Synthesis of carboxylate derivatives of molybdenum and tungsten based on joint insertion of CO2 and PhNCS or N, N′- dicyclohexylcarbodiimide into M-Cl bonds

Article abstract of DOI:10.1134/S0020168513050105

Reactions of the higher molybdenum and tungsten chlorides with phenyl isothiocyanate or with N, N′-dicyclohexylcarbodiimide and carbon dioxide in dichloroethane are the first to demonstrate the possibility of insertion of carbon dioxide in combination wit

Full text of DOI:10.1134/S0020168513050105

ISSN 0020ꢀ1685, Inorganic Materials, 2013, Vol. 49, No. 6, pp. 638–642. © Pleiades Publishing, Ltd., 2013.
Original Russian Text © N.A. Ovchinnikova, E.A. Martynova, N.A. Minaeva, O.G. Ellert, 2013, published in Neorganicheskie Materialy, 2013, Vol. 49, No. 6, pp. 680–684.
Synthesis of Carboxylate Derivatives of Molybdenum
and Tungsten Based on Joint Insertion of CO2 and PhNCS
or N,N'ꢀDicyclohexylcarbodiimide into M–Cl Bonds
N. A. Ovchinnikova, E. A. Martynova, N. A. Minaeva, and O. G. Ellert
Kurnakov Institute of General and Inorganic Chemistry, Russian Academy of Sciences,
Leninskii pr. 31, Moscow, 119991 Russia
eꢀmail: talan@igic.ras.ru
Received November 16, 2012
Abstract—Reactions of the higher molybdenum and tungsten chlorides with phenyl isothiocyanate or with
N'ꢀdicyclohexylcarbodiimide and carbon dioxide in dichloroethane are the first to demonstrate the possiꢀ
N
,
bility of insertion of carbon dioxide in combination with other heterocumulenes into transition metal–haloꢀ
gen bonds. IR spectroscopy and elemental analysis data show that the reactions result in the attachment of
the ligands at the same metal–chlorine bond and the formation of heteromolecular insertion products with
the compositions
[MoOCl3{N(Ph)C(S)}2NC(Me)Cl]
and
MClx{OC(O)[(Hex)NCN(Hex)]2}Cl,
where x = 4 and 5 for the Mo and W derivatives, respectively.
DOI: 10.1134/S0020168513050105
structed can be used as key components of drugs [6, 7]
and thermally stable polymers and can find application
as sources of difficultꢀtoꢀreach organic materials.
INTRODUCTION
As shown earlier, heterocumulenes in combination
with other unsaturated molecules are capable of being
attached to a bond between a transition metal (Group V
[1, 2], VI [3], or VII [4]) and chlorine, which according
to NMR and Xꢀray diffraction date, to form heterocyꢀ
clic ligands or compounds in the case of partial or comꢀ
plete hydrolysis, respectively.
The goal of this work was to carboxylate molybdeꢀ
num and tungsten complexes by way of heteromolecuꢀ
lar insertion of carbon dioxide in combination with
another, isoelectronic heterocumulene (an isothiocyꢀ
anate or carbodiimide) into a metal–halogen (metal =
molybdenum or tungsten) bond, on the example of
addition of carbon dioxide and phenyl isothiocyanate
(or N,N'ꢀdicyclohexylcarbodiimide) to molybdenum
pentachloride and tungsten hexachloride.
Even though transition metal compounds are conꢀ
venient object for carbon dioxide conversion to carboxꢀ
ylates or carbamates, there is only one known example
of the carboxylation of combinations of СО2 with other
heterocumulenes: the insertion of the carbon dioxide
into the La–O bond of the lanthanide complex in the
La(OPr)2–PhNCO–CO2 system [5].
EXPERIMENTAL
All manipulations related to the synthesis and isolaꢀ
tion of the complexes and sampling were carried out
under a dry argon atmosphere because the starting
molybdenum and tungsten chlorides and their derivaꢀ
tives hydrolyze in air.
The heteromolecular insertion of carbon dioxide in
combination with an isoelectronic heterocumulene
into the metal–chlorine (metal = molybdenum or
tungsten) bond opens up new possibilities for advances
in the combinatorial synthesis of carboxylate comꢀ
The completeness of the reaction determined by the
pounds with complex ligands. The complexes thus conꢀ disappearance of the stretching bands of free ligands in
638

SYNTHESIS OF CARBOXYLATE DERIVATIVES OF MOLYBDENUM AND TUNGSTEN
639
the range 2100–2300 cm–1 in the IR spectrum of the
Calculated for WCl6C27H44N4O2 (%): N, 6.50; C,
reaction mixture, and insertion into the complex was 36.5; H, 5.2; Cl, 24.9.
registered on the appearance of new bands in the range
µeff = 0 at 293 K.
1500–1800 cm–1, typical for stretching modes of the
Reaction of MoCl5 with PhNCS and CO2. Bubbling
double bonds in the inserted ligands.
CO2 for 7 h through a MoCl5 (1 g, 3.66 mmol) suspenꢀ
sion in dichloroethane (10 mL) containing PhNCS
(1 mL, 9.47 mmol) at the boiling point of the reaction
mixture led to the formation of a dark brown viscous
substance. IR spectroscopic characterization of the
reaction product showed that ligand insertion did not
reach completion. In view of this, the sample was
heated further after the addition of acetonitrile, which
can act not only as a medium but also as a reagent proꢀ
moting the insertion process.
In our syntheses, we used molybdenum pentachloꢀ
ride and tungsten hexachloride purified by highꢀtemꢀ
perature vacuum sublimation, N,N'ꢀdicyclohexylcarꢀ
bodiimide (99%, Fluka), phenyl isothiocyanate (98%,
Fluka), and acetonitrile and dichloroethane purified by
standard procedures.
Chloride ions were determined by way of silver chloꢀ
ride precipitation: an excess of a titrated silver nitrate
solution was added, and the excess was then titrated by
the Volhard method. Hydrogen, carbon, nitrogen, and
sulfur were determined on a Carlo Erba EAꢀ1108
CHNS analyzer (Shared Physical Characterization
Facilities Center, Kurnakov Institute of General and
Inorganic Chemistry (IGIC), Russian Academy of Sciꢀ
ences).
Boiling the acetonitrile solution for 2 h led to the
formation of a brownꢀblack viscous substance, which
was dried under vacuum, repeatedly washed with carꢀ
bon tetrachloride, and again dried to constant
weight. The reaction product had the form of blackꢀ
brown powder (III).
IR spectra were registered on Specord 75 IR (400–
4000 cm–1) and Specord 80 (200–4000 cm–1) spectroꢀ
photometers using KBr plates and samples prepared as
Vaseline mulls.
Found for III (%): N, 6.01; C, 30.51; H, 1.86; S,
9.44; Cl, 23.24.
Calculated for MoCl4C14H10N2S2O3 (%): N, 4.92;
C, 31.67; H, 1.76; S, 11.26; Cl, 24.95.
Magnetic susceptibility was measured using a
setup designed at IGIC by a procedure described
elsewhere [8].
µeff = 0 at 293 K.
Reaction of MoCl5 with С6Н11СNCC6H11 and CO2
.
DISCUSSION
Bubbling СО2 for 2 h through a МоСl5 (1.040 g,
3.81 mmol) suspension in dichloroethane (10 mL) conꢀ
taining С6Н11СNCC6H11 (1.571 g, 7.6 mmol) led to
heat release, and the solution changed color from dark
brown to green. The resultant solution was dried under
vacuum, repeatedly washed with carbon tetrachloride,
and again dried under vacuum to constant weight. As a
The present results demonstrate that the reaction of
molybdenum pentachloride with N,N'ꢀdicyclohexylꢀ
carbodiimide and carbon dioxide in dichloroethane at
room temperature leads to the formation of a complex
containing both types of molecules.
The IR spectrum of the isolated compound (Fig. 1a)
contains strong absorption bands at 1610 cm–1, correꢀ
result, we obtained a dark brown viscous substance (
I)
sponding to the
at 1560 and 1520 cm–1, corresponding to the
of the inserted carbodiimide. The presence of a single
band at 896 cm–1, characteristic of
(C–Cl), indicates
ν
(С=О) of the carboxylate group, and
with a green tinge.
ν
(С=N)
Found for I (%): N, 7.40; C, 42.39; H, 6.6; Cl, 17.5.
Calculated for MoCl5C27H44N4O2 (%): N, 8.20; C,
45.9; H, 6.5; Cl, 15.6.
ν
that all molecules are inserted into the same Mo–Cl
bond, forming a chain ligand.
µeff = 1.95µB at 293 K.
That the IR spectrum of the complex contains a
Reaction of WCl6 with С6Н11СNCC6H11 and CO2.
Bubbling СО2 for 2 h through a WCl5 (9.686 g,
1.73 mmol) suspension in dichloroethane (10 mL) conꢀ
taining С6Н11СNCC6H11 (0.713 g, 3.45 mmol) caused
the solution to turn dark brown with an emerald tinge.
strong
(М–N) absorption band at 560 cm–1 indicates
ν
that the reaction involves the formation of a bond
between one of the N,N'ꢀcarbodiimide groups of the
chain and a metal atom. The weaker band at 440 cm–1,
corresponding to (M–О), suggests that the ligand is
ν
The resultant solution was dried under vacuum,
repeatedly washed with carbon tetrachloride, and again
dried to constant weight. The product was a thermally
stable dark brown viscous substance (II) with an emerꢀ
ald tinge.
also coordinated to the metal atom through the oxygen
of the carbonyl group.
The high thermal stability of the insertion product
MoCl4 {OC(O)[(Hex)NCN(Hex)]2}Cl
(I) and the staꢀ
bilization of the oxidation state of the metal (5+) lead us
Found for II (%): N, 6.17; C, 36.6; H, 3.86; Cl, 28.8. to assume that it has a polymeric structure.
INORGANIC MATERIALS Vol. 49
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640
OVCHINNIKOVA et al.
Based on elemental analysis data, we conclude that molecules and one carbon dioxide molecule occurs
the addition of two N,N'ꢀdicyclohexylcarbodiimide according to the following scheme:
C6H11
C6H11 C6H11
N
C
O
N
N
t
= 20
C H Cl
2
°C
MoCl5 + H11C6ꢀN=C=NꢀC6H11 + CO2
Cl4Mo
C
O
C
2
4
N
Cl
C6H11
(I
)
Comparison of the IR spectra of the readily forming inserted N,N'ꢀdicyclohexylcarbodiimide. The presence
carbodiimide insertion product and (Figs. 1b, 1a) sugꢀ
(С–Сl) at 880 cm–1 indiꢀ
I
of a single band typical for
cates that, like in , all of the molecules are inserted into
the same Mo–Cl bond, forming a chain ligand.
ν
gests that the first reaction step is the insertion of two
N,N'ꢀdicyclohexylcarbodiimide molecules into the
Mo–Cl bond. Subsequently, a carbon dioxide molecule
is attached due to the breaking of the C–N bond
between the two inserted carbodiimide fragments.
The reaction of tungsten hexachloride with
N,N'ꢀdicyclohexylcarbodiimide and carbon dioxide
in dichloroethane also occurs at room temperature
and leads to the attachment of both types of moleꢀ
I
The presence of a strong ν(М–N) absorption band
at 560 cm–1 in the IR spectrum of II indicates that this
insertion product contains a bond between the N,N'
dicyclohexylcarbodiimide and a metal atom. The
weaker band at 420 cm–1, corresponding to
(М–О)
ꢀ
ν
,
leads us to conclude that the ligand is also coordinated
to the same or a neighboring metal atom through the
oxygen atom of the carbonyl group.
cules
and
the
formation
of
the
WCl5{OC(O)[(Hex)N=C=N(Hex)]2}Cl adduct (II).
The IR spectrum of II (Fig. 2) contains strong
absorption bands at 1640 cm–1, corresponding to the
Based on elemental analysis data, we conclude that
the addition of two N,N'ꢀdicyclohexylcarbodiimide
molecules and one carbon dioxide molecule to the same
ν
(С=О) of the carboxylate ligand, and at 1560 and
1520 cm–1, corresponding to the
ν
(С=N) of the W–Cl bond occurs according to the following scheme:
C6H11
C6H11 C6H11
N
C
O
N
N
t
C H Cl
= 20 С
°
WCl6 + H11C6ꢀN=C=NꢀC6H11 + CO2
Cl5W
C
O
C
2
4
2
N
Cl
C6H11
(
II)
Studies have shown, that the reaction of molybdeꢀ spectrum
of
MoOCl3{N(Ph)C(S)OC(O)N(Ph)C(S)}Cl
(Fig. 3). The presence of strong bands at 1620 cm–1,
corresponding to the (С=O) of the carboxylate ligand,
and at 1560 and 1520 cm–1, corresponding to the
(С=N) of the inserted phenyl isothiocyanate, and a
single
(С–Сl) band at 890 cm–1 leads us to conclude
the
synthesized
compound
num pentachloride with phenyl isothiocyanate in
dichloroethane does not take place completely even
during prolonged boiling reaction mixture, as eviꢀ
denced by the fact that the IR spectrum of the reaction
(III
)
ν
mixture contains the (N=C=S) bands at 2100 and
ν
2400 cm–1, corresponding to vibrations of bonds in free
and coordinated phenyl isothiocyanates, respectively.
As has shown experiment, the addition of a donor
solvent (acetonitrile) allows one to completely move the
reaction toward the formation of a heteromolecular
ligand insertion product.
ν
ν
that the phenyl isothiocyanate and carbon dioxide molꢀ
ecules are inserted into the same Mo–Cl bond, forming
a chain ligand.
Coupled with elemental analysis data, the reaction
Thus, are not found absorption bands corresponding
to free or coordinated phenyl isothiocyanate in the IR scheme can be represented as follows:
Ph
N
Ph
N
Cl
O
Cl
t
°
Cl
Cl
b
MoCl5 + PhꢀN=C=S + CO2
Mo
C
S
C
O
C
S
C H Cl
2
2
CH CN
4
3
O
(III)
INORGANIC MATERIALS Vol. 49
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SYNTHESIS OF CARBOXYLATE DERIVATIVES OF MOLYBDENUM AND TUNGSTEN
641
(а)
2000 1800 1600 1400 1200 1000 800 600 400
Wavenumber, cm–1
2000 1800 1600 1400 1200 1000 800 600 400
Wavenumber, cm–1
Fig. 2.
IR
spectrum
of
the
WCl {OC(O)[(Hex)N=C=N(Hex)] }Cl complex (II).
(b)
5
2
2000 1800 1600 1400 1200 1000 800 600
Wavenumber, cm–1
1800 1600 1400 1200 1000 800 600 400
Wavenumber, cm–1
Fig.
1.
IR
spectra
of
(a)
the
) and
MoCl {OC(O)[(Hex)NCN(Hex)] }Cl complex (
I
5
4
2
(b) the product of the reaction between MoCl and
2C H CNCC H .
Fig. 3.
IR
spectrum
of
the
MoOCl {N(Ph)C(S)OC(O)N(Ph)C(S)}Cl complex (III).
6
11
6
11
3
It has been found, that after СО2 bubbling for 12.5 h
through a boiling suspension of tungsten hexachloride
and phenyl isothiocyanate in dichloroethane, the IR
spectrum of the reaction mixture contained strong
absorption bands at 1580 and 2096 cm–1, correꢀ
sponding to bonds in the inserted and coordinated
phenyl isothiocyanates, respectively. The addition of
acetonitrile to the reaction mixture did not improve
the results, suggesting that, in the case of the tungsten
analog, the insertion reaction was reversible.
Note that reversibility of phenyl isothiocyanate
insertion into metal–ligand bonds was also pointed out
by Gibson et al. [9] for the Mo–O bond by the example
of reactions of alkoxy amide derivatives of molybdenum
with PhNCS.
CONCLUSIONS
The presented results indicate that reactions of
Мо(W)Сlx with PhNCS and СО2 in dichloroethane are
reversible, whereas the addition of a donor solvent (aceꢀ
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OVCHINNIKOVA et al.
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СО2 into the Mo–Cl bond in the ratio 2 : 1 totally.
We have for the first time demonstrated heteromoꢀ
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combination with СО2 into the Mo(W)–Cl bond; that
is, we have performed the first intramolecular condenꢀ
sation of carbon dioxide with an aryl iso(thio)cyanate or
carbodiimide on the basis of the heteromolecular inserꢀ
tion of their combinations into chloro derivatives of
molybdenum and tungsten. This opens up new possibilꢀ
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from the coordination sphere of the complex, makes it
possible to design and engineer novel and difficultꢀtoꢀ
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into alkoxo and imido ligands, Chem. Commun., 1994,
no. 22, pp. 2635–2636.
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INORGANIC MATERIALS Vol. 49
No. 6
2013