Dehydrogenative Cross-coupling And Addition Reactions Of Boranes And Hydrosilanes

The dehydrogenative cross-coupling and addition reactions of boranes and silanes are very important in organic and polymer synthesis. This thesis focused on the dehydrogenative coupling and addition reactions of boranes and silanes mediated by rare-earth complexes and N-heterocyclic carbenes.The major contents as follows:1) Sterically hindered amino borane ArNH2-BH3(Ar=2,6-(3,55-Me2C6H3)2C6H3) have been synthesized. Its reactions with rare earth trialkyl complexes M(CH2SiMe3)3(THF)2(M=Y, Sm) afforded two borane-stablized rare earth imino complexes [ArN(BH3)YCH2SiMe3]2and [ArN(BH3)SmCH2SiMe3]2, which were fully characterized by1H,13C NMR, IR and X-ray crystallographic analysis. The stability, catalytic activity and reactivity of those two imino complexes were explored. ArNH2-BH3reacted with yttrium amine complex Y[N(SiMe3)2]3affording a complicated dehydrogenate product [ArN(BHNHAr)]2Y(BH4)(THF). The reaction of ArNH2-BH3with NHC stabilized ytterbium amide complex resultes in the formation of (μ2-ArNH)2[YbN(SiMe3)2][Yb(BH3)N(SiMe3)2], in which a BH3insert into a Yb-N bond.2) The synthesis of rare earth dihydride has been explored. The isolation of NHC-stablized ytterbium dihydride was searched. A serial of rare earth adducts were prepared and their properties were explored. Two chelated rare earth dialkyl complexes were synthesized, which exhibited excellent catalytic activity for lactide polymerization with3,4-selectivity.3) The dehydrogenative cross-coupling reaction of silanes and various alcohols has been studied. Different carbenes have been screened, and N-heterocyclic carbene has been found to be highly efficient. The carbene catalyzed reaction of hydrosilanes and alcohols can achieve good selectity and efficiency under mild conditions under solvent free conditions. The catalytic reactions is tolerant to a wide range of functional groups such as amine, halides, imine carbonyl groups. The solvent effects on the reactivity has also been investigated. 4) The dehydrogenative coupling reaction of silanes and water has been investigated. N-heterocyclic carbenes have been found to catalyze the reaction under relatively mild conditions. The coupling reaction of tertiary silanes with water leads to the exclusive formation of silyl ethers.The reaction of secondary silanes with water results in cyclosiloxanes with good selectivity. As the widely applications of the hydrolysis products siloxanes, the method is valuable for practical application. The carbene catalyzed ring-open polymerization of cyclosiloxanes have been researched.