The invention concerns a catalytic composition comprising: at least one nickel precursor with an oxidation number of (+II), at least one phosphine ligand with formula PR1R2R3 in which the groups R1, R2 and R3, which may be identical or different and which may or may not be bonded together, and at least one Lewis base, said composition having a molar ratio of the phosphine ligand to the nickel precursor of less than or equal to 5 and a molar ratio of the Lewis base and phosphine ligand together to the nickel precursor of greater than or equal to 5.