Insights into a nontoxic and high-yielding synthesis of methyltrioxorhenium (MTO)

Article abstract of DOI:10.1002/ejic.200800524

The versatile catalyst methyltrioxorhenium(VII) (MTO) is now available in high yields by utilizing easily accessible nontoxic starting materials. The new synthetic pathway allows an inexpensive, large-scale production of MTO, paving the way for industrial applications. A variety of starting materials is compared with respect to their applicability, availability and ease of handling. The reaction times and the by-products formed are compared under different reaction conditions. It was seen that silver perrhenate in combination with methylzinc acetate, which was derived from trimethylaluminum and zinc acetate, are the best starting materials for a high-yielding large-scale synthesis of MTO. Wiley-VCH Verlag GmbH & Co. KGaA, 2008.

Full text of DOI:10.1002/ejic.200800524

FULL PAPER
DOI: 10.1002/ejic.200800524
Insights into a Nontoxic and High-Yielding Synthesis of Methyltrioxorhenium
(MTO)
Josef K. M. Mitterpleininger,[a] Normen Szesni,[b] Stefanie Sturm,[b] Richard W. Fischer,[b]
and Fritz E. Kühn*[a]
Dedicated to Wolfgang A. Herrmann on the occasion of his 60th birthday
Keywords: Rhenium / Alkylzinc compounds / IR spectroscopy / Synthesis
The versatile catalyst methyltrioxorhenium(VII) (MTO) is
now available in high yields by utilizing easily accessible
nontoxic starting materials. The new synthetic pathway al-
lows an inexpensive, large-scale production of MTO, paving
the way for industrial applications. A variety of starting mate-
products formed are compared under different reaction con-
ditions. It was seen that silver perrhenate in combination
with methylzinc acetate, which was derived from trimeth-
ylaluminum and zinc acetate, are the best starting materials
for a high-yielding large-scale synthesis of MTO.
rials is compared with respect to their applicability, availabil- (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
ity and ease of handling. The reaction times and the by-
Germany, 2008)
MTO is a highly active catalyst for olefin metathesis as well
as for the olefination of aldehydes and has even found entry
into the field of material science.[11–13]
Introduction
High oxidation state organometallic oxides have been es-
tablished as important catalysts in many organic transfor-
mations.[1] This is especially true for catalytic oxidation re-
actions.[2] One of the best studied pre-catalysts in this field
is methyltrioxorhenium (MTO).[3] It was first mentioned in
the literature Ϫ almost 30 years ago Ϫ by Beattie and Jones
in 1979 who isolated tiny amounts of MTO from the decay
of trimethyldioxorhenium(VII) exposed to air.[4] Because
this method of access was time consuming (weeks) and re-
stricted to low scale (milligrams), MTO was originally re-
garded as another mere lab curiosity. This situation re-
mained unchanged until 1988, when Herrmann et al. found
a much better synthetic procedure for the preparation of
MTO. The alkylation of dirhenium heptoxide (Re2O7) with
the nonreducing alkylating agent tetramethyltin gave MTO
(1) in almost quantitative yield on scales of up to ca. 10 g
(Scheme 1).[5] This discovery was the starting point for the
exploration of the catalytic potential of MTO, which has
shown to be considerable. MTO is particularly stable and
therefore easy to handle, and it has been proven to be an
extremely versatile and powerful catalyst.[3] MTO can be
used in the epoxidation of olefins and in the oxidation of
aromatics, ethers, alcohols or amines.[3,6–10] Moreover,
Scheme 1. The first literature reported multigram-scale synthesis of
methyltrioxorhenium.[5]
The multitude of applications led to a steady increase in
the interest in MTO, and it was soon revealed that the syn-
thetic pathway established in 1988 was not satisfactory, as
half the employed rhenium was converted into a catalyti-
cally inactive compound Ϫ trimethylstannyl perrhenate (2).
The reason for the formation of this byproduct was as-
cribed to the heterolytic cleavage of the Re–O–Re moiety in
dirhenium heptoxide.[14]
It is known that dirhenium heptoxide, being the anhy-
dride of perrhenic acid, reacts with carboxylic anhydrides
to form mixed anhydrides of type 3 (Scheme 2). In this reac-
tion, the heterolytic cleavage of dirhenium heptoxide into a
“perrhenyl perrhenate” is avoided. The preparation of com-
plexes of type 3 is quite generally applicable and the corre-
sponding carboxyl perrhenates are usually obtained in very
high yields.[15] The subsequent treatment of carbonyl per-
rhenates with methyl tin reagents gives MTO in moderate
to excellent yields,[16] and the outcome of the reaction is
strongly dependent on the nature of the employed carbox-
[a] Lehrstuhl für Anorganische Chemie und Molekulare Katalyse,
Fakultät für Chemie, Technische Universität München
Lichtenbergstr. 4, 85747 Garching, Germany
Fax: +49-89-289-13473
E-mail: fritz.kuehn@ch.tum.de
[b] R & D Catalytic Technologies, Süd-Chemie AG
Waldheimer Str. 13, 83052 Bruckmühl, Germany
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J. K. M. Mitterpleininger, N. Szesni, S. Sturm, R. W. Fischer, F. E. Kühn
FULL PAPER
ylic acid derivative. The carboxylate ligands in such com-
plexes are either mono- or bidentate. Electron-rich alkyl
substituents in 3 lead to an η2-coordination geometry,
whereas the electron-withdrawing character of halogenated
substituents results in monodentate (η1) coordination.[15]
Concomitantly with the change of the coordination mode
a significant change in the reactivity can be observed. When
acetyl perrhenate is allowed to react with tetramethyltin,
MTO is obtained in only moderate yields of about 50%.
In contrast, the reactions of trifluoroacetyl perrhenate with
methyltin reagents give MTO in yields of up to 90%.[15,16]
Following this methodology, even the considerably less-re-
Results and Discussion
Preparation of Methylzinc Acetate
The methylating agent methylzinc acetate, which is used
for the transformation of the carboxyl perrhenates into
MTO, can be prepared by three different routes: (i) The
reaction of dimethylzinc with acetic acid[21] [Equation (1)].
(ii) The comproportionation of equimolar amounts
of dimethylzinc and zinc acetate [Equation (2)]. (iii) The re-
action of trimethylaluminum with zinc acetate [Equa-
tion (3)].
active trimethylstannyl perrhenate can be activated and Me2Zn + HOAc Ǟ MeZn(OAc) + CH4Ȇ
(1)
(2)
(3)
transformed into MTO with good yields.[15,16]
Me2Zn + Zn(OAc)2 Ǟ 2 MeZn(OAc)
2 Me3Al + 3 Zn(OAc)2 Ǟ 3 MeZn(OAc) + 2 Al(OAc)3ȇ
For the preparation of methylzinc acetate according to
Equation (1), dimethylzinc is added slowly to a precooled
suspension (–78 °C) of acetic acid in toluene. When kept at
this temperature, no reaction can be observed. Therefore,
the reaction mixture must be warmed slowly to room tem-
perature. During this period, vivid evolution of stoichiomet-
ric amounts of methane can be observed. After evolution
of the gas stops, the solvent is removed in vacuo to afford
methylzinc acetate in an excellent yield of 95%. However,
due to formation of large quantities of gas, which might
become a considerable safety issue, and because the loss of
“active” methyl groups is not economical, the reaction is
not very well suited for scale up.
The comproportionation of dimethylzinc and dehydrated
zinc acetate [Equation (2)] proceeds smoothly at room tem-
perature. After removal of the solvent, methylzinc acetate is
obtained in near quantitative yield. Nevertheless, dimeth-
ylzinc is pyrophoric and expensive, and therefore, it is desir-
able to replace dimethylzinc by more cost effective methyl
sources.
Scheme 2. Synthesis of MTO with mixed anhydrides of perrhenic
acid.[15]
In spite of further synthetic progress made since
1992,[17,18] one major drawback of all the established syn-
thetic procedures towards MTO remained: volatile, highly
toxic, carcinogenic tin reagents must be utilized. Thus, both
the synthesis and the purification of MTO require high
safety precautions. Alternative alkylating agents like dialk-
ylzinc, Grignard, organolithium or organocopper reagents
lead to poor yields of the desired product as a result of the
partial reduction of the rhenium species and the formation
of inorganic perrhenates.[19]
Recently, we reported on a new and efficient synthesis of
MTO by utilizing the stable and easy to prepare methylzinc
acetate as the alkylating agent (Scheme 3). The alkylation
of the less-reactive acetyl perrhenate proceeds cleanly with-
out any reduction of the ReVII species and gives MTO in
up to 90% isolated yield.[20]
The reaction of dehydrated zinc acetate with trimeth-
ylaluminum (which is considerably less expensive than the
above-described methylating agents) likewise delivers meth-
ylzinc acetate in high yields (up to 90%) and of very good
quality at room temperature. The reaction can be per-
formed on any scale without loss of yield. To study the reac-
tion in more detail, its pathway was followed by in situ IR
spectroscopy (Figure 1).
Upon addition of trimethylaluminum to a suspension of
zinc acetate in toluene, the ν(CO) vibrations seen at 1458
and 1543 cm–1 immediately diminish. After a short induc-
tion period, a set of two new bands is formed at 1477 and
Scheme 3. Synthesis of MTO with the use of acetyl perrhenate and
methylzinc acetate.[20]
The findings described above indicate that the choice of 1589 cm–1 (Figure 1). The data are consistent with those
the combination of the reactive rhenium intermediate and obtained from an authentic sample of methylzinc acetate.
the alkylating agent is crucial for the success of the quanti- After 3 h at room temperature the reaction reaches comple-
tative formation of MTO. In order to further optimize the tion and no further change in the intensities can be ob-
current synthetic procedure of MTO, the reactions of vari- served. Precipitated aluminum acetate cannot be observed
ous nonactivated carboxyl perrhenates with methylzinc ace- in the spectra due to the extremely poor solubility of this
tate were studied in detail and the results are presented be- compound. Therefore, byproduct formation (e.g., alumi-
low.
nates) due to reactions with MeZnOAc does not occur.
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Insights into a Nontoxic and High-Yielding Synthesis of MTO
rapid decomposition of the desired product, which is unfor-
tunately thermally labile. Because polymerization of THF
occurs after prolonged reaction times, acetonitrile proved
to be the solvent of choice for such reactions.
However, another severe problem for the large-scale syn-
thesis of MTO is the pronounced sensitivity of dirhenium
heptoxide towards water. Even trace amounts of moisture
readily react with dirhenium heptoxide to yield perrhenic
acid. Inorganic perrhenates, however, are readily available
in large quantities directly from rhenium metal, are stable
towards air and water and can be stored over long periods
of time without any signs of decomposition. The reaction
of silver perrhenate with acetic chloride also delivers acetyl
perrhenate in quantitative yield (Figure 2). The reaction is
fast and occurs with a quantitative precipitation of silver
chloride. A selected set of other synthesized carboxyl per-
rhenates is displayed in Scheme 4.
Figure 1. In situ IR spectra for the synthesis of methylzinc acetate
from the reaction of zinc acetate with trimethylaluminum.
The spectroscopic data of carboxyl perrhenates 3a–i are
in good accordance with those previously reported in the
literature.[15] The ν(CO) vibration mode at rather low ener-
gies confirms the η2-coordination geometry of all tested
perrhenates (Table 1). The ν(CO) vibration mode of the
carboxylic ligands with η1-coordination is usually found
at a considerably higher wavenumber (1792 cm–1 for
CF3COOReO3). Although, perrhenyl carboxylates are
known to be significantly moisture and temperature sensi-
tive, they are stable in solution for several hours when kept
under an inert atmosphere (IR evidence), (Figure 2). As iso-
lation of the pure perrhenyl carboxylates proved to be diffi-
cult due to their sensitivity, selected examples were isolated
as bipyridine adducts [RCOORe(bipy)O3; R = Me (4a), Et
(4b), nPr (4c), tBu (4d), Ph (4e)] and were characterized by
elemental analysis and spectroscopic methods (see Experi-
mental Section).
1
When the reaction is monitored by H NMR spectroscopy
only the starting compounds and the product can be ob-
served during the course of the reaction.
Synthesis of MTO
The synthetic procedure for the preparation of MTO is
as follows: In a first step, carboxyl perrhenate is prepared.
Following the established method, dirhenium heptoxide is
dissolved in a donor solvent like THF or acetonitrile and
allowed to react with a carboxylic anhydride. The progress
of the reaction can be monitored by in situ IR spectroscopy.
The time needed to obtain complete conversion ranges be-
tween seconds and hours, according to the electronic and
steric requirements of the carboxylic anhydrides. In general,
aliphatic carboxylic anhydrides react smoothly to give
For the conversion into MTO, the perrhenyl carboxylates
mixed anhydrides in quantitative yields. In contrast, the re- are treated with one equivalent of solid methylzinc acetate,
action of Re2O7 with 2-naphthalene carboxylic anhydride added in small portions at ambient temperature. Upon ad-
remains incomplete even after 24 h at ambient temperature. dition of the alkylating agent the clear reaction solution
The reaction at elevated temperatures (40 °C) leads to the immediately darkens from red to violet and Zn(OAc)2 is
Figure 2. Series of IR spectra obtained from the reaction of silver perrhenate with acetic chloride (left) and Re2O7 with acetic anhydride
(right), indicating the formation of acetyl perrhenate. Both spectra show the product at 940 cm–1.
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J. K. M. Mitterpleininger, N. Szesni, S. Sturm, R. W. Fischer, F. E. Kühn
FULL PAPER
Figure 3. Series of IR spectra obtained from the reaction of acetyl
perrhenate with methylzinc acetate (successive addition of small
portions of methylzinc acetate is indicated by black arrows). MTO
shows a pronounced vibration at 961 cm–1.
and obtained from the different perrhenates cannot be ex-
plained in all detail yet, but it is assumed that the steric
hindrance as well as the varying solubility of the resulting
zinc salts (precipitation of the byproduct as one of the driv-
ing forces of the reaction) play a role. However, for econ-
omic reasons, acetic chloride or anhydride are clearly pre-
ferred. It is noteworthy that the yields obtained from silver
Scheme 4. Selected set of perrhenyl carboxylates 3a–i.
Table 1. ν(CO) Vibration of perrhenyl carboxylates 3a–i in acetoni-
trile at room temperature.
Compound
νasymm.(CO)
νasymm.(CO)
perrhenate as starting materials are always higher (about 2–
5%) than those obtained with dirhenium heptoxide as a
rhenium source.
[cm–1]
[cm–1]
CH3(C=O)OReO3 (3a)
C2H5(C=O)OReO3 (3b)
C3H7(C=O)OReO3 (3c)
C4H9(C=O)OReO3 (3d)
(CH3)2CH(C=O)OReO3 (3e)
(CH3)C(C=O)OReO3 (3f)
C6H5(C=O)OReO3 (3g)
C10H7(C=O)OReO3 (3h)
o-C6H4[(C=O)OReO3]2 (3i)
1493
1490
1487
1487
1495
1499
1509
1512
1501
1448
1440
1435
1435
1452
1456
1487
1489
1456
Table 2. Synthesis of MTO from carboxyl perrhenates 3a–g, 3i,
Re2O7 (5), ClReO3 (6) and (CH3)3SiOReO3 (7) with methylzinc ace-
tate as alkylating agent.
Reactive rhenium(VII) precursor
Isolated yield [%]
CH3(C=O)OReO3 (3a)
C2H5(C=O)OReO3 (3b)
C3H7(C=O)OReO3 (3c)
C4H9(C=O)OReO3 (3d)
90
66
76
69
precipitated. Again, the progress of the reaction is followed
by in situ-IR spectroscopy. As can be seen from the spectra, (CH3)2CH(C=O)OReO3 (3e)
92
(CH3)C(C=O)OReO3 (3f)
75
73
acetyl perrhenate is smoothly converted into MTO. Only
C6H5(C=O)OReO3 (3g)
trace amounts of zinc perrhenate and ReO3 are formed dur-
o-C6H4[(C=O)OReO3]2 (3i)
73
ing the reaction as byproducts. The waterfall plot obtained
Re2O7 (5)
26 (52 % of theory)
from a typical reaction is displayed in Figure 3. Unfortu-
nately, kinetic data could not be obtained with this method,
as the conversion to MTO happens virtually immediately
with the addition of the methylating agent.
ClReO3 (6)
55
48
(CH3)3SiOReO3 (7)
For purification, the resulting suspension can be filtered
The formation of the bis[dimethyl(µ-oxo)oxorhenium-
from the precipitated Zn(OAc)2. After removal of the sol- (VI)] and (µ-oxo)bis[trimethyloxorhenium(VI)] byproducts
vent, pure MTO can easily be obtained by recrystallization due to the partial reduction and higher alkylation of the
or sublimation. The employed rhenium precursors gave rhenium entity has already been described in the litera-
generally good yields ranging from 66–92% and are, by far, ture.[11] This side reaction was reported as dominant for
superior to dirhenium heptoxide (5), chloro trioxorhen- stronger alkylating agents like aluminum reagents or MeTi-
ium[22] (6) or trimethylsilyl perrhenate[23] (7) as more reac- (OiPr)3 (8q). In fact, bis[dimethyl(µ-oxo)oxorhenium(VI)]
tive rhenium sources (Table 2). The best results were ob- can be prepared in high yields by reaction of dirhenium
tained with acetic and isobutyric acid derivatives. The dif- heptoxide with MeTi(OiPr)3 (8q). In order to investigate the
ferences in the reactivities and product yields observed for selectivity of the alkylating agent methylzinc acetate, the
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Insights into a Nontoxic and High-Yielding Synthesis of MTO
Table 3. Product distribution for the synthesis of MTO from carboxyl perrhenates 3a and 3e–g with methylzinc acetate as alkylating
agent.
Reactive rhenium(VII)
precursor
MTO
[%]
Bis[dimethyl(µ-oxo)oxorhenium(VI)]
(µ-Oxo)bis[trimethyloxorhenium(VI)]
[%]
[%]
CH3(C=O)OReO3 (3a)[a]
CH3(C=O)OReO3 (3a)[b]
(CH3)2CH(C=O)OReO3 (3e)[a]
(CH3)C(C=O)OReO3 (3f)[a]
C6H5(C=O)OReO3 (3g)[a]
90
84
92
75
73
Ͻ1
5
2
4
4
0
2
0
0
0
[a] Obtained by the reaction of silver perrhenate with acetyl chloride. [b] Obtained by the reaction of dirhenium heptoxide with acetic
anhydride.
as an internal standard. In situ IR spectroscopy was performed
with a Bruker-Optics Matrix-M “IR-Cube” FT-NIR spectrometer
couple with a diamond ATR-probe IN350.
product distribution was determined by quantitative GC
and H NMR spectroscopy. The results are summarized in
Table 3.
1
Preparation of MeZnOAc: Finely ground zinc acetate dihydrate
(11.1 g, 60.06 mmol) was dried at 70 °C for 3 h. The loss of water
was determined gravimetrically. The obtained anhydrous zinc ace-
tate was then suspended in dry toluene (50 mL) and a stoichiomet-
Conclusions
After many years of research, an industrially applicable ric amount of Al(CH3)3 was added at –10 °C. After stirring for 5 h,
the resulting reaction mixture was separated from the precipitated
Al(OAc)3, and the solvent of the filtrate was evaporated in vacuo.
MeZnOAc was obtained as a colourless powder (7.5 g, 90%). 1H
NMR (400 MHz, CDCl3, 25 °C): δ = 2.14 (s, 3 H, C-CH3), –0.68
(Zn-CH3) ppm. 13C NMR (400 MHz, CDCl3, 25 °C): δ = 180.4
(C=O), 25.0 (C-CH3), –15.2 (Zn-CH3) ppm.
preparation of MTO has finally been found. The combina-
tion of the efficient alkylating agent methylzinc acetate with
carboxyl perrhenates as reactive rhenium intermediates is
highly efficient and elegantly eliminates the two major
drawbacks for the large-scale preparation of MTO, namely,
the sensitivity of dirhenium heptoxide and the expensive
and highly toxic methyltin reagents. Furthermore, easily ac-
cessible rhenium sources can now be relied upon, such as
silver perrhenates, which can be synthesized in a simple way
from rhenium metal or as a product of catalyst recycling.
Perrhenates are Ϫ in contrast to rhenium heptoxide Ϫ
stable towards moisture. The sensitivity of rhenium hep-
taoxide to hydrolysis does not pose a significant problem at
the laboratory scale, but it is of critical importance in an
industrial context. The acyl perrhenates, which are at least
in part sensitive to elevated temperatures, need not be iso-
lated. In situ they are Ϫ as reaction intermediates Ϫ easy
to handle.
Preparation of Perrhenyl Carboxylates from Re2O7: Dirhenium hep-
toxide (Re2O7; 1 g, 2.06 mmol) was suspended in acetonitrile
(10 mL). Then, one equivalent of the corresponding carboxylic an-
hydride was slowly added. The end of the reaction was indicated
by the complete dissolution of dirhenium heptoxide.
Preparation of Perrhenyl Carboxylates from AgReO4: AgReO4 (1 g,
2.79 mmol) was dissolved in acetonitrile (10 mL) and on equivalent
of the corresponding carboxylic chloride was added. AgCl precipi-
tated immediately. After 10 min of stirring, the solution was fil-
tered.
NMR Spectroscopic Data for Selected Perrhenyl Carboxylates
1
MeCOOReO3: H NMR (400 MHz, CD3CN, 25 °C): δ = 2.16 [s,
3 H, C(=O)-CH3] ppm.
In this context, IR spectroscopic methods proved to be
a very useful tool for monitoring the reactions quickly and
directly, whereas “traditional” methods, which require the
preparation of separate samples, are in comparison quite
cumbersome due to the considerable sensitivity of some of
the species under examination.
1
EtCOOReO3: H NMR (400 MHz, CD3CN, 25 °C): δ = 2.52 [q, 2
H, C(=O)-CH2-], 1.16 (t, 3 H, -CH3) ppm.
nPrCOOReO3: 1H NMR (400 MHz, CD3CN, 25 °C): δ = 2.47 [m,
2 H, C(=O)-CH2-], 1.67 [m, 2 H, C(=O)-CH2-CH2-], 0.97 (t, 3 H,
-CH3) ppm.
1
tBuCOOReO3: H NMR (400 MHz, CD3CN, 25 °C): δ = 2.66 (s,
9 H, CH3) ppm.
1
Experimental Section
PhCOOReO3: H NMR (400 MHz, CD3CN, 25 °C): δ = 8.12 (d,
2 H, o-H), 7.77 (t, 1 H, p-H), 7.58 (dd, 2 H, m-H) ppm.
General: All experiments were performed under an atmosphere of
argon or nitrogen purified over molecular sieves and BTS catalyst
in flame-dried standard Schlenk-type glassware. Dry solvents were
obtained from an MBraun SPS system. Chemicals were purchased
from Merck, Acros Organics and Aldrich, and in case of liquids,
distilled under an inert gas prior to use. NMR spectra were re-
corded with a JEOL JMX-GX 400 (400 MHz). Chemicals shifts
are reported in ppm, referenced to the residual solvent signal. IR
spectra were recorded with a JASCO FT/IR-460 spectrometer. For
ex situ liquid IR, KBr cells were used. Solids were prepared as
Typical Procedure for the Synthesis of MTO from Acyl Perrhenates:
To a previously stirred solution of the appropriate acyl perrhenate
in acetonitrile, solid MeZnOAc (1 equiv.) was added in small por-
tions. The solution immediately turned turbid and its colour
changed from light yellow to dark red. After complete addition of
the methylating agent, stirring was continued for a further 30 min.
The reaction mixture was then filtered, and the solvent was re-
moved in vacuo from the filtrate. The remaining solid was sublimed
(10–1 mbar, 40 °C). MTO was obtained as a colourless crystalline
nujol mulls. GC analyses were performed with a Varian CP-3800 solid. The analytical data correspond with those reported in the
equipped with a VF-5ms column and an FID and with mesitylene
literature.[2]
Eur. J. Inorg. Chem. 2008, 3929–3934
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FULL PAPER
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pared perrhenyl carboxylate (1 mmol) was treated with 2,2Ј-bipyr-
idine (1 equiv.) with vigorous stirring. The product was immedi-
ately formed as a voluminous precipitate. After filtration, the re-
maining solid was washed with benzene (2ϫ) and dried in vacuo.
NMR spectroscopic data cannot be provided due to the poor solu-
bility of the bipyridine adducts.
[4]
[5]
MeCOOReO3·bipy (4a): Yield: 0.35 g (0.78 mmol; 78%). IR (nu-
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[7]
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1598 (vs), 1560 (m), 1551 (w), 1497 (m), 1473 (m), 1449 (s), 1272
(w), 1176 (m), 1110 (m), 1032 (m), 1024 (w), 987 (w), 961 (w), 918
(vs), 660 (w), 544 (w), 420 (m) cm–1. C12H11N2O5Re (449.43): calcd.
C 32.07, H 2.47, N 6.23; found C 31.98, H 2.54, N 6.51.
[8]
[9]
EtCOOReO3·bipy (4b): Yield: 0.37 g (0.79 mmol; 79%). IR (nujol):
ν = 3110 (w), 3065 (w), 2724 (w), 1651 (s), 1601 (m), 1496 (m),
˜
[10]
[11]
[12]
[13]
1317 (m), 1286 (s), 1233 (m), 1172 (w), 1152 (w), 1118 (w), 1103
(w), 1079 (w), 1065 (m), 1035 (w), 1024 (w), 999 (w), 943 (s), 922
(s), 908 (vs), 893 (s), 804 (w), 773 (s), 731 (m), 658 (w) cm–1.
C13H13N2O5Re (463.46): calcd. C 33.69, H 2.83, N 6.04; found C
33.57, H 2.64, N 5.91.
W. A. Herrmann, F. E. Kühn, Acc. Chem. Res. 1997, 30, 169–
180.
R. Miller, E. W. Scheidt, G. Eickerling, C. Helbig, F. Mayr, R.
Herrmann, W. Scherer, H. A. K. v. Nidda, V. Eyert, P. Schwab,
Phys. Rev. B 2006, 73, 165113-1–116113-14.
W. A. Herrmann, P. W. Roesky, F. E. Kühn, W. Scherer, M.
Kleine, Angew. Chem. 1993, 105, 1768–1770; Angew. Chem. Int.
Ed. Engl. 1993, 32, 1714–1716.
W. A. Herrmann, W. R. Thiel, F. E. Kühn, R. W. Fischer, M.
Kleine, E. Herdtweck, W. Scherer, J. Mink, Inorg. Chem. 1993,
32, 5188–5194.
W. A. Herrmann, F. E. Kühn, R. W. Fischer, W. R. Thiel, C. C.
Romão, Inorg. Chem. 1992, 31, 4431–4432.
W. A. Herrmann, R. M. Kratzer, R. W. Fischer, Angew. Chem.
Int. Ed. Engl. 1997, 36, 2652–2654.
W. A. Herrmann, R. M. Kratzer, Inorg. Synthesis 2002, 33,
110–112.
nPrCOOReO3·bipy (4c): Yield: 0.39 g (0.81 mmol; 81%). IR (nu-
jol): ν = 1649 (m), 1600 (m), 1315 (m), 1260 (m), 1213 (w), 1171
˜
(w), 1101 (m), 1034 (m), 944 (s), 921 (s), 890 (s), 798 (m), 773 (m),
721 (m) cm–1. C14H15N2O5Re (477.49): calcd. C 35.22, H 3.17, N
5.87; found C 35.22, H 2.94, N 5.82.
[14]
[15]
tBuCOOReO3·bipy (4d): Yield: 0.38 g (0.78 mmol; 78%). IR (nu-
jol): ν = 3112 (w), 1646 (m), 1601 (m), 1315 (w), 1302 (m), 1196
˜
(m), 1169 (w), 1155 (w), 1102 (m), 1061 (m), 1033 (m), 942 (s), 922
(s), 893 (s), 776 (m), 732 (m) cm–1. C15H17N2O5Re (491.51): calcd.
C 36.65, H 3.49, N 5.70; found C 36.87, H 3.33, N 5.51.
[16]
[17]
[18]
[19]
[20]
PhCOOReO3·bipy (4e): Yield: 0.39 g (0.77 mmol; 77%). IR (nujol):
ν = 3113 (s), 2359 (m), 1660 (vs), 1601 (s), 1580 (m), 1497 (m),
˜
1445 (s), 1311 (vs), 1295 (s), 1171 (w), 1158 (w), 1124 (m), 1106
(m), 1079 (w), 1067 (w), 1035 (w), 1023 (m), 943 (s), 914 (s), 903
(s), 765 (s), 717 (s), 689 (w), 669 (w) cm–1. C17H13N2O5Re (511.50):
calcd. C 39.92, H 2.56, N 5.48; found C 39.56, H 2.23, N 5.40.
A. M. J. Rost, W. A. Herrmann, F. E. Kühn, Tetrahedron Lett.
2007, 48, 1775–1779.
W. A. Herrmann, A. M. J. Rost, J. K. M. Mitterpleininger, N.
Szesni, S. Sturm, R. W. Fischer, F. E. Kühn, Angew. Chem.
2007, 119, 7440–7442; W. A. Herrmann, A. M. J. Rost, J. K. M.
Mitterpleininger, N. Szesni, S. Sturm, R. W. Fischer, F. E.
Kühn, Angew. Chem. Int. Ed. 2007, 46, 7301–7303.
G. E. Coates, D. Ridley, J. Chem. Soc. 1965, 1870–1877.
W. A. Herrmann, F. E. Kühn, C. C. Romão, M. Kleine, J.
Mink, Chem. Ber. 1994, 127, 47–54.
Acknowledgments
[21]
[22]
The authors are grateful to the Bavarian Research Foundation for
financial support.
[23]
M. Schmidt, H. Schmidbaur, Chem. Ber. 1959, 92, 2667–2670.
[1] F. E. Kühn, A. M. Santos, M. Abrantes, Chem. Rev. 2006, 106,
2455–2457.
Received: May 25, 2008
Published Online: July 24, 2008
3934
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© 2008 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Eur. J. Inorg. Chem. 2008, 3929–3934