RESUMO
2,6-Bis(3,5-dimethylpyrazoylmethyl)-4-methylphenol LH was readily synthesized by the reaction between 2,6-bis[(dimethylamino)methyl]-4-methylphenol and 3,5-dimethylpyrazole. The X-ray structure of the trisodium complex of LH showed the benzene-like planar Na3O3 ring with alternative shorter (2.181-2.185 Å) and longer (2.244-2.263 Å) bonds. The reaction of anionic ligand L with [PdCl2(COD)] yielded three Pd(II) complexes: [Pd{OC6H2(CH2PzMe2)2-2,6-Me-4-κ N, O}2] (1), [PdCl{µ-OC6H2(CH2PzMe2)2-2,6-Me-4-κ N, O, N}]2 (2), and [PdCl2{µ-OC6H2(CH2PzMe2)2-2,6-Me-4-κ N, O, N}2Pd] (3) (PzMe2 = 3,5-dimethylpyrazole). Conversely, the neutral ligand LH reacts with [PdCl2(PhCN)2] to give the 20-membered palladacycle, [Pd2Cl4{µ-HOC6H2(CH2PzMe2)2-2,6-Me-4-κ N, N}2] (4). 2 and 3 are structural isomers and rigid molecules, whereas 1 and 4 are fluxional, as shown by their 1H NMR spectra. Hence, the dynamic behaviors of 1 and 4 were studied by variable-temperature 1H NMR methods and are proposed to be interconversion processes: cis-trans for 1 and two chiral enantiomers for 4. The structures of all complexes were determined by single crystal X-ray diffraction methods, which showed the presence of two different conformations of LH (trans and semitrans) bound to metal atoms. In addition, complexes 2-4 were found to be excellent precatalysts for the vinyl polymerization of norbornene in the presence of varying amount of MMAO and EtAlCl2 in toluene or CH2Cl2.Within a short period of time (1 min), almost all monomers are changed to polymers with one micromole of precatalyst. The optimized conditions of 1000 molar excess of MMAO gave 1.20 × 108 g PNB mol-1 h-1 at room temperature. These addition polymers are completely insoluble in several organic solvents and hence were only characterized by 1H, IR, powder XRD, and TGA methods.
