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:
• R5 attached to N is independently C1-40 substituted or unsubstituted alkyl, C1-40 substituted or unsubstituted aryl;
• each R5 attached to the phenyl group is independently halogen, C1-40 substituted or unsubstituted alkyl, C1-40 substituted or unsubstituted aryl;
• n is an integer from 0 to 5;
• and 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.