Steric Effect Of The Amido Ligand On The Synthesis, Structures And Reactivity Of Lanthanide Amides

The steric effect of amido ligands on the synthesis, structures and reactivity of the lanthanide amide complexes were studied by use of the two kinds of amido ligands, bridged diamido ([Me2Si(NPh)2]2- and [o-(Me3SiN)2C6H4]2-) and unbridged monoamido ((C6H5)(SiMe3)N- and (C6H3-iPr2-2,6)(SiMe3)N-). The main results obtained in this thesis are as follows.1. The reactions of PhLiNSiMe2NLiPh and Li2-o-(Me3SiN)2C6H4 with YbCl3 in 1:1 molar ratio, respectively, afforded three lanthanide chlorides, {[Me2Si(NPh)2]YbCl(TMEDA)}2·3C7H8 (1), [o-(Me3SiN)2C6H4]Yb(THF)2Cl2Li(TMEDA)·THF·0.5C6H12 (2) and {[o-(Me3SiN)2C6H4]Yb(THF)Cl2Li(DME)}2·2THF·C7H8 (3). The effect of the diamido ligand on structure of lanthanide(III) chlorides was observed.2. The reactions of PhLiNSiMe2NLiPh / Li2-o-(Me3SiN)2C6H4, LnCl3 and Cp'Na (Cp'= C5H5, MeC5H4) in 1:1:2 molar ratio afforded six new anionic complexes, {[Me2Si(NPh)2]LnCp'2}{Li(DME)3} [Cp'= C5H5, Ln = Yb (4); Sm (5); Cp'= MeC5H4, Ln = Yb (6)] and {[o-(Me3SiN)2C6H4]Ln(MeC5H4)2}{Li(DME)3} [Ln = Yb (7), Sm (8), Nd (9)]. These anionic complexes were found to be efficient single-component initiators for the polymerization of MMA at r.t.. The polymerization gave the syndiotactic rich polymers. The ligand and center metal exhibit a great influence on the catalytic activity, the active order is [o-(Me3SiN)2C6H4]2- > [Me2Si(NPh)2]2- and Yb > Sm > Nd. Among them, 7 shows the highest activity. Moreover, the polymerization of MMA initiated by 7 has"living character"at -40°C. The polymerization was supposed to proceed by anionic mechanism.3. The reaction of PhLiNSiMe2NLiPh, LnCl3 and NaN(SiMe3)2 in 1:1:2 molar ratio afforded the complex {[Me2Si(PhN)2]2Yb(THF)2}{Li(THF)} (10), while the reaction of Li2-o-(Me3SiN)2C6H4, YbCl3 and NaN(SiMe3)2 in 1:1:2 molar ratio yielded the complex [o-(Me3SiN)2C6H4]Yb[N(SiMe3)2]Li(THF) (11). It showed the amido ligand exhibits great influence on the structure of the product.4. Reduction reaction of 3 with Na-K alloy gave a ytterbium(II) cluster [o-(Me3SiN)2C6H4]5Yb6Li4Cl6(DME)4·6C7H8 (13), which was formed via both Ln-N and Ln-Cl bond cleavages. Reduction reactions of 2 formed in situ by Na-K alloy yielded another ytterbium(II) cluster [o-(Me3SiN)2C6H4]2[o-(Me3SiN)(Me2SiN)C6H4]2Yb3(THF)2Cl2Li2(TMEDA)2·2C7H8 (14).5. The metathesis reactions of LnCl3 with LiN(C6H5)(SiMe3) and LiN(C6H3-iPr2-2,6)(SiMe3) in 1:2 molar ratio, respectively, afforded three bisamide lanthanide(III) chlorides {[(C6H5)(Me3Si)N]2YbCl(THF)}2·C7H8 (16), [(C6H3-iPr2-2,6)(SiMe3)N]2YbCl(μ-Cl)Li(THF)3?PhCH3 (17) and [(C6H3-iPr2-2,6)(SiMe3)N]2SmCl3Li2(THF)4 (18). The metathesis reactions of LnCl3 with LiN(C6H5)(SiMe3) and LiN(C6H3-iPr2-2,6)(SiMe3) in 1:1 molar ratio, respectively, afforded two monoamide lanthanide(III) chlorides [(C6H3-iPr2-2,6)(SiMe3)N]YbCl2(THF)3 (19) and {[(C6H3-iPr2-2,6)(SiMe3)N]Sm(THF)Cl3Li(THF)}2 (20). The effect of the center metal and amido ligand on the structure of lanthanide(III) chlorides was observed.6. Reduction reactions of trivalent bisamide lanthanide chlorides by Na-K alloy were studied. Great influence of the center metal and amido ligand on the products was observed. The reduction reaction of 16 with Na-K alloy afforded a bisamide ytterbium(II) complex {[(C6H5)(Me3Si)N]2Yb(DME)2} (21) via Yb-Cl bond cleavage. The reduction reaction of ytterbium chloride 17 with bulky amide ligand afforded a monoamide chloride {[(C6H3-iPr2-2,6)(SiMe3)N]Yb(μ-Cl)(THF)2}2 (22) via the cleavage of Yb-N bond. However the bisamide samarium(II) complexes can be obtained by reduction reaction, using the less bulky amido (C6H5)(SiMe3)N- or bulky amido (C6H3-iPr2-2,6)(SiMe3)N- as ligand. This is the first example for the steric effect of amido ligand and central metal on the outcome of reduction reaction in lanthanide(II) chemistry. Complex 22, which is the first example of ytterbium(II) amide chloride, can also be synthesized by the Na/K alloy reduction reaction of 19.7. The reactions of lanthanide(II) complexes with carbodiimides were studied. The reaction of Sm[N(SiMe3)2]2(THF)2 with CyN=C=NCy gave the trivalent lanthanide diamidine complex [(Me3Si)2N)]2Sm[μ-η2-(CyN)2-C-C-(NCy)2-η2-μ]Sm[N(SiMe3)2)]2 (26), while Yb(NPh2)2(THF)4 and 22 didn't react with carbodiimides.8. The lanthanide(II) complexes supported by monoamido ligands, {[(C6H5)(Me3Si)N]2Yb(DME)2} (21), [(C6H3-iPr2-2,6)(SiMe3)N]2Sm(THF)2 (23), {[Ph(Me3Si)N]2Sm(DME)2 (24) and [(C6H3-iPr2-2,6)(SiMe3)N]2Yb(THF)2 (25) were found to be efficient single-component initiators for the polymerization of methyl methacrylate (MMA). The systems yielded syndiotactic rich polymers. The polymerization systems of MMA initiated by 23 and 25 at -40°C have"living character". The center metal and ligand exhibit a great influence on the catalytic activity with the active order of Yb > Sm and (C6H3-iPr2-2,6)(SiMe3)N- > (C6H5)(SiMe3)N-.9. The lanthanide(II) complexes supported by monoamido ligands, {[(C6H5)(Me3Si)N]2Yb(DME)2} (21), [(C6H3-iPr2-2,6)(SiMe3)N]2Sm(THF)2 (23), {[Ph(Me3Si)N]2Sm(DME)2 (24) and [(C6H3-iPr2-2,6)(SiMe3)N]2Yb(THF)2 (25) were found to be efficient single-component initiators for the polymerization ofε-CL. Their catalytic activity are much higher than those of lanthanide(II) complexes reported previously. The center metal and ligand exhibit a great influence on the catalytic activity with the active order of Sm > Yb , (C6H5)(SiMe3)N- > (C6H3-iPr2-2,6)(SiMe3)N-.