Olefin polymerisation catalyst

A catalyst for polymerizing olefins, corresponding to the following formula:

• in which:
• E is an oxygen or sulfur atom;
• X is a phosphorus, arsenic or antimony atom;
• M is a nickel, palladium or platinum atom comprising an unattributed valency;
• a is 1 or 2;
• R1, R2 and R3, which may be identical or different, may be chosen from hydrogen, alkyl, cycloalkyl, aryl, alkylaryl and arylalkyl radicals, each generally containing from 1 to 20 carbon atoms, the hydroxyl radical, alkoxide radicals with from 1 to 20 carbon atoms, C(O)OR′ in which R′ represents a hydrocarbon-based radical that may contain from 1 to 15 carbon atoms, —SO3Y in which Y is chosen from Li, Na, K, NH4, NR4 in which R represents a hydrocarbon-based radical that may contain from 1 to 15 carbon atoms;
• Rf represents a pentafluorophenyl, trifluoromethyl or heptafluoropropyl group;
• and
• R4 is a group —C(O)OR′wherein R′ is an ethyl, tert-butyl or benzyl group, further wherein:
• when R′ is an ethyl, tert-butyl or benzyl group, Rf is a pentafluorophenyl group;
• and when R′ is an ethyl group, Rf is a trifluoromethyl group or a heptafluoropropyl group.