The Crystal Structure of the THF Adduct of Monolithioferrocene

Article abstract of DOI:10.1002/zaac.201400548

Single crystals of [Fe(η⁵-C₅H₄)(η⁵-C₅H₅)]₂Li₂(thf)₄ (1) were obtained from a tetrahydrofuran solution containing monolithioferrocene. The title compound crystallizes in the monoclinic space group P2₁ with a = 9.6589(5) ?, b = 17.4285(9) ?, c = 30.3116(15) ?, β = 91.911(2)° and V = 5099.8(5) ?³ with three independent molecules of 1. All individual molecules feature a non- symmetric almost planar Li₂C₂ four-membered ring with two shorter (2.118-2.215 ?) and two longer Li-C distances (2.257-2.309 ?). The lithium cations are each coordinated by two carbanionic atoms of two ferrocenyl substituents and two tetrahydrofuran molecules in a distorted tetrahedral fashion. All ferrocenyl moieties display an eclipsed conformation of the C₅ rings.

Full text of DOI:10.1002/zaac.201400548

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Zeitschrift für anorganische und allgemeine Chemie
DOI: 10.1002/zaac.201400548
The Crystal Structure of the THF Adduct of Monolithioferrocene
Christoph Förster[a] and Katja Heinze*[a]
Keywords: Ferrocene; Crystal structure; Lithium; Organolithium compound; X-ray diffraction
Abstract. Single crystals of [Fe(η5-C5H4)(η5-C5H5)]2Li2(thf)4 (1) metric almost planar Li2C2 four-membered ring with two shorter
were obtained from a tetrahydrofuran solution containing mono-
(2.118–2.215 Å) and two longer Li–C distances (2.257–2.309 Å). The
lithioferrocene. The title compound crystallizes in the monoclinic lithium cations are each coordinated by two carbanionic atoms of two
space group P21 with a = 9.6589(5) Å, b = 17.4285(9) Å, c =
30.3116(15) Å, β = 91.911(2)° and V = 5099.8(5) Å3 with three inde-
pendent molecules of 1. All individual molecules feature a non- sym-
ferrocenyl substituents and two tetrahydrofuran molecules in a dis-
torted tetrahedral fashion. All ferrocenyl moieties display an eclipsed
conformation of the C5 rings.
have not been reported. However, a few solid-state structures
of ortho-substituted monolithiated ferrocenes have been de-
scribed in the literature by the groups of Edelmann, Jacob,
Erker and Strohmann.[10–13] The basic structural motif is the
well-known Li2C2 four-membered ring.[14] Typically, the lith-
ium cation is three or four coordinate by the chelating amine
side arm, sometimes assisted by a solvent molecule such as
diethyl ether. The solid-state structures of the tmeda and pmdta
adducts of 1,1’-dilithiated ferrocene (tmeda = N,N,N’,N’-tetra-
methylethane-1,2-diamine,[15a] pmdta = N,N,N’,N’,N’’-penta-
methyldiethylenetriamine[15b]) have been reported as well. The
tetrahydrofuran adduct [Fe(η5-C5H4)2]2Li4(thf)6 has been pre-
pared and structurally characterized by Wagner.[16] Basically,
all 1,1’-dilithiated ferrocenes display a central Li2C2 four-
membered ring and two terminal base-coordinated lithium cat-
ions. The substituted dilithio derivative [(η5-C5H4Li)Fe(η5-
1,2-C5H3Li(CHMeNMe2))]4(LiOEt)2(tmeda)2 features a more
complicated structure due to the presence of several different
Introduction
Substituted ferrocenes have found widespread interest in a
variety of applications ranging from fundamental research to
biology, catalysis and materials science.[1–3] The selective
monofunctionalization of ferrocene is one of the most impor-
tant reactions of organometallic chemistry.[1] Standard organic
transformations such as Friedel–Crafts or Mannich reactions
are quite often employed while the most versatile reaction is
probably the lithiation of ferrocene giving access to e.g. B, C,
Si, Sn, N, P, O, S and halide substituted ferrocenes after
quenching with suitable electrophiles.[1] The most convenient
method to monolithioferrocene is probably the metallation of
ferrocene with tBuLi/KOtBu in tetrahydrofuran according to
Mueller-Westerhoff’s[4] optimized Kagan procedure.[5] To ac-
cess highly pure and donor base-free monolithioferrocene lith-
ium-halogen exchange is feasible from FcI or FcBr with nBuLi
in ethyl ether at low temperatures[6] while FcCl yields a mix-
ture of ferrocene, chloroferrocene, n-butylferrocene and bifer-
rocene.[7]
donor ligands.[17]
A
1,1’,3,3’-tetrametallated ferrocene
[{Fe(η5-C5H3)2}Na4Mg4{iPr2N}8 has been reported by Mul-
vey displaying a crown of sodium and magnesium amide
units.[18] To the best of our knowledge solid-state structures of
simple monolithio ferrocenes are unknown up to now.
The base-free monolithioferrocene LiFc is poorly soluble in
non-coordinating solvents and is presumably a polymeric ma-
terial, possibly similar to [LiCp]ϱ,[8] but its structure in the
solid state is at present unknown. With coordinating solvents
the polymeric structure is certainly disrupted giving soluble
and solvated [LiFc]n(solv)m which can be characterized by Results and Discussion
NMR spectroscopy.[9] In spite of its tremendous utility and its
extensive application in organometallic synthesis the solid-
state structures of base-free and donor-base coordinated LiFc
Monolithioferrocene has been prepared from ferrocene and
the super base tBuLi/KOtBu at low temperature according to
Mueller-Westerhoff.[4] Quenching with iodine gave the pure
iodoferrocene.[19] The latter was lithiated by nBuLi in petro-
leum ether (b.p. 40–60 °C) at room temperature.[6,7] The pre-
cipitated LiFc was thoroughly washed with petroleum ether
(b.p. 40–60 °C).
Solid LiFc easily dissolved in THF and was fully charac-
terized by multinuclear and two-dimensional NMR spec-
troscopy (Exp. Section, Supporting Information). After a few
days, orange crystals precipitated from the solution at room
* Prof. Dr. K. Heinze
Fax: +49-6131-39-27-277
E-Mail: katja.heinze@uni-mainz.de
[a] Institute of Inorganic Chemistry and Analytical Chemistry
Johannes Gutenberg-University of Mainz
Duesbergweg 10–14
55128 Mainz, Germany
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/zaac.201400548 or from the au-
thor.
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temperature. The tetrahydrofuran adduct of LiFc crystallized bulk of the ferrocenyl carbanion assists in reducing the cluster
in the chiral monoclinic space group P21 as a racemic twin size to a dimeric structure. In contrast to ((thf)2LiMes)2,[20]
with three independent molecular entities [Fe(η5-C5H4)(η5-
C5H5)]2Li2(thf)4 (1) in the unit cell (Figure 1).
((tmeda)LiPh)2,[21a] and (((–)-sparteine)LiPh)2,[21b] the Li2C2
rings of 1 are not C2 or Ci symmetric but feature a pair of
longer (2.257–2.309 Å) and a pair of shorter Li–C distances
(2.118–2.215 Å). The lithium cations are approximately tetra-
hedrally surrounded with a κ2O κ2C coordination. All ferro-
cenyl moieties display an essentially eclipsed conformation of
the co-planar C5 rings (Figure 1, Table 1). No further unusual
intermolecular contacts are observed. The solid state 7Li NMR
spectrum[22] reveals a broad resonance at around δ = 3.5 ppm
probably enclosing several close-lying resonances of the lith-
ium ions in slightly different chemical environments in crystal-
line 1.
DFT (B3LYP, LANL2DZ, IEFPCM THF) calculations[23]
on 1 reveal a similar geometry as found in the solid state with
an essentially centrosymmetric Li2C2 ring with a longer and a
shorter Li-C distance (Table 2). The C5 rings of the ferrocenyl
moieties are eclipsed and co-planar. A hypothetical monomeric
species (thf)3LiFc (2) has been calculated as well (Table 2).
Apart from the lone pairs of the oxygen atoms of the thf mo-
lecules significant accessible electron density is found on top
of the C5H4 and C5H5 rings (Figure 2). Hence, one can specu-
late that upon removal of the coordinating thf ligands the lith-
ium cation of the unsaturated LiFc fragment will attach to the
C5H4 or C5H5 ring of a neighbouring molecule. This bridging
(η5-C5H4)/(η5-C5H5) and (η1-C5H4) coordination of the lith-
ium ion could give rise to a polymeric one-dimensional struc-
ture [LiFc]ϱ 3 similar to cyclopentadienyllithium [LiCp]ϱ.[8]
However, the experimental verification of this hypothesis must
Figure 1. Molecular structures of the three independent molecules of
1 in the solid state.
The three independent molecules differ only slightly in their
metrical data (Figure 1, Table 1). All display a non-symmetric
almost planar Li2C2 four-membered ring similar to the struc-
tures of ((thf)2LiMes)2,[20] ((tmeda)LiPh)2,[21a] and (((–)-spar-
[21b]
teine)LiPh)2
and different to the tetrameric assembly of
phenyllithium etherate ((Et2O)LiPh)4.[21c] Possibly the steric await the structure determination of donor base-free 3.
Table 1. Selected bond lengths /Å and angles /° of 1 from XRD data.
Fe1/Fe2
Fe3/Fe4
Fe5/Fe6
Li1···Li2
2.4876 (0.0289)
2.2064 (0.0217)
2.3092 (0.0297)
2.2708 (0.0225)
2.1184 (0.0219)
1.9752 (0.0228)
1.9784 (0.0216)
2.0188 (0.0201)
2.0484 (0.0229)
3.4568 (0.0200)
3.5258 (0.0197)
1.634
1.657
1.652
1.647
109.74 (1.16)
114.56 (0.98)
67.49 (0.88)
68.21 (0.77)
–3.2
Li3···Li4
2.5355 (0.0223)
2.1909 (0.0202)
2.2589 (0.0191)
2.2817 (0.0228)
2.2150 (0.0214)
1.9884 (0.0208)
1.9541 (0.0197)
2.0120 (0.0217)
1.9478 (0.0221)
3.4808 (0.0172)
3.5242 (0.0192)
1.656
1.669
1.648
1.647
111.82 (0.86)
110.07 (0.98)
69.03 (0.68)
69.04 (0.70)
1.3
Li5···Li6
2.5236 (0.0225)
2.1857 (0.0194)
2.2570 (0.0202)
2.2766 (0.0234)
2.1784 (0.0210)
2.0012 (0.0216)
1.9974 (0.0195)
2.0357 (0.0211)
1.9560 (0.0252)
3.5010 (0.0173)
3.5311 (0.0194)
1.650
1.664
1.643
1.658
111.08 (0.86)
110.61 (1.01)
68.85 (0.68)
69.33 (0.73)
0.4
Li1–C106
Li1–C116
Li2–C106
Li2–C116
Li1–O1
Li1–O2
Li2–O3
Li2–O4
Li1···Fe1
Li3–C206
Li3–C216
Li4–C206
Li4–C216
Li3–O5
Li3–O6
Li4–O7
Li4–O8
Li3···Fe3
Li5–C306
Li5–C316
Li6–C306
Li6–C316
Li5–O9
Li5–O10
Li6–O11
Li6–O12
Li5···Fe5
Li2···Fe2
Li4···Fe4
Li6···Fe6
Fe1–X1a)
Fe1–X2b)
Fe2–X1a)
Fe2–X2b)
C106-Li1–C116
C106-Li2–C116
Li1–C106-Li2
Li1–C116-Li2
ω(Fe1)c)
Fe3–X1a)
Fe3–X2b)
Fe4–X1a)
Fe4–X2b)
C206-Li3–C216
C206-Li4–C216
Li3–C206-Li4
Li3–C216-Li4
ω(Fe3)e)
Fe5–X1a)
Fe5–X2b)
Fe6–X1a)
Fe6–X2b)
C306-Li5–C316
C306-Li6–C316
Li5–C306-Li6
Li5–C316-Li6
ω(Fe5)g)
ω(Fe2)d)
–0.7
178.6
179.5
ω(Fe4)f)
–0.8
179.6
178.0
ω(Fe6)h)
–0.2
179.0
178.0
τ(Fe1)i)
τ(Fe3)i)
τ(Fe5)i)
τ(Fe2)i)
τ(Fe4)i)
τ(Fe6)i)
a) X1 = centroid of the coordinated C5H5 ring. b) X2 = centroid of the coordinated C5H4 ring. c) ω(Fe1) = C106-X2–X1–C102.a,b) d) ω(Fe2)
= C116–X2–X1–C111.a,b) e) ω(Fe3) = C206–X2–X1–C204.a,b) f) ω(Fe4) = C216–X2–X1–C212.a,b) g) ω(Fe5) = C306–X2–X1–C303.a,b)
h) ω(Fe6) = C316–X2–X1–C311.a,b) i) τ(Fe) = X2–Fe–X1.a,b)
Z. Anorg. Allg. Chem. 2015, 517–520
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Table 2. Selected bond lengths /Å and angles /° of 1 and 2 from DFT
calculations.
Experimental Section
Solution NMR spectra were recorded with a Bruker Avance DRX
400 spectrometer at 400.31 MHz (1H), 100.657 MHz (13C) and
155.575 MHz (7Li). All resonances are reported in ppm vs. the solvent
signal as internal standard [THF (1H: δ = 1.73, 3.58 ppm; 13C: δ =
25.37, 67.57 ppm)]. Solid state NMR measurements were conducted
using a 400 MHz Bruker Avance spectrometer at a frequency of
155.40 MHz and 8 kHz spinning at the magic angle for 7Li. 5 μs pulse
length for the 90° single pulse excitation experiment and recycle delays
of 120 s were used in all cases. 8 transients were averaged when
acquiring the 7Li NMR signal. A commercial 3-channels Bruker 4 mm
probe-head, capable of fast MAS was used for all measurements. The
spectra were referenced to external aqueous 3 m LiCl solution.
1
2
Li1···Li2
2.565
2.189
2.375
2.190
2.376
1.998
1.993
1.998
1.993
3.644
3.637
1.741
1.734
1.741
1.734
111.4
111.4
68.2
Li1–C106
Li1–C116
Li2–C106
Li2–C116
Li1–O1
Li1–O2
Li2–O3
Li2–O4
Li1···Fe1
Li1–C106
2.134
Li1–O1
Li1–O2
Li1–O3
2.027
1.989
2.009
Li1···Fe1
4.000
Li2···Fe2
Fe1–X1a)
Fe1–X2b)
Fe2–X1a)
Fe2–X2b)
C106-Li1–C116
C106-Li2–C116
Li1–C106-Li2
Li1–C116-Li2
ω(Fe1)c)
Fe1–X1a)
Fe1–X2b)
1.740
1.734
X-ray diffraction data were collected with a Bruker AXS Smart 1000
CCD diffractometer with an APEX II detector and an Oxford cooling
system and corrected for absorption and other effects using Mo-Kα
radiation (λ = 0.71073 Å) at 173(2) K. The diffraction frames were
integrated using the SAINT package, and most were corrected for ab-
sorption with MULABS.[24,25] The structure was solved by direct
methods and refined by the full-matrix method based on F2 using the
SHELXTL software package.[26,27] All non-hydrogen atoms were re-
fined anisotropically, while the positions of carbon bonded hydrogen
atoms were generated with appropriate geometric constraints and al-
lowed to ride on their respective parent atoms with fixed isotropic
thermal parameters. For the refinement of the structure SADI, SAME,
RIGU and SIMU restraints have been used. Split models were applied
for disordered tetrahydrofuran molecules. The occupancies of the dis-
ordered atom sites were as follows: C121 (0.65), C21A (0.35); C128
(0.50), C28A (0.50); C129 (0.50), C29A (0.50); C135 (0.65), C035
(0.35); C232 (0.70), C32A (0.30); C235 (0.80), C35B (0.20); C328
(0.55), C08A (0.45); O12···C336 (0.70); O12A···C36A (0.30). Crystal-
lographic data (excluding structure factors) for the structure reported
in this paper have been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no CCDC-1035257. Copies
of the data can be obtained free of charge upon application to CCDC,
12 Union Road, Cambridge CB2 1EZ, U.K. (Fax: +44-1223-336-033;
E-mail deposit@ccdc.cam.ac.uk).
68.2
1.5
1.8
179.9
179.9
ω(Fe1)c)
τ(Fe1)e)
–0.01
179.3
ω(Fe2)d)
τ(Fe1)e)
τ(Fe2)e)
a) X1 = centroid of the coordinated C5H5 ring. b) X2 = centroid of
the coordinated C5H4 ring. c) ω(Fe1) = C6–X2–X1–C1.a,b) d) ω(Fe2)
= C16–X2–X1–C11.a,b) e) τ(Fe) = X2–Fe–X1.a,b)
DFT calculations were carried out with the Gaussian09/DFT[28] series
of programs. The B3LYP formulation of DFT was used employing the
LANL2DZ basis set. No symmetry constraints were imposed on the
molecules. The presence of energy minima was checked by analytical
frequency calculations. The integral-equation-formalism polarizable
continuum model (IEFPCM, THF) was employed for solvent model-
ing.
Crystallographic data of 1: C36H50Fe2Li2O4 (672.34); monoclinic; P21;
a = 9.6589(5) Å, b = 17.4285(9) Å, c = 30.3116(15) Å, β = 91.911(2)°,
V = 5099.8(5) Å3; Z = 6; density, calcd. = 1.314 g cm–3, μ = 0.889 mm–1;
F(000) = 2136; crystal size 0.28ϫ 0.24ϫ 0.14 mm; θ = 1.34 to 26.48
deg.; –12 Յ h Յ 12, –20 Յ k Յ 21, –38 Յ l Յ 38; rfln collected =
52804; rfln unique = 18772 [R(int) = 0.0997]; completeness to θ =
26.48 = 99.7%; semi-empirical absorption correction from equiva-
lents; max. and min. transmission 0.883 and 0.780; data 18762; re-
straints 1218, parameters 1244; goodness-of-fit on F2 = 0.922; final R
indices [I Ͼ 2σ(I)] R1 = 0.0676, wR2 = 0.1444; R indices (all data)
R1 = 0.1408, wR2 = 0.1696; largest diff. peak and hole 1.02 and
–1.26 e·Å–3; absolute structure parameter 0.55(6).
Figure 2. Electrostatic potential of 2 calculated by DFT (contour value
0.07 a.u.; negative = blue, positive = yellow).
Conclusions
The thf adduct of monolithioferrocene crystallizes as
[Fe(η5-C5H4)(η5-C5H5)]2Li2(thf)4 in the monoclinic space
group P21 featuring Li2C2 four-membered rings. Together with
the solid-state structure of the thf adduct of dilithiated ferro-
cene [Fe(η5-C5H4)2]2Li4(thf)6 reported by Wagner[16] the two
probably most often employed lithiated ferrocenes are now
structurally characterized.
Synthesis of 1: Solid LiFc[4] prepared from FcI[19] and nBuLi (2.5 m in
hexane) was dissolved in THF. For NMR spectroscopic measurements
Z. Anorg. Allg. Chem. 2015, 517–520
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Weinheim, 2004, pp. 47–120; b) V. H. Gessner, C. Däschlein, C.
Strohmann, Chem. Eur. J. 2009, 15, 3320–3334; c) K. Gregory,
P. v. Ragué Schleyer, R. Snaith, Adv. Inorg. Chem. 1991, 37, 47–
142; d) R. E. Mulvey, Chem. Soc. Rev. 1991, 20, 167–209.
[15] a) I. R. Butler, W. R. Cullen, J. Ni, S. J. Rettig, Organometallics
1985, 4, 2196–2201; b) M. Walczak, K. Walczak, R. Mink, M. D.
Rausch, G. Stucky, J. Am. Chem. Soc. 1978, 100, 6382–6388.
[16] A. S. Perucha, J. Heilmann-Brohl, M. Bolte, H.-W. Lerner, M.
Wagner, Organometallics 2008, 27, 6170–6177.
[D8]THF was used. Crystals of 1 suitable for X-ray diffraction studies
precipitated from the solution upon standing at –28 °C.
1H NMR ([D8]THF): δ = 3.73 (s, 2 H, H3), 3.79 (s, 5 H, H4), 4.02 (s,
2 H, H2) ppm. 13C{1H} NMR ([D8]THF): δ = 66.6 (C4), 69.9 (C2),
80.5 (C3), 96.0 (C1) ppm. 7Li{1H} NMR ([D8]THF): δ = 1.89 ppm.
7
MAS Li NMR: δ = 3.5 (br) ppm.
Supporting Information (see footnote on the first page of this article):
selected NMR spectra of 1; Cartesian coordinates of optimized geome-
tries of 1 and 2.
[17] I. R. Butler, W. R. Cullen, J. Reglinski, S. J. Rettig, J. Organomet.
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Acknowledgments
The Internal University Research Funding of the Johannes Gutenberg
University, Mainz (Germany) is gratefully acknowledged. We thank
Sebastian Seibert for preparative assistance and Dr. Dieter Schollmeyer
for giving useful hints to resolve the disorder.
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Received: November 20, 2014
Published Online: January 20, 2015
Z. Anorg. Allg. Chem. 2015, 517–520
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