Studies On The Hydroboration Of Carbonyl Compounds Catalyzed By Tris(methylcyclopentadienyl)lanthanide Complexes And The Hydroboration Of Imines Catalyzed By Lithium Compounds

In this paper,the hydroboration of carbonyl compounds catalyzed by tris(methylcyclopentadienyl)lanthanide complexes was investigated.Besides,hydroboration of imines catalyzed by lithium compounds was studied.It mainly includes the following two aspects:1.Homoleptic lanthanide complexes coordinated by Me-substituted Cp ligand(MeCp)3RE demonstrated unprecedently high efficience in catalyzing the hydroboration of aldehydes and ketones with pinacolborane(HBpin),respectively.The catalytic system is an extension of the hydroboration of aldehydes and ketones catalyzed by tris(cyclopentadienyl)lanthanide complexes.The reaction conditions,such as solvent,the ratio of reaction substrate,and different rare earth metals,were screened.The experiment shows that the progress of the reaction is closely related to the radius of rare earth ions(La>Nd>Yb,Y).The larger the radius,the faster the reaction rate.The hydroborations of ketones and aldehydes with HBpin were carried out using 0.001-1 mol%of(MeCp)3La at room temperature.After work up,1° and 2° alcohols were achieved.In addition,catalyst(MeCp)3RE exhibits remarkable hydroboration selectivity toward aldehydes over ketones in the competitive study.The catalyst shows functional group tolerance even toward CN and OH groups.One possible mechanism is presented on the basis of DFT study.2.Lithium cmpounds(n-BuLi,PhNHLi,2-CH3PhNHLi,2-CH3OPhNHLi,4-CH3OPhNHLi and 2,6-iPr2PhNHLi)have been firstly employed as efficient catalysts for the hydroboration of a wide range of imines with HBpin at room temperature.The protocol requires low catalyst loadings(6 mol%of n-BuLi)and proceeds rapidly(99%conversion in 60 min).After work up,1° and 2° imines were obtained in high yields.A wide range of substrate scopes with high functional group tolerance was proved in the current system.Moreover,the system was also used in catalyzing the hydroboration of alkynes.Chemoselective hydroboration of imines over alkynes is attained under the mild conditions.DFT calculations were carried out to get the deep insight into the mechanism of hydroboration.The results show that lithium compounds smoothly catalyzed the hydroboration of imines by capturing HBpin and imine gradually,followed by hydrogen migration and ligand exchange.