Rare-Earth Metal Alkyl Complexes Bearing A Thienyl Functionalized β-Diketiminato Ligand:Synthesis,Characterization And Catalytic Application

In this paper,two tridentate thienyl functionalizedβ-diketiminato ligands H₂L¹and H₂L²[L¹=Me C（NDipp）CHC（Me）NCH₂-2-C₄H₂S,L²=Me C（NDipp）CHC（Me）NCH₂CH₂-2-C₄H₂S,Dipp=2,6-ⁱPr₂C₆H₃]were designed and synthesized.A series of rare-earth metal monoalkyl complexes bearing a thienyl functionalizedβ-diketiminato ligand were prepared via the reactions of the ligands with rare-earth metal trialkyl compounds RE（CH₂Si Me₃）₃（THF）₂（RE=Y,Er,Yb,Lu）and their catalytic activities toward Tishchenko reaction were also investigated.1.Five mononuclear rare-earth metal monoalkyl complexes bearing a thienyl functionalizedβ-diketiminato ligand formulated as L²RE（CH₂Si Me₃）（THF）[RE=Y（2）,Er（3）,Yb（4）,Lu（5）]and L¹Yb（CH₂Si Me₃）（THF）（6）were synthesized through the reactions of H₂L¹or H₂L²with the rare-earth metal alkyls RE（CH₂Si Me₃）₃（THF）₂in toluene at room temperature.During this process,the activation of the C–H bond on 3-position of the thienyl ring resulted in the formation of the dianion species[Me C（NDipp）CHC（Me）N（CH₂）_n-2-C₄H₂S]^2-（n=1 or 2）,forming the rare-earth metal monoalkyl complexes with a N,N,C-tridentate coordination to the rare earth ions.The complexes have a good solubility in toluene and tetrahydrofuran,but a poor solubility in n-hexane.2.Further investigation showed that these rare-earth metal momoalkyl complexes supported by a thienyl functionalizedβ-Diketiminato ligand were used as catalysts for the dimerization of aldehydes（or named as Tishchenko reaction）,affording the corresponding esters in moderate to high yields.The catalysts have good compatibility with aromatic,heteroaromatic,and aliphatic aldehydes and different substituents on the phenyl rings.We attempted the cross-coupling of two different aldehydes（aliphatic and aromatic aldehydes）and four different types of esters were obtained in the presence of complex 2 as the catalyst.The results show that the aliphatic aldehyde is easier to dimerize and to be oxidation compared to the aromatic aldehyde.Hydroboration of esters from the catalytic products catalyzed by the complex 2 were investigated,and the final products of primary alcohols were obtained in high yields.The structures of all the above complexes were characterized by single-crystal X-ray diffraction,elemental analysis and IR spectroscopy.The structures of the ligands H₂L¹,H₂L²,complex 2,and 5 were further confirmed by NMR analyses.