US Patent 7273959 Catalytic trimerization of olefinic monomers

A catalyst composition suitable for the trimerization of olefinic monomers, wherein the catalyst composition comprises:a) a source of chromium, molybdenum or tungsten;b) a ligand of general formula (I);(R1)(R2)P—X—P(R3)(R4)  (I)wherein:X is a bivalent organic bridging group;R1 and R3 are independently selected from, hydrocarbyl, substituted hydrocarbyl, heterohydrocarbyl and substituted heterohydrocarbyl groups, with the proviso that when R1 and R3 are cycloaromatic groups they do not contain a polar substituent at any of the ortho-positions;R2 and R4 are independently selected from optionally substituted cycloaromatic groups, each R2 and R4 bearing a polar substituent on at least one of the ortho-positions; andc) a cocatalyst.