Searching for New Four-membered Palladacycles Derived from Anilines: Influence of the N-Substituents in the Reaction Outcome

Abstract

The reactions of iodoanilines IC₆H₄NRR′-2 with [Pd(PPh₃)₄] gave complexes [Pd(C₆H₄NRR′-2}I(PPh₃)₂] [R=H, R’=H (1 a), Me (1 b); R=R’=Me (1 c)] while a mixture of 1 a, and the dimeric [Pd{μ-C,N-C₆H₄NH₂-2)I(PPh₃)]₂ (2 a) was obtained when the appropriate iodoaniline was reacted with [Pd(dba)₂] (dba=dibenzylideneacetone) and 1 equiv. of PPh₃. The phosphonium salts [Ph₃PC₆H₄NRMe-2]OTf [R=H (3 b), Me (3 c)] formed upon reacting complexes 1 b,c with TlOTf (OTf=CF₃SO₃). Complexes of the type [Pd(C₆H₄NRR′-2}I(N N)] (4) were obtained from the reaction of [Pd(dba)₂] with the appropriate iodoaniline and a N N bidentate ligand (N N=4,4′-di-tert-butyl-2,2′-bipyridine or N,N,N′,N′-tetramethylethylenediamine). Complexes 4 reacted with TlOTf and PPh₃ or XyNC (Xy=C₄H₄Me₂-2,6) to give [Pd(C₆H₄NRR′-2)(N N)(PPh₃)]OTf (5) or [Pd{C,N-C(=NHXy)C₆H₄NRR′-2)(N N)]OTf (6), respectively. In the absence of any added ligand, the reactions of complexes 4 with TlOTf produced the dimeric complexes [Pd{μ-C,N-C₆H₄NHR-2)(N N)]₂(OTf)₂ (7) or the four-membered palladacycles [Pd(κ²-C₆H₄NMe₂-2)(N N)]OTf (8), depending on the substitution degree of the aniline reagent.