851539-80-5Relevant articles and documents
Reactions of vinyl acetate and vinyl trifluoroacetate with cationic diimine Pd(II) and Ni(II) alkyl complexes: Identification of problems connected with copolymerizations of these monomers with ethylene
Williams, B. Scott,Leatherman, Mark D.,White, Peter S.,Brookhart, Maurice
, p. 5132 - 5146 (2007/10/03)
Vinyl acetate (VA) and vinyl trifluoroacetate (VAf) react with [(NAN)Pd(Me)(L)][X] (M = Pd, Ni, (N∧N) = N,N′-1,2- acenaphthylenediylidene bis(2,6-dimethyl aniline), Arf = 3,5-trifluoromethyl phenyl, L = ArfCN, Et2O; X = B(Ar f)4-, SbF6-) to form π-adducts 3 and 5 at -40 °C. Binding affinities relative to ethylene have been determined. Migratory insertion occurs in a 2,1 fashion (ΔG ? = 19.4 kcal/mol, 0 °C for VA, and 17.4 kcal/mol, -40 °C for VAf) to yield five-membered chelate complexes [(N∧N)Pd(κ2-CH(Kt)(OC(O)-CH3))]+, 4, and [(N∧N)Pd(κ2-CH(Et)(OC(O)CF3))]+, 6. When VA is added to [(N∧N)Ni(CH3)]+, an equilibrium mixture of an η2 olefin complex, 8c, and a κ-oxygen complex, 8o, results. Insertion occurs from the η2 olefin complex, 8c (ΔG? = 15.5 kcal/mol, -51 °C), in both a 2,1 and a 1,2 fashion to generate a mixture of five- and six-membered chelates, 92,1 and 91,2. VAf inserts into the Ni-CH 3 bond (-80 °C) to form a five-membered chelate with no detectable intermediate. Thermolysis of the Pd chelates results in β-acetate elimination from 4 (ΔG? = 25.5 kcal/mol, 60 °C) and β-trifluoroacetate elimination from 6 (ΔG ? = 20.5 kcal/mol, 10 °C). The five-membered Ni chelate, 92,1, is quite stable at room temperature, but the six-membered chelate, 91,2, undergoes β-elimination at -34 °C. Treatment of the OAcf containing Pd chelate 6 with ethylene results in complete opening to the π-complex [(N∧N)Pd(κ2-CH(Et)(OAc f))(CH2CH2)]+ (OAcf = OC(O)CF3), 18, while reaction of the OAc containing Pd chelate 4 with ethylene establishes an equilibrium between 4 and the open form 16, strongly favoring the closed chelate 4 (ΔH= -4.1 kcal/mol, ΔS = -23 eu, K = 0.009 M-1 at 25 °C). The open chelates undergo migratory insertion at much slower rates relative to those of the simple (N∧N)Pd(CH3)(CH2CH2)+ analogue. These quantitative studies provide an explanation for the behavior of VA and VAf in attempted copolymerizations with ethylene.
