Oxasmaragdyrin–Ferrocene and Oxacorrole–Ferrocene Conjugates: Synthesis, Structure, and Nonlinear Optical Properties

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Abstract

Ferrocenyl macrocyclic conjugates involving 22π oxasmaragdyrins and 18π oxacorroles have been synthesized and characterized. The direct covalent linkage of the ferrocenyl moiety to the meso position of the macrocycle is achieved by simple oxidative coupling of appropriate precursors with trifluoroacetic acid as catalyst. The electronic coupling between the ferrocenyl moiety and the macrocyclic π system is apparent from: a) the red shifts (293–718 cm−1) of the Soret and Q-bands in the electronic absorption spectra of ferrocenyl conjugates; b) the shift of oxidation potentials (50–130 mV) of both the ferrocene and the corrole rings to the positive potentials; and c) considerable shortening of the C[BOND]C bond which connects the ferrocene and the meso-carbon atom of the macrocycle. The single-crystal X-ray structure of oxasmaragdyrin–ferrocene conjugate 9 reveals the planarity of the 22π skeleton with very small deviations of the meso-carbon atoms. The meso-ferrocenyl substituent has a small dihedral angle of 38°, making way for mixing of the molecular orbitals of the ferrocene and the macrocycle. However, the other two meso substituents are almost perpendicular to the mean plane, defined by the three meso carbon atoms. Classical C[BOND]H⋅⋅⋅O and nonclassical C[BOND]H⋅⋅⋅π interactions lead to a two-dimensional supramolecular network. Ferrocene–smaragdyrin conjugate 9 bonds to a chloride ion in the protonated form and a rhodium(i) ion in the free base form. Nonlinear optical measurements reveal a larger nonlinear refractive index (−5.83×10−8 cm2 W−1) and figure of merit (2.28×10−8 cm3 W−1) for the rhodium smaragdyrin–ferrocene conjugate 19 than for the others, suggesting its possible application in optical devices.

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