The syntheses of new cationic nickel complexes {[eta(3)-methallyl]Ni[ kappa (2) P,O-Ph-2 P(X)P(O)Ph-2]}SbF6, (1)-(2) [X = (o-C6H4) (1), (NH), (2)1 have been accomplished. The complexes oligomerize ethylene to linear cl-olefins with selectivities as high as 89%. A dependence of oligomerization grade and activity on backbone geometry was shown. New cationic allyl and methyl complexes of palladium(II) [(CH3CN)(Me)Pd(kappa(2)P,O-Ar2P(CH2)(n)P(O)Ar-2)]X [n = 1-3, X = BF4, Ar = C6H5 (18-20)] [n = 1, X = SbF6, Ar =p-tolyl (23); n = 1 or 2, X = SbF6, Ar = C6H5 (21) or (22)]; [( eta(3)-C3H5Pd(kappa(2)P,O-Ph2P(CH2)(n)P(O)Ph-2)]X, [n = 2, X=triflate (10), tosylate (13); n=3, X=triflate (11), tosylate (14)], ([ eta(3)-C3H5)]Pd(kappa(2)P,O-Ar2P(CH2)(n)P(O)Ar-2)]X, [n = 1, X = SbF6, Ar =p-tolyl (17); n = 2, X = SbF6 Ar = C6H5(16)] have been synthesized in good yields. These complexes have been used in the catalytic oligomerization of ethylene, and in the catalytic alternating copolymerization of ethylene and carbon monoxide, to yield polyketones.