Influence of Schiff base and lanthanide metals on the synthesis, stability, and reactivity of monoamido lanthanide complexes bearing two Schiff bases.

The monoamido lanthanide complexes stabilized by Schiff base ligand L(2)LnN(TMS)(2) (L = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-8-C(9)H(6)N, Ln = Yb (1), Y (2), Eu (3), Nd (4), and La (5)) were synthesized in good yields by the reactions of Ln[N(TMS)(2)](3) with 1.8 equiv of HL in hexane at room temperature. It was found that the stability of 1-5 depends greatly on the size of the lanthanide metals with the increasing trend of Yb ≈ Y < Nd < La. The amine elimination of Ln[N(TMS)(2)](3) with the bulky bidentate Schiff base HL' (L' = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-2,6-Pr(i)(2)-C(6)H(3)) afforded the monoamido lanthanide complexes L'(2)LnN(TMS)(2) (Ln = Yb (9), Y (10), Nd (11), and La (12)). While the amine elimination with the less bulky Schiff base HL'' (L'' = 3,5-Bu(t)(2)-2-(O)-C(6)H(2)CH═N-2,6-Me(2)-C(6)H(3)) yielded the desired monoamido complexes with the small metals of Y and Yb, L''(2)LnN(TMS)(2) (Ln = Yb (13) and Y (14)), and the more stable tris-Schiff base complexes with the large metals of La and Nd, yielded L''(3)Ln as the only product. Complexes 1-14 were fully characterized including X-ray crystal structural analysis. Complexes 1-5, 10, and 14 can serve as the efficient catalysts for addition of amines to carbodiimides, and the catalytic activity is greatly affected by the lanthanide metals with the active sequence of Yb < Y < Eu ≈ Nd ≈ La.

[Determination of trace germanium in coal by spectrophotometry with 2,4-dichlorophenylfluorone].

A method for the determination of germanium in coal samples by spectrophotometry has been developed. The color reaction of germanium with 2,4-dichlorophenylfluorone (2,4-DCIPF) in the presence of cetyltrimethylammonium bromide (CTMAB) has been studied. The results show that Ge(IV) reacts on 2,4-DCIPF and CTMAB to form a multicomponent complex in a 1.8-2.5 mol x L(-1) H2SO4 medium. The complex has the maximum absorption wavelength at 516 nm and its apparent molar absorptivity epsilon is 1.38 x 10(5) L x mol(-1) x cm(-1). Beer's law is obeyed in the range of 0-12.5 microg x (25 mL)(-1) for Ge(IV). The recovery of standard addition is 103%-106% and the relative standard deviation (RSD) is 1.1%-1.7%. This method has been applied to the determination of Ge(IV) in coal samples with satisfactory results.

Migration of amide to imine group of lanthanide Schiff base complexes: effect of amido group.

The protonolysis of anionic lanthanide amide complexes (THF)LiLn(NPri2)4 with two equiv. of tridentate Schiff base HL (L=3,5-But(2)-2-O-C6H2CH=N-C5H4N) afforded the unanticipated products LiL'2Ln(THF) (L'=3,5-But(2)-2-O-C6H2CH(NPri2)-N-C5H4N; Ln=Y 1, Sm 2 and Yb 3) formed by intramolecular nucleophilic attack of the amide groups at the imine carbon atoms of the original ligand, L. The protonolysis is greatly affected by the amide group. When amine elimination was carried out with a mixture of Ln[N(TMS)2]3(micro-Cl)Li(THF)3 (TMS=SiMe3) and LiN(TMS)2, the expected lanthanide amide complexes with two Schiff base ligands, L2Ln[N(TMS)2] (Ln=Sm 4 and Nd 5), were isolated and no migration of the N(TMS)2 group was observed because of steric hindrance. Complexes 1-5 were well characterized including X-ray structural analyses.