Study On Catalytic Performance Of Rare-Earth /Sodium Metal Alkoxide Complexes With Acid-Base Bifunctionality

Six heterobimetallic rare-earth/sodium metal alkoxide complexes were synthesized in high yield with HOCH2CH2NMe2 and (CH3)3COH as ligand respectively. The catalytic activity of heterobimetallic rare-earth/sodium metal alkoxide complexes for transesterification, synthesis of carbamates from aminolysis of carbonates and transamidation was investigated. The results are as follows:1. Sodium alkoxide NaOCH2CH2NMe2 reacted with LnCL3 in a molar ratio of 6:1 in the presence of one equiv of NaOH, giving the rare-earth/sodium metal alkoxide complexes Ln2Na8(OCH2CH2NMe2)12(OH)2 [Ln= Nd (Ⅰ), Sm (Ⅱ), Yb(Ⅲ),Y(Ⅳ)].2. Sodium alkoxide NaOC(CH3)3 reacted with LnCl3 in a molar ratio of 10:1 in the presence of one equiv of NaOH, giving the rare-earth/sodium metal alkoxide complexes LnNa8(OtBu)10(OH) [Ln= Nd (ⅰ), Yb (ⅱ)].3. The catalytic activity of Ln2Nag(OCH2CH2NMe2)i2(OH)2 [Ln= Nd (Ⅰ), Sm (Ⅱ), Yb (Ⅲ)] for transesterification was studied. The results showed that heterobimetallic dinuclear lanthanide alkoxide complexes could highly catalyze transesterification of carboxylic esters, weakly reactive carbonates and much less-reactive ethyl silicate with primary and secondary alcohols. The catalysts showed high catalytic activity and a wide scope of substrates for transesterification with good to excellent yields under mild reaction conditions. Selectivity experiments revealed that primary alcohols can be acylated efficiently over secondary alcohols in the presence of the catalyst.4. The comparative study on the aminolysis of carbonates between Ln2Na8(OCH2CH2NMe2)i2(OH)2 [Ln= Nd (Ⅰ), Sm (Ⅱ), Yb (Ⅲ), Y (Ⅳ)] and LnNa8(OTBu)io(OH) [Ln= Nd (ⅰ), Yb (ⅱ)] was examined. The results showed that heterobimetallic dinuclear lanthanide alkoxide complexes were used as the efficient acid-base bifunctional catalysts for the synthesis of carbamates from dialkyl carbonates and amines as well as the N-Boc protection of various amines. The cooperative catalysts showed the high catalytic activity and a wide scope of substrates with good to excellent yields under solvent-free conditions. The comparison of catalytic efficiency between the mono- and dinuclear heterobimetallic lanthanide alkoxide complexes was investigated as well, indicating dinuclear systems have the higher catalytic activities due to the noteworthy synergistic interactions of Ln center-Ln center.5. The study on transamidation of Ln2Na8(OCH2CH2NMe2)12(OH)2 [Ln= Nd (Ⅰ), Sm (Ⅱ), Yb (Ⅲ), Y (Ⅳ)] was conducted. The results showed that heterobimetallic dinuclear lanthanide alkoxide complexes were used as the efficient acid-base bifunctional catalysts for the transamidation of several primary, secondary, and tertiary amides with aliphatic and aromatic amines. The reaction is performed in the presence of low loading of catalyst with a wide scope of substrates with good to excellent yields.