Patent ID: 7867938

Claim:
A catalyst precursor composition comprising: a) a source of chromium, molybdenum or tungsten; b) a first ligand having the general formula (I); (R 1 )(R 2 )P—X—P(R 3 )(R 4 ) (I) wherein: X is a bridging group of the formula —N(R 5 )—, wherein R 5 is selected from hydrogen, a hydrocarbyl group, a substituted hydrocarbyl group, a heterohydrocarbyl group, a substituted heterohydrocarbyl group, a silyl group or derivative thereof; at least three of R 1 to R 4 are independently selected from optionally substituted aromatic groups, each bearing a polar substituent on at least one of the ortho-positions; and optionally one of R 1 to R 4 is 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; c) a second ligand having the general formula (II); (R 1′ )(R 2′ )P—X′—P(R 3′ )(R 4′ ) (II) wherein: X′ is a bridging group as defined for X of the first ligand, component (b), of general formula (I); at least R 1′ and R 2′ of R 1′ to R 4′ 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; and none, one or both of R 3′ and R 4′ are independently selected from an optionally substituted aromatic group bearing a polar substituent on at least one of the ortho-positions.