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 (N⌒N)Pd(C( N-2,6-Me 2 C 6 H 3 )Me)X (X = Cl ( 1 ), Br ( 2 ), I ( 3 ); N⌒N = 2,2‘-bipyridine (bpy, a ), 1,10-phenanthroline (phen, b )) afforded quantitatively the novel and stable complexes [(N⌒N)Pd(C 7 H 8 C( NR)Me)]X and [(N⌒N)Pd(C 7 H 10 C( NR)Me)]X (R = 2,6-Me 2 C 6 H 3 ). Insertion reactions of the unstrained unsaturated hydrocarbons ethylene, propylene, 3-methyl-1,2-butadiene, and acetylene with the cationic complexes [(N⌒N)Pd(C( NR)Me)]X (N⌒N = bpy, phen; R = 2,6-Me 2 C 6 H 3; X = BF 4 ) provided the complexes [(N⌒N)Pd(C 2 H 4 C( NR)Me)]X, [(N⌒N)Pd(C 3 H 6 C( NR)Me)]X, [(N⌒N)Pd(C 5 H 8 C( NR)Me)]X, and [(bpy)Pd(C 2 H 2 C( 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 1a and 1b with HC⋮CCOOMe gave, instead of an insertion product, the Michael addition product (N⌒N)Pd[C( CH 2 )N(2,6-Me 2 C 6 H 3 )(CH CHCOOMe)]Cl. Kinetic measurements carried out on the norbornadiene insertion reactions with 1a, 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.
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Delis et al. (1997) studied this question.