Nickel-based catalytic composition, and its use in a process for the oligomerization of olefins

A composition comprising:

• at least one precursor of nickel with an oxidation number of (0) or (+II),
• at least one ligand with formula 1a), 1b) or 1c)
• in which
• A and A′, which may be identical or different, are independently O, S, NR3 or a single bond between the phosphorus atom and a carbon atom,
• the group R3 is either a hydrogen atom or an alkyl group, which may or may not be cyclic, which may or may not be substituted and which may or may not contain heteroelements, or an aromatic group, which may or may not be substituted and which may or may not contain heteroelements,
• the groups R1a and R1b being mutually identical or different and which may or may not be bonded together, are selected from alkyl groups which may or may not be cyclic, which may or may not be substituted and which may or may not contain heteroelements, and aromatic groups which may or may not be substituted and which may or may not contain heteroelements,
• the group R2 is selected from alkyl groups which may or may not be cyclic, which may or may not be substituted and which may or may not contain heteroelements, and aromatic groups which may or may not be substituted and which may or may not contain heteroelements,
• with the condition that when a precursor of nickel with an oxidation number of (+II) is in the composition, it is in the presence of a reducing agent or in the presence of a Brönsted base.