Structural Studies of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. 2. Ionic Aggregation Modes in Solution and PEO Matrix

In this paper, we present complementary spectroscopic analyses of lithium 2-trifluoromethyl-4,5-dicyanoimidazole adducts with aprotic solvents like dimethyl ethers of poly­(ethylene glycols) (i.e., glymes) and crown ethers. Comparing the XRD structures with Raman spectra we have found fingerprints of various structural motifs such as ionic pairs, dimers, “free ions”, and higher aggregates. Comprehensive analysis of crystalline materials has been performed to correlate molecular structures with spectroscopic data, which give valuable information about the coordination preferences of substituted 4,5-dicyanoimidazolato anions and provide the basis for further developing a model for poly­(ethylene oxide) electrolytes. Complementary and systematic X-ray studies of glyme adducts enable precise interpretation of the anion–cation and cation–solvent interactions from experimental Raman spectra. This information provides a convenient tool for the characterization of the ionic association interactions within electrolytes

Snapshots of the Hydrolysis of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. Impact of Water Molecules on Aggregation Processes in Lithium-Ion Battery Electrolytes

Despite that 4,5-dicyano-2-(trifluoromethyl)­imidazole lithium salt (LiTDI) exhibits several interesting features in aprotic solvents such as glymes or carbonate esters, little is known about its structural rearrangement after exposure to water. Since the LiTDI salt has been verified as an effective moisture scavenger able to suppress degradation of the LiPF₆-based electrolyte, comprehensive knowledge of coordination modes in the LiTDI–H₂O system, as well as information about the structure of formed hydrates, is desirable. In the present study, we report the impact of water on the LiTDI glyme-based electrolytes investigated by means of the single-crystal X-ray diffraction technique and Raman spectroscopy. We have found that the exposure of lithium 4,5-dicyanoimidazolate–glyme solvates to humid air gives rise to the hydrolysis products arising from stepwise addition of water molecules to the lithium coordination sphere. Several structural motifs have been distinguished as preferred coordination modes in the LiTDI–H₂O system. A high number of available ether oxygen donor center water molecules cause dissociation of ionic contact pairs and aggregation of cationic species stabilized by crown ethers. Low O:Li molar ratio leads to the formation of LiTDI–glyme–water solvates and LiTDI hydrates. The air-stable LiTDI trihydrate comprises ionic pairs formed by a lithium cation coordinated to an imidazole nitrogen of TDI. A lithium cation coordinated via nitrile groups and bearing water molecules is a basic motif constituting dimeric species of formula [Li­(H₂O)₂TDI]₂ which are present in aggregated [Li­(H₂O)­TDI]<i>_n</i> chains making up the structure of a monohydrate. The discovered motifs have been proved to occur in both the solid and melted hydrated systems of LiTDI. They will be helpful for conducting molecular dynamic calculations and for obtaining information how to manipulate the structure of a Li⁺-solvation sheath in both hydrated and liquid aqueous electrolytes based on heterocyclic anions

Structural Studies of Lithium 4,5-Dicyanoimidazolate–Glyme Solvates. 1. From Isolated Free Ions to Conductive Aggregated Systems

We present complementary series of crystal structures of lithium salts containing 4,5-dicyanoimidazolato anions substituted with perfluoroalkyl groups. Single-crystal X-ray analysis of 10 adducts with aprotic solvents, glymes (dimethyl ethers of poly­(ethylene glycols)) and crown ethers, have been performed to correlate their molecular structures and properties with spectroscopic and thermal data. Comprehensive structure analysis of crystalline materials reveals valuable information about the coordination ability of substituted 4,5-dicyanoimidazolato anions and provides the basis for developing the model of poly­(ethylene oxide) electrolytes and liquid systems. Presented results reveal new aggregation modes at high concentrations of lithium salts involving the release of cations by self-assembly of an anionic subnetwork and provide some insight into the electrochemical performance of TDI anions

Effect of In–C_NHC Bonds on the Synthesis, Structure, and Reactivity of Dialkylindium Alkoxides: How Indium Compares to Gallium

The investigation of the reactivity of dialkylindium alkoxides toward N-heterocyclic carbenes (NHCs) has shown that both the character of the In–C_NHC bond and alkyl and alkoxide substituents have a significant effect on the formation of R₂InOR­(NHC) complexes and the distribution of products. The reactions of simple dimethylindium alkoxides with the N-heterocyclic carbenes 1,3-bis­(2,4,6-trimethylphenyl)­imidazolin-2-ylidene (SIMes) and 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes) lead to the monomeric complexes Me₂InOR­(NHC), as shown by the isolation of Me₂InOMe­(NHC) (NHC = IMes (<b>3</b>), SIMes (<b>4</b>)). Compounds Me₂InOR­(NHC) are unstable in solution and instantly disproportionate, which can be associated with a weaker In–C_NHC bond in comparison with stable gallium analogues. As a result, Me₃In­(NHC) (NHC = IMes (<b>1</b>), SIMes (<b>2</b>)) adducts, as well as Mitsubishi-type methylindium alkoxides, are formed. The exchange of a simple alkoxy group with chelating (<i>S</i>)-methyl lactate (<i>S-melac</i>) has resulted in the more stable Me₂In­(OCH­(Me)­CO₂Me)­(NHC) complexes. The use of the bulky alkoxide ligand OCPh₂Me allows for the synthesis of stable Me₂In­(OCPh₂Me)­(NHC) (NHC = IMes (<b>6</b>), SIMes (<b>7</b>)) from [Me₂In­(μ-OCPh₂Me)]₂ (<b>5</b>). While the strongest In–C_NHC bond, among the characterized Me₂In­(OR)­(NHC) complexes, is crucial for the stability of <b>6</b> and <b>7</b>, it is still weaker in comparison with Ga–C_NHC bonds in the analogous gallium complexes Me₂Ga­(OCPh₂Me)­(NHC) (NHC = IMes (<b>8</b>), SIMes (<b>9</b>)). For [^<i>t</i>Bu₂In­(μ-OCH₂CH₂OMe)]₂, the introduction of a bulky <i>tert</i>-butyl group has resulted in a lack of reactivity toward NHCs. However, the structure of ^<i>t</i>Bu₂In­(OCPh₂Me)­(IMes) has confirmed the substantial effect of bulky alkyl substituents on the strength of the In–C_NHC bond. The structures of <b>1</b>, <b>2</b>, <b>4</b>–<b>6</b>, and <b>8</b> have been determined using both spectroscopic methods in solution and X-ray diffraction studies. Similarly to their gallium analogues, Me₂In­(OCH­(Me)­CO₂Me)­(NHC) complexes are highly active in the ring-opening polymerization of <i>rac</i>-lactide already at −20 °C, leading to isotactically enriched PLA (<i>P</i>_m = 0.67–0.76). However, in contrast to the gallium complexes Me₂GaOR­(NHC), the noninnocent role of an NHC ligand, resulting in the formation of cyclic PLA, has been demonstrated for <b>6</b> and <b>7</b>

Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure

Methods for the synthesis of dialkylgalium compounds with alkoxide or aryloxide ligands possessing N-heterocyclic carbene functionalities have been established. As a result, the synthesis of a series of dialkylgallium complexes Me₂Ga­(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me₂Ga­(O,C)·Me₃Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic carbene functionality. All complexes have been fully characterized using spectroscopic and X-ray techniques. The presence of a strongly basic NHC functionality in alkoxide or aryloxide ligands resulted in the formation of monomeric Me₂Ga­(O,C) species. The reaction of those complexes with the Lewis acid Me₃Ga leads to Me₂Ga­(O,C)·Me₃Ga adducts (<b>2</b> and <b>6</b>) with a strong Me₃Ga–O dative bond. The effect of (O,C) ligands with various steric and electronic properties on the structure of obtained Me₂Ga­(O,C) and Me₂Ga­(O,C)·Me₃Ga has been discussed on the basis of spectroscopic data. Finally, the bond valence vector model has been used to estimate the effect of a chelating (O,C) ligand on strains in complexes <b>1</b>–<b>6</b> on the basis of X-ray data

Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure

Methods for the synthesis of dialkylgalium compounds with alkoxide or aryloxide ligands possessing N-heterocyclic carbene functionalities have been established. As a result, the synthesis of a series of dialkylgallium complexes Me₂Ga­(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me₂Ga­(O,C)·Me₃Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic carbene functionality. All complexes have been fully characterized using spectroscopic and X-ray techniques. The presence of a strongly basic NHC functionality in alkoxide or aryloxide ligands resulted in the formation of monomeric Me₂Ga­(O,C) species. The reaction of those complexes with the Lewis acid Me₃Ga leads to Me₂Ga­(O,C)·Me₃Ga adducts (<b>2</b> and <b>6</b>) with a strong Me₃Ga–O dative bond. The effect of (O,C) ligands with various steric and electronic properties on the structure of obtained Me₂Ga­(O,C) and Me₂Ga­(O,C)·Me₃Ga has been discussed on the basis of spectroscopic data. Finally, the bond valence vector model has been used to estimate the effect of a chelating (O,C) ligand on strains in complexes <b>1</b>–<b>6</b> on the basis of X-ray data

Dialkylgallium Alkoxides Stabilized with <i>N</i>‑Heterocyclic Carbenes: Opportunities and Limitations for the Controlled and Stereoselective Polymerization of <i>rac</i>-Lactide

The structure of a series of Me₂GaOR­(NHC) complexes with <i>N</i>-heterocyclic carbenes (1,3-bis­(2,4,6-trimethylphenyl)­imidazolin-2-ylidene (SIMes) and 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes)) have been characterized using spectroscopic and X-ray techniques and discussed in view of their reactivity in the polymerization of <i>rac</i>-lactide (<i>rac</i>-LA). Both structure studies and density functional theory (DFT) calculations show the significant influence of NHC and OR on the structure of investigated complexes and has indicated that the Ga–C_NHC bond (32.6–39.6 kcal mol^–1) is strong enough to form stable Me₂GaOR­(NHC) complexes in the form of monomeric species. The reactivity of Me₂Ga­((<i>S</i>)-OCH­(Me)­CO₂Me)­(SIMes) (<b>1</b>) and Me₂Ga­((<i>S</i>)-OCH­(Me)­CO₂Me)­(IMes) (<b>5</b>) toward Lewis acids such as CO₂ and GaMe₃ has resulted in breaking of the Ga–C_NHC bond with the formation of (NHC)­CO₂ and Me₃Ga­(NHC) (<b>8</b> and <b>10</b>) and [Me₂Ga­(μ-(<i>S</i>)-OCH­(Me)­CO₂Me)]₂. Different results have been obtained for l,3-bis­(2,6-diisopropylphenyl)-imidazolin-2-ylidene (SIPr), which coordinates more weakly to gallium, as demonstrated by the Ga–C_NHC bond strength for model Me₃GaSIMes, Me₃GaIMes (<b>8</b>), and Me₃GaSIPr (<b>10</b>) adducts. The reaction of SIPr with [Me₂Ga­(μ-OR)]₂ has not allowed for the breaking of Ga₂O₂ bridges and the formation of monomeric Me₂GaOR­(SIPr) complexes, contrary to SIMes and IMes. In the case of the reaction with [Me₂Ga­(μ-(<i>S</i>)-OCH­(Me)­CO₂Me)]₂, the ionic compound [Me₂Ga­(OCH­(Me)­CO₂)]⁻[SIPrH]⁺ (<b>9</b>) has been isolated. The investigated Me₂GaOR­(NHC) complexes are highly active and stereoselective in the ring-opening polymerization of <i>rac</i>-lactide from −20 °C to room temperature, due to the insertion of <i>rac</i>-LA exclusively into the Ga–O_alkoxide bond, leading to isotactically enriched polylactide (PLA) (<i>P</i>_m = 0.65–0.78). It has been shown that the polymerization of lactide at low temperature is influenced by the chelate interaction of (<i>S</i>)-OCH­(Me)­CO₂Me or (OCH­(Me)­C­(O))₂OR resulting from the primary insertion of <i>rac</i>-LA into the Ga–O_alkoxide bond, with the Ga center, which can be responsible for the low control over the molecular weight of the obtained PLA. The latter effect can be eliminated by the initial synthesis of Me₂Ga­((PLA)_<i>n</i>OR)­(NHC) with short PLA chains, which allows for controlled polymerization. Although the adverse chelate effect can be also eliminated by the polymerization of <i>rac</i>-LA at room temperature, the stereoselectivity of <i>rac</i>-LA polymerization is strongly affected by transesterification reactions. Out of investigated Me₂GaOR­(SIMes) and Me₂GaOR­(IMes) complexes, only the latter allowed for the immortal ring opening polymerization of <i>rac</i>-LA in the presence of ^<i>i</i>PrOH

Dialkylgallium Alkoxides Stabilized with <i>N</i>‑Heterocyclic Carbenes: Opportunities and Limitations for the Controlled and Stereoselective Polymerization of <i>rac</i>-Lactide

The structure of a series of Me₂GaOR­(NHC) complexes with <i>N</i>-heterocyclic carbenes (1,3-bis­(2,4,6-trimethylphenyl)­imidazolin-2-ylidene (SIMes) and 1,3-bis­(2,4,6-trimethylphenyl)­imidazol-2-ylidene (IMes)) have been characterized using spectroscopic and X-ray techniques and discussed in view of their reactivity in the polymerization of <i>rac</i>-lactide (<i>rac</i>-LA). Both structure studies and density functional theory (DFT) calculations show the significant influence of NHC and OR on the structure of investigated complexes and has indicated that the Ga–C_NHC bond (32.6–39.6 kcal mol^–1) is strong enough to form stable Me₂GaOR­(NHC) complexes in the form of monomeric species. The reactivity of Me₂Ga­((<i>S</i>)-OCH­(Me)­CO₂Me)­(SIMes) (<b>1</b>) and Me₂Ga­((<i>S</i>)-OCH­(Me)­CO₂Me)­(IMes) (<b>5</b>) toward Lewis acids such as CO₂ and GaMe₃ has resulted in breaking of the Ga–C_NHC bond with the formation of (NHC)­CO₂ and Me₃Ga­(NHC) (<b>8</b> and <b>10</b>) and [Me₂Ga­(μ-(<i>S</i>)-OCH­(Me)­CO₂Me)]₂. Different results have been obtained for l,3-bis­(2,6-diisopropylphenyl)-imidazolin-2-ylidene (SIPr), which coordinates more weakly to gallium, as demonstrated by the Ga–C_NHC bond strength for model Me₃GaSIMes, Me₃GaIMes (<b>8</b>), and Me₃GaSIPr (<b>10</b>) adducts. The reaction of SIPr with [Me₂Ga­(μ-OR)]₂ has not allowed for the breaking of Ga₂O₂ bridges and the formation of monomeric Me₂GaOR­(SIPr) complexes, contrary to SIMes and IMes. In the case of the reaction with [Me₂Ga­(μ-(<i>S</i>)-OCH­(Me)­CO₂Me)]₂, the ionic compound [Me₂Ga­(OCH­(Me)­CO₂)]⁻[SIPrH]⁺ (<b>9</b>) has been isolated. The investigated Me₂GaOR­(NHC) complexes are highly active and stereoselective in the ring-opening polymerization of <i>rac</i>-lactide from −20 °C to room temperature, due to the insertion of <i>rac</i>-LA exclusively into the Ga–O_alkoxide bond, leading to isotactically enriched polylactide (PLA) (<i>P</i>_m = 0.65–0.78). It has been shown that the polymerization of lactide at low temperature is influenced by the chelate interaction of (<i>S</i>)-OCH­(Me)­CO₂Me or (OCH­(Me)­C­(O))₂OR resulting from the primary insertion of <i>rac</i>-LA into the Ga–O_alkoxide bond, with the Ga center, which can be responsible for the low control over the molecular weight of the obtained PLA. The latter effect can be eliminated by the initial synthesis of Me₂Ga­((PLA)_<i>n</i>OR)­(NHC) with short PLA chains, which allows for controlled polymerization. Although the adverse chelate effect can be also eliminated by the polymerization of <i>rac</i>-LA at room temperature, the stereoselectivity of <i>rac</i>-LA polymerization is strongly affected by transesterification reactions. Out of investigated Me₂GaOR­(SIMes) and Me₂GaOR­(IMes) complexes, only the latter allowed for the immortal ring opening polymerization of <i>rac</i>-LA in the presence of ^<i>i</i>PrOH

Coordination Abilities of 4,5-Dicyano-2-(trifluoromethyl)imidazolate Anion toward Sodium Cation: Structural and Spectroscopic Studies of Solid and Liquid Glyme-Solvated Electrolyte Systems

Comprehensive structural analysis of sodium 4,5-dicyano-2-(trifluoromethyl)­imidazolate (NaTDI) solvates with glymes (1–4), tetrahydrofuran, and crown ethers has been performed. Several structural motifs obtained from single-crystal X-ray analysis of complementary series of crystalline adducts with varying O:Na ratios were correlated with spectroscopic and thermal data to provide new information about the coordination ability of heterocyclic anions toward sodium cations. Presented results provide a basis for developing models of poly­(ethylene oxide) electrolytes and liquid systems for sodium ion battery electrolytes. We have found a wide variety of anion–cation coordination types which allow us to compare them with analogous lithium solvates in terms of Brown’s valence-matching principle and Lewis acid strength (<i>S</i>_a) parameters. Noticed aggregation modes of sodium salts confirm the occurrence of a solvate disproportionation conductivity mechanism at high salt concentrations which can be used for developing new heterocyclic salt systems for sodium batteries

Dialkylgallium Complexes with Alkoxide and Aryloxide Ligands Possessing N‑Heterocyclic Carbene Functionalities: Synthesis and Structure

Methods for the synthesis of dialkylgalium compounds with alkoxide or aryloxide ligands possessing N-heterocyclic carbene functionalities have been established. As a result, the synthesis of a series of dialkylgallium complexes Me₂Ga­(O,C) (<b>1</b>, <b>3</b>–<b>5</b>), and Me₂Ga­(O,C)·Me₃Ga (<b>2</b>, <b>6</b>) is described, where (O,C) represents an alkoxide or aryloxide monoanionic chelate ligand with an N-heterocyclic carbene functionality. All complexes have been fully characterized using spectroscopic and X-ray techniques. The presence of a strongly basic NHC functionality in alkoxide or aryloxide ligands resulted in the formation of monomeric Me₂Ga­(O,C) species. The reaction of those complexes with the Lewis acid Me₃Ga leads to Me₂Ga­(O,C)·Me₃Ga adducts (<b>2</b> and <b>6</b>) with a strong Me₃Ga–O dative bond. The effect of (O,C) ligands with various steric and electronic properties on the structure of obtained Me₂Ga­(O,C) and Me₂Ga­(O,C)·Me₃Ga has been discussed on the basis of spectroscopic data. Finally, the bond valence vector model has been used to estimate the effect of a chelating (O,C) ligand on strains in complexes <b>1</b>–<b>6</b> on the basis of X-ray data