Rare Earth Metal Alkyls Catalyzed Dehydrogenation Of Amine-Boranes

Aminoboranes are a significant complex with great potential in the fields of energy and material science.However,current methods for synthesizing aminoboranes exist many limitations.In addition,there remains a lot of space for development in the amineborane dehydrogenation catalyzed by rare earth metal complexes.This dissertation presents the application of rare earth metal complexes in catalyzing dehydrocoupling of amines and boranes and amine-borane dehydropolymerization,including the following:1.The dehydrocoupling reaction of amines and boranes is firstly catalyzed by rare earth metal alkyl complex.In the study,we find that the scandocene alkyl complex(1)Cp*2ScCH2SiMe3(Cp*=C5Me5)can efficiently catalyze the dehydrocoupling reaction of amines and boranes to generate the corresponding aminoborane products.The noncyclic secondary borane Cy2BH(2)and the primary borane Me2CHCMe2BH2(3)are firstly used in the dehydrocoupling reaction.At the same time,a wide range of amines can be applied in the study as well,including aliphatic amines and aromatic amines.And the analysis of the active intermediate indicates the reaction undergoes a classicβ-H elimination process.In addition,kinetic studies show that the dehydrocoupling reaction exhibits first-order kinetic behavior for rare earth catalyst,and zero-order kinetic behavior for both substrate amine and borane.Deuteration experiments show that the cleavage of the B-H bond is the rate-determining step of the reaction.2.Rare earth metal alkyl complexes are used to achieve the dehydropolymerization of amine-borane for the first time.Dicyclopentadiene rare earth metal alkyl complexes can catalyze the dehydropolymerization of MeNH2-BH3(MAB)to afford PMAB.With the increase of ion radius of the metal center or the decrease of the steric hindrance of the substituents on the cyclopentadienyl,the polymerization activity will decrease.However,when using large sterically hindered amine-borane EtNH2·BH3(EtAB),nBuNH2·BH3(BuAB),2-MeOEtNH2-BH3(2-MeOEtAB),BzNH2·BH3(BzAB)as the substrate,the polymer is not observed,but the dehydrogenation trimerization cyclization products are obtained.Interestingly,the dehydrogenation of MAB can selectively obtain dehydrogenation trimerization cyclization product when catalyzed by a monocene constrained geometry catalysts(CGC)type rare earth metal alkyl complex.Mechanism studies indicate that the dehydrogenation of amine-borane undergoes a β-H elimination process.In the dicyclopentadiene rare earth metal catalyst system,the metal hydride is obtained by the elimination of β-H which will further undergo a coordination nucleophilic reaction with the free aminoborane to obtain a polymer.In the CGC-type catalytic system,there is a competitive coordination of THF in the reaction,which prevents the coordination process of the subsequent monomers,leading to the trimeric cyclization product.Kinetic studies show that dehydropolymerization reaction exhibits first-order kinetic behavior for rare earth catalyst,and zero-order kinetic behavior for monomer MAB.