A series of symmetric and unsymmetric N,N-bis(diarylphosphino)amine (‘PNP’) ligands (Ar₂PN(R)PNAr′₂: R = Me, Ar₂ = o-anisyl, Ar′₂ = Ph, 1, R = Me, Ar₂ = o-tolyl, Ar′₂ = Ph, 2, R = Me, Ar₂ = Ph(o-ethyl), Ar′₂ = Ph, 3, R = Me, Ar₂ = Ar′₂ = o-anisyl, 4, R = ⁱPr, Ar₂ = Ar′₂ = Ph, 5) and symmetric N,N′-bis(diarylphosphino)dimethylhydrazine (‘PNNP’) ligands (Ar₂PN(Me)N(Me)PAr₂: Ar₂ = o-tolyl, 6, Ar₂ = o-anisyl, 7) have been synthesised. Catalytic screening for ethene/styrene co-trimerisation and isoprene trimerisation was performed via the in situ complexation to [CrCl₃(THF)₃] followed by activation with methylaluminoxane (MAO). PNNP catalytic systems showed a significant increase in activity and selectivity over previously reported PNP systems in isoprene trimerisation. Comparing the symmetric and unsymmetric variants in ethene and styrene co-trimerisation resulted in a switch in selectivity, an unsymmetric catalytic (o-anisyl)₂PN(Me)PPh₂ (1) ligand system affording unique incorporation of two styrenic monomers into the co-trimer product distribution differing from the familiar two ethene and one styrene ω-substituted alkenes. Complexes of the type [(diphosphine)Cr(CO)₄] 8–11 were also synthesised, the single-crystal X-ray diffraction of which are reported. We propose the mechanisms of these catalytic transformations and an insight into the effect of the ligand series on the chromacyclic catalytic intermediates.