Multiple bonds between main-group elements and transition metals. 166. Oxo/imido complexes of heptavalent rhenium: Structures, reactivity, and behavior in solution

Article abstract of DOI:10.1021/om971062+

Mixed imido/oxo rhenium(VII) complexes, formal derivatives of methyltrioxorhenium(VII) (1) with (2,6-diisopropylphenyl)imido ligands of general formula CH₃ReO_3-x(NR)_x (x = 1, and 2; compounds 2 and 3, respectively), have been synthesized. Their structures and behavior in solution have been studied by dynamic ¹H and ¹⁷O NMR spectroscopy. In the solid state, compounds 2 and 3 display dimeric structures, as shown by X-ray crystallography. In solution, monomeric and dimeric forms exist in equilibria. At elevated temperatures, the monomers are dominant. In the solid state, the dimeric compounds are bridged by oxygen ligands, forming Re₂O₂ units, while in solution, nitrogen bridging is also evident. Formal replacement of all three oxo groups in 1 by (2,6-diisopropylphenyl)imido ligands leads to a compound of formula CH₃Re(NR)₃ (4). Complex 4 is monomeric both in solution, regardless of the temperature, and in the solid state. Ligand exchange processes take place via dimeric intermediates if organorhenium oxides are mixed with organorhenium(VII) imido/oxo species or organorhenium(VII) imides. Reaction of methylbis(imido)monooxorhenium(VII) (3) with (methylcyclopentadienyl) trioxorhenium (5) leads to a dimer with mixed methyl/cyclopentadienyl and imido/oxo groups (6). Reaction of 2-4 with water slowly leads to the formation of 1, perrhenate, and amines.

Full text of DOI:10.1021/om971062+

Organometallics 1998, 17, 2751-2757
2751
Mu ltip le Bon d s betw een Ma in -Gr ou p Elem en ts a n d
Tr a n sition Meta ls. 166.1 Oxo/Im id o Com p lexes of
Hep ta va len t Rh en iu m : Str u ctu r es, Rea ctivity, a n d
Beh a vior in Solu tion †
Wolfgang A. Herrmann,* Hao Ding,‡ Fritz E. Ku¨hn,* and Wolfgang Scherer
Anorganisch-chemisches Institut der Technischen Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
D-85747 Garching b. Mu¨nchen, Germany
Received December 3, 1997
Mixed imido/oxo rhenium(VII) complexes, formal derivatives of methyltrioxorhenium(VII)
(1) with (2,6-diisopropylphenyl)imido ligands of general formula CH3ReO3-x(NR)x (x ) 1,
and 2; compounds 2 and 3, respectively), have been synthesized. Their structures and
1
behavior in solution have been studied by dynamic H and 17O NMR spectroscopy. In the
solid state, compounds 2 and 3 display dimeric structures, as shown by X-ray crystallography.
In solution, monomeric and dimeric forms exist in equilibria. At elevated temperatures,
the monomers are dominant. In the solid state, the dimeric compounds are bridged by oxygen
ligands, forming Re2O2 units, while in solution, nitrogen bridging is also evident. Formal
replacement of all three oxo groups in 1 by (2,6-diisopropylphenyl)imido ligands leads to a
compound of formula CH3Re(NR)3 (4). Complex 4 is monomeric both in solution, regardless
of the temperature, and in the solid state. Ligand exchange processes take place via dimeric
intermediates if organorhenium oxides are mixed with organorhenium(VII) imido/oxo species
or organorhenium(VII) imides. Reaction of methylbis(imido)monooxorhenium(VII) (3) with
(methylcyclopentadienyl) trioxorhenium (5) leads to a dimer with mixed methyl/cyclopen-
tadienyl and imido/oxo groups (6). Reaction of 2-4 with water slowly leads to the formation
of 1, perrhenate, and amines.
In tr od u ction
of imidorhenium(VII) complexes to understand the
gradual change of behavior between rhenium-oxo and
-imido species. Some unexpected and interesting find-
ings from both a structural and synthetic point of view,
including an easy synthetic approach to rhenium imido/
oxo complexes with mixed organic ligands, resulted from
this work.
Organorhenium oxides such as methyltrioxorhenium
(1) have recently been extensively studied. Applications
as active, selective catalysts for organic syntheses as
well as in material sciences were discovered.2 A simi-
larly detailed examination of organorhenium(VII) imido
complexes has not yet been performed.2b Organorhe-
nium(VII) imido and organorhenium(VII) imido/oxo
complexes may have catalytic activity in certain organic
reactions, such as hydroamination and oxyamination.3
Imidorhenium(VII) complexes also offer the possibility
for chiral modification with chiral organic groups on the
nitrogen, which of course is not possible with divalent
oxo ligands. On the basis of an earlier report,4 we
examined structural aspects and the dynamic behavior
Resu lts a n d Discu ssion
Syn th esis a n d NMR Sp ectr oscop y. To examine
the gradual changes in the physical properties and
chemical behavior of compounds of the general type
[CH3ReOn(NR)3-n
]
(n ) 0-3; m ) 1, 2; R ) 2,6-
m
diisopropylphenyl) (Scheme 1), we first synthesized
these complexes according to literature procedures.2,4
CH3ReO3 (1) was refluxed with the corresponding
amount of 2,6-diisopropylphenyl isocyanate (DIPP-NCO)
in 1,2-dimethoxyethane (DME). The products were
obtained as orange crystals in the case of CH3ReO(NR)2
(3) and dark red crystals in the case of CH3Re(NR)3 (4)
by recrystallization at -30 °C. However, the prepara-
tion of 2 by the reaction between 1 and DIPP-NCO
turned out to be problematic. Impurities with higher
numbers of imido groups were present in all cases.
When 3 is mixed with 1 in solution, their oxo and imido
groups exchange rapidly. Therefore 2 can be synthe-
* Corresponding authors.
† Dedicated to Professor Carlos C. Roma˜o on occasion of his 50th
birthday.
‡ Alexander von Humboldt Fellow (1997-1998).
(1) Preceding paper of this series: Ku¨hn, F. E.; Rauch, M. U.;
Lobmaier, G. L. M.; Artus, G. R. J .; Herrmann, W. A. Chem. Ber. 1997,
130, 1427.
(2) Recent reviews: (a) Herrmann, W. A.; Ku¨hn, F. E. Acc. Chem.
Res. 1997, 130, 1169. (b) Roma˜o, C. C.; Ku¨hn, F. E.; Herrmann, W. A.
Chem. Rev. 1997, 97, 3197. (c) Herrmann, W. A. J . Organomet. Chem.
1995, 500, 149.
(3) (a) Taube, R. In Applied Homogeneous Catalysis with Organo-
metallic Compounds; Cornils, B., Herrmann, W. A., Eds.; VCH:
Weinheim, Germany, 1996; Vol. 1, pp 507-520 and literature cited
therein. (b) Beller, M.; Sharpless, K. B. In Applied Homogeneous
Catalysis with Organometallic Compounds; Cornils, B., Herrmann, W.
A., Eds.; VCH: Weinheim, Germany, 1996; Vol. 2, pp 1009-1024 and
literature cited therein.
(4) Herrmann, W. A.; Weichselbaumer, G.; Paciello, R. A.; Fischer,
R. A.; Herdtweck, E.; Okuda, J .; Marz, D. W. Organometallics 1990,
9, 489.
S0276-7333(97)01062-5 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 06/05/1998

2752 Organometallics, Vol. 17, No. 13, 1998
Herrmann et al.
Sch em e 1
Sch em e 2
Sch em e 3
dimerization behavior of these compounds,4 is not
significant. Namely, only monomers, without any bridg-
1
ing groups, were observed at room temperature by H
NMR after long standing in either polar or nonpolar
solvents. The previously claimed dimeric derivatives
turned out to be a mixture of the monomeric compounds
and decomposition products caused by the reaction of
monomer with trace amounts of water (Scheme 3).
However, both 2 and 3 show, also in contrast to earlier
reports, a temperature-dependent dynamic behavior.
The 17O NMR spectra at 100 °C in toluene-d8 2 show a
single peak at δ(17O) ) 770 ppm. Cooling to room
temperature leads to a significant broadening of the
signal and a high-field shift to δ(17O) ) 747 ppm.
Further cooling causes again a broadening and a shift
to higher field. At -90 °C, no signal is detectable.
Using diethyl ether as solvent, similar observations can
be made at low temperatures. At -110 °C, two broad
signals appear, one at δ(17O) ) 670 ppm and one at δ-
sized by mixing either the bis(imido)rhenium complex
3 or the tris(imido)rhenium complex 4 with 1 in the
correct stoichiometry (Scheme 2). This result indicates
that intermolecular oxo and imido ligand exchange is
quite common in this chemistry (see NMR results below)
and can be utilized in the preparation of mixed oxo/
imido complexes. The reaction between 1 and 3 to
generate 2 is much faster than that between 1 and the
tris(imido) derivative 4. It is particularly interesting
to monitor the progress of the reaction of 1 with 1 equiv
of 4 by 1H NMR. The reaction initially (in 10 min)
generated only 2 with excess 4, while 3 was not observed
until a much later stage of the reaction (after several
hours). This perhaps indicates once 3 is generated as
the byproduct, it reacts with 1 at a much faster rate
than 1 reacts with 4. Consequently, 1 is totally con-
sumed, the reaction is temporarily stopped, and eventu-
ally 3 is regenerated by the ligand exchange between 2
and 4. The fact that 3 reacts more readily with 1
compared to the reaction of 4 with 1 is very likely due
to the steric bulk of the imido ligands in 4 (see for
comparison the X-ray section).
1
(17O) ) 267 ppm. The H NMR shows three high-field
signals at room temperature and above: a septet at δ-
(1H) ) 3.64 ppm (belonging to the isopropyl proton), a
doublet at δ(1H) ) 1.08 ppm (CH3 groups of the imido
ligand), and a singlet at δ(1H) ) 1.85 (belonging to the
Re-CH3 group). At -90 °C, the signal of the Re-CH3
group has shifted to 0.95 ppm, the doublet to 1.14 ppm,
and the multiplet to 3.81 ppm.
In the case of compound 3, the situation is similar.
The 17O NMR signal at room temperature observed at
δ(17O) ) 738 ppm in toluene-d8 broadens during cooling
and disappears at ca. -10 °C. At -30 °C, two broad
signals can be observed, one at δ(17O) ) 748 ppm and
one at δ(17O) ) 297 ppm. Both signals become sharper
when the solution is further cooled, leading to signals
Compounds 2-4 are moisture sensitive but thermally
stable. We found that the influence of the polarity of
the solvent, which was previously believed to dictate the

Oxo/ Imido Complexes of Heptavalent Rhenium
Organometallics, Vol. 17, No. 13, 1998 2753
at δ(17O) ) 766 and 276 ppm at -90 °C. The situation
in CD2Cl2 as a solvent is similar. The low-field signal
is less pronounced at lower temperatures, and the high-
field signal increases with falling temperature. The 1H
NMR of 3 shows also three high-field signals: a septet
at δ(1H) ) 3.56 ppm, belonging to the isopropyl H, two
doublets at 1.06 and 1.08 ppm, representing the isopro-
pyl CH3 groups, and a singlet at 1.51 ppm for the Re-
CH3 group. At -90 °C, the Re-CH3 signal has shifted
to δ(1H) ) 1.43 ppm, the signal of the isopropyl proton
has split into two septets, one at 3.80 and the other at
3.64 ppm, and the doublet at 1.07 ppm has also split
into three doublets at 1.12, 1.08, and 1.09 ppm.
In our opinion, the interpretation of these observa-
tions is as follows: in solution, equilibria exist between
the monomeric and dimeric forms of complexes 2 and
3. Cooling the solutions shifts the equilibria to the
dimeric forms. Above a certain temperature (above
-100 °C for 2; around -30 °C for 3), the monomers
become the predominant species (see also the IR sec-
tion). The bridging oxygen atoms give rise to the 17O
NMR signals below δ(17O) ) 300 ppm, and the terminal
oxygens the signal above ca. 700 ppm. These data are
in good accord with published data for related complexes
with bridging and terminal oxo ligands.2,5 It is also
interesting to note that the dimer in the case of 3 is
observable at higher temperatures than the dimer in
the case of 2. It seems that the presence of a higher
number of bulky imido ligands is helpful for the dimer-
ization of the complexes by oxo bridges. This assump-
tion is supported by our X-ray structure determinations
and results of Wilkinson et al., who examined mixed
imido/oxo rhenium complexes with aryl ligands in the
solid state.6 The 17O NMR results prove that the imido
ligands are stronger donors than the oxo ligands. The
17O NMR signal at room temperature is found for 1 at
δ(17O) ) 830 ppm, for 2 at δ(17O) ) 747 ppm, and for 3
at δ(17O) ) 738 ppm in toluene.
Dimerization of compound 1 or its higher congeners
of the formula R-ReO3 (R ) alkyl, aryl) has never been
observed in solution.2 However, there is evidence that
oxygen ligand exchange takes place in solution between
17O-labeled and unlabeled organorhenium(VII) oxides
and OsO4, respectively.5c It was not clear before this
study whether traces of water or intramolecular oxo
bridges are responsible for this phenomenum.5c In view
of the above-mentioned results for mixed imido/oxo
complexes, exchange between labeled and unlabeled
oxygen ligands via oxygen bridges seems to be most
likely. It is also possible that dimerization processes
such as those described here play an important part in
the polymerization of 1 in water.2 In the case of the
tris(imido) derivative 4, however, we found no indica-
tions for the presence of bridging groups by NMR
spectroscopy. Only three high-field sets of 1H NMR
signals can be observed, regardless of the temperature
(+100 °C, δ(1H) ) 3.55 (septet, isopropyl H), 2.54
(singlet, Re-CH3), 1.06 ppm (doublet, isopropyl CH3);
-90 °C, δ(1H) ) 3.69, 2.79, 1.06 ppm). The previously
reported “dimer”4 turned out to be a mixture of com-
pounds 3 and 4. Although it cannot be totally ruled out
that a quick exchange between the terminal and bridg-
ing imido groups of 4 as a dimer takes place over the
examined temperature range, our (see below) and
Wilkinson’s6 X-ray examinations of 4 and related com-
plexes give no indication of dimeric species of organotris-
(imido)rhenium(VII) compounds. The steric bulk of the
imido ligands probably prevents the dimerization of 4.
The results presented also shed light on earlier
examinations of intermetallic exchange of oxo and imido
ligands.7,8 The observed structures (see below) may be
regarded as model complexes for the exchange inter-
mediates of oxo/imido ligands as proposed by Gibson et
al.7a The 17O NMR results and the preparation of
complex 2 (which requires intermolecular oxygen and
imido ligand exchange by means of bridging) strongly
support the assumptions concerning the four-center
ligand exchange mechanism and also verify Gibson’s
predictions concerning the synthetic applications of such
exchanges.7a
Another noteworthy fact is the temperature-depend-
ent shift of the Re-CH3 signal in the 1H NMR in toluene
in the cases of 1-3. The Re-CH3 protons of 1 are
observed at 1.55 ppm at +100 °C and at 0.80 ppm at
-90 °C. In the case of 2, the signals shift from 1.90 to
0.95 ppm; in the case of 3, they shift from 1.51 to 1.43
ppm in the same temperature range. For compound 4,
which contains no oxygen atoms, a comparable high-
field shift is not observed. In contrast, the signal is
shifted from 2.54 to 2.79 ppm. In no other solvents
(except benzene) has a comparatively strong shift
change of the Re-CH3 protons been observed.5,7 One
possible explanation is the formation of a charge trans-
fer complex between the aromatic solvent and the
electron-deficient Re center. The higher the electron
deficiency of the Re center, the stronger is the effect.
UV/vis spectroscopic results also show significant dif-
ferences in the absorption maxima of these complexes
between aromatic and nonaromatic solvents.2b
Rea ction s. Although bulky aromatic imido com-
plexes of rhenium(VII) oxides can be handled in air
briefly without noticeable decomposition, compounds
2-4 are susceptible to hydrolysis in solution. In all
cases, these compounds react with H2O slowly to
decrease the imido-to-oxo ratio by liberating amines and
eventually converting to 1 (Scheme 3; see also IR
results).
Mixed oxo/imido complexes, such as 3, can also
exchange oxo and imido ligands with other organorhe-
nium oxides, such as (methylcyclopentadienyl)rhenium
trioxide (5). There is an immediate reaction of 3 and 5
in a 1/1 stoichiometric ratio (eq 1). In about 2 h, the
exchange of oxo and imido ligands is complete and
compound 6 is generated. Even with a bulky (2,6-
(5) (a) Herrmann, W. A.; Thiel, W. R.; Ku¨hn, F. E.; Fischer, R. W.;
Kleine, M.; Herdtweck, E.; Scherer, W.; Mink, J . Inorg. Chem. 1993,
32, 5188. (b) Herrmann, W. A.; Ku¨hn, F. E.; Roesky, P. W. J .
Organomet. Chem. 1995, 485, 243. (c) Herrmann, W. A.; Ku¨hn, F. E.;
Rauch, M. U.; Correia, J . D. G.; Artus, G. R. J . Inorg. Chem. 1995, 34,
2914. (d) Herrmann, W. A.; Correia, J . D. G.; Ku¨hn, F. E.; Artus, G. R.
J . Chem. Eur. J . 1996, 2, 168. (e) Herrmann, W. A.; Wojtczak, W. A.;
Artus, G. R. J .; Ku¨hn, F. E.; Mattner, M. R. Inorg. Chem. 1997, 36,
465.
(7) (a) J olly, M.; Mitchel, J . P.; Gibson, V. C. J . Chem. Soc., Dalton
Trans. 1992, 1331. (b) Wolf, J . R.; Bazan, G. C.; Schrock, R. R. Inorg.
Chem. 1993, 32, 4155. (c) Cummins, C. C.; Schrock, R. R.; Davies, W.
M. Inorg. Chem. 1994, 33, 1448. (d) Holm, R. H. Chem. Rev. 1987, 87,
1401. (e) Nugent, W. A.; Mayer, J . M. Metal-Ligand Multiple Bonds;
Wiley: New York, 1983.
(6) Gutierrez, A.; Wilkinson, G.; Hussain-Bates, B.; Hursthouse, M.
B. Polyhedron 1990, 9, 2081.
(8) Ku¨hn, F. E.; Herrmann, W. A.; Hahn, R.; Elison, M.; Blu¨mel, J .;
Herdtweck, E. Organometallics 1994, 13, 1601.

2754 Organometallics, Vol. 17, No. 13, 1998
Herrmann et al.
diisopropylphenyl)imido group, 6 retains the η5 coordi-
nation with the substituted cyclopentadienyl ring. In
solution, 6 exchanges its oxo and imido ligands intramo-
1
lecularly. The H NMR spectrum of 6 at room temper-
3
ature shows only one doublet (δ ) 1.17 ppm, J H-H
)
6.96 Hz) for the methyl substituent on the (diisopropyl-
phenyl)imido groups. The exchange slows at lower
temperatures, and the doublet splits into two sets of
doublets below -30 °C.
IR Sp ectr oscop y. In agreement with the solid-state
structures of 2 and 3, their IR spectra show the presence
of terminal and bridging oxo groups. The IR spectrum
of 2 (KBr) shows a very strong band at 953 cm-1. This
band can be assigned to the terminal oxo stretching
vibration.9 A strong absorption at 703 cm-1 indicates
that 2 contains bridging oxo groups in the solid state.9
Exposure of compound 2 to air or moisture leads to two
new RedO vibrations (958 and 934 cm-1) due to the
formation of 1A. After 12 h in air, the band at 934 cm-1
is the most pronounced RedO vibration while the
vibrations at 953 and 703 cm-1 decrease significantly
in intensity. Compound 3 has a very strong band at
680 cm-1 representing the bridging oxo groups, ν(Re-
O-Re), while no terminal oxo-rhenium stretching
modes are observed. Complex 3 also decomposes slowly
during exposure to air or moisture under formation of
1A, as detectable from the changes in the IR spectrum.
In the case of derivative 6, the ν(RedO) IR frequencies
are shifted to even lower wavenumbers (921 (CH3RedO)
and 907 cm-1 (CpRedO)) due to the presence of the
methylcyclopentadienyl group. Two bridging Re-O-
Re vibrations are observed, as expected from the lower
symmetry of the complex (772, 747 cm-1). All com-
pounds have a number of bands in the frequency range
in which rhenium-imido stretching modes ν(RedN) are
expected. The assignment of these bands is tentative
(see Experimental Section) due to the uncertainty in the
assignment of metal-nitrogen stretching modes, caused
by its coupling to the nitrogen-carbon stretching and
even to C-C and C-H modes.6,10 IR spectra recorded
in diethyl ether solution at room temperature do not
show bridging Re-O-Re vibrations. Instead, in the
case of compound 3, a strong band can be observed at
924 cm-1, due to the terminal RedO stretching vibra-
tion. In the case of 2, two RedO bands can be observed
in solution, one at 928 cm-1 and one at 985 cm-1. In
this case, the Re-O-Re band is also conspicuously
absent. These results strongly support the conclusions
drawn from the NMR measurements (see above).
X-r a y Cr ysta llogr a p h y. To be able to compare the
NMR measurements in solution with the solid-state
structures, we determined the structures of compounds
F igu r e 1. PLATON representation of 2. Thermal el-
lipsoids are shown at the 50% probability level; hydrogen
atoms are omitted for clarity.
F igu r e 2. PLATON representation of 3. Thermal el-
lipsoids are shown at the 30% probability level; hydrogen
atoms are omitted for clarity. A symmetry operation (-x,
-y, -z) is applied to atoms labeled by “a”.
2-4 by X-ray structure analysis. PLATON18 represen-
tations of molecules 2-4 are shown in Figures 1-3, and
selected bond distances and bond angles are given in
Tables 1-3.
Compounds 2 and 3 display dimeric structures. In
both cases, pentagonally coordinated Re centers are
linked by two bridging oxygen atoms. The Re-Re
distance is rather long and indicates only a very weak
bonding interaction (3.0902(10)-3.1186(3) Å). Com-
pound 4 is monomeric with a distorted tetrahedral
coordination sphere for the Re center. These results are
in accord with some earlier structural examinations of
related compounds.6,10 3 is the first bis(imido)mono-
oxoorganorhenium(VII) complex characterized by X-ray
crystallography. Up to now, only two monoimidodioxoor-
ganorhenium(VII) structures have been published,
namely [Re(NtBu)(O)(µ-O)(xylyl)]2 and [Re(NtBu)(O)(µ-
O)(mesityl)]2.6 Both complexes have unsymmetrical
Re-O bridges (2.081(8)/1.867(8) Å in the xylyl case and
1.791(7)/2.364(7) Å in the mesityl case). In the methyl
derivative 2, the bridges are less unsymmetrical (1.891-
(8)/1.997(8) Å) but still significantly different. Wilkin-
(9) (a) Mink, J .; Keresztury, G.; Stirling, A.; Herrmann, W. A.
Spectrochim. Acta 1994, 50A, 2039. (b) Ku¨hn, F. E.; Mink, J .;
Herrmann, W. A. Chem. Ber. 1997, 130, 295.
(10) (a) Saboonchian, V.; Danopoulos, A. A.; Guiterrez, A.; Wilkinson,
G.; Williams, D. J . Polyhedron 1991, 10, 2241. (b) Danopoulos, A. A.;
Wilkinson, G.; Williams, D. J . J . Chem. Soc., Chem. Commun. 1991,
181.

Oxo/ Imido Complexes of Heptavalent Rhenium
Organometallics, Vol. 17, No. 13, 1998 2755
(ca. 1.68-1.72 Å).2 Concerning the bridging Re-O
bonds, two significantly different bond lengths can be
observed (see above). However, both of them are still
in the usual range of Re-O single bonds. Re-O bond
distances for OfRe(VII) donor interactions are known
to range between 2.30 and 2.45 Å.2,5c,11 The asymmetry
of the Re2O2 units could therefore be formally inter-
preted in terms of a dimer, consisting of two strongly
interacting “monomeric units”. Thus, the observed
cleavage of the dimers in solution is in agreement with
the structural findings in the solid state: thermal
movements at higher temperatures are obviously able
to cleave the two weaker of the four Re-O single bonds
of the crystalline compounds, leading to the monomeric
compounds in solution.
Packing effects due to bulky ligands and donor effects
of the imido and organyl substituents might also influ-
ence the Re-O bond lengths as observed in the two
crystallographically independent molecules in the unit
cell of compound 3 (see above). We have also observed
the formation of unsymmetric ReVII2O2 units in related
complexes, namely [ReO2(µ-O)C2H4C(CH3)HO(CH3)]2
and [ReO3(µ-OCH3)(CH3OH)]2 in the solid state.5e,12
There are two possible explanations for the mono-
meric structures of 4 and the related published and
structurally very similar derivatives ([C6H5Re(NC6H3-
(i-C3H7)3] and [C6H2(CH3)3Re(NC(CH3)3)3]).9,13 First,
the imido ligands used to date are too bulky to favor
dimerization. The other reason might be that imido
groups are stronger donors than oxygen atoms. Thus,
three imido groups in one molecule may be sufficient to
provide steric and electronic saturation of the metal
center.
It should be noted, in this context, that several
analogous Tc complexes, most notably (η1-C5H5)Tc(NAr)3
and CH3Tc(NAr)3, are known.14 All bond distances and
bond angles of the latter compound are identical to those
of 4 within estimated error. The entire class RM(NR′)3
(M ) Tc, Re) display very similar structural features.
This kind of structural similarity has already been noted
for the RMO3 (M ) Tc, Re) complexes. The chemical
and spectroscopic similarities of the latter class of
compounds are extremely widespread,2 and the same
seems to be true for the RM(NR′)3 compounds.
F igu r e 3. PLATON representation of 4. Thermal el-
lipsoids are shown at the 30% probability level; hydrogen
atoms are omitted for clarity.
Ta ble 1. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for th e Dim er ic Com p ou n d 2
Re(1)-O(1)
Re(1)-N(1)
Re(1)-O(2)
Re(1)-O(4)
Re(1)-C(1)
Re(1)-Re(2)
Re(2)-O(3)
Re(2)-N(2)
Re(2)-O(4)
Re(2)-O(2)
Re(2)-C(14)
1.702(9)
1.730(8)
1.891(8)
1.997(8)
2.135(12)
3.0902(10)
1.686(10)
1.738(9)
1.895(8)
1.999(8)
2.106(14)
Re(1)-O(2)-Re(2)
Re(2)-O(4)-Re(2)
O(1)-Re(1)-N(2)
O(1)-Re(1)-O(2)
N(1)-Re(1)-O(2)
N(1)-Re(1)-O(4)
O(2)-Re(1)-O(4)
O(1)-Re(1)-C(1)
N(1)-Re(1)-C(1)
O(2)-Re(1)-C(1)
O(4)-Re(1)-C(1)
105.2(4)
105.2(4)
106.9(4)
113.9(4)
98.5(4)
144.3(4)
74.7(3)
102.7(4)
87.3(4)
139.1(4)
77.3(4)
Ta ble 2. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for th e Dim er ic Com p ou n d 3a
Re(1)-O(1)
Re(1)-O(1)a
Re(1)-N(11)
Re(1)-N(12)
Re(1)-C(1)
Re(1)-Re(1)
N(11)-C(2)
N(12)-C(14)
1.885(4) Re(1)-O(1)-Re(1)
2.022(3) O(1)-Re(1)-N(11)
1.740(4) O(1)-Re(1)-N(12)
1.730(4) O(1)-Re(1)-C(1)
2.141(6) Re(1)a-Re(1)-O(1)
105.9(2)
98.8(2)
114.5(2)
137.4(2)
38.6(1)
3.1190(3) Re(1)a-Re(1)-N(12) 113.1(1)
1.368(7) Re(1)a-Re(1)-C(1) 107.6(2)
1.412(7) Re(1)-N(11)-C(2)
172.1(4)
Re(1)-N(12)-C(14) 157.7(4)
O(1)a-Re(1)-N(12) 102.6(2)
O(1)a-Re(1)-N(11) 147.4(2)
O(1)a-Re(1)-C(1)
77.2(2)
a
A symmetry operation (-x, -y, -z) is applied to atoms labeled
by “a”.
Con clu sion s
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for th e Mon om er ic Com p ou n d 4
Imido/oxo rhenium(VII) organyl complexes can be
easily synthesized by mixing organorhenium(VII) tri-
oxides with organorhenium(VII) tris(imides). Oxo and
imido ligand exchange takes place via bridging ligand
groups. In solution, there is an equilibrium between
monomers (main product at high temperatures) and
dimers (low temperatures). In the solid state, dimeric
Re(1)-N(3)
Re(1)-N(4)
Re(1)-N(2)
Re(1)-C(1)
N(2)-C(2)
N(3)-C(14)
N(4)-C(26)
1.748(3)
1.758(4)
1.766(3)
2.109(5)
1.373(5)
1.391(5)
1.390(5)
N(3)-Re(1)-N(4)
N(3)-Re(1)-N(2)
N(4)-Re(1)-N(2)
N(3)-Re(1)-C(1)
N(4)-Re(1)-C(1)
N(2)-Re(1)-C(1)
C(2)-N(2)-Re(1)
C(14)-N(3)-Re(1)
C(26)-N(4)-Re(1)
115.6(2)
114.8(2)
116.2(2)
101.8(2)
103.0(2)
102.4(2)
166.3(3)
168.8(3)
169.5(3)
(11) (a) Herrmann, W. A.; Roesky, P. W.; Wang, M.; Scherer, W.
Organometallics 1994, 13, 4536. (b) de Me´ric de Bellefon, C.; Her-
rmann, W. A.; Kiprof, P.; Whitaker, C. R. Organometallics 1992, 11,
1072. (c) Kiprof, P.; Herrmann, W. A.; Ku¨hn, F. E.; Scherer, W.; Kleine,
M.; Elison, M.; Rypdal, K.; Volden, H. V.; Gundersen, S.; Haaland, A.
Bull. Soc. Chim. Fr. 1992, 129, 655.
(12) Herrmann, W. A.; Correia, J . D. G.; Rauch, M. U.; Artus, G. R.
J .; Ku¨hn, F. E. J . Mol. Catal. 1997, 118, 33.
(13) Schoop, T.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H. G.
Organometallics 1993, 12, 571.
son et al. argued that the longer Re-O bond distance
in the axial case might be due to either a trans influence
of the imido group or packing effects. In complex 3, the
Re2O2 units of the two crystallographically independent
molecules are also rather asymmetric (1.885(4)/2.022-
(3) and 1.916(3)/1.994(3) Å).
(14) (a) Burrell, A. K.; Bryan, J . C. Organometallics 1992, 11, 3501.
(b) Burrell, A. K.; Clark, D. L.; Gordon, P. L.; Sattelberger, A. P.; Bryan,
J . C. J . Am. Chem. Soc. 1994, 116, 3813. (c) Benson, M. T.; Bryan, J .
C.; Burrell, A. K.; Cundari, T. R. Inorg. Chem. 1995, 34, 2348.
The terminal RedO bond lengths (1.69(1) and 1.70-
(1) Å) in the case of 2 are in the usual range of RedO
double bonds observed in organorhenium(VII) oxides

2756 Organometallics, Vol. 17, No. 13, 1998
Herrmann et al.
1384 s, 749 s. CI MS, m/z: 569, [M/2]+; peaks at higher mass
indicate a dimeric compound. Anal. Found: C, 52.76; H, 6.59;
N, 4.72. Calcd for C50H74N4O2Re2 (Mr ) 1135.58): C, 52.89;
H, 6.57; N, 4.93.
compounds with bridging oxygen atoms can be isolated.
These dimers can formally be regarded as consisting of
two very strongly interacting monomeric units, leading
to one shorter and one longer Re-O bond in the bridges.
Mixing compounds with different organyl ligands leads
to defined products with mixed ligands. By means of
this method, a broad variety of yet unknown derivatives
with interesting characteristics and applications should
be accessible.
Tr is((2,6-d iisop r op ylp h en yl)im id o)m et h ylr h en iu m -
(VII) (4). A solution of 100 mg (0.40 mmol) of 1 and 284 µL
(1.33 mmol, 269 mg) of 2,6-diisopropylphenyl isocyanate in 30
mL of 1,2-dimethoxyethane was refluxed for 12 h. The solvent
in the resulting deep red solution was then removed. The
viscous red residue was dried under vacuum at 65 °C for 10 h
to remove unreacted isocynate. Yield: 280 mg (96%) of 4 as a
dark red solid. Further recrystallization in hexanes at -30
°C afforded dark red crystals in about 85% yield. 1H NMR
Exp er im en ta l Section
3
(400 MHz, 23 °C, CDCl3): δ 1.08 (d, J H-H ) 6.96 Hz, 36 H),
All reactions were performed with standard Schlenk tech-
niques under oxygen-free and water-free nitrogen or argon
atmospheres. Solvents were dried with standard methods and
distilled under N2 or argon. Infrared spectra were recorded
on a Perkin-Elmer 1600 series FTIR spectrometer (resolution
3
2.46 (s, 3 H), 3.45 (sept, J H-H ) 6.96 Hz, 6 H), 7.02-7.10 (m,
9 H). 13C NMR (100 MHz, 23 °C, CDCl3): δ 23.1 (s, 12 C),
28.5 (s, 7 C), 122.0 (s, 6 C), 125.3 (s, 6 C), 140.5 (s, 3 C), 153.0
(s, 3 C). IR (KBr), cm-1: ν(RedN) 1334 vs, 1292 vs, ν(C-H)
2961 vs, 2924 m, 2870 m, 1384 s, 752 s. CI MS, m/z: 728,
M+. Anal. Found: C, 59.44; H, 7.52; N, 5.44. Calcd for
1
4 cm-1); the H and 17O NMR spectra were acquired at 399.78
and 54.21 MHz, respectively, on FT-J EOL GX 400 and Bruker
DPX 400 instruments. All NMR solvents were “freeze-
pump-thaw” degassed and stored over molecular sieves before
use. Elemental analyses were performed in the microanalyti-
cal laboratory of our institute. Mass spectra were obtained
with Finnigan MAT 311A- and MAT 90 spectrometers. 17O
labeled 1 was prepared according to refs 5b and 15.15 For 17O
NMR experiments, 2 and 3 were also prepared 17O labeled
from 17O-labeled 1 according to the procedures described below.
Compound 5 was prepared according to ref 8. For in situ NMR
studies, each component was weighted separately and trans-
ferred to an NMR tube under Ar atmosphere. The NMR
sample tube was stored under Ar in a Schlenk tube when the
sample needed to be kept for longer periods of time.
C
37H54N3Re (Mr ) 727.06): C, 61.12; H, 7.49; N, 5.78.
[((2,6-Diisop r op ylp h en yl)im id o)m et h yloxor h en iu m -
(VII)]bis(µ-oxo)[((2,6-d iisop r op ylp h en yl)im id o)(m eth yl-
cyclop en ta d ien yl)oxor h en iu m (VII)] (6). A 40 mg (0.128
mmol) sample of (methylcyclopentadienyl)trioxorhenium(VII)
and 73 mg (0.128 mmol) of 3 were dissolved in 8 mL of CH2-
Cl2. The red-brown solution gradually became be dark brown.
The solvent was removed at room temperature under vacuum
after 6 h. The resulting brown solid was recrystallized in CH2-
Cl2 and hexanes (1/10 v/v) to give 80 mg (70%) of 6 as brown
microcrystals. 1H NMR (400 MHz, 23 °C, CDCl3): δ 1.17 (d,
3J H-H ) 6.96 Hz, 24 H), 2.44 (s, 3 H), 2.73 (s, 3 H), 3.14 (sept,
3
3J H-H ) 6.96 Hz, 4 H), 6.61 (t, J H-H ) 2.56 Hz, 2 H), 6.87 (t,
3J H-H ) 2.56 Hz, 2 H), 7.2-7.3 (m 6 H). 13C NMR (100 MHz,
23 °C, CDCl3): δ 14.0 (s, 1 C), 23.8 (s, 4 C), 23.9 (s, 4 C), 28.6
(s, 5 C), 107.4 (s, 2 C), 109.8 (s, 2 C), 123.3 (s, 4 C), 130.7 (s,
1 C), 131.7 (s, 4 C), 144.1 (s, 2 C), 150.8 (s, 2 C). IR (KBr),
cm-1: ν(RedO) 921 m, 907 vs, 852 m, ν(Re-O-Re) 772 m,
747 m, ν(RedN) 1384 s, 1325 m, ν(C-H) 2965 s, 2925 m, 2869
m, 1384 s, 746 s. CI MS, m/z: 706, [M - NR]+; 569, [M -
MeCpReO3]+. Anal. Found: C, 42.11; H, 4.98; N, 3.09. Calcd
for C31H44N2O4Re2 (Mr ) 881.12): C, 42.26; H, 5.03; N, 3.18.
X-r a y Cr ysta llogr a p h y. Suitable single crystals for X-ray
diffraction studies were obtained by slowly cooling saturated
solutions of complexes 2-4 to -30 °C. All structures were
solved and refined by a combination of direct methods,
difference Fourier syntheses, and least-squares methods.
Neutral-atom scattering factors for all atoms and anomalous
dispersion corrections for the non-hydrogen atoms were taken
from the ref 16.16 All calculations were performed on a DEC
3000 AXP workstation with the STRUX-V system,17 including
the programs PLATON-92,18 PLUTON-92,18 SIR-92,19and
SHELXL-93.20
B is [(µ-o x o )(2,6-d iis o p r o p y lp h e n y lim id o )m e t h y l-
oxor h en iu m (VII)] (2). A 100 mg (0.08 mmol) sample of 3
and 48 mg (0.18 mmol) of 1 were dissolved in 5 mL of CH2Cl2,
and the solution was stirred for 1 h, resulting in a yellow
solution. The solvent was then removed by vacuum, and the
residue was recrystallized in pentane and methylene chloride
(9/1 vol/vol) at -60 °C. A 120 mg (90%) quantity of analytically
pure 2 as yellow-brown microcrystals was collected. 1H NMR
3
(400 MHz, 23 °C, CDCl3): δ 1.29 (d, J H-H ) 6.96 Hz, 24 H),
3
2.45 (s, 6 H), 3.66 (sept, J H-H ) 6.96 Hz, 4 H), 7.2-7.4 (m, 6
H). 13C NMR (100 MHz, 23 °C, CDCl3): δ 23.3 (s, 8 C), 28.7
(s, 6 C), 122.8 (s, 4 C), 132.0 (s, 4 C), 146.6 (s, 2 C), 151.7 (s,
2 C). 17O NMR (54 MHz, 23 °C, CDCl3): δ 747 (s). IR (KBr),
cm-1: ν(RedO) 953 s, ν(Re-O-Re) 703 vs, ν(RedN) 1384 s,
1341 m, ν(C-H) 2962 s, 2925 m, 2870 m, 1384 s, 744 s. CI
MS, m/z: 818, M+. Anal. Found: C, 38.16; H, 4.96; N, 3.35.
Calcd for C26H40N2O4Re2 (Mr 817.03): C, 38.22; H, 4.93; N,
3.43.
Bis[(µ-oxo)b is(2,6-d iisop r op ylp h e n ylim id o)m e t h yl-
r h en iu m (VII)] (3). A solution of 200 mg (0.80 mmol) of 1
and 343 µL (1.6 mmol, 327 mg) of 2,6-diisopropylphenyl
isocyanate in 30 mL of 1,2-dimethoxyethane was refluxed for
16 h. The solvent in the resulting deep red solution was then
removed under vacuum at 50 °C. The residue was redissolved
in 16 mL of diethyl ether and hexanes (1/1 vol/vol), and the
solution was cooled to -30 °C to produce the analytically pure
product as orange microcrystals, which were then collected by
filtration and dried. Yield: 390 mg (86%). 1H NMR (400 MHz,
23 °C, CDCl3): δ 1.13 (d, 3J H-H ) 6.96 Hz, 24 H), 1.16 (d, 3J H-H
Da ta Collection a n d Str u ctu r e Solu tion a n d Refin e-
m en t for Com p lexes 2-4. A summary of the collection and
refinement data is reported in Table 4. Preliminary examina-
tion and data collection for compounds 3 and 4 were carried
(16) International Tables for Crystallography; Wilson, A. J . C., Ed.;
Kluwer Academic Publishers: Dordrecht, The Netherlands, 1992; Vol.
C, Tables 6.1.1.4 (pp 500-502), 4.2.6.8 (pp 219-222), and 4.2.4.2 (pp
193-199).
(17) Artus, G.; Scherer, W.; Priermeier, T.; Herdtweck, E. STRUX-
V: A Program System to Handle X-ray Data. TU Mu¨nchen, Germany,
1997.
(18) Spek, A. L. PLATON-92-PLUTON-92: An Integrated Tool for
the Analysis of the Results of a Single-Crystal Structure Determina-
tion. Acta Crystallogr., Sect. A 1990, 46, C34.
(19) Altomare, A.; Cascarano, G.; Giacovazzo, C.; Guagliardi, A.;
Burla, M. C.; Polidori, G.; Camalli M. SIR-92. University Bari, Italy,
1992.
3
) 6.96 Hz, 24 H), 2.43 (s, 6 H), 3.42 (sept, J H-H ) 6.96 Hz, 8
H), 7.14 (br s, 12 H). 13C NMR (100 MHz, 23 °C, CDCl3): δ
22.8 (s, 8 C), 23.4 (s, 8 C), 28.5 (s, 10 C), 122.3 (s, 8 C), 127.8
(s, 8 C), 142.6 (s, 4 C), 151.9 (s, 4 C). 17O NMR (54 MHz, 25
°C, Tol-d8): δ 738 (br s). IR (KBr), cm-1: ν(Re-O-Re) 680
vs, ν(RedN) 1332 s, 1290 s, ν(C-H) 2962 s, 2923 m, 2870 m,
(20) Sheldrick, G. M. SHELXL-93. In Crystallographic Computing
3; Sheldrick, G. M., Kru¨ger, C., Goddard, R., Eds.; Oxford University
Press: Oxford, England, 1993; pp 175-189.
(15) Herrmann, W. A.; Ku¨hn, F. E.; Fischer, R. W.; Thiel, W. R.;
Roma˜o, C. C. Inorg. Chem. 1992, 31, 4431.

Oxo/ Imido Complexes of Heptavalent Rhenium
Organometallics, Vol. 17, No. 13, 1998 2757
Ta ble 4. Cr ysta llogr a p h ic Da ta for Com p ou n d s 2-4
2
3
4
Crystal Data
empirical formula
fw
C
26H40N2O4Re2
C50H74N4O2Re2
1135.56
C37H54N3Re
727.05
817.01
color
brown
orange
orange
cryst size (mm)
cryst system
space group
a (Å)
b (Å)
c (Å)
0.38 × 0.13 × 0.05
monoclinic
P21/c
19.922(3)
13.138(3)
11.357(3)
93.324(8)
2967.5(11)
4
0.28 × 0.04 × 0.04
monoclinic
P21/c
19.0347(12)
15.2465(8)
18.0530(12)
105.828(6)
5040.8(6)
4
0.40 × 0.32 × 0.14
orthorhombic
Fdd2
36.8535(8)
39.9810(17)
10.5930(3)
â (deg)
V (Å3)
15608.2(9)
16
Z
T (K)
293
1.829
81.8
1568
200
1.496
48.4
2272
173
1.238
31.4
Fcalcd (g cm-3
)
µ (cm-1
F000
)
5952
Data Collection
Refinementa
λ (Å)
0.710 73
ω scan
1.0-25.0
+23,+15,(13
0.710 73
0.710 73
scan method
imaging plate
1.5-25.1
(22,(17,(21
imaging plate
2.43-27.77
(46,(52,(13
θ range (deg)
data collcd (h,k,l)
no. of rflns collcd
no. of indep rflns
no. of obsd rflns
Rint
R1
wR2
5622
5202
58 174
8132
8132 (all data)
0.0652
0.0252
51 671
9031
9031 (all data)
0.0324
0.0222
5202 (all data)
0.0169
0.0354
0.1047
1.072
0.0482
0.830
0.0712
GOF
1.121
Flack param, ø
0.000(8)b
+1.14/-0.50
∆Fmax/min (e Å-3
)
+2.35/-2.13
+0.88/-0.93
R1 ) Σ||Fo| - |Fc||/Σ|Fo|; wR2 ) [Σw(Fo - Fc2)2/Σw(Fo2)2]1/2; GOF ) [Σw(Fo - Fc2)2/(NO - NV)]1/2; w ≡ SHELXL-93 weights.
a
2
2
b
Refinements of the enantiomorphic model resulted in larger R values (wR2 ) 0.1175).
out on an imaging plate diffraction system (IPDS; Stoe&Cie)
equipped with a rotating anode (Enraf-Nonius FR591) and
graphite monochromated Mo KR radiation. The data collection
was performed at 200 K (173 K) within the θ range 1.55°< θ
< 25.1° (2.43° < θ < 27.77°) with an exposure time of 5.0 (3.0)
min per image (either oscillation or rotation scan modes from
æ ) 25.0 to 360° (0 to 264°) with ∆æ ) 1° (0.5°). A total number
of 58 174 (51 671) reflections were collected; 1157 (744)
systematically absent reflections were rejected from the origi-
nal data set. After merging, 8132 (9031) independent reflec-
tions remained and were used for all calculations. Data were
corrected for Lorentz and polarization effects. Corrections for
intensity decay and/or absorption effects with the program
Decay21 were applied for 3. The unit cell parameters were
obtained by least-squares refinements of 4448 (4590) reflec-
tions with the program Cell.21 Final cell constants for 2 were
obtained by least-squares refinement of 25 automatically
centered reflections (7.1° < θ < 22.54°) on an Enraf-Nonius
CAD4 diffractometer (λ ) 0.710 73 Å; graphite monochroma-
tor): range of measurement 1.0° < θ < 25.0°; ω-scan, scan
width (1.0 + 0.25 tan θ)o ((25%) before and after each
reflection to determine the background; tmax ) 60 s; orientation
control reflections were monitored every 200 reflections, and
the intensities of three reflections were checked every 3600 s
(5622 measured reflections, 5202 independent reflections). A
semiempirical absorption correction based on six ψ-scan reflec-
tions was made (Tmax/Tmin: 99.9/49.2%).
All “heavy atoms” of the asymmetric unit were anisotropi-
cally refined. All hydrogen atoms were calculated in ideal
positions (riding model) for 2-4. Full-matrix least-squares
2
2 2
refinements were carried out by minimizing ∑w(Fo - Fc
)
with SHELXL weighting schemes and stopped at shift/error
< 0.001 in the case of compound 4. A potential solvent area
volume of 242.1 Å3 was found. The solvent molecule was not
resolved due to low residual electron densities (<1 e/Å3).
Ack n ow led gm en t. This work was supported by the
Alexander von Humboldt Foundation through a Fel-
lowship for H.D.
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
crystal data and refinement details, atomic positional and
thermal parameters, bond lengths and angles, and tempera-
ture-dependent 17O NMR data (58 pages). Ordering informa-
tion is given on any current masthead page.
(21) IPDS Operating System, Version 2.8; Stoe&Cie. GmbH: Darm-
stadt, Germany, 1997.
OM971062+