Abstract
The reactivity of a mixed-ligand alkylamino-β-ketoenolato decanoatophthalocyaninate of hafnium was investigated by 1H NMR spectroscopy via substitution of axial ligands in reactions with para-isopropoxybenzoic acid and dibenzoylmethane. The initial complex PcHf(C₉H₁₉COO)L was shown to exhibit high reactivity. It was established that the presence of different axial ligands enables their selective or complete substitution depending on the nature of the reagent. In the reaction with para-isopropoxybenzoic acid, only the decanoate ligand is replaced, leading to the formation of a new mixed-ligand complex PcHf(C₁₀H₁₁O₃)L. The 1H NMR spectrum of the obtained complex displays signals of the phthalocyanine macrocycle protons (9.5–8.1 ppm) and the para-substituted benzoate fragment (7.5–7.4 ppm). Signals corresponding to the alkylamino-β-ketoenol ligand are observed in the region 7.2–5.5 ppm, as well as in the aliphatic region. The absence of signals corresponding to the decanoate chain protons (0.0–0.5 ppm) and the appearance of signals of the isopropyl methyl protons (2.27 ppm) confirm the completion of the ligand exchange reaction. In contrast, the reaction of PcHf(C₉H₁₉COO)L with dibenzoylmethane results in complete substitution of both axial ligands (decanoate and alkylamino-β-ketoenolate), yielding bis(dibenzoylmethanato)hafnium phthalocyaninate. The 1H NMR spectrum of the product shows no signals of either decanoate or alkylamino-β-ketoenolate protons and matches the previously reported spectrum of PcHf(dbm)₂. A stability series of chelate rings in the coordination sphere of hafnium phthalocyaninates was established. The strength of ligand binding to the central metal atom increases in the following order: aliphatic carboxylate < aromatic carboxylate < alkylamino-β-ketoenolate < β-diketonate. The obtained results expand the possibilities for the targeted synthesis of out-of-plane coordinated phthalocyanine complexes, enabling the tuning of their physicochemical properties (such as solubility and spectral characteristics) for potential applications in photodynamic therapy, organic semiconductors, and sensors.
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