Periodic Reporting for period 4 - MultiBD-CHALLENGE (The Pursuit of Group 13-Group 15 (E13≡E15) Triple Bonds. Their Reactivity and Applications for Materials)
Okres sprawozdawczy: 2023-08-01 do 2024-07-31
The chemical bond is a core concept in all areas of chemistry. The modern quest for smaller and more efficient devices can be approached comprehensively from a molecular perspective (bottom-up). Given the direct technological impact, deliberate tailoring bonding properties, such as strength, reactivity/stability, and light interaction, has become of paramount interest. Thus, current endeavors aim to establish structure-activity guidelines and produce reliable models based on a deep understanding of bonding interactions.
This project focuses on the fundamental aspects and applications of chemical bonding properties. The central point is the engineering of unsaturated main group compounds chemistry combining groups 13 and 15 elements of the periodic table. The systems offer a great diversity of bonding situations and directly connect to materials science applications (III−V semiconductor, small molecules activation/fixation).
Although multiple bonds between carbon atoms are well-known, the heavier analogues had long remained inaccessible. The double-bond rule emerged, formalizing the impossibility of achieving them given the π-bonds weakness. Eventually, synthetic strategies based on bulky substituents to provide kinetic and thermodynamic stability brought homodiatomic examples (Sn=Sn), disproving the rule. This approach has been then exploited to accomplish many exotic unsaturated compounds. Nonetheless, the isoelectronic heteroatomic motifs are preparatively more challenging as they are prone to oligomerization.
Compounds featuring double/triple-bond character between groups 13 and 15 elements are rare. Traditional synthetic approaches are limited to double-bond character, leaving higher-order multiple-bond examples elusive. The challenge of the project is to build compounds with hitherto unknown multiple bonds, overcoming these limitations. The hypothesis rests not only on the stabilization provided by the Lewis base species but also on the electronic structure twist caused by the dative interaction.
These target motifs present a multifunctional character, given a unique bonding situation, able to serve as reagents for the activation of organic small molecules and versatile coordination ligands toward transition metals. Furthermore, these compounds are expected to act as precursors for growing high-quality III-V semiconductor films.
The specific aims of this project are to assess these unique compounds, explore their reactivity, and harvest their potential in materials science.
This project focuses on the fundamental aspects and applications of chemical bonding properties. The central point is the engineering of unsaturated main group compounds chemistry combining groups 13 and 15 elements of the periodic table. The systems offer a great diversity of bonding situations and directly connect to materials science applications (III−V semiconductor, small molecules activation/fixation).
Although multiple bonds between carbon atoms are well-known, the heavier analogues had long remained inaccessible. The double-bond rule emerged, formalizing the impossibility of achieving them given the π-bonds weakness. Eventually, synthetic strategies based on bulky substituents to provide kinetic and thermodynamic stability brought homodiatomic examples (Sn=Sn), disproving the rule. This approach has been then exploited to accomplish many exotic unsaturated compounds. Nonetheless, the isoelectronic heteroatomic motifs are preparatively more challenging as they are prone to oligomerization.
Compounds featuring double/triple-bond character between groups 13 and 15 elements are rare. Traditional synthetic approaches are limited to double-bond character, leaving higher-order multiple-bond examples elusive. The challenge of the project is to build compounds with hitherto unknown multiple bonds, overcoming these limitations. The hypothesis rests not only on the stabilization provided by the Lewis base species but also on the electronic structure twist caused by the dative interaction.
These target motifs present a multifunctional character, given a unique bonding situation, able to serve as reagents for the activation of organic small molecules and versatile coordination ligands toward transition metals. Furthermore, these compounds are expected to act as precursors for growing high-quality III-V semiconductor films.
The specific aims of this project are to assess these unique compounds, explore their reactivity, and harvest their potential in materials science.
This project focused on the molecular design and synthesis of compounds where B, Al, and Ga atoms are combined with N or P atoms via two/three electron pairs.
At the outset, we studied the target chemical bonds computationally. The origins of chemical bonds are inaccessible by experiments but can be approached theoretically. Since no exclusive approach exists to describe it unequivocally, there are continued debates on its definition. An approach to analyze it consists of classifying the electron-pair interactions as electron-sharing and dative. We demonstrated that there is a bonding situation manifested in metals, a so-called spin-polarized bond, which can also be used to describe the nature of the chemical bond in main group compounds.
Additionally, we have developed a combined molecular orbital theory-based method with topological analysis (EDA-IQA). This work provides an interesting approach for analyzing the directionality of bonding interactions such as orbital relaxation, Pauli repulsion, and electrostatic interaction.
The boron chemistry has been explored intensively from the experimental part. The isoelectronic relationship between C=C and B=N units has been exploited to prepare hybrid (in)organic polycyclic aromatic hydrocarbons (PAHs). The BN units, as traditionally incorporated, are described as electron sharing σ-bond and π-donation of the lone pair of nitrogen into an empty p-orbital of boron. We envisage that π-electronic systems of iminoborane-Lewis base adducts may provide a different kind of BN-unit. The bonding description consists of a double bond where the σ- and π-systems are electron-sharing with a strong dipolar moment. This bonding gives a twist since we obtained unprecedented thermal stability by introducing Lewis-base coordinated iminoborane adducts into pre-established cyclic geometry. Notably, the nature of the electronic situation unit differs from previous examples; having a HOMO-LUMO gap is significantly reduced. In addition, the pending N atom allows functionalization by a series of electrophiles, which can be used as a link to tune optoelectronic properties.
Analogues compounds containing B=P units are very scarce. Monomeric species need extra kinetic stabilization by blocking the P lone pair with a Lewis acid, or the B empty p-orbital with a Lewis base. We have successfully prepared new Lewis base-stabilized phosphaborenes by promoting TMSCl elimination. The attractive approach avoids the dimerization step observed in other synthetic protocols, allowing less bulky groups on the P atom. The B=P units can be transferred to organic, inorganic, and organometallic electrophiles. Unfortunately, our efforts to increase the unsaturation degree were unsuccessful.
We also pursued the formation of Al and Ga-containing analogues. These combinations bring experimental difficulties because of the big electronegativity difference in the atoms involved, which makes the species very reactive. Besides, conventional functionalization of aluminium species relies on small molecule elimination, salt elimination, and the activation of molecules with Al(I) species. Our focal point is to generate low-valent aluminium compounds with extremely rigid scaffolds with less sterical protection by side groups. Interestingly, instead of generating a nucleophilic aluminyl anion, we formed aluminium radicals which reduced benzene. We have also investigated the aluminium hydride chemistry with a counter ion (alkaline metal), envisioning application in catalysis for hydroborilation and hydrosilylation. We found particular use of boron-based substituents as pseudo-halide functionalities. This ligand is adaptable to multiple chemical environments and leads to valuable precursors for building sophisticated compounds.
Finally, the chemistry of gallium compounds leads to the preparation of monocoordinate species as a key intermediate for accessing GaN unsaturated functionalities.
At the outset, we studied the target chemical bonds computationally. The origins of chemical bonds are inaccessible by experiments but can be approached theoretically. Since no exclusive approach exists to describe it unequivocally, there are continued debates on its definition. An approach to analyze it consists of classifying the electron-pair interactions as electron-sharing and dative. We demonstrated that there is a bonding situation manifested in metals, a so-called spin-polarized bond, which can also be used to describe the nature of the chemical bond in main group compounds.
Additionally, we have developed a combined molecular orbital theory-based method with topological analysis (EDA-IQA). This work provides an interesting approach for analyzing the directionality of bonding interactions such as orbital relaxation, Pauli repulsion, and electrostatic interaction.
The boron chemistry has been explored intensively from the experimental part. The isoelectronic relationship between C=C and B=N units has been exploited to prepare hybrid (in)organic polycyclic aromatic hydrocarbons (PAHs). The BN units, as traditionally incorporated, are described as electron sharing σ-bond and π-donation of the lone pair of nitrogen into an empty p-orbital of boron. We envisage that π-electronic systems of iminoborane-Lewis base adducts may provide a different kind of BN-unit. The bonding description consists of a double bond where the σ- and π-systems are electron-sharing with a strong dipolar moment. This bonding gives a twist since we obtained unprecedented thermal stability by introducing Lewis-base coordinated iminoborane adducts into pre-established cyclic geometry. Notably, the nature of the electronic situation unit differs from previous examples; having a HOMO-LUMO gap is significantly reduced. In addition, the pending N atom allows functionalization by a series of electrophiles, which can be used as a link to tune optoelectronic properties.
Analogues compounds containing B=P units are very scarce. Monomeric species need extra kinetic stabilization by blocking the P lone pair with a Lewis acid, or the B empty p-orbital with a Lewis base. We have successfully prepared new Lewis base-stabilized phosphaborenes by promoting TMSCl elimination. The attractive approach avoids the dimerization step observed in other synthetic protocols, allowing less bulky groups on the P atom. The B=P units can be transferred to organic, inorganic, and organometallic electrophiles. Unfortunately, our efforts to increase the unsaturation degree were unsuccessful.
We also pursued the formation of Al and Ga-containing analogues. These combinations bring experimental difficulties because of the big electronegativity difference in the atoms involved, which makes the species very reactive. Besides, conventional functionalization of aluminium species relies on small molecule elimination, salt elimination, and the activation of molecules with Al(I) species. Our focal point is to generate low-valent aluminium compounds with extremely rigid scaffolds with less sterical protection by side groups. Interestingly, instead of generating a nucleophilic aluminyl anion, we formed aluminium radicals which reduced benzene. We have also investigated the aluminium hydride chemistry with a counter ion (alkaline metal), envisioning application in catalysis for hydroborilation and hydrosilylation. We found particular use of boron-based substituents as pseudo-halide functionalities. This ligand is adaptable to multiple chemical environments and leads to valuable precursors for building sophisticated compounds.
Finally, the chemistry of gallium compounds leads to the preparation of monocoordinate species as a key intermediate for accessing GaN unsaturated functionalities.
The main effort tackled the chemical bond concept. We provided an understanding of exotic bonding situations in main group compounds. Thus, the specific electronic structure of the pursed molecules yields a highly exotic situation beyond the traditional knowledge, allowing us to provide guidelines for molecular design.
The preparative approach towards compounds with unsaturated units between group 13 and 15 elements consisted of a combination of bulky groups to improve the kinetic and thermodynamic stability and Lewis acid/base pairs to mitigate their reactivity. We accessed examples of BN, BP, and GaN multiple bonds, and Al compounds generate different species that are used in catalysis and redox chemistry. These methodologies are limited to genuine double bonds, but the insight into the chemistry is valuable for our constant quest for multiple bonds.
The preparative approach towards compounds with unsaturated units between group 13 and 15 elements consisted of a combination of bulky groups to improve the kinetic and thermodynamic stability and Lewis acid/base pairs to mitigate their reactivity. We accessed examples of BN, BP, and GaN multiple bonds, and Al compounds generate different species that are used in catalysis and redox chemistry. These methodologies are limited to genuine double bonds, but the insight into the chemistry is valuable for our constant quest for multiple bonds.