Reactions of 2,2 '-methylenebis(4-chloro-6-isopropyl-3-methylphenol) with trimethylaluminum: Highly efficient catalysts for the ring-opening polymerization of lactones

The reaction of 2,2 ' -methylenebis(4-chloro-6-isopropyl-3-methylphenol) (M CIMP-H-2) with 1.2 molar equiv of AlMe3 in THF yields [(MCIMP)AlMe(THF)] (1 ), which further reacts with a stoichiometric amount of 2-propanol (IPA), a ffording the isopropoxy-bridged dimer [(MCIMPAl(mu -(OPr)-Pr-i)](2) (2). Co mpound 2 can also be obtained by the treatment of MCIMP-H-2 with a stoichio metric amount of Al((OPr)-Pr-i)(3) in refluxing toluene. However, the react ion of 1 with another 1 equiv of AlMe3 in CH2Cl2 furnishes [Me2Al(mu -MCIMP )AlMe2(THF)] (3), in which the MCIMP2- ligand is acting as a bridging ligan d. Further treatment of compound 3 with 2 molar equiv of 2-propanol results in the formation of the isopropoxy-bridged dinuclear aluminum complex [(MC IMP)Al(mu -(OPr)-Pr-i)(2)AlMe2] (4). Compound 4 can be directly obtained fr om the reaction of 1 with AlMe3 in the presence of 2-propanol. However, in the presence of a stoichiometric amount of H2O, hydrolysis of 1 in THF give s the trimeric aluminum compound [(MCIMP)Al(mu -(OHTHF)-T-. . .)](3) (5), i n which the hydroxy group acts as a chelating group bridging to two aluminu m atoms. Compounds 2 and 4 have shown excellent catalytic activity toward t he ring-opening polymerization of epsilon -caprolactone and delta -valerola ctone.