Preparation and structure of the 17-electron (η5-C5R5)Mo(OH)2(dppe) (R = Me, Et) organometallic compounds containing two gem-terminal hydroxide ligands

Article abstract of DOI:10.1016/S0022-328X(99)00539-2

Oxidation of (η⁵-C₅R₅)MoH₃(dppe) (R = Me, Et) by Cp₂Fe⁺ in wet THF leads to the formation of the corresponding (η⁵-C₅R₅)Mo(OH)₂(dppe). These compounds show a low-potential reversible oxidation wave. The structure of the C₅Et₅ complex has been confirmed by X-ray diffraction methods: triclinic; space group P1; a = 11.030(1); b = 12.533(1); c = 16.241 (1) A?; α = 68.585(7); β = 75.197(5); γ = 83.991(7)°; V = 2020.6(3) A?³; Z = 2; D_calc = 1.324 g cm^-3, μ(Mo-K_α) = 0.441 mm^-1; R₁ = 0.0325; wR₂ = 0.0875 for 415 parameters and 6823 independent reflections [R_int = 0.0177] with I = 2σ(I). The molecule shows a four-legged piano-stool geometry with two terminal OH ligands in a relative trans configuration. The complex EPR properties indicate that an equilibrium mixture of various species is present in solution.

Full text of DOI:10.1016/S0022-328X(99)00539-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 596 (2000) 64–69
Preparation and structure of the 17-electron
(h5-C5R5)Mo(OH)2(dppe) (R=Me, Et) organometallic compounds
containing two gem-terminal hydroxide ligands
Dolores Morales a, Brett Pleune b, Rinaldo Poli a,*, Philippe Richard a
a Laboratoire de Synthe`se et d’Electrosynthe`se Organome´talliques, Faculte´ des Sciences ‘Gabriel’, Uni6ersite´ de Bourgogne, 6 Boule6ard Gabriel,
F-21100 Dijon, France
b Department of Chemistry and Biochemistry, Uni6ersity of Maryland, College Park, MD 20742, USA
Received 30 August 1999
Dedicated to Al Cotton on the occasion of his 70th birthday for his outstanding contributions to chemistry.
Abstract
Oxidation of (h5-C5R5)MoH3(dppe) (R=Me, Et) by Cp2Fe+ in wet THF leads to the formation of the corresponding
(h5-C5R5)Mo(OH)2(dppe). These compounds show a low-potential reversible oxidation wave. The structure of the C5Et5 complex
(
,
has been confirmed by X-ray diffraction methods: triclinic; space group P1; a=11.030(1); b=12.533(1); c=16.241 (1) A;
3
h=68.585(7); i=75.197(5); k=83.991(7)°; V=2020.6(3) A ; Z=2; Dcalc=1.324 g cm−3, v(Mo–Kh)=0.441 mm−1; R1=
,
0.0325; wR2=0.0875 for 415 parameters and 6823 independent reflections [Rint=0.0177] with I=2|(I). The molecule shows a
four-legged piano-stool geometry with two terminal OH ligands in a relative trans configuration. The complex EPR properties
indicate that an equilibrium mixture of various species is present in solution. © 2000 Elsevier Science S.A. All rights reserved.
Keywords: Half-sandwich complexes; Hydride complexes; Hydroxide complexes; Molybdenum; Oxidation
1. Introduction
oxidation may occur, generating a doubly oxidized,
even more acidic hydride complex. Under suitable con-
ditions, water can act as a ligand (L), being the source
of the hydroxide ligand for the metal center, and also
as a Brønsted base [5,6]. Additional external bases,
however, may also be used. In this process, both the
hydride and one of the water H atoms are lost as
protons. This method has allowed the preparation of
[CpMo(OH)(PMe3)3]+ from CpMoH(PMe3)3 in wet
THF [4,7], while the use of dry MeCN as solvent leads
There has been wide interest in organometallic hy-
droxide complexes, because of their role in catalysis and
in materials chemistry [1–3]. In a recent review, it has
been pointed out that these complexes often form ad-
ventitiously and that the understanding of these forma-
tion reactions is incomplete [3]. Recently, we have
reported on a new method that leads to the formation
of hydroxide complexes, namely the oxidation of hy-
dride complexes in a wet, poorly coordinating organic
solvent (see Scheme 1) [4]. One-electron oxidation ren-
ders the hydride species more acidic and susceptible to
both deprotonation by an external base [5] and coordi-
nation by a two-electron donor ligand. Electron-donat-
ing and sterically protecting ligands, however, kine-
tically disfavor the deprotonation process and further
* Corresponding author. Tel.: +33-380396881; fax: +33-
380396098.
E-mail address: rinaldo.poli@u-bourgogne.fr (R. Poli)
Scheme 1.
0022-328X/00/$ - see front matter © 2000 Elsevier Science S.A. All rights reserved.
PII: S0022-328X(99)00539-2

D. Morales et al. / Journal of Organometallic Chemistry 596 (2000) 64–69
65
rocene standard, which was added to each solution and
measured at the end of the experiments. The elemental
analyses were carried out by the analytical service of
the Laboratoire de Synthe`se et d’Electrosynthe`se
Organome´talliques with a Fisons Instruments EA1108
analyzer. Compound Cp*MoH3(dppe) was prepared as
described elsewhere [10], while compound (C5Et5)MoH3
(dppe) was prepared by an extension of this procedure
from (C5Et5)MoCl4, dppe and LiAlH4 [11]. In turn,
(C5Et5)MoCl4 was obtained from (C5Et5)Mo(CO)3CH3
[12] and PCl5 by the same procedure reported for the
Cp* analogue [13].
Fig. 1. EPR spectra in pentane solutions of compound 1 at room
temperature (a) and at −40°C (b), and of compound 2 at room
temperature (c) and at −68°C (d).
2.2. Preparation of compounds (p-C5R5)Mo(OH)2(dppe)
(R=Me, 1; Et, 2)
to the stable doubly oxidized complex [CpMoH(MeCN)-
(PMe3)]2+ [8].
2.2.1. R=Et
In the above example, only one open coordination
site is made available by the two-electron oxidation
process. In parallel studies, we have recently discovered
that oxidation of the trihydride complex Cp*MoH3
(dppe) induces the reductive elimination of H2 to pro-
duce the solvated complexes [Cp*MoH(dppe)(S)]+
[9,10]. This process, therefore, makes available two
potential coordination sites to the intervention of water
as a ligand, with the possibility of obtaining a gem-ter-
minal bis(hydroxo) or an oxo complex. In this contri-
bution, we describe the extention of our oxidation
studies in wet THF to the (h-C5R5)MoH3(dppe) (R=
Me, Et) systems, which indeed proves the validity of
this concept.
A solution of (C5Et5)MoH3(dppe) (0.420 g, 0.59
mmol) in 10 ml of THF at −78°C was transferred to a
suspension of Cp2FeBF4 (0.246 g, 0.885 mmol). The
violet solution exhibited a triplet of quartets in the EPR
spectrum (g=2.016, aP(t)=28.9 G, aH(q)=11.6 G)
attributable to [(C5Et5)MoH3(dppe)]+ [11]. This solu-
tion was stirred at room temperature (r.t.) for ca. 15
min. The solvent was evaporated in vacuo and the
residue was washed with pentane (5×10 ml) in order
to eliminate the Cp2Fe. The residue was redissolved in
20 ml of THF and NEt3 (246 ml, 1.77 mmol) was added.
The brown–yellow solution was stirred for 90 min,
followed by evaporation to dryness. The residue was
extracted with pentane (ca. 150 ml) and the resulting
suspension was filtered through Celite. The solution
was concentrated in vacuo to ca. 10 ml and placed at
−12°C overnight, resulting in the formation of 2 as a
yellow–green microcrystalline solid: yield: 0.239 g,
55%. The sample used for the elemental analysis had
been thoroughly dried under vacuum. Anal. Calc. for
C41H51MoO2P2: C, 67.11; H, 7.01; Found: C, 67.43, H,
7.15. Single crystals were obtained by slow evaporation
(12 h) at r.t. of a pentane solution under argon and
contained an interstitial pentane molecule (see below).
The product is stable as a solid in air for days. It is very
soluble in all common organic solvents and stable in
MeCN or MeCN–water mixtures. The addition of a
large excess of water only induces the reprecipitation of
2. The compound is also stable in CH2Cl2 under an
inert atmosphere for a short period of time but decom-
poses rapidly in CHCl3 to afford an EPR silent solu-
tion. EPR (THF, r.t.): g=1.997 (apparent quintet, with
Mo satellites, aP=19.7 G, aMo= 44.8 G, see Fig. 1).
Cyclic voltammetry (THF, r.t.): reversible oxidation at
2. Experimental
2.1. General procedures
Unless otherwise stated, all manipulations were car-
ried out under an inert atmosphere of dinitrogen or
argon by the use of Schlenk-line or glove-box tech-
niques. Solvents were dried by conventional methods
and distilled under dinitrogen prior to use. NEt3 was
distilled under dinitrogen prior to use. Deuterated sol-
vents were dried over molecular sieves and degassed by
three freeze–pump–thaw cycles prior to use. EPR mea-
surements were carried out at the X-band microwave
frequency on a Bruker ESP300 spectrometer. The spec-
trometer frequency was calibrated with DPPH (g=
2.0037). Cyclic voltammograms were carried out at
20°C with an EG&G 283 analogue potentiostat con-
nected to a Macintosh computer via a MacLab ana-
logue–digital converter. The electrochemical cell was
fitted with a Ag ꢀ AgCl reference electrode, a platinum
disk working electrode and a Pt wire counterelectrode.
Bu4NPF6 (ca. 0.1 M) was used as supporting elec-
trolyte. All potentials are reported relative to the fer-
E1/2= −0.64 V.
Compound 2 was also obtained by an alternative
procedure where an excess of water was used in place of
triethylamine. Cp2FeBF4 (0.012 g, 0.043 mmol) was

66
D. Morales et al. / Journal of Organometallic Chemistry 596 (2000) 64–69
added to a stirred solution of (C5Et5)MoH3(dppe)
(0.020 g, 0.029 mmol) in 4 ml of THF at −80°C. The
solution showed the spectrum corresponding to
[(C5Et5)MoH3(dppe)]BF4. This solution was stirred for
15 min at r.t., followed by the addition of distilled and
deoxygenated water (10 ml, 0.55 mmol) and stirring was
continued for 45 min. The EPR properties of the
resulting yellow–brown solution matched those de-
scribed above for compound 2.
Table 1
Crystal data and refinement parameters for (h-C5Et5)Mo(OH)2(dppe)
Formula
M
C41H51O2P2Mo.C5H12
805.84
T (K)
Crystal system
293(2)
Triclinic
2.2.2. R=Me
By an identical procedure to that described above for
R=Et, compound 1 (71 mg, 30% yield) was prepared
from Cp*MoH3(dppe) (0.23 g; 0.36 mmol) and
Cp2FePF6 (0.12 g, 0.36 mmol). EPR (C6H6, r.t.): g=
1.999 (apparent quintet, with Mo satellites, aP=21.0 G,
(
Space group
P1
,
a (A)
11.030(1)
12.533(1)
16.241(1)
68.585(7)
75.197(5)
83.991(7)
2020.6(3)
2
,
b (A)
,
c (A)
h (°)
i (°)
k (°)
aMo= 38.0 G, see Fig. 1). Cyclic voltammetry (THF,
room temperature): reversible oxidation at E1/2
−0.72 V.
=
3
,
V (A )
Z
F(000)
854
1.324
Dcalc (g cm−3
)
2.3. X-ray crystallography for compound
(p-C5Et5)Mo(OH)2(dppe) (2)
,
u (A)
0.71073
0.441
0.3×0.2×0.2
0.62
v (mm−1
)
Crystal size (mm3)
sin(q)/u max (A
Index ranges
Crystals for the X-ray structure analysis were grown
by a slow evaporation at 0°C from a pentane solution.
A green crystal (0.3×0.2×0.2 mm3) was mounted in
the presence of solvent vapours in a capillary on an
Enraf–Nonius CAD4 diffractometer. A total of 8563
reflections (8122 unique) were collected at r.t. up to
−1
,
)
H
K
L
−13, 0
−15, 15
−20, 19
0
psi scan
PLATON (see text)
8582
8135 [Rint=0.0177]
6823
Decay (%)
Absorption correction
Solvent correction
RC=reflections collected
IRC=independent RC
IRCGT=IRC and [I\2|(I)]
Refinement method
sin(q)/u=0.62 A−1. The data were corrected for
,
Lorentz and polarization effects and for absorption
(psi-scan method) [14]. No decay was observed. The
structure was solved via a Patterson search program
Full-matrix least-squares on
(
[15] and refined (space group P1) with full-matrix least-
F2
squares methods [15] based on ꢀF2ꢀ. All non-hydrogen
atoms were refined with anisotropic thermal parame-
ters. The hydrogen atoms of the complex, except for
those of the hydroxyl groups, were included in their
calculated positions and refined with a riding model.
Any attempt to locate the hydrogen atoms of the
hydroxyl groups failed. At the end of this refinement
the agreement indices were wR2=0.145 for all data and
R1=0.0394 for intensities with I=2|(I). The final
difference electron density map exhibited peaks near the
Data/restraints/parameters
R for IRCGT
8135/0/415
R1=0.0325a, wR2=0.0875b
R1=0.0464a, wR2=0.0914b
1.037
R for IRC
Goodness-of-fitc
Largest difference peak and hole
(e A
0.624 and −0.364
−3
,
)
a R1=ꢁ(ꢀꢀFoꢀ−ꢀFcꢀꢀ)/ꢁꢀFoꢀ.
b wR2=[ꢁ w(Fo2−Fc2)2/ꢁ[w(Fo2)2]1/2
where
w=1/[|2(F2o)+
(0.0512*P)2+0.75*P] where P=(max(Fo2, 0)+2*Fc2)/3.
c Goodness-of-fit=[ꢁ w(F2o−F2c)2/(No−Nv)]1/2
.
oxygen atoms (ca. 0.6 e A−3) but also in a region far
,
from the model (ca. 1 e A−3). A PLATON [14] run
Table 2
,
,
Selected bond lengths [A] and angles (°) for (h-C5Et5)-
3
,
indicated a potential solvent region of 280 A . The
Mo(OH)2(dppe)a
electron difference density map was not sufficiently
clear to successfully model a badly disordered solvent
molecule and the BYPASS procedure, implemented in
the PLATON program [16] was used to handle this
problem. In this procedure the contribution of the
solvent (one molecule of pentane) electron density is
subtracted to the structure factors. The refinement with
the solvent-corrected data set led to the final agreement
indices: wR2=0.0914 for all data, R1=0.0325 for 6823
data with I=2|(I) and GoF=1.037. Crystal data are
reported in Table 1, while selected bond distances and
angles are listed in Table 2.
Bond lengths
Mo–CNT
Mo–P(1)
Mo–P(2)
2.020(2)
2.4954(6)
2.4951(5)
Mo–O(1)
Mo–O(2)
1.984(2)
2.0111(14)
Bond angles
O(1)–Mo–O(2)
O(1)–Mo–P(1)
O(1)–Mo–P(2)
O(1)–Mo–CNT
O(2)–Mo–P(1)
148.28(6)
79.56(5)
77.26(5)
106.0(2)
74.31(4)
O(2)–Mo–P(2)
O(2)–Mo-CNT
P(1)–Mo–P(2)
P(1)–Mo–CNT
P(2)–Mo–CNT
80.76(4)
105.6(2)
80.05(2)
142.9(3)
137.0(2)
a CNT is the centroid of the cyclopentadienyl ring.

D. Morales et al. / Journal of Organometallic Chemistry 596 (2000) 64–69
67
oped the analogous C5Et5 derivative. Oxidation of com-
pound (h-C5Et5)MoH3(dppe) in dry THF, CH2Cl2, or
MeCN follows the same pattern already described for
the Cp* analogue. The EPR spectrum of [(h-
C5Et5)MoH3(dppe)]+ shows a triplet of quartets at
g=2.016, aP(t)=28.9 G, aH(q)=11.6 G, and thus
compares very closely to the spectrum of the Cp*
analogue [10]. The ferrocenium oxidation of (h-
C5Et5)MoH3(dppe) in wet THF parallels the pattern
described above for the Cp* species, affording again an
apparent quintet resonance in the EPR spectrum (Fig.
1). By an analogous work-up procedure, compound
(h-C5Et5)Mo(OH)2(dppe), 2, was isolated in 55% yields.
Thus, the oxidation of the C5Me5 and C5Et5 parent
trihydride species is identical in all respects. However,
the C5Et5 product 2 readily afforded single crystals
which were suitable for an X-ray investigation.
Fig. 2. An ORTEP [33] view of compound 2 with thermal ellipsoids
drawn at the 30% probability level. Hydrogen atoms are omitted for
clarity.
The structure of compound 2 exhibits individual
molecules of the bis-hydroxo complex (see Fig. 2) in
general positions without any intermolecular hydrogen
bonding interactions (shortest O···O separation=5.073
3. Results and discussion
,
A). The absence of these interactions may be attributed
We have recently reported [10] that the oxidation of
compound Cp*MoH3(dppe) in dry THF, CH2Cl2 or
MeCN affords the one-electron oxidation product,
[Cp*MoH3(dppe)]+, which is characterized by a triplet
of quartets signal in the EPR spectrum. This coupling
pattern is due to two equivalent phosphorus donors
and three rapidly exchanging hydride ligands. This
paramagnetic trihydride complex decomposes by H2
reductive elimination in the first two solvents and by a
combination of proton transfer and disproportionation
mechanisms in the last one [10]. We now report that,
when the oxidation is carried out in wet THF, the
solution evolves to a product which is characterized by
an EPR signal having the apparent shape of a quintet
(Fig. 1). Work-up of the solution affords a pentane-sol-
uble fraction from which the bis-hydroxo product
Cp*Mo(OH)2(dppe), 1, is recovered by crystallization
from pentane at low temperature. The product was
initially obtained from procedures carried out in ‘dry’
THF, the hydroxo ligands presumably originating from
small amounts of adventitious water which also acts as
a deprotonating base (see Section 1) [17]. We find,
however, that the use of NEt3 as an additional external
base as described in Section 2 affords more satisfactory
results. The mechanism of formation of 1 must involve
a number of electron and proton transfer and water
coordination processes. Any attempt to analyze this
mechanism in greater detail would be wildly specula-
tive. The product of the first one-electron transfer,
[Cp*MoH3(dppe)]+, decomposes by H2 reductive elimi-
nation in dry solvents, but the presence of water may
well trigger alternative reaction pathways.
to steric encumberance. A space-filling model shows
that the hydroxide ligands are sterically protected by a
shield of the dppe phenyl groups and the C5Et5 ligand.
The conformation adopted by the C5Et5 ligand has all
five substituents bent toward the same side of the ring
and away from the metal. According to the Cambridge
Crystallographic Database, this ligand has only been
previously investigated in the decaethylferrocenium
cation (with two different counterions, namely the
7,7%,8,8%-tetracyano-p-quinodimethanide at two differ-
ent temperatures [18,19], and the 2,3,5,6-tetrafluoro-
7,7%,8,8%-tetracyano-p-quinodimethanide [20]). In all
cases, the same conformation of the C5Et5 ligand was
observed.
The four-legged piano-stool geometry around the
central metal atom is characteristic of the wide class of
17-electron half-sandwich Mo(III) derivatives [21]. In
particular, the trans relative arrangement of the OH
ligands and the phosphorus donors is identical with
that observed for the related complex Cp*MoCl2(dppe)
[22]. The metric parameters of compound 2 (distances
and angles) are indeed quite close to those of the
Cp*-dichloride analogue, confirming the metal oxida-
tion state assignment as a bis(hydroxo) derivative, even
though the H atoms on the hydroxide ligands could not
be located from the X-ray diffraction data. In terms of
bond distances, the Mo–CNT separation (CNT=C5R5
,
,
ring centroid) is 2.020(2) A for 2 and 2.046(3) A for
Cp*MoCl2(dppe), while the average Mo–P distance is
2.4952(6) for 2 and 2.499(3) for the dichloride complex.
In terms of bond angles, the CNT–Mo–X angles also
show a remarkable similarity: X=P, 142.9(3) and
137.0(2)° for 2, 140.1(1) and 139.3(1)° for the dichloride
complex; X=O/Cl, 106.0(2) and 105.6(2)° for 2,
In spite of several attempts, we were not able to grow
single crystals of compound 1. We have therefore devel-

68
D. Morales et al. / Journal of Organometallic Chemistry 596 (2000) 64–69
107.2(1) and 104.9(1)° for the dichloride complex. As
previously shown [23], these angular parameters are
quite sensitive to the metal electronic configuration.
The identity of the hydroxide ligands is further ascer-
[22] and CpMoCl2(PMePh2)2 [28], while the closely
related complexes CpMoBr2(dppe) and Cp*MoCl2-
(dppe) adopt cis and trans structures in the solid state,
respectively [22,26]. A closer look at the room-tempera-
ture spectra of the two complexes (Fig. 1(a) and (c)),
reveals that the satellites on the right-hand side of the
main resonance have a greater intensity relative to
those on the left hand side. This was reproducibly
observed on recrystallized samples of both compounds.
Cooling the samples (Fig. 1(b) and (d)) permits the
right-hand side features to be distinguished more clearly
as new signals with the apparent shape of binomial
triplets (g=1.948, aP=18.7 G for 1; g=1.943, aP=
18.8 G for 2). The low-temperature spectra also show
the appearance of yet another broad signal, which is
located to the left of the main ‘quintet’ signal. This is
more evident for compound 1 (Fig. 1(b)) but can also
be noticed for compound 2 (Fig. 1(d)). All these tem-
perature-dependent spectral changes are fully reversible,
consistent with reversible equilibria between different
species. It is to be noticed that similar temperature-de-
pendent spectral characteristics were previously ob-
served for Cp*MoCl2(dppe) [22], whose solid-state
structure is related to that described here for 2. The
EPR properties of compounds 1 and 2 may also be
complicated by solution equilibria between a bis(hy-
droxo) form and an oxo form. In fact, bis(hydroxo)
compounds are often unstable species with respect to
loss of water [29,30]. The room-temperature spectrum
of 2 obtained in the presence of a large excess of D2O
shows a slight increase of the triplet resonance at
g=1.943, but this change is not sufficiently pro-
nounced to be considered significant.
,
tained by the Mo–O distances (average 1.998(13) A)
which favorably compare with that of the previously
reported [CpMo(OH)(PMe3)3]+ (2.080(3) A) [4]. A re-
,
lated distance in a terminal Mo(IV)–OH organometal-
,
lic complex is 2.050(5) A for complex [Cp2Mo(NH2Me)
(OH)]PF6 [24], while Mo–oxo distances are much
+
,
shorter, for instance 1.674(13) A in [CpMoO(PMe3)2]
5
,
or 1.710(3) A for [CH3C(CH2-h -C5H4)(CH2PPh2)2
MoO]+ [4,25].
No O–H stretching vibration could be identified in
the IR spectrum, presumably because these are masked
by the stronger aromatic C–H stretching bands. The
cyclic voltammetric studies show a facile and reversible
one-electron oxidation process (E1/2= −0.72 V for 1
and −0.64 V for 2). A comparison of these values
shows similar electron-donating properties for C5Et5
and C5Me5. Most half-sandwich, 17-electron Mo(III)
complexes undergo a reversible one-electron oxidation
process, for instance at E1/2= −0.33, −0.26 and
−0.20 V for CpMoX2(dppe) (X=Cl, Br, and I, respec-
tively) [26], and at E1/2= −0.58 V for Cp*MoCl2
(dppe) [27]. The low E1/2 values for 1 and 2, relative to
the dihalide analogues, may seem unusual because the
higher electronegativity of oxygen would be expected to
lead to a greater effective positive charge on the metal
center and consequently to higher oxidation potentials.
However, as previously discussed [26], the HOMO for
this system has a relatively strong Mo–X p antibonding
component. Thus, a stronger p donor such as the
hydroxide will result in a higher HOMO energy, com-
pensating for the energetically stabilizing s effect. Fur-
thermore, the E1/2 value also reflect the stabilization of
the Mo(IV) oxidation product, which is greater for the
more strongly p-donating OH ligand.
The deceiving EPR spectra deserve a brief discussion,
although we cannot offer an unambiguous rationaliza-
tion. Both compounds 1 and 2 show a pattern which
resembles a binomial quintet. This pattern could be
accounted for by accidental degeneracy of the hyperfine
coupling to the two equivalent P nuclei and the two
equivalent hydroxo H nuclei. In order to probe for this
possibility, an H/D exchange experiment with D2O was
attempted. The addition of excess D2O to a THF
solution of 2 did not affect the shape nor the intensity
of the EPR spectrum over 30 min, until addition of a
larger excess induced the reprecipitation of the com-
pound. We cannot rule out, however, that H/D ex-
change is too slow under our conditions. The observed
patterns may also result from the overlap of different
resonances due to isomers of the compounds. In this
respect, we note that the presence of different isomers
in solution has been established for Cp*MoCl2(dppe)
In conclusion, we have extended a new method for
obtaining organometallic hydroxo complexes, which in-
volves the oxidation of hydride precursor complexes in
wet THF, to the formation of geminal bis(hydroxo)
derivatives. It is to be remarked that the complexes
described here join a very limited family of terminal
gem-M(OH)2 compounds. Cp*W(OH)2Cl2 [31] seems to
constitute the only precedent for organometallic deriva-
tives of the Group 6 metals. The only other structurally
characterized organometallic terminal gem-bis(hy-
droxo) complex appears to be Cp*2 Zr(OH)2 [32].
4. Supplementary material
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 132464. Copies of this infor-
mation may be obtained free of charge from The
Director, CCDC, 12 Union Road, Cambridge, CB2
1EZ, UK (Fax: +44-1223-336033; e-mail: deposit-
@ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).

D. Morales et al. / Journal of Organometallic Chemistry 596 (2000) 64–69
69
[13] R.C. Murray, L. Blum, A.H. Liu, R.R. Schrock, Organometal-
lics 4 (1985) 953.
Acknowledgements
[14] A.L. Spek, Acta Crystallogr. Sect. A Found. Crystallogr. 46
(1990) C34.
[15] G.M. Sheldrick, University of Go¨ttingen, Go¨ttingen, Germany,
1997.
[16] P. van der Sluis, A.L. Spek, Acta Crystallogr. Sect. A Found.
Crystallogr. 46 (1990) 194.
[17] In synthetic procedures where the oxidation of the trihydride
precursor is incomplete, the remaining amount of the latter may
also act as a proton scavenger, affording [Cp*MoH4(dppe)]+
which is eliminated during the pentane extraction procedure.
[18] K.-M. Chi, J.C. Calabrese, W.M. Reiff, J.S. Miller,
Organometallics 10 (1991) 688.
We are grateful to the Conseil Re´gional de Bour-
gogne, the MENRT and the CNRS for support of this
work. We thank the Conseil Re´gional de Bourgogne
and the II Plan Regional de Investigation del Princi-
pado de Asturias (Spain) for postoctoral fellowships to
D.M. We also thank Professor H. Sitzmann for a
generous gift of the (C5Et5)Mo(CO)3CH3 starting
material.
[19] D. Stein, H. Sitzmann, R. Boese, J. Organomet. Chem. 421
(1991) 275.
References
[20] D. Stein, H. Sitzmann, E. Dormann, H. Winter, J. Organomet.
Chem. 412 (1991) 143.
[21] R. Poli, J. Coord. Chem. B 29 (1993) 121.
[22] J.C. Fettinger, D.W. Keogh, B. Pleune, R. Poli, Inorg. Chim.
Acta 261 (1997) 1.
[23] R. Poli, Organometallics 9 (1990) 1892.
[24] K. Prout, T.S. Cameron, R.A. Forder, S.R. Critchley, B. Den-
ton, G.V. Rees, Acta Crystallogr. B30 (1974) 2290.
[25] B. Antelmann, G. Huttner, U. Winterhalter, J. Organomet.
Chem. 555 (1998) 119.
[1] F. Bottomley, L. Sutin, Adv. Organomet. Chem. 26 (1988) 339.
[2] H.E. Bryndza, W. Tam, Chem. Rev. 88 (1988) 1163.
[3] J.W. Gilje, H.W. Roesky, Chem. Rev. 94 (1994) 895.
[4] J.C. Fettinger, H.-B. Kraatz, R. Poli, E.A. Quadrelli, J. Chem.
Soc. Dalton Trans. (1999) 497.
[5] O.B. Ryan, M. Tilset, V.D. Parker, J. Am. Chem. Soc. 112
(1990) 2618.
[6] E.A. Quadrelli, H.-B. Kraatz, R. Poli, Inorg. Chem. 35 (1996)
5154.
[7] J.C. Fettinger, H.-B. Kraatz, R. Poli, E.A. Quadrelli, Chem.
Commun. (Cambridge) (1997) 889.
[8] J.C. Fettinger, H.-B. Kraatz, R. Poli, E.A. Quadrelli, R.C.
Torralba, Organometallics 17 (1998) 5767.
[9] B. Pleune, R. Poli, J.C. Fettinger, J. Am. Chem. Soc. 120 (1998)
3257.
[10] B. Pleune, D. Morales, R. Meunier-Prest, P. Richard, E. Col-
lange, J.C. Fettinger, R. Poli, J. Am. Chem. Soc. 121 (1999)
2209.
[26] S.T. Krueger, B.E. Owens, R. Poli, Inorg. Chem. 29 (1990) 2001.
[27] J.C. Fettinger, D.W. Keogh, R. Poli, J. Am. Chem. Soc. 118
(1996) 3617.
[28] R. Poli, B.E. Owens, S.T. Krueger, A.L. Rheingold, Polyhedron
11 (1992) 2301.
[29] G. Parkin, J.E. Bercaw, Polyhedron 7 (1988) 2053.
[30] M. Yoon, D.R. Tyler, Chem. Commun. (Cambridge) (1997) 639.
[31] M.S. Rau, C.M. Kretz, G.L. Geoffroy, A.L. Rheingold,
Organometallics 12 (1993) 3447.
[11] D. Morales, R. Poli, J. Andriev, Inorg. Chim. Acta, submitted
for publication.
[32] R. Bortolin, V. Patel, I. Munday, N.J. Taulor, A.J. Carty, J.
Chem. Soc. Chem. Commun. (1985) 456.
[12] K.N. Anisimov, N.E. Kolobova, I.B. Zlotina, Izv. Akad. Nauk.
SSSR Ser. Khim. (1964) 1326.
[33] C.K. Johnson, Oak Ridge National Laboratory, Oak Ridge, TN,
1976.
.
.