6533b839fe1ef96bd12a5a97

RESEARCH PRODUCT

Mechanism of oxidative allyl transfer from allylic ammonium cations to palladium(0) α-diimine complexes

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Abstract The palladium(0) complex [Pd(η2-fn)(NN′)] (1, fn = fumaronitrile; NN′ = C5H4N-2-CH=NC6H4OME-4) reacts slowly and reversibly with A +  CH 2  CH=CH 2 (2a, A = NEt 3 ; 2 b , A = C 5 H 5 N ) to yield the cationic η3-allypalladium(II) derivative [ Pd (η[ 3 - C 3 H 5 )( N  N ′)] + (3) the free amine A and fn. The equilibrium constant Ke is (2.6 ± 0.1) × 10−3 for 2a and 1.0 ± 0.4 for 2b. Kinetic studies of these oxidative allyl-transfer reactions show that the rates increase with increasing concentration of 2 and with decreasing concentration of fn. A stepwise mechanism is proposed which involves slow and reversible displacement of fn by 2 to give a labile intermediate [ Pd (η 2 - CH 2 = CH  CH 2  A + ( N  N ′)] . This undergoes slow and reversible intramolecular allyl transfer through nucleophilic attack by the palladium(0) metal centre on the nitrogen-bound allyl carbon. The kinetic parameters evaluated by a steady-state treatment satisfactorily generate the observed equilibrium constant Ke. The rate of formation of the intermediate and the relative rate of its decay to the starting reactants and final products are virtually independent of the nature of the amine A.