New air stable cationic methallyl Ni complexes bearing imidoyl-indazole carboxylate ligand: Synthesis, characterization and their reactivity towards ethylene
Alan R. Cabreraa, d, , ,Ivan Martineza,
Constantin G. Daniliucb,
Griselda B. Gallandc,
Cristian O. Salasa,
Rene S. Rojasa,
a Nucleus Millennium of Chemical Processes and Catalysis, Faculty of Chemistry, Pontificia Universidad Católica de Chile, Casilla 306, Santiago, Chile
b Chemisches Institut der Universität Münster, Corrensstrasse 40, 48149 Münster, Germany
c Instituto de Química, Universidade Federal do Rio Grande do Sul, Porto Alegre, Brazil
d Universidad Bernardo O Higgins, Departamento de Ciencias Químicas y Biológicas, Laboratorio de Bionanotecnología, General Gana 1702, Santiago, Chile
Received 4 December 2015, Revised 23 December 2015, Accepted 27 December 2015, Available online 31 December 2015
Three new neutral N,N imidoyl-indazole ligands with a methoxycarbonyl functional group (1–3) and three new air-stable cationic methallyl nickel complexes (4–6) were prepared. These compounds were characterized by NMR, FT-IR and elemental analyses. In addition, compounds 1, 2, 3 and 4 were analyzed using X-ray diffraction. An evaluation of the reactivity of complexes 4–6 toward ethylene was conducted by using 5 equivalents of B(C6F5)3. At 1 bar of ethylene and 20 °C, only complexes 4 and 6 were able to produce butene, showing unusual air stability and dimerizing ethylene even after exposure to air for 48 h. By increasing the pressure to 12 bar at 20 °C, complex 6 showed a catalytic activity of 401 Kg product (mol Ni)−1 h−1, producing a low molecular weight polyethylene (26.6 Kg/mol) with almost exclusively methyl branches (2.3 mol%). By increasing the temperature to 60 °C at 12 bar of ethylene, the system 6/B(C6F5)3 increased its catalytic activity to 487 Kg product (mol Ni−1) h−1, but produced a significant decrease in the molecular weight of the polymer (1.8 Kg/mol) and a broad distribution of branches.
