Ethylene oligomerization method with reduced polymer generation and improved productivity

An ethylene oligomerization method comprising reacting a chromium complex represented by the following Chemical Formula 1, an organoaluminum compound represented by the following Chemical Formula 2, and an organozinc compound represented by the following Chemical Formula 3 with ethylene in the presence of an organic solvent to prepare an ethylene oligomer,

• wherein a mole ratio (Cr:Zn) between the chromium complex and the organozinc compound is 1:100 to 1500, and the reaction is performed at a temperature of 0 to 80° C. under a pressure of 1 to 100 bar:
• Wherein
• R is C1-C60 alkyl, C6-C60 aryl, or C2-C60 heteroaryl;
• R1 to R4 are independently of one another C1-C60 alkyl, C6-C60 aryl, or C2-C60 heteroaryl;
• X1 and X2 are independently of each other a halogen, C1-C30 alkyl, C1-C30 alkylcarboxylate, acetylacetonate, or C1-C30 hydrocarbyl including one or more selected from ether and amino;
• A is boron or aluminum;
• Y1 to Y4 are independently of one another fluorine-substituted C6-C60 aryl, fluorine-substituted C2-C60 heteroaryl, fluorine-substituted C6-C60 aryloxy, or fluorine-substituted C6-C60 alkoxy;
• R11 to R13 are independently of one another C4-C8 alkyl;
• R21 to R22 are independently of each other C1-C8 alkyl;
• the alkyl, aryl, or heteroaryl of R and R1 to R4 may be further substituted by one or more selected from C1-C30 alkyl, C6-C30 aryl, C1-C30 alkoxy, monoC1-C30 alkylamino, diC1-C30 alkylamino, monoC6-C30 arylamino, diC6-C30 arylamino, monoC1-C30 alkylsilyl, diC1-C30 alkylsilyl, triC1-C30 alkylsilyl, monoC6-C30 arylsilyl, diC6-C30 arylsilyl, and triC6-C30 arylsilyl;
• and
• the heteroaryl includes at least one heteroatom selected from the group consisting of O, N, S, Si, and P.