Process for oligomerization

A process for oligomerizing an olefin comprising:

• contacting at least one olefin with a catalyst system under olefin oligomerization conditions sufficient to convert at least a portion of the at least one olefin to a product comprising at least one oligomer of the at least one olefin, the catalyst system comprising:
• a) a source of chromium;
• b) one or more activators;
• and,
• c) at least one phosphacycle-containing ligating compound of the formula:
• wherein:
• L and L1 are C;
• q is 1 or 2;
• p is 1 or 2;
• R5 attached to L1 is independently H, C1-40 substituted or unsubstituted alkyl, C1-40 substituted or unsubstituted aryl;
• each R5 attached to the C or L group is independently H, halogen, C1-40 substituted or unsubstituted alkyl, C1-40 substituted or unsubstituted aryl;
• R3 and R4 independently are represented by alkyl, substituted alkyl, phenyl, substituted phenyl, furanyl, substituted furanyl, thienyl, substituted thienyl, pyrrolyl, substituted pyrrolyl, pyridinyl, and substituted pyridinyl;
• and
• two or more R3, R4 or R5 groups are optionally linked together to form cyclic structures containing 4 to 10 ring atoms;
• two or more R5 groups linked to separate L atoms in a phosphacycle moiety are optionally linked together to form a cyclic structure that contains from 3 to 10 ring atoms;
• and
• two R5 groups attached to the same L atom may be optionally linked together to form a cyclic structure that contains from 3 to 10 ring atoms.