Synthesis and crystal structure of the 16 e- cationic tungsten(IV) complex [WCp*(4,4′-Me2bipy)Cl2]+BPh 4-

Article abstract of DOI:10.1039/a902743b

A general synthetic route to electron rich half-sandwich tungsten(IV) complexes with a series of 4,4′-disubstituted 2,2′-bipyridyl (R₂bipy) donor ligands of the type [W^IVCp*(R₂bipy)Cl₃] has been elaborated. The crystal structure and conductivity measurements of the R = methyl derivative evidenced quite weak bonding of the chloride ligands in these complexes. This propensity has been utilized to prepare the novel square pyramidal, 16e^- Lewis acid [WCp*(Me₂bipy)Cl₂]⁺BPh₄ ^- through halide abstraction from [WCp*(Me₂bipy)Cl₃] with NaBPh₄. The crystal structures of the cationic complex and its 18e^- CO adduct [WCp*(Me₂bipy)(CO)Cl₂]⁺BPh ₄^- obtained through carbon monoxide addition to the former have been determined.

Full text of DOI:10.1039/a902743b

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Synthesis and crystal structure of the 16 e؊ cationic tungsten(IV)
؊
complex [WCp*(4,4Ј-Me2bipy)Cl2]؉BPh4 †
Christian Cremer and Peter Burger*
Anorganisch-chemisches Institut der Universität Zürich, Winterthurerstr. 190, 8057 Zürich,
Switzerland. E-mail: chburger@aci.unizh.ch
Received 16th December 1998, Accepted 23rd April 1999
A general synthetic route to electron rich half-sandwich tungsten() complexes with a series of 4,4Ј-disubstituted
2,2Ј-bipyridyl (R2bipy) donor ligands of the type [WIVCp*(R2bipy)Cl3] has been elaborated. The crystal structure
and conductivity measurements of the R = methyl derivative evidenced quite weak bonding of the chloride ligands
in these complexes. This propensity has been utilized to prepare the novel square pyramidal, 16eϪ Lewis acid
[WCp*(Me2bipy)Cl2]ϩBPh4Ϫ through halide abstraction from [WCp*(Me2bipy)Cl3] with NaBPh4. The crystal
structures of the cationic complex and its 18eϪ CO adduct [WCp*(Me2bipy)(CO)Cl2]ϩBPh4Ϫ obtained through
carbon monoxide addition to the former have been determined.
Lewis acid obtained from it through halide abstraction, i.e.
Introduction
[WCp*(Me2bipy)Cl2]ϩ, will be reported.
The chemistry of monocyclopentadienyl (Cp) transition metal
halide complexes is in general well developed and has quite
recently been reviewed by Poli.1 His group has largely con-
tributed to and in particular extended the chemistry of half-
sandwich Cp molybdenum complexes in higher oxidation
Results and discussion
Since the synthesis, isolation, electronic and magnetic prop-
erties of [(WCp*Cl3)2] 1 will be described in some detail in a
forthcoming publication, we will just briefly review some
aspects of its preparation. Compound 1 can be obtained
according to eqn. (1) by one-electron reduction through careful
states, i.e. MoIV–VI 2–8
For the higher tungsten homologue there
.
have been numerous publications from the groups of Schrock
and Green mostly dedicated to tungsten in its WIII,V,VI oxidation
state.1,9–17 The latter compounds have frequently been obtained
from the very versatile and readily available starting materials
[W(CpR)Cp*Cl4].1,9–19
On the other hand, little was known about tungsten() half-
sandwich complexes when we started to work in this area.20–25
To the best of our knowledge, the single electron reduction of
[W(CpR)Cp*Cl4] to yield “[W(CpR)Cp*Cl3]” had so far not
been carried out with success; Schrock et al.17 have even pro-
vided some limited evidence that “[WCp*Cl3]” might undergo
disproportionation to tungsten-() and -() species. Related
redox chemistry of the PMe3 adduct of [WCp*Cl4], [WCp*-
Cl4(PMe3)], in the presence of phosphine donors has recently
been described by Baker et al.23 It is noteworthy that the corre-
sponding molybdenum() complex “[MoCp*Cl3]” has very
recently been prepared by Poli and co-workers4 by a one-
electron reductive route from [MoCp*Cl4]. The crystal structure
analysis showed that the molybdenum() compound is actually
a doubly µ-chloride bridged dimer, i.e. [{MoCp*Cl2(µ-Cl)}2],
which can be cleaved to monomeric complexes by addition of
phosphine ligands.4
In the search for a route to electron rich half-sandwich tung-
sten() complexes with a series of 4,4Ј-disubstituted 2,2Ј-bipyr-
idyl (R2bipy) donor ligands of the type [WIVCp*(R2bipy)Cl3] the
aforementioned route for molybdenum seemed attractive since
a common starting material, i.e. “[WCp*Cl3]”, could be used in
these syntheses. We have hence turned to the synthesis of this
material from [WCp*Cl4] under reductive conditions and have
briefly reported on its preparation and dimeric crystal structure
in a recent communication.26 In this publication, we will present
a general route to [WIVCp*(R2bipy)Cl3] complexes from this
hitherto unknown starting material. The crystal structures of
the 4,4Ј-dimethylbipyridyl representative and the cationic 16eϪ
controlled addition of NaHg to [WCp*Cl4] in toluene, to avoid
formation of [(WCp*Cl2)2]. However, the isolation of pure com-
pound 1 from this reaction mixture is rather cumbersome
owing to its extremely high air-sensitivity and limited solu-
bility in innocent solvents, such as toluene, which have to be
used to prevent decomposition. We have therefore prepared
complexes 2-R from compound 1 generated in situ according to
eqn. (2). Preferably, 1/2 equivalent of the mild reducing agent,
the electron rich tetrakis(dimethylamino) substituted olefin,
(NMe ) C᎐C(NMe ) (TDAE), is used in this reaction.
᎐
2
2
2 2
Complexes 2-R were prepared by this route in good to
excellent yields as microcrystalline materials; depending on the
bipyridyl substituent R their colours vary from yellow to dark
violet (see Experimental section). Although the quite low
solubility of most compounds posed some problems to their
† Monocyclopentadienyl complexes. Part 1.
J. Chem. Soc., Dalton Trans., 1999, 1967–1974
1967

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isolation pure, we have obtained correct elemental analysis data
for all novel complexes 2-R shown in eqn. (2).
The related Cp molybdenum complex to 2-R, [MoCp-
(bipy)Br3], had been reported by Haines et al.27 some years ago
and has been prepared through thermal decarbonylation of the
dicarbonyl starting material, [MoCp(CO)2Br3], in the presence
of the N-donor. Owing to the low solubility, however, this
compound has been characterized only by elemental analysis.
Adaptation of this synthesis for the tungsten analogues
required [WCp*(CO)2Cl3], which just recently has become
available.24 The compound 2-Me could be prepared according
to this route in reasonable yield, eqn. (2).
It should be noted that the reductive pathway shown in
eqn. (2) is clearly superior to the latter preparation, since
isolation from carbonyl containing by-products is not required,
higher overall yields are obtained and the more readily available
starting material [WCp*Cl4] can be utilized.
structure of complexes 2-R unambiguously, we have therefore
performed a crystal structure analysis of the methyl derivative
2-Me.
Crystal structure of complex 2Et-Me
Analytically pure compounds 2-R are weakly paramagnetic
Although the collected data for complex 2-Me allowed us to
establish clearly the geometric arrangement around the tung-
sten centre as the facial isomer a, disorder in the Cp* rings led
to severe problems with the data refinement. We have therefore
prepared and collected a crystal data set for the ethyltetra-
methyl analogue [W(C5Me4Et)(Me2bipy)Cl3] 2Et-Me. This small
variation allowed us to obtain better data and to solve and
refine the molecular structure of 2Et-Me which is presented in
Fig. 1. Selected bond distances and angles are given in Table 1.
Although the W central atom in complex 2Et-Me is formally
eight-co-ordinate, the structure is described better in terms of a
pseudo-octahedral geometry with the ethyltetramethylcyclo-
pentadienyl (C5Me4Et) ligand occupying one co-ordination site.
The equatorial plane then includes the nitrogen atoms of the
4,4Ј-dimethylbipyridyl (N1, N2) and the Cl ligands, Cl1 and
Cl2. This is best illustrated through the Cl3–W1–Z1 angle of
174.8Њ (Z1 = ring centroid). Notably, we observed significant
variations in the W–CCp bond lengths (Table 1) which are in the
range of 2.244(9) to 2.453(8) Å. Distortions of this type have
been observed by Poli and co-workers6 in the crystal structures
of Cp molybdenum complexes and have been interpreted in
electronic terms, i.e. W–Cp δ bonding.31 Since additional bend-
ing of the Cp-ring substituents out of the cyclopentadienyl ring
plane away from the metal centre is observed, we anticipate
that steric congestion at the metal centre is also contributing.
However, by comparison with tungsten–chlorine bonds in other
18 eϪ tungsten complexes,32 the most prominent feature of this
with magnetic moments, µeff, of 0.5–0.8 µB at RT. This explains
1
the broad lines observed in the H NMR spectra and leads in
most cases to unresolved H–H coupling due to line broadening
of the bipyridyl resonances. It is interesting, however, that the
1
chemical shifts of the bipyridyl and the Cp* methyl H NMR
resonances are still in the expected range for the presumed
diamagnetic complexes. The measurement of 13C NMR spectra
was limited to the tert-butyl substituted complex 2-tBu owing to
the very low solubilities of the other complexes 2-R. However,
even at 10Ϫ1 M concentration of 2-tBu in CD2Cl2 at 75.1 MHz
and using polarization transfer techniques, we could merely
detect the rather broad resonance of the peripheral tert-butyl
methyl groups. Hence, although the NMR data allowed only
1
limited structural assignments, the H NMR spectra provided
evidence for Cs symmetry in complexes 2-R. The chemical
equivalence of the equivalent positions in the bipyridyl rings
suggested that of two possible isomers (mer and fac) for 2-R
shown, only the facial isomer a was present in solution.
This was also in accordance with steric arguments, since an
energetically less favourable structure for the meridional isomer
b was anticipated due to steric repulsion between the Cp*
and one of the bipyridyl rings. It deserves special mention,
however, that in the cyclopentadienyl molybdenum series, i.e.
for complexes of the type [MoCpL2X3] where L is a mono- or
bi-dentate phosphine donor and X = halide, both types of
isomers a, b have been observed.5,8,28,29 In order to establish the
1968
J. Chem. Soc., Dalton Trans., 1999, 1967–1974

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Fig. 2 Concentration dependent molar conductivity of complex 2-Me
in dichloromethane.
Fig. 1 An ORTEP30 plot of complex 2Et-Me (ellipsoids are at the 50%
probability level).
Table 1 Selected bond distances (Å) and angles (Њ) with estimated
standard deviations (e.s.d.s) for complex 2Et-Me
W1–Cl1
W1–Cl3
W1–N2
W1–C2
W1–C4
W1–Z1a
2.487(2)
2.534(7)
2.164(7)
2.453(8)
2.244(9)
2.20
W1–Cl2
W1–N1
W1–C1
W1–C3
W1–C5
2.470(2)
2.163(7)
2.436(8)
2.345(9)
2.307(8)
1.423(12)
C–C (Cp*)av
Cl1–W1–Cl2
Cl2–W1–Cl3
Cl1–W1–N2
Cl3–W1–N1
Cl3–W1–N1
N1–W1–N2
Cl2–W1–Z1
N1–W1–Z1
85.7(1)
77.7(1)
92.8(2)
74.4(2)
74.4(2)
75.8(3)
106.5
Cl1–W1–Cl3
Cl1–W1–N1
Cl2–W1–N1
Cl3–W1–N2
Cl3–W1–N2
Cl1–W1–Z1
Cl3–W1–Z1
N2–W1–Z1
76.7(1)
151.0(2)
91.1(2)
72.5(2)
72.5(2)
106.3
174.8
103.0
102.3
a Z1 is the midpoint of carbon atoms C1 to C5.
trichloro complex is the rather long W–Cl bond distances [W1–
Cl1 2.487(2), W1–Cl2 2.470(2) Å] with the Cl ligand Cl3 in
“trans” position to the C5Me4Et group having an even 5 pm
longer W–Cl bond [W1–Cl3 2.534(7) Å]. Considering the
pronounced elongation of the W–Cl bonds, we anticipated that
facile ionization of the unique Cl3 ligand might occur in solu-
tion and have hence turned to conductivity measurements
which are described in the next paragraph.
Synthesis of the cationic complexes 3-R
We had anticipated that the cationic complexes 3-R might be
directly obtained from compounds 2-R by addition of NaX
Ϫ
Ϫ
salts, where X = BPh4 , PF6Ϫ or SbF6 , forcing the equilibrium
(3) to the right through formation of insoluble sodium chloride,
eqn. (4). Upon addition of NaBPh4 to a violet solution of 2-Me
in dichloromethane according to eqn. (4) indeed an immediate
change to dark green was noticed. From the reaction mixture,
the cationic complex 3-Me could be isolated as an analytically
pure microcrystalline green solid in excellent yields. Conduc-
Conductivity measurements
Ionization of one of the Cl ligands would lead to the equi-
librium (3). The results of a concentration dependent molar
tivity measurements in dichloromethane at 10Ϫ3 and 10Ϫ4
M
[WCp*(R2bipy)Cl3]
[WCp*(R2bipy)Cl2]ϩ ϩ ClϪ (3)
gave molar conductivity values of 32 and 58 S cm2 molϪ1. This
clearly evidenced that 3-Me was a 1:1 electrolyte consistent
with the description as a formal 16-electron complex. The
NMR characterization was difficult due to the observed para-
magnetism (µeff = 2.18 µB at RT), which gives rise to broad and
conductivity study for 2-Me in CH2Cl2 solution presented in
Fig. 2 clearly established that 2-Me is only partially dissociated
at 10Ϫ3 M concentration (Λm = 1.4 S cm2 molϪ1, c = 10Ϫ3 M) and
therefore is not a 1:1 electrolyte. However, in full agreement
with the equilibrium (3), complex 2-Me behaves as an iono-
phore33 and is completely dissociated at low concentrations
(c < 10Ϫ5 M, Λm = 32 S cm2 molϪ1 at 5 × 10Ϫ6 M). The outcome
of these measurements suggested that the cationic complexes
[WCp*(R2bipy)Cl2]ϩ had indeed some inherent stability. Owing
to the latter considerations and, also, since these cations were
deemed synthetically valuable Lewis acids, we made efforts to
establish the synthetic access to this type of compounds.
1
strongly shifted, temperature dependent H NMR resonances.
Since the NMR spectroscopy allowed little structural assign-
ment, we have performed a single crystal X-ray diffraction
study to establish the molecular structure of 3-Me.
Crystal structure of complex 3-Me
Attempts to grow suitable single crystals of the cationic com-
plexes were rather cumbersome and only successful for the
J. Chem. Soc., Dalton Trans., 1999, 1967–1974
1969

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chemistry. Even under very careful conditions, i.e. using high
vacuum and dry-box techniques and thoroughly dried solvents,
the formation of the violet, diamagnetic, dinuclear µ-oxo, bis-µ-
Cl bridged complex, [{WCp*(Me2bipy)}2(µ-O)(µ-Cl)2]2ϩ 4,35
was noticed in the presence of even trace amounts of water. So
far, we were therefore restricted to reactions which proved to be
sufficiently fast to intercept the irreversible formation of the
undesired hydrolysed product 4. The CO addition to complex
3-Me, which quite surprisingly is only moderately fast and
complete within 45 min at RT, fulfils this requirement and gives
the cationic carbonyl complex 5-Me in excellent yield, eqn. (5).
Ϫ
Fig. 3 Molecular structure of the cationic complex 3-Me; the BPh4
counter ion has been omitted for clarity (ellipsoids are at the 50% prob-
ability level).
Table 2 Selected bond distances (Å) and angles (Њ) with e.s.d.s for
complex 3-Me
W1–Cl1
W1–N1
W1–C1
W1–C3
W1–C5
2.355(1)
2.134(3)
2.305(4)
2.334(4)
2.372(3)
1.408(5)
W1–Cl2
W1–N2
W1–C2
W1–C4
W1–Z1a
2.366(1)
2.143(2)
2.302(3)
2.405(4)
2.02
C–C (Cp*)av
Cl1–W1–Cl2
Cl1–W1–N2
Cl2–W1–N2
Cl1–W1–Z1
N1–W1–Z1
83.1(4)
85.0(1)
132.8(1)
110.7
Cl1–W1–N1
Cl2–W1–N1
N1–W1–N2
Cl2–W1–Z1
N2–W1–Z1
135.7(1)
83.9(8)
73.6(1)
113.7
113.4
113.3
a Z1 is the midpoint of carbon atoms C1 to C5.
In contrast to the other mononuclear tungsten() complexes
described herein, the carbonyl complex 5-Me is diamagnetic, as
BPh4Ϫ salt, [WCp*(Me2bipy)Cl2]ϩBPh4Ϫ 3-Me. Thecrystalstruc-
ture of this complex is presented in Fig. 3; selected distances
and angles are given in Table 2.
1
evidenced through sharp well resolved H and 13C NMR spec-
tra. This quite likely reflects the larger ligand field splitting due
1
to the carbonyl ligand. The inequivalence of the H and 13C
The shortest contact between the BPh4Ϫ counter ion and the
W atom is 4.7 Å which suggests that there is just coulombic
interaction between the cationic metal complex and the anion.
A formal 16-electron configuration can therefore be ascribed
to 3-Me. The complex adopts a square pyramidal structure,
i.e. a four-legged piano stool structure, which is corroborated
through the angles at the tungsten centre between the Cp* cen-
troid, Z1, and the bipyridyl and chloride ligands (Cl1–W1–Z1
110.7; Cl2–W1–Z1 113.7; N1–W1–Z1 113.4; N2–W1–Z1
113.3Њ). The bipyridyl donor and the chloride ligands form the
basal ligands; the tungsten centre is located 0.087 Å above the
basal plane. As expected, the tungsten–chloride bonds W1–Cl1
2.355(1) and W1–Cl2 2.366(1) Å in the cationic complex are
significantly shorter than in the corresponding trichloro com-
plex 2-Me suggesting π donation of the chloride ligands to the
Lewis acidic tungsten centre. In addition, stronger donation
from the Cp* ring to the metal centre is implied through the
shorter Cp*centroid–W distance (3-Me: W1–Z1 2.02 vs. 2.20 Å
in 2-Me). Overall, the structural parameters of complex 3-Me
strongly resemble those reported by Poli34 for the afore-
mentioned cationic molybdenum [MoCp(PMe3)2Cl2]ϩ complex,
which also displays a square pyramidal structure.
NMR resonances of the equivalent positions in the bipyridyl
rings immediately allowed us to establish that 5-Me no longer
possessed Cs symmetry. This clearly evidenced that the CO
ligand was not incorporated into the vacant co-ordination site
of the square-pyramidal complex, i.e. trans to the Cp* ring, but
rather was co-ordinated in the equatorial plane of the pseudo-
octahedral complex. The IR spectrum displays a single stretch-
ing frequency at ν(CO) 2004 cmϪ1 in the carbonyl range, which
suggests sizeable back donation from the metal centre to the
CO ligand and also rules out the presence of another isomer in
solution. The spectroscopic assignment was confirmed later by
the results of a crystal structure analysis (Fig. 4); selected bond
lengths and angles in Table 3.
Crystal structure investigation of complex 5-Me
Despite some minor crystallographic problems due to pos-
itional disorder of the equatorial CO and Cl ligands (see
Experimental section for details), the equatorial position of the
CO ligand in the carbonyl complex could be unambiguously
demonstrated through the results of the crystal structure analy-
sis. The co-ordination geometry around the tungsten centre in
complex 5-Me is best described as a pseudo-octahedron with
the bipyridyl, the CO and Cl(1) ligands in the equatorial plane
and the Cp* ring and Cl(2) in the axial positions. The averaged
W–Cl(1,2) distances of 2.42 Å are intermediate between those
found in the trichloro complex 2-Me and the corresponding
Reactivity of complex 3-Me
The exceedingly high water sensitivity of the cationic complex
3-Me imposed difficult problems to the study of its reaction
1970
J. Chem. Soc., Dalton Trans., 1999, 1967–1974

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Conclusion
We have demonstrated that bipyridyl substituted half-sandwich
tungsten() 2-Me complexes are readily obtained through one
electron reduction of the versatile starting material [WCp*Cl4]
in the presence of the bipyridyl donors. Facile ionization of one
chloride ligand in these electron rich complexes allowed us to
isolate the corresponding cationic tungsten() complex 3-Me.
Most of the d2 tungsten() complexes described herein are
paramagnetic; the investigation of the paramagnetic origin by
both experimental and theoretical methods will be reported in
due course.
Experimental
Reactions were carried out under a dinitrogen atmosphere
with thoroughly dried solvents using glove-box and Schlenk
techniques. The compounds [WCp*Cl4],12 [W(C5Me4Et)Cl4],12
[WCp*(CO)2Cl3]24 and tBu2bipy36 were prepared according
to published methods. The rather cumbersome synthesis of
(NMe2)2bipy has been described previously.37 We have prepared
this ligand by a straightforward albeit low-yield (15%) route
through reductive coupling of the commercially available p-
Fig. 4 Molecular structure of the carbonyl complex 5-Me; only one of
the disordered positions of atoms Cl1,2 and the carbonyl ligand are
Ϫ
presented. The BPh4 counter ion has been omitted for clarity (ellips-
oids are at the 50% probability level).
Table 3 Selected bond distances (Å) and angles (Њ) with e.s.d.s for
complex 5-Me
1
dimethylaminopyridine with Raney nickel. The H NMR and
13C NMR spectra were recorded on Varian Gemini 200 and 300
spectrometers. Chemical shifts are given in ppm and referenced
W1–Cl1a,ba
W1–N1
W1–C1
W1–C3
W1–C6
2.41
W1–Cl2a,b
W1–N2
W1–C2
2.45
1
to the residual H or 13C NMR solvent shifts. The assignment
2.187(3)
2.394(6)
2.295(6)
2.432(6)
1.14
2.176(3)
2.320(5)
2.350(5)
2.00
of resonances is based on DEPT and selective 1H NMR homo
decoupling experiments. The IR spectra were measured on a
Bio-Rad FTS-45 Fourier IR spectrometer. The CHN analyses
were carried out with a LECO CHNS-932 elemental analyser
in our institute. Some of the compounds contained solvents
from recrystallization in the analytically pure material; this
has been confirmed independently by integration of the solvent
W1–C4
W1–C23a,b
C23a,b–O1a,b
C–C (Cp*)av
W1–Z1b
2.03
1.413(8)
Cl1a,b–W1–Cl2a,b
C23a,b–W1–Cl1a,b
W1–C23a,b–O1a,b
Cl1a,b–W1–Z1
78.4
87.5
170.8
105.7
105.1
N1–W1–N2
Cl2a,b–W1–C23a,b
74.4(1)
75.9
1
in the H NMR spectrum. Conductivity measurements were
Cl2a,b–W1–Z1
N2–W1–Z1
171.4
106.0
performed with an Amel-160 conductometer using a glass cell
with platinum electrodes (K = 1.0). Magnetic moments have
been determined at room temperature with a Johnson-Matthey
laboratory magnetic susceptibility balance and were corrected
for diamagnetic contributions.
N1–W1–Z1
a Averaged values for disordered positions given. b Z1 is the midpoint of
carbon atoms C1 to C5.
cationic complex 3-Me, which implies that the CO ligand
can remove electron density from the rather electron rich d2
system.
Syntheses
[WCp*(Me2bipy)Cl3] 2-Me. From [WCp*Cl4]. At room tem-
In order to establish whether co-ordination of CO occurs
initially at the axial position, which is then followed by isomeri-
zation (path a), or alternatively, through isomerization prior
to CO addition (path b), we have monitored the reaction of
3-Me with CO by variable temperature 1H NMR spectroscopy.
Within detection limits, we could only observe the resonances
of the starting material 3-Me and the product 5-Me in these
experiments, which suggests that the reaction proceeds via
path b. It should be noted, however, that the absence of NMR
signals arising from a (undetected) Cs symmetrical intermediate
with the CO ligand in trans position to the Cp* ring does not
completely rule out path a since the latter transient might just
be present at very low concentration. Nevertheless, it is deemed
that co-ordination of the CO ligand in the equatorial plane of
complex 5-Me is thermodynamically preferred on both (1)
steric and (2) more relevant electronic grounds. Item (1) can be
rationalized based on the steric encumbrance in the related
trichloro complex 2-Me, which has been used in the latter con-
text to explain the out-of-plane bending of the Cp* methyl
groups (see above). The smaller (slimmer) CO ligand thus can
orient in a way that just one of the sterically more demanding
Cl ligands is oriented in cis position to the Cp* ring. For item
(2) it has to be considered that in an unperturbed octahedral d2
system (Oh symmetry) the two electrons reside in the basal
plane, the dxy orbital. On these grounds π-back donation to
the CO ligand can only be established if the CO group is
co-ordinated in the basal plane.
perature, a solution of 183 mg (0.91 mmol) (NMe ) C᎐
᎐
2 2
C(NMe2) (TDAE) in 10 ml dichloromethane was added to an
orange suspension of 842 mg (1.83 mmol) [WCp*Cl4] and 336
mg (1.83 mmol) Me2bipy in 100 ml dichloromethane upon
which a change to dark violet was observed. The suspension
was stirred for 1 h at this temperature, then filtered through a
pad of Celite and the Celite washed with a small amount of
CH2Cl2. After concentration of the filtrate to ca. 40 ml the
product was precipitated through addition of 40 ml of diethyl
ether. The solid was collected by filtration, washed twice with
ether and pentane and finally dried in high vacuo to give com-
plex 2-Me as an analytically pure violet microcrystalline solid.
Yield: 1.01 g, 1.66 mmol, 91% (based on [WCp*Cl4]. 1H NMR
(CD2Cl2, RT, 300 MHz): δ 8.7 (br, ω1/2 ≈ 32, 2 H, Me2bipy), 8.1
(br, ω1/2 ≈ 13, 2 H, Me2bipy), 7.5 (br, ω1/2 ≈ 13, 2 H, Me2bipy), 2.8
(br, ω1/2 ≈ 24, 6 H, Me2bipy) and 1.7 (br, ω1/2 ≈ 6 Hz, 15 H,
C5Me5). MS (EI): m/z 608 (Mϩ Ϫ 2H) and 575 (Mϩ Ϫ Cl) (Calc.
for C22H27Cl3N2W: C, 43.34; H, 4.46; N, 4.59. Found: C, 43.13;
H, 4.30; N, 4.50%).
From [WCp*(CO)2Cl3]. A suspension of 80 mg (0.170
mmol) [WCp*(CO)2Cl3] and 31 mg (0.170 mmol) Me2bipy in 20
ml toluene was heated in vacuum for 6 h to 110 ЊC leading to a
change from yellow to dark brown. After this time the reaction
mixture was allowed to cool to RT, the solid collected by cen-
trifugation and washed with small portions of ether until the
washing solutions remained colourless. The residue was then
dried in high vacuo and recrystallized at –36 ЊC from a pentane
J. Chem. Soc., Dalton Trans., 1999, 1967–1974
1971

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layered solution of the crude product in CH2Cl2. Yield: 66 mg,
64%.
2.35 mmol 3-Me, 76% based on [WCp*(Me2bipy)Cl3]. Single
crystals suitable for X-ray diffraction were obtained at RT by
crystallization from an ether–1,2-dichloroethane solution. H
1
[W(ç5-C5Me4Et)(Me2bipy)Cl3] 2Et-Me. A solution of 58 mg
(0.290 mmol) TDAE in 3 ml dichloromethane was slowly
dropped on to a solution of 276 mg (0.581 mmol) [W(η5-
C5Me4Et)Cl4] and 108 mg (0.587 mmol) Me2bipy in 15 ml
CH2Cl2 at RT giving a violet suspension which was stirred for
1 h at RT. Upon filtration through Celite the filtrate was concen-
trated to ca. 10 ml, then cooled to Ϫ36 ЊC. At this temperature
complex 2Et-Me was obtained as violet needles which were
isolated by decantation of the mother-liquor. The crystals were
washed with a small amount of pentane, then dried in high
vacuo to give 309 mg, 0.495 mmol, 85% 2Et-Me {based on
[W(η5-C5Me4Et)Cl4]}. Crystals suitable for X-ray diffraction
were obtained by slow diffusion of diethyl ether into a solution
NMR (CD2Cl2, 300 MHz, 293 K): δ 106 (br, ω1/2 ≈ 105), 43 (br,
ω1/2 ≈ 40), 28 (br, ω1/2 ≈ 30), 17.5 (br, ω1/2 ≈ 40), 7.4 (m, 8 H,
Ϫ
Ϫ
Ϫ
BPh4 ), 7.0 (m, 8 H, BPh4 ), 6.9 (m, 4 H, BPh4 ) and Ϫ85 (br,
ω1/2 ≈ 110 Hz). MS: FABϩ m/z 535 (Mϩ Ϫ Cl); FABϪ m/z 319
Ϫ
(BPh4 ). Molar conductivity, Λm(CH2Cl2): c = 10Ϫ4, 58; 10Ϫ3 M,
32 S cm2 molϪ1 (Calc. for C46H47BCl2N2W: C, 61.84; H, 5.30;
N, 3.14. Found: C, 61.49; H, 5.33; N, 3.10%).
[WCp*{(NMe2)2bipy}Cl2][BPh4] 3-NMe2. A solution of 102
mg NaBPh4 (0.30 mmol) in 10 ml THF was added to a suspen-
sion of 199 mg (0.30 mmol) [WCp*{(NMe2)2bipy}Cl3] in 10 ml
THF. After stirring for 30 min at RT the reaction mixture
was evaporated to dryness in high vacuum. The residue was
extracted into 15 ml 1,2-dichloroethane, and filtered through a
fine frit covered with a pad of Celite. Diethyl ether was added
to the filtrate until precipitation of the product was observed.
Overnight the product crystallized from this mixture as a
dark green microcrystalline solid. The solid was collected by
filtration, washed with ether and dried in high vacuum. Yield:
160 mg, 0.17 mmol, 56% based on [WCp*{(NMe2)2bipy}Cl3].
1
of 2Et-Me in dichloromethane at room temperature. H NMR
(CD2Cl2, RT, 300 MHz): δ 8.6 (br, ω1/2 ≈ 69, 2 H, Me2bipy), 8.1
(br, ω1/2 ≈ 11, 2 H, Me2bipy), 7.5 (br, ω1/2 ≈ 23, 2 H, Me2bipy), 2.9
(br, ω1/2 ≈ 56 Hz, 6 H, Me2bipy), 1.80 (s, 6 H, C5Me4Et), 1.75
(s, 6 H, C5Me4Et), 1.45 (q, 2 H, C5Me4CH2CH3, J = 7) and 1.03
(t, 3 H, C5Me4CH2CH3, J = 7 Hz) (Calc. for C23H29Cl3N2W: C,
44.29; H, 4.69; N, 4.49. Found: C, 44.18; H, 4.72; N, 4.64%).
3
4
1H NMR (CD2Cl2, 293 K): δ 8.64 [dd, J = 7, J = 2, 2 H,
Ϫ
Ϫ
[WCp*(tBu2bipy)Cl3] 2-tBu. To a suspension of 1.73 g (3.75
mmol) [WCp*Cl4] and 1.01 g (3.77 mmol) tBu2bipy in 150 ml
CH2Cl2, a solution of 375 mg (1.88 mmol) TDAE in 15 ml
CH2Cl2 was slowly added at RT. After stirring for 1 h the violet
suspension was filtered through Celite and the volume of
filtrate reduced to ca. 50 ml in vacuo. Upon addition of 100 ml
diethyl ether to the filtrate the product precipitated and was
collected by filtration and washed with ether and pentane. The
solid was finally dried in high vacuo to yield 2.47 g, 3.56 mmol,
(NMe2)2bipy], 7.31 (m, 8 H, BPh4 ), 7.01 (m, 8 H, BPh4 ),
Ϫ
6.85 (m, 4 H, BPh4 ), 6.58 [d, 4J = 2 Hz, 2 H, (NMe2)2bipy], 6.30
[br, ω1/2 = 30, 6 H, (NMe2)2bipy], 5.85 [br, ω1/2 = 30 Hz, 6 H,
(NMe2)2bipy], 4.85 [d, 3J = 7 Hz, 2 H, (NMe2)2bipy] and 3.26 (s,
ω1/2 = 4 Hz, 15 H, C5Me5) (Calc. for C48H53BCl2N4WؒCH2Cl2:
C, 56.78; H, 5.35; N, 5.41. Found: C, 56.40; H, 5.22; N, 5.39%).
[WCp*(Me2bipy)(CO)Cl2]؉BPh4؊ 5-Me. In the dry-box, 363
Ϫ
mg (0.41 mmol) [WCp*(Me2bipy)Cl2]ϩBPh4 3-Me were dis-
1
95% 2-tBu based on [WCp*Cl4]. H NMR (CD2Cl2, RT, 300
solved in 30 ml 1,2-dichloroethane in a 200 ml high-vacuum
Young tap-sealed Schlenk tube and transferred to a high
vacuum manifold. The solution was frozen out at liquid nitro-
gen temperature, evacuated, then refilled with 1 bar of carbon
monoxide and warmed to RT. Within 45 min of stirring at this
temperature a change from dark green to red was observed.
After stirring for 90 min the solution was concentrated to 10 ml
in vacuo and the product precipitated as a microcrystalline
orange-red solid by slow addition of diethyl ether. It was
collected by filtration, washed twice with ether and pentane,
then dried in high vacuo. The CO complex 5-Me is insoluble in
THF but dissolves well in CH2Cl2. Yield: 325 mg, 0.35 mmol,
MHz): δ 8.8 (br, ω1/2 ≈ 35, 2 H, tBu2bipy), 8.2 (br, ω1/2 ≈ 10, 2 H,
tBu2bipy), 7.7 (br, ω1/2 ≈ 40, 2 H, tBu2bipy), 1.71 (br, ω1/2 ≈ 15
Hz, 15 H, C5Me5) and 1.45 (s, 18 H, CMe3). MS (EI): m/z 692
(Mϩ) and 657 (Mϩ Ϫ Cl) (Calc. for C28H39Cl3N2W: C, 48.47;
H, 5.67; N, 4.04. Found: C, 48.10; H, 5.49; N, 4.07%).
[WCp*{(NMe2)2bipy}Cl3] 2-NMe2. A solution of 76 mg (0.38
mmol) TDAE in 20 ml dichloromethane was added dropwise to
a solution of 350 mg (0.76 mmol) [WCp*Cl4] and 185 mg (0.76
mmol) (NMe2)2bipy in 60 ml CH2Cl2 giving a yellow-orange
suspension. After stirring for 2 h at RT the reaction mixture was
filtered through a pad of Celite and washed with a small
amount of CH2Cl2. The collected filtrates were concentrated
in vacuo to ca. 10 ml, upon which the product precipitated as a
yellow-orange solid; precipitation was completed through
addition of 40 ml ether. The solid was collected by filtration,
washed with toluene and ether and finally dried in high
vacuum. Yield: 450 mg, 0.67 mmol, 89% based on [WCp*Cl4].
1H NMR (CD2Cl2, 298 K): δ 8.37 [d, 4J = 2, 2 H, (NMe2)2bipy],
7.46 [m, 2 H, (NMe2)2bipy], 7.0 [d, 3J = 7 Hz, 2H, (NMe2)2bipy],
4.84 [br, ω1/2 = 20, 12 H, (NMe2)2bipy] and 2.61 (br, ω1/2 = 6 Hz,
15 H, C5Me5) (Calc. for C24H33Cl3N4W: C, 43.17; H, 4.98; N,
8.39. Found: C, 43.22; H, 5.25; N, 8.01%).
3
87%. 1H NMR (CD2Cl2, 300 MHz, 293 K): δ 9.03 (d, J = 6, 1
3
H, Me2bipy), 8.33 (d, 1 H, J = 6, Me2bipy), 7.91 (m, 1 H,
3
4
Me2bipy), 7.89 (m, 1 H, Me2bipy), 7.56 (dd, J = 6, J = 2, 1 H,
Ϫ
Me2bipy), 7.35 (m, 8 H, BPh4 ), 7.28 (dd, 3J = 6, 4J = 2 Hz, 1 H,
Ϫ
Ϫ
Me2bipy), 6.99 (m, 8 H, BPh4 ), 6.83 (m, 4 H, BPh4 ), 2.52 (s,
3 H, Me2bipy), 2.48 (s, 3 H, Me2bipy) and 1.78 (s, 15 H, C5Me5).
13C-{1H} NMR (CD2Cl2, 75.4 MHz, 298 K): δ 214.1 (s, CO),
Ϫ
164.3 [q, B(C6H5)4 , 1JB-C = 50], 156.8 (s, quart. Carom, Me2bipy),
156.1 (s, quart. Carom, Me2bipy), 155.7 (s, CHarom, Me2bipy),
154.9 (s, quart. Carom, Me2bipy), 154.5 (s, quart. Carom, Me2bipy),
Ϫ
149.7 (s, CHarom, Me2bipy), 136.4 [q, CHarom, B(C6H5)4 ,
JB-C = 2], 131.3 (s, CHarom, Me2bipy), 129.8 (s, CHarom, Me2bipy),
Ϫ
126.4 (s, CHarom, Me2bipy), 126.2 [q, CHarom, B(C6H5)4 ,
[WCp*(Me2bipy)Cl2]؉BPh4؊ 3-Me. A solution of 1.05 g (3.08
mmol) NaBPh4 in 30 ml THF was added to a stirred suspension
of 1.88 g (3.08 mmol) [WCp*(Me2bipy)Cl3] in 100 ml THF at
RT. After stirring for 30 min at this temperature a clear brown
solution was obtained which was evacuated to dryness. The
residue was extracted into 150 ml of 1,2-dichloroethane and
filtered through a fine porous frit covered with a pad of Celite.
After concentration of the green filtrate to 80 ml in vacuo, 180
ml ether were slowly added. From this mixture, the product
crystallized overnight as a microcrystalline dark green solid at
RT. The mother-liquor was decanted off, the solid washed
with ether and finally dried in high vacuum to give 2.1 g,
JB-C = 3 Hz], 122.3 [q, CHarom, B(C6H5)4Ϫ], 110.2 (s, quart.
Carom, C5Me5), 22.2 (s, Me2bipy), 22.0 (s, Me2bipy) and 10.9
(s, C5Me5). IR (CH2Cl2): ν(CO) 2004 cmϪ1 (Calc. for C47H47-
BCl2N2OWؒC2H4Cl2: C, 57.68; H, 5.04; N, 2.75. Found: C,
58.04; H, 4.66; N, 2.70%). Single crystals suitable for X-ray
diffraction were obtained by slow diffusion of ether into a
solution of 5-Me in 1,2-dichloroethane at RT.
Crystal structure analyses
General remarks. Suitable single crystals of complexes 2Et-Me,
3-Me and 5-Me were mounted on a glass fibre in Paratone-N
1972
J. Chem. Soc., Dalton Trans., 1999, 1967–1974

View Article Online
Table 4 Crystal and data collection parameters for compounds 2Et-Me, 3-Me and 5-Me
2Et-Me
3-Me
5-Me
Formula
M
C23H29Cl3N2Wؒ2CH2Cl2
793.5
C46H47BCl2N2W
893.4
C47H47BCl2N2OWؒC2H4Cl2
1020.4
Crystal system
Space group
a/Å
b/Å
Monoclinic
P21/n (no. 14)
8.324(1)
17.879(3)
20.464(4)
100.92(1)
2990.4(9)
4
Monoclinic
P21/c (no. 14)
11.672(1)
16.362(2)
21.122(2)
99.61(1)
3977.2(7)
4
Monoclinic
P21/n (no. 14)
22.428(2)
9.264(1)
23.646(2)
115.13(1)
4448.0(7)
4
c/Å
β/Њ
V/Å3
Z
µ/mmϪ1
4.50
3.07
2.88
T/K
2θ range/Њ
193
4–52
193
4–52
193
4–52
No. measured reflections
(total, unique)
R1 [F2 > 2σ(F2)]
wR2 [F2 > 2σ(F2)]
5749, 5339
36931, 7678
34876, 8462
0.0563
0.1463
0.0192
0.0372
0.0280
0.0770
(oil), transferred on the goniometer head to the diffractometer
and cooled to Ϫ80 ЊC in a nitrogen cryostream. The data sets
were collected with graphite monochromated Mo-Kα radiation
(λ 0.71073 Å) on Siemens P4 four-circle (2Et-Me) and Stoe
IPDS image plate diffractometers (3-Me and 5-Me). Intensities
were corrected for Lorentz-polarization effects and absorption
corrections performed either empirically from ψ scans (2Et-Me)
or numerically with the faces and corresponding crystal dimen-
sions determined using the STOE Faceit-Video CCD camera
microscope system (3-Me and 5-Me). The structures were
solved using direct methods with the SHELXS 86 program
package.38 The refinements were carried out with SHELXL 93
support. We thank Mr Thomas Hiltebrand for working out
the details of the synthesis of (NMe2)2bipy. Funding of this
project by the Swiss National Science Foundation is gratefully
acknowledged.
References
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2 39
using all unique Fo . Except for complex 5-Me all non-
hydrogen atoms were refined anisotropically. The positions of
the hydrogen atoms were calculated in idealized positions (C–H
bonds fixed at 0.96 Å) and refined as a riding model with a fixed
isotropic displacement factor of U = 0.08 Å2. The details of
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10 R. R. Schrock, T. E. Glassman, M. G. Vale and M. Kol, J. Am.
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Complex 5-Me. One disordered molecule of 1,2-dichloro-
ethane from recrystallization was contained per molecule of
complex and was refined with two split positions with occu-
pation factors of 0.55 and 0.45 for the disordered Cl3 atom.
The CO ligand and atom Cl1 were positionally disordered; this
was indicated in the Fourier-difference map through a large
peak between the C23–O1 bond vector and by another peak
located on the W1–Cl1 axis (distant from W1) in close prox-
imity to Cl1 (0.56 Å apart from Cl1). The disorder was resolved
and refined with split positions for atoms C23 and O1 (denoted
as C23a,b and O1a,b) and two split positions for Cl1, denoted
as Cl1a,b, with their occupational parameters refined as an
independent variable. The positions of C23a,b and O1a,b were
refined isotropically using identical displacement parameters
(EADP card) while Cl1a,b was treated anisotropically. The
refinement of the occupational parameter converged at final
values of 0.44 and 0.56. In addition, a strong thermal mobility
of Cl2 was noticed. This could be refined with two split posi-
tions, i.e. Cl2a,b, and using the occupational parameters
obtained for the aforementioned positional disorder of the
CO and Cl1 ligands. The residual non-hydrogen atoms were
refined anisotropically; the positions of the hydrogen atoms
were calculated in idealized positions and refined as above.
CCDC reference number 186/1438.
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See http://www.rsc.org/suppdata/dt/1999/1967/ for crystallo-
graphic files in .cif format.
Acknowledgements
We are indebted to Professor Heinz Berke for his generous
J. Chem. Soc., Dalton Trans., 1999, 1967–1974
1973

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Paper 9/02743B
1974
J. Chem. Soc., Dalton Trans., 1999, 1967–1974