Reactivity studies on lanthanum and cerium hydrido metallocenes.

Alkyl complexes [η5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) (Ln = La 1 and Ce 2) react with 9-borabicyclo[3.3.1]nonane (9-BBN) in THF to afford the lanthanum boroxide complex [η5-1,3-(Me3C)2C5H3]2La(µ-OBC8H14)(THF) (3) and cerium boroxide complex [η5-1,3-(Me3C)2C5H3]2Ce(µ-OBC8H14)(THF) (4). However, the reaction of alkyl complexes [η5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) with cyclohexene oxide followed by the addition of 9-BBN resulted in the formation of ring-opened products [η5-1,3-(Me3C)2C5H3]2Ln(OC6H11)(THF) (Ln = La 5 and Ce 6) concomitant with C8H14BCH2C6H4N(CH3)2 release, indicating that lanthanum and cerium hydride complexes formed in situ by treating alkyl complexes with 9-BBN may be the reactive species. Therefore, further studies on the reactivity of lanthanum and cerium hydride complexes generated in situ were carried out. The reaction of lanthanum and cerium hydride complexes with Me3SiCl provided lanthanide chloride complexes [η5-1,3-(Me3C)2C5H3]2LnCl (Ln = La 7and Ce 8) as well as Me3SiH. Each lanthanide hydride complex reduces phenazine and white phosphorus to produce {[η5-1,3-(Me3C)2C5H3]2Ln}2(µ-η3:η3-C12H8N2) (Ln = La 9 and Ce 10) and {[η5-1,3-Me3C)2C5H3]2Ln}3P7 (Ln = La 11 and Ce 12), respectively. All the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses.

Cerocene and Lanthanocene Chalcogenides: Synthesis, Structure, and Luminescence.

A series of lanthanide chalcogenides {[η5-1,3-(Me3C)2C5H3]2Ln}2(µ-η2:η2-Te2) (Ln = Ce 1, La 2), {[η5-1,3-(Me3C)2C5H3]2Ln(THF)}2(µ-Se) (Ln = Ce 3, La 4), and {[η5-1,3-(Me3C)2C5H3]2Ln(THF)}2(µ-Te) (Ln = Ce 5, La 6) can be readily obtained by the reaction of the alkyl complexes [η5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) with elemental selenium or tellurium in the presence of 9-borabicyclo[3.3.1]nonane (9-BBN). The reaction of the alkyl complexes [η5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) with 9-BBN in 1:2 molar ratio afforded the lanthanide (cyclooctane-1,5-diyl)dihydroborate complexes [η5-1,3-(Me3C)2C5H3]2Ln[(µ-H)2BC8H14] (Ln = Ce 7, La 8) concomitant with the (Me2N-o-C6H4CH2)BC8H14 release, indicating that [η5-1,3-(Me3C)2C5H3]2LnH may be the reactive species for the synthesis of lanthanide chalcogenides. All the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses. Luminescence spectroscopy was also employed to characterize complexes 1-6. The Ce(III) complexes 3 and 5 display distinct luminescence properties at room temperature, as compared to the corresponding La(III) complexes 4 and 6. The complex {[η5-1,3-(Me3C)2C5H3]2Ce(THF)}2(µ-Te) (5) exhibits unexpectedly red emission in solution which is found to depend strongly on the excitation wavelength.

Lanthanocene and Cerocene Alkyl Complexes: Synthesis, Structure, and Reactivity Studies.

Lanthanocene and cerocene alkyl complexes [η5-1,3-(Me3C)2C5H3]2Ln(CH2C6H4-o-NMe2) (Ln = La 3 and Ce 4) were obtained from the salt metathesis of {[η5-1,3-(Me3C)2C5H3]2Ln(µ3-κ3-O3SCF3)2K(THF)2}2·THF (Ln = La 1·THF and Ce 2·THF) with LiCH2C6H4-o-NMe2. Reactivity of 3 and 4 toward various small molecules provides access to a series of lanthanide derivatives. For example, reactions of 3 and 4 with elemental chalcogens (sulfur and selenium) in 1:1 molar ratio give the lanthanide thiolates {[η5-1,3-(Me3C)2C5H3]2Ln(µ-SCH2C6H4-o-NMe2)}2 (Ln = La 5 and Ce 6) and selenolates {[η5-1,3-(Me3C)2C5H3]2Ln(µ-SeCH2C6H4-o-NMe2)}2 (Ln = La 7 and Ce 8). The compounds 3 and 4 react with two equivalents of elemental chalcogens (sulfur and selenium) to afford the lanthanide disulfides {[η5-1,3-(Me3C)2C5H3]2Ln}2(µ-η2:η2-S2) (Ln = La 9 and Ce 10) and diselenides {[η5-1,3-(Me3C)2C5H3]2Ln}2(µ-η2:η2-Se2) (Ln = La 11 and Ce 12). The lanthanide disulfides (9 and 10) or diselenides (11 and 12) can also be readily obtained through oxidation of the corresponding lanthanide thiolates (5 and 6) or selenolates (7 and 8) by elemental chalcogens concomitant with the (Me2N-o-C6H4CH2)2E2 (E = S or Se) release. Treatment of 3 and 4 with one equivalent or two equivalents of benzonitrile produces the serendipitous lanthanum and cerium-1-azaallyl complexes [η5-1,3-(Me3C)2C5H3]2Ln[N(H)C(Ph)═CHC6H4-o-NMe2] (Ln = La 13 and Ce 14) or amidine complexes [η5-1,3-(Me3C)2C5H3]2Ln[N(H)C(Ph)NC(Ph)═CHC6H4-o-NMe2]·C7H8 (Ln = La 15·C7H8 and Ce 16·C7H8), respectively. The compound 15 or 16 can also be readily synthesized by further insertion of one benzonitrile molecule into the 1-azaallyl complex 13 or 14. Insertion of N,N'-dicyclohexylcarbodiimide or phenyl isothiocyanate into Ln-C bonds within 3 and 4 results in the formation of the amidine complexes [η5-1,3-(Me3C)2C5H3]2Ln[CyNC(CH2C6H4-o-NMe2)NCy] (Cy = cyclohexyl, Ln = La 17 and Ce 18) or thioamidato complexes [η5-1,3-(Me3C)2C5H3]2Ln[SC(CH2C6H4-o-NMe2)NPh] (Ln = La 19 and Ce 20). All of the new compounds were characterized by various spectroscopic methods, and their solid-state structures were further confirmed by single-crystal X-ray diffraction analyses.

Preparation Methods and Antioxidant Activities of Polysaccharides and Their Derivatives.

BACKGROUND: In recent years, the antioxidant effects of polysaccharides have become a hot spot in the field of polysaccharide research. METHOD: Herein, the action mechanisms of polysaccharide antioxidation and scavenging free radicals were analyzed. The research progresses on the preparation methods and antioxidant properties of polysaccharides and their derivatives were summarized. CONCLUSION: Investigating the antioxidant activities of polysaccharides and their derivatives can find useful polysaccharides and their derivatives, which have great potential as natural antioxidants used in functional foods or medicines.