Dipolar sesquifulvalene compounds with (tetraaryl-η4- cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I)complex units as electron donors

Article abstract of DOI:10.1021/om300710x

Mononuclear monohydro sequifulvalene complexes of cobalt and their vinylogous derivatives [(Ar₄CBD)Co(Cp-Z-C₇H₇)] (Ar₄CBD = C₄Ar₄; Ar = p-X-C₆H ₄; X = H, Z = - (4); X = H, -C₂H₂- (9a); X = Cl, Z = -C₂H₂- (9b); X = Me, Z = -C₂H ₂- (9c); X = OMe, Z = -C₂H₂- (9d); X = NMe ₂, Z = -C₂H₂- (9e); X = H, Z = -(C ₂H₂)₂- (10); X = H, Z = -(C₂H ₂)₃- (11)) were synthesized and transformed by hydride abstraction to the corresponding dipolar sesquifulvalene complexes of [(Ar ₄CBD)Co(Cp-Z-C₇H₆)]⁺ (Ar ₄CBD = C₄Ar₄; Ar = p-X-C₆H ₄; X = H, Z = - (5); X = H, Z = -C₂H₂- (12a); X = Cl, Z = -C₂H₂- (12b); X = Me, Z = -C₂H ₂- (12c); X = H, Z = -(C₂H₂)₂- (13)) featuring a (tetraaryl-η⁴-cyclobutadiene)(η⁵- cyclopentadienediyl)cobalt(I) sandwich complex as an electron donor and the cationic tropylium part as an electron acceptor. Hydride abstraction to form the complexes [(Ar₄-η⁴-CBD)Co{(η⁵-C ₅H₄)Z(C₇H₆)]⁺ (Ar = p-C₆H₄X; X = OMe, NMe₂; Z = -C ₂H₂-) and [(Ar₄-η⁴-CBD) Co{(η⁵-C₅H₄)Z(C₇H ₆)}]⁺ (Ar = C₆H₅; Z = -(C ₂H₂)₃- (14)) failed and led to decomposition. The mononuclear archetypal sesquifulvalene complex 5 was obtained by nucleophilic addition of the monolithiated complex (Ar₄CBD)Co(CpLi) (3) to tropylium cation and subsequent hydride abstraction from the seven-membered ring. The vinylogous derivatives 9a-e, 10, and 11 were prepared by Horner-Wadsworth-Emmons (HWE) reactions of the suitable carbaldehydes (Ar₄CBD)Co(Cp-Z-CHO) (Z = -(C₂H₂)_n-) with the HWE reagent cyclohepta-1′,3′,5′-trien-1′- ylmethylphosphonate diethyl ester in a phase transfer catalyzed reaction. The donor-acceptor interaction was studied by means of ¹H and ¹³C NMR and UV-vis spectroscopy, cyclic voltammetry, X-ray structure determination, and hyper-Rayleigh scattering (HRS) measurements. For analysis of electronic excitations DFT calculations were performed on the complexes, revealing the cyclobutadiene metal complex fragment to be the donor and the metal complex Cp-bridge-cycloheptatrienylium fragment to be the acceptor.

Full text of DOI:10.1021/om300710x

Article
pubs.acs.org/Organometallics
Dipolar Sesquifulvalene Compounds with
(Tetraaryl‑η4‑cyclobutadiene)(η5- cyclopentadienediyl)cobalt(I)
Complex Units as Electron Donors
Sven Dabek,† Marc Heinrich Prosenc,*,‡ and Jurgen Heck*,§
̈
†Deutsches Patentamt Munchen, Zweibruckenstraße 12, 80331 Munchen, Germany
̈
̈
̈
‡Fachbereich Chemie, Technische Universitat Kaiserslautern, Erwin-Schrodinger-Straße 52, 67663 Kaiserslautern, Germany
̈
̈
§Fachbereich Chemie, Universitat Hamburg, Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
̈
S
* Supporting Information
ABSTRACT: Mononuclear monohydro sequifulvalene complexes of
cobalt and their vinylogous derivatives [(Ar4CBD)Co(Cp-Z-C7H7)]
(Ar4CBD = C4Ar4; Ar = p-X-C6H4; X = H, Z = − (4); X = H,
−C2H2− (9a); X = Cl, Z = −C2H2− (9b); X = Me, Z = −C2H2−
(9c); X = OMe, Z = −C2H2− (9d); X = NMe2, Z = −C2H2− (9e); X
= H, Z = −(C2H2)2− (10); X = H, Z = −(C2H2)3− (11)) were
synthesized and transformed by hydride abstraction to the
corresponding dipolar sesquifulvalene complexes of [(Ar4CBD)Co-
(Cp-Z-C7H6)]+ (Ar4CBD = C4Ar4; Ar = p-X-C6H4; X = H, Z = − (5); X = H, Z = −C2H2− (12a); X = Cl, Z = −C2H2− (12b);
X = Me, Z = −C2H2− (12c); X = H, Z = −(C2H2)2− (13)) featuring a (tetraaryl-η4-cyclobutadiene)(η5-cyclopentadienediyl)-
cobalt(I) sandwich complex as an electron donor and the cationic tropylium part as an electron acceptor. Hydride abstraction to
form the complexes [(Ar4-η4-CBD)Co{(η5-C5H4)Z(C7H6)]+ (Ar = p-C6H4X; X = OMe, NMe2; Z = −C2H2−) and [(Ar4-η4-
CBD)Co{(η5-C5H4)Z(C7H6)}]+ (Ar = C6H5; Z = −(C2H2)3− (14)) failed and led to decomposition. The mononuclear
archetypal sesquifulvalene complex 5 was obtained by nucleophilic addition of the monolithiated complex (Ar4CBD)Co(CpLi)
(3) to tropylium cation and subsequent hydride abstraction from the seven-membered ring. The vinylogous derivatives 9a−e, 10,
and 11 were prepared by Horner−Wadsworth−Emmons (HWE) reactions of the suitable carbaldehydes (Ar4CBD)Co(Cp-Z-
CHO) (Z = −(C2H2)n−) with the HWE reagent cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester in a phase
1
transfer catalyzed reaction. The donor−acceptor interaction was studied by means of H and 13C NMR and UV−vis
spectroscopy, cyclic voltammetry, X-ray structure determination, and hyper-Rayleigh scattering (HRS) measurements. For
analysis of electronic excitations DFT calculations were performed on the complexes, revealing the cyclobutadiene metal complex
fragment to be the donor and the metal complex Cp-bridge-cycloheptatrienylium fragment to be the acceptor.
electron donor yet in dipolar complexes directed toward NLO
properties, except for a short note in a review article.1l In a
previous paper we presented a strategy to build up
mononuclear and dinuclear sesquifulvalene complexes and
vinylogous congeners on the basis of ferrocene and
ruthenocene derivatives. These are synthesized straightfor-
wardly by starting with the appropriate cyclopentadienyl
carboxaldehyde sandwich complex. Subsequent Horner−Wads-
worth−Emmons (HWE) reactions are used to extend the
olefinic bridge between the donor and the acceptor of a dipolar
sesquifulvalene complex.1l,4h,6e
In this paper we present the syntheses, molecular structures,
and spectroscopic properties of dipolar mononuclear sesqui-
fulvalene cobalt complexes and their vinylogous derivatives with
a (tetraaryl-η4-cyclobutadiene)(η5-cyclopentadiendiyl)cobalt(I)
entities as electron-donating groups. Moreover, to fine-tune the
electronic properties, the cyclobutadiene ligands are provided
INTRODUCTION
■
The concept of employing dipolar organometallic complexes
for compounds with nonlinear optical (NLO) properties,1 e.g.
second harmonic generation (SHG), has been shown to be very
fruitful. In a simplified model, these complexes are commonly
composed of an organometallic electron-donating and/or
-accepting group connected by a π bridge, which enables
electronic communication between them. For organometallic
electron-accepting groups carbonyl and nitrosyl complexes
were applied2 as well as Fischer-type carbene complexes3 and
cationic compounds of organic π ligands.4 The most widely
used organometallic donating units are half-sandwich5 and
sandwich complexes and in particular ferrocenes and
ruthenocenes, due to their inertness and facile synthetic
availability of derivatives.6 Isoelectronic with ferrocene are
sandwich complexes of the type (η4-cyclobutadiene)(η5-
cyclopentadienyl)cobalt(I), which are stable in air as well and
can be electronically fine-tuned by the aryl substituents at the
cyclobutadiene ligand. However, a (η4-cyclobutadiene)(η5-
cyclopentadienyl)cobalt(I) unit has not been reported as an
Received: July 27, 2012
Published: September 24, 2012
© 2012 American Chemical Society
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with four aryl substituents whose para position is modified by
different groups X (Figure 1).
demonstrated in Scheme 2, the corresponding tropylium
compounds were obtained by hydride abstraction. When the
cycloheptatriene compounds were treated with trityl cation,
decomposition was observed for 11 with n = 3 and for 9d,e.
The instability of 11 with the hexatriene linker between the
donor and the acceptor is in agreement with the instability of
the corresponding ferrocene derivative.6e The decomposition of
9d,e may be due to an increasing oxidation sensitivity, which
ends up in an irreversible (vide infra) oxidation reaction of the
(Ar4CBD)CoCp entity. In principle, there are two different
paths concerning the mechanism of the hydride abstraction.
For easily oxidized complexes such as ferrocenes, the hydride
abstraction proceeds presumably via an oxidation of the metal
complex first, followed by an intermolecular hydrogen
abstraction.12 If the oxidized complex is sufficiently stable, as
for ferrocenium cation, it is even possible to isolate and
characterize it.1l,13 For complexes with a higher oxidation
potential such as ruthenocene or (Ar4CBD)CoCp complexes
(Ar = phenyl)14 with less electron releasing aryl substituents
(vide infra), the hydride abstraction is assumed to occur
directly.12 This mechanism needs more free space around the
hydride for abstraction and explains the necessity to isomerize
the cycloheptatriene substituent of cobalt complexes, bringing
the hydridic function via a 1,5-hydrogen shift13 in a more
distant position relative to the ipso carbon atom of the seven-
membered ring. While the hydride abstraction via the redox
mechanism mostly needs low temperature to stabilize the
radical cation, the direct hydride elimination can be performed
at room temperature.
Figure 1. Mononuclear sesquifulvalene complexes of (tetraaryl-η4-
cyclobutadiene)(η5-cyclopentadienediyl)cobalt(I) units and vinylo-
gous derivatives as target compounds.
RESULTS AND DISCUSSION
■
Synthesis. From earlier work it was known that a direct
coupling between a five- and seven-membered ring receiving an
archetypal sesquifulvalene ligand is successful, when the
metallocene is monometalated and acts as a nucleophile upon
addition to the tropylium ring.1l,6e
Since an application of a direct monometalation of the Cp
ring in 1 by organolithium compounds failed, a chloromercura-
tion reaction was performed first to obtain the monomercu-
rated complex 2.7 After a mercury−lithium exchange reaction
the lithiated complex 3 was subjected to a nucleophilic addition
on tropylium hexafluorophosphate (Scheme 1). The product
yielded the cycloheptatrienyl-substituted complex 4 contami-
nated with 10% of the starting material 1, which could not be
separated from the desired compound 4 by means of
recrystallization or column chromatography. However, the
formation of the compound 5 as a salt allows an easy
separation, due to different solubilities of the neutral, weakly
polar complex 1 in comparison to the salt of 5.
Former results indicate that a hydride abstraction is more
easily performed from the seven-membered ring to form the
tropylium compound 5, when the cycloheptatriene is linked to
the Cp ligand through an sp2 carbon atom.8 Hence, compound
4 was heated in mesitylene, to induce isomerization via a 1,5-
hydrogen migration.9
Solid-State Structure. For two tropylium compounds (5
and 12c) crystals could be obtained suitable for X-ray structure
determination (Figures 2−4). The sesquifulvalene complex 12c
crystallizes in the triclinic space group P1, and for 5 the
̅
monoclinic space group P21/c is found. The molecular
structure of complex 12c reveals a disorder in the
sesquifulvalene part. Both structures of the complexes 5 and
12c display very similar Co−CCBD distances (1.987(2)−
2.013(2) Å for 5 and 1.982(6)−2.002(6) Å for 12c). The
Co−C distances of the CBD part are distinctly shorter than for
the cobalt−cyclopentadienyl coordination (2.053(3)−2.095(3)
Å for 5 and 2.000(10)−2.083(8) A for 12c) (Table 1). The
structural data of the sandwich core of 5 and 12c are quite
comparable to those of other molecular structures of (η4-
cyclobutadiene)(η5-cyclopentadienyl)cobalt(I) complexes re-
ported in the literature.15−18 The difference in Co−C bond
lengths suggests a stronger cobalt bonding to the C4-ring than
The synthesis of the vinyloguous sesquifulvalene complexes
was performed by reaction of the appropriate carbaldehyde10
with the HWE reagent cycloheptatrienylmethyl phosphonate
diethyl ester6e in a phase transfer catalysis11 (Scheme 2). As
Scheme 1. Synthesis of the Archetypal Sesquifulvalene Complex 5 with (Ar4CBD)(Cp)Co as the Electron-Donating Complex
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Scheme 2. Synthesis of Dipolar, Mononuclear, Vinylogous Sesquifulvalene Complexes with a (Ar4CBD)Co(Cp) Unit As
Electron Donor
reason for the relatively small tilt angle of about 20° for the aryl
substituent C10−C15 of derivative 5 (see Figure 3) may be
caused by the steric demand of the tropylium substituent,
which is tilted only about 14° relative to the best plane of the
Cp ligand and is placed in an almost van der Waals contact with
this aryl substituent (compare Table 2).
It is interesting to note that the crystal packing of compound
12c forms a layered structure, wherein the sesquifulvalene
moieties of one layer of molecules is facing the sesquifulvalene
parts of another layer of molecules. The same holds true for the
cyclobutadiene entity (Figure 5).
Spectroscopic and Electrochemical Properties of the
Tropylium Compounds. All sandwich compounds under
study have been characterized by 1H and 13C NMR
spectroscopy. The assignment of the resonance signals has
been done by means of one- and two-dimensional NMR
spectroscopy.
For the neutral monohydro sesquifulvalene complexes 4,
9a−e, 10, and 11 the proton resonance signals of the seven-
membered ring appear in the range of 5.2−7.3 ppm and the
signals of the Cp protons in the range of 4.58−4.72 ppm (Table
3). The corresponding two shift ranges are found for the 13C
signals (Table 4). The resonance signals of the hydrogen-
bearing carbon nuclei of these neutral compounds range from
80 to 85 ppm for the Cp ligands and from 122 to 131 ppm for
the cycloheptatriene moiety, respectively. A distinct high-
frequency shift of all of these signals is observed upon hydride
abstraction, which is caused by the positive charge of the
cationic tropylium unit. The signals of the Cp protons shift
about 1 ppm to higher frequency. The degree of high-frequency
shift Δδ of the Cp protons depends on the conjugation length
of the π linker between donor and acceptor: i.e., for n = 0, Δδ =
∼1 ppm, for n = 1, Δδ = 0.7 ppm, and for n = 2, Δδ = ∼0.5
ppm (Table 3). The tendency of decreasing interaction upon
increasing conjugation lengths is also verified by 13C NMR
results (Table 4). Even on the 13C resonance signal of the CBD
ligand a small effect of the conjugation length can be
considered for the sesquifulvalene cation. The shift of the
Figure 2. Molecular structure of the archetypal sesquifuvalene
complex 5. The counterion and the hydrogen atoms are omitted for
clarity.
to the C5-ring ligand, which is in agreement with theoretical
calculations.10,19,20 In contrast, the distance between the Co
atom and the centroid Xcp of the five-membered ring is slightly
reduced (1.684 Å for 5 and 1.683 and 1.682 Å for 12c)
compared to the distance between the Co atom and the
centroid of the C4-ring (1.704 Å for 5 and 1.683 12c,
respectively) (Table 2). Due to the larger ring size, the five-
membered ring immerses better into the coordination sphere of
the Co center than the four-membered ring.
The aryl substituents of the cyclobutadiene ligands in 5 and
12c are all tilted in the ranges of 22.7−64.7 and 23.2−51.8°,
respectively, relative to the plane of the four-membered ring,
and form a four-bladed propeller as found for other arylated η4-
cyclobutadiene ligands in Co complexes (Figure 2).10,15,18 The
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Figure 3. Top view of the molecular structure of the archetypal sesquifulvalene complex 5, illustrating the relative position of the tropylium ring and
the obverse arene substituent. The remaining arene substituents, the counterion, and hydrogen atoms are omitted for clarity.
Figure 4. Molecular structure of 12c. The counterion and the hydrogen atoms are omitted for clarity. Note the disorder in the sesquifulvalene part!
protons of the seven-membered ring amounts to 7.9−8.6 ppm.
A high-frequency shift of more than 20 ppm in comparison to
the neutral complexes is induced by the positive charge for the
signals of the 13C nuclei of the cationic species.
electronic arrangement of the ground state has to be taken into
account in the order Me > H > Cl, indicating a slight decrease
of electron-donating capability in this order, which is in
agreement with the order of the Hammett parameters σp
(Table 5).21
A comparable behavior is found for the redox activity. The
cyclic voltammograms of the cationic tropylium compounds
reveal an electrochemically irreversible oxidation and an
irreversible reduction step. The oxidation occurs in the
characteristic range for (tetraaryl-η4-cyclobutadiene)(η5-
cyclopentadienyl)cobalt(I) complexes10,22,23 and illustrates an
influence of the aryl substituents X, as is observed for the
corresponding carbonyl complexes 6a−e.10 The change of X =
Me to X = Cl induces an anodic shift of the oxidation potential
of about 220 mV, due to the −I effect of the Cl and the +I
hyperconjugative influence of the methyl group.
As for sesquifulvalenes themselves, the bonding situation in
their vinylogous derivatives can in principle be described in
terms of two mesomeric forms: the bis-aromatic form A and the
cross-conjugated form B, which is composed of a η6-fulvene
complex and a cycloheptatriene moiety (Figure 6). In order to
get a deeper insight into the electronic effects of the aryl
substituents X on the ground-state electronic arrangement, the
1H41−1H42 coupling constants across the C41−C42 bond linking
the five- and seven-membered rings of the vinylogous
sesquifulvalene unit have been determined, since the proton
coupling constant 3J(1H41−1H42) increases as the C41−C42
bond order increases.4g From Table 5 a subtle change of
3J(1H41−1H42) can be found in the order X = Cl > H > Me,
which goes along with the corresponding Hammett parameter
σp.21
As a result of the increasing conjugation length between the
electron-donating complex entity and the electron-accepting
tropylium fragment in the complexes 5, 12a and 13 the
electronic interaction decreases in this order. The potential gap
Considering the two limiting mesomeric forms A and B
(Figure 6), a small contribution of the mesomeric form B to the
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a
Table 1. Selected Bond Lengths (Å) of the Tropylium Complexes 5 and 12c
5
12c
13
DFT
Cp ring
exptl
DFT
exptl (A)
exptl (B)
DFT
Co−C(1)
Co−C(2)
Co−C(3)
Co−C(4)
2.073(2)
2.095(3)
2.092(3)
2.077(3)
2.053(3)
1.465(3)
1.471(3)
1.479(3)
1.477(3)
2.013(2)
1.987(2)
1.988(2)
1.990(2)
1.415(4)
1.411(4)
1.374(4)
1.406(5)
1.354(6)
1.400(5)
1.369(4)
2.1352
2.1160
2.1343
2.1363
2.1114
1.4640
1.4641
1.4656
1.4639
2.0098
2.0125
1.9974
2.0025
1.4238
1.4238
1.3717
1.4120
1.3692
1.4118
1.3718
1.999(8)
2.016(9)
2.109(8)
2.148(8)
2.083(8)
2.062(8)
2.074(9)
2.081(8)
2.083(8)
2.046(8)
2.1244
2.1150
2.1412
2.1167
2.1291
1.449
2.1416
2.1161
2.1268
2.1278
2.1162
1.467
Co−C(5)
C(6)−C(10)
C(7)−C(16)
C(8)−C(22)
C(9)−C(28)
Co−C(6)
Co−C(7)
Co−C(8)
Co−C(9)
C(34)−C(35)
C(34)−C(40)
C(35)−C(36)
C(36)−C(37)
C(37)−C(38)
C(38)−C(39)
C(39)−C(40)
1.448(9)
1.464(9)
1.458(9)
1.480(9)
1.991(6)
2.002(6)
1.991(7)
1.982(6)
1.4584
1.4680
1.4678
1.9867
2.0057
2.0140
2.0282
1.4310
1.4304
1.3673
1.4178
1.3647
1.4191
1.3663
1.4608
1.4653
1.4607
1.9899
2.0049
2.0143
2.0191
1.4315
1.4332
1.3654
1.4202
1.3631
1.4215
1.3647
1.457(7)
1.430(7)
1.368(11)
1.151(13)
1.546(6)
1.578(9)
1.542(8)
1.457(2)
1.368(2)
1.557(3)
1.328(4)
1.557(3)
1.587(3)
1.352(2)
a
The notations A and B define the two disordered fragments in the asymmetric unit. The errors for 12c correspond to a restraint to the distances of
the other disordered fragment (see also the Experimental Section).
Table 2. Selected Interatomic Distances (Å) and Angles
a
(deg) of the Tropylium Complexes 5 and 12c
5
12c (A)
12c (B)
22.70
39.80
31.30
64.70
6.50
33.40
23.20
51.80
36.00
b
b
b
CBD(6−9)/Ph(16−21)
CBD(6−9)/Ph(22−27)
CBD(6−9)/Ph(28−33)
b
Cp(1−5)/CBD(6−9)
177.00
177.50
b
Cp(1−5)/Trop(34−40)
13.90
175.20
179.60
c
XCp−C(1)−C(34)
c
XTrop−C(34)−C(1)
XCp−C(1)−C(41)
c
175.00
177.50
1.683
177.50
178.30
1.682
c
XTrop−C(34)−C(42)
b
Co−Cp(1−5)
Co−CBD(6−9)
XPh(10−15)−XTrop
1.689
1.704
3.975
4.159
3.721
b
1.697
c
Figure 5. Crystal packing of 12c.
c
XPh(10−15)−C(34)
C(10)−C(34)
XPh(16−21)−C(41)
XPh(16−21)−C(42)
c
fragment orbital. The major contribution to the LUMO comes
from a C5 bridge−C7 π fragment orbital.
3.774
3.770
3.328
c
In the HOMO the C4 ring and two of the phenyl π orbitals
dominate together with a Co dxz orbital. The C5 bridge−C7 π
orbitals have also significant coefficients in the HOMO, which
is in accord with the electrochemical studies which revealed the
oxidation as well as the reduction to be dependent on the
length of the bridge between the five- and seven-membered
rings.
C(16)−C(34)
a
The notations A and B define the disordered fragments within the
b
asymmetric unit. Angles between the best planes of CBD, Cp, phenyl,
and tropylium. X = centroid of the corresponding cycle: XCp
centroid of the C5-ring ligand; XCBD = centroid of the C4-ring ligand;
Xtrop = centroid of the tropylium ring.
c
=
Along these lines are the electrochemical data for complexes
12a−c, in which the shift of the oxidation potential is within the
expected direction of electronic influence of the phenyl
substituents, which is 220 mV for the oxidation and only
about 40 mV for the reduction potential.
Electronic Excitation. The most remarkable feature during
the synthesis of the dipolar mononuclear tropylium complexes
is the dramatic change of color upon hydride abstraction. In all
for 13 is found to be about ∼480 mV smaller than observed for
5 (Table 6, Figure7)
Calculation of the molecular orbitals of the complexes
revealed the frontier orbitals depicted in Figure 8. The LUMO
2
results from a combination of a Co dz type orbital with the z
axis in the equatorial plane spanned by the C4 and C5 ring
ligands and a small contribution of a nonbonding C4 ring π
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Table 3. 1H NMR Shifts of the Cyclopentadienyl Signals of the Neutral Cycloheptatriene and Cationic Tropylium Compounds
a
b
cycloheptatriene
X = Me
tropylium
X = Cl
c
d
n
X
= H
X = Cl
X = OMe
X = NMe2
X = H
X = Me
0
4.63
4.86
4.66
4.72
4.67
4.69
4.67
4.70
5.62
5.88
5.36
5.42
5.16
5.25
1
2
3
4.65
4.71
4.64
4.67
4.63
4.68
4.58
4.64
5.36
5.46
5.35
5.39
a
b
c
Measured in dichloromethane-d2. Measured in nitromethane-d3. n = number of C−C double bonds between the five- and seven-membered ring.
d
X = substituent in para position of the aryl group.
Table 4. 13C NMR Shifts of the Cyclopentadienyl Signals of the Neutral Cycloheptatriene and Cationic Tropylium Compounds
a
b
cycloheptatriene
tropylium
Cp
CBD
Cp
CBD
c
d
n
X
= H
X = Cl
X = Me
X = H
75.6
X = Cl
X = Me
75.4
X = H
X = Cl
X = Me
X = H
82.2
X = Cl
X = Me
80.9
0
79.7
85.2
80.9
85.3
81.3
84.9
85.8
94.5
85.9
91.7
85.1
90.6
1
2
81.1
85.2
80.6
84.8
75.9
76.0
74.7
86.1
92.2
85.9
92.1
80.6
79.8
78.9
a
b
c
Measured in dichloromethane-d2. Measured in nitromethane-d3. n = number of C−C double bonds between the five- and seven-membered rings.
d
X = substituent in para position of the aryl group.
Figure 6. Bis-aromatic (A) and cross-conjugated (B) mesomeric forms
of the dipolar mononuclear vinylogous sesquifulvalene derivatives of
(η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt(I).
1
Table 5. Correlation between the H NMR Coupling
Constants and the σp Values of the Aryl Substituents X
Figure 7. Cyclic voltammograms of the tropylium compounds 5, 12a,
and 13.
b
X
σp
3J (Hz)
a
a
12a
H
0
15.48
15.63
15.14
hexafluoridophosphate is added to a solution of the cyclo-
heptatriene compounds. The color change is in accord with a
strong increase of the donor−acceptor interaction.4a,6c The
enhancement of the electronic communication between
electron donor and acceptor can be observed in UV−vis
studies, which were performed with solutions of different
solvent polarities, i.e. dichloromethane and nitromethane, to
12b
Cl
0.23
−0.17
a
12c
CH3
a
b
In CD2Cl2. σp values from ref 21.
cases the color immediately changes from orange-red to dark
blue or green, when the light yellow solution of trityl
Table 6. Cyclic Voltammetric Data of the Tropylium-Substituted (Tetraaryl-η4-cyclobutadiene)(η5-cyclopentadiendiyl)cobalt(I)
Complexes
b
ce
,
cf
,
d
compd
X
n
σp
Epa (mV)
Epc (mV)
ΔE (mV)
ΔE(LUMO−HOMO) (hartree)
5
H
0
1
2
1
1
0
0
0
841
626
535
781
558
−779
−660
−611
−635
−678
1620
1286
1146
1416
1236
0.076
0.067
0.060
12a
13
H
H
12b
12c
Cl
0.23
CH3
−0.17
0.064
a
b
c
Scan rate 200 mV s−1. σp values from ref 21. Condtions: vs FcH/FcH+ in MeNO2, 0.4 M [n-Bu4N][PF6], room temperature, reference electrode
d
e
f
Ag/AgCl. ΔE = Epa − Epc. Irreversible oxidation. Irreversible reduction.
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Figure 10 displays the influence of the conjugation length n
between the donor and the acceptor: with the increase of the
conjugation length n, the absorption maxima shift to lower
wavelength. Remarkably, the extinction coefficient ε of the low-
energy absorption grows with the extent of the bathochromic
shift, which is in accord with the results from the
solvatochromic measurements. The ratio of charge localization
(dipole) and delocalization in the excited state would lead to an
increased transition dipole moment and thus to a higher
extinction coefficient.
In accordance with the results of others27 and from our
results28 with a ferrocene and ruthenocene moiety and in
particular with our MO calculations (vide supra) of the
(Ar4CBD)CoCp complexes as the electron donor, the high-
energy absorption band is assigned to a metal-donor-ligand to
acceptor charge-transfer (DL-A CT) transition, whereas the
low-energy absorption band is caused by a cyclobutadiene-
metal-donor to acceptor charge-transfer (DM-A CT) transition.
An experimental indication for the assignment of the high-
energy absorption band to the DL-A CT band is the influence
of the conjugation length on the solvatochromic effect, which
almost doubles on going from the archetypal sesquifulvalene
complex 5 (Δν = −689 cm−1) to the butadiene-bridged
derivative 13 (Δν = −1357 cm−1), since the polarizability is
increased with growing conjugation length of the π-bonding
system, whereas the low-energy CT absorption reveals a change
of Δν = −1139 cm−1 for 5 and Δν = −1526 cm−1 for 13. A
comparison of the positions of the absorption maxima for the
cobalt sandwich compounds illustrates a weak dependence of
λmax on the electron-releasing capability of the aryl substituent
X (Figure 10). However, a closer look at the UV−vis
spectroscopic data (Table 7) discloses that the absorption
coefficient of the low-energy absorption band is considerably
stronger for the Co species in comparison to the Fe congeners.
The extinction coefficient of the long-wavelength absorption of
the chromophore 13 exceeds that of the corresponding Fe
complex by a factor of 2.6e This must have a strong influence on
the first hyperpolarizability β, since the electronic transition
moment directly depends on the absorption coefficient and,
according to the two-level model, the first hyperpolarizability β
is proportional to the square of the electronic transition
moment.
To reveal information on the character of electronic
excitations, we performed calculations on the density functional
level of theory on optimized structures in the gas phase (see
below). The resulting calculated excitations are in good
agreement with the experimental data and are given in Table
7. For interpretation a natural transition orbital analysis was
performed,38 revealing orbitals depicted in Figure 10 for the
low-energy and Figure 11 for the high-energy transition. While
for the low-energy transition an almost pure one natural orbital
to one natural orbital transition is found, the high-energy
transition consists of two transitions with contributions of 83%
and 11% (Figure 11). Some conclusions can be drawn from the
calculations.
Figure 8. LUMO (top) and HOMO (bottom) of complex 12c.
elucidate solvatochromism, which gives a clue to the dipole
change Δμ between the ground and excited states upon
electronic excitation24 and is thus relevant for the first
hyperpolarizability β according to the two-level approxima-
tion.25
The UV−vis spectra of the complexes under study contain
two strong absorption bands in the visible and near-UV region,
which are characteristic for dipolar sandwich complexes bearing
NLO chromophores. The solvatochromism of the cobalt
complexes is negative and is quite similar to those found for
the corresponding ferrocene derivatives (Figure 9, Table 7).6c
This implies the positive charge to be mainly localized on the
seven-membered ring in the electronic ground state, whereas it
is delocalized over the complex entity in the electronic excited
state.26
In the low-energy transition the cyclobutadiene ligand as well
as the metal center and the C5 bridge−C7 fragment contribute
to the hole of the transition, while the particle is mainly located
on the acceptor site with small contributions of the metal
center and cyclobutadiene ligand.
Upon extension of the bridge the hole appears to be more
localized on the metal complex site while the particle remains
from the metal center to the acceptor fragment. A strong
Figure 9. UV−vis spectra of the vinylogous sesquifulvalene complex
12a recorded in solvents of different polarities to illustrate the
solvatochromic effect.
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Table 7. UV−Vis Data of the Dipolar, Mononuclear Sesquifulvalene CBDCo Complexes
DL-A CT
DM-ACT
TD-DFT nm,
TD-DFT nm,
cm−1
a
b
a
b
a
b
a
b
X
n
CH2Cl2 νmax
̃
(ε)
CH3NO2 νmax
̃
(ε)
Δν
̃
cm−1
CH2Cl2 νmax
̃
(ε)
CH3NO2 νmax
̃
(ε)
Δν
̃
5
H
0
1
2
1
1
25 907 (21 420)
22 075 (17 577)
19 920 (21 646)
22 222 (35 870)
21 277 (25 426)
26 596 (14 745)
23 041 (8 276)
21 277 (18 589)
23 364 (15 393)
22 321 (15 228)
−689
−966
−1357
−1142
−1044
414, 24 155
433 23 095
457 21 882
15 528 (8 526)
13 908 (19 427)
12 821 (40 385)
14 164 (35 656)
13 228 (23 530)
16 667 (7 135)
15 128 (9578)
14 347 (32 918)
15 383 (15 335)
14 327 (14 163)
−1139 719, 13908
−1220 786, 12 723
−1526 808, 12 376
−1221
−1099 832, 12 019
852, 11 737
12a
13
H
H
12b
12c
13c
Cl
CH3
436, 22 936
499, 20 040
CH3
a
b
c
In cm−1. In M−1 cm−1. Δν
̃
= 1/λmax(CH2Cl2) − 1/λmax(CH3NO2).
state) of the transition. Generally, in the MO picture an
extension of a π system will lower the energy of the LUMO and
increase the energy of the HOMO. Here an extension of the
bridge leads to a large effect on the low-energy transition due to
stabilization of the LUMO and also on the high-energy
transition due to an increase of the HOMO and decrease of the
LUMO upon bridge extension as well as variation of
substituents on the phenyl rings of the cyclobutadiene ring
(Figure 12).
Figure 10. Representative UV−vis spectra of the mononuclear cationic
vinylogous sesquifulvalene complexes with different conjugation
lengths n.
Figure 12. Natural transition orbital pairs of DL-A CT transition in 13.
The natural orbital pairs contribute 11% (top) and 83% (bottom) to
the excitation.
Figure 11. Natural transition orbital pairs of DMA-CT transitions. The
natural orbital pairs contribute to 96% (5), 98% (12a) and 98% (13)
to the excitations.
Figure 13. UV−vis spectra of [Ar4(CBD)Co(Cp-Z-C7H6)]+ com-
plexes with different aryl substituents X and the same olefinic linker (Z
= −(C2H2)−).
influence of the phenyl substituents on the hole and thus on the
transition is anticipated, since only one state is influenced. This
is in agreement with the observed bathochromic shift upon
extension of the π-conjugated bridge. These influences to a
different extent can be observed in a significant decrease of the
HOMO−LUMO (Table 6).
For the high-energy transition a mixture of two transitions
with strong metal complex contribution in the hole and strong
π-acceptor orbitals on the particle site was found from the
natural transition orbital analysis. In accord with previous
conclusions the influence of the bridge length on the high-
energy transition can be envisaged due to the different
contributions of metal complex fragment and the C5 bridge−
C7 fragment to the hole (ground state) and the particle (excited
Nonlinear Optical Studies. The low-lying excited states,
the facile polarizability concluded from the pronounced
solvatochromism, and the assignment of the intense charge
transfer transition bands in the near-UV and, in particular, the
visible region, which are both assigned to donor−acceptor
transitions, make these sesquifulvalene cobalt complexes very
promising for second harmonic generation (SHG). Therefore,
these cationic complexes were subjected to hyper-Rayleigh
scattering (HRS)29 studies, which is the only method for
determining the first hyperpolarizability β of charged
compounds. However, an intrinsic drawback of this method
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Figure 14. Absorption and emission spectra of compounds 12a (A), 13 (B), and 12b (C).
is the fluorescence due to two-photon absorption. This
problem has been discussed in previous publications4e,6e and
can be partially solved, among other means,30 by introducing
band-pass filters with peak transmittance at different wave-
lengths in front of the photomultiplier of the HRS setup.1l,4e
The broad fluorescence signal, which reveals the emission
maximum at λ/2 of the fundamental wavelength, is easily
discriminated from the narrow second harmonic signal.
Figure 14 displays the absorption spectra and the emission
spectra obtained from HRS experiments, which indicate that a
weak intensity of fluorescence is overlapping the λ/2 signal. As
a consequence, the β values in Table 8, which are very large
compared to those of other sandwich-type NLO chromo-
phores, are too large when calculated. However, another
important conclusion can be drawn from the HRS study: the
low-energy CT transition plays an important role in the SHG
effect. It is quite obvious that in more polar solvents the SHG
Table 8. First Hyperpolarizability β of the Compounds 11,
12a−c, and 13 Determined by HRS Measurements
compd
X
n
solvent
λmax (nm)
β (10−30 esu)
11
H
0
CH2Cl2
MeNO2
CH2Cl2
MeNO2
CH2Cl2
MeNO2
CH2Cl2
MeNO2
CH2Cl2
MeNO2
386/644
376/600
453/719
434/661
502/780
470/697
450/706
428/650
470/756
448/698
b
b
a
12a
13
H
1
2
1
1
−504
−600
−448
−881
−400
−665
−498
−613
a
a
H
a
a
12b
12c
Cl
a
CH3
a
a
b
Two-photon absorption−fluorescence. No HRS intensity detect-
able.
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signal is distinctly larger (Table 8). This effect is caused by the
resonance enhancement due to the hypsochromic shift of the
low-energy CT transition, which thus becomes less separated
from the λ/2 value and contributes more to the intensity of the
SHG signal.
excitation in the near-UV and vis region is coupled with a
dipole change.
EXPERIMENTAL SECTION
■
Manipulations were carried out under a dry nitrogen atmosphere using
standard Schlenk techniques. All solvents were saturated with nitrogen.
Diethyl ether (Et2O), tetrahydrofuran (THF), n-hexane, and toluene
were freshly distilled from the appropriate alkali metal or metal alloy.
Dichloromethane (CH2Cl2) and nitromethane (MeNO2) were dried
over calcium hydride. NMR: Varian Gemini 200 BB; Bruker AM 360;
measured at 295 K relative to TMS. UV−vis: Perkin-Elmer Model 554.
IR: KBr pellets, FT-IR, Perkin-Elmer Model 325. MS: Finnigan MAT
311 A (EI-MS). Elemental analyses: CHN-O-Rapid, Fa. Heraeus,
CONCLUSIONS
■
A series of cationic monometallic dipolar sesquifulvalene
complexes [(Ar4-η4-CBD)Co{(η5-C5H4)Z(C7H6)]+ (Ar = p-
C6H4X, X = Cl, H, Me; Z = −(C2H2)n−, n = 0−2) were
synthesized and spectroscopically and (for two of them, 5 and
12c) also structurally characterized. Attempts to prepare the
complexes [(Ar4-η4-CBD)Co{(η5-C5H4)Z(C7H6)}]+ (Ar = p-
C6H4X, X = OMe, NMe2; Z = −C2H2−) and [(Ar4-η4-
CBD)Co{(η5-C5H4)Z(C7H6)}]+ (Ar = C6H5; Z = −(C2H2)3−)
failed and led to decomposition of the products, probably due
to an irreversible oxidation and sensitivity to strong Lewis
acidity, respectively. In the sesquifulvalene complexes the
sandwich units (Ar4CBD)CoCp act as electron donors and the
positively charged tropylium moieties as electron acceptors.
From NMR spectroscopic and cyclic voltammetric data a
decreased donating ability of the sandwich unit is concluded:
12c (X = Me) > 12a (X = H) > 12b (X = Cl). The decreased
donating capability in this order is confirmed by the UV−vis
measurements, where two strong absorption bands are
recorded and absorption maxima are slightly bathochromically
shifted with growing donor capability. In accordance with our
DFT calculations, the high-energy band is assigned to a donor
ligand (DL)−acceptor ligand (A) charge transfer (CT)
transition while the low-energy band is caused by a donor
cyclobutadiene metal (DM)−A CT transition. It is worth
mentioning that the extinction coefficient for the DM-A CT
transition for 13 (X = H, Z = −(CHCH)2−) is about 2 times
more intense than for the DM-A CT transition of the
corresponding ferrocene derivative. The spectroscopic results
indicate that NLO chromophores with (CBD)CoCp as donor
functionalities are very promising. The SHG effect was
measured at the fundamental wavelength of λ = 1064 nm by
means of hyper-Rayleigh scattering (HRS) and reveal values for
the first hyperpolarizabilities β, which belong to the largest ever
obtained for sandwich-type NLO chromophores despite a weak
fluorescence overlapping at λ/2. The reason for the exception-
ally large SHG effect is a strong resonance enhancement caused
by two CT transitions which are coupled with a large dipole
change.
Zentrale Elementanalytik, Fachbereich Chemie, Universitat Hamburg.
̈
The (tetraaryl-η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt(I) car-
baldehyde complexes 6a−e,10 cycloheptatrienylmethyl phosphonate
diethyl ester,6e and (tetraphenyl-η4-cyclobutadiene)(chloromercurio-
η5-cyclopentadienediyl)cobalt(I) (2)7 were synthesized as published.
X-ray Structure Determination. Crystals of the compounds 5
and 12c suitable for a structure determination were obtained by gas-
phase diffusion of Et2O into a CH2Cl2 solution of the corresponding
complex. The data were collected on a Hilger and Watts Y290 four-
circle diffractometer at 293 K (5) and 173 K (12c) (Mo Kα radiation,
λ = 0.710 73 Å). The structures were solved by direct methods
(SHELXS-86), and the refinement on F2 was carried out by full-matrix
least-squares techniques (SHELXL-97).31 All non-hydrogen atoms
were refined with anisotropic thermal parameters. The hydrogen
atoms were refined with a fixed isotropic thermal parameter related by
a factor of 1.2 to the value of the equivalent isotropic parameter of
their carrier atom. Weights were optimized in the final refinement
cycles. For the structure of compound 12c the disorder was resolved
and disordered fragments were constrained to have similar distances
within σ = 0.001.
Crystallographic data for the structures reported in this paper (see
also Table 9 in the Supporting Information) have been deposited at
the Cambridge Crystallographic Data Centre as supplementary
publication nos. CCDC-891916 (5) and CCDC-891923 (12c).
Copies of the data can be obtained free of charge on application to
the CCDC, 12 Union Road, Cambridge CB2 1EZ, U.K. (fax,
(internat.) +44-1223/336-033; e-mail, deposit@ccdc.cam.ac.uk].
Hyper-Rayleigh Scattering. Hyper-Rayleigh scattering measure-
ments were performed with a pulsed Nd:YAG laser at a wavelength of
λ 1064 nm. For the experimental setup see ref 29. Solutions of the
complexes in MeNO2 with concentrations in the range of 10−4−10−6
M were used with p-nitroaniline as a reference (β(MeNO2) = 34.6 ×
10−30 esu).32 Fluorescence checks were made by replacement of the
interference filter at the entrance of the photomultiplier tube using
filters with transmittances at 400, 450, 500, 532, 560, 600, 650, and
700 nm.6e
DFT Calculations. Geometry optimization of complex 5, 12c, and
13 revealed the geometrical parameters given in Table 1 in agreement
with experimental data. To reveal information on bonding and charge
transfer in these complexes, NBO analyses were performed.33
For all calculations at the density functional theory level, the
program Gaussian09 was used.34 For geometry optimization the
energies were corrected for nonlocal exchange and for nonlocal
correlation according to Becke's three-parameter functional B3LYP.35
The def2-TZVP-split valence basis set was used for all atoms.36
Optical excitations were calculated employing the TD-DFT37
method on optimized geometries of complexes 5, 12c, and 13. All
stationary points were checked by second-derivative calculations,
revealing no imaginary frequencies.
Cyclic Voltammetry. Measurements were performed in MeNO2
with 0.4 M [N(n-Bu)4]PF6 as supporting electrolyte. An Amel 5000
system was used with a Pt wire as working electrode and a Pt plate (0.6
cm2) as an auxiliary electrode. The potentials were measured against
Ag/AgCl and are referenced against E1/2([Fe(C5H5)2]/[Fe(C5H5)2]+)
= 0.
The results from the DFT calculations and subsequent
natural transition orbital analysis further allow a reliable
assignment of the electronic excitation. The DFT calculations
confirm the HOMOs to be mainly donor localized, whereas the
LUMOs are predominantly acceptor based. The cyclobutadiene
ligand has a strong influence on the donor orbitals, while the
tropylium ligand has a strong influence on the acceptor unit.
Thus, the absorption depends on the substituents on the
cyclobutadiene ligand. The length of the bridge has an influence
on the hole and particle orbitals. Upon extension of the bridge
the hole orbital becomes destabilized while the particle state
becomes more stabilized, resulting in a bathochromic shift of
the excitations. Due to the strong charge transfer character
from the cyclobutadiene metal donor to the Cp bridge
tropylium acceptor, the transition dipole moment increases
upon extension of the bridge, thus increasing the absorption
intensity of the electronic excitation. Hence, every electronic
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(Tetraphenyl-η4-cyclobutadiene)(cyclohepta-2′,4′,6′-trien-
1′-yl-η5-cyclopentadienyl)cobalt(I) (4a). [{(C6H5)4CBD}Co-
(CpHgCl)] (2; 140 mg, 0.20 mmol) was dissolved in diethyl ether
(15 mL) and cooled to −70 °C. A hexane solution of Li-n-Bu (1.5 M,
0.26 mL, 0.39 mmol) was added at −70 °C. The reaction mixture was
warmed to room temperature and was stirred for an additional 15 min.
The yellow solution was cooled again to −70 °C. Tropylium
hexafluorophosphate (47 mg, 0.20 mmol) was added, and the reaction
mixture was warmed to room temperature. After the mixture was
stirred for an additional 3 h the solvent was evaporated. The solid
residue was purified by column chromatography (Al2O3 neutral, 5%
water, hexane).
5.97 (dd, 3J = 9.40 Hz, 6.00 Hz, H-3′ (4b)), 6.40 (d, 3J = 6.20 Hz, H-
2′ (4b)), 7.11−7.25 (m, Hm,p (4b,c), Hm,p (1)), 7.34−7.55 (m, Ho
(4b,c), Ho (1)). Since the product consists of three different
complexes, assignment of the number of hydrogen atoms was not
carried out. 13C NMR: (50 MHz, CD2Cl2, δ in ppm): 28.01 (C-5′
(4b)), 75.56 (CBD (4b,c), CBD (1)), 79.74 (Cp (4b,c)), 83.50 (Cp
(1)), 85.18 (Cp (4b,c)), 93.80 (Cq-Cp (1)), 100.05 (Cq-Cp (4b)),
120.64 (C-4′ (4b)), 120.70 (C-6′ (4b)), 126.40 (Cp (4b,c)), 126.40
(C-2′ (4b)), 126.45 (C-7′ (4b)), 126.60 (Cp (1)), 126.87 (C-3′ (4b)),
128.25 (Cm (4b,c)), 128.28 (Cm (1)), 129.06 (Co (4b,c)), 129.18 (Co
(1)), 135.78 (C-1′ (4b)), 136.31 (Ci (4b,c), Ci (1)).
General Synthesis of the Vinylogous Cycloheptatriene
Complexes: [{(4-XC6H4)4CBD}Co{Cp-(E)-(CHCH)nCHT}] (n = 1,
X = H, Cl, Me, OMe, NMe2; n = 2, X = H; n = 3, X = H). The
aldehyde complexes (6a − 6e, 7, 8) and two equivalents of cyclohepta-
1′,3′,5′-trien-1′-ylmethyl-phosphonate diethylester are dissolved in
benzene. The same volume of soda lye (50%) and a small amount of
tetrabutylammonium bromide was added. The reaction mixture was
vigorously stirred under reflux for 2.5 until 10 h. The progress of the
reaction was monitored by thin layer chromatography. Finally, the
reaction mixture was hydrolyzed and extracted with diethyl ether. The
organic layers were combined, dried over magnesium sulfate,
concentrated and chromatographed. The numbering scheme is given
in Chart 2.
1
A H NMR spectrum (see Chart 1 for numbering scheme) of the
product revealed a mixture of (tetraphenyl-η4-cyclobutadiene)-
Chart 1. Numbering Scheme of the Cycloheptatrienyl
Substituent and the Related Isomers 4a−c
(cyclohepta-2′,4′,6′-trien-1′-yl-η5-cyclopentadienediyl)cobalt(I) (4a)
and the starting material (tetraphenyl-η4-cyclobutadiene)(η5-
cyclopentadienyl)cobalt(I) (1) in a ratio of 9:1. Yield: 60 mg of a
mixture of [{(C6H5)4CBD}Co(Cp-2′,4′,6′-CHT)] (4a; CHT =
cacloheptatriene) and [{(C6H5)4CBD}CoCp] (1). Since the solubil-
ities of the starting compound 1 and the desired cation 5 would be
quite different, further purification of complex 4a was not carried out.
1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.21 (t, 3J = 5.74 Hz, 1 H,
H-1′ (4a)), 4.56 (m, 2 H, Cp (4a)), 4.63 (s, Cp (1)), 4.68 (m, 2 H,
Chart 2. Numbering Scheme for the Unsaturated Bridge
Connecting the Five- and Seven-Membered Rings and for
the Cycloheptatrienyl Substituent
3
Cp (4a)), 5.02 (dd, J = 8.79 Hz, 5.86 Hz, 2 H, H-2′/7′ (4a)), 5.91
(m, 2 H, H-3′/6′ (4a)), 6.55 (dd, 3J = 3.41 Hz, 2.69 Hz, 2 H, H-4′/5′
(4a)), 7.15−7.26 (m, 12 H, Hm,p (4a), Hm,p (1)), 7.39−7.47 (m, Ho
(4a), Ho (1)). For the remaining starting material 1 and in cases when
the resonance signals of the desired complex 4a display a superposition
with the signals of compound 1, no number of protons are assigned.
13C NMR: (50 MHz, CD2Cl2, δ in ppm): 37.53 (C-1′ (4a)), 75.17
(CBD (4a), CBD (1)), 81.52 (Cp (4a)), 83.48 (Cp (1)), 83.71 (Cp
(4a)), 101.68 (Cq-Cp (4a)), 124.13 (C-3′/6′ (4a)), 125.83 (C-2′/7′
(4a)), 126.44 (Cp (4a), Cp (1)), 128.26 (Cm (4a), Cm (1)), 129.14
(Co (4a), Co (1)), 131.05 (C-4′/5′ (4a)), 136.68 (Ci (4a), Ci (1)). EI-
MS (m/z (%)): 570 (47) [M+ (4a)], 480 (56) [M− -CHT (4a), M+
(1)], 415 (12) [{(C6H5)4-CBD}Co+], 214 (67) [CoCpCHT+], 91
(34) [CHT+ (26)], 58 (26) [Co+].
(E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)-
cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9a):
[{(C6H5)4CBD}CoCpCHO] (6a; 526 mg, 1.03 mmol), cyclohepta-
1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (498 mg, 2.06
mmol), benzene (25 mL), soda lye (50%) (5 mL), 9 h reflux, column
chromatography Al2O3 neutral, 5% water, hexane/diethyl ether 2/1.
Yield: 466 mg (0.78 mmol, 75.5%) orange-red solid material of 9a.
Anal. Calcd for C42H33Co (596.5): C, 84.54; H, 5.58. Found: C, 84.38;
H, 5.86. Mp: 164 °C. IR (KBr, cm−1): 3080, 3059, 3019 (CH)Ph, 2953,
2922, 2874 (CH2), 1676 (CC), 1596, 1498, 1443 (CC)Ph, 1125,
1026 (CC)Cp, 970 (CCH), 747, 706 (CH). EI-MS (m/z, (%)):
597 (5) [M+], 357 (16) [{(C6H5)4CBD}+], 180 (4) [Cp(CH
Isomerization of (Tetraphenyl-η4-cyclobutadiene)-
(cyclohepta-2′,4′,6′-trien-1′-yl-η5-cyclopentadienediyl)cobalt-
(I) (4a) to (Tetraphenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,6′-
trien-1′-yl-η5-cyclopentadienediyl)cobalt(I) (4b) and (Tetra-
phenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,5′-trien-1′-yl-η5-
cyclopentadienyl)cobalt(I) (4c). The isomer [{(C6H5)4CBD}Co-
(Cp-2′,4′,6′-CHT)] (4a; 15 mg, 0.03 mmol) was dissolved in p-xylene
(2 mL). After the mixture was heated at 140 °C for 1 day, the solvent
1
CH)CHT+], 124 (23) [CpCo+]. H NMR (200 MHz, CD2Cl2, δ in
ppm): 2.30 (d, 3J = 7.1 Hz, 2 H, H-7′exo/endo), 4.66 (m, 2 H, Cp), 4.72
(m, 2 H, Cp), 5.20 (dt, 3J = 9.28 Hz, 7.08 Hz, 1 H, H-6′), 5.98 (d, 3J =
5.13 Hz, 1 H, H-2′), 6.07 (d, 3J = 16.11 Hz, 1 H, H-2), 6.17 (dd, 3J =
9.52 Hz, 4.40 Hz, 1 H, H-5′), 6.18 (d, 3J = 16.11 Hz, 1 H, H-1), 6.53
(2dd, 3J = 9.90 Hz, 5.01 Hz, 4.39 Hz, 2 H, H-3′/4′), 7.16−7.23 (m, 12
H, Hm,p), 7.37−7.43 (m, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ in
ppm): 27.84 (C-7′), 75.94 (CBD), 80.93 (Cp), 85.30 (Cp), 95.96
(Cq-Cp), 122.33 (C-6′), 123.59 (C-2), 125.53 (C-2′), 126.55 (Cp),
127.60 (C-1), 128.28 (Cm), 129.06 (Co), 129.93 (C-4′), 130.08 (C-
5′), 131.05 (C-3′), 132.31 (C-1′), 136.34 (Ci).
1
was stripped off in vacuo. H NMR spectra show that a mixture of
(tetraphenyl-η4-cyclobutadiene)(cyclohepta-1′,3′,6′-trien-1′-yl-η5-cy-
clopentadienediyl)cobalt (4b), (tetraphenyl-η4-cyclobutadiene)-
(cyclohepta-1′,3′,5′-trien-1′-yl-η5-cyclopentadienediyl)cobalt (4c),
and (tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienyl)cobalt (1)
is formed in a ratio of 8:1:1. For 4c not all resonance signals could
be assigned, due to low content and superposition with other signals.
Yield: 15 mg of a mixture of [{(C6H5)4CBD}Co(Cp-1′,3′,6′-
CHT)] (4b), [{(C6H5)4CBD}CoCp-1′,3′,5′-CHT] (4c) and
[{(C6H5)4CBD}CoCp] (1)). EI-MS (m/z (%)): 570 (100) [M+
(4b,c)], 480 (12) [M+ − CHT (4b,c), M+ (1)]. 1H NMR (200
MHz, CD2Cl2, δ in ppm): 1.96 (t, 3J = 6.80 Hz, H-5′exo/endo (4b), 2.07
(d, 3J = 7.08 Hz, H-7′exo/endo (4c)), 4.63 (m, Cp (4b,c), Cp (1)), 4.86
(m, Cp (4b,c)), 5.14 (dt, 3J = 9.60 Hz, 7.00 Hz, H-6′ (4b)), 5.35 (dt,
(E,E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)-
cobalt(I)]-4-(cyclohepta-1′,3′,5′-trien-1′-yl)-1,3-butadiene (10):
{(C6H5)4CBD}CoCp-(E)-(CHCH)CHO (7; 134 mg, 0.24
mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester
(121 mg, 0.48 mmol), benzene (15 mL), soda lye (50%) (5 mL), 6 h
reflux, column chromatography Alox neutral, 5% water, hexane/diethyl
ether 5/1.
Yield: 124 mg (0.20 mmol, 79.5%) orange-red solid material. Anal.
Calcd for C44H35Co(H2O) (640.71): C, 82.48; H, 5.82. Found: C,
3
3J = 9.20 Hz, 6.80 Hz, H-4′ (4b)), 5.87 (d, J = 9.52 Hz, H-7′ (4b)),
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82.63; H, 5.88. Mp: 130 °C. IR (KBr, cm−1): 3022 (CH)Ph, 2924, 2851
(CH2), 1596, 1498, 1443 (CC)Ph, 1025 (CC)Cp, 979 (CCH),
744, 705 (CH). EI-MS m/z (%): 623 (79) [M+], 416 (94)
[{(C6H5)4CBD}Co+], 266 (67) [CoCp(CHCH)2CHT+]. 1H
Yield: 31 mg (0.05 mmol) orange-red solid material (67.4%). Mp:
230 °C. Anal. Calcd for C46H41Co (H2O) (M = 670.78): C, 82.37; H,
6.46. Found: C, 82.44; H, 6.82. IR (KBr, cm−1): 3084, 3025 (CH)Ph,
2918, 2855 (CH3), 1654 (CC), 1618, 1516, 1438 (CC)Ph, 1380
(CH3), 1110, 1018 (CC)Cp, 952 (CCH), 809 (CH). EI-MS (m/z
(%)): 652 (100) [M+], 471.6 (43) [{(4-CH3C6H4)4CBD}Co+], 240.3
(91) [CoCp-(CHCH)CHT+], 57 (79) [Co+]. 1H NMR (200 MHz,
CD2Cl2, δ in ppm): 2.26 (s, 12 H, CH3), 2.30 (d, 3J = 7.10 Hz, 2 H, 1
H-7′exo/endo), 4.62 (m, 2 H, Cp), 4.67 (m, 2 H, Cp), 5.21 (dt, 3J = 9.03
3
NMR (200 MHz, CD2Cl2, δ in ppm): 2.59 (d, J = 7.08 Hz, 2 H,
H-7′exo/endo), 4.67 (m, 3J = 2.00 Hz, 2 H, Cp), 4.69 (m, 2 H, Cp), 5.44
(m, 7.20 Hz, 1 H, H-6′), 5.75 (d, 3J = 15.63 Hz, 1 H, H-4), 6.02−6.32
3
(m, 5 H, H-1/2/3, H-2′/5′), 6.56 (2dd, J = 10.07 Hz, 5.86 Hz, 4.27
Hz, 2 H, H-3′/4′), 7.16−7.24 (m, 12 H, Hm,p), 7.36−7.42 (m, 8 H,
Ho). 13C NMR (50 MHz, CD2Cl2, δ in ppm): 28.18 (C-7′), 76.00
(CBD), 81.29 (Cp), 84.88 (Cp), 96.06 (Cq-Cp), 122.74 (C-6′),
126.01 (C-4), 126.52 (Cp), 127.06, 127.88, 128.84, 130.32, 132.97 (C-
2′/5′, C-1,2,3), 128.28 (Cm), 129.10 (Co), 131.12 (C-3′/4′), 132.63
(C-1′), 136.24 (Ci).
3
Hz, 7.20 Hz, 1 H, H-6′), 5.93 (d, J = 5.10 Hz, 1 H, H-2′), 6.09 (s, 2
3
3
H, H-1/2), 6.18 (dd, J = 9.28 Hz, 3.78 Hz, H, C-5′), 6.52 (2dd, J =
9.77 Hz, 4.88 Hz, 4.30 Hz, 2 H, H-3′/4′), 6.98 (d, 3J = 7.81 Hz, 8 H,
Hm), 7.26 (d, 3J = 8.06 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2, δ
in ppm): 21.21 (CH3); 27.51 (C-7′), 75.42 (CBD), 80.64 (Cp), 84.77
(Cp), 95.32 (Cq-Cp), 122.01 (C-6′), 123.60 (C-2), 125.02 (C-2′),
127.29 (C-5′), 128.62 (Cm), 128.67 (Co), 129.08 (C-1), 129.57 (C-
4′), 130.81 (C-3′), 132.20 (C-1′), 133.05 (Cp), 135.93 (Ci).
( E , E , E ) - 1 - [ ( T e t r a p h e n y l - η 4 - c y c l o b u t a d i e n e ) ( η 5 -
cyclopentadienediyl)cobalt(I)]-6-(cyclohepta-1′,3′,5′-trien-1′-yl)-
1,3,5-hexatriene (11): {(C6H5)4CBD}CoCp-(E)-(CHCH)2CHO
(8; 41 mg, 0.07 mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosph-
onate diethyl ester (34 mg, 0.14 mmol), benzene (4 mL), soda lye
(50%) (4 mL), 4 h reflux, column chromatography Al2O3 neutral, 5%
water, hexane/diethyl ether 3/1.
(E)-1-[{Tetrakis(4-methoxyphenyl)-η4-cyclobutadiene}(η5-
cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)-
ethene (9d): {(4-MeOC6H4)4CBD}CoCpCHO (6d; 30 mg, 0.05
mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester
(27 mg, 0.11 mmol), benzene (3 mL), 50% soda lye (3 mL), 4 h
reflux, column chromatography Al2O3 neutral, 5% water/95% toluene.
Yield: 32 mg (0.04 mmol, 93.6%) orange-red solid material. Mp:
226 °C. Anal. Calcd for C46H41CoO4 (Et2O) (M = 790.88): C, 75.93;
H, 6.50. Found: C, 75.69; H, 6.78. EI-MS (m/z (%)): 716.5 (100)
[M+], 702 (M+ − CH2), 535.2 (12) [{(4-CH3OC6H4)4CBD}Co+],
240.1 (52) [CoCp(CHCH)CHT+]. IR (KBr, cm−1): 2999, 2952,
2928 (CH2, CH3), 2833 (COCH3), 1607, 1513, 1450 (CC)Ph, 1382
(CH3), 1243 (COCH3), 1173, 1033 (CC)Cp, 954 (CCH), 809
(CH). 1H NMR (200 MHz, CD2Cl2, δ in ppm): 2.34 (d, 3J = 7.08 Hz,
2 H, H-7′exo/endo), 3.77 (s, 12 H, OCH3), 4.62 (m, 2 H, Cp), 4.68 (m,
2 H, Cp), 5.24 (dt, 3J = 9.27 Hz, 7.00 Hz, 1H, H-6′), 5.96 (d, 3J = 5.37
Hz, 1 H, H-2′), 6.07 (d, 3J = 15.78 Hz, 1 H, H-2), 6.16 (d, 3J = 15.78
Hz, 1 H, H-1), 6.18 (dd, 3J = 9.28 Hz, 4.40 Hz, 1 H, C-5′), 6.53 (2dd,
3J = 10.55 Hz, 5.58 Hz, 4.80 Hz, 2 H, H-3′/4′), 6.72 (d, 3J = 8.79 Hz, 8
Yield: 41 mg (0.06 mmol, 91%) orange-red solid material. Anal.
Calcd for C46H37Co (4H2O) (720.79): C, 76.65; H, 6.29. Found: C,
76.70; H, 6.47. Mp: 129 °C. IR (KBr, cm−1): 3079, 3055, 3021
(CH)Ph, 2924, 2850 (CH2), 1724, 1675 (CC), 1597, 1498, 1443
(CC)Ph, 1156, 1026 (CC)Cp, 993 (CCH), 744, 705 (CH). EI-
MS (m/z (%)): 648 (17) [M+], 415 (13) [{(C6H5)4CBD}Co+], 356
+
(55) [{(C6H5)4CBD}+], 278 (14) [CoCp(CHCH)3C6H6 ]. 1H
3
NMR (200 MHz, CD2Cl2, δ in ppm): 2.63 (d, J = 7.14 Hz, 2 H, H-
3
7′exo/endo), 4.67 (m, 2 H, Cp), 4.70 (m, 2 H, Cp), 5.44 (dt, J = 8.80
Hz, 6.80 Hz, 1 H, H-6′), 5.75 (d, 3J = 14.00 Hz, 1 H, H-6), 6.02−6.37
(m, 6 H, H-2′/5′, H-2/3/4/5), 6.53−6.61 (m, 3 H, H-1, H-3′/4′),
7.14−7.25 (m, 12 H, Hm,p), 7.36−7.43 (m, 8 H, Ho). 13C NMR (50
MHz, CD2Cl2, δ in ppm): 28.14 (C-7′), 75.94 (CBD), 81.11 (Cp),
85.12 (Cp), 96.03 (Cq-Cp), 122.70 (C-6′), 126.49 (Cp), 126.49,
127.88, 128.93, 132.06, 133.51, 134.44 (C-2′/5′, C-2/3/4/5), 126.83
(C-6), 128.25 (Cm), 129.05 (Co), 130.53 (C-1), 130.91 (C-4′), 131.04
(C-3′), 132.81 (C-1′), 136.21 (Ci).
H, Hm), 7.30 (d, 3J = 8.79 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2,
δ in ppm): 27.87 (C-7′), 55.54 (OCH3), 75.29 (CBD), 80.70 (Cp),
84.86 (Cp), 95.58 (Cq-Cp), 113.77 (Cm), 122.22 (C-6′), 124.22 (C-
2), 125.14 (C-2′), 127.65 (C-5′), 128.45 (Ci), 129.13 (C-1), 129.86
(C-4′), 130.07 (Co), 131.14 (C-3′), 132.55 (C-1′), 158.43 (Cp).
(E)-1-[Tetrakis(4-dimethylaminophenyl)(η4-cyclobutadiene)(η5-
cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)-
ethene (9e). {(4-(CH3)2NC6H4)4CBD}CoCpCHO (6e; 80 mg, 0.12
mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester
(57 mg, 0.42 mmol), benzene (6 mL), 50% soda lye (3 mL), 10 h
reflux, column chromatography Al2O3 neutral, 5% water, hexane/
diethyl ether 1/1.
(E)-1-[(Tetrakis(4-chlorophenyl)-η4-cyclobutadiene)(η5-
cyclopentadienediyl)cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)-
ethene (9b). {(4-ClC6H4)4CBD}CoCpCHO (6b; 100 mg, 0.15
mmol), cyclohepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester
(90 mg, 0.36 mmol), benzene (4 mL), 50% soda lye (4 mL), 2.5 h
reflux, column chromatography Al2O3 neutral, 5% water, hexane/
diethyl ether 5/1.
Yield: 110 mg (0.15 mmol, 96.5%) orange-red solid material. Anal.
Calcd for C42H29Cl4Co (0.5H2O) (M = 743.45): C, 67.85; H, 3.98.
Found: C, 67.99; H, 4.24. Mp: 190 °C. IR (KBr, cm−1): 3017 (CH)Ph,
2922, 2851 (CH2), 1601, 1495, 1443 (CC)Ph, 1117, 1011 (C
C)Cp, 1081 (CCl), 952 (CCH), 818 (CH). EI-MS (m/z (%)): 736
(2), 734 (6), 732 (4) [M+ − (Cl, isotopic pattern) 722 (2), 720 (6),
Yield: 48 mg (0.06 mmol) red solid material (53.1%). Mp: 305 °C.
Anal. Calcd for C50H53CoN4 (1/2CH2Cl2) (M = 811.40): C, 74.75; H,
6.71, N 6.90. Found: C, 75.20; H, 6.86, N 7.02. EI-MS (m/z (%)):
767.9 (100) [M+], 586.9 (12) [{(4-(CH3)2NC6H4)4CBD}Co+], 528.1
(26) [{(4-(CH3)2NC6H4)4CBD}+], 240.1 (26) [CoCp(CHCH)-
CHT+]. IR (KBr, cm−1): 3085, 3015 (CH)Ph, 2993, 2976, 2888, 2850
(CH2,CH3), 1609, 1524, 1444 (CC)Ph, 1388 (CH3), 1195 (CN),
1126, 1004 (CC)Cp, 945 (CCH), 814 (CH). 1H NMR (200
1
718 (4) [M+ − CH2 − (Cl-isotopic pattern)], 91 (100) [CHT+]. H
3
NMR (200 MHz, CD2Cl2, δ in ppm): 2.36 (d, J = 7.08 Hz, 2 H, H-
3
7′exo/endo), 4.65 (m, 2 H, Cp), 4.71 (m, 2 H, Cp), 5.25 (dt, J = 9.00
Hz, 7.10 Hz, 1 H, H-6′), 6.01 (dd, 3J = 4.15 Hz, 2.00 Hz, 1.71 Hz, 1 H,
H-2′), 6.04 (d, 3J = 16.11 Hz, 1 H, H-2), 6.15 (d, 3J = 16.11 Hz, 1 H,
H-1), 6.21 (ddd, 3J = 9.34 Hz, 3.60 Hz, 2.00 Hz, 1 H, H-5′), 6.55 (2dd,
3J = 8.85 Hz, 4.40 Hz, 3.15 Hz, 2 H, H-3′/4′), 7.17 (d, 3J = 8.79 Hz, 8
3
MHz, CD2Cl2, δ in ppm): 2.34 (d, J = 7.22 Hz, 2 H, H-7′exo/endo),
2.92 (s, 24 H, N(CH3)2), 4.58 (m, 2 H, Cp), 4.64 (m, 2 H, Cp), 5.24
(dt, 3J = 8.23 Hz, 7.20 Hz, H, H-6′), 5.94 (d, 3J = 5.82 Hz, 1 H, H-2′),
6.07 (d, 3J = 16.00 Hz, H, H-2), 6.10−6.20 (m, H, H-5′), 6.20 (d, 3J =
16.00 Hz, 1 H, H-1), 6.40−6.60 (m, 2 H, H-3′/4′), 6.54 (d, 3J = 11.67
H, Hm), 7.28 (d, 3J = 8.79 Hz, 8 H, Ho). 13C NMR (50 MHz, CD2Cl2,
δ in ppm): 27.69 (C-7′), 74.66 (CBD), 81.05 (Cp), 85.22 (Cp), 96.23
(Cq-Cp), 122.30 (C-2), 127.84 (C-6′), 126.24 (C-2′), 127.84 (C-5′),
128.73 (Cm), 130.12 (Co), 130.44 (C-4′), 130.58 (C-1), 131.09 (C-
3′), 131.85 (C-1′), 132.26 (Ci), 134.330 (Cp).
3
Hz, 8 H, Hm), 7.26 (d, J = 11.67 Hz, 8 H, Ho). 13C NMR (50 MHz,
CD2Cl2, δ in ppm): 27.99 (C-7′), 40.61 (N(CH3)2), 75.64 (CBD),
80.36 (Cp), 84.54 (Cp), 95.26 (Cq-Cp), 112.10 (Cm), 122.09 (C-6′),
124.40 (Ci), 124.51 (C-2′), 125.35 (C-5′), 127.48 (C-2), 128.31 (C-
4′), 129.37 (C-3′), 129.72 (Co), 131.22 (C-1), 132.86 (C-1′), 149.12
(Cp).
General Synthesis of Cationic, Mononuclear (Ar4CBD)CoCp
Complexes with Tropylium Substitution. The cycloheptatrienyl-
substituted complexes 4b,c, 9a−e, 10, and 11 were dissolved in
(E)-1-[(Tetra-p-tolyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)-
cobalt(I)]-2-(cyclohepta-1′,3′,5′-trien-1′-yl)ethene (9c): {(4-
CH3C6H4)4CBD}CoCpCHO (6c) (40 mg, 0.07 mmol), Cyclo-
hepta-1′,3′,5′-trien-1′-ylmethylphosphonate diethyl ester (40 mg,
0.16 mmol), benzene (5 mL), 50% soda lye (5 mL), 6 h reflux,
column chromatography Al2O3 neutral, 5% water, hexane/diethyl
ether 2/1.
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dichloromethane. A solution of trityl hexafluorophosphate (0.9−1
equiv) in dichloromethane was added. The reaction mixture was
stirred for 5−10 min at room temperature. During this time the color
changed from orange-red to dark green or blue. Afterward diethyl
ether was poured into the reaction mixture, to precipitate the
tropylium salts. The precipitate was collected on a filter and dried in
vacuo. The solid material was recrystallized from dichloromethane
solution and gas-phase diffusion with diethyl ether. The numbering
scheme is given in Chart 3.
{(C6H5)4CBD}Co{Cp-(E)-(CHCH)2CHT} (10; 60 mg, 0.10
mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (30
mg, 0.08 mmol) in dichloromethane (2 mL), stirring at room
temperature for 5 min, color change from orange-red to blue, addition
of diethyl ether (20 mL) to provide the desired tropylium salt,
recrystallization from dichloromethane solution and gas-phase
diffusion of diethyl ether.
Yield: 21 mg (0.03 mmol) black-green cubes (28.4%). Mp: 340 °C
dec. Anal. Calcd for C44H34CoF6P (M = 766.65): C, 68.93; H, 4.47.
Found: C, 68.33; H, 4.53. FAB-MS (m/z (%)): 621 (5) [M+], 415 (3)
[{(C6H5)4CBD}Co+], 356 (100) [{(C6H5)4CBD}+]. IR (KBr, cm−1):
1586, 1498, 1437 (CC)Ph, 1124, 1002 (CC)Cp, 929 (CCH),
Chart 3. Numbering Scheme of the Tropylium Substituent in
5 and 12−14
1
846, 545 (PF6), 747, 705 (CH). H NMR (200 MHz, CD3NO2, δ in
ppm): 5.16 (m, 2 H, Cp), 5.25 (m, 2 H, Cp), 6.34 (dd, 3J = 14.89 Hz,
3
3
11.23 Hz, 1H, H-2), 6.62 (d, J = 14.89 Hz, 1H, H-4), 6.85 (d, J =
14.65 Hz, 1H, H-1), 7.24−7.32 (m, 12 1H, Hm,p), 7.44−7.59 (m, 9 H,
H-3, Ho), 8.36−8.46 (m, 4 H, H-3′/3′,4′/4′), 8.62 (d, 3J = 9.03 Hz, 2
H, H-2′/2′). 13C NMR (50 MHz, CD3NO2, δ in ppm) 79.75 (CBD),
85.13 (Cp), 90.56 (Cp), 95.80 (Cq-Cp), 128.66 (Cp), 128.82 (C-2),
129.85 (Cm), 130.47 (Co), 131.44 (C-4), 136.54 (Ci), 148.17 (C-2′/
2′), 148.33 (C-1), 149.60 (C-3′/3′), 150.21 (C-4′/4′), 152.94 (C-3),
167.49 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2, 502 (21
646), 780 (40 385); in MeNO2, 470 (18 589), 697 (32 918).
(Tetraphenyl-η4 -cyclobutadiene)(1′-tropylium-η5 -
cyclopentadienediyl)cobalt(I) Hexafluorophosphate (5):
{(C6H5)4CBD}Co(Cp-1′,3′,5′-CHT) (4b) and {(C6H5)4CBD}Co-
(Cp-1′,3′,6′-CHT) (4c) (132 mg, 0.23 mmol) in dichloromethane (7
mL), trityl hexafluorophosphate (80 mg, 0.21 mmol) in dichloro-
methane (3 mL), stirring at room temperature for 10 min, color
change from orange-red to blue, addition of diethyl ether (20 mL) to
provide the desired tropylium salt, recrystallization from dichloro-
methane solution and gas-phase diffusion of diethyl ether.
Attempt To Synthesize (E,E,E)-1-[(Tetraphenyl-η4 -
cyclobutadiene)(η5-cyclopentadienediyl)cobalt]-6-(tropylium)-
1,3,5-hexatriene Hexafluorophosphate (14): {(C6H5)4CBD}Co{Cp-
(E)-(CHCH)3CHT} (11; 20 mg, 0.03 mmol) in dichloromethane
(2 mL), trityl hexafluorophosphate (11 mg, 0.03 mmol) in
dichloromethane (1 mL), stirring at room temperature for 5 min,
color change from orange-red to green-brown, addition of diethyl
ether (20 mL) revealed a green-brown solid material that is almost
Yield: 120 mg (0.17 mmol, 81.6%), black blue crystals. Mp: 245 °C
dec. Anal. Calcd for C40H30CoF6P (1/4CH2Cl2) (M = 726.70): C,
65.70; H, 4.18. Found: C, 66.04; H, 4.26. FAB-MS (m/z (%)): 569
(100) [M+], 415 (15) [{(C6H5)4CBD}Co+], 213 (15) [CoCpTrop+].
IR (KBr, cm−1): 3052, 3031 (CH)Ph, 1611, 1492, 1442 (CC)Ph,
1126, 1003 (CC)Cp, 834, 547 (PF6), 747, 705 (CH). 1H NMR (200
MHz, CD3NO2, δ in ppm): 5.62 (m, 2 H, Cp), 5.88 (m, 2 H, Cp),
7.18−7.30 (m, 8 H, Ho3), 7.34−7.38 (m, 12 H, Hm,p), 7.91−8.02 (m, 2
1
insoluble in dichloromethane. The corresponding H NMR spectrum
gave no indication for the desired product 14.
(E)-1-[Tetrakis(4-chlorophenyl)(η4-cyclobutadiene)(η5-
cyclopentadienediyl)cobalt(I)]-2-(tropylium)ethene Hexafluoro-
phosphate (12b): {(4-ClC6H4)4CBD}CoCp-(E)-(CHCH)CHT
(9b; 63 mg, 0.09 mmol) in dichloromethane (4 mL), trityl
hexafluorophosphate (33 mg, 0.08 mmol) in dichloromethane (2
mL), stirring at room temperature for 5 min, color change from
orange-red to dark green, addition of diethyl ether (20 mL) to provide
the desired tropylium salt 12b, recrystallization from dichloromethane
solution and gas-phase diffusion of diethyl ether.
3
H, H-3′/3′), 8.14 (d, J = 10.62 Hz, 2 H, H-2′/2′), 8.28 (dd, J =
10.07 Hz, 4.03 Hz, 2 H, H-4′/4′). 13C NMR: (50 MHz, CD3NO2, δ in
ppm): 82.17 (CBD), 85.79 (Cp), 94.51 (Cp), 96.60 (Cq-Cp), 128.83
(Cp), 130.14 (Co,m), 135.01 (Ci), 146.89 (C-2′/2′), 148.64 (C-4′/4′),
150.67 (C-3′/3′), 165.93 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in
CH2Cl2, 386 (21 420), 644 (8526); in MeNO2, 376 (14 745), 600
(7135).
Yield: 30 mg (0.03 mmol, 40%) black-green cubes. Mp: 285 °C dec.
Anal. Calcd for C42H28Cl4CoF6P (M = 878.39): C, 57.43; H, 3.21.
Found: C, 57.95; H, 3.74. FAB-MS (m/z (%)): 735 (55), 733 (92),
731 (68) [M+ − (isotopic pattern of 35/37Cl)], 554 (25), 552 (43), 550
(27) [{(4-ClC6H4)4CBD}Co+(isotopic pattern of 35/37Cl)]. IR (KBr,
cm−1): 1598, 1496, 1457 (CC)Ph, 1176, 1012 (CC)Cp, 1082
(CCl), 968 (CCH), 837, 558 (PF6). 1H NMR (200 MHz, CD3NO2,
δ in ppm): 5.36 (m, 2 H, Cp), 5.46 (m, 2 H, Cp), 6.69 (d, 3J = 15.38
Hz, 1H, H-2), 7.22 (d, 3J = 6.76 Hz, 8 H, Hm), 7.42 (d, 3J = 6.76 Hz, 8
H, Ho), 7.46 (d, 3J = 15.38 Hz, 1H, H-1), 8.30 (d, 3J = 10.44 Hz, 2 H,
H-2′/2′), 8.43−8.52 (m, 4 H, H-3′/3′,4′/4′). 13C NMR (50 MHz,
CD3NO2, δ in ppm): 78.90 (CBD), 86.05 (Cp), 92.20 (Cp), 94.80
(Cq-Cp), 127.70 (C-2), 129.91 (Cm), 131.59 (Co), 133.49 (Ci), 134.30
(Cp), 147.51 (C-1), 147.85 (C-2′/2′), 150.02 (C-3′/3′), 151.23 (C-
4′/4′), 166.11 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in CH2Cl2,
450 (35 870), 706 (35 656); in MeNO2, 428 (15 393), 650 (15 335).
(E)-1-[(Tetra-p-tolyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)-
cobalt(I)]-2-(tropylium)ethene Hexafluorophosphate (12c): {(4-
CH3C6H4)4CBD}CoCp-(E)-(CHCH)CHT (9c; 38 mg, 0.06
mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (20
mg, 0.05 mmol) in dichloromethane (1 mL), stirring at room
temperature for 5 min, color change from orange-red to blue, addition
of diethyl ether (20 mL) to provide the desired tropylium salt.
Recrystallization from dichloromethane solution and gas-phase
diffusion with diethyl ether.
(E)-1-[(Tetraphenyl-η4-cyclobutadiene)(1′-tropylum-η5-
cyclopentadienediyl)cobalt(I)]-2-(tropylium)ethene Hexafluoro-
phosphate (12e): {(C6H5)4CBD}Co{Cp-(E)-(CHCH)CHT}
(9a; 77 mg, 0.13 mmol) in dichloromethane (5 mL), trityl
hexafluorophosphate (31 mg, 0.13 mmol) in dichloromethane (2
mL), stirring at room temperature for 5 min, color change from
orange-red to blue, addition of diethyl ether (20 mL) to provide the
desired tropylium salt, recrystallization from dichloromethane solution
and gas-phase diffusion of diethyl ether.
Yield: 50 mg (0.07 mmol, 52.3%) black-violet cubes. Mp: 275 °C
dec. Anal. Calcd for C42H32CoF6P (1/4CH2Cl2) (M = 752.73): C,
66.61; H, 4.30. Found: C, 66.33; H, 4.44. FAB-MS (m/z (%)): 595
(24) [M+], 415 (16) [{(C6H5)4CBD}Co+], 356 (100)
[{(C6H5)4CBD}+]. IR (KBr, cm−1): 3057 (CH), 1599, 1498, 1457
(CC)Ph, 1122, 1025 (CC)Cp, 962 (CCH), 848, 545 (PF6), 749,
1
708 (CH). H NMR (200 MHz, CD3NO2, δ in ppm): 5.36 (m, 2 H,
3
Cp), 5.42 (m, 2 H, Cp), 6.52 (d, J = 15.44 Hz, H, H-2), 7.15−7.35
(m, 13 H, H-1, Hm,p), 7.42−7.47 (m, 8 H, Ho), 8.07 (d, 3J = 8.84 Hz, 2
H, H-2′/2′), 8.39−8.49 (m, 4 H, H-3′/3′,4′/4′). 13C NMR (50 MHz,
CD3NO2, δ in ppm): 80.57 (CBD), 85.89 (Cp), 91.72 (Cp), 95.08
(Cq-Cp), 126.91 (C-2), 128.47 (Cp), 129.91 (Cm), 130.01 (Co),
135.87 (Ci), 147.73 (C-2′/2′), 148.38 (C-1), 149.23 (C-3′/3′), 150.20
(C-4′/4′), 166.47 (C-1′). UV−vis (λmax, nm (ε, M−1 cm−1)): in
CH2Cl2, 453 (17 577) nm, 719 (19427) nm; in MeNO2, 432 (14 868),
670 (16 299).
Yield: 30 mg (0.04 mmol, 73%) black-green solid material. Mp: 222
°C dec. Anal. Calcd for C46H40CoF6P(CH2Cl2)(H2O) (M = 899.67):
C, 62,65; H, 4,93. Found: C, 62.72; H, 5.23. FAB-MS (m/z (%)): 651
(E,E)-1-[(Tetraphenyl-η4-cyclobutadiene)(η5-cyclopentadienediyl)-
cobalt]-4-(tropylium)-1,3-butadiene Hexafluorophosphate (13):
6923
dx.doi.org/10.1021/om300710x | Organometallics 2012, 31, 6911−6925

Organometallics
Article
(35) [M+], 471 (100) [{(4-CH3C6H4)4CBD}Co+], 412 (5) [{(4-
CH3C6H4)4CBD}+]. IR (KBr, cm−1): 2919 (CH3), 1595, 1496, 1455
(CC)Ph, 1385 (CH3), 1129, 1056 (CC)Cp, 962 (CCH), 848,
1217−1254. (m) Coe, B. J. In Comprehensive Coordination Chemistry;
McCleverty, J. A., Meyer, T. J., Eds.; Elsevier Science: Amsterdam,
2003; Chapter 9.14, pp 621−687. (n) Coe, B. J.; Curati, N. R. M.
Comments Inorg. Chem. 2004, 25, 147−184. (o) Coe, B. J. Acc. Chem.
Res. 2006, 39, 383−393. (p) Cariati, E.; Pizzotti, M.; Roberto, D.;
Tessore, F.; Ugo, R. Coord. Chem. Rev. 2006, 250, 1210−1233.
(q) Humphrey, M. G.; Samoc, M. Adv. Organomet. Chem. 2008, 55,
61−136. (r) Di Bella, S.; Dragonetti, C.; Pizzotti, M.; Roberto, D.;
Tessore, F.; Ugo, R. In Molecular Organometallic Materials for Optics;
Le Bozec, H., Guerchais, V., Eds.; Springer Verlag: Berlin, Heidelberg,
2010; Topics in Organometallic Chemistry 28, pp 1−55. (s) Kuzyk,
M. G. J. Mater. Chem. 2009, 19, 7444−7465. (t) Maury, O.; Le Bosec,
H. In Molecular Materials; Bruce, D. W., O’Hare, D., Walton, I. R.,
Eds.; Wiley: New York, 2010.
1
558 (PF6). H NMR (200 MHz, CD3NO2, δ in ppm): 2.23 (s, 12 H,
3
3
CH3), 5.35 (pt, J = 2.10 Hz, 2 H, Cp), 5.39 (pt, J = 2.10 Hz, 2 H,
Cp), 6.52 (d, 3J = 15.38 Hz, H, H-2), 7.04 (d, 3J = 7.90 Hz, 8 H, Hm),
7.33 (d, 3J = 7.90 Hz, 8 H, Ho), 7.46 (d, 3J = 15.38 Hz, H, H-1), 8.04
3
(d, J = 9.03 Hz, 2 H, H-2′/2′), 8.29−8.33 (m, 4 H, H-3′/3′,4′/4′).
13C NMR: (50 MHz, CD2Cl2, δ in ppm): 21.62 (CH3), 80.88 (CBD),
85.85 (Cp), 92.10 (Cp), 105.23 (Cq-Cp), 126.86 (C-2), 130.07 (Cm),
130.31 (Co), 132.81 (Cp), 138.55 (Ci), 147.18 (C-2′/2′), 148.48 (C-
3′/3′), 149.16 (C-1), 149.63 (C-4′/4′), 166.08 (C-1′). UV−vis (λmax
,
nm (ε, M−1 cm−1)): in CH2Cl2, 470 (25 426), 756 (23 530); in
MeNO2, 448 (15 228), 698 (14 163).
Attempt To Synthesize (E)-1-[{Tetrakis(p-methoxyphenyl)-η4-
cyclobutadiene}(η5-cyclopentadienediyl)cobalt}-2-(tropylium)-
ethene Hexafluorophosphate (12d): {(4-CH3OC6H4)4CBD}CoCp-
(E)-(CHCH)CHT (9d; 42 mg, 0.06 mmol) in dichloromethane (2
mL), trityl hexafluorophosphate (21 mg, 0.06 mmol) in dichloro-
methane (1 mL), stirring at room temperature for 5 min, color change
from orange-red to deep red, addition of diethyl ether (20 mL)
(2) For example see: (a) Bourgault, M.; Baum, K.; Le Bosec, H.;
Pucetty, G.; Ledouox, I.; Zyss, J. New J. Chem. 1998, 517−522.
(b) Mata, J.; Uriel, S.; Peris, E.; Llusar, R.; Houbrechts, S.; Persoons, A.
J. Organomet. Chem. 1998, 562, 197−202. (c) Lee, I. S.; Lee, S.;
Chung, Y. K.; Kim, D.; Song, N. W. Inorg. Chim. Acta 1998, 279, 243−
248. (d) Briel, O.; Sunkel, K.; Krossing, I.; Noth, H.; Schmalzlin, E.;
̈
̈
̈
1
Meerholz, K.; Brauchle, C.; Beck, W. Eur. J. Inorg. Chem. 1999, 483−
̈
revealed a brown solid material, whose H NMR spectrum gave no
490. (e) Cadierno, V.; Conejero, S.; Gamasa, M. P.; Gimeno, J.;
Asselberghs, I.; Houbrechts, S.; Clays, K.; Persoons, A.; Borge, J.;
Garcia-Granda, S. Organometallics 1999, 18, 582−597. (f) Mata, J. A.;
Peris, E.; Asselberghs, I.; van Boxel, R.; Persoons, A. New. J. Chem.
2001, 25, 1043−1046.
(3) For example see: (a) Roth, G.; Fischer, H.; Meyer-Friedrichsen,
T.; Heck, J.; Houbrechts, S.; Persoons, A. Organometallics 1998, 17,
1511. (b) Licandro, E.; Maiorana, S.; Papagni, A.; Hellier, P.; Capella,
L.; Persoons, A.; Houbrechts, S. J. Organomet. Chem. 1999, 583, 111−
119. (c) Jayaprakash, K. N.; Ray, P. C.; Matsuoka, I.; Bhadbhade, M.
M.; Puranik, V. G.; Das, P. K.; Nishihara, H.; Sarkar, A. Organometallics
hint of the desired tropylium salt.
Attempt To Synthesize (E)-1-[{Tetrakis(4-(dimethylamino)-
phenyl)-η4-cyclobutadiene}(η5-cyclopentadienediyl)cobalt]-2-(η7-
tropylium)ethene Hexafluorophosphate (12e): {(4-
(CH3)2NC6H4)4CBD}CoCp-(E)-(CHCH)CHT (9e; 30 mg, 0.04
mmol) in dichloromethane (2 mL), trityl hexafluorophosphate (13
mg, 0.03 mmol) in dichloromethane (1 mL), stirring at room
temperature for 5 min, color change from orange-red to deep red,
addition of diethyl ether (20 mL) revealed a brown solid material,
1
whose H NMR spectrum gave no hint of the desired tropylium salt.
ASSOCIATED CONTENT
* Supporting Information
1999, 18, 3851−3858. (d) Ipaktschi, J.; Mohseni-Ala, J.; Dulmer, A.;
̈
■
Steffens, S.; Wittenburg, C.; Heck, J. Organometallics 2004, 23, 4902−
4909. (e) Szesni, N.; Drexler, M.; Maurer, J.; Winter, R. F.; de
Montigny, F.; Lapinte, C.; Steffens, S.; Heck, J.; Weibert, B.; Fischer,
H. Organometallics 2006, 25, 5774−5787.
S
CIF files giving crystallographic data for 5 and 12c. This
material is available free of charge via the Internet at http://
pubs.acs.org.
(4) For example see: (a) Behrens, U.; Brussaard, H.; Hagenau, U.;
Heck, J.; Hendrickx, E.; Kornich, J.; van der Linden, J. G. M.;
̈
AUTHOR INFORMATION
■
Persoons, A.; Spek, A. L.; Veldman, N.; Voss, B.; Wong, H. Chem. Eur.
J. 1996, 2, 98. (b) Hendrickx, E.; Persoons, A.; Samson, S.;
Stephenson, G. R. J. Organomet. Chem. 1997, 542, 295. (c) Farrell,
T.; Meyer-Friedrichsen, T.; Malessa, M.; Haase, D.; Saak, W.;
Asselberghs, I.; Wostyn, K.; Clays, K.; Persoons, A.; Heck, J.;
Manning, A. R. Dalton Trans. 2001, 29. (d) Malaun, M.; Kowallick,
R.; McDonagh, A. M.; Marcaccio, M.; Paul, R. L.; Asselberghs, I.;
Clays, K.; Persoons, A.; Bildstein, B.; Fiorini, C.; Nunzi, J.-M.; Ward,
M. D.; McCleverty, J. A. Dalton Trans. 2001, 3025. (e) Farrell, T.;
Manning, A. R.; Murphy, T. C.; Meyer-Friedrichsen, T.; Heck, J.;
Asselberghs, I.; Persoons, A. Eur. J. Inorg. Chem. 2001, 2365.
(f) Meyer-Friedrichsen, T.; Mecker, C.; Prosenc, M. H.; Heck, J.
Eur. J. Inorg. Chem. 2002, 239−248. (g) Farrell, T.; Manning, A. R.;
Mitchell, G.; Heck, J.; Meyer-Friedrichsen, T.; Malessa, M.;
Wittenburg, C.; Prosenc, M. H.; Cunningham, D.; McArdle, P. Eur.
J. Inorg. Chem. 2002, 1677−1686. (h) Meyer-Friedrichsen, T.; Wong,
H.; Prosenc, M. H.; Heck, J. Eur. J. Inorg. Chem. 2003, 936.
(i) Steffens, S.; Prosenc, M. H.; Heck, J.; Asselgerghs, I.; Clays, K. Eur.
J. Inorg. Chem. 2008, 1999−2006. (j) Coe, B. J.; Essex-Lopresti, J. P.;
Harris, J. A.; Houbrechts, S.; Persoons, A. Chem. Commun. 1997,
1645−1646.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Deutsche Forschungsgemein-
schaft (DFG, HE 1309/3) by the European Community
(COST D 14, TMR FMRX-CT-98-0166). M.H.P. thanks the
Deutsche Forschungsgemeinschaft for a fellowship (DFG, PR
654/1-1).
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