Synthesis of mono- and geminal dimetalated carbanions of bis(phenylsulfonyl)methane using alkali metal bases and structural comparisons with lithiated bis(phenylsulfonyl)imides

The alpha,alpha'-stabilized carbanion complexes [(PhSO2)2CHLi.THF]1, [(PhSO2)2CHNa.THF]2 and [(PhSO2)2CHK]3 were prepared by the direct deprotonation of bis(phenylsulfonyl)methane I in THF with one molar equivalent of MeLi, BuNa and BnK respectively. The geminal dianionic complexes [(PhSO2)2CLi2.THF]4, [(PhSO2)2CNa2.0.55THF]5 and [(PhSO2)2CK2]6 were similarly prepared by the reaction of I with two molar equivalents of MeLi, BuNa and BnK respectively in THF. NMR and MS solution studies of 1-3 are consistent with the formation of charge-separated species in DMSO media. Solutions studies of 4-6, in conjunction with trapping experiments, indicate that the dianions deprotonate DMSO and regenerate the monoanions 1-3. Crystallographic analysis of 1 revealed a 1D chain polymer in which the metal centers are chelated by the bis(sulfonyl) ligands and connect to neighboring units through Li-O(S) interactions. An unexpected feature of 1 is that the polymeric chains are homochiral, since the chelating ligands of the backbone adopt the same relative configuration. Also, the phenyl substituents of each chelate in 1 are oriented in a cisoid manner. The sodium derivative 2 adopts a related solid-state structure, where enantiomeric pairs of chains combine to give a 1D ribbon motif. The lithium bis(phenylsulfonyl)imides [(PhSO2)2NLi.THF]9 and [(PhSO2)2NLi.Pyr2]10 were also prepared and structurally characterized. In the solid state 9 has a similar connectivity to that found for 1 but with heterochiral chains. In comparison, the more highly solvated complex 10 forms a 1D polymeric arrangement without chelation of the ligands and with the phenyl substituents oriented in a transoid fashion.

Hetero-Aggregate Compounds of Aryl and Alkyl Lithium Reagents: A Structurally Intriguing Aspect of Organolithium Chemistry

Organolithium compounds are often depicted as mononuclear species. However, such compounds are in fact aggregated species and can form hetero-aggregates containing different organic groups, including heteroatom groups. In reactions involving organolithium reagents, the "pure" homo-aggregate organolithium compound can change into a hetero-aggregate, which has a different structure and reactivity to the homo-aggregate. This fact is often overlooked. When there are chiral centers in the organolithium reagent or the substrate, diastereoselective self-assembly (the preferential formation of a particular diastereoisomeric aggregate) plays a role. The importance of these contributions in understanding the structure and reactivity patterns of organolithium reagents is the focus of this Minireview.

Formation of Organolithium Hetero-Aggregates [Li4Ar2(nBu)2] (Ar=C6H4CH(Me)NMe2-2) during the Directedortho-Lithiation of [1-(Dimethylamino)ethyl]benzene

(R)-[1-(Dimethylamino)ethyl]benzene reacts with nBuLi in a 1:1 molar ratio in pentane to quantitatively yield a unique hetero-aggregate (2 a) containing the lithiated arene, unreacted nBuLi, and the complexed parent arene in a 1:1:1 ratio. As a model compound, [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)] (2 b) was prepared from the quantitative redistribution reaction of the parent lithiated arene Li(C(6)H(4)CH(Me)NMe(2)-2) with nBuLi in a 1:1 molar ratio. The mono-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))] (2 c) and the bis-Et(2)O adduct [Li(4)(C(6)H(4)CH(Me)NMe(2)-2)(2)(nBu)(2)(OEt(2))(2)] (2 d) were obtained by re-crystallization of 2 b from pentane/Et(2)O and pure Et(2)O, respectively. The single-crystal X-ray structure determinations of 2 b-d show that the overall structural motifs of all three derivatives are closely related. They are all tetranuclear Li aggregates in which the four Li atoms are arranged in an almost regular tetrahedron. These structures can be described as consisting of two linked dimeric units: one Li(2)Ar(2) dimer and a hypothetical Li(2)nBu(2) dimer. The stereochemical aspects of the chiral Li(2)Ar(2) fragment are discussed. The structures as observed in the solid state are apparently retained in solution as revealed by a combination of cryoscopy and (1)H, (13)C, and (6)Li NMR spectroscopy.

The Crystal Structures of a Chiral Aminoalkoxide Cluster and Its Adduct with Benzyllithium

The crystal structures of the chiral aminoalkoxide cluster (S)-2 and its unexpected adduct with benzyllithium (S)-3 have been determined. For compound (S)-2, a hexameric cyclic ring-ladder is observed in the solid state, which leads to an unshielded coordination site in a chiral pocket that is only accessible from one direction. The presence of (S)-2 leads to the deprotonation of toluene by n-butyllithium, giving benzyllithium. In contrast to earlier studies on lithium alkoxides, the resulting adduct (S)-3 between benzyllithium and (S)-2 is not formed by the exchange of alkoxy groups for alkanide units, as has been observed for a multitude of examples. Compound (S)-3 therefore represents a thus far unconsidered type of structure: the unshielded "top side" of the aminoalkoxide cluster (S)-2 capped by the lithium center of benzyllithium via three Li-O interactions.

Lithiation of tris(alkyl- and arylamido)orthophosphates EP[N(H)R]3 (E = O, S, Se): imido substituent effects and P=E bond cleavage

In the solid state, OP[N(H)Me](3) (1a) and OP[N(H)(t)Bu](3) (1b) have hydrogen-bonded structures that exhibit three-dimensional and one-dimensional arrays, respectively. The lithiation of 1b with 1 equiv of (n)BuLi generates the trimeric monolithiated complex (THF)[LiOP(N(t)Bu)[N(H)(t)Bu](2)](3) (4), whereas reaction with an excess of (n)BuLi produces the dimeric dilithium complex [(THF)(2)Li(2)OP(N(t)Bu)(2)[N(H)(t)Bu]](2) (5). Complex 4 contains a Li(2)O(2) ring in an open-ladder structure, whereas 5 embraces a central Li(2)O(2) ring in a closed-ladder arrangement. Investigations of the lithiation of tris(alkyl or arylamido)thiophosphates, SP[N(H)R](3) (2a, R = (i)Pr; 2b, R = (t)Bu; 2c, R = p-tol) with (n)BuLi reveal interesting imido substituent effects. For the alkyl derivatives, only mono- or dilithiation is observed. In the case of R = (t)Bu, lithiation is accompanied by P-S bond cleavage to give the dilithiated cyclodiphosph(V/V)azane [(THF)(2)Li(2)[((t)BuN)(2)P(micro-N(t)Bu)(2)P(N(t)Bu)(2)]] (9). Trilithiation occurs for the triaryl derivatives EP[N(H)Ar](3) (E = S, Ar = p-tolyl; E = Se, Ar = Ph), as demonstrated by the preparation of [(THF)(4)Li(3)[SP(Np-tol)(3)]](2) (10) and [(THF)(4)Li(3)[SeP(NPh)(3)]](2) (11), which are accompanied by the formation of small amounts of 10.[LiOH(THF)](2) and 11.Li(2)Se(2)(THF)(2), respectively.

Aggregation patterns in alpha,alpha'-stabilized carbanions: assembly of a sodium cage polymer by slip-stacking of dimers

The alpha,alpha'-stabilized carbanion complexes [PhSO(2)CHCNNa.THF], 3, [t-BuSO(2)CHCNNa], 4, [PhSO(2)CHCNK], 5, [t-BuSO(2)CHCNK], 6, and [MeSO(2)CHCNLi.TMEDA], 7, have been synthesized via the metalation of the parent (organo)sulfonylacetonitriles by BuLi, BuNa, or BnK in THF solution (or THF/TMEDA in the case of 7). In addition, complexes 3 and 7 have been characterized by single-crystal X-ray analyses and have been found to adopt related structures in the solid state. Complex 7 is a molecular dimer containing a central 12-membered (OSCCNLi)(2) ring core, with each metal rendered tetracoordinate by binding to a chelating TMEDA molecule. As found in related complexes, no direct carbanion to lithium contacts are present in the structure of 7. Complex 3 forms a polymeric cage structure composed of associated "dimeric" (OSCCNNa)(2) rings, similar to those found in 7. The larger sodium cations, and the presence of only one THF molecule/metal, allow additional contacts with the anions, leading to hexacoordination at the metal centers. These contacts include long-range transannular Na-N interactions (2.8042(14) A) across the central dimeric ring and "interdimer" Na-C connections (2.8718(15) A). Dissolution of complexes 3-6 and their lithiated derivatives [PhSO(2)CHCNLi.TMEDA], 1, and [t-BuSO(2)CHCNLi.THF], 2, in DMSO-d(6) results in almost identical chemical shifts for each type of ligand. This suggests that charge-separated complexes of the form [RSO(2)CHCN](-)[M(DMSO-d(6))(n)()](+) are formed in highly polar solution.

Understanding the formation of new clusters of alkali and alkaline Earth metals: a new synthetic approach, single-crystal structures, and theoretical calculations

A new synthetic approach, reacting alkaline earth metal iodides with butyllithium, lithium hydroxide, and/or lithium butoxide under salt elimination, is presented, giving access to some interesting clusters of calcium, strontium, and barium, partially in combination with lithium. The so far largest calcium cluster Li[[Ca(7)(mu(3)-OH)(8)I(6)(thf)(12)](2)(mu(2)-I)].3THF, 4, and the new strontium compound [Sr(3)I(3)(OH)(2)(thf)(9)]I, 5, are shown to feature common building blocks of OH-capped M(3) triangles. On the basis of mainly electrostatic interactions, these clusters are not volatile. By introducing LiO(t)Bu, the two clusters [IM(O(t)Bu)(4)[Li(thf)](4)(OH)] (6, M = Sr; 7, M = Ba) are prepared, 7 exhibiting volatility as an important physical property, which makes it a potential precursor for chemical vapor deposition. The structural relationship between 4, 5, 6, and 7 and their respective starting materials is shown, and possible reaction mechanisms are proposed. Exhibiting surprising and new structural motifs, the bonding modes of these clusters are investigated by the electron localization function as well as by ab initio calculations.

Molecular mechanics (MM3) calculations on lithium amide compounds

The MM3 force field has been extended to deal with the lithium amide molecules that are widely used as efficient catalysts for stereoselective asymmetric synthesis. The MM3 force field parameters have been determined on the basis of the ab initio MP2/6-31G* and/or DFT (B3LYP/6-31G*, B3-PW91/6-31G*) geometry optimization calculations. To evaluate the electronic interactions specific to the lithium amides derived from the diamine molecules properly, the Lewis bonding potential term for the interaction between the lithium atom and the nonbonded adjacent electronegative atom such as nitrogen was introduced into the MM3 force field. The bond dipoles were evaluated correctly from the electronic charges on the atoms calculated by fitting to the electrostatic potential at points selected. The MM3 results on the molecular structures, conformational energies, and vibrational spectra show good agreement with those from the quantum mechanical calculations.

First synthesis and structural determination of a monomeric, unsolvated lithium amide, LiNH(2)

Alkali metal amides typically aggregate in solution and the solid phase, and even in the gas phase. In addition, even in the few known monomeric structures, the coordination number of the alkali metal is raised by binding of Lewis-basic solvent molecules, with concomitant changes in structure. In contrast, the simplest lithium amide LiNH(2) has never been made in a monomeric form, even though its structure has been theoretically predicted several times. Here, the first experimental structural data for a monomeric, unsolvated lithium amide are determined using a combination of gas-phase synthesis and millimeter/submillimeter-wave spectroscopy. All data point to a planar structure for LiNH(2). The r(o) structure of LiNH(2) has a Li-N distance of 1.736(3) A, an N-H distance of 1.022(3) A, and a H-N-H angle of 106.9(1) degrees. These results are compared with theoretical predictions for LiNH(2), and experimental data for oligomeric, solid-phase samples, which could not resolve the question of whether LiNH(2) is planar or not. In addition, comparisons are made with revised gas-phase and solid-phase data and calculated structures of NaNH(2).

The pi complexation of alkali and alkaline earth ions by the use of meso-octaalkylporphyrinogen and aromatic hydrocarbons

The full metallation of meso-octaalkylporphyrinogens [R8N4H4] (R=Et, 1; nBu, 2; CH2Ph, 3; (CH2)4, 4) with heavy alkali metals (M = K, Rb, Cs) leads to the porphyrinogen-M4 compounds, in which the solvation of the alkali cations is largely assured by the intra- and intermolecular phi-interactions with the pyrrolyl anions. Such a mode of complexation results in a structural diversity as a function of the meso substituents, the size of the metal ion, and the solvent. The structure of the unsolvated polymers [R8N4M4]n (R= Et, M=K, 5; M=Rb, 6; M=Cs, 7; R= (CH2)4, M = Rb, 8; M = Cs, 9) have been clarified through the X-ray analysis of 7 recrystallized from diglyme. The structure shows that the tetraanion binds two Cs ions inside the cavity, which display in one case eta1:eta1:eta1:eta1 and in the other eta5:eta5:eta5:eta5 interaction modes. Bidimensional polymerization is assured by four Cs ions, which each bind at the eta5 position on the exo face of each pyrrole. With bulkier meso substituents, different polymeric forms are obtained (R = nBu, M = K, 10; M = Rb, 11; M = Cs, 12), and their structures were clarified through the X-ray analysis of 10, which was recrystallized from dimethoxyethane. The polymeric units are made up by the monomeric units [Bu8N4K2]2-, in which one potassium is eta1:eta1:eta1:eta5 and the other eta5:eta1:eta5:eta1 bonded inside the porphyrinogen cavity. In the case of R=CH2Ph, the monomeric anion [(PhCH2)8N4K2]2- (13) has been structurally identified. The metallation of 1 and 2 with active forms of alkaline earth metals (M' = Ca, Sr, Ba) led to dinuclear compounds [R,N4M'2] (R = Et, M' = Ca, 14; M'=Sr, 15; M'=Ba, 16; R=nBu. M'=Ba, 18), in which both metals inside the cavity are eta1:eta3:eta1:eta3 (Ca) and eta1:eta5:eta1:eta5 (Sr and Ba) bonded to the porphyrinogen tetraanion. The coordination sphere of each metal ion is completed by two THF molecules, which, in the case of Ba, are easily replaced by an arene ring [Bu8N4Ba2(eta6-arene)2] (arene=durene, 22; naphthalene, 23; toluene, 24; benzene, 25). The X-ray structures of 14, 15, 18, 22, and 23 are described in detail. We have tried to establish a relationship between the solid-state and solution structures by analyzing the 1H NMR spectra of the porphyrinogen complexes.

Titanium alkali metal nitrido complexes

Treatment of [(Ti(eta5-C5Me5)(mu-NH))3(mu3-N)] with alkali metal bis(trimethylsilyl)amido reagents in toluene afforded the complexes [M(mu3-N)(mu3-NH)2[Ti3(mu5-C5Me5)3(mu3-N)]]2 (M = Li (2), Na, (3), K (4)). The molecular structures of 2 and 3 have been determined by X-ray crystallographic studies and show two azaheterometallocubane cores [MTi3N4] linked by metal-nitrogen bonds. Reaction of the lithium derivative 2 with chlorotrimethylsilane or trimethyltin chloride in toluene gave the incomplete cube nitrido complexes [Ti3(eta5-C5Me5)3(mu-NH)2(mu-NMMe3)(mu3-N)] (M = Si (5), Sn (6)). A similar reaction with indium(I) or thallium(I) chlorides yielded cube-type derivatives [M(mu3-N)(mu3-NH)2[Ti(eta5-C5Me5)3(mu3-N)] (M=In (7), Tl (8)).

Steric and Solvation Effects on the Aggregation of Lithium Thioamidates: Single-Strand Polymers with (LiS)(n)() and (LiNCS)(n)() Backbones

The addition of methyllithium or n-butyllithium to alkyl isothiocyanates produces lithium thioamidates {Li[RCS(NR')]}(n)(). Three such compounds were structurally characterized after recrystallization from THF. When R = n-Bu and R' = t-Bu, an unsolvated hexamer {Li[n-BuCS(N-t-Bu)]}(6) (1) is obtained. By contrast, the solvated derivatives {Li.THF[MeCS(N-t-Bu)]}(infinity) (2.THF) and {Li.2THF[MeCS(NMe)]}(infinity) (3.2THF) form single-strand polymers. The monosolvated complex 2.THF involves four-membered rings with an (LiS)(n)() backbone whereas the disolvate 3.2THF is comprised of LiNCS repeating units. The structures of all three aggregates can be generated via sterically directed solvation of a common dimeric precursor. Crystal data for 2.THF: C(10)H(20)NLiOS, monoclinic, P2(1)/a (#14), a = 9.129(2) Å, b = 11.099(2) Å, c = 12.537(2) Å, beta = 94.14(2) degrees, V = 1267.0(4) Å(3), Z = 4. Crystal data for 3.2THF: C(11)H(22)NLiSO(2), monoclinic, P2(1)/a (#14), a = 10.974(3) Å, b = 8.575(5) Å, c = 14.898(5) Å, beta = 91.33(3) degrees, V = 1401.6(10) Å(3), Z = 4.