Naphthalene-bridged ansa-nickelocene: Synthesis, structure, electrochemical, and magnetic measurements

Article abstract of DOI:10.1002/ejic.201200698

The reaction of naphthalene-1,8-diylbis(cyclopentadienylsodium) (1) with the nickel triple-decker compound [Ni₂Cp₃]BF₄ affords the paramagnetic ansa-nickelocene 1,1'-(naphthalene-1″,8″- diyl)nickelocene (2). Alternatively, 2 can directly be obtained by a salt metathesis reaction of the disodium salt 1 with hexaammine nickel(II) dichloride [Ni(NH₃)₆]Cl₂. For magnetic dilution experiments, the corresponding but diamagnetic ansa-ruthenocene 3 was synthesized by reaction of the disodium salt 1 with dichloridotetrakis(dimethyl sulfoxide)ruthenium(II). The solid-state molecular structures of 2 and 3 were determined by single-crystal X-ray diffraction analysis and revealed bent sandwich complexes. Cyclic voltammetry studies of 2 indicate three oxidation states. The electronic structure of complex 2 has been investigated by variable-temperature ¹H NMR spectroscopy, magnetic measurements, and DFT calculations. Superconducting quantum interference device (SQUID) magnetometry has been performed for the neat and diluted samples of 2. The neat crystalline material of 2 displays antiferromagnetic behavior, whereas the susceptibility of the magnetically diluted sample runs into saturation at T < 4 K. This property is in agreement with an intermolecular antiferromagnetic interaction in the bulk material of compound 2 and the triplet ground state calculated by broken-symmetry (BS)-DFT calculations. Copyright

Full text of DOI:10.1002/ejic.201200698

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DOI: 10.1002/ejic.201200698
Naphthalene-Bridged ansa-Nickelocene: Synthesis, Structure, Electrochemical,
and Magnetic Measurements
Sabrina Trtica,[a] Enno Meyer,[a] Marc Heinrich Prosenc,*[a] Jürgen Heck,*[a]
Tim Böhnert,[b] and Detlef Görlitz[b]
Dedicated to Professor Dieter Fenske on the occasion of his 70th birthday
Keywords: Metallocenes / Sandwich complexes / Nickel / Magnetic properties
The reaction of naphthalene-1,8-diylbis(cyclopentadienyl-
The electronic structure of complex 2 has been investigated
sodium) (1) with the nickel triple-decker compound [Ni2Cp3]- by variable-temperature 1H NMR spectroscopy, magnetic
BF4 affords the paramagnetic ansa-nickelocene 1,1Ј-(naphth-
alene-1ЈЈ,8ЈЈ-diyl)nickelocene (2). Alternatively, 2 can directly
be obtained by a salt metathesis reaction of the disodium salt
measurements, and DFT calculations. Superconducting
quantum interference device (SQUID) magnetometry has
been performed for the neat and diluted samples of 2. The
neat crystalline material of 2 displays antiferromagnetic be-
havior, whereas the susceptibility of the magnetically diluted
sample runs into saturation at T Ͻ 4 K. This property is in
agreement with an intermolecular antiferromagnetic interac-
tion in the bulk material of compound 2 and the triplet
ground state calculated by broken-symmetry (BS)-DFT cal-
culations.
1
with hexaammine nickel(II) dichloride [Ni(NH3)6]-
Cl2. For magnetic dilution experiments, the corresponding
but diamagnetic ansa-ruthenocene 3 was synthesized by re-
action of the disodium salt 1 with dichloridotetrakis(dimeth-
ylsulfoxide)ruthenium(II). The solid-state molecular struc-
tures of 2 and 3 were determined by single-crystal X-ray dif-
fraction analysis and revealed bent sandwich complexes. Cy-
clic voltammetry studies of 2 indicate three oxidation states.
been investigated extensively, studies on ansa-nickelocenes
with a linker between the Cp rings are still rare, although
ansa-metallocenes have received great attention over the last
20 years due to their markedly different structural and elec-
tronic properties and their particular reactivity relative to
nonbridged metallocenes.[7] Mainly ferrocene complexes
with different bridging functions were reported. Most com-
monly, these complexes are synthesized by salt elimination
reactions from dimetallated metallocenes and suitable di-
halides. This synthetic route is obstructed for nickelocene
due to the reactivity of nickelocene toward organolithium
compounds.[8a] However, in very special cases, deproton-
ation reactions in the distant ligand sphere of nickelocene
derivatives are possible.[8b] With respect to these difficulties
in synthesis, only very few nickelocenophanes were known.
The first nickelocenophane synthesized in 1976 exhibits
a 3-oxopentamethylene bridge.[9] Recently, two [n]carba-
nickelocenophanes (n = 4, 6) were synthesized by ring-clos-
ing metathesis of 1,1Ј-bis(alkenyl)-substituted nickel-
ocenes.[10] A peculiar type of nickelocenophane is the dinu-
clear nickel complex bis(fulvalene)dinickel,[11a] which dis-
plays a reduced paramagnetism, although it is composed
of two nickelocenes.[11b] These complexes have a relatively
nonstrained structure due to their long handle between the
two cyclopentadienyl (Cp) ligands. Recently, the first
Introduction
Nickelocene is a very prominent example of paramag-
netic metallocenes because it contains 20 valence electrons,
but is stable under inert-gas conditions. The lowest anti-
bonding orbitals in nickelocene are twofold-degenerated
and occupied by two electrons to result in a triplet ground
state.[1] Since its discovery in 1953,[2] many groups have in-
vestigated the magnetic properties and discussed the lack of
an EPR signal that results from a strong zero-field splitting
in the triplet ground state.[3] Magnetic susceptibility mea-
surements on nickelocene revealed a deviation from normal
Curie–Weiss behavior below 70 K.[4] The origin of this devi-
ation was interpreted by Prins et al., who attributed it to
the zero-field splitting,[5] whereas Baltzer et al. ascribed it to
a predominantly ferromagnetic coupling of the nickelocene
molecules to its nearest neighbors in the crystalline state.[6]
Whereas nickelocene and substituted derivatives have
[a] Institute of Inorganic and Analytical Chemistry, University of
Hamburg,
Martin-Luther-King-Platz 6, 20146 Hamburg, Germany
Homepage: http://www.chemie.uni-hamburg.de/ac/heck/
index.html
[b] Institute of Applied Physics and Microstructure Research
Centre, University of Hamburg,
Jungiusstrasse 11, 20355 Hamburg, Germany
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M. H. Prosenc, J. Heck et al.
FULL PAPER
strained [2]nickelocenophane was prepared with a tet- 1,1Ј-diyl)]dinickel(Ni–Ni) to the [5]nickelocenophan-8-one
ramethyldisilane bridge.[12]
in the presence of triphenylphosphane.[9]
Here we report the synthesis of the first ansa-nickelocene
In a more straightforward synthesis of compound 2, an
with a rigid bridge and a strained structure in which the equimolar amount of hexaammine nickel(II) chloride was
two Cp units are linked by a naphthalene molecule. We de- subjected to reaction with the disodium salt 1 (Scheme 1).
scribe the structural parameters and redox as well as mag- In the same manner, the corresponding Ru complex 3 was
netic properties.
synthesized with dichloridotetrakis(dimethylsulfoxide)ru-
thenium(II) (Scheme 1). Complex 3 was taken as a diamag-
netic host material for compound 2 in doping experiments.
Results and Discussion
Synthesis
Molecular Structure
In our ongoing research on stacked nickelocene com-
plexes, we attempted to synthesize the unmethylated deriva-
tive of 1,8-bis(pentamethylnickelocenyl)naphthalene.[13]
As starting materials, naphthalene-1,8-diylbis(cyclopenta-
dienylsodium) (1) and [Cp3Ni2]+ triple-decker as CpNi
transfer reagent[14] were used. But instead of the desired
unmethylated 1,8-bis(nickelocenyl)naphthalene (Scheme 1),
nickelocenophane complex 2 and nickelocene were ob-
tained.
Suitable crystals of the complex 2 and 3 for X-ray struc-
ture analysis were obtained by crystallization from n-pent-
ane solution, with data listed in Table 1. Compound 2 crys-
¯
tallizes in the triclinic space group P1 with two independent
molecules in the asymmetric unit, and compound 3 crys-
tallizes in the monoclinic space group P21/c with four inde-
pendent molecules in the asymmetric unit.
Table 1. Selected interatomic distances [pm] and angles [°] of 2 and
3 obtained from X-ray structure analysis and DFT calculations.
2: X-ray
2: DFT
3: X-ray
M = NiII
M = NiII M = Ru
C1–C11
C8–C16
C1–C8
149.4(5)
149.9(5)
259.6(5)
309.1(10)
387.0(12)
387.0(12)
210.6(5)
211.0(5)
216.4(7)
213.4(5)
212.3(5)
216.2(6)
219.4(6)
217.1(5)
217.1(5)
219.4(7)
178.3(5)
178.2(5)
353.2(11)
148.9
148.9
258.7
311.0
404.1
404.1
213.6
213.6
218.7
218.8
218.8
218.7
224.9
224.8
224.8
224.9
184.0
184.0
363.9
149.5(4)
148.5(4)
261.7(7)
311.9(9)
388.4(9)
388.2(10)
209.4(4)
210.3(4)
216.0(6)
215.6(5)
215.4(4)
216.2(6)
221.8(6)
220.0(4)
221.1(4)
221.3(6)
178.9(5)
179.2(5)
356.0(1)
C11–C16
C13–C18
C14–C19
M1–C11
M1–C16
M1–C12
M1–C15
M1–C17
M1–C20
M1–C13
M1–C14
M1–C18
M1–C19
M1–XCp1
M1–XCp2
XCp1–XCp2
Scheme 1. Synthesis of ansa-nickelocene 2 and ansa-ruthenocene 3.
C11–C1–C2
C16–C8–C7
C11–C1–C9
C16–C8–C9
C2–C1–C9
C7–C8–C9
C1–C9–C8
114.5(19)
114.3(19)
125.3(18)
126.0(18)
120.1(19)
119.8(18)
127.3(16)
164.4(14)
20.2(6)
113.8
113.8
126.6
126.6
119.6
119.6
127.0
162.9
26.7
114.5(17)
114.1(17)
125.8(16)
126.2(16)
119.7(15)
119.7(15)
127.2(15)
167.6(12)
19.4(8)
The mechanism for the reaction depicted in Scheme 1 is
still unknown. However, this reaction very much resembles
the formation of the corresponding Co complex by the re-
duction of 1,8-bis(cobaltocenyl)naphthalene.[15] The inter-
mediately formed bis(cyclopentadienyl)cobaltate is isoelec-
tronic to nickelocene. Presumably, a naphthalene-bound
nickelocene intermediate was achieved, but cleavage of the
unsubstituted Cp ligand and subsequent intramolecular re-
arrangement might precede formation of the ansa-nickel-
ocene compound 2. The driving force of this reaction might
be the chelating effect of the naphthalene-1,8-diylbis(cyclo-
pentadienyl) ligand. A related dismutation reaction was re-
ported by Köhler and co-workers from fulvalene-bridged
binickelocene to form bis(fulvalene)dinickel and nickelo-
[a]
δ(XCp1–M1–XCp2
)
α(plane Cp1–plane Cp2)
Plane(Cp)–plane(naph)
C11–C1–C8–C16; ring
slippage [pm]
80.6(4)/81.4
7.9(2); 7.8/8.8 7.0;
89.5/89.5 83.5/83.2
5.4(15);
10.7/12.7
[a] XCp: Centroid of the corresponding 5 carbon atoms of the Cp
ligand.
The ansa-metallocene entities demonstrate a slightly dis-
cene.[16] Eilbracht found a ligand exchange from the di-µ- torted structure caused by bridging of the two Cp units with
carbonyl-µ-[3-oxopentamethylenebis(η5-cyclopentadiene- the rigid naphthalene linker (Figure 1).
2
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Naphthalene-Bridged ansa-Nickelocene
alene is about 81° for 2 and 83° for 3, respectively. The
distances between the metal and the bridgehead carbon
atoms are significantly shorter (Ni1–C11 210.6 pm, Ni1–
C16 211.0 pm, Ru1–C11 209.4 pm, and Ru1–C16 210.3 pm,
respectively) than the other metal–carbon(Cp) distances,
which range between 217.1 and 219.6 pm for 2 and between
215.4 and 221.3 pm for 3 (Table 1). The most significant
structural features for strained metallocenophanes are the
tilt angle α between the best planes of the Cp ligands and
the angle δ between the two axes defined by the metal center
and the centroid XCp, which describe the extent of the dis-
tortion from a perfect sandwich structure (Figure 2).[17]
Figure 1. Left: Molecular structure of compound 2. Right: Projec-
tion of the molecule of complex 2 along the C11–C17 axis (hydro-
gen atoms are omitted for clarity; anisotropic displacement ellip-
soids are depicted at the 50% probability level). The molecular
structure of the Ru complex 3 looks very much the same.
Figure 2. Geometric parameters of the ring slippage in ansa-
metallocenes.
Angles of α = 20.2 and 19.4°, and of δ = 164.4 and 167.6°
The dihedral angle C1–C11–C8–C16 amounts to 7.9 and for 2 and 3, respectively, are indicative of a considerably
5.4° for 2 and 3, respectively (Figure 1, Table 1). The angle bent metallocene structure. Complex 2 exhibits a somewhat
between the best planes of the Cp ligands and the naphth- larger distortion than the tetramethyldisilane bridged com-
Figure 3. Plot of the crystal structure of 2 (a), intermolecular Ni–Ni distances (b) and shortest intermolecular C–Ni distances (c).
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FULL PAPER
pound (α = 9.37°, δ = 171.4°).[12] The fixation of the Cp
fragments by the nonflexible naphthalene clamp appeared
to be the reason. Due to the distortion of the metallocene
units, the metal atoms are shifted away from the naphth-
alene bridge (Figure 1, right). On the whole, the geometric
parameters of the molecular structure of the ansa-nickelo-
cene 2 very much resemble those of the corresponding ansa-
ruthenocene 3, which makes 3 an ideal diamagnetic host for
the paramagnetic guest 2.[6]
A distinctive feature of the crystal packing is the antipar-
allel alignment of the nickelocenophane complexes depicted
in Figure 3. The shortest intermolecular nickel–nickel dis-
tance amounts to 521.1 pm.
Figure 4. Frontier molecular orbitals of complex 2: LUMO (top),
SOMO1 (center, left), SOMO2 (center, right), and HOMO (bot-
tom) obtained from DFT calculations.
DFT Calculations
To investigate the influence of the XCp–Ni–XCp bend an-
gle and the naphthyl substitution on the electronic structure
in the ansa-nickelocene complex 2, quantum chemical cal-
culations were performed using the density functional
theory (DFT) method, which has been successfully em-
ployed on calculations of related complexes.[13] Initial opti-
mization of complex 2 revealed a nearly C2v-symmetric
structure. Calculated bond lengths and angles are in good
agreement with the structural parameters obtained by
means of X-ray structure analysis (Table 1). The main dif-
ference between the calculated and X-ray structure is ob-
served in the distance of the β-carbon atoms (C13/C14 to
C18/C19) of the Cp ligands, which indicates a less deformed
metallocene unit in the experimental structure. The stronger
deviation of the structure from the ideal C2v symmetry and
a twist of the Cp rings might be caused by packing forces
and does not affect other structural parameters such as the
Magnetic Measurements
The magnetic behavior of complex 2 was investigated in
solution by variable-temperature (VT) 1H NMR spec-
troscopy in toluene in the range of 203 to 343 K (see Fig-
ures 5 and 6). The assignment of the proton NMR spec-
troscopy signals have been performed following the spin
densities of the different carbon atoms obtained from DFT
calculations. They result in two sets of Fermi contact terms:
two large and negative values for the Cp rings and three of
an order of magnitude smaller, assigned to the naphthalene
protons. Hence, the signals for the Cp protons of compound
2 are shifted to high field (δ
ure 5) as a consequence of the two unpaired electrons delo-
calized on the Ni atom and the Cp rings (compare Fig-
293 K
= –248.8, –280.1 ppm; Fig-
para
ure 4). The dispersion for the mean chemical shift of the Cp
protons of compound 2 (δ
than found for the unsubstituted nickelocene (δ
293 K
X
Cp–Ni–XCp bend angle.
= –265 ppm) is even larger
para
293 K
Calculations on the electronic ground state revealed a
=
para
triplet state to be most energetically favorable. Higher sing-
let states calculated by broken symmetry and an unrestric-
ted (U)-DFT approach were calculated to be +34 kJmol–1
for an open-shell singlet and +69 kJmol–1 for a closed-shell
singlet state above the triplet ground state.
–255.2 ppm). The assignment of the resonance signals to
the Cp protons H-12/15 and H-13/14 occurred in accord
with Köhler et al.[16]
The frontier molecular orbitals of the triplet ground state
are depicted in Figure 4. The splitting of the two (in
nickelocene) degenerate orbitals was calculated to be
15 kJmol–1.[18] The influence of the naphthyl bridge on the
splitting can be deduced from the SOMOs. The SOMO that
is higher in energy (SOMO1) exhibits an antibonding inter-
action between the naphthyl σ orbitals with the π system of
the Cp rings, which causes an increase in energy. In ad-
dition, due to the bending of the nickelocene fragment, the
antibonding overlap between the π system of the Cp ring
and the nickel 3dyz orbital increases, which also destabilizes
the SOMO1. Due to the nonbonding interaction between
the π system of the Cp ring and the naphthyl ring and lower
1
Figure 5. H NMR spectrum of compound 2 in toluene at 293 K.
The solvent signals are marked with an S. The sample contains
minor impurities, most likely due to solvent traces from the synthe-
sis.
The proton signals of the naphthalene bridge were
increase in the antibonding contribution between the π sys- shifted to low field in the range 10 Ͻ δ Ͻ 15 ppm. This
tem of the Cp ring and the 3dxz orbital at the Ni center, the slight low-field shift proves a subtle spin density in the
SOMO2 (Figure 4) is less destabilized. In total, this resulted naphthalene scaffold, which is in harmony with the DFT
in a splitting of SOMO1 and SOMO2.[18]
calculation.
4
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Naphthalene-Bridged ansa-Nickelocene
Figure 6. Curie plot of the chemical shift (δ) versus reciprocal tem-
perature.
Figure 7. The molar magnetic susceptibility (χm) and effective mag-
netic moment (μeff) of pure ansa-nickelocene complex 2.
The highest SOMO (SOMO1; Figure 4) displays a cer-
tain spin density on the carbon atoms of the naphthalene the theoretical value quite well for SNi = 1 (μeff = 2.83 at
bridge (+0.008 e at C2, +0.0001 e at C3, and +0.001 e at room temperature for g = 2, using the spin-only approxi-
C4) that is predominantly due to small σ-spin delocaliza- mation).
tion effects. This order implies the proximal protons H-2/7
The antiferromagnetic behavior was unexpected for a
to be most low-field-shifted. Nevertheless, when the relax- mononuclear nickelocene complex and can be explained by
ation is affected by the dipolar interaction, the line width an intramolecular singlet–triplet change, or alternatively, by
of the signal should distinctly increase as the distance be- an intermolecular coupling through space. However, our
tween the paramagnetic center and the related proton de- DFT calculations for an isolated molecule reveal a triplet
creases. Therefore, the signal at δ = 10 ppm is assigned to ground state as was found for nickelocene itself. The anti-
H-2/7.
ferromagnetic coupling through an intermolecular magnetic
The VT 1H NMR spectra demonstrate a linear corre- interaction between two molecules is corroborated by the
lation between the chemical shifts of the proton-resonance crystal structure determination, which demonstrates a pair-
signals of 2 and the reciprocal temperature (Figure 6). The wise packing order of the molecules in the crystal. The clos-
linear slope proves a Curie behavior in the temperature est distance between two molecules amounts to 393.3 pm,
range of 203 Ͻ T Ͻ 343 K. The large temperature-depend- which is calculated between a hydrogen-bearing carbon
ent shift difference in the Cp signals exhibits a large spin atom of the Cp ligands of one molecule and the Ni center
density as is suggested by the frontier molecular orbitals in of the second molecule and vice versa (Figure 3, c).
Figure 4.
To prove the intermolecular magnetic interaction attrib-
To obtain more information about the magnetic behavior uted to crystal packing, diluted samples of 2 in a diamag-
of 2, the susceptibility of a microcrystalline sample was de- netic host were investigated by SQUID measurements. The
termined by superconducting quantum interference device molecular structure of ruthenocene very much resembles
(SQUID) measurements in the temperature range 2–300 K. the geometry of the molecular structure of nickelocene and,
From the magnetic susceptibility of compound 2 depicted hence, allows the application of the ansa-ruthenocene 3 as
in Figure 7, a paramagnetic behavior above approximately a diamagnetic host for the corresponding nickelocene 2 in
30 K can be deduced. Below 30 K a deviation from the Cu- magnetic measurements.[6] Crystals of diluted samples of
rie–Weiss law is observed. Complex 2 (Figure 7) exhibits complex 2 in the diamagnetic ansa-ruthenocene 3 with dif-
antiferromagnetic behavior with a maximum of the suscep- ferent doping rates could be obtained from toluene solu-
tibility χm at about T ≈ 25 K. The magnetic behavior of 2 tions. The exact doping rates were determined by flame
can be rationalized by magnetic interaction between two atomic absorption spectroscopy. The doped samples show
molecules arranged in pairs. The susceptibility data could paramagnetic behavior above approximately 10 K (Fig-
be simulated satisfactory (Figure 7, solid line) by using the ure 8). Below T = 10 K, a deviation from the Curie–Weiss
ˆ
ˆ
ˆ
ˆ
ˆ
spin Hamiltonian H = –2J12 ΣS1·S2, in which S1 = S2 = 1, law was obtained and the susceptibility runs into saturation
J12 = –10.07 cm–1, Θ = –0.2 K and g = 2.029, and consider- below T = 4 K (Figure 8).
ing pairs of complexes as the paramagnetic unit. An ad-
The lack of the maximum in the χm versus T curve at
ditional paramagnetic “impurity” of 9.9% with a spin S = 25 K, which was observed from the neat complex 2 (Fig-
1 has to be taken in account, which may be due to ansa- ure 7), indicate an intermolecular antiferromagnetic interac-
nickelocene species without a coupling counterpart.
tion between the nickelocene units, and from X-ray struc-
The magnetic moment μeff calculated from χm data of the ture determination it is clear that the interaction occurs
neat sample is equal to 2.92 at room temperature, which fits pairwise, which is in agreement with the fitting procedure.
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Table 2. Cyclic voltammetry data[a] of 2.
[b]
[c]
Redox couples E1/2
Epa
Epc
ΔEp
–1/0
0/+1
+1/+2
–
–
–2.294
–
–0.522 –0.485 –0.558 0.073 ΔEpc(2–1)[d] 1.736
0.487 0.523 0.450 0.073 ΔE1/2(3–2)[e] 1.009
[a] In acetonitrile at room temperature, [nBu4N]PF6 (0.2 m) as the
supporting electrolyte, Pt as the standard electrode referenced ver-
sus E1/2(FcH/FcH+) = 0 V, scan rate 200 mVs–1. Potentials E in
volts (Ϯ0.005 V). [b] E1/2 = (Epa + Epc)/2. [c] ΔEp = |Epc – Epa|.
[d] ΔEpc(2–1) = |Epc(0/+1) – Epc(–1/0)|. [e] ΔE1/2(3–2) = |E1/2(+1/
+2) – E1/2(0/+1)|.
The small reduction wave at –0.960 V (Figure 9, solid
line) only appears in connection with the oxidation of com-
plex 2 to the dication beyond 0.485 V, which is confirmed
by the additional cyclic voltammogram from the first redox
couple (Figure 9, dotted line).
Figure 8. The molar magnetic susceptibility (χm) and effective mag-
netic moment (μeff) of the ansa-nickelocene complex 2 doped into
3. The χm values take into account the dilution of 2 of about
26 mol-% of the diamagnetic ruthenium congener 3.
Conclusion
Redox Properties
The synthesis of new ansa-metallocenes of nickel (2) and
ruthenium (3) has been shown. Complex 2 and 3 have been
characterized by single-crystal structure determination and
established a very similar molecular structure for both com-
plexes.
The redox chemistry of ansa-nickelocene 2 was investi-
gated by means of cyclic voltammetry (Figure 9). The cyclic
voltammogram of 2 in acetonitrile displays two redox cou-
ples with a separation of about 1 V and an additional
irreversible reduction in the range of the archetype nickelo-
cene.[19] All redox couples correspond to a one-electron
transfer that results in three different oxidation states of
complex 2 (0, +1, +2; Scheme 2). In contrast to the redox
properties of the parent nickelocenes, only the first oxi-
dation step at E1/2 = –0.522 V is electrochemically revers-
ible, whereas the second oxidation step at E1/2 = 0.487 V is
only partially reversible, and the reduction to the anion at
Epc = –2.294 V is electrochemically irreversible (Table 2).
1
VT H NMR spectroscopy revealed a Curie behavior in
the temperature range for the paramagnetic nickel com-
pound 2 that has been additionally investigated by SQUID
measurements in the solid state. The neat sample exhibits
antiferromagnetic coupling with a maximum of the molar
magnetic susceptibility at about T ≈ 25 K. SQUID measure-
ments of diluted samples of 2 in the diamagnetic ruthenium
host prove it as an intermolecular coupling. The intermo-
lecular coupling can be rationalized by a pairwise magnetic
interaction as shown by the fitting procedure of the molar
susceptibility and the result of the X-ray structure analysis.
Cyclic voltammetry presented a close electronic relationship
to nickelocene, although the structural distortion caused by
the 1,1Ј-disubstitution yields a considerably bent metallo-
cene, in which the twofold degeneracy of the former e1g or-
bitals is broken. DFT calculations revealed a triplet ground
state with a SOMO1–SOMO2 gap of 15 kJmol–1 for com-
plex 2.
Experimental Section
General: Unless otherwise noted, the reactions were carried out
under dry nitrogen using standard Schlenk techniques. Solvents
were saturated with nitrogen. THF and n-hexane were dried by
sodium potassium alloy. Naphthalene-1,8-diylbis(cyclopentadienyl-
sodium) (1)[13] and hexaamminenickel(II) dichloride [Ni-
Figure 9. Cyclic voltammogram of 2: overview (solid line); 0/+1
[20]
(NH3)6]Cl2 were synthesized according to literature procedures.
(dotted line).
Dichloridotetrakis(dimethylsulfoxide)ruthenium(II) was purchased
and used without further purification. NMR spectroscopy was car-
ried out with a Bruker AVANCE 400 instrument; variable-tempera-
ture 1H NMR spectra of the paramagnetic compound 2 were mea-
sured in an NMR Young tube. MS: Finnigan MAT 311 A (FAB).
Elemental analysis: CHN-O-Rapid, F. Heraeus, Zentrale Element-
aranalytik, Fachbereich Chemie, Universität Hamburg.
Scheme 2. Redox cascade of compound 2.
6
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/KAP1
Date: 03-09-12 15:41:15
Pages: 9
Naphthalene-Bridged ansa-Nickelocene
Cyclic Voltammetry: Measurements were performed in acetonitrile
with 0.2 m [nBu4N]PF6 as supporting electrolyte. A Metrohm Auto-
lab PGSTAT-101 system was used with a Pt disk as working elec-
trode, Pt wire as reference electrode, and Pt rod as counter elec-
trode. The potentials were referenced to E1/2(ferrocene/ferrocen-
ium) = 0 V.
CCDC-844818 (for 2) and -844819 (for 3) contain the supplemen-
tary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data
Centre via www.ccdc.cam.ac.uk/data_request/cif.
1,1Ј-(Naphthalene-1ЈЈ,8ЈЈ-diyl)nickelocene (2) from [Cp3Ni2]BF4:
Naphthalene-1,8-diylbis(cyclopentadienylsodium)·THF (1) (182 mg,
0.49 mmol) was dissolved in THF (30 mL) and cooled to –78 °C.
The triple-decker complex tris(cyclopentadienyl)dinickel tetrafluor-
idoborate [Cp3Ni2]BF4 (395 mg, 0.99 mmol) was added and stirred
for one hour. The volatiles were removed under reduced pressure,
and the solid residue was extracted with hexane. The solvent was
removed and a part of nickelocene was sublimated from the residue.
The separation was not quantitative and efforts led to a mixture of
nickelocene and ansa-nickelocene 2. Hence, no exact yield could be
determined.
Magnetic Measurements: The magnetic susceptibility data of com-
pound 2 were collected in a temperature range of 2–300 K under
an applied field of 10 kG on powdered microcrystalline samples
with a SQUID magnetometer (MPMS-XL, Quantum Design). The
samples were sealed in quartz tubes under vacuum or were mea-
sured in gelatin capsules. Experimental susceptibility data were cor-
rected for the underlying diamagnetism using Pascal’s constants.[21]
The temperature-dependent magnetic contribution of the holder
was experimentally determined and subtracted from the measured
susceptibility data. The resulting molar susceptibility data were
plotted in χM versus T and μeff versus T. The program julx31 was
used for spin-Hamiltonian simulations of the data (E. Bill, Max-
Planck Institute for Bioinorganic Chemistry, Mülheim, http://
www.mpi-muelheim.mpg.de/bac/logins/bill/julX_en.php). The sus-
ceptibility data could be simulated using the spin Hamiltonian
1,1Ј-(Naphthalene-1ЈЈ,8ЈЈ-diyl)nickelocene (2) from Hexaammine-
nickel(II) Dichloride: Naphthalene-1,8-diylbis(cyclopentadienyl-
sodium)·THF (1) (641 mg, 1.73 mmol) and hexaammine-
nickel(II) dichloride (401 mg, 1.73 mmol) were dissolved in THF
(60 mL). The resulting solution was heated at reflux overnight. The
volatiles were removed under reduced pressure, and the solid resi-
due was extracted with pentane. The extract was reduced in volume
and crystallization at –20 °C afforded green crystalline needles
H = –2J12 ΣS1·S2, with S1 = S2 = 1, J12 = –10.07 cm–1, Θ = –0.2 K
and g = 2.029, and considering pairs of complexes as the paramag-
netic unit.
ˆ
ˆ
ˆ
ˆ
ˆ
1
(403 mg, 74%). H NMR (400 MHz, C6D6, 293 K): δ = 17.6 (s, 2
H, 3-H, 6-H), 14.3 (s, 2 H, 4-H, 5-H), 10.5 (s, 2 H,2-H, 7-H), –248.8
(s, 2 H, 13-H, 14-H), –280.1 (s, 2 H, 12-H, 15-H) ppm. MS (FAB):
m/z [%]: 312.1 (100), 314.1 (46), 313.01 (31). HRMS (FAB): m/z:
calcd. for C10H14Ni [M]+: 312.04623; found: 312.04489. Elemental
analysis calcd. C 76.74, H 4.51; found C 76.30, H 4.57.
X-ray Structure Determination: The data were collected with a
Bruker AXS Smart APEX CCD, Mo-Kα, λ = 0.71073 Å (for crys-
tallographic data of 2 and 3, see Table 3). The structures were
solved by direct methods (SHELXS-86)[22] and the refinements on
F2 were carried out by full-matrix least-squares techniques
(SHELXL-97).[23] All non-hydrogen atoms were refined with aniso-
tropic 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 atoms.
Weights were optimized in the final refinement cycles.
1,1Ј-(Naphthalene-1ЈЈ,8ЈЈ-diyl)ruthenocene (3): Naphthalene-1,8-
diylbis(cyclopentadienylsodium)·THF (1) (207 mg, 0.559 mmol)
was dissolved in THF (15 mL) and cooled to –78 °C. Dichlorido-
tetrakis(dimethylsulfoxide)ruthenium(II) (240 mg, 0.495 mmol)
was added in five portions, and the solution was additionally stirred
at ambient temperature for two days. A white precipitate formed,
and to complete the reaction the mixture was heated at reflux over-
night. The solvent was removed under reduced pressure, and the
crude product was subjected to chromatography [toluene, alumina
(5% water)] to give the ansa-ruthenocene 3 in pale yellow crystals
(156 mg, 0.438 mmol, 89%). 1H NMR (400 MHz, CD2Cl2) [the as-
signment of the Cp signals has been performed by assuming an
anisotropy of the aromatic ring current of the naphthalene in-
ducing a stronger shielding effect at the protons in position 12 and
15 compared to H-13 and H-14 (Figure 10); multiplicities of high-
order signals were described as first-order and marked with the
prefix m~]: δ = 7.92 (m~dd, J = 1.4, 8.3 Hz, 2 H, H-2, H-7 or H4,
H-5), 7.80 (m~dd, J = 1.5, 7.0 Hz, 2 H, H-4, H-5 or H-2, H-7),
7.46 (m~dd, J = 7.0, 8.1 Hz, 2 H, H-3, H-6), 4.90 (m~dd, J = 1.7,
1.7 Hz, 2 H, H-13, H-14), 4.66 (m~dd, J = 1.7, 1.7 Hz, 2 H, H-12,
H-15) ppm. 13C NMR (200 MHz, CD2Cl2): δ = 132.53 (C-2, C-7
or C-4, C-5), 130.13 (C-4, C-5 or C-2, C-7), 124.39 (C-3, C-6),
Table 3. Crystallographic data of the dinuclear complex 2 and 3.
2
3
Empirical formula
Mr [gmol–1]
T [K]
C20H14Ni
313.02
100(2)
C20H14Ru
355.40
100(2)
λ [pm]
71.073
71.073
Crystal system
Space group
a [pm]
b [pm]
c [pm]
α [°]
β [°]
triclinic
P1
monoclinic
P21/c
771.8(2)
1882.5(6)
966.4(3)
¯
777.5(3)
963.6(3)
990.7(3)
107.100(1)
75.097(4)
76.607(4)
670.8(4)
2
106.246(3)
γ [°]
V [106 pm3]
Z
1347.9(7)
4
1.751
1.151
712
ρcalcd. [Mgm–3]
μ [mm–1]
F(000)
1.550
1.434
324
Crystal size [mm]
2θ [°]
Total reflections
Rint
0.31ϫ0.07ϫ0.03
4.34–50
3141
0.24ϫ0.07ϫ0.02
4.32–53.98
10155
0.0490
0.0723
Independent reflections 2145
2872
206
Parameters
190
GOF
R1/wR2 [IϾ2σ(I)]
R1/wR2 (all data)
1.100
0.0543/0.1367
0.0633/0.1429
1.094
0.0492/0.0910
0.0852/0.1045
Figure 10. Atom labeling for NMR spectroscopy.
Eur. J. Inorg. Chem. 0000, 0–0
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/KAP1
Date: 03-09-12 15:41:15
Pages: 9
M. H. Prosenc, J. Heck et al.
FULL PAPER
[11] a) P. R. Sharp, K. N. Raymond, J. C. Smart, R. J. McKinney,
J. Am. Chem. Soc. 1981, 103, 753–757; b) F. H. Köhler, K. H.
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2007, 26, 6688–669.
86.63 (C-11), 73.62 (C-13, C-4), 73.10 (C-12, C-15) ppm. MS
(FAB): m/z (%): 356.1 (100), 355.1 (68), 358.1 (55), 354.1 (51), 357.1
(44), 353.1 (41), 359.1 (28), 350.1 (22), 360.2 (4). HRMS (FAB):
m/z: calcd. for C10H14Ru [M]+: 356.01390; found 356.01459.
[13] S. Trtica, M. H. Prosenc, M. Schmidt, J. Heck, O. Albrecht, D.
Görlitz, F. Reuter, E. Rentschler, Inorg. Chem. 2010, 49, 1667–
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Computational Details: All calculations on complexes were per-
formed at the DFT level of theory and by employing the B3LYP
hybrid functional.[24] For all atoms the def2-TZVP basis set was
used.[25] The ground state of the complex was calculated to be an
open-shell singlet state in which the geometry optimization was
performed in the frame of broken-symmetry formalism. The
broken-symmetry solution was obtained by using the solution for
the triplet state, and adjustment of the spin orbitals as a guess for
the singlet-state. For all calculations the Gaussian 09 program suite
was used.[26]
[17] D. E. Herbert, U. F. J. Mayer, I. Manners, Angew. Chem. 2007,
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[18] J. W. Lauher, R. Hoffmann, J. Am. Chem. Soc. 1976, 98, 1729–
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Acknowledgments
[19] R. J. Wilson, L. F. Warren Jr, M. F. Hawthorn, J. Am. Chem.
Soc. 1969, 91, 758–759; J. D. L. Holloway, W. E. Geiger, J. Am.
Chem. Soc. 1979, 101, 2038–2044; D. Chong, J. Slote, W. E.
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[20] B. Heyn, B. Hipler, G. Kreisel, H. Schreer, D. Walther, Anor-
ganische Synthesechemie, Springer-Verlag, Berlin, 1999, p. 101.
[21] G. A. Bain, J. F. Berry, J. Chem. Educ. 2008, 85, 532–536.
[22] G. M. Sheldrick, SHELXL-86 Program for crystal structure de-
termination, University of Göttingen, Germany, 1986.
[23] M. Sheldrick, SHELXL-97 Program for crystal structure refine-
ment, University of Göttingen, Germany, 1997.
This work was supported by the Collaborative Research Center
SFB 668 (TP A4) of the Deutsche Forschungsgemeinschaft
(DFG). We thank Dr. E. T. K. Haupt for the measurement of the
NMR spectra and F. H. Köhler for helpful discussion.
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Received: June 25, 2012
Published Online: ᭿
8
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Eur. J. Inorg. Chem. 0000, 0–0

Job/Unit: I20698
/KAP1
Date: 03-09-12 15:41:15
Pages: 9
Naphthalene-Bridged ansa-Nickelocene
ansa-Nickelocene
A paramagnetic naphthalene-bridged ansa-
nickelocene has been synthesized. Al-
though DFT calculations indicate a triplet
ground state for the isolated single mo-
lecules, SQUID measurements with the
neat compound reveal an antiferromag-
netic interaction due to an intermolecular
coupling between two molecules arranged
in pairs.
S. Trtica, E. Meyer, M. H. Prosenc,*
J. Heck,* T. Böhnert, D. Görlitz ....... 1–9
Naphthalene-Bridged
ansa-Nickelocene:
Synthesis, Structure, Electrochemical, and
Magnetic Measurements
Keywords: Metallocenes / Sandwich com-
plexes / Nickel / Magnetic properties
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9