Bridging azines in the coordination sphere of low-valent vanadocene derivatives

Article abstract of DOI:10.1021/om100612e

Complexes of vanadocene(II) and -(III) derivatives with aromatic N-heterocyclic ligands are scarcely known. Here we present the first syntheses of several mono-, di-, and trinuclear complexes of this type and their detailed characterization. Reactions of vanadocene(II) derivatives are limited to N-heterocycles with distinct π-acceptor ability such as 4,4'-azobis(pyridine) , which reacts as a bridging ligand to form [(Cp₂V) ₂(μ₂-Py₂N₂)] (13). In contrast Cp₂V^II reacts with, for example, 1,2-bis(4-pyridiyl) acetylene (C₂Py₂) solely to give the corresponding metallacyclopropene [Cp₂V(η²-C₂Py ₂)] (12) without affecting the pyridyl moieties. On the other hand, the reactivity of vanadocene(III) cations with this class of ligands is unrestricted and dominated by the acid-base properties of the reactants. The application of permethylated cyclopentadienyl ligands (Cp*) significantly enhances the solubility of those complexes, which leads to a better crystallizability. Due to the cationic properties of vanadocenium(III) derivatives, reactions with the smallest aromatic bridging N-heterocycle, pyrazine, afforded the rarely known mononuclear pyrazine complexes [Cp' ₂V(Pz)][BPh₄] (Cp' = Cp (17), Cp* (20); Pz = C ₄H₄N₂), whereas other N-heterocycles with expanded π-systems such as 4,4'-bipyridine (4-Bipy), C₂Py ₂, and 1,3,5-tris(4-pyridyl)-2,4,6-triazine (4-TPT) grant access to multinuclear vanadocenium(III) derivatives ([(Cp*₂V) ₂(μ₂-4-Bipy)][BPh₄]₂ (21), [(Cp*₂V)₂(μ₂-Py₂C ₂)][BPh₄]₂ (24), [(Cp*₂V) ₃(μ₃-4-TPT)][BPh₄]₃ (26)). Compositions of all these complexes were confirmed by single-crystal X-ray diffraction.

Full text of DOI:10.1021/om100612e

Organometallics 2010, 29, 5859–5870 5859
DOI: 10.1021/om100612e
Bridging Azines in the Coordination Sphere of Low-Valent Vanadocene
Derivatives†
€
Markus Jordan, Wolfgang Saak, Detlev Haase, and Rudiger Beckhaus*
Institute of Pure and Applied Chemistry, Carl von Ossietzky University Oldenburg, P.O. Box 2503, D-26111
Oldenburg, Germany
Received June 24, 2010
Complexes of vanadocene(II) and -(III) derivatives with aromatic N-heterocyclic ligands are scarcely
known. Here we present the first syntheses of several mono-, di-, and trinuclear complexes of this type and
their detailed characterization. Reactions of vanadocene(II) derivatives are limited to N-heterocycles
with distinct π-acceptor ability such as 4,40-azobis(pyridine), which reacts as a bridging ligand to form
[(Cp2V)2(μ2-Py2N2)] (13). In contrast Cp2VII reacts with, for example, 1,2-bis(4-pyridiyl)acetylene
(C2Py2) solely to give the corresponding metallacyclopropene [Cp2V(η2-C2Py2)] (12) without affecting
the pyridyl moieties. On the other hand, the reactivity of vanadocene(III) cations with this class of ligands
is unrestricted and dominated by the acid-base properties of the reactants. The application of perme-
thylated cyclopentadienyl ligands (Cp*) significantly enhances the solubility of those complexes, which
leads to a better crystallizability. Due to the cationic properties of vanadocenium(III) derivatives,
reactions with the smallest aromatic bridging N-heterocycle, pyrazine, afforded the rarely known mono-
nuclear pyrazine complexes [Cp02V(Pz)][BPh4] (Cp0 =Cp (17), Cp* (20); Pz=C4H4N2), whereas other
N-heterocycles with expanded π-systems such as 4,40-bipyridine (4-Bipy), C2Py2, and 1,3,5-tris(4-pyridyl)-
2,4,6-triazine(4-TPT) grantaccesstomultinuclearvanadocenium(III) derivatives([(Cp*2V)2(μ2-4-Bipy)]-
[BPh4]2 (21), [(Cp*2V)2(μ2-Py2C2)][BPh4]2 (24), [(Cp*2V)3(μ3-4-TPT)][BPh4]3 (26)). Compositions of all
these complexes were confirmed by single-crystal X-ray diffraction.
Introduction
this class of ligands is of particular interest, which can effect
electron transfer and delocalization between the metal cen-
ters.10,12-17 In contrast to the highly developed supramolecular
chemistry of late transition metals, only a few examples are
known of well-defined multinuclear architectures of early
transition metals.15-21
Within the scope of our investigations on the reactivity
of low-valent titanocene precursors22,23 with aromatic
N-heterocyclic ligands, we could establish new routes to form
The design of highly ordered supramolecular architectures
by metal-directed self-assembly has attracted more and more
attention over the last few decades. Due to this concept, it is
possible to create a wide variety of two- and three-dimensional
structures by combining simple building blocks.1-9 Bridging
ligands in those complexes are often based on aromatic N-het-
erocycles because of their great electronic and steric versatil-
ity.10,11 Among their ability to connect metal centers by form-
ing metal-ligand bonds, the π-back-bonding properties of
(12) Launay, J.-P. Chem. Soc. Rev. 2001, 30, 386–397.
(13) Serroni, S.; Campagna, S.; Puntoriero, F.; Di Pietro, C.;
McClenaghan, N. D.; Loiseau, F. Chem. Soc. Rev. 2001, 30, 367–375.
(14) Petersen, J. D.; Murphy, W. R., Jr.; Sahai, R.; Brewer, K. J.;
Ruminski, R. R. Coord. Chem. Rev. 1985, 64, 261–272.
(15) Kraft, S.; Beckhaus, R.; Haase, D.; Saak, W. Angew. Chem., Int.
Ed. 2004, 43, 1583–1587.
† Dedicated to Prof. Dr. J€urgen Heck on the occasion of his 60th birthday.
*To whom correspondence should be addressed. Tel: þ49 441
798 3656. Fax: þ49 441 798 3851. E-mail: ruediger.beckhaus@
uni-oldenburg.de.
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r
2010 American Chemical Society
Published on Web 10/25/2010
pubs.acs.org/Organometallics

5860 Organometallics, Vol. 29, No. 22, 2010
Jordan et al.
molecular squares and rectangles with formally tetrahedral
coordinated metal corners,15,16 as well as squares with end-
on and side-on coordinated metal centers.17 The latter is the
first example of a trans to cis rearrangement of 4,40-azobis-
(pyridine) in metal complexes due to side-on coordination
of the azo group, which is induced by the electronic prop-
erties of titanocene fragments. Furthermore, we described
the synthesis and characterization of trinuclear titanocene
chelate complexes with interesting redox and electronic
properties.24,25
Although a rich chemistry of titanocene derivatives is
known, the metallocene chemistry of the adjacent group 5
element vanadium is much less developed. The lack of
knowledge is primarily based on the odd electron numbers
of vanadocene complexes, which induce paramagnetism and
hence hinder further spectroscopic analysis. Therefore, the
characterization of vanadocene derivatives is dominated by
IR spectroscopy and especially by X-ray diffraction.
However, there are also some advantages of vanadocene
chemistry in comparison to that of its titanium analogues.
Vanadocene(II) (1) is the first stable metallocene of the 3d
early transition metals,26-28 whereas titanocene(II) deriva-
tives need π-acceptor ligands to stabilize the highly reactive
complexes in a bent metallocene structure.29 The same
applies to vanadocene(III) cations, in spite of being isoelec-
tronic with titanocene(II); thus, there are no competitive
ligands in the reactions of 1.30,31 Owing to their one addi-
tional electron in comparison to corresponding titanocene
complexes, interesting electronic effects in multinuclear van-
adocene complexes should be observed.
Figure 1. Known low-valent vanadocene(II) and -(III) com-
plexes with aromatic N-heterocyclic ligands.
and activated nitrile groups38,42 just as lithiated hydrocarbons43
as binding sites. Multinuclear low-valent vanadocene com-
plexes with, for example, aromatic N-heterocycles, one of the
most common class of ligands in coordination chemistry, are
still unknown.
Here we report on the synthesis and characterization of
new bi- and trinuclear decamethylvanadocene(II) and -(III)
complexes with some popular bridging aromatic N-heterocycles.
Additionally, we present several mononuclear (decamethyl)-
vanadocenium(III) complexes with pyridine as well as pyrazine,
which is quite inconvenient for the simplest six-membered
aromatic N-heterocyclic bridging ligand. All structures have
been confirmed by single-crystal X-ray diffraction.
Surprisingly, only two mononuclear low-valent vanadocene
complexes with aromatic N-heterocyclic ligands (2 and 3)
had been reported first by Floriani et al. until the beginning of
our studies (Figure 1);37,44 therefore, new routes had to be
established to enter this kind of vanadocene chemistry.
Results and Discussion
Thanks to the high-spin configurations of free low-valent
vanadium sandwich compounds,30-33 coordination of more
than one additional ligand is scarcely observed.29,34-38 Be-
cause of this, only a few binuclear vanadocene(II) and -(III)
complexes are known in literature, using keto,39 acetylene,40,41
To gain access to vanadocene azine chemistry, we ini-
tially reproduced the 2,20-bipyridine (2-Bipy) complex 2 of
Floriani et al., in which the authors assumed a monodentate
2,20-bipyridine coordination to avoid an unfavorable 19e
complex, due to the lack of structural information. We were
able to prove the bidentate coordination of the chelate ligand
by X-ray diffraction; however, one cyclopentadienyl ring
(Cp) performed a rarely observed ring slippage to η3 coordi-
nation, even in the solid state to form the preferred 17e
complex.45 Formal one-electron oxidation of 2 by ferro-
cenium salt led to the stable 18e complex cation in which both
Cp ligands were arranged in the usual η5 coordination. Sub-
sequently, we intensified our studies in vanadocene complexes
with bridging N-heterocyclic ligands. In the following, we
describe the synthesis and characterization of neutral com-
plexes of vanadocene(II) derivatives and cationic complexes
of vanadocenium(III) derivatives.
Complexes of Vanadocene(II) Derivatives. Vanadocene(II)
derivatives are well-known 15e complexes with three unpaired
electrons.32,33 This results in the occupation of all bonding
orbitals of the metallocene with at least one electron. Thus,
only donor ligands with certain π-back-donating properties
have the ability to coordinate to the vanadium center by partial
reduction. As mentioned above, this generally includes aro-
matic N-heterocycles. On the basis of redox potentials, which
can be generally determined by cyclic voltammetry (CV), a
(24) Piglosiewicz, I. M.; Beckhaus, R.; Saak, W.; Haase, D. J. Am.
Chem. Soc. 2005, 127, 14190–14191.
(25) Piglosiewicz, I. M.; Beckhaus, R.; Wittstock, G.; Saak, W.;
Haase, D. Inorg. Chem. 2007, 46, 7610–7620.
(26) Kowaleski, R. M.; Basolo, F.; Trogler, W. C.; Gedridge, R. W.;
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9b, 503–504.
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(29) Togni, A.; Halterman, R. L. Metallocenes; Wiley-VCH:
Weinheim, Germany, 1998.
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metallics 1999, 18, 2452–2458.
(31) Bouwkamp, M. W.; Budzelaar, P. H. M.; Gercama, J.; Morales,
I. D. H.; de Wolf, J.; Meetsma, A.; Troyanov, S. I.; Teuben, J. H.;
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Chem. Soc. 1982, 104, 1882–1893.
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(34) Curtis, C. J.; Smart, J. C.; Robbins, J. L. Organometallics 1985, 4,
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(35) Gambarotta, S.; Floriani, C.; Chiesi-Villa, A.; Guastini, C.
Inorg. Chem. 1984, 23, 1739–1747.
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Article
Organometallics, Vol. 29, No. 22, 2010 5861
Table 1. First Redox Potentials (E1 2) of Applied Aromatic
/
N-Heterocycles Converted to Fc/Fcþ Standard
compd
E1/2 (V)a
solvent
ref
Py (5)
Pz (6)
-3.215
-2.584
-2.617
-2.320
-2.232
-1.249
-1.720
DMF
DMF
DMF
DMF
MeCN
DMF
PhCN
50
50
50
50
51
52
53
2-Bipy (7)
4-Bipy (8)
4-C2Py2 (9)
4-N2Py2 (10)
4-TPT (11)
a Vs Fc/Fcþ standard.
qualitative valuation of the capability of vanadocene(II) deriva-
tives to transfer electrons on these N-heterocycles should give an
indication for suitable reactant combinations. However, it
should be outlined that this method of comparison is by rule
of thumb, due to great influences on the shape and orientation of
cyclic voltammograms by experimental parameters such as the
choice of solvent, scan rate, and the choice of electrodes. Though
the much more positive redox potentials of the vanadocene(II)
derivatives compared to those of most of the azine derivatives
should limit the choice of potential ligands, because electron
transfer can formally occur from the reactant with more negative
potential to the reactant with more positive redox potential.
Table 1 shows the redox potentials of applied aromatic
N-heterocycles versus the Fc/Fcþ couple46 compared to vanado-
cene(II) (1, E1/2=-1.134 V vs Fc/Fcþ, thf)47 and decamethyl-
vanadocene(II) (4).48 In contrast to that, more strongly reducing
properties are found, as expected, in the case of titanocene
complexes (Cp2TiCl2, E1/2 = -1.38, -2.68, -2.96 V vs Fc/
Fcþ, thf).49
Figure 2. ORTEP plot of the solid-state molecular structure of 12.
Thermal ellipsoids are drawn at the 50% probability level. Hydro-
gen atoms are omitted for clarity; one of two independent molecules
˚
in the asymmetric unit is shown. Selected bond lengths (A) and
angles (deg): V1-C1 = 2.129(2), V1-C2 = 2.080(2), V1-Ct1=
1.97, V1-Ct2=1.97, C1-C2=1.290(3), N1-C3=1.351(3), C3-
C4 = 1.379(3), C4-C5 = 1.400(3), C5-C1 = 1.460(3), C5-
C6=1.396(3), C6-C7=1.386(3), C7-N1=1.337(3), C2-C10 =
1.468(3), N2-C8 = 1.343(3), C8-C9 = 1.385(3), C9-C10 =
1.385(3), C10-C11=1.397(3), C11-C12=1.383(3), C12-N2 =
1.338(3); C1-V1-C2=35.67(8), Ct1-V1-Ct2=139.6 (Ct1 =ring
centroid of C13-C17, Ct2=ring centroid of C18-C22).
Scheme 1. Reaction of 1 and 9 To Give Metallacyclopropene 12
The low affinity of vanadocene(II) derivatives to aromatic
N-heterocycles was exemplified in the reaction of 1 with 1,2-
bis(4-pyridyl)acetylene (9, 4-C2Py2), exhibiting an acetylene
spacer as a second sort of binding site between the pyridyl
rings. Owing to the highly negative redox potential of N-
heterocyclic ligand 9, vanadocene(II) (1) exclusively coordinated
to the C-C-triple bond to form, even with an excess of the
metal complex, the corresponding acetylene complex 12, best
described as metallacyclopropene (Scheme 1), which could be
proved by X-ray diffraction (Figure 2). Furthermore, the side-
on coordination of the acetylene moiety was shown by IR
spectroscopy (ν~(CtC) 1782, 1771, 1745 cm-1). For a com-
plete characterization, the decomposition point (134-136 °C),
mass spectra, and elemental analysis were determined.
The best yields were achieved by equimolar mixing of
vanadocene(II) (1) and ligand 9 in toluene. During stirring of
the resulting solution for 1 day at room temperature, its color
changed from violet to yellow-brown. Brown crystals of 12,
which were suitable for X-ray diffraction, could be obtained in
55% yield by cooling the reaction mixture to -40 °C for several
days. Complex 12 crystallizes in the triclinic space group P1 with
four complex molecules per unit cell and two independent
complex molecules in the asymmetric unit. The coordinated
˚
acetylene bridge is widened to 1.290 A due to π-back-donation
to the vanadium center, and the V-C bond lengths are in
the range of comparable vanadocene(II) acetylene complexes
(average 2.102 A).54-56 In accordance with the changed hybri-
˚
dization of the coordinated C atoms C1 and C2, an C5-C1-C2
angle of 144.7(2)° (C1-C2-C10=139.5(2)°) was found. This
value is comparable to those for typical acetylene complexes of
early transition metals (e.g., Cp2V(η2-C2(C6F5)2) 142.3(4)°,55
Cp2Ti(η2-C2(SiMe3)2) average 146.7(4)°).23
To the best of our knowledge, there is only one additional
complex of 9 exhibiting an exclusively C-C coordination
mode, found for the Co2CO6 fragment.57,58 Generally, deri-
vatives of 9 are often used as building blocks employing late
transition metals which have high affinity to the pyridyl
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(48) The CV of decamethylvanadocene(II) exhibits no reversible one-
electron wave but should be much more easily oxidizable than
vanadocene(II) due to the enhanced electron-donating properties of
the CpMe5 ligand (cf. ref 32).
(49) Mugnier, Y.; Moise, C.; Laviron, E. J. Organomet. Chem. 1981,
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Organometallics 2005, 24, 6464–6471.

5862 Organometallics, Vol. 29, No. 22, 2010
Jordan et al.
Figure 3. ORTEP plot of the solid-state molecular structure of 13. Thermal ellipsoids are drawn at the 50% probability level.
˚
Hydrogen atoms and solvent molecules are omitted for clarity. Selected bond lengths (A) and angles (deg): V1-N1 = 2.126(2),
V1-Ct1 = 2.01, V1-Ct2 = 2.01, N1-C1 = 1.383(4), C1-C2 = 1.370(4), C2-C3 = 1.436(5), C3-C4 = 1.461(5), C4-C5 =
1.396(4), C5-N1 = 1.368(4), C3-N2 = 1.365(4), N2-N20 = 1.372(6); Ct1-V1-Ct2 = 145.9 (Ct1 = ring centroid of C6-C10,
Ct2=ring centroid of C16-C20). Symmetry transformation for the generation of equivalent atoms: -x þ 1, -y þ 1, -z.
Scheme 2. Reaction of 4 with 10 Leading to the Formation of Binuclear Complex 13
moieties to form bi-59 or multinuclear complexes, particu-
larly in self-assembling processes.57,60,61
˚
Table 2. Comparison of Selected Bond Lengths (A) of the 4-N2Py2
Ligand (10) and Complex 13
In contrast to most of the N-heterocyclic ligands, the redox
10a
13
potential of 4,40-azobis(pyridine) (10, 4-N2Py2) seems to be
located in an acceptable range with respect to the potentials of
vanadocene(II) (1) and decamethylvanadocene(II) (4) to force
a metal-to-ligand electron transfer which in turn afforded the
complexation of the ligand to the metal center by the pyridyl
moieties (vide supra). Reaction of 1 with 10 resulted in the
precipitation of a brown amorphous solid that could not be
identified. Due to the higher solubility of the permethylated
vanadocene(II) derivative 4, we were able to grow crystals of
the new binuclear complex 13 (mp 165-166 °C dec) by slow
diffusion of a layered n-hexane solution of 10 into a toluene
solution of decamethylvanadocene(II) (4). The color of the
solution at the phase interphase changed immediately to dark
brown, and black crystals of 13 grew over a period of a few
days. The structural characterization proved the coordination
of 4 to the pyridyl moieties of 4-N2Py2 (10), which led to the
formation of the first binuclear decamethylvanadocene(II)
complex 13 with an N-heterocyclic bridging ligand in 56%
yield (Scheme 2). In contrast to titanocene chemistry17 the usual
trans modification of introduced 10 remained in the complex
and complexation of the azo bridge by 4 was not observed,
although side-on azo coordination of related azobenzene with
vanadocene(II) (1) had been explored.62,63
C3-N2
N2-N20
N1-C1
N1-C5
C1-C2
C2-C3
C3-C4
C4-C5
1.444(2)
1.251(2)
1.340(2)
1.336(2)
1.384(2)
1.393(2)
1.383(2)
1.388(2)
1.365(4)
1.372(6)
1.383(4)
1.368(4)
1.370(4)
1.436(5)
1.461(5)
1.396(4)
a Reference 17.
˚
The V-N bond length in 13 (2.126(2) A) is significantly
˚
longer than in 2-Bipy complex 2 (average 2.04 A) due to the
rigid chelate coordination of 2-bipy (7),45 and the distances
of η5-coordinated 1,2,3,4,5-pentamethylcyclopentadienyl
(Cp*) ligands are within the expected range of decamethylvan-
64
˚
docene complexes (2.01 A).
An activation of the azo bridge is observable in regard to a
significant widening of the azo double bond (N2dN20) from
0
˚
˚
1.251(2) A in free 4,4 -azobis(pyridine) (10) to 1.372(2) A,
which is almost as long as the N-N single-bond length in 1,2-
bis(4-pyridyl)hydrazine (1.3934(1) A).17 In conjunction with
˚
˚
the shortening of adjacent C3-N2 bonds (1.444(2) A in 10 to
1.365(4) A in 13) a reduction of the ligand by the metal
˚
centers can be assumed. A slight chinoid distortion of the
pyridyl moieties in 13 confirms this assumption (Table 2).
Hence, in principle the proposed relation of redox poten-
tials of vanadocene(II) derivatives and aromatic N-hetero-
cycles to their coordination ability could give an indication
of feasible reactant combinations in these reactions.
Owing to the activation of the azo bridge in 13, an N-N
bond cleavage was found in the CI mass spectra. Even in
high-resolution mode a decamethylvanadocene(II) complex
Binuclear complex 13 crystallizes in the monoclinic space
group P21/n with two complex molecules and four toluene
molecules per unit cell. The crystal structure of 13 is shown
in Figure 3.
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metallics 2002, 21, 685–693.
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D. G.; Taylor, R. J. Chem. Soc., Dalton Trans. 1989, S1–S83.

Article
Organometallics, Vol. 29, No. 22, 2010 5863
Scheme 4. Formation of Mononuclear Complex 17 by Reaction
of [Cp2V][BPh4] (16) with Pyrazine (6)
vanadocene(II) derivatives, the coordination of N-heterocy-
clic ligands to vanadocenium(III) derivatives is not hindered,
thanks to the lack of one electron in this oxidation state.
Hence, free electron pairs of N-heterocycles are allowed to
donate into the unoccupied bonding orbital.
The crystal structure of 3 shows that the V1-N1 bond length
is not significantly longer than in decamethylvanadocene(II)
˚
complex 13 (2.1389(18) A) and V-Ct distances are within the
expected range (average 1.94 A). The decomposition point was
˚
determined to be 210-212 °C.
Figure 4. ORTEP plot of the solid-state molecular structure of 3.
Thermal ellipsoids are drawn at the 50% probability level. Hydro-
Application of the salt metathesis concept to other N-
heterocyclic ligands such as pyrazine (6, Pz) or 4,40-bipyridine
(8, 4-Bipy) failed because of the poor solubility of the formed
cationic vanadocenium(III) complexes. However, a proce-
dure we recently established for reactions of vanadocenium-
(III) cations with chelating aromatic N-heterocycles led to a
crystalline product for the reaction with Pz (6).45 Therefore, a
thf solution of vanadocenium(III) tetraphenylborate (16,
[Cp2V][BPh4])30 was layered with a small amount of diethyl
ether that was layered with an n-hexane solution of 6 as well.
In spite of the solubility properties of the uncoordinated
metallocenium salt as well as the product, dark blue crystals,
which were suitable for X-ray diffraction, were grown after
several days on the wall of the flask. The crystal structure
confirmed the formation of mononuclear complex 17 in
43% yield (Scheme 4), even with an excess of vanadium(III)
compound 16. This behavior is in contrast to that of the
isoelectronic titanium(II) fragments, which form tetranu-
clear complexes with pyrazine.15,16
Compound 17 crystallizes in the orthorhombic space
group Pna21 with cell parameters almost identical with those
of the very similar pyridine complex 3 (Figure 5). The mono-
nuclear coordination of pyrazine seems to be a result of the
deactivation of its second nitrogen moiety, thanks to the positive
charge introduced by the vanadocenium(III) cation. To the best
of our knowledge, this coordination mode of pyrazine is
completely unknown for early transition metals, but there are
several examples of singly coordinated pyrazine complexes with
late transition metals in the literature.67-74
˚
gen atoms are omitted for clarity. Selected bond lengths (A) and
angles (deg): V1-N1 = 2.1389(18), V1-Ct1 = 1.94, V1-Ct2 =
1.94, N1-C1 = 1.350(3), C1-C2 = 1.377(3), C2-C3 = 1.378(3),
C3-C4 = 1.382(3), C4-C5 = 1.374(3), C5-N1 = 1.341(2), B1-
C16 = 1.655(3), B1-C22 = 1.649(4), B1-C28 = 1.669(3), B1-
C34 = 1.651(3); Ct1-V1-Ct2 = 143.1 (Ct1 = ring centroid of
C6-C10, Ct2 = ring centroid of C11-C15).
Scheme 3. Preparation of 3 via Salt Metathesis of 14 and 15
Initiated by Pyridine Addition
with coordinated protonated 4-aminopyridine ligand was
identified as the base peak (m/z 415.2). This was evidenced by
the identification of the protonated 4-aminopyridine frag-
ment (m/z 95.1) as well as the ionic decamethylvanadocene
fragment (m/z 321.2).
Complexes of Cationic Vanadocenium(III) Derivatives. Up to
now, there have only been two examples of vanadocenium(III)
complexes with aromatic N-heterocyclic ligands. In addition to
our recently reported 2-Bipy complex of vanadocenium(III)
cation,45 Floriani et al. produced the cationic vanadocenium(III)
pyridine complex 3 by salt metathesis of vanadocene(III) chlor-
ide (14)65 with sodium tetraphenylborate (15) initiated by an
excess of basic pyridine (5, Py) (Scheme 3).37
In order to confirm their results by X-ray diffraction, we
succeeded in growing crystals of the complex by slight mod-
ification of the literature procedure. Complex 3 crystallizes
in the orthorhombic space groupPna21 with four ion pairs per
unit cell. The crystal structure confirms the coordination of
one pyridine ligand to form a cationic 16e complex (Figure 4).
This behavior is quite usual for vanadocenium(III) deriva-
tives. Coordination of one additional ligand to build up
a stable 18e complex is not preferred, because of the low
energy gap between the two singly occupied orbitals, making
spin pairing unfavorable.66 Furthermore, in contrast to
The second nitrogen does not have any effect on the V1-N1
bond length (2.135(3) A) in 17 compared to pyridine complex 3
˚
˚
(2.1389(18) A), but the cell parameters of both crystal structures
(67) Watanabe, M.; Motoyama, I.; Takayama, T.; Sato, M.
J. Organomet. Chem. 1997, 549, 13–23.
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Inorg. Chem. 1999, 38, 5027–5033.
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658.
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Freisinger, E.; Miguel, P. J. S.; Roitzsch, M.; Lippert, B. Inorg. Chem.
2006, 45, 2093–2099.
(71) Stang, P. J.; Cao, D. H.; Saito, S.; Arif, A. M. J. Am. Chem. Soc.
1995, 117, 6273–6283.
(72) Cavaglioni, A.; Cini, R. Polyhedron 1997, 16, 4045–4054.
(73) Gress, M. E.; Creutz, C.; Quicksall, C. O. Inorg. Chem. 1981, 20,
1522–1528.
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Acta 2002, 330, 128–135.
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203–210.

5864 Organometallics, Vol. 29, No. 22, 2010
Jordan et al.
detailed structural information, the crystal structures of 19 and
20 are given in the Supporting Information. Furthermore, the
characterization of these complexes was completed by mass
spectrometry, infrared spectroscopy, and determination of de-
composition points as well as elemental analysis.
Owing to the interesting inhibition of a second (decamethyl)-
vanadocenium(III) coordination at the pyrazine ligand, the
influence of the bridge length of N-heterocycles on the coordina-
tion behavior of decamethylvanadocenium(III) cations was
explored.
4,40-Bipyridine (8, 4-Bipy) is a very common bridging
ligand in coordination chemistry.4,16,75,76 The reaction with
[Cp*2V][BPh4] (18) in thf at 60 °C afforded the first binuclear
decamethylvanadocenium(III) complex, 21 (mp 258-260 °C
dec) with an N-heterocyclic bridging ligand within several
days (Scheme 6). By layering of the green reaction mixture with
n-hexane at room temperature, 21 crystallized as green-brown
blocks in 51% yield. The expanded π system of 4-Bipy (8)
compared to Pz (6) allows complexation of both binding sites;
thus, the inhibition effect of the first cationic decamethylvana-
docenium(III) complexation no longer influences the coordina-
tion of the nitrogen moiety in the second pyridyl ring. Dicationic
complex 21 crystallizes in the monoclinic space group C2/c with
4 dications and 8 tetraphenylborate anions as well as 16
disordered thf molecules in the unit cell (Figure 6).
Figure 5. ORTEP plot of the solid-state molecular structure of
17. Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms are omitted for clarity. Selected bond lengths
˚
(A) and angles (deg): V1-N1 = 2.135(3), N1-C1 = 1.372(4),
C1-C2 = 1.398(6), C2-N2 = 1.300(6), N2-C3 = 1.295(6),
C3-C4 = 1.373(6), C4-N1 = 1.372(4), B1-C15 = 1.702(4),
B1-C21 = 1.709(4), B1-C27 = 1.717(3), B1-C33 = 1.707(4),
V1-Ct1 = 1.94, V1-Ct2 = 1.95; Ct1-V1-Ct2 = 142.6 (Ct1 =
ring centroid of C5-C9, Ct2 = ring centroid of C10-C14).
˚
The V-N bond lengths in complex 21 (2.142(2) A) are
almost as long as in vanadocenium(III) complexes 3 and 17.
A closer look at the bond lengths of the bridging ligand confirms
that an electron transfer from the metal on the ligand is prohib-
ited in 21. In contrast, for the isoelectronic neutral decamethyl-
titanocene 4-Bipy complex, a metal-ligand charge transfer
(MLCT) band is observed.77 The reduction was verified by a
shortening of the C-C bond between both pyridyl rings
give detailed information about the steric demands of both
heterocyclic ligands (Table 4). The volume of the unit cell of
3
pyridine complex 3 is 14.2 A larger than of the pyrazine
˚
complex 17. Because the C-H group is spatially larger than
the nitrogen with its free electron pair, the Py ligand needs
3
approximately 3.5 A more space in the crystal lattice than the Pz
˚
˚
ligand calculated for four ion pairs per unit cell. In addition, a
significant distortion of the coordinated Pz ligand in 17 is visible.
(1.392(7) A) and coplanarity of the bridging ligand, due to the
formation of a chinoid ligand π system (Scheme 7).16
˚
The N-C bonds of the coordinated N1 atom (1.372(4) A) are
However, in the decamethylvanadocenium(III) complex
21 the C3-C30 bond length is comparable to that of free
4-Bipy (8) as well as the twist angle of the pyridyl rings
against each other. Table 3 compares the structural param-
eters of 21 with corresponding datas of free 4-Bipy (8) and
reduced trimethylsilyl-substituted derivative 23, which have
already been reported by our group.16
Additionally, mass spectrometric and infrared spectro-
scopic investigations as well as elemental analysis confirmed
the composition of complex 21.
1,2-Bis(4-pyridyl)acetylene (9) is another suitable bridging
ligand. Although the reactivity of the pyridyl moieties to
vanadocene(II) derivatives is low (vide supra), the complexa-
tion of vandocenium(III) derivatives to the pyridyl nitrogens
was successful. Reaction of [Cp*2V][BPh4] (18) with 9 in thf
afforded small brown needles of binuclear complex 24 (mp
265-267 °C dec), which precipitated directly from the solu-
tion in 6% yield (Scheme 8).
We were able to prove the composition of 24 by X-ray
diffraction, but due to the small size of the crystals, a discussion
of bond lengths and angles was not reasonable. Therefore, the
synthesis of 24 had to be modified to obtain larger crystals. In
the end we were able to get larger crystals as well as a higher yield
˚
0.072-0.077 A longer than those of the uncoordinated N2 atom
(1.295(6), 1.300(6) A).
˚
To explore the coordination behavior of the other bridging
N-heterocycles with extended π systems, it was mainly necessary
to increase the solubility of the applied vanadocenium(III) salts.
The substitution of the Cp ligand with Cp* led to success.
Decamethylvanadocenium(III) tetraphenylborate (18, [Cp*2V]-
[BPh4])31 is quite soluble in thf and other polar solvents. Hence,
for comparison reasons we tested the reactivity of 18 to already
described simple N-heterocycles Py (5) and Pz (6). Reactions
occurred in thf solution by heating at 60 °C for several days
without stirring. In contrast to the reactions with unsubstituted
[Cp2V][BPh4] (16), reaction products remained in solution,
whose color changed from brown to green. The resulting com-
plexes are more soluble than free 18. After they were cooled to
room temperature, the reaction mixtures were filtered from
the remaining solids and the solutions were layered with the same
amount of n-hexane, which forced crystallization of the products.
Both pyridine complex 19 (48%) and pyrazine complex 20 (32%)
had compositions identical with those of their unsubstituted
derivatives (Scheme 5).
Especially, the renewed formation of mononuclear pyrazine
complex 20 confirms the great influence of oxidized vanadium-
(III) centers on the donating properties of the second nitrogen
moiety of the bis(azine) ligand 6. However, a comparison of cell
parameters is not possible. Due to certain solvent insertions, the
permethylated complexes crystallize in different space groups.
All molecular parameters are within the expected ranges. For
(75) Biradha, K.; Sarkar, M.; Rajput, L. Chem. Commun. 2006, 4169–
4179.
(76) Wang, J.-Q.; Ren, C.-X.; Jin, G.-X. Organometallics 2006, 25,
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€
(77) Kraft, S. Ph.D. Thesis, Carl von Ossietzky Universitat Oldenburg,
2004.

Article
Organometallics, Vol. 29, No. 22, 2010 5865
Scheme 5. Reaction of [Cp*2V][BPh4] (18) with Pyridine (5) and Pyrazine (6) to Give Mononuclear Decamethylvanadocenium(III)
Complexes 19 and 20
Scheme 7. General Reduction of 4,40-Bipyridine
Table 3. Bond Lengths and Twist Angles for Free (8), Reduced
(23), and Coordinated 4,40-Bipyridine (21)
Scheme 8. Reaction of [Cp*2V][BPh4] (18) and 4-C2Py2 (9) to
Give Binuclear Complex 24
Figure 6. ORTEP plot of the solid-state molecular structure of 21.
Thermal ellipsoids are drawn at the 50% probability level. Hydro-
gen atoms and solvent molecules are omitted for clarity. Selected
˚
bond lengths (A) and angles (deg): V1-N1=2.142(2), N1-C1 =
1.360(3), C1-C2 = 1.389(3), C2-C3 = 1.394(4), C3-C4 =
1.403(3), C4-C5 = 1.382(4), C5-N1 = 1.351(3), C3-C30 =
1.495(5), V1-Ct1=1.99, V1-Ct2=1.99; Ct1-V1-Ct2 = 147.5;
B1-C26=1.656(4), B1-C32=1.655(4), B1-C38=1.662(4), B1-
C44=1.664(4) (Ct1=ring centroid of C6-C10, Ct2=ring centroid
of C16-C20). Symmetry transformation for the generation of
1
equivalent atoms: -x þ 1, y, -z þ /2.
Scheme 6. Formation of Binuclear Complex 21 by Reaction of 18
with N-heterocyclic Ligand 8
of 24 by a totally unexpected route. The main purpose of the
reaction of acetylene complex 12 with [Cp*2V][BPh4] (18) was
the formation of the trinuclear mixed-valent complex 25, in
which two V(III) centers were connected via pyridyl coordina-
tion with the side-on-coordinated V(II) center (Scheme 9).
However, 24 crystallized solely as large brown needles directly
from the reaction mixture. After that observation the reaction
procedure was optimized by starting with an in situ reaction of
vanadocene(II) (1) with ligand 9 in thf to form the acetylene
complex 12. Subsequent addition of a thf solution of [Cp*2V]
[BPh4] (18) and heating to 60 °C for several days without stirring
caused a slow precipitation of 24 in 42% yield, which was
suitable for X-ray diffraction (Scheme 9). We presume that the

5866 Organometallics, Vol. 29, No. 22, 2010
Jordan et al.

Article
Organometallics, Vol. 29, No. 22, 2010 5867
Figure 7. ORTEP plot of the solid-state molecular structure of 24. Thermal ellipsoids are drawn at the 50% probability level.
˚
Hydrogen atoms are omitted for clarity. Selected bond lengths (A) and angles (deg): V1-N1 = 2.1311(13), N1-C1 = 1.3468(19),
C1-C2 = 1.378(2), C2-C3 = 1.399(2), C3-C4 = 1.403(2), C3-C6 = 1.432(2), C4-C5 = 1.378(2), C5-N1 = 1.350(2), C6-C60 =
1.197(3), V1-Ct1 = 1.99, V1-Ct2 = 1.99; Ct1-V1-Ct2 = 148.1; B1-C27 = 1.648(2), B1-C33 = 1.6564(19), B1-C39 = 1.651(2),
B1-C45 = 1.638(2) (Ct1 = ring centroid of C7-C11, Ct2 = ring centroid of C17-C21). Symmetry transformation for the generation
of equivalent atoms: -x, -y þ 2, -z.
Scheme 9. Synthesis of 24 by Reaction of Acetylene Complex 12 with [Cp*2V][BPh4] (18)
reaction starts with the coordination of decamethylvanado-
cenium(III) cations to the nitrogen binding sites of the pyridyl
rings. As in pyrazine complexes 17 and 20, the complexation
provokes a deactivation of the acetylene bridge, by which the
dissociation of already complexed vanadocene(II) (1) occurs,
accompanied by a back-formation of the C-C triple bond. This
was also confirmed by the infrared spectrum of 24, in which the
characteristic band for the complexed acetylene moiety of 12
disappeared.
positions by a central triazine ring.53,79-81 A mixture of
4-TPT (11) with 18 in thf was heated to 60 °C for several
days without stirring, which led to a green solution. After
filtration of the reaction mixture from the remaining poorly
soluble ligand 11 at room temperature, the solution was layered
with n-hexane. Yellow-green crystalline needles of trinuclear
complex 26 grew slowly at the phase interphase. The results of
our X-ray structural analysis of 26, despite the inclusion of
considerable thf in the lattice, were sufficient to establish
unequivocally its atom connectivity but not to discuss bond
lengths and angles of the complex. By substitution of the
reaction solvent thf with the more polar, but also more rigid,
noncoordinating 1,2-difluorobenzene,31,82 we obtained dark
green needles of 26 (mp 248-250 °C dec) in 26% yield, which
were suitable for X-ray diffraction (Scheme 10).
Complex 24 crystallizes in the monoclinic space group P21/c,
exhibiting two complex dications and four tetraphenylborate
anions per unit cell (Figure 7). The V-N bond lengths are within
the range of already presented decamethylvanadocenium(III)
˚
˚
complexes (2.1311(13) A) aswellastheV-Ct distances (1.99 A).
The bond lengths of the bridging ligand 9 hardly differ from the
values for the free ligand 9.78 Hence, as expected, a reduction of
the C-C triple bond by metal-to-ligand charge transfer which
would lead to bond alternations is not observed.51 Also, the
pyridyl rings in 24 prefer, as in free 9, a coplanar orientation,
because there is no steric hindrance of ortho hydrogens next to
the pyridyl connecting bond as in 4,40-bipyridine, thanks to the
acetylene spacer.
Complex 26 crystallizes from 1,2-difluorobenzene/n-hex-
ane in the trigonal space group P3c1, exhibiting two tricat-
ionic complexes and six tetraphenylborate anions in the unit
cell (Figure 8). Owing to symmetry generation of the com-
plex cation a disorder of the central triazine ring is observ-
able, which effects a bending of pyridyl rings toward the
triazine plane (13.4°) and a relatively large elongation of the
The presented complexes show that a connection of a
vanadocene center with two additional vanadocene com-
plexes is not possible. Because of that, the only chance to
create multinuclear vanadocene complexes with more than
two vanadium centers is to enhance the number of pyridyl
binding sites of the ligand. In that case, a very well-known
example is 1,3,5-tris(4-pyridyl)-2,4,6-triazine (11, 4-TPT),
which exhibits three pyridyl moieties connected in para
C4-C1a bond length in comparison to that of the free ligand
83
11 (average 1.490(2) A; 26, average 1.535(9) A). In addi-
˚
˚
tion, the distortion of the pyridyl rings to the triazine plane is
(79) Fujita, M.; Tominaga, M.; Hori, A.; Therrien, B. Acc. Chem.
Res. 2005, 38, 369–378.
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Perkin Trans. 1 1995, 2231–2245.
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(78) Zaman, M. B.; Tomura, M.; Yamashita, Y. J. Org. Chem. 2001,
66, 5987–5995.
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5868 Organometallics, Vol. 29, No. 22, 2010
Jordan et al.
Figure 8. ORTEP plot of the solid-state molecular structure of
26. Thermal ellipsoids are drawn at the 50% probability level.
Hydrogen atoms, solvent molecules, and tetraphenylborate
˚
anions are omitted for clarity. Selected bond lengths (A) and angles
(deg): V1-N2=2.135(3), N2-C2=1.360(5), C2-C3=1.379(6),
C3-C4=1.374(6), C4-C5=1.386(7), C5-C6 =1.386(6), C6-
N2 = 1.348(5), C4-C1a = 1.526(8), C4-C1b = 1.543(9), C1a-
N1a=1.351(9), C1b-N1b=1.331(10) V1-Ct1=1.98, V1-Ct2 =
2.00; Ct1-V1-Ct2=148.1 (Ct1=ring centroid of C7-C11, Ct2=
ring centroid of C17-C21). Symmetry transformation for the
generation of equivalent atoms: (a) -y, x - y, z; (b) -x þ y, -x, z.
Figure 9. Diamond plot of the solid-state structure of 26,
showing the orientations of 1,2-difluorobenzene molecules
(green) and tetraphenylborate anions (purple) with respect to
the complex cation.
˚
(3.35-4.14 A), respectively, and additionally C-H
interactions with corresponding methyl Cp*-groups are
F
3 3 3
Scheme 10. Reaction of [Cp*2V][BPh4] (18) and 4-TPT (11) To
Give Trinuclear Complex 26
˚
found (2.33 A). Particularly, one 1,2-difluorobenzene mole-
cule is oriented parallel to the central triazine ring of the
˚
4-TPT ligand (π stacking: 3.35 A). Furthermore, C-H
interactions of one phenyl substituent of the tetraphenylbo-
F
3 3 3
rate anions and 1,2-difluorobenzene occur (C-H F =
3 3 3
˚
2.28 A). The tetraphenylborate anions are located next to the
Cp* ligands, which do not interact with 1,2-difluorobenzene
molecules (Figure 9). In turn, the space between them is filled
with the adjacent complex cation, which can also be regarded
as a structure-defining motive.
The triply charged cation of 26 was also identified by CI
and HR-CI mass spectrometry (m/z 425.2162).
Conclusions and Outlook
Aromatic N-heterocycles are useful building blocks in
coordination chemistry. Especially, bis(azines) are applica-
ble to build up molecular architectures, which can be par-
tially accompanied by C-C coupling reactions. The latter
dominates the chemistry of strongly reducing titanocene
derivatives, which is caused by the distinct donor-acceptor
properties of the applied complexes and ligands. In contrast,
the presented vanadium(II) and -(III) complexes showed a
decreased reactivity. Generally, due to the lower reducing
properties, no metal-induced C-C couplings were observ-
able. However, N-heterocycles with a certain electron affinity,
such as 4-N2Py2 (10), are able to form binuclear complexes
with vanadocene(II) derivatives, which, for example, led to
the formation of 13. Furthermore, acetylene coordination of
vanadocene(II) is preferred in comparison to N-coordination,
as can be seen in complex 12. On the other hand, the chemistry
of vanadocenium(III) cations is dominated by their Lewis
acidity, accompanied by comparably low back-bonding proper-
ties. In contrast to the isoelectronic titanocene(II) fragments
with their tetrahedral coordination sphere, the vanadocene units
11.9°, which is also larger than in the crystal structure of free
4-TPT (11: 6.8, 7.9°). However, the V-N bond lengths are
again within the range of already presented complexes
(2.135(3) A). An inclusion of 4 equiv of 1,2-difluorobenzene
is observed. Three of them undergo π-π interactions with
one Cp* ligand of the decamethylvanadocenium(III) centers
˚

Article
Organometallics, Vol. 29, No. 22, 2010 5869
formed solely complexes with trigonally coordinated V(III)
centers. In addition, the formation of multinuclear vanadocene-
(III) complexes required N-heterocyclic ligands with extended
π systems, which means with more than one aromatic ring, such
as 4-Bipy (8), 4-C2Py2 (9), and 4-TPT (11). However, smaller
bis(azines) such as Pz (6) were not suitable; hence, only the
mononuclear complexes 17 and 20 were formed. Further
analytical explorations about electronic and magnetic proper-
ties of these complexes are in progress.
Synthesis of [Cp2V(η2-C2Py2)] (12). Vanadocene(II) (1; 37 mg,
0.2 mmol) and 36 mg (0.2 mmol) of 1,2-bis(4-pyridyl)acetylene
(9) were dissolved in 20 mL of toluene and stirred overnight. The
solution changed immediately from violet to yellow-brown. The
product was obtained by crystallization at -40 °C as brown
crystals, which were suitable for X-ray diffraction. After the
mother liquor was decanted, the product was washed with 5 mL
of n-hexane and dried under vacuum to afford 12 in 55% yield
(40 mg, 0.11 mmol). Mp: 134-136 °C dec. IR (KBr; cm-1): ν~
3067 (w), 1782 (m), 1771 (m), 1745 (m), 1579 (s), 1526 (m), 1479
(m), 1432 (w), 1408 (m), 1385 (w), 1308 (w), 1267 (w), 1212 (w),
1019 (w), 1010 (w), 989 (m), 814 (s), 684 (w), 558 (m), 550 (m).
MS (CI, isobutane): m/z (relative intensity, %) 363.2 (9), 362.2
(39), 361.2 (100) [M]þ. HR-MS (CI, isobutane): m/z calcd for
C22H18N2Vþ 361.0910, found 361.0912 (100). Anal. Calcd for
C22H18N2V: C, 73.13; H, 5.02; N, 7.75. Found: C, 72.66; H, 5.40;
N, 7.69.
Synthesis of [(Cp*2V)2(μ2-Py2N2)] (13). Decamethylvanado-
cene(II) (4; 80 mg, 0.25 mmol) was dissolved in 10 mL of
toluene and layered with 5 mL of a 1:1 mixture of toluene/
n-hexane. Then a solution of 47 mg (0.25 mmol) of 4,40-azobis-
(pyridine) (10) in 18 mL of n-hexane was layered. After several
days black crystals of 12 were formed, which were suitable for
X-ray diffraction. The mother liquor was decanted, and the
crystals were washed with 5 mL of n-hexane. Drying under
vacuum afforded 70 mg (0.07 mmol, 56% relating to 4) of 13. Mp:
165-166 °C dec. IR (KBr; cm-1): ν~ 3020 (w), 2962 (m), 2904 (m),
2852 (m), 1604 (s), 1512 (m), 1493 (m), 1429 (m), 1379 (m), 1300 (m),
1261 (w), 1201 (w), 1178 (m), 1065 (w), 1005 (s), 943 (w), 802 (m),
731 (w), 694 (w), 613 (w), 534 (w), 505 (w), 465 (w), 422 (w). MS
(CI, isobutane): m/z (relative intensity, %) 417.2 (4), 416.2 (24),
415.2 (100) [(Cp*2V(4-PyNH2))]þ; 323.2 (1), 322.2 (13), 321.2 (58)
[(Cp*2V)]þ; 95.1 (24) [(4-PyNH2þH)]þ. HR-MS (CI, isobutane):
m/z calcd for C25H36N2Vþ 415.2313, found 415.2320 (100). Anal.
Calcd for C50H68N4V2: C, 72.62; H, 8.29; N, 6.77. Found: C, 72.40;
H, 8.74; N, 7.15.
Synthesis of [Cp2V(Pz)][BPh4] (17). [Cp2V][BPh4] (16; 20 mg,
0.04 mmol) was dissolved in 20 mL of thf. The solution was
filtered from the remaining solid and layered with 3 mL of
diethyl ether. Then a solution of 6 mg (0.08 mmol) of pyrazine
(6) in 10 mL of n-hexane was layered. Dark blue crystals of 17
formed after several days, which were suitable for X-ray diffrac-
tion. The mother liquor was decanted, and the product was
washed with 5 mL of n-hexane. Drying under vacuum afforded 9
mg (0.015 mmol, 43%) of 17. Mp: 197-199 °C. IR (KBr; cm-1):
ν~ 3105 (w), 3049 (m), 2995 (m), 2981 (m), 2895 (w), 1579 (w),
1477 (m), 1425 (m), 1265 (w), 1182 (w), 1149 (w), 1122 (w), 1066
(w), 1020 (m), 874 (m), 824 (s), 743 (s), 735 (s), 708 (s), 625 (w),
604 (m), 478 (w), 461 (w).
Synthesis of [Cp*2V(Py)][BPh4] (19). [Cp*2V][BPh4] (18; 100 mg,
0.16 mmol) was suspended in 20 mL of thf, and 30 μL (30 mg,
0.37 mmol) of pyridine (5) was added via syringe. When the
resulting suspension was heated to 60 °C for 2 weeks without
stirring, its color changed from brown to green and most of the
solid 18 was dissolved. The solution was filtered from the
remaining solids at room temperature and layered with 20 mL
of n-hexane to get green plates of 19, which were suitable for X-ray
diffraction. After decanting of the mother liquor the crystals were
washed with 5 mL of n-hexane and dried under vacuum to obtain
30 mg (0.08 mmol, 48% relating to 18) of pure 19. Mp: 217-
219 °C dec. IR (KBr; cm-1): ν~ 3051 (m), 3034 (m), 2978 (m), 2910
(m), 2852 (m), 1943 (w), 1867 (w), 1803 (w), 1759 (w), 1643 (w),
1603 (m), 1578 (m), 1478 (m), 1443 (m), 1421 (m), 1381 (m), 1309
(m), 1259 (m), 1211 (m), 1182 (m), 1155 (m), 1120 (m), 1065 (m),
1032 (m), 1018 (m), 985 (m), 860 (w), 841 (m), 804 (w), 762 (m),
744 (m), 731 (s), 710 (s), 698 (s), 623 (w), 611 (s), 500 (w), 467 (w),
432 (w). MS (CI, isobutane): m/z (relative intensity, %) 402.3 (3),
401.3 (23), 400.3 (68) [M]þ; 323.3 (9), 322.3 (38), 321.3 (100)
[(Cp*2V)]þ;80.1(12) [(PyH)]þ. HR-MS(CI,isobutane):m/zcalcd
for C25H35NVþ 400.2209, found 400.2207 (100). Anal. Calcd for
Experimental Section
Reagents and General Techniques. All operations were per-
formed under a nitrogen atmosphere with rigorous exclusion of
oxygen and moisture using glovebox and Schlenk techniques.
All chemicals used were reagent grade or higher and were
purified according to standard protocols. Solvents were distilled
over Na/K alloy and benzophenone under a nitrogen atmo-
sphere. Chemical ionization (CI) mass spectra were taken on a
Finnigan-MAT 95 spectrometer. Isobutane was used as ioniza-
tion gas. Electrospray ionization (ESI) mass spectra were mea-
sured on a Finnigan-LCQ spectrometer. IR spectra were
recorded on a Bruker VECTOR 22 spectrometer using KBr
pellets. Elemental analyses were carried out by using an EA
Euro 3000 from EuroVector, Milan, Italy. Melting points were deter-
mined using a Mel-Temp by Laboratory Devices, Cambridge, U.K.
Pyridine (5), pyrazine (6),4,40-bipyridine (8), and sodium tetraphenyl
borate (15) were purchased from Aldrich. Vanadocene(II) (1),26
decamethylvanadocene(II) (4),32 vanadocene(III) chloride (14),65
[Cp2VIII][BPh4] (16),30 [Cp*2VIII][BPh4] (18),31 1,2-bis(4-pyridyl)-
acetylene (9),84 4,40-azobis(pyridine) (10),85 and 1,3,5-tris(4-pyridyl)-
2,4,6-triazine (11)81 were prepared according to literature procedures.
X-ray Diffraction. Single-crystal experiments were carried out
on a STOE IPDS diffractometer and a Bruker AXS Χ8 Apex II
diffractometer with graphite-monochromated Mo KR radiation
˚
(λ = 0.71073 A). The structures were solved by direct phase determi-
nation with SHELXS-97 and refined by full-matrix least-squares
techniques against F2 with the SHELXL-97 program system.86
Crystallographic details of presented crystal structures are given in
Table 4. Crystallographic data of the solid-state structures of
complexes 19 ([Cp*2V(Py)][BPh4]) and 20 ([Cp*2V(Pz)][BPh4])
are given in the Supporting Information.
Synthesis of [Cp2V(Py)][BPh4] (3).37 Vanadocene(III) chlo-
ride (14, 50 mg, 0.23 mmol) and 79 mg (0.23 mmol) of sodium
tetraphenylborate (15) were suspended in 7 mL of thf, and 75 μL
(0.92 mmol) of pyridine (5) was added via syringe. The supension
was stirred for 30 s and left overnight at room temperature.
The solution turned slowly from blue to blue-violet, and amor-
phous NaCl precipitated. After 18 h blue-violet plates of 3, which
were suitable for X-ray diffraction, were separated from the
suspension on a large-pored frit by hot filtration. Washing with
n-hexane and drying under vacuum afforded 54 mg (0.09 mmol,
41%) of 3. Mp: 210-212 °C dec. IR (KBr; cm-1): ν~ 3450 (br),
3090 (w), 3054 (m), 2989 (w), 1604 (m), 1578 (m), 1477 (m), 1444
(m), 1422 (m), 1359 (w), 1250 (w), 1175 (w), 1152 (w), 1129 (w),
1068 (m), 1032 (w), 1017 (m), 1005 (m), 828 (s), 751 (m),
734 (s), 704 (s), 610 (m), 458 (w). MS (CI, isobutane): m/z
(relative intensity, %) 262.0 (2), 261.0 (19), 260.0 (100) [M]þ;
181.0 (14) [Cp2V]þ; 80.0 (100) [(pyH)]þ. HR-MS (CI, iso-
butane): m/z calcd for C15H15NVþ 260.0644, found 260.0648
(100). Anal. Calcd for C39H35BNV: C, 80.84; H, 6.09; N,
2.42. Found: C, 80.12; H, 6.51; N, 2.44.
(84) Coe, B. J.; Harries, J. L.; Harris, J. A.; Brunschwig, B. S.; Coles,
S. J.; Light, M. E.; Hursthouse, M. B. Dalton Trans. 2004, 2935–2942.
(85) Launay, J. P.; Tourrel-Pagis, M.; Lipskier, J. F.; Marvaud, V.;
Joachim, C. Inorg. Chem. 1991, 30, 1033–1038.
(86) Sheldrick, G. M. SHELXL-97: A Program for Refining Crystal
€
€
Structures; University of Gottingen, Gottingen, Germany, 1997.

5870 Organometallics, Vol. 29, No. 22, 2010
Jordan et al.
C49H55BNV: C, 81.77; H, 7.70; N, 1.95. Found: C, 80.86; H, 8.49;
N, 1.64.
needles which were suitable for X-ray diffraction. After cooling
to room temperature the mother liquor was decanted and the
crystals were washed with 5 mL of n-hexane. Drying under
vacuum afforded 61 mg (0.04 mmol, 42% relating to 18) of pure
24. Mp: 265-267 °C dec. IR (KBr; cm-1): ν~ 3053 (m), 2998 (m),
2982 (m), 2904 (m), 1607 (m), 1581 (w), 1501 (w), 1478 (m), 1427
(m), 1411 (m), 1379 (m), 1318 (w), 1262 (m), 1207 (w), 1181 (w),
1147 (w), 1059 (w), 1018 (m), 844 (m), 804 (w), 741 (m), 729 (s),
704 (s), 604 (m), 552 (w), 481 (w), 461 (w), 439 (w). MS (CI,
isobutane): m/z (relative intensity, %) 841.7 (7), 840.7 (31), 839.7
(52) [(M þ CH3 þ 2H)]þ; 323.1 (5), 322.1 (48), 321.1 (100), 320.1
(31) [(Cp*2V)]þ, [(BPh4 þ 2H)]þ; 181.1 (38) [(C2Py2 þ H)]þ;
165.1 (65) [(BPh2)]þ; 135.2 (27) [Cp*]þ. Anal. Calcd for
C100H108B2N2V2: C, 82.18; H, 7.45; N, 1.92. Found: C, 81.43;
H, 8.18; N, 2.14.
Synthesis of [Cp*2V(Pz)][BPh4] (20). [Cp*2V][BPh4] (18; 96
mg, 0.15 mmol) and 12 mg (0.15 mmol) of pyrazine (6) were
suspended in 20 mL of thf and heated to 60 °C without stirring.
The solution changed slowly from brown to green, and most of
the solid 18 was dissolved during the reaction. After 2 weeks the
solution was filtered from the remaining solids at room temperature
and layered with 20 mL of n-hexane to obtain yellow-brown plates
of 20, which were suitable for X-ray diffraction. After decanting of
the mother liquor the crystals were washed with 5 mL of n-hexane
and dried under vacuum to obtain 38 mg (0.05 mmol, 33%) of pure
20. Mp: 211-213 °C dec. IR (KBr; cm-1): ν~ 3051 (m), 3037 (m),
2980 (m), 2906 (m), 2856 (m), 1944 (w), 1879 (w), 1817 (w), 1764
(w), 1579 (m), 1478 (m), 1451 (w), 1426 (m), 1412 (m), 1381 (w),
1309 (m), 1241 (m), 1182 (w), 1146 (m), 1064 (w), 1050 (w), 1031
(w), 1018 (m), 985 (m), 914 (w), 841 (w), 809 (m), 731 (s), 705 (s),
612 (m), 604 (m), 480 (w), 440 (w). MS (CI, isobutane): m/z (rela-
tive intensity, %) 401.1 (4), 400.1 (23), 399.1 (63) [(M-2H)]þ; 323.1
(3), 322.1 (27), 321.1 (100) [(Cp*2V)]þ. MS (ESI, thf; pos): m/z
(relative intensity, %) 388.2 (5), 387.2 (22), 386.2 (29), 385.2 (100)
[(M - CH2 - H)]þ, [(M - CH2 - 2H)]þ. HR-MS (CI, isobutane):
m/z calcd for C24H34N2Vþ 401.2162, found 401.2165 (100). Anal.
Synthesis of [(Cp*2V)3(μ3-4-TPT)][BPh4]3 (26). [Cp*2V][BPh4]
(18; 100 mg, 0.16 mmol) and 16 mg (0.05 mmol) of 4-TPT (11) were
suspended in 30 mL of 1,2-difluorobenzene and heated to 60 °C
without stirring. The color of the solution changed slowly from
brown to green, and most of the solid 18 was dissolved during the
reaction. After 2 weeks the solution was filtered from the remaining
solids at room temperature and layered with 30 mL of n-hexane to
give green-black needles of 25, which were suitable for X-ray
diffraction. After decanting of the mother liquor the crystals were
washed with 5 mL of n-hexane and dried under vacuum to obtain
30 mg (0.01 mmol, 26% relating to 18) ofpure26.Mp:248-250 °C.
IR (KBr; cm-1): ν~ 3053 (m), 3032 (m), 2997 (m), 2981 (m), 2908
(m), 2854 (w), 1940 (w), 1876 (w), 1817 (w), 1759 (w), 1616 (w),
1570 (m), 1516 (s), 1508 (s), 1479 (m), 1450 (m), 1425 (m), 1371 (s),
1315 (w), 1263 (m), 1182 (w), 1138 (w), 1099 (w), 1057 (m), 1032
(m), 1018 (m), 964 (w), 845 (w), 812 (m), 733 (s), 704 (s), 656 (w),
611(m), 532(w), 469(w), 440(w). MS(CI, isobutane):m/z(relative
intensity, %) 417.1 (4), 416.1 (20), 415.1 (100) [M - (2CH2) -
Calcd for C48H54BN2V 0.5C6H14: C, 80.20; H, 8.05; N, 3.67.
3
Found: C, 78.40; H, 8.17; N, 3.69.
Synthesis of [(Cp*2V)2(μ2-4-Bipy)][BPh4]2 (21). [Cp*2V][BPh4]
(18; 96 mg, 0.15 mmol) and 24 mg (0.15 mmol) of 4,40-bipyridine (8)
were suspended in 20 mL of thf and heated to 60 °C without
stirring. The color of the solution changed slowly from brown to
green, and most of the solid 18 was dissolved during the reaction.
After 3 days the solution was filtered from the remaining solids at
room temperature and layered with 20 mL of n-hexane to give
green-brown blocks of 21, which were suitable for X-ray diffrac-
tion. After decanting of the mother liquor the crystals were washed
with 5 mL of n-hexane and dried under vacuum to obtain 60 mg
(0.04 mmol, 51% relating to 18) of pure 21. Mp: 258-260 °C dec.
IR (KBr; cm-1): ν~ 3052 (m), 3035 (m), 2996 (m), 2982 (m), 2904
(m), 1939 (w), 1878 (w), 1816 (w), 1606 (m), 1579 (m), 1479 (m),
1450 (m), 1426 (m), 1410 (m), 1380 (m), 1308 (w), 1261 (m), 1211
(w), 1182 (m), 1148 (m), 1064 (m), 1031 (m), 1018 (m), 845 (w), 821
(m), 731 (s), 704 (s), 612 (m), 604 (m), 439 (w). MS (CI, isobutane):
m/z (relative intensity, %) 842.8 (2), 841.8 (11), 840.8 (50), 839.7
(100) [(M þ C3H6)]þ. HR-MS (CI, isobutane): m/z calcd for
(2H)]3þ. HR-MS (CI, isobutane): m/z calcd for C78H102N6V3
425.2162, found 425.2164 (100). Anal. Calcd for C150H162B3N6V3
3þ
3
C6H14: C, 80.75; H, 7.65; N, 3.62. Found: C, 79.38; H, 7.67; N, 3.70.
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft (DFG, SPP 1118) for financial support.
Supporting Information Available: Tables of crystal data and
ORTEP drawings of 19 and 20 and CIF files giving crystal-
lographic data for structures 3, 12, 13, 17, 19, 20, 21, 24, and 26.
This material is available free of charge via the Internet at http://
pubs.acs.org. Crystallographic data have also been deposited
with the Cambridge Crystallographic Data Centre as supple-
mentary publication nos. CCDC 736231 (26), CCDC 736232
(12), CCDC 736233 (24), CCDC 736234 (3), CCDC 736235 (13),
CCDC 736236 (17), CCDC 736237 (21), CCDC 736238 (19),
and CCDC 736239 (20). Copies of data can be obtained free of
charge on application to the CCDC, 12 Union Road, Cambridge
CB21EZ, U.K. (fax, þ44 1223 336 033; e-mail, deposit@
ccdc.cam.ac.uk).
2þ
C50H68N2V2 399.2131, found 399.2127 (100). Anal. Calcd for
C98H108B2N2V2 2C4H8O: C, 80.49; H, 7.90; N, 1.77. Found: C,
3
81.18; H, 8.07; N, 2.03.
Synthesis of [(Cp*2V)2(μ2-Py2C2)][BPh4]2 (24). Vanadocene(II)
(1; 18 mg, 0.1 mmol) and 18 mg (0.1 mmol) of 1,2-bis(4-
pyridyl)acetylene (9) were dissolved in 20 mL of thf and stirred
overnight to form complex 12 in situ. A suspension of 128 mg
(0.2 mmol) of [Cp*2V][BPh4] (18) in 20 mL of thf was added, and
the resulting reaction mixture was heated to 60 °C for 2 weeks
without stirring. During that time 24 precipitated as brown