Insertion of unsaturated hydrocarbons into the palladium-carbon bond of complexes (N N)Pd(C(=N-2,6-Me2Ph)Me)X (N N = bpy, phen; X = Cl, Br, I, BF4): A structural and mechanistic study

The reactivity of Pd-carboimine complexes toward unsaturated hydrocarbon bonds has been studied. Insertion of norbornadiene and norbornene into the Pd-C bond of the neutral complexes (NN)Pd(C(=N-2,6-Me2C6H3)Me)X (X = Cl (1), Br (2), I (3); NN = 2,2'-bipyridine (hpy, a), 1,10-phenanthroline (phen, b)) afforded quantitatively the novel and stable complexes [(NN)Pd(C7H8(=NR)Me)]X and [(NN)Pd(C7H10C(=NR)Me)]X (R = 2,6-Me2C6H3). Insertion reactions of the unstrained unsaturated hydrocarbons ethylene, propylene, 3-methyl-1,2-butadiene, and acetylene with the cationic complexes [(NN)Pd-(C(=NR)Me)]X(NN = bpy, phen; R = 2,6-Me2C6H3; X = BF4) provided the complexes [(NN)Pd(C2H4C(=NR)Me)]X, [(NN)Pd(C3H6C(=NR)Me)]X, [(NN)Pd(C5H8C(=NR)Me)]X, and [(bpy)Pd(C2H2C(=NR)Me)]X. The remarkable stability of these products is caused by the strong coordination of the carboimine nitrogen to the palladium center, Reaction of Ba and Ib with HC=CCOOMe gave, instead of an insertion product, the Michael addition product (NN)Pd[C(=CH2)N(2,6-Me2C6H3)(CH=CHCOOMe)]Cl. Kinetic measurements carried out on the norbornadiene insertion reactions with Pa,b, 2a, and 3a revealed that the reactions are first order in the palladium concentration and occur via a norbornadiene concentration-independent and dependent pathway.