Metal Coordination-Induced Electronic Tuning in Fused Polyheterocycles: Synthesis and Characterization of Cu, Zn and Fe Complexes of Benzo[a]furo[2,3-c]phenazine, Furo[3′,2′:3,4]naphtho[1,2-d]imidazole and Naphtho[1,2-b]furan-4,5-dione

We report the synthesis, characterisation and electronic modulation of three novel fused polyheterocyclic ligands—naphtho[1,2-b]furan-4,5-dione (1), furo[3′,2′:3,4]naphtho[1,2-d]imidazole (2), and benzo[a]furo[2,3-c]phenazine (3)—and their Cu(II), Zn(II) and Fe(II/III) complexes. Compound (1) was isolated at 96.5% yield using fulvic acid as a green organocatalyst. 57Fe Mössbauer spectroscopy identified two high-spin Fe(III) environments in a 37:63 ratio (δ = 0.377 mm s−1; Δ = 0.62 and 1.01 mm s−1), with no evidence of magnetically ordered oxide phases. Six enantiomeric metal malate salts were synthesised at 86–93% yield for spectrophotometric titrations. The key finding is a striking Cu(II)-specific enantioselective molecular recognition: (3) binds (S)-(−)-malate Cu(II) with log K = 9.02, a factor of 2.5× higher than the (R)-(+)-malate complex (log K = 8.62), while Fe(II) and Zn(II) show no enantioselectivity. These results establish chiral counter-ion engineering combined with π-conjugated polyheterocyclic scaffolds as a powerful strategy for chiroptical sensing and asymmetric catalysis.