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).