氟化物催化硅氢化合物和取代酚的脱氢偶联反应

FLUORIDE CATALYZED DEHYDROCOUPLING REACTION OF HYDROSILANE AND SUBSTITUTED PHENOLS

通过等摩尔竞争反应研究了氟化物催化的硅氢化合物和取代酚的脱氢偶联反应机理．研究表明，ｐ－ＸＣ６Ｈ４ＯＨ在反应中的取代基效应与氟化物催化取代苯甲醛ｐ－ＸＣ６Ｈ４ＣＨＯ的硅氢化反应中的不同．这表明它们的反应机理存在差异．在这两种反应中，虽然Ｆ－对Ｓｉ的配位都促进了硅氢化合物中的Ｈ对底物中带正电荷原子的亲核进攻，但是在催化酚解反应中，由于没有四中心过渡态的形成，因此下一步取代酚中的氧原子对Ｆ－配位的Ｓｉ原子的进攻不是协同过程．硅氢化合物酚解反应的速度是由这两步反应的速度常数ｋ１和ｋ２共同决定的．依此对氟化物催化的硅氢化物的酚解（包括醇解）反应提出了新的机理．

he mechanism of the fluoride catalyzed dehydrocoupling of hydrosilane and phenols has been studied by equal mole competition reaction. It is shown that the substituent effect in p--XC6H4OH is differentfrom that observed in the fluoride catalyzed hydrosilylation of substituted benzaldehydes P--XC,H,CHO with hydrosilane (C2H5O)3SiH. It is indicated that there are differences in the mechanism of both type of reaction. Although, in the course of both reaction, the coordination of Fanion to St atom promotes the foregoing nucleophilic attacking of Hatom in hydrosilane on positive charged atom in the substrates, but incatalytic phenolysis because of no formation of four--center transitionstate, therefore next nucleophilic attacking of oxygen atom of substituted phenols on Si atom coordinated by F anion is not a concerted process.The reaction rate of phenolysis of hydrosilane is controlled combinatively by two--step reaction rate constants hi and k2. A new mechanism forfluoride-catalyzed phenolysis (including alcoholysis) of hydrosilane has been suggested.