Catalyst composition and process for di-, tri-and/or tetramerization of ethylene

A catalyst composition, obtainable by combining at least:

• (a) a chromium compound;
• (b) a ligand of the general structure
• R1R2P—N(R3)—P(R4)—N(R5)—PR6R7,
• wherein R1, R2, R3, R4, R5, R6 and R7 are independently selected from halogen, amino, trimethylsilyl, C1-C10-alkyl, aryl and substituted aryl, and said ligand may be a cyclic derivative, wherein at least one of the P or N atoms of the PNPNP-unit is a member of a ring system, the ring system being formed from one or more constituent compounds of the ligand by substitution;
• and
• (c) an activator or co-catalyst.