Catalytic process for the oligomerization of olefinic monomers

A process for the simultaneous trimerization and tetramerization of olefinic monomers, wherein the process comprises contacting at least one olefinic monomer with a catalyst system comprising:

• a) a source of chromium, molybdenum or tungsten;
• b) a ligand having the general formula (I);
• (R1)2P—X—P(R1)m(R2)n (I)
• wherein:
• X is a bridging group of the formula —N(R3)—, wherein R3 is selected from hydrogen, a hydrocarbyl group, a substituted hydrocarbyl group, a heterohydrocarbyl group, a substituted heterohydrocarbyl group, a silyl group or derivative thereof;
• the R1 groups are independently selected from an optionally substituted aromatic group bearing a polar substituent on at least one of the ortho-positions;
• and
• the R2 groups are independently selected from hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl groups with the proviso that when the group is aromatic it does not contain a polar substituent at any of the ortho-positions;
• with the proviso that m is 0 or 1, n is 1 or 2 and the total of m+n is 2;
• optionally, any of the R1 and R2 groups may independently be linked to one or more of each other or to the bridging group X to form a cyclic structure;
• and
• c) a cocatalyst,
• at a pressure in the range of from below atmospheric to 40 barg and at a temperature in the range of from 0° C. to 120° C.