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Novel Lanthanide Amides Incorporating Neutral Pyrrole Ligand in a Constrained Geometry Architecture: Synthesis, Characterization, Reaction, and Catalytic Activity

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posted on 22.07.2013, 00:00 by Fenhua Wang, Shaowu Wang, Xiancui Zhu, Shuangliu Zhou, Hui Miao, Xiaoxia Gu, Yun Wei, Qingbing Yuan
The first series of lanthanide amido complexes incorporating a neutral pyrrole ligand in a constrained geometry architecture were synthesized, and their bonding, reactions, and catalytic activities were studied. Treatment of [(Me3Si)2N]3Ln­(μ-Cl)­Li­(THF)3 with 1 equiv of (N-C6H5NHCH2CH2)­(2,5-Me2C4H2N) (1) afforded the first example of bisamido lanthanide complexes having the neutral pyrrole η5-bonded to the metal formulated as [η51-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)]­Ln­[N­(SiMe3)2]2 (Ln = La (2) and Nd (3)). Reaction of [(Me3Si)2N]3Sm­(μ-Cl)­Li­(THF)3 with 2 equiv of 1 produced the complex [η51-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)]­[η1-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)]]­SmN­(SiMe3)2 (4). Treatment of 3 with 2 equiv of 1 gave the sandwich neodymium complex [η51-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)]2Nd­[η1-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)] (5), in which two neutral pyrroles bonded with metal in an η5 mode. Complex 5 could also be prepared by reaction of [(Me3Si)2N]3Nd­(μ-Cl)­Li­(THF)3 with 3 equiv of 1. Reactivities of the lanthanide bisamido complexes were further investigated. Reaction of complex 2 with pyrrolyl-functionalized imine [2-(2,6-iPr2C6H3NCH)­C4H3NH] afforded a mixed η5-bonded neutral pyrrole and η1-bonded anionic pyrrolyl lanthanum complex [η51-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)]­{η1-2-[(2,6-iPr2C6H3)­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 [η51-(N-C6H5NCH2CH2)­(2,5-Me2C4H2N)]­[(η1-2-tBuNCH)­C4H3N]2Ln (Ln = La (7), Nd (8)) with dehydrogenation of the secondary amine. Investigation of the catalytic properties of complexes 28 indicated that all complexes exhibited a high activity with a high chemo- and regioselectivity on the addition of dialkyl phosphite to α,β-unsaturated carbonyl derivatives. An interesting result was found that 1,2-hydrophosphonylation substrates could be catalytically converted to 1,4-hydrophosphinylation products when the substrates are the substituted benzylideneacetones by controlling the reaction conditions.