloreversion, as confirmed by comprehensive spectroscopic and chemical analyses. Such reactivity offers the opportunity to develop triazoles as mechanically labile protecting groups or for use in readily accessible materials that respond to mechanical force.
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http://dx.doi.org/10.1126/science.1207934DOI Listing
September 2011

Mechanically facilitated retro [4+2] cycloadditions.

J Am Chem Soc 2011 May 19;133(18):7180-9. Epub 2011 Apr 19.

Department of Chemistry and Biochemistry, The University of Texas, Austin, Texas 78712, USA.

Poly(methyl acrylate)s (PMAs) of varying molecular weights were grown from a [4+2] cycloaddition adduct of maleimide with furan containing two polymerization initiators. Subjecting the corresponding PMA (>30 kDa) chains to ultrasound at 0 °C resulted in a retro [4+2] cycloaddition reaction, as observed by gel permeation chromatography (GPC) and UV-vis spectroscopy, as well as labeling of the liberated maleimide and furan moieties with appropriate chromophores featuring complementary functional groups. Similar results were obtained by sonicating analogous polymers that were grown from a thermally robust [4+2] cycloaddition adduct of maleimide with anthracene. The generation of anthracenyl species from these latter adducts allowed for the rate of the corresponding mechanically activated retro [4+2] cycloaddition reaction to be measured. No reduction in the number average molecular weight (M(n)) or liberation of the maleimide, furan, or anthracene moieties was observed (i) for polymers containing the cycloaddition adducts with M(n) < 20 kDa, (ii) for high molecular weight PMAs (M(n) > 60 kDa) featuring terminal cycloaddition adducts, or (iii) when the cycloaddition adducts were not covalently linked to a high molecular weight PMA. Collectively, these results support the notion that the aforementioned retro [4+2] cycloaddition processes were derived from a vectorially opposed mechanical force applied to adducts embedded within the polymer chains.
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http://dx.doi.org/10.1021/ja201135yDOI Listing
May 2011

Mechanical activation of catalysts for C-C bond forming and anionic polymerization reactions from a single macromolecular reagent.

J Am Chem Soc 2010 Nov 2;132(46):16631-6. Epub 2010 Nov 2.

Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, United States.

Coupling of pyridine-capped poly(methyl acrylate)s, PyP(M) (where M corresponds to the number average molecular weight in kDa), to the SCS-cyclometalated dipalladium complex [(1)(CH(3)CN)(2)] afforded organometallic polymers [(1)(PyP(M))(2)] with a concomitant doubling in molecular weight. Ultrasonication of solutions containing [(1)(PyP(M))(2)] effected the mechanical scission of a palladium-pyridine bond, where the liberated PyP(M) was trapped with excess HBF(4) as the corresponding pyridinium salt, harnessed to effect the stoichiometric deprotonation of a colorimetric indicator, or used to catalyze the anionic polymerization of α-trifluoromethyl-2,2,2-trifluoroethyl acrylate. The mechanically induced chain scission also unmasked a catalytically active palladium species which was used to facilitate carbon-carbon bond formation between benzyl cyanide and N-tosyl imines. Spectroscopic and macromolecular analyses as well as a series of control experiments demonstrated that the aforementioned structural changes were derived from mechanical forces that originated from ultrasound-induced dissociation of the polymer chains connected to the aforementioned Pd complexes.
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http://dx.doi.org/10.1021/ja107620yDOI Listing
November 2010

Mechanical reconfiguration of stereoisomers.

J Am Chem Soc 2010 Mar;132(10):3256-7

Department of Chemistry and Biochemistry, The University of Texas at Austin, Austin, Texas 78712, USA.

Poly(methyl acrylate) of varying molecular weight was grown from the enantiopure ditopic initiator (R)- or (S)-1,1'-binaphthyl-2,2'-bis-(2-bromoisobutyrate). Subjecting CH(3)CN solutions of high-molecular-weight derivatives (M(N) > 25 kDa) to sonication at 0 degrees C resulted in >95% racemization after 24 h, as determined by circular dichroism; no appreciable racemization was observed in low-molecular-weight derivatives. Control experiments excluded the possibility of a thermal racemization mechanism.
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http://dx.doi.org/10.1021/ja910716sDOI Listing
March 2010

A systematic investigation of factors influencing the decarboxylation of imidazolium carboxylates.

J Org Chem 2009 Oct;74(20):7935-42

Department of Chemistry, Henry Eyring Building, University of Utah, 315 S. 1400 East, Salt Lake City, Utah 84112-0850, USA.

A series of 1,3-disubstituted-2-imidazolium carboxylates, an adduct of CO(2) and N-heterocyclic carbenes, were synthesized and characterized using single crystal X-ray, thermogravimetric, IR, and NMR analysis. The TGA analysis of the NHC-CO(2)'s shows that as steric bulk on the N-substituent increases, the ability of the NHC-CO(2) to decarboxylate increases. The comparison of NHC-CO(2)'s with and without methyls at the 4,5-position indicate that extra electron density in the imidazolium ring enhances the stability of an NHC-CO(2) thereby making it less prone to decarboxylation. Single crystal X-ray analysis shows that the torsional angle of the carboxylate group and the C-CO(2) bond length with respect to the imidazolium ring is dependent on the steric bulk of the N-substituent. Rotamers in the unit cell of a single crystal of I(t)BuPrCO(2) (2f) indicate that the C-CO(2) bond length increases as the N-substituents rotate toward the carboxylate moiety, which suggests that rotation of the N-substituents through the plane of the C-CO(2) bond may be involved in the bond breaking event to release CO(2).
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http://dx.doi.org/10.1021/jo901791kDOI Listing
October 2009
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