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A breakthrough in electronic structure! How to use aluminum-based compounds to achieve ultra-stable structures?
In recent years, aluminum-based compounds, especially those related to gallium (Ga), have become important research objects in the field of chemistry. The unique electronic structures of these compounds make them show excellent potential in various applications. For example, low-valent species of gallium, the so-called gallylenes, have been found in recent years to possess remarkable stability and chemical reactivity, which makes them play an important role in synthetic chemistry and transition metal chemistry.
The unique electronic properties of these compounds make them comparable to compounds of other main-group elements, such as borylenes and carbenes.
Common Gallylenes
β-diketiminate ligands
β-diketiminate ligands (commonly referred to as NacNac ligands) are widely used to stabilize gallylenes. These ligands have lone electron pairs, which enable them to act as Lewis bases and form sigma bonds with gallylene, which has Lewis acid properties. Power et al. synthesized a monomeric Ga(I) compound coordinated with a Dipp-substituted NacNac ligand. The resulting gallylene exhibits surprising stability below 150 °C, a property attributed to the steric protection of the β-diketiminate ligand.
NacNacGa(I) is capable of oxidative addition reactions, activation of C-H bonds, and dual action with certain substrates.
Clamp Ligand
Pinch ligands are used to stabilize the gallylene-derived complexes by preventing the loss of metallylene during the reaction. Iwasawa and co-workers synthesized an Ir complex with a pincer-like ligand. The reaction of this complex shows that gallium is reduced to Ga(I) upon addition of Ir(I). The reaction of the pincer Ir complex with tetrabutylammonium salt resulted in the exchange and decarboxylation of the resident ligand.
Transition Metal Ligands
Gallylenes are frequently used as ligands in transition metal chemistry. An early example is the Ga-Fe triple bond reported by Robinson et al., although Albert Cotton refuted this claim, arguing that there is a coordination bond to Ga and the excess bond order is the return of Fe electrons to Ga atoms. Resonance. With advances in computation, studies of such boundaries have confirmed the coordination properties of gallylene.
This enables gallylene to act as a transition metal ligand and exhibit different reactivities depending on the ligand.
Reactivity
CO and CN breakage
Gallylenes can undergo [1+2] cycloaddition reactions with isocyanates and cleave C=O and C=N bonds. The behavior of this reaction is influenced by the isocyanate substituent. Hydrogen transferGallylenes can be used to prepare gallium hydrides, which can serve as a source of hydrogen and are strong electron donors that can stabilize high oxidation state transition metal hydride complexes.
C-H activation
Fischer and colleagues demonstrated that a NacNacGa(I) complex can break the C-H bonds of organoplatinum and stabilize the resulting platinum species.
Cycloadducts
Fedushkin et al. demonstrated the reactivity of a series of gallylenes stabilized with 1,2-bis[(2,6-diisopropylphenyl)imine] anhydride ligands that led to new cycloadditions. Into product.Azide
Fedushkin et al. showed that gallylene dimers with α-diimine ligands can react with organic azides, and the electronic structure of nitrogen plays a promoting role in the reaction.
Carbodiimide
Treatment of the α-diimine ligand gallylene with carbodiimide yields an amino derivative, demonstrating the “no-effect” nature of the ligand system.
Computational studies and electronic structure
Computational modeling of the five-membered gallylene heterocycle showed that its singlet-triplet excitation energy gap is about 52 kcal/mol. At the same time, the study also pointed out that the stability of ternary gallylene is better than its aluminum-based counterpart, which is also related to its electronic structure.
For applications using gallylene as a transition metal ligand, the structure of the ligand itself has an important influence on its chemical behavior.
With the in-depth study of gallylene and its derivatives, we may see more application potentials of these compounds in catalysis, synthetic chemistry and materials science. This also leads people to think about the role of aluminum-based compounds in innovative technologies in the future?
