Doubly cyclopalladated complexes of N,N,N′,N′-tetraethylbenzene-1,3-bis(methylamine)

Abstract

N,N,N′,N′-Tetraethylbenzene-1,3-bis(methylamine)(L) undergoes regiospecific double cyclopalladation with Li₂[PdCl₄] at the 4,6 positions of the benzene ring to produce the chloro-bridged polymeric complex [Pd₂(L – 2H)Cl₂]. Reactions of this complex with PPh₃, methylpyridines, acetylacetone, ethylacetoacetate, monothiodibenzoylmethane and trifluoro(thenoyl)acetone have been studied and the products characterized by ¹H and ¹³C NMR spectroscopy. Treatment of [Pd₂(L – 2H)(PPh₃)₂Cl₂] with MeCO₂H and LiCl produces at room temperature the nitrogen-protonated species [Pd₂L(PPh₃)₂Cl₄], but trans-[Pd₂(PPh₃)₂Cl₄] and the metal-free ligand (L) are formed at 80 °C. The complex [Pd₂(L – 2H)Cl₂] undergoes exchange reaction with ligands capable of forming monocyclopalladated complexes. The crystal structure of [Pd₂(L – 2H)(PPh₃)₂Cl₂] has been determined: monoclinic, space group C2/c, a= 20.676(4), b= 12.436(3), c= 19.445(4)Å, β= 104.29(3)° and Z= 4; refinement led to R= 0.035 and R′= 0.043 using 3533 unique reflections with I > 2σ(I).