Nickel-based complexes and their use in a process for the transformation of olefins

A nickel-based complex having formula (I)

• in which
• the atoms P, N, S, O constitute a ligand fragment,
• 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 of R1a or R1b,
• 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 R1, represented in the formula by R1a and R1b, with 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,
• L1 and L2, which may be identical or different, represent a Lewis base,
• X1 is a carbon atom bonded to or forming part of at least one alkyl group, which may or may not be cyclic, which may or may not be unsaturated, which may or may not be substituted and which may or may not contain heteroelements, and an aromatic group which may or may not be substituted and which may or may not contain heteroelements,
• L1, L2 and X1 are such that the oxidation number of the nickel is respected, and δ− represents the delocalisation of the negative charge over the ligand fragment constituted by the atoms P, N, S and O.