The metathesis reactions of [SNS][SbF6] and [SN][AsF6] with Li[Al(OC(CF3)3)4] in liquid SO2

The small di- and triatomic molecules [SN]⁺ and [SNS]⁺ have shown versatile chemistries and [SNS]⁺ is an important starting reagent for many sulfur-nitrogen radicals. However, their chemistry is limited to the more polar solvents (e.g. SO₂). In this work an attempt is made to increase their solubility in less polar solvents by exchange of the usual [MF₆]⁻ (M = As, Sb) anions by the large and weakly coordinating [Al(OC(CF₃)₃)₄]⁻. As expected the metathesis reactions of [SN][AsF₆] and [SNS][SbF₆] with Li[Al(OC(CF₃)₃)₄] in liquid sulfur dioxide resulted in the formation of the insoluble Li[SbF₆], which is the driving force for these metathesis reactions. The characterization of the compounds by IR and multinuclear NMR revealed that [SNS]⁺ formed a [Al(OC(CF₃)₃)₄]⁻ salt in a clean reaction. A preliminary crystal structure of [SNS][Al(OC(CF₃)₃)₄] is presented. The solubility of [SNS][Al(OC(CF₃)₃)₄] in CH₂Cl₂ is significantly increased with respect to the corresponding [MF₆]⁻ salts, and potentially opens up new areas of [SNS]⁺ chemistry. The reaction of the more reactive [SN]⁺ with Li[Al(OC(CF₃)₃)₄] was less clear. Multinuclear NMR and IR spectra were consistent with the formation of [SN][Al(OC(CF₃)₃)₄], which also showed significant decomposition.     

Snapshots of the Hydrolysis of the Lithium Alkoxide [Li{OC(CF3)3}]4

Exposure of the tetrameric, heterocubane‐like perfluorinated lithium alkoxide [Li{OC(CF₃)₃}]₄ to humid air gaverise to the hydrolysis products [{(CF₃)₃CO}Li(H₂O)₂‐μ‐(H₂O)‐Li(H₂O)₂{OC(CF₃)₃}], [{(CF₃)₃CO}Li(H₂O)₂‐μ‐(H₂O)‐Li‐(H₂O)₃]⁺[OC(CF₃)₃]^– and [Li(H₂O)₄]⁺[OC(CF₃)₃]^– because of stepwise addition of water molecules in a gas‐solid reaction without solvent. All compounds were studied by X‐ray crystallography and their solid‐state structures are strongly influenced by hydrogen bonding and fluorophilic interactions.     

Silver–Ethene Complexes [Ag(η2‐C2H4)n][Al(ORF)4] with n=1, 2, 3 (RF=Fluorine‐Substituted Group)

Compounds including the free or coordinated gas‐phase cations [Ag(η²‐C₂H₄)_n]⁺ (n=1–3) were stabilized with very weakly coordinating anions [A]^? (A=Al{OC(CH₃)(CF₃)₂}₄, n=1 ( 1 ); Al{OC(H)(CF₃)₂}₄, n=2 ( 3 ); Al{OC(CF₃)₃}₄, n=3 ( 5 ); {(F₃C)₃CO}₃Al‐F‐Al{OC(CF₃)₃}₃, n=3 ( 6 )). They were prepared by reaction of the respective silver(I) salts with stoichiometric amounts of ethene in CH₂Cl₂ solution. As a reference we also prepared the isobutene complex [(Me₂C?CH₂)Ag(Al{OC(CH₃)(CF₃)₂}₄)] ( 2 ). The compounds were characterized by multinuclear solution‐NMR, solid‐state MAS‐NMR, IR and Raman spectroscopy as well as by their single crystal X‐ray structures. MAS‐NMR spectroscopy shows that the [Ag(η²‐C₂H₄)₃]⁺ cation in its [Al{OC(CF₃)₃}₄]^? salt exhibits time‐averaged D_3h‐symmetry and freely rotates around its principal z‐axis in the solid state. All routine X‐ray structures (2θ_max.<55°) converged within the 3σ limit at C?C double bond lengths that were shorter or similar to that of free ethene. In contrast, the respective Raman active C?C stretching modes indicated red‐shifts of 38 to 45 cm^?1, suggesting a slight C?C bond elongation. This mismatch is owed to residual librational motion at 100 K, the temperature of the data collection, as well as the lack of high angular data owing to the anisotropic electron distribution in the ethene molecule. Therefore, a method for the extraction of the C?C distance in [M(C₂H₄)] complexes from experimental Raman data was developed and meaningful C?C distances were obtained. These spectroscopic C?C distances compare well to newly collected X‐ray data obtained at high resolution (2θ_max.=100°) and low temperature (100 K). To complement the experimental data as well as to obtain further insight into bond formation, the complexes with up to three ligands were studied theoretically. The calculations were performed with DFT (BP86/TZVPP, PBE0/TZVPP), MP2/TZVPP and partly CCSD(T)/AUG‐cc‐pVTZ methods. In most cases several isomers were considered. Additionally, [M(C₂H₄)₃] (M=Cu⁺, Ag⁺, Au⁺, Ni⁰, Pd⁰, Pt⁰, Na⁺) were investigated with AIM theory to substantiate the preference for a planar conformation and to estimate the importance of σ donation and π back donation. Comparing the group 10 and 11 analogues, we find that the lack of π back bonding in the group 11 cations is almost compensated by increased σ donation.     

The Parent Cyclopentadienyltin Cation,Its Toluene Adduct,and the Quadruple‐Decker [Sn3Cp4]2+

Truly cationic metallocenes with the parent cyclopentadienyl ligand are so far unknown for the Group 14 elements. Herein we report on an almost “naked” [SnCp]⁺ cation with the weakly coordinating [Al{OC(CF₃)₃}₄]⁻ and [{(F₃C)₃CO}₃Al−F−Al{OC(CF₃)₃}₃]⁻ anions. [SnCp][Al{OC(CF₃)₃}₄] was used to prepare the first main‐group quadruple‐decker cation [Sn₃Cp₄]²⁺ again as the [Al{OC(CF₃)₃}₄]⁻ salt. Additionally, the toluene adduct [CpSn(C₇H₈)][Al{OC(CF₃)₃}₄] was obtained.     

The Parent Cyclopentadienyltin Cation,Its Toluene Adduct,and the Quadruple‐Decker [Sn3Cp4]2+

Truly cationic metallocenes with the parent cyclopentadienyl ligand are so far unknown for the Group 14 elements. Herein we report on an almost “naked” [SnCp]⁺ cation with the weakly coordinating [Al{OC(CF₃)₃}₄]⁻ and [{(F₃C)₃CO}₃Al−F−Al{OC(CF₃)₃}₃]⁻ anions. [SnCp][Al{OC(CF₃)₃}₄] was used to prepare the first main‐group quadruple‐decker cation [Sn₃Cp₄]²⁺ again as the [Al{OC(CF₃)₃}₄]⁻ salt. Additionally, the toluene adduct [CpSn(C₇H₈)][Al{OC(CF₃)₃}₄] was obtained.     

Copper(I) Complexes of Anionic Tridentate CNC Pincer Ligands

New monoanionic CNC pincer ligands, [N{SiMe₂CH₂(RIm)}₂]^– (R = tBu, iPr, Ph) featuring three different N-heterocyclic carbenes and a disilylamido moiety is reported. Treatment of the lithium salt of [N{SiMe₂CH₂(RIm)}₂]^– with Cu^IOTf afforded the corresponding copper complexes [N{SiMe₂CH₂(RIm)}₂]Cu in 41–56 % yield. X-ray crystal structures of [N{SiMe₂CH₂(RIm)}₂]Cu show that they are monomeric and feature three-coordinate, pseudo T-shaped copper(I) sites. The X-ray crystal structure of one of the precursor lithium complexes, [N{SiMe₂CH₂(tBuIm)}₂]Li is also presented.     

From Ion‐Like Ethylzinc Aluminates to [EtZn(arene)2]+[Al(ORF)4]− Salts

Attempts to prepare previously unknown simple and very Lewis acidic [RZn]⁺[Al(OR^F)₄]^? salts from ZnR₂, AlR₃, and HO?R^F delivered the ion‐like RZn(Al(OR^F)₄) (R=Me, Et; R^F=C(CF₃)₃) with a coordinated counterion, but never the ionic compound. Increasing the steric bulk in RZn⁺ to R=CH₂CMe₃, CH₂SiMe₃, or Cp*, thus attempting to induce ionization, failed and led only to reaction mixtures including anion decomposition. However, ionization of the ion‐like EtZn(Al(OR^F)₄) compound with arenes yielded the [EtZn(arene)₂]⁺[Al(OR^F)₄]^? salts with arene=toluene, mesitylene, or o‐difluorobenzene (o‐DFB)/toluene. In contrast to the ion‐like EtZn(η³‐C₆H₆)(CHB₁₁Cl₁₁), which co‐crystallizes with one benzene molecule, the less coordinating nature of the [Al(OR^F)₄]^? anion allowed the ionization and preparation of the purely organometallic [EtZn(arene)₂]⁺ cation. These stable materials have further applications as, for example, initiators of isobutene polymerization. DFT calculations to compare the Lewis acidities of the zinc cations to those of a large number of organometallic cations were performed on the basis of fluoride ion affinity. The complexation energetics of EtZn⁺ with arenes and THF was assessed and related to the experiments.     

Using Me3Si–F–Al(ORF)3 and Me3Si–Cl as Methylating Agents – Synthesis and Characterization of SeMeCl2[F{Al(ORF)3}2]

Upon reacting SeCl₄ with Me₃Si–F–Al(OR^F)₃, the selenonium salt SeMeCl₂[al‐f‐al] ( 1 ) {[al‐f‐al]^– = [F[Al(OC(CF₃)₃)₃]₂]^–} was obtained and characterized by NMR, IR, and Raman spectroscopy as well as single crystal XRD experiments. Despite the [SeX₃]⁺ (X = F, Cl, Br, I) and [SeR₃]⁺ salts (R = aliphatic organic residue) being well known and thoroughly studied, the mixed cations are scarce. The only previous example of a salt with the [SeMeCl₂]⁺ cation is SeMeCl₂[SbCl₆], which was never structurally characterized and is unstable in solution over hours. Only ¹H‐NMR studies and IR spectra of this compound are known. The unexpected use of Me₃Si–F–Al(OR^F)₃ as a methylating agent was investigated via DFT calculations and NMR experiments of the reaction solution. The reaction of SeCl₃[al‐f‐al] with Me₃Si‐Cl at room temperature in CH₂Cl₂ proved to yield the same product with Me₃Si–Cl acting as a methylating agent.     

On the Reactivity of Silylated Ge9 Clusters: Synthesis and Characterization of [ZnCp*(Ge9{Si(SiMe3)3}3)], [CuPiPr3(Ge9{Si(SiMe3)3}3)], and [(CuPiPr3)4{Ge9(SiPh3)2}2]

We report on the synthesis of new derivatives of silylated clusters of the type [Ge₉(SiR₃)₃]^? (R = SiMe₃, Me = CH₃; R = Ph, Ph = C₆H₅) as well as on their reactivity towards copper and zinc compounds. The silylated cluster compounds were synthesized by heterogeneous reactions starting from the Zintl phase K₄Ge₉. Reaction of K[Ge₉{Si(SiMe₃)₃}₃] with ZnCl₂ leads to the already known dimeric compound [Zn(Ge₉{Si(SiMe₃)₃}₃)₂] ( 1 ), whereas upon the reaction with [ZnCp*₂] the coordination of [ZnCp*]⁺ to the cluster takes place (Cp*=1,2,3,4,5‐pentamethylcyclopentadienyl) under the formation of [ZnCp*(Ge₉{Si(SiMe₃)₃}₃)] ( 2 ). A similar reaction leads to [CuPiPr₃(Ge₉{Si(SiMe₃)₃}₃)] ( 3 ) from [CuPiPr₃Cl] (iPr=isopropyl). Further we investigated the novel silylated cluster units [Ge₉(SiPh₃)₃]^? ( 4 ) and [Ge₉(SiPh₃)₂]^? ( 5 ), which could be identified by mass spectroscopy. Bis‐ and tris‐silylated species can be synthesized by the respective stoichiometric reactions, and the products were characterized by ESI‐MS and NMR experiments. These clusters show rather different reactivity. The reaction of the tris‐silylated anion 4 with [CuPiPr₃Cl] leads to [(CuPiPr₃)₃Ge₉(SiPh₃)₂]⁺ as shown from NMR experiments and to [(CuPiPr₃)₄{Ge₉(SiPh₃)₂}₂] ( 6 ), which was characterized by single‐crystal X‐ray diffraction. Compound 6 shows a new type of coordination of the Cu atoms to the silylated Zintl clusters.     

Treatment of a Methylene‐Bridged Dialuminium Compound with Lithium Alkanides and Alkynides ‐ Single vs. Twofold Terminal Coordination

We have investigated the coordination of alkanide and alkynide anions to the coordinatively unsaturated aluminium atoms of the methylene‐bridged dialuminium compound R₂Al‐CH₂‐AlR₂ [ 1 , R = CH(SiMe₃)₂]. Treatment of 1 with the corresponding lithium derivatives in the presence of a small excess of TMEN (TMEN = tetramethylethylenediamine) yielded mono‐adducts [M]⁺[R₂Al‐CH₂‐AlR₂R']^– [ 2a , M = Li(TMEN)₂, R' = Me; 2b , M = Li(TMEN)₂, R' = n‐Bu; 3a , M = Li(TMEN)₂, R' = C≡C‐SiMe₃; 3b , M = Li(TMEN)₂, R' = C≡C‐t‐Bu; 3d , M = Li(DME)₃, R' = C≡C‐Ph; 3e , M = Li(TMEN)₂, R' = C≡C‐PPh₂)] and bis‐adducts [Li(TMEN)₂]⁺[LiCH₂(AlR₂R')₂]^– [ 4a , R' = C≡C‐CH₂‐NEt₂; 4b , R' = C≡C‐t‐Bu]. In the solid state the mono‐adducts have clearly separated coordinatively saturated (coordination number four) and unsaturated aluminium atoms (coordination number three). In solution the groups R' show a fast exchange between both aluminium atoms as evident from the room temperature NMR spectra that showed in most cases equivalent CH(SiMe₃)₂ groups despite different coordination spheres of the metal atoms. Only 2b gave the expected splitting of resonances at ambient temperature, while cooling was required to prevent the dynamic process for 3a . The dialkynide 4a has a unique molecular structure with one of the lithium cations bonded to the α‐carbon atoms of the alkynido ligands and to the carbon atom of the methylene bridge which is five‐coordinate with a distorted trigonal bipyramidal coordination sphere.     

One‐Dimensional Polymers Based on Silver(I) Cations and Organometallic cyclo‐P3 Ligand Complexes

The synthesis and characterization of the first supramolecular aggregates incorporating the organometallic cyclo‐P₃ ligand complexes [Cp^RMo(CO)₂(η³‐P₃)] (Cp^R=Cp (C₅H₅; 1a ), Cp* (C₅(CH₃)₅; 1b )) as linking units is described. The reaction of the Cp derivative 1a with AgX (X=CF₃SO₃, Al{OC(CF₃)₃}₄) yields the one‐dimensional (1D) coordination polymers [Ag{CpMo(CO)₂(μ,η³:η¹:η¹‐P₃)}₂]_n[Al{OC(CF₃)₃}₄]_n ( 2 ) and [Ag{CpMo(CO)₂(μ,η³:η¹:η¹‐P₃)}₃]_n[X]_n (X=CF₃SO₃ ( 3a ), Al{OC(CF₃)₃}₄ ( 3b )). The solid‐state structures of these polymers were revealed by X‐ray crystallography and shown to comprise polycationic chains well‐separated from the weakly coordinating anions. If AgCF₃SO₃ is used, polymer 3a is obtained regardless of reactant stoichiometry whereas in the case of Ag[Al{OC(CF₃)₃}₄], reactant stoichiometry plays a decisive role in determining the structure and composition of the resulting product. Moreover, polymers 3a, b are the first examples of homoleptic silver complexes in which Ag^I centers are found octahedrally coordinated to six phosphorus atoms. The Cp* derivative 1b reacts with Ag[Al{OC(CF₃)₃}₄] to yield the 1D polymer [Ag{Cp*Mo(CO)₂(μ,η³:η²:η¹‐P₃)}₂]_n[Al{OC(CF₃)₃}₄]_n ( 4 ), the crystal structure of which differs from that of polymer 2 in the coordination mode of the cyclo‐P₃ ligands: in 2 , the Ag⁺ cations are bridged by the cyclo‐P₃ ligands in a η¹:η¹ (edge bridging) fashion whereas in 4 , they are bridged exclusively in a η²:η¹ mode (face bridging). Thus, one third of the phosphorus atoms in 2 are not coordinated to silver while in 4 , all phosphorus atoms are engaged in coordination with silver. Comprehensive spectroscopic and analytical measurements revealed that the polymers 2 , 3a , b , and 4 depolymerize extensively upon dissolution and display dynamic behavior in solution, as evidenced in particular by variable temperature ³¹P NMR spectroscopy. Solid‐state ³¹P magic angle spinning (MAS) NMR measurements, performed on the polymers 2 , 3b , and 4 , demonstrated that the polymers 2 and 3b also display dynamic behavior in the solid state at room temperature. The X‐ray crystallographic characterisation of 1b is also reported.     

Univalent Gallium and Indium Phosphane Complexes: From Pyramidal M(PPh3)3+ to Carbene‐Analogous Bent M(PtBu3)2+ (M=Ga,In) Complexes

In a new oxidative route, Ag⁺[Al(OR^F)₄]^? (R^F=C(CF₃)₃) and metallic indium were sonicated in aromatic solvents, such as fluorobenzene (PhF), to give a precipitate of silver metal and highly soluble [In(PhF)_n]⁺ salts (n=2, 3) with the weakly coordinating [Al(OR^F)₄]^? anion in quantitative yield. The In⁺ salt and the known analogous Ga⁺[Al(OR^F)₄]^? were used to synthesize a series of homoleptic PR₃ phosphane complexes [M(PR₃)_n]⁺, that is, the weakly PPh₃‐bridged [(Ph₃P)₃In–(PPh₃)–In(PPh₃)₃]²⁺ that essentially contains two independent [In(PPh₃)₃]⁺ cations or, with increasing bulk of the phosphane, the carbene‐analogous [M(PtBu₃)₂]⁺ (M=Ga, In) cations. The M^I? P distances are 27 to 29 pm longer for indium, and thus considerably longer than the difference between their tabulated radii (18 pm). The structure, formation, and frontier orbitals of these complexes were investigated by calculations at the BP86/SV(P), B3LYP/def2‐TZVPP, MP2/def2‐TZVPP, and SCS‐MP2/def2‐TZVPP levels.     

Homoleptic Gold Acetonitrile Complexes with Medium to Very Weakly Coordinating Counterions: Effect on Aurophilicity?

A series of gold acetonitrile complexes [Au(NCMe)₂]⁺[WCA]^? with weakly coordinating counterions (WCAs) was synthesized by the reaction of elemental gold and nitrosyl salts [NO]⁺[WCA]^? in acetonitrile ([WCA]^? = [GaCl₄]^?, [B(CF₃)₄]^?, [Al(OR^F)₄]^?; R^F = C(CF₃)₃). In the crystal structures, the [Au(NCMe)₂]⁺ units appeared as monomers, dimers, or chains. A clear correlation between the aurophilicity and the coordinating ability of counterions was observed, with more strongly coordinating WCAs leading to stronger aurophilic contacts (distances, C?N stretching frequencies of [Au(NCMe)₂]⁺ units). An attempt to prepare [Au(L)₂]⁺ units, even with less weakly basic solvents like CH₂Cl₂, led to decomposition of the [Al(OR^F)₄]^? anion and formation of [NO(CH₂Cl₂)₂]⁺[F(Al(OR^F)₃)₂]^?. All nitrosyl reagents [NO]⁺[WCA]^? were generated according to an optimized procedure and were thoroughly characterized by Raman and NMR spectroscopy. Moreover, the to date unknown species [NO]⁺[B(CF₃)₃CN]^? was prepared. Its reaction with gold unexpectedly produced [Au(NCMe)₂]⁺[Au(NCB(CF₃)₃)₂]^?, in which the cyanoborate counterion acts as an anionic ligand itself. Interestingly, the auroborate anion [Au(NCB(CF₃)₃)₂]^? behaves as a weakly coordinating counterion, which becomes evident from the crystallographic data and the vibrational spectral characteristics of the [Au(NCMe)₂]⁺ cation in this complex. Ligand exchange in the only room temperature stable salt of this series, [Au(NCMe)₂]⁺[Al(OR^F)₄]^?, is facile and, for example, [Au(PPh₃)(NCMe)]⁺[Al(OR^F)₄]^? can be selectively generated. This reactivity opens the possibility to generate various [AuL¹L²]⁺[Al(OR^F)₄]^? salts through consecutive ligand‐exchange reactions that offer access to a huge variety of Au^I complexes for gold catalysis.     

Synthesis and Crystal Structure of the two Lithium Hypersilylcuprates LiCu2[Si(SiMe3)3]3 and [Li7(OtBu)6][Cu2{Si(SiMe3)3}3]

The two hypersilylcuprates LiCu₂Hyp₃ ( 2 ) and [Li₇(O^tBu)₆][Cu₂Hyp₃] ( 3 ) (Hyp = Si(SiMe₃)₃) were synthesized by reactions of unsolvated lithium hypersilanide, LiHyp with hypersilylcopper and CuO^tBu, respectively. Both contain the novel A‐frame trihypersilyldicuprate anion [Cu₂Hyp₃]^–. In the former case a molecular compound is produced containing intimate ion pairs. In the latter case the cuprate anion and the unique large [Li₇(O^tBu)₆]⁺ cation form a salt‐like compound, only sparingly soluble in unpolar solvents. According to NBO analyses the bonding within the trihypersilyldicuprate moiety is best described by interaction of a bridging lewis‐basic hypersilanide anion with two lewis‐acidic hypersilyl copper fragments.     

Synthesis and crystal structures of organometallic compounds containing the ligands C(SiMe3)2(SiMe2H) and C(SiMe2Ph)2(SiMe2H)

Metallation of (HMe₂Si)(Me₃Si)₂CH (1) by LiMe gave the organolithium compound Li(THF)₂C(SiMe₃)₂(SiMe₂H) (2a), which exists in toluene solution as a mixture of covalent species and ion pairs [Li(THF)₄][Li{C(SiMe₃)₂(SiMe₂H)}₂] (2b). Treatment of a mixture of 1 and LiMe with KOBu^t gave KC(SiMe₃)₂(SiMe₂H) (3). This reacted with AlMe₂Cl in hexane/THF to give Al(THF)Me₂{C(SiMe₃)₂(Si Me₂H)} (4). Treatment of (HMe₂Si)(PhMe₂Si)₂CH (5) with LiMe in Et₂O/THF gave the THF adduct [Li(THF)₂C(SiMe₂Ph)₂(SiMe₂H)] (6); in the presence of KOBu^t the solvent-free [K][C(SiMe₂Ph)₂(SiMe₂H)] (7) was obtained. Crystal structure determinations showed that 6 crystallizes in a molecular lattice and 7 in an ionic lattice in which the coordination sphere of the potassium comprises phenyl groups and hydrogen atoms attached to silicon, as well as the central carbon of the bulky carbanion. Compound 7 reacted with an excess of AlMe₂Cl to give [AlClMe{C(SiMe₂Ph)₂(SiMe₂H)}]₂ (8) and AlMe₃. A small amount of the methoxo derivative [Al(OMe)Me{C(SiMe₂Ph)₂(SiMe₂H)}]₂ (9) was obtained as a byproduct, presumably after the accidental admission of traces of air. X-ray structural determinations showed that 8 forms halogen-bridged dimers, with the bulky ligands in the anti-configuration, and 9 forms methoxo-bridged species in which the bulky ligands are syn.     

From Weakly Coordinating to Non‐Coordinating Anions? A Simple Preparation of the Silver Salt of the Least Coordinating Anion and Its Application To Determine the Ground State Structure of the Ag(η2‐P4)2+ Cation

The unexpected but facile preparation of the silver salt of the least coordinating [(RO)₃Al‐F‐Al(OR)₃]^? anion (R=C(CF₃)₃) by reaction of Ag[Al(OR)₄] with one equivalent of PCl₃ is described. The mechanism of the formation of Ag[(RO)₃Al‐F‐Al(OR)₃] is explained based on the available experimental data as well as on quantum chemical calculations with the inclusion of entropy and COSMO solvation enthalpies. The crystal structures of (RO)₃Al←OC₄H₈, Cs⁺[(RO)₂(Me)Al‐F‐Al(Me)(OR)₂]^?, Ag(CH₂Cl₂)₃⁺[(RO)₃Al‐F‐Al(OR)₃]^? and Ag(η²‐P₄)₂⁺[(RO)₃Al‐F‐Al(OR)₃]^? are described. From the collected data it will be shown that the [(RO)₃Al‐F‐Al(OR)₃]^? anion is the least coordinating anion currently known. With respect to the fluoride ion affinity of two parent Lewis acids Al(OR)₃ of 685 kJ mol^?1, the ligand affinity (441 kJ mol^?1), the proton and copper decomposition reactions (?983 and ?297 kJ mol^?1) as well as HOMO level and HOMO–LUMO gap and in comparison with [Sb₄F₂₁]^?, [Sb(OTeF₅)₆]^?, [Al(OR)₄]^? as well as [B(R^F)₄]^? (R^F=CF₃ or C₆F₅) the [(RO)₃Al‐F‐Al(OR)₃]^? anion is among the best weakly coordinating anions (WCAs) according to each value. In contrast to most of the other cited anions, the [(RO)₃Al‐F‐Al(OR)₃] anion is available by a simple preparation in conventional inorganic laboratories. The least coordinating character of this anion was employed to clarify the question of the ground state geometry of the Ag(η²‐P₄)₂⁺ cation (D_2h, D₂ or D_2d?). In agreement with computational data and NMR spectra it could be shown that the rotation along the Ag‐(P‐P‐centroid) vector has no barrier and that the structure adopted in the solid state depends on packing effects which lead to an almost D_2h symmetric Ag(η²‐P₄)₂⁺ cation (0 to 10.6° torsion) for the more symmetrical [Al(OR)₄]^? anion, but to a D₂ symmetric Ag(η²‐P₄)₂⁺ cation with a 44° twist angle of the two AgP₂ planes for the less symmetrical [(RO)₃Al‐F‐Al(OR)₃]^? anion. This implies that silver back bonding, suggested by quantum chemical population analyses to be of importance, is only weak.     

Synthese und Kristallstruktur eines μ-Methylen-μ-hydrido-dialanats [R2Al(μ-CH2)(μ-H)AlR2]− (R = CH(SiMe3)2)

Synthesis and Crystal Structure of a μ-Methylene-μ-hydrido-dialanate [R₂Al(μ-CH₂)(μ-H)AlR₂]^? (R = CH(SiMe₃)₂) tert-Butyl lithium reacts with the recently synthesized methylene bridged dialuminium compound [(Me₃Si)₂CH]₂Al? CH₂? Al[CH(SiMe₃)₂]₂ 2 in the presence of TMEDA under β-elimination; the thereby formed hydride anion is bound in a chelating manner by both unsaturated aluminium atoms forming a 3c–2e–Al? H? Al bond. The crystal structure of the product shows two independent molecules differing only slightly in bond lengths and angles, but significantly in conformation. While one of the Al₂CH heterocycles deviates little from planarity with a rough C₂ symmetry for the whole anion, the other one is folded with an angle of 21.1° and the arrangement of the substituents is best described by C_s symmetry.     

Die Reaktion des [(Me3Si)2CH]2Al?CH2?Al [CH(SiMe3)2]2 mit Neopentyllithium: Bildung des {[(Me3Si)2CH]2Al?CH2?Al [CH(SiMe3)2]2CH2CMe3}⊖ [Li(TMEDA)2]⊕

Reaction of [(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂ with Neopentyllithium: Formation of {[(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂CH₂CMe₃} ? [Li(TMEDA)₂]⊕ The recently synthesized methylene bridged dialuminium compound [(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂ reacts with neopentyl lithium in the presence of TMEDA to give the stable {[(Me₃Si)₂CH]₂Al? CH₂? Al [CH(SiMe₃)₂]₂CH₂ · CMe₃}? [Li(TMEDA)₂]⊕ decomposing at 115°C. The aluminium atoms therein are not additionally bridged, but the new substituent is occupying a terminal position as detected by crystal structure determination. A compound is formed containing a saturated, fourfold coordinated neighbouring a formally unsaturated, threefold coordinated aluminium atom. Due to high sterical restrictions the Al? C bonds are lengthened up to 209.0(3) pm at the alanate site and the Al? C? Al angle in the methylene bridge is extraordinarily enlarged to 144.4(2)°.     

Dynamics and counterion-dependence of the structures of weakly bound Ag+-P4S3 complexes

In an earlier publication (J. Am. Chem. Soc. 2002 , 124, 7111) we showed that polymeric cationic [Ag(P₄S₃)_n]⁺ complexes (n=1, 2) are accessible if partnered with a suitable weakly coordinating counterion of the type [Al(OR^F)₄]^? (OR^F: poly‐ or perfluorinated alkoxide). The present work addresses the following questions that could not be answered in the initial report: How many P₄S₃ cages can be bound to a Ag⁺ ion? Why are these complexes completely dynamic in solution in the ³¹P NMR experiments? Can these dynamics be frozen out in a low‐temperature ³¹P MAS NMR experiment? What are the principal binding sites of the P₄S₃ cage towards the Ag⁺ ion? What are likely other isomers on the [Ag(P₄S₃)_n]⁺ potential energy surface? Counterion influence: Reactions of P₄S₃ with Ag[Al{OC(CH₃)(CF₃)₂}₄] (Ag[hftb]) and Ag[{(CF₃)₃CO}₃Al‐F‐Al{OC(CF₃)₃)}₃] (Ag[al‐f‐al]) gave [(P₄S₃)Ag[hftb]]_∞ ( 7 ) as a molecular species, whereas [Ag₂(P₄S₃)₆]²⁺[al‐f‐al]^?₂ ( 8 ) is an isolated 2:1 salt. We suggest that a maximum of three P₄S₃ cages may be bound on average to an Ag⁺ ion. Only isolated dimeric dications are formed with the largest cation, but polymeric species are obtained with all other smaller aluminates. Thermodynamic Born–Haber cycles, DFT calculations, as well as solution NMR and ESI mass spectrometry indicate that 8 exhibits an equilibrium between the dication [Ag₂(P₄S₃)₆]²⁺ (in the solid state) and two [Ag(P₄S₃)₃]⁺ monocations (in the gas phase and in solution). Dynamics: ³¹P MAS NMR spectroscopy showed these solid adducts to be highly dynamic, to an extent that the ²J_P,P coupling within the cages could be resolved (J‐res experiment). This is supported by DFT calculations, which show that the extended PES of [Ag(P₄S₃)_n]⁺ (n=1–3) and [Ag₂(P₄S₃)₂]⁺ is very flat. The structures of α‐ and γ‐P₄S₃ were redetermined. Their variable‐temperature ³¹P MAS NMR spectra are discussed jointly with those of all four currently known [Ag(P₄S₃)_n]⁺ adducts with n=1, 2, and 3.     

A Thallium Coated Dianion: Trigonal Bipyramidal [F2Al(OR)3]2— Coordinated to Three Tl+ Cations in the Ion Pair [Tl3F2Al(OR)3]+[Al(OR)4]— [R = CH(CF3)2]

The reproducible synthesis of the unusual ionic aluminum compound [Tl₃F₂Al(OR)₃]⁺[Al(OR)₄]^— ( 1 ) is reported. In the reaction of Li[Al(OR)₄] [R = C(H)(CF₃)₂] with TlF the initially desired Tl[Al(OR)₄] only formed with an exact 1:1 stoichiometry, while an excess of TlF led to [Tl₃F₂Al(OR)₃]⁺[Al(OR)₄]^— ( 1 ). Additionally the x‐ray single crystal structure of the byproduct [(R‐OH)TlAl(OR)₃(μ‐F)]₂ ( 2 ) was determined. Compounds 1 and 2 were characterized by X‐ray single crystal structure determinations and 1 also by NMR spectroscopy and an elemental analysis. In 1 the [Tl₃F₂Al(OR)₃]⁺ cation forms a trigonal bipyramid with a pentacoordinate aluminum atom. Three Tl⁺ cations cover the [F₂Al(OR)₃]^2— dianion core and the charge of the resulting [Tl₃F₂Al(OR)₃]⁺ cation is compensated by a weakly coordinating [Al(OR)₄]^— anion. Compound 2 contains a centrosymmetric [Al(OR)₃(μ‐F)]₂^2— dianion core with pentacoordinate aluminum atoms building a distorted edge sharing double trigonal bipyramid. The [Al(OR)₃(μ‐F)]₂^2— dianion coordinates two [Tl(R‐OH)]⁺ cations giving the non charged molecular [(R‐OH)TlAl(OR)₃(μ‐F)]₂ ( 2 ). Based on BP86/SVP (DFT‐) and lattice enthalpy calculations a pathway of the reaction was proposed to rationalize the formation of the [M₃F₂Al(OR)₃]⁺ cation upon reaction of Li[Al(OR)₄] with MF for M = Tl but not for M = Cs (cf. Cs⁺ and Tl⁺ have very similar ionic radii). Using a suitable BorñHaber cycle and in agreement with the experiment, the enthalpies of the reaction of 2 M[Al(OR)₄] with 2 MF giving [M₃F₂Al(OR)₃]⁺[Al(OR)₄]^— and MOR were shown to be favorable for M = Tl by 127 kJ/mol but endothermic for the formation of the hypothetical [Cs₃F₂Al(OR)₃]⁺[Al(OR)₄]^— by 95 kJ/mol. It is suggested that in the reaction leading to 1 initially Tl[Al(OR)₄] is formed, followed by an abstraction of TlOR and Al(OR)₃. The latter very strong Lewis acid reacts subsequently with an excess of TlF yielding 1 .