Palladium-catalyzed annulation of 9-halophenanthrenes with alkynes: Synthesis, structural analysis, and properties of acephenanthrylene-based derivatives

Article abstract of DOI:10.1002/chem.201405763

The palladium-catalyzed annulation of 9-bromoand 9-chlorophenanthrenes with alkynes gave 4,5-disubstituted acephenanthrylenes in yields of 58-95% (9 examples). Asymmetric alkynes, such as 1-phenyl-1-propyne, 1-phenyl-1-hexyne, and 1-cyclopropyl-2-phenylethyne, regioselectively form (cyclo)alkyl-substituted products, following the regular rule that governs the carbopalladation of alkynes. This synthetic protocol can also be utilized in annulations with several p-extended bromoarenes, such as 7-bromo[5]helicene, 5-bromo[4]helicene, 9-bromoanthracene, 3-bromoperylene, and 3-bromofluoranthene, to give the corresponding annulated products in moderate to good yields (51-86%; 6 examples). Similarly, bromocorannulene produced highly curved 1,2-disubstituted cyclopentacorannulenes. Reactions of 6,12-dibromochrysene and 4,7-dibromo[4]helicene with di(4-tolyl) ethyne provided the twofold annulated products in moderate yields. 4,5-Diphenylacephenanthrylene and 6,7-diphenylbenzo[ a]acephenanthrylene thus generated were converted into phenanthro[9,10-e]acephenanthrylene and benzo[ a]phenanthro[9,10-e]acephenanthrylene, respectively, by oxidative cyclodehydrogenation. The structures of 4,5-diphenylacephenanthrylene, 4,5-diphenyldibenzo[a,l]acephenanthrylene, 1,2-diarylcyclopentacorannulenes, and benzo[ a]-phenanthro[9,10-e]acephenanthrylene were verified by X-ray crystallography. The photophysical and electrochemical properties of the selected annulated products were investigated.

Full text of DOI:10.1002/chem.201405763

DOI: 10.1002/chem.201405763
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Macrocycles |Hot Paper|
Palladium-Catalyzed Annulation of 9-Halophenanthrenes with
Alkynes: Synthesis, Structural Analysis, and Properties of
Acephenanthrylene-Based Derivatives**
En-Chih Liu, Min-Kuan Chen, Jen-Yi Li, and Yao-Ting Wu*[a]
Abstract: The palladium-catalyzed annulation of 9-bromo-
and 9-chlorophenanthrenes with alkynes gave 4,5-disubsti-
tuted acephenanthrylenes in 58–95% yield (9 examples).
Asymmetric alkynes, such as 1-phenyl-1-propyne, 1-phenyl-
1-hexyne, and 1-cyclopropyl-2-phenylethyne, regioselectively
form (cyclo)alkyl-substituted products, following the regular
rule that governs the carbopalladation of alkynes. This syn-
thetic protocol can also be utilized in annulations with sever-
al p-extended bromoarenes, such as 7-bromo[5]helicene, 5-
bromo[4]helicene, 9-bromoanthracene, 3-bromoperylene,
and 3-bromofluoranthene, to give the corresponding annu-
lated products in moderate to good yields (51–86%; 6 exam-
ples). Similarly, bromocorannulene produced highly curved
1,2-disubstituted cyclopentacorannulenes. Reactions of 6,12-
dibromochrysene and 4,7-dibromo[4]helicene with di(4-tol-
yl)ethyne provided the twofold annulated products in mod-
erate yields. 4,5-Diphenylacephenanthrylene and 6,7-diphe-
nylbenzo[a]acephenanthrylene thus generated were con-
verted into phenanthro[9,10-e]acephenanthrylene and ben-
zo[a]phenanthro[9,10-e]acephenanthrylene, respectively, by
oxidative cyclodehydrogenation. The structures of 4,5-diphe-
nylacephenanthrylene, 4,5-diphenyldibenzo[a,l]acephenan-
thrylene, 1,2-diarylcyclopentacorannulenes, and benzo[a]-
phenanthro[9,10-e]acephenanthrylene were verified by X-ray
crystallography. The photophysical and electrochemical
properties of the selected annulated products were investi-
gated.
ing materials.[5] A metal-catalyzed reaction for the formation of
carbon–carbon bonds may provide an efficient means of over-
coming these issues.[6] The formal [3+2] annulation of a haloar-
ene with an alkyne is effective for enlarging existing aromatic
systems in the synthesis of cyclopentene-fused PAHs. This syn-
thetic strategy has been utilized in the preparation of acenaph-
thylenes,[7] aceanthrylenes,[8] cyclopenta[cd]pyrenes, and
Introduction
The chemical and physical properties of cyclopentene-fused
polycyclic aromatic hydrocarbons (PAHs), in which a five-mem-
bered ring cannot exhibit aromaticity associated with a Kekulꢀ
structure, differ from those of standard benzenoid PAHs.[1] Ace-
naphthylene is the simplest of this class of compounds, and it
has been extensively studied.[2] In contrast, the chemistry of
the two next higher-order benzo derivatives, aceanthrylene
and acephenanthrylene, is largely unknown. This relative lack
of investigations arises mainly from the poor availability of the
compound. The main methods for the preparation of acephe-
nanthrylene include high-temperature flash vacuum pyrolysis
(FVP)[3] or solution-phase synthesis with Friedel–Crafts cycliza-
tion as a key step.[4] The required conditions for FVP considera-
bly limit the range of functional groups, and cause thermal re-
arrangement of the molecular framework[3] owing to the low
stability of acephenanthrylene.[5] The solution-phase synthesis
requires many steps that involve commercially available start-
others.[9] However, established palladium-catalyzed protocols
cannot be used to synthesize acephenanthrylene efficiently.[9]
According to Euler’s rule[10] and the results of experimental
investigations,[11] the cyclopentene annulation of corannulene,
which is the elementary bowl-shaped fragment of fullerene, in-
creases its curvature. Highly curved bowl-shaped polyarenes
(so-called buckybowls) have a high inherent strain, so their
preparation is challenging. This study presents a general proto-
col for synthesizing various planar, twisted, and bowl-shaped
acephenanthrylene-based PAHs. The structures and properties
of the prepared products were elucidated.
[a] E.-C. Liu, M.-K. Chen, J.-Y. Li, Prof. Y.-T. Wu
Department of Chemistry, National Cheng Kung University
No.1 Ta-Hsueh Road, 70101 Tainan (Taiwan)
E-mail: ytwuchem@mail.ncku.edu.tw
[**] Metal-Catalyzed Reactions of Alkynes. Part XVII. For Part XVI see: Y.-C.
Hsieh, H.-Y. Fang, Y.-T. Chen, R. Yang, C.-I. Yang, P.-T. Chou, M.-Y. Kuo, Y.-T.
Wu, Angew. Chem. Int. Ed. 2015, DOI: 10.1002/anie.201410316.
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201405763.
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products 3 were obtained in
moderate to excellent yields
(Table 2, entries 1–10). Generally,
diarylacetylenes provided better
results than (cyclo)alkyl-substi-
tuted alkynes. Asymmetric al-
kynes, such as 1-phenyl-1-pro-
pyne (2 f), 1-phenyl-1-hexyne
(2g), and 1-cyclopropyl-2-phe-
nylethyne (2h), regioselectively
formed 3 f, 3g, and 3h, respec-
tively (Table 2, entries 8–10).
Their structures were confirmed
by using 2D NMR spectroscopy
techniques (see the Supporting
Information). The regioselectivi-
ty is consistent with the regular
rule that governs the carbopal-
ladation of alkynes.[12] Unlike in
the other examples, compounds
2g and 2h can only be added
to the reaction mixture by
Table 1. Optimization of reaction conditions for the preparation of 4,5-diphenylacephenanthrylene 3a.[a]
Catalyst
[mol%]
Solvent
Base
Additive
([equiv])
Conversion
[%]
Ratio of
1-H/3a/4a
Yield
[%][b]
1
2
3
4
5
6
7
8
[PdCl2(PCy3)2] (10)
Pd(OAc)2 (10)
Pd(OAc)2 (10)
Pd(OAc)2 (10)
Pd(OAc)2 (10)
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
NMP
CH3CN
DMF
dioxane
dioxane
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
DBU
NEt3
K2CO3
DBU
DBU
DBU
DBU
NEt3
DBU
–
73
100
100
100
100
100
42
100
100
100
100
100
100
100
100
100
100
92:8:0
–
–
–
–
–
–
–
–
–
–
–
–
89
–
–
–
85
IPr·HCl (0.2)
P(o-tol)3 (0.2)
BINAP (0.1)
dppm (0.1)
dppe (0.1)
–
PPh3 (0.2)
–
–
63:37:0
12:88:0
25:75:0
20:80:0
27:72:1
18:73:9
6:78:16
3:73:21
33:50:17
100:0:0
8:85:7
2:96:2
62:38:0
5:95:0
23:14:63
2:98:0
Pd(OAc)2 (10)
[PdCl2(PPh3)2] (10)
[PdCl2(PPh3)2] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (10)
[PdCl2(dppf)] (5)
9
10
11
12
13
14
15
16
17
–
CsOPiv[c]
CsOPiv (1.1)
CsOPiv (1.1)
CsOPiv (1.1)
–
CsOPiv (1.1)
using
a syringe pump over
a period of 5 h to suppress the
formation of the corresponding
triphenylenes 4. Rather than an-
nulation, 1,2-bis(trimethylsilyl)-
ethyne (2i) underwent Sonoga-
shira couplings to give di(9-phe-
nanthyl)ethyne. When catalyst
[PdCl2(dppf)] was replaced with
[PdCl2(PCy3)2] (Method C), 9-
[a] A mixture of 9-bromophenanthrene (1-Br, 0.25 mmol), alkyne 2a (1.2 equiv), base (3.0 equiv), and a solvent
(1 mL) in a sealed tube was heated for 24 h. The conversion of 1-Br and the ratio of the compounds was deter-
mined by GC–MS. Cy=cyclohexyl, NMP=N-methylpyrrolidone, DBU=1,5-diazabicyclo[5.4.0]undec-5-ene,
BINAP=2,2’-bis(diphenylphosphino)-1,1’-binaphthyl,
dppm=1,1-bis(diphenylphosphino)methane, dppf=1,1’-bis(diphenylphosphino)ferrocene,
tol=tolyl,
dppe=1,2-bis(diphenylphosphino)ethane,
Piv=pivaloyl.
[b] Yields are given of products isolated after the reaction. [c] CsOPiv was prepared in situ by using Cs2CO3
(0.55 equiv) and PivOH (1.1 equiv).
Results and Discussion
chlorophenanthrene (1-Cl) could be applied in the annulation,
but the products were obtained in slightly lower yields than
those generated by Method B (Table 2, entries 2 and 5). The
palladium-catalyzed annulations of several p-extended bro-
moarenes, including 7-bromo[5]helicene (5), 5-bromo[4]heli-
cene (7), 9-bromoanthrene (9), 3-bromoperylene (11), and 3-
bromofluoranthene (13), with 2a produced the corresponding
annulated products in moderate to good yields (45–86%;
Table 2, entries 12–16, and Scheme 1). In the synthesis of
Heating 9-bromophenanthrene (1-Br) with diphenylacetylene
(2a) and a palladium catalyst generated a mixture of debromi-
nated phenanthrene 1-H, 4,5-diphenylacephenanthrylene 3a,
and triphenylene 4a (Table 1). The palladium catalyst, ligand,
solvent, base and additive all have critical roles in this reaction.
Catalyst [PdCl2(dppf)] was found to be superior to
[PdCl2(PCy3)2], [PdCl2(PPh3)2], and the other catalytic systems
presented in Table 1 in suppressing the formation of phenan-
threne (1-H; Table 1, entries 1–9). DBU appeared to outperform
other bases, such as K2CO3 and NEt3, in the selective genera-
tion of 3a (Table 1, entries 9–11). The additive CsOPiv strongly
reduced the amount of 4a (Table 1, entries 9 and 13–15), and
provided a better result than a combination of Cs2CO3 and
PivOH (Table 1, entry 12). The reaction was performed with
acetonitrile, NMP, or DMF as the solvent, and the last two were
observed to improve the debromination of the starting materi-
al (Table 1, entries 13–15). Under the optimal conditions, the
desired product 3a was obtained in 89% yield (Method A;
Table 1, entry 13). Notably, the reaction conducted in dioxane
with a lower catalyst loading (5 mol%) also gave a satisfactory
result (Method B; Table 1, entry 17).
Scheme 1. Annulations of bromo[4]helicenes with diphenylethyne. The
1
ratios were determined according to the H NMR spectrum.
naphth[1,2-a]acephenanthrylene 6a, Method B is more effi-
cient than Method A, and requires less catalyst loading
(Table 2, entry 12). Regioisomeric bromo[4]helicenes 7 and 17
exhibited different reactivities in annulation. When a mixture
of 7 and 17 (ratio 37:63) was heated with 2a under the opti-
The reactivity of alkynes 2 in annulation was examined by
using 1-Br under conditions of Method A and/or B, and most
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Presumably, the highly curved
structure was responsible for
the unsatisfactory results.[11] The
bowl-to-bowl inversion barrier
(DG°inv) for the parent cyclopen-
tacorannulene was theoretically
predicted to be 27.7–30.9 kcal
molÀ1).[14] In both the 1H and
13C NMR spectra, the signals for
the two methyl and isopropyl
groups in 16e and 16j, respec-
tively, are identical, although
they are diastereotopic. Annu-
lated products 10a, 12a, and
14a, which are not acephenan-
thrylene-based derivatives, were
prepared from bromoarenes 9,
11, and 13, respectively, in mod-
erate yields (Table 2, entries 14–
16). As reported in the litera-
ture, compounds 10a and 12a
were generated in 76 and 30%
yields, respectively, by using
a catalytic system that com-
Table 2. Preparation of cyclopentene-fused PAHs.[a]
ArÀX
Alkyne
Product
Method (Yield [%])
1
2
3
4
5
6
7
8
1-Br
1-Cl
1-Br
1-Br
1-Cl
1-Br
1-Br
1-Br
1-Br
1-Br
1-Br
2a (R1 =R2 =Ph)
2a
3a
3a
3b
3c
3d
3d
3e
3 f
3g
3h
3i
A (89), B (85, 82[b]
C (79)
)
2b (R1 =R2 =4-CH3-C6H4)
2c (R1 =R2 =4-OCH3-C6H4)
2d (R1 =R2 =3-CF3-C6H4)
2d (R1 =R2 =3-CF3-C6H4)
2e [R1 =R2 =3,5-C6H3(CH3)2]
2 f (R1 =Me, R2 =Ph)
2g (R1 =nBu, R2 =Ph)
2h (R1 =cPr, R2 =Ph)
2i (R1 =R2 =SiMe3)
A (93)
A (81), B (63)
C (61)
A (95)
A (70)
A (89), B (53)
A (73)[c]
A (58)[c]
A (0)[d]
9
10
11
12
2a (R1 =R2 =Ph)
A (58), B (76)
13
14
2a (R1 =R2 =Ph)
2a (R1 =R2 =Ph)
B (86)
prised
Pd(dba)2
(10 mol%;
A (45), B (69)[e]
dba=dibenzylideneacetone)
and P(o-tol)3 (15 mol%) under
highly dilute conditions (ca.
10À2 m) in toluene.[9] One ad-
vantage of our protocol is a re-
duction in the amounts of sol-
vents used.
15
16
2a (R1 =R2 =Ph)
2a (R1 =R2 =Ph)
A (51)
B (51)[f]
The synthetic method devel-
oped herein was also utilized in
twofold annulations of dibro-
moarenes (Scheme 2). The reac-
tion of 6,12-dibromochrysene
(19) with di(4-tolyl)acetylene
(2b) generated cyclopenta[hi]-
chrysene 20b and dicyclopen-
ta[hi,qr]chrysene 21b in 10 and
50% yields, respectively. Similar-
ly, benzo[l]acephenanthrylene
8b and 23b were prepared by
the annulation of dibromo[4]he-
licene 22 with 2b. Notably, al-
though both 21b and 23b con-
17
18
19
15
15
15
2b (R1 =R2 =4-CH3-C6H4)
2e [R1 =R2 =3,5-C6H3(CH3)2]
2j [R1 =R2 =3,5-C6(iPr)2H3]
16b
16e
16j
B (32)[f]
B (31)[f]
B (44)[f]
[a] Reaction conditions: Method A: [PdCl2(dppf)] (10 mol%), bromoarene (0.25 mmol), alkyne (1.2 equiv), DBU
(3 equiv), CsOPiv (1.1 equiv), NMP, 1308C, 24 h. Method B: [PdCl2(dppf)] (5 mol%), bromoarene (0.25 mmol),
alkyne (1.2 equiv), DBU (3 equiv), CsOPiv (1.1 equiv), dioxane, 1308C, 24 h. Method C: [PdCl2(PCy3)2] (5 mol%),
9-chlorophenanthrene (1-Cl; 0.25 mmol), alkyne (1.2 equiv), DBU (3 equiv), CsOPiv (1.1 equiv), anisole, 1508C,
36 h. [b] The reaction was conducted with 1.50 mmol of 1-Br. [c] Alkyne (1.5 equiv) was slowly added within
5 h by using a syringe pump. [d] Di(9-phenanthyl)ethyne was obtained. [e] The reaction was conducted in diox-
ane in the absence of CsOPiv. [f] Reaction was conducted with 0.2 equivalents of CsOPiv.
mal conditions (Method B), compounds 8a and 18a (ratio
55:45) were obtained in a total yield of 74%; this reveals the
higher reaction efficiency of 7 (Scheme 1). Compounds 8a and
18a cannot be separated by column chromatography. Both
compounds were obtained in pure form by recrystallization of
the mixture. The high reactivity of 7 is also verified by the high
yield of 8a (86%; Table 2, entry 13). Unlike in the examples de-
scribed above, 1,2-diaryl-substituted cyclopentacorannulenes
16b, 16e, and 16j were acquired in yields of 31–44%, which
are much lower than those of the other examples in Table 2.[13]
tain four 4-tolyl groups, their solubility in common organic sol-
vents is poor.
4,5-Diphenylacephenanthrylene (3a) was converted into
phenanthro[9,10-e]acephenanthrylene (24a) in 72% yield by
oxidative cyclodehydrogenation (Scheme 3).[15] The low solubil-
ity of 24a in common organic solvents was probably responsi-
ble for the low yield because some of the material was irrever-
sibly lost during chromatography. It has been reported that
the AlCl3-mediated cyclodimerization of phenanthrene easily
generates a mixture of 24a and dibenzo[fg,qr]pentacene in
Chem. Eur. J. 2015, 21, 1 – 8
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Figure 1. Molecular structures of 3a (a) and 6a (b). Only carbon atoms are
shown for clarity, the thermal ellipsoids are set at the 30% probability level.
Scheme 2. Twofold annulations of dibromoarenes 21 and 23.
a solution in benzene. Cyclopentene annulation caused the
phenanthrene moiety in 3a to be slightly more twisted than
the parent phenanthrene,[18] as revealed by a comparison of
the dihedral angles between rings A and C (4.5 vs. 2.48). Al-
though the shortest intermolecular carbon–carbon distance
was determined to be 3.33 ꢂ, p–p stacking in 3a could be
negligible.
The helical structure of 6a was analyzed by X-ray crystallog-
raphy. The dihedral angle between the extremities (rings D and
H) and the torsion angle measured for bay carbon atoms II–III–
IV–V were determined to be 42.8 and 27.78, respectively. The
nonbonded contact between carbon atoms I and VI was found
to be 2.96 ꢂ. These structural data of the [5]helicene moiety
described above are very similar to those of 3,12-disubstituted
[5]helicenes 27 (Table 4).[19] Therefore, cyclopentene annulation
does not significantly alter the structure of the [5]helicene frag-
ment. Molecules of 6a lack p–p stacking.
Scheme 3. The Scholl reaction of 3a and 18a. DDQ=2,3-dichloro-5,6-dicya-
no-1,4-benzoquinone.
a ratio of approximately 7:3, but the purification of the former
requires many steps.[16] An attempt was made to close both
the six- and the five-membered rings in 18a, but only ben-
zo[a]phenanthro[9,10-e]acephenanthrylene (25a) was ob-
tained.
Table 4. Structural data of [5]helicene derivatives.
6a
2.96
27.7
42.8
27-Cl
27-Ph
Single crystals of 3a, 6a, 16j, and 25a for X-ray crystallo-
graphic analysis were grown by the diffusion of MeOH into sol-
utions of the compounds in CH2Cl2 at room temperature
(Table 3 and Figure 1).[17] Unlike in the examples above, single
crystals of 16b were acquired by the diffusion of MeOH into
distance (I···VI) [ꢂ]
torsion angle (II-III-IV-V) [8]
dihedral angle (rings D/H) [8]
ref.
2.93
29.5
49.9
[19]
2.90
26.7
42.8
[19]
this work
In the solid state, two molecules of 16b and two
benzene solvent molecules form two asymmetric
units. The two species of molecules 16b have very
similar structural data. The p-orbital axis vector
(POAV) pyramidalization angle is a useful metric of
buckybowl curvature: its values for planar benzene
and C60 are 0 and 11.68, respectively.[20] As presented
in Table 5, the POAV pyramidalization angle is high-
est at the hub carbon atoms of a corannulene core,
at which it is 11.28. This value exceeds the corre-
sponding value for corannulene (8.28). The bowl
depth of the corannulene fragment in 16b was de-
termined as 1.10 ꢂ, which also exceeds that of coran-
nulene (0.87 ꢂ). Molecules of 16b cannot form col-
umnar stacks (Figure 2). The important interaction
was the CH/p interaction, for which the distance be-
tween the center of a corannulenyl benzenoid and
Table 3. Crystal structure data for 3a, 6a, 16b, 16j, and 25a.
3a
6a
16b
16j
25a
CCDC no.
formula
Mr
1022047
C28H18
354.42
100(2)
1022048
C36H33
454.54
100(2)
1022049
C36H22·C6H6 C46H42
532.64
100(2)
1022050
1022051
C32H18
402.46
100(2)
orthorhombic
Pccn
594.79
100(2)
T [K]
crystal system triclinic
orthorhombic monoclinic triclinic
¯
¯
space group
Z
P1
2
Pbca
8
P21/c
8
P1
2
4
a [ꢀ]
b [ꢀ]
c [ꢀ]
7.2764(4)
10.6347(5) 16.5090(10)
12.1668(6) 17.9379(9)
15.9909(10)
19.9061(17) 10.4145(7) 3.8982(4)
16.3419(13) 11.8605(6) 18.1566(17)
17.9187(15) 13.8603(9) 26.409(2)
a [8]
b [8]
g [8]
83.123(2)
79.033(2)
74.640(2)8 90
644.72(14) 4735.5(5)
4.82
90
90
90
77.237(3)
76.768(3
83.744(3)
1622.33(17) 1869.2(3)
4.71 3.67
90
90
90
105.902(2)
90
5605.9(8)
5.62
V [ꢂ3]
R factor [%]
4.12
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Table 5. Structural data of cyclopentacorannulene derivatives.[a]
Parent[b]
16b
16j
POAV [8]
(atoms 1, 2, 3)
bowl depth [ꢂ]
9.3, 10.0, 10.9
9.7, 10.2, 11.0
9.7, 10.3, 11.2
1.08, 1.10 [1.08]
9.7, 10.3, 11.5
1.06 [1.08]
1.11 [1.08]
bond length [ꢂ]
a
b
c
1.344 [1.361]
1.374 [1.395]
1.467 [1.487]
1.388 [1.370]
1.353, 1.360 [1.361]
1.392, 1.387 [1.397]
1.493, 1.493 [1.498]
1.381,1.382 [1.391]
1.352 [1.361]
1.386 [1.396]
1.491 [1.498]
1.379 [1.390]
d
[a] The values were obtained by averaging the symmetry-related data.
The optimized structures at the B3LYP/cc-pVDZ level are shown in brack-
ets. Bowl depths determined from the corannulene core. [b] Ref. [14b].
Figure 3. Crystal packing in 16j. Only carbon atoms are shown for clarity;
the thermal ellipsoids are set at 30% probability.
a hydrogen of benzene was 2.88 ꢂ. This value is slightly shorter
than the sum of the van der Waals radii of the corresponding
atoms (2.90 ꢂ).[21]
16b>parent compound, as verified by both the maximum
POAV angle and bowl depth of the corannulenyl fragment. The
lengths of some of the bonds in 16b/16j significantly differed
from those in the parent cyclopentacorannulene, as summar-
ized in Table 5. To gain an insight into these structural differen-
ces, the optimized structures for three compounds were ob-
tained by using DFT at the B3LYP/cc-pVDZ level. In contrast to
the parent cyclopentacorannulene, the results for 16b and 16j
agree more closely with crystallographic analysis. The signifi-
cant structural derivation of the parent compound should be
caused by the crystal packing and/or quasi-bowl-in-bowl
stacks.
Figure 2. Crystal packing in 16b. Only carbon atoms are shown for clarity;
the thermal ellipsoids are set at the 30% probability level.
Compound 25a is not planar, as confirmed by X-ray analysis
(Figure 4). The dihedral angle between the extremities (rings I
and L) and the torsion angle measured for bay carbon atoms
VII-VIII-IX-X were determined to be 23.8 and 26.38, respectively.
The nonbonded contact between carbon atoms VII and X was
found to be 2.96 ꢂ. The p–p stacks were observed in crystals
of 25a. The molecules in each stack are slightly slipped from
the stacking axis. Therefore, the separation between two
neighboring molecules is 3.90 ꢂ, but the shortest distance be-
tween any two closed carbon atoms is 3.44 ꢂ.
X-ray crystallography revealed that the maximum POAV
angle and the bowl depth of the corannulene fragment in 16j
were 11.58 and 1.11 ꢂ, respectively. The former value is very
close to that of C60. All molecules of 16j, with concave faces,
formed a “dimer” pair through CH/p interactions between iso-
propyl hydrogen and corannulene carbon atoms, and the
short contact distances for these interactions were determined
to be 2.84–2.89 ꢂ (Figure 3). The distance between a methyl
carbon atom and the center of the corannulenyl five-mem-
bered ring is 3.42 ꢂ.
A significant difference between the parent[14b] and diaryl-
substituted cyclopentacorannulenes 16 is in the molecular
packing. Unlike 16b/16j, all bowl molecules of the unsubsti-
tuted cyclopentacorannulene form quasi-bowl-in-bowl stacks,
but crystals are apolar because half of the columns are orient-
ed in opposite directions. Additionally, the curvature of the
three cyclopentacorannulenes follows the order of 16j>
The photoabsorption properties of selected compounds in
CH2Cl2 (10 mm) at room temperature were studied (Table 6 and
the Supporting Information), and they were found to be
strongly influenced by the aromatic p system in the backbone.
The cyclopentene annulation redshifts lmax. For example, phen-
Figure 4. Illustration of the molecular structure (a) and crystal packing (b) in
25a. Only carbon atoms are shown for clarity; the thermal ellipsoids are set
at the 30% probability level.
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derivatives have not been determined experimentally, the
preparation and chiral resolution of suitable compounds are
underway to study the inversion dynamics. In light of the
good reactivity of 1-Cl in annulation, this synthetic protocol
opens up a possible route to construct the highly curved
buckybowl 28 (C30R10)[25] from 1,3,5,7,9-pentachlorocorannu-
lene.
Table 6. Physical properties of the cyclopentene-annulated products.[a]
ox
1=2
red
Compound
labs [nm]
E
[V]
E
[V]
1=2
1
2
3
4
5
6
7
8
9
3a
6a
8a
14a
16j
18a
20b
21b
23b
24a
357, 376, 411 (sh)
360, 402, 426
377, 396, 450 (sh)
390, 410
349, 477 (sh)
388, 409
369, 381, 439 (sh)
388, 410, 476 (sh)
338, 354, 421 (sh)
344, 379, 397, 464 (sh)
1.11
1.03
1.08
0.93, 1.27
0.90
1.06
0.95
0.94
0.94
–
–
–
À1.54
–
–
–
–
–
–
Experimental Section
General procedures for the Pd-catalyzed annulation of
a haloarene with an alkyne
10
1.15
[a] Photophysical properties were measured at a concentration of about
10À5 m in CH2Cl2, and absorption bands over l=340 nm are listed. Redox
properties were investigated with compounds (concentration ca. 10À3 m)
Method A:
A
mixture of bromoarene (0.25 mmol), alkyne
(0.30 mmol), [PdCl2(dppf)]·CH2Cl2 (20.4 mg, 25.0 mmol, 10 mmol%),
DBU (114 mg, 0.75 mmol), CsOPiv (65.5 mg, 0.28 mmol), and NMP
(1 mL) in a thick-walled Pyrex tube was purged with nitrogen for
5 min. The sealed tube was kept in an oil bath at 1308C for 24 h.
After cooling to room temperature, the suspension was filtered
through a 3 cm thick layer of Celite. The Celite was rinsed well
with CH2Cl2 (40 mL). The solution was washed with 2n HCl (3ꢃ
10 mL), and dried over MgSO4. The solvent of the filtrate was re-
moved under reduced pressure, and the residue was subjected to
chromatography on silica gel.
in background electrolyte solution of 0.1m tetrabutylammonium hexa-
red
fluorophosphate (TBAPF6) in CH2Cl2. Eo1=x2 and E are half-wave potentials
1=2
of the oxidative and reductive waves, respectively, with potentials versus
the ferrocene (Fc/Fc+) couple.
anthrene does not exhibit any significant absorption bands at
wavelengths of greater than l=300 nm,[22] whereas 3a exhib-
its strong absorptions at l=376 and 411 nm (Table 6, entry 1).
Results concerning corannulene/cyclopentacorannulene 16j
(l=320[23] vs. 349 nm) and monoannulated 20b/bisannulated
21b (l=439 vs. 477 nm) also support this conclusion (Table 6,
entries 5, 7, and 8). In contrast to 3a, the oxidative cyclodehy-
drogenation product 24a has a bathochromic shift of lmax
(Table 6, entries 1 and 10).
Method B: Similar to Method A, but the reaction was conducted
with 1,4-dioxane (1 mL) and less [PdCl2(dppf)]·CH2Cl2 (10.2 mg,
12.5mmol, 5 mmol%).
Method C: Similar to Method A, but the reaction was conducted
with chloroarene (0.25 mmol), [PdCl2(PCy3)2] (9.2 mg, 25.0mmol,
10 mmol%) and anisole (1 mL) at 1508C for 36 h.
The redox properties of selected annulated products were
characterized by cyclic voltammetry, and the results are shown
in Table 6. The oxidation waves of all compounds are observed,
but only 14a exhibits a reversible reduction signal (Table 6,
entry 4). All oxidation signals are irreversible,[24] which indicates
the low thermodynamic stability of these cationic species.
Compounds 24a (1.15 V vs. Fc/Fc+) and 16j (0.90 V) have the
highest and lowest oxidation potentials, respectively (Table 6,
entries 5 and 10). The oxidation potential of the annulated
products is not very sensitive to the aromatic p system in the
backbone, as revealed by the following three examples. The
members of each pair of compounds, annulated [4]- and
[5]helicenes 8a/6a (1.08 vs. 1.03 V), mono- and bisannulated
chrysenes 20b/21b (0.95 vs. 0.94 V), and 3a and its cyclization
product 24a (1.11 vs. 1.15 V), have very similar oxidation po-
tentials (Table 6, entries 1–3, 7, 8, and 10). The oxidation poten-
tials for isomers 8a/18a and 21b/23b are (almost) identical
(Table 6, entries 3, 6, 8, and 9).
Acknowledgements
This work was supported by the Ministry of Science and Tech-
nology of Taiwan (NSC 101-2628M-006-002-MY3). We also
thank Prof. Sue-Lein Wang and Pei-Lin Chen (National Tsing-
Hua University, Taiwan) for the X-ray structure analyses.
Keywords: alkynes · annulation · macrocycles · palladium ·
synthesis design
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We developed a simple method for synthesizing acephenan-
thrylene-based derivatives, including 1,2-disubstituted cyclo-
pentacorannulenes, by the palladium-catalyzed annulation of
9-halophenanthrenes with alkynes. The diaryl-substituted ace-
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the bowl-to-bowl inversion barriers to cyclopentacorannulene
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Received: October 21, 2014
Published online on && &&, 0000
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FULL PAPER
&
Macrocycles
E.-C. Liu, M.-K. Chen, J.-Y. Li, Y.-T. Wu*
&& – &&
Put a ring on it: The palladium-cata-
lyzed annulation of 9-halophenan-
threnes with alkynes produced 4,5-di-
substituted acephenanthrylenes (see
scheme). The annulated diphenyl-sub-
stituted acephenanthrylene derivatives
were converted into phenanthro[9,10-
e]acephenanthrylenes by oxidative cy-
clodehydrogenation. The photophysical
and electrochemical properties of se-
lected compounds were investigated.
Palladium-Catalyzed Annulation of 9-
Halophenanthrenes with Alkynes:
Synthesis, Structural Analysis, and
Properties of Acephenanthrylene-
Based Derivatives
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ÝÝ These are not the final page numbers!