Oligomerization to alpha-olefins

An oligomerization or cooligomerization process comprising passing ethylene or a mixture of ethylene and propylene in contact with a catalyst, in the liquid phase, said catalyst comprising the reaction product of (i) a transition metal compound wherein the transition metal is selected from the group consisting of nickel, chromium, cobalt, iron, and copper, and mixtures thereof;

• (ii) in the event that (a) the transition metal is not in the oxidation state of zero or (b) the transition metal compound does not have a hydride or an alkyl, alkenyl, alkynyl, or aryl group bonded to the transition metal, a catalyst activator consisting of a compound or compounds capable of transferring a hydride or an alkyl, alkenyl, alkynyl, or aryl group from itself to the transition metal/ligand, hereinafter defined, complex formed by the reaction of the transition metal compound with the ligand and bonding the group to the transition metal, said activator being present in a sufficient amount to activate the catalyst;
• and (iii) at least one organophosphorus sulfonate ligand containing (a) at least one benzene ring having a trivalent phosphorus atom located at one position on the benzene ring and an SO.sub.3 M group located at a position on the benzene ring ortho thereto, or at least one benzene ring having a trivalent phosphorus atom connected through a methylene group to a first position on the benzene ring and an SO.sub.3 M group connected through a methylene group to a second position on the benzene ring ortho to the first position, or at least one bridging or fused aromatic ring system having a trivalent phosphorus atom and and SO.sub.3 M group, each located on a different aromatic ring in the system at substituent positions adjacent to one another, or at least one aromatic ring, other than a benzene ring, or heteroaromatic ring, each ring having a trivalent phosphorus atom and an SO.sub.3 M group located at substituent positions adjacent to one another, wherein M is selected from the group consisting of hydrogen, alkali metals, alkaline earth metals, and NR.sub.4 and PR.sub.4 wherein R is a hydrogen atom or a substituted or unsubstituted hydrocarbyl radical having 1 to 15 carbon atoms and each R can be alike or different or (b) a trivalent phosphorus atom connected through a group having the formula ##STR36## wherein A is an oxygen atom, an NH radical, or an NR radical;
• R.sup.2 and R.sup.3 are hydrogen atoms or a substituted or unsubstituted hydrocarbyl radical having 1 to 6 carbon atoms and can be alike or different;
• x is an integer 0 or 1;
• y is an integer from 1 to 3;
• and R and M are as defined above.