Trovacene chemistry. 10. The [1]- and [2]silatrovacenophanes (η7-C7H6)V(η5-C 5H4SiR2) and (η7-C7H6)V(η5-C5H4SiR 2SiR2 (R = Me, Ph): Synthesis, structure, and ring opening

Article abstract of DOI:10.1002/zaac.200400247

Heteroannular dilithiation of trovacene, (η⁷-C ₇H₇)V(η⁵-C₅H₅) (1^?), and subsequent reaction with the respective dichlorosilane yielded the [1]silatrovacenophanes (η⁷-C₇H ₆)V(η⁵-C₅H₄SiR₂) (2^?, R = Ph; 3^?, R = Me) and the [2]silatrovacenophane (η⁷-C₇H₆) V(η⁵-C₅H₄SiMe₂SiMe₂) (4^?). Structural studies by X-ray diffraction revealed sandwich tilt angles of 17.3° (2^?) and 3.8° (4^?), respectively, and considerable strain in the ring-link-ring region. EPR spectroscopy responds to these distortions in that the g-tensor is tetragonal (g_x = g_y ≠ g_z) for 4^? but rhombic (g_x ≠ g_y ≠ g_z) for 2 ^? and 3^?. With increasing tilt, increases slightly towards g_fs = 2.0023 and a(⁵¹V) decreases, the latter response to tilting being more pronounced. These trends are plausible in view of distortion-induced mixing of the V(3d_z2) SOMO with π orbitals. Whereas cyclic voltammetry of undistorted 4 ^? displays reversible oxidation and reduction, the strained sandwich 2^? shows irreversible behavior, probably caused by cleavage of the interannular bridge. [1]Silatrovacenophanes are thermally more robust than [1]silaferrocenophanes in that 2^?, exposed to 280°C, fails to show indications of ring-opening polymerization (ROP).

Full text of DOI:10.1002/zaac.200400247

Trovacene Chemistry. 10 [1]
The [1]- and [2]Silatrovacenophanes (η7-CT7H6)V(η5-C5H4SUiR2) and
(η7-CT7H6)V(η5-C5H4SiR2SUiR2 (R ؍ Me, Ph): Synthesis, Structure, and Ring
Opening
Christoph Elschenbroich*, Francesca Paganelli, Mathias Nowotny, Bernhard Neumüller, and Olaf Burghaus
Marburg, Fachbereich Chemie der Philipps-Universität
Received June 18th, 2004.
Dedicated to Professor Albrecht Salzer on the Occasion of his 60th Birthday
Abstract. Heteroannular dilithiation of trovacene, (η7-C7H7)V(η5-
C5H5) (1•), and subsequent reaction with the respective dichlorosil-
more pronounced. These trends are plausible in view of distortion-
2
induced mixing of the V(3d ) SOMO with ligand π orbitals.
z
ane yielded the [1]silatrovacenophanes (η7-C7
T
H6)V(η5-C5H4S
U
iR2)
(2•, R ϭ Ph; 3•, R ϭ Me) and the [2]silatrovacenophane (η7-
C7
H6)V(η5-C5H4SiMe2SiMe2) (4•). Structural studies by X-ray dif-
Whereas cyclic voltammetry of undistorted 4• displays reversible
oxidation and reduction, the strained sandwich 2• shows irrevers-
ible behavior, probably caused by cleavage of the interannular
bridge. [1]Silatrovacenophanes are thermally more robust than
[1]silaferrocenophanes in that 2•, exposed to 280 °C, fails to show
indications of ring-opening polymerization (ROP).
T
U
fraction revealed sandwich tilt angles of 17.3° (2•) and 3.8° (4•),
respectively, and considerable strain in the ring-link-ring region.
EPR spectroscopy responds to these distortions in that the g-tensor
is tetragonal (gx ϭ gy ϶ gz) for 4• but rhombic (gx ϶ gy ϶ gz) for
2• and 3•. With increasing tilt, ϽgϾ increases slightly towards gfs ϭ
2.0023 and a(51V) decreases, the latter response to tilting being
Keywords: Metallocenophanes; Mixed-ligand sandwich; EPR-spec-
troscopy; Cyclic voltammetry; Ring-opening polymerization
Trovacenchemie. 10 [1]
Die [1]- und [2]Silatrovacenophane (η7-CT7H6)V(η5-C5H4SUiR2) und
(η7-CT7H6)V(η5-C5H4SiR2SUiR2 (R ؍ Me, Ph): Synthese, Struktur und Ringöffnung
Inhaltsübersicht. Heteroannulare Dilithiierung von Trovacen, (η7-
C7H7)V(η5-C5H5) (1•), und anschließende Reaktion mit den ent-
sprechenden Dihalogensilanen lieferte die [1]Silatrovacenophane
Kippung nimmt g geringfügig in Richtung auf gfs ϭ 2.0023 hin zu
und a(51V) deutlich ab. Diese Trends erklären sich aus der verzer-
2
rungsinduzierten Mischung des SOMO V(3d ) mit Ligand-π-Orbi-
z
(η7-C7
T
H6)V(η5-C5H4S
U
iR2) (2•, R ϭ Ph; 3•, R ϭ Me) und das [2]Si-
talen. Während die cyclische Voltammetrie für das unverzerrte 4•
reversible Oxidation und Reduktion anzeigt, weist das gespannte
[1]Trovacenophan 2• irreversibles Redoxverhalten auf, welches sich
auf die Spaltung der interannularen Brücke zurückführen läßt.
[1]Silatrovacenophane sind thermisch robuster als [1]Ferroceno-
phane, denn 2• bietet, auch nach thermischer Belastung auf 280°,
keine Hinweise auf ringöffnende Polymerisation (ROP).
latrovacenophan (η7-C7
T
H6)V(η5-C5H4SiMe2SiMe2) (4•). Struktur-
U
untersuchungen mittels Röntgenbeugung ergaben Sandwich-Kipp-
winkel von 17.3° (2•) und 3.8° (4•) und beträchtliche Spannung im
Ring-Brücke-Ring-Bereich. Die EPR-Spektren zeigen diese Verzer-
rungen an, indem der g-Tensor für 4• tetragonal (gx ϭ gy ϶ gz), für
2• und 3• hingegen rhombisch (gx ϶ gy ϶ gz) ist. Mit zunehmender
1 Introduction
by the short interannular links responsible for tilting of the
sandwich backbone also modifies chemical reactivity as has
been amply demonstrated by Manners et al. [2]. The latter
have exploited this effect in the preparation of metallocene
containing polymers formed by ring opening polymeriz-
ation (ROP) of [1]silaferrocenophanes.
Interannular links at bis(arene)metal complexes have
played an important role in our own work over the years
[3]. Our recent focus on paramagnetic (η7-tropylium)vanad-
ium(η5-cyclopentadienyl), trovacene 1•, as a probe in stud-
ies of intramolecular communication initiated the plan of
synthesizing tilted derivatives of parent 1•. Apart from the
fact that this type of metallocyclophane was hitherto un-
known, motivation also derived from the question whether
Tilted sandwich complexes are of interest for a variety of
reasons. With regard to electronic structure, loss of axial
symmetry with attendant raising of orbital degeneracies
should effect changes in spectroscopic, magnetic, and redox
properties. In a different vein, the strain which is introduced
* Prof. Dr. Ch. Elschenbroich
Fachbereich Chemie
Philipps-Universität Marburg
D-35032 Marburg/Germany
Fax: ϩ49(0)6421/2825653
E-Mail: eb@chemie.uni-marburg.de
Z. Anorg. Allg. Chem. 2004, 630, 1599Ϫ1606
DOI: 10.1002/zaac.200400247
 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1599

Ch. Elschenbroich, F. Paganelli, M. Nowotny, B. Neumüller, O. Burghaus
Scheme 1
Figure 1 Molecular structure of 2• in the crystal, SHELXTL draw-
ing with 50 % probability ellipsoids.
tilted [1]trovacenophanes would readily undergo ROP.
While [1]metallocenophanes in fact display ROP, in our
hands interannularly bridged, tilted bis(arene)metal com-
plexes failed to do so, probably for the reason that metal-
ring bond-cleavage competes with polymerization [3m]. We
therefore set out to prepare [1]- and [2]silatrovacenophanes,
the outcome of this endeavour being reported in the sequel.
X-Ray Crystallographic Study
The structures of the [1]silatrovacenophane 2• and the [2]sil-
atrovacenophane 4• are displayed in Figures 1 and 2, selec-
ted bond lengths and angles are given in Table 1. The angles
describing the bending distortions are defined in Figure 3.
Tilting of the sandwich axes is, of course, the prominent
structural feature, it gives rise to the interplanar angles
(2•) ϭ 17.26(9)° and (4•) ϭ 3.8(3)°, respectively. The tilt an-
gle σ is defined as the angle of the axes connecting the two
ring centroids with the central metal atom. Distortion par-
ameters for a few related molecules are also given in Figure
3. In accordance with the larger atomic radius of vanadium,
compared to chromium, interannular ϪSiR2Ϫ and
ϪGeR2Ϫ links cause more extensive tilting for the va-
nadium sandwich complexes than for the chromium species.
The effect of the size of the bridging atom is illustrated by
the [1]zirconavanadarenophane 8• which, despite the pres-
ence of a one-atom bridge, is tilted only marginally [3m].
Surprisingly, although the inter-ring distance of parent (η7-
C7H7)V(η5-C5H5) (338 pm) is somewhat larger than in the
symmetrical isomer (η6-C6H6)2V (322 pm), α(2•) falls short
of α(7•). This must be a consequence of the disparate ring
sizes in 2•. The latter are also responsible for differing
angles βTr(2•) and βCp(2•): the absence of ring slippage and
identical bond distances C1ϪSi and C8ϪSi necessarily re-
sult in the gradation βTr (2•) ϭ 45° > βCp (2•) ϭ 33°.
2 Results and Discussion
Synthesis
A suitable precursor in the preparation of interannularly
linked trovacene derivatives would be the dilithiated species
(η7-C7H6Li)V(η5-C5H4Li). At the start of the present study,
only the monolithiated complex (η7-C7H7)V(η5-C5H4Li)
had been obtained, however. The factors which govern re-
activity, regioselectivity of monolithiation, and the control
of mono- versus dilithiation of mixed sandwich complexes
(η7-C7H7)M(η5-C5H5), M ϭ Ti, V, Cr, still are not well
understood [4]. Under mild lithiation conditions (n-BuLi,
hexane/Et2O, room temperature) (C7H7)Ti(C5H5) is mono-
lithiated at η7-C7H7 and (C7H7)V(C5H5) at η5-C5H5. For
unknown reasons, monolithiation of trovacene 1• stops at
50 % conversion. Heteroannular dilithiation of (η7-
C7H7)Ti(η5-C5H5) is effected by n-butyl lithium in the pres-
ence of N,N,NЈ,NЈ-tetramethylethylenediamine (TMEDA)
[4e]. This procedure also generates (η7-C7H6Li)V(η5-
C5H4Li), which subsequently by means of the respective or-
ganohalosilane R2SiCl2 can be transformed into the silatro-
vacenophanes 1,8-diphenylsilanediyl(η7-cycloheptatrienyl)-
(η5-cyclopentadienyl)vanadium 2•, 1,8-dimethylsilanediyl-
In addition to sandwich tilting, strain also manifests itself
(η7-cycloheptatrienyl)(η5-cyclopentadienyl)vanadium
and 1,8-tetramethyldisilane-1,2-diyl(η7-cycloheptatrienyl)-
(η5-cyclopentadienyl)vanadium 4• (Scheme I) [5]. Exhaus-
tive heteroannular dilithiation of trovacene requires an ex-
cess of n-BuLi/TMEDA. In general, it is advisable to separ-
ate insoluble dilithiotrovacene by decantation before use in
subsequent reactions. In the present application, however,
this step proved to be superfluous, possibly because dilithi-
otrovacene reacts with halosilanes faster than n-butyllith-
ium.
3•,
in the deviation of the angle θ at the bridging atom E from
the value appropriate for sp3 hybridization and in the bend-
ing β of the CipsoϪE bond vectors out of the π-perimeter
planes. Chemical lability of the interannular links is there-
fore expected and found as will be discussed in a later sec-
tion.
Structural details for the ϪSiMe2Ϫ bridged complex 3•
are unavailable because this material at ambient tempera-
ture is obtained as an oil which resisted all crystallization
attempts.
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Z. Anorg. Allg. Chem. 2004, 630, 1599Ϫ1606

Trovacene Chemistry. 10
Figure 2 Molecular structure of 4• in the crystal, SHELXTL draw-
ing with 50 % probability ellipsoids.
Metallocene derivatives or similar ligand systems with a
ϪSiMe2ϪSiMe2Ϫ bridge are known for typical sandwich
compounds with almost parallel ligand-ring arrangements
(M ϭ Cr [3d], Fe [6], Ru [7]) as well as for Cp2TiCl2-type
complexes (M ϭ Ti [8], Zr [8b, 9], Hf [10]). The SiϪSi dis-
tance for the first mentioned type of compound can vary
between 233.4(8) and 237.0(2) pm [6d, 7] depending on the
steric conditions generated by the metals and the aromatic
ligand system. The value of 235.5(2) pm in 4• fits into this
range. For the latter type of complex usually a somewhat
shorter SiϪSi bond was observed caused by the reduced
steric stress in the pseudo-tetrahedral environment. Typical
values lie between 232.4(3) and 233.1(3) pm [8b].
Electron Paramagnetic Resonance
EPR spectroscopy has proved to be an invaluable tool in
the study of V0(d5) sandwich complexes. While for oligonu-
clear V0 complexes 51V hyperfine analysis reveals intramol-
ecular magnetic interaction [11], in the case of mononuclear
derivatives substituent effects and structural distortions are
assessed [3]. With regard to the silatrovacenes 2•-4•, which
form the topic of the present investigation, the effect of tilt-
ing on g- and hyperfine anisotropy are at stake. Rigid solu-
tion EPR spectra of 2• and 4• are depicted in Figure 4, the
data are collected in Table 2. As expected, the spectral re-
cord for 4• (α ϭ 3.8°) closely matches that observed for
parent 1• (α ϭ 0°); the small changes of the parameters
ϽgϾ, a(51V), gʈ, gЌ, Aʈ(51V), and AЌ(51V) reflect the
weakly electron withdrawing nature of organosilyl substi-
tution in 4•. Even for the more extensively tilted complex 2•
(α ϭ 17.3°), loss of axial symmetry is barely resolved in
the rigid solution X-band EPR spectrum; resort to Q-band
measurements was therefore taken, which form the basis for
the data collected in Table 2. Inspection of the parameters
extracted for the species 1•, 2•, and 4• reveals that ϽgϾ in-
creases and a(51V) decreases with increasing tilt. The same
gradation had been observed previously for the couple 11ϩ·
Figure 3 Schematics of interannularly bridged symmetrical (a) and
unsymmetrical (b) sandwich complexes and designations of the rel-
evant angles which describe the distortions: 2•, 4• (this paper) and
5-12 (as reported previously).
Z. Anorg. Allg. Chem. 2004, 630, 1599Ϫ1606
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 2004 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
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Ch. Elschenbroich, F. Paganelli, M. Nowotny, B. Neumüller, O. Burghaus
Table 1 Selected bond lengths/pm and bond angles/° in 2• and 4•a)
2•
V1···Si1
V1ϪC1
V1ϪC2
V1ϪC3
V1ϪC4
V1ϪC5
V1ϪC6
V1ϪC7
V1ϪC8
V1ϪC9
288.00(7) C1ϪSi1ϪC8
213.6(2) C1ϪSi1ϪC13
216.3(2) C8ϪSi1ϪC13
220.6(2) Si1ϪC1ϪC2
221.0(2) C2ϪC1ϪC7
220.3(2) C2ϪC3ϪC4
220.3(2) C4ϪC5ϪC6
217.8(2) C1ϪC7ϪC6
221.6(2) Si1ϪC8ϪC12
223.2(2) C8ϪC9ϪC10
98.17(8) C13ϪSi1ϪC19 111.67(9)
111.69(9) C1ϪSi1ϪC19 113.58(8)
110.88(8) C8ϪSi1ϪC19 110.11(9)
111.6(1) Si1ϪC1ϪC7
124.2(2) C1ϪC2ϪC3
129.4(2) C3ϪC4ϪC5
127.7(2) C5ϪC6ϪC7
129.8(2) Si1ϪC8ϪC9
110.1(1)
130.1(2)
128.0(2)
130.0(2)
121.8(1)
120.7(1) C9ϪC8ϪC12 105.0(2)
109.4(2) C9ϪC10ϪC11 108.4(2)
V1ϪC10 227.3(2) C10ϪC11ϪC12 107.5(2) C11ϪC12ϪC8 109.7(2)
V1ϪC11 228.4(2)
V1ϪC12 224.0(2)
Si1ϪC1
188.9(2) Si1ϪC8
187.7(2) Si1ϪC13
143.6(3) C1ϪC7
140.9(3) C4ϪC5
140.9(3) C8ϪC9
141.0(3) C10ϪC11
186.6(2)
143.5(3)
140.9(3)
143.6(3)
141.3(3)
Si1ϪC19 186.3(2) C1ϪC2
C2ϪC3
C5ϪC6
141.4(3) C3ϪC4
141.0(3) C6ϪC7
C8ϪC12 144.0(3) C9ϪC10
C11ϪC12 141.1(3)
4•
V1ϪC1
V1ϪC2
V1ϪC3
V1ϪC4
V1ϪC5
V1ϪC6
V1ϪC7
V1ϪC8
V1ϪC9
219.1(4) C1ϪSi1ϪSi2
219.1(5) Si1ϪC1ϪC2
218.9(6) C2ϪC1ϪC7
219.6(6) C2ϪC3ϪC4
219.9(5) C4ϪC5ϪC6
219.4(5) C6ϪC7ϪC1
219.1(5) Si2ϪC8ϪC12
226.2(6) C8ϪC9ϪC10
102.9(1) C8ϪSi2ϪSi1
115.6(3) Si1ϪC1ϪC7
125.9(4) C1ϪC2ϪC3
128.8(6) C3ϪC4ϪC5
128.5(6) C5ϪC6ϪC7
129.3(5) Si2ϪC8ϪC9
105.4(2)
116.3(3)
129.7(5)
128.1(6)
129.6(6)
126.2(5)
126.2(5) C9ϪC8ϪC12 107.2(5)
109.0(6) C9ϪC10ϪC11 107.1(6)
226.7(6) C10ϪC11ϪC12 108.0(6) C11ϪC12ϪC8 108.7(6)
V1ϪC10 226.7(6)
V1ϪC11 226.6(6)
V1ϪC12 225.5(6)
Si1ϪSi2 235.5(2) Si1ϪC1
Figure 4 EPR spectra of 2• and 4• in rigid solution (toluene, 110 K;
Q band ν ϭ 34.0137 GHz)
Experimental (ᎏ) and simulated (····)
189.4(6) Si2ϪC8
143.1(7) C2ϪC3
140.5(9) C5ϪC6
141.9(8) C8ϪC12
189.0(6)
141.0(8)
140.4(9)
141.4(8)
143(1)
C1ϪC2
C3ϪC4
C6ϪC7
143.3(7) C1ϪC7
143.1(8) C4ϪC5
141.6(8) C8ϪC9
C9ϪC10 142.9(9) C10ϪC11
142(1)
C11ϪC12
a) Further details can be obtained from the Cambridge Crystallographic
Data Center, 12 Union Road, Cambridge CB2 1EZ by quoting the numbers
CCDC 237109 and CCDC 237110 (Fax: (ϩ44) 1223-3 36-0 33; e-mail: de-
posit@ccdc.cam.ac.uk).
Table 2 EPR parameters for axially symmetric 1• and tilted 2•
and 4•.
1•
4•
2•
(α ϭ 0°) and 12ϩ· (α ϭ 18°), which features Crϩ·(d5) instead
of V•(d5) as the central metal [3c]. The inverse response of
ϽgϾ and a(51V) to tilting suggests that this distortion is
accompanied by a slight increase in metalǞligand spin de-
localization, which would serve to reduce the spin-orbit
coupling contribution to the g factor and the extent of cen-
tral metal hyperfine coupling. Axially symmetric bis(arene)-
metal(d5) sandwich complexes possess the frontier orbital
α
0°
1.9815
3.8°
17.3°
1.9832
1.9737
1.9715
1.9993
1.9815
6.76
9.62
10.08
0.6
giso
1.9816
1.9724
1.9718
1.998
1.9813
7.03
g1
g2 [gЌ]
g3 [gʈ]
1.9725
1.9994
1.9815
7.20
10.26
10.37
0.97
ϽgϾ (calcd)
a(51V)/mT
A1(51V)/mT
A2(51V) [AЌ(51V)]/mT
A3(51V) [Aʈ(51V)]/mT
ϽA(51V)Ͼ (calcd)/mT
10.19
10.36
0.53
4
1
0
sequence e2 a1 e1 . The SOMO a1 is an essentially non
7.20
7.03
6.76
2
bonding M(dz ) function, metal ligand overlap being almost
nil because the ligand π-orbitals are positioned in the nodal
2
plane of the M(dz ) orbital. This situation changes upon
central metal atom and a reduction of hyperfine coupling
as actually observed for tilted 2•. It is worth mentioning
that the extent of δ-backbonding from filled metal dxy and
tilting distortion, a modified molecular orbital diagram for
bent metallocenes has been proposed by Green [12] and re-
fined by Hoffmann [13]. Accordingly, the degeneracies of
the e2- and e1 levels are raised and the new sequence
1a1b22a1b1a2 emerges [13], in which the SOMO 2a1 can now
mix with 1a1. Since 1a1 is of e2 origin (δ-bonding in the
undistorted sandwich), mixing of metal-dominated 2a1 with
1a1 is expected to cause a decrease of spin density on the
2
2
dx -y orbitals to unoccupied ligand orbitals increases with
increasing π-perimeter size. Therefore, the composition
(C7H7)M(C5H5) should be comparable to (C6H6)M(C6H6),
where bonding is thought to be dominated by the
δ
MǞCnHn contribution [14].
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Trovacene Chemistry. 10
also serves to rationalize the more robust nature of 4• under
oxidizing and reducing conditions (absence of strain) and
of 2• and 5•-7• under reducing conditions (attenuation of
susceptibility to nucleophilic attack).
Experiments Directed at Ring Opening
Polymerization (ROP)
Chemically induced cleavage of the interannular link in
[1]silametallocenophanes is complemented by thermal ring
opening, which can lead to macromolecules in which
1,1Ј-metallocenediyl units alternate with ϪSiR2Ϫ groups
[2]. It therefore was of interest to inquire whether this type
of ring opening polymerization also proceeds with [1]sila-
trovacenophanes 2• and 3•. An attractive feature of this sys-
tem is the fact that a silyltrovacenyl based organometallic
polymer would contain a paramagnetic repeating unit
which would trigger questions of magnetic coupling along
this polyradical chain. Spin exchange is expected to profit
from the known ability of organosilanes to promote conju-
gation [17]. In fact, we have previously observed antiferro-
magnetic exchange in dinuclear bis(η6-benzene)vanadium
derivatives, mediated by organosilicon spacers [3i]. Even in
the case of a disilyl spacer, the exchange coupling constant
J exceeded the value of the hyperfine coupling constant
a(51V) by a factor of 100, which renders exchange moder-
ately strong on the 51V hyperfine scale still keeping it in a
range where it noticeably shapes the hyperfine pattern.
Since the ϪSiMe2Ϫ bridged complex 3• could not be
fully characterized as a pure material, thermolysis experi-
ments were inconclusive. EI-MS mass spectrometric analy-
sis pointed to the presence of the trimer
TVCϪSiMe2ϪTVCϪSiMe2ϪTVC together with the target
molecule 3•. However, it is not clear whether the trimer
arose during the synthesis in a reaction competing with
[1]silatrovacenophane formation or whether it constitutes a
ring opening oligomerization product generated during the
EI-MS experiment. The latter alternative gains some sup-
port from the observation that the initial product in the
synthesis of 3• furnishes an EPR spectrum which advocates
the presence of mononuclear TVC derivatives only, whereas
after heating to 80 °C in the presence of a trace of PtCl2 for
2 h, the EPR spectrum of a dinuclear trovacene derivative
is superimposed on the monomer spectrum (Figure 6a). Pt
catalyzed ROP has been reported for the [1]silaferroceno-
phane 10 [2c].
Figure 5 Cyclic voltammograms for 2• and 4 in DME/n-Bu4NClO4
at Ϫ40 °C and 100 mV/s vs. SCE. Compound 2: Epa(ϩ/0)a
ϭ
0.376 V; E1/2(0/Ϫ) ϭ Ϫ2.473 V, ∆Ep ϭ 41 mV, r ϭ 1. Compound
4: E1/2(ϩ/0) ϭ 0.260 V, ∆Ep ϭ 76 mV, r ϭ 1; E1/2(0/Ϫ) ϭ Ϫ2.489 V,
∆Ep ϭ 66 mV, r ϭ 1. Compound 1 [10]: E1/2(ϩ/0) ϭ 0.260 V, ∆Ep ϭ
a
64 mV, r ϭ 0.9; E1/2(0/Ϫ) ϭ Ϫ2.55 V, ∆Ep ϭ 66 mV, r ϭ 1. Irre-
versible process.
Redox properties
Parent trovacene 1• undergoes two reversible redox pro-
cesses, which according to cyclic voltammetry (CV vs SCE)
proceed at the potentials
E1/2(ϩ/0)ϭϩ0.26 V and
E
1/2(0/Ϫ) ϭ Ϫ2.55 V [15]. Again, as in the case of the EPR
spectra, the weakly tilted complex 4• mimicks parent 1•
whereas the strongly tilted complex 2• differs in that oxi-
dation is irreversible and reduction is ill defined. The CV
traces for 2• and 4• are shown in Figure 5, electrochemical
data are found in the respective captions. The observation
that the redox potentials of 4• are almost the same as
those of 1• may be explained by the fact that in 4• the anodic
shift typical for silyl substitution is compensated by
SiϪSi(σ)Ηηn-CnHn(π) conjugation. The latter should be par-
ticularly effective in the [2]silatrovacenophane structure
since the SiϪSi σ-bond vector is parallel to the axes of the
π-perimeter ligand orbitals. Precedent for the electrochemi-
cal behavior of 2• exists with the complexes 5• [3e], 6• [3m],
and 7• [3j], which also display totally irreversible oxidation.
In view of the well-known sensitivity of the η6-arene-Si
bond to solvodesilylation [16], the strain inherent in the
one-atom ansa-sandwich structure and the higher suscepti-
bility of cations to nucleophilic attack, the ready cleavage of
the one-atom interannularly bridges in 2• and 5•-7• during
electrochemical oxidation is not surprising. This picture
Dimers, trimers, and possibly oligomers comprised of the
units ϪTVCϪSiMe2Ϫ are also found if the synthesis is car-
ried out in refluxing tetrahydrofuran. In different runs of
this experiment, the respective products displayed EPR
spectra which attest to the presence of exchange coupled
dinuclear [15 lines, splitting a(51V, 1•)/2] and trinuclear [22
lines, splitting a(51V, 1•)/3] trovacene derivatives (Figure 6b).
Again, it is not apparent whether the latter are formed in-
itially or whether they are the products of secondary ring
opening.
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Ch. Elschenbroich, F. Paganelli, M. Nowotny, B. Neumüller, O. Burghaus
Table 3 Crystallographic data of 2• and 4•
instrument
radiation
formula
formular weight/g·mol
crystal size/mm
a/pm
IPDS II (Stoe)
Mo-Kα
C24H20SiV
387.45
0.23ϫ0.20ϫ0.08
1114.3(2)
1527.0(2)
1190.7(2)
111.91(1)
1879.7(5)
4
IPDS II
Mo-Kα
C16H22Si2V
321.47
0.40ϫ0.34ϫ0.12
664.0(1)
1310.9(1)
944.8(1)
104.72(1)
795.4(2)
2
b/pm
c/pm
β/°
unit cell volume/106 pm3
Z
dcalc
1.369
1.342
monoclinic
P21
numerical
7.6
crystal system
space group (No.)
absorption correction
µ/cmϪ1
monoclinic
P21/n (14 [22])
numerical
6.0
temperature/K
2θmax/°
193
52.51
Ϫ13 Յ h Յ 13
Ϫ18 Յ k Յ 18
Ϫ14 Յ l Յ 14
26752
193
52.37
Ϫ8 Յ h Յ 8
Ϫ18 Յ k Յ 18
Ϫ14 Յ l Յ 14
11497
hkl values
measured reflection
unique reflections
Rint
3770
0.0668
3064
0.0731
reflections with Fo>4σ(Fo)
parameter
structure solution
2544
315
direct methods
(SIR-92 [23])
2917
217
direct methods
(SHELXS-97 [24])
refinement against F2
H atoms
Ϫ SHELXL-97 [25] Ϫ
a)
a)
Flack-Parameter
R1
wR2 (all data)
max. residual electron density
/10Ϫ6 e·pm3
Ϫ
0.02(4)
0.0631
0.1755c)
1.57
Figure 6 EPR spectra (X band, 298 K) of solutions obtained during
attempted ring opening polymerization (ROP); a 3• in toluene, trace
of PtCl2, 80 °C for 2h; b 3• in THF, reflux for 8 h. The observation
of 15 and 22 line 51V hyperfine patterns displaying splittings one
half and one third of that of monomeric 3• attest to the presence
of exchange coupled diradicals and triradicals, respectively, in solu-
tion.
0.0284
0.0604b)
0.26
a) Free refinement. b) w ϭ 1/[σ2(Fo2)ϩ(0.0323·P)2]; P ϭ [max(Fo2, 0)ϩ2·Fc2]/3.
c) w ϭ 1/[σ2(Fo2)ϩ(0.1297·P)2ϩ(0.32·P)].
viously [18]. Trovacene (η7-C7H7)V(η5-C5H5) (1•) was prepared as
described in the literature [20].
[1]Silaferrocenophane 9 bearing an ϪSiPh2Ϫ interannu-
lar link was shown to engage in quantitative ring opening
polymerization, albeit at higher temperature than the
ϪSiMe2Ϫ analogue [2]. Contrarily, in our hands the
ϪSiPh2Ϫ bridged [1]trovacenophane 2• fails to undergo
ROP even at 280 °C since, after thermal treatment, MS-
und EPR analysis revealed the presence of the unchanged
monomer 2•. It may therefore be concluded that [1]silatrov-
acenophanes are considerably more robust than [1]silaferro-
cenphanes, which is surprising in view of the fact that the
tiltingangles differ only marginally. More extensive steric
shielding of the silicon atom in 2•, compared to 3• and 4•,
comes to mind as an explanation for the more robust nature
of 2•. Possibly, a two component ROP, utilizing 3• and 10,
X-ray data collection
The crystals were covered with a perfluorinated polyether and
mounted at the top of a glass capillary under a flow of cold gaseous
nitrogen. The reflection were collected with a IPDS II dif-
fractometer (Stoe; λ ϭ 71.073 pm). The intensities were corrected
for Lorentz and polarization effects (for absorption correction, cell
parameters, and collecting of the intensities, see Table 3). 4• crys-
tallizes in the Sohncke space group P21 [21]. Transformation in
P21/m is not possible (see also Flack-Parameter in Table 1). Selec-
ted bond lengths and angles of 2• and 4• are listed in Table 1.
(η7-C7H6)V(η5-C5H4SiPh2) (2•). A 100 mL flask equipped with a
T U
magnetic stirring bar was charged with (η7-cycloheptatrienyl)-
(η5-cyclopentadienyl)vanadium (0.20 g, 0.97 mmol), diethyl ether
(30 mL), and N,N,NЈ,NЈ-tetramethylethylenediamine (TMEDA)
(0.58 mL, 3.83 mmol). n-BuLi (2.41 mL, 3.83 mmol, solution 1.6 M
in hexane) was added dropwise and the mixture was refluxed for
4 h. After cooling to Ϫ20 °C dichlorodiphenylsilane (0.2 mL,
0.97 mmol) dissolved in petroleum ether (10 mL) was added during
2 h to the dark-violet suspension. The color of the mixture turned
from dark-brown to violet and LiCl precipitated. The mixture was
stirred at room temperature overnight. Filtration and storing of the
solution at Ϫ20 °C yielded violet crystals which were suitable for
X-ray diffraction.
will lead to organometallic polymers in which
a
(ϪC5H4)Fe(C5H4ϪSiMe2Ϫ) backbone is interspersed with
paramagnetic (ϪC7H6)V(C5H4ϪSiMe2Ϫ) units. This ap-
proach
had
been
chosen
to
incorporate
(ϪC6H5)Cr(C6H5ϪSiMe2Ϫ) blocks into a polysilaferrocen-
ophane chain [19] while neat [1]silachromarenophanes 5
failed to yield a ROP product.
Experimental Section
Chemical manipulations and physical measurements were per-
formed using standard techniques and instruments specified pre-
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Z. Anorg. Allg. Chem. 2004, 630, 1599Ϫ1606

Trovacene Chemistry. 10
Yield: 0.24 g, 64 %.
Wocadlo, E. Reijerse, Inorg. Chem. 1995, 34, 743; l) Ch. Elsch-
enbroich, Th. Isenburg , A. Behrendt, Inorg. Chem. 1995, 34,
6565; m) Ch. Elschenbroich, E. Schmidt, B. Metz, K. Harms,
Organometallics 1995, 14, 4043; n) Ch. Elschenbroich, E.
Schmidt, R. Gondrum, B. Metz, O. Burghaus, W. Massa, S.
Wocadlo, Organometallics 1997, 16, 4589.
Elemental analysis: C24H20SiV (387.45): calcd C 74.70, H 5.20;
found C 73.14, H 5.78 %.
EI-MS (70 ev) m/z ϭ 387 [Mϩ] (100 %); 309 [Mϩ-Ph] (14 %); 232
[Mϩ-2Ph] (14 %); 205 [Mϩ-SiPh2] (3 %).
(η7-C7H6)V(η5-C5H4SiMe2SiMe2) (4•). The preparation was car-
T U
[4] a) C. J. Groenenboom, H. J. de Liefde Meijer, F. Jellinek, Rec.
Trav. Chim. Pays-Bas 1974, 93, 6; b) C. J. Groenenboom, H.
J. de Liefde Meijer, F. Jellinek, J. Organomet. Chem. 1974, 69,
235; c) C. J. Groenenboom, F. Jellinek, J. Organomet. Chem.
1974, 80, 229; d) M. Vliek, C. J. Groenenboom, H. J. de Liefde
Meijer, F. Jellinek, J. Organomet. Chem. 1975, 97, 67; e) L. B.
Kool, M. Ogasa, M. D. Rausch, R. D. Rogers, Organometallics
1989, 8, 1785; f) M. Ogasa, M. D. Rausch, R. D. Rogers, J.
Organomet. Chem. 1991, 403, 279; g) M. L. H. Green, D. K.
P. N g , Chem. Rev. 1995, 95, 439; h) N. Kaltsoyannis, J. Chem.
Soc., Dalton Trans. 1995, 3727; i) For the electron-density dis-
tribution in mixed sandwiches (η7-C7H7)M(η5-C5H5), M ϭ Ti,
V, Cr, see K. A. Lyssenko, M. Yu. Antipin, S. Yu. Ketkov,
Russ. Chem. Bull., Int. Ed. 2001, 50, 130.
ried out in analogy to that of 2•, this time using
(η7-C7H7)V(η5-C5H5) (0.15 g, 0.72 mmol), TMEDA (0.43 mL,
2.88 mmol), n-BuLi (1.81 mL, 2.88 mmol, sol. 1.6 M in hexane),
1,2-dichlorotetramethyldisilane (0.13 mL, 0.72 mmol).
Yield: 0.10 g, 45 %.
Elemental analysis: C16H22Si2V (321.46): calcd C 59.78, H 6.90;
found C 56.83, H 7.04. EI-MS (70 eV) m/z ϭ 321 [Mϩ] (9 %); 205
[Mϩ-Si2Me4] (37 %); 116 [C5H5Vϩ] (54 %); 91 [C7H7ϩ] (20 %).
(η7-C7H6)V(η5-C5H4SiMe2) (3•). The synthesis of 3• was attempted
T U
in the same way as that of 2•, replacing Ph2SiCl2 by Me2SiCl2
(0.12 mL, 0.97 mmol), dissolved in petroleum ether (10 mL). The
product was a violet oil which resisted further purification. Column
chromatography led to deposition of insoluble material. Heating to
150 °C for 1 h in an evacuated tube resulted in no visible change.
Microanalysis revealed a small content (ഠ 3 %) of nitrogen, which
points to coordinated TMEDA. EI-MS (70 eV) m/z ϭ 734
[TVCϪSiMe2ϪTVCϪSiMe2ϪTVC] (50 %); 264 [3ϩ] (15 %); 207
[TVCϩ] (2 %); 91 [C7H7ϩ] (100 %).
[5] F. Paganelli, PhD Thesis, Univ. Marburg 2003.
[6] a) P. Jutzi, R. Krallmann, G. Wolf, B. Neumann, H.-G.
Stammler, Chem. Ber. 1991, 124, 2391; b) W. Finckh, B.-Z.
Tang, D. A. Foucher, D. B. Zamble, R. Ziembinski, A. Lough,
I. Manners, Organometallics 1993, 12, 823; c) V. V. Dement’ev,
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Acknowledgement. This work was supported by the
Volkswagen-Stiftung, the Deutsche Forschungsgemeinschaft, and
the Fonds der Chemischen Industrie. We thank Tina Schmidt for
technical assistance.
[7] J. M. Nelson, A. J. Lough, I. Manners, Organometallics 1994,
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