1,1'-Ferrocenedicarboxylate-bridged redox-active organotin and -tellurium-containing 16-membered macrocycles: synthesis, structure, and electrochemistry

Abstract

The reaction of 1,1'-ferrocenedicarboxylic acid, LH₂, with diorganotin halides R₂SnCl₂ (R = n-Bu and Bn) or Ar₂TeCl₂ (Ar = 4-OMe-C₆H₄) in the presence of triethylamine afforded, in nearly quantitative yields, heterobimetallic tetranuclear macrocycles [R₂SnL]₂ and [Ar₂TeL]₂. The molecular structures of these compounds have been confirmed by single-crystal X-ray analysis and show that the two main-group metal atoms within each macrocycle are bridged to each other by two ferrocene carboxylate ligands. In the case of the organotin derivatives the ferrocenedicarboxylate ligand acts in an anisobidentate chelating manner, leading to a hexacoordinate tin present in a skewed trapezoidal bipyramid geometry. In contrast, in the tellurium analogue the ferrocenecarboxylate ligand is monodentate, leading to a tetracoordinate tellurium in a seesaw geometry. ESI-MS studies on these macrocylic complexes reveal that they retain their structural integrity in solution. Electrochemcial studies reveal that [n-Bu₂SnL]₂ and [Ar₂TeL]₂ show two quasi-reversible oxidation processes. These compounds have low comproportionation constants (K_c) and can be described as being intermediate between noncoupling and weakly coupled systems. [Bn₂SnL]₂ also shows two oxidation processes. However, in this instance, the second event is irreversible.