Synthesis and characterisation of the new diaza ferrocene macrocycle 1,1′-( 2,6-diazahepta-1,6-diene) ferrocene and its parent amine 1,1′-( 2,6-diazaheptane ) ferrocene

Reaction of ferrocene-1,1′-dicarbaldehy de and propylenediamine yields the Schiff-base derivative 1,1′-(2,6-diazahepta-1,6-diene)-ferrocene (1). The molecular structure of 1 has been determined by single crystal X-ray analysis. It crystallises in the monoclinic system, space group P2₁/c, a=13.507(3), b=9.800(2), c=10.086(2) Å, β=110.81(3)°, Z=4 and V=1248.0(5) ų. Refinement of the atomic parameters by least-squares techniques gave a final R factor of 0.074 for 1588 observed reflections having 1>2σ(1), Hydrogenation of 1 with LiA1H₄ results in the parent amine 1,1′-(2,6-diazaheptane)ferrocene (2). The protonation of 2 has been investigated by potentiometry in water in the pH range 11-6. At pH lower than 6, 2 is unstable in solution. The E_1/2 potential for 2 is pH-dependent (E_1/2(pH 11) = 255, E_1/2(pH 6) =435 mV). A similar behaviour was also observed in THF:water (60:40 vol./vol.). The electrochemical behaviour for 1 and 2 has also been studied in CH₂Cl₂.