Axial zero-field splitting in mononuclear Co(ii) 2-N substituted N-confused porphyrin: Co(2-NC3H5-21-Y-CH2C6H4CH3-NCTPP)Cl (Y = o, m, p) and Co(2-NC3H5-21-CH2C6H5-NCTPP)Cl

Abstract

The inner C-benzyl- and C-o-xylyl (or m-xylyl, p-xylyl)-substituted cobalt(II) complexes of a 2-N-substituted N-confused porphyrin were synthesized from the reaction of 2-NC₃H₅NCTPPH (1) and CoCl₂·6H₂O in toluene (or o-xylene, m-xylene, p-xylene). The crystal structures of diamagnetic chloro(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-hydrogen-21-carbaporphyrinato-N,N′,N′′)zinc(II) [Zn(2-NC₃H₅-21-H-NCTPP)Cl; 3 ] and paramagnetic chloro(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-benzyl-21-carbaporphyrinato-N,N′,N′′)cobalt(II) [Co(2-NC₃H₅-21-CH₂C₆H₅NCTPP)Cl; 7], and chloro(2-aza-2-allyl-5,10,15,20-tetraphenyl-21-Y-xylyl-21-carbaporphyrinato-N,N′,N′′)cobalt(II) [Co(2-NC₃H₅-21-Y-CH₂C₆H₄CH₃NCTPP)Cl] [Y = o (8), m (9), p (10)] were determined. The coordination sphere around the Zn²⁺ (or Co²⁺) ion in 3 (or 7–10) is a distorted tetrahedron (DT). The free energy of activation at the coalescence temperature T_c for the exchange of phenyl ortho protons o-H (26) with o-H (22) in 3 in a CDCl₃ solvent is found to be ΔG^‡₂₉₃ = 61.4 kJ mol⁻¹ through ¹H NMR temperature-dependent measurements. The axial zero-field splitting parameter |D| was found to vary from 35.6 cm⁻¹ in 7 (or 30.7 cm⁻¹ in 8) to 42.0 cm⁻¹ in 9 and 46.9 cm⁻¹ in 10 through paramagnetic susceptibility measurements. The magnitude of |D| can be related to the coordination sphere at the cobalt sites.