1,1‘-Ferrocenedicarboxylate-Bridged Redox-Active Organotin and -tellurium-Containing 16-Membered Macrocycles: Synthesis, Structure, and Electrochemistry

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 (Kc)
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.