Five new nonsymmetric 1-diphenylphosphino-3-{bisarylphosphino}propane ligands 1b−f aryl:  b = 3,5-bis(trifluoromethyl)phenyl, c = 3,5-dimethylphenyl, d = 3,5-difluorophenyl, e = 2-(trifluoromethyl)phenyl, f = 2,4,6-trifluorophenyl and their corresponding neutral dichloro palladium(II) 2b−f, diiodo palladium(II) 3d,e, and dicationic diacetonitrile palladium(II) ditetrafluoroborate complexes 4b−f were synthesized. The symmetric ligand 1,3-bis{bis3,5-bis(trifluoromethyl)phenylphosphino}propane (1a) and the related palladium(II) complexes 2a and 4a were prepared for comparison. Solid state structures of new ligands were determined by X-ray structure analysis in the form of the dichloro (2a−c,f) and diiodo (3d,e) compounds. The properties of the symmetric (4a) and nonsymmetric catalysts (4b−f) were tested in propene/CO copolymerization experiments. A clear correlation between primarily steric effects of these ligands and the catalyst activity as well as the molecular weight of the resulting polyketone materials was observed. The nonsymmetric structure 4b, bearing CF3 groups in the 3,5-position of two aryl units on one phosphorus side, proved to be the most effective catalyst, which reached an activity maximum (12.7 kgmol(Pd) × h-1) and led at the same time to propene/CO copolymers of high molecular weight (M̄ w ≈ 5 × 105 g mol-1). The same catalyst species 4b affords even ultrahigh molecular weight ethene/propene/CO terpolymers with M̄ w ≈ 8 × 105 g mol-1. These novel polyketones possess a predominantly regioirregular microstructure, leading to interesting flexible material properties in contrast to already known regioregular and thereby brittle propene/CO copolymers.