The Synthesis of Novel Gallium Carbenes, Nitrenes, Phosphinidenes and Alkoxides

<p>In the present study, synthetic routes to formal double bonds between gallium and carbon (fig 1), nitrogen (fig 2), and phosphorus (fig 3) have been investigated. These synthetic routes utilised the monoanionic, four electron donor, β-diketiminate (BDI) ligand to provide both steric and electronic stabilisation to three coordinate gallium complexes. The known di-substituted β-diketiminatogallium complexes: [(BDI)GaMe₂] and [(BDI)Ga(NHPh)₂], as well the new complexes: [(BDI)GaBn₂], [(BDI)Ga(NHDMP)₂] (DMP = 2,6-Me₂C₆H₃), [(BDI)Ga(NHDIPP)₂] (DIPP = 2,6-iPr₂C₆H₃), [(BDI)Ga(PHPh)₂] were examined for their reactivity towards the α-proton elimination mechanism for the formation of multiple bonds that is observed in transition metals. All of these complexes were shown to be unreactive towards α-proton elimination. The di-substituted β-diketiminato-gallium complex [(BDI)GaMe₂] was subjected to various aniline derivatives to investigate if the methyl ligands exhibited the same reactivity as di-methyl transition metal complexes, where the methyl ligands could deprotonate the aniline to form a metal-imido complex. This complex was found to have no reactivity with anilines. The mono-substituted β-diketiminato-gallium complex [(BDI)Ga(NHDMP)Cl] was tested for its reactivity with ⁿBuLi to abstract the amide proton and eliminate LiCl to form a gallium imido complex. While the ¹H NMR spectrum of the reaction mixture showed that a reaction had occurred, the products could not be isolated for characterisation. Another mono-substituted β-diketiminato-gallium complex [(BDI)Ga(PHPh)Cl] was also tested for its reactivity with ⁿBuLi to abstract the phosphide proton and eliminate LiCl to form a gallium phosphinidene complex. The ¹H NMR spectrum and ³¹P NMR spectrum of the isolated complex revealed that it still contained a phosphide proton, however the gallium centre now appeared to be bonded to a former methine carbon of an isopropyl group of the BDI ligand (fig 32). This bond may have formed through metathesis between an intermediate containing a gallium-phosphorus double bond, and the C-H bond of the isopropyl group. Further mechanistic studies could confirm if an intermediate such as [fig 3] is formed, and the synthetic strategy altered to isolate it. The synthesis of β-diketiminato-gallium-alkoxide complexes was also attempted, however the products of these synthesises could not be isolated due to solubility issues, potentially due to polymerisation.</p>

The Synthesis of Novel Gallium Carbenes, Nitrenes, Phosphinidenes and Alkoxides

<p>In the present study, synthetic routes to formal double bonds between gallium and carbon (fig 1), nitrogen (fig 2), and phosphorus (fig 3) have been investigated. These synthetic routes utilised the monoanionic, four electron donor, β-diketiminate (BDI) ligand to provide both steric and electronic stabilisation to three coordinate gallium complexes. The known di-substituted β-diketiminatogallium complexes: [(BDI)GaMe₂] and [(BDI)Ga(NHPh)₂], as well the new complexes: [(BDI)GaBn₂], [(BDI)Ga(NHDMP)₂] (DMP = 2,6-Me₂C₆H₃), [(BDI)Ga(NHDIPP)₂] (DIPP = 2,6-iPr₂C₆H₃), [(BDI)Ga(PHPh)₂] were examined for their reactivity towards the α-proton elimination mechanism for the formation of multiple bonds that is observed in transition metals. All of these complexes were shown to be unreactive towards α-proton elimination. The di-substituted β-diketiminato-gallium complex [(BDI)GaMe₂] was subjected to various aniline derivatives to investigate if the methyl ligands exhibited the same reactivity as di-methyl transition metal complexes, where the methyl ligands could deprotonate the aniline to form a metal-imido complex. This complex was found to have no reactivity with anilines. The mono-substituted β-diketiminato-gallium complex [(BDI)Ga(NHDMP)Cl] was tested for its reactivity with ⁿBuLi to abstract the amide proton and eliminate LiCl to form a gallium imido complex. While the ¹H NMR spectrum of the reaction mixture showed that a reaction had occurred, the products could not be isolated for characterisation. Another mono-substituted β-diketiminato-gallium complex [(BDI)Ga(PHPh)Cl] was also tested for its reactivity with ⁿBuLi to abstract the phosphide proton and eliminate LiCl to form a gallium phosphinidene complex. The ¹H NMR spectrum and ³¹P NMR spectrum of the isolated complex revealed that it still contained a phosphide proton, however the gallium centre now appeared to be bonded to a former methine carbon of an isopropyl group of the BDI ligand (fig 32). This bond may have formed through metathesis between an intermediate containing a gallium-phosphorus double bond, and the C-H bond of the isopropyl group. Further mechanistic studies could confirm if an intermediate such as [fig 3] is formed, and the synthetic strategy altered to isolate it. The synthesis of β-diketiminato-gallium-alkoxide complexes was also attempted, however the products of these synthesises could not be isolated due to solubility issues, potentially due to polymerisation.</p>

SYNTHESIS OF GALLIUM COMPLEXES OF TERT-BUTYLSUBSTITUTED ACYCLIC AND CYCLIC COMPOUNDS BASED ON 3,5-DIAMINO-1,2,4-TRIAZOLE

Synthetic methods of organic chemistry which are currently available in scientific literature allow obtaining a large number macroheterocycles with structurally different internal coordination cavities. They also provide a number of convenient ways to attach to a macrocyclic platform various biologically active heterocyclic fragments such as guanazol. This paper discusses the synthesis and composition of gallium complexes of cyclic and acyclic compounds based on 3,5-diamino-1H-1,2,4-triazol (guanazol), which is itself widely used in medical practice and, most importantly, for the treatment of cancer, in particular, breast cancer ("Anastrozole", "Letrozole"). Interest in gallium compounds is associated with the discovery of a high tropicity of this element to the DNA of tumor cells, as well as cells of the reticuloendothelial system (macrophages and lymphocytes). Therefore, the synthesis of new potential drugs with gallium salts for tumor chemotherapy is an urgent task. The gallium complex of a macroheterocyclic compound of symmetrical structure based on guanazole was obtained through the formation of a three-unit product - 3,5-bis - (5 (6)-tert-butyl-3-iminoisoindoline-1-ilidenamino)-1,2,4-triazole and its complex, followed by cyclization of 3,5-diamino-1H-1,2,4-triazole in phenol. The structure of the obtained compounds was proved using modern physicochemical research methods (UV, IR, NMR spectroscopy, mass spectrometry, and elemental analysis). In the mass spectra of the obtained compounds there are peaks of molecular ions of the target products and their fragmentation products. The coincidence of the m/z values with the mass of molecular ions, as well as the characteristic distributions of molecular ions with the calculated values, confirms the composition of the synthesized gallium complexes.

Synthesis, crystal structures, photoluminescence, electrochemistry and DFT study of aluminium(III) and gallium(III) complexes containing a novel tetradentate Schiff base ligand

Single crystals of the aluminium and gallium complexes of 6,6′-{(1E,1′E)-[1,2-phenylenebis(azanylylidene)]bis(methanylylidene)}bis(2-methoxyphenol), namely diaqua(6,6′-{(1E,1′E)-[1,2-phenylenebis(azanylylidene)]bis(methanylylidene)}bis(2-methoxyphenolato)-κ4 O 1,N,N′,O 1′)aluminium(III) nitrate ethanol monosolvate, [Al(C22H18N2O4)(H2O)2]NO3·C2H5OH, 1, and diaqua(6,6′-{(1E,1′E)-[1,2-phenylenebis(azanylylidene)]bis(methanylylidene)}bis(2-methoxyphenolato)-κ4 O 1,N,N′,O 1′)gallium(III) nitrate ethanol monosolvate, [Ga(C22H18N2O4)(H2O)2]NO3·C2H5OH, 2, were obtained after successful synthesis in ethanol. Both complexes crystallized in the triclinic space group P\overline{1}, with two molecules in the asymmetric unit. In both structures, in one of the independent molecules the tetradentate ligand is almost planar while in the other independent molecule the ligand shows significant distortions from planarity, as illustrated by the largest distance from the plane constructed through the central metal atom and the O,N,N′,O′-coordinating atoms of the ligand in 1 of 1.155 (3) Å and a distance of 1.1707 (3) Å in 2. The possible reason for this is that there are various strong π-interactions in the structures. This was confirmed by density functional theory (DFT) calculations, as were the other crystallographic data. DFT was also used to predict the outcome of cyclic voltammetry experiments. Ligand oxidation is more stabilized in the gallium complex. Solid-state photoluminescence gave an 80 nm red-shifted spectrum for the gallium complex, whereas the aluminium complex maintains the ligand curve with a smaller red shift of 40 nm.

Insights into the reaction mechanism of n-hexane dehydroaromatization to benzene over gallium embedded HZSM-5: effect of H2 incorporated on active sites

This work clearly confirms the existence of dihydrido gallium complex (GaH2+) as one of the most active species for the n-hexane dehydroaromatization into benzene.

Photophysical properties and photodynamic anti-tumor activity of corrole-coumarin dyads

A new non-conjugated corrole-coumarin dyad and its gallium complex has been synthesized. Photophysical properties of the dyads were tested in two solvents, exhibiting strong solvent effect on the absorption and fluorescence spectra. Absorption spectra of the dyads are a linear combination of the spectra of their corresponding monomers, demonstrating a negligible electronic communication between coumarin and corrole moiety. However, fluorescence emission of coumarin entity in all dyads were quenched significantly as compared to pristine coumarin; this was attributed to intramolecular energy transfer from coumarin to the corrole. Photodynamic anti-tumor tests revealed that gallium corrole-coumarin dyads (2-Ga) exhibited good PDT activity towards SiHa cells. After PDT treatment, 2-Ga could induce apoptosis in SiHa cells, which was associated to cell S phase arrest, collapse of the mitochondrial membrane potential and increase of the intracellular ROS level.