VANADIUM(II) CHLORIDE

1

Vanadium(II) Chloride

VCl

2

[10580-52-6]

Cl

2

V

(MW 121.84)

InChI = 1/2ClH.V/h2*1H;/q;;+2/p-2/f2Cl.V/h2*1h;/q2*-1;m
InChIKey = ITAKKORXEUJTBC-OUXHBNONCC

(nitro group to carbonyl conversion; hydrodehalogenation of
α

-halo ketones; reductions; reductive cleavage of oximes;

reductive hydrolysis of 2,4-DNP derivatives)

Alternate Names:

vanadium dichloride; vanadium chloride.

Physical Data:

mp 910

◦

C (subl); d 3.23 g cm

−3

.

Solubility:

sol with decomposition in hot and cold water; sol

alcohols, DMF, THF, ethers.

Form Supplied in:

commercially available as a green deliquescent

solid.

Vanadium(II) Chloride.

Many reagents based on chro-

mium(II), titanium(II), and titanium(III) ions have found utility
in organic synthesis because of their redox potentials (Table 1).
Vanadium(II) chloride has found application in modern organic
synthesis in part because its redox potential (+0.255 V) is
greater than the Sn

II

–Sn

III

couple (−0.15 V) although lower than

Cr

II

– Cr

III

(+0.41 V) or Ti

II

–Ti

III

(+0.37 V).

1

A variety of syn-

thetic transformations have been documented.

Conversion of the Nitro Group to the Carbonyl Group.

When an aqueous solution of vanadium chloride is added to a pri-
mary or secondary aliphatic nitro compound dissolved in a mix-
ture of water, hydrochloric acid, and DMF, a moderate to good
yield (50–70% typically) of the corresponding ketone is isolated
(eq 1).

2

The pH-dependent procedure involves initial reduction

and subsequent hydrolysis of the resulting carbonyl imine.
Several alternative methods are known

3

which will effect the

same transformation.

NO

2

O

VCl

2

DMF, H

2

O

(1)

53%

Hydrodehalogenation of α

α

α

-Halo Ketones. When an aqueous

solution of vanadium chloride is added to α-halo ketones

1

in THF,

a mildly exothermic reaction ensues which yields the halogen-free
product after extractive workup (eq 2). Yields are generally quite
high, ranging between 80 and 98%.

O

Br

Br

VCl

2

THF, H

2

O

O

Br

(2)

98%

Reductions.

This reagent also reduces benzils to ben-

zoins (THF–H

2

O, 80–90% yield),

4

quinones to hydroquinones

(90–95% yield),

4

and aryl azides to the corresponding amines

and N

2

(70–95% yield) (eq 3).

5

N

3

R

VCl

2

NH

2

R

(3)

R = H, 2-Me, 4-Cl, 4-F, 2-CF

3

THF, H

2

O

Reductive Cleavage of Oximes. Aqueous solutions of VCl

2

have been employed in the mildly exothermic deoximation of
oximes to the corresponding carbonyl compounds in 75–90%
yield (eq 4).

6

N

OH

N

OVCl

2

VCl

2

NH

(4)

O

– VOCl

2

87%

H

+

THF, H

2

O

H

2

O

Reductive Hydrolysis of 2,4-Dinitrophenylhydrazones.

The regeneration of carbonyl compounds from 2,4-dinitrophenyl-
hydrazones is often problematic owing to the acid stability of the
parent molecules. Vanadium chloride promotes the hydrolysis to
the respective carbonyl moiety in 67–95% yield via initial reduc-
tion of the nitro group.

7

Other Vanadium(II) Reagents. Aryl and alkyl halides are re-

duced by a number of low-valent transition metals.

8

The complex

9

VCl

2

(py)

4

reduces activated (e.g. Bn–Cl) but not unactivated

halo compounds (e.g. vinyl halides). This reagent is selective
towards the formation of coupled R–R products to the exclu-
sion of R–H-type products. In contrast, Cr

II

reduces

10

Bn–Cl

to various ratios of bibenzyl and toluene (dependent on the re-
action conditions). Bis(cyclopentadienyl)vanadium

11

(Cp

2

V) is

also effective in these reactions. In an extension of earlier work,

12

2,2,2-trichloroacetanilide has been selectively reduced to 2,2-
dichloroacetanilide using VCl

2

(py)

4

. Other complexes

13

of di-

valent vanadium having the general formula V(amine)

4

X

2

are

also known. The amine can be either aromatic (e.g. picoline) or
aliphatic (e.g. ethylenediamine). The V(amine)

4

X

2

chemistry

remains largely unexplored.

Recently, a bimetallic V

II

species, [V

2

Cl

3

(THF)

6

]

2

[Zn

2

Cl

6

],

prepared in situ from V

III

, has been introduced

14

to achieve the

stereoselective cross coupling of two different alkanals under mild
conditions. The intermolecular pinacol cross-coupling reaction
has been modified

15

to include chiral aldehydes which yield syn-

diols in a 91:9 diastereoisomeric ratio (up to 84% ee). Reduc-
tive cyclization of δ,ε-enals has also been demonstrated

16

to pro-

ceed with excellent stereoselectivity (eq 5), in contrast to what is
obtained with other reagents such as Sm

II

.

Avoid Skin Contact with All Reagents

2

VANADIUM(II) CHLORIDE

CHO

CO

2

Me

CO

2

Me

OH

CO

2

Me

OH

(5)

+

24:1

68%

[V

2

Cl

3

(THF)

6

]

2

[Zn

2

Cl

6

]

CH

2

Cl

2

1.

Ho, T.-L.; Olah, G. A., Synthesis 1976, 807.

2.

Kirchoff, R., Tetrahedron Lett. 1976, 2533.

3.

(a) McMurry, J.; Melton, J., J. Am. Chem. Soc. 1971, 93, 5309.
(b) McMurry, J.; Melton, J.; Padgett, H., J. Org. Chem. 1974, 39, 259.

4.

Ho, T.-L.; Olah, G. A., Synthesis 1976, 815.

5.

Ho, T.-L.; Henninger, M.; Olah, G. A., Synthesis 1976, 815.

6.

Olah, G. A.; Arvanaghi, M.; Surya, G. K., Synthesis 1980, 220.

7.

Olah, G. A.; Chao, Y.-L.; Arvanaghi, M.; Surya Prakash, G. K., Synthesis
1981, 476.

8.

Kustin, K., Prog. Inorg. Chem. 1969, 13, 107.

9.

Cooper, T. A., J. Am. Chem. Soc. 1973, 95, 4158.

10.

de Liefde Meijer, H. J.; Janssen, M. J.; van der Kerk, G. J. M., Recl. Trav.
Chim. Pays-Bas 1961

, 80, 831.

11.

Eisch, J. J.; King, R. B., Org. Synth. 1965, 1, 65.

12.

Cooper, T. A.; Sonneberg, F. M., J. Org. Chem. 1975, 40, 55.

13.

Kamar, M. M.; Larkworthy, L. F.; Patel, K. C.; Philips, D. J.; Beech, G.,
Aust. J. Chem. 1974

, 27, 41.

14.

Raw, A. S.; Pedersen, S. F., J. Org. Chem. 1991, 56, 830.

15.

Annunziata, R.; Cinquini, M.; Cozzi, F.; Giaroni, P.; Benaglia, M.,
Tetrahedron 1991

, 47, 5737.

16.

Inokuchi, T.; Kawafuchi, H.; Torii, S., J. Org. Chem. 1991, 56, 4983.

Benoit Vanasse & Michael K. O’Brien

Rhône-Poulenc Rorer Pharmaceuticals, Collegeville, PA, USA

A list of General Abbreviations appears on the front Endpapers