Negishi's Reagent Versus Rosenthal's Reagent in the Formation of Zirconacyclopentadienes

Article abstract of DOI:10.1002/chem.201902255

Zirconacyclopentadienes are versatile precursors for a large number of heteroles, which are accessible by Zr-element exchange reactions. The vast majority of reports describe their preparation by the use of Negishi′s reagent, which is a species that is fo

Full text of DOI:10.1002/chem.201902255

A Journal of
Accepted Article
Title: Negishi’s Reagent Versus Rosenthal’s Reagent in the Formation
of Zirconacyclopentadienes
Authors: Sara Urrego-Riveros, Isabel-Maria Ramirez y Medina, Daniel
Duvinage, Enno Lork, Frank Sönnichsen, and Anne Staubitz
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10.1002/chem.201902255
Chemistry - A European Journal
Negishi’s Reagent Versus Rosenthal’s Reagent in the Formation
of Zirconacyclopentadienes
Sara Urrego-Riveros,[a, ] Isabel-Maria Ramirez y Medina,[a, ] Daniel Duvinage,[b] Enno Lork,[b] Frank D.
Sönnichsen[c] and Anne Staubitz*[a]
§
§
Abstract: Zirconacyclopentadienes are versatile precursors for a
large number of heteroles that are accessible by Zr-element exchange
reactions. The vast majority of reports describe their preparation by
the use of Negishi´s reagent, which is a species that is formed in situ.
The zirconacyclopentadiene is then formed by the addition of one
equivalent of a diyne or two equivalents of a monoyne moiety to this
Negishi species. Another route involves Rosenthal´s reagent
(Cp2Zr(py)Me3SiCCSiMe3), which then reacts with a diyne or
monoyne moiety. In this work, the efficiency of both routes was
compared in terms of reaction time, stability of the product in the
reaction mixture and yield. The synthetic implications of using both
routes are evaluated. Novel zirconacyclopentadienes were
synthesized, characterized directly from the reaction mixture and
crystal structures could be obtained in most cases.
coordination sphere of the zirconium. These ligands are Cp rings
in most cases. Starting with a zirconacyclopentadiene (e.g. 1a),
many metalloles can be synthesized, in which group 14 elements
(E= Si, Ge, Sn, Pb) or other main group elements are introduced
9]
into the cycle by transmetallation reactions.[5a,
Moreover,
zirconacyclopentadienes show other synthetic uses (Scheme 1).
For example, if the zirconacyclopentadiene core (e.g. 1b) is part
of a large polyaromatic system, the protonation with HCl gives
dienes as compound 3 that are otherwise difficult to access.[10]
Furthermore, if zirconacyclopentadienes are included into
polymeric systems (e.g. 1c), they can be converted into stable
aromatic building blocks as in polymer 4.[11]
Introduction
Heteroles are five membered cycles derived from
cyclopentadiene or its derivatives. In these molecules, the sp3
carbon is replaced by a heteroatom. They have become very
important during the past few decades in the areas of biology,[1]
materials science[2] and medicinal chemistry.[1]
The most common of these heterocycles are aromatic (e. g.
thiophene, pyrrole, or furan),[3] while others are formally anti-
aromatic (e.g. boroles).[4] Some are non-aromatic with other forms
of conjugations such as σ*-π*-conjugation, which is exclusive to
heavier element containing heterocycles (for example group 14
metalloles).[5]
There are many established routes for the synthesis of these
classical aromatic heteroles,[6] but the breakthrough to access the
non-classical non- or antiaromatic congeners was achieved by
the
use
of
zirconacyclopentadienes
or
other
metallacyclopentadienes[7] as precursor molecules.[8] In
zirconacyclopentadienes, the sp3 atom of a cyclopentadiene is
replaced by a Zr atom with further ligands saturating the
[a]
S. Urrego-Riveros, I.-M. Ramirez y Medina; both authors contributed
equally to the paper
Prof. Dr. A. Staubitz
University of Bremen
Institute for Organic and Analytical Chemistry/ MAPEX Center for
Materials and Processes
Leobener Str. 7/ Bibliothekstr. 1, 28359 Bremen, Germany
E-mail: staubitz@uni-bremen.de
Scheme 1. Transformation of zirconacyclopentadienes into metalloles and
extended diene systems.[9b-d] Use of polyzirconacyclopentadienes for the
synthesis of stable polymers.[10-11]
[b]
[c]
D. Duvinage, Dr. E. Lork
University of Bremen
Institute for Inorganic Chemistry and Crystallography/ MAPEX
Center for Materials and Processes
Leobener Str. 7/ Bibliothekstr. 1, 28359 Bremen, Germany
F. D. Sönnichsen
Zirconacyclopentadienes 1 are typically formed by a reductive
coupling of alkynes 5 by the zirconocene species “Cp2Zr” 8
(Scheme 2).[12] Such zirconacyclopentadienes can be also
University of Kiel
Otto-Diels-Institute for Organic Chemistry
Otto-Hahn-Platz 4, 24098 Kiel, Germany
1
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synthesized by the reaction of two monoynes with the active
zirconocene species 8.
and co-workers exchanged THF by pyridine, because the
zirconocene complex of THF is not as stable as with pyridine in
solution and in pure form. There are two ways to prepare such a
complex: One is based on the reduction of Cp2ZrCl2 with
magnesium in the presence of bis-(trimethylsilyl) acetylene in
THF at room temperature (in a yield of 66%).[15b] An improved
method is based on the formation of the complex via Negishi’s
conditions (Scheme 3), elaborated by Tilley and co-workers (in a
yield of 85%).
The “Cp2Zr” species, stabilized by a pyridine and a bis-
(trimethylsilyl)acetylene ligand, produces a thermally stable
compound that can be easily crystallized and stored under inert
conditions.[10b, 19]
Scheme 2. General synthesis of zirconacyclopentadienes of type 1.
In general, there are different methods to form this “Cp2Zr”
species from reagents that are mixtures of Cp2ZrCl2 / Na,
Cp2ZrCl2 / Mg or Cp2ZrCl2 / Ln.[9c] Further reagents are the
Takahashi´s (“Cp2ZrEt2”)[13]
,
Negishi’s (“Cp2ZrBu2”)[14] and
Rosenthal’s reagent (Cp2Zr(py)Me3SiCCSiMe3).[15] However, the
vast majority of reports describe the formation of the active “Cp2Zr”
species using either of the latter two methods.
Figure 1. Structure of the Rosenthal’s reagent 9.
The synthesis of zirconacyclopentadienes via Negishi´s reagent
includes an in-situ formed Zr-reagent, coordinated by THF, which
This means that for further syntheses with the Rosenthal reagent,
much milder reaction conditions will be given to form further
metalloles in general; some examples for the synthesis of
functionalized metalloles already exist.[20] The great solubility in
different solvents including nonpolar ones renders this reagent
particularly useful for applications in macrocyclic and polymer
chemistry, but mostly non-coordinating solvents are used in the
literature. Furthermore, just volatile by-products (pyridine and bis-
trimethylsilylacetylene) are formed during the reaction and can be
therefore easily removed compared to LiCl.[10b, 18a, 21]
However, a direct, quantitative and practicability comparison
between the two reagents has not been made so far. The aim of
this work was to investigate the exact differences between the use
of two sources of “Cp2Zr” in the preparation of
zirconacyclopentadienes 11a–11h starting with eight dialkynes
10a-10h (Scheme 4) and zirconacyclopentadienes 11i-11l from
four alkynes 10i-10l (Scheme 5).[22] A particular focus was the
compatibility of the reagents with alkynes that are functionalized.
is not stable for longer times at room temperature and which can
14, 16]
be not isolated in pure form.[12,
The reaction between
Cp2ZrCl2 (6) and two equivalents of nBuLi yields the intermediate
7 and insoluble LiCl (Scheme 3). The zirconocene 7 then
decomposes into n-butane and a number of active species
collectively labelled as “Cp2Zr” (8),[17] which is Negishi´s reagent.
The advantages of using this reagent include the use of relatively
cheap precursors, time saving in-situ handling of the precursor
reagents and the high reactivity of the Negishi species. However,
the latter may turn into a disadvantage when the dialkynes bear
functional groups like aromatic rings with halogen atoms. In a side
reaction, these can undergo halogen-lithium exchange reactions
if the concentration of nBuLi is not exactly known and an excess
is used. Also the tolerance towards other functional groups and
heterocycles as substituents is often not given.[10b] Finally, the
reaction conditions limit the choice of solvent, because Cp2ZrCl2
(6) is insoluble in nonpolar solvents as n-pentane or n-hexane.[10b]
Scheme 3. Formation of the “Cp2Zr”-Negishi’s reagent 8.[12]
Another possibility for the formation of zirconacyclopentadienes is
the use of Rosenthal´s reagent 9 (Figure 1).[15, 18] The synthesis
of Rosenthal’s zirconocene is based on the substitution of THF by
pyridine of the complex Cp2Zr(THF)Me3SiCCSiMe3. Rosenthal
2
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In the case of the dialkynes 10a and 10b, the use of Negishi´s
reagent for the formation of the zirconacyclopentadienes has
already been documented; the isolated yields are 55% for
zirconacyclopentadiene 11a[23] and 48% for compound 11b.[9d]
They are included in this study as benchmarks.
Results and Discussion
The “Results and Discussion” part of the synthesis of the alkynes
can be found as a part of the SI.
Synthesis of Zirconacyclopentadienes: Monitoring of
Reaction Progress by 1H NMR
Reaction of the diynes and monoynes 10a-10l respectively with
the “Cp2Zr” species, derived either from Negishi’s or Rosenthal´s
reagent,
should
lead
to
the
formation
of
the
zirconacyclopentadienes 11a-11l (Schemes 4 and 5). The
progress of the reactions under both conditions was followed by
1H NMR spectroscopy using naphthalene as an internal standard
for quantification.
In the case of Negishi´s reagent, the reactive “Cp2Zr” species was
formed by adding nBuLi to a solution of zirconocene dichloride in
THF at -78°C. The time reaction started with the addition of the
solution of the respective alkynes 10a-10l in THF. The cooling
bath was then removed allowing the reaction to reach room
temperature (ca. 22 °C in our laboratories, see SI for details). A
defined sample was taken out after 10 min, 30 min, 1 h, 3 h and
22 h and the solvent was removed immediately under reduced
pressure at 22 °C. Then, naphthalene in C6D6 as an internal
standard was added in equimolar proportions for the 1H NMR
measurements.
Scheme 4. Synthetic path to form the zirconacyclopentadienes 11a-11h using
two different sources of “Cp2Zr” and eight types of dialkynes 10a-10h.
The formation of the zirconacyclopentadiene 11a via this route
was confirmed as reported by literature;[23] after 30 min of reaction
the product was formed with a yield of 85%. The 1H NMR
spectrum showed a resonance at 6.00 ppm, which was indicative
for the cyclopentadienyl groups (Cp) of zirconacyclopentadiene
1
11a (Figure 2). Such a downfield shift of the Cp-signal in the H
NMR spectrum in comparison to the chemical shift of these
protons of the starting material (Cp2ZrCl2 δ(C6D6): 5.88 ppm)
suggests zirconacyclopentadiene ring formation, because the
shift is affected by the C-C double bonds inside the
zirconacyclopentadiene.
However, over 22 h the Cp signal shifted from 6.00 ppm to
6.04 ppm and the methylene groups were not as well defined as
before, which may indicate that the product was not stable in the
reaction mixture.
Scheme 5. Synthetic path to form the zirconacyclopentadienes 11i-11l using
two different sources of “Cp2Zr” and four alkynes 10i-10l.
3
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Figure 2. 1H NMR spectra (recorded at 300 K, 200 MHz in C6D6) of the reaction
monitoring for the synthesis of zirconacyclopentadiene 11a (Negishi’s reagent)
with naphthalene as standard (1 eq.). a) starting material Cp2ZrCl2, b)
naphthalene, c) starting material 10a at t = 0 min. Reaction monitoring after d) t
Figure 3. 1H NMR spectra (recorded at 300 K, 200 MHz in C6D6) of the reaction
monitoring for the synthesis of zirconacyclopentadiene 11c (Negishi’s reagent)
with naphthalene as standard (1 eq.). a) starting material Cp2ZrCl2, b)
naphthalene. c) starting material 10c. Reaction monitoring after d) t = 10 min,
e) t = 30 min, f) t = 1 h, g) t = 3 h and h) t = 22 h. i) zirconacyclopentadiene 11c
that was previously isolated.
=
10 min, e)
t = 30 min, f) t = 1 h, g) t = 3 h and h) t = 22 h. i)
zirconacyclopentadiene 11a previously isolated.[23]
In the case of zirconacyclopentadiene 11b with BPin moieties
attached, 20% yield was observed after 10 min of reaction; after
3 h the yield increased to 58%. However, after 22 h, the
zirconacyclopentadiene decomposed (for the corresponding 1H
NMR spectra see Figure S61 in the supporting information SI).
For the reaction of Negishi’s reagent and the dialkynes 10c -10f
with thiophene moieties, quite a different outcome was observed.
In the case of the reaction of diyne 10c, the
zirconacyclopentadiene 11c was formed after 10 min with a yield
of 15%, but after 30 min the yield decreased to 9% and after 1 h
to 2% (Figure 3). After 3 h of reaction, the product appeared to be
entirely decomposed to the starting material 10c indicating that
the zirconacyclopentadiene 11c was unstable under the
conditions of the synthetic route. This finding was confirmed by
integration of the peak corresponding to the methoxy group
compared with the standard which indicated that 98% of the
starting material was present in the reaction mixture at 3 h.
For the formation of the zirconacyclopentadienes 11d and 11f by
the reaction of the Negishi´s reagent and diynes 10d or 10f,
respectively, something similar could be observed. After 10 min
reaction time, 26% was generated for compound 11d and 82% for
11f. After 30 min, the yield increased to 28% for 11d while for 11f,
it decreased to 80%. The yield decreased after 1 h to 21% for 11d
and after 3 h to 65% for 11f. After 22h, the signals present were
attributed to the starting materials 10d and 10f and decomposition
of the zirconium part into different structures[16] was observed; a
spectrum of different Cp-signals appeared in the 1H NMR spectra
(see Figures S63 and S66 in the SI). The zirconacyclopentadiene
11e was not formed at any time of reaction, just starting material
10e and decomposition of the zirconium reagent was observed
1
throughout the reaction monitoring by H NMR (see Figure S64
from the SI).
However, if bis(trimethylsilyl)acetylene (BTMSA) is first added to
the Negishi´s reagent followed by the diyne 10e, it could be
observed that the zirconacyclopentadiene 11e was formed in a
yield of 41% after 60 min. Still, after 22 h, the
zirconacyclopentadiene 11e was decomposed again (Figure 4).
The difference in both reactions of diyne 10e with Negishi´s
reagent was the BTMSA, which seemed to be the crucial factor if
the product 11e can be formed or not.
4
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1
proportions and the reactions were monitored immediately by H
NMR spectroscopy. Rosenthal´s reagent is mostly used in non-
coordinating solvents (n-pentane, n-hexane, toluene or benzene)
in the literature, a reason could be that the original zirconium
complex undergoes ligand-exchange reactions and might be less
stable again. Also for further transmetalation reactions, which can
be made by one-pot reaction it is often desired to have non-
coordinating solvents. Therefore toluene was used as solvent, but
two further experiments in THF were also conducted.
Figure
5 shows the progress of the formation of the
zirconacyclopentadiene 11a. After 10 min, a signal at 6.00 ppm
appears, which can be assigned to the Cp protons of the desired
zirconacyclopentadiene, whereas the Cp signals at 5.44 ppm of
the Rosenthal’s reagent disappear. Compared to the synthesis
with the Negishi´s reagent, the product was still stable after 22 h.
Figure 4. 1H NMR spectra (recorded at 300 K, 600 MHz in C6D6) of the reaction
monitoring of the formation of zirconacyclopentadiene 11e at 22 °C with
naphthalene as an internal standard. a) starting material Cp2ZrCl2. b)
naphthalene c) starting material 10e at t = 0 min. Reaction monitoring after d) t
=
10 min, e)
t = 30 min, f) t = 1 h, g) t = 3 h and h) t = 22 h. i)
zirconacyclopentadiene 11e previously isolated.
In the case of the reaction of the Negishi’s reagent with the
starting materials 10h and 10k, their respective
zirconacyclopentadienes 11h and 11k were formed with high
yields of 99% and 97% after 10 min respectively (see Figures S67
and S70). Compared to previous results, both were still stable
within the reaction mixture after 22 h with yields of 99% and 70%.
For the conversion of the alkynes 10i, 10j and 10l into the
zirconacyclopentadienes 11i, 11j and 11l, the yield rose until 94%,
88% and 80% after 10 min, 10 min and 30 min respectively, but
decreased after 22 h to 67%, 65% and 26% (see Figures S68,
S69 and S71). This means that these particular
zirconacyclopentadienes were insufficiently stable within the
reaction mixture over time: care would need to be taken to
terminate the reaction with the appropriate Zr-element exchange
at an optimal reaction time.[24]
Figure 5. 1H NMR spectra (recorded at 300 K, 200 MHz in C6D6) of the reaction
monitoring of the formation of zirconacyclopentadiene 11a at 22 °C with
naphthalene as an internal standard. a) Rosenthal’s reagent 9. b) naphthalene
c) starting material 10a. d) monitoring after 10 min. e) zirconacyclopentadiene
11a.[23]
The yield of zirconacyclopentadiene 11g could not be determined
by 1H NMR measurements (monitoring of reaction progress by 1H
NMR), because this compound could not be completely
redissolved after isolation. The compound was forming gel-like
needles with the NMR solvents. Therefore, the yield of the
zirconacyclopentadiene 11g had to be determined after complete
isolation after 3 h from the reaction mixture. It could be
successfully synthesized with a yield of 88% (purity 90%). A long
1H NMR measurement and HR-MS confirm the identity of the
product.
Thus, Negishi´s reagent proved to be incompatible with all
compounds that bear thiophenyl motifs. In general, the synthesis
was successful with yields between 28% and 98% for all other
zirconacyclopentadienes.
The reactions with Rosenthal’s reagent were placed inside a
glove box under a nitrogen atmosphere. To a solution of
The transformation of the alkynes 10b-l in toluene to their
respective zirconacyclopentadienes 11b-l proceeded in the same
manner and were completed in all cases after 10 min; the
products were stable for more than 22 h with yields ranging from
83% to 99% (For the 1H NMR spectra of the reaction monitoring
of the zirconacyclopentadienes 11b-l see the SI). In the cases of
the zirconacyclopentadienes 11i and 11l the yield dropped down
from 97% and 95% to 83% and 90% respectively after 22 h (see
Figures S82 and S85); it appears that these two compounds might
undergo a reversion of the cyclization as it was observed in most
of the synthesis examples under the Negishi´s conditions.
Zirconacyclopentadiene 11g could be obtained with a yield of
91% (purity 92%) after 3 h of reaction time after complete isolation
from the reaction mixture. Because of the solubility problems, the
identity was determined again with a long-time 1H NMR and a HR-
MS measurement. Zirconacyclopentadienes 11d and 11h were
also synthesized with Rosenthal´s reagent in THF. The yield for
both reactions was >99% after 10 min, but dropped after 22 h to
63% and 83% respectively. After 22 h, both 1H NMR spectra
5
Rosenthal’s zirconocene
9 in toluene, the alkynes 10a-l
respectively were added as a solution in toluene. To each sample
of the reaction monitoring after removing the solvent, naphthalene
in C6D6 as an internal standard was added in equimolar
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10.1002/chem.201902255
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showed again signals of the alkyne starting materials 10d and 10h,
thus, the zirconium complex is not quite as stable as in toluene.
This might arise because the coordinating THF in excess can
induce the reverse reaction.
To investigate the stability of the zirconacyclopentadienes in
solution in the presence of lithium chloride (which is a by-product
of the Negishi reagent), isolated zirconacyclopentadiene 11e was
stirred in a mixture of LiCl in toluene for 22 h and defined samples
were taken after 10 min, 30 min, 60 min, 180 min and 22 h. It was
observed that
a precipitate formed and after 22 h, the
zirconacyclopentadiene 11e was completely decomposed (Figure
6).
Figure 6. 1H NMR spectra (recorded at 300 K, 600 MHz in C6D6) of the reaction
monitoring of the stability test of zirconacyclopentadiene 11e with naphthalene
as standard (1 eq.). a) Naphthalene. b) Starting material 10e. Reaction
monitoring after. c) 10 min. d) 30 min. e) 1 h. f) 3 h. g) 22 h. and h) isolated
zirconacyclopentadiene 11e.
Table 1 summarizes the 1H NMR signals of the Cp groups and the
analytical yields of all zirconacyclopentadienes obtained with both
routes.
6
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Table 1. Summary of 1H NMR signals of the Cp rings in C6D6 and the highest % conversion for the zirconacyclopentadienes 11a-l synthesized using the Rosenthal
and Negishi reagent.
Entry
Product
1H
ppm
δ
Cp/
Rosenthal
Negishi
t/ min
Max. conversion/
%1 in toluene
t/
min
Remaining yield
after 22 h/ %
Max. conversion/ %
Remaining yield
after 22 h/ %
1
2
3
4
5
6
7
8
11a
11b
11c
11d
11e
11f
6.00
6.37
6.05
5.84
5.85
6.00
5.93
5.70
> 99
10
10
> 99
85
10
180
0
0
97
97
56
98
10
96
15
30
0
91 (> 99% in THF)
10
88 (63% in THF)
28
30
0
> 99
93
10
> 99
93
-
0 (41% with BTMSA)
- (60 min)
10
0
10
83
88
98
0
11g
11h
91
1802
10
1803
10
-
> 99
> 99
98
(> 99% in THF)
(83% in THF)
9
11i
11j
11k
11l
6.09
5.94
6.01
6.35
97
96
10
10
10
10
90
96
94
88
97
80
10
10
10
30
67
65
70
26
10
11
12
> 99
95
> 99
83
1 The conversion was calculated based on the consumption of the starting material.
2 Yield obtained after complete isolation of the product after 3 h.
3 Yield obtained after complete isolation of the product after 3 h.
7
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In general, it seems that for longer reaction times, the Rosenthal’s
reagent is more stable in solution than the Negishi’s reagent. This
is most likely due to the stabilizing ligands (bis-(trimethylsilyl)
acetylene and pyridine). This might be also explained by the
slower and lower conversion for five (11a-11e) of the examples,
because a certain amount of the active “Cp2Zr” species might
decompose before it can undergo the cyclisation reaction. The
extra experiment of Negishi´s reagent with diyne 10e, where
BTMSA was added beforehand, shows also that stabilizing
ligands are important for the prevention of decomposition of the
active zirconium species and the formation of the
the active “Cp2Zr” species over the time, the yield decreases and
new zirconacyclopentadiene cannot be formed.
The visible formation of a solid after 22 h in all of the reactions
with Negishi’s reagent might result from the LiCl that slowly
precipitated; however, it could also be the decomposition of the
“Cp2Zr” species and the reversibility of the cyclization reaction to
the starting materials.[19] Another point in terms of decomposition
of the zirconacyclopentadienes under Negishi´s conditions can be
the LiCl in the solution. Zirconacyclopentadiene 11e, which
performed worst with Negishi’s reagent, was tested for its stability.
In a mixture of LiCl in toluene, we observed indeed that LiCl could
zirconacyclopentadienes. For the other seven (11f-11l) examples, induce decomposition. It appears again the stability of the alkyne
the conversion with the Negishi´s reagent was nearly as fast and
high-yielding as with Rosenthal´s reagent (Table 1).
complex in the reaction mixture is crucial, because in the study
with Negishi´s reagent, the zirconacyclopentadiene did not
decompose in all cases. The choice of solvent also clearly has an
effect on the overall stability, which can be seen from the
reactions with Rosenthal´s reagent in THF.
In addition, comparing both methods, the handling of the
Rosenthal’s reagent was much easier compared to Negishi’s
reagent; especially when exact stoichiometry is needed. In one
hand, it was sufficient to prepare merely one stock solutions for
several reactions without the need for lower temperatures for the
formation of such zirconacyclopentadienes. The in-situ formation
of Negishi´s reagent on the other hand requires lower
temperatures and therefore temperature controls to prevent the
reagent from decomposition.[16]
An important fact to recognize is also that the
zirconacyclopentadienes (11a-11f) were more stable over the
time (monitoring until 22 h) under the mild Rosenthal’s conditions
than under the harsher Negishi conditions. In all the six examples
11a-11f, the product was completely decomposed under
Negishi’s conditions. However, in the case of the compounds 11h-
11l, with less reactive motifs such as phenyl groups or
trimethylsilyl groups, the stability under the Negishi conditions
was almost equal; the remaining yields after 22 h were higher
than 26%. The maximum conversion for all reactions with
Rosenthal´s reagent reached nearly quantitative after only 10 min
and the remaining yields were higher than 83% (toluene) and 63%
(THF).
Additionally, air stability tests were conducted for all products and
can be found as a part of the SI.
For each of the two reagents it could be observed that the
conversion for all alkynes was different. One point could be the
stability of the alkyne-complex with the Zr-species in general. The
Structures in the Solid State
formation of the zirconacyclopentadiene is an equilibrium reaction, The molecular structures of 11d, 11f, 11h, 11i, 11j, 11k and 11l
which means for some of the alkynes the equilibrium might be on
the side of the alkyne-complex, but for some it might be on the
side of the starting material. This can be seen by the fact that the
maximal conversion for all the alkynes is different for the reaction
with Rosenthal´s reagent and the same is also for the route with
Negishi´s reagent. This observation may be explained by the
different binding behavior of the alkynes to the zirconium, which
means the yield of the zirconacyclopentadiene should be higher
for a good-binding alkyne. For the reaction with Negishi´s reagent,
this can be seen more extremely in term of yields (Table1, max.
conversion and remaining yield after 22 h) than for the reaction
with Rosenthal´s reagent due to the fact that there are stabilizing
ligands as pyridine and/or bis-(trimethylsilyl) acetylene from
Rosenthal´s reagent remaining in solution. Therefore, in the
equilibrium, there are stable starting materials and products. In
the case of the Negishi reagent, the starting material is unstable;
thus, if the reverse reaction occurs, decomposition of the alkyne-
complex cannot be prevented. Because of the decomposition of
are shown in Figure 7 (and are also part of the SI) and confirm the
identity of the compounds. Single crystals were obtained from a
saturated toluene solution. A table with selected bond lengths and
angles of all structures can be found as a part of the SI (Tables
S6-8). In all compounds, the Zr atom is incorporated into almost
planar five-membered central rings (e.g. Zr(1)-C(1)-C(2)-C(7) is
8.3(2) ° for 11d). In all cases where the zirconacyclopentadiene
ring bears aryl groups in the 2- and 5- position, these groups are
twisted to the plane (e.g. Zr(1)-C(1)-C(10)-C(11) is -23.0(3) ° for
11d). In the compounds 11i, 11j, 11k and 11l, the aryl groups in
the 3- and 4- position of the zirconacyclopentadiene ring are
nearly completely twisted with respect to the plane (e.g. C(1)-
C(2)-C(20)-C(21) is 83.36(2) ° for 11l), whereas the annulated
six- or five-membered rings in that position show puckered
confirmations.
8
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10.1002/chem.201902255
Chemistry - A European Journal
Figure 7. Molecular structures of 11d, 11f, 11h, 11i, 11j, 11k and 11l showing 50% probability ellipsoids and the crystallographic numbering scheme. Only the
major parts of the disordered molecule of 11f is shown for clarity. For 11h only one independent molecule is shown. Only the major parts of the disordered molecule
of 11i is shown for clarity
available and were used without further purification unless noted otherwise.
n-BuLi was titrated by Lin and Paquette method[25] for exact concentrations.
Conclusions
In summary, it could be observed that the use of Rosenthal´s
reagent was much more efficient for the synthesis of
zirconacyclopentadienes in most of the cases with respect to yield,
Analytical Instruments
stability of the zirconacyclopentadiene and reaction time when
compared to Negishi´s reagent. More particularly, with our study
1H NMR, 13C{1H} NMR, 11B{1H} NMR, 119Sn{1H} NMR, 19F NMR and
has been shown the high importance of stabilizing ligands in the
29Si{1H} NMR spectra were recorded on a Bruker Avance Neo 500, Bruker
Avance Neo 600 or Bruker DPX-200 spectrometer at 300 K. All H NMR
reaction mixture. In addition to reliably producing high yields,
1
Rosenthal’s reagent is very functional group tolerant; but in
general, it was shown that halides do also not react under
Negishi´s conditions, when n-BuLi is titrated and used in exact
amounts. However, the advantages of using Negishi´s reagent
mean using relatively cheap precursors, time saving in-situ
handling of the precursor reagents and a highly reactive species;
but finally, Rosenthal´s zirconocene is a thermally stable reagent
that can be prepared with great convenience.
and 13C{1H} NMR were referenced against the solvent residual proton
signals (1H), or the solvent itself (13C). The reference for the 119Sn{1H} NMR
spectra was calculated based on the 1H NMR spectrum of TMS. 11B{1H}
NMR and 19F NMR spectra were referenced against BF3·Et2O in CDCl3.
29Si{1H} NMR spectra were referenced against TMS in CDCl3. All chemical
δ shifts are given in parts per million (ppm) and all coupling constants J in
Hz. Electron Impact (EI) ionization mass spectra were obtained on the
double focusing mass spectrometer MAT 95+ or MAT 8200 from
FINNIGAN mat. Samples were measured by direct inlet or indirect inlet
method with a source temperature of 200° C. The ionization energy of the
electron impact ionization was 70 eV. All signals were reported with the
quotient from mass to charge m/z.
Experimental Section
Crystallography. Intensity data of 11d, 11f, 11h, 11i, 11j, 11k and 11l
were collected on a Bruker Venture D8 diffractometer at 100 K with Mo-K
(0.7107 Å) radiation. All structures were solved by Intrinsic phasing and
refined based on F2 by use of the SHELX [26]program package as
implemented in OLex21.2.[27] All non-hydrogen atoms were refined using
anisotropic displacement parameters. Hydrogen atoms attached to carbon
atoms were included in geometrically calculated positions using a riding
model. Crystal and refinement data are collected in Table S3-5.
General Methods and Materials
All reactions were carried out using standard Schlenk techniques under a
dry, inert nitrogen or argon atmosphere unless noted otherwise. Some
reactions were performed inside a nitrogen filled glovebox from Inert,
Innovative Technology, Inc. Company ( < 0.1 ppm O2 and < 0.1 ppm H2O).
All dry solvents were taken from the solvent purification system (SPS),
degassed by freeze-pump-thaw cycles and stored under a nitrogen
atmosphere unless noted otherwise. All chemicals were commercially
A rotational disorder was resolved for the thiophene groups of compound
11f. The refinement led to a split atom model for each group with refined
9
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10.1002/chem.201902255
Chemistry - A European Journal
occupancies of 76:24 and 53:47, respectively. Compound 11h comprises
two crystallographic independent conformers. The fluorine atoms of the
two CF3-groups of compound 11i were disordered and were refined with
split occupancies of 71:29 and 57:43, respectively. The C-F-distances
were restrained to be equal. Compound 11k crystallized with one molecule
of toluene per asymmetric unit. The toluene solvate molecule was
disordered over two positions with split occupancies of 65:35. Compound
11l crystallized with a half molecule in the asymmetric unit. The Zr-atom is
located on the Wyckoff-Position 4e of space group C2/c.
δ 176.9 (a), 156.1 (e), 142.8 (b), 137.1 (g), 129. (f), 112.1 (Cp), 70.0 (h),
29.9 (c), 23.6 (d) ppm; HR-MS (EI, C26H22I2S290Zr): m/z calcd. 741.82939,
found 741.82934 (R = 10000); MS (EI, 70 eV, direct inlet, 200 °C): m/z (%
relative intensity) = 742 (44) [M]+., 347 (100).
11f. 10f (150 mg, 555 µmol), Rosenthal´s reagent (261 mg, 555 µmol),
toluene (6 mL), 22 °C, (259 mg, 95%). 1H NMR (500.1 MHz, C6D6): δ 6.96
(dd, 3J = 5.2 Hz, 4J = 1.0 Hz, 2H, h), 6.90 (dd, 3J = 5.2, 3.5 Hz, 2H, g), 6.21
(dd, 3J = 3.5 Hz, 4J =1.0 Hz, 2H, f), 6.00 (s, 10H, Cp), 2.70-2.64 (m, 2H, c),
1.57-1.54 (m, 2H, d) ppm; 13C{1H} NMR (126 MHz, C6D6): δ 177.9 (a),
150.3 (e), 142.4 (b), 127.3 (g), 123.0 (h), 121.4 (f), 112.2 (Cp), 30.1 (c),
24.0 (d) ppm; HR-MS (EI, C26H24S290Zr): m/z calcd. 490.03610, found
490.03669 (R = 10000); MS (EI, 70 eV, direct inlet, 200 °C): m/z (% relative
intensity) = 490 (19) [M]+., 220 (100) [Cp2Zr]+..
Crystallographic data for the structural analyses have been deposited with
the Cambridge Crystallographic Data Centre. Copies of this information
may be obtained free of charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033; e-mail:
deposit@ccdc.cam.ac.uk or http://www.ccdc.cam.ac.uk).
11g. 10g (150 mg, 551 µmol), Rosenthal´s reagent (259 mg, 552 µmol),
toluene (6 mL), 22 °C, (248 mg, 91%, 92% purity). 1H NMR (500 MHz,
C6D6): δ 7.42-7.23 (m, 4H, g, g’), 7.09-6.95 (m, 6H, h, h’, i), 5.93 (s, 10H,
Cp), 2.38-2.31 (m, 4H, c), 1.61-1.50 (m, 6H, d, e) ppm; 13C{1H} NMR
(126 MHz, C6D6): δ 189.3 (a), 149.6 (b), 137.9 (f), 128.6 (g, g’), 126.3,
123.3 (h, h, I’), 112.2 (Cp), 31.6 (c), 31.1 (d, e) ppm; HR-MS (EI,
C31H3090Zr): m/z calcd. 492.13891, found 492.13982 (R = 10000); MS (EI,
70 eV, direct inlet, 200 °C): m/z (% relative intensity) = 492 (8) [M]+., 220
(100) [Cp2Zr]+..
General procedure for the synthesis of the zirconacyclopentadienes (11a-
l)
An equimolar solution of Rosenthal’s reagent (9), and alkyne (10a-l) in
toluene was stirred at 22 °C for 10 min. The solvent was removed under
inert conditions. After filtration over Celite, the final product was afforded.
11a. 10a (100 mg, 230 µmol), Rosenthal´s reagent (109 mg, 230 µmol),
toluene (5 mL), 22 °C, (141 mg, 94%). 1H NMR (500 MHz, C6D6) δ 6.00 (s,
10H, Cp), 2.22-2.15 (m, 4H, c), 1.57-1.50 (m, 4H, d), 0.20 (d, 18H, e; 2JSn-
H= 24 Hz) ppm; 13C{1H} NMR (126 MHz, C6D6): δ 206.1 (a), 150.7 (b),
111.4 (Cp), 38.7 (c), 23.1(d), -6.7 (e; 1JSn-C = 146 Hz) ppm; 119Sn{1H} NMR
(187 MHz, CDCl3): δ -81.3 ppm; HR-MS (EI, C24H36Sn2Zr): m/z calcd
653.99153, found 653.99188 (R = 10000); MS (EI, 70 eV, direct inlet,
200 °C): m/z (% relative intensity) = 654 (5) [M]+., 155 [M-C12H12]+., (100).
11h. 10h (150 mg, 373 µmol), Rosenthal´s reagent (176 mg, 373 µmol),
toluene (6 mL), 22 °C, (223 mg, 96%).1H NMR (600 MHz, C6D6): δ 7.49-
7.44 (m, 4H, g, g´), 6.80-6.74 (m, 4H, f, f´), 5.70 (s, 10H, Cp), 2.33 (t, 3J =
7.1 Hz, 4H, c), 1.26 (p, 3J = 7.1 Hz, 2H, d) ppm; 13C{1H} NMR (151 MHz,
C6D6): δ 182.2 (a), 149.0 (b), 131.7 (g, g’), 128.0 (f, f’), 126.2 (e), 117.8 (h),
110.4 (Cp), 35.6 (c), 22.5 (d) ppm; HR-MS (EI, C29H2479/80Br290Zr): m/z
calcd. 621.92728, found 621.92652 (R = 10000); MS (EI, 70 eV, direct inlet,
200 °C): m/z (% relative intensity) = 620 (69) [M]+., 220 (100) [Cp2Zr]+..
11b. 10b (100 mg, 280 µmol), Rosenthal´s reagent (132 mg, 280 µmol),
toluene (5 mL), 22 °C, (151 mg, 93%). 1H NMR (500 MHz, C6D6): δ 6.37
(s, 10, Cp), 2.59-2.54 (m, 4H, c), 1.65-1.58 (m, 4H, d), 1.10 (s, 24H, f) ppm;
13C{1H} NMR (126 MHz, C6D6): δ 147.0 (b), 111.7 (Cp), 81.5(e), 35.4 (c),
24.9 (f), 23.5 (d) ppm;4 11B NMR (160 MHz, C6D6): δ 30.9 ppm; HR-MS (EI,
C30H4210/11B2O490Zr): m/z calcd. 577.23471, found 577.23484 (R = 10000);
MS (EI, 70 eV, direct inlet, 200 °C): m/z (% relative intensity) = 578 (13)
[M]+., 83 (100).
11i. 10i (150 mg, 650 µmol), Rosenthal´s reagent (146 mg, 310 µmol),
toluene (6 mL), 22 °C, (206 mg, 94%). 1H NMR (600 MHz, C6D6): δ 7.10
3
(d, 3J = 7.8 Hz, 4H, e, e´), 6.48 (d, J = 7.98 Hz, 4H, d, d´), 6.08 (s, 10H,
Cp), -0.28 (s, 18H, SiMe3) ppm; 13C{1H} NMR (151 MHz, C6D6): δ 206.3
2
(a), 149.4 (c) 148.2 (b), 130.2 (d, d´), 127.5 (q, JC-F = 32.2 Hz, f)5, 125.0
1
3
(q, JC-F = 271.7 Hz, g), 124.0 (q, JC-F = 3.8 Hz, e, e´), 111.7 (Cp), 2.70
(SiMe3) ppm; 19F NMR (471 MHz, C6D6): δ -62.1 ppm; 29Si{1H} NMR
(99 MHz, C6D6): δ -14.9 ppm; MS (EI, 70 eV, direct inlet, 200 °C):
compound shows no molecule ion.
11c. 10c (150 mg, 454 µmol), Rosenthal´s reagent (213 mg, 454 µmol),
toluene (6 mL), 22 °C, (233 mg, 93%). 1H NMR (500 MHz, C6D6): δ 6.07
(d, 3J = 3.8 Hz, 2H, g), 6.05 (s, 10H, Cp), 5.77 (d, 3J = 3.7 Hz, 2H, f), 3.44
(s, 6H, i), 2.80-2.74 (m, 4H, c), 1.63-1.57 (m, 2H, d) ppm; 13C{1H} NMR
(126 MHz, C6D6): δ 177.9 (a), 165.7 (h), 141.3 (b), 136.8 (e), 119.9 (f),
112.1 (Cp), 104.1 (g), 59.7 (i), 30.7 (c), 24.4 (d) ppm; HR-MS (EI,
C28H28O2S290Zr): m/z calcd. 550.05723, found 550.05796 (R = 10000); MS
(EI, 70 eV, direct inlet, 200 °C): m/z (% relative intensity) = 550 (74) [M]+.,
220 (100) [Cp2Zr]+..
11j. 10j (122 mg, 352 µmol), Rosenthal´s reagent (166 mg, 352 µmol),
toluene (3 mL), 22 °C, (192 mg, 96%). 1H NMR (600 MHz, C6D6): δ 7.60
(dd, 3J = 7.6 Hz, 4J = 1.3 Hz, 2H, e), 7.51 (dd, 3J = 7.6 Hz, 4J = 1.3 Hz, h),
7.14 (td, 3J = 7.6 Hz, 4J = 1.3 Hz, 2H, f), 7.07 (td, 3J = 7.6 Hz, 4J = 1.3 Hz,
2H, g), 5.94 (s, 10H, Cp), 0.21 (s, 18H, SiMe3) ppm; 13C{1H} NMR
(151 MHz, C6D6): δ 208.9 (a), 137.5 (b), 136.2 (c or d), 133.7 (d or c), 129.7
(h), 128.8 (f), 126.9 (g), 123.7 (e), 110.2 (Cp), 3.8 (SiMe3) ppm; HR-MS
(EI, C32H3628Si290Zr); m/z calcd. 566.13971, found 566.13966 (R = 10000);
MS (EI, 70 eV, direct inlet, 200 °C): m/z (% relative intensity) = 566 (5)
[M]+., 220 (100) [Cp2Zr]+.
11d. 10d (150 mg, 352 µmol), Rosenthal´s reagent (166 mg, 352 µmol),
toluene (6 mL), 22 °C, (210 mg, 93%). 1H NMR (600 MHz, C6D6): δ 6.82
(d, 3J = 3.8 Hz, 2H, g), 5.84 (s, 10H, Cp), 5.69 (d, 3J = 3.8 Hz, 1H, f), 2.49
(m, 4H, c), 1.50-1.46 (m, 4H, d) ppm; 13C{1H} NMR (126 MHz, C6D6): δ
177.0 (a), 151.8 (e), 143.0 (b), 130.2 (g), 121.8 (f), 112.3 (Cp), 109.4 (h),
30.1 (c), 23.8 (d) ppm; HR-MS (EI, C26H2279Br2S290Zr): m/z calcd.
645.85712, found 645.85714 (R = 10000); MS (EI, 70 eV, direct inlet,
200 °C): m/z (% relative intensity) = 646 (38) [M]+., 301 (100).
11k. 10k (150 mg, 842 µmol), Rosenthal´s reagent (198 mg, 421 µmol),
toluene (6 mL), 22 °C, (231 mg, 95%).1H NMR (500 MHz, C6D6): δ 7.06-
7.01 (m, 4H, i, i´), 7.00-6.93 (m, 4H, d, d´), 6.86-6.82 (m, 4H, e, e´), 6.82-
6.79 (m, 2H, j), 6.76-6.71 (m, 2H, f), 6.71-6.66 (m, 4H, h, h´), 6.01 (s, 10H,
Cp) ppm; 13C{1H} NMR (126 MHz, C6D6): δ 194.8 (a), 148.6 (g), 142.8 (b),
141.7 (c), 131.3 (i, i´), 128.3 (h, h´), 127.7 (d, d´), 127.2 (e, e´), 125.1 (f),
123.4 (j), 112.3 (Cp) ppm; HR-MS (EI, C38H3090Zr); m/z calcd. 576.13891,
11e. 10e (150 mg, 287 µmol), Rosenthal´s reagent (137 mg, 287 µmol),
toluene (6 mL), 22 °C, (194 mg, 91%). 1H NMR (500 MHz, C6D6): δ 7.03
(d, 3J = 3.7 Hz, 2H, g), 5.85 (s, 10H, Cp), 5.66 (d, 3J = 3.7 Hz, 2H, f), 2.52-
2.45 (m, 4H, c), 1.50-1.45 (m, 4H, d) ppm; 13C{1H} NMR (126 MHz, C6D6):
4 The signal from the carbon atom bond to boron was not visible due to the
high quadrupole moment of the boron nucleus.
5 The signal is overlapping with the solvent signal.
10
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10.1002/chem.201902255
Chemistry - A European Journal
found 576.13987 (R = 10000); MS (EI, 70 eV, direct inlet, 200 °C): m/z (%
relative intensity) = 576 (18) [M]+., 220 (100) [Cp2Zr]+..
Matano, H. Ohkubo, T. Miyata, Y. Watanabe, Y. Hayashi, T. Umeyama,
H. Imahori, Eur. J. Inorg. Chem. 2014, 2014, 1620-1624.
[3]
[4]
K. E. Horner, P. B. Karadakov, The Journal of Organic Chemistry 2013,
78, 8037-8043.
11l. 10l (150 mg, 669 µmol), Rosenthal´s reagent (158 mg, 335 µmol),
toluene (6 mL), 22 °C, (202 mg, 90%). 1H NMR (600 MHz, C6D6): δ 8.32
(dq, 3J = 8.4 Hz, 4J = 0.9 Hz, 2H, k), 7.46 (ddd, 3J = 8.4 Hz, 3J = 6.8 Hz, 4J
= 1.3 Hz, 2H, j), 7.38 (ddt, 3J = 8.1 Hz, 4J = 1.2 Hz, 0.6 Hz, 2H, h), 7.21
(ddd, 3J = 8.1 Hz, 3J = 6.8 Hz, 4J = 1.3 Hz, 2H, i), 7.02 (d, 3J = 8.1 Hz, 2H,
f), 6.84 (dd, 3J = 7.0 Hz, 4J = 1.3 Hz, 2H, d), 6.59 (dd, 3J = 8.2 Hz, 3J =
7.0 Hz, 2H, e), 6.34 (s, 10H, Cp), -0.39 (m, 18H, SiMe3) ppm; 13C{1H} NMR
(151 MHz, C6D6): δ 207.7 (a), 150.0 (b), 142.6 (c), 133.4 (l), 132.8 (g),
128.0 (h), 126.8 (k), 126.0 (d), 125.8 (f), 124.8 (j), 124.6 (i), 124.0 (e), 111.1
(Cp), 2.1 (SiMe3) ppm; 29Si{1H} NMR (99 MHz, C6D6): δ -14.9 ppm; MS (EI,
70 eV, direct inlet, 200 °C): compound shows no molecule ion.
a) J. O. C. Jimenez-Halla, E. Matito, M. Solà, H. Braunschweig, C. Hörl,
I. Krummenacher, J. Wahler, Dalton Transactions 2015, 44, 6740-6747;
b) A. Iida, S. Yamaguchi, J. Am. Chem. Soc. 2011, 133, 6952-6955.
a) S. Yamaguchi, Y. Itami, K. Tamao, Organometallics 1998, 17, 4910-
4916; b) B. Goldfuss, P. v. R. Schleyer, Organometallics 1997, 16, 1543-
1552; c) M. Saito, M. Sakaguchi, T. Tajima, K. Ishimura, S. Nagase,
Phosphorus, Sulfur, and Silicon and the Related Elements 2010, 185,
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[5]
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a) S. Khaghaninejad, M. M. Heravi, in Adv. Heterocycl. Chem., Vol. 111
(Ed.: A. R. Katritzky), Academic Press, 2014, pp. 95-146; b) A. J. Ashe,
L. L. Lohr, S. M. Al-Taweel, Organometallics 1991, 10, 2424-2431; c) G.
Mross, E. Holtz, P. Langer, The Journal of Organic Chemistry 2006, 71,
8045-8049.
Monitoring of Reaction Progress of the zirconacyclopentadienes (11a-l) by
1H NMR
[7]
[8]
a) Y. Zhang, L. Liu, T. Chen, Z. Huang, W.-X. Zhang, Z. Xi,
Organometallics 2019, 38, 2174-2178; b) J. Wei, L. Liu, M. Zhan, L. Xu,
W.-X. Zhang, Z. Xi, Angew. Chem. Int. Ed. 2014, 53, 5634-5638.
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2017, 46, 1160-1192; c) L. Liu, W. Geng, Q. Yang, W.-X. Zhang, Z. Xi,
Organometallics 2015, 34, 4198-4201.
Procedure for Negishi’s condition: example 11a
To a solution of Cp2ZrCl2 (67.7 mg, 231 µmol) in THF (2.0 mL) at -78 °C,
n-butyllithium (180 µL, 463 µmol; 2.59 M in hexanes) was added dropwise
over the course of 1 min. The reaction mixture was stirred at -78°C for 1 h
and a solution of 10a (100 mg, 231 µmol) in THF (1.0 mL) was added. The
cooling bath was removed, and the reaction’s time started to run. A sample
(0.30 mL, 14 µmol) was taken after 10 min, 30 min, 1 h, 3 h and 22 h and
the solvent was removed immediately under inert conditions. Naphthalene
in C6D6 was added (0.2 mL, 0.06 M, 14 µmol) to the sample and used as
an internal standard. The reaction progress was analyzed by 1H NMR
spectroscopic measurements of each sample.
[9]
a) Z. Xi, R. Hara, T. Takahashi, The Journal of Organic Chemistry 1995,
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McDonald, E. Rivard, J. Am. Chem. Soc. 2013, 135, 5360-5363; e) I.-M.
Ramirez y Medina, M. Rohdenburg, F. Mostaghimi, S. Grabowsky, P.
Swiderek, J. Beckmann, J. Hoffmann, V. Dorcet, M. Hissler, A. Staubitz,
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Int. Ed. 2018, 57, 13319-13324.
Procedure for Rosenthal’s condition: example 11a
In a GB, a solution of 9 (109 mg, 230 μmol) and 10a (100 mg, 230 μmol)
in toluene (5 mL) was stirred at 22 °C. A sample of the reaction (0.3 mL,
14 µmol) was taken after 10 min, 30 min, 1 h, 3 h and 22 h and the solvent
was removed immediately under inert conditions. Naphthalene in C6D6
was added (0.2 mL, 0.06 M, 14 µmol) to the sample and used as an
internal standard. The reaction progress was analyzed by 1H NMR
spectroscopic measurements of each sample.
[10] a) G. R. Kiel, M. S. Ziegler, T. Tilley, Angew. Chem. Int. Ed. 2017, 122,
4839-4844; b) J. R. Nitschke, S. Zürcher, T. D. Tilley, J. Am. Chem. Soc.
2000, 122, 10345-10352.
[11] S. S. H. Mao, T. D. Tilley, Macromolecules 1997, 30, 5566-5569.
[12] E. Negishi, S. J. Holmes, J. M. Tour, J. A. Miller, F. E. Cederbaum, D. R.
Swanson, T. Takahashi, J. Am. Chem. Soc. 1989, 111, 3336-3346.
[13] T. Takahashi, M. Kageyama, V. Denisov, R. Hara, E. Negishi,
Tetrahedron Lett. 1993, 34, 687-690.
More detailed reaction monitoring conditions of both routes for the
zirconacyclopentadienes 11b-l can be found in the SI.
[14] E.-i. Negishi, F. E. Cederbaum, T. Takahashi, Tetrahedron Lett. 1986,
27, 2829-2832.
[15] a) U. Rosenthal, A. Ohff, M. Michalik, H. Görls, V. V. Burlakov, V. B. Shur,
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Acknowledgements
S.U-R thanks the German Academic Exchange Service (DAAD)
and the Colfuturo Foundation for a PhD scholarship. Grant
number A/13/72356.
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This research has been supported by the Institutional Strategy of
the University of Bremen, funded by the German Excellence
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Keywords: Zirconium • Metallacycles • Substituent effects •
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10.1002/chem.201902255
Chemistry - A European Journal
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10.1002/chem.201902255
Chemistry - A European Journal
FULL PAPER
In this study, two “Cp2Zr” sources, the
Negishi´s and the Rosenthal´s reagent
were compared with respect to yield,
reaction time and product stability. In
total, twelve compounds with different
substituents were used for the
reductive coupling by these zirconium
sources.
Sara Urrego-Riveros[a,§], Isabel-Maria
Ramirez y Medina[a,§], Daniel
Duvinage[b], Enno Lork[b], Frank D.
Sönnichsen[c] and Anne Staubitz*[a]
1 – 10
Negishi´s Reagent Versus
Rosenthal´s Reagent in the Formation
of Zirconacyclopentadienes
13
This article is protected by copyright. All rights reserved.