A systematic study on the activation of simple polyethers by MoCl 5 and WCl6

Article abstract of DOI:10.1039/c001377c

MoCl₅, 1a, and WCl₆, 1b, activate 1,3-dioxolane at room temperature in chlorinated solvents: the compound [MoOCl ₃{OC(H)OCH₂CH₂Cl}]₂, 2, has been isolated from MoCl₅/dioxolane. The mixed oxo-chloro species WOCl ₄, 1c, reacts with 1,3-dioxolane, selectively giving the coordination adduct WOCl₄(κ¹-C₃H₆O ₂), 3. Dimethoxymethane, CH₂(OMe)₂, undergoes activation including C-H bond cleavage when reacted with 1a to give the molybdenum complexes [MoOCl₃{OC(H)OMe}]₂, 4, and Mo ₂Cl₅(OMe)₅, 5. The reactions of 1b with CH ₂(OR)₂ (R = Me, Et) proceed via O-abstraction with formation of the oxo-derivatives WOCl₄[O(R)CH₂Cl] (R = Me, 6a; R = Et, 6b) in admixture with equimolar amounts of RCl. The reactions of 1a,b with CMe₂(OMe)₂ lead to mesityl oxide, MeC(O)CHC(Me)₂. A series of simple diethers of general formula ROCH₂(CHR′)OR′′ are activated by 1a,b in CDCl ₃, usually via cleavage of C-O bonds at high temperature. The complex WCl₅(OCH₂CH₂OMe), 7, has been detected in solution as an intermediate species in the course of the degradation of 1,2-dimethoxyethane (dme) by 1b. The activation of CH(OMe)₃ by 1 is limited to C-O bonds and selectively gives methyl chloride and methylformate, which has been found coordinated in WOCl₄[OC(H)OMe], 8. The organic fragments produced in the reactions have been detected by GC-MS and NMR analyses, upon hydrolysis of the reaction mixtures. Compounds 2 and 5, which have had their molecular structures ascertained by X-ray diffraction, represent rare examples of crystallographically-characterized dinuclear Mo(v) species containing both halides and oxygen ligands.

Full text of DOI:10.1039/c001377c

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PAPER
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A systematic study on the activation of simple polyethers by MoCl5
and WCl6†
a
a
a
b
Sara Dolci, Fabio Marchetti,‡ Guido Pampaloni* and Stefano Zacchini
Received 22nd January 2010, Accepted 13th April 2010
First published as an Advance Article on the web 7th May 2010
DOI: 10.1039/c001377c
MoCl
5
, 1a, and WCl
6
, 1b, activate 1,3-dioxolane at room temperature in chlorinated solvents: the
CH , 2, has been isolated from MoCl /dioxolane. The mixed
, 1c, reacts with 1,3-dioxolane, selectively giving the coordination adduct
(OMe) , undergoes activation including C–H bond
{O=C(H)OMe}]
, 4, and
(R = Me, Et) proceed via O-abstraction with
Cl] (R = Me, 6a; R = Et, 6b) in admixture with
equimolar amounts of RCl. The reactions of 1a,b with CMe (OMe) lead to mesityl oxide,
MeC(O)CH=C(Me)
. A series of simple diethers of general formula ROCH (CHR¢)OR¢¢ are activated
by 1a,b in CDCl , usually via cleavage of C–O bonds at high temperature. The complex
WCl (OCH CH OMe), 7, has been detected in solution as an intermediate species in the course of the
degradation of 1,2-dimethoxyethane (dme) by 1b. The activation of CH(OMe) by 1 is limited to C–O
bonds and selectively gives methyl chloride and methylformate, which has been found coordinated in
WOCl
compound [MoOCl
3
{O=C(H)OCH
2
2
Cl}]
2
5
oxo-chloro species WOCl
4
1
WOCl
4
(k -C
3
H
6
O
2
), 3. Dimethoxymethane, CH
2
2
cleavage when reacted with 1a to give the molybdenum complexes [MoOCl
Mo Cl (OMe) , 5. The reactions of 1b with CH (OR)
formation of the oxo-derivatives WOCl [O(R)CH
3
2
2
5
5
2
2
4
2
2
2
2
2
3
5
2
2
3
[O=C(H)OMe], 8. The organic fragments produced in the reactions have been detected by
4
GC-MS and NMR analyses, upon hydrolysis of the reaction mixtures. Compounds 2 and 5, which have
had their molecular structures ascertained by X-ray diffraction, represent rare examples of
crystallographically-characterized dinuclear Mo(V) species containing both halides and oxygen ligands.
Introduction
complicate the comprehension of this chemistry: (a) the high air-
and moisture-sensitivity of 1, providing difficulties in the storage
and in the manipulation of these materials; (b) when organic
substrates are allowed to contact with 1, activation of the former
Early transition metal halides in high oxidation states have
been efficiently employed in a huge number of metal-directed
1-3
reactions.
In this context, the most accessible halides of the group
heavier metals in high oxidation state, i.e. MoCl , 1a, and
WCl
variety of processes, including polymerization of alkynes, alkenes
20
may take place even at room temperature; and (c) compounds
1
may reduce to lower oxidation states by reaction with different
6
5
21
types of ligands. More specifically, the behaviour of MoCl
5
in
6
, 1b, have found application as catalytic precursors in a
oxygen-containing organic solvents, L, was subject to investigation
4
5
22
a long time ago. It was proposed that two main reactivity patterns
6
7
8
and cyclic esters, alkene metathesis, ROMP polymerization,
20b
could be followed depending on L: (i) O-abstraction from L (see
9
10
alkene fluorination, thioacetalizations, and oxidative coupling
point (b) above), resulting in formation of chloro-oxo derivatives
11
of sulfides. In particular, the high oxophilicity of 1a and 1b
has been exploited for performing different types of transforma-
tions involving oxygen species; relevant examples are oxidative
23
MoOCl
3
L
2
;
and (ii) metal reduction with consequent generation
(see point (c) above). It may sound impressive
that only two crystallographically-characterized compounds, i.e.
of adducts MoCl
4
L
2
1
2
coupling of alkoxyarenes, chlorination of alcohols, aldehydes
24
20c
WCl
6
(S
8
), and MoCl
5
(OPCl ), as obtained by simple Lewis-
3
13
14
and epoxides, N-acylation of sulfonamides, acylative cleavage
base addition to compounds 1a and 1b, have been reported.
A better knowledge of the stoichiometric chemistry of 1 may
help the understanding and, hopefully, improve the catalytic
processes. This is particularly true on considering that the catalytic
activity of 1 is often reported to be associated with the presence
of an “oxygen modifier” (ether, amide, DMSO, etc.) acting as
15
16
17
of ethers, deoxygenation, C–C coupling, and conversion of
18
ketones into vinyl-chlorides.
In spite of the interesting performances that compounds 1a and
b may exhibit in catalysis, their coordination chemistry is still
1
19
far from being well elucidated. There are some factors which
4d,5,13c
a promoter.
For example, the ring opening polymerization
a
of various cyclic olefins has been efficiently performed in the
Universit a` di Pisa, Dipartimento di Chimica e Chimica Industriale,
25
Via Risorgimento 35, I-56126, Pisa, Italy. E-mail: pampa@dcci.unipi.it;
Fax: +39 050 2219246; Tel: +39 050 2219219
presence of oxygen Lewis bases. Nevertheless, no information
about the interaction of the modifier with the metal species has
been provided.
b
Universit a` di Bologna, Dipartimento di Chimica Fisica e Inorganica, Viale
Risorgimento 4, I-40136, Bologna, Italy
In recent years, we have carried out a systematic study on
†
CCDC reference numbers 758020 and 758021. For crystallographic data
in CIF or other electronic format see DOI: 10.1039/c001377c
Born in Bologna (Italy) in 1974.
the reactivity of the heavier group 5 pentahalides MX
5
(M =
‡
Nb, Ta; X = F, Cl, Br) with controlled amounts of oxygen
Dalton Trans., 2010, 39, 5367–5376 | 5367
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2
6
◦
species. The study has pointed out interesting features, in
particular we have found that simple diethers may undergo
unusual, noticeable transformations, when allowed to react with
Table 1 Selected bond distances ( A˚ ) and angles ( ) for 2
Mo(1)–O(1)
Mo(1)–Cl(1)
Mo(1)–Cl(2)
O(2)–C(1)
O(3)–C(2)
Cl(4)–C(3)
1.6532(14) Mo(1)–O(2)
2.2924(14)
2.4790(6)
2.3170(6)
1.311(3)
2.4749(6)
2.3029(6)
1.217(3)
1.455(3)
1.799(2)
Mo(1)–Cl(1)#1
Mo(1)–Cl(3)
C(1)–O(3)
27
MX in chlorinated solvents. Therefore, we decided to extend
our investigation, concerning the chemistry of oxophilic metal
halides with oxygen species, to molybdenum pentachloride, 1a,
5
C(2)–C(3)
1.496(3)
28
and tungsten hexachloride, 1b. The purpose is to increase the
knowledge about the direct interaction of the halides 1a and 1b
with oxygen-containing compounds, in the view of contributing
to the development of the exploitation of these metal derivatives
in organic synthesis.
The present paper focuses on the reactions of 1a and 1b
with a variety of simple, multifunctional, oxygen molecules, in-
cluding 1,1-dialkoxyalkanes [CRR¢(OR¢¢)
Cl(1)–Mo(1)–Cl(1)#1
O(1)–Mo(1)–O(2)
O(3)–C(2)–C(3)
83.826(18) Cl(2)–Mo(1)–Cl(3)
169.59(6) O(2)–C(1)–O(3)
110.68(17) C(2)–C(3)–Cl(4)
92.75(2)
123.9(2)
110.87(15)
Symmetry transformations used to generate equivalent atoms: #1 -x + 1,
-y + 2, -z + 2.
29
2
], 1,2-dialkoxyalkanes
]. The
[
ROCH CH(R¢)OR¢¢], and trimethoxymethane [CH(OMe)
2
3
Only half of 2 is present within the asymmetric unit, the rest of
the molecule being generated by an inversion centre. The Mo(V)-
centres display distorted octahedral geometry being coordinated
by four chloride ligands (two of which are in the bridging position),
one oxo and a chloroethylformate ligand. The Mo
the dimer is perfectly planar, and the terminal chloride ligands lie
structural and spectroscopic features of the isolated metal-
containing products will be presented, moreover the fragmenta-
tions operative in the various reactions will be discussed. The clear
detection of the organic fragments generated in the distinct cases
has been practicable upon hydrolysis of the reaction mixtures, and
2
(m-Cl) core of
2
˚ ˚
considerably out of the plane [Cl(2) 0.623 A and Cl(3) 0.666 A].
the quantification has been based on NMR analyses using CH
as standard.
2
Cl
2
˚
Due to the long separation [3.687(3) A] between the molybdenum
centres, no bonding has to be envisaged between them. The oxo
and the chloroethylformate ligands, bound respectively to distinct
metal centres, are in a relative trans position. The Mo(1)–O(1)
distance [1.6532(14) A˚ ] is considerably shorter than Mo(1)–O(2)
Results and discussion
Activation of 1,3-dioxolane by means of molybdenum and tungsten
chlorides
[2.2924(14) A˚ ], in view of the double bond character of the former.
Dimolybdenum complexes of general formula [MoOX
3
L]
2
(X =
When MoCl
in CH Cl , slow turning of the mixture from brown to green was
observed. The successive work-up afforded moderate yields of the
dinuclear oxo-chloroethylformate complex [MoOCl
{O=C(H)O-
CH CH , 2, see Scheme 1. The product has been character-
5
was treated with two equivalents of 1,3-dioxolane
halogen; L = neutral ligand) are rarely discussed in the literature,
and to the best of our knowledge the X-ray structure determined
for 2 is the first one reported for this class of compounds. The
2
2
3
derivatives [MoOCl
3
L]
2
may form via reaction of MoCl with
5
2
2
Cl}]
2
two equivalents of the oxygen donor ligand L (including O-
abstraction regarding one equivalent), and can be considered as
ized by elemental analysis, IR spectroscopy and X-ray diffraction.
precursors of mononuclear MoOCl
been described (see Introduction).
3
2
L species, which have already
Interestingly, it was reported that the 1 : 2 molar ratio reaction
of MoCl with ethanol afforded the stable pentacoordinated
MoOCl (EtOH), whose solid state structure was determined.
This adduct is actually an example of a mononuclear equivalent
of [MoOCl L] (see above).
Salient IR features for 2 (see Experimental) are given by two
5
30
3
Scheme 1 Synthesis of compound 2.
3
2
Fig. 1 represents a view of the molecular structure of 2, while a
selection of bond distances and angles is reported in Table 1.
-
1
strong absorptions at 1644 and 1000 cm , which have been
associated with the coordinated carbonyl group and the Mo=O
20b,31
moiety,
respectively.
The presence of the chloroethylformate unit in 2 is clearly the
result of dioxolane ring opening, proceeding with the activation
of C–O and C–H bonds (Scheme 2, pathway b). This feature
is not entirely new, since the generation of non-cyclic esters
from dioxolanes by means of acidic transition-metal species was
32
formerly proposed.
On account of the fact that 2 is obtained in relatively modest
amount, the reaction was also carried out in CDCl and mon-
3
itored by NMR. However, certain recognition of the products
was not possible due to the presence of paramagnetic centres.
Therefore, the mixture was hydrolyzed with the aim to clearly
detect the organic products. Indeed this procedure, which favours
the isolation of an organic phase consisting of the O-substrates
released from the metal centres, has proved to be effective in
Fig. 1 View of the molecular structure of 2. Displacement ellipsoids are
at the 50% probability level. Only independent atoms are labelled.
5
368 | Dalton Trans., 2010, 39, 5367–5376
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Scheme 3 Reaction of 1,3-dioxolane with WCl
6
, 1b.
Scheme 2 Reaction of 1,3-dioxolane with MoCl , 1a.
5
see Scheme 4, which has been characterized in CDCl
3
solution
by NMR spectroscopy. The spectra display three resonances
2
7a-c,33
related studies regarding group 5 pentahalides.
resulting from treatment with water was analyzed by NMR and
GC-MS: O(CH Cl) and O(CH Cl)(CH CH Cl) were identified in
admixture with minor amounts of HCO CH CH Cl and MeCl.
This result has suggested that the fragmentation of the dioxolane
molecule by means of MoCl is not selective, and might proceed
according to several pathways.
The solution
1
[
(
e.g. in the H NMR spectrum: 5.86 (OCH
CH CH )], thus indicating that 1,3-dioxolane acts here as a
monodentate, non-symmetric, oxygen ligand. It is noteworthy that
compound 3 is stable upon thermal treatment in CDCl solution,
2
O), 5.77, 4.50 ppm
2
2
2
2
2
2
2
2
2
2
3
and uncoordinated 1,3-dioxolane has been cleanly recovered after
hydrolysis.
5
On considering that the reactions have been carried out in
strictly anhydrous conditions, we believe that the oxo unit found in
complex 2 reasonably originates from the organic material, rather
than from adventitious water (Scheme 2, pathways d and e). Co-
herently with this point, the formation of O(CH
2
Cl)(CH
2
CH Cl)
2
could be the consequence of O-abstraction by molybdenum and
chloride transfer from molybdenum to the organic substrate
Scheme 4 Reaction of 1,3-dioxolane with WOCl , 1c.
4
(
Scheme 2, pathway d). Likewise, O(CH
2
Cl) might generate via
2
Although WOCl
state, the presence of one oxo-unit makes 1c less oxophilic than
b, and considerably less efficient for the activation of C–O bonds.
Similar results were reported for the reactivity of azoxybenzenes
4
contains a tungsten centre in +6 oxidation
C–O and C–C bond breaking, and chloride transfer (Scheme 2,
pathway c). Notwithstanding it should not be ruled out in
principle the possibility that alternative routes are operative to
give the Cl-ethers, including the formation of paramagnetic metal
compounds containing the alkoxo unit M–OR. This latter may
afford chloroalkanes, Cl–R, upon treatment with water (HCl is
produced during the hydrolysis).
The reaction of WCl
monitored by NMR spectroscopy, in view of the diamagnetism
of the W(VI) system. Hence the uncoordinated ethers O(CH Cl)
O(CH CH Cl) and O(CH Cl)(CH CH Cl) were identified, in
admixture with presumably a W(VI) complex containing the
alkoxo frame [–O(CH OCH Cl], derived from dioxolane single
1
with WCl
using WCl
6
/WOCl
4
: N–O bond activation was achieved only by
34
6
.
When considering that NbCl
dioxolane at room temperature, the results reported in this
5
is not effective in activating 1,3-
27b
6
with dioxolane in CDCl
3
could be
section indicate that MoCl is more efficient than the correspond-
5
ing group 5 congener in promoting C–O bond activation. This
agrees with the fact that a prominent feature of the chemistry
of molybdenum and tungsten is the formation of numerous
polymolybdate(VI) and polytungstate(VI) salts; the corresponding
2
2
,
2
2
2
2
2
2
2
)
2
2
35
group 5 elements show this tendency to a more limited extent.
C–O bond breaking. The complete characterization of the latter
complex failed (see Experimental).
C–O and C–H bond activation in the reaction of MoCl
CH (OMe)
5
with
The same ethers were recovered after hydrolysis, and, in contrast
2
2
with the reaction involving MoCl
found. Reasonable pathways for the non-selective activation of
,3-dioxolane by WCl are given in Scheme 3. Interestingly, C–C
breaking could be a process operative in the course of the activa-
tion (Scheme 3, pathway c), like we have seen for MoCl /dioxolane
see above). On the other hand, the possibility exists that the
symmetric ethers O(CH Cl) and O(CH CH Cl) form from some
interaction with O(CH Cl)(CH CH Cl) molecules with the metal
species involved in the process, through C–O bond cleavages and
couplings, according to the reaction 2ORR¢ → OR + OR¢
Actually O(CH Cl) and O(CH CH Cl) have been found in
comparable amounts in the mixture after hydrolysis.
The behaviour of 1,3-dioxolane with WCl , 1b, has been
compared with that of the tungsten(VI) oxychloride WOCl , 1c.
5
, no chloroethylformate was
Molybdenum pentachloride, 1a, reacts with one equivalent of
dimethoxymethane in dichloromethane solution at room temper-
ature, affording a dark-green solution. By layering with heptane, a
mixture of dark-green microcrystals and red crystals was obtained.
The two solids were separated mechanically, thus the dark-green
one was analyzed by IR spectroscopy and elemental analyses.
1
6
5
(
2
2
2
2
2
-
1
2
2
2
The IR spectrum exhibited two strong absorptions at 1643 cm
-
1
and 987 cm , the latter within the range typical of the Mo=O
-
1
.
bond. The absorption at 1643 cm has been assigned to the C=O
stretching vibration of coordinated methylformate. Really this
molecule has been identified by NMR after dissolution of the solid
2
2
2
2
2
2
2
6
in CDCl followed by addition of water. Crystals were obtained
3
4
after several attempts, but their low quality prevented an accurate
crystal structure determination. Nevertheless, the connectivity was
This latter adds dioxolane to give the coordination compound 3,
This journal is © The Royal Society of Chemistry 2010
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◦
Table 2 Selected bond distances ( A˚ ) and angles ( ) for 5
when CH
(OMe)
is treated with MoCl
. Indeed the treatment
2
2
5
with water of the reaction mixture gave a solution containing
, OMe(CH Cl) and O(CH Cl) (see
Cl(1)–Mo(1)
Mo(1)–O(1)
Cl(2)–Mo(1)
Cl(3)–Mo(1)
Mo(1)–O(2)
Mo(1)–O(3)
Mo(1)–Mo(2)
C(2)–O(2)
2.4876(6)
2.0154(16)
2.3297(6)
2.3902(6)
1.8157(16)
1.8157(16)
2.8509(3)
1.414(3)
Cl(1)–Mo(2)
Mo(2)–O(1)
Cl(4)–Mo(2)
Cl(5)–Mo(2)
Mo(2)–O(4)
Mo(2)–O(5)
C(1)–O(1)
2.4196(6)
2.0285(16)
2.3905(7)
2.3881(6)
1.8153(16)
1.8115(16)
1.439(3)
O=C(H)OMe, MeCl, OMe
2
2
2
2
Experimental and Scheme 5). This suggests that C–O bond
cleavage is the main process operative in the course of the reaction.
For the symmetric ethers OMe and O(CH Cl) , these may form
2
2
2
by C–O cleavages and couplings starting from OMe(CH
2
Cl),
analogously to what was discussed above for the WCl /dioxolane
6
C(4)–O(4)
C(5)–O(5)
1.413(3)
1.421(3)
C(3)–O(3)
1.426(3)
interaction. Besides, the generation of O=C(H)OMe requires a
C–H breaking step.
O(1)–Mo(1)–Cl(1)
Cl(2)–Mo(1)–Cl(3)
O(3)–Mo(1)–O(2)
98.73(5)
88.02(2)
165.11(8)
O(1)–Mo(2)-Cl(1)
Cl(5)–Mo(2)–Cl(4)
O(5)–Mo(2)–O(4)
100.58(5)
86.69(2)
170.37(7)
established to be that of [MoOCl
Mo(V) species analogous to 2.
3
{O=C(H)OMe}]
2
, 4, a dinuclear
Scheme 5 Reaction of dimethoxymethane with MoCl , 1a.
5
We were also able to characterize the minor component of
the solid mixture which, on the basis of a single-crystal X ray
diffraction study, resulted in the mixed chloro-methoxy complex
The reactivity of WCl
oxo-ether compounds
6
with dialkoxymethanes: formation of
Mo
2
Cl
4
(m-Cl)(m-OMe)(OMe) , 5. The X ray molecular structure
4
is drawn in Fig. 2, and the main bond distances and angles are
reported in Table 2.
The reactions of WCl
molar ratio, afford the complexes WOCl
a; R = Et, 6b) in good yields. The latter have been isolated
as microcrystalline solids and characterized by IR and NMR
6
, 1b, with CH
2
(OR)
2
(R = Me, Et), in 1 : 2
4
[O(R)CH
2
Cl] (R = Me,
6
41
spectroscopy and elemental analysis. A common feature in the IR
spectra is the typical absorption due to the W=O interaction (e.g.
-
1
20h,42
at 980 cm in the case of 6b).
The NMR spectra (in CDCl )
3
display the resonances due to the coordinated chloromethyl-alkyl
ether, for instance the [CH Cl] moiety is seen as a singlet at ca.
.70 ppm in the H NMR spectra.
The reactions leading to 6a and 6b seemed to be quite
2
1
5
selective, and we were interested in understanding what kind of
fragmentation was operative. In order to investigate the point,
we carried out the reactions of 1b with CH
2
(OR)
2
(R = Me,
Et) in CDCl . The ether ROCH Cl and the alkylchloride RCl
3
2
were the only compounds present in the mixtures after hydrolysis,
in comparable ratio. This feature suggests that the reaction of
Fig. 2 View of the molecular structure of 5. Displacement ellipsoids are
at the 50% probability level.
CH
2
(OR)
2
with WCl proceeds selectively via oxygen abstraction
6
by the metal centre. The abstraction takes place with contextual
chlorine transfer from tungsten to the organic fragments, affording
Compound
5
belongs to the restricted family of
RCl and ROCH
2
Cl, with the latter capable of coordination to the
moiety (see Scheme 6).
crystallographically-characterized mixed halo-alkoxo compounds
of Mo(V), the only previously reported examples being
newly formed WOCl
4
3
6
37
38
Mo
Mo
2
Cl
2
(OMe)
8
,
Mo
2
Cl
4
39
(OMe)
6
,
Mo
2
Cl
4
(OPh)
6
,
and
i
2
X
4
(O Pr)
6
(X = Cl, Br). The Mo
2
(m-Cl)(m-OMe)Cl
4
core of
the dinuclear species is almost planar [mean deviation from the
least square plane Mo(1) Mo(2) Cl(1) Cl(2) Cl(3) Cl(4) Cl(5) O(1)
˚
0
.0156 A], with the two terminal alkoxo ligands in a relative trans
˚
position. The Mo(1)–Mo(2) contact [2.8509(3) A] is indicative
for a Mo–Mo single bond.
36-40
Scheme 6 Reaction of dioxyalkanes with WCl , 1b.
6
The Mo–O contacts with terminal
˚
alkoxide ligands fall in the range 1.8115(16)–1.8157(16) A, and are
significantly shorter compared to the Mo–O(bridging) distances
Interestingly, fragmentation routes completely different from
that presented in Scheme 6 occur when using MoCl in the place
of WCl . The non-selective reaction of MoCl with CH (OMe) has
been discussed in the previous paragraph. Otherwise, the reaction
of MoCl with CH (OEt) gave a mixture of unidentified products,
˚
[
2.0154(16)–2.0285(16) A]. Moreover, the former contacts are
5
intermediate between the distances found in 2 for Mo=O
6
5
2
2
˚
˚
[
1.6532(14) A] and Mo–O(chloroethylformate) [2.2924(14) A].
The formation of the units Cl
in complex 4, and of the methoxy-containing derivative 5, indi-
3
Mo=O and O=C(H)OMe, found
5
2
2
and EtCl was recognised as the major component after hydrolysis
(see Experimental).
cates that more than one fragmentation pathway are concurrent
5
370 | Dalton Trans., 2010, 39, 5367–5376
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C–C bond formation in the reactions of 1a and 1b with
,2-dialkoxypropanes
2
The reactivity of CMe
2
(OMe)
2
with equimolar amounts of 1a and
1b was investigated. The mixtures of the reactions carried out in
CDCl in sealed NMR tubes gave, after treatment with water,
3
solutions for which GC-MS analysis evidenced the presence of
MeCl and mesityl oxide, Me
C=CHC(O)Me, see Scheme 7. The
2
first step is presumably the formation of acetone, that is a well-
known reaction in the field of ketal to ketone transformations
4
3
promoted by acidic species. Then, mesityl oxide is produced by
successive aldol condensation of acetone.
Scheme 8 Reactions of 1a, 1b and 1d with dme.
compounds MeO(CH
Scheme 8(b)).
The possibility to activate dme by means of a group 6 halide
2
)
2
Cl, Cl(CH ) Cl and MeCl were detected
2
2
(
Scheme 7 Reaction of 2,2-dimethoxypropane with 1a and 1b.
was also evaluated by using WCl
out in CDCl
Successive hydrolysis gave a solution containing dme only, thus
indicating that the W(IV) species 1d is not effective in performing
fragmentation of dme (Scheme 8(c)).
4
, 1d. The reaction was carried
in a sealed NMR tube heated at 100 C for 2 h.
◦
The possibility that mesityl oxide is generated during hydrolysis
should be discharged on the basis of the fact that the IR spectra
of the solid mixtures isolated from the reactions before hydrolysis
3
display absorptions ascribable to the Me
Experimental).
2
C=CHC(O)Me unit (see
The study of the reactivity of 1a and 1b with 1,2-
Analogously, the reaction of 1a with CHMe(OEt)
2
afforded a
dialkoxyalkanes was extended to MeOCH
MeOCH CH OCH Cl. At room temperature in CDCl
partial fragmentation of MeOCH CH OCH Cl was observed,
whereas MeOCH CH(Me)OMe was recovered nearly quantita-
2
CH(Me)OMe and
dark-green solid after work-up. The solid was dried, dissolved
in CDCl and treated with water. Thus, NMR/GC-MS analyses
2
2
2
3
, only
3
2
2
2
evidenced the presence of a mixture of ethyl chloride and
several carbonylic compounds. Among the latter, trans-2-butenal,
HC(O)C(H)=C(H)Me, was detected unambiguously in small
2
tively from the respective reaction mixtures after treatment with
water. These reactions were repeated at 90 C (see Experimental):
◦
amounts. The formation of trans-2-butenal may take place by a
two-step process, including the formation of acetaldehyde, and
resembling that shown in Scheme 7. On the other hand, the
presence of ethyl chloride suggests the previous formation of Mo-
ethoxide species, which afford EtCl upon hydrolysis.
in these conditions, fragmentation of the diethers took place in
a few hours. NMR analyses did not allow to identify unam-
biguously the inorganic products. Conversely, organic substrates
derived from the fragmentation reactions could be detected after
hydrolysis. The products recognized after hydrolysis of the reaction
mixtures obtained by high temperature reactions of 1a and 1b with
The reactivity of 1a and 1b with 1,2-dialkoxyalkanes,
1,2-dialkoxyalkanes are listed in Table 3.
ROCH
2
(CHR¢)OR¢¢
According to the results shown in Table 3, the fragmentations of
,2-diethers by means of the group 6 chlorides 1a and 1b generally
1
The reactivity of 1a and 1b with a series of 1,2-dialkoxyalkanes,
proceed at high temperatures via the cleavage of C–O bonds. The
higher reactivity of MeOCH CH OCH Cl is manifested in the
room temperature, non-selective, reaction with WCl , which may
ROCH (CHR¢)OR¢¢ (R = R¢¢ = Me, R¢ = H (dme); R = R¢ =
R¢¢ = Me; R = Me, R¢ = H, R¢¢ = CH Cl), was investigated.
It is known that MoCl undergoes reduction in the presence
of dme, affording the Mo(IV) derivative MoCl
have confirmed this result and we have investigated the stability
of this product in CDCl solution. After being stored at room
temperature for several days, the mixture was treated with water,
giving a solution containing dme, Cl(CH Cl and MeCl, in 9 : 2 : 4
ratio (see Scheme 8(a)). This fact points out that the compound
2
2
2
2
2
6
5
2
21a
include the coupling of C–O bonds. These outcomes can be com-
pared to the chemistry exhibited by niobium and tantalum pen-
4
(k -dme). We
tahalides with MeOCH
2
CH OMe. The unique behaviour of such
2
3
group 5 derivatives determines the selective activation of dme,
)
2 2
Table 3 Compounds detected by NMR/GC-MS after hydrolysis of the
reaction mixtures obtained from 1/ROCH (CHR¢)OR¢¢
2
2
MoCl (k -dme) is not indefinitely stable in solution, thus slow
4
degradation of the organic moiety takes place via multiple C–O
bond cleavage. The degradation is complete in 4 h at 90 C, then
Metal
◦
compound 1,2-Dialkoxyalkane
Products of the fragmentation
Cl(CH
final mixture after hydrolysis (see Experimental).
The reaction between WCl and dme in CDCl
by NMR spectroscopy. After a few hours, the starting materials
had disappeared, and the NMR spectra revealed the probable
2
) Cl and MeCl have been recognized in ca. 1 : 2 ratio in the
2
MoCl
5
, 1a MeOCH
2
CH
CH
2
2
OMe
OMe
MeCl, ClCH
MeCl, ClCH
2
2
CH
CH
2
2
Cl
Cl,
WCl
6
, 1b MeOCH
2
6
3
was monitored
OMe(CH
MeOCH
CH
CH
Cl)
OMe
2
2
WCl
MoCl
4
, 1d MeOCH
5
2
2
2
CH
2
OMe
2
2
, 1a MeOCH
CH(Me)OMe MeCl, ClCH
CH(Me)OMe MeCl, ClCH
2
CH(Me)Cl
CH(Me)Cl,
WCl , 1b MeOCH
6
2
formation of the alkoxo-complex WCl
admixture with MeCl, as a result of single C–O bond cleavage
Scheme 8(b)). However, compound 7 is not stable in solution:
5
(OCH
2
CH OMe), 7, in
2
MeOCH
HOCH CH(Me)OMe
2
CH(Me)OH,
2
MoCl
5
, 1a MeOCH
2
CH
CH
2
2
OCH
OCH
2
Cl MeCl, ClCH
Cl MeCl, ClCH
2
CH
CH
2
Cl
(
WCl , 1b MeOCH
6
2
2
2
2
Cl, O(CH
2
Cl)
2
,
after 12 days NMR evidenced the absence of 7 and the formation
of non-identified products. The mixture was hydrolyzed, then
OMe(CH
2
Cl), O(CH
2
CH
2
Cl)
2
, OMe
2
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consisting of multiple C–O bond cleavage followed by C–O
coupling.
Experimental
2
7a,d
General
The reactivity of 1a and 1b with trimethylformate, CH(OMe)
3
All manipulations of air and/or moisture sensitive compounds
were performed under an atmosphere of pre-purified argon using
The study of the reactivity of chlorides 1a and 1b with polyethers
was extended to trimethoxymethane. The reactions proceed se-
lectively through multiple C–O bond cleavage, including probable
O-abstraction by the metal centre, see Scheme 9. Indeed, methyl
formate and methyl chloride have been found in ca. 1 : 2 ratio in
the reaction mixtures, see Experimental. Moreover, the complex
standard Schlenk techniques. The reaction vessels were oven dried
◦
-2
at 150 C prior to use, evacuated (10 mmHg) and then filled with
argon. MoCl
mercial products (Aldrich) of the highest purity available, stored
under argon atmosphere as received. 1,3-Dioxolane, CH (OMe)
CH (OEt) , CMe (OMe) , CHMe(OEt) , MeOCH CH(Me)OMe,
MeO(CH OCH Cl and CH(OMe) were commercial products
Aldrich) stored under argon atmosphere as received. CH Cl
CDCl and 1,2-dimethoxyethane (dme) were distilled before use
under argon atmosphere from P 10, while pentane and heptane
were distilled from LiAlH . Infrared spectra were recorded at
93 K on a Spectrum One Perkin Elmer Spectrometer, equipped
5
, 1a, WCl
6
, 1b, WOCl
4
, 1c, and WCl
4
, 1d, were com-
2
2
,
2
2
2
2
2
2
WOCl
good yield from the reaction of 1b with a two-fold excess of
CH(OMe) (Scheme 9(b)).
4
[O=C(H)OMe], 8, has been isolated as a brown solid in
2
)
2
2
3
(
2
2
,
3
3
4
O
4
2
with a UATR sampling accessory. NMR measurements were
recorded on Varian Gemini 200BB instrument at 293 K. The
1
13
chemical shifts of H and C NMR spectra were referenced to
the non-deuterated aliquot of the solvent. Ratios were calculated
1
on the basis of H NMR peak integrals. GC-MS analyses were
Scheme 9 Reaction of trimethylformate with 1a and 1b.
performed on a HP6890 instrument, interfaced with MSD-
HP5973 detector and equipped with a Phenonex Zebron column.
Carbon and hydrogen analyses were performed on a Carlo Erba
mod. 1106 instrument, paying particular attention to the more
sensitive compounds which were weighed and directly introduced
into the analyzer. The halide content was determined by the
Volhardt method after exhaustive hydrolysis of the sample.
The halogen analyses were repeated twice in order to check for
reproducibility.
Major features of the IR spectrum (solid state) are two intense
bands at 1652 cm-1 and 1056 cm-1, attributed to the coordinated
carbonyl and the W=O moiety, respectively. The NMR spectra
show the resonances related to the methylformate ligand at higher
44
chemical shifts with respect to the uncoordinated molecule [e.g.
1
for the H spectrum: d = 8.67 (CH), 4.19 (CH
3
) ppm].
Conclusions
Reactivity of 1a–c with 1,3-dioxolane; synthesis and isolation of
This paper reports the systematic investigation on the reactivity
of the highly oxophilic early transition metal chlorides MoCl
and WCl towards simple polyethers, such as acetals, ketals,
,2-dialkoxyalkanes and trimethylformate. The reactions result
[
MoOCl
3
{O=C(H)OCH
2
CH
2
Cl}]
2
, 2, and detection in solution of
5
1
WOCl
4
(j -C
3
H
6
O ), 3
2
6
1
1,3-Dioxolane (80 mL, 1.1 mmol) was added to MoCl
5
, 1a (0.150 g,
in fragmentation of the organic species, and the two metal
compounds behave similarly in most cases. It is remarkable that
the room temperature reactions of acetals and ketals with 1a and
0.549 mmol), in CH Cl (12 mL). The resulting brown mixture was
2
2
stirred at room temperature for 24 h, during which progressive
turning to green was observed. The final solution was layered with
◦
1b do not generally follow the usual pathway expected on the basis
heptane (15 mL) and stored at -30 C, thus green crystals of 2
of the acidity of 1, i.e. generation of the “deprotected” carbonylic
compound. Conversely, more complicated reaction patterns are
operative, including cleavage of C–H and, possibly, C–C bonds,
and formation of new C–C bonds.
suitable for X ray analysis were collected after some days. Yield:
0.072 g, 40%. Anal. Calcd. for C
6
H
10Cl
8
Mo
2
6
O : C, 11.03; H, 1.54;
Cl, 43.39. Found: C, 11.17; H, 1.49; Cl, 43.16. IR (solid state):
n = 2968 w, 1644 m-s (nC=O), 1614 s, 1440 m, 1429 w-m, 1391
w-m, 1374 m, 1302 s, 1288 s, 1271 s, 1238 m-s, 1196 m, 1065 w-m,
1000 s (nMo=O), 959 m, 942 s, 825 w-m, 805 m, 782 w-m, 736 w-m,
Interestingly, MoCl
wards 1,3-dioxolane than the corresponding pentahalides
of group 5, namely NbCl and TaCl The compound
MoOCl CH , resulting from a dioxolane
Cl}]
5
and WCl
6
show higher reactivity to-
-
1
5
5
.
661 s cm .
[
3
{O=C(H)OCH
2
2
2
In a different experiment, MoCl , 1a (0.075 g, 0.28 mmol),
5
ring-opening reaction, represents the first crystallographically-
characterized dimeric oxo-chloro Mo(V) derivative.
in CDCl
with CH
3
(0.75 mL) inside an NMR tube, was treated firstly
Cl (0.018 mL, 0.28 mmol) and then with 1,3-dioxolane
2
2
The results presented here may provide more information in
(21 mL, 0.30 mmol). The tube was sealed, briefly shaken so to
the reactivity of the highly oxophilic MoCl
5
and WCl
6
with
homogenize the content, and stored at room temperature for
72 h. Afterwards, the tube was cooled to -20 C, opened, and
water (ca. 5 mmol) was added. A dark-green solid precipitated
from a green solution; the solution was analysed by NMR/GC-
◦
oxygen substrates, in order to further exploit these easily-accessible
materials in metal-directed syntheses involving oxygen species.
Development in this area is really desirable, on account of the
availability of such metal compounds and of the substantial low-
toxicity of the elements.
MS, which evidenced the presence of CH
2
Cl
2
, CH
3
Cl, O(CH
2
Cl) ,
2
Cl(CH OCH Cl and HCO (CH Cl (ratio 20 : 2 : 7 : 10 : 1).
2
)
2
2
2
)
2 2
5
372 | Dalton Trans., 2010, 39, 5367–5376
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The 1 : 1 reactions of 1,3-dioxolane (0.50 mmol) with WCl
6
,
6 was obtained as a light-green microcrystalline solid after
1
b, or WOCl , 1c, in CDCl (0.75 mL) were carried out by
4
3
3 days.
1
the same procedure described for 1a. The H NMR spectrum
of the mixture obtained from 1b and dioxolane, after 8 days,
6a. Yield: 0.102 g, 66%. Anal. Calcd. for C
H, 1.19; Cl, 41.99. Found: C, 5.76; H, 1.13; Cl, 41.77. IR (solid
2
H
5
Cl
5
O W: C, 5.69;
2
showed the presence of CH
Cl(CH OCH Cl and, presumably, a W(VI) complex contain-
ing the ligand [–OCH CH OCH Cl] (ratio 10 : 3 : 2 : 1 : 3). The
resonances related to the latter appeared as follows: H NMR
2
Cl
2
, O(CH
2
Cl)
2
, O(CH
2
CH
2
Cl)
2
,
state): n = 2955 w, 1442 m, 1374 m-s, 1152 m, 1109 m, 1068 s, 999
-
1
1
2
)
2
2
m, 970 vs (nW=O) cm . H NMR (CDCl
3
): d = 5.71 (s, 2 H, CH
2
),
),
1
3
1
2
2
2
3.82 (s, 3 H, CH
57.7 (CH ) ppm.
6b. Yield: 0.109 g, 68%. Anal. Calcd. for C
3
) ppm. C NMR{ H} (CDCl
3
): d = 84.8 (CH
2
1
3
3
d = 5.84 (s, 2 H, CH
2
Cl), 5.74 (t, 2 H,
J
HH = 5.5 Hz,
3
H
7
Cl
5
O
2
W: C, 8.26;
3
OCH
2
CH
2
O), 4.48 (t, 2 H, JHH = 5.5 Hz, OCH
2
CH
2
O) ppm;
O), 70.5
H, 1.62; Cl, 40.64. Found: C, 8.31; H, 1.59; Cl, 40.15. IR (solid
1
3
1
C NMR{ H} d = 80.6 (CH
2
Cl), 78.1 (OCH
2
CH
2
state): n = 2963 w, 1441 m, 1396 m, 1379 m, 1351 m, 1260 s, 1086
-
1
(
OCH
After treatment with water, a light-yellow solution was sepa-
rated from a blue precipitate and analysed by NMR/GC-MS:
CH Cl , O(CH Cl) , O(CH CH Cl) and Cl(CH OCH Cl were
found in 10 : 3 : 3 : 4 ratio. Compound WOCl ), 3, and
were detected by H NMR in ca. 1 : 1 ratio in the yellow
solution obtained from 1c (0.25 mmol), 1,3-dioxolane (0.25 mmol)
2
CH
2
O) ppm.
m-s, 1018 s, 980 m-s (nW=O), 935 m-s, 934 m-s, 855 s, 793 vs cm .
1
3
H NMR (CDCl
2 H, CH
(CDCl
All the attempts to isolate products from the reaction of
MoCl with CH (OEt) gave brown, very air-sensitive, oily-solids
which could not be characterised. MoCl , 1a (0.25 mmol), in
CDCl (0.75 mL), was treated in an NMR tube with CH Cl
(0.25 mmol) and then with CH (OEt) (0.25 mmol). The tube was
3
): d = 5.69 (s, 2 H, CH
2
), 4.48 (q, JHH = 5 Hz,
3
13
1
2
), 1.41 (t, JHH = 5 Hz, 3 H, CH
3
) ppm. C NMR{ H}
2
2
2
2
2
2
2
2
)
2
2
3
): d = 84.0 (CH
2
), 69.8 (CH
2
), 14.4 (CH ) ppm.
3
1
4
(k -C
3
H
6
O
2
1
CH
2
Cl
2
5
2
2
5
1
and CH
2
Cl
2
(0.25 mmol) after 12 days. H NMR (CDCl
3
): d =
HH = 5.5 Hz,
): d = 80.6 (OCH O), 78.2,
) ppm. 1,3-Dioxolane was recovered cleanly after
3
2
2
3
5
CH
.86 (s, 2 H, OCH
2
O), 5.77, 4.50 (t, 4 H,
J
2
2
1
3
1
2
CH
2
) ppm. C NMR{ H} (CDCl
3
2
sealed, shaken so to homogenize the content, and stored at room
◦
70.9 (CH
2
CH
2
temperature for ca. 7 days. After cooling at ca. -30 C, the tube
hydrolysis. Complex 3 in CDCl
after thermal treatment at 90 C for 60 min.
3
in a sealed tube was unchanged
was opened, and water (ca. 5 mmol) was added. A brown solid
precipitated from a brown solution. The solution was analysed by
◦
NMR/GC-MS: CH
ratio.
2
Cl
2
, CH
3
Cl and EtCl were found in 10 : 1 : 8
Reactivity of 1a with CH
2
(OMe)
2
; synthesis and isolation of
Cl (OMe) , 5
The reactions of WCl
in CDCl (0.75 mL), were carried out by the same procedure
described above for the reaction of 1a with CH
NMR/GC-MS analyses of the mixture obtained from 1b and
CH (OMe) , after 2 days, showed the presence of CH Cl and
WOCl [O(Me)CH Cl], 6a (ratio ca. 1 : 1) After treatment with wa-
ter, a brown solution was separated from a colourless precipitate,
and analysed by NMR/GC-MS: CH Cl and MeOCH Cl were
found in ca. 1 : 1 ratio. Instead, H NMR/GC-MS analyses of the
mixture obtained from 1b and CH (OEt) , after 12 days, showed
the presence of CH Cl , EtCl, ClCH OEt, WOCl [O(Et)CH Cl],
6
, 1b, with CH
2
(OR)
2
(R = Me, Et),
[MoOCl
3
{O=C(H)OMe}]
2
, 4, and Mo
2
5
5
3
1
MoCl
5
, 1a (0.168 g, 0.615 mmol), CH Cl
2
2
(7 mL) and CH
2
(OMe)
2
2
(OEt) . H
2
(
0.615 mmol) were introduced into a Schlenk tube. The mixture
was stirred for 20 h, then it was filtrated in order to remove some
solid. The filtrated dark-green solution was layered with heptane
2
2
3
4
2
◦
and stored at -30 C for 7 days. Hence, a mixture of a few red
X-ray quality crystals and a dark-green microcrystalline solid was
3
2
1
obtained. Part of this mixture was dissolved in CDCl
with water: a solution containing HCO Me and MeOH (ratio
0 : 1, H NMR) was obtained. The red crystals of compound
Mo Cl (OMe) , 5, were separated mechanically from the solid
mixture and studied by X-ray diffraction and elemental analysis.
Anal. Calcd. for C Mo : C, 11.45; H, 2.88; Cl, 33.81.
Found: C, 11.36; H, 2.73; Cl, 32.90. The dark green solid consisted
of [MoOCl , 4. Yield: 0.068 g (40%). Anal.
{O=C(H)OMe}]
Calcd. for C Cl Mo : C, 8.63; H, 1.45; Cl, 38.21. Found:
C, 8.50; H, 1.39; Cl, 37.60. IR (solid state): n = 2967 w, 1643 m-s
C=O), 1445 w-m, 1429 m, 1369 m, 1285 s, 1174 w, 1044 m, 987
3
and treated
2
2
2
1
1
2
2
2
4
2
2
5
5
6b. After treatment with water, a light-brown solution was
separated from a yellow precipitate and analysed by NMR/GC-
5
H
15Cl
5
2
O
5
MS: CH
2
Cl
2
, EtCl, ClCH OEt were found in ca. 10 : 8 : 9 ratio.
2
3
2
Reactivity of 1a and 1b with CMe
2
(OMe) . General procedure
2
4
H
8
6
2
O
6
CMe
2
(OMe)
2
(0.550 mmol) was added to 1a or 1b (0.500 mmol),
(
n
in CH
2
2
Cl (20 mL), and the mixture was stirred for ca. 24 h.
-
1
m-s (nMo=O), 963 s, 884 s, 794 m, 730 w cm .
The reaction of 1a (0.20 mmol) with CH
in CDCl (0.70 mL) in a sealed NMR tube, afforded a green-
brown mixture after 24 h. Hydrolysis gave a light-green solution
of HCO Me, MeCl, OMe , OMe(CH Cl) and O(CH Cl) (ratio
0 : 60 : 12 : 6 : 8).
Hence, the resulting orange-brown solution was layered with
heptane (30 mL) and stored at -30 C for 10 days. Thus, the
final products were obtained as dark solids, which were analyzed
by IR spectroscopy. From 1a and CMe
◦
2
(OMe)
2
(0.20 mmol),
3
2
(OMe) , IR (solid state):
2
2
2
2
2
2
n = 2954 w-m, 2844 w, 1584 s (nC=O), 1519 m (nC=C), 1484 m, 1448
1
m-s, 1428 m, 1361 m-s, 1337 m-s, 1302 m-s, 1299 w-m, 1101 m,
-
1
9
(
1
78 s (nMo=O), 893 m, 735 m cm . From 1b and CMe
solid state): n = 2941 w, 1595 s (nC=O), 1506 s (nC=C), 1453 m,
437 m, 1403 w-m, 1378 w, 1342 m-s, 1294 w-m, 1029 w-m, 981 s
2
(OMe) , IR
2
Reactivity of 1a and 1b with CH
2
(OR)
2
; synthesis and isolation of
WOCl [O(R)CH
4
2
Cl] (R = Me, 6a; R = Et, 6b). General procedure
-
1
(
n
W=O), 932 m, 872 vs, 847 m, 792 m, 733 m cm .
An NMR tube was charged with MoCl , 1a (0.180 mmol),
CDCl (0.65 mL), CH Cl (0.180 mmol) and CMe (OMe)
CH (OR) (0.74 mmol) was added to WCl , 1b (0.145 g,
2
2
6
5
0
.366 mmol), in CH Cl (15 mL), and the resulting mixture was
2
2
3
2
2
2
2
stirred overnight. Hence, the final yellow solution was layered with
heptane (15 mL) and stored at room temperature. Thus, compound
(0.185 mmol). The tube was sealed and shaken in order to obtain a
homogeneous mixture. The tube was stored at room temperature
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View Online
for 7 days, obtaining an orange solution. Then the tube was cooled
to ca. -20 C and opened. A large excess of water (ca. 5 mmol) was
added, so producing a dark precipitate and a light-yellow solution.
Reactivity of 1a and 1b with CH(OMe)
3
: synthesis of
◦
WOCl
4
[O=C(H)OMe], 8. General procedure
Trimethylformate (0.65 mmol) was added to 1a or 1b (0.32 mmol),
in CDCl (0.70 mL)/CH Cl (0.35 mmol) in an NMR tube. The
The latter was analyzed by NMR/GC-MS: CH
2
Cl
2
, MeCl (ratio
1
3
2
2
1
: 1, H NMR) and MeC(O)CH=C(Me)
identified.
The reaction of 1b (0.250 mmol) and CMe
0.253 mmol), in sealed NMR tube, was carried out similarly.
After 6 days, the reaction mixture was hydrolysed, thus CH Cl
(GC-MS)
2
(GC-MS) were clearly
tube was shaken to homogenize the mixture, and then maintained
at room temperature for 24 h. The final mixture was treated with
water (ca. 5 mmol): immediate precipitation of a green solid from
a solution took place. NMR analysis of the latter pointed out the
2
(OMe)
2
(
2
2
,
1
presence of CH
ratio from 1b: 5 : 7 : 4). NMR spectrum of the mixture obtained
from 1b and CH(OMe) , before hydrolysis, evidenced the presence
of complex 8. The latter was isolated according to the following
procedure: WCl , 1b (0.180 g, 0.454 mmol), in CH Cl (15 mL),
was treated with CH(OMe) (0.100 mL, 0.914 mmol). The mixture
2
Cl
2
, MeCl and HCO
2
Me (ratio from 1a: 1 : 2 : 1;
MeCl (ratio 1 : 1, H NMR) and MeC(O)CH=C(Me)
2
were found in the resulting solution.
3
Reactivity of 1a and 1b with CHMe(OEt) . General procedure
2
6
2
2
3
CHMe(OEt)
2
(0.550 mmol) was added to 1a or 1b (0.500 mmol),
was stirred for 18 h. Thus, the final orange solution was layered
in CH Cl (20 mL), and the mixture was stirred for ca. 24 h. Hence,
2
2
◦
with heptane and stored at -30 C for 10 days. A brown solid
the resulting solution was layered with heptane (30 mL) and stored
◦
corresponding to 8 was collected. Yield: 0.137 g, 75%. Anal. Calcd.
at -30 C for 72 h. Precipitation of a solid occurred. The solid
for C
.04; Cl, 35.06. IR (solid state): n = 2963 w, 1652 s (nC=O), 1431
m, 1417 m, 1371 w-m, 1289 s, 1262 m, 1148 m, 1056 s (nW=O),
2
H
4
Cl
4
3
O W: C, 5.98; H, 1.00; Cl, 35.30. Found: C, 6.06; H,
was dried under vacuo, dissolved in CDCl
with a large excess of H O. The resulting mixture was analyzed
by GC-MS and NMR spectroscopy. From 1a and CHMe(OEt)
trans-HC(O)C(H)=C(H)CH
and EtCl (ratio 2 : 3). From 1b and
CHMe(OEt) : EtCl.
3
(0.80 mL) and treated
1
2
2
:
-
1
1
9
86 s, 886 vs, 808 vs, 675 s cm . H NMR (CDCl
3
): d = 8.67
3
1
3
1
(CH), 4.19 (CH
3
) ppm. C NMR{ H} (CDCl
3
): d = 170.5 (CH),
2
55.8 (CH
3
) ppm.
Reactivity of 1a, 1b and 1d with ROCH
2
(CHR¢)OR¢¢ (R = R¢¢ =
X-Ray crystallographic study
Crystal data and collection details for [MoOCl
Me, R¢ = H (dme); R = R¢ = R¢¢ = Me; R = Me, R¢ = H, R¢¢ =
CH
2
Cl). General procedure
{O=C(H)-
3
OCH CH , 2, and Mo Cl (OMe) , 5, are reported in Table 4.
2
2
Cl}]
2
2
5
5
CH
2
Cl (0.300 mmol) and ROCH
2
2
(CHR¢)OR¢¢ (0.300 mmol) were
(0.70 mL), in an
The diffraction experiments were carried out on a Bruker APEX II
diffractometer equipped with a CCD detector using Mo-Ka
radiation. Data were corrected for Lorentz polarization and
added to a suspension of 1 (0.300 mmol) in CDCl
NMR tube. Then the tube was sealed, shaken in order to homog-
enize the mixture, and maintained at different temperatures for
variable times. Hence, the tube was cooled to -20 C and opened,
then H O (ca. 5 mmol) was added causing the precipitation of a
3
45
◦
absorption effects (empirical absorption correction SADABS)
Structures were solved by direct methods and refined by
2
solid from a solution. Combined GC-MS/NMR analysis of the
latter was carried out.
Table 4 Crystal data and experimental details for [MoOCl
OCH CH , 2, and Mo Cl (OMe) , 5
Cl}]
3
{O=C(H)-
2
2
2
2
5
5
From 1a and MeOCH
2
CH
2
OMe (reaction time: 4 h; tempera-
Cl (3 : 4 : 2 ratio).
OMe (12 d, room temperature):
◦
ture: 90 C): CH
2
Cl
2
, MeCl and Cl(CH
CH
Cl, Cl(CH
From 1d and MeOCH CH
MeOCH CH OMe (1 : 1).
From 1a and MeOCH
MeCl and ClCH CH(Me)Cl (5 : 8 : 4).
From 1b and MeOCH CH(Me)OMe (3 h, 100 C):
CH Cl , MeCl, ClCH CH(Me)Cl, MeOCH CH(Me)OH and
HOCH CH(Me)OMe (10 : 8 : 2 : 3 : 3).
From 1a and MeOCH CH OCH Cl (2 h, 90 C): CH
and Cl(CH Cl (5 : 3 : 2).
From 1b and MeOCH
ature): CH Cl , MeCl, Cl(CH
O(CH CH Cl) and Me O (50 : 15 : 15 4 : 2 : 13 : 6).
2
)
2
2
5
From 1b and MeOCH
CH Cl , MeO(CH
2
2
2
2
2
)
2
2
)
2
Cl and MeCl (7 : 2 : 3 : 8).
Formula
Fw
C
6
H
10Cl
8
Mo
2
O
6
C
5 5 2 5
H15Cl Mo O
◦
653.62
0.71073
100(2)
Monoclinic
C2/c
21.043(4)
6.1669(10)
14.915(3)
93.412(2)
1932.0(6)
4
2.247
2.421
1256
1.94–26.00
6369
524.30
0.71073
100(2)
2
2
OMe (2 h, 100 C): CH
2
Cl
2
and
Cl
l/A˚
2
2
Temperature/K
Crystal system
Space group
◦
2
CH(Me)OMe (10 h, 110 C): CH
2
2
,
Monoclinic
P2 /c
2
1
◦
˚
a/A
b/A˚
12.7518(9)
12.8342(9)
10.3363(7)
109.041(1)
1599.1(2)
4
2
2
2
2
2
c/A˚
2
◦
b/
◦
2
2
2
2
Cl
2
, MeCl
Cell volume/A
˚
3
2
)
2
Z
-
3
D
c
/g cm
2.178
2.406
1016
2
CH
2
OCH
2
Cl (12 h, room temper-
Cl) , MeOCH Cl,
-
1
m/mm
F(000)
q limits/
Reflections collected
2
2
2
)
2
Cl, O(CH
2
2
2
◦
2
2
2
2
1.69–26.00
15987
The NMR spectra of the mixture obtained from 1b and
dme, before hydrolysis, exhibited resonances attributed to the
Independent reflections
1900 (Rint = 0.0228) 3142 (Rint = 0.0159)
Data/restraints/parameters 1900/1/103
3142/68/154
1.117
compound WCl
5
(OCH
2
CH
2
OMe), 7 (ratio CH
2
Cl
2
: 7 : CH
3
Cl =
2
Goodness on fit on F
1
1.176
0.0181
0.0417
0.303 and -0.682
1
3
1
0 : 8 : 9). H NMR(CDCl
3
): d = 5.72 (t, 2 H, JHH = 5.0 Hz,
R (I > 2s(I))
0.0188
0.0468
3
wR
2
(all data)
WOCH
2
), 4.27 (t, 2 H, JHH = 5.0 Hz, CH
2
), 4.03 (s, 3 H, Me) ppm.
), 75.6 (CH ), 63.5
1
3
1
Largest diff. peak and
0.651 and -0.480
C NMR{ H} (CDCl
3
): d = 79.0 (WOCH
2
2
hole/e A˚ -
3
(
Me) ppm.
5
374 | Dalton Trans., 2010, 39, 5367–5376
This journal is © The Royal Society of Chemistry 2010

View Online
2
46
full-matrix least-squares based on all data using F . Hydrogen
atoms bonded to C-atoms were fixed at calculated positions and
refined by a riding model, except H(1) in 2 which was located in the
Fourier map and refined isotropically using the 1.2 fold Uiso value
of the parent C(1) atom; the C(1)–H(1) distance was restrained to
Tetrahedron Lett., 1971, 12, 787; (d) Q. Guo, L. Li, L. Chen, Y. Wang,
S. Ren and B. Shen, Energy Fuels, 2009, 23, 51; (e) T. Hirao, S. Kohno,
J. Enda, Y. Ohshiro and T. Agawa, Tetrahedron Lett., 1981, 22, 3633.
8 M. E. Jung and J. I. Wasserman, Tetrahedron Lett., 2003, 44,
7273.
1
19 (a) C. D. Garner and J. M. Charnock, Molybdenum(III), (IV) and
(
V), in Comprehensive Coordination Chemistry, ed. G. Wilkinson,
˚
0
.93 A [s.u. 0.01]. The asymmetric unit of 2 contains only half of
a molecule, the rest being generated by an inversion centre. Rigid
bond restraints were applied to all atoms in 5 (s.u. 0.005).
R. D. Gillard and J. A. McCleverty, Pergamon, Oxford, 1987, vol. 3,
pp. 1329–1374; (b) Z. Dori, Tungsten in Comprehensive Coordination
Chemistry, ed. G. Wilkinson, R. D. Gillard and J. A. McCleverty,
Pergamon, Oxford, 1987, vol. 3, pp. 973–1022; (c) C. G. Young,
Molybdenum in Comprehensive Coordination Chemistry II, ed. J. A.
McCleverty and T. J. Meyer, Pergamon, Oxford, 2003, Vol 4, pp. 415–
Acknowledgements
5
27; (d) T. Okamura and N. Ueyama, Tungsten in Comprehensive
Coordination Chemistry II, ed. J. A. McCleverty and T. J. Meyer,
Pergamon, Oxford, 2003, Vol 4, pp. 529–573.
The authors wish to thank the Ministero dell’Istruzione,
dell’Universit a` e della Ricerca (MIUR, Roma), Programmi di
Ricerca Scientifica di Notevole Interesse Nazionale 2007-2008,
for financial support.
2
5
0 MoCl : (a) M. L. Larson, J. Am. Chem. Soc., 1960, 82, 1223; (b) D. L.
Kepert and R. Mandyczewsky, J. Chem. Soc. A, 1968, 530; (c) T. Ernst,
A. El-Kholi, U. M u¨ ller and K. Dehnicke, Z. Anorg. Allg. Chem., 1988,
5
66, 7; (d) J. Hyde, L. Magin and J. Zubieta, Chem. Commun., 1980, 204;
e) S. M. Horner and S. Y. Tyree, Jr., Inorg. Chem., 1962, 1, 122. WCl
(f) B. J. Brisdon, G. W. A. Fowles and B. P. Osborne, J. Chem. Soc.,
962, 1330; (g) C. M. Mikulski, L. L. Pytlewski and N. M. Karayannis,
(
6
:
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376 | Dalton Trans., 2010, 39, 5367–5376
This journal is © The Royal Society of Chemistry 2010