Vinyl acetate (VA) and vinyl trifluoroacetate (VA(f)) react with [(N boolean AND N)Pd(Me)(Q][X] (M = Pd, Ni, (N boolean AND N) = N,N'-1,2-acenaphthylenediylidene bis(2,6-dimethyl aniline), Ar-f = 3,5-trifluoromethyl phenyl, L = ArfCN, Et2O; X = B(Ar-f)(4)(-), SbF6-) to form pi-adducts 3 and 5 at -40 degrees C. Binding affinities relative to ethylene have been determined. Migratory insertion occurs in a 2,1 fashion (Delta G(double dagger) = 19.4 kcal/mol, 0 degrees C for VA, and 17.4 kcal/mol, -40 degrees C for VA(f)) to yield five-membered chelate complexes [(N boolean AND N)Pd(kappa(2)-CH(Et)(OC(O)CH3))](+), 4, and [(N boolean AND N) Pd(kappa(2)-CH(Et)(OC(O)CF3))](+), 6. When VA is added to [(N boolean AND N)Ni(CH3)](+), an equilibrium mixture of an eta(2) olefin complex, 8c, and a kappa-oxygen complex, 8o, results. Insertion occurs from the eta(2) olefin complex, 8c (Delta G(double dagger) = 15.5 kcal/mol, -51 degrees C), in both a 2,1 and a 1,2 fashion to generate a mixture of five- and six-membered chelates, 9(2,1), and 9(2,1). VA(f) inserts into the Ni-CH3 bond (-80 degrees C) to form a five-membered chelate with no detectable intermediate. Thermolysis of the Pd chelates results in beta-acetate elimination from 4 (Delta G(double dagger) = 25.5 kcal/mol, 60 degrees C) and beta-trifluoroacetate elimination from 6 (Delta G(double dagger) = 20.5 kcal/mol, 10 degrees C). The five-membered Ni chelate, 92,1, is quite stable at room temperature, but the six-membered chelate, 91,2, undergoes beta-elimination at -34 degrees C. Treatment of the OAcf containing Pd chelate 6 with ethylene results in complete opening to the pi-complex [(N boolean AND N) Pd(kappa(2)-CH(Et)(OAcf))(CH2CH2)](+) (OAcf = OC(O)CF3), 18, while reaction of the OAcf containing Pd chelate 4 with ethylene establishes an equilibrium between 4 and the open form 16, strongly favoring the closed chelate 4 (Delta H = -4.1 kcal/mol, Delta S = -23 eu, K = 0.009 M-1 at 25 degrees C). The open chelates undergo migratory insertion at much slower rates relative to those of the simple (N boolean AND N)Pd(CH3)(CH2CH2)(+) analogue. These quantitative studies provide an explanation for the behavior of VA and VA(f) in attempted copolymerizations with ethylene.