Aromatic Interactions Frontiers in Knowledge and Application

295 Pages·2016·25.12 MB·English

by  Darren W Johnson

Aromatic Interactions
Frontiers in Knowledge and Application
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Monographs in Supramolecular Chemistry
Series Editors:
Professor Philip Gale, University of Southampton, UK
1
00 Professor Jonathan Steed, Durham University, UK
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2 Titles in this Series:
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62 1: Cyclophanes
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78 2: Calixarenes
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78 3: Crown Ethers and Cryptands
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9/ 4: Container Molecules and Their Guests
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1 5: Membranes and Molecular Assemblies: The Synkinetic Approach
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oi:1 6: Calixarenes Revisited
d 7: Self-assembly in Supramolecular Systems
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or 8: Anion Receptor Chemistry
sc. 9: Boronic Acids in Saccharide Recognition
bs.r 10: Calixarenes: An Introduction, 2nd Edition
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htt Understanding to Applications
on 12: Molecular Logic-based Computation
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1 13: Supramolecular Systems in Biomedical Fields
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m 15: Polyrotaxane and Slide-Ring Materials
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5 17: Porous Polymers: Design, Synthesis and Applications
on 1 18: Pillararenes
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Aromatic Interactions
Frontiers in Knowledge and Application
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1 University of Oregon, Eugene, Oregon, USA
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org | Fraser Hof
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s University of Victoria, Victoria, British Columbia, Canada
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d Monographs in Supramolecular Chemistry No. 20
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c. Print ISBN: 978-1-78262-417-2
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on A catalogue record for this book is available from the British Library
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2 © The Royal Society of Chemistry 2017
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66 Preface
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oi: Aromatic rings are prevalent throughout nature, found in hydrocarbons,
g | d nucleic acids, proteins, metabolites, and drugs. Aromatic groups are also
or ubiquitous in materials science, where they are prized for their programmed
s.rsc. reactivity and chemical stability.1,2 The interactions of aromatic groups
ub with their surroundings are central to their properties and functions in all
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p:// of these settings. In this book we seek to introduce the reader to modern
htt research on aromatic interactions. This monograph should not be viewed
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o as a comprehensive review of all knowledge on aromatic systems, but rather
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01 we aspire to highlight topics of current interest that have emerged in the last
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er several years. The scope of topics to be covered fits into three main catego-
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m ries, including: (i) new developments in our fundamental understanding of
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o aromatic interactions (substituent effects, electronic effects, thermodynam-
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5 ics), (ii) discovery and characterization of new kinds of aromatic interactions
on 1 (anion–π interactions, aromatic interactions on surfaces), and (iii) emerging
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he applications of aromatic interactions (biological sciences, catalysis, organic
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bli electronics, and materials science).
u
P The field of aromatic interactions has generated significant new content,
and with it renewed controversy in recent years. The fundamental nature of
substituent effects in aromatic interactions has been discussed, the term
“π-stacking” itself has been reconsidered, the understanding of the nature of
the interaction between ions and aromatic rings continues to evolve, and new
theoretical frameworks have been developed and tested against experiment.
Against this backdrop of an evolving basic knowledge, aromatic interactions
have repeatedly appeared among the applied solutions found for problems
in biology and materials science.
While many other weak interactions have been well understood for
decades, our fundamental understanding of aromatic interactions has con-
tinued to evolve in the last 10 years. Early models for aromatic interactions
Monographs in Supramolecular Chemistry No. 20
Aromatic Interactions: Frontiers in Knowledge and Application
Edited by Darren W. Johnson and Fraser Hof
© The Royal Society of Chemistry 2017
Published by the Royal Society of Chemistry, www.rsc.org
v
View Online
vi Preface
were based primarily on electrostatics; however, in order to explain the
observed strengths of interactions, van der Waals forces and desolva-
tion were also highlighted as playing significant energetic roles.3,4 When
dealing with polarized aromatic systems, the early model by Hunter and
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0 Sanders broke the electrostatic contributions down into πσ–πσ (present in non-
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F polarized systems), atom–atom (partial atomic charge attraction or repulsion),
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2 and atom–πσ (the interaction of the partial atomic charge of one molecule with
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2 the out-of-plane π electron cloud of another molecule). Such a model accu-
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8 rately predicts the strengths of benzene dimer interactions, as well as ben-
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8 zene–hexafluorobenzene, but breaks down with more complex systems.
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9/ Since this initial model, there have been many advances in understanding
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10 the phenomenon of “aromatic interactions” through detailed physical organic
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1 studies on solutions, solid-state investigations, and quantum mechanical
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d computations. Such an understanding has enabled the rational design of
org | new functional molecular systems relying on aromatic interactions.5 Stoddart
sc. has made rotaxanes that depend on aromatic interactions to control molecu-
bs.r lar movements and locations;6 Sharpless has utilized host ligands that bind
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http://p faeraotmuraitnicg gπu–eπs ststa icnk dinegfi nareed u gseeodm ine tsreiems itchoantd fuavcotirn rge achctairvgitey-;t7r aonrgsafenri cm mataetreirailasl,s8
on just to name a few. Practical advances like these have progressed in lockstep
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1 with studies that reveal the fundamental nature of aromatic interactions.
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er Aromatic interactions remain a vibrant area of study because of their com-
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m plexity. This book dives into further theoretical understanding of the nature
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ov of these interactions, with several chapters describing the latest approaches
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5 to arene–arene, cation–π, anion–π, and main group lone pair–π interactions.
n 1 In Chapter 1, Lewis goes beyond the quadrupolar electrostatic distribution
o
ed of aromatic systems and brings in aromatic polarizability, induction, disper-
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blis sion, exchange, and substituent-dominated effects to improve the under-
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P standing of aromatic interactions. The strength of the contributing factors,
as well as their individual contributions to the overall energy of the interac-
tion, are further discussed for simple arene–arene interactions as well as cat-
ion–π. And in Chapter 2, Maji and Wheeler expand on how this fundamental
understanding of aromatic interactions can be harnessed to direct organic
reactions with new organocatalysts.
The list of canonical types of aromatic interactions is still expanding. Since
the last publication of this Monographs series, anion–π (Chapters 2 and 3)
and main group–π (Chapter 4) interactions have entered the scene. The
strength of anion–π interactions is enhanced with an increase in electron
deficiency of the out-of-plane π electron cloud; however, the strength is also
increased by the anion’s ability to induce a dipole in the π-electron cloud.
Anion–π and related interactions have been found to be a powerful directing
effect for organic reactions, and catalysis, as mentioned in Chapter 2 and
highlighted in greater detail in Chapter 3. Harnessing the understanding
of anion–π interactions led Frontera and Ballester to propose that extended
π-systems should be used in anion–π complexes due to their increased
polarizability.
View Online
Preface vii
Even more recently, main group element lone pair–π interactions have
been defined, characterized, and exploited for self-assembly (Chapter 4).
Many examples of such contacts have been discovered through searches of
the Cambridge Structural Database (CSD). Much like cation–π interactions,
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0 the polarizability of the participating electrons is key for the interaction to
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F take place. However, given the ambipolar-type nature of some main group
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2 complexes, the main group element can in some cases donate its electron as
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2 a π-base to a π-acidic aromatic ring, or alternately, serve as the Lewis acidic
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8 cation in a cation–π complex, thereby exhibiting features of both anion–π
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8 and cation–π interactions, sometimes even within the same complex.
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9/ Changes in the way the field has modeled aromatic interactions compu-
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10 tationally, and the changes advanced by that understanding, are driven by
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1 trying to accurately predict what is experimentally observed in solution. This
oi:
d has driven work aimed at understanding how simple model systems can be
org | used for quantitative measurement and the study of non-covalent interac-
sc. tions between aromatic rings in solution. In Chapter 5, Shimizu and Hwang
bs.r describe a series of such systems carefully designed to control and under-
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p
p:// stand different contributing factors such as electrostatics, dispersion, repul-
htt sion, and solvent effects. There are key challenges that must be overcome,
on such as defining a system where other weak forces such as dipole effects, ste-
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1 rics, and secondary interactions are not mistaken for aromatic interactions.
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er The models that have been studied vary from simple fixed interactions of
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m aromatics to adapting biomolecular frameworks for physical organic models.
e
ov The combinations of these studies, both simple and complex, have and
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5 continue to contribute greatly to the fundamental understanding of these
n 1 interactions. Paired with computational studies and single crystal X-ray dif-
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ed fraction, these solution state studies have benefitted biological understand-
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blis ing and biomimetic design of molecular structures and systems.
u
P The inspiration for using subtle aromatic interactions to direct and/or
catalyze organic reactions (Chapters 2 and 3) is derived in part from studying
biological systems. We devote two chapters to biological examples of aro-
matic interactions: in Chapter 6, Bockus and Urbach describe aromatic inter-
actions of amino acids and proteins; in Chapter 7, Koenig and Waters focus
on cation–π interactions in biological chemistry. Both chapters describe
efforts to understand the fundamental nature of interactions, while also
describing the progression to creating synthetic molecules that can bind to
and modulate natural, biological partners. A definitive fundamental lesson
highlighted in Chapter 7 explores the use of isosteric R-NMe + and R-C(Me)
3 3
ligands to understand the role of cation–π interactions in natural protein–
protein interactions. Chapter 6 highlights a seminal example of the type of
synthetic recognition systems enabled by aromatic interactions in viologen-
bound hosts that co-encapsulate aromatic side chains of amino acids, pep-
tides, and whole proteins.
The principles that allow aromatic interactions to be utilized in molecular
systems have also advanced into the realm of materials chemistry. This
application in materials chemistry can take on different forms: aromatic
View Online
viii Preface
interactions can be used for functionalizing materials surfaces, molecular
receptors can be applied to a surface, and favorable interactions with the
surface can help facilitate organized self-assembly on the surface.8–10 Apply-
ing aromatic molecules to metallic surfaces has afforded new characteriza-
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0 tion methods, as well as novel reactivity. In Chapter 8, Marangoni, Cloke and
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F Fischer introduce such surface characterization methods, with a focus on the
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2 techniques that allow visualization at submolecular resolution. These meth-
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2 ods are powerful tools in advancing the understanding of aromatic mole-
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8 cules and their interactions. The metallic substrates can also be utilized to
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8 control reactivity of the adsorbed aromatic compounds, including reactions
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9/ that are unprecedented in the solution phase. By “building up” complexity
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10 on the surface, the creation of 2D and 3D molecules is now possible. This
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1 further advances extended π surfaces, with promise for improved electronic
oi:
d devices such as organic light emitting diodes, organic thin film transistors,
org | and organic photovoltaics.
sc. Structural investigations of aromatic molecules on crystalline surfaces has
bs.r resulted in novel reactivity and new applications in materials chemistry. The
u
p
p:// designed use of predictive aromatic interactions has impacted fields ranging
htt from catalysis (through conformational control), drug design (molecular
on recognition), and materials chemistry (surface functionalization), among
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1 others. Such designs would not be possible without the continued evolu-
0
2
er tion of fundamental understandings furthered by computational chemistry
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m informed by solution-state models—both synthetic and biological—as well
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ov as data from solid state structural investigations.
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5 As can be seen from the content described above, this book does not aim
n 1 to be a tutorial review on aromatic interactions. We have aimed instead to
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ed include content that describes the last 10 years of progress—the newest
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blis classes of interactions, latest ways of understanding interactions, and the
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P cutting edge of experimental systems that exploit this knowledge to drive
new science. It is clear that the field of Aromatic Interactions is not yet
settled. We look forward to the next decade of discovery.
Kara M. Nell, University of Oregon, Eugene, USA
Fraser Hof, University of Victoria, Victoria, Canada
Darren W. Johnson, University of Oregon, Eugene, USA
References
1. K. A. Wilson, J. L. Kellie and S. D. Wetmore, Nucleic Acids Res., 2014, 10,
6726–6741.
2. C. A. Hunter, J. Mol. Biol., 1993, 230, 1025–1053.
3. C. A. Hunter and J. K. M. Sanders, J. Am. Chem. Soc., 1990, 112, 5525–5534.
4. C. A. Hunter, Chem. Soc. Rev., 1994, 23, 101–109.
5. C. A. Hunter, K. R. Lawson, J. Perkins and C. J. Urch, J. Chem. Soc., Perkin
Trans. 2, 2001, 651–669.
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Preface ix
6. R. A. Bissell, E. Cordova, A. E. Kaifer and J. F. Stoddart, Nature, 1994, 369,
133.
7. M. R. Bryce, Adv. Mater, 1999, 11, 11.
8. H. C. Kolb, P. G. Andersson and K. B. Sharpless, J. Am. Chem. Soc., 1994,
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0 116, 1278.
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F 9. K. M. Nell, S. A. Fontenot, T. G. Carter, M. G. Warner, C. L. Warner, R. S.
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2 Addleman and D. W. Johnson, Environ. Sci.: Nano, 2016, 3, 138–145.
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2 10. S. Lee, B. E. Hirsch, Y. Liu, J. R. Dobscha, D. W. Burke, S. L. Tait and A. H.
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8 Flood, Chem.–Eur. J., 2016, 22, 560–569.
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66 Contents
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1 Chapter 1 Modern Computational Approaches to Understanding
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oi:1 Interactions of Aromatics 1
g | d Michael Lewis, Christina Bagwill, Laura Hardebeck
or and Selina Wireduaah
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ub 1.1 Introduction and Background 1
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p:// 1.1.1 Arene–Arene Interactions 2
htt 1.1.2 Cation–Arene Interactions 3
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o 1.1.3 Beyond the Aromatic Quadrupole Moment 4
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01 1.2 Computational Approaches to Understanding
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er Arene–Arene Interactions 5
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m 1.2.1 The Nature of Arene–Arene Interactions 5
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o 1.2.2 Predicting the Strength of Arene–Arene
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5 Interactions 9
on 1 1.3 Computational Approaches to Understanding
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he Cation–Arene Interactions 10
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bli 1.3.1 The Nature of Cation–Arene Interactions 10
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Interactions 13
1.4 Summary 14
References 15
Chapter 2 Role of Aromatic Interactions in Directing Organic
Reactions 18
Rajat Maji and Steven E. Wheeler
2.1 Introduction and Background 18
2.2 Aromatic Interactions of Relevance to Organic
Reactions 19
Monographs in Supramolecular Chemistry No. 20
Aromatic Interactions: Frontiers in Knowledge and Application
Edited by Darren W. Johnson and Fraser Hof
© The Royal Society of Chemistry 2017
Published by the Royal Society of Chemistry, www.rsc.org
xi