Half-open ferrocenes and ruthenocenes containing an edge-bridged open indenyl ligand

Article abstract of DOI:10.1021/om400485a

Potassium 1,1-dimethyl-1,2-dihydronaphthalenide, K(eboInd) (1), was synthesized in three steps from 4,4-dimethyl-1-tetralone and used for the synthesis of half-open metallocenes containing an edge-bridged open indenyl ligand (eboInd). Successive treatment of [(THF)FeI₂] with Li(C ₅Me₅) and 1 at low temperatures afforded [(η⁵-C₅Me₅)Fe(η⁵-eboInd)] (2), whereas [(η⁵-C₅Me₅) Ru(η⁵-eboInd)] (3) was synthesized by reaction of 1 with [(C ₅Me₅)RuCl]₄. Both compounds reacted with CO and 2,6-dimethylphenyl isocyanide (CN-o-Xy) to form [(η⁵-C ₅Me₅)M(η³-eboInd)L] (4: M = Fe, L = CO; 5: M = Ru, L = CO; 6: M = Fe, L = CN-o-Xy; 7: M = Ru, L = CN-o-Xy), in which the eboInd ligand has undergone an η⁵-to-η³ hapticity conversion. In contrast, the N-heterocyclic carbene 1,3,4,5- tetramethylimidazolin-2-ylidene (IMe) only reacted with the ruthenocene derivative 3 to give [(η⁵-C₅Me₅) Ru(η³-eboInd)(IMe)] (8). The molecular structures of 2-7 were determined by X-ray diffraction analysis. None of the iron-ruthenium pairs are isotypic.

Full text of DOI:10.1021/om400485a

Article
pubs.acs.org/Organometallics
Half-Open Ferrocenes and Ruthenocenes Containing an Edge-
Bridged Open Indenyl Ligand
Jeroen Volbeda, Constantin G. Daniliuc, Peter G. Jones, and Matthias Tamm*
Institut fur Anorganische und Analytische Chemie, Technische Universitat Braunschweig, Hagenring 30, 38106 Braunschweig,
̈
̈
Germany
S
* Supporting Information
ABSTRACT: Potassium 1,1-dimethyl-1,2-dihydronaphthalenide, K-
(eboInd) (1), was synthesized in three steps from 4,4-dimethyl-1-
tetralone and used for the synthesis of half-open metallocenes containing
an edge-bridged open indenyl ligand (eboInd). Successive treatment of
[(THF)FeI2] with Li(C5Me5) and 1 at low temperatures afforded [(η5-
C5Me5)Fe(η5-eboInd)] (2), whereas [(η5-C5Me5)Ru(η5-eboInd)] (3)
was synthesized by reaction of 1 with [(C5Me5)RuCl]4. Both compounds
reacted with CO and 2,6-dimethylphenyl isocyanide (CN-o-Xy) to form [(η5-C5Me5)M(η3-eboInd)L] (4: M = Fe, L = CO; 5: M
= Ru, L = CO; 6: M = Fe, L = CN-o-Xy; 7: M = Ru, L = CN-o-Xy), in which the eboInd ligand has undergone an η5-to-η3
hapticity conversion. In contrast, the N-heterocyclic carbene 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe) only reacted with the
ruthenocene derivative 3 to give [(η5-C5Me5)Ru(η3-eboInd)(IMe)] (8). The molecular structures of 2−7 were determined by X-
ray diffraction analysis. None of the iron−ruthenium pairs are isotypic.
Scheme 1. Conceptualization of Open Indenyl Ligands from
Known Pentadienyl Ligands
INTRODUCTION
■
Metal−pentadienyl chemistry has received considerable
attention over the past few decades, and pentadienyl (“open
cyclopentadienyl”, oCp) ligands are well known for their wide
range of coordination modes; notably η5, η3, and η1 are
accessible.1 Switching between these coordination modes is
easier once one of the π-bonds is less strongly coordinated to
the metal atom, as is the case for instance in heteropentadienyl-
transition-metal complexes, which are known to undergo a
hapticity switch upon addition of an additional ligand under
mildly forcing conditions.2 Similarly, our group recently
employed a phenylmethallyl (“open indenyl”, oIndMe) ligand
for the preparation of half-open metallocenes of the type [(η5-
C5Me5)M(η5-oIndMe)] (M = Fe, Ru), which readily underwent
η5-to-η3 hapticity interconversion and formed the complexes
[(η5-C5Me5)M(η3-oIndMe)L] (M = Fe, Ru with L= CO, PMe3;
M = Ru with L = 2,6-dimethylphenyl isocyanide (CN-o-Xy); M
= Fe with L = 1,3,4,5-tetramethylimidazolin-2-ylidene (IMe))
upon addition of two-electron donor ligands.3 The oIndMe
ligand can be viewed as the indenyl analogue of the widely used
2,4-dimethylpentadienyl (2,4-C7H11) ligand (Scheme 1), while
benzannulation weakens coordination through the endocyclic
π-bond and facilitates the switch to the η3-coordination mode
by rearomatization of the benzene ring. This could be
considered a more extreme example of the indenyl effect,4
where the rate increase in ligand exchange is also attributed to a
hapticity switch.5
such that, unlike pentadienyl ligands, they are able to stabilize
group 4 metals in high oxidation states.7 Just as eboCp ligands
may be considered as more strongly bound ancillary ligands,
one should also expect edge-bridged open indenyl (eboInd)
ligands to afford less reactive transition metal complexes with a
reduced propensity to undergo η5-to-η3 hapticity conversion in
comparison with their open indenyl (oIndMe) counterparts.
Therefore, we were interested in investigating the coordination
chemistry of the eboInd ligand, which can be formally derived
from the dmCh system by benzannulation (“dimethylbenzocy-
clohexadienyl”, Scheme 1), and report herein the preparation of
the potassium salt K(eboInd) (1) and its use for the synthesis
of the sandwich complexes [(η5-C5Me5)M(η5-eboInd)] and
[(η5-C5Me5)M(η3-eboInd)L] (M = Fe, L = CO, CN-o-Xy; M =
Ru, CO, CN-o-Xy, IMe).
An important pentadienyl subclass is formed by so-called
edge-bridged open cyclopentadienyls (eboCp), for which 6,6-
dimethylcyclohexadienyl (dmCh) is a prominent example.
These species have properties in between those of pentadienyl
and cyclopentadienyl ligands;6 for instance, their reactivity is
Special Issue: Ferrocene - Beauty and Function
Received: May 29, 2013
© XXXX American Chemical Society
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Even though eboInd and transition metal complexes thereof
are unknown, it should be noted that several related 1H-
hydronaphthalene (or more precisely 1,2-dihydro-2-naphtha-
lenyl) complexes are known, in which the (formally) anionic
ligand is usually generated in the metal coordination sphere by
addition of electrophiles or nucleophiles to a coordinated
naphthalene ligand.8 As an example, the cymantrene derivative
[(η5-C10H9)Mn(CO)3] can be accessed either from anionic
[(η4-C10H8)Mn(CO)3]− by protonation8d,g or from cationic
[(η6-C10H8)Mn(CO)3]+ by hydride addition,8a,f,h respectively.
Several of these 1,2-dihydro-2-naphthalenyl complexes undergo
facile η5−η3 ring slippage,9 and this ability was also held
responsible for the observation that [(η5-C10H9)Mn(CO)3]
catalyzes the hydrosilylation of ketones in a far more efficient
manner than other cymantrene derivatives.9a
H2O) under an argon atmosphere. This gave the fairly pure
product in 53% yield as a green oil, which still contained a small
amount of decamethylferrocene. An analytically pure sample
could be obtained after recrystallization from hexamethyldisi-
loxane (HMDSO). The half-open ruthenocene 3 was
conveniently prepared by reacting [(C5Me5)RuCl]4 with 1 in
THF at −78 °C. After column chromatography with pentane
over neutral alumina (4 wt % H2O) under an argon
atmosphere, the product was isolated as an orange, slowly
solidifying oil in 69% yield.
Scheme 3. Synthesis of Half-Open Metallocenes
RESULTS AND DISCUSSION
■
Ligand Synthesis. 4,4-Dimethyl-1-tetralone was synthe-
sized according to a published procedure from ethyl levulinate
via γ,γ-dimethylbutyrolactone, which reacted with benzene in
the presence of excess aluminum trichloride.10 The resulting
tetralone was reduced to the corresponding alcohol by reaction
with NaBH4 and subsequently dehydrated to afford the 1,1-
dimethyl-1,2-dihydronaphthalene.11 Treatment with Schlosser’s
base12 afforded the desired potassium 1,1-dimethyl-1,2-
dihydronaphthalenide (1) as a pyrophoric orange powder
(Scheme 2). The 1H NMR spectrum shows the expected
The 1H NMR spectra of both 2 and 3 provide clear evidence
for η5-coordination of the eboInd ligand to the metal atoms.
The signals found for the hydrogen atoms of the bridgehead
methyl groups are particularly diagnostic, since a pronounced
high-field shift is observed for the exo-methyl groups (Fe:
−0.14; Ru: 0.30 ppm) relative to the endo-methyl groups (Fe:
1.73; Ru: 1.57 ppm). Similar shifts were reported for complexes
of the related 6,6-dimethylcyclohexadienyl (dmCh) ligand.6a
The signals for the allylic part of the eboInd ligand are found in
similar regions for both 2 and 3, although the signals for the
iron compound are spread over a larger area (2: H1: 2.07, H2:
3.62, H3: 5.77 ppm; 3: H1: 2.32, H2: 4.07, H3: 5.54 ppm).
It was previously found that half-open, open, and edge-
bridged open ferrocenes are more readily oxidized than
ferrocene.6c,14 In cyclic voltammetry experiments, the oxida-
tions of 2 and 3 were investigated, showing a quasi-reversible
oxidation of 2 at E1/2 = −0.06 V vs SCE in THF as shown in
Figure 1. The cyclic voltammogram of 3 shows a quasi-
reversible oxidation at E1/2 = 0.46 V vs SCE and an irreversible
oxidation at Epox = 0.74 V vs SCE (see Supporting Information)
in THF. For related half-open ruthenocenes bearing either a
pentadienyl or a heteropentadienyl ligand, it was found that
Scheme 2. Synthesis of the Potassium Salt K(eboInd) (1)
signals for the potassium salt; the bridgehead methyl groups
give rise to a singlet at 1.03 ppm, and three characteristic
multiplets are found at 5.90 (H2), 4.25 (H3), and 3.39 ppm
(H1) for the allylic hydrogen atoms (for the numbering
scheme, refer to Chart 1, vide infra). These chemical shifts are
very similar to those observed for the related 6,6-dimethylcy-
clohexadienyl potassium salt.13
Synthesis and Characterization of Half-Open Metal-
locenes. In analogy to our previous reports on the
coordination chemistry of the open indenyl ligand oIndMe, we
aimed at the preparation of the half-open ferrocene and
ruthenocene derivatives [(η5-C5Me5)M(η5-eboInd)] (M = Fe,
2; M = Ru, 3). 2 was obtained by subsequent addition of
(C5Me5)Li and 1 to a THF solution of [(THF)2FeI2] at −78
°C, which afforded a dark green solution. After filtration and
removal of the volatiles, a dark green, air-sensitive oil is
1
obtained. According to the H NMR spectrum, the product
contains significant amounts of decamethylferrocene (approx-
imately 10%) as well as other impurities, which is in contrast to
the previously reported synthesis of the corresponding oIndMe
complex,3b which was selectively formed under similar reaction
conditions. The product could be purified by column
chromatography with pentane over neutral alumina (4 wt %
Figure 1. Cyclic voltammogram (CV) for 2. CV recorded at ambient
temperature in THF with 0.1 M [n-Bu4N][PF6] supporting electrolyte.
Scan rate: 100 mV/s.
B
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oxidation leads to coordination of an acetonitrile solvent
molecule concomitant with a change in hapticity.15
bond lengths ranging from 2.0250(19) Å (Fe−C2) to
2.2074(17) Å (Fe−C5) and from 2.169(2) Å (Ru−C2) to
2.2958(18) Å (Ru−C5), respectively. These distances are
slightly shorter than those in the corresponding oIndMe
complexes, where the Fe−C and Ru−C bond lengths fall in
the ranges 2.055(2)−2.254(2) Å and 2.178(3)−2.312(3) Å.3
The eboInd ligand plane in both complexes approaches the
metal atom much more closely than the C5Me5 does (1.565 vs
1.646 Å in 2 and 1.713 vs 1.815 Å in 3), which is similar, albeit
less pronounced, to the situation found in the corresponding
ferrocene (1.486 vs 1.688 Å) and ruthenocene (1.616 vs 1.821
Å) derivatives bearing the oIndMe ligand.3 These structural
differences between the eboInd and oIndMe systems are in
agreement with those observed for edge-bridged pentadienyl
and pentadienyl systems.6
Single crystals of 2 for X-ray diffraction analysis were isolated
from a concentrated HMDSO solution at −30 °C, whereas
storing the oil obtained after column chromatography overnight
at −30 °C afforded suitable crystals of 3. Both compounds
crystallize in the monoclinic space group P21/c (but are not
isotypic), and the molecular structures are shown in Figures 2
Coordination of a benzene ring to the metal atoms via the
C4 and C5 carbon atoms results in bending of the eboInd
ligand, as indicated by fold angles between the C4−C5−C7−
C8−C9−C10 and C1−C2−C3 planes of 9.8° in 2 and 9.7° in
3. These angles are smaller than those found in the
corresponding oIndMe complexes (11.7° for M = Fe and
14.8° for M = Ru). In addition, benzene coordination leads to a
perturbed electron delocalization within the six-membered ring
and affords a distinct long−short−long−short−long pattern of
the C−C bond lengths along the C5−C7−C8−C9−C10−C4
moieties in both complexes. Overall, the compounds show
similar structural features to those observed for related edged-
bridged half-open ferrocenes16 and ruthenocenes.17,18
Figure 2. ORTEP drawing of 2 with thermal displacement parameters
drawn at 30% probability. The alternative disordered position of the
C5Me5 ligand and the hydrogen atoms are omitted for clarity. Selected
bond lengths [Å] and angles [deg]: Fe−C(C5Me5) 1.983(5)−
2.105(5), Fe−C1 2.0621(19), Fe−C2 2.0250(19), Fe−C3 2.050(2),
Fe−C4 2.1015(19), Fe−C5 2.2074(17), C1−C2 1.401(3), C2−C3
1.415(3), C3−C4 1.429(3), C4−C5 1.439(3), C5−C7 1.424(3), C7−
C8 1.368(3), C8−C9 1.411(3), C9−C10 1.347(3), C10−C4
1.437(3); C1−C2−C3 118.61(17), C2−C3−C4 118.63(19), C3−
C4−C5 119.08(17).
η5-to-η3 Hapticity Interconversion by Ligand Addi-
tion. As was shown in previous studies by our group,3 the half-
open indenyl complexes [(η5-C5Me5)M(η5-oIndMe)] (M = Fe,
Ru) readily switch between the η5- and η3-coordination modes
upon addition of suitable two-electron donor ligands. Naturally,
we were interested to see whether the new edge-bridged open
indenyl complexes 2 and 3 would show a similar behavior,
despite their higher rigidity and potentially greater stability.
Upon subjecting toluene solutions of 2 and 3 to an atmosphere
of carbon monoxide (Scheme 4), gradual color changes could
and 3, confirming the expected formation of half-open
metallocenes. In both cases, the eboInd ligand exhibits a
distorted η5-coordination mode, with the Fe−C and Ru−C
Scheme 4. Ligand Addition to the Half-Open Metallocenes 2
and 3
Figure 3. ORTEP drawing of 3 with thermal displacement parameters
drawn at 30% probability. The hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: Ru−C(C5Me5)
2.1595(19)−2.203(2), Ru−C1 2.1870(19), Ru−C2 2.169(2), Ru−
C3 2.185(2), Ru−C4 2.2295(19), Ru−C5 2.2958(18), C1−C2
1.410(3), C2−C3 1.425(3), C3−C4 1.433(3), C4−C5 1.442(3),
C5−C7 1.428(3), C7−C8 1.359(3), C8−C9 1.416(3), C9−C10
1.355(3), C10−C4 1.441(3); C1−C2−C3 118.28(18), C2−C3−C4
118.99(18), C3−C4−C5 118.63(18).
be observed for both compounds within a couple of days.
Whereas the solution of the iron complex 2 changed from
green to orange after heating at 70 °C for three days, its
ruthenium congener 3 switched more readily, changing from
orange to yellow after stirring for two days at room
temperature. These observations indicate significantly lower
reaction rates than those observed for the oIndMe systems,
which show immediate color changes upon exposure to CO
C
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under ambient conditions.3 For comparison, the half-open
ferrocene [(η5-C5H4tBu)Fe{η5-C10H6(OMe)2}] containing a
related 5,8-dimethoxy-1,2-dihydro-2-naphthalenyl ligand adds
CO with rearrangement to an η3-coordination mode within 5 h
at room temperature under 4.5 bar CO pressure.8b
Evaporation of the toluene solutions afforded the carbonyl
complexes 4 and 5 as orange and yellow solids, which could be
further purified by recrystallization from diethyl ether.
Coordination of CO is clearly indicated by 13C NMR
resonances at 223.5 (4) and 209.7 ppm (5); the accompanying
1
hapticity switch is particularly well illustrated by the H NMR
signals assigned to the hydrogen atoms of the bridgehead
methyl groups, which are now observed between ca. 1.5−1.6
ppm for both the exo- and endo-methyl groups, whereas the
signals for the exo-CH3 groups in the parent complexes 2 and 3
were found at significantly higher field (vide supra).
Single crystals suitable for X-ray diffraction analysis were
obtained by storing concentrated diethyl ether solutions of 4
and 5 at −30 °C. The molecular structures clearly reveal the
eboInd ligand bound in an η3-fashion with the additional
carbonyl ligand coordinating toward the open edge of the allyl
ligand, which corresponds to an exo-conformation.19 The
metal−CO bond lengths of 1.746(3) Å (Fe−C23) and
1.8650(16) Å (Ru−C23) are comparable to those found in
similar CO adducts of cyclopentadienyl-allyl metal com-
plexes,20,21 and they are nearly identical to the bond lengths
previously established for [(η5-C5Me5)Fe(η3-oIndMe)(CO)]
(1.7464(14) Å)3b and [(η5-C5Me5)Ru(η3-oIndMe)(CO)]
(1.855(2) Å).3a As expected, η5-to-η3 hapticity interconversion
goes along with a significantly stronger folding of the eboInd
ligand with an increase of the angle between the allyl (C1−C2−
C3) and benzene (C4−C5−C7−C8−C9−C10) planes from
9.8° and 9.7° in 2 and 3 to 36.2° and 31.5° in 4 and 5,
respectively. Additionally the bond length alteration of the
benzene ring observed in 2 and 3 is not present in complexes 4
and 5.
Figure 5. ORTEP drawing of 5 with thermal displacement parameters
drawn at 30% probability. The hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: Ru−C(C5Me5)
2.2079(14)−2.2476(14), Ru−C1 2.2149(14), Ru−C2 2.1176(14),
Ru−C3 2.2511(15), Ru−C23 1.8650(16), C23−O 1.1544(19), C1−
C2 1.417(2), C2−C3 1.420(2), C3−C4 1.479(2), C4−C5 1.410(2),
C5−C7 1.392(2), C7−C8 1.390(2), C8−C9 1.383(2), C9−C10
1.388(2), C10−C4 1.398(2); Ru−C23−O 173.54(13), C1−C2−C3
115.34(13), C2−C3−C4 117.93(13), C3−C4−C5 120.25(13).
Addition of 2,6-dimethylphenyl isocyanide to 2 and 3
resulted in similar color changes. Again, compound 2 required
heating at 70 °C for three days to achieve full conversion,
whereas compound 3 switched at room temperature over the
course of two days. The changes in the NMR spectra of the
resulting isocyanide complexes 6 and 7 were analogous to those
observed for compounds 4 and 5, and again, the resonances of
the bridgehead methyl groups are most notably affected by
switching from a η5- to a η3-coordination mode (vide supra).
The CN resonance in 6 is found at 197.6 ppm, whereas the
corresponding signal could not be resolved for 7. Single crystals
of 6 and 7 suitable for X-ray diffraction analysis were grown
from saturated diethyl ether solutions at −30 °C. The
molecular structures are very similar to those established for
4 and 5, with the eboInd ligand bound in an η3-fashion and
adopting an exo-conformation relative to the isocyanide ligand
(Figures 6 and 7). The metal to isocyanide bond lengths are
1.790(5) Å (Fe−C23) and 1.9044(13) Å (Ru−C23), with the
latter value being similar to the distance found for [(η5-
C5Me5)Ru(η3-oIndMe)(CN-o-Xy)] (1.8943(17) Å).3a,22
Addition of the N-heterocyclic carbene 1,3,4,5-tetramethyli-
midazol-2-ylidene (IMe) proved to be more difficult, and
indeed, no reaction with 2 was observed even upon heating for
a prolonged period of time, eventually resulting in the
decomposition of the starting material. This could be due to
the small size of the iron atom, not offering sufficient space for
the addition of the carbene ligand. The ruthenium complex 3,
however, was capable of accommodating the carbene, and the
carbene complex 8 was isolated as a yellow solid after heating at
60 °C for three days. The 1H NMR spectrum of 8 clearly shows
the expected signal shifts for the eboInd ligand binding in an η3-
fashion, although the shifts of signals assigned to the bridgehead
methyl groups are not quite as pronounced as those observed
for the previous allyl-ruthenium species 5 and 7. The carbene
carbon signal is found at 194.1 ppm in the 13C NMR spectrum,
and it is worth mentioning that, apart from this resonance, the
Figure 4. ORTEP drawing of 4 with thermal displacement parameters
drawn at 30% probability. The alternative disordered positions of the
C5Me5 ligand and hydrogen atoms are omitted for clarity. Selected
bond lengths [Å] and angles [deg]: Fe−C(C5Me5) 2.088(6)−
2.1249(7), Fe−C1 2.104(3), Fe−C2 1.984(3), Fe−C3 2.122(3),
Fe−C23 1.746(3), C23−O 1.157(3), C1−C2 1.400(4), C2−C3
1.411(4), C3−C4 1.471(4), C4−C5 1.409(4), C5−C7 1.391(4), C7−
C8 1.393(4), C8−C9 1.375(4), C9−C10 1.384(4), C10−C4
1.396(4); O−C23−Fe 173.3(2), C1−C2−C3 114.8(3), C2−C3−C4
118.3(3), C3−C4−C5 119.9(2).
1
carbene fragment gives rise to a duplicate set of H and 13C
D
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Ru) provides evidence for the ability of the eboInd ligand to
coordinate to transition metals in an η5-fashion, despite the
presumably weak π-interaction with the annelated benzene ring.
The presence of this weaker bond allows these half-open
metallocenes to change their hapticity upon addition of a two-
electron donor ligand and to switch readily from an η5- to an
η3-coordination mode. However, these switches were signifi-
cantly slower than previously observed for the unbridged open
indenyl (oIndMe) system, and this lower reactivity is probably
associated with the greater rigidity of the eboInd ligand.
EXPERIMENTAL SECTION
■
All synthetic and spectroscopic manipulations were carried out under
an atmosphere of purified nitrogen, either in a Schlenk apparatus or in
a glovebox. Solvents were dried and deoxygenated either by distillation
under a nitrogen atmosphere from sodium benzophenone ketyl
(THF) or by an MBraun GmbH solvent purification system (all other
solvents). NMR spectra were obtained on a Bruker DRX 400 or a
Bruker Avance III 400 spectrometer at 400 or 300 MHz (1H) and 101
or 75 MHz (13C). The residual solvent signal was used as a chemical
shift reference (δH = 7.16 ppm for C6D6, δH = 1.72, 3.58 ppm for
Figure 6. ORTEP drawing of 6 with thermal displacement parameters
drawn at 30% probability. The hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: Fe−C(C5Me5)
2.084(5)−2.119(5), Fe−C1 2.110(5), Fe−C2 1.993(5), Fe−C3
2.146(5), Fe−C23 1.790(5), C23−N 1.194, C1−C2 1.418(7), C2−
C3 1.404(7), C3−C4 1.457(7), C4−C5 1.409(7), C5−C7 1.384(7),
C7−C8 1.390(7), C8−C9 1.399(7), C9−C10 1.384(7), C10−C4
1.400(7); Fe−C23−N 170.9(5), C1−C2−C3 115.3(5), C2−C3−C4
118.7(5), C3−C4−C5 120.7(5).
[D8]THF) for the 1H NMR spectra and the solvent signal (δC
=
128.04 ppm for C6D6, δH = 25.31, 67.21 ppm for [D8]THF) for the
13C NMR spectra. The number of protons attached to each carbon was
determined by 13C-DEPT135 experiments. If required, signal assign-
ment was achieved by two-dimensional H,H-COSY, H,H-NOESY,
H,C-HSQC, and H,C-HMBC NMR spectra. They were recorded
using standard Bruker pulse programs; sweep widths, digital
resolution, and pulse delays were optimized for the samples under
investigation. Mixing times of 1000 and 2000 ms were used for the
H,H-NOESY experiments. A Bruker Vertex 70 spectrometer was used
for recording IR spectra. Elemental analyses were performed by
combustion and gas chromatographic analysis with an Elementar
VarioMICRO instrument. Cyclic voltammograms were recorded on a
Metrohm μAutolab Type III potentiostat/galvanostat in a THF
solution containing 0.1 M [n-Bu4N][PF6] as supporting electrolyte;
99.9% platinum wires (φ 0.6 mm, Chempur) were used as working
and counter electrode, and the potentials were measured against a
99.9% silver wire (φ 0.6 mm, Chempur). Redox potentials were
calculated using the formula ΔE1/2 = 1/2(Epox + Epred), where Epox and
red
Figure 7. ORTEP drawing of 7 with thermal displacement parameters
drawn at 30% probability. The hydrogen atoms are omitted for clarity.
Selected bond lengths [Å] and angles [deg]: Ru−C(C5Me5)
2.2153(12)−2.2483(12), Ru−C1 2.2182(13), Ru−C2 2.0969(13),
Ru−C3 2.2309(12), Ru−C23 1.9044(13), C23−N 1.1828(16), C1−
C2 1.420(2), C2−C3 1.4216(18), C3−C4 1.4731(17), C4−C5
1.4096(18), C5−C7 1.3924(18), C7−C8 1.393(2), C8−C9
1.383(2), C9−C10 1.3874(18), C10−C4 1.4007(17); Ru−C23−N
177.97(11), C1−C2−C3 114.71(11), C2−C3−C4 117.88(12), C3−
C4−C5 120.70(11).
Ep are peak potentials. Ferrocene was used as a standard for the
measurement of 2. The couple [(η5-C5H5)2Fe]+/[(η5-C5H5)2Fe]
displayed a reversible cyclic voltammetric trace with a redox potential
ΔE1/2 = +0.56 V (in THF) under these conditions.23 Cobaltocene was
used as a standard for 3, which was itself referenced to ferrocene. The
couple [(η5-C5H5)2Co]+/[(η5-C5H5)2Co] displayed a reversible cyclic
voltammetric trace with a redox potential ΔE1/2 = −0.82 V (in THF)
under the chosen measuring conditions. 4,4-Dimethyl-1-tetralone,10
1,1-dimethyl-1,2-dihydronaphthalene,11 [FeI2(thf)2],24 Li(C5Me5),25
26
and [(C5Me5)RuCl]4 were prepared according to the literature; all
other reagents were obtained commercially and used as received.
X-ray Diffraction Studies. Data were recorded at 100 K on
Oxford Diffraction diffractometers using monochromated Mo Kα or
mirror-focused Cu Kα radiation (Table 1). The structures were refined
anisotropically using the SHELXL-97 program.27 Hydrogen atoms
were either (i) located and refined isotropically (H1, H2, H3 for all
structures); (ii) included as idealized methyl groups allowed to rotate,
but not tip; or (iii) placed geometrically and allowed to ride on their
attached carbon atoms. Special features: In the iron complexes 2 and 4,
the C5Me5 ligand was disordered over two positions. Appropriate
restraints and constraints were used to ensure stability of refinement
(for details see the Supporting Information). Data for 6 were weak,
and the R values are correspondingly poor, but the structure serves as
proof of the nature of 6. Complete data have been deposited at the
Cambridge Crystallographic Data Centre under the numbers CCDC
941708 (2), 941709 (3), 941710 (4), 941711 (5), 941712 (6), and
941713 (7). These data can be obtained free of charge from www.ccdc.
cam.ac.uk/data_request/cif.
NMR signals, indicating hindered rotation around the
ruthenium−carbene bond at room temperature on the NMR
time scale. Finally it should be noted that neither 2 nor 3
reacted with PMe3, even at elevated temperatures. Apparently,
the metal atoms in 2 and 3 are quite efficiently shielded by the
bulky C5Me5 and eboInd ligands, so that only rod-like or flat
molecules readily coordinate and induce switching of the
eboInd ligand.
CONCLUSIONS
■
Potassium 1,1-dimethyl-1,2-dihydronaphthalenide, K(eboInd)
(1), provides convenient access to half-open metallocenes
containing a novel edge-bridged open indenyl ligand. The
isolation and structural characterization of the sandwich
complexes [(η5-C5Me5)M(η5-eboInd)] (2, M = Fe; 3, M =
E
dx.doi.org/10.1021/om400485a | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
Table 1. Crystallographic Data
2
3
4
5
6
7
empirical formula
fw
C22H28Fe
348.29
C22H28Ru
393.51
C23H28FeO
376.30
C23H28ORu
421.52
C31H37FeN
479.47
C31H37NRu
524.69
temperature (K)
wavelength λ (Å)
cryst syst
100(2)
100(2)
100(2)
100(2)
100(2)
100(2)
0.71073
monoclinic
P21/c
0.71073
0.71073
triclinic
1.54184
monoclinic
P21/n
0.71073
triclinic
0.71073
triclinic
monoclinic
P21/c
space group
a [Å]
P1
P1
̅
P1
̅
̅
8.1835(4)
24.1385(12)
9.9365(6)
90
13.6723(4)
8.5436(2)
16.0804(4)
90
8.2042(8)
10.1965(8)
13.3248(12)
108.566(8)
98.077(8)
108.480(8)
965.37(15)
2
8.1412(2)
18.4127(2)
13.4624(2)
90
8.5368(8)
10.486(2)
15.658(3)
79.902(18)
85.608(12)
66.907(14)
1269.3(4)
2
8.49475(18)
11.27251(18)
14.7874(4)
92.387(2)
103.370(2)
109.317(2)
1289.25(5)
2
b [Å]
c [Å]
α [deg]
β [deg]
112.222(6)
90
103.142(2)
90
98.800(2)
90
γ [deg]
volume [Å3]
1817.04(17)
4
1829.17(8)
4
1994.28(6)
4
Z
reflns collected
independent reflns
46 155
77 440
33 473
33 698
39 518
62 483
4004 [Rint = 0.0580] 4193 [Rint = 0.0472] 3966 [Rint = 0.1060] 4075 [Rint = 0.0291] 4486 [Rint = 0.1631] 7416 [Rint = 0.0319]
goodness of fit on F2 1.025
1.097
1.059
1.060
1.099
1.074
ρcalcd [g cm−3
]
1.273
1.429
1.295
1.404
1.254
1.352
μ [mm−1
]
0.828
0.855
0.788
6.396
0.613
0.627
2
R(Fo ), [I > 2σ(I)]
0.0356
0.0246
0.0581
1.739/−0.429
0.0523
0.1005
0.551/−0.385
0.0182
0.0470
0.381/−0.427
0.0823
0.1981
1.159/−0.472
0.0214
0.0543
0.540/−0.393
2
Rw (Fo )
0.0851
Δρ [e Å−3
]
0.810/−0.329
concentrated solution of 2 in HMDSO at −30 °C for several weeks.
1H NMR (400 MHz; C6D6): δ 7.20 (d, JHH 8.6 Hz, 1H, H10), 6.94−
6.78 (m, 3H, H7, 8, 9), 5.77 (d, JHH 5.2 Hz, 1H, H3), 3.62 (t, JHH 5.9
Hz, 1H, H2), 2.07 (d, JHH 6.4 Hz, 1H, H1), 1.73 (s, 3H, H12), 1.42 (s,
15H, C5Me5), −0.14 (s, 3H, H11) ppm. 13C NMR (100 MHz; C6D6):
δ 133.6 (phenyl), 127.5 (C10), 125.6 (phenyl), 122.5 (phenyl), 97.7
(C4), 83.3 (C2), 80.1 (C5Me5), 75.9 (C3), 63.9 (C5), 44.2 (C1), 35.4
(C6), 33.9 (C11), 27.4 (C12), 9.8 (C5Me5) ppm. Anal. Calcd for
C22H28Fe: C, 75.86; H, 8.10. Found: C, 75.19; H, 7.88.
Chart 1. Numbering Scheme for the Assignment of NMR
Resonances to the eboInd Fragment
[(η5-C5Me5)Ru(η5-eboInd)] (3). To a suspension of 271.9 mg
(0.25 mmol) of [(C5Me5)RuCl]4 in 10 mL of THF at −78 °C was
slowly added by syringe a solution of 196.3 mg (1 mmol) of 1 in 10
mL of THF. After removing the cooling bath and stirring overnight a
dark red suspension was obtained. The solvent was removed in vacuo,
and the residue extracted with 20 mL of pentane followed by another
10 mL of pentane. After removing the solvent in vacuo a dark red oil
was obtained. Column chromatography under argon over neutral
alumina (4 wt % H2O) with pentane gave after removal of the solvent
in vacuo 272.6 mg (0.69 mmol, 69%) of a bright orange oil, which
Potassium 1,1-Dimethyl-1,2-dihydronaphthalenide (Ke-
boInd) (1). To a suspension of 1.2 g of potassium tert-butoxide
(10.7 mmol) in pentane was added 1.7 g of 1,1-dimethyl-1,2-
dihydronaphthalene (10.7 mmol). The mixture was stirred and cooled
to −78 °C. Then 4.8 mL of n-butyllithium (2.5 M in hexane, 12
mmol) was added slowly by syringe. The mixture was allowed to warm
to room temperature while stirring overnight. The orange precipitate
thus formed on a frit and washed three times with 20 mL of pentane.
After drying in vacuo 1.9 g (9.7 mmol, 90% yield) of orange pyrophoric
1 was obtained. 1H NMR (400 MHz; [D8]THF): δ 6.74 (dd, 1H, JHH
0.9, 7.5 Hz, H7), 6.42 (dt, 1H, JHH 1.4, 7.5 Hz, H9), 6.22 (dd, 1H, JHH
1.4, 8.0 Hz, H10), 5.95 (dt, 1H, JHH 1.3, 7.1 Hz, H8), 5.90 (dd, 1H,
JHH 6.5, 8.0 Hz, H2), 4.25 (d, 1H, JHH 6.5 Hz, H3), 3.39 (d, 1H, JHH
8.0 Hz, H1), 1.03 (s, 6H, H11) ppm. 13C NMR (100 MHz;
[D8]THF): δ 141.8 (C4), 128.0 (C2), 124.9 (C5), 124.8 (C9), 124.6
(C7), 116.6 (C10), 110.9 (C8), 92.1 (C1), 79.1 (C3), 36.7 (C6), 30.3
(C11) ppm. The extremely air-sensitive nature of the product made it
impossible to obtain an accurate elemental analysis.
1
slowly crystallized at room temperature. H NMR (400 MHz; C6D6):
δ 6.84−6.70 (m, 4H, H7, 8, 9, 10), 5.54 (d, JHH 4.8 Hz, 1H, H3), 4.06
(dd, JHH 4.8, 6.2 Hz, 1H, H2), 2.32 (dd, JHH 0.9, 6.2 Hz, 1H, H1), 1.57
(s, 3H, H12), 1.50 (s, 15H, C5Me5), 0.30 (s, 3H, H11) ppm. 13C NMR
(100 MHz; C6D6): δ 131.8 (C7), 125.5 (C10), 124.1 (C8), 120.8
(C9), 98.0 (C4), 85.0 (C5Me5), 81.6 (C2), 76.0 (C3), 67.7 (C5), 45.4
(C1), 38.9 (C6), 35.2 (C11), 27.7 (C12), 10.3 (C5Me5) ppm. Anal.
Calcd for C22H28Ru: C, 67.15; H, 7.17. Found: C, 67.33; H, 7.17.
[(η5-C5Me5)Fe(η3-eboInd)(CO)] (4). CO gas was passed through a
solution of 50 mg (0.14 mmol) of 2 in 20 mL of toluene for 5 min.
The closed vessel was stirred at 70 °C for 3 d. This resulted in a color
change from green to orange. After removing the solvent in vacuo the
orange solid was dissolved in Et2O. Upon concentrating the solution
and storing at −30 °C overnight 29 mg (0.08 mmol, 55%) of orange
[(η5-C5Me5)Fe(η5-eboInd)] (2). A dark purple solution of 454 mg
(1.0 mmol) of [(THF)2FeI2] in 10 mL of THF was cooled to −78 °C.
A suspension of 142 mg (1.0 mmol) of [Li(C5Me5)] in 10 mL of THF
was added by syringe. After stirring for 10 min at −78 °C a yellow
solution was obtained. To this was added slowly by syringe a solution
of 196 mg (1.0 mmol) of K(eboInd) 1 in 10 mL of THF. After stirring
overnight and allowing the mixture to slowly reach room temperature,
a green solution was obtained. After removing the solvent in vacuo the
green residue was extracted three times with 20 mL of pentane. The
pentane was removed in vacuo, and the resulting green oil was further
purified by column chromatography under an argon atmosphere over
neutral alumina (4 wt % H2O) with pentane. The product was
obtained as a green oil (183 mg, 0.53 mmol, 53% yield). Single crystals
suitable for X-ray diffraction analysis could be obtained by storing a
1
crystals was obtained. H NMR (400 MHz; C6D6): δ 7.00 (d, JHH 6.8
Hz, 1H, H7), 6.90 (d, JHH 6.6 Hz, H10), 6.87 (dt, 2.3, 7.2 JHH Hz, 1H,
H8), 6.84 (dt, JHH 1.8, 7.2 Hz, 1H, H9), 3.91 (t, JHH 5.8 Hz, 1H, H2),
3.89 (d, JHH 2.7 Hz, 1H, H3), 3.32 (dd, JHH 2.9, 5.8 Hz, 1H, H1), 1.55
(s, 3H, CMe2), 1.49 (s, 3H, CMe2), 1.46 (s, 15H, C5Me5) ppm. 13C
NMR (100 MHz; C6D6): δ 223.5 (CO), 143.9 (C4), 140.2 (C5),
126.0 (C10), 125.9 (C8), 124.2 (C7,9), 89.0 (C5Me5), 76.6 (C2), 69.4
(C1), 58.2 (C3), 40.1 (C6), 38.3 (CMe2), 30.2 (CMe2), 9.7 (C5Me5)
F
dx.doi.org/10.1021/om400485a | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
ppm. Anal. Calcd for C23H28FeO: C, 73.41; H, 7.50. Found: C, 73.53;
H, 7.54. IR (ATR): ν(CO/cm−1) = 1918.
3H, CMe), 1.15 (s, 3H, H11) ppm. 13C NMR (100 MHz; C6D6): δ
194.1 (NCN), 147.5 (C4), 142.0 (C5), 125.5 (C10), 124.0 (CMe),
123.5 (C9), 123.3 (C7), 123.2 (CMe), 120.8 (C8), 85.7 (C5Me5), 67.3
(C2), 53.3 (C1), 46.2 (C3), 42.1 (C12), 39.3 (NMe), 39.2 (C6), 36.3
(NMe), 27.8 (C11), 10.1 (C5Me5), 9.7 (CMe), 9.4 (CMe) ppm. Anal.
Calcd for C29H40N2Ru: C, 67.28; H, 7.79; N, 5.41. Found: C, 67.36;
H, 7.68; N, 5.35.
[(η5-C5Me5)Ru(η3-eboInd)(CO)] (5). CO gas was passed through a
solution of 50 mg (0.13 mmol) of 3 in 20 mL of toluene for 5 min.
After this the closed vessel was stirred at room temperature for 2 d,
after which a color change from orange to yellow had occurred. After
removing the solvent in vacuo the yellow solid was dissolved in diethyl
ether. After concentrating the solution and storing at −30 °C
overnight 29 mg (0.07 mmol, 54%) of yellow crystals was obtained. 1H
NMR (400 MHz; C6D6): δ 7.08 (dd, JHH 1.6, 7.2 Hz, 1H, H10), 7.04
(dd, JHH 1.7, 7.2 Hz, 1H, H7), 6.92 (dt, JHH 1.8, 7.3 Hz, 1H, H9), 6.87
(dt, JHH 1.6, 7.3 Hz, 1H, H8), 4.34 (dd, JHH 2.0, 5.2 Hz, 1H, H3), 3.36
(d, JHH 5.2 Hz, 1H, H1), 3.35 (dt, JHH 2.1, 6.9 Hz, 1H, H2), 1.62 (s,
3H, CMe2), 1.59 (s, 3H, CMe2), 1.57 (s, 15H, C5Me5) ppm. 13C NMR
(100 MHz; C6D6): δ 209.7 (CO), 144.0 (C4), 140.3 (C5), 126.0
(C7), 125.8 (C9), 124.3 (C8, 10), 93.1 (C5Me5), 73.4 (C1), 67.8
(C2), 56.2 (C3), 40.2 (C6), 38.0 (CMe2), 31.1 (CMe2), 10.1 (C5Me5)
ppm. Anal. Calcd for C23H28RuO: C, 65.53; H, 6.70. Found: C, 65.48;
H, 6.66. IR (ATR): ν(CO/cm−1) = 1922.
ASSOCIATED CONTENT
* Supporting Information
■
S
Crystallographic information files (CIF), NMR spectra, the
cyclovoltammetric data for 3, and the crystal structure data for
[(η5-C5Me5)Ru(η3-oIndMe)(CN-o-Xy)]. This material is avail-
able free of charge via the Internet at http://pubs.acs.org.
AUTHOR INFORMATION
Notes
The authors declare no competing financial interest.
■
[(η5-C5Me5)Fe(η3-eboInd)(CN-o-Xy)] (6). A 44.6 mg (0.34 mmol)
amount of 2,6-dimethylphenyl isocyanide was added to a solution of
120 mg (0.34 mmol) of 2 in 20 mL of toluene. The solution was
heated at 70 °C for 3 d, resulting in an orange solution. After removal
of the solvent in vacuo the compound was obtained as an orange solid,
which was recrystallized by cooling a concentrated Et2O solution to
−30 °C overnight. This gave 6 as an orange crystalline solid (72 mg,
ACKNOWLEDGMENTS
■
We thank Dr. Andreas Glockner for helpful discussions.
̈
REFERENCES
■
1
(1) (a) Ernst, R. D. Acc. Chem. Res. 1985, 18, 56−62. (b) Ernst, R. D.
Chem. Rev. 1988, 88, 1255−1291. (c) Ernst, R. D. Comments Inorg.
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0.15 mmol, 44% yield). H NMR (400 MHz; C6D6): δ 6.89 (dd, JHH
1.5, 7.5 Hz, 1H, H10), 6.80−6.70 (m, 3H, phenyl), 6.66 (d, JHH 7.6
Hz, 1H, H7), 6.61 (dt, JHH 1.4, 7.4 Hz, 1H, H9), 6.44 (dt, JHH 1.4, 7.4
Hz, 1H, H8), 4.13 (t, JHH 6.4 Hz, 1H, H2), 3.88 (dd, JHH 1.4, 6.0 Hz,
1H, H3), 3.34 (dd, JHH 1.4, 7.0 Hz, 1H, H1), 2.30 (s, 6H, C6H4-o-
Me2), 1.58 (s, 6H, CMe2), 1.57 (s, 15H, C5Me5) ppm. 13C NMR (100
MHz; C6D6): δ 197.6 (oXyNC), 145.3 (C4),140.8 (C5), 134.6 (ipso-
phenyl), 132.0 (ipso-C-NC), 127.7 (phenyl), 125.3 (phenyl), 125.0
(C7), 124.9 (C9), 124.3 (C10), 122.7 (C8), 87.2 (C5Me5), 75.6 (C2),
66.4 (C1), 55.5 (C3), 40.0 (C6), 38.9 (CMe2), 30.1 (CMe2), 19.5
(C6H4-o-Me2), 10.0 (C5Me5) ppm. Anal. Calcd for C31H37FeN: C,
77.65; H, 7.78; N, 2.92. Found: C, 77.47; H, 7.73; N, 2.88. IR (ATR):
ν(CN/cm−1) = 1990.
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[(η5-C5Me5)Ru(η3-eboInd)(CN-o-Xy)] (7). Toluene was added to
a mixture of 50 mg (0.13 mmol) of 3 and 17 mg (0.13 mmol) of 2,6-
dimethylphenyl isocyanide. Full conversion of the starting materials
was observed after 2 d at room temperature. The solvent was removed
in vacuo. Recrystallization from a concentrated Et2O solution at −30
1
(5) (a) Calhorda, M. J.; Romao, C. C.; Veiros, L. F. Chem.Eur. J.
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°C gave 39 mg (0.08 mmol, 58%) of yellow crystals. H NMR (400
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MHz; C6D6): δ 6.98 (dd, JHH 1.5, 7.5 Hz, 1H, H10), 6.83 (t, JHH 7.5
Hz, 1H, H7), 6.75 (t, 1H, phenyl), 6.74 (d, 2H, phenyl), 6.64 (dt, JHH
1.4, 7.5 Hz, 1H, H9), 6.48 (dt, JHH 1.5, 7.5 Hz, 1H, H8), 4.25 (d, JHH
5.8 Hz, 1H, H3), 3.51 (dd, JHH 5.8, 6.8 Hz, 1H, H2), 3.28 (dd, JHH 1.3,
6.8 Hz, 1H, H1) 2.24 (s, 6H, C6H4-o-Me2), 1.69 (s, 15H, C5Me5), 1.68
(s, 3H, CMe2), 1.66 (s, 3H, CMe2) ppm. 13C NMR (100 MHz; C6D6):
δ 145.5 (C4), 141.0 (C5), 134.6 (ipso-phenyl), 131.5 (ipso-C-NC),
127.6 (phenyl), 125.5 (phenyl), 125.2 (C7), 124.9 (C9), 123.9 (C10),
122.6 (C8), 91.0 (C5Me5), 71.3 (C2), 64.9 (C1), 53.6 (C3), 40.0
(C6), 38.3 (CMe2), 31.0 (CMe2), 19.2 (C6H4-o-Me2), 10.3 (C5Me5)
ppm. The signal for the isocyanide carbon could not be observed.
Anal. Calcd for C31H37NRu: C, 70.96; H, 7.11; N, 2.67. Found: C,
71.01; H, 7.09; N, 2.63. IR (ATR): ν(CN/cm−1) 1955.
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[(η5-C5Me5)Ru(η3-eboInd)(IMe)] (8). C6D6 was added to a
mixture of 50 mg (0.13 mmol) of 3 and 16 mg (0.13 mmol) of
1,3,4,5-tetramethylimidazol-2-ylidene. Full conversion of the starting
materials was observed after 3 d at 60 °C. The solvent was removed in
vacuo, and the compound was precipitated from pentane/hexame-
thyldisiloxane at −30 °C. This gave 51 mg (0.10 mmol, 78% yield) of a
yellow solid. 1H NMR (400 MHz; C6D6): δ 6.98 (dd, JHH 1.5, 7.5 Hz,
1H, H10), 6.73 (dt, JHH 1.5, 7.3 Hz, 1H, H9), 6.67 (dt, JHH 1.5, 7.3 Hz,
1H, H8), 6.57 (dd, JHH 1.5, 7.5 Hz, 1H, H7), 3.59 (s, 3H, NMe), 3.56
(d, JHH 6.3 Hz, 1H, H3), 3.55 (dt, JHH 1.8, 5.7 Hz, 1H, H2), 3.47 (s,
3H, NMe), 2.99 (dd, JHH 1.7, 6.3 Hz, 1H, H1), 1.74 (s, 3H, H12), 1.55
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