Synthesis of rhenabenzenes from the reactions of rhenacyclobutadienes with ethoxyethyne

Article abstract of DOI:10.1002/chem.201403186

Treatment of Na[Re(CO)₅] with RC≡CCO₂Et (R= phenyl, naphthalen-1-yl, phenanthren-9-yl and pyren-1-yl) followed by reaction with acetyl chloride and ethanol afforded the rhenacyclobutadienes Re{-C(R)=C(CO₂Et)C(OEt)= }(CO)₄. Reactions of these rhenacyclobutadienes with HC≡ COEt produced rhenabenzenes Re{-C(R)=C(CO ₂Et)C(OEt)= CHC(OEt)=}(CO)₄. Except for R = Ph, new rhenacyclobutadienes with pendant alkenyl substituents Re{-C(R)=C(C(OEt)= CH(CO₂Et))C(OEt)=}(CO)₄ were also isolated from these reactions. The NMR spectroscopic and X-ray structural data, as well as the aromatic stabilization energy (ASE) values suggest that the rhenabenzenes are aromatic, with extensive delocalized character.

Full text of DOI:10.1002/chem.201403186

DOI: 10.1002/chem.201403186
Full Paper
&
Metallacycles
Synthesis of Rhenabenzenes from the Reactions of
Rhenacyclobutadienes with Ethoxyethyne
Ran Lin, Ka-Ho Lee, Ka Chun Poon, Herman H. Y. Sung, Ian D. Williams,* Zhenyang Lin,* and
[a]
Guochen Jia*
Abstract: Treatment of Na[Re(CO) ] with RCꢀCCO Et (R=
dienes with pendant alkenyl substituents Re{-C(R)=C(C(OEt)=
CH(CO Et))C(OEt)=}(CO) were also isolated from these reac-
5
2
phenyl, naphthalen-1-yl, phenanthren-9-yl and pyren-1-yl)
followed by reaction with acetyl chloride and ethanol afford-
2
4
tions. The NMR spectroscopic and X-ray structural data, as
ed the rhenacyclobutadienes Re{-C(R)=C(CO Et)C(OEt)= well as the aromatic stabilization energy (ASE) values sug-
2
}
(CO) . Reactions of these rhenacyclobutadienes with HCꢀ gest that the rhenabenzenes are aromatic, with extensive
4
COEt produced rhenabenzenes Re{-C(R)=C(CO Et)C(OEt)= delocalized p character.
2
CHC(OEt)=}(CO) . Except for R=Ph, new rhenacyclobuta-
4
Introduction
reaction intermediates, isolated and well-characterized metalla-
benzenes with an early or middle transition metal (Group 3–7)
are very rare and are limited to only a few 1,3-dimetallaben-
There has been much interest in the development of chemistry
of metallabenzenes, or more generally, metallaaromatics de-
rived from formal replacement of a CH group in benzene by
[37]
zenes of Nb and Ta. In this work, we report the preparation
and structural characterization of rhenabenzenes. A preliminary
[
1]
[38]
an isolobal transition-metal fragment. Previous studies have
led to the isolation of a number of metallabenzenes, especially
report on this work has been published.
[2–4]
those with a late transition metal such as platinum,
iridi-
It has been demon-
strated that metallabenzenes can have properties of typical or-
[
5–17]
[18–26]
[27–30]
um,
osmium,
or ruthenium.
ganic aromatic systems. For example, they can undergo elec- Results and Discussion
[
16–18,21,22]
trophilic substitution reactions
and nucleophilic aro-
An overview of the strategy used in the synthesis of rhena-
benzenes
[
19,23,24,30]
6
matic substitution reactions,
and function as h -ligands
[
3,4,10,11,12,31]
to form half-sandwich and sandwich complexes.
They can also display properties of nonaromatic systems. For
example, they can undergo migratory insertion reactions to
Our synthetic work was inspired by the report that the reac-
tion of a tethered iridacyclobutadiene complex with methyl
propiolate in the presence of silver triflate produced a tethered
[
3,4,12–14,26,28]
give cyclopentadienyl complexes,
cycloaddition re-
[8,9,25]
[
4,6,7]
[15]
actions,
and nucleophilic addition reactions.
iridabenzene and by the report that reactions of rhenacyclo-
Most of the previous studies have focused on metallaben-
zenes containing a late transition metal, and the chemistry of
metallabenzenes containing early or middle transition metals is
underdeveloped. For example, whereas manganabenzenes
butadienes with alkynes gave cyclopentadienyl complexes,
which were proposed to be formed via thermally unstable rhe-
[33,34,39]
nabenzene intermediates.
In our previous work on the chemistry of osmabenzynes, we
found that a methoxy substituent at the a-carbon of a metalla-
benzene can stabilize the metallabenzene relative to the corre-
[
32]
were predicted theoretically 35 years ago and metallaben-
[
33]
[34]
zenes such as rhenabenzene,
rhenaphenanthrene,
chro-
[
35]
[36]
[40]
mabenzene, and tungstabenzene have been suggested as
sponding cyclopentadienyl complex. Computational studies
[41]
[42]
by Iron et. al and also by ourselves suggest that electron-
donating groups such as alkoxy and amido at ortho and/or
para positions of a metallabenzene ring can increase the stabil-
ity of the metallabenzene with respect to the formation of the
corresponding cyclopentadienyl complex. We therefore envi-
sioned that reactions of an alkoxy- or amido-containing rhena-
cyclobutadiene complex A with RCꢀCOR’ may give rhenaben-
zene B or C with alkoxy or amido substituents at an ortho or
the para position of the metallabenzene ring, which may be
stable enough to be isolated [Eq. (1)].
[
a] Dr. R. Lin, K.-H. Lee, Dr. K. C. Poon, Dr. H. H. Y. Sung, Prof. I. D. Williams,
Prof. Z. Lin, Prof. G. Jia
Department of Chemistry
The Hong Kong University of Science and Technology
Clear Water Bay, Kowloon (Hong Kong)
Fax: (+852)2358-1594
E-mail: ianduncanw@gmail.com
chzlin@ust.hk
chjiag@ust.hk
Supporting information for this article is available on the WWW under
http://dx.doi.org/10.1002/chem.201403186.
Chem. Eur. J. 2014, 20, 1 – 16
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Full Paper
Synthesis of alkoxy-containing rhenacyclobutadiene com-
plexes
The required alkoxy-containing rhenacyclobutadienes were
prepared by following the route developed by Wojcicki et.
[
43]
al, starting from the reaction of Na[Re(CO) ] with RCꢀCCO Et.
5
2
For easy isolation, we have used RCꢀCCO Et with R=aryl or
2
polyaromatic group. A solution of Na[Re(CO) ] (1) in THF was
5
Figure 1. Molecular structure of 4 (thermal ellipsoids set at 30% probability).
Selected bond lengths [ꢁ] and angles [8]: Re1–C1 2.191(5), Re1–C3 2.144(5),
C1–C2 1.373(8), C2–C3 1.432(7); C1–Re1–C3 60.5(2), Re1–C3–C2 98.6(3), Re1–
C1–C2 98.4(4), C1–C2–C3 102.3(4).
generated from the reaction of [Re (CO) ] with Na. Reaction of
2
10
Na[Re(CO) ] (1) with PhCꢀCCO Et in THF produced the anionic
5
2
rhenacyclobutadiene complex Na[Re{-C(Ph)=C(CO Et)C(O)=
2
}
(CO) ] (2). Treatment of 2 with acetyl chloride at À158C fol-
4
lowed by ethanol afforded, after workup, rhenacyclobutadiene
4
as an orange solid in an overall yield of 37% (based on
Na[Re(CO) ]). The reaction presumably proceeds via intermedi-
5
ate 3.
Similarly, treatment of 1 with ethyl 3-(naphthalen-1-yl)pro-
piolate, ethyl 3-(phenanthren-9-yl)propiolate, and ethyl 3-
(pyren-1-yl)propiolate followed by acetyl chloride and ethanol
produced the analogous rhenacyclobutadienes 5, 6, and 7, re-
spectively, with isolated yields of 46, 35, and 60% (Scheme 1).
In all the complexes 4–7, the CO Et group is at the b-carbon of
2
the metallacycle.
Figure 2. Molecular structure of 5 (thermal ellipsoids set at 30% probability).
Selected bond lengths [ꢁ] and angles [8]:Re1–C1 2.188(3), Re1–C3 2.145(3),
C1–C2 1.383(4), C2–C3 1.432(4); C1–Re1–C3 60.63(11), Re1–C3–C2 98.8(2),
Re1–C1–C2 98.50(19), C1–C2–C3 102.0(3).
Table 1. Selected bond lengths [ꢁ] and angles [8] for the rhenacyclobuta-
diene complexes 4–6, 11 and 16.
4
5
6
11
16
Re1–C1
Re1–C3
C1–C2
C2–C3
C1–Re1–C3
Re1–C3–C2
Re1–C1–C2
C1–C2–C3
2.191(5)
2.144(5)
1.373(8)
1.432(7)
60.5(2)
98.6(3)
98.4(4)
102.3(4)
2.188(3)
2.145(3)
1.383(4)
1.432(4)
60.63(11)
98.8(2)
2.176(3)
2.146(4)
1.374(5)
1.430(6)
60.32(15)
98.8(3)
2.169(4)
2.186(3)
1.376(5)
1.464(5)
61.18(13)
96.2(2)
2.187(4)
2.178(9)
1.374(6)
1.449(7)
60.4(2)
97.6(4)
99.7(3)
102.1(5)
Scheme 1. Synthesis of alkoxy-containing rhenacyclobutadiene complexes
98.50(19)
102.0(3)
99.3(3)
101.5(3)
99.8(2)
102.6(3)
1
Complexes 4–6 have been characterized by
H and
1
3
1
C{ H} NMR spectroscopy, chemical analysis, and single-crystal
X-ray diffraction; the molecular structures of the complexes 4,
, and 6, are shown in Figure 1, Figure 2, and Figure 3, respec-
dihedral angles between the planes of the metallacycles and
the aromatic substituents are 27.6, 46.8, and 51.98 for the com-
plexes 4, 5, and 6, respectively. The two ReÀC bond lengths in
each of the complexes are only slightly different, with the ReÀ
5
tively. Selected bond distances and angles are given in Table 1.
All the complexes have an essentially planar metallacycle. The
&
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Reactions of 4 with alkynes
Stirring a mixture of rhenacyclobutadiene 4 and ethoxyethyne
in acetonitrile at room temperature for 12 h produced a red-
1
brown solution. The H NMR spectrum recorded in situ sug-
gests that the reaction generated a complex mixture of spe-
cies. Nevertheless, rhenabenzene complex 8 could be isolated
from the reaction mixture as a bright-orange solid in 5% isolat-
ed yield (Scheme 2).
1
13
1
Complex 8 has been characterized by H and C{ H} NMR
spectroscopy, chemical analysis, and by a single-crystal X-ray
diffraction study. The molecular structure of complex 8 is
shown in Figure 4. The complex contains an essentially planar
six-membered metallacycle. The mean deviation from the least
squares plane through Re1 and C1–C5 is 0.10 ꢁ. The maximum
deviation from the least-squares plane through Re1 and C1–C5
is 0.16 ꢁ for Re1. The ReÀC(OEt) bond (2.142(4) ꢁ) is slightly
shorter than the ReÀC(Ph) bond (2.184(3) ꢁ). A similar pattern
for the ReÀC bond lengths is found for rhenacyclobutadiene
complex 4. The dihedral angle of the metallacycle with respect
to the phenyl plane (71.58) in complex 8 is larger than that in
the related rhenacyclobutadiene complex 4 (27.68), likely due
to the fact that complex 8 experiences greater repulsive inter-
Figure 3. Molecular structure of 6 (thermal ellipsoids set at 30% probability).
Selected bond lengths [ꢁ] and angles [8]: Re1–C1 2.176(3), Re1–C3 2.146(4),
C1–C2 1.374(5), C2–C3 1.430(6); C1–Re1–C3 60.32(15), Re1–C3–C2 98.8(3),
Re1–C1–C2 99.3(3), C1–C2–C3 101.5(3).
action between the phenyl and CO Et substituents. The ReÀC1
2
C(OEt) bond being slightly shorter than the ReÀC(Ar) bond. For
example, in complex 4, the ReÀC(OEt) and ReÀC(Ar) distances
are 2.144(5) and 2.191(5) ꢁ, respectively. The CÀC bonds of the
rhenacyclobutadienes also support a predominantly delocal-
ized electronic arrangement, but with some weak double/
and ReÀC5 bond lengths lie within the large range reported
[
44,45]
for ReÀC (vinyl) bond lengths (1.996–2.305 ꢁ)
and at the
high end of those reported for typical Re=CHR (carbene)
[44,46]
bonds (1.850–2.263 ꢁ).
The ring CÀC distances are in the
range of 1.356–1.444 ꢁ, which are intermediate between single
and double carbon–carbon bonds. These structural features
suggest that the metallacycle of 8 has a delocalized structure
with contributions from the resonance structures 8 and 8A,
with the former predominating (Scheme 2).
single bond alternation character. The C(OEt)ÀC(CO Et) bonds
2
are consistently longer than C(Ar)ÀC(CO Et) bonds. For exam-
2
ple, in complex 4, the C(OEt)ÀC(CO Et) and C(Ar)ÀC(CO Et) dis-
2
2
tances are 1.432(7) and 1.373(8) ꢁ, respectively. The structural
features associated with the metallacycles are similar
to that of the related rhenacyclobutadiene complex
1
3
1
Re{-C(Me)=C(CO Me)C(OEt)=}(CO) reported by Woj-
Table 2. Selected C{ H} NMR data for the rhenacyclobutadiene complexes Re{-C(R)=
2
4
[
a]
[43b]
C(CO Et)C(R’)=}(CO) (4–7 and 16).
cicki and co-workers.
2
4
The solution NMR data are consistent with the
[b]
4
5
6
7
16
solid-state structures for complexes 4, 5, and 6. For
example, the H NMR spectrum of 4 showed two
R
R’
phenyl
OEt
naphthanenyl phenanthrenyl pyrenyl
phenyl
NEt
2
1
OEt
OEt
OEt
OCH signals at d=4.09 and 4.87 ppm; the
C1
C2
C3
CO
221.8
153.0
241.9
159.3
227.9
155.3
245.5
228.7
156.9
246.2
158.7
231.2
156.4
246.7
159.4
190.4
147.8
189.2
2
13
1
C{ H} NMR spectrum of 4 showed signals of the ring
carbon atoms at d=241.9, 221.8, and 153.0 ppm for
2
Et
157.8
167.3
ReC(OEt), ReC(Ph), and C(CO Et), respectively, and
2
CO
2
Et
12.8 (CH
3
), 12.1 (CH
3
),
13.4 (CH
3
),
13.9 (CH
3
3
), 14.7 (CH ),
those of the carbonyl carbon atoms at d=193.3 (cis
CO), 190.8 (cis CO), and 189.7 ppm (two trans COs).
Although the X-ray structure of complex 7 was not
determined, its structure could be readily assigned
59.0 (CH2) 58.6 (CH2)
59.6 (CH2)
60.3 (CH2) 61.2 (CH2)
R’=OEt, 13.5 (CH
or NEt 79.4 (CH
3
), 13.5 (CH
80.2 (CH
3
),
)
14.8 (CH
81.4 (CH
3
),
)
15.8 (CH
81.4 (CH
3
), 14.0, 14.1 (CH
48.5, 57.3 (CH
3
),
)
2
2
)
2
2
2
)
2
2
[a] C1=C(R); C2=C(CO Et); C3=C(R’). Unless otherwise stated, the spectrum was re-
1
corded in [D ]acetone. [b] The spectrum was recorded in CD Cl .
based on its NMR data. The H NMR spectrum of 7
6
2
2
showed two OCH signals at d=3.68 and 4.90 ppm;
2
13
1
the C{ H} NMR spectrum of 7 showed signals of the
ring carbon atoms at d=246.7, 231.2, and 156.4 ppm for ReC-
(
OEt), ReC(pyren-1-yl), and C(CO Et), respectively, and those of
2
the carbonyl carbons at d=193.9 (cis CO), 192.5 (cis CO), and
91.6 ppm (two trans COs). The NMR data associated with the
metallacycles are similar to those of complexes 4, 5, and 6 as
1
13
1
illustrated by the C{ H} NMR data listed in Table 2.
Scheme 2. The reaction of 4 with ethoxyethyne.
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Scheme 3. The reaction of 5 with ethoxyethyne.
The structure of 9 was confirmed by single-crystal X-ray dif-
fraction (Figure 5). As shown in Table 3, the structural parame-
ters associated with the metallacycle of complex 9 are similar
to those of 8. The NMR data associated with the metallacycle
of complex 9 are also similar to those of 8 (see Table 4), as ex-
pected.
Figure 4. Molecular structure of 8 (thermal ellipsoids set at 30% probability)
Selected bond lengths [ꢁ] and angles [8]: Re1–C1 2.184(3), Re1–C5 2.142(4),
C1–C2 1.356(5), C2–C3 1.444(5), C3–C4 1.392(5), C4–C5 1.391(5); C1–Re1–C5
85.57(13), C2–C1–Re1 125.0(3), C1–C2–C3 125.7(3), C2–C3–C4 127.9(3), C3–
C4–C5 122.0(3), C4–C5–Re1 128.5(3).
The structure of the oily compound 10 was assigned based
on the observation that it reacts with 4-methoxyanilline to
give the crystalline vinyl-substituted rhenacyclobutadiene com-
plex 11, which could be isolated in 65% yield (Scheme 3). Simi-
lar substitution reactions of the rhenacyclobutadiene Re{-
The solution NMR data are also consistent with the solid-
1
state structure. For example, the H NMR spectrum of 8 dis-
1
played a characteristic H signal at d=6.18 ppm due to the
13
1
proton on the metallacyclic ring. The C{ H} NMR spectrum
showed ReC(OEt) and ReC(Ph) signals at d=258.5 and
C(Me)C=(CO Me)C(OEt)=}(CO)4 with amines R2NH to give
2
13
205.1 ppm, respectively. The other C signals of the metallacy-
amino-rhenacyclobutadienes
Re{-C(Me)=C(CO Me)C(NR )=}
2 2
cle were found at d=103.6 (CH), 137.0 (C(CO Et)), and
2
13
1
1
87.9 ppm (C(OEt)). As expected, the C{ H} NMR spectrum of
8
showed three carbonyl signals at d=187.6 (two trans COs),
190.8 (cis CO), and 191.0 ppm (cis CO).
Complex 8 can be regarded as being formed by formal in-
sertion of HCꢀCOEt into the ReÀC(OEt) bond of rhenacyclobu-
tadiene 4. In principle, HCꢀCOEt could also insert into the ReÀ
C(Ph) bond of rhenacyclobutadiene 4 to give the isomeric rhe-
nabenzene complex Re{-C(OEt)=CHC(Ph)=C(CO Et)C(OEt)=
2
}
(CO) . Unfortunately, our attempts to isolate such a complex
4
or its rearranged product were unsuccessful.
We have also carried out the reactions of 4 with alkynes
such as PhCꢀCH, EtCꢀCEt, PhCꢀCOEt, and EtCꢀCOEt. Under
similar condition, no reactions were observed for these al-
kynes. The reactions did not proceed in acetonitrile at room
temperature even after a week.
Reaction of 5 with HCꢀCOEt
Treatment of 5 with HCꢀCOEt also produced a mixture of spe-
cies, from which we were able to isolate two pure compounds,
one in the form of an orange solid and the second in the form
of a yellow oil, in 10 and 15% isolated yields, respectively. The
orange solid was identified as rhenabenzene complex 9 and
the oily compound was identified as rhenacyclobutadiene
Figure 5. Molecular structure of 9 (thermal ellipsoids set at 30% probability)
Selected bond lengths [ꢁ] and angles [8]. Re1–C1 2.175(7), Re1–C5 2.153(7),
C1–C2 1.363(10), C2–C3 1.451(10), C3–C4 1.372(10), C4–C5 1.416(10); C1–
Re1–C5 86.0(3), C2-C1–Re1 126.1(5), C1–C2–C3 125.9(7), C2–C3–C4 127.6(7),
C3–C4–C5 122.8(7), C4–C5–Re1 128.2(6). The mean deviation from the least
squares plane through Re1 and C1–C5=0.08 ꢁ. The maximum deviation
from the least squares plane through Re1 and C1–C5 is À0.14 ꢁ for C5. The
dihedral angle of the metallacycle with respect to the naphthalenyl plane is
93.48.
[
47]
1
complex 10 (Scheme 3). H NMR analysis of spectra recorded
in situ suggested that 9 and 10 were produced in a molar
ratio of 1:1.4.
&
&
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Table 3. Selected bond lengths [ꢁ] and angles [8] for the rhenabenzenes
2 4
Re{-C(R)C(CO Et)=C(OEt)CHC(OEt)=}(CO) (8, 9, and 12).
8
9
12
R
phenyl
naphthelenyl
phenanthrenyl
Re1–C1
Re1–C5
C1–C2
C2–C3
C3–C4
C4–C5
C1–Re1–C5
C2–C1–Re1
C1–C2–C3
C2–C3–C4
C3–C4–C5
C4–C5–Re1
2.184(3)
2.142(4)
1.356(5)
1.444(5)
1.392(5)
1.391(5)
85.57(13)
125.0(3)
125.7(3)
127.9(3)
122.0(3)
128.5(3)
2.175(7)
2.153(7)
1.363(10)
1.451(10)
1.372(10)
1.416(10)
86.0(3)
126.1(5)
125.9(7)
127.6(7)
122.8(7)
128.2(6)
2.163(6)
2.145(6)
1.364(7)
1.456(8)
1.364(8)
1.399(8)
85.5(2)
127.6(4)
124.9(5)
127.5(5)
123.9(5)
129.4(4)
Table 4. Selected NMR chemical shifts for the rhenabenzene complexes
[
a]
Re{-C(R)=C(CO
2
Et)C(OEt)=CHC(OEt)=}(CO)
4
(8, 9, 12, and 14).
8
9
12
14
R
phenyl
naphthelenyl
phenanthrenyl
pyrenyl
C1
C2
C3
C4
C5
CO
205.1
137.0
187.9
103.6
258.5
167.4
13.4 (CH
204.1
137.7
187.3
104.1
259.7
167.6
13.2 (CH
60.0 (CH
13.9 (CH
69.3 (CH
13.7 (CH
67.2 (CH
6.27
203.2
137.8
187.4
104.3
259.8
167.7
13.3 (CH
60.0 (CH
14.0 (CH
69.4 (CH
13.8 (CH
67.3 (CH
6.30
204.8
138.1
188.3
104.4
259.9
167.8
13.2 (CH
60.1 (CH
14.1 (CH
69.5 (CH
13.9 (CH
67.4 (CH
6.33
Figure 6. Molecular structure of 11 (thermal ellipsoids set at 30% probabili-
ty). Selected bond lengths [ꢁ] and angles [8]: Re1–C1 2.169(4), Re1–C3
2
Et
Et
CO
2
3
2
3
2
3
2
),
)
),
)
),
)
3
2
3
2
3
2
),
)
),
)
),
)
3
2
3
2
3
2
),
)
),
)
),
)
3
2
3
2
3
2
),
)
),
)
),
)
2
.186(3), C1–C2 1.376(5), C2–C3 1.464(5), C2–C4 1.483(5), C4–C5 1.351(5);
C1–Re1–C3 61.18(13) Re1–C3–C2 96.2(2), Re1–C1–C2 99.8(2), C1–C2–C3
02.6(3). The mean deviation from the least squares plane through Re1 and
6
0.0 (CH
13.7 (CH
8.9 (CH
13.4 (CH
6.9 (CH
6.18
para-OEt
ReC(OEt)
1
6
C1–C3 is 0.02 ꢁ. The dihedral angle of the metallacycle with respect to the
naphthalenyl plane is 63.98.
6
[
b]
CH
with the four-membered metallacycle are similar to those of
[
3
a] The spectrum was recorded in CD CN. Unless otherwise stated, the
1
3
data are C NMR chemical shifts. The labeling scheme is the same as that
used for the X-ray structures. [b] The data in this row are H NMR chemi-
cal shifts.
the rhenacyclobutadiene complexes 4, 5, and 6 (see Table 1).
1
1
Consistent with the solid-state structure, the H NMR spec-
1
trum of 11 displayed a characteristic H signal at d=4.99 ppm
13
1
for the =CH proton. The C{ H} NMR showed two ReC signals
at d=198.0 (ReC(NHAr)) and 196.0 ppm (ReC(naphthalenyl)),
a CH signal at d=95.1 ppm, a C(OEt) signal at d=161.9 ppm,
and a CC(OEt) signal at d=153.6 ppm.
[
43]
(
CO)4 are known.
The NMR data are consistent with the
1
structure. In particular, the H NMR spectrum showed a CH
13
1
signal at d=4.92 ppm. The C{ H} NMR spectrum showed
a CH signal at d=93.5 ppm, two ReC signals at d=241.4 and
2
13.3 ppm assignable to ReC(OEt) and ReC(naphthalenyl), re-
Reactions of 6 and 7 with HCꢀCOEt
spectively, and two signals at d=160.4 and 160.2 ppm, assign-
able to C(OEt) and CC(OEt), respectively. The cis arrangement
Similar reactions occurred when the metallacyclobutadiene
complexes 6 and 7 were treated with HCꢀCOEt. The reaction
of 6 produced rhenabenzene 12 (isolated in 8% yield) and the
vinyl-substituted metallacyclobutadiene complex 13 (isolated
in 15.3% yield); the reaction of 7 produced rhenabenzene 14
(isolated in 5% yield) and vinyl-substituted metallacyclobuta-
of OEt and H in the vinyl group -C(OEt)=CH(CO Et) was con-
2
1
firmed by an NOE experiment. When the H signal of =CH at
d=4.92 ppm was irradiated, the OCH signal of C(OEt) at d=
2
3.16 ppm was enhanced by 5.7%.
The structure of complex 11 was subsequently determined
1
by a single-crystal X-ray diffraction study. As shown in Figure 6,
the complex contains a four-membered metallacycle with the
diene complex 15 (isolated in 6% yield) (Scheme 4). H NMR
spectra measured in situ showed that 12 and 13 were pro-
duced in a molar ratio of 1:1.3; and 14 and 15 were produced
in a molar ratio of 1:1.1. The ratios are similar to (or slightly
less than) that of complexes 9 and 10 produced from the reac-
tion of HCꢀCOEt with 5 (1:1.4).
vinyl substituent -C(OEt)=CH(CO Et) at the b-carbon. In the
2
vinyl substituent, the OEt and CO Et groups are confirmed to
2
be trans to each other. The structural parameters associated
Chem. Eur. J. 2014, 20, 1 – 16
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Table 5. Selected NMR chemical shifts for rhenacyclobutadiene com-
[
a]
2 4
plexes Re{-C(R)=C(C(OEt)=CH(CO Et))C(X)=}(CO) (10, 11, 13 and 15).
[
b]
1
0
11
13
15
R
X
naphthelenyl naphthelenyl
phenanthrenyl pyrenyl
OEt
p-NHC
6
H
4
OMe OEt
OEt
C1
C2
C3
C4
C5
CO
213.3
160.2
241.4
160.4
93.5
166.2
13.2 (CH
58.7 (CH
13.5 (CH
196.0
153.6
198.0
161.9
95.1
212.9
160.2
241.4
160.3
93.5
166.2
13.2 (CH
58.7 (CH
13.5 (CH
79.1 (CH
12.0 (CH
63.6 (CH
4.90
213.6
160.7
241.5
160.7
93.8
166.4
13.4 (CH
59.0 (CH
13.7 (CH
79.3 (CH
12.0 (CH
63.7 (CH
4.96
2
Et
Et
167.1
CO
2
3
2
3
2
3
2
),
)
),
)
),
)
15.1 (CH
60.6 (CH
3
),
)
3
2
3
2
3
2
),
)
),
)
),
)
3
2
3
2
3
2
),
)
),
)
),
)
Scheme 4. Reactions of 6 and 7 with ethoxyethyne.
2
[
d]
ReCOEt
7
9.1 (CH
OEt at C4 12.0 (CH
3.6 (CH
4.92
1
14.1 (CH
65.3 (CH
4.99
3
),
)
Interestingly, we were not able to identify, by H NMR meas-
urements in situ, the signal of a similar vinyl-substituted metal-
lacyclobutadiene complex from the reaction of HCꢀCOEt with
6
2
[c]
CH
[
3
a] The spectrum was recorded in CD CN. Unless otherwise stated, the
data are C{ H} NMR chemical shifts. The labeling scheme is the same as
4
. It appears that the aryl substituents of the starting metalla-
13
1
cyclobutadiene complexes have an appreciable effect on the
relative amounts of rhenabenzenes and vinyl-substituted rhe-
nacyclobutadiene complexes, although the exact cause for the
effect is still not clear to us.
that used for the X-ray structures. [b] The spectrum was recorded in
1
CD
2
Cl
2
. [c] The data in this row are H NMR chemical shifts. [d] See experi-
6 4
mental section for the NMR data of p-NHC H OMe.
The structure of the rhenabenzene 12 was confirmed by X-
ray diffraction analysis (Figure 7). The solution NMR data are
consistent with the solid-state structure (see Table 4). The
structure of rhenabenzene 14 can be assigned based on the
NMR data. In particular, the NMR signals associated with the
metallacycle are similar to those of the analogous rhenaben-
zenes 8 and 9 (see Table 4). The structures of complexes 13
and 15 were assigned based on the fact that the NMR data as-
sociated with the respective metallacycles are similar to those
of analogous rhenacyclobutadiene 10, as illustrated by the
Reaction of an amino-rhenacyclobutadiene with HCꢀCOEt
After the successful preparation of rhenabenzenes from the re-
actions of alkoxyrhenacyclobutadienes with HCꢀCOEt, we then
examined the reaction of amino-rhenacyclobutadiene 16 with
HCꢀCOEt. Compound 16 could be readily prepared in 85% iso-
lated yield by the reaction of 4 with Et NH (Scheme 5). The
2
complex has been characterized by NMR spectroscopy and by
X-ray diffraction analysis (Figure 8). When complex 16 was
treated with HCꢀCOEt, no reaction was observed.
13
1
C{ H} NMR data shown in Table 5.
Scheme 5. Synthesis of amino-rhenacyclobutadiene 16.
[48]
Mechanism for the formation of rhenabenzene complexes
Rhenabenzenes are produced from the reactions of HCꢀCOEt
with alkoxy-containing rhenacyclobutadienes at room temper-
ature; therefore, a reaction involving dissociation/association
of carbonyl is unlikely. Indeed, our DFT calculations show that
the substitution reaction of the model rhenacyclobutadiene
complex Re{-C(Ph)=C(CO Et)C(OEt)=}(CO)4 with the alkyne
2
HCꢀCOMe to give the alkyne–rhenacyclobutadiene complex
Figure 7. Molecular structure of 12 (thermal ellipsoids set at 30% probabili-
ty). Selected bond lengths [ꢁ] and angles [8]: Re1–C1 2.163(6), Re1–C5
2
Re(h -HCꢀCOMe) {-C(Ph)=C(CO Et)C(OEt)=}(CO) is thermody-
2
4
À1
namically unfavorable by 22.7 kcalmol . The [2+2] cycloaddi-
2
.145(6), C1–C2 1.364(7), C2–C3 1.456(8), C3–C4 1.364(8), C4–C5 1.399(8);
C1–Re1–C5 85.5(2), C2–C1–Re1 127.6(4), C1–C2–C3 124.9(5), C2–C3–C4
27.5(5), C3–C4–C(5) 123.9(5), C4–C5–Re1 129.4(4). The mean deviation from
tion reaction of alkyne–rhenacyclobutadiene complex to give
1
À1
a metallabenzene complex has a barrier of 8.4 kcalmol (see
the least squares plane through Re1 and C1–C5=0.05 ꢁ. The maximum de-
viation from the least squares plane through Re1 and C1–C5 is 0.08 ꢁ for
Re1. The dihedral angle of the metallacycle with respect to the phenan-
threnyl plane is 91.08
the Supporting Information). The overall barrier for the forma-
À1
tion of the metallabenzene complex (31.1 kcalmol ) is higher
than that calculated for the pathway described below.
&
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Scheme 6. A proposed mechanism for the formation of rhenabenzenes.
can also rearrange through an even lower energy barrier to
give the five-membered metallacycle 22, which contains
a free-carbene group stabilized by the OMe substituent. Com-
plex 22 eventually evolves to the metallabenzene complex 23
À1
via TS22–23 with a small reaction barrier of 7.4 kcalmol . The re-
sults shown in Figure 9 indicate that the addition of alkyne to
the a-carbon of the rhenacyclobutadiene complex 20 is a cru-
cial step for the reaction.
Figure 8. Molecular structure of 16 (thermal ellipsoids set at 30% probabili-
ty). Selected bond lengths [ꢁ] and angles [8]: Re1–C1 2.187(4), Re1–C3
We have also investigated the energetics for nucleophilic ad-
dition through the terminal carbon of HCꢀCOMe to the C(Ph)
carbene carbon of metallacycle 20. The reaction was also
2
9
.178(9), C1–C2 1.374(6), C2–C3 1.449(7); C1–Re1–C3 60.4(2), Re1–C3–C(2)
7.6(4), Re1–C1–C2 99.7(3), C1–C2–C3 102.1(5). The mean deviation from the
least squares plane through Re1 and C1–C3 is 0.01 ꢁ. The dihedral angle of
the metallacycle with respect to the phenyl plane is 31.18.
À1
found to have a reaction barrier of 26.7 kcalmol , which is the
same as that for the nucleophilic addition of the terminal
carbon of HCꢀCOMe to the C(OMe) carbene carbon of metalla-
cycle 20. The calculated results suggest that reaction of HCꢀ
COEt with rhenacyclobutadiene 4 at the ReÀC(Ph) bond to
give the isomeric rhenabenzene complex Re{-C(OEt)=CHC(Ph)=
We noted that alkynes such as PhCꢀCH, EtCꢀCEt, PhCꢀCOEt,
and EtCꢀCOEt do not undergo analogous reactions under simi-
lar conditions. Therefore, the higher reactivity of HCꢀCOEt
must be related to its special properties. It is known that the
b-carbon of an alkoxyalkyne RCꢀCOR is nucleophilic, and that
a Fischer carbene carbon is electrophilic. Therefore, we pro-
pose that the reaction is initiated by direct nucleophilic attack
of the b-carbon of HCꢀCOEt on the carbene carbon of the rhe-
nacyclobutadienes, as illustrated by the mechanism shown in
Scheme 6 with a rhenacyclobutadiene represented as 17. Such
a direct nucleophilic attack could
C(CO Et)C(OEt)=}(CO)4 could also occur, although we have
2
failed to isolate the related rhenabenzene or its rearranged
products from the reaction mixture. The low yield of isolated
rhenabenzenes and complex appearance of the NMR spectra
measured in situ may indicate that such a reaction indeed oc-
curred.
give intermediate 18, which
could rearrange to the final rhe-
nabenzene 19. Nucleophilic
attack on the vinylidene a-
carbon of M(CO) (=C=CAr ) by
5
2
[
49]
HCꢀCOR has been reported.
The proposed reaction mecha-
nism is supported by a computa-
tional study. Figure 9 shows the
calculated energy profile for the
reaction of the model rhenacy-
clobutadiene complex 20 with
HCꢀCOMe. As shown in Figure 9,
nucleophilic addition through
the terminal carbon of HCꢀ
COMe to the C(OMe) carbene
carbon of metallacycle 20 to
give the zwitterionic complex 21
via TS20–21 has a moderate reac-
À1
tion barrier of 26.7 kcalmol .
The rearrangement through the
bicyclo-transition state TS21–23 to
give the metallabenzene com-
Figure 9. Energy profile calculated for the reaction of the model complex 20 with HCꢀCOMe to give the rhena-
plex 23 has an overall barrier of
benzene complex 23. The relative Gibbs free energies (298 K) and electronic energies (in parentheses) are given in
À1
À1
2
8.8 kcalmol . Interestingly, 21 kcalmol
.
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Figure 11. Energy profile calculated for the reaction of the model complex
2
5 with HCꢀCOMe to give the rhenabenzenes complex 26. The relative
Gibbs free energies (298 K) and electronic energies (in parentheses) are
given in kcalmol
À1
.
Figure 10. Energy profiles calculated for the reactions of the model complex
2
0 with RCꢀCR’ to give the rhenabenzene complexes 24A, 24B, and 24C.
The relative Gibbs free energies (298 K) and electronic energies (in parenthe-
ses) are given in kcalmol
À1
.
pears to be related to the energies of the LUMOs of Re{-C(Ph)=
C(CO Me)C(OMe)=}(CO) (20) and Re{-C(Ph)=C(CO Me)C(NMe )=
2
4
2
2
To understand why alkoxyalkynes such as PhCꢀCOEt and
EtCꢀCOEt and simple aryl- and alkylalkynes such as PhCꢀCH,
EtCꢀCEt do not undergo analogous reactions under similar
conditions, the addition barriers for the reactions of 20 with al-
kynes such as PhCꢀCH, MeCꢀCMe, and MeCꢀCOEt were also
calculated (Figure 10). Our calculations confirm that reactions
}(CO) (25), and to the NBO charge of the ReC(OMe) carbon of
4
Re{-C(Ph)=C(CO Me)C(OMe)=}(CO) (20) and that of the ReC-
2
4
(NMe ) carbon of Re{-C(Ph)=C(CO Me)C(NMe )=}(CO) (25). Cal-
2
2
2
4
culations show that the compositions of the LUMOs calculated
for the two complexes are similar and are mainly composed of
the p orbitals of the two a-carbon atoms and O for 20 or N
p
of the model complex 20 with PhCꢀCH, MeCꢀCMe, and MeCꢀ for 25 (Figure 12). The energy of the LUMO of 20 (À2.46 eV) is
COMe to give analogous rhenabenzene complexes are thermo-
dynamically feasible. However, they all have substantially
À1
higher addition barriers (the barriers are 45.0 kcalmol for
À1
À1
MeCꢀCMe, 34.0 kcalmol for PhCꢀCH, and 33.8 kcalmol for
MeCꢀCOMe). The results suggest that the lower reactivity of al-
kynes PhCꢀCOEt, EtCꢀCOEt, PhCꢀCH, and EtCꢀCEt in their re-
actions with rhenacyclobutadiene 4 is due to kinetics. The
lower reactivity of PhCꢀCOEt and EtCꢀCOEt could be related
to steric effects. It is also understandable that PhCꢀCH and
EtCꢀCEt are much less reactive than HCꢀCOEt, because these
alkynes are less nucleophilic and the expected transition states
or the resulting intermediates could not be stabilized because
of the lack of p-donor substituents.
Figure 12. Plots of LUMOs of complexes 20 and 25 and their corresponding
energy, and selected NBO charges.
To understand why the amino-rhenacyclobutadiene 16 does
not react with HCꢀCOMe under similar conditions to give the
analogous rhenabenzene, we also calculated the addition bar-
rier for the reaction of the model rhenacyclobutadiene com-
plex Re{-C(Ph)=C(CO Me)C(NMe )=}(CO) (25) with HCꢀCOMe.
significantly lower than that of 25 (À1.95 eV). The NBO charge
of the ReC(OMe) carbon of Re{-C(Ph)=C(CO Me)C(OMe)=}(CO)
2
4
(20) (0.488) is larger than that of the ReC(NMe ) carbon of Re{-
2
C(Ph)=C(CO Me)C(NMe )-}(CO) (25) (0.249). The results are con-
2
2
4
2
2
4
Our computational results suggest that the reaction of 25 with
HCꢀCOMe to give the analogous rhenabenzene complex Re{-
C(Ph)=C(CO Me)C(NMe )=CHC(OMe)=}(CO) (26) is thermody-
sistent with the experimental observation that 16 is less reac-
tive than 4 in their reactions with HCꢀCOEt under similar con-
ditions to give rhanabenzenes, if one assumes that the reac-
tions of amino-rhenacyclobutadienes and alkoxy-rhenacyclobu-
tadienes (electrophiles) towards HCꢀCOR (nucleophiles) are
charge-controlled and/or frontier-orbital controlled, that is,
LUMO-controlled.
2
2
4
À1
namically favorable by 35.5 kcalmol (Figure 11). However, nu-
cleophilic addition through the terminal carbon of HCꢀCOMe
to the C(NMe ) carbene carbon of metallacycle 25 was found
2
À1
to have a noticeably higher addition barrier of 34.4 kcalmol ,
suggesting that the lower reactivity of the amino-rhenacyclo-
butadiene Re{-C(Ph)=C(CO Et)C(NEt )=}(CO) (16) towards HCꢀ
2
2
4
Comments on the aromatic nature of the rhenabenzenes
COEt is of kinetic origin.
The difference in the reactivity of amino-rhenacyclobuta-
Organic aromatic systems such as benzene have a delocalized
dienes and alkoxy-rhenacyclobutadienes towards HCꢀCOR ap-
planar ring structure with bonds of equal or similar CÀC
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lengths intermediate between single and double carbon–
carbon bonds. As mentioned above, the structurally character-
ized rhenabenzenes have an essentially planar metallacycle.
The ReÀC bond distances are intermediate between those of
Re=C carbene and ReÀC vinyl bonds. The ring CÀC distances
are in the range of 1.350–1.469 ꢁ, which are intermediate be-
tween single and double carbon–carbon bonds. We noted that
the structurally characterized rhenabenzenes do show some-
what unequal ReÀC, C ÀC , and C ÀC bond distances. The ex-
that proton chemical shifts are not generally reliable aromatici-
[53]
ty indicators.
To further support the aromatic character of the rhenaben-
zenes, we have estimated the aromatic stabilization energy
(ASE) values of several model rhenabenzenes by using the iso-
[54]
merization method introduced by Schleyer et al. The model
rhenabenzene complex 30 was estimated to have an ASE
À1
value of 21.5 kcalmol at the B3LYP/6-311+G** + lanl2dz
level (Figure 15). In contrast, the reaction energy for the con-
a
b
b
g
perimentally observed structural features are in agreement
with the calculated structural parameters of the model rhene-
benzenes, as illustrated by those calculated for complex 8
(Figure 13). The unequal bond distances are expected consid-
Figure 13. Selected calculated bond distances [ꢁ] of the rhenabenzenes 8
and 27, calculated at the B3LYP/6-311+G** + lanl2dz level in the gas phase.
The experimentally observed bond distances of 8 are in parentheses.
ering the unsymmetrical nature of the metallacycles. Our calcu-
lations confirm that symmetric rhenabenzene model complex
2
7 indeed has equal ReÀC, C ÀC , and C ÀC bond distances
a
b
b
g
(Figure 13). This structural feature indicates that the metallacy-
cle has a delocalized structure, and has aromatic character.
Protons of aromatic compounds usually have a relatively
large downfield NMR spectroscopic shift due to aromatic ring
1
current. The H signals of ReC(OEt)CH of the rhenabenzene
complexes 8, 9, 12, and 14 appeared at approximately d=6.2–
6
.3 ppm. The chemical shift is close to that (d=6.48 ppm) of
[50]
the proton at the C2 carbon of 1,3-dimethoxybenzene (28a),
Figure 15. ASE values of toluene and metallabenzenes derived from the iso-
merization method, calculated at the B3LYP/6-311+G** + lanl2dz level in
the gas phase.
and downfield with respect to that of the proton (d=4.5 ppm)
at the C2 carbon of 1,3-dimethoxy-5-methyl-cyclohexa-1,3-
[
51]
diene (28b) (Figure 14). The similarity in the chemical shifts
version of partially unsaturated metallacycle 32 into 33 was
À1
calculated to be only 2.0 kcalmol . The results clearly show
that the model rhenabenzene complex 30 has appreciable ASE
and therefore shows aromatic character. The calculations also
indicate that analogous rhenabenzenes with an OEt substitu-
ent (34, 36, and 38) and phosphine ligand (40) have slightly
lower ASE values. The ASE value of toluene (42) was found to
1
Figure 14. H NMR data of 1,3-dimethoxybenzene (28a) and 1,3-dimethoxy-
5
-methyl-cyclohexa-1,3-diene (28b), and the alkoxy carbene complex 29.
À1
be 33.7 kcalmol in our calculations. Thus, the aromatic char-
acter of rhenabenzenes is substantially less than that of ben-
zene.
of the CH signals of the rhenabenzenes and 1,3-dimethoxyben-
zene may also be taken as an indication of aromaticity of the
rhenabenzenes. However, we notice that the b-CH of alkoxy
For comparison, we have also calculated ASE values of relat-
[55]
ed metallabenzenes with Pt, Ir, and Os (Figure 16). The calcu-
lated results suggest that the model rhenabenzene 30 has an
ASE value slightly smaller than those calculated for platinaben-
zene 44 and iridabenzene 48, comparable to that of osmaben-
[
52]
complex 29 has a chemical shift of d=6.25 ppm. Thus, we
feel that the NMR evidence is not conclusive for their aromatic
character. In this regard, Schleyer et al. recently pointed out
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used as purchased from Aldrich Chemical Co. The starting materi-
[43]
[56]
[57]
als Na[Re(CO)5], PhCꢀCOEt, and EtCꢀCOEt were synthesized
by using reported procedures. Microanalyses were performed by
M-H-W Laboratories (Phoenix, AZ). NMR spectra were collected
1
13
with a Bruker AV-300 spectrometer ( H 300.1 MHz; C 75.5 MHz) or
1
13
a Bruker AV-400 spectrometer ( H 400.1 MHz; C 100.6 MHz).
General procedure for the preparation of alkyl arylpropio-
late
To a solution of arylacetylene (13.8 mmol) in THF (50 mL) was
slowly added a solution of n-butyllithium (2.0m in cyclohexane,
1
5.2 mmol) at À788C. After stirring for 1 h, ethyl chloroformate
(1.32 mL, 13.8 mmol) was added. The reaction mixture was stirred
at this temperature for 30 min and for 3 h at RT to give a brown
suspension. This suspension was poured into a separating funnel
and washed successively with water and brine. The organic layer
was collected, dried with MgSO , and filtered. The filtrate was con-
4
centrated under reduced pressure to give a dark-brown oil, which
was subjected to chromatography with a silica gel column. The
column was eluted with a mixture of n-hexane and dichlorome-
thane in various ratios (a mixture with a 5:1 (v/v) ratio proved to
[58]
be effective in most cases).
General procedure for the preparation of rhenacyclobuta-
diene complexes
To a solution of Na[Re(CO) ] (0.500 g, 1.43 mmol) in THF (20 mL)
5
was slowly added one equivalent of an alkyl arylpropiolate in THF
(20 mL) at RT. The mixture was stirred for 12 h to give a red-brown
solution. The solvent was removed under vacuum to give an
orange-brown sticky residue, which was subsequently dissolved in
CH Cl . The solution was cooled to À158C and acetyl chloride
2
2
(
0.15 mL, 2.10 mmol) was added. The mixture turned dark-red im-
Figure 16. ASE values of metallabenzenes derived from the isomerization
method, calculated at the B3LYP/6-311+G** + lanl2dz level in the gas
phase.
mediately. After 20 min stirring, ethanol (10 equiv) was added and
the mixture was allowed to warm to RT. A yellow-brown residue
was obtained after removal of the solvent under reduced pressure.
The product was purified by silica gel column chromatography to
give the desired complex as a bright-orange or red solid. The
column was eluted with a mixture of n-hexane and diethyl ether in
various ratios (a mixture with a 7:1 (v/v) ratio proved to be effec-
tive in many cases).
zene 54, and slightly larger than those for iridabenzenes 46
and 50.
Re{-C(Ph)=C(CO Et)C(OEt)=}(CO) (4): Obtained from Na[Re(CO)5]
2
4
Conclusion
(0.50 g, 1.43 mmol), ethyl 3-phenylpropiolate (0.27 g, 1.43 mmol),
and ethanol (0.8 mL, 13.7 mmol). Yield: 0.28 g (37%); bright-
We have successfully isolated and characterized a series of rhe-
nabenzene complexes. The NMR spectroscopic and X-ray struc-
tural data, as well as the ASE values, suggest that these rhena-
benzenes do have aromatic character, although the aromatic
character is substantially less than that of benzene. Most of the
rhenabenzenes show only a weak alternating double/single
bond character around the ring, but most of this can be attrib-
uted to the electronic asymmetry in the substituent groups fa-
voring one resonance form over another.
1
orange solid; H NMR (400.1 MHz, CD COCD ): d=1.15 (t, J=
3
3
7
.2 Hz, 3H; CO CH CH ), 1.62 (t, J=7.2 Hz, 3H; OCH CH ), 4.09 (q,
2 2 3 2 3
J=7.2 Hz, 2H; CO CH CH ), 4.87 (q, J=7.2 Hz, 2H; OCH CH ), 7.47–
2
2
3
13
2
3
1
7
.55 ppm (m, 5H; Ph); C{ H} NMR (100.6 MHz, CD COCD ): d=
3 3
12.8 (s, CO CH CH ), 13.5 (s, OCH CH ), 59.0 (s, CO CH CH ), 79.4 (s,
2
2
3
2
3
2
2
3
OCH
CH ), 127.6, 128.1, 130.0, 144.9 (all s, C of Ph), 153.0 (s,
3
2
C(CO Et)), 159.3 (s, CO Et), 189.7 (s, trans Re(CO)), 190.8 (s, Re(CO)),
2
2
1
93.3 (s, Re(CO)), 221.8 (s, ReC(Ph)), 241.9 (s, ReC(OEt)); elemental
analysis (%) calcd for C H O Re: C 40.83, H 2.86; found: C 41.03, H
18
15
7
3
.03.
Re{C-(naphthalen-1-yl)=C(CO Et)C(OEt)=}(CO) (5): Obtained from
2
4
Na[Re(CO) ] (0.50 g, 1.43 mmol), ethyl 3-(naphthalen-1-yl)propiolate
5
Experimental Section
(
0.32 g, 1.43 mmol), and ethanol (0.8 mL, 13.7 mmol). Yield: 0.39 g
1
All manipulations were carried out at RT under a nitrogen atmos-
phere by using standard Schlenk techniques, unless otherwise
stated. Solvents were distilled under nitrogen from sodium benzo-
phenone (n-hexane, cyclohexane, diethyl ether, tetrahydrofuran), or
calcium hydride (acetonitrile, dichloromethane). Reagents were
(46%); bright-orange solid; H NMR (400.1 MHz, CD COCD ): d=
3 3
0.57 (t, J=7.2 Hz, 3H; CO CH CH ), 1.63 (t, J=7.2 Hz, 3H;
2
2
3
OCH CH ), 3.66 (q, J=7.2 Hz, 2H; CO CH CH ), 4.86 (q, J=7.2 Hz,
2
3
2
2
3
2H; OCH CH ), 7.33 (d, J=6.8 Hz, 1H; naphthalen-1-yl), 7.4–7.6 (m,
2
3
3H; naphthalen-1-yl), 7.78 (d, J=8 Hz, 1H; naphthalen-1-yl), 7.85
&
&
Chem. Eur. J. 2014, 20, 1 – 16
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10
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
(
d, J=8 Hz, 1H; naphthalen-1-yl), 7.93 ppm (d, J=7.6 Hz, 1H;
(1:1 v/v) gave two fractions (one red and the second orange). The
1
3
1
1
naphthalen-1-yl); C{ H} NMR (100.6 MHz, CD COCD ): d=12.1 (s,
CO CH CH ), 13.5 (s, OCH CH ), 58.6 (s, CO CH CH ), 80.2 (s,
red fraction showed no H NMR signals in the region d=5–7 ppm
3
3
1
in the H NMR spectrum, and was discarded. The solvent of the
2
2
3
2
3
2
2
3
OCH CH ), 121.5, 124.6, 124.7, 125.5, 125.6, 127.6, 127.7, 132.7,
orange fraction was removed under reduced pressure to give
a dark-orange sticky material. The residue was extracted with
hexane and stored in a freezer at À308C for 48 h to afford red-
orange needle-shaped crystals. The crystalline solid was collected
by filtration, washed with cold hexane, and dried under vacuum.
2
3
1
46.3 ( all s, C of naphthalen-1-yl), 155.3 (s, C(CO Et)), 157.8 (s,
2
CO Et), 189.9 (s, trans Re(CO)), 191.0 (s, Re(CO)), 192.8 (s, Re(CO)),
2
2
27.9 (s, ReC(naphthalen-1-yl)), 245.5 (s, ReC(OEt)); elemental analy-
sis (%) calcd for C H O Re·H O: C 44.22, H 3.20; found: C 43.49, H
2
2
17
7
2
1
3
.00.
Yield: 53 mg (5%); bright-orange solid; H NMR (400.1 MHz,
CD CN): d=0.94 (t, J=7.2 Hz, 3H; CO CH CH ), 1.37 (t, J=7.2 Hz,
Re{-C(phenanthren-9-yl)=C(CO Et)C(OEt)=}(CO)4 (6): Obtained
3
2
2
3
2
3
7
H; ReC(OCH CH )), 1.51 (t, J=7.2 Hz, 3H; C(OCH CH )), 3.76 (q, J=
2 3 2 3
from Na[Re(CO) ] (0.50 g, 1.43 mmol), ethyl 3-(phenanthren-9-yl)-
5
.2 Hz, 2H; CO CH CH ), 4.29 (q, J=7.2 Hz, 2H; ReC(OCH CH )),
propiolate (0.39 g, 1.43 mmol), and ethanol (0.8 mL, 13.7 mmol).
2
2
3
2
3
1
4.42 (q, J=7.2 Hz, 2H; C(OCH CH )), 6.18 (s, 1H; CH), 6.84 (d, J=
2 3
Yield: 0.31 g (35%); bright-orange solid; H NMR (400.1 MHz,
7
2
.6 Hz, 2H; Ph), 7.01 (t, J=7.6 Hz, 1H; Ph), 7.28 ppm (t, J=7.6 Hz,
CD COCD ): d=0.51 (t, J=7.2 Hz, 3H; CO CH CH ), 1.69 (t, J=
3
3
2
2
3
13
1
H; Ph); C{ H} NMR (75.7 MHz, CD CN): d=13.4 (s, CO CH CH
3
7
.2 Hz, 3H; OCH CH ), 3.63 (q, J=7.2 Hz, 2H; CO CH CH ), 4.99 (q,
3
2
2
2
3
2
2
3
and ReC(OCH CH )), 13.7 (s, C(OCH CH )), 60.0 (s, CO CH CH ), 66.9
J=7.2 Hz, 2H; OCH CH ), 7.64--7.74 (m, 5H; phenanthren-9-yl),
2
3
2
3
2
2
3
2
3
(
s, ReC(OCH CH )), 68.9 (s, C(OCH CH )), 103.6 (s, CH), 121.8, 124.5,
7
.89 (d, J=8.0 Hz, 1H; phenanthren-9-yl), 8.10 (d, J=7.6 Hz, 1H;
2 3 2 3
1
27.6, 158.9 (s, C of Ph), 137.0 (s, C(CO Et)), 167.4 (s, CO Et), 187.9
2 2
phenanthren-9-yl), 8.82 (d, J=8.4 Hz, 1H; phenanthren-9-yl),
13
1
(s, C(OEt)), 187.6 (s, trans Re(CO)), 190.8 (s, Re(CO)), 191.0 (s,
Re(CO)), 205.1 (s, ReC(Ph)), 258.5 (s, ReC(OEt)); elemental analysis
8
.90 ppm (d, J=8.1 Hz, 1H; phenanthren-9-yl);
C{ H} NMR
(
100.6 MHz, CD COCD ): d=13.4 (s, CO CH CH ), 14.8 (s, OCH CH ),
3
3
2
2
3
2
3
(
%) calcd for C H O Re: C 44.07, H 3.53; found: C 44.28, H 3.72.
5
1
9.6 (s, CO CH CH ), 81.4 (s, OCH CH ), 123.3, 123.4, 123.9, 126.6,
27.2, 127.3, 127.6, 127.9, 128.0, 130.0, 130.7, 130.8, 132.0, 146.6 (all
22 21 8
2
2
3
2
3
Re{-C(naphthalen-1-yl)=C(CO Et)C(OEt)=CHC(OEt)=}(CO) (9): Ob-
2
4
s, C of phenanthren-9-yl), 156.9 (s, C(CO Et)), 158.7 (s, CO Et), 191.4
2
2
tained from Re{C(naphthalen-1-yl)C(CO Et)C(OEt)}(CO)4 (5; 1.04 g,
2
(
s, trans Re(CO)), 192.2 (s, Re(CO)), 193.9 (s, Re(CO)), 228.7 (s, Re-
1
.80 mmol). Purified by column chromatography (n-hexane/diethyl
C(phenanthren-9-yl)), 246.2 (s, ReC(OEt)); elemental analysis (%)
ether, 1:1 v/v). The fraction was a reddish orange solution. A dark-
orange sticky material was obtained after removing the solvents.
The residue was extracted with a minimal amount of petroleum
ether/dichloromethane [v/v=20:1]. Storing the resultant orange
solution in a freezer at À308C for 48 h afforded bright-orange crys-
tals. The crystalline solid was collected by filtration, washed with
calcd for C H O Re: C 49.60, H 3.04; found: C 49.43, H 3.24.
2
6
19
7
Re{-C(pyren-1-yl)=C(CO Et)C(OEt)=}(CO)
(7): Obtained from
2
4
Na[Re(CO)5] (0.50 g, 1.43 mmol), ethyl 3-(pyren-1-yl)propiolate
(
(
0.43 g, 1.43 mmol), and ethanol (0.8 mL, 13.7 mmol). Yield: 0.56 g
1
60%); bright-red solid; H NMR (400.1 MHz, CD Cl ): d=0.48 (t, J=
2
2
7
.2 Hz, 3H; CO CH CH ), 1.72 (t, J=7.2 Hz, 3H; OCH CH ), 3.68 (q,
cold hexane, and dried under vacuum. Yield: 116 mg (10%);
2
2
3
2
3
1
J=7.2 Hz, 2H; CO CH CH ), 4.90 (q, J=7.2 Hz, 2H; OCH CH ), 7.87
bright-orange solid; H NMR (400.1 MHz, CD CN): d=0.57 (t, J=
2
2
3
2
3
3
(
8
d, J=8.0 Hz, 1H; pyren-1-yl), 8.02–8.15 (m, 5H; pyren-1-yl), 8.22–
7.2 Hz, 3H; CO CH CH ), 1.39 (t, J=7.2 Hz, 3H; ReC(OCH CH )), 1.54
(t, J=7.2 Hz, 3H; C(OCH CH )), 3.56 (q, J=7.2 Hz, 2H; CO CH CH ),
2 3 2 2 3
2
2
3
2
3
13
1
.28 ppm (m, 3H; pyren-1-yl); C{ H} NMR (100.6 MHz, CD Cl ): d=
2
2
1
3.9 (s, CO CH CH ), 15.5 (s, OCH CH ), 60.3 (s, CO CH CH ), 81.4 (s,
4.35 (q, J=7.2 Hz, 2H; ReC(OCH CH )), 4.46 (q, J=7.2 Hz, 2H;
2 3
2
2
3
2
3
2
2
3
OCH CH ), 123.8, 124.6, 125.1, 125.3, 125.6, 125.8, 126.1, 126.4,
C(OCH CH )), 6.27 (s, 1H; CH), 6.83 (d, J=7.2 Hz, 1H; naphthalen-1-
2 3
2
3
1
27.1, 128.2, 128.3, 128.7, 131.7, 132.0, 132.4, 145.0 (all s, C of
yl), 7.41 (m, 3H; naphthalen-1-yl), 7.57 (d, J=8.4 Hz, 1H; naphtha-
len-1-yl), 7.70 (d, J=8.0 Hz, 1H; naphthalen-1-yl), 7.75 ppm (d, J=
pyren-1-yl), 156.4 (s, C(CO Et)), 159.4 (s, CO Et), 191.6 (s, trans
2
2
13
1
Re(CO)), 192.5 (s, Re(CO)), 193.9 (s, Re(CO)), 231.2 (s, ReC(pyren-1-
yl)), 246.7 (s, ReC(OEt)); elemental analysis (%) calcd for
C H O Re·0.5CH Cl : C 49.17, H 2.90; found: C 49.47, H 3.22.
8.4 Hz, 1H; naphthalen-1-yl); C{ H} NMR (100.6 MHz, CD CN): d=
3
13.2 (s, CO CH CH ), 13.7 (s, ReC(OCH CH )), 13.9 (s, C(OCH CH )),
2
2
3
2
3
2
3
2
8
19
7
2
2
60.0 (s, CO CH CH ), 67.2 (s, ReC(OCH CH )), 69.3 (s, C(OCH CH )),
2
2
3
2
3
2
3
1
1
04.1 (s, CH), 124.9, 125.0, 125.4, 126.0, 127.2, 127.3, 128.3, 133.8,
56.1 (all s, C of naphthalen-1-yl), 137.7 (s, C(CO Et)), 167.6 (s,
2
General procedure for the isolation of rhenabenzenes and
vinyl-substituted rhenacyclobutadiene complexes
CO Et), 187.3 (s, C(OEt)), 188.2 (s, Re(CO)), 188.4 (s, Re(CO)), 190.7 (s,
trans Re(CO)), 204.1 (s, ReC(naphthalen-1-yl)), 259.7 (s, ReC(OEt)); el-
2
emental analysis (%) calcd for C H O Re: C 48.07, H 3.57; found: C
26
23
8
A solution of HCꢀCOEt (40wt% solution in hexanes, 1.32 mL,
4
8.00, H 3.81.
5
.42 mmol) was added to a solution of rhenacyclobutadiene
(
1.80 mmol) in acetonitrile (80 mL). The resulting mixture was
Re{-C(naphthalen-1-yl)=C(C(OEt)=CH(CO Et))C(OEt)=}(CO)4 (10):
2
stirred in an ice bath for 1 h, then warmed slowly to RT and stirred
at RT for ca. 12 h to give a dark red-brown suspension. A dark-
brown residue was obtained after removal of the solvent under re-
duced pressure. The product was purified by silica gel column
chromatography to give the desired complex as a bright-orange
solid or a yellow oil. The eluents used for column chromatography
were mixtures of n-hexane and diethyl ether in various ratios.
Obtained from Re{C(naphthalen-1-yl)C(CO Et)C(OEt)}(CO)
(5;
2
4
1
.04 g, 1.80 mmol). Purified by column chromatography (n-hexane/
diethyl ether, 10:1 v/v). The fraction was a light-yellow solution. A
yellow oil was obtained after removal of the solvents. Yield:
1
1
78 mg (15%); yellow oil; H NMR (400.1 MHz, CD CN): d=0.41 (t,
3
J=7.2 Hz, 3H; C(OCH CH )), 1.24 (t, J=7.2 Hz, 3H; CO CH CH ),
2
3
2
2
3
1
.53 (t, J=7.2 Hz, 3H; ReC(OCH CH )), 3.16 (d, J=6.0 Hz, 2H;
2 3
Re{-C(Ph)=C(CO Et)C(OEt)=CHC(OEt)=}(CO)4 (8): Obtained from
C(OCH CH )), 4.10 (q, J=7.2 Hz, 2H; CO CH CH ), 4.76 (q, J=7.2 Hz,
2 3 2 2 3
2
Re{C(Ph)C(CO Et)C(OEt)}(CO)4 (4; 0.95 g, 1.80 mmol). To isolate 8,
2H; ReC(OCH CH )), 4.92 (s, 1H; CH), 7.37–7.56 (m, 4H; naphtha-
2 3
2
the column was first eluted with a mixture of n-hexane and diethyl
ether (10:1 v/v) to give a light-yellow solution [this fraction gave
a yellow oil upon removal of solvents. However, we have failed to
len-1-yl), 7.83 (d, J=8.1 Hz, 1H; naphthalen-1-yl), 7.90 (d, J=8.1 Hz,
1H; naphthalen-1-yl), 7.97 ppm (d, J=8.1 Hz, 1H; naphthalen-1-yl);
13
1
C{ H} NMR (100.6 MHz, CD CN): d=12.0 (s, C(OCH CH )), 13.2 (s,
3
2
3
1
identify compounds for this fraction because the H NMR spectrum
CO CH CH ), 13.5 (s, ReC(OCH CH )), 58.7 (s, CO CH CH ), 63.6 (s,
2 2 3 2 3 2 2 3
was complex and showed many unidentified signals]. Further elu-
C(OCH CH )), 79.1 (s, ReC(OCH CH )), 93.5 (s, CH), 122.7, 124,7,
2 3 2 3
tion of the column with mixtures of n-hexane and diethyl ether
125.2, 125.6, 126.1, 127.2, 127.4, 127.5, 132.7, 145.4 (all s, C of
Chem. Eur. J. 2014, 20, 1 – 16
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ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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Full Paper
naphthalen-1-yl), 160.2 (s, C(C(OEt)), 160.4 (s, C(OEt)), 166.2 (s,
CO CH CH ), 67.4 (s, ReC(OCH CH )), 69.5 (s, C(OCH CH )), 104.4 (s,
2
2
3
2
3
2
3
CO Et), 190.2 (s, trans Re(CO)), 191.3 (s, Re(CO)), 193.6 (s, Re(CO)),
CH), 120.7, 122.4, 124.8, 124.9, 125.0, 125.3, 125.4, 126.2, 126.6,
126.7, 126.8, 127.8 128.9, 131.6, 132.0, 154.3 (all s, C of pyren-1-yl),
138.1 (s, C(CO Et)), 167.8 (s, CO Et), 187.4 (s, trans Re(CO)), 188.3 (s,
2
2
13.3 (s, ReC(naphthalen-1-yl)), 241.4 ppm (s, ReC(OEt)); elemental
analysis (%) calcd for C H O Re: C 48.07, H 3.57; found: C 48.22, H
26
23
8
2
2
3
.76.
C(OEt)), 188.4 (s, Re(CO)), 190.8 (s, Re(CO)), 204.8 (s, ReC(pyren-1-
yl)), 259.9 ppm (s, ReC(OEt)); elemental analysis (%) calcd for
C H O Re: C 53.10, H 3.48; found: C 53.06, H 3.55.
Re{-C(phenanthren-9-yl)=C(CO Et)C(OEt)=CHC(OEt)=}(CO)4 (12):
Obtained from Re{C(phenanthren-9-yl)C(CO Et)C(OEt)}(CO)4 (6;
2
32
25
8
2
Re{-C(pyren-1-yl)=C(C(OEt)=CH(CO Et))C(OEt)=}(CO) (15): Ob-
1
.13 g, 1.80 mmol). Purified by column chromatography (n-hexane/
2
4
tained from Re[C(pyren-1-yl)C(CO Et)C(OEt)](CO)4 (7; 1.18 g,
diethyl ether, 1:1 v/v). The fraction was a light-orange solution. A
bright-orange solid was formed after refrigerating a solution of the
crude mixture in n-hexanes overnight. The product was collected
2
1
.80 mmol). Purified by column chromatography (n-hexane/diethyl
ether, 10:1 v/v]. The fraction was a light-yellow solution. A yellow
oil was obtained after removal of the solvents. Yield: 78 mg (6%);
by filtration and dried under vacuum. Yield: 100 mg (8%); bright-
1
1
bright-orange solid; H NMR (400.1 MHz, CD CN): d=0.21 (t, J=
orange solid; H NMR (400.1 MHz, CD CN): d=0.53 (t, J=7.2 Hz,
3
3
7
.2 Hz, 3H; C(OCH CH )), 1.24 (t, J=7.2 Hz, 3H; CO CH CH ), 1.57 (t,
2 3 2 2 3
3
7
7
6
H; CO CH CH ), 1.40 (t, J=7.2 Hz, 3H; ReC(OCH CH )), 1.55 (t, J=
2
2
3
2
3
J=7.2 Hz, 3H; ReC(OCH CH )), 3.16 (d, J=6.0 Hz, 2H; C(OCH CH )),
4
.2 Hz, 3H; C(OCH CH )), 3.56 (m, 2H; CO CH CH ), 4.36 (q, J=
2
3
2
3
2
3
2
2
3
.13 (q, J=7.2 Hz, 2H; CO CH CH ), 4.81 (q, J=7.2 Hz, 2H; ReC-
2 2 3
.2 Hz, 2H; ReC(OCH CH )), 4.48 (q, J=7.2 Hz, 2H; C(OCH CH )),
2
3
2
3
(OCH CH )), 4.96 (s, 1H; ReC(OEt)CH), 7.92 (d, J=8.0 Hz, 1H; Py),
2 3
.30 (s, 1H; CH), 7.05 (s, 1H; phenanthren-9-yl), 7.55–7.86 (m, 6H;
13
1
8
.03–8.29 ppm (m, 8H; pyren-1-yl); C{ H} NMR (75.5 MHz, CD CN):
3
phenanthren-9-yl), 8.70–8.77 ppm (m, 2H; phenanthren-9-yl);
1
3
1
d=12.0 (s, C(OCH CH )), 13.4 (s, CO CH CH ), 13.7 (s, ReC-
C{ H} NMR (100.6 MHz, CD CN): d=13.3 (s, CO CH CH ), 13.8 (s,
2
3
2
2
3
3
2
2
3
(
OCH CH )), 59.0 (s, CO CH CH ), 63.7 (s, C(OCH CH )), 79.3 (s, ReC-
ReC(OCH CH )), 14.0 (s, C(OCH CH )), 60.0 (s, CO CH CH ), 67.3 (s,
2 3 2 2 3 2 3
2
3
2
3
2
2
3
(
OCH CH )), 93.8 (s, CH), 122.9, 123.9, 124.2, 124.7, 124.9, 125.0,
ReC(OCH CH )), 69.4 (s, C(OCH CH )), 104.3 (s, CH), 116.1, 122.8,
2 3
2
3
2
3
1
26.0, 126.4, 126.5, 126.8, 127.0, 127.2, 130.4, 130.5, 131.0, 145.0 (all
1
1
23.3, 126.0, 126.1, 126.9, 127.2, 128.1, 128.4, 128.7, 129.0, 130.5,
s, C of pyren-1-yl), 160.7 (s, C(OEt) and C(C(OEt)), 166.4 (s, CO Et),
32.0, 154.4 (all s, C of phenanthren-9-yl), 137.8 (s, C(CO Et)), 167.7
2
2
1
90.4 (s, trans Re(CO)), 191.4 (s, Re(CO)), 193.3 (s, Re(CO)), 213.6 (s,
ReC(pyren-1-yl)), 241.5 ppm (s, ReC(OEt)); elemental analysis (%)
calcd for C H O Re: C 53.10, H 3.48; found: C 53.16, H 3.72.
(
2
s, CO Et), 187.4 (s, C(OEt)), 188.1, 188.4, 190.5, 191.0 (s, Re(CO)),
2
03.2 (s, ReC(phenanthren-9-yl)), 259.8 ppm (s, ReC(OEt)); elemental
analysis (%) calcd for C H O Re: C 51.49, H 3.60; found: C 51.29, H
32 25
8
30
25
8
3
.86.
Re{-C(phenanthren-9-yl)=C(C(OEt)=CH(CO Et))C(OEt)=}(CO) (13):
2
4
General procedure for the isolation of vinyl-substituted
amino-rhenacyclobutadiene complexes
Obtained from Re{C(phenanthren-9-yl)C(CO Et)C(OEt)}(CO)4 (6;
2
1
.04 g, 1.80 mmol). Purified by column chromatography (n-hexane
and diethyl ether, 8:1 v/v). The fraction was a light-yellow solution.
A
NH
mixture of vinyl-substituted rhenacyclobutadiene with p-
OMe or Et NH in THF was stirred at RT for 12 h to give
A yellow oil was obtained after removal of the solvents. Yield:
2
C
6
H
4
2
1
1
78 mg (15.3%); yellow oil; H NMR (400.1 MHz, CD CN): d=0.34
a brown-yellow solution. The solvent was removed under vacuum
and a yellow solid was formed after refrigerating a solution of the
crude mixture in tetrahydrofuran/cyclohexane (1:30) for two days.
The product was collected by filtration, washed with n-hexane, and
dried under vacuum.
3
(
t, J=7.2 Hz, 3H; C(OCH CH )), 1.21 (t, J=7.2 Hz, 3H; CO CH CH ),
2 3 2 2 3
1
.54 (t, J=7.2 Hz, 3H; ReC(OCH CH ), 3.13 (d, J=6.0 Hz, 2H;
2 3
C(OCH CH )), 4.10 (q, J=7.2 Hz, 2H; CO CH CH ), 4.78 (q, J=7.2 Hz,
2
3
2
2
3
2
H; ReC(OCH CH )), 4.90 (s, 1H; CH), 7.52–7.56 (m, 1H; phenanth-
2 3
ren-9-yl), 7.62–7.72 (m, 4H; phenanthren-9-yl), 8.00–8.05 (m, 2H;
Re{-C(naphthalen-1-yl)=C(C(OEt)=CH(CO Et))C(p-NHC H OMe)=
2
6
4
phenanthren-9-yl), 8.72 (d, J=8.1 Hz, 1H; phenanthren-9-yl),
}
(CO)4 (11): Obtained from Re{C(naphthalen-1-yl)C(C(OEt)=CH-
13
1
8
.77 ppm (d, J=8.1 Hz, 1H; phenanthren-9-yl);
C{ H} NMR
(CO Et))C(OEt)}(CO)4 (10; 52 mg, 0.08 mmol) and p-NH C H OMe
2
2
6
4
1
(
100.6 MHz, CD CN): d=12.0 (s, C(OCH CH )), 13.2 (s, CO CH CH ),
3
2
3
2
2
3
(12 mg, 0.10 mmol). Yield: 38 mg (65%); H NMR (400.1 MHz,
1
7
1
3.5 (s, ReC(OCH CH )), 58.7 (s, CO CH CH ), 63.6 (s, C(OCH CH )),
2 3 2 2 3 2 3
CD Cl ): d=0.66 (t, J=7.2 Hz, 3H; OCH CH ), 1.23 (t, J=7.2 Hz, 3H;
CO CH CH ), 3.33 (q, J=7.2 Hz, 2H; OCH CH ), 3.87 (s, 3H; p-
2 2 3 2 3
2
2
2
3
9.1 (s, ReC(OCH CH )), 93.5 (s, CH), 122.1, 122.3, 125.6, 126.1,
2
3
26.2, 126.4, 126.5, 126.6, 128.4, 129.3, 129.4, 130.7, 144.3 (all s, C
NHC H OCH ), 4.11 (q, J=7.2 Hz, 2H; CO CH CH ), 4.99 (s, 1H; CH),
6
4
3
2
2
3
of phenanthren-9-yl), 160.2 (s, C(C(OEt)), 160.3 (s, C(OEt)), 166.2 (s,
CO Et), 190.2 (s, trans Re(CO)), 191.3 (s, Re(CO)), 193.6 (s, Re(CO)),
7
.05 (d, J=8.8 Hz, 2H; C H ), 7.32 (d, J=6.8 Hz, 1H; naphthalen-1-
6 4
2
yl), 7.40–7.52 (m, 5H; naphthalen-1-yl and C H ), 7.73 (d, J=8.4 Hz,
6 4
2
12.9 (s, ReC(phenanthren-9-yl)), 241.4 ppm (s, ReC(OEt)); elemental
1
H; naphthalen-1-yl), 7.85 (d, J=8.4 Hz, 1H; naphthalen-1-yl), 8.00
analysis (%) calcd for C H O Re: C 51.49, H 3.60; found: C 51.25, H
30
25
8
(d, J=8.4 Hz, 1H; naphthalen-1-yl), 9.79 ppm (s, 1H; NH);
13
1
3
.88.
C{ H} NMR (100.6 MHz, CD Cl ): d=14.1 (s, OCH CH ), 15.1 (s,
2
2
2
3
CO CH CH ), 56.4 (s, p-NHC H OCH ), 60.6 (s, CO CH CH ), 65.3 (s,
Re{-C(pyren-1-yl)=C(CO Et)C(OEt)=CHC(OEt)=}(CO)
(14): Ob-
2
2
3
6
4
3
2
2
3
2
4
OCH CH ), 95.1 (s, CH), 115.5, 123.7, 125.8, 126.0, 126.1, 126.5,
tained from Re{C(pyren-1-yl)C(CO Et)C(OEt)} (7; 1.18 g, 1.80 mmol).
2
3
2
1
27.0, 127.5, 128.3, 128.7, 134.2, 134.4, 146.7, 160.3 (all s, C of
naphthalen-1-yl and Ph), 153.6 (s, C(C(OEt))), 161.9 (s, C(OEt)), 167.1
s, CO Et), 192.3 (s, Re(CO)), 192.4 (s, trans Re(CO)), 195.1 (s,
Purified by column chromatography (n-hexane/diethyl ether, 1:1 v/
v]. The fraction was a light-orange solution. A bright-orange solid
was formed after refrigerating a solution of the crude mixture in n-
hexanes overnight. The product was collected by filtration and
dried under vacuum. Yield: 65 mg (5%); bright-orange solid;
(
2
Re(CO)), 196.0 (s, ReC(naphthalen-1-yl)), 198.0 ppm (s, ReC(p-
NH C H OMe)); elemental analysis (%) calcd for
C H NO Re·0.25C H O: C 51.61, H 3.79, N 1.88; found: C 52.00, H
2
6
4
1
H NMR (400.1 MHz, CD CN): d=0.41 (t, J=7.2 Hz, 3H; CO CH CH ),
31 26
8
4
8
3
2
2
3
4
.09, N, 1.94.
1
.40 (t, J=7.2 Hz, 3H; ReC(OCH CH )), 1.56 (t, J=7.2 Hz, 3H;
2 3
C(OCH CH )), 3.42 (t, J=7.2 Hz, 2H; CO CH CH ), 4.38 (q, J=7.2 Hz,
Re{-C(Ph)=C(CO Et)C(NEt )=}(CO) (16): Obtained from Re{C(Ph)C-
2
3
2
2
3
2
2
4
2
1
H; ReC(OCH CH )), 4.49 (q, J=7.2 Hz, 2H; C(OCH CH )), 6.33 (s,
(CO Et)C(OEt)}(CO)4 (4; 0.11 g, 0.20 mmol) and Et NH (0.3 mL,
2 2
0.30 mmol). Yield: 95 mg (85%); yellow solid; H NMR (400.1 MHz,
2
3
2
3
1
H; CH), 7.47 (d, J=8.0 Hz, 1H; pyren-1-yl), 7.90–8.10 ppm (m, 1H;
1
3
1
pyren-1-yl);
C{ H} NMR (75.5 MHz, CD CN): d=13.2 (s,
CD COCD ): d=1.07 (t, J=7.2 Hz, 3H; OCH CH ), 1.32 (t, J=7.2 Hz,
3
3
3
2
3
CO CH CH ), 13.9 (s, ReC(OCH CH )), 14.1 (s, C(OCH CH )), 60.1 (s,
3H; NCH CH ), 1.44 (t, J=7.2 Hz, 3H; NCH CH ), 3.82 (m, 4H;
2 3 2 3
2
2
3
2
3
2
3
&
&
Chem. Eur. J. 2014, 20, 1 – 16
www.chemeurj.org
12
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!

Full Paper
[
62]
NCH ), 4.04 (q, J=7.2 Hz, 2H; OCH ), 7.30–7.42 ppm (m, 5H; Ph);
Pt. Polarization functions were added for P (z (d)=0.387), Cl (z
(d)=0.640), I (z (d)=0.289), Re (z (f)=0.869), Os (z (f)=0.886), Ir (z
2
2
1
3
1
C{ H} NMR (100.6 MHz, CD COCD ): d=14.0 (s, NCH CH ), 14.1 (s,
3
3
2
3
[63]
NCH CH ), 14.7 (s, OCH CH ), 48.5 (s, NCH ), 57.3 (s, NCH ), 61.2 (s,
(f)=0.938), and Pt (z (f)=0.993). All the calculations were per-
formed with the Gaussian 03 software package.
2
3
2
3
2
2
[67]
OCH ), 127.7, 128.9, 146.6 (all s, C of Ph), 147.8 (s, C(CO Et)), 167.3
2
2
(
s, CO Et), 189.2 (s, ReC(NEt )), 190.4 (s, ReC(Ph)), 192.3 (s, trans
2 2
Re(CO)), 193.4 (s, Re(CO)), 194.8 ppm (s, Re(CO)); elemental analysis
(
%) calcd for C H NO Re: C 43.16, H 3.62, N 2.52; found: C 43.02, Acknowledgements
2
0
20
6
H 3.89, N 2.54.
This work was supported by the Hong Kong Research Grant
Council (Project No.: 602611, 601812, CUHK7/CRF/12G-2).
X-ray crystallography
Crystals of 4–6, 8, 9, 11, and 16 were obtained by refrigerating sol-
utions of the rhenacyclobutadiene complexes in tetrahydrofuran/
cyclohexane (1:30) for one week. Crystals of 12 were grown by
slow evaporation of an acetonitrile/methanol solution. The diffrac-
tion intensity data were collected with an Oxford Diffraction
Gemini S Ultra X-ray Diffractometer with either monochromatized
MoKa radiation (l=0.71073 ꢁ) or (CuKa radiation (l=1.54178 ꢁ) at
Keywords: aromaticity · metallabenzene · metallacycles ·
rhenium · structure elucidation
[1] For reviews, see: a) X. Y. Cao, Q. Zhao, Z. Lin, H. Xia, Acc. Chem. Res.
2014, 47, 341; b) J. Chen, G. Jia, Coord. Chem. Rev. 2013, 257, 2491;
c) A. F. Dalebrook, L. J. Wright, Adv. Organomet. Chem. 2012, 60, 93;
d) M. Paneque, M. L. Poveda, N. Rendꢂn, Eur. J. Inorg. Chem. 2011, 19;
e) C. W. Landorf, M. M. Haley, Angew. Chem. 2006, 118, 4018; Angew.
Chem. Int. Ed. 2006, 45, 3914; f) L. J. Wright, Dalton Trans. 2006, 1821;
g) J. R. Bleeke, Chem. Rev. 2001, 101, 1205.
1
73 or 100 K. Diffraction data were collected and processed by
using the CrysAlisPro software (version 1.171.35.19). Empirical ab-
sorption corrections were performed by using spherical harmonics,
implemented in SCALE3 ABSPACK scaling algorithm in the CrysAlis-
Pro software suite. Structure solution and refinement for all com-
[
2] V. Jacob, C. W. Landorf, L. N. Zakharov, T. J. R. Weakley, M. M. Haley, Or-
ganometallics 2009, 28, 5183.
[
59]
pounds were performed by using the Olex2 software package
which embedded the structure refinement program SHELXTL).
[
3] C. W. Landorf, V. Jacob, T. J. R. Weakley, M. M. Haley, Organometallics
2004, 23, 1174.
[60]
(
All the structures were solved by direct methods, expanded by dif-
ference Fourier syntheses and refined by full matrix least-squares
on F . All non-hydrogen atoms were refined anisotropically with
a riding model for the hydrogen atoms except where noted sepa-
rately. Complexes 6 and 12 include solvent of crystallization, which
were refined as molecules of cyclohexane and acetonitrile respec-
tively, each with fractional (0.25) occupancy. CCDC-994857(4),
[4] V. Jacob, T. J. R. Weakley, M. M. Haley, Angew. Chem. 2002, 114, 3620;
Angew. Chem. Int. Ed. 2002, 41, 3470.
2
[
5] a) A. Vivancos, M. Paneque, M. L. Poveda, E. Alvarez, Angew. Chem.
013, 125, 10252; Angew. Chem. Int. Ed. 2013, 52, 10068; b) M. Paneque,
M. L. Poveda, N. Rendꢂn, E. ꢃlvarez, E. Carmona, Eur. J. Inorg. Chem.
007, 2711; c) E. ꢃlvarez, M. Paneque, M. L. Poveda, N. Rendꢂn, Angew.
2
2
Chem. 2006, 118, 488; Angew. Chem. Int. Ed. 2006, 45, 474; d) C. S. Chin,
H. Lee, M. S. Eum, Organometallics 2005, 24, 4849; e) C. S. Chin, H. Lee,
Chem. Eur. J. 2004, 10, 4518; f) R. D. Gilbertson, T. L. S. Lau, S. Lanza,
H. P. Wu, T. J. R. Weakley, M. M. Haley, Organometallics 2003, 22, 3279;
g) J. R. Bleeke, R. Behm, J. Am. Chem. Soc. 1997, 119, 8503; h) J. R.
Bleeke, Y. F. J. Xie, W. J. Peng, M. Chiang, J. Am. Chem. Soc. 1989, 111,
-
-
757667(5), -994858(6), -757669(8), -757668(9), -994859(11),
994860(12), and -994861(16) contain the supplementary crystallo-
graphic 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.
4118.
[
6] J. R. Bleeke, R. Behm, Y. F. Xie, M. Y. Chiang, K. D. Robinson, A. M. Beatty,
Organometallics 1997, 16, 606.
Computational details
[7] R. D. Gilbertson, T. J. R. Weakley, M. M. Haley, J. Am. Chem. Soc. 1999,
21, 2597.
1
All structures were optimized without any constraint at the B3LYP
[8] M. Paneque, C. M. Posadas, M. L. Poveda, N. Rendꢂn, V. Salazar, E.
OÇate, K. Mereiter, J. Am. Chem. Soc. 2003, 125, 9898.
[9] M. Paneque, C. M. Posadas, M. L. Poveda, N. Rendꢂn, L. L. Santos, E. ꢃl-
varez, V. Salazar, K. Mereiter, E. OÇate, Organometallics 2007, 26, 3403.
10] J. R. Bleeke, Y. F. Xie, L. Bass, M. Y. Chiang, J. Am. Chem. Soc. 1991, 113,
[61]
level of density functional theory. Frequency calculations were
also performed to confirm all the stationary points as minima (zero
imaginary frequency) or transition states (one imaginary frequen-
cy), and to provide free energies at 298.15 K.
[
[
4
703.
11] J. R. Bleeke, L. A. Bass, Y. F. Xie, M. Y. Chiang, J. Am. Chem. Soc. 1992, 114,
213.
In the DFT calculations, the standard 6–31G* basis set was used for
C, N, O, and H atoms. The effective core potentials (ECPs) of
4
[62]
Lanl2dz was used to describe Re,
Re(z (f)=0.869) being added.
with polarization functions
[12] H. P. Wu, D. H. Ess, S. Lanza, T. J. R. Weakley, K. N. Houk, K. K. Baldridge,
[63]
M. M. Haley, Organometallics 2007, 26, 3957.
[
13] H. P. Wu, S. Lanza, T. J. R. Weakley, M. M. Haley, Organometallics 2002,
21, 2824.
To reduce the overestimation of the entropy contribution in the
À1
gas-phase results, corrections of À2.6 kcalmol in free energies
[
[
14] H. P. Wu, T. J. R. Weakley, M. M. Haley, Chem. Eur. J. 2005, 11, 1191.
15] G. R. Clark, G. Lu, W. R. Roper, L. J. Wright, Organometallics 2007, 26,
[64]
were made for 2-to-1 transformations. This correction was em-
[65]
ployed in a number of earlier theoretical studies. To obtain solva-
tion-corrected relative free energies, we employed a continuum
medium for single-point calculations for all model complexes,
using UAKS radii on the conductor polarizable continuum model
2167.
[
16] G. R. Clark, P. M. Johns, W. R. Roper, L. J. Wright, Organometallics 2008,
27, 451.
[17] G. R. Clark, P. M. Johns, W. R. Roper, T. Soehnel, L. J. Wright, Organome-
tallics 2011, 30, 129.
[66]
(
CPCM). Acetonitrile was employed as the solvent, according to
[
[
[
18] T. Wang, H. Zhang, F. Han, L. Long, Z. Lin, H. Xia, Angew. Chem. 2013,
25, 9421; Angew. Chem. Int. Ed. 2013, 52, 9251.
19] T. Wang, H. Zhang, F. Han, L. Long, Z. Lin, H. Xia, Chem. Eur. J. 2013, 19,
0982.
20] a) J. Chen, C. Zhang, T. Xie, T. B. Wen, H. Zhang, H. Xia, Organometallics
2013, 32, 3993; b) T. Wang, H. Zhang, F. Han, R. Lin, Z. Lin, H. Xia,
Angew. Chem. 2012, 124, 9976; Angew. Chem. Int. Ed. 2012, 51, 9838;
the reaction conditions, in the CPCM calculations. Unless specifical-
ly noted, entropy-corrected and solvation-corrected free energies
were used in all of the discussions in this article.
1
1
For the ASE calculations, larger basis set 6–311+G** was used for
B, C, N, O and H atoms. The effective core potentials (ECPs) of
Lanl2dz and basis sets were used to describe P, Cl, I, Re, Os, Ir, and
Chem. Eur. J. 2014, 20, 1 – 16
www.chemeurj.org
13
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
&
&
These are not the final page numbers! ÞÞ

Full Paper
c) W. Y. Hung, B. Liu, W. Shou, T. B. Wen, C. Shi, H. H. Y. Sung, I. D. Wil-
liams, Z. Lin, G. Jia, J. Am. Chem. Soc. 2011, 133, 18350; d) L. Gong, Y.
Lin, T. B. Wen, H. Zhang, B. Zeng, H. Xia, Organometallics 2008, 27,
c) L. L. Padolik, J. Gallucci, A. Wojcicki, J. Organomet. Chem. 1990, 383,
C1.
[44] Based on a search of the Cambridge Structural Database, CSD version
5.32 (Nov. 2011).
2584; e) H. Xia, G. He, H. Zhang, T. B. Wen, H. H. Y. Sung, I. D. Williams,
G. Jia, J. Am. Chem. Soc. 2004, 126, 6862; f) P. Barrio, M. A. Esteruelas, E.
OÇate, J. Am. Chem. Soc. 2004, 126, 1946; g) C. E. F. Rickard, W. R. Roper,
S. D. Woodgate, L. J. Wright, J. Organomet. Chem. 2001, 623, 109;
h) G. P. Elliott, W. R. Roper, J. M. Waters, J. Chem. Soc. Chem. Commun.
[45] For recent examples, see: a) M. N. Uddin, M. A. Mottalib, N. Begum, S.
Ghosh, A. K. Raha, D. T. Haworth, S. V. Lindeman, T. A. Siddiquee, D. W.
Bennett, G. Hogarth, E. Nordlander, S. E. Kabir, Organometallics 2009, 28,
1514; b) O. V. Ozerov, M. Pink, L. A. Watson, K. G. Caulton, J. Am. Chem.
Soc. 2004, 126, 2105.
[46] For recent examples, see: a) Y. Jiang, O. Blaccque, T. Fox, C. M. Frech, H.
Berke, Organometallics 2009, 28, 4670; b) P. R. Elowe, N. M. West, J. A.
Labinger, J. E. Bercaw, Organometallics 2009, 28, 6218.
1
982, 811.
21] C. E. F. Rickard, W. R. Roper, S. D. Woodgate, L. J. Wright, Angew. Chem.
000, 112, 766; Angew. Chem. Int. Ed. 2000, 39, 750.
22] G. R. Clark, P. M. Johns, W. R. Roper, L. J. Wright, Organometallics 2006,
5, 1771.
[
[
[
[
[
[
[
2
2
[47] Based on the analytical and NMR data, the yellow oil was previously in-
correctly postulated to be an isomer of rhenabenzene 11 with two OEt
groups in our preliminary report (see ref. [38]).
23] T. Wang, S. Li, H. Zhang, R. Lin, F. Han, Y. Lin, T. B. Wen, H. Xia, Angew.
Chem. 2009, 121, 6575; Angew. Chem. Int. Ed. 2009, 48, 6453.
24] G. R. Clark, L. A. Ferguson, A. E. McIntosh, T. Sohnel, L. J. Wright, J. Am.
Chem. Soc. 2010, 132, 13443.
[48] As the main concern of this work is the chemistry of rhenabenzenes,
the mechanism for the formation of the vinylcyclobutadiene complexes
is not discussed in this work. Our preliminary experimental and theoret-
ical studies indicate that the vinyl-substituted metallacyclobutadienes
are formed by initial direct nucleophilic attack of the b-carbon of HCꢀ
COEt on the carbene carbon of the starting rhenacyclobutadienes to
give zwitterionic carbene intermediates, which rearrange to the final
vinyl-substituted rhenacyclobutadiene products. Details of these inter-
esting findings will be reported in a separate manuscript.
[49] S. Hagmayer, A. Frꢄh, T. Haas, M. Drexler, H. Fischer, Organometallics
2007, 26, 3791.
25] H. Zhang, R. Lin, G. Hong, T. Wang, T. B. Wen, H. Xia, Chem. Eur. J. 2010,
1
6, 6999.
26] P. M. Johns, W. R. Roper, S. D. Woodgate, L. J. Wright, Organometallics
010, 29, 5358.
27] a) L. Wu, L. Feng, H. Zhang, Q. Liu, X. He, F. Yang, H. Xia, J. Org. Chem.
008, 73, 2883; b) H. Zhang, L. Feng, L. Gong, L. Wu, G. He, T. B. Wen, F.
2
2
Yang, H. Xia, Organometallics 2007, 26, 2705; c) H. Zhang, H. Xia, G. He,
T. B. Wen, L. Gong, G. Jia, Angew. Chem. 2006, 118, 2986; Angew. Chem.
Int. Ed. 2006, 45, 2920.
[
[
[
28] J. Yang, W. M. Jones, J. K. Dixon, N. T. Allison, J. Am. Chem. Soc. 1995,
[50] N. Mathivanan, F. Cozens, R. A. McClelland, S. Steeden, J. Am. Chem. Soc.
1992, 114, 2198.
[51] A. J. Birch, G. S. R. S. Rao, Aust. J.Chem. 1970, 23, 1641.
[52] K. Osowska, K. Mierzwicki, S. Szafert, Organometallics 2006, 25, 3544.
[53] C. S. Wannere, C. Corminboeuf, W. D. Allen, H. E. Schaefer, P. R. Schleyer,
Org. Lett. 2005, 7, 1457.
117, 9776.
29] G. R. Clark, T. R. O’Neale, W. R. Roper, D. M. Tonei, L. J. Wright, Organo-
metallics 2009, 28, 567.
30] a) R. Lin, J. Zhao, H. Chen, H. Zhang, H. Xia, Chem. Asian J. 2012, 7,
1
4
915; b) R. Lin, H. Zhang, S. Li, J. Wang, H. Xia, Chem. Eur. J. 2011, 17,
223.
[54] P. R. Schleyer, F. Puhlhofer, Org. Lett. 2002, 4, 2873.
[
31] a) S. H. Liu, W. S. Ng, H. S. Chu, T. B. Wen, H. Xia, Z. Y. Zhou, C. P. Lau, G.
[55] For previous work on the ASEs of other model metallabenzene com-
plexes evaluated by the isomerization methods, see: a) F. De Proft, P.
Geerlings, Phys. Chem. Chem. Phys. 2004, 6, 242; b) M. Mauksch, S. B.
Tsogoeva, Chem. Eur. J. 2010, 16, 7843; for ASE values of metallaben-
zenes evaluated with other methods, see: homodesmic reaction: c) T. Z.
Huang, S. Y. Yang, X. Y. Li, J. Organomet. Chem. 2004, 689, 1050; energy
decomposition analysis (EDA) calculations: d) I. Fernꢅndez, G. Frenking,
Chem. Eur. J. 2007, 13, 5873.
Jia, Angew. Chem. 2002, 114, 1659; Angew. Chem. Int. Ed. 2002, 41,
1589; b) Y. Ohki, H. Suzuki, Angew. Chem. 2000, 112, 3605; Angew.
Chem. Int. Ed. 2000, 39, 3463; c) U. Englert, F. Podewils, I. Schiffers, A.
Salzer, Angew. Chem. 1998, 110, 2196; Angew. Chem. Int. Ed. 1998, 37,
2
2
134; d) W. Lin, S. R. Wilson, G. S. Girolami, Organometallics 1997, 16,
356; e) U. Bertling, U. Englert, A. Salzer, Angew. Chem. 1994, 106, 1026;
Angew. Chem. Int. Ed. Engl. 1994, 33, 1003; f) M. S. Kralik, A. L. Rheingold,
J. P. Hutchinson, J. W. Freeman, R. D. Ernst, Organometallics 1996, 15,
[56] R. Tanaka, S. I. Miller, Tetrahedron Lett. 1971, 12, 1753.
[57] D. K. Whelligan, D. W. Thomson, D. Taylor, S. Hoelder, J. Org. Chem.
2010, 75, 11.
551; g) H. W. Bosch, H. U. Hung, D. Nietlispach, A. Salzer, Organometal-
lics 1992, 11, 2087.
[
[
32] D. L. Thorn, R. Hoffmann, Nouv. J. Chim. 1979, 3, 39.
33] a) V. Plantevin, A. Wojcicki, J. Organomet. Chem. 2004, 689, 2013; b) R.
Ferede, J. F. Hinton, W. A. Korfmacher, J. P. Freeman, N. T. Allison, Orga-
nometallics 1985, 4, 614.
[58] All the spectroscopic data are provided in the Supporting Information.
[59] O. V. Dolomanov, L. J. Bourhis, R. J. Gildea, J. A. K. Howard, H. Pusch-
mann, J. Appl. Crystallogr. 2009, 42, 339. OLEX2: a complete structure
solution, refinement, and analysis program.
[
[
[
34] C. A. Mike, R. Ferede, N. T. Allison, Organometallics 1988, 7, 1457.
35] T. M. Sivavec, T. J. Katz, Tetrahedron Lett. 1985, 26, 2159.
36] a) J. Zhu, G. Jia, Z. Lin, Organometallics 2006, 25, 1812; b) R. R. Schrock,
Acc. Chem. Res. 1986, 19, 342; c) R. R. Schrock, S. F. Pederson, M. R.
Churchill, J. W. Ziller, Organometallics 1984, 3, 1574; d) J. H. Freuden-
berger, R. R. Schrock, M. R. Churchill, A. L. Rheingold, J. W. Ziller, Organo-
metallics 1984, 3, 1563.
[60] G. M. Sheldrick, Acta Crystallogr. A, 2008, 64, 112.
[61] a) P. J. Stephens, F. J. Devlin, C. F. Chabalowski, M. J. Frisch, J. Phys.
Chem. 1994, 98, 11623; b) A. D. Becke, J. Chem. Phys. 1993, 98, 5648;
c) B. Miehlich, A. Savin, H. Stoll, H. Preuss, Chem. Phys. Lett. 1989, 157,
200; d) C. Lee, W. Yang, R. G. Parr, Phys. Rev. B 1988, 37, 785; e) A. D.
Becke, Phys. Rev. A 1988, 38, 3098.
[62] a) P. J. Hay, W. R. Wadt, J. Chem. Phys. 1985, 82, 299; b) W. R. Wadt, P. J.
Hay, J. Chem. Phys. 1985, 82, 284.
[63] A. Hçllwarth, M. Bohme, S. Dapprich, A. W. Ehlers, A. Gobbi, V. Jonas,
K. F. Kohler, R. Stegmann, A. Veldkamp, G. Frenking, Chem. Phys. Lett.
1993, 208, 237.
[
37] a) P. N. Riley, R. D. Profilet, M. M. Salberg, P. E. Fanwick, I. P. Rothwell,
Polyhedron 1998, 17, 773; b) R. D. Profilet, P. E. Fanwick, I. P. Rothwell,
Angew. Chem. 1992, 104, 1277; Angew. Chem. Int. Ed. Engl. 1992, 31,
1261.
[
[
[
[
38] K. C. Poon, L. Liu, T. Guo, J. Li, H. H. Y. Sung, I. D. Williams, Z. Lin, G. Jia,
Angew. Chem. 2010, 122, 2819; Angew. Chem. Int. Ed. 2010, 49, 2759.
39] a) C. Lçwe, V. Shklover, H. W. Bosch, H. Berke, Chem. Ber. 1993, 126,
[64] S. W. Benson, The Foundations of Chemical Kinetics, Krieger, Malabar,
1982.
[65] See for example: a) Y. Okuno, Chem. Eur. J. 1997, 3, 212; b) D. Ardura, R.
Lꢂpez, T. L. Sordo, J. Phys. Chem. B. 2005, 109, 23618; c) F. Schoenebeck,
K. N. Houk, J. Am. Chem. Soc. 2010, 132, 2496; d) Q. Liu, Y. Lan, J. Liu, G.
Li, Y. D. Wu, A. Lei, J. Am. Chem. Soc. 2009, 131, 10201; e) A. Ariafard,
N. J. Brookes, R. Stanger, B. F. Yates, Organometallics 2011, 30, 1340;
f) H. Yu, Q. Lu, Z. Dang, Y. Fu, Chem. Asian J. 2013, 8, 2262; g) A. Aria-
fard, N. M. Ghohe, K. K. Abbasi, A. J. Canty, B. F. Yates, Inorg. Chem.
2013, 52, 707.
1769; b) C. Lçwe, V. Shklover, H. Berke, Organometallics 1991, 10, 3396.
40] W. Y. Hung, J. Zhu, T. B. Wen, K. P. Yu, H. H. Y. Sung, I. D. Williams, Z. Lin,
G. Jia, J. Am. Chem. Soc. 2006, 128, 13742.
41] a) M. A. Iron, A. C. B. Lucassen, H. Cohen, M. E. Boom, J. M. L. Martin, J.
Am. Chem. Soc. 2004, 126, 11699; b) M. A. Iron, J. M. L. Martin, M. E.
Boom, J. Am. Chem. Soc. 2003, 125, 13020.
[
42] C. Shi, T. Guo, K. C. Poon, Z. Lin, G. Jia, Dalton Trans. 2011, 40, 11315.
43] a) V. Plantevin, A. Wojcicki, J. Organomet. Chem. 2004, 689, 2000; b) L. L.
Padolik, J. C. Gallucci, A. Wojcicki, J. Am. Chem. Soc. 1993, 115, 9986;
[
[66] a) M. Cossi, N. Rega, G. Scalmani, V. Barone, J. Comput. Chem. 2003, 24,
669; b) M. Cossi, V. Barone, M. A. Robb, J. Chem. Phys. 1999, 111, 5295;
&
&
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www.chemeurj.org
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c) M. Cossi, V. Barone, B. Mennucci, J. Tomasi, Chem. Phys. Lett. 1998,
86, 253; d) M. Cossi, V. Barone, R. Cammi, J. Tomasi, Chem. Phys. Lett.
996, 255, 327.
V. G. Zakrzewski, S. Dapprich, A. D. Daniels, M. C. Strain, O. Farkas, D. K.
Malick, A. D. Rabuck, K. Raghavachari, J. B. Foresman, J. V. Ortiz, Q. Cui,
A. G. Baboul, S. Clifford, J. Cioslowski, B. B. Stefanov, G. Liu, A. Liashenko,
P. Piskorz, I. Komaromi, R. L. Martin, D. J. Fox, T. Keith, M. A. Al-Laham,
C. Y. Peng, A. Nanayakkara, M. Challacombe, P. M. W. Gill, B. Johnson, W.
Chen, M. W. Wong, C. Gonzalez, and J. A. Pople, Gaussian, Inc., Walling-
ford CT, 2004.
2
1
[
67] Gaussian 03, Revision E.01, M. J. Frisch, G. W. Trucks, H. B. Schlegel, G. E.
Scuseria, M. A. Robb, J. R. Cheeseman, J. A. Montgomery, Jr., T. Vreven,
K. N. Kudin, J. C. Burant, J. M. Millam, S. S. Iyengar, J. Tomasi, V. Barone,
B. Mennucci, M. Cossi, G. Scalmani, N. Rega, G. A. Petersson, H. Nakatsu-
ji, M. Hada, M. Ehara, K. Toyota, R. Fukuda, J. Hasegawa, M. Ishida, T. Na-
kajima, Y. Honda, O. Kitao, H. Nakai, M. Klene, X. Li, J. E. Knox, H. P.
Hratchian, J. B. Cross, V. Bakken, C. Adamo, J. Jaramillo, R. Gomperts,
R. E. Stratmann, O. Yazyev, A. J. Austin, R. Cammi, C. Pomelli, J. W. Och-
terski, P. Y. Ayala, K. Morokuma, G. A. Voth, P. Salvador, J. J. Dannenberg,
Received: April 21, 2014
Published online on && &&, 0000
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FULL PAPER
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Metallacycles
R. Lin, K.-H. Lee, K. C. Poon, H. H. Y. Sung,
I. D. Williams,* Z. Lin,* G. Jia*
&& – &&
Question answered? Group 7 metalla-
benzenes were predicted theoretically
dienes with ethoxyethyne (see scheme).
The NMR spectroscopic and X-ray struc-
tural data, as well as the aromatic stabi-
lization energy (ASE) values suggest
that these rhenabenzenes have aromat-
ic character.
Synthesis of Rhenabenzenes from the
Reactions of Rhenacyclobutadienes
with Ethoxyethyne
3
5 years ago. This work reports the iso-
lation, characterization, and properties
of rhenabenzenes, which were obtained
from the reactions of rhenacyclobuta-
&
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Chem. Eur. J. 2014, 20, 1 – 16
www.chemeurj.org
16
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
ÝÝ These are not the final page numbers!