Synthesis And Reactivity Of NHC-Stabilized Silylene

The dissertation described the synthesis and chemical properties of silylenes,especially the synthesis and reactivity of N-heterocyclic carbene-stablized silylenes.The results are summarized below:1. For the first time, it has been found that N-heterocyclic carbenes （NHCs）reduce substituted chlorosilanes to yield stable and transient silylenes under mildconditions. This is a novel, reliable and facile route for the generation of silylenes.Reactions of variuos cyclic diaminochlorosilanes with1,3-bis（tert-butyl）imidazol-2-ylidene （ItBu） yielded the corresponding N-heterocyclic silylenes, disilanes andsilyl-functionalized NHCs depending on the substituents on the nitrogen atoms andring sizes. In the later two cases for the formation of disilanes and silyl-functionalizedcarbenes, transient silylenes have been proposed as intermediates, which undergoSi-Cl bond insertion and C-H bond insertion reactions to give disilanes andfunctionalized carbenes, respectively. These reactions provide novel routes to silylfunctionalized NHCs and disilanes.2. Reactions of the aminodichlorosilane R¹R²NSiHCl₂（R¹=2,6-iPr₂C₆H₃, R²=SiMe₃） with different N-substituted of N-heterocyclic carbenes （NHCs） have beenstudied. It has been observed that the resulting products largely depend on thereaction conditions and the steric effects of NHCs. The reaction of R¹R²NSiHCl₂withthe bulky N-heterocyclic carbene ItBu gave disilane R¹R²NSi（HCl）Si（Cl₂）NR¹R²atroom temperature and4-silyl-NHC R¹R²NSi（HCl）-ItBu at high temperature. Thereaction of R¹R²NSiHCl₂with1,3,4,5-tetramethylimidazol-2-ylidene （IMe） affordedthe first donor-stablized1-hydrosilanimine IMe-R¹R²NHSi=NR¹and the trimericsix-membered product （HClSiNR¹）3, respectively, under different reaction conditions.When1,3-diisopropyl-4,5-dimethyl-imidazol-2-ylidene （IPr） was employed, thereaction yielded the first NHC-stablized monoaminochlorosilylene R¹R²NSi（Cl）（IPr）in good yield. The small IMe can replace the relative bukyl IPr from the silyleneR¹R²NSi（Cl）IPr to yield the similar NHC-stabilized chlorosilylene, indicating thesteric factors afforded by NHCs have significant effects on the dehydrochlorinationpathways. 3. The reactivity of NHC-stablized aminochlorosilylene R¹R²NSi（Cl）-IPr hasbeen investigated in detail. It can acts as Lewis base to form complexes withtransition metals and Lewis acids like borane. Most importantly, the silylene is highlynucleophilic and exhibits pronounced silyl anionic character and might be an efficientsilylation reagents for unsaturated organic substartes.A facile route for the disilylation of activated alkynes without transiton metalcatalysis has been developed. The reaction of RSi（Cl）-IPr with activated alkyneefficiently give cis-disilylation products. This novel method is stereo-andregioselective and atom economic and represents the first metal-free silylationreactions.The first donor-free2-hydrophosphasilene R¹R²NSiH=PAr （Ar=2,6-Mes2C3H6）has been synthesized from the silylene. The reaction of R¹R²NSi（Cl）IPr with ArPHLigave the aminophosphasilylene LSi（II）（IPr）-PHAr as meta stable product, whichsubsequently undergoes hydrogen migration from phosphorus to silicon atom to yieldphosphasilene R¹R²N（IPr）HSi=PAr. The coordinated NHC can be removed by theborane BPh3to afford R¹R²NSiH=PAr. The reaction of RSiCl（IPr） with the boraneBH3·THF affored the air stable adduct R¹R²NSi（Cl）（IPr）（BH3）. The reaction ofR¹R²NSi（Cl）（IPr） with SiCl4afforded NHC-stablized dichlorosilanimineR¹N=SiCl₂（IPr） and aminotrichlorosilane R¹R²NSiCl3under different conditions,respectively. The first Si=Fe double bond compound was synthesized by the reactionof R¹R²NSi（Cl）（IPr） with CpFe（CO）₂K. NHC-stablized silylene LSi（IPr）（PPh₂） wasprepared via the reaction of R¹R²NSi（Cl）（IPr） with Ph₂PLi and has been fullycharacterized. Its reaction with dioxygen afforded two productsR¹N=Si（IPr）（OTMS）PPh₂and R¹N=Si（IPr）（OTMS）OPPh₂under different conditionsby controlling the temperature and dioxygen concentration. The selective formationof the two products have been realized and the mechanisms have been proposed.