Catalysis And Reactivity Of Lanthanide Thiolate Complexes

It is well known that lanthanide thiolate complexes possess good application in semiconductor and optical materials. Besides, lanthanide thiolate complexes also display special catalytic activity for Michael reaction, olefin polymerization, phenyl isocyanate polymerization, ring-opening polymerization ofε-caprolactone and insertion reaction. In this thesis, a series of lanthanide thiolate complexes were prepared and characterized and their catalytic activities toward the ROP of ?-caprolactone or cyclodimerization, cyclotrimerization of isocyanates were investigated. The catalytic activities of lanthanide 4,6-dimethylpyrimidine-2-thionate complexes toward the cyclodimerization of isocyanates were reported. They are briefly summarized as follows:1. The reaction of Pr[(Me3Si)2N]3 with 3 equiv of PhSH afforded one praseodymium benzenethiolate complex [Pr(SPh)3(THF)3] (1). The cyclotrimerization (2a-2f) of aryl isocyanates and the cyclodimerization (3a-3e) of alkyl isocyanates initiated by [Pr(SPh)3(THF)3] were investigated. Comparative runs with [Pr(SPh)3(THF)3] and its precursor Pr[(Me3Si)2N]3 showed that the former has the advantages of a higher selectivity towards isocyanates, easy preparation, low catalyst loading, high conversion as well as mild reaction conditions. The formation of the intermediate 4 supported our initial assumption that [Pr(SPh)3(THF)3] was formed and isocyanate was inserted into the Pr-S bond. To our knowledge, it represents the first example to employ lanthanide thiolate complexes to catalyze the cyclotrimerization of isocyanates.2. The reaction of Sm[(Me3Si)2N]3 with 3 equiv of iPrSH afforded one samarium isopropanethiol complex [Sm(SiPr)3(THF)3] (5). This complex exhibited very high activity toward the polymerization of ?-caprolactone and produced poly(?-caprolactone) with narrower molecular weight distribution. Besides, The ring-opening polymerization of ?-caprolactone initiated by Sm[(Me3Si)2N]3 in the presence of different equiv isopropanethiol were also investigated. This initiating system also showed very high activity toward the polymerization of ?-caprolactone, excess isopropanethiol could be used as an effective chain transfer agent for this initiator. The first-order kinetic action was observed in the polymerization of ?-caprolactone.3. Lanthanide 4,6-dimethylpyrimidine-2-thionate complexes ( Ln = Pr; Nd; Sm; Eu) displayed excellent catalytic performances on cyclodimerization of isocyanates to produce substituted ureas (6, 7, 3a, 3c, 3d) via elimination of CO, which represents the first example of lanthanide thiolates exhibiting a high catalytic activity and a high selectivity on cyclodimerization of isocyanates. The solvents, temperatures, catalyst loading, and the rare earth metal effects on the catalytic activities of the complexes were examined.