Ethylene oligomerization promoted by chromium complexes bearing pyrrolide-imine-amine/ether tridentate ligands.
Chromium(iii) complexes [CrCl2(L)(THF)] based on monoanionic tridentate ligands [, L = {2-(C4H3N-2'-CH[double bond, length as m-dash]N)C2H4NHPh}; , L = {5-tert-butyl-2-(C4H2N-2'-CH[double bond, length as m-dash]N)C2H3NHPh}; , L = {2-(C4H3N-2'-CH[double bond, length as m-dash]N)C2H4OPh}] have been prepared. Complexes and were converted into the monomeric acetonitrile adducts [CrCl2(L)(NCMe)] [, L = {2-(C4H3N-2'-CH[double bond, length as m-dash]N)C2H4NHPh}; , L = {5-tert-butyl-2-(C4H2N-2'-CH[double bond, length as m-dash]N)C2H3NHPh}] by reaction with acetonitrile at room temperature. All Cr complexes were characterized by IR spectroscopy, elemental analysis, magnetochemistry for , and by X-ray crystallography for and . Upon activation with methylaluminoxane (MAO), chromium precatalysts and showed good activity in ethylene oligomerization (TOF = 47.0-57.0 × 10(3) (mol ethylene)(mol Cr)(-1) h(-1) at 80 °C), producing mostly oligomers (93.0-95.6 wt% of total products). On the other hand, under identical oligomerization conditions, /MAO behaved as a polymerization catalyst generating predominantly polyethylene (73.0 wt%). However, the catalytic behavior of the precatalyst can be adjusted by varying the MAO-to-Cr ratio. Thus, the use of 500 equiv. causes a dramatic shift from polymerization to ethylene oligomerization, eventually producing mainly lighter α-olefin fractions [α-C4 (68.7 wt%) and α-C6 (19.2 wt%)]. A further increase in the amount of MAO (1000 equiv.) leads to a more balanced distribution of oligomers, with a drastic decrease in the α-C4 and increase in the α-C8 fractions.
Laboratory of Molecular Catalysis, Instituto de Química, Universidade Federal do Rio Grande do Sul, Avenida Bento Gonçalves, 9500, RS, 90501-970, Brazil. osvaldo.casagrande@ufrgs.br.
A C
AC
Pinheiro
T
T
Roisnel
E
E
Kirillov
J-F
JF
Carpentier
Osvaldo L
OL
Casagrande
D000588:Amines / Q000737:chemistry; D002857:Chromium / Q000737:chemistry; D004987:Ethers / Q000737:chemistry; D005030:Ethylenes / Q000737:chemistry*; D007097:Imines / Q000737:chemistry; D008024:Ligands; D008958:Models, Molecular; D015394:Molecular Structure; D009942:Organometallic Compounds / Q000138:chemical synthesis / Q000737:chemistry*; D011758:Pyrroles / Q000737:chemistry
D000588:Amines; D004987:Ethers; D005030:Ethylenes; D007097:Imines; D008024:Ligands; D009942:Organometallic Compounds; D011758:Pyrroles; D002857:Chromium; C036216:ethylene