Synthesis and Structural Characterization of Various N,O,N-Chelated Aluminum and Gallium Complexes for the Efficient ROP of Cyclic Esters and Carbonates: How Do Aluminum and Gallium Derivatives Compar

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• 作者：Fr茅d茅ric Hild ; Nirvana Neehaul ; Fr茅d茅ric Bier ; Morgane Wirsum ; Christophe Gourlaouen ; Samuel Dagorne
• 刊名：Organometallics
• 出版年：2013
• 出版时间：January 28, 2013
• 年：2013
• 卷：32
• 期：2
• 页码：587-598
• 全文大小：456K
• 年卷期：v.32,no.2(January 28, 2013)
• ISSN：1520-6041

文摘

The novel Al and Ga coordination compounds 4, 5, 7, and 8 of the type (NON)AlX (NON^{2鈥?/sup> = {RNC₆H₄}₂O2鈥?/sup>; 4, R = Cy, X = Me; 5, R = C₅H₉, X = OCH₂Ph; 7, R = C₆F₅, X = Me) and (NON)GaX (NON2鈥?/sup> = {R₂NHC₆H₄}₂O2鈥?/sup>; 8, R = C₆F₅, X = Me) have been synthesized via, in the case of 4, 7, and 8, a methane elimination reaction between the corresponding protio ligands (NON)H₂ and MMe₃ precursors (M = Al, Ga). The Al alkoxide derivative 5 was prepared via an alcoholysis reaction between 魏3-N,O,N-{(C₅H₉)NC₆H₄}₂O}₂AlNMe₂ and PhCH₂OH. The tetracoordinate Al鈥揟HF adduct 魏2-N,N鈥?/i>-{(C₅H₉)NC₆H₄}₂O}₂Al(Me)(THF) (6) was prepared via a methane elimination reaction between the protio ligand TfNONH₂ (Tf = CF₃SO₂, 1c) and AlMe₃ in a CH₂Cl₂/THF solvent mixture. As determined from X-ray studies, complexes 4, 7, and 8 are monomeric in the solid state and feature a central tetracoordinate metal center effectively 魏3-N,O,N鈥?/i> chelated and adopting a trigonal-monopyramidal geometry. The presence of Ga路路路F(o-C₆F₅) contacts in the solid-state structure of compound 8 are likely to reflect the Lewis acidity of the Ga center. The Al alkoxide derivative [魏3-N,O,N-{(C₅H₉)NC₆H₄}₂O}₂AlOCH₂Ph]₂ (5) was isolated as a dimer containing two five-coordinate (trigonal-pyramidal) Al centers and retains its dimeric structure in solution, while the Al鈥揟HF adduct 6 crystallizes in a monomeric form with an Al center in a tetrahedral geometry. The catalytic performances of the Al and Ga species 4, 5, 7, and 8 as ROP initiators of rac-lactide (rac-LA), 蔚-caprolactone (蔚-CL), and trimethylene carbonate (TMC) were estimated, and most of them efficiently mediate the controlled and immortal ROP of these three monomers in the presence of BnOH, such an alcohol acting as an effective chain transfer agent. Of particular interest, the Ga amido species 魏3-N,O,N-{(C₅H₉)NC₆H₄}₂O}₂Ga-NMe₂ (3) outperforms its Al counterpart 魏3-N,O,N-{(C₅H₉)NC₆H₄}₂O}₂AlNMe₂ (2) in the ROP of rac-LA, whether in terms of control or activity, to afford isotactically enriched PLA (P_m = 0.7). In contrast, all the Al derivatives are more efficient catalysts for the polymerization of 蔚-CL or TMC than the Ga analogues. For the ROP of TMC initiated by the Al and Ga complexes 2鈥?b>5, an increased Lewis acidity of the metal center is clearly beneficial to both the activity and the ROP control. Notably, the C₆F₅N Ga species 8 was found to be inactive in the ROP of rac-LA, 蔚-CL, and TMC, which may be related to both electronic (C鈥揊路路路Ga interactions) and steric factors.}