Selective alpha-olefin trimerisation catalysts are of substantial and increasing commercial significance. Novel chromium based catalyst systems, based on derivatives and analogues of the previously developed chromium III complexes of 1,3,5-triazacyclohexanes, have been investigated, with particular emphasis on the synthesis and reactivity of the potential ligand type RB(R’NCH2)2, and on the incorporation of weakly coordinating anionic functionalities into the active complexes.