Aromaticity: From Organics
to Inorganics, From 2D to 3D
吕鑫 (X. Lu)
2013. 07. 24
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Outline







Overview
Practical Criteria of Aromaticity
p-aromaticity (2D)
Möbius aromaticity
Homoaromaticity
s-aromaticity
Spherical aromaticity and 3D aromaticity
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1.
Overview
• Few concepts are as frequently used as
AROMATICITY in the current chemical literature.
• Since 1981, ca. 300,000 papers dealing with the
aromatic properties of chemical systems have been
published.
• A thematic issue on Aromaticity: P. v. R. Schleyer,
Chem. Rev. 2001, 101(5), 1115.
• A recent thematic issue on aromaticity: P. v. R.
Schleyer, Chem. Rev. 2005, 105(10).
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• The history of aromaticity can be traced
back to 1825 when M. Faraday isolated for
the first time benzene.
Benzene
(M. Faraday, 1825)
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• The term “aromatic” was first used by
chemists in the early 19th century to designate a
specific class of organic substances (e.g.,
benzene), which are initially distinguished from
those belonging to the aliphatic class by virtue
of their pleasant olfactory properties.
• Aromaticity --- extra stability --- remarkable
electron delocalization /conjugation.
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1.1 Types of Aromatic Systems
• Before 1958, 2D planar polycyclic aromatic
hydrocarbons (PAHs) reducible to molecules
containing six p-electrons, e.g.,
p-aromaticity of
PAH fulfilling
the Huckel 4N+2
or Clar sextet
(6N) rule
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After 1958
1) Monocyclic hydrocarbons containing up to
30 p-electrons, e.g., [n]annulenes
14
10
18
Huckel & Möbius p-aromaticity of annulenes
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2) 3D boron and carborane cluster molecules
based upon triangular face polyhedra, e.g.,
C2B3H5
B6H62-
2B7H7
C2B4H6 C2B5H7
B12H122C2B10H12
3D aromaticity of clusters (ions)
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3) Large carbon clusters illustrated by the
famous buckminsterfullerene C60 and its
homologues.
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4) Analogues of PAHs containing metal
atoms, such as gallium, or full metal
clusters. E.g., metallabenzenes.
Predicted by Hoffman
Synthesized in
in 1979.
1982.
1) Thorn, D. L.; Hoffman, R. Nouv. J. Chim. 1979, 3, 39-45.
2) Elliott, G. P. et al. J. Chem. Soc., Chem. Commun. 1982, 811-813.
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5) Molecules stabilized by s-electron
delocalization (s-aromaticity), e.g.,
cyclopentane.
Dewar, M. J. S. Bul. Soc. Chim. Belg. 1979, 88, 957
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6) transition-metal clusters stabilized by delectron delocalization (-aromaticity), e.g.,
CunHn
(n=4,5,6)
M4Li2
(M=Cu,Ag,
Au)
1) Tsipis et al. J. Am. Chem. Soc. 2003, 125, 1136.
2) Schleyer et al. J. Am. Chem. Soc. 2005, 127, 5701.
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1.2 Main developments about aromaticity
1980 Lu JX et al,
quasi-aromaticity
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1.3 Nature of the aromaticity concept
1) Like other useful and popular chemical concepts
(chemical bonds, charges, electronegativities,
hyperconjugations etc.), aromaticity is nonreductive, and lacks of clear physical bases.
2) Aromaticity is not a physical observable, having no
precise experimental definition.
3) Aromaticity is just like to define beauty in our daily
life!
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•
•
•
•
•
•
Easily to recognize (but not always)
Many kinds
Hard to compare
Difficult to quantify
Various opinions, no general agreement
Interpreted differently
Beauty (Aromaticity) is in the eye of the
beholder!
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4) Aromaticity is a time-dependent concept,
of which new aspects are pending for
discovery.
5) Aromaticity is a property associated with
extra stability and many other unusual
manifestation!!!
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1.4 Main categories of criteria
characterizing aromaticity
• Structural - planarity and equal bond length
tendencies (simple, but unreliable!)
• Energetic – enhanced stability (indirect, but
impractical!)
• Reactivity – lower reactivity, electrophilic aromatic
substitution (neither direct nor reliable!)
• Spectroscopic– UV, proton chemical shifts, magnetic
susceptibility exaltation (indirect, mostly reliable,
but sometimes impractical!)
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Four classes of aromaticity criteria
•Sructural bond length equalization
1.39
1.47
1.34
•More stable than their acyclic analogues
selection of reference systems, isodesmic or homodesmotic reaction !
•Chemical behavior: electrophilic aromatic substitution
prefered to addition but C60addition,
anthracene/phenantrene  Diels-Alder !
•Magnetic: ring current effects
a) Increased values of the magnetic
susceptibility (ctot)
b) Large
magnetic
anisotropies
(caniso
)
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c) Diamagnetic susceptibility exaltation ()
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Drawbacks exist with these criteria:
1) Structural Criterion
Bond length equalization should not be used alone
as a criterion for aromaticity as some bondequalized systems are not aromatic. e.g.,
B3N3H6: isoelectronic with benzene, equalized B-N
bond lengths, not aromatic due to electron
localization on the N atoms.
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2) Energetic criterion.
•
The aromatic stabilization energy (ASE) and
resonance energy (RE) have been well recognized
as the cornerstone of aromaticity.
•
However, ASEs and REs of strained and more
complicated systems are difficult to evaluate.
•
Such energy estimates vary significantly, strongly
depending on the equations used and on the
choice of reference molecules.
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(1)
-32 kcal/mol
+2
3
Dewar Resonance Energy
+ 3
+3
-
3(
)
CH3
-50 kcal/mol
-21 kcal/mol
s-trans
(2)
(3)
Aromatic Stabilization Energy
+
3
CH3
2
-35 kcal/mol
(4)
-34 kcal/mol
(5)
cisoid
+
3
3
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cisoid
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3) Reactivity criterion
• The key characteristic reactivity feature:
electrophilic aromatic substitution, not addition
reaction.
• However, aromaticity criteria based on chemical
reactivity are not straightforward to apply!!
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4) 1H NMR chemical shifts:
------- A magnetic criterion
• A criterion most often used experimentally.
• Due to the ring current induced by an external
magnetic field, the inner protons are shifted upfield,
and the outer protons are downfield-shifted.
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But !!!
H1
H3
H1
O
H2
H3
H2
H1: 5.78
4-5
H1: 6.10
H2: 6.26
antiaromatic
H2: 7.71
H3: 6.36
nonaromatic 4-membered ring
is antiaromatic
H1
H1: 8.6
H2: 8.1
H3: 8.5
Nonaromatic
PW91/IGLOIII
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H2
Important criteria for aromaticity and key
developments
Time
Contributors Contributions
<1825
Type
Aromatic smell
1825
Faraday
isolation of Benzene, stable, but high
unsaturation
1861
Loschmidt
1865
Kekulé
A ring of carbon atoms suggested for
benzene.
Benzene structure
1866
Erlenmeyer
Substitution is more favorable than
addition for benzene.
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R
Time
Contributors Contributions
1910
Pascal
1922
Crocker
1925
Armit/
Robinson
Electron sextet and heteroaromaticity.
1931
Hückel
Theory of cyclic (4n+2) systems
1933
Pauling et al.
Resonance energy.
R
1936
Pauling et al.
Ring current theory
M
1937
London et al. QM treatment of ring current, London
diamagnetism, GIAO method
Increment system for diamagnetic
susceptibility, aromatic exaltation
Aromatic sextet
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Type
M
M
Time
Contributors Contributions
1953
Meyer et al.
The difference in the proton magnetic
shielding between benzene and
noncyclic olefins observed
M
1956
Pople
Ring current effects on NMR
chemical shifts: deshielding of
benzene protons– manifestation of
moleuclar ring current induced by
external magnetic field.
M
1969
Dewar
Dewar resonance energy.
E
1967
Garratt
Define molecules with an induced
diamagnetic ring current as diatropic
M
1967
Jug et al.
Jug structural index
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Type
S
Time Contributors Contributions
1968
Dauben
1970 Flygare
1971
Hess, Schaad
Diamagnetic susceptibility exaltaion
as a criterion of aromaticity
Microwave spectroscopy, aromatic
systems shown diamagnetic
anisotropies.
Hess-Schaad resonance energy.
1972 Clar
Clar “aromatic sextet” rule
1972
Harmonic oscillator model or
aromaticity (HOMA) as structural
index of aromaticity
Fringuelli structural index
Krygowski
1974 Fringuelli
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Type
M
M
E
S
S
Time Contributors Contributions
1975
Aihara et al.
1980 Kutzelnigg
1981
1983
Lazzeretti,
Zanasi
Jug
1985
1985
Type
Topological resonance energy
E
IGLO calculation of magnetic
properties: chemical shifts, magnetic
susceptibilities and magnetic
susceptibility anisotropies
Ab initio current density plots.
M
M
Jug structural index
S
Pozharskki
Pozharskki structural index
S
Bird
Bird structural index
S
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Time Contributors Contributions
1987
Type
Mizoguchi
Magnetic susceptibility of Huckel and
Mobius annulenes show an opposite
tendency
M
Zhou, Parr,
Garst
1990- Schleyer
1995
Hardness (low reactivity) as aromatic
index
Extensively using Li+ NMR to study
aromaticity.
R
1988
M
1994- Schleyer, Jiao Extensively using magnetic
1996
susceptibility exaltation to study
aromaticity
M
1994 Saunders et al. Experimental endohedral 3He NMR to
measure aromaticity in fullerenes and
their derivatives
M
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Time Contributors Contributions
1994
Buhl et al.
Computed endohedral 3He NMR to
measure aromaticity in fullerenes and
their derivatives
1995
krygowski
1996
Schleyer
Bond alteration coefficient (BAC)
structural index
Nucleus-independent chemical
shifts(NICS)
1996
Fowler,
Steiner
Schleyer
1997
Extensive application of current
density plots to study aromaticity
Dissected NICS for localized MOs
1997 Bohmann,
NBO-GIAO dissected canonical MOs
Weinhold,
(CMO) and LMO NICS
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Farrar
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Type
M
S
M
M
M
M
Time Contributors Contributions
1998
Bean et al.
1998 Chesnut
1999 Mo
Application of NBO analysis to
delocalization and aromaticity
Difference in ring proton shieldings
between the fully unsaturated species
and its monoene counterpart
recommended as aromaticity measure
Block-localized wavefunction (BLW)
method based on modern ab initio VB
theory to approach the absolute RSE
Type
M
E
1999
Sundholm
Aromatic Ring-Current
Shielding(ARCS)
M
2000
Thiel
Computing NICS using MNDO
M
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Time Contributors Contributions
2001
Herges
2002 Schleyer
Anisotropy of the current induced
density (ACID)
Isomerization Stabilization
Energy(ISE)
CiLC(CI/LMO/CASSCF) analysis;
index of deviation from the
aromaticity (IDA)
Type
M
E
2002
Sakai
2003
Schleyer et al. GIAO-CMO NICS
M
2004
Heine et al.
M
2005
Sola
Induced magnetic field as aromatic
index
Aromatic fluctuation index (FLU)
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Aromaticity criteria
historically
Structure criteria
Reactivity criteria
Energy criteria
Magnetic criteria
aromatic smell
(before 1825) Discovery of benzene
Faraday (1825)
High carbon ratio
(before 1865)
Nucleus-Independent chemical
shift (NICS) --Schleyer (1996)
Magnetic sucseptibility
anisotropy -- Flygare (1970)
Benzene structure
Kekulé 1865
Aromaticity
Magnetic sucseptibility
exaltation --Dauben (1969)
Ring current effect on NMR
chemical shift--Pople (1956)
p electron to contribution to magnetic
susceptibilty -- London (1937)
Substitution > addition
Erlenmeyer (1866)
Exalted diamagnetic
susceptibility--Pascal
(1910)
Electron sextet
Armit-Robinson (1925)
4n+2 electron
Hückel (1931)
Ring current theory
Pauling (1936)
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Schleyer and Jiao, Pure Appl. Chem. 1996, 68, 209-218
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2 Key Criteria for Aromaticity
2.1 Energetic criteria
• 2.1.1 RE-Resonance Energy (VB theory).
RE or Edelocalization = E(LS) – E(DS)
Case study: Benzene
Delocalized
Key Localized Structures
benzene
Kekule Structures
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Dewar Structures
HMO predictions
E
Delocalized
Localized
benzene
1,3,5-cyclohexatriene


0
Edelocalized = |8-6= |2

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HMO Predictions
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Ab initio MO predictions
• The MO calculation on the “unrealistic”
localized structure is impossible in practice.
• Isodesmic reactions were proposed to
evaluate RE.
+2
3
(1)
-32 kcal/mol
Dewar Resonance Energy
+ 3
+3
CH3
CH3
-50 kcal/mol
(2)
An isodesmic reaction is a chemical reaction in which the type of
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in theChemistry
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are the
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formed in the reaction product
• The ab initio MO-based RE depends
strongly on the choice of isodesmic
reactions.
• It is far from trivial to balance strain,
hyperconjugative effects, as well as
differences in the types of bonds and atom
hybridizations, using energy evaluation
schemes.
• Impractical for complex systems such as
those with a large number of p-electrons or
s-aromaticity.
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VB treatment
• VB/STO-6G
C-C
benzene
TRE = VRE + B
RE(kcal/mol)
1
1.404
2
1.404
74.28
3
1.343/
1.521
44.48
VRE
B
Kekule
stable cyclohexatriene
Mo, Y et al, JPC, 1994, 98, 10048.
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2.1.2 ASE (aromatic stabilization energy)
-
3(
)
-21 kcal/mol
s-trans
Aromatic Stabilization Energy
+
3
(3)
2
-35 kcal/mol
(4)
-34 kcal/mol
(5)
cisoid
+
3
cisoid
3
Cryanski et al, Tetrahedron, 2003, 59, 1657.
Homodesmic reactions for the evaluation of ASE.
Homodesmic reactions are an improved form of isodesmic reactions in
whichState
all formal
bonds
and types
of each
carbon
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in the reactants and products.
2.1.3 ISE (Isomerization stabilization energy):
-------the difference between the total energies of a
methyl derivative of the aromatic system and its
nonaromatic exocyclic methylene isomer.
Schleyer, P. v. R.; Puhlhofer, F. Org. Lett. 2002, 4 ,
2873.
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2.2 Magnetic Criteria
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The ring current induces
magnetic shielding within the
ring, but deshielding out of
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the ring.
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2.2.1 Diamagnetic Susceptibility
exaltation (MSE, )
• Pioneering work by Pascal in 1910
• Benzene and its derivatives exhibited larger
diamagnetic susceptibilities than would be
expected for them from the susceptibilities of
other unsaturated compounds.
Pascal, P. Ann. Chim. Phys. 1910, 19, 5.
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• Pacault handled the discrepancy of magnetic
susceptibility in the “Pascal system” by
introducing a special benzene-ring parameter
called “exaltation”.
• Pink et al. hypothesized that the exaltation of
diamagnetic susceptibility can be used to
identify aromatic systems.
Pacault, A. Ann. Chim., Ser. XII. 1946, 1, 567.
Pink, R. C. Trans. Faraday Soc., 1948, 4, 407.
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• Exaltation of diamagnetic susceptibility
results from the presence of cyclic
delocalization of electrons, i.e. ring current.
• Definition of exaltation of magnetic
susceptibility:
 
cM

c 'M
susceptibility
exaltation
delocalized system
non delocalized isomer
• A systematic survey of MSE of aromatic
hydrocarbons was done by Dauben in 1968.
Pacault, A. Ann. Chim., Ser. XII. 1946, 1, 567.
Dauben, H. J. Jr. et al. J. Am. Chem. Soc.1968, 90, 811.
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Magnetic susceptibility anisotropies
• The tensor component perpendicular to the
aromatic ring is much larger than the average of
the others two components
c anis  c zz  ( c xx  c yy ) / 2
Aromatic / Antiaromatic = negative / positive canis, 
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Calculation of magnetic susceptibility
• The magnetic susceptibility (MS) is a global
property of the molecule.
• Calculation of MS can be readily computed
with the CSGT (Continuous Set of Gauge
Transformations) method available in the
Gaussian package.
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Example 1
Cyclopropane is s-aromatic
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Example 2: Double aromaticity in C6H3+
•  plane: 6pe
2e
• In-plane: 2se
Schleyer, P. v. R. et al. J. Am. Chem. Soc. 1994, 116,
10129.
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Schleyer, P. v. R. et al. J. Am. Chem. Soc. 1994, 116, 10129.
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Compounds which exhibit significant
exalted diamagnetic susceptibility
are aromatic. Those compound with
exalted paramagnetic susceptibility
may be antiaromatic.
Schleyer, P. v. R.; Jiao, H. Pure Appl. Chem. 1996, 68,
209
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Example 3: Calculated canis and 
Schleyer and Jiao, Pure Appl. Chem. 1996, 68, 209-218
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2.2.2 Li+ NMR Chemical Shift
• Lithium bonding is primarily electrostatic, experimental
7Li chemical shifts generally shows little variation
among different compounds.
• Lithium cations, typically complex to the π faces of
aromatic (or anti-aromatic) systems.
• This complexation results in a significant shielding (or
deshielding) of the 7Li NMR signal due to ring current
effects.
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2.2.2 Li+ NMR Chemical Shift
Experiments
• Aromatic
• Paquette, L. A. et
al, JACS, 1990,
112, 8776.
• Antiaromatic
• Sekiguchi et al,
JACS, 1991, 113,
7081.
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• Experimental 7Li NMR chemical shifts can be well
reproduced by modern computations.
• The clear advantage of using δ(7Li) as a
theoretical probe lies in the possibility to provide a
comparison with 7Li NMR spectrum of experimental
Li+ complexes.
• However, the number of Li+ complexes and
therefore the utility of Li+ as a computational probe
are rather limited.
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2.2.3 NICS
(Nucleas-Independent Chemical Shifts)
• Motivated by the analysis of the ring current
effects on 7Li+ chemical shifts.
• The ring current induced in aromatic molecules
affects the magnetic environment of nuclei quite
sensitively.
• However, inversely the physical existence of the
probe nucleus could also affect the properties of
the system under consideration.
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Why not use the absolute chemical
shielding of a virtual nucleus to
probe
(the ring current effects of)
aromaticity?
--Schleyer et al, JACS, 1996, 118, 6317.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Ab initio calculations of NICS
• NICS indices correspond to the negative
value of the magnetic shielding computed
at chosen points in the vicinity of molecules.
• Typically computed at ring centers, at
points above, and even as grids in and
around the molecule.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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NICS(0) and Aromaticity
NICS
Magnetism
Ring Current
Aromaticity
Significantly
Negative
Magnetically
Shielded
Diatropic
Aromatic
Positive
Magnetically
Deshielded
Paratropic
Antiaromatic
Around Zero
NonAromatic
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Computation of NICS with Gaussian
Optimize the molecule structure
Place "dummy" (Bq) atoms at the
positions where NICS should be
computed
Request an NMR type calculation
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Case Study: Benzene
(GIAO-B3LYP/6-311+G**)
State Key Laboratory for Physical Chemistry of Solid Surfaces
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C6H6 vs. C4H4
• The NICS grid plot of benzene and
cyclobutadiene at the GIAO-B3LYP/6311+G*//B3LYP/6-311+G* level of theory. The red
and green dots denote diatropic (aromatic) and
paratropic (antiaromatic) ring currents,
respectively.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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NICS experimental validation
Endohedral 3He Chemical Shifts (ppm) of Fullerenes.
Cages
C60 (1, Ih)
C70 (1, D5h)
C606- (1, Ih)
C706- (1, D5h)
C76 (1, D2)
C766- (1, D2)
B3LYP/6-31G*
-2.8
-27.2
-50.0
10.3
-16.2
-18.2
He)
–6.3b
-28.2c
-48.7c
8.3c
-18.7e
-20.6f
Bühl, M. Chem. Rev. 2001, 101,
1153.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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More Examples
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Bergman cyclization = aromatization reaction
NICS [ppm]
TS -17.9
2 -19.0
B3LYP/6-311+G*
Schleyer J. Org. Chem. 2002.
P. Schreiner J. Am. Chem. Soc. 1998.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Iso-Chemical-Shielding Surfaces
(ICSS)
• The shape of the magnetic shielding
function provides the same information
about electron delocalization and
molecular aromaticity.
• ICSS are actually isosurfaces of NICS
values.
Klod,
S et al. J. Chem. Soc. Perkin Trans. 2, 2001, 1893.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
• Calculated ring current effect of benzene. (shielding
surfaces at 0.1 ppm in yellow, at 0.5 ppm in green,
at 1 ppm in green-blue, at 2 ppm in cyan, and 5
ppm in blue, respectively; deshielding surface at
0.1 ppmState
in Key
red).
View
from
perpendicular
to
the
Laboratory for Physical Chemistry of Solid Surfaces
molecule and
in the plane of the molecule.
厦门大学固体表面物理化学国家重点实验室
Advantages of NICS
1. Does not require reference standards, increment
schemes, calibrating, and calibrating (homodesmic )
equations for evaluation.
2. Importantly, in several sets of related molecules,
NICS correlates well with other aromaticity
indexes based on energetic, geometric, and
other magnetic criteria.
3. Much less size-dependent than diamagnetic
susceptibility exaltation.
4. Easily computed with standard QM packages,
such as Gaussian, ADF, DeMon etc.
State P.
Keyv.
Laboratory
for Physical
Chemistry
of Solid
Surfaces
Schleyer,
R. J. Am.
Chem.
Soc.
1999,
121, 6872.
The numbers厦门大学固体表面物理化学国家重点实验室
of citations of the original NICS paper
Disadvantages of NICS
1. The total NICS does not depend purely on the p
system, but also on other magnetic shielding
contributions due to local circulations of
electrons in bonds, lone pairs and core electrons.
2. Refined alternatives of the original NICS
technique are highly desirable to offer a
better control of the contributions.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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2.2.4 Dissected NICS
• By definition, the chemical shielding tensors can be
described by a sum of partial chemical shifts
arising from occupied molecular orbitals (MOs). So
do the NICS tensors.
1
σ 2
2c
rrN I  rN  r
occ

k
k0
r  RN
3
| k 0
(L N )
2 occ
   k0
c k
r  RN
diamagnetic term
3
(ψ k1 )
paramagnetic term
where L N  rN 
and rN  r  R N
Eschrig, H.; Seifert, G.; Ziesche, P. Solid State Commun. 1985, 56,
777.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Two alternative ways of Dissected NICS
• Localized MO-NICS (LMO-NICS
Schleyer, P. v. R.et al. J. Am. Chem. Soc. 1997, 119,
12669.
• Canonical MO-NICS (CMO-NICS)
Heine, T.et al. PCCP. 2003, 5, 246; JPCA 2003, 107,
6470.
Bohmann, T.et al. JCP. 1997, 107, 1173.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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LMO NICS
NICStot=
NICSC-C(s)+NICSC-H+NICSLP
+NICSp
State Key Laboratory for Physical Chemistry of Solid Surfaces
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NICS(tot), NICS (p) and NICS (s) at the ring centers
Molecules
R
NICS(p)
NICS(s)
NICS(tot)
C6H6 (D6h)
1.396
-20.7
13.8
-8.9
Si6H6 (D6h)
2.217
-15.0
0.6
-13.1
Si6H6 (D3d)
2.240
Ge6H6 (D6h)
2.305
Ge6H6 (D3d)
2.384
B3N3H6 (D3h)
1.431
-11.2
-15.0
-1.5
-14.6
-10.0
-12.0
11.4
• SOS-DEPT-IGLO/III//B3LYP/6-311+G**
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
-2.1
State Key Laboratory for Physical Chemistry of Solid Surfaces
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3
2D p-Aromaticity
3.1 Benzene & other 6p-e aromatics
3.2 PAHs (Polycyclic aromatic
hydrocarbons)
3.3 [n]Annulenes
3.4 [n]Trannulenes
State Key Laboratory for Physical Chemistry of Solid Surfaces
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3.1 Benzene & other 6pe aromatics
2-
X
X
(X=O,S,NH)
(X=N)
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Benzene: MO-NICS Analysis
-5.1
-15.2
• Poater, J. et al. Chem. Eur. J., 2003, 9, 1113.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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NICS(total) RB3LYP/6-311+G** values for aza
pyrroles.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
NICS(total) RB3LYP/6-311+G** values for phospha
pyrroles.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
NICS(total) RB3LYP/6-311+G** values for aza
thiophenes.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
NICS(total) RB3LYP/6-311+G** values for
azapyridines.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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3.2 PAHs
(Randic, M. Chem. Rev. 2003, 103, 3449.)
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Misuse of circle notation!
Chrysene
Kekule Structures
Circle notation
Clar Structures
Wrong!!!
• Belloli, R. C. J. Chem. Educ. 1983, 60, 190.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Electron Rules for PAHs
Clar 6n rule versus Hückel (4n+2) rule
• Hückel (4n+2) rule holds strictly for monocyclic
aromatic systems.
• Clar 6n rule holds faithfully for benzenoid PAHs
having 6n p-electrons which always show extra
stability.
Clar, E. The Aromatic Sextet; J. Wiley & Sons: London, 1972.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Clar Sextet Structures of PAHs
•Extra stability
1
2
3
•Large HOMOLUMO gap
4
•Unusually high
excitation energy
5
6
7
Each circle represents 6 p-electrons exclusively!
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Giant Benzenoids
All fulfill Clar 6n rule.
Müllen, K. et al, Chem.
Rev. 2001, 101, 1267;
Angew. Chem. Int.
Ed., 1997, 36, 631,
1604, 1607.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Further Support for Clar’s Aromatic Sextet
NICS grid of C42H18
• Clar sextet rings have large negative NICS
values.
----Moran, D.et al, J. Am. Chem. Soc. 2003, 125,
6746.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Further Support for Clar’s Aromatic Sextet
NICS
Hexaradical Clar
formula
Fully Benzenoid
Clar formula
C48H24
Moran, D.et al, J. Am. Chem. Soc. 2003, 125, 6746
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Further Support for Clar’s Aromatic Sextet
For all PBHs, there is
perfect agreement
between Clar and
NICS electron
topologies.
Moran, D.et al, J. Am.
Chem. Soc. 2003, 125,
6746.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Clar Sextet model for SWCNTs
• Length-dependence of finite armchair (n,n)
SWCNTs.
(3m+1)-layered (3m+2)-layered
a) Kekule
3m-layered
b) Incomplete Clar c) Complete Clar
Matsuo,
Y.; Tahara, K.; Nakamura, E. Org. Lett. 2003, 5, 3181
State Key Laboratory for Physical Chemistry of Solid Surfaces
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State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
The finite
(n,n) tubes having complete
LUMO
Clar aromatic sextet structures have
smaller
HOMO-LUMO gaps!
DG
HOMO
HOMO,
LUMO and DG of finite (5,5)
State Key Laboratory for Physical Chemistry of Solid Surfaces
SWCNTs (PM3 predictions)
厦门大学固体表面物理化学国家重点实验室
Clar Sextet model for infinite (n,m) SWCNTs
R(n,m)
Conductivity
Clar VB Model
0
Metallic
complete Clar sextet &
fully benzenoid
1, 2
Semiconductor
Incomplete Clar
Structure with a seam
of double bonds.
R(n,m) = n- m modulo 3
Ormsby,
L.; King,
B. T. J.Chemistry
Org. Chem.,
2004,
69, 4287.
State Key J.
Laboratory
for Physical
of Solid
Surfaces
厦门大学固体表面物理化学国家重点实验室
(19,0)
(12,8)
(12,7)
(12,9)
Clar VB representation of (12,9), (12,8), (12,7)
and (19,0) SWCNTs
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Important application of Clar VB
• The Clar VB models of SWCNTs were
demonstrated to be consistent with the
patterns exhibited by SMT images.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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3.3 [n]Annulenes
• Examples of aromatic [n]annulenes
State Key Laboratory for Physical Chemistry of Solid Surfaces
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• Examples of antiaromatic [n]annulenes
State Key Laboratory for Physical Chemistry of Solid Surfaces
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ISE of Aromatic [n]annulenes
• Wannere, C. S.; Schleyer, P. v. R. Org. Lett. 2003, 5,
865.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Magnetic properties of [18]-annulenes
H
The six inner hydrogens
resonate at  =-3.0 ppm
H
H
H
Upfield of TMS !!!
H
H
H
H
H
H
H
H
Nucleus-Independent Chemical Shifts
(14.ppm)
H
H
H
H
H
The twelve outside hydrogens
resonate at  = 9.0 ppm
H
1996 Schleyer: Nucleus-Independent Chemical Shifts (NICS):
J. Am. Chem. Soc. 1996, 118, 6317.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Calculated Properties of [n]annulenes
• B3—B3LYP/6-31G* ; HF – HF/6-31G*
Wannere,
C. S.; Schleyer, P. v. R. Org. Lett. 2003, 5,
State Key Laboratory for Physical Chemistry of Solid Surfaces
865. 厦门大学固体表面物理化学国家重点实验室
• However, large annulenes such as [54]- and
[66]-annulenes behave more like long
chain cyclic polyenes.
Wannere, C. S.; Schleyer, P. v. R. Org. Lett. 2003, 5,
865.
Schleyer, P. V. R. et al., Chem. Rev. 2005, 105, in press.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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3.4 [n]Trannulenes
• [n]trannulenes --- all-trans-[n]annulenes with inplane pp-orbital conjugation.
Annulenes
(all cis-)
or cis,trans-
Annulenes
(cis,trans)
Trannulenes
(all-trans)
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Predicted model molecules
Dodecahedrapentaene & [10]trannulene
NICS= -16.5 ppm
NICS= -14.0 ppm
McEwen, et al. J. Org. Chem. 1986, 51, 4357.
State Key Laboratory for Physical Chemistry of Solid Surfaces
Fokin, 厦门大学固体表面物理化学国家重点实验室
et al. J. Am. Chem. Soc. 1998, 120, 9364.
Aromaticity of [n]trannulenes
1. The [n]trannulenes, CnHn, have uniform
configurations (Dn and Dnd symmetries) and are
higher in energy than the corresponding
[n]annulenes.
2. All of the [n]trannulenes follow the Hückel rule
exactly.
4n + 2 electron singlets--------aromatic
4n singlets ------------------antiaromatic
4n triplet ---------------------- aromatic.
Fokin, et al. J. Am. Chem. Soc. 1998, 120, 9364.
State Key Laboratory for Physical Chemistry of Solid Surfaces
Burley,厦门大学固体表面物理化学国家重点实验室
et al., Angew. Chem. Int. Ed., 2005, 44, 3176.
Magnetic Properties of Aromatic
[n]Trannulenes (B3LYP/6-31G*)
Formula
Sym.

NICS
(H)
C10H10
D5d
-29.3
-14.0
2.0
C14H14
D7d
-105.8
-17.2
1.8
C18H18
D9d
-232.5
-17.9
1.0
C22H22
D11d
-426.9
-17.9
0.4
C26H26
D13d
-705.0
-17.8
-0.1
Laboratory for Physical
Chemistry of
Solid Surfaces
C30H30State KeyD
-1082.3
-17.8
-0.5
15d
厦门大学固体表面物理化学国家重点实验室
Magnetic Properties of Antiaromatic
[n]Trannulenes (B3LYP/6-31G*)
Formula
Sym.

NICS
(H)
C12H12
D6
113.7
35.7
10.6
C16H16
D8
221.3
27.8
10.7
C20H20
D10
349.0
21.6
10.3
C24H24
D12
487.4
17.0
9.8
C28H28
D14
619.6
13.4
9.1
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Magnetic Properties of Triplet-aromatic
[n]Trannulenes (B3LYP/6-31G*)
Formula
Sym.

NICS
(H)
C12H12
D6d
-58.9
-15.3
2.7
C16H16
D8d
-157.4
-17.2
1.5
C20H20
D10d
-315.6
-17.6
0.6
C24H24
D12d
-548.9
-17.7
0.2
C28H28
D14d
-874.9
-17.7
-0.1
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
Synthesized [n]Trannulenes
[18]trannulenes----Derivatives of C60
Wei et al., Angew. Chem. Int. Ed. 2001, 40, 2989.
State Key
forChem.
Physical
Chemistry
of Solid
Troshin,
etLaboratory
al. Angew.
Int.
Ed. 2005,
44, Surfaces
234.
厦门大学固体表面物理化学国家重点实验室
Chiang et al., J. Am. Chem. Soc. 2005, 127, 26.
4 Möbius Aromaticity
• Möbius Strip: A ribbon with a 180 twist, named
after the theoretical astronomer and mathematician
August F. Möbius (1790-1868).
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
• Craig-type p-conjugation & aromaticity: Möbius
topologies in electronic wave functions, i.e., introducing
the essential 180°(p) half-twist into a cyclic array of
atomic orbital (AO) basis functions.
HMO calculations by Craig et al. revealed that in such planar cyclic
(AB)n, n=3,4, molecules with equal numbers of p- and d-functions,
the delocalization energies were smooth functions of n, and leading in
the limit of large rings to the same delocalization energy per pelectron as pp-pp overlaps.
Craig, D. P. et al. Nature 1958, 181, 1052; J. Chem. Soc. 1959, 997.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Heilbronner-type Möbius Aromaticity
• In 1964, Heilbronner predicted that
singlet [4n]annulenes would be aromatic
systems in twisted conformations where
the pp orbitals lie on the surface of a
Möbius strip.
C2
Heilbronner, E. Tetrahedron Lett. 1964, 1923.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
p-system of Benzene
A Möbius p-system
with a 180°twist --Heilbronner-type
Möbius aromaticity
Critical Features in
Geometry &
Electronic Structure
C2
State Key Laboratory for Physical Chemistry of Solid Surfaces
Heilbronner,
E. Tetrahedron Lett. 1964, 1923.
厦门大学固体表面物理化学国家重点实验室
p-MO occupations
(a) planar 4n+2
(b) planar 4n
(c) one-half twisted 4n
Heilbronner, E. Tetrahedron Lett. 1964, 1923.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
C9H9+
(c = -188.8)
Mauksch, M. et al. Angew. Chem., Int. Ed. 1998, 37, 2395.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Möbius [4n]annulenes
C12H12
NICS = -14.3 ppm
C16H16
NICS = -14.5 ppm
Castro, C. et al.. Org. Lett. 2002, 4, 3431
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Synthesized Möbius-type [16]annulene
Ajami, D. et al. Nature 2003, 426, 819.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Is this molecule möbius-aromatic ?
• This möbius-shaped
[16]annulene is nonaromatic
and that any aromatic character
of it is confined to the benzene
rings!!
NICS= -3.4 ppm
• The goal of preparing an
unambiguously aromatic
neutral Möbius [4n]annulene
remains to be realized!!
Castro et al. J. Am. Chem. Soc. 2005, 127, 2425.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
New metallacycles of Craig-Möbius aromaticity
arising from 8c-8e d-p p-conjugation.
Resonance of VB
structures
Xia, H.P. et al, Nature Chem. DOI: 10.1038/NCHEM.1690.
State Key Laboratory for Physical Chemistry of Solid Surfaces
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Trend for dp-pp conjugation within fused ring
compounds with one transition metal atom
• Simplified as a [n]-polyenic chain + a TM atom! (n =odd)
• The occupied p-MOs of a [n]-polyene (n=odd) is always aligned
as,
ne , (n-1)/2 MOs doubly occupied
…
E
E(n+3)/2
…
E(n-1)/2
…
and one non-bonding SOMO!
(n+3)/2
(n+1)/2
(n-1)/2
E(n+1)/2
E2
E1
p
n= 4k+1
(n+1)/2= 2k+1
(n+3)/2= 2k+2
LUMO
2 Asymm. SOMO
1 Symm.
n= 4k+3
(n+1)/2= 2k+2
(n+3)/2= 2k+3
Asymm.
Symm.
Symm.
Asymm.
State Key Laboratory for Physical Chemistry of Solid Surfaces
厦门大学固体表面物理化学国家重点实验室
• Based on HMO theory, the [n]polyene (n=odd) has a nn bond,
whose SOMO adopts the form,
n
ψ SOMO  A ( φ1  φ3  φ5  ...)
k 1
Simplified diagram of SOMO:
n=4k+1
n=4k+3
Asymm.
Symm.
• To form a closed ring system with dp-pp (n+1)c(n+1)e conjugation,
the symmetry of d(AO) of the TM atom should be compatible with
that of the SOMO of [n]polyenic fragment. Thus,
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5. Homoaromaticity
• In 1959 Winstein introduced the term
"homoaromatic" to describe compounds that
display aromaticity despite one or more
saturated linkages interrupting the formal
cyclic conjugation.
•Winstein, S. J. Am. Chem. Soc. 1959, 81, 6524 & 6523.
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•Williams, R. V. Chem. Rev.
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2001, 101, 1185.
Homoaromaticity & Homoantiaromaticity
Hückel-type:
•Homoaromaticity: homoconjugative interaction(s) with
cyclic delocalization of (4n+2) electrons.
•Homoantiaromaticity: homoconjugative interaction(s)
with cyclic delocalization of 4n electrons.
Similarly, Möbius-type homoaromaticity arising from
Möbius-manner homoconjugation involving 4n electrons.
•Williams, R. V. Chem. Rev. 2001, 101, 1185.
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The first suggestion of homoaromatic system
Homoallylic cation
cholesteryl p-toluenesulfonate
Winstein, S.; Adams, R. J. Am. Chem. Soc. 1948, 70, 838.
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Types of Homoaromaticity
Number of saturated
insertions
Monohomoaromatic
1
Bishomoaromatic
2
Homoaromatic
3
4
Trishomoaromaticity
Tetrahomoaromaticity
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Criteria for Homoaromaticity
• The presence of homoconjugative interaction(s)
(either through-bond or through-space) closing
cyclic conjugation.
• Electron delocalization.
• 4n+2 Huckel rule
• RE > 2 kcal/mol.
• exceptional magnetic properties.
Note that through-bond homoconjugation invloves the
hyperconjugation around the saturated linkage!
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5.1 Cationic homoaromaticity
5.1.1 2e systems:
monohomoaromatic
Homocyclopropenium cation
Applequist, D. E. et al. J. Am. Chem. Soc. 1956, 78, 4012.
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Cationic homoaromaticity
bishomocyclopropenium cations
Bishomoaromatic
non-homoaromatic
Winstein, S. Chem. Soc. Spec. Publ. 1967, 21, 5.
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More examples of 2e-bishomoaromatics
• Laube, T. Acc. Chem. Res. 1995, 28, 399.
• Evans, W. J. et al. J. Am. Chem. Soc. 1995, 117, 12635.
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Double bishomoaromatics
Bishomoaromatic
• Prakash, G. K. S.et al. J. Am. Chem. Soc. 1987, 109, 911.
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Trishomocyclopropenium Cations
Trishomoaromatic
Szabo, K. J. et al. J. Org. Chem. 1996, 61, 2783
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Pagodane Dications
4c2e homoaromatics
(C…C distance 2.3~2.4 Å)
Prinzbach, H.et al. Pure Appl. Chem. 1995, 67, 673.
Etzkorn, M. et al. J. Org. Chem. 1998, 63, 6080.
Prakash, G. K. S. et al. Chem. Commun. 1999, 1029.
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Syn-Periplanar Bisdiazene-Tetroxide Dication
2.55
-2e
Exner, K. et al. J. Am. Chem. Soc. 1999, 121, 1964.
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5.1.2 6e systems
Homotropylium cations
a) equalized C-C bonds
b) equalized (13C)
c) NICS(0) = 11.3 ppm
Reindl, B.et al. JPCA 1998, 102, 8953.
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5.1.3 dehydroadamantyl dication
NICS = 50.1
 = -50.1
• 4c2e Tetrahomoaromatic
Bremer, M. et al. ACIE. 1987, 26, 761.
Schleyer, P. v. R. JACS, 1996, 118, 6317.
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5.1.4 Antihomoaromatic Cations
• Jiao, H.et al. In AIP Conference
Proceedings 330: E.C.C.C. 1,
Computational Chemistry;
American Institute of Physics:
Woodbury, NY, 1995; p 107.
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5.2 Neutral Homoaromatics
• Hypothetic neutral homoaromatics
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• Few examples of neutral homoaromatic molecules
has been predicted theoretically.
• Thus far, neutral homoaromaticity has been
widely recognized in the transitions states of a lot
of chemical pericyclic reactions, such as DielsAlder, 1,3-dipolar cycloaddition, cope
rearrangement and so on.!
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5.3 Aromaticity of Transition States of
Pericyclic Reactions & Homoaromaticity
5.3.1 Diels-Alder reactions
6e homoaromaticity
• Evans, M. G..; Warhurst, E. Trans. Faraday Soc. 1938, 34, 614.
• Cossio, F. P. et al. J. Am. Chem. Soc. 1999, 121, 6737.
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5.3.2 Sigmatropic shifts
6e homoaromaticity
• Jiao, H.; Schleyer, P. v. R. J. Phys. Org. Chem. 1998, 11, 655.
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5.3.3 Cope rearrangements
6e homoaromaticity
• Navarro-Vazquez, A. et al. Org. Lett. 2004, 6, 2981.
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5.3.4 Claisen rearrangements
6e homoaromaticity
• Yoo, H. Y.; Houk, K. N. J. Am. Chem. Soc. 1997, 119, 2877.
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5.3.5 Electrocyclic reactions
6e homoaromatic TSs
• Jiao, H.; Schleyer, P. v. R. J. Phys. Org. Chem. 1998, 11, 655.
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5.3.6 Ene reactions
6e homoaromaticity
• Loncharich, R.; Houk, K. N. J. Am. Chem. Soc. 1987, 109, 6947.
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5.3.7 Reactions involving TS’s of Möbius
Homoaromaticity
4ne Möbius homoaromaticity
[1,7] Sigmatropic Shift
•
Ring opening of cyclobutene
Jiao, H.; Schleyer, P. v. R. Angew. Chem., Int. Ed. Engl. 1993, 32,1763.
• Lee, P. S. et al. J. Am. Chem. Soc. 2003, 125, 5839.
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6 s-Aromaticity
•Dewar, M. J. S. Bul. Soc.
Chim. Belg. 1979, 88, 957.
•Exner, K. et al, J. Phys.
Chem A 2001, 105, 3407.
NICS
Grid
•Moran, D. et al. Org. Lett.
2003, 5, 23.
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• Dissected NICS data of cycloalkanes.
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Super s-(anti) aromaticity
Symm.
NICS
D3h
Oh
Cage -48.3
-0.1
+23.1
3MR
-33.0
-0.8
+13.1
Td
4MR
-46.1
• Moran, D. et al. Org. Lett. 2003, 5, 23.
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Related Inorganics: P4 and P8
P
P
P
P
P
P
P
P
P
PP
Symm.
NICS
P
Td
Cage -59.7
3MR
Oh
+43.4
-57.4
4MR
+26.6
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7
Spherical Aromaticity
• Fullerenes
• Polyhedral boranes and carboranes
• Other inorganic cage compounds and
Clusters
• Aihara, J. J. Am. Chem. Soc. 1978, 100, 3339.
• Bühl, M.；Hirsch, A.; Chem. Rev. 2001, 101, 1153.
• King, R. B. et al, Chem. Rev., 2005, 105, in press.
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7.1 The Sphericity
of Fullerenes
p-MOs of C60
The spherical
harmonic pattern for
C60 MOs
Tang, A. C. et al. Chem. Phys. Lett.
1994, 227, 579.
Reiher, M.; Hirsch, A. Chem. Eur.
J. 2003, 9, 5442.
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Noble-gas configuration of C6010+
2(N+1)2 electron-counting rule for
spherical aromaticity of Ih fullerenes,
e.g., C202+ and C6010+
NICS(C202+) = -73.1 ppm
NICS(C6010+) = -81.4 ppm
• Hirsch, A. Angew. Chem, Int. Ed. 2000, 39, 3915-3917
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7.2 Duality of Fullerenes and Deltahedral Boranes
• Fullerene polyhedra and borane deltahedra
have an interesting dual relationship.
• A given polyhedron P can be converted into
its dual P* by locating the centers of the
faces of P* at the vertices of P and the
vertices of P* above the centers of the faces
of P.
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Example: Cube Octahedron dualization
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Dualization of C60 and B32H322-
C60
(v = 60, e = 90,
and f = 32)
Dual
B32H322–
(v = 32, e = 90,
and f = 60)
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7.3 Aromaticity of fullerenes
Symmetry
Ne
l
NICS
C284-
Td
32
3
-35.5
C32
D3
32
3
-53.2
C482-
(199)C2
50
4
-40.4
C6010+
Ih
50
4
-81.7
C808+
Ih
72
5
-82.9
** GIAO-SCF/6-31G*
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Chemical Shifts of Endohedral 3He in C60 and C70
3He@Cn
3He2@Cn
C60
-6.40
-6.40
C606-
-49.27
-49.17
C70
-28.82
-28.81
C706-
+8.20
+8.04
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7.4 Aromaticity of boranes and derivatives
• The deltahedral closo-boranes BnHn–2 (6 ≤ n ≤
12) and their carboranes are well-accepted as
aromatic.
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NICS(B5H52-) = -28.1 ppm
NICS (N2B3H5) = -10.1 ppm
• Schleyer, P. v. R. et al. J. Am. Chem. Soc. 1996, 118, 9988
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NICS of Boranes and derivatives
(CSGT-B3LYP/6-311+G**)
BnHn2-
CBn-1Hn-
NBn-1Hn
6 vertex
-26.5
-26.6
-25.9
7 vertex
-19.7
-20.3
-15.7
8 vertex
-16.7
-16.8
-14.7
9 vertex
-21.1
-20.2
-16.7
10 vertex
-27.5
-24.9
-20.0
11 vertex
-26.2
-24.0
-19.4
12 vertex
-28.4
-28.0
-26.3
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Najafian K.et al. Inorg. Chem.
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2003, 42, 4190.
7.5 Other inorganic clusters
7.5.1 E4q (q=0, E=N,As,Sb,Bi; q=-4, E=Si,Ge,Sn,Pb)
Both the s and p MO shells of P4 fulfill the 2(N+1)2
rule, attaining daul spherical aromaticity.
State Key Laboratory for Physical Chemistry of Solid Surfaces
Hirsch,厦门大学固体表面物理化学国家重点实验室
A. ACIE 2000, 39,
NICS (ppm) of E4q clusters
NICSa
NICSb
a
P4
As4
Sb4
Bi4
-54.6
-55.3
-40.3
-37.3
Si44-
Ge44-
Sn44-
Pb44-
-41.9
-39.3
-32.3
-29.1
GIAO-MP2/6-31G*; b GIAO-MP2/LANL2DZp
Hirsch, A. et al. Angew. Chem, Int. Ed. 2001, 40, 2834.
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7.5.2 Zintl ions
>
E94- (E= Si, Ge, Sn, Pb) and Bi95+
double spherical aromaticity = 32 (s) + 8 (p)
Corbett, J.D. Angew. Chem. Int. Ed. 2000, 39, 670
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E9q Clusters (GIAO-MP2)
Si94Ge94-
Sn94Pb94Bi95+
Symmetry
closo(D3h)
NICS
Erel(kcal/mol)
-87.7
nido(C4v)
-86.7
closo(D3h)
-81.0
nido(C4v)
-80.3
closo(D3h)
-68.9
nido(C4v)
-68.2
closo(D3h)
-68.9
nido(C4v)
-68.3
closo(D3h)
-28.1
nido(Cfor
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-28.1
4v)Physical Chemistry
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0.0
1.1
0.0
0.8
0.0
0.8
0.0
1.0
0.0
0.4
Kuznetsov, A. N. et al. Chem. Eur. J. 2001,7,2821.
7.6 Spherically aromatic gold clusters
NICS=-36 ppm
• King, R. B. et al. Inorg. Chem. 2004, 43, 4564.
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MOs of Au20(Td)
Spherically Aromatic
• King, R. B. et al. Inorg. Chem. 2004, 43, 4564.
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icosahedral “golden” fullerene Au32
The dual of C60
32 s-electrons
Spherical
s-aromaticity
NICS=-100ppm
•State
Johansson,
M. P. et al. Angew. Chem., Int. Ed. 2004, 43, 2678.
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8. Aromaticities in Metal Clusters
• Ga32-
NICS(0) =-45.4 ppm
NICS(1) =- 23.5 ppm
• Li, X. W. et al. J. Am. Chem. Soc.,1995, 117, 7578.
•厦门大学固体表面物理化学国家重点实验室
Xie, Y. M. et al. J. Am. Chem. Soc. 1996, 118, 10635.
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Hg46-
• A 2pe aromatic inorganic cluster
•State
Kuznetsov,
A.E. et al. Angew. Chem., Int. Ed. 2001, 40,
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3369.
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Au5Zn+
• 6se aromatic
• Tanaka, H. et al, J. Am. Chem. Soc. 2003, 125, 2862.
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8 Through-space Aromaticity of Inorganic Ions
8.1 Pericyclic Transition-State-Like Aromaticity
E
Selected MOs of Se2I42+
LUMO
HOMO
HOMO-1
HOMO-6
HOMO-7
10e homoaromatic
Zhang, Q.; Lu, X. et al. Inorg. Chem., 2006,
45, 2457. JACS, 2009, 131, 9781.
HOMO-11
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Three VB structures of Se2I42+
The resonance of these VB structures results
in 6c10e through-space conjugation!
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(I2+)2 with PTS-like
aromaticity
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8.2 S2I42+ with dual
PTS-like aromaticity
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8.3 Bishomoaromatic Inorganic Ions
6c10e through-space
homoconjugation
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
S
State Key
Laboratory for Physical Chemistry of Solid Surfaces
VB
description
MO description
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8.4 Neutral Bishomoaromatic Inorganics
1,5-diphoshadithiazocines
14aa
14bb
14ca
S….S
(Å)
2.62
(2.55)
2.77
(2.53)
2.62
(2.53)
NICS
(ppm)
-18.4
-18.7
-17.3
c
ppm cgs
-135.8
-251.9 -235.6
a
B3LYP/6-311+G(3df);
b B3LYP/6-31G(d);
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6c10e homoconjugation
8.5 Spherically Aromatic TS Conjugation
Te64+
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6c8e
spherical through-space conjugation
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Concluding Remarks
Aromaticity is a timedependent concept, of which
new aspects are pending for
discovery.
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厦门大学校主--陈嘉庚先生
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Questions
• 同芳香性和常规芳香性体系的异同点有哪些?
• Möbius芳香性区别于Hückel芳香性的关键特征有哪些?
• 上述Nature Chem文献中的Metallapentalyne为何在杂金
属后具有Möbius芳香性? 当金属原子不位于其中间桥
位时是否仍可能具有类似的Möbius芳香性？
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