Bisphosphine ligand compound, chromium compound, ethylene oligomerization catalyst system, and ethylene oligomer preparation method

A chromium compound represented by Formula 1:

• wherein Formula 1, R is a substituted or unsubstituted C1 to C60 alkyl group or a substituted or unsubstituted C6 to C60 aryl group;
• R1s are a substituted or unsubstituted C1 to C60 alkyl group or a substituted or unsubstituted C6 to C60 aryl group;
• Xs are each independently a halogen atom, a C2 to C30 carboxylate, acetylacetonate, or a C1 to C30 hydrocarbyl group containing or free from at least one selected from among an ether group and an amine group;
• A is boron or aluminum;
• and Y is a fluorine-substituted C6 to C20 aryl group, a fluorine-substituted C6 to C20 aryloxy group, or a fluorine-substituted C1 to C20 alkoxy group.

An ethylene oligomerization catalyst system comprising:

• a chromium compound represented by Formula 1;
• and
• an organic aluminum compound represented by Formula 2;
• wherein Formula 1, R is a substituted or unsubstituted C1 to C60 alkyl group or a substituted or unsubstituted C6 to C60 aryl group;
• R1s are a substituted or unsubstituted C1 to C60 alkyl group or a substituted or unsubstituted C6 to C60 aryl group;
• Xs are each independently a halogen atom, a C2 to C30 carboxylate, acetylacetonate, or a C1 to C30 hydrocarbyl group containing or free from at least one selected from among an ether group and an amine group;
• A is boron or aluminum;
• and Y is a fluorine-substituted C6 to C20 aryl group, a fluorine-substituted C6 to C20 aryloxy group, or a fluorine-substituted C1 to C20 alkoxy group;
• (R2)3Al [Formula 2]
• wherein Formula 2, R2 is a C1 to C20 alkyl group.