Synthesis Of Low-Coordinate Unsaturated Compounds With Heavier Main Group Elements Ga,Ge And Sn By Novel α-Diketimine

Thermodynamically stable low-valent and low-coordinate unsaturated complexes with heavier main group elements have unique bonding nature,novel molecular structures and abundant reactivity.In the past three decades,the synthesis and isolation of these species have become a rapidly developing research field in inorganic synthetic chemistry,the synthesis of heavier carbene analogues and the study of their coordination chemistry is a typical field.Heavier carbene molecules have typical Lewis acid-base amphiphic,so choosing ligands with steric and electronic effects is the key to stabilizing such highly active molecules with low oxidation states.On the other hand,the unique electronic structures of heavier carbene molecules prompt them to react with a variety of electrophilic and nucleophilic reagents,showing abundant chemical reactivity.With the discovery of some heavier carbene molecules,the investigation of their reactivity has been further deepened,and many unsaturated compounds of main group elements with novel structures have been isolated,which provides support for the completeness of the current chemical bond theory.Based on this,a rigidα-diimine and three bulky monodentate silylamino compounds were selected as ligands for this doctoral work to explore the synthesis and reactivity of stable low-valent gallium,germanium,and tin complexes,in an attempt to obtain systematic experimental results and summarize the innovative findings.This doctoral work mainly covers the following parts:1.Theα-diimine ligand 1 with imino-enamine conjugated structure was used to assemble with Ge Cl₂﹒dioxane to synthesizeα-diimino chlorogermylene 2.On this basis,the reactivity of germylene chloride 2 was explored,including the reaction with bulky silylamino bases,Lewis acids,reducing agents,and its activation reaction with trace water molecules.（1）Using（^tBu Me₂Si）₂NK and germylene chloride 2 to carry out dehydrochlorination to generate germylene 3.Compound 3 is an example of non-aromatic germylene whose backbone has conjugated structure,and has good structural symmetry and molecular stability.（2）Two equiv.of Al Cl₃ and germylene chloride 2 were used for dechlorinate to generate Al₂Cl₇^-paired cationic germylene 4 in high yield.Theoretical calculations show that the cationic character of germylene 4 causes the contraction of all molecular orbitals,the energy of its Ge^II lone pair（-9.986 e V）is remarkably lower than those in 3.The germylene cation 4 has high coordination chemical activity due to its Lewis acid-base amphoteric and good electrophilicity.（3）Single-electron reduction of germylene chloride 2 with metal K to generate C-C radical coupled digermylene 5 and its diastereomer5’.The five-membered rings on both sides of the C-C bond in digermylene 5 are arranged in trans-parallel,while the two five-membered rings of its isomer 5’have trans-twisted configuration with a dihedral angle of 55.42°.The formation mechanism of digermylene 5proves that the stability of carbon radicals is significantly higher than that of germanium radicals.（4）Hydrolysis of germylene chloride 2 with N-Heterocyclic Carbene and water generates digermylene oxide 6 and its conformation isomer 6’.Molecule 6 has conformational and cis-trans isomerous conversion because the steric hindrance for rotation of chemical bonds.The isolation of digermylene oxide 6 demonstrates the reactivity of the Ge-Cl bond in germylene chloride 2 which is first disrupted during hydrolysis.2.Three bulky monodentate silylamino alkali metal compounds 11,15 and 22 were selected as ligands,and they assemble with Ge Cl₄,Ge Cl₂﹒dioxane and Sn Cl₂ in different molar ratios were explored respectively.A series of low-valent germanium and tin complexes with novel structures were isolated.（1）Monodentate silylamido potassium salt11,15 and 22 were monosubstituted with Ge Cl₄ in a molar ratio of 1:1 to obtain silylamino germanium trichloride compounds 12,16 and 23.These compounds have similar structures,all of which having tetrahedral geometry on Ge atoms.However,the corresponding bond lengths and angles are slightly different due to the steric hindrance of the ligands.The successful isolation of these compounds lays the foundation for the reduction of low-valent oligomeric unsaturated germanium compounds.（2）The monosubstituted germanium compound 12 was reduced by excess metal potassium,and the hexanuclear germanium cluster 13 with cage structure was isolated.（3）Using monodentate ligands 11 and 15 to carry out double-substituted reactions with Ge Cl₂ at a molar ratio of 2:1,respectively,obtaining disilylamino germylenes 14 and 17.The structures of the two double-substituted products are similar,both of which are curved two-coordinated chain configurations on the Ge atoms.The synthesis of these compounds is the first to achieve the use of bulky monodentate silylamino to stabilize double-substituted germylenes,which provides an experimental basis for exploring the electronic arrangement and orbital energy state of more stretched chain germylene.（4）Monodentate silylamino ligand 15 and Sn Cl₂ in a molar ratio of 1:1 were used for monosubstitute to obtain chlorostannylene 18.The Lewis acid-base adduct 19 was isolated in high yield by reacting an excess of pyridine with chlorostannylene.This acid-base addition reaction demonstrates the Lewis acidity of tricoordinated chlorostannylene 18.3.Theα-diimine ligand 1 with imino-enamine conjugated structure is used to assemble with Ga Cl₃ to synthesize theα-diimine dichlorogallium complex 24.On this basis,the reactivity of complex 24 was explored,including single and double electron reduction and activation reaction of small molecules by Ga=Ga bond.（1）Single electron reduction of complex 24 using 1.2 equivalents of metal K to generate dimer 25 containing a Ga-Ga single bond.Different from digermylene 5,the gallium radicals in this compound are coupled to each other to form dimers in trans-parallel arrangement separated by Ga-Ga bond.（2）Double electron reduction of 24 was performed using 2.2 equiv of metal K to obtain a dimer26 containing a Ga=Ga double bond.The Ga=Ga bond length is 2.3613（?）,which is a relatively short distance among such double bonds reported in the literature,which is a valuable academic discovery in the field of unsaturated covalent bonds between metals.（3）Theα-diimido gallium-gallium double bond compound 26 was dissolved in toluene,and the reaction was heated at 60°C under sunlight,and the activation product 27 of the gallium-gallium double bond to the saturated C-H bond of toluene was found.The Ga-Ga bond length in this molecule is 2.4688（?）,which is obviously longer than the corresponding distance of26 and is within the normal range of Ga-Ga single bonds.The successful isolation of this compound proves that the Ga=Ga double bond has the ability to activate small molecules.（4）Pouring an appropriate amount of O₂ into the toluene solution of the complex 26 to generate the product 28 with activated O₂ molecules.The core of this compound has a[Ga O₂Ga]four-membered ring,and the molecule presents a zigzag configuration.This work further verified the sensitivity of the Ga=Ga double bond to O₂,and found an exact path for the addition reaction between the metallic unsaturated bond and the O₂ molecules.In summary,this doctoral work has successfully synthesized 22 new compounds within the scope of the designed subject,and achieved the preparation of single crystals and molecular structure characterization,as well as the molecular stability and chemical bonding of 12 low-valent main group elements with high academic value unsaturated compounds were investigated,especially the reactivity of germylene chloride molecules was systematically explored,which enriched the research direction of main group element synthesis chemistry and further expanded the experimental methods and exploration ideas of synthesize unsaturated compounds with heavier group 14 elements.