Depalladation of Neutral Monoalkyne- and Dialkyne-Inserted Palladacycles and Alkyne Insertion/Depalladation Reactions of Cationic Palladacycles Derived from N,N′,N″-Triarylguanidines as Facile Routes for Guanidine-Containing Heterocycles/Carbocycles: Synthetic, Structural, and Mechanistic Aspects

Abstract

Depalladation of the monoalkyne-inserted cyclopalladated guanidines [κ2(C,N)Pd(2,6-Me2C5H3N)Br] (I and II) in PhCl under reflux conditions and that of the dialkyne-inserted cyclopalladated guanidine [κ2(C,N):η2(C═C)PdBr] (III) in pyridine under reflux conditions afforded a guanidine-containing indole (1), imidazoindole (2), and benzazepine (3) in 80%, 67%, and 76%, yields, respectively. trans-[L2PdBr2] species (L = 2,6-Me2C5H3N, C5H5N) were also isolated in the aforementioned reactions in 35%, 42%, and 40% yields. Further, the reaction of the cyclopalladated guanidine [κ2(C,N)Pd(μ-Br)]2 (IV) with AgBF4 in a CH2Cl2/MeCN mixture afforded the cationic pincer type cyclopalladated guanidine [κ3(C,N,O)Pd(MeCN)][BF4] (4) in 85% yield and this palladacycle upon crystallization in MeCN and the reaction of [κ2(C,N)Pd(μ-Br)]2 (V) with AgBF4 in a CH2Cl2/MeCN mixture afforded the cationic palladacycles [{κ2(C,N)Pd(MeCN)2][BF4] (5 and 6) in 89% and 91% yields, respectively. The separate reactions of 4 with 2 equiv of m...