Syntheses and Crystal Structures of Phenyl-Lithium Derivatives

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Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX

Syntheses and Crystal Structures of Phenyl-Lithium Derivatives Alexander Bodach,† René Hebestreit, Michael Bolte, and Lothar Fink* Institut für Anorganische und Analytische Chemie, Goethe-Universität Frankfurt, Max-von-Laue-Strasse 7, D-60438 Frankfurt/Main, Germany

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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 2methylphenyl-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 (3,5dimethyl-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.

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trimethylphenyl)phenyl-lithium,22 or even leads to tetramers, e.g., [iPr3(C6H2)Li]421 by Li···π interactions only, or results in hexamers, e.g., [2,5-tBu2(C6H3)Li]6,23 similar to [n-BuLi]624 and other alkyl-lithium compounds. Although organolithium compounds are used preferentially in solution and for syntheses, they also might be applied in mechanosyntheses.25 This dramatically hints for the need for donor-unsupported and solid organolithium compounds. Therefore, structure determination from powder expands our basic understanding of well-known and widely used simple organolithium compounds. Here we report on the syntheses of two polymeric tolyllithium (para-TolLi, ortho-TolLi) compounds and a 5-metaxylyl-lithium cage [(5-m-XyLi)3(MTBE)3LiBr] (MTBE = methyl-tert-butylether). The corresponding crystal structures were determined from X-ray powder diffraction data, due to insolubility in saturated and aromatic hydrocarbons. Single crystals of [(5-m-XyLi)3(MTBE)3LiBr] could be grown while no polymeric m-XyLi was observed.

INTRODUCTION Since the early work of Schlenk et al.,1 organolithium compounds matured to indispensable reagents for the syntheses of organic, organometallic, and polymeric compounds, even on an industrial scale.2−5 Their structures and reactivities are distinct, manifold, and directly correlated,6 whereas our fundamental understanding is mainly limited by the knowledge of structures. However, many organolithium compounds are used exclusively in solution, often in the presence of Lewis-bases, such as amines or ethers. Therefore, most of the known structures consist of organolithiums stabilized by Lewis-bases.7−9 Hitherto, only ∼30 crystal structures of pure, unsolvated organolithium compounds (only Li, C, H) were reported.10 A remarkably high number of these structures were determined from X-ray powder diffraction (XRPD) data, due to their polymeric structure and insolubility in hydrocarbons. MeLi (Me = methyl),11−13 PhLi (Ph = phenyl),14 indenylLi,15 Licp (cp = cyclopentadienyl),16 and Licp* (cp* = 1,2,3,4,5 pentamethylcyclopentadienyl)17 were determined from synchrotron data, whereas mesitylLi18 and Li[CH2P(tBu)2]19 (tBu = tert-butyl) were determined from laboratory data. 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-trimethylphenyl) 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© XXXX American Chemical Society

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RESULTS AND DISCUSSION 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 measured in sealed capillaries in Debye−Scherrer geometry. The Received: April 19, 2018

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DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry

differences are also accompanied by different unit cell settings and monoclinic axes (Table S1). 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)

Scheme 1. General Lithium−Bromide Exchange Reaction of Bromo-(di)methylbenzene and n-Butyl-lithium

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 insoluble 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 pTolLi 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

DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX

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Inorganic Chemistry 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. 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 noncentrosymmetric 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 oTolLi 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. 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). 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. 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. The crystal structure was determined in space group Pa3̅. Four lithium atoms form a trigonal pyramid, whose basal plane is capped by bromine, while opposite to the bromine atom is

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

Figure 5. Molecular model of [(5-m-XyLi)3(MTBE)3LiBr], view tilted along 3̅-axis parallel to [111]. Ellipsoids are shown with 50% probability.

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 equivalent lithium atom by 1̅ 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-mxylyl ligands, which are oriented staggered to each other, according to the 3̅ symmetry. The bromine atom is sterically hindered by three tBu groups of MTBE molecules from different cages (Figure 6).

Figure 6. Packing motif of [(5-m-XyLi)3(MTBE)3LiBr] view nearly perpendicular to the 3̅-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 3̅ 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 C

DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX

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the case of 5-m-XyLi and, for both of the tolyl-lithium compounds, in the precipitation of coordination polymers.

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 parasubstitution, 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 “TurboGrignards”,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 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

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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 Ph2Te242 in THF, frequently. Caution! Alkyl-lithium solutions and neat aryl-lithium compounds are generally classif ied 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, 2H-aryl), 7.24 (d, J = 6.8 Hz, 2H-aryl), 2.31 (s, 3H). 7Li (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-mXyLi)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).

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

DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX

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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 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 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 Järvinen.50 For all non-hydrogen atoms one isotropic Debye−Wallerfactor 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. Single Crystal X-ray Diffraction and Structure Determination. 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 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. Crystallographic data of the reported crystal structures have been deposited at the Cambridge Crystallographic Data Centre. NMR Spectroscopy. NMR spectra (1H, 7Li, 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, 13C 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.

Article

ASSOCIATED CONTENT

S Supporting Information *

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.inorgchem.8b01041. (PDF) Accession Codes

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 [email protected]. uk, or by contacting The Cambridge Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ, UK; fax: +44 1223 336033.

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AUTHOR INFORMATION

Corresponding Author

*E-mail: fi[email protected]. ORCID

Lothar Fink: 0000-0001-8369-1756 Present Address †

Max-Planck-Institut für Kohlenforschung, Kaiser-WilhelmPlatz 1, D-45470 Mülheim/Ruhr, Germany.

Notes

The authors declare no competing financial interest.

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ACKNOWLEDGMENTS We gratefully acknowledge Dr. Peter Rittmeyer from Albemarle/Rockwood Lithium GmbH for donating butyllithium 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.

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REFERENCES

(1) Schlenk, W.; Holtz, J. Ü ber 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. (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. (6) Reich, H. J. Role of Organolithium Aggregates and Mixed Aggregates in Organolithium Mechanisms. Chem. Rev. 2013, 113 (9), 7130−7178. (7) Weiss, E. Structures of organo alkali metal complexes and related compounds. Angew. Chem., Int. Ed. Engl. 1993, 32 (11), 1501−1523. (8) Gessner, V. H.; Däschlein, C.; Strohmann, C. Structure formation principles and reactivity of organolithium compounds. Chem. - Eur. J. 2009, 15 (14), 3320−3334. (9) Götz, K.; Gessner, V. H.; Unkelbach, C.; Kaupp, M.; Strohmann, C. Understanding Structure Formation in Organolithium Compounds: An Experimental and Quantum-Chemical Approach. Z. Anorg. Allg. Chem. 2013, 639 (11), 2077−2085. (10) Allen, F. H. The Cambridge Structural Database: a quarter of a million crystal structures and rising. Acta Crystallogr., Sect. B: Struct. Sci. 2002, 58 (3), 380−388.

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CONCLUSIONS 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 configuration. 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, 5m-XyLi could only be isolated as a contact-dimer forming [(5m-XyLi)3(MTBE)3LiBr] instead of a coordination polymer, probably due to electronic effects of the substitution pattern. Surprisingly, the stable ether adduct [(5-m-XyLi)3(MTBE)3LiBr] is not soluble in benzene. E

DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX

Article

Inorganic Chemistry

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DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX

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DOI: 10.1021/acs.inorgchem.8b01041 Inorg. Chem. XXXX, XXX, XXX−XXX