1172124-01-4Relevant academic research and scientific papers
Synthesis and structure of neutral and cationic aluminum complexes supported by bidentate O,P-phosphinophenolate ligands and their reactivity with propylene oxide and ε-caprolactone
Haddad, Mansour,Laghzaoui, Mohamed,Welter, Richard,Dagorne, Samuel
, p. 4584 - 4592 (2009/12/08)
The O,P-type phosphinophenol ligands 1a-c were found to readily react with 1 equiv of AlMe3 to afford in high yields the corresponding Al chelate complexes {η2-O,P-(2-PPh2-4-R′-6-R- C6H2O)}-AlMe2, 2a-c (R = Me, R′ = H, 2a; R = Ph, R′ = H, 2b; R = tBu, R′ = Me, 2c). The bis-adduct Al methyl complexes {η2-O,P-(2-PPh2-4-R′-6-R- C6H2O)}2AlMe (R = Ph, R′ = H, 3b; R = tBu, R′ = Me, 3c) also formed quantitatively upon reaction of phosphinophenols 1b,c with 0.5 equiv of AlMe3. Both the mono- and bis-adduct Al methyl species 2a-c and 3b,c are stable monomeric species whether in solution or in the solid state and remain stable in coordinating solvents such as thf. In contrast, the bis-adduct Al methyl complex 3c undergoes a ligand exchange reaction in the presence of an alcohol source (tPrOH, BnOH) to generate the homoleptic tris-adduct Al complex {η2-O,P-(2- PPh2-4-Me-6-tBu-C6H3O)} 3Al (5c), as determined from X-ray crystallographic studies. Both the mono- and bis-adduct Al methyl species 2b,c and 3b,c react fast with B(C 6F5)3 via a methide abstraction reaction to afford the stable and well-defined Al cationic species {η2-O,P- (2-PPh2-6-Ph-C6H3O)}Al(Me) (THF)+ (6b,c+) and {η2-O,P-(2-PPh2-4-R′-6-R- C6H3O)}2Al+ (7b,c+), respectively, which were found to be highly active in propylene oxide polymerization to afford atactic poly(propylene oxide). These cations also readily initiate the ring-opening polymerization of e-caprolactone via successive ring-opening insertions of the monomer into the Al-O phenoxide bond of the phosphinophenolate chelating ligand to exclusively afford linear poly(e-caprolactone) capped, at the ester end, with a (phosphino oxide)phenolate group, as deduced from NMR and MALDI-TOF data. In these cationic systems, the PO- chelating moiety may thus act as both a supporting ligand and an initiating group for the ROP of ε-CL.
