Synthesis of dibromobenzobarrelene derivatives and catalytic activity of their rhodium complexes

Article abstract of DOI:10.1002/ejic.201300161

A novel synthetic route based on [4+2] cycloaddition for dibromobenzobarrelene derivatives starting from in situ generated 3,5-dibromo-1,2-didehydrobenzene and mesitylene, 1,2,4,5-tetramethylbenzene, 1,2,3,5-tetramethylbenzene, pentamethylbenzene, 1,3-dimethoxybenzene, and 2,4,6-trimethylbromobenzene, respectively, was developed. Thus, six novel dibromobenzobarrelenes with diverse substitution patterns at the barrelene framework including chiral derivatives are reported. The benzobarrelene 6,8-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene (1a) was functionalized at the annulated benzene ring to give three novel carboxylic acids and two novel phosphonic acid esters. Selected benzobarrelene complexes with Rh^ICl were tested for their catalytic activity in the 1,4-addition of phenylboronic acid towards cyclohex-2-enone. Turnover frequencies up to 3405 h^-1 were observed, which are among the highest reported so far for Rh-diene complexes in this type of C-C coupling reaction. The synthesis by means of a [4+2] cycloaddition approach of six novel dibromobenzobarrelenes with diverse substitution patterns at the barrelene framework, including chiral derivatives, is reported as well as the functionalization of 6,8-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4- ethenonaphthalene to give carboxylic acid and phosphonic acid ester derivatives. Copyright

Full text of DOI:10.1002/ejic.201300161

FULL PAPER
DOI:10.1002/ejic.201300161
Synthesis of Dibromobenzobarrelene Derivatives and
Catalytic Activity of Their Rhodium Complexes
Maik Schlesinger,[a] Max Hofmann,[a] Tobias Rüffer,[b]
Dieter Schaarschmidt,[b] Heinrich Lang,[b] Sergio Theilacker,[c]
Markus Schürmann,[c] Klaus Jurkschat,[c] and Michael Mehring*[a]
Keywords: Homogeneous catalysis / C–C coupling / Diene ligands / Rhodium
A novel synthetic route based on [4+2] cycloaddition for di-
bromobenzobarrelene derivatives starting from in situ gener-
ated 3,5-dibromo-1,2-didehydrobenzene and mesitylene,
methyl-1,4-dihydro-1,4-ethenonaphthalene (1a) was func-
tionalized at the annulated benzene ring to give three novel
carboxylic acids and two novel phosphonic acid esters. Se-
lected benzobarrelene complexes with RhICl were tested for
their catalytic activity in the 1,4-addition of phenylboronic
acid towards cyclohex-2-enone. Turnover frequencies up to
3405 h–1 were observed, which are among the highest re-
ported so far for Rh–diene complexes in this type of C–C cou-
pling reaction.
1,2,4,5-tetramethylbenzene,
1,2,3,5-tetramethylbenzene,
pentamethylbenzene, 1,3-dimethoxybenzene, and 2,4,6-tri-
methylbromobenzene, respectively, was developed. Thus, six
novel dibromobenzobarrelenes with diverse substitution pat-
terns at the barrelene framework including chiral derivatives
are reported. The benzobarrelene 6,8-dibromo-1,3,10-tri-
als).[7] For example, halogen atoms in perhalogenobenzo-
barrelene derivatives (Scheme 1, C) act as electron-with-
drawing groups that enhance the coordination strength of
the strained olefins in complexes with late-transition metals,
whereas substitution at the double bonds allows the fine-
tuning of the bite angle of the dienes and provides steric
and stereochemical control of the coordination.[7] Since
1985, a rich coordination chemistry with achiral perfluori-
nated benzobarrelenes was developed,[8] whereas the grow-
ing interest in chiral benzobarrelene ligands and their use
in asymmetric catalysis is more recent.[9] With regard to im-
mobilization of diene-based catalysts, it is of interest to
post-functionalize the benzene ring of a benzobarrelene li-
gand (e.g., with carboxylic or phosphonic acid moieties).
However, so far only the synthesis of perhalogenated deriv-
atives was reported, which are not suitable for such post-
functionalization strategies. Herein, we present a one-pot
synthesis for partially bromo-substituted benzobarrelenes,
which are subsequently transformed into phosphonic acid
esters and carboxylic acids, respectively. The potential of
Introduction
Since the first report by Zimmerman and Paufler on bi-
cyclo[2.2.2]-2,5,7-octatriene (Scheme 1, A) in 1960,[1] di-
verse synthetic routes have been developed for this class of
bicyclic olefins.[2] In particular, their reactivity as a result of
the ring strain has gained considerable interest.[2b,2c] The
key step to prepare these so-called barrelenes is a [4+2] cy-
cloaddition of acetylene and benzene derivatives.[2a,3] Re-
cently, alternative synthetic routes starting from cis-3,5-cy-
clohexadiene-1,2-diol have been reported.[4] The replace-
ment of acetylene by benzyne derivatives and the reaction
of acetylene derivatives with naphthalene give access to
strained olefins attached to a substituted benzene ring, so-
called benzobarrelenes (Scheme 1, B).[2a,5] The substitution
pattern at the olefin as well as at the annulated benzene ring
does significantly influence the reactivity of the com-
pounds[6] as well as their electronic properties and thus their
coordination behavior (e.g., towards late-transition met-
[a] Technische Universität Chemnitz, Fakultät für
Naturwissenschaften, Institut für Chemie,
Koordinationschemie,
Strasse der Nationen 62, 09111 Chemnitz, Germany
Fax: +49-371-531-21219
E-mail: michael.mehring@chemie.tu-chemnitz.de
Homepage: http://www.tu-chemnitz.de/chemie/koord/
[b] Technische Universität Chemnitz, Fakultät für
Naturwissenschaften, Institut für Chemie, Anorganische
Chemie,
Strasse der Nationen 62, 09111 Chemnitz, Germany
[c] Technische Universität Dortmund, Anorganische Chemie,
Otto-Hahn-Strasse 6, 44227 Dortmund, Germany
Supporting information for this article is available on the
WWW under http://dx.doi.org/10.1002/ejic.201300161.
Scheme 1. Selected examples of different types of barrelenes.[1,2,5,6]
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the benzobarrelenes to act as diene ligands is demonstrated stituted benzene derivatives. Upon heating the Grignard
by the isolation of the rhodium complex μ-dichloridodi(6,8- reagent in THF, 3,5-dibromo-1,2-didehydrobenzene is re-
dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphth- leased and reacts with the benzene derivative to give a
alene)dirhodium(I). The 1,4-addition of phenylboronic acid benzobarrelene as illustrated in Scheme 2.
to 2-cyclohexen-1-one was chosen as a catalytic test reac-
tion to study the potential of in situ formed rhodium com-
plexes with benzobarrelene ligands in homogeneous cataly-
sis.
To identify suitable benzene derivatives for the [4+2] cy-
cloaddition, various diene components such as mesitylene
(1), 1,2,4,5-tetramethylbenzene (2), 1,2,3,5-tetramethylbenz-
ene (3), 2,4,6-trimethylbromobenzene (4), pentamethylbenz-
ene (5), and 1,3-dimethoxybenzene (6) were investigated
and the degree of conversion was determined by NMR
spectroscopy. Electron-rich benzenes such as 1,3-dimeth-
oxybenzene and 1,2,3,5-tetramethylbenzene show a high de-
gree of conversion (58–62%, based on 2,4,6-tribromoiodo-
benzene) to the respective benzobarrelene derivatives,
whereas electron-poor systems (e.g., 2,4,6-trimethylbromo-
benzene; 17% conversion) did react, but only sluggishly.
Depending on the workup procedure, we were able to iso-
late benzobarrelenes with yields up to 37% (e.g., compound
6). The number of isomers formed depends on the identity
of the starting benzene derivatives. In the case of mesit-
ylene, the two regioisomers 1a and 1b (76:24) were separated
by precipitation to give 6,8-dibromo-1,3,10-trimethyl-1,4-
dihydro-1,4-ethenonaphthalene 1a as solid material, which
was additionally purified by sublimation (20% yield). Kug-
elrohr distillation and column chromatography of the resi-
due afforded 5,7-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-
ethenonaphthalene (1b) with a yield of 8%. The NMR
spectra of both isomers 1a and 1b do not differ significantly
except for a signal that is observed at δ = 4.64 ppm for 1b
and at δ = 4.00 ppm for 1a. The latter is assigned on the
basis of a NOESY 1D-NMR spectroscopic experiment that
revealed an interaction (NOE 1.7%) between the aromatic
proton Ha(C4) at δ = 7.18 ppm and the bridgehead proton
Hb(C7) at δ = 4.00 ppm (Scheme S1 in the Supporting In-
formation). In the isomer 1b the bridgehead proton Hc is
located in proximity to Brd and does not show any interac-
tion with an aromatic proton.
Results and Discussion
Synthesis of Benzobarrelene Derivatives
Our synthetic approach towards bromo-substituted
benzobarrelene derivatives is based on the Diels–Alder re-
action of 3,5-dibromo-1,2-didehydrobenzene with different
benzene derivatives. Typically, arynes are accessible either
by means of decomposition of anthranilic acid deriva-
tives,[5,10] oxidation of 1-aminobenzotriazole,[11] or elimi-
nation of metal salts starting from ortho-metalated halo-
benzenes.[12] With respect to the latter method, and as a
result of higher stability, Grignard reagents are much easier
to handle than organolithium compounds, especially in the
case of a high halogen content in the halobenzenes. Thus,
they allow a “controlled” release of the benzyne upon gen-
tle heating, which ensures high conversion rates upon reac-
tion with benzene derivatives. So far, studies on the synthe-
sis of partially substituted benzobarrelenes using benzynes
are scarce, presumably because the elimination of metal hal-
ides from ortho-metalated halobenzenes results in the for-
mation of different isomeric benzynes. These might react
with unsymmetrical benzenes to give a large number of
benzobarrelene isomers. Thus, we used symmetrically sub-
stituted 2,4,6-tribromoiodobenzene as starting material,
which reacts with isopropylmagnesium bromide[13] to afford
the Grignard reagent 2,4,6-Br3C6H2MgBr. The latter is
stable in THF at room temperature in the presence of sub-
Scheme 2. Synthesis of dibromo-substituted benzobarrelene derivatives.
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The reaction of the in situ prepared 3,5-dibromo-1,2-di-
dehydrobenzene with 1,2,4,5-tetramethylbenzene gave, ac-
cording to NMR spectroscopic experiments, three different
isomers of 2, two of which were stereoisomers. Conversion
into the symmetrical regioisomer 2a bearing two hydrogen
atoms in the bridgehead position is favored, but isolation
of the pure compound 2a was difficult. Thus, a mixture of
all isomers with an overall yield of 24% was isolated. Using
the more complex 1,2,3,5-tetramethylbenzene gave two chi-
ral regioisomers (3a/b; 3c/d), of which compound 3a/b was
isolated by column chromatography with a yield of 31%.
Crystallization from hexane gave single crystals that con-
1
sisted of a racemic mixture of 3a/b. H NMR spectroscopy
revealed the absence of an achiral regioisomer with two
methyl groups in the bridgehead position. This might be
explained as the result of steric hindrance and unfavorable
electronic properties in the starting material 1,2,3,5-tet-
ramethylbenzene. According to the frontier orbitals overlap
concept developed by Fukui for Diels–Alder reactions, it is
most likely that the methyl groups in the 2- and 5-position
in 1,2,3,5-tetramethylbenzene disfavor the reaction with 3,5-
dibromo-1,2-didehydrobenzene to give the above-men-
tioned achiral regioisomer.[14] A similar situation was ob-
served upon reaction of 3,5-dibromo-1,2-didehydrobenzene
with 2,4,6-trimethylbromobenzene, which results in the for-
mation of two chiral regioisomers, 4a/b and 4c/d (62:38).
The stereochemical outcome of the reaction does not differ
significantly relative to 1,2,3,5-tetramethylbenzene, but the
conversion drops to 17%. Single crystals of 4a/b were iso-
lated with the bromo substituent located at the 2-position
of the corresponding benzobarrelene derivative (Figure 1).
Bromo-substituted derivatives similar to 4 have been re-
ported earlier. A bromination–elimination sequence starting
from unsubstituted or fully halogenated benzobarrelene de-
rivatives was used. Such a reaction sequence might allow
additional functionalization of the novel benzobarrelenes
reported here.[6a,15] Starting from pentamethylbenzene, the
reaction is even more complex and provides three regioiso-
mers of compound 5 including one chiral isomer. After the
workup procedure including column chromatography, sub-
limation, and crystallization, we did obtain single crystals
composed of the regioisomers 5a and 5b and the stereoiso-
mers 5c/d with a ratio of 53:25:22 (Figure S1 in the Sup-
porting Information). As expected, the reaction of 3,5-di-
bromo-1,2-didehydrobenzene with the electron-rich 1,3-di-
methoxybenzene gave the best conversion of 76% yield, but
isolation of the pure compound 6 was difficult. However,
from a mixture of two racemic regioisomers (6a/b:6c/d;
84:16) dissolved in hexane/acetone, racemic single crystals
of the regioisomer 6a/b crystallized with low yield (Fig-
ure 1).
Figure 1. Ball-and-stick representation (DIAMOND) of the molec-
ular structures of compounds 1a (left top), 3a (right top), 4a (left
bottom), and 6a (right bottom). Hydrogen atoms are omitted for
clarity.
compound 4a) a large difference is observed (3.86°). These
values demonstrate that a fine-tuning of the bite angle of
the dienes is possible through substitution at the barrelene
framework.
Functionalization
The substituent pattern of the dibromobenzobarrelene
derivatives reported here allows further substitution at the
annulated benzene ring. We have chosen compound 1a as a
model compound to study the reactivity of dibromobenzo-
barrelenes. With regard to our previous work on organo-
phosphonate synthesis, we have chosen functionalization of
compound 1a by a nickel-promoted phosphonation with
triisopropylphosphite (Tavs reaction).[16] Additionally, we
studied the synthesis of the corresponding carboxylic acids.
The reaction of 1a with triisopropyl phosphite at a tempera-
ture of 160 °C gave tetraisopropyl 1,3,10-trimethyl-1,4-
dihydro-1,4-ethenonaphthalene-6,8-diphosphonate
(7a),
which was isolated with a yield of 52% (Scheme 3).
Crystallization from ethyl acetate afforded single crystals
that were suitable for X-ray diffraction analysis (Figure 2).
Purification of the crude product by column chromatog-
raphy gave a second product, diisopropyl 8-bromo-1,3,10-
trimethyl-1,4-dihydro-1,4-ethenonaphthalene-6-phosphon-
1
ate (7b), with an isolated yield of 14%. The H NMR spec-
The molecular structures show different angles at the
diene. For example, in compound 1a the angles C9–C10–
C12 105.2(4)° and C8–C7–C11 107.4(4)° differ by 2.20°
(Figure 1), which is a consequence of both electronic and
steric properties of the diene system. Electron-rich com-
pounds, such as compound 6a, do not show a significant
difference (0.13°), whereas for electron-poor systems (e.g., Scheme 3. Functionalization of compound 1a by the Tavs reaction.
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tra show a shift to higher frequencies for both aromatic atom of compound 1a using the Tavs reaction failed; in-
protons from δ = 7.14 and 7.23 ppm in compound 1a to δ stead, mixtures of 7a and 7b were always obtained.
= 7.43 and 7.51 ppm in compound 7b, respectively. Further-
The reaction of one molar equivalent of n-butyllithium
more, both aromatic protons show a 3J(1H,31P) coupling of with compound 1a gave a mixture of products as a result
14.3 Hz. Crystallization from ethyl acetate gave single crys- of metal/halogen exchange in the 6- and 8-position. Quanti-
tals of 7b. The molecular structure (Figure S2 in the Sup- tative and selective metal–halogen exchange at the 8-posi-
porting Information) confirms the substitution at the steri- tion was realized by the use of tert-butyllithium at –78 °C.
cally less-hindered bromine substituent in the 6-position. It The addition of methanol gave 6-bromo-1,3,10-trimethyl-
is worth noting that selective substitution of one bromine 1,4-dihydro-1,4-ethenonaphthalene (8) with a yield of 98%
(Scheme 4). Worthy of note, and in contrast to the synthesis
of compound 7b, substitution at the sterically hindered
bromine atom in the 8-position is observed. The bromine
atom of compound 8 in the 6-position was removed quanti-
tatively by the reaction of the latter with one equivalent of
tert-butyllithium at –50 to –60 °C followed by the addition
of methanol to give 1,3,10-trimethyl-1,4-dihydro-1,4-
ethenonaphthalene (9) with a yield of 91%. The latter was
directly prepared with a yield of 93% by reaction of 1,3,10-
trimethyl-1,4-dihydro-1,4-ethenonaphthalene (1a) with two
equivalents of n-butyllithium in hexane under reflux condi-
tions followed by the addition of methanol. Starting from
compound 1a the use of tert-butyllithium even in large ex-
cess amount in a one-pot reaction did not result in quanti-
tative metal–halogen exchange of both bromine atoms.
Based on the results of the metal–halogen exchange stud-
ies, three benzobarrelene carboxylic acid derivatives (10–12)
were synthesized by the addition of carbon dioxide to the
Figure 2. Ball-and-stick representation (DIAMOND) of the mole-
cular structure of compound 7a. Hydrogen atoms are omitted for
clarity.
Scheme 4. Metal–halogen exchange studies of compound 1a.
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organolithium species with yields in the range 70–77%
Crystallization from dichloromethane resulted in the for-
(Scheme 4). The monocarboxylic acid 10 was obtained as a mation of single crystals suitable for X-ray diffraction
crystalline material (Figure 3). The molecular structure is analysis (Figure 4). Formation of a nonsymmetrically
composed of a dimer as a result of hydrogen bonds with an chlorido-bridged rhodium dimer [Rh1–Cl1 2.4033(2) Å;
O1···O2A distance of 2.653 Å. The characteristic absorp- Rh1–Cl1A 2.4075(2) Å] is observed. The carbon–carbon
tion band assigned to the asymmetric stretching vibration double bonds are elongated from 1.315(7) (C8–C9) and
of the carbonyl group at ν = 1697 cm–1, the broad band at 1.321(7) Å (C11–C12) in compound 1a to 1.4146(1) (C2–
˜
ν = 2962 cm–1, and the O–H···O out-of-plane vibrations at C3) and 1.4141(1) Å (C6–C7) in complex 13. The C3–C4–
˜
ν = 960 cm–1 support the assignment of strong hydrogen C6 angle of 98.1(6)° is significantly compressed relative to
˜
1
bonds. Furthermore, the H NMR spectra show a shift to compound 1a [C9–C10–C12 105.2(3)°]. This is in good
higher frequency for the aromatic proton at C2 from δ = agreement with other known bis(μ-chlorido)bis(benzo-
7.23 ppm in compound 1a to δ = 7.41 ppm in compound barrelene)dirhodium complexes, such as bis(μ-chlorido)-
10, respectively. Similarly, in the 1H NMR spectrum of bis{η2,η2-(R,R)-5,6,7,8-tetrafluoro-2,9-bis[(–)menthoxy-
compound 11 the aromatic protons are shifted to δ = 7.63 methyl]-1,4-dihydro-1,4-ethenonaphthalene}dirhodium,[9e]
and 7.80 ppm. The IR spectrum indicates the formation of which shows a bite angle of approximately 98.2° and a C–
hydrogen bonds by the asymmetric stretching vibration of C bond length of 1.406 Å.
the carbonyl group at ν = 1688 cm–1 and the broad band
˜
absorption at ν = 3040 cm–1. The monocarboxylic acid 12,
˜
synthesized starting from compound 1a by means of 8, also
shows characteristic absorption bands for the asymmetric
stretching vibration of the carbonyl group at ν = 1694 cm–1
˜
and a broad absorption band at ν = 3020 cm–1 that is in-
˜
dicative of a supramolecular assembly through hydrogen
1
bonds. The H NMR spectrum shows a shift to higher fre-
quencies for the corresponding aromatic protons from δ =
6.95, 7.07, and 7.27 ppm in compound 8 to δ = 7.15, 7.56,
Figure 4. Ball-and-stick representation (DIAMOND) of the mole-
and 7.70 ppm in compound 12, respectively. These observa-
tions are in good agreement with values described in the
literature.[17]
cular structure of complex 13. Hydrogen atoms are omitted for
clarity. Symmetry transformations used: A = –x + 1, –y + 1, –z +
2.
Catalysis
Catalyst screening was performed on the basis of the 1,4-
addition of phenylboronic acid towards 2-cyclohexen-1-one
(Table 1), a reaction that is catalyzed by rhodium complexes
that contain diene ligands (Figure 5).[9b,9d,9e,18] Therefore,
compounds 1a, 3a/b, 7a, and 11 were treated with di-μ-
chloridotetraethylenedirhodium(I) to induce the exchange
of ethylene by the corresponding benzobarrelene ligand. In
the case of compound 1a, this reaction was monitored by
1H NMR spectroscopy to reveal quantitative exchange. The
Figure 3. Ball-and-stick representation (DIAMOND) of the mole-
cular structure of compound 10. Symmetry transformations used:
A = –x + 1, –y + 1, –z + 2. O2···O1A 2.653 Å.
RhI Complex
Benzobarrelene derivatives offer the possibility of diene complex composed of 1a–RhI gave, after 6 min, quantita-
coordination to late-transition metals to give complexes tive conversion of cyclehex-2-enone to 3-phenylcyclohex-
that hold potential in homogeneous catalysis.[9a,9c,9d] Thus, enone with a maximum turnover frequency (TOF) of
the reaction of compound 1a with di-μ-chloridotetraethy- 2900 h–1 after 30 s (Table 1). The complexes composed of
lenedirhodium(I) was studied and gave di-μ-chloridodi-8- 7a–RhI and 11–RhI, respectively, gave quantitative conver-
Adibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphth- sion after 10 min (TOF of 600 h–1). The maximum TOF of
alenedirhodium(I) (13) and ethylene. The progress of the 3405 h–1 after 30 s was observed for 11–RhI (7a–RhI,
1
reaction was indicated by a disappearance of the H NMR 2011 h–1) and was the highest of all samples tested. The
spectroscopic signal in CDCl3 at δ = 3.16 ppm (coordinated complex 3a/b–RhI gave quantitative conversion after 20 min
ethylene) and the appearance of a new signal at δ = (TOF of 300 h–1) and a maximum TOF of 1821 h–1 after
5.34 ppm (free ethylene). Furthermore, an upfield shift of 30 s. The lowest catalytic activity was observed for the 3a/
the signal for the diene hydrogen atoms from δ = 6.00 ppm b–RhI complex (quantitative conversion after 20 min),
in compound 1a to δ = 3.18 ppm in compound 13 was ob- which is more sterically hindered at the diene system as a
served.
result of the additional methyl group.
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Table 1. Rhodium-catalyzed 1,4-addition of phenylboronic acid to
2-cyclohexen-1-one by the use of compounds 1a, 3a/b, 7a, and 11
as diene ligands.
Figure 5. Catalytic activity of RhI complexes with 1a, 3a/b, 7a, and
11 in the 1,4-addition of phenylboronic acid to 2-cyclohexen-1-one.
Conclusion
A new synthetic approach towards dibromobenzobarre-
lene derivatives is reported. The Diels–Alder reaction of
3,5-dibromo-1,2-didehydrobenzene, which was prepared
from the Grignard reagent 2,4,6-Br3C6H2MgBr, allows the
synthesis of dibromobenzobarrelenes including achiral as
well as chiral derivatives. Metal–halogen exchange studies
using the model compound 6,8-dibromo-1,3,10-trimethyl-
1,4-dihydro-1,4-ethenonaphthalene (1a) and butyllithium
reagents show a higher reactivity of the bromine atom in
the sterically more-hindered 8-position. Interestingly, con-
trary results were obtained by using the Tavs reaction,
which showed a higher reactivity of the bromine atom in
the 6-position. By utilizing these two synthetic procedures
five additional benzobarrelene derivatives including three
carboxylic acids and two phosphonic acid esters were syn-
thesized. They hold potential for the immobilization of
benzobarrelenes on solid supports. Exchange experiments
with μ-dichloridotetraethylenedirhodium(I) and the benzo-
barrelene ligand 1a confirm the straightforward formation
of the novel benzobarrelene-substituted rhodium complex
[{Rh(1a)Cl}2]. Such complexes are very active in the rho-
dium-catalyzed 1,4-addition of phenylboronic acid to 2-cy-
clohexen-1-on as exemplified by the use of benzobarrelene
ligands 1a, 3a/b, 7a, and 11. An excellent catalytic perform-
ance that resulted in high turnover frequencies with values
up to 3405 h–1 and quantitative conversions after 6 to
10 min was observed. The catalytic activity was much
higher than reported for other diene ligands, which typically
give quantitative yields after a reaction time of one to three
hours.[18c–18g] Notably, the catalytic reaction tolerates func-
tional groups such as carboxylic acid and phosphonic acid
ester.
Time
[min]
Conversion [%] (TOF [h–1])
1a
3a/b
7a
11
0.5
1.0
1.5
2.0
3.0
4.0
6.0
10.0
20.0
24.2
(2900)
36.1
(2163)
49.4
(1977)
59.1
(1699)
71.8
(1437)
94.3
(1414)
100
(1000)
100
15.2
(1821)
29.5
(1772)
37.2
16.8
(2011)
26.7
(1604)
42.2
28.4
(3405)
46.9
(2812)
59.8
(2392)
79.3
(2379)
85.6
(1713)
91.2
(1368)
95.2
(952)
100
(600)
100
(1488)
45.2
(1355)
56.0
(1668)
49.4
(1483)
66.6
(1121)
66.1
(992)
84.0
(1332)
79.6
(1194)
94.6
(840)
96.5
(579)
100
(946)
100
(600)
100
100
(300)
Note that the use of complex 1a–RhI as catalyst and
0.5 equiv. of KOH, an amount that is typically used in lit-
erature procedures, gave a conversion of approximately 85%
after 1 h with a maximum TOF of 3142 h–1 after 60 s. The
amount of conversion is below those reported for other bi-
cyclo[2.2.2]octa-2,5-dienes, which give 96 to 100% yield af-
ter a reaction time of 1 h.[18c,18e] However, under optimized
reaction conditions (1.5 equiv. KOH) we did observe quan-
titative conversion within 6 min for complex 1a–RhI. Thus,
the optimized conditions were used for catalytic investi-
gations of the benzobarrelene derivatives reported here and
result in high TOFs and quantitative yields.
Experimental Section
General: All solvents were dried and distilled before use. Column
chromatography was performed on silica gel 60 (70–230 mesh, Ma-
Eur. J. Inorg. Chem. 2013, 2930–2939
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cherey-Nagel). 2,4,6-Tribromoiodobenzene was synthesized ac-
cording to literature methods.[19] Melting points were determined
with a Büchi Melting Point B-540 melting apparatus and are uncor-
rected. Infrared spectra were recorded with a Spectromat FTS-165
spectrometer. 1H and 13C NMR spectra were recorded with a
Bruker Avance III 500 spectrometer (500 MHz) at room tempera-
ture. NOESY 1D NMR spectroscopic experiments were carried out
with a Varian Inova 400 spectrometer. Quantitative gas chromato-
graphic analysis was performed with a 5890 Series II Plus from
Hewlett–Packard equipped with a flame ionization detector (FID).
An apolar J&W HP-5 column from Agilent Technologies, which
consisted of polymethylphenylsiloxane (95% methyl, 5% phenyl
groups), was used. The injector temperature was set to 270 °C, a
split of 1:50, and a volume flow of the carrier gas nitrogen of
1.8 mLmin–1 was used. After 5 min at 50 °C, the temperature was
increased to 275 °C with a rate of 10 °Cmin–1 and then remained
at this temperature for 14.5 min. For each sample a fivefold GC
analysis was performed. The data sets for the single-crystal X-ray
studies of the compounds 3a/b, 5a–d, 6a/b, 7b, 9, and 13 were col-
lected with Mo-Kα radiation (0.71073 Å) with an Oxford Gemini S
diffractometer at 110 K. The data sets for the single-crystal X-ray
studies of the compounds 1a, 4a/b, and 7a were collected with Mo-
evaporated from the filtrate and the residue was purified by Kugel-
rohr distillation under high vacuum (Ͻ10–3 mbar) at 180 °C to give
crude compound 1b. Column chromatography (silica, hexane) af-
forded a colorless oil of compound 1b with a yield of 8% (1.5 g,
4.2 mmol). Compound 1a: 1H NMR (500.30 MHz, CDCl3): δ =
1.93 (d, J = 1.7 Hz, 6 H), 2.11 (s, 3 H), 4.03 (t, J = 1.9 Hz,1 H),
6.00 (m, 2 H), 7.17 (d, J = 1.9 Hz, 1 H), 7.24 (d, J = 1.9 Hz, 1 H)
ppm. 13C NMR (125.81 MHz, CDCl3): δ = 19.0, 21.8, 52.8, 60.6,
115.2, 116.8, 124.0, 132.1, 138.2, 146.2, 150.3, 153.9 ppm. Calcd.
for C15H14Br2 (354.08): C 50.9, H 4.0; found C 50.9, H 3.8. Com-
pound 1b: 1H NMR (500.30 MHz, CDCl3): δ = 1.93 (d, J = 1.7 Hz,
6 H), 2.29 (s, 3 H), 4.64 (t, J = 1.8 Hz, 1 H), 5.99 (m, 2 H), 7.14
(d, J = 1.5 Hz, 1 H), 7.23 (d, J = 1.6 Hz, 1 H) ppm. 13C NMR
(125.81 MHz, CDCl3): δ = 19.5, 21.3, 50.9, 58.8, 126.9, 128.3,
137.0, 150.3 ppm. Calcd. for C15H14Br2 (354.08): C 50.9, H 4.0;
found 50.6, H 3.9.
5,7-Dibromo-2,3,9,10-tetramethyl-1,4-dihydro-1,4-ethenonaphth-
alene (2a), (S,S)-5,7-Dibromo-1,2,4,10-tetramethyl-1,4-dihydro-1,4-
ethenonaphthalene (2b), and (R,R)-5,7-Dibromo-1,2,4,10-
tetramethyl-1,4-dihydro-1,4-ethenonaphthalene (2c): Compounds
2a–c were prepared according to the general procedure given above
using 1,2,4,5-tetramethylbenzene (8.0 g, 60.0 mmol). The crude
product was purified by column chromatography (silica, hexane).
Sublimation under high vacuum (Ͻ10–3 mbar) at 85 °C afforded
the product as colorless crystals that contained both isomers with
a yield of 24 % (4.4 g, 12.0 mmol). Compound 2a: 1H NMR
(500.30 MHz, CDCl3): δ = 1.78 (d, J = 1.1 Hz, 6 H), 1.81 (d, J =
1.1 Hz, 6 H), 4.06 (s, 1 H), 4.54 (s, 2 H), 7.15 (d, J = 1.9 Hz, 1
H), 7.23 (d, J = 1.8 Hz, 1 H) ppm. Compound 2b/2c: 1H NMR
(500.30 MHz, CDCl3): δ = 1.76 (d, J = 1.2 Hz, 3 H), 1.81 (d, J =
1.2 Hz, 3 H), 2.10 (s, 3 H), 2.20 (s, 3 H), 6.04 (m, 2 H), 7.12 (d, J
= 1.6 Hz, 1 H), 7.23 (d, J = 1.6 Hz, 1 H) ppm. Calcd. for C16H16Br2
(368.11): C 52.2, H 4.4; found C 51.9, H 4.2.
Kα radiation (0.71073 Å) with
a Nonius–Kappa CCD dif-
fractometer at 173 K. All calculations were performed using the
SHELXTL program.[20] The structures were solved by direct meth-
ods and refined by full-matrix least-squares on F2.
Comment to Refinement of Structure 13: The highest unrefined elec-
tron-density peak is located approximately 0.50 Å away from atom
C17, and the next highest unrefined electron-density peak is located
approximately 1.66 Å away from atom Cl5 of one and the same
CH2Cl2 molecule, which acts as packing solvent. Any attempts to
refine the mentioned CH2Cl2 molecule disordered failed or gave
unreliable results.
CCDC-817508 (for 1a), -817512 (for 3a/b), -817509 (for 4a/b),
-817510 (for 5a–d), -517511 (for 6a/b), -900721 (for 7a), -900720
(for 7b), -900718 (for 10), and -900719 (for 13) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
(S,R)-6,8-Dibromo-1,2,3,10-tetramethyl-1,4-dihydro-1,4-etheno-
naphthalene (3a), (R,S)-6,8-Dibromo-1,2,3,10-tetramethyl-1,4-di-
hydro-1,4-ethenonaphthalene (3b), (R,S)-5,7-Dibromo-1,2,3,10-
tetramethyl-1,4-dihydro-1,4-ethenonaphthalene (3c), and (S,R)-5,7-
Dibromo-1,2,3,10-tetramethyl-1,4-dihydro-1,4-ethenonaphthalene
(3d): Compounds 3a–d were prepared according to the general pro-
cedure given above using 1,2,3,5-tetramethylbenzene (10.0 g,
75.0 mmol). The crude product was purified by column chromatog-
raphy (silica, hexane). Colorless crystals that contained a mixture
of compounds 3a and 3b were obtained with a yield of 26% (4.8 g,
13.0 mmol) and a melting point of 115–116 °C. Compounds 3c and
3d were not isolated. Compounds 3a/3b: 1H NMR (500.30 MHz,
CDCl3): δ = 1.69 (d, J = 1.2 Hz, 3 H), 1.81 (d, J = 1.2 Hz, 3 H),
1.88 (d, J = 1.2 Hz, 3 H), 2.10 (s, 3 H), 3.98 (d, J = 2.1 Hz, 1 H),
5.89 (m, 2 H),7.14 (d, J = 1.9 Hz, 1 H), 7.22 (d, J = 1.9 Hz, 1 H)
ppm. 13C NMR (125.80 MHz, CDCl3): δ = 12.6, 17.1, 19.0, 20.4,
55.1, 60.7, 117.0, 123.7, 132.0, 138.3, 140.5, 141.2, 148.7, 153.8
ppm. Calcd. for C16H16Br2 (368.1): C 52.2, H 4.4; found C 51.9, H
General Procedure for the Synthesis of Dibromobenzobarrelene De-
rivatives: Isopropylmagnesium bromide was prepared by the reac-
tion of isopropyl bromide (7.4 g, 50.0 mmol) and magnesium turn-
ings (1.8 g, 74.0 mmol) in tetrahydrofuran (100 mL). The solution
was added dropwise to a mixture of 2,4,6-tribromoiodobenzene
(22.0 g, 50.0 mmol) in tetrahydrofuran (75 mL) and the benzene
derivative at 0 °C. After stirring for 48 h under reflux conditions
(except for compound 1), the solvents were evaporated under vac-
uum at 70 °C. After dissolving the residue in diethyl ether
(200 mL), the organic phase was washed three times with water
(50 mL) and dried with magnesium sulfate. After removing the lat-
ter, evaporation of the solvent provided the crude product that was
purified according to the methods presented below.
1
4.4. Compounds 3c/3d: H NMR (500.30 MHz, CDCl3): δ = 1.65
(d, J = 1 Hz, 3 H), 1.85 (d, J = 1.1 Hz, 3 H), 1.91 (s, J = 1.7 Hz,
3 H), 2.25 (s, 3 H), 4.59 (d, J = 1.9 Hz, 1 H), 5.91 (m, 2 H),7.10 (d,
J = 1.7 Hz, 1 H), 7.23 (d, J = 1.7 Hz, 1 H) ppm.
6,8-Dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene
(1a) and 5,7-Dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-etheno-
naphthalene (1b): Compounds 1a and 1b were prepared according
to the general procedure given above by using mesitylene (75 mL).
In this case, no additional tetrahydrofuran was used. The reaction
mixture was stirred at 130 °C. Compound 1a was precipitated as
solid material by adding hexane. It was removed by filtration and
purified by sublimation under high vacuum (Ͻ10–3 mbar) at 150 °C
to give colorless crystals of compound 1a with a yield of 20%
(3.5 g, 9.9 mmol) and a melting point of 144–145 °C. Hexane was
(R,S)-2,6,8-Tribromo-1,3,10-trimethyl-1,4-dihydro-1,4-etheno-
naphthalene (4a), (S,R)-2,6,8-Tribromo-1,3,10-trimethyl-1,4-di-
hydro-1,4-ethenonaphthalene (4b), (S,R)-2,5,7-Tribromo-1,3,10-tri-
methyl-1,4-dihydro-1,4-ethenonaphthalene (4c), and (R,S)-2,5,7-Tri-
bromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene (4d):
Compounds 4a–d were prepared according to the general pro-
cedure given above using 2,4,6-trimethylbromobenzene (10.5 mL,
Eur. J. Inorg. Chem. 2013, 2930–2939
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75.0 mmol). The crude product was purified by column chromatog-
raphy (silica, hexane). The product was obtained as colorless single-
crystalline material with a yield of 7% (1.5 g, 3.5 mmol) and con-
87 °C as the second phase of the column chromatography. Com-
pound 7b was obtained as colorless crystals with a yield of 14%
and a melting point of 119–121 °C as the first phase of the column
1
tained all isomers. Compounds 4a/4b: 1H NMR (500.30 MHz, chromatography. Compound 7a: H NMR (500.30 MHz, CDCl3):
CDCl3): δ = 1.90 (d, J = 1.8 Hz, 3 H), 1.95 (s, 3 H), 2.18 (s, 3 H),
4.15 (d, J = 2.0 Hz, 1 H), 5.98 (m, 1 H), 7.18 (d, J = 1.9 Hz, 1
H), 7.29 (d, J = 1.9 Hz, 1 H) ppm. Compounds 4c/4d: 1H NMR
(500.30 MHz, CDCl3): δ = 1.94 (d, J = 1.7 Hz, 3 H), 1.98 (s, 3 H),
δ = 1.23 (d, J = 6.2 Hz, 6 H), 1.33 (d, J = 6.2 Hz, 6 H), 1.35 (d, J
= 1.5 Hz, 6 H), 1.36 (d, J = 1.5 Hz, 6 H), 1.88 (d, J = 1.6 Hz, 6
H), 2.29 (s, 3 H), 4.17 (q, J = 1.8 Hz, 1 H), 4.65 (m, 4 H), 5.94 (m,
2 H), 7.64 (m, 1 H), 8.07 (m, 1 H) ppm. 31P NMR (202.53 MHz,
2.21 (s, 3 H), 4.77 (d, J = 2.1 Hz, 1 H), 5.99 (m, 1 H), 7.17 (d, J = CDCl3): δ = 17.32 (s) ppm. Calcd. for C27H42O6P2 (524.57): C 61.8,
1.6 Hz, 1 H), 7.29 (d, J = 1.6 Hz, 1 H) ppm. Calcd. for C15H13Br3 H 8.1; found C 61.5, H 8.2. Compound 7b: 1H NMR (500.30 MHz,
(432.98): C 41.6; H 3.0; found C 40.9, H 3.3.
CDCl3): δ = 1.23 (d, J = 1.7 Hz, 6 H), 1.36 (d, J = 6.2 Hz, 6 H),
1.89 (d, J = 6.2 Hz, 6 H), 2.14 (s, 3 H), 4.13 (t, J = 1.9 Hz, 1 H),
4.66 (m, 4 H), 5.98 (m, 2 H), 7.43 (dd, J = 14.0, 1.3 Hz, 1 H), 7.51
(dd, J = 14.0, 1.3 Hz, 1 H) ppm. 31P NMR (202.53 MHz, CDCl3):
δ = 15.41 (s) ppm. Calcd. for C21H28BrO3P (439.32): C 57.4, H 6.1;
found C 57.0, H 6.1.
6,8-Dibromo-1,2,3,9,10-pentamethyl-1,4-dihydro-1,4-ethenonaphth-
alene (5a), 5,7-Dibromo-1,2,3,9,10-pentamethyl-1,4-dihydro-1,4-
ethenonaphthalene (5b), (S,R)-5,7-Dibromo-1,2,3,4,9-pentamethyl-
1,4-dihydro-1,4-ethenonaphthalene (5c), and (R,S)-5,7-Dibromo-
1,2,3,4,9-pentamethyl-1,4-dihydro-1,4-ethenonaphthalene (5d):
Compounds 5a–d were prepared according to the general pro-
cedure given above using pentamethylbenzene (8.9 g, 60.0 mmol).
The crude product was purified by column chromatography (silica,
hexane). The product was obtained as colorless crystals with a yield
of 29% (5.6 g, 14.6 mmol) and contained all isomers. Compound
6-Bromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene (8):
Compound 1 (5.0 g, 14.1 mmol) was dissolved in tetrahydrofuran
(60 mL), and tert-butyllithium (1.6 m, 9.71 mL, 15.5 mmol) was
added dropwise at –78 °C. The reaction mixture was stirred for 2 h
at –60 to –70 °C. After adding methanol (20 mL), the solvents were
5a: 1H NMR (500.30 MHz, CDCl3): δ = 1.67 (d, J = 1.2 Hz, 6 H), evaporated, and the residue was dissolved in diethyl ether (100 mL).
1.82 (d, J = 1.2 Hz, 6 H), 2.10 (s, 1 H), 3.96 (s, 1 H), 7.12 (d, J = The organic phase was extracted three times with water (20 mL)
1.9 Hz, 1 H), 7.23 (d, J = 1.9 Hz, 1 H) ppm. Compound 5b: 1H
NMR (500.30 MHz, CDCl3): δ = 1.63 (d, J = 1.2 Hz, 6 H), 1.84
(d, J = 1.2 Hz, 6 H), 2.11 (s, 1 H), 4.57 (s, 1 H), 7.10 (d, J = 1.9 Hz,
and dried with magnesium sulfate. After removing the latter by
filtration, evaporation of the solvent gave the product as a colorless
solid with a yield of 98% (3.8 g, 13.8 mmol) and a melting point
1
1
1 H), 7.23 (d, J = 1.9 Hz, 1 H) ppm. Compound 5c/5d: H NMR
of 139 °C. H NMR (500.30 MHz, CDCl3): δ = 1.82 (s, 3 H), 1.89
(500.30 MHz, CDCl3): δ = 1.73–1.75 (m, 15 H), 6.03 (s, 1 H), 7.05
(d, J = 1.9 Hz, 1 H), 7.22 (d, J = 1.9 Hz, 1 H) ppm. Calcd. for
C17H18Br2 (382.13): C 53.4, H 4.8; found C 52.8, H 4.4.
(d, J = 1.7 Hz, 6 H), 4.10 (t, J = 1.8 Hz, 1 H), 6.00 (m, 2 H), 6.95
(d, J = 7.8 Hz, 1 H), 7.07 (dd, J = 7.8 Hz, 1.9 Hz, 1 H), 7.27 (d, J
= 1.9 Hz, 1 H) ppm. 13C NMR (125.81 MHz, CDCl3): δ = 17.3,
19.2, 49.9, 59.9, 119.4, 124.6, 126.1, 137.1, 150.1 ppm. Calcd. for
C15H15Br (275.18): C 65.5, H 5.5; found C 65.3, H 5.4.
(R,S)-6,8-Dibromo-1,3-dimethoxy-1,4-dihydro-1,4-ethenonaphth-
alene (6a), (S,R)-6,8-Dibromo-1,3-dimethoxy-1,4-dihydro-1,4-
ethenonaphthalene (6b), (R,S)-5,7-Dibromo-1,3-dimethoxy-1,4-di- 1,3,10-Trimethyl-1,4-dihydro-1,4-ethenonaphthalene (9): Compound
hydro-1,4-ethenonaphthalene (6c), and (S,R)-5,7-Dibromo-1,3-di- 1 (2.0 g, 5.6 mmol) was dissolved in dry hexane (160 mL), and n-
methoxy-1,4-dihydro-1,4-ethenonaphthalene (6d): Compounds 6a–d
were prepared according to the general procedure given above
using 1,3-dimethoxybenzene (10 mL, 77.0 mmol). The crude prod-
uct was purified by column chromatography (silica, 10:1 mixture
of hexane/acetone). The product was obtained as a colorless to
butyllithium (2.6 m, 4.73 mL, 12.3 mmol) was added dropwise at
0 °C. The reaction mixture was heated at reflux for 1 h. After ad-
dition of methanol (50 mL), the solvents were evaporated, and the
residue was dissolved in ethyl ether (50 mL). The organic phase
was extracted three times with water (20 mL) and dried with mag-
light yellow single-crystalline material with a yield of 37% (6.9 g, nesium sulfate. After removing the latter by filtration, evaporation
18.5 mmol) and contained all isomers. Compounds 6a/6b: 1H
NMR (500.30 MHz, CDCl3): δ = 3.50 (s, 3 H), 3.74 (s, 3 H), 4.32
(ddd, J = 6.0, 1.6, 2.5 Hz, 1 H), 5.53 (d, J = 2.6 Hz, 2 H), 6.84 (dd,
of the solvent gave the product as a colorless solid with a yield of
93% (1.0 g, 5.2 mmol) and a melting point of 44–47 °C. H NMR
(500.30 MHz, CDCl3): δ = 1.85 (s, 3 H), 1.89 (d, J = 1.7 Hz, 6 H),
4.15 (t, J = 1.7 Hz, 1 H), 6.00 (m, 2 H), 6.86 (dt, J = 7.2 Hz, 1.2 Hz,
1
J = 6.1, 7.2 Hz, 1 H), 7.07 (dd, J = 7.3, 1.4 Hz, 1 H), 7.19 (d, J =
1
1.8 Hz, 1 H), 7.29 (d, J = 1.8 Hz, 1 H) ppm. Compound 6c/6d: H 1 H), 6.94 (dt, J = 7.2 Hz, 1.2 Hz, 1 H), 7.12 (dd, J = 7.2 Hz,
NMR (500.30 MHz, CDCl3): δ = 3.50 (s, 3 H), 3.77 (s, 3 H), 4.82
(ddd, J = 6.1, 1.5, 1.9 Hz, 1 H), 5.46 (d, J = 2.4 Hz, 2 H), 6.88 (dd,
J = 6.2, 7.2 Hz, 1 H), 7.04 (dd, J = 7.2, 1.4 Hz, 1 H), 7.25 (d, J =
1.2 Hz, 1 H), 7.15 (dd, J = 7.2 Hz, 1.2 Hz, 1 H) ppm. 13C NMR
(125.81 MHz, CDCl3): δ = 17.6, 19.5, 50.2, 60.6, 118.1, 121.5,
122.8, 123.6, 137.3, 148.4, 150.6, 151.1 ppm. Calcd. for C15H16
(196.29); C 91.8, H 8.2; found C 91.4, H 7.7
1.8 Hz, 1 H), 7.43 (d, J = 1.8 Hz, 1 H) ppm. Compound 6a/6b: 13
C
NMR (125.80 MHz, CDCl3): δ = 54.3, 56.7, 59.7, 89.5, 101.7,
117.4, 120.5, 124.5, 132.6, 136.1, 139.9, 143.4 ppm. Calcd. for
C14H12Br2O2 (372.05): C 45.2, H 3.3; found C 45.7, H 3.4.
6-Bromo-1,3,10-trimethyl-1,4-dihydro-1,4-ethenonaphthalene-8-carb-
oxylic Acid (10): Compound 1 (2.0 g, 5.6 mmol) was dissolved in
tetrahydrofuran (35 mL), and tert-butyllithium (1.6 m, 3.88 mL,
6.2 mmol) was added dropwise at –78 °C. The reaction mixture was
Tetraisopropyl 1,3,10-Trimethyl-1,4-dihydro-1,4-ethenonaphthalene-
6,8-diphosphonate (7a) and Diisopropyl 8-Bromo-1,3,10-trimethyl- stirred for 2 h at –60 to –70 °C. Gaseous carbon dioxide was
1,4-dihydro-1,4-ethenonaphthalene-6-phosphonate (7b): Compound
1 (5.0 g, 14.1 mmol) was mixed with nickel(II) bromide (1.23 g,
5.6 mmol). After heating to 160 °C, triisopropyl phosphite (8.8 g,
42.3 mmol) was added, and the reaction mixture was stirred over
a period of 4 h at the same temperature. Cooling to room tempera-
ture afforded the crude product, which was purified by column
chromatography (silica, ethyl acetate). Compound 7a was obtained
as colorless crystals with a yield of 52% and a melting point of 86–
dumped through a drain tube over a period of 2 h at the same
temperature. After the solvents had been evaporated, the residue
was dissolved in diethyl ether (60 mL). The organic phase was ex-
tracted three times with diluted hydrochloric acid (20 mL) and
dried with magnesium sulfate. After removing the latter by fil-
tration, evaporation of the solvent provided the crude product,
which was dissolved in a diluted sodium hydroxide solution and
filtered through Celite. Acidification of the filtrate with diluted hy-
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drochloric acid gave a colorless precipitate that was removed by
filtration and dried under vacuum at 60 °C. The product was ob-
tained as a colorless powder with a yield of 76% (1.4 g, 4.3 mmol)
(s), 1337 (w), 1296 (s), 1262 (m), 1175 (w), 1093 (w), 1045 (w), 957
(w), 924 (w), 873 (w), 813 (m), 775 (m), 669 (m), 642 (m), 550 (w),
514 (w) cm–1. Calcd. for C16H16O2 (240.30): C 80.0, H 6.7; found
and a decomposition temperature of 189 °C. 1H NMR (500.30 C 79.2, H 6.7.
MHz, [D6]acetone): δ = 1.88 (d, J = 1.7 Hz, 6 H), 1.91 (s, 3 H),
μ-Dichloridodi(6,8-dibromo-1,3,10-trimethyl-1,4-dihydro-1,4-etheno-
4.31 (t, J = 1.8 Hz, 1 H), 5.97 (m, 2 H), 7.05 (d, J = 1.9 Hz, 1 H),
7.41 (d, J = 1.9 Hz, 1 H) ppm. 13C NMR (125.81 MHz, [D6]-
acetone): δ = 18.1, 18.2, 59.7, 124.4, 125.3, 137.3, 149.9, 169.4 ppm.
naphthalene)dirhodium(I) (13): In a typical synthesis, μ-dichlorido-
tetraethylenedirhodium(I) (50.0 mg, 0.13 mmol) was suspended in
dry toluene (5 mL) and then cooled to –70 °C. After compound 1a
(100.1 mg, 0.28 mmol) had been added, the solution was warmed
to room temperature and stirred overnight. The precipitate was re-
moved by filtration and dissolved in dry chloroform. Filtration and
evaporation of the solvent gave a solid residue that was recrys-
tallized from dry dichloromethane at –40 °C. The product was ob-
tained as yellow-orange crystals with a yield of 96% (122.9 mg).
1H NMR (500.30 MHz, CDCl3): δ = 1.52 (s, 6 H), 2.93 (s, 3 H),
3.18 (s, 2 H), 4.52 (s, 1 H), 7.26 (d, J = 1.9 Hz, 1 H), 7.51 (d, J =
IR: ν = 3420 (w), 2970 (m) , 2927 (m), 2902 (m), 2957 (w), 2560
˜
(w), 1694 (s), 1603 (m), 1576 (w), 1508 (w), 1475 (w), 1432 (m),
1378 (w), 1337 (w), 1296 (s), 1262 (s), 1175 (w), 1116 (w), 1092 (w),
1045 (w), 957 (w), 924 (w), 874 (w), 813 (m), 775 (m), 669 (w), 642
(w), 550 (w), 514 (w) cm–1. Calcd. for C16H15BrO2 (319.19); C 60.2,
H 4.7; found C 60.3, H 4.8.
1,3,10-Trimethyl-1,4-dihydro-1,4-ethenonaphthalene-6,8-dicarboxy-
lic Acid (11): n-Butyllithium (2.6 m, 4.73 mL, 12.3 mmol) was
added dropwise at 0 °C to a solution of compound 1 (2.0 g,
5.6 mmol) in dry hexane (160 mL). The reaction mixture was
heated at reflux for 1 h. After cooling to room temperature, gaseous
carbon dioxide was added with a drain tube over a period of 2 h.
After the solvent had been evaporated, the residue was dissolved
in diethyl ether (80 mL). The organic phase was extracted three
times with diluted hydrochloric acid (20 mL) and dried with mag-
nesium sulfate. After removing the latter by filtration, evaporation
of the solvent provided the crude product, which was dissolved in
a diluted sodium hydroxide solution and filtered over Celite. Acidi-
fication of the filtrate with diluted hydrochloric acid gave a color-
less precipitate that was removed by filtration and dried under vac-
uum at 60 °C. The product was obtained as a colorless powder with
a yield of 70% (1.1 g, 3.9 mmol) and a decomposition temperature
1.9 Hz, 1 H) ppm. IR: ν = 2960 (w), 2925 (w), 2876 (w), 2853 (w),
˜
1574 (m), 1536 (m), 1417 (m), 1379 (m), 1367 (m), 1252 (s), 1138
(w), 1091 (s), 1015 (s), 912 (w), 870 (w), 839 (w), 789 (s), 774 (s),
751 (s), 693 (m), 674 (m), 663 (m), 617 (m), 567 (w), 537 (m), 521
(w), 495 (w), 464 (w) cm–1. Calcd. for C30H28Br4Cl2Rh2·3CH2Cl2
(1239.49): C 32.0, H 2.8; found C 32.0, H 2.6.
General Procedure for Catalytic Investigations: Phenylboronic acid
(226.8 mg, 1.9 μmol), [{RhCl(C2H4)2}2] (1.2 mg, 3.1 μmol), and the
appropriate benzobarrelene derivative (1a 2.4 mg, 3a/b 2.5 mg, 7a
3.6 mg, 10 1.9 mg; 6.8 μmol) were dissolved in degassed and dry
dioxane (10 mL) and stirred for 45 min at 30 °C. The catalysis was
initiated by addition of a degassed, aqueous potassium hydroxide
solution (4.5 m, 0.21 mL) and cyclohex-2-enone (0.06 mL,
0.62 mmol). After t = 0.5, 1, 1.5, 2, 3, 4, 6, 10, and 20 min, samples
of 0.5 mL were removed, and the catalysis of each sample was
stopped by the addition of ice-cold saturated sodium bicarbonate
solution (1 mL). The aqueous phase was extracted five times with
diethyl ether and then combined. After evaporating the diethyl
ether (760 mbar, 40 °C) the GC flame ionization detector (FID)
analysis was performed.
1
of 223 °C. H NMR (500.30 MHz, [D6]acetone): δ = 1.91 (d, J =
1.7 Hz, 6 H), 1.96 (s, 3 H), 4.41 (t, J = 1.9 Hz, 1 H), 5.97 (m, 2 H),
7.63 (d, J = 1.7 Hz, 1 H), 7.80 (d, J = 1.7 Hz, 1 H) ppm. 13C NMR
(125.80 MHz, CDCl3): 18.2, 18.3, 51.3, 60.1, 122.4, 125.0, 136.7,
150.4, 151.1, 166.1 ppm. IR: ν = 3040 (m), 2958 (m), 2930 (m),
˜
2902 (m), 2857 (w), 2647 (w), 2547 (w), 2358 (w), 2325 (m), 1688
(s), 1605 (m), 1461 (w), 1430 (m), 1390 (m), 1259 (s), 1179 (m),
1115 (w), 1047 (m), 903 (w), 874 (w), 811 (m), 766 (m), 702 (w),
668 (w), 646 (m), 536 (w), 208 (w), 479 (w), 422 (w) cm–1. Calcd.
for C17H16O4 (284.31): C 71.8, H 5.7; found C 71.4, H 6.2
Supporting Information (see footnote on the first page of this arti-
cle): It contains Scheme S1, Figure S1, Figure S2, and Table S1
(crystallographic data).
1,3,10-Trimethyl-1,4-dihydro-1,4-ethenonaphthalene-6-carboxylic
Acid (12): tert-Butyllithium (1.6 m, 4.99 mL, 8.0 mmol) was added
dropwise at –78 °C to a solution of compound 3 (2.0 g, 7.3 mmol)
in tetrahydrofuran (125 mL). The reaction mixture was stirred for
2 h at –50 to –60 °C. Gaseous carbon dioxide was dumped through
a drain tube over a period of 2 h at the same temperature. After
the solvents had been evaporated, the residue was dissolved in di-
ethyl ether (80 mL). The organic phase was extracted three times
with diluted hydrochloric acid (20 mL) and dried with magnesium
sulfate. After removing the latter by filtration, evaporation of the
solvent provided the crude product, which was dissolved in a di-
luted sodium hydroxide solution and filtered through Celite. Acidi-
fication of the filtrate with diluted hydrochloric acid gave a color-
less precipitate that was removed by filtration and dried under vac-
uum at 60 °C. The product was obtained as colorless powder with
a yield of 77% (1.4 g, 5.6 mmol) and a decomposition temperature
of 245–250 °C. 1H NMR (500.30 MHz, [D6]DMSO): δ = 1.80 (s, 3
H), 1.83 (d, J = 1.7 Hz, 6 H), 4.32 (t, J = 1.8 Hz, 1 H), 5.96 (m, 2
H), 7.15 (d, J = 7.7 Hz, 1 H), 7.56 (dd, J = 7.7 Hz, 1.7 Hz, 1 H),
7.70 (d, J = 1.7 Hz, 1 H) ppm. 13C NMR (125.81 MHz, CDCl3): δ
= 17.7, 19.4, 50.4, 59.6, 118.1, 122.1, 125.5, 126.2, 150.3, 167.9
Acknowledgments
The authors thank Prof. Dr. Stefan Spange for giving access to
ATR-FT-infrared spectroscopy, Dr. Enrico Dietzsch for access to
gas chromatographic analysis, and Janine Fritzsch for performing
CHN analyses.
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Published Online: April 17, 2013
Eur. J. Inorg. Chem. 2013, 2930–2939
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© 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim