Catalytic activity of asymmetric monobenzoylmonobenzotetraazacyclo[14]tetradecinatonickel(II) complexes: X-ray crystal structure of monobenzo-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclo[14]tetradecinatonickel(II)

Abstract

The complexes, 3-(p-Ymonobenzoyl)-Xmonobenzo-2,4,9,11-tetramethyl-1,5,8,12-tetraazacyclo [14]tetradecinato(2−)nickel(II), Y = CH₃, H, Cl, NO₂ or OCH₃, X = H (A) or NO₂ (B) have been synthesized and characterized. IR spectra of the complexes show intense bands in the region 1641–1647 cm⁻¹ attributed to the stretching modes of C=O. Electronic absorption spectra for the A series exhibit π → π* and ligand to metal charge transfer (LMCT) transitions, while for the B series an additional band appears between 440 and 452 nm, which might be due to another charge transfer. ¹H NMR spectra show an anisotropic magnetic effect due to the benzoyl group. Voltammograms of the complexes show two one-electron irreversible oxidation peaks in the range +100 to +800 mV and two, three or four reduction peaks between −1200 and −2800 mV, depending on substituents. Hammett plots of first and second oxidation potentials for the A series had slopes of 37 and 54 mV (22 and 39 mV for the B series), respectively. In oxidations of p-Zstyrenes (Z = OCH₃, CH₃, H, F or Cl) catalyzed by the complexes, conversion yields of substrates are appreciably affected by substituents of substrates and complexes. The structure of the precursor complex 1 with X = H and without any attached benzoyl group (orthorhombic, P2₁2₁2₁, a = 7.923(6), b = 8.429(7), c = 24.18(2) Å, Z = 4, R1 = 0.0224 and wR2 = 0.0577) was characterized using single-crystal X-ray diffraction methods.

Keywords:

• Monobenzoylmonobenzotetraazacyclo[14]annulenenickel(II)
• LMCT and redox potential
• X-Ray structure

Acknowledgments

This work was supported by a Korea Research Foundation Grant (KRF-2004-005-C00009).