[NBu4][ReNCl4]: Facile synthesis, structure, electron paramagnetic resonance spectroscopy and reactions

Article abstract of DOI:10.1039/a705881k

The compound [NBu₄][ReNCl₄] has been found to be easily accessible by the reaction of [NBu₄][ReO₄] with sodium azide and HCl gas in ethanol and represents an excellent precursor for the synthesis of further rhenium nitrido complexes. It has been studied by X-ray crystallography. Rhenium(VI) compounds of the general formula [ReNX₄₍₅₎]^-,2- (X = Br or NCS) were obtained when [NBu₄][ReNCl₄] reacts with HBr or KSCN. The products as well as mixed-ligand intermediates which are formed during the ligand exchange have been studied by EPR spectroscopy. The EPR parameters of the individual mixed-ligand compounds are clearly correlated to the composition of the co-ordination sphere and can be used to characterize the mixed-ligand species unambiguously. This is shown by a nearly linear dependence of g₀, g_∥, a₀^Re and A_∥^Re on the spin-orbit coupling constants of the equatorial donors. Reactions of [NBu₄][ReNCl₄] with most organic ligands yielded rhenium(V) compounds. A number of phosphine complexes and chelates with sulfur-containing ligands have been prepared and spectroscopically characterized. A crystallographic study on [ReN(Hdetcb)₂] (Hdetcb^- = N²-diethylthiocarbamoylbenzamidinate) shows cis co-ordination for the chelating S,N-donor ligands. Weak intermolecular hydrogen bridges have been found between the co-ordinated nitrogen atoms and the lone pair of the nitrido nitrogen. A comparison between the crystal structural data of [NBu₄]₂[ReN(mnt)₂] (mnt^2- = 1,2-dicyanoethene-1,2-dithiolate), prepared from [NBu₄][ReNCl₄] and Na₂mnt, and [NBu₄][ReO(mnt)₂] shows longer Re-S bonds in the nitrido anion but markedly higher O-Re-S bond angles indicating higher steric requirements of the oxo ligand compared with 'N^3-'.

Full text of DOI:10.1039/a705881k

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[NBu4][ReNCl4]: Facile synthesis, structure, electron paramagnetic
resonance spectroscopy and reactions
Ulrich Abram,*,a Martin Braun,b Sonja Abram,b Reinhard Kirmsea and Andreas Voigtc
a Forschungszentrum Rossendorf, Institute of Radiochemistry, c/o Dresden University of
Technology, Institute of Analytical Chemistry, D-01062 Dresden, Germany
b Institute of Inorganic Chemistry, University of Tübingen, Auf der Morgenstelle 18,
D-72076 Tübingen, Germany
c Institute of Inorganic Chemistry, University of Leipzig, Talstrasse 35, D-04103 Leipzig, Germany
The compound [NBu4][ReNCl4] has been found to be easily accessible by the reaction of [NBu4][ReO4] with
sodium azide and HCl gas in ethanol and represents an excellent precursor for the synthesis of further rhenium
nitrido complexes. It has been studied by X-ray crystallography. Rhenium() compounds of the general formula
[ReNX4(5)]
Ϫ,2Ϫ (X = Br or NCS) were obtained when [NBu4][ReNCl4] reacts with HBr or KSCN. The products as
well as mixed-ligand intermediates which are formed during the ligand exchange have been studied by EPR
spectroscopy. The EPR parameters of the individual mixed-ligand compounds are clearly correlated to the
composition of the co-ordination sphere and can be used to characterize the mixed-ligand species unambiguously.
Re
||
This is shown by a nearly linear dependence of g0, g||, a0Re and A on the spin–orbit coupling constants of the
equatorial donors. Reactions of [NBu4][ReNCl4] with most organic ligands yielded rhenium() compounds. A
number of phosphine complexes and chelates with sulfur-containing ligands have been prepared and spectro-
scopically characterized. A crystallographic study on [ReN(Hdetcb)2] (HdetcbϪ = N2-diethylthiocarbamoyl-
benzamidinate) shows cis co-ordination for the chelating S,N-donor ligands. Weak intermolecular hydrogen
bridges have been found between the co-ordinated nitrogen atoms and the lone pair of the nitrido nitrogen.
A comparison between the crystal structural data of [NBu4]2[ReN(mnt)2] (mnt2Ϫ = 1,2-dicyanoethene-1,2-
dithiolate), prepared from [NBu4][ReNCl4] and Na2mnt, and [NBu4][ReO(mnt)2] shows longer Re᎐S bonds in the
nitrido anion but markedly higher O᎐Re᎐S bond angles indicating higher steric requirements of the oxo ligand
compared with ‘N3Ϫ’.
The tetrachloronitridorhenate anion, [ReNCl4]Ϫ, was first
prepared about 20 years ago by reaction of the neutral
rhenium() nitride chloride ReNCl4 with tetraphenylarsonium
chloride.1 The compound has been fully characterised, its
crystal structure elucidated2 and ligand-exchange reactions
with BrϪ and NCSϪ reported which lead to the rhenium()
ordination sphere of the metal and particularly its low solu-
bility in most common solvents restrict the applicability of this
starting material.
In the present paper we describe a facile synthesis of
[NBu4][ReNCl4] from perrhenate, sodium azide and HCl. Its
crystal structure and a detailed analysis of the EPR spectra of
the d1 system are reported. We demonstrate that [ReNCl4]Ϫ is
a suitable starting material for the synthesis of new rhenium
nitrido complexes and discuss the structures of the neutral
anions [ReNBr4]Ϫ and [ReN(NCS)5]2Ϫ 3,4
For a large-scale
.
synthesis, however, the approach via the neutral rhenium nitride
chlorides ReNCl3 or ReNCl4 [equations (1) and (2)] seems to
[ReN(Hdetcb)2]
(HdetcbϪ = N2-diethylthiocarbamoylbenz-
amidinate) and of the complex anion [ReN(mnt)2]2Ϫ (mnt2Ϫ
=
ReNCl3 ϩ AsPh4Cl → [AsPh4][ReNCl4]
(1)
1,2-dicyanoethene-1,2-dithiolate). The structure of [ReN-
(mnt)2]2Ϫ is compared with that of its oxo analogue
[ReO(mnt)2]Ϫ.
ReNCl4 ϩ AsPh4Cl → [AsPh4][ReNCl4] ϩ ¹Cl2 (2)
¯
²
be less appropriate with regard to their syntheses from ReCl5
and nitrogen trichloride and chlorine azide, respectively.1,5 The
reaction of [ReCl4(NSCl)(POCl3)] with AsPh4Cl [equation (3)]
Results and Discussion
Tetrachloronitridorhenate() can be prepared in good yields
in a single-pot synthesis from tetrabutylammonium perrhenate,
HCl gas and sodium azide. The synthesis follows a general
route for the preparation of tetrahalogenonitridometalates10,11
and has also been applied for the lighter equivalent of rhenium.
Baldas et al.15 demonstrated that [TcNCl4]Ϫ and [TcNBr4]Ϫ can
be prepared from pertechnetate and sodium azide in excellent
yields even in hot aqueous HCl or HBr without any hydrolysis.
The anionic complexes can easily be precipitated with bulky
cations. When the same protocol is applied to rhenium, a mix-
ture of mainly rhenium-() and -() compounds is obtained
and [ReNCl4]Ϫ is only formed as a minor side-product. To
increase the amount of the nitrido complex it is necessary to
keep the temperature of the reaction mixture low and to add
several small portions of azide rather than one big amount.
When the reaction is interrupted after addition of the first
[ReCl4(NSCl)(POCl3)] ϩ AsPh4Cl →
[AsPh4][ReNCl4] ϩ POCl3 ϩ SCl2 (3)
avoids the use of these vigorous reagents, but the rhenium
starting material has to be prepared in a multistep synthesis
from ReCl5 and trithiazyl chloride (SNCl)3.6–8 Therefore, com-
monly the triphenylphosphine complex [ReNCl2(Ph3P)2], which
can be prepared in good yields from [ReOCl3(Ph3P)3] and
phenylhydrazine9 or from perrhenate, aqueous HCl, NaN3 and
Ph3P,† is used as precursor for the synthesis of nitridorhenium
compounds.10–14 However, the presence of Ph3P in the co-
† The synthesis of [ReNCl2(Ph3P)2] via the reaction ReO4Ϫ ϩ N3Ϫ ϩ
HCl(aq) ϩ Ph3P ϩ EtOH → [ReNCl2(Ph3P)2] was suggested by one
of the referees and works well.
J. Chem. Soc., Dalton Trans., 1998, Pages 231–238
231

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Ϫ
portion of azide considerable amounts of ReO4 and
[ReOCl4]Ϫ are observed.
The mechanism of the reaction is not completely clear. The
assumption in ref. 15 that the [MNX4]Ϫ anions are finally
formed via a metal() transition state is sound with regard to
the fact that the formation of a nitrido function from a co-
ordinated azide requires a two-electron oxidation of the metal.
Attempts to isolate [TcNCl4]Ϫ or [ReNCl4]Ϫ from isolated hexa-
chlorometalates(), however, gave unsatisfactory results with
only small amounts of impure technetium() or rhenium()
complexes.16 On the other hand, tetrachloronitridotechne-
tate() can be isolated in good yields from [TcOCl4]Ϫ (refs. 17
and 18) which is the product of the reaction of TcO4Ϫ with HCl
at ambient temperature. This suggests an intermediate form-
ation of the unstable technetium() nitrido compound which
is rapidly reduced by ClϪ to give the very stable TcVIN core. It is
the extraordinary stability of the TcN core (which even resists
an aqueous hydrolysis19 or reactions with H2O2 20,21) which
makes the one-step synthesis of [TcNCl4]Ϫ possible. For the syn-
thesis of pure [ReNCl4]Ϫ, however, several portions of azide must
be added subsequently. Obviously, the intermediately formed
rhenium() compound (ReNCl4 or [ReNCl5]Ϫ) is less resistant
to acidic hydrolysis than its technetium analogue and/or the
higher reduction potential of ReVII prevents a rapid reduction
to ReVI and prefers hydrolysis. Thus, considerable amounts of
perrhenate are reformed which react with the HCl gas to give
[ReOCl4]Ϫ and, thus, are transferred back to the formation of
the nitrido complex when more azide is provided. Usually, three
additions of sodium azide are sufficient to obtain [NBu4]-
[ReNCl4] in good yields and high purity. The absence of the
Fig. 1 Molecular structure of the complex anion in [NBu4][ReNCl4]
together with the bond lengths and angles [symmetry codes (Ј) 0.5 Ϫ y,
x, z; (Љ) 0.5 Ϫ x, 0.5 Ϫ y, z; (ٞ) 0.5 Ϫ x, 0.5 Ϫ y, z]. The thermal ellip-
soids represent 50% probability23
possible impurities [NBu4][ReO4] and [NBu4][ReOCl4] can
᎐
easily be checked by IR spectroscopy. The ν(Re᎐N) vibration at
᎐
1103 cmϪ1 is well separated from the regions where the Re᎐O
᎐
Ϫ
frequencies of [ReOCl4]Ϫ (1033 cmϪ1) and ReO4 (913 cmϪ1
)
can be detected.
The caesium salt Cs2[ReNCl5] precipitates on addition of
CsCl to the reaction mixture described above. The complex
anion is six-co-ordinate. This is in accordance with the situation
in other oxo- or nitrido-metalates with halide ligands, where
with alkali-metal cations preferably [MYX5]2Ϫ anions (Y = N or
O, X = Cl or Br) are precipitated from solutions which contain
excess of XϪ, whereas [MYX4]Ϫ or [MYX4(solv)]Ϫ are preferred
with large organic cations.22 The compound Cs2[ReNCl5] is a
yellow solid which is stable in air, but more sensitive to
᎐
hydrolysis than the tetrabutylammonium salt. The Re᎐N fre-
᎐
quency of the six-co-ordinate compound is found at 1053 cmϪ1
.
The use of Cs2[ReNCl5] for ligand exchange is particularly
useful when strong ligands are used and water is required as
solvent.
Sodium azide can be replaced by SiMe3N3 in the formation
of [NBu4][ReNCl4]. This allows one to work in dichloro-
methane. Using this approach the reformation of ReO4Ϫ can be
minimized by careful drying of the solvent. The overall yield
of the nitrido complex, however, is less than when using several
portions of sodium azide.
Fig. 2 (a) Experimental X-band EPR spectrum of [AsPh4]2[ReN-
(NCS)5] in CH2Cl2, T = 130 K. (b) Simulated spectrum
Rhenium() compounds of the type [ReNX4(5)]
Ϫ,2Ϫ (X = Cl,
Br or NCS) are favoured for EPR studies because of their 5d1
(S = ¹) configuration. The spectra of the parent complexes
¯
²
The compound [NBu4][ReNCl4] is air-stable and does not
hydrolyse under ambient conditions. In water, however, a black-
brown, insoluble solid is rapidly formed. When this product is
treated with HCl or SOCl2 only a few percent can be retrans-
ferred to [ReNCl4]Ϫ. The same can be observed during the
hydrolysis of Cs2[ReNCl5] which undergoes disproportionation
[ReNCl4(5)
]
Ϫ,2Ϫ and [ReNBr4]Ϫ are known.24,25 As found for the
Ϫ,2Ϫ
nitridorhenium compounds [ReNX4(5)
]
(X = Cl or Br) the
[ReN(NCS)5]2Ϫ species gives a well resolved room-temperature
X-band EPR spectrum consisting of six 185,187Re hyperfine
structure (h.f.s.) lines. This sextet arises from the interaction of
the unpaired electron with the nuclear spin of both rhenium
Ϫ
5
isotopes 185Re and 187Re (IRe = ; natural abundance 185Re 37.4%
–
to ReO4 and insoluble rhenium() species when treated with
2
water.
and 187Re 62.6%). The frozen-solution EPR spectrum of
The compound [NBu4][ReNCl4] crystallises in the tetragonal
space group P4/n and the anion (see Fig. 1) shows the expected
C4v symmetry. The Re᎐N and Re᎐Cl bond lengths of 1.612(8)
and 2.323(1) Å are the same as observed in the tetraphenyl-
arsonium salt.2 The Re᎐N distance is consistent with a
rhenium–nitrogen triple bond. There are no exceptional bond-
ing features for the tetrabutylammonium cation.
[AsPh4]2[ReN(NCS)5] and its simulation are reproduced in Fig.
2. This spectrum shows a typical axially symmetric pattern with
six 185,187Re h.f.s. lines in the parallel and the perpendicular
part. For the spectrum at T = 130 K as well as for the room-
temperature spectrum, ligand h.f.s. splittings were not resolved
because of the comparatively large linewidth of ∆Bpp = 9–19
mT. Owing to the magnitude of the 185,187Re h.f.s. coupling
232
J. Chem. Soc., Dalton Trans., 1998, Pages 231–238

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Table 1 Experimentally obtaineda and calculatedb EPR parameters
(g0, g||, a0 and A ) for [ReNBr4ϪpClp]Ϫ mixed-ligand complexes.
Re
Re
||
Hyperfine couplings are given in 10Ϫ4 cmϪ1; solvent CH2Cl2 (T = 295 K)
or MeCN (T = 130 K)
Re
g0
a0
Compound
Found
Calculated
Found
Calculated
[ReNBr4]Ϫ
2.005
1.984
1.962
1.944
1.924
2.005
1.984
1.964
1.944
1.924
447
461
483
494
513
447
464
480
497
513
[ReNBr3Cl]Ϫ
[ReNBr2Cl2]Ϫ
[ReNBrCl3]Ϫ
[ReNCl4]Ϫ
Re
g||
A
||
Found
Calculated
Found
Calculated
[ReNBr4]Ϫ
2.069
2.034
1.994
1.944
1.908
2.069
2.029
1.988
1.948
1.908
665
695
721
744
768
665
694
720
745
768
[ReNBr3Cl]Ϫ
[ReNBr2Cl2]Ϫ
[ReNBrCl3]Ϫ
[ReNCl4]Ϫ
a Experimental error: g0, g|| 0.003; a0Re, A
3. b By using y([ReN-
Re
||
Ϫ
Ϫ
Ϫ
1
–
Br4ϪpClp] ) = 4{(4 Ϫ p)y([ReNBr4] ) ϩ py([ReNCl4] )} with y = g0,
g||, a0Re or A
.
Re
||
Fig. 4 (a) Experimental X-band EPR spectrum of [ReNBr4ϪpClp]Ϫ
(p = 0–4) complexes in MeCN, T = 130 K. In the high-field region of
the parallel part all three mixed-ligand species and the parent com-
pounds are detected. (b) Simulated spectrum
As mentioned above the room-temperature EPR spectra
of [ReNCl4]Ϫ and [ReNBr4]Ϫ consist of six h.f.s. lines. In the
spectra of [ReNCl4]Ϫ–[ReNBr4]Ϫ mixtures in addition to the
signals of the parent compounds there are several new signals
which indicate the formation of mixed-ligand complexes of the
type [ReNBr4ϪpClp]Ϫ with p = 1–3. A typical spectrum revealing
the formation of ReVIN mixed-ligand complexes is shown in
Fig. 3. In contrast to the EPR investigation of the ligand-
exchange reaction on the related nitridotechnetium compounds
5
[TcNX4]Ϫ (X = C or Br),26 only the high-field line (mIRe = ) is
–
2
clearly split. Owing to the comparatively large linewidth of
∆Bpp ≈ 7 mT for the remaining lines, the signals of the indi-
vidual complexes nearly coincide, which complicates the spec-
tral analysis. Therefore, the EPR parameters of the individual
spectra were obtained by simulation. They are listed in Table 1
together with the values of their parent compounds.
In frozen-solution spectra of [ReNCl4]Ϫ–[ReNBr4]Ϫ mix-
tures, in addition to the signals of the parent complexes, new
signals are to be seen in the high-field region of the parallel part
which must be attributed to rhenium() mixed-ligand species
as found in the liquid-solution spectra. A typical spectrum is
shown in Fig. 4. The perpendicular part of the spectrum is very
Fig. 3 (a) Experimental X-band EPR spectrum of [ReNBr4ϪpClp]Ϫ
(p = 0–4) complexes in CH2Cl2, T = 295 K. The well resolved high-field
5
line (mIRe = ϩ2) shows the presence of all three possible mixed-ligand
–
species and the parent compounds. (b) Simulated spectrum
constants and the nuclear quadrupole moments in both cases
the equidistance of the h.f.s. lines is disturbed.
complex due to many overlappings; therefore, no attempts have
Re
been made to derive the parameters g⊥ and A⊥Re. The g|| and A
Rhenium() compounds of the general formula
||
[ReNX4(5)
Hamiltonian (4). All symbols have their usual meanings. The
]
Ϫ,2Ϫ (X = Cl, Br or NCS) can be described by the spin
of the parallel part of the spectra are listed also in Table 1.
Ligand h.f.s. due to the interaction of the unpaired electron
with the 35.37Cl, 79,81Br and 14N nuclei were not resolved.
Hsp = gؒµBؒSؒB0 ϩ SؒAReؒIRe ϩ IReؒQReؒIRe
(4)
The investigation of ligand-exchange reactions by means
of EPR spectroscopy requires knowledge about the dependence
of the EPR parameters on the type (composition, symmetry)
of the co-ordination sphere. Extensive investigations have
been made e.g. for the d1 systems CrO3ϩ, MoO3ϩ, WO3ϩ, VO2ϩ
and on related nitridotechnetium() compounds of general
formula [TcNX4]Ϫ (X = Cl or Br).26,27 According to the study on
the TcVIN complexes, a nearly linear dependence of the EPR
obtained principal values of the g tensors and the 185,187Re h.f.s.
tensors ARe for [AsPh4]2[ReN(NCS)5] are g|| = 1.817, g⊥ = 1.958,
gav = 1.911, A = 681.1 × 10Ϫ4 cmϪ1, A⊥Re = 379.1 × 10Ϫ4 cmϪ1
Re
||
Re
Re
and AavRe = 479.9 × 10Ϫ4 cmϪ1 (g||, g⊥ 0.003; A , A⊥
||
3.0 × 10Ϫ4 cmϪ1). The values for [NBu4][ReNCl4] and [NBu4]-
[ReNBr4] are summarized in Table 1.
J. Chem. Soc., Dalton Trans., 1998, Pages 231–238
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Fig. 5 Dependence of g0, g||, a0Re and A of [ReNBr4ϪpClp]Ϫ (p = 0–4)
Re
||
1
–
species on the effective spin–orbit coupling λL = 4[(4 Ϫ p)λBr ϩ pλCl].
λCl = 586 cmϪ1 and λBr = 2460 cmϪ1
Fig. 6 Molecular structure of [ReN(Hdetcb)2] along with the atomic
Re
spectral quantities, g0, g||, a0Re and A on the ‘heaviness’ of the
numbering scheme (thermal ellipsoids represent 50% probability)23
||
first co-ordination sphere is expected. This can be defined for
the present [ReNBr4ϪpClp]Ϫ complexes with p = 0–4 as in
equation (5) where λCl, λBr and λRe are the spin–orbit coupling
constants of chlorine, bromine and rhenium, respectively.
Ϫ
and diethyldithiocarbamate (S2CNEt2
) which gave the
previously reported rhenium() complexes [ReNCl2(Ph3P)2],
[ReNCl2(Me2PhP)3] and [ReN(S2CNEt2)2],31 we attempted reac-
tions with N2-diethylthiocarbamoylbenzamidine (H2detcb) and
sodium 1,2-dicyanoethene-1,2-dithiolate (Na2mnt). Our recent
attempts to isolate crystalline samples of [ReN(Hdetcb)2]
and [ReN(mnt)2]2Ϫ from reactions of [ReNCl2(Ph3P)2] or
[ReNCl2(Me2PhP)3] failed. In the former case only oily prod-
ucts were obtained and in the latter case the ligand exchange
stopped at the stages [ReN(Cl)(Me2PhP)2(Hdetcb)]32 and
[ReN(Me2PhP)2(mnt)],33 respectively. The structures of both
products have been solved.32,34 With [NBu4][ReNCl4], however,
[ReN(Hdetcb)2] and [NBu4]2[ReN(mnt)2] could be easily iso-
lated and structurally characterized.
Re
g0, g||, a0Re, A|| ≈ λL/λRe = [pλCl ϩ (4 Ϫ p)λBr]/λRe (5)
1
4
–
The proportionality [equation (5)] holds true if there are no
significant differences concerning the structure and bonding
properties of the complexes considered. Thus, if the g values
and the h.f.s. coupling parameters ARe of the parent complexes
Re
Re
are known the g0, g||, a0 and A values of the mixed-ligand
||
complexes can be estimated simply by using the ‘additivity rule’
Re
Re
given in equation (6), with y = g0, g||, a0 or A . In Table 1
||
Ϫ
Ϫ
1
–
y = ([ReNBr4ϪpClp] ) = 4{(4 Ϫ p)y([ReNBr4] ) ϩ
py([ReNCl4]Ϫ)} (6)
Et
NaS
CN
CN
C
C
N
N
Re
Re
the g0, g||, a0 and A values estimated for [ReNBr4ϪpClp]Ϫ
||
Et
C
S
C
mixed-ligand complexes with p = 1–3 according to equation
(6) are compared with the experimentally derived ones. It can
be seen that the experimental values are well reproduced by
equation (6). Fig. 5 illustrates the nearly linear dependence of
the observed EPR quantities of the [ReNBr4ϪpClp]Ϫ complexes
with p = 0–4 on the composition of the first co-ordination
sphere.
It should be noted that in solution the co-ordination of a
sixth ligand X (X = Cl, Br or solvent) in trans position to the
nitrogen may occur. However, according to several studies
made on other d1 systems the influence of a trans-co-ordinated
ligand in the species of general formula [ReNBr4ϪpClpX]Ϫ
(X = Cl, Br or solvent) with p = 0–4 should be vanishingly
small.26,27
The EPR spectroscopically detected ligand exchange demon-
strates that [ReNCl4]Ϫ is a suitable starting material for the syn-
thesis of rhenium nitrido complexes. The oxidation state ‘ϩ6’ is
maintained during the reaction with halides and NCSϪ. With
excess of organic ligands reduction to rhenium() complexes
can be observed. The previously reported formation of the
rhenium() species with co-ordinated Ph3P, bipyridine (bipy)
and pyridine (py)28 obviously results from the very mild condi-
tions applied and is in good agreement with our observations
that rhenium() species with co-ordinated organic ligands can
also be detected by EPR spectroscopy when an only small
excess of ligand is used. Similar observations could be made for
technetium, where the crystal structure of [TcNCl3(bipy)]29 has
been elucidated and EPR spectra of technetium() species with
co-ordinated Ph3P and Ph3As ligands have been reported.30
Besides of reactions of [NBu4][ReNCl4] with Ph3P, Me2PhP
NH2
NaS
H2detcb
Na2mnt
The compound [ReN(Hdetcb)2] is an orange-red solid which
crystallizes directly from [ReNCl4]Ϫ–H2detcb–Et3N reaction
mixtures. It is readily soluble in CHCl3 and CH2Cl2, but only
slightly soluble in alcohols. The NMR and mass spectra are
in agreement with the formulation of a five-co-ordinate
rhenium() complex with two HdetcbϪ ligands. This is con-
firmed by the crystal structure. Fig. 6 shows an ellipsoid repre-
sentation of the molecular structure along with the atomic
labeling scheme. Selected bond lengths and angles are con-
tained in Table 2. The rhenium atom has a distorted square-
pyramidal co-ordination sphere with the nitrido nitrogen at the
apical position. The metal is displaced by 0.511(3) Å from the
basal plane which is formed by the donor atoms of the chelat-
ing ligands. In accordance with other rhenium nitrido com-
plexes, the Re᎐N bond is short [1.657(4) Å]. Almost equal
᎐
᎐
lengths (≈1.33 Å) are observed for all C᎐N bonds in the chelate
ring systems. This also includes the C᎐N bonds between the
diethylamino substituents and the chelate rings [C(1)᎐N(3)
1.343(7), C(22)᎐N(6) 1.344(6) Å], indicating a noticeable devi-
ation from a normal single C᎐N bond length of the latter and
the presence of an extended conjugated π system.
The bond lengths of the equatorial donors are longer by a
mean value of about 0.05 Å compared with the situation in the
corresponding cationic oxo complex [ReO(Hdetcb)2]ϩ.35 In
both compounds the thiocarbamoylbenzamidinates are cis co-
ordinated. The same has been found previously for the corre-
234
J. Chem. Soc., Dalton Trans., 1998, Pages 231–238