Tin(IV) and Antimony(V) Complexes Bearing Catecholate Ligands Connected to Ferrocene – Syntheses, Molecular Structures, and Electrochemical Properties

The ferrocenyl‐containing 3,5‐di‐tert‐butylcatechol Fc‐L‐CatH₂ (2) was synthesized by the condensation of the precursor 6‐(hydrazonomethyl)‐3,5‐di‐tert‐butylcatechol 6‐(H₂N–N=CH)CatH₂ (1) with ferrocenecarboxaldehyde (L = –CH=N–N=CH–, Cat = 3,5‐di‐tert‐butylcatecholate, Fc = ferrocene). The exchange reaction between catechol 2 and Ph₃SbBr₂ in the presence of a base (Et₃N) in toluene leads to the formation of the triphenylantimony(V) catecholate (Fc‐L‐Cat)SbPh₃ (3) as the main product and the ionic bromotriphenylantimony(V) catecholate (Fc‐LH‐Cat)SbPh₃Br (4) containing a hydraziniumylidene cation (LH = –CH=NH⁺–N=CH–) as the byproduct. The change of toluene to tetrahydrofuran (THF) results in the formation of 4 as the main product in nearly quantitative yield. The exchange reactions of catechol 2 with Ph₂SnCl₂ and SnCl₄ give anionic catecholate complexes bridged with hydraziniumylidene cations even in the presence of excess base. Complexes (Fc‐LH‐Cat)SnPh₂Cl (5), (Fc‐LH‐Cat)₂SnPh₂ (6), and (Fc‐LH‐Cat)₂SnCl₂ (7) were synthesized. The compounds obtained were characterized by IR spectroscopy, ¹H and ¹³C NMR spectroscopy, elemental analysis, and cyclic voltammetry. The molecular structures of crystals of 5–7 were determined by X‐ray diffraction analysis. The formation of catecholates 4–7 with hydraziniumylidene cations is caused by intramolecular hydrogen bonding between the hydroxy and imine groups, which leads to proton transfer from the oxygen atom to the nitrogen atom of the hydrazine linker.