Mono-, di- and poly-nuclear transition-metal complexes of a bis(tridentate) ligand: towards p-phenylenediamine-bridged co-ordination polymers

Abstract

The bis(tridentate) ligand N,N,N′,N′-tetrakis(2-pyridylmethyl)benzene-1,4-diamine (1,4-tpbd) is multifunctional in that mono-, di- and poly-nuclear transition-metal complexes as well as bis-co-ordinated complexes can be prepared. A prototype example of each class of complex has been characterized. In [ZnCl₂(2,4-tpbd)] the 1,4-tpbd is co-ordinated via only one of its tridentate ends. Both ends of 1,4-tpbd are bound in a dipalladium complex. [Pd₂Cl₂(1,4-tpbd)][PdCl₃(dmso)]₂. This structure constitutes the first example of a crystal structure of the counter anion [PdCl₃(dmso)]^–. The chloride salt of the [Pd₂Cl₂(tpbd)]²⁺ cation has also been isolated. In the structures of both [ZnCl₂(1,4-tpbd)] and [Pd₂Cl₂(tpbd)]²⁺ quinoid character of the benzene linker of the 1,4-tpbd is evident. The compound [Ru(1,4-tpbd)₂][PF₆]₂ is an example of a bis-co-ordinated complex. One tridentate end of each ligand is co-ordinated to the ruthenium(II) ion while the other end is unco-ordinated. These three contrasting complexes demonstrate the versatility of 1,4-tpbd as a ligand for transition-metal complexes and the series represent the structural elements required for the construction of homo- and hetero-nuclear co-ordination oligo- or poly-mers. The compositions of the products isolated from the reaction of 1,4-tpbd with iron and nickel are consistent with the polymeric formulations [M(1,4-tpbd)]_nA_2n (M = Fe, A = Cl; M = Ni, A = NO₃).