Synthesis Of Tridentate β-diketiminato Rare-Earth Metal Complexes And Their Catalytic Behaviors For Hydroalkoxylation And Tandem Hydroalkoxylation/Cyclohydroamination Of Isocyanates

In this paper,a pyrrolidine-functionalized β-diketiminato ligand and the resulting N,N,N-tridentate β-diketiminato rare-earth metal dialkyl complexes were prepared.Furthermore,we developed the first rare-earth-metal complex-catalyzed protocol for the synthesis of carbamates and oxazolidinones by the reactions of isocyanates with alcohols and propargylic alcohols,respectively.(1)The N,N,N-tridentate β-diketiminato ligand HL(L=MeC(NDipp)CHC(Me)N(CH2)2NC4H8,Dipp=2,6-iPr2C6H3)was synthesized by a two-step reaction.Novel N,N,N-tridentate,β-diketiminato rare earth metal dialkyl complexes LRE(CH2SiMe3)2(RE=Y(1a),Gd(1b),Yb(1c),Lu(1d);L=MeC(NDipp)CHC(Me)N(CH2)2NC4H8,Dipp=2,6-iPr2C6H3)were synthesized by the reaction of rare earth metal trialkyl complexes RE(CH2SiMe3)3(THF)2 with the proligand.These complexes are soluble in n-hexane,toluene,and tetrahy drofuran.(2)It was found that the N,N,N-tridentate β-diketiminato rare earth metal dialkyl complexes can efficiently catalyze the hydroalkoxylation of isocyanates and alcohols.Primary,secondary and tertiary alcohols were applicable in the addition to react with aryl or aliphatic substituted isocyanates,affording a series of N-alkyl and N-aryl carbamate derivatives under a rather low catalyst loading(0.04 mol%)at room temperature.(3)Further studies found that when the reaction temperature was elevated,1 mol%of the rare earth catalyst can catalyze a tandem hydroalkoxylation/cyclohydroamination reaction between terminal and internal propargylic alcohols with substituted arylisocyanates,leading to the efficient synthesis of methylene and(Z)-selective arylidene oxazolidinones in high yields.(4)When the reaction of rare earth metal complex la with two equimolar amount of p-tolyl isocyanate,an unusual binuclear yttrium complex{[η2-(p-tosylNCO)(CH2SiMe3)]Y[μ-η2:η1:η1-(p-tosylNCO)CC(Me)(NDipp)C(Me)N(CH2)2NC4H8]}2(7a)with two different amidate units was isolated.The molecular structure of 7a show that the activation of an sp2 C-H bond on the β-diketimine backbone and the insertion of a molecule of isocyanate to the Y-C bond.On the basis of the result of 1H NMR mornitoring the catalytic reaction,we proposed a plausible reaction mechanism for the synthesis of oxazolidinones via hydroalkoxylation/cyclohydroamination reaction of aryl-substituted isocyanates catalyzed by tridentate β-diketiminato rare earth metal dialkyl complexes.The structures of rare earth metal complexes were characterized by elemental analysis and single crystal X-ray diffraction.The structures of catalytic products were confirmed by 1H NMR,13C NMR and HR-MS analysis.