Half-sandwich molybdenum compounds with phosphine-alkylthiolate and phosphine-thioether ligands. Crystal structure of [CpMo(SCH2CH2PPh2)2][BPh 4]

Article abstract of DOI:10.1039/a809903k

The reaction of CpMoCl₂ with Ph₂PCH₂CH₂SR (R = H, CH₃) yields the corresponding addition products CpMoCl₂(Ph₂PCH₂CH₂SR), but only the derivative with R = CH₃ (compound 5) is sufficiently stable to be isolated as a crystalline solid. The derivative with R = H evolves rapidly to afford a mixture of compounds [CpMo(SCH₂CH₂-PPh₂)₂]⁺Cl 1, and [CpMoCl(SCH₂CH₂PPh₂)]₂ 2, the former being favored by a larger ligand: Mo ratio. Compound 1 undergoes metathesis with NaBPh₄ to afford [CpMo(SCH₂CH₂PPh₂)₂] ⁺BPh₄^- 3, which has been characterized by X-ray crystallography. The reaction of CpMoCl₂ with 2 equivalents of Ph₂PCH₂CH₂S^-Li⁺ affords the paramagnetic complex CpMo(SCH₂CH₂PPh₂)₂ 4, which is readily oxidized by Cp₂Fe⁺ or by H⁺ to the corresponding cation. The salts 1 and 3, in turn, may be reduced by Na amalgam, MeLi, or Bu^tOK to compound 4. The reversible redox process interconverting 4 and its cation occurs at E_1/2 = -1.23 V relative to the ferrocene standard, while compound 5 shows a reversible oxidation process at E_1/2 = 0.12 V by cyclic voltammetry. The comparison between these potentials and that previously reported for CpMoCl₂(dppe) indicates relative donor abilities in the order Ph₂P > MeS and RS^- > Cl^-. Compound 5 can also be synthesized by Na amalgam or Zn reduction of CpMoCl₄(Ph₂PCH₂CH₂SCH₃) 6, which is obtained by addition of the ligand to CpMoCl₄.

Full text of DOI:10.1039/a809903k

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Half-sandwich molybdenum compounds with phosphine–
alkylthiolate and phosphine–thioether ligands. Crystal structure
of [CpMo(SCH2CH2PPh2)2][BPh4]
Dolores Morales, Rinaldo Poli,* Philippe Richard, Jacques Andrieu and Edmond Collange
Laboratoire de Synthèse et d’Electrosynthèse Organométalliques, Faculté des Sciences
“Gabriel”, Université de Bourgogne, 6 Boulevard Gabriel, 21100 Dijon, France.
E-mail: Rinaldo.Poli@u-bourgogne.fr
Received 21st December 1998, Accepted 21st January 1999
The reaction of CpMoCl2 with Ph2PCH2CH2SR (R = H, CH3) yields the corresponding addition products
CpMoCl2(Ph2PCH2CH2SR), but only the derivative with R = CH3 (compound 5) is sufficiently stable to be isolated as
a crystalline solid. The derivative with R = H evolves rapidly to afford a mixture of compounds [CpMo(SCH2CH2-
PPh2)2]ϩClϪ 1, and [CpMoCl(SCH2CH2PPh2)]2 2, the former being favored by a larger ligand:Mo ratio. Compound
1 undergoes metathesis with NaBPh4 to afford [CpMo(SCH2CH2PPh2)2]ϩBPh4Ϫ 3, which has been characterized by
X-ray crystallography. The reaction of CpMoCl2 with 2 equivalents of Ph2PCH2CH2SϪLiϩ affords the paramagnetic
complex CpMo(SCH2CH2PPh2)2 4, which is readily oxidized by Cp2Feϩ or by Hϩ to the corresponding cation. The
salts 1 and 3, in turn, may be reduced by Na amalgam, MeLi, or ButOK to compound 4. The reversible redox process
₁
interconverting 4 and its cation occurs at E = Ϫ1.23 V relative to the ferrocene standard, while compound 5 shows a
₂
₁
reversible oxidation process at E = 0.12 V by cyclic voltammetry. The comparison between these potentials and that
₂
previously reported for CpMoCl2(dppe) indicates relative donor abilities in the order Ph2P > MeS and RSϪ > ClϪ.
Compound 5 can also be synthesized by Na amalgam or Zn reduction of CpMoCl4(Ph2PCH2CH2SCH3) 6, which is
obtained by addition of the ligand to CpMoCl4.
intermediate which disappears within a few minutes. The EPR
properties of this intermediate indicate its probable com-
Introduction
Molybdenum complexes with sulfide, thiolate, or thioether
position as the addition product, CpMoCl2(Ph2PCH2CH2SH),
ligands are extensively used models for understanding the
by comparison with those of the stable thioether analogue
mechanism of action of fossil fuel hydrotreating catalysts and
CpMoCl2(Ph2PCH2CH2SCH3), compound 5, see below. When
a larger excess of the ligand was used (3.5 equivalents), how-
ever, compound 1 was recovered in a greater yield (57% relative
to 40% when 2 equivalents were used) and product 2 was
absent. The yield of compound 1 was even lower (20%) when
using a 1:1 Mo:ligand ratio.
Compound 1, which is obtained as a yellow precipitate from
metalloenzymes involved in the nitrogen cycle.1–10 In both areas,
useful information has been obtained from fundamental
investigations of the effect of the coordination environment on
the stability, redox properties, and reactivity. A great many
studies have been devoted to dinuclear half-sandwich com-
plexes of Mo() and Mo(),6,7,10 generally containing only
anionic ligands (halides, thiolates, sulfide) or a combination of
these and neutral π-acceptor ligands (carbonyl, isocyanides,
thioethers). In our laboratory, we have investigated in detail
reactivity and redox properties as a function of the ligands for a
the reaction mixture, is insoluble in all common solvents
and only slightly soluble in MeOH. A 31P-{1H} NMR spectrum
in MeOH shows a single resonance at δ 85.1, indicating its
diamagnetic nature. Methathesis of 1 with NaBPh4 yields a
class of mononuclear complexes of formula CpMoX2L2 where
more soluble tetraphenylborate salt, 3, which was amenable to a
X is a halide ligand and L is typically a tertiary phosphine.11–18
more detailed characterization. The 31P-{1H} NMR resonance
These are stable paramagnetic compounds characterized by a
17-electron configuration and sharp room temperature iso-
of 3 compares with that of 1, while the triplet 1H NMR reson-
ance for the Cp ring at δ 4.40 (JPH = 1.83 Hz) is direct evidence
tropic EPR resonances. Here we extend the above class to
for the presence of two ligands per metal atom. These spectral
thiolate and thioether derivatives.
data suggest a four-legged piano stool structure for the cation,
leaving uncertain the stereochemistry (cis vs. trans). The trans
configuration is shown by the X-ray structural characterization
(see below).
Results
Reactions with the Ph2PCH2CH2SH ligand
Compound 2 is obtained as a microcrystalline brown solid by
diffusion of pentane into the CH2Cl2 solution after separation
of compound 1. This compound is insoluble in hydrocarbon
solvents but soluble in CH2Cl2, CHCl3 and THF. Elemental
analyses (C, H, S) and NMR investigations (1H and 31P) help
in the structural assignment of the compound. The doublet Cp
The reaction between CpMoCl2 and the bifunctional ligand
Ph2PCH2CH2SH in a 1:1 or 1:2 ratio produces compounds
[CpMo(SCH2CH2PPh2)2]Cl 1, and [CpMoCl(SCH2CH2PPh2)]2
2 [eqn. (1)]. The interaction initially affords an EPR active
1
resonance in the H NMR spectrum indicates the presence of
only one ligand per metal atom and the diamagnetism requires
CpMoCl2 ϩ Ph2PCH2CH2SH → [CpMo(SCH2CH2PPh2)2]Cl
1
a
dimeric formulation, since mononuclear half-sandwich
ϩ [CpMoCl(SCH2CH2PPh2)]2 (1)
Mo() complexes are paramagnetic and EPR active.17 A satur-
ated electronic configuration can be reached by adopting a
2
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bridged structure with a metal–metal bond, as described for the
isoelectronic complex {[CpMo(µ-SBut)(CO)2]2}2ϩ 19
In prin-
.
ciple, either the two chloride ligands or the two thiolate func-
tions may occupy the bridging positions. The superior bridging
ability of thiolates relative to halides lead us to propose struc-
ture I for compound 2. The isoelectronic Mo() complexes
[CpM(SMe)X(CO)]2 (M = Mo, W; X = Cl, Br) have also been
proposed to adopt a thiolato-bridged structure with terminal
halide ligands,20 and complexes with bridging thiolato or hydro-
sulfide and terminal chlorides are known for other metals.21,22
The single 31P-{1H} NMR resonance at δ 78.5 indicates the
equivalence of the two phosphorus atoms and the chelating
nature of the ligand, but cannot distinguish between the P–S
and the P–(µ-S) binding modes. Unfortunately, suitable crystals
for an X-ray investigation could not be obtained.
S
S
Fig. 1 An ORTEP45 view of the cation of compound 3 with thermal
ellipsoids drawn at the 30% probability level. Hydrogen atoms are
omitted for clarity.
Mo
Mo
Cl
Ph2P
P
Ph2
Cl
I
Ph2
P
Mo
S
The reaction between CpMoCl2 and 1 equivalent of Ph2P-
CH2CH2SϪLiϩ leads to a mixture of unidentified paramagnetic
products. However, the reaction with 2 equivalents of the same
reagent produces a stable paramagnetic Mo() compound,
namely CpMo(SCH2CH2PPh2)2 4, see eqn. (2). Compound 4
P
S
Ph2
4
CpMoCl2 ϩ 2 Ph2PCH2CH2SϪLiϩ →
(i) [Cp2Fe]BF4 or HBF4 (X= BF4)
(ii) Na (X= BPh4) or 2MeLi (X=Cl) or ButOK (X=Cl)
CpMo(SCH2CH2PPh2)2 ϩ 2 LiCl (2)
4
(i) (ii)
also forms upon treatment of compound 2 with Ph2PCH2-
CH2SϪLiϩ, see eqn. (3). The identity of this complex as a 17-
[CpMoCl(SCH2CH2PPh2)]2 ϩ 2 Ph2PCH2CH2SϪLiϩ →
+
2
2 CpMo(SCH2CH2PPh2)2 ϩ 2 LiCl (3)
(4)
4
X –
Ph2
P
Mo
S
electron monomer is confirmed by the EPR spectrum which
shows a binomial triplet (g = 1.987, aP = 3.9 G, aMo = 32.4 G) in
hexane (other solvents yield a broader resonance which does
not permit the observation of the phosphorus coupling). It is
interesting to note the unusually small phosphorus hyperfine
coupling. In previously reported bis(phosphine) dichloro
complexes of half-sandwich Mo(), the aP values are smaller
when the two P donors adopt a relative trans configuration (in
the 9–16 G range) than when they are located cis to each other
(greater than 23 G).12,14,23 A trans geometry seems therefore
most reasonable for compound 4.
This compound can be also synthesized by reduction
of compounds 1 and 3, eqn. (4). The reduction of the THF-
soluble 3 can be easily accomplished with sodium, while the
reduction of the insoluble 1 can conveniently be carried out by
the use of THF-soluble reducing agents. One such reagent is
MeLi, which is known to display single electron transfer prop-
erties.24 The reduction process with this reagent is instantaneous
in THF. Somewhat surprisingly, a clean reduction process also
occurs, albeit more slowly (12 h), with ButOK. Conversely,
compound 4 can be chemically oxidized to the corresponding
cation by a ferrocenium salt, [Cp2Fe]BF4, or by the proton of
HBF4ؒOEt2, as shown by EPR and NMR spectroscopic
monitoring. Oxidation with HBF4ؒOEt2 in C6D6 led to the
immediate evolution of H2, which was identified by the charac-
teristic NMR resonance at δ 4.5.
P
Ph2
S
1 (X = Cl)
3 (X = BPh4)
witnessed by electrochemical investigations. The cyclic voltam-
mogram of compound 4 shows a reversible oxidation wave at
E = Ϫ1.23 V, which is quite close to the potential of the revers-
ible reduction wave measured for compound 3 (E = Ϫ1.25 V).
₁
₂
₁
₂
This value is an indicator of the electron richness of this system
relative to the CpMoCl2L2 complexes (L = tertiary phosphine),
whose oxidation potentials are in the range Ϫ0.33 V (for L2 =
dppe) to Ϫ0.63 V (for L = PPrn ).14 This illustrates the greater
3
donor capability of a thiolate ligand relative to a chloride. Since
compound 3 is shown by the X-ray analysis to adopt a trans
geometry, the reversibility of the redox process indicates the
same relative configuration for compound 4, confirming
the prediction previously made on the basis of the aP value in
the EPR spectrum.
A view of the cation of compound 3 is shown in Fig. 1, and
bond lengths and angles in Table 1. The geometry can be
described as a four-legged piano stool, with the pairs of sulfur
and phosphorus atoms occupying relative trans positions to
yield an approximate C2 local symmetry. The CNT–Mo–L
angles (CNT = center of gravity of the Cp ring) are larger for
The reversibility of the redox process in eqn. (4) can also be
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Table 1 Selected bond distances (Å) and angles (Њ) for compound 3a
is correspondingly slightly greater (29 and 33 G for dppe and
dmpe analogues, respectively). The alternative trans arrange-
ment, observed for the bulkier Cp*MoCl2(dppe) derivative,
leads to completely different spectral parameters.23 The g factor
was shown to be highly dependent on the nature of the halide
ligands but rather independent of the phosphine substituents
(in the 1.978–1.994 range for the dichloride complexes). The g
value recorded for compound 5 is at the low end of this range,
and a direct comparison with the value for CpMoCl2(dppe)
(g = 1.986)12 indicates a rather small low-field shift caused by
the replacement of a PPh2 donor with a SMe donor. Com-
Mo–CNT
Mo–S(1)
Mo–P(2)
1.98(2)
2.3261(9)
2.4824(9)
Mo–S(2)
Mo–P(1)
2.3134(9)
2.4770(9)
CNT–Mo–S(1)
CNT–Mo–S(2)
CNT–Mo–P(1)
CNT–Mo–P(2)
S(1)–Mo–S(2)
125(1)
116(1)
111(1)
108(1)
118.82(3)
S(1)–Mo–P(1)
S(1)–Mo–P(2)
S(2)–Mo–P(1)
S(2)–Mo–P(2)
P(1)–Mo–P(2)
77.84(3)
82.22(3)
82.72(3)
77.64(3)
140.56(3)
a CNT is the centroid of the cyclopentadienyl ring.
₁
pound 5 shows a reversible oxidation wave at E = 0.12 V in the
₂
cyclic voltammogram. This is 0.45 V more positive relative
to the oxidation process of the analogous CpMoCl2(dppe)
complex,14 indicating that the SMe group is a weaker electron
donor relative to the PPh2 group, as expected from the different
electronegativity of the two donor elements.
the thiolate donors than for the phosphorus donors, as pre-
dicted on the basis of the π-donor/acceptor properties of these
ligands and the diamagnetic configuration of the complex.25
The geometry and metric parameters can be best compared
with those of the isoelectronic oxo compound MoO(SCH2-
CH2PPh2)2.26 Both are compounds of Mo() with the same
bifunctional ligand, the O2Ϫ and CpϪ ligands being both
capable of establishing three bonding interactions (σ ϩ 2π)
and, therefore, being able to donate 6 electrons to the metal
center. The Mo–P distances are comparable in the two
compounds, whereas the Mo–S distances are significantly
shorter in the cation of 3 relative to the oxo analogue (2.372(4)
Å and 2.348(4) Å).26 This difference can be rationalized by
the stronger electron donating capability of the O2Ϫ ligand
relative to the CpϪ, as also indirectly established from other
comparisons.27
Compound 5 has also been prepared by an alternative pro-
cedure (Scheme 1). The reaction between CpMoCl4 and one
equivalent of the ligand in CH2Cl2 affords the corresponding
addition product CpMoCl4(Ph2PCH2CH2SCH3), 6, in good
yields. Reduction of compound 6 in THF with either 2 equiv-
alents of sodium amalgam or 1 equivalent of Zn gives the
Mo() complex 5. The EPR spectrum of compound 6 does not
show coupling to the phosphorus atom (singlet at g = 1.954,
aMo = 51.8 G). Previously reported phosphine adducts of alkyl-
substituted cyclopentadienyl derivatives of Mo() display
rather large phosphorus hyperfine constants (greater than 24
G),29–31 thus indicating the possibility that the bifunctional
ligand binds the metal in a monodentate fashion via the sulfur
donor in compound 6. However, we find that the addition of
the electronically similar PMePh2 ligand to CpMoCl4 affords an
EPR spectrum which consists of a single resonance with no
observable hyperfine coupling to the P nucleus. The g value and
aMo hyperfine coupling of this spectrum are very similar to
those of the Ph2PCH2CH2SMe adduct (see Experimental sec-
tion). Therefore, phosphorus coordination to the metal center
remains a structural possibility. We have also considered the
possibility of a bidentate coordination mode for the phosphine–
thioether ligand. This alternative arrangement would likely
induce the displacement of a chloro ligand, to afford an ionic
isomer, [CpMoCl3(η2-Ph2PCH2CH2SMe-P,S)]ϩClϪ. Electrical
conductivity measurements indicate the presence of ionic
species (Λ∞ = 9.3 and 90.5 S cm2 molϪ1 in THF and MeCN
solutions, respectively). The values measured, however, are
slightly smaller than those typically observed for fully dissoci-
ated 1:1 salts.32 A possible rationalization of this result is the
existence of an equilibrium between ionic and neutral isomeric
forms.
Reactions with the Ph2PCH2CH2SCH3 ligand
The reaction between CpMoCl2 and the phosphine–thioether
ligand Ph2PCH2CH2SCH3 leads to the addition product 5, see
Scheme 1, which was isolated as a microcrystalline brown-red
Ph2PCH2CH2SMe
CpMoCl2
Ph2
Mo
P
Cl
Cl
S
Me
5
2Na–Hg
or Zn
Ph2PCH2CH2SMe
An attempt was made to methylate compound 5 with methyl-
lithium. The reaction with 1 equivalent of MeLi carried out
at Ϫ80 ЊC in THF led to the disappearance of the starting
material without the appearance of new EPR-active species.
The 31P-{1H} NMR spectrum showed the formation of a com-
plex mixture of several products, which was not further investi-
gated. When 2 equivalents of MeLi were used, the immediately
recorded EPR spectrum showed a new doublet resonance
(g = 1.987, aP = 24.3 G, aMo = 38.6 G), which we tentatively
assign to the dimethyl product CpMo(CH3)2(Ph2PCH2CH2-
SMe), but the signal disappeared after ca. 1/2 h at room tem-
perature. The 31P-{1H} NMR spectrum showed the release of
the free ligand Ph2PCH2CH2SMe. An analogous alkylation
attempt had been carried out previously for the compound
CpMoCl2(PMe3)2, also resulting in decomposition of the
alkylation product,13 whereas the alkylation of CpMoCl2(η4-
C4H6) affords thermally stable dialkyl derivatives.33 The positive
shift of the g value upon methylation of compound 5 (from
1.973 to 1.987) parallels those observed upon methylation of
CpMoCl2(PMe3)2 (from 1.982 to 2.003) and CpMoCl2(η4-C4-
H6) (from 1.994 to 2.012).
CpMoCl4(Ph2PCH2CH2SMe)
CpMoCl4
6
Scheme 1
solid and characterized by elemental analysis, EPR spectro-
scopy, and cyclic voltammetry. The compound is indefinitely
stable under an argon atmosphere at Ϫ80 ЊC, but decomposes
at room temperature rather quickly even under an inert atmos-
phere. The EPR spectrum shows the expected doublet due to
coupling with a phosphorus atom (g = 1.973, aP = 24.7 G,
aMo = 35.9 G). These properties compare quite well with those
of the diphosphine derivatives CpMoCl2(L–L) (L–L = dppe,
dmpe) for which a four legged piano-stool structure with a cis
arrangement of the two phosphorus donors was demon-
strated.12,28 An analogous structure is therefore also proposed
for compound 5. In particular, the phosphorus hyperfine coup-
ling constant of 5 is only slightly smaller than those of the
diphosphine analogues (26 G for the dppe complex and 28 G
for the dmpe complex) and the Mo hyperfine coupling constant
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Ph2PCH2CH2SH
Ph2
P
Mo
H
Ph2
P
Mo
CpMoCl2
Cl
Cl
Cl
S
S
HCl
III
II
Ph2PCH2CH2SH
x 2
S
S
HCl
+
Cl-
Mo
Mo
HCl
Ph2
P
Mo
S
Ph2
P
Mo
S
Cl
P
Ph2
Ph2P
Cl
P
Ph2
S
P
1/2 H2
S
Ph2
2
4
1
Scheme 2
properties in the order RSϪ > ClϪ and RSMe < RPPh2. Both
these two effects contribute to render compound 4 much more
easily oxidized relative to compound 5.
Discussion
The addition of neutral ligands to CpMoCl2 to form 17-
electron CpMoCl2L2 adducts had previously been established
when L = tertiary phosphine11,14 or L2 = diphosphine12 or
diene.34 In this contribution, we have analyzed the results of the
addition of the bifunctional ligands Ph2PCH2CH2SR (R = H,
CH3). An isolable addition product (compound 5) is only
obtained for R = CH3. When R = H, the addition intermediate
(which can be spectroscopically observed) rapidly evolves to
lead to the isolation of two different products, 1 and 2, in a
relative ratio that depends on the amount of ligand used. The
results of the electrochemical investigations help us formulate a
mechanism for the formation of these compounds (see Scheme
2).
The difference between the two addition products is likely
due to the acidity of the SH function, especially once this is
coordinated to the metal center. Thus, deprotonation of the
intermediate II and loss of chloride would lead to the unsatur-
ated complex III. A related deprotonation process has been
described for a very similar reaction, namely the addition of
HS(CH2)nSH (n = 2, 3) to Cp2Mo2(µ-SMe)3(µ-Cl), whereby
the dinuclear product Cp2Mo2(µ-SMe)3[µ-S(CH2)nSH] is
obtained with elimination of HCl.35 Compound CpMoCl2
is also a dinuclear compound with four bridging chloro
ligands.36–38 Intermediate III can evolve to a saturated product
either by dimerization, leading directly to the observed product
2, or by addition of a second molecule of the ligand Ph2PCH2-
CH2SH. Further deprotonation and chloride loss would afford
compound 4, but the redox properties of this 17-electron
Mo() product make it susceptible to oxidation by the available
protons, as it has independently been verified, to afford the
observed Mo() product 1. The essential features of this
proposed mechanism are consistent with the observation that
the use of an increased amount of the ligand Ph2PCH2CH2SH
increases the yield of 1 and decreases the yield of 2. In addition,
compound 2 converts into compound 4 upon treatment with
Ph2PCH2CH2SϪ.
Conclusions
The present study is relevant in comparison with previous
investigations of electron-poor half-sandwich Mo() com-
plexes, which by and large prefer to adopt a dinuclear structure
with a metal–metal bond. The combination of a sulfur ligand
(alkylthiolate or thioether) with a phosphorus donor in a
chelating bifunctional ligand leads to stable mononuclear,
electron-rich compounds. This greater electron-richness is
clearly manifested in the oxidation of Mo() to Mo() by the
protons generated from coordinated mercaptans, to yield H2.
Similar oxidation of dinuclear, thiolate-bridged cyclopenta-
dienyl derivatives of Mo() by the proton have been reported.7
Experimental
All reactions were carried out in dry solvents under a dinitrogen
or argon atmosphere by the use of Schlenk line or glove-box
techniques. The solvents were dried by conventional methods
(CH2Cl2 from CaH2, THF from Na–K, pentane and toluene
from Na–benzophenone) and distilled under nitrogen prior to
use. Deuteriated solvents were dried over molecular sieves and
1
degassed by 3 freeze–pump–thaw cycles prior to use. H and
31P-{1H} NMR measurements were carried out on a Bruker
AC200 spectrometer. The peak positions are reported with
positive shifts downfield of SiMe4 as calculated from the
residual solvent peaks (1H) or downfield of external 85% H3PO4
(31P). EPR measurements were carried out at the X-band
microwave frequency on a Bruker ESP300 spectrometer. The
spectrometer frequency was calibrated with diphenylpicryl-
hydrazyl (g = 2.0037). Cyclic voltammograms were carried out
at room temperature with a Radiometer digital electrochemical
analyzer (model DEA332). The electrochemical cell was fitted
with an SCE reference electrode, a platinum disc working elec-
trode and a Pt wire counter electrode. Bu4NPF6 (ca. 0.1 M)
was used as supporting electrolyte. All potentials are reported
relative to the ferrocene standard, which was added to each
solution and measured at the end of the experiments. The solu-
tion conductivity measurements were carried out at 25 ЊC with
a Tacussel type CD6 N conductimeter equipped with an XE
110 cell which had been calibrated with a 0.1 M KCl solution.
The elemental analyses were carried out by the analytical
service of the Laboratoire de Synthèse et d’Electrosynthèse
Organométalliques. NaBPh4, HBF4ؒOEt2, MeLi (1 M solution
in diethyl ether), BunLi (1.6 M solution in hexanes), ButOK and
It is notable that intermediate II has the same electronic
configuration as compound 4, but is not oxidized under the
reaction conditions that lead to products 1 and 2. The electro-
chemical investigation of the analogous thioether complex 5
indicates that the potential at which its oxidation would occur is
much more positive relative to that of compound 4 (ca. 1.3 V
more positive), revealing a dramatic effect of the ligand’s nature
on the redox properties in this system. A comparison of the
redox potentials for the Mo()/Mo() processes in compounds
3/4 and 5 with that already reported in the literature for com-
pound CpMoCl2(dppe) (Ϫ0.33 V) shows trends in ligand donor
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Zn powder were used as received, without further purification.
CpMoCl4,39 CpMoCl2,40 Ph2PCH2CH2SH,26 and [Cp2Fe]BF4,41
were prepared according to literature procedures. Ph2PCH2-
CH2SCH3 was prepared by a slight modification of the method
described in the literature:42 to a solution of Ph2PCH2CH2SH
(1.057 mL, 4.57 mmol) in 20 mL of THF at 0 ЊC was added a
solution of 1.6 M BunLi (2.85 mL, 4.57 mmol) and MeI (284 µl,
4.57 mmol). The mixture was stirred overnight. The solvent was
evaporated in vacuo, the residue was extracted with pentane,
filtered through Celite, and concentrated in vacuo to ca. 20 mL.
Cooling to Ϫ80 ЊC for 24 h afforded white crystals of Ph2-
PCH2CH2SCH3. The 1H and 31P NMR properties of this
product are identical with those previously reported.42 Yield:
0.845 g, 71%.
CpMoCl2 (0.255 g, 1.07 mmol) in 40 mL of THF. The mixture
was stirred overnight at room temperature. The brown-red solu-
tion was evaporated under reduced pressure. The residue was
extracted in toluene and filtered through Celite. The solvent was
evaporated in vacuo, the residue was washed with cold pentane
(3 × 5 mL) and dried under vacuum. Yield: 0.382 g, 55%. EPR
(hexane): g = 1.987 (triplet with Mo satellites, aP = 3.94 G,
aMo = 32.4 G). Cyclic voltammetry (THF, room temperature):
₁
reversible oxidation at E = Ϫ1.23 V.
₂
(B) By reduction of compound 1. By MeLi. To a suspension of
compound 1 (0.091 g, 0.132 mmol) in 20 mL of toluene was
added dropwise 264 µL (0.264 mmol) of a MeLi solution (1 M
in diethyl ether) causing the dissolution of the yellow starting
material within 30 min and formation of a brown-red solution.
The solution was evaporated under reduced pressure to ca. 10
mL and filtered through Celite. The solvent was further evapor-
ated to dryness and the residue was washed with cold pentane
(3 × 5 mL) and dried under reduced pressure. Yield: 0.060 g,
69.83%. This product had spectroscopic (EPR) and electro-
chemical properties identical to those of the material obtained
by method A.
Synthesis of [CpMo(SCH2CH2PPh2)2]Cl 1
A solution of Ph2PCH2CH2SH (474 µL, 2.17 mmol) in 5 mL of
CH2Cl2 was added to a suspension of CpMoCl2 (0.143 g, 0.62
mmol) in 10 mL of CH2Cl2 and the mixture was stirred over-
night at room temperature. An immediate analysis of the
supernatant solution by EPR spectroscopy revealed a doublet
resonance (aP = 26.20 G) at g = 1.982. After a few minutes this
EPR signal was no longer present. Compound 1 precipitated as
a very insoluble yellow solid, which was collected on a filter,
washed with CH2Cl2 (4 × 5 mL) and dried in vacuo. Yield: 0.244
g, 57%. (Calc. for C33H33ClMoP2S2: C, 57.69; H, 4.84; S, 9.33.
Found: C, 57.27; H, 4.87; S, 8.96%). 31P-{1H} NMR (CH3OH,
with external D2O capillary): δ 85.1.
By ButOK. To a suspension of compound 1 (0.084 g, 0.122
mmol) in 20 mL of THF was added ButOK (0.027 g, 0.244
mmol). After 24 h of stirring at room temperature the solvent
was removed in vacuo. The residue was extracted with toluene
and filtered through Celite, the solution was evaporated to dry-
ness under reduced pressure and the residue was washed with
cold pentane (3 × 5 mL) and dried under vacuum. Yield: 0.185
g, 72.88%. (Calc. for C33H33MoP2S2: C, 60.83; H, 5.10; S, 9.84.
Found: C, 61.15; H, 5.36; S, 9.31%).
Synthesis of [CpMoCl(SCH2CH2PPh2)]2 2
A solution of Ph2PCH2CH2SH (628 µL, 2.88 mmol) in 5 mL of
CH2Cl2 was added to a suspension of CpMoCl2 (0.668 g, 2.88
mmol) in 20 mL of CH2Cl2 and the mixture was stirred over-
night at room temperature. A yellow microcrystalline precipi-
tate corresponding to compound 1 was filtered off (yield: 0.402
g, 20%). The solution was filtered again through Celite, concen-
trated in vacuo to ca. 5 mL, layered with pentane (20 mL) and
kept in a refrigerator at Ϫ20 ЊC for several days. When the
diffusion was complete compound 2 was obtained as a micro-
crystalline brown solid. Yield: 0.589 g, 46%. (Calc. for C19H19-
ClMoPS: C, 51.66; H, 4.33; S, 7.26. Found: C, 51.28; H, 4.69; S,
(C) By reduction of compound 3. To a solution of [CpMo-
(SCH2CH2PPh2)2]BPh4 (0.010 g, 0.01 mmol) in 2 mL of THF
was added Na (0.023 g, 0.01 mmol) and the mixture was stirred
at room temperature for 45 min. During this time, the yellow
solution became red and the EPR spectrum showed the signal
corresponding to compound 4. The EPR properties matched
those described above for the product of method A.
(D) From compound 2 and 2 equivalents of Ph2PCH2-
CH2S؊Li؉. To a solution of compound 2 (0.007 g, 0.009 mmol)
in 1mL of THF was added a solution of Ph2PCH2CH2SϪLiϩ,
prepared in situ from Ph2PCH2CH2SH (5 µL, 0.018 mmol) and
MeLi (18 µL, 0.018 mmol) in 1 mL of THF. The brown solution
became red. The EPR spectrum shows the signal corresponding
to compound 4.
1
6.97%). 31P-{1H} NMR (CDCl3): δ 78.5. H NMR (CDCl3):
δ 7.88–7.32 (m, 10H, Ph), 4.92 (d, JPH = 2.20 Hz 5H, Cp), 4.08–
3.07 (m, 4H, SCH2CH2P).
Synthesis of [CpMo(SCH2CH2PPh2)2]BPh4 3
To a suspension of [CpMo(SCH2CH2PPh2)2]Cl (0.034 g, 0.05
mmol) in 10 mL of THF was added NaBPh4 (0.016 g, 0.05
mmol) and the mixture was stirred overnight at room temper-
ature, resulting in the solubilization of the yellow starting
material to yield an orange solution. After evaporation, the
residue was redissolved in 10 mL of CH2Cl2. The resulting
orange solution was filtered through Celite and concentrated
under reduced pressure to ca. 5 mL. Slow diffusion of pentane
into this solution at Ϫ20 ЊC produced orange crystals after 3
days. Yield: 0.038 g, 80%. A suitable crystal obtained in this way
was used for the X-ray analysis. (Calc. for C57H53BMoP2S2: C,
70.52; H, 5.50; S, 6.60. Found: C, 70.37; H, 5.40; S, 6.31%).
NMR study of the chemical oxidation of compound 4
(A) By ferrocenium. To a solution of compound 4 (0.006 g,
0.01 mmol) in 5 mL of THF was added [Cp2Fe]BF4 (0.027 g,
0.01 mmol) and the mixture was stirred for 15 min. The red
solution changes to yellow and it becomes EPR silent. The
31P-{1H} NMR (THF) shows one sharp peak at δ 84.7 attrib-
uted to [CpMo(SCH2CH2PPh2)2]BF4.
(B) By HBF4. To a solution of compound 4 (41.65 g, 0.064
mmol) in 1 mL of C6D6 was added HBF4ؒOEt2 (0.064 mmol, 69
µL) at 0 ЊC. Gas evolution was immediately observed, dis-
charging the red colour of the solution and yielding a yellow
precipitate. 1H NMR (C6D6): δ 4.50 (s, H2). The suspension was
filtered and the yellow solid was dissolved in THF. 31P-{1H}
NMR (THF): δ 84.7.
1
31P-{1H} NMR (CD2Cl2): δ 83.4. H NMR (CD2Cl2): δ 7.48–
6.79 (m, 40H, Ph), 4.40 (t, JPH = 1.83 Hz, 5H, Cp), 3.68–
2.90 (m, 8H, SCH2CH2P). Cyclic voltammetry (THF, room
₁
temperature): reversible reduction at E = Ϫ1.25 V.
₂
Synthesis of CpMo(SCH2CH2PPh2)2 4
Synthesis of CpMoCl2(Ph2PCH2CH2SCH3) 5 from CpMoCl2
and Ph2PCH2CH2SCH3
(A) From CpMoCl2 and 2 equivalents of Ph2PCH2CH2S؊Li؉.
A solution of Ph2PCH2CH2SϪLiϩ, prepared in situ from
Ph2PCH2CH2SH (496 µL, 2.15 mmol) and MeLi (2.15 mL,
2.15 mmol) in 10 mL of THF, was added to a suspension of
To a suspension of CpMoCl2 (0.185 g, 0.8 mmol) in 15 mL of
CH2Cl2 was added a solution of Ph2PCH2CH2SCH3 (0.209 g,
0.8 mmol) in 5 mL of CH2Cl2 at room temperature. The mix-
J. Chem. Soc., Dalton Trans., 1999, 867–873
871

View Article Online
ture was stirred for 2 h, filtered through Celite and concentrated
under reduced pressure to ca. 5 mL. Addition of pentane (20
mL) gave 6 as a brown-red microcrystalline solid. Yield: 0.324
g, 82% (Calc. for C20H22Cl2MoPS: C, 48.80; H, 4.50; S, 6.51.
Found: C, 48.76; H, 4.87; S, 5.91%). EPR (hexane): g = 1.973
(doublet, with Mo satellites, aP = 24.7 G, aMo = 35.9 G). Cyclic
voltammetry (CH2Cl2, room temperature): reversible oxidation
Crystal structure determination of compound 3
Crystal data. C57H53BMoP2S2, M = 970.80, monoclinic, a =
18.943(2), b = 12.397(1), c = 20.508(2) Å, β = 91.138(7)Њ, U =
4815.1(8) Å3, T = 293(2) K, space group = P21/c (no. 14), Z = 4,
µ = 0.463 mmϪ1, 8365 reflections measured up to sinθ/λ = 0.59
Å
Ϫ1, 8108 unique (Rint = 0.0302), which were used in all the
calculations.
₁
at E = 0.12 V.
The data were corrected for absorption (ψ scan).43 No decay
was observed. The structure was solved via a Patterson search
program44 and refined (space group P21/c) with full-matrix
least-squares methods44 based on |F2|. All non-hydrogen atoms
were refined with anisotropic thermal parameters. Hydrogen
atoms of the complex were included in their calculated posi-
tions and refined with a riding model. The cyclopentadienyl
ligand was found to be disordered around its geometrical center
and was modelled as lying in two positions with occupancies
m1 = 0.624 and m2 = 1 Ϫ m1 = 0.376. The cyclopentadienyl
rings were refined as variable metric groups (the shape is
retained but the group may shrink or expand uniformly). The
final agreement indices are Rw(F2) = 0.0885 and R(F) = 0.0987
for all data and 600 parameters; R(F) = 0.0336 for 5311 data
with I > 2σ(I); goodness of fit = 1.043. The final Fourier differ-
₂
Synthesis of CpMoCl4(Ph2PCH2CH2SCH3) 6
A solution of Ph2PCH2CH2SCH3 (0.551 g, 2.11 mmol) in 5 mL
of CH2Cl2 was added to a suspension of CpMoCl4 (0.669 g,
2.21 mmol) in 20 mL of CH2Cl2 at Ϫ80 ЊC. The solution was
warmed to room temperature, stirred for 3 h and filtered
through Celite. The filtrate was concentrated under reduced
pressure to ca. 5 mL. Addition of pentane (20 mL) gave 6 as a
brown-red microcrystalline solid. Yield: 1.152 g, 96% (Calc. for
C20H22Cl4MoPS: C, 42.65; H, 3.94; S, 5.69. Found: C, 42.28; H,
3.82; S, 5.65%). EPR (CH2Cl2): g = 1.954 (s, with Mo satellites,
aMo = 51.82 G). Molar conductivity (Λ, S cm2 molϪ1) in THF
2.6 (8.9 × 10Ϫ3 M), 7.2 (8.9 × 10Ϫ4 M), Λ∞ = 9.3 S cm2 molϪ1; in
MeCN 48.9 (9.05 × 10Ϫ3 M), 75.7 (9.05 × 10Ϫ4 M), Λ∞ = 90.5 S
ence map is featureless: ∆ρ = 0.335 and Ϫ0.273 e ÅϪ3
CCDC reference number 186/1324.
.
cm2 molϪ1
.
See http://www.rsc.org/suppdata/dt/1999/867/ for crystallo-
graphic files in .cif format.
Reduction of compound 6 to compound 5
(A) With sodium amalgam. Compound 6 (0.400 g, 0.71
mmol) was dissolved in THF (20 mL) and the solution was
cooled to 0 ЊC. Freshly prepared sodium amalgam (1% w/w,
0.032 g, 1.42 mmol) was added and the mixture was stirred for
45 min. The mixture was decanted and the solution was filtered
(via cannula). The solvent was removed in vacuo and the solid
residue was extracted with CH2Cl2 and filtered through Celite.
The solution was evaporated and the precipitate was washed
with pentane and dried under vacuum. Yield: 0.162 g, 46%.
This product had spectroscopic (EPR) properties identical to
those of the material obtained from CpMoCl2 and Ph2PCH2-
CH2SMe as described above.
Acknowledgements
We are grateful to the Conseil Régional de Bourgogne, the
MENRT and the CNRS for support of this work. We also
thank the Conseil Régional de Bourgogne and the II Plan
Regional de Investigation del Principado de Asturias (Spain)
for postdoctoral fellowships to D. M.
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