Synthesis, Structures And Reactivity Of Aminopyrrolyl Alkali-metal Compounds

Aminopyrrolyl metal compounds exhibited high catalytic activities toward olefin polymerization, ring-opening polymerization of lactide and ε-caprolatone by virtue of its strong metal-ligand bonds and exceptional tunable steric and electronic features required for compensating coordinative unsaturation of metal centers. Recently, many examples of organometallic complexes containing pyrrolyl ligands have been synthesized and applied to varied reactions as catalysts. But alkali-metal aminopyrrolyl compounds have rarely been isolated from reaction solution and poorly characterized in the solid state, let alone concerns their structural features because they are generally prepared and employed in situ as metal transfer reagents. However, structure elucidation is a crucial part of the understanding of reactivities and reaction mechanisms and for selective and specific applications in organolithium chemistry. Herein, the series of lithium compounds containing substituted pyrrolyl ligands were synthesized and characterized by satisfactory C, H, and N microanalysis,1H,13C{1H}, and 7Li NMR spectra, and single crystal X-ray structural data. The relativity between their structural features and catalytic organic reactions for the cyclotrimerization of isocyanate, the amidation reaction of aldehydes with amines and Tishchenko reaction has been investigated. The results will provide a greater understanding of the mechanisms involved in activation of small molecules and catalytic organic reactions and may contribute to further advances in this area. The main research contents are described as follows.1. Six animopyrrolyl ligands and their lithium compounds were synthesized and were characterized by satisfactory C, H, and N microanalysis, 1H,13C{1H} NMR spectra in C6D6 at ambient temperature, and single crystal X-ray structural data. All lithium compounds show high catalytic activities for the cyclotrimerization of isocyanate to corresponding isocyanurate. Among them, compound 2a exhibited the highest activities and selectivities in the cyclotrimerization reaction. The reaction can proceeded almost quantitatively in Et2O for 30 min at room temperature in the presence of 0.1% mol loading.2. Five dilithium compounds containing bidentate dianionic pyrrolyl ligands, [{2-(CH3NCH2)C4H3N}Li2(TMEDA)3] (3a),{[μ-η5-2-[CH3CH2NCH 2]C4H3N]Li2(TMEDA)}2 (3b),{[μ-η1-2-[(CH3)3NCH2]C4H3N]Li1(TME DA)}2 (3c),{[η5-2-[(CH3)2CHNCH2]C4H3N]Li2(TMEDA)}2 (3d), and {[η5-2-[(CH2)5CHNCH2]C4H3N]Li2(TMEDA)}2 (3e), were synthesized and characterized by satisfactory C, H, and N microanalysis,1H,13C{1H}, and 7Li NMR spectra in C6D6 at ambient temperature, and single crystal X-ray structural data. The X-ray diffraction analysis indicated that the compounds exhibited structural diversity with different substituents.The catalytic results indicate the compound 3a shows the highest activities in Tishchenko reaction as the catalyst at 2% mol loading in solvent-free condition under 70℃. And the best result of amidation reactions of aldehydes with amines was obtained when diethyl ether was employed as solvent in the presence of 10% mol of compound 3c at room temperature.3. We demonstrated a simple and efficient method for synthesis of 2 or 5-substituted benzoylpyrrole derivatives by alkali metallised pyrrole with benzaldehydes using 2,6-dimethylaniline as additive. This method shows good functional group tolerance and the C-C bond is formed simultaneously to afford these benzoylpyrrole derivatives in moderate to good yields. The traditional synthetic protocols involving uncommonly used acylated reagents or unbenign reaction conditions, such as highly toxic acyl chloride and halogenated solvents, was avoided. It represents a promising protocol for organic synthesis and industrial applications.