A 13C and 1H NMR spectroscopic investigation of the structure of the iminium ion with a dipolar form in metal complexes of 2-N-substituted N-confused porphyrins

Abstract

The crystal structures of chloro(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′) zinc(II) [Zn(2-NCH₂COOC₂H₅NCTPP)Cl; 4], (2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′) palladium(II) [Pd(2-NCH₂COOC₂H₅NCTPP); 5], bromo(2-aza-2-ethoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′) manganese(III) [Mn(2-NCH₂COOC₂H₅NCTPP)Br; 6], [2-aza-(3′-phenoxypropyl)-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′] nickel(II) [Ni(2-NCH₂CH₂CH₂OC₆H₅NCTPP); 7] and chloro(2-aza-2-methoxycarbonylmethyl-5,10,15,20-tetraphenyl-21-carbaporphyrinato-N,N′N′′) zinc(II) [Zn(2-NCH₂COOCH₃NCTPP)Cl; 8] have been established. The g value of 9.54, which was measured from the parallel polarization of the X-band EPR spectra in CHCl₃ at 4 K, is consistent with the high spin mononuclear manganese(III) centre (S = 2) in 6. The magnitude of the axial (D) zero-field splitting (ZFS) for the mononuclear Mn(III) centre in 6 was determined approximately to be 1.63 cm⁻¹ by paramagnetic susceptibility measurements. The NMR spectroscopic investigation of the iminium ion with a dipolar canonical contribution to the metal complexes 5–7, Pd(2-NCH₂C₆H₅NCTPP) (10) and Ni(2-NCH₂C₆H₅NCTPP) (11) in CDCl₃ is reported. A resonance between the dipolar canonical form II and covalent canonical form I exists for complexes 5–7, 10 and 11 in CDCl₃. To develop the correlations between δ¹³C [C(3)], δ¹H [H(3)] and the canonical form II in 5–7, 10 and 11, this work thoroughly examines the ¹³C and ¹H NMR of N⁺CH(Ar) fragment on seven metal complexes of 2-N substituted N-confused porphyrin. According to these results, the ¹³C [C(3)] and ¹H [H(3)] chemical shifts of the N⁺CH(Ar) fragment at 20 °C in CDCl₃ are separately located at 152.6 ± 0.5 and 8.30 ± 0.15 ppm respectively for the iminium ion. This exists as a dipolar canonical form II for complexes 5–7, 10 and 11, and the N–CH(Ar) group appears at 121.1 ± 0.1 ppm and 6.35 ± 0.01 ppm, which is in a covalent canonical form I contribution to complexes 4 and 8. X-Ray diffraction data indicate that N(2)–C(3) = 1.315 ± 0.011 Å for the dipolar contribution of 5–7, 10–13, while N(2)–C(3) = 1.331 ± 0.008 Å for the covalent contribution of 4 and 8.