The O,P-type phosphinophenol ligands 1a-c were found to readily react with 1 equiv of AlMe 3 to afford in high yields the corresponding Al chelate complexes {η 2 3c) also formed quantitatively upon reaction of phosphinophenols 1b,c with 0.5 equiv of AlMe 3 . 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 ( i PrOH, BnOH) to generate the homoleptic tris-adduct Al complex {η 2 -O,P-(2-PPh 2 -4-Me-6-t Bu-C 6 H 3 O)} 3 Al (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 6 F 5 ) 3 via a methide abstraction reaction to afford the stable and well-defined Al cationic species {η 2 -O,P-( 2, 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 ε-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(ε-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 POchelating moiety may thus act as both a supporting ligand and an initiating group for the ROP of ε-CL.

No abstract

No abstract

No abstract