Synthesis, Structure And Reactivity Of Rare-Earth Metal Amido And Alkyl Complexes Incorporating Neutral Pyrrole Ligands

This thesis focuses on the synthesis, structure and catalytic reactivity of rare-earth complexes incorporating neutral pyrrole ligand and consists of three parts:synthesis, reactivity and catalytic activity of novel lanthanide amides incorporating neutral pyrrole ligand in a constrained geometry architecture for the addition of dialkyl phosphite to a,β-unsaturated carbonyl derivatives; synthesis, reactivity and catalytic activity of lanthanide amides incorporating bridged neutral bispyrrole ligand for the cyanosilylation of ketones; synthesis of rare-earth alkyl complexes supported by a bridged neutral bis(pyrrole) ligand.1. Synthesis, reaction and catalytic activity of novel lanthanide amides incorporating neutral pyrrole ligand in a constrained geometry architecture for addition of dialkyl phosphite to a,β-unsaturated carbonyl derivatives.Reactions of rare-earth metal [(Me3Si)2N]3RE(μ-Cl)Li(THF)3] with 1 equiv of (N-C6H5NHCH2CH2)(2,5-Me2C4H2N) (1) produced bisamido lanthanide complexes with a neutral pyrrole η5-bonded to the metal formulated as [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]RE[N(SiMe3)2]2 (RE= La (2) and Nd (3)). Reaction of [(Me3Si)2N]3Sm(μ-Cl)Li(THF)3 with 2 equiv of 1 produced the complex [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)][η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]] SmN(SiMe3)2 (4) with two ligands. Reactivities of the constrained geometry lanthanide bisamido complexes incorporating neutral pyrrole were investigated. Treatment of 3 with 2 equiv of 1 gave a novel neodymium complex [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2c4H2N)]Nd[η2:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H 2N)][η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)] (5), in which the three neutral pyrroles were bonded to the metal in different modes. Reaction of complex 2 with pyrrolyl-functionalized imine [2-(2,6-’Pr2C6H3N=CH)C4H3NH] afforded a mixed η5-bonded neutral pyrrole and η1-bonded anionic pyrrolyl lanthanum complex [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)]{η1-2-[(2,6-’Pr2C6H3)NCH]C4H3N}La[N( SiMe3)2] (6). Reactions of complexes 2 and 3 with pyrrolyl-functionalized secondary amine afforded the mixed η5-bonded neutral pyrrole and the η1-bonded anionic pyrrolyl lanthanide complexes [η5:η1-(N-C6H5NCH2CH2)(2,5-Me2C4H2N)][(η1-2-’BuNCH)C4H3N]2RE (RE=La (7), Nd (8)) with the dehydrogenation of the secondary amine, observed and comfirmed by NMR and X-ray analysis results.Reactions of (N-C6H5NHCH2CH2)(2,5-Me2C4H2N) (1) with heavy rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3] (RE=Dy, Er, Y, Yb) were also investigated. Reaction of [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 with 3 equiv of 1 produced the complexes (η5:η1-[N-C6HSNCH2CH2(2,5-Me2C4H2N)]}RE{η1-[N-C6HSNCH2CH2(2,5-Me2C4H2 N)]}2[N(TMS)2] (RE= Dy (11), Er (12), Y (13), Yb (14)) in a constrained geometry architecture. Complexes 11-14 contain three neutral pyrrole ligands, one neutral pyrrole ligand coordinated to rare-earth metal in an η5:η1 mode, the other two neutral pyrrole ligands served as amido ligands.The catalytic activities of neutral pyrrole supported rare-earth complexes in the reaction of diethyl phosphite and a,β-unsaturated carbonyl derivatives were investigated. These results indicated that these complexes have a high catalytic activities and high regioselectivity for this type of reaction. The substrates of a,β-unsaturated carbonyl compounds can effect the regioselectivity of this addition reaction. This catalytic reaction regioselectively provided only 1,4-addition products for chalcones, α,β-unsaturated esters, amide, and 2-cyclopenten-l-one, and 1,2-addition for α,β-unsaturated aldehydes and 2-cyclohexen-l-one. It is interesting that the reaction conditions also have a great effect on the regioselectivity of this catalytic addition of diethyl phosphite to substituted benzylideneacetones, and the 1,2-addition products could be transferred to the 1,4-addition products in the presence of the neutral pyrrole supported lanthanide amides as catalysts.2. Synthesis, reactivity and catalytic activity of lanthanide amides incorporating bridged neutral bis(pyrrole) ligand for cyanosilylation of ketones.Reactions of [(2,5-Me2C4H2N)CH2CH2]2NH (15) with [(Me3Si)2N]3RE(μ-Cl)Li(THF)3 afforded the corresponding lanthanide amides having one neutral pyrrole η5-bonded to the metal formulated as [η5:η1-(2,5-Me2C4H2N)CH2CH2]2NRE[N(SiMe3)2]2 (RE= La (16), Nd (17)). Reactivities of complexes 16 and 17 were investigated. Treatment of 16 or 17 with N,N’-dicyclohexylcarbodiimide (CyN=C=NCy) gave carbodiimide selectively insertion into the appended RE-N bond product formulated as CyNC{[N, N-(2,5-Me2C4H2N)CH2CH2]2N}NCyRE[N(SiMe3)2]2 (RE= La (18), Nd (19)). Reaction of heavy rare-earth metal amides [(Me3Si)2N]3RE(μ-Cl)Li(THF)3] (RE= Er, Y, Yb) with 2 equiv of [(2,5-Me2C4H2N)CH2CH2]2NH (15) produced the complexes formulated as [η5:η1-(2,5-Me2C4H2NCH2CH2)2N][η1-(2,5-Me2C4H2NCH2CH2)2N]REN(SiMe3)2 (RE= Er (20), Y (21), Yb (22)) in a constrained geometry architecture. Complexes 20-22 contains one N(SiMe3)2, one ligand coordinated to rare-earth metal η5:η1 modes, another ligand served as an amido ligand in η1 mode.The lanthanide amido complexes 16,17,20-22 as catalysts for the cyanosilylation of ketones were investigated. Results showed that complexes 16 and 17 exhibited a high catalytic activity for the cyanosilylation of ketones with an employment of a low catalyst loadings (0.1 mol%), and a good compatibility with a wide range of substrates, solvent-free conditions and under room temperature. It provides a direct, atom economic way for the preparation of cyanohydrinsilylethers. In order to furtherly study the mechanism of the catalytic reaction, The stoichiometric reactions of lanthanide amides 16 or 17 with Me3SiCN were performed, from which the novel trinuclear lanthanum and neodymium complexes {(η5:η1-[(2,5-Me2C4H2NCH2CH2)2N]RE[N(SiMe3)2](μ-CN)}3 (RE= La (25), Nd (26)). These complexes 25 and 26 represent the first example of compounds through σ-bond metathesis reaction between the La-N [(N(SiMe3)2] and Si-C of Me3SiCN on addition of Me3SiCN to ketones. It was also the first example of rare earth complexes containing neutral pyrrole ligand and CN group. Kinetic study and’H NMR. probe of the catalytic reaction indicated that they might be the key intermediates in the catalytic cycle of the cyanosilylation of ketones. It was the first application of rare earth organic complexes as catalysts for cyanosilylation of ketones.3. Synthesis of rare-earth alkyl complexes supported by bridged neutral bis(pyrrole) ligand.Reactions of [(2,5-Me2C4H2N)CH2CH2]2NH (15) with alkyl reare-earth metal complexes RE(CH2SiMe3)3(thf)3 at room temperature afforded the corresponding alkyl rare-earth complexes formulated as [η1-(2,5-Me2C4H2N)CH2CH2]2NRE(CH2SiMe3)2(thf)2 (RE=Y(27), Yb, (28), Er (29)). X-ray analyses revealed that neutral pyrrole didn’t bond with rare-earth metal. Heating the hexane solution of 27,28 or 29 to 50℃ for 4 h, gave the corresponding new alkyl complexes removal of THF [η5:η1-(2,5-Me2C4H2N)CH2CH2]NRE(CH2SiMe3)2(RE= Y (30), Yb, (31), Er (32)), in which one neutral pyrrole bonded with metal in an η5 mode. This is the first example of alkyl complexes containing neutral pyrrole ligand.