スライド 1

Synthesis and Properties of
Cyclooctatetraene Congeners
2014. 12. 3
Tobe Lab.
Kazuya Fujita
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Contents
• Introduction
Aromaticity- Hückel’s Rule and NICS(0) value
Structure and physical properties of cyclooctatetraene and its
congeners
Biradical character
• Twisted cyclooctatetraene congeners
Synthesis and physical properties
My work and results
• Summary
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Hückel’s Rule and NICS(0) Value
• Hückel’s Rule: a rule to distinguish whether cyclic conjugated
polyenes will have aromatic property on the basis
of stabilization energy
• NICS(0) value: a value by theoretical calculations to estimate
aromatic property
p-conjugated
cyclic compounds
structure
number of
p electrons
planar
4N + 2
4N
aromatic (芳香族)
NICS(0)
Value
negative
anti-aromatic (反芳香族) positive
( N = 0, 1, 2, …)
non-planar
non-aromatic (非芳香族)
zero
• larger absolute value means stronger aromaticity/anti-aromaticity
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Hückel’s Rule and NICS(0) Value
cyclic conjugated
polyenes
planar
number of
p electrons
NICS(0) Value
negative
aromatic (芳香族)
anti-aromatic (反芳香族) positive
4N + 2
4N
( N = 0, 1, 2, …)
non-planar
• benzene
non-aromatic (非芳香族)
NICS(0): -11.5
• planar
• has 6 p electrons
aromatic
zero
Calculatied by HF/6-31G*//B3LYP/6-31G*
resonance (共鳴):
• two forms are not under equilibrate (平衡)
• the true structure is the mixture of two forms
all bond lengths are equal (1.39 Å)
• aromatic compound is stabilized by resonance energy
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Cyclooctatetraene (COT)
NICS(0): +1.9
=
=
126.1 °
• has 8 p electrons
• alternating single and double bonds
• non planar tub-shaped structure
non-aromatic
1.34 Å
1.48 Å
• tub-to-tub inversion in solution
flexible p conjugated skeleton
equilibrate (平衡),
not resonance (共鳴)
5
COT Congeners and NICS(0) Value
NICS(0): +1.9
• has 8 p electrons
• non-planar
non-aromatic
• Planarized COT by introducing substituents
NICS(0): +17.4
Crystal structure of 1
anti-aromatic
Nishinaga, T. et al. J. Am. Chem. Soc. 2010, 132, 1066.
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Biradical Character
• Ethylene
cleavage of p bond (double bond)
leads to loss of bonding energy
closed shell
open shell
• o-Quinodimethane
open shell structure is stabilized by
forming benzene ring
resonance (共鳴)
closed shell
open shell
open shell structure contributes to
resonance hybride and has diradical
character
• Formal [4+4] dimerization of o-quinodimethane
Boekelheide, V. et al. J. Am. Chem. Soc. 1981, 103, 1777.
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Dimerization of Indeno[2,1-a]fluorenes
• dimerization and formation of COT ring undergo one step
• more p conjugated system having COT ring can be synthesized
new synthetic method of COT congeners
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Crystal Structure and NICS(0) Value of Dimer 5
torsion angle
C1-C1’-C4’-C4
C2-C3-C3’-C2’
C4
C2
C3
C3’
29.2 °
38.6 °
C1
C1’
C2’
C4’
steric repulsion
COT ring is twisted
NICS(0): +11.9
decreased
anti-aromaticity
An ORTEP drawing of Dimer 5.
Single crystals of 5 suitable for X-ray
analysis
were
obtained
from
benzene/methanol.
Calculatied by HF/6-31G*//B3LYP/6-31G*
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My Work
Tobe, Y. et al. Angew. Chem. Int. Ed. 2013, 52, 4184.
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Structures of Dimer 7 and 8’
Optimized structure by DFT
(B3LYP/6-31G* )
HOMO
LUMO
HOMOtorsion angle torsion angle
LUMO gap
red
orange
NICS(0)
7
-4.89 eV -2.81 eV
2.08 eV
42.7 °
33.6 °
+12.7
8’
-5.10 eV -2.30 eV
2.80 eV
4.5 °
5.5 °
+12.2
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Synthesis of dibromodihydroindenofluorene 12
Mataka, S. et al. New. J. Chem. 2003, 27, 1377.
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Attempted Synthesis of Dimer 7
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Reaction Mechanism of Dimerization
Calculated at RB3LYP/6-31G(d) + LanL2DZ (for Br) (TS1, INT2)
Calculated at UB3LYP/6-31G(d) + LanL2DZ (for Br) (INT1, TS2)
by Dr. Nobusue, S
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Reaction Mechanism of Dimerization
Structure of TS1
Calculated at RB3LYP/6-31G(d) + LanL2DZ (for Br) 15
Energy Diagram of Dimerization
30
TS2
Relative energy / kcal mol-1
20
10
0
TS1
INT1
3
-10
-20
INT2
-30
= Ph
-40
5
TS1
reaction coordinate
Calculated at RB3LYP/6-31G(d) + LanL2DZ (for Br) (TS1, INT2); Calculated at UB3LYP/6-31G(d) +
LanL2DZ (for Br) (INT1, TS2) by Dr. Nobusue, S
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Energy Diagram of Dimerization
30
TS2
higher activation barrier
Relative energy / kcal mol-1
20
10
0
TS1
INT1
3
-10
-20
INT2
-30
= Ph
-40
5
TS1
reaction coordinate
Calculated at RB3LYP/6-31G(d) + LanL2DZ (for Br) (TS1, INT2); Calculated at UB3LYP/6-31G(d) +
LanL2DZ (for Br) (INT1, TS2) by Dr. Nobusue, S
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Synthetic Scheme of Dimer 8 and 8’
† Steven, G. N. et al. PCT Int. Appl. US 03/022898, A1, 2003.
‡ Lai, Y-H. et al. J. Chem. Soc. Perkin Trans. 2 1993, 7, 1377.
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Summary
• Non-planar tub-shaped COT exhibits non-aromaticity and
planarized COT exhibits anti-aromaticity.
• Twisted COT congener was formed by dimerization of indeno[2,1a]fluorenes and its twisted COT ring exhibits decreased antiaromaticity.
• Synthesis of Ph-substituted indenofluorene dimer was attempted,
but unexpected reaction occurred.
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