Syntheses and characterisation of methyltrioxorhenium adducts of low-valence organometallic Lewis bases

Article abstract of DOI:10.1039/b004640j

Methyltrioxorhenium(vii) forms air and moisture stable trigonal-bipyramidal adducts with several organometallic Lewis bases having a pyridine nitrogen atom as the donor moiety. These complexes have been isolated and fully characterised. A single-crystal structure of one of the products has been determined. Whilst the Re-N interaction is weaker than in some simple organic Lewis base adducts of Re(CH3)O3, e.g. with pyridine or 4-/e/7-butylpyridine, the more pronounced stability of the complexes described in this work is probably due to steric crowding and the moderate donor capability of the organometallic ligands. The donor capability of the ligands applied increases in the order Re(CO)3Br(4,4'-bpy)2 < l,l'-bis(4-pyridylethynyl)ferrocene < ferrocenyl-4-pyridylacetylene. The Royal Society of Chemistry 2000.

Full text of DOI:10.1039/b004640j

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Syntheses and characterisation of methyltrioxorhenium adducts of
low-valence organometallic Lewis bases
Ana M. Santos, Fritz E. Kühn,* Wen-Mei Xue and Eberhardt Herdtweck
Anorganisch-Chemisches Institut der Technischen Universität München, Lichtenbergstrasse 4,
D-85747 Garching b. München, Germany. Fax: 0049(0)89 289 13473;
E-mail: fritz.kuehn@ch.tum.de
Received 12th June 2000, Accepted 30th August 2000
First published as an Advance Article on the web 28th September 2000
Methyltrioxorhenium() forms air and moisture stable trigonal-bipyramidal adducts with several organometallic
Lewis bases having a pyridine nitrogen atom as the donor moiety. These complexes have been isolated and fully
characterised. A single-crystal structure of one of the products has been determined. Whilst the Re–N interaction
is weaker than in some simple organic Lewis base adducts of Re(CH3)O3, e.g. with pyridine or 4-tert-butylpyridine,
the more pronounced stability of the complexes described in this work is probably due to steric crowding and the
moderate donor capability of the organometallic ligands. The donor capability of the ligands applied increases in
the order Re(CO)3Br(4,4Ј-bpy)2 < 1,1Ј-bis(4-pyridylethynyl)ferrocene < ferrocenyl-4-pyridylacetylene.
Introduction
Methyltrioxorhenium() 1 has been found to be a very useful
catalyst for a broad variety of processes during the last decade.1
Among the best examined of these is the epoxidation of
olefins.2 The most important drawback was the concomitant
formation of diols instead of the desired epoxides, most notably
in the case of more sensitive substrates.3 It has been found that
the use of organic Lewis base adducts of complex 1 signifi-
cantly decreases the formation of diols as a consequence of the
reduced Lewis acidity of the catalytic system. Especially pyrid-
ine derivatives and pyrazole are very useful Lewis bases for this
purpose.4 Only recently Lewis base adducts of compound 1
were characterised properly. Despite the sensitivity of com-
plexes of that type these attempts have been quite successful for
organic Lewis bases.5 Organometallic Lewis base adducts of 1,
still being very rare and in principle interesting as charge trans-
fer complexes, turned out to be even more sensitive in several
cases and therefore no structurally characterised example is
known to date.6 All known organometallic Lewis base adducts
of 1 are unstable towards oxidation of the organometallic
ligand. In some cases an intramolecular redox reaction can be
observed. Since we have recently worked on stable, one dimen-
sional organometallic chain molecules utilising the Lewis bases
ferrocenyl-4-pyridylacetylene 2, 1,1Ј-bis(4-pyridylethynyl)ferro-
cene 3 and Re(CO)3Br(4,4Ј-bpy)2 4 as interconnecting units of
metal–metal bonded molecules, we applied the same organo-
(1)
of decomposition when exposed to air for several hours. It is
metallic ligands for reactions with compound 1.
soluble in polar organic solvents, e.g. THF and acetonitrile.
In this work we shall present the first stable and fully charac-
terised organometallic Lewis base adducts of 1. These com-
pounds will be compared to the known reaction products of 1
with organic Lewis bases mentioned above.
Ϫ1
᎐
The IR active C᎐C stretching vibration occurs at 2208 cm
,
᎐
with a deviation within the measurement error range (4 cmϪ1
)
in comparison to that of the “free” ligand (2210 cmϪ1). The
pyridyl ring stretching vibration appears at 1603 cmϪ1, the
corresponding band of 2 at 1594 cmϪ1. The Re᎐O stretching
᎐
vibrations are shifted from 958 (asym.) and 1005 cmϪ1 (sym.) in
the case of 1 to 920 and 960 cmϪ1 in the case of complex 5,
reflecting the donor capacity of ligand 2. From these IR
Results and discussion
Preparation and characterisation
The addition of one equivalent of compound 2 to 1 in diethyl
ether or CH2Cl2 at room temperature (eqn. 1) immediately leads
to the formation of complex 5, which can be isolated from the
orange suspension as a light orange solid in good yield. This
compound is stable at room temperature and shows no signs
vibrational frequencies the force constant of the Re᎐O
᎐
vibration can be calculated according to ref. 7 to be 7.55
mdyn ÅϪ1. This value indicates a weakening of the Re–O bonds
in comparison to that of complex 1 ( f(Re᎐O) = 8.58 mdyn ÅϪ1
)
᎐
(Table 1). The additional electron density donated from the
3570
J. Chem. Soc., Dalton Trans., 2000, 3570–3574
DOI: 10.1039/b004640j
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Table 1 Selected IR (in KBr), 1H and 17O NMR (in CD2Cl2) data, and
calculated force constants f(ReO) for 5–7 and related complexes
Table 2 Crystallographic data comparison for complex 5, 1 and two
known organic pyridine adducts of 1
ν(Re᎐O)/
f(ReO)/
Compound
Σ O–Re᎐O/Њ
Re–N/pm
Re–C/pm
᎐
᎐
Compound
cmϪ1
δ(1H) δ(17O) mdyn ÅϪ1
5
355.2(3)
241.7(6)
240.7(5)
250.4(5)
208.9(8)
208.3(7)
207.9(7)
206.3(2)
1
5
6
7
958, 1005
920, 960
925, 964
930, 964
2.67
2.01
2.11
2.27
1.80
829
865
860
855
868
863
8.58
7.55
7.63
7.68
7.38
7.53
Re(CH3)O3–4-t-butylpyridine 355.9(2)
[Re(CH3)O3]2bpy
1
353.2(3)
338.8(1)
Re(CH3)O3–4-t-butylpyridine 921, 929
[Re(CH3)O3]2bpy 928, 940
Fig. 1 PLATON12b plot of the solid state structure of complex 5.
Thermal ellipsoids are at the 50% probability level. Hydrogens omitted
for clarity.
protons [δ(Hα) 8.21, δ(Hβ) 7.25] also do not show a significant
difference compared to the free ligand 3 [δ(Hα) 8.25, δ(Hβ) 7.19].
Concerning the 17O NMR shift a significant difference between
the chemical shift of compound 1 (δ 17O 829) and 6 (δ 17O 860)
is evident, reflecting the fact that Lewis base adducts show a
strong low field shift due to the pronounced σ donor character
of the co-ordinating nitrogen.9
The reaction of one equivalent of ligand 410 with two of 1 in
CH2Cl2 at room temperature affords promptly complex 7 as a
yellow solid soluble in common polar organic solvents, e.g.
THF. Compound 7 does not decompose when exposed to
air for some hours. In the IR spectrum the bands corresponding
to the CO stretching vibrations, 1903 and 1887 cmϪ1, show no
significant difference from the non-co-ordinated 4, indicating
that the effect of the co-ordination of 1 to the 4,4Ј-bipyridine
does not influence significantly the back donation to the CO
ligands by the ReI. This would be expected if the pyridine
rings are twisted and therefore in different planes. Although
in this case we have not obtained single crystal X-ray data for
the complex, this is known to happen in similar rhenium()
ligand to the ReVII significantly weakens the Re–O bonds. It has
been argued that the formally 14e system 1 should be regarded
as an 18e system with three Re–O bonds of order 22/3.8 If
additional electron density is introduced in the system, for
example by a Lewis base ligand, the Re–O bond order is
reduced and less electron density is withdrawn from the
terminal oxygen ligands. The value obtained for the force con-
stant is also in accordance with the 17O NMR shift of δ(17O) 865
which is observed at significantly lower field than for free 17O-
labelled 1 (δ17O), 829.9a,b The pyridyl protons of 5 [δ(Hα) 8.24,
δ(Hβ) 7.42] differ in their chemical shift also notably from those
free 2 [δ(Hα) 8.53, δ(Hβ) 7.32]. The ferrocene proton resonances
are comparable to those of the “free” ligand, because they are
far apart from the ReVII. The proton NMR signal correspond-
ing to the methyl group of 5 appears at δ 2.01 which is shifted
upfield with regard to the un-coordinated compound 1 (δ 2.67)
as a result of the electron density donated by the N-donor
complexes.11 The values ν(Re᎐O)
930 and ν(Re᎐O)
964
᎐
᎐
asym
sym
cmϪ1 show a similar deviation from those of free 1 as found
1
for complex 5 (see Table 1). The H NMR chemical shift of
the CH3 group of 7 is shifted to higher field δ(1H) 2.27 in
comparison to complex 1, δ(1H) 2.67.
Table 2 gives a comparison of the crystallographic data for
the complexes examined here and the two known organic pyri-
dine adducts of 1.5 It can be seen that all of the Lewis base
ligands used in complexes 5–7 have a weaker influence on the
CH3ReO3 moiety than the organic ligand 4-tert-butylpyridine.
The complex of 1 with 4-tert-butylpyridine shows the weakest
ligand to the Lewis acidic ReVII
.
The addition of one equivalent of ligand 3 to two of 1 affords
the high yield formation of complex 6 in CH2Cl2 at room
temperature as a dark orange solid, soluble in polar organic
solvents (CH3CN, CH2Cl2, THF) and stable at room temper-
ature. Complex 6 does not show signs of decomposition when
Re᎐O force constant, the most pronounced low field shift in 17
O
᎐
NMR and the strongest high field shift in 1H NMR. The values
obtained for the complexes 5–7 are closer to the values of the
not ligated 1, but still well within the range for Lewis base
adducts of 1. The results obtained are quite similar to that
of (CH3ReO3)2–4,4Ј-bipyridine.5 In this complex the donor
capability of the organic ligand is relatively weak due to its
co-ordination to two electron withdrawing molecules of com-
pound 1. It is interesting that the organometallic ligands
utilised here to coordinate to 1 do not have a stronger electron
donor capability than simple organic ligands, especially since
exposed to air for several hours. Its solid state IR spectrum
᎐
exhibits the characteristic C᎐C stretching vibration at 2213
᎐
cmϪ1. In relation to free 3 [ν(C᎐C) 2208 cmϪ1] the deviation
᎐
᎐
is not significant. The strong band at 1592 cmϪ1 of free 3
attributed to the pyridyl ring is shifted to 1603 cmϪ1 after co-
ordination. The IR bands corresponding to the Re᎐O stretch-
᎐
ing vibrations appear at 925 (asym.) and 964 cmϪ1 (sym.), the
force constant being in this case f = 7.63 mdyn ÅϪ1, in good
accordance with values obtained for other bis(CH3ReO3) com-
the C H C᎐CC H N unit is not tilted. The two rings are
᎐
᎐
5
4
5
4
coplanar as can be seen from the X-ray crystal structure of
5 (Fig. 1). The structural data of this complex are very similar
to those of the 4-tert-butylpyridine adduct of 1; within the
given error range the Re–C and the Re–N bond distances as well
1
plexes.5 The H NMR chemical shifts of the ferrocene protons
of complex 6 are similar to those of free 3. The pyridyl
J. Chem. Soc., Dalton Trans., 2000, 3570–3574
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as the sum of the O–Re᎐O angles can be regarded as identical.
Complex 6 decomposes in four steps, the onset temperature
᎐
This again shows the significantly larger sensitivity of IR and
NMR spectroscopy to small, but important interaction dif-
ferences compared to X-ray crystallography. We therefore
regarded the failed attempt to crystallise compounds 6 and 7 as
of little consequence since spectroscopic methods give a closer
insight on the donor capabilities of the ligands applied. The
Re–N interaction is strongest in 5 and weakest in 7 according to
both NMR(17O, 1H) and IR spectroscopy (see Table 1). Accord-
of the first decomposition step being 50 ЊC above the sublim-
ation onset temperature for 1, which denotes increased stability
of 6.
Complex 7 starts decomposing at 134 ЊC; this value is situ-
ated between the decomposition onset temperatures of 1 and 4
(222 ЊC).17 The decomposition follows in 6 steps of which the
first can be regarded as loss of one molecule of 1 corresponding
to ca. 24% weight loss. At 730 ЊC only 17% remains as residual
weight.
ingly, complex 7 has the largest Re᎐O force constant, the most
᎐
high field shifted Re–CH3 1H NMR signal and the most low
field shifted Re᎐O 17O NMR signal. Additionally, ligand 3 is a
᎐
Electronic absorption spectroscopy and cyclic voltammetry
slightly stronger donor than 4 according to Table 1. However,
since both complexes 6 and 7 show co-ordination to two elec-
tron withdrawing CH3ReO3 units the ligands are weaker donors
than 2, interacting with only one molecule of complex 1. Form-
ing stable Lewis base adducts of 1 seems to be a difficult task.
Strong donor ligands shift too much electron density to the
ReVII causing disruption of the Re–C bond (usually recognised
by the formation of dark residues of ReO3), whereas too weakly
co-ordinating ligands can be exchanged quite easily by the
moisture of the air (usually recognised by the formation of
colourless residues of “HOReO3”(perrhenic acid)).4a,6,9,13 The
complexes described in this work are quite obviously on the
borderline between these two decomposition pathways and
therefore comparatively stable.
It should be emphasised in this context that the relatively
weak interaction between the organometallic Lewis base
ligands and the ReVII is very likely due to the large distance
between the ReVII and the FeII or ReI and not to the lack of
similar orbitals at the Re and N atoms, enabling charge transfer.
The possibility of the formation of charge transfer complexes
of this type has been stated in a theoretical work.14
The adducts 5–7 show their characteristic absorptions at
similar wavelengths to those of their Lewis base precursors.
Not only the absorption energies but also the absorption
coefficients of the adducts are not significantly different (see
Table 3).
Mixed-valence compounds, which contain a metal in low
oxidation state and another metal in a high oxidation state, may
be intriguing in their electronic communications between metal
centres. A unique property of these species is the presence
of a metal-to-metal charge-transfer (MMЈCT) band in their
electronic spectra which is absent from the spectra of the pure
starting materials. However, for the binuclear and trinuclear
compounds investigated here no MMЈCT bands are identified
from their electronic spectra even on scanning a concentrated
solution of ca. 5 × 10Ϫ3 M in CH2Cl2 over 1100 nm. It seems
that no significant intramolecular electronic communication
occurs between the metal centres.
The cyclic voltammograms of the adducts were measured
and the data are summarised in Table 4. According to the elec-
tronic spectra and cyclic voltammograms, the co-ordination of
the organometallic Lewis bases utilised in this investigation to
compound 1 does not significantly change the electronic struc-
Thermogravimetry
tures from those of the parent molecular fragments; the high-
18
valence metal (Re7ϩ
)
and low-valence metal (Fe2ϩ, Reϩ) are
Complexes 5–7 and the precursors for which no literature data
were available were examined by thermogravimetry (TG).
Compound 1 sublimes below 100 ЊC under TG conditions,15
ligand 2 starts decomposing at 229 ЊC and ligand 3 at 480 ЊC.16
Complex 5 decomposes below 100 ЊC, in the same temper-
ature range in which 1 sublimes. Obviously Re–N rupture leads
to an immediate sublimation of the now un-coordinated 1.
obviously not communicating electronically. This is in good
accordance with the spectroscopic and crystallographic results
described above.
Conclusions
Organometallic Lewis-base adducts of compound 1 can be
prepared very easily by treating organometallic Lewis bases
with 1 at room temperature. The adducts with ligand 2 (mono-
adduct) and with 3 and 4 (bis adducts) are stable against air and
moisture for several hours. Most of the known organic Lewis
base adducts of 1 are significantly less stable. However, no
detectable charge transfer between the two involved metal
centres in different oxidation states can be observed. The
organometallic Lewis base ligands applied in this work are
weaker donors than simple organic molecules like pyridine,
4-tert-butylpyridine and 4-methylpyridine, according to our
spectroscopic data. This is probably due to the distance between
the metal centres which hampers proper electron transfer from
the electron rich to the electron deficient metal atom. Anyway,
Table 3 UV/Vis Absorption spectral data measured in CH2Cl2 at
room temperature
Compound
λmax/nm (ε/MϪ1 cmϪ1
)
1
2
3
236 (1700), 258 (980)
252 (13700), 304 (12800), 352 (2320), 449 (760)
261 (26100), 281 (20900), 311 (19600), 350 (4160),
457 (1040)
4
5
6
246 (38700), 320 (14100)
252 (15700), 304 (13800), 351 (2760), 449 (950)
262 (33700), 282 (27000), 311 (24800), 350 (5680),
456 (1510)
7
245 (43000), 320 (15000)
Table 4 Cyclic voltammetric dataa measured in deoxygenated CH2Cl2 solutions at room temperature
Compound
Re7ϩ/6ϩ
Fe3ϩ/2ϩ
Re2ϩ/ϩ
Reduction of pyridyl
1
2
3
4
5
6
7
Ϫ1.24(ir)
0.12(72)
0.20(83)
ϩ1.39(ir)
ϩ1.37(ir)
Ϫ1.66(103), Ϫ1.98(100), Ϫ2.16(ir)
Ϫ1.68(107), Ϫ1.99(103), Ϫ2.17(ir)
Ϫ1.33(ir)
Ϫ1.38(ir)
Ϫ1.27(ir)
a Potentials in volts vs. the ferrocene–ferrocenium couple; scan rate is 50 mV sϪ1; ∆Ep = Epa Ϫ Epc (mV) are included in parentheses.
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J. Chem. Soc., Dalton Trans., 2000, 3570–3574

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Table 5 Summary of data for crystal structure analysis of compound 5
the apparent lack of communication between the metal centres
together with the steric crowding of the rhenium() core might
be responsible for the enhanced stability of these adducts that
enables easy handling and characterisation. More work to
synthesize complexes with shorter bridges between the metal
centres in order to get measurable charge transfer between them
is currently underway in our laboratories.
Formula
M
C18H16FeNO3Re
536.38
Crystal system
Space group
Triclinic
P1 (no. 2)
¯
a/pm
b/pm
c/pm
α/Њ
598.09(6)
1149.5(2)
1371.9(2)
68.94(2)
77.44(2)
75.59(1)
843.9(2)
2
β/Њ
Experimental
General
γ/Њ
V/106 pm3
Z
All preparations and manipulations were carried out under
an oxygen and water free argon atmosphere using standard
Schlenk techniques. Solvents were dried by standard pro-
cedures, distilled and kept under argon over 4 Å molecular
µ/mmϪ1
8.040
λ/pm
T/K
71.073
173
No. reflections collected
No. independent/observed I > 2σI
R1, wR2 indices [I > 2σI]
(all data)
11532
sieves. Complexes 1,19 2,15,20 15,21 and 410 were prepared accord-
3
2945/2654
0.0276, 0.0653
0.0329, 0.0663
ing to the literature. All the other chemicals mentioned were
used as received from Aldrich. Elemental analyses were per-
formed in the Mikroanalytisches Labor of the TU München in
Garching. 1H, 13C and 17O NMR spectra were recorded using a
FT-JEOL GX 400 spectrometer, IR spectra on a Perkin-Elmer
FT-IR spectrometer using KBr pellets as matrix. TGA was
performed using a Perkin-Elmer TGA 7 Thermogravimetric
Analyzer. Electronic absorption spectra were run using
a Perkin-Elmer Lambda 2 UV/VIS spectrometer. Cyclic
voltammograms were recorded with a computer-controlled
Model 173 Potentiostat/Galvanostat (EG&G Princeton
Applied Research) in argon saturated and dried solutions
with tetrabutylammonium hexafluorophosphate (0.1 M) as
supporting electrolyte. The working electrode was platinum
and the reference electrode was silver wire. Potentials are
quoted vs. the ferrocene–ferrocenium couple as an internal
standard.
Re(CO)3Br[(4,4Ј-bipy)Re(CH3)O3]2 7. To a solution of Re-
(CH3)O3 (100 mg, 0.4 mmol) in 10 mL of CH2Cl2, Re(CO)3-
Br(4,4Ј-bipy)2 (132 mg, 0.2 mmol) was added. The solvent was
removed by oil pump vacuum and the resulting yellow precipi-
tate washed twice with hexane. Yield 195 mg (84%). Calc. for
C25H22BrN4O9Re3: C 25.86, H 1.91, N 4.83%. Found C 25.77,
H 1.92, N 4.80%. Selected IR (KBr): 2022s, 1903s, 1887s, 1607s,
1
930s and 814s. H NMR (CD2Cl2, RT): δ 2.27 (CH3ReO3, s,
6 H), 7.64 (Hβ of C10H8N2, m, 8 H), 8.57 (Hα of C10H8N2ReVII
,
d, 4 H) and 8.98 (Hα of C10H8N2ReI, d, 4 H). 13C NMR
(CD2Cl2, RT): δ 23.8 (CH3ReO3), 122.3 (Cβ of C10H8N2), 146.6
(Cγ of C10H8N2), 148.7 (Cα of C10H8N2) and 155.2 (CO). 17O
NMR (CD2Cl2, RT): δ 855.
Crystal structure determination
Preparations
Details are given in Table 5. Preliminary examination and data
collection on compound 5 were carried out on an imaging plate
diffraction system (IPDS; STOE&CIE) equipped with a rotating
anode (NONIUS FR591; 50 kV; 80 mA; 4.0 kW) and graphite
monochromated Mo-Kα radiation. Data were corrected for
Lorentz and polarisation effects.12a Corrections for absorption
(DIFABS)12b and decay effects (DECAY)12a were applied. The
unit cell parameters were obtained by full-matrix least-squares
refinements of 5000 reflections (CELL).12a The structure was
solved by a combination of direct methods12c and Fourier-
difference syntheses All non-hydrogen atoms of the asymmetric
unit were refined anisotropically. All hydrogen atoms were
placed in ideal geometry and allowed to ride on the parent
carbon atom. Full-matrix least-squares refinements were
carried out by minimising Σw(Fo2 Ϫ Fc2)2 with the weighting
scheme of SHELXL-97.12d,e
(4-Ferrocenylethynylpyridine)methyltrioxorhenium 5. To
a
solution of Re(CH3)O3 (200 mg, 0.8 mmol) in 10 mL of diethyl
ether, ferrocenyl-4-pyridylacetylene (222 mg, 0.8 mmol) was
added. An orange precipitate formed immediately. After stir-
ring for 30 min the diethyl ether was removed by oil pump
vacuum and the precipitate washed with n-hexane. Yield: 380
mg (90%). Calc. for C18H16FeNO3Re: C 40.31, H 3.01, N 2.61%.
Found: C 40.20, H 3.20, N 2.40%. Selected IR (KBr): 2208s
1
᎐
(C᎐C), 1603s, 1436s, 1109s, 997m, 960m, 920s and 884s. H
᎐
NMR (CD2Cl2, RT): δ 2.01 (CH3ReO3, s, 3 H), 4.26 (C5H5, s,
5 H), 4.35 (Hβ of C5H4, t, 2 H), 4.57 (Hα of C5H4, t, 2 H), 7.42
(Hβ of C5H4N, d, 2 H) and 8.24 (Hα of C5H4N, d, 2 H). 13C
NMR (CDCl3, RT): δ 27.7 (CH3ReO3), 71.6, 72.6, 74.4 (C5H5
and C5H4), 85.3 (C5H4CC), 100.2 (CCC5H4N), 128.8 (Cβ of
C5H4N), 137.5 (Cγ of C5H4N) and 149.1 (Cα of C5H4N). 17O
NMR (CD2Cl2, RT): δ 865.
CCDC reference number 186/2167.
See http://www.rsc.org/suppdata/dt/b0/b004640j/ for crystal-
lographic files in .cif format.
[ꢀ-1,1Ј-Bis(4-pyridylethynyl)ferrocene]-bis(methyltrioxo-
rhenium) 6. To a solution of Re(CH3)O3 (200 mg, 0.8 mmol) in
15 mL of CH2Cl2, 1,1Ј-bis(4-pyridylethynyl)ferrocene (155 mg,
0.4 mmol) was added. The solution became dark red; after ca.
15 min an orange solid started to precipitate. The solvent was
removed by oil pump vacuum. The resulting orange powder
was washed twice with diethyl ether. Yield 315 mg (88%). Calc.
References
1 C. C. Romão, F. E. Kühn and W. A. Herrmann, Chem. Rev., 1997,
97, 3197 and references cited therein.
2 F. E. Kühn and W. A. Herrmann, Struct. Bonding (Berlin), 2000,
97, 211 and references cited therein; G. S. Owens, J. Arias and
M. M. Abu-Omar, Catal. Today, 2000, 65, 317 and references
cited therein.
for C26H22FeN2O6Re2: C 35.22, H 2.50, N 3.16%. Found: C
᎐
35.17, H 2.48, N 3.16%. Selected IR (KBr): 2213s (C᎐C),
᎐
1603vs and 925vs. 1H NMR (CD2Cl2, RT): δ 2.11 (CH3ReO3, s,
6 H), 4.43 (Hβ of C5H4, t, 4 H), 4.61 (Hα of C5H4, t, 4 H), 7.25
(Hβ of C5H4N, d, 4 H) and 8.21 (Hα of C5H4N, d, 4 H). 13C
NMR (CD2Cl2, RT): δ 23.7 (CH3ReO3), 65.8, 72.1, 73.9 (C5H4),
84.3 (C5H4CC), 95.2 (CCC5H4N), 126.4 (Cβ of C5H4N), 134.5
(Cγ of C5H4N) and 147.7 (Cα of C5H4N); 17O NMR (CD2Cl2,
RT): δ 860.
3 W. A. Herrmann, R. W. Fischer, M. U. Rauch and W. Scherer,
J. Mol. Catal. A, 1994, 86, 243.
4 (a) W. A. Herrmann, F. E. Kühn, M. R. Mattner, G. R. J. Artus,
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