Superbasicity of silylene derivatives achieved via non-covalent intramolecular cation⋯π interactions and exploited as molecular containers for CO2

Abstract

We have reported for the first time designed silylene superbases involving intramolecular H(+)···π interaction using density functional theory (DFT) calculations. The non-covalent interactions augment the proton affinity values by 13 kcal mol−1 in the designed superbase (1) compared to the acyclic silylene, [:Si(NMe2)2]. These divalent Si(II) compounds can act as powerful neutral organic superbases in gas and solvent phases. The DFT calculations performed at the B3LYP/6-311+G**//B3LYP/6-31+G* level of theory showed that the gas phase proton affinity of the paracyclophane based silylene superbase (8) reaches up to ~271.0 kcal mol(−1), which is the highest in paracyclophane Si(II) compounds. In tetrahydrofuran solvent medium, the calculated proton affinity of 8 was found to be 301.4 kcal mol(−1). The paracyclophane-based silylene systems are used for binding with small alkali metal ions. The calculated results showed that these systems selectively bind to lithium ions over sodium ions due to the small size of lithium ions which is well fitted in the space between the silicon atom and the phenyl ring. Furthermore, we have used the lithiated silylene 1 and 9 (which exhibits bis-protonation) for gas storage (CO and CO2). The calculated results showed both the lithiated silylene 1 and 9 bind preferentially to CO2 than CO. The calculated gravimetric density of CO2 is found to be 26.97 wt% for 9-Li2–(CO2)4. The energy decomposition analysis (EDA) has been performed to investigate the role of various contributing factors to the total binding strength of the CO2 or CO molecules with lithiated silylene superbases. EDA reveals that the electrostatic energy and polarization energy are the major driving force for higher total interaction energy of the lithiated-silylene–CO2 complex than the lithiated-silylene–CO complex. The lithiated silylene systems showed a higher binding energy with CO2 than the previously reported imidazopyridamine at the same level of theory. These results suggest that the lithiated silylene systems can be used as a more efficient CO2 storage material than the aforementioned system. The calculated desorption energies per CO2 and CO (ΔEDE) also indicate the recyclable property of the materials.

Basicity Limits of Neutral Organic Superbases

“…[13] More recently different innovative bases have been proposed, such as cyclopropeneimines [14] and silylene bases. [15] Despite av ast range of potential applications, [1] many classes of superbases (guanidino proton sponges, [7] phosphorus ylides [16] )a re still almost unexplored.An early Minireview by Schwesinger [17] summarizes the principal approaches to enhancing the basicity of organosuperbases:1 )the "battery cell" principle, [3] that is,s tepwise expansion of the molecular scaffold by forming alternating formal single and double bonds and thereby enhancing the structure where the positive charge can be delocalized (Scheme 1);2 )stabilization of the protonated form by intramolecular hydrogen bond (chelation);a nd 3) structures that become aromatic on protonation. It was concluded that the most fruitful approach to design of superbases is the battery cell principle.T he best known practical example is the phosphazene family of superbases.…”

“…[13] More recently different innovative bases have been proposed, such as cyclopropeneimines [14] and silylene bases. [15] Despite av ast range of potential applications, [1] many classes of superbases (guanidino proton sponges, [7] phosphorus ylides [16] )a re still almost unexplored.…”

Probing the bent bonds in cyclopropane systems for gas storage and separation process: A computational study

“…Such materials can also be used for the separation of CO 2 and CO gas mixture . CO 2 separation from the flue gas of coal‐burning power plants can be work as one of the solution for managing CO 2 emission in the atmosphere.…”

“…Such materials can also be used for the separation of CO 2 and CO gas mixture. [35,36] CO 2 separation from the flue gas of coalburning power plants can be work as one of the solution for managing CO 2 emission in the atmosphere. Graphene, graphene derivatives [37] and lithium doped materials [38][39][40] are extensively studied for CO2 adsorption process.…”

Revealing Germylene Compounds to Attain Superbasicity with Sigma Donor Substituents: A Density Functional Theory Study

“…[48] They have been used in many applications such as catalysis in organic reactions, diabetes medication,g ene therapy,c apture of CO 2 , and conversiont ou seful materials. [49][50][51][52][53][54]60] Therefore,d esign of novel superbasic molecules is an active area of research.M any new classes of nonionics uperbases have been designed and preparedd uringt he past decades, such as guanidinophosphazenes,s uperbasic guanidine derivatives, chiral phosphazenes, quinones,p hosphonium ylides, and azap hosphatranes. [55][56][57][58] The basicities of carbenes have been found to be higher than normal nitrogen containing organic bases [56,59] and their basicity has also been examined within the conceptual framework of non-covalent interactions with p-systems.…”