Ion pairs from redox reaction of decamethylchromocene with
cyclopentadienyltitanium trichlorides
Vojtech Varga
a
, Róbert Gyepes
b
, Jiří Pinkas
c
, Michal Horáček
c
, Jiří Kubišta
c
, Karel Mach
c,
⁎
a
Research Institute of Inorganic Chemistry, Revoluční 84, 400 01 Ústí nad Labem, Czech Republic
b
J. Selye University, Faculty of Education, Bratislavská cesta 3322, 94501 Komárno, Slovak Republic
c
J. Heyrovský Institute of Physical Chemistry,v.v.i., Academy of Sciences of the Czech Republic, Dolejškova 3, 182 23 Prague 8, Czech Republic
abstract article info
Article history:
Received 19 December 2011
Accepted 8 February 2012
Available online 16 February 2012
Keywords:
Chromium
Chromocenium
Titanium
Titanate
NMR spectra
Crystal structure
Decamethylchromocene [Cr(η
5
-C
5
Me
5
)
2
] reacted with cyclopentadienyltitanium trichlorides [Ti(η
5
-C
5
H
5-n
Me
n
)
Cl
3
](n =0–5) in toluene to precipitate yellow finely crystalline ion pairs [Cr(η
5
-C
5
Me
5
)
2
]
+
[Ti(η
5
-C
5
H
5-n
Me
n
)
Cl
3
]
−
(1–6). Evidence for the chromocenium cation and titanate anions was obtained by paramagnetic
1
H
NMR spectra of 1–6 in CD
2
Cl
2
. The resonance of the cation was invariant at δ 6.9 ppm (Δν
1/2
~0.4 kHz) whereas
resonances of the titanate anions were shifting in response to the number of methyl groups (δ 10.5–8.4 ppm
(CpMe) and δ 26.6–39.0 ppm (CpH)). The presence of toluene of crystallization in 1–6 was observed by
1
H
NMR spectra, and in the crystal structure of 6. Crystallization of 6 from tetrahydrofuran afforded solvent-free
crystals of 6A. In crystal structures of both 6 and 6A the [Ti(η
5
-C
5
Me
5
)Cl
3
]
–
titanate anion possessed shorter
Ti–Cg distances and longer Ti–Cl bonds than the neutral species.
© 2012 Elsevier B.V. All rights reserved.
Late transition metal decamethylmetallocenes are known to be
electron donors capable to form stable donor-acceptor complexes,
aka charge-transfer salts with strong organic electron acceptors as
well as complex inorganic anions (A) according to general Eq. (1) [1].
M η
5
−C
5
Me
5
2
h i
þ A ¼ M η
5
−C
5
Me
5
2
h i
þ
A ½
–
ð1Þ
This property has been evaluated electrochemically by the half-
wave reduction potentials of metallocenium salts with hexafluoro-
phosphate [M(η
5
-C
5
Me
5
)
2
]
+
[PF
6
]
–
for reaction (2) giving E
1/2
for
M=Co −1.47 V, Cr −1.04 V, Ni −0.65 V, and Fe −0.12 V. The corre-
sponding non-methylated metallocenes are weaker electron donors
since their E
1/2
values were found by about 0.6 V more positive [2].
M η
5
−C
5
Me
5
2
h i
þ
þ e ¼ M η
5
−C
5
Me
5
2
h i
ð2Þ
The charge-transfer salts of these metallocenes and manganocene
with tetracyanoquinodimethane (TCNQ) [3a], tetracyanoethene
(TCNE) [3b], dialkyl dicyanofumarates [3c], and others, involving
fullerene [3d] or metal-containing electron acceptors [3e] were inves-
tigated as promising ferromagnetic materials. In organometallic
chemistry, mixing of cobaltocene with neutral complexes in solution
was used to prepare low soluble complex anions in charge-transfer
salts with [Co(η
5
-C
5
H
5
)
2
]
+
[4]. Related to this work, ion pairs of
cobaltocenium with methylcyclopentadienyltitanium trichloride and
methylcyclopentadienylvanadium trichloride anions were prepared,
and the paramagnetically shifted
1
H NMR spectra of the vanadate
and titanate species were observed [5]. Similarly, the [Co(η
5
-
C
5
H
5
)
2
]
+
[Ti(η
5
-C
5
H
5
)Cl
3
]
–
ion pair was obtained in dichloromethane,
and its X-ray crystal structure revealed that the Co–Cg (Cg – centroid
of gravity of the cyclopentadienyl ring) distance in cobaltocenium is
remarkably shorter than that in cobaltocene, and Ti–Cl bonds in the
titanate anion are distinctly longer than in the neutral CpTiCl
3
[6].
Chromocene [Cr(η
5
-C
5
H
5
)
2
] was known to react with alkyl or hy-
drogen halides to produce the chromocenium cation coupled with the
[CpCrX
3
]
–
(X = Cl, Br, or I) anion [7a,b], and [Cr(η
5
-C
5
Me
5
)
2
] reacted
with gaseous iodine to give [Cr(η
5
-C
5
Me
5
)
2
]
+
[Cr(η
5
-C
5
Me
5
)I
3
]
–
, the
evidence obtained mostly from paramagnetic
1
H and
13
C NMR spec-
tra [7c]. The crystal structure of serendipitously obtained decamethyl-
chromocene iodide revealed that it is the ionic compound [Cr(η
5
-
C
5
Me
5
)
2
]
+
I
–
where the chromocenium retains parallel planes of the
cyclopentadienyl rings [8].
Here we report the synthesis and some properties of ion pairs aris-
ing from the redox reaction of [Cr(η
5
-C
5
Me
5
)
2
] with a whole series of
methyl-substituted half-sandwich titanocene trichlorides [Ti(η
5
-
C
5
H
5-n
Me
n
)Cl
3
](n =0–5). Mixing of equimolar amounts of the both
reagents in toluene solutions resulted in virtually quantitative precip-
itation of lustrous golden-yellow microcrystalline powders of ion
pairs [Cr(η
5
-C
5
Me
5
)
2
]
+
[Ti(η
5
-C
5
H
5-n
Me
n
)Cl
3
]
–
(1–6) (Scheme 1).
Inorganic Chemistry Communications 19 (2012) 61–65
⁎ Corresponding author. Tel.: + 420 2 266053735; fax: + 420 2 286582307.
E-mail address: mach@jh-inst.cas.cz (K. Mach).
1387-7003/$ – see front matter © 2012 Elsevier B.V. All rights reserved.
doi:10.1016/j.inoche.2012.02.003
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