Organometallic complexes comprising iminophosphorane ligands have recently found an increasing application in both coordination chemistry and catalysis. The integration of supplemental donor sites D into the iminophosphorane structure yields polydentate mixed ligands of type A or B. Ligands of this type are of particular interest due to the analogy of the iminophosphorane unit with imines, ubiquitous in coordination chemistry. New ligands of type A and B with either anionic or neutral oxygen or sulfur donor atoms have been synthesized via two different pathways, both straightforward and easy to scale up. The coordination of these ligands to NiIIBr2(DME) (DME = dimethoxyethane) has been evaluated and preliminary results in the catalyzed oligomerization reaction of ethylene employing these complexes are reported.