Neodymium and dysprosium diiodides in the synthesis of vanadocene and cobaltocene

Article abstract of DOI:10.1007/s11172-005-0094-x

The reaction of NdI₂ or DyI₂ with VCl₃ and cyclopentadiene in THF at 65-70°C without isolation of the intermediates afforded vanadocene in 55 and 68% yields, respectively. An analogous reaction of DyI₂ with CoCl

Full text of DOI:10.1007/s11172-005-0094-x

Russian Chemical Bulletin, International Edition, Vol. 53, No. 10, pp. 2179—2181, October, 2004
2179
Neodymium and dysprosium diiodides
in the synthesis of vanadocene and cobaltocene
ꢀ
M. N. Bochkarev and M. E. Burin
G. A. Razuvaev Institute of Organometallic Chemistry of the Russian Academy of Sciences,
49 ul. Tropinina, 603950 Nizhny Novgorod, Russian Federation.
Fax: +7 (831 2) 12 7497. Eꢀmail: mboch@imoc.sinn.ru
The reaction of NdI2 or DyI2 with VCl3 and cyclopentadiene in THF at 65—70 °C without
isolation of the intermediates afforded vanadocene in 55 and 68% yields, respectively. An
analogous reaction of DyI2 with CoCl2 at 50 °C produced Cp2Co in 38% yield.
Key words: neodymium diiodide, dysprosium diiodide, vanadocene, cobaltocene, synꢀ
thesis.
Due to high reduction potentials of divalent
neodymium and dysprosium diiodides, these compounds
(a simple procedure for their synthesis has been debeloped
recently1) can be used as a convenient and safe alternative
to alkali metals. In particular, we have demonstrated that
the LnI2 salts (Ln = Nd (1) or Dy (2)) can be used for the
preparation of Cp2V without isolation of intermediates
(Scheme 1).
It should be noted that an increase in the temperature
to 80—90 °C in the second step of the synthesis caused
further changes, resulting in a decrease in the yield of
Cp2V. Under these conditions, cyclopentadienyl iodide
Cp2VI was isolated from the reaction mixture in low yield
along with vanadocene. The possibility of the formaꢀ
tion of this complex from Cp2V and neodymium
trihalide, NdI2Cl, which is one of the products generated
in the second step, was confirmed by the reaction of
vanadocene with NdI3, which also gave green iodide
Cp2VI at 80—90 °C.
Scheme 1
Taking into account the reduction potentials of
vanadium (E°(V3+/V2+) = –0.255 V), neodymium
(E°(Nd3+/Nd2+
)
=
–2.6 V), and dysprosium
(E°(Dy3+/Dy2+) = –2.5 V),3 it can be hypothesized that
the formation of vanadocene in the aboveꢀmentioned sysꢀ
tem involves also the step of reduction of vanadium
trichloride to VCl2 with iodides 1 and 2. This leads to a
sharp increase in the yield of Cp2V in the synthesis inꢀ
volving DyI2 compared to the reaction of VCl3 with
CpDyI2(THF)3. Earlier, it has been demonstrated4,5 that
preliminary reduction of VCl3 to VCl2 with zinc dust or
LiAlH4 in the conventional synthesis of vanadocene
through CpNa made it possible to increase the yield of the
target product from 40 to 60—78%. Actually, we found
that diiodide 2 reacts with VCl3 in THF even at –30 °C.
However, this reaction afforded a darkꢀbrown solution of
several organodysprosium products instead of the expected
VCl2(THF)2.6 We failed to isolate individual compounds
(except for dysprosium trihalides) from this mixture. Earꢀ
lier,7 analogous changes have been observed upon the
addition of aromatic compounds to solutions of comꢀ
pounds 1 and 2 in THF or DME. To explain the observed
effect, we hypothesize that LnI2 undergoes disproporꢀ
tionation in a solvating medium to give triiodide and exꢀ
The monocyclopentadienyl complex CpLnI2(THF)x
is generated in the first step proceeding at room temperaꢀ
ture. The formation of such compounds in the reactions
of LnI2 (Ln = Nd or Dy) with cyclopentadiene has been
observed in our earlier study.2 Subsequent heating of the
reaction mixture at 60—65 °C afforded vanadocene
through metathesis between CpLnI2(THF)x and vanaꢀ
dium trichloride. The reactions with salts 1 and 2 proꢀ
duced Cp2V in 55 and 68% yields, respectively. This
vanadocene was easily isolated by vacuum sublimation of
a mixture of solid products obtained after the removal of
the solvent, an excess of CpH, and volatile products.
Interestingly, the reaction of CpDyI2(THF)3 with VCl3
performed separately afforded vanadocene in a yield of no
higher than 17% (Scheme 2).
Scheme 2
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 10, pp. 2086—2088, October, 2004.
1066ꢀ5285/04/5310ꢀ2179 © 2004 Springer Science+Business Media, Inc.

2180
Russ.Chem.Bull., Int.Ed., Vol. 53, No. 10, October, 2004
Bochkarev and Burin
tremely active monovalent iodide (LnI). The reaction of
the latter with the solvent affords7 a mixture of brown
σꢀcomplexes of composition RR´LnI (R and R´ are fragꢀ
ments of the solvent molecules). Apparently, vanadium
chloride, like benzene, promotes disproportionation
of LnI2. It was demonstrated that LiI, ScI3, and YI3 exert
the same effect on solutions of neodymium and dysproꢀ
sium diiodides. The formation of the intermediates
RR´LnI in the synthesis of Cp2V cannot have a substanꢀ
tial effect on the yield of the target product, because the
subsequent replacement of R and R´ with more acidic Cp
groups, which is inevitable under the synthesis conꢀ
ditions, would give rise to cyclopentadienyl derivaꢀ
tives Cp2LnI. It should be noted that the Cp2LnI comꢀ
plexes can also be generated in the direct reaction of
LnI with cyclopentadiene. The reaction of these prodꢀ
ucts with VCl3, analogously to the reaction with CpLnI2,
afforded vanadocene. We believe that the synthesis of
Cp2V involves both pathways, viz., through CpLnI2 and
Cp2LnI.
The reaction of diiodide 1 with CoCl2 and CpH in
THF at 20 °C produced a green solution, from which only
trace amounts of Cp2Co were isolated by sublimation. An
increase in the reaction temperature to 50—60 °C did not
lead to an increase in the yield of the product. By conꢀ
trast, the use of dysprosium iodide 2 under the same conꢀ
ditions made it possible to synthesize cobaltocene in 38%
yield. The characteristic brownishꢀgreen color of the soꢀ
lution as well as precipitation of dysprosium triiodide
(which occurs upon disproportionation of LnI2),7 which
were observed in the first step, indicate that this reaction
follows primarily the pathway
Experimental
All operations were carried out in vacuo or under argon
using the Schlenk technique. Tetrahydrofuran was distilled
over NaOH, degassed, dried with neodymium diiodide (THF
(500 mL), NdI2 (2 g), 20 °C, 30 min), and condensed into a
reaction tube immediately before use. Anhydrous VCl3 and
CoCl2 were purchased from Aldrich. Iodides NdI2 (1) and DyI2
(2) were purchased from Synor (Nizhny Novgorod, Russia).
The CpDyI2(THF)3 complex was prepared according to a proꢀ
cedure described earlier.2 The IR spectra were recorded on a
Perkin Elmer 577 spectrometer. The samples were prepared as
Nujol mulls. The ESR spectra were measured on a BrukerꢀER
200Dꢀ1SRC instrument.
Vanadocene, Cp2V. А. A solution of CpH (1.32 g, 20 mmol)
in THF (30 mL) was placed in an evacuated tube containing
DyI2 (3.58 g, 8.6 mmol) and VCl3 (0.31 g, 1.97 mmol) at ~20 °C.
Gas evolution started immediately. The gas was periodically
vented to atmosphere. The reaction mixture was stirred for 1.5 h
until evolution of hydrogen completely ceased. The tube was
evacuated, sealed, and heated with vigorous stirring at 65—70 °C
for 2 h, resulting in dissolution of the violet precipitate of VCl3
to give a colorless DyI2Cl(THF)x precipitate. The solution turned
violetꢀbrown. The reaction mixture was transferred to a subliꢀ
mation apparatus, and the solvent and volatile products were
removed by vacuum condensation. Further heating of the solid
residue to 80—100 °C (0.1 Torr) led to sublimation of darkꢀ
violet crystals of Cp2V. The yield was 0.24 g (68%). IR, ν/cm–1
:
1100 m, 1005 m, 820 w. ESR (77 K): g⊥ = 4.0, a⊥(51V) =
2.8 mT, g|| = 2.0.
B. Under analogous conditions, Cp2V was prepared from
NdI2 (2.8 g, 7.0 mmol), VCl3 (0.25 g, 1.5 mmol), and cycloꢀ
pentadiene (1.0 g, 15.1 mmol) in THF (10 mL) in a yield of
0.16 g (55%).
C. A mixture of CpDyI2(THF)3 (0.74 g, 1.06 mmol) and
VCl3 (0.05 g, 0.32 mmol) in THF (20 mL) was heated with
stirring to 65 °C for 2 h, after which the solution turned green.
Vanadocene was isolated from solid products by vacuum subliꢀ
mation at 90—100 °C in a yield of 0.01 g (17%).
LnI2 → LnI → RR´LnI → Cp2LnI → Cp2Co.
Taking into account the simplicity of the procedure,
availability of iodides 1 and 2, and relatively high yields of
metallocenes comparable to the yields achieved in conꢀ
ventional synthesis methods,4,5,8 the proposed method
can be recommended as a preparative approach. An imꢀ
portant advantage of this approach is that it does not
require inflammable alkali metals and LiAlH4, which warꢀ
rants the slightly higher prices of neodymium or dysproꢀ
sium compared to sodium. The ease of the reactions and
the preliminary data provide evidence that this procedure
can be extended to cyclopentadienyl and related comꢀ
plexes of other dꢀtransition metals. Studies in this field
are currently underway.
To summarize, we demonstrated for the first time that
divalent lanthanide diiodides, in particular, neodymium
and dysprosium diiodides, can successfully be used for
the synthesis of metallocenes of dꢀtransition metals. The
new procedure offers a number of advantages over conꢀ
ventional methods.
Cobaltocene, Cp2Co. The first step of the reaction of
DyI2 (1.89 g, 4.54 mmol), CoCl2 (0.2 g, 1.54 mmol), and
cyclopentadiene (1 g, 15.1 mmol) in THF (30 mL) was carried
out as described above for the reaction of DyI2 with VCl3. The
resulting greenishꢀbrown mixture was heated with stirring at
55 °C for 1 h. The solvent and volatile products were reꢀ
moved in vacuo, and red crystals of cobaltocene were sublimed
from a grayꢀbrown solid residue at 40—50 °C (0.1 Torr). The
yield was 0.11 g (38%), m.p. 173—174 °C (cf. lit. data9: m.p.
171—173 °C).
Dicyclopentadienylvanadium iodide, Cp2VI. А. A violet reacꢀ
tion mixture, which was prepared from DyI2 (1.54 g, 3.70 mmol),
VCl3 (0.13 g, 0.83 mmol), and cyclopentadiene (0.53 g,
8.03 mmol) in THF (30 mL) under the conditions of the aboveꢀ
described experiment, was heated with stirring at 90 °C for 4 h.
The solution gradually turned blueꢀgreen. After removal of the
solvent, the gray solid residue was heated in vacuo. At 80—100 °C
(0.1 Torr), trace amounts of Cp2V sublimed. Darkꢀgreen crysꢀ
tals of Cp2VI sublimed when the temperature was raised to
170—180 °C. The yield was 52 mg (20%), m.p. 215—217 °C (cf.
lit. data10: m.p. 214—215 °C). IR, ν/cm–1: 1100 m, 1005 m, 820.

Synthesis of vanadocene through lanthanide diiodides Russ.Chem.Bull., Int.Ed., Vol. 53, No. 10, October, 2004
2181
B. A mixture of Cp2V (210 mg, 1.16 mmol) and NdI3(THF)3
(860 mg, 1.16 mmol) in THF (10 mL) was heated with stirring
in a sealed tube at 80 °C for 3 h. The color of the solution
gradually changed from violet to blue and then to blueꢀgreen.
The solvent was removed in vacuo and the residue was extracted
with toluene (3×10 mL). After removal of the toluene from
the extract, the grayꢀgreen residue was heated in vacuo. At
170—180 °C (0.1 Torr), green crystals of Cp2VI sublimed. The
yield was 21 mg (6%), m.p. 215—217 °C. The IR spectrum of
the product was identical to the spectrum of the compound
prepared in the above experiment.
2. G. V. Khoroshen´kov, A. A. Fagin, M. N. Bochkarev,
S. Dechert, and H. Schumann, Izv. Akad. Nauk, Ser. Khim.,
2003, 1627 [Russ. Chem. Bull., Int. Ed., 2003, 52, 1715].
3. F. A. Cotton and G. Wilkinson, Adv. Inorg. Chem., 5th ed.,
J. Wiley and Sons, New York (USA), 1988.
4. G. Wilkinson, F. A. Cotton, and J. M. Bormingham, J. Inorg.
Nucl. Chem., 1956, 2, 95.
5. K. Handlir, J. Holecek, and J. Klikorka, Z. Chem., 1979,
19, 265.
6. F. H. Köhler and W. Prössdorf, Z. Naturforsch., 1977,
32b, 1026.
7. M. N. Bochkarev, A. A. Fagin, and G. V. Khoroshen´kov,
Izv. Akad. Nauk, Ser. Khim., 2002, 1757 [Russ. Chem. Bull.,
Int. Ed., 2002, 51, 1909].
8. E. O. Fisher and R. Jira, Z. Naturforsch., 1953, 8b, 327;
Comprehensive Organometallic Chemistry, Eds G. Wilkinson,
F. Gordon, A. Stone, and E. W. Abel, Pergamon Press,
Oxford, 1982, 5.
This study was financially supported by the Foundaꢀ
tion of the President of the Russian Federation (Program
"Leading Scientific Schools," Grant NShꢀ58.2003.3), the
Russian Foundation for Basic Research (Project No. 04ꢀ
03ꢀ32093), and the US Civilian Research and Developꢀ
ment Foundation (CRDF, Grant RC1ꢀ2322ꢀNNꢀ02).
9. G. Wilkinson, P. Pauson, and F. A. Cotton, J. Am. Chem.
Soc., 1954, 76, 1970.
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1. M. N. Bochkarev and A. A. Fagin, Izv. Akad. Nauk, Ser.
Khim., 1999, 1200 [Russ. Chem. Bull., 1999, 48, 1187 (Engl.
Transl.)]; M. N. Bochkarev and A. A. Fagin, Chem. Eur. J.,
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Received January 28, 2004;
in revised form May 5, 2004