Syntheses and Crystal Structures of Phenyl-Lithium Derivatives

Article abstract of DOI:10.1021/acs.inorgchem.8b01041

Although organolithium compounds have been studied and applied for ～100 years, only few crystal structures of pure, unsolvated organolithium compounds have been reported so far. Therefore, several phenyl-lithium derivatives were synthesized by lithium-hal

Full text of DOI:10.1021/acs.inorgchem.8b01041

Article
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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Syntheses and Crystal Structures of Phenyl-Lithium Derivatives
†
́
Alexander Bodach, Rene Hebestreit, Michael Bolte, and Lothar Fink*
Institut fur Anorganische und Analytische Chemie, Goethe-Universitat Frankfurt, Max-von-Laue-Strasse 7, D-60438
̈
̈
Frankfurt/Main, Germany
S
* Supporting Information
ABSTRACT: Although organolithium compounds have been
studied and applied for ∼100 years, only few crystal structures
of pure, unsolvated organolithium compounds have been
reported so far. Therefore, several phenyl-lithium derivatives
were synthesized by lithium−halogen exchange reactions,
yielding fairly soluble polymers in the cases of 4- and 2-
methylphenyl-lithium (p-TolLi and o-TolLi). Their crystal
structures have been determined by X-ray powder diffraction.
Remarkably, o-TolLi crystallizes in the noncentrosymmetric
space group P212121 with two independent monomers,
whereas the crystal structure of p-TolLi is described in
spacegroup P21/a. In contrast, no polymer of 5-m-XyLi (3,5-
dimethyl-phenyl-lithium) could be observed, but single
crystals of a [(5-m-XyLi)3(MTBE)3LiBr] adduct were isolated (MTBE = methyl-tert-butylether). This gives hints on the
nature of lithium−halogen exchange reactions. Steric and electronic effects of the phenyl-lithium substitution are further
discussed in conjunction with related compounds.
trimethylphenyl)phenyl-lithium,22 or even leads to tetramers,
INTRODUCTION
■
e.g., [iPr3(C6H2)Li]421 by Li···π interactions only, or results in
Since the early work of Schlenk et al.,1 organolithium
24
hexamers, e.g., [2,5-tBu2(C6H3)Li]6,23 similar to [n-BuLi]6
compounds matured to indispensable reagents for the
and other alkyl-lithium compounds.
syntheses of organic, organometallic, and polymeric com-
Although organolithium compounds are used preferentially
pounds, even on an industrial scale.2−5 Their structures and
in solution and for syntheses, they also might be applied in
reactivities are distinct, manifold, and directly correlated,6
mechanosyntheses.25
whereas our fundamental understanding is mainly limited by
This dramatically hints for the need for donor-unsupported
the knowledge of structures. However, many organolithium
and solid organolithium compounds. Therefore, structure
compounds are used exclusively in solution, often in the
determination from powder expands our basic understanding
presence of Lewis-bases, such as amines or ethers. Therefore,
of well-known and widely used simple organolithium
most of the known structures consist of organolithiums
compounds.
stabilized by Lewis-bases.7−9 Hitherto, only ∼30 crystal
Here we report on the syntheses of two polymeric tolyl-
structures of pure, unsolvated organolithium compounds
lithium (para-TolLi, ortho-TolLi) compounds and a 5-meta-
(only Li, C, H) were reported.10 A remarkably high number
xylyl-lithium cage [(5-m-XyLi)3(MTBE)3LiBr] (MTBE =
of these structures were determined from X-ray powder
methyl-tert-butylether). The corresponding crystal structures
diffraction (XRPD) data, due to their polymeric structure and
were determined from X-ray powder diffraction data, due to
insolubility in hydrocarbons. MeLi (Me = methyl),11−13 PhLi
insolubility in saturated and aromatic hydrocarbons. Single
(Ph = phenyl),14 indenylLi,15 Licp (cp = cyclopentadienyl),16
crystals of [(5-m-XyLi)3(MTBE)3LiBr] could be grown while
and Licp* (cp* = 1,2,3,4,5 pentamethylcyclopentadienyl)17
no polymeric m-XyLi was observed.
were determined from synchrotron data, whereas mesitylLi18
and Li[CH2P(tBu)2]19 (tBu = tert-butyl) were determined
RESULTS AND DISCUSSION
■
from laboratory data.
All compounds were synthesized by lithium−bromide
exchange reaction (Schlosser26 method), based on the
known synthesis of MesLi18 (Scheme 1). XRPD data of all
samples, consisting of microcrystalline powders, were meas-
ured in sealed capillaries in Debye−Scherrer geometry. The
The general motif of the aromatic organolithium compounds
is the Li···π interaction leading to polymeric structures.
Additionally, PhLi and MesLi (Mes = mesityl/2,4,6-trimethyl-
phenyl) exhibit dimers by the formation of Li2C2-rings. Among
all the structural variety of aryl-lithium compounds, an
increased sterical demand of the ligand hinders the formation
of polymeric chains and allows the isolation of the naked
dimer, e.g., [Xy2(C6H3)Li]2,20 Mes2(C6H3)Li,21 bis(2,3,5-
Received: April 19, 2018
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.8b01041
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Article
differences are also accompanied by different unit cell settings
and monoclinic axes (Table S1).
Scheme 1. General Lithium−Bromide Exchange Reaction of
Bromo-(di)methylbenzene and n-Butyl-lithium
ortho-Tolyl-lithium, o-TolLi. Many attempts to prepare
pure o-TolLi yielded the desired product with varying yields
and purities. A minor amount of nanocrystalline LiBr (3.5%,
determined by Rietveld method, Figure S1, ESI) could not be
avoided. Both, LiBr and o-TolLi are poorly soluble in Et2O and
MTBE; extraction yielded o-TolLi and amorphous LiBr, which
recrystallized during the measurements.
Indexing of the reflections led to an orthorhombic unit cell
with 2.17 times the volume compared to the para isomer.
Structure solution with two independent o-TolLi moieties in
Sohncke space group P212121 revealed polymeric chains,
similar to p-TolLi, exhibiting both relative configurations
with respect to the methyl groups (trans and cis) and a slight
preference for the trans configuration. (Figure 3)
structures were solved in real space by simulated annealing
with DASH27 and refined with Rietveld methods28,29 using
TOPAS.30
para-Tolyl-lithium, p-TolLi. para-Tolyl-lithium is insolu-
ble in hydrocarbons and aromatics. Upon addition of Et2O, a
small amount of an ether adduct is formed in benzene (Et =
ethyl). This can be explained by its polymeric structure (Figure
1): Two p-TolLi moieties form a dimer built-up by a C2Li2-
Figure 1. Packing motif of p-TolLi, with C (black), Li (gray), H
(white), and Li···π coordination shown.
Figure 3. Packing motif of o-TolLi, C (black), Li (gray), and H
(omitted).
ring. These dimers are Li···π coordinated to two adjacent p-
TolLi dimers to build up polymeric chains. In contrast to
[(thp)4(p-TolLi)LiBr]31 (thp = tetrahydropyrane), which also
forms a four-membered ring, but consists of CLi2Br, the Li
coordination is saturated by thp molecules to form isolated
complexes.
Structure determination proceeded without peculiarity, and
Rietveld refinement converged with appropriate quality criteria
and a smooth difference curve (Figure 2 and Table S1).
The crystal structure of p-TolLi is isotypic to that of PhLi14
and homotypic to that of MesLi.18 They all share a similar
constitution of the chains with respect to the methyl groups,
while the chains of MesLi are packed differently. These
Rietveld refinement confirmed the crystal structure of the
trans configured dimer (trans, Rwp = 2.22, GOF = 2.12; cis, Rwp
= 3.85, GOF = 3.50) with moderate quality criteria and a
sufficient difference curve (Table S1 and Figure S1).
The crystal structure of o-TolLi exhibits pseudoinversion
symmetry within the dimers. Therefore, one would expect a
structure description in a centrosymmetric super group, but
the methyl groups of the tolyl moiety are oriented differently
with respect to the next coordination polymer chain, Figure 4.
Figure 2. Rietveld-plot of the crystal structure of p-TolLi: Iexp
(measured intensity, black circles), Icalc (caluculated intensity, red),
Iexp − Icalc (blue), positions of Bragg reflections (tick marks).
Figure 4. Packing motif of o-TolLi; symmetrically identical tolyl
moieties drawn in blue and black, respectively. Li (gray) view along c.
B
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The reduced density and the moderate fit from Rietveld
refinement could indicate disorder. Several approaches for a
proper description of a disordered phase failed. Most of the
structural models did not even improve the fit, while only a
small improvement came with a high prize of additional
parameters. Therefore, all models were rejected.
located the fourth lithium atom. Three of the four lithium
triangles are capped by 5-m-XyLi ligands, while the fourth
lithium atom is exposed, Figure 5. This results in a distorted
The comparison of the crystal structure of o-TolLi to those
of PhLi,14 MesLi,18 and p-TolLi exhibits similar chains for all,
while only the chains of o-TolLi are packed in a non-
centrosymmetric structure. Further, the structures of o-TolLi,
p-TolLi, PhLi,14 and MesLi18 with their laterally connected
dimeric Li2C2 rings fit to the laddering principle by Snaith and
Mulvey et al.32,33
However, the packing of the o-TolLi chains is totally
different from those of p-TolLi, MesLi,18 and PhLi14 (Figures
S2−S4). This results in a double-sized unit cell with two
independent monomers in the asymmetric unit. The crystal
structure of o-TolLi is described with Sohncke space group
P212121, which shares the common subgroup P21 with the
above-mentioned aryl-lithium compounds. The density of o-
TolLi is ∼8% smaller compared to that of p-TolLi, which is
due to a packing effect from the ortho-methyl group leading to
the noncentrosymmetric space group.
Figure 5. Molecular model of [(5-m-XyLi)3(MTBE)3LiBr], view
̅
tilted along 3-axis parallel to [111]. Ellipsoids are shown with 50%
probability.
Although the density and, therefore, the packing of o-TolLi
are expected to be worse compared to those of p-TolLi, it is
not forming an ether adduct. Surprisingly, within the compared
phenyl-lithium derivatives, p-TolLi is packed most efficiently
by means of density, while o-TolLi is the least dense (Table
S1).
Li4C3Br cubane-like motif, which can also be described as stack
of two dilithium rings, Li2C2 and Li2CBr, according to Snaith
et al.32 Bromine and one lithium atom are located on the 3-fold
axis, above and below the Li3-triangle, whose corners are
coordinated by MTBE ligands (d(Li−O) = 1.962(7) Å; d =
distance). The exposed lithium atom is related to the next
A closer look at the bond lengths with respect to the
differences of the user generated constraints and restraints
during Rietveld refinement reveals small differences. The Li−C
bonds and Li−Li and Li−phenyl distances should be very
similar. However, MesLi18 exhibits the shortest of all of them,
which might be due to stronger Li−π interactions and a
stronger Li−C bond induced by the +I effect of the mesityl
group (Table S1). The weakening of the Li−C bond by less + I
effect is supported by elongated Li−C bonds (MesLi < p-TolLi
< o-TolLi < PhLi). In principle the same holds true for the
Li−π interaction: Remarkably, p-TolLi has a Li−π distance
similar to that of PhLi, while the Li−π distance for o-TolLi is
close to the average of the distances in MesLi and PhLi. The
Li−Li distances of PhLi and p-TolLi are again very similar,
while MesLi exhibits the shortest and o-TolLi by far the
longest. The elongated Li−Li distance in o-TolLi is the result
of the different packing; e.g., there is a slight shift between the
phenyl planes in Sohncke space group P212121. The bond
angles φ (C−Li−C) compensate geometrically for the bond
length differences ranging from 109.6(2)° for o-TolLi to
121.0(3)° for MesLi.
̅
equivalent lithium atom by 1 symmetry with a distance of
6.30(2) Å, leading to a contact dimer of two cages. These
lithium atoms are sterically hindered by the packing of the 5-m-
xylyl ligands, which are oriented staggered to each other,
̅
according to the 3 symmetry. The bromine atom is sterically
hindered by three tBu groups of MTBE molecules from
different cages (Figure 6).
5-m-Xylyl-lithium, 5-m-XyLi. The synthesis of 5-m-XyLi
was performed in a manner similar to those of both TolLi
compounds. However, only a product with the composition
[(5-m-XyLi)3(MTBE)3LiBr] (MTBE = methyl-tert-butylether)
could be isolated and single crystals grown. The “standard
synthesis” in Et2O led to a phase mixture of LiBr and an
unknown product; reliable indexing of the XRPD pattern
failed. However, the XRPD pattern looks different in
comparison to those of all polymeric PhLi derivatives; no
single crystals could be grown.
Figure 6. Packing motif of [(5-m-XyLi)3(MTBE)3LiBr] view nearly
̅
perpendicular to the 3-axis (along [111]), Li (gray), C (black), O
(red), Br (orange), H (omitted). The three detached MTBE
molecules belong to three separate cages.
The displacement ellipsoids of the alkyl carbon atoms are
enlarged and distorted, probably due to deformations,
̅
vibrations, or a slight displacement from the 3 symmetry. In
comparison with [(PhLi)3(Et2O)3LiBr]34 (space group P21/c,
all atoms on general position), the molecular geometry and
bond lengths are similar (Table S1), while the Li−C bond
length of the exposed Li is significantly shorter. However, the
̅
The crystal structure was determined in space group Pa3.
Four lithium atoms form a trigonal pyramid, whose basal plane
is capped by bromine, while opposite to the bromine atom is
C
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Inorganic Chemistry
Article
symmetry and packing of both cage structures differ
significantly in the formation of contact dimers, with Li
oriented to Li in the case of [(5-m-XyLi)3(MTBE)3LiBr] and
Li toward Br for [(PhLi)3(Et2O)3LiBr].34 This is probably
caused by the steric demand of the ligands.
For validation purpose the structure was also refined against
the XRPD data of the crude product with Rietveld methods to
prove the purity and stability of the phase from −100 °C to
ambient. The refinement converged with appropriate quality
criteria and a smooth difference curve (Table S1 and Figure
S5).
Since [(5-m-XyLi)3(MTBE)3LiBr] precipitates from the
reaction solution it is at least a stable reaction intermediate
in the Li−Br exchange reaction. This stable cage compound
forms a contact dimer and hinders full conversion to 5-m-XyLi
and polymerization, as known from other PhLi derivatives.
This also leads to an “increased” solubility, compared to PhLi,
p-TolLi, o-TolLi, and MesLi, which all precipitate nearly
quantitatively from ethereal solutions by the formation of
polymeric chains. This might be understood due to electronic
effects of the substitution pattern on the aromatic ring, e.g.,
double-meta substitution vs no substitution, ortho- and para-
substitution, and trisubstitution. However, there is a chance
that similar cage aggregates also exist in solution. These
aggregates could explain the unavoidable LiBr formation in the
o-TolLi synthesis from a nonstable cage compound, as well as
the moderate solubility of o-TolLi in Et2O in the presence of
LiBr. A similar behavior is known from so-called “Turbo-
Grignards”,35 which incorporate lithium halides and exhibit
higher reactivities and solubilities. Hitherto, only little is
known about their crystal structures from two examples.36,37
However, their occurring aggregates are rather complicated,
due to the Schlenk equilibrium. So far only nuclear magnetic
resonance (NMR) techniques were widely and successfully
applied.38−40
the case of 5-m-XyLi and, for both of the tolyl-lithium
compounds, in the precipitation of coordination polymers.
EXPERIMENTAL SECTION
■
All preparations and manipulations were done under severe inert gas
(Ar 99.999%) conditions using Schlenk techniques. Powders were
transferred using glass trousers and attached capillaries (Figures S6
and S7). Et2O, MTBE, and THF (all pro analysis, p.a.) were dried
over NaK alloy/benzophenone and stored over molecular sieves (4 Å)
at 0 °C, while n-pentane and n-hexane (both p.a.) were dried and
stored over molecular sieves (4 Å). C6D6 was dried over molecular
sieves (4 Å) and degassed by three freeze−pump−thaw cycles.
All commercial chemicals were purchased and used as received
(>95%, for synthesis). Solutions of organolithium compounds were
obtained from Rockwood/Albemarle Lithium and titrated with
42
Ph2Te2 in THF, frequently.
Caution! Alkyl-lithium solutions and neat aryl-lithium compounds are
generally classified as pyrophoric.
Syntheses. All syntheses were carried out by Li−halogen
exchange reaction (Schlosser26 method) via a modified procedure
based on the synthesis of MesLi.18
4-Methylphenyl-lithium (p-TolLi). 4-Bromotoluene (3.0 mL, ρ =
1.41 g mL−1, 4.2 g, 25 mmol) was dissolved in 5 mL of Et2O and
cooled to −75 °C with CO2/iso-propanol bath, and n-BuLi (9.0 mL,
2.3 mol L−1 in hexane, 21 mmol, 0.8 equiv) was added within 10 min
via syringe and septum. The reaction mixture was stirred at −75 °C
for 2 h and allowed to reach ambient overnight, at which point a
colorless powder was obtained. After filtration and two washes with 4
mL of n-pentane, the product was dried in vacuo. Isolated yield: 760
mg (7.7 mmol, 37%), insoluble in C6D6. NMR data for the Et2O
adduct (Figures S8 and S9, 13C could not be measured, due to poor
solubility) follow. 1H (300 MHz, C6D6) δ/ppm = 8.21 (d, J = 7.2 Hz,
7
2H-aryl), 7.24 (d, J = 6.8 Hz, 2H-aryl), 2.31 (s, 3H). Li (194 MHz,
C6D6) δ/ppm = 1.94.
2-Methylphenyl-lithium (o-TolLi). 2-Bromotoluene (0.70 mL, ρ =
1.42 g mL−1, 0.99 g, 5.8 mmol) was dissolved in 5 mL of MTBE and
cooled to −80 °C with liquid N2/iso-propanol bath, and n-BuLi (0.7
mL, 2.3 mol L−1 in hexane, 1.6 mmol, 0.3 equiv) was added within 25
min via syringe and septum. The reaction mixture was stirred at −80
°C for 2 h and allowed to reach ambient overnight. The reaction
solution was then dried in vacuo, at which point a colorless powder
was obtained with about 3.5% LiBr and a purity of approximate >95%.
Isolated (corrected) yield: 110 mg (1.1 mmol, 69%). This material is
insoluble in C6D6; NMR of an Et2O adduct failed.
3,5-Dimethylphenyl-lithium (5-m-XyLi)/[(5-m-
XyLi)3(MTBE)3LiBr]. Bromo-3,5-dimethylbenzene (0.70 mL, ρ =
1.36 g mL−1, 0.95 g, 5.1 mmol) was dissolved in 5 mL of MTBE and
cooled to −80 °C with liquid N2/iso-propanol bath, and n-BuLi (2.0
mL, 2.3 mol L−1 in hexane, 4.6 mmol, 0.9 Eq) was added within 25
min via syringe and septum. The reaction mixture was stirred at −80
°C for 2 h and allowed to reach ambient overnight, at which point a
colorless powder was obtained. After filtration and two washes with 5
mL of n-hexane, the product was dried in vacuo. Single crystals,
suitable for XRD, were grown from an MTBE solution within a week
by slow addition of hexane. Isolated yield of [(5-m-XyLi)3-
(MTBE)3LiBr]: 503 mg (0.77 mmol, 67% (based on n-BuLi)).
This material decomposes in C6D6 to MTBE and an insoluble
residue; NMR of an ether adduct failed. The purity was confirmed by
Rietveld refinement of the XRPD data of the crude product.
X-ray Powder Diffraction and Structure Determination.
Measurement. All samples, consisting of microcrystalline powders,
were sealed in borosilicate glass capillaries and measured in Debye−
Scherrer geometry on a STOE Stadi P diffractometer. Radiation was
generated by a classical sealed tube with Cu-anode (40 kV, 30 mA);
its line focus beam was monochromated to Cu Kα1 (λ = 1.5406 Å)
with a curved Ge(111) single crystal. The intensity of the diffracted
beam was detected by a linear position sensitive detector (lin PSD, Kr/
CH4).
The presence of small amounts of LiBr in o-TolLi and the
incorporation in [(5-m-XyLi)3(MTBE)3LiBr] result from the
presence of both direct coupling and lithium−halogen
exchange reaction. This probably indicates for a four-centered
transition state, as proposed by Wakefield4 (Scheme 2a), in the
Scheme 2. (a) Four-Centered Transition State Proposed by
Wakefield4 and (b) Proposed Extension of Wakefield’s
Mechanism Involving the Aggregation (R = Alkyl, Ar = Aryl,
D = Donor Molecule/Ether)
discussed lithium−halogen exchange reaction mechanism.41
However, the truth within this unclear reaction mechanism
might be more complex and definitely involves the aggregation
equilibria of the organolithium compounds (Scheme 2b). First,
the hexameric n-BuLi should disaggregate in a hexane−ether
mixture to a tetramer and maybe to a dimer. We assume this is
followed by a tetramer of the type [(BuLi)4−n(Ar−Br)n] (Ar =
aryl), which undergoes lithium−halogen exchange and
eliminates/exchanges BuBr (and Ar−Br) by “fresh” BuLi and
ArBr. This results in isolated [(5-m-XyLi)3(MTBE)3LiBr] in
D
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The spun samples were measured several times within a few days to
check the stability during the entire measurement. Data processing
was carried out with the software package WinXPOW.43
ASSOCIATED CONTENT
* Supporting Information
■
S
Additional Rietveld-Plots, crystallographic data, packing
diagrams, NMR spectra and sketches of some applied
glassware are given in the Supporting Information.The
Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.8b01041.
Structure Determination. The Bragg reflections were indexed with
DICVOL44 to yield reliable unit cell parameters. These parameters
were then refined with Pawley45 methods. With the volume
increments of Hofmann,46 Z and Z′ (Z, Z′ = number of formula
units in the unit cell/asymmetric unit) were estimated, and due to
systematic extinctions the most reliable space groups were
determined. The structures were solved in real space with the
program DASH,27 molecular models of the compounds were derived
from the known structures of PhLi14 and MesLi.18
(PDF)
Accession Codes
The solved structures were refined with Rietveld28,29 methods in
program TOPAS.30,47 Both, bond lengths and angles were restrained;
in addition, the phenyl rings were restrained to be flat. The
background was fitted with at least 20 parameters of a Chebychev48
polynomial function. The asymmetry was described by three
fundamental parameters,49 and the anisotropic broadening of the
reflections was described by spherical harmonics in conjunction to
CCDC 1540481−1540482, 1819589, and 1819714 contain the
supplementary crystallographic data for this paper. These data
can be obtained free of charge via www.ccdc.cam.ac.uk/
data_request/cif, or by emailing data_request@ccdc.cam.ac.
uk, or by contacting The Cambridge Crystallographic Data
Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44
1223 336033.
Jarvinen.50 For all non-hydrogen atoms one isotropic Debye−Waller-
̈
factor Biso was used, while the one for hydrogen atoms was
constrained to be 1.2·Biso. If necessary, an additional Biso for selected
atoms/moieties was applied.
AUTHOR INFORMATION
Corresponding Author
*E-mail: fink@chemie.uni-frankfurt.de.
ORCID
■
Single Crystal X-ray Diffraction and Structure Determi-
nation. Measurement. A single crystal was selected and prepared
under perfluorated oil on a glass fiber. The crystal was measured on a
STOE IPDS-II diffractometer at −100 °C in a N2 stream of a
Cryostream 700 (OXFORD CRYOSYSTEMS). Mo Kα (λ = 0.71073
Å) radiation was generated by a XENOCS GeniX3D microfocus
source and focused on the crystal by multilayer optics. The intensity
of the diffracted beam was detected by an image plate detector.
Indexing and data processing were carried out with software package
X-Area.51
Lothar Fink: 0000-0001-8369-1756
Present Address
†Max-Planck-Institut fu
̈
r Kohlenforschung, Kaiser-Wilhelm-
Platz 1, D-45470 Mu
̈
lheim/Ruhr, Germany.
Notes
The authors declare no competing financial interest.
Structure Determination. The structure was solved by direct
methods52 and refined against F2 by full-matrix least-squares
techniques (F = structure factor).53 H atoms were refined using a
riding model. The molecule is located on a 3-fold rotation axis with
only one-third of it in the asymmetric unit.
ACKNOWLEDGMENTS
■
We gratefully acknowledge Dr. Peter Rittmeyer from
Albemarle/Rockwood Lithium GmbH for donating butyl-
lithium solutions. In addition we thank Dr. Hans-Wolfram
Lerner, Edith Alig, and Laura Remmel for helpful discussions.
A.B. thanks Prof. Dr. Martin U. Schmidt for the opportunity to
write the master thesis using the equipment of the group.
Crystallographic data of the reported crystal structures have been
deposited at the Cambridge Crystallographic Data Centre.
7
NMR Spectroscopy. NMR spectra (1H, Li, 13C) were recorded
in sealed borosilicate glass tubes (d = 0.5 mm) on a BRUKER
Avance-300 (1H 300.03 MHz) and Avance-500 (7Li 194.39 MHz, 13
C
REFERENCES
125.77 MHz). Chemical shifts δ are given in ppm relative to external
tetramethylsilane or LiCl in H2O and, if possible, calibrated to the
residual signal of C6D6 (δ(1H) = 7.16 ppm, δ(13H) = 128.06 ppm).54
Multiplicities are given with the common abbreviations (e.g., s singlet,
d doublet); J coupling constants are given in Hz.
■
̈
(1) Schlenk, W.; Holtz, J. Uber die einfachsten metallorganischen
Alkaliverbindungen. Ber. Dtsch. Chem. Ges. 1917, 50 (1), 262−274.
(2) Schlosser, M. Organometallics in Synthesis: A Manual; Wiley:
Chichester, U.K., 1994.
(3) Schlosser, M. Organometallics in Synthesis, Third Manual; Wiley:
NJ, 2013.
CONCLUSIONS
■
(4) Wakefield, B. J. The Chemistry of Organolithium Compounds;
Pergamon Press: Oxford, U.K., 1974.
(5) Clayden, J. Organolithiums: Selectivity for Synthesis; Elsevier:
Oxford, U.K., 2002.
X-ray powder diffraction and single crystal diffraction together
revealed the crystal structure and purity of organolithium
compounds, which are insoluble in noncoordinating solvents.
Two tolyl-lithium isomers (para and ortho) form polymeric
chains, while the ortho-isomer exhibits pseudoinversion
symmetry with two independent monomers in trans config-
uration. This leads to a reduced density and solubility nearly
equal to that of LiBr or probably the formation of an o-TolLi·
LiBr cage with moderate solubility. However, in benzene only
an Et2O adduct of p-TolLi is slightly soluble, while o-TolLi is
not forming a similar adduct. In contrast to o- and p-TolLi, 5-
m-XyLi could only be isolated as a contact-dimer forming [(5-
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