1350733-26-4Relevant articles and documents
Aluminum complexes of bidentate fluorinated alkoxy-imino ligands: Syntheses, structures, and use in ring-opening polymerization of cyclic esters
Bouyahyi, Miloud,Roisnel, Thierry,Carpentier, Jean-Francois
, p. 1458 - 1466 (2012/04/10)
The coordination chemistry of bidentate fluorinated alkoxy-imino ligands onto Al(III) centers has been studied. The proligands (CF3) 2C(OH)CH2C(R1)=N-R2 ({ON R1,R2}H; R1 = Me, Ph; R2 = Ph, CH 2Ph, cyclohexyl; 1a-d) react selectively with AlMe3 (0.5 or 1.0 equiv) and AlMe2(OiPr) or Al(OiPr)3 (0.5 equiv) to give the corresponding monoligand compounds {ONR1,R2}AlMe2 (2a-d) and the bis-ligand compounds {ONR1,R2}2AlMe (3a-d) and {ONR1,R2}2Al(OiPr) (4a-c). X-ray diffraction studies revealed that {ONPh,Bn}AlMe2 (2a), {ONMe,Bn} AlMe2 (2b), {ONMe,Bn}2AlMe (3b), {ON Ph,Ph}2AlMe (3c), {ONMe,Bn}2Al(OiPr) (4b), and {ONPh,Ph}2Al(OiPr) (4c) all adopt a mononuclear structure in the solid state; four-coordinate {ONR1,R2}AlMe 2 and five-coordinate {ONMe,Bn}2Al(OiPr) feature respectively distorted-tetrahedral and trigonal-bipyramidal geometries. The 1H, 13C{1H}, and 19F{ 1H} NMR data indicate that the structures observed in the solid state are retained in CD2Cl2 or C6D6 solution at room temperature. The binary systems {ONR1,R2}AlMe 2 (2)/BnOH and discrete {ONR1,R2}2Al(OiPr) (4) are effective catalysts for the controlled ROP of ε-caprolactone and rac-lactide, both in bulk molten monomer and in toluene solution/slurry. In contrast to the case for {ONRNO}Al(OiPr), having a bridged tetradentate fluorinated dialkoxy-diimino ligand that provides isotactic-enriched polylactides, the unbridged compounds {ONR1,R2} 2Al(OiPr) (4) produce atactic PLAs. The key element which appears to be at the origin of the absence of stereocontrol is the lack of bridge between the two imino-alkoxy moieties, possibly via a decrease in the rigidity of the compounds and/or a different positioning of N,O vs N,N heteroatoms in axial sites.
