Ethylene Oligomerization Study Bearing Nickel (II) and Cobalt (II) Complexes with N, O‐Donor Schiff Bases as Ligands

Abstract

A series of novel nickel 1–4 {[Ni(L1)] (1); [Ni(L2)Cl2] (2); [Ni(L3)Cl2] (3); [Ni(L4)Cl2] (4)} and cobalt complexes 5–8 {[Co(L1)] (5); [Co(L2)Cl2] (6); [Co(L3)Cl2] (7); [Co(L4)Cl2] (8)}bearing N, O‐donor Schiff bases as ligands L1‐L4 (L1= (E)‐2‐(((2‐phenoxyethyl)imino)methyl)‐phenol; L2= (E)‐5‐methoxy‐2‐(((2‐phenoxyethyl)imino)methyl)phenol; L3= (E)‐2‐(((2‐(2‐methox yphenoxy)ethyl)imino)methyl)phenol; L4= (E)‐5‐methoxy‐2‐(((2‐(2‐methoxyphenoxy)ethyl)imino) methyl)phenol) were synthesized from the complex reaction between salicylaldehyde and phenoxye‐thylamine analogues and characterized by UV‐Vis, IR, 1H NMR, ESI‐MS and elemental analysis. All the nickel complexes (1‐4) and cobalt complexes (5‐8) as catalyst precursors were evaluated in detail with methylaluminoxane (MAO) as an activator in the ethylene oligomerization. At the same time, the effects of reaction parameters, catalyst structures and solvent on ethylene oligomerization were investigated too. As a result, complexes 5–8 showed a better catalytic activity (2.05‐3.38×105 g/(mol(Co)•h) and a higher selectivity of 34.44% toward the valuable C8 compound using toluene as the solvent than complexes 1–4.

Ethylene Oligomerization Catalyzed by Different Homogeneous or Heterogeneous Catalysts

“…Further investigations of nickel complexes bearing α-diimine ligands have involved the modification of the ligand to alter its spatial site resistance and electronic effects. In addition, other types of bidentate ligands (including (N, O) [25][26][27][28][29], (P, N) [30][31][32], (P, P) [33][34][35], (P, S) [36], and (N, S) [37]) as well as tridentate ligands (including (N, N, N) [38][39][40], (N, N, O) [41,42], (N, O, O) [43,44], etc.) were synthesized.…”

“…In addition, other types of bidentate ligands (including (N, O) [25][26][27][28][29], (P, N) [30][31][32], (P, P) [33][34][35], (P, S) [36], and (N, S) [37]) as well as tridentate ligands (including (N, N, N) [38][39][40], (N, N, O) [41,42], (N, O, O) [43,44], etc.) were synthesized.…”

“…To summarize the three types of cobalt complexes of salicylaldimine ligands mentioned above, the backbone structure affects the activity and product selectivity of ethylene oligomerization. Wang and co-workers [25] explored a series of cobalt complexes as catalyst precursors and reported their performance in the ethylene oligomerization with MAO as an activator (Figure 14). Under the optimum conditions (n (catalyst) = 7 µmol, T = 50 • C, P (ethylene pressure) = 2.0 MPa, n(Al)/n(M) = 300, toluene as solvent), complex 55 produced the selectivity of 34.44% to C 8 and activity of 3.38 × 10 5 g•mol −1 Co •h).…”