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

• Published in: Organometallics 1997-09, Vol.16 (19), p.4150-4160
• Main Authors: Delis, Johannes G. P, Aubel, Peter G, Vrieze, Kees, van Leeuwen, Piet W. N. M, Veldman, Nora, Spek, Anthony L
• Format: Article
• Language: English
• ISSN: 0276-7333; 1520-6041
• DOI: 10.1021/om9701940

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-Me2C6H3)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(C7H8C(NR)Me)]X and [(N⌒N)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 [(N⌒N)Pd(C(NR)Me)]X (N⌒N = bpy, phen; R = 2,6-Me2C6H3; X = BF4) provided the complexes [(N⌒N)Pd(C2H4C(NR)Me)]X, [(N⌒N)Pd(C3H6C(NR)Me)]X, [(N⌒N)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 1a and 1b with HC⋮CCOOMe gave, instead of an insertion product, the Michael addition product (N⌒N)Pd[C(CH2)N(2,6-Me2C6H3)(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.