Structural nonrigidity of N-(cycloheptatrienyl)phthalimide

Full text of DOI:10.1134/S0012500810010040

ISSN 0012ꢀ5008, Doklady Chemistry, 2010, Vol. 430, Part 1, pp. 11–17. © Pleiades Publishing, Ltd., 2010.
Original Russian Text © G.A. Dushenko, O.I. Mikhailova, I.E. Mikhailov, R.M. Minyaev, V.I. Minkin, 2010, published in Doklady Akademii Nauk, 2010, Vol. 430, No. 2,
pp. 195–201.
CHEMISTRY
Structural Nonrigidity of Nꢀ(Cycloheptatrienyl)phthalimide
G. A. Dushenko, O. I. Mikhailova, I. E. Mikhailov, R. M. Minyaev, and Academician V. I. Minkin
Received July 29, 2009
DOI: 10.1134/S0012500810010040
Functionalized cycloheptatrienes, widely used as compound
1 in crystal has a boat conformation with
ligands for synthesizing catalytically active metal comꢀ the phthalimido group in the quasiꢀequatorial posiꢀ
plexes [1, 2], are stereochemically nonrigid systems tion, which is supported by the spin coupling conꢀ
3
4
that undergo lowꢀbarrier shifts of substituents (H, stants J(Hꢀ1,Hꢀ7) = 5.10 Hz and J(Hꢀ2,Hꢀ7) =
BPr , NCO, NCS, NCSe, N , OMe, SR, Cl, and
1
2
3
1.66 Hz in H NMR spectra.
organometallic groups) along the sevenꢀmembered
ring perimeter [3, 4]. No information has heretofore
been available on migrations of amino groups. The
introduction of electronꢀwithdrawing substituents
into the amino group made it possible to considerably
decrease the activation barrier and detect migrations
of the phthalimido group in the cycloheptatriene ring,
which are fast on the NMR time scale.
1
In the H NMR spectra (300 and 80 MHz) of comꢀ
pound 1 in nitrobenzeneꢀd5 (Fig. 1), heating the soluꢀ
tion to 140 C leads to synchronous reversible broadꢀ
ening of the indicator signals of the cyclotrienyl proꢀ
tons Hꢀ7, Hꢀ1 and Hꢀ6, Hꢀ2 and Hꢀ5, and Hꢀ3 and
°
Hꢀ4, and at 200 C the coalescence of these signals is
°
1
observed ( H NMR at 80 MHz). This spectral behavꢀ
ior is evidence of phthalimido group shifts along the
cycloheptatriene ring perimeter, proceeding by the
Nꢀ(1,3,5ꢀCycloheptatrienꢀ7ꢀyl)phthalimide
(1)
was synthesized by the reaction of tropylium tetrafluꢀ dissociation–recombination mechanism with interꢀ
oroborate with potassium phthalimide in acetonitrile. mediate formation of the zwitterion tropylium catꢀ
1
13
IR and H and C NMR spectra demonstrate that ion–phthalimide anion
2
(Scheme 1).
…
…
…
O
H
H
1
O
3
4
7
1
5
–
O
N
2
1
3
2
14
N
N
13
5
…
12
5
6
8
6
7 O
9
O
O
10
11
+
1
2
…
…
Scheme 1.
The dominating dissociation–recombination compound
1, which shows exchange crossꢀpeaks
mechanism of phthalimido group migrations is also between all pairs of signals of the sevenꢀmembered
1
confirmed by the 2D (EXSY) H NMR spectrum of ring at 160
C. The rate of this dynamic process is indeꢀ
°
pendent of the solution concentration within the
1
range 0.007–0.2 mol/L. From the H NMR line shape
analysis, we calculated the activation parameters of
of Sciences, pr. Stachki 194/2, RostovꢀonꢀDon, 344090 Russia degenerate migrations of the phthalimido group along
Institute of Physical and Organic Chemistry, Southern Federal
University, Southern Scientific Center, Russian Academy
11

12
DUSHENKO et al.
200°C (80 MHz)
200
°
C
1
80
°
C
C
160
°
140
°
C
24°C
8.0
7.5
7.0
6.5
6.0
5.5
5.0
4.5
, ppm
δ
Fig. 1. 1H NMR spectra (300 and 80 MHz) of compound
1 in deuterated nitrobenzene.
the cycloheptatriene ring perimeter in a solution in group in the equatorial position perpendicular of the
≠
sevenꢀmembered ring plane of
formation of ꢀ(cycloheptatrienꢀ7ꢀyl)phthalimide, which
is 3.5 kcal/mol more favorable than conformation with
1, is the most stable conꢀ
nitrobenzeneꢀd5
k180°C = 9.4 s–1
To confirm the mechanism of structural nonrigidꢀ
ity of compound for which the activation parameters
: ΔG180°C = 25.1 kcal/mol and
N
.
5
the phthalimido substituent in the axial position. The calꢀ
≠
1
culated barrier ΔEZPE to the inversion of the sevenꢀ
correspond to the upper limit of the NMR time scale,
possible rearrangement paths were theoretically modꢀ
eled using density functional theory DFT B3LYP/6ꢀ
membered ring (
with the almost flat cycloheptatriene ring, is rather low
5.5 kcal/mol), which is consistent with the literature
data on unsubstituted cycloheptatriene [6]. The calcuꢀ
In agreement with the experimental data, the calꢀ lated barrier to the rotation of the phthalimido group in
culations demonstrate that the boat structure of conformation through TS is also low (4.5 kcal/mol)
cycloheptatrienylphthalimide, with the phthalimido (Scheme 2, Tables 1 and 2, Fig. 2). Such inversion and
1
→
5) through transition state (TS) 3,
(
3
1G** calculations [5].
1
4
DOKLADY CHEMISTRY Vol. 430
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2010

STRUCTURAL NONRIGIDITY OF
N
ꢀ(CYCLOHEPTATRIENYL)PHTHALIMIDE
13
Table 1. Total and relative energies of the ground state structures of cycloheptatrienylphthalimide in the gas phase and niꢀ
tromethane calculated by the B3LYP/6ꢀ31G** methoda
Δ
E
Δ
EZPE
Compound
Etotal, au
ω
, cm–1
1
kcal/mol
1
5
–783.4195
–783.4146
0
0
37
34
3.1
3.5
7
2
(see b)
(see b)
–783.4208
–783.3782
0
0
35
15
26.7
25.1
a
b
Etotal is the total energy, 1 au = 627.5095 kcal/mol; ΔEZPE is the relative energy with inclusion of the zeroꢀpoint energy; ω is the lowest harꢀ
1
monic vibrational frequency.
PCM, nitromethane.
rotation barriers point to the possibility of fast interconꢀ for migrations of the phthalimido group along the sevenꢀ
version of the conformers yielding the structure favorable membered ring perimeter.
O
H
*
H
O
O
Ring
inversion
N
N
H
N
O
H
O
O
1
TS 3
5
Rotation
H
O
O
N
N
O
*
O
TS 4
Scheme 2.
On the potential energy surface (PES) of conꢀ the cycloheptatriene ring with an energy barrier of
former in the gas phase, structure TS was localꢀ 30.2 kcal/mol (26.5 kcal/mol at the B3LYP/6ꢀ
ized for 1,7ꢀshifts of the phthalimido group along 311++G** level) (Scheme 3, Tables 1 and 2, Fig. 2).
5
6
O
1,7ꢀshift
O
N
O
–
O
7
N
O
N
1
H
7
1
7
O
+
1
H
5
TS 6
Scheme 3.
In the structure of zwitterionic TS 6, the cyclohepꢀ phthalimido group is at a distance of 2.499 Å from the
tatriene ring is almost planar, the nitrogen atom of the nearest carbon atoms of the sevenꢀmembered ring,
DOKLADY CHEMISTRY Vol. 430
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14
DUSHENKO et al.
Table 2. Total energies of the transition state structures and energy barrier to structural nonrigidity processes of cyclohepꢀ
tatrienylphthalimide in the gas phase and nitromethane calculated by the B3LYP/6ꢀ31G** methoda
≠
≠
≠
ΔEZPE
Δ
H
ΔG298
TS
Etotal, au
ω
, cm–1
kcal/mol
TS 3
TS 4
TS 6
–783.4111
–783.4122
–783.3636
5.5
4.5
5.1
3.8
6.0
5.8
49
22
30.2
(26.5b)
25.5
0.6
30.4
(26.8b)
25.8
0.2
28.3
(24.4b)
23.4
1.2
155
(142b)
(
–783.5599b)
–783.3773
–783.3768
TS 8 (see c)
TS 9 (see c)
53
35
a
b
c
See notes to Table 1 for designations; ω is the single imaginary harmonic vibrational frequency.
B3LYP/6ꢀ311++G**.
PCM, nitromethane.
and the overall charge of this group is –0.67
ing to the Mulliken population analysis). Analogous (the charge on the chlorine atom, –0.53
e
(accordꢀ structure of the zwitterionic TS of chlorine 1,7ꢀshifts
); therefore,
e
calculations for 1,7,7ꢀtrichlorocycloheptatriene [7] chlorine migrations occur contrary to the orbital symꢀ
showed that electrostatic interaction stabilizes the metry conservation rules. No TS structures correꢀ
O
C
C
O
C
C
C
C
C
C
C
C
C
N
C
C
N
C
C
C
1
.446
C
1.351
C
C
C
C
C
1.367
C
C
C
C
O
1.453
C
C
1
O
C
.
4
4
C
6
1
,
C1
3
, Cs (TS)
C
C
C
C
C
C
C
O
C
C
C
C
C
C
O
C
N
1
9
C
.4
C
C
1
N
C
C
C
C
1
C
O
1.370
C
C
6
C
C
C
C
C
.441
1.353
C
4,
Cs
(TS
)
, Cs (TS)
Fig. 2. Geometric parameters of the ground state structure of cycloheptatrienylphthalimide 1 and TSs of the processes of its steꢀ
reochemical and structural nonrigidity in the gas phase calculated by the DFT B3LYP/6ꢀ31G** method. Hereinafter, bond
lengths are in angstroms.
DOKLADY CHEMISTRY Vol. 430
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2010

STRUCTURAL NONRIGIDITY OF
N
ꢀ(CYCLOHEPTATRIENYL)PHTHALIMIDE
15
sponding to the 1,5ꢀ and 1,3ꢀsigmatropic shifts or to ido moiety (the overall charge on this group is –0.87e),
the ion dissociation mechanism for migrations of the long bonds between the carbon atoms of the ring and
N
ꢀphthalimido group in the gas phase were found on
the nitrogen atom of the phthalimide group (3.337 Å),
and large dipole moment ( = 11.2 D). The total
energy of structure is 4.9 kcal/mol lower than the
sum of the energies of the tropylium cation (Etotal
the PES of the molecule. Thus, the mechanism of 1,7ꢀ
shifts of the phthalimido group in the gas phase is the
borderline case between the sigmatropic rearrangeꢀ
ment and the rearrangement by the ion pair mechaꢀ
nism.
μ
2
=
=
⎯
270.75728 au) and the phthalimide anion (Etotal
⎯
512.61313 au) in nitromethane. The calculated actiꢀ
process through TS 8 in
nitromethane is 25.5 kcal/mol. Ion pair intermediate
undergoes very rapid topomerization (the calculated
The calculation using the polarizable continuum
vation barrier of the
7
→
2
model (PCM) revealed that compound
vents (nitromethane) rearranges through intermediꢀ
ate corresponding to a zwitterion structure. It forms
from ground state structure through TS 8 in which
the cleavage and formation of the C–N bond (phthalꢀ
imido group–sevenꢀmembered ring) occurs at the
same carbon atom (the
Tables 1 and 2, Fig. 3). Zwitterion structure
acterized by almost complete charge separation tions of the phthalimido group by the ion pair mechaꢀ
between the sevenꢀmembered ring and the phthalimꢀ nism should have a random character.
1 in polar solꢀ
2
2
≠
≠
7
energy barrier ΔEZPE = 0.6 kcal/mol, ΔG298 K
.2 kcal/mol) due to sliding of the phthalimide anion
over the sevenꢀmembered ring plane through TS 9 of
symmetry Cs (the ꢀtype shift); therefore, migraꢀ
=
1
σ,
πꢀtype shift) (Scheme 4,
π,π
2
is charꢀ
O
O
O
–
N
N
N
7
1
O
O
O
1
H
1
7
7
H
+
7
TS 8
2
O
O
N
–
1
7
+
O
TS 9 (Cs)
O
O
N
1
–
H
N
N
O
H 1
O
O
7
1
7
7
+
Scheme 4.
The calculated energy barriers to migration of the
phthalimido group in nitromethane are consistent
with the experimental value in deuterated nitrobenꢀ
≠
EXPERIMENTAL
1
Experimental and computational methods. The H
and 1 C NMR spectra were recorded on Bruker AM
3
1
zene (ΔG180°C = 25.1 kcal/mol), which is evidence in
favor of the dissociation–recombination mechanism and 75.47 ( C) MHz. TMS was used as the internal
with intermediate formation of tropylium cation– reference. Deuterated solvents were dried over calꢀ
and Varian Unity spectrometers operating at 300 ( H)
13
phthalimide anion zwitterion
2.
cined molecular sieves. The IR spectra were recorded
DOKLADY CHEMISTRY Vol. 430
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2010

16
DUSHENKO et al.
C
C
C
C
O
C
C
C
C
C
C
C
C
1
.
3
6
O
C
O
N
8
C
C
C
N
1.349
C
C
C
C
O
C
C
1.356
C
C
C
C
C
C
C
C
7,
C1
8, C1 (TS)
C
C
C
C
C
C
O
C
C
N
O
3.337
1.403
1.388
1
.389
C
C
C
C
1.402
C
1.402
C
C
1.403
1.388
2
, C1
Fig. 3. Geometric parameters of the covalent (
7) and ionic (2) structure of cycloheptatrienylphthalimide and TS 8 of ionization–
recombination in nitromethane calculated by the DFT B3LYP/6ꢀ31G** method.
as mineral oil mulls on a Specord IRꢀ75 spectrophoꢀ (5 mmol) in 20 mL of dry acetonitrile at 20 C, a soluꢀ
°
tometer. The EI mass spectra (70 eV) were recorded on tion of 5 mmol of potassium phthalimide in 20 mL of
an HP 5995A mass spectrometer with direct sample
injection.
dry acetonitrile was added dropwise. The mixture was
refluxed with stirring for 15 min. The resulting precipꢀ
Quantumꢀchemical calculations were performed itate of KBF4 was filtered off. The solvent was removed
using the Gaussian 03 program package by the DFT
method [5] with the threeꢀparameter potential B3LYP
and the 6ꢀ31G** splitꢀvalence basis set. All stationary
points were identified by calculation of the Hessian
matrix.
in vacuo. The residue was recrystallized two times
from acetonitrile with hot filtration. The yield of
1 as
colorless crystals with mp 175–176 C was 1.08 g
°
(
91%).
Quantumꢀchemical calculations were performed
with the use of facilities of the supercomputer center of
the Institute of Physical and Organic chemistry,
Southern Federal University.
1
H NMR (300 MHz, CDCl ), , ppm: 4.48 (tt, 1H,
δ
3
3J1,7 = 5.10 Hz, 4J2,7 = 1.66 Hz, Hꢀ7), 5.53 (m, 2H,
3J1,2 = 9.01 Hz, 4J1,3 = 0.68 Hz, Hꢀ1,6), 5.96 (m, 2H,
3J2,3= 3.66 Hz, Hꢀ2,5), 6.44 (m, 2H, Hꢀ3,5), 6.93–
Synthesis of Nꢀ(1,3,5ꢀcycloheptatrienꢀ7ꢀyl)phthalꢀ
imide (1). To a solution of tropylium tetrafluoroborate 7.47 (m, 4H, Ar).
DOKLADY CHEMISTRY Vol. 430
Part 1
2010

STRUCTURAL NONRIGIDITY OF
N
ꢀ(CYCLOHEPTATRIENYL)PHTHALIMIDE
17
1
3
C NMR (75.47 MHz, CDCl ),
δ
, ppm: 50.31
ACKNOWLEDGMENTS
This work was supported by the Ministry of Educaꢀ
3
(
1
1
Cꢀ7), 123.14 (Cꢀ1,6), 123.71 (Cꢀ2,5), 124.08 (Cꢀ3,4),
31.50 (Cꢀ10,13), 132.51 (Cꢀ9,14), 133.64 (Cꢀ11,12), tion and Science (Russian National Program project
67.55 (Cꢀ8,15).
nos. 2.2.1.1.2348 and 2.1.1.2371) and the Council for
Grants of the President of the Russian Federation for
For C H NO anal. calcd. (%): C, 75.94; H, 4.67; Support of Leading Scientific Schools (grant no.
15
11
2
NShꢀ363.2008.3).
N, 5.90. Found (%): C, 75.88; H, 4.58; N, 5.98.
–1
IR (mineral oil),
ν
, cm : 1760, 1710 (C=O), 1620,
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[
(
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7 7 7 6 6 6
+
+
+
C H ] , 76 (88.7) [C H ] , 65 (17.0) [C H ] , 50
6
5
6
4
5
5
7
+
+
+
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4
2
3
3
2
DOKLADY CHEMISTRY Vol. 430
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2010