New Porphyrins Bearing Pyridyl Peripheral Groups Linked by Secondary or Tertiary Sulfonamide Groups: Synthesis and Structural Characterization

New pyridyl meso-tetraarylporphyrins (TArP, Ar = -C6H4-) of the general formula, T(R1R2NSO2Ar)P (R1 = N-py-n-CH2 (n = 2 or 4) and R2 = CH3), have been synthesized by the versatile approach of utilizing meso-tetra(4-chlorosulfonylphenyl)porphyrin. After characterization by mass spectrometry and by visible absorption and 1H NMR spectroscopy, the porphyrins were converted to various metalloderivatives, including Cu(II) and Zn(II). Treatment of T(N-py-4-CH2(CH3)NSO2Ar)P (5) or TpyP(4) (meso-tetra(4-pyridyl)porphyrin) with CH3Co(DH)2H2O (DH = monoanion of dimethylglyoxime) afforded [CH3Co(DH)2]4T(N-py-4-CH2(CH3)NSO2Ar)P (6) and [CH3Co(DH)2]4TpyP(4) (7). Typically, basic pyridines shift the axial methyl 1H NMR signal of CH3Co(DH)2L upfield but leave the equatorial methyl signal unshifted. However, both signals for [CH3Co(DH)2]4TpyP(4) are ∼0.2 ppm more downfield than normal, suggesting perhaps an extremely non-basic pyridyl group. However, TpyP(4) forms CH3Co(DH)2py adducts with binding ability comparable to that of other pyridine ligands with normal basicity and to that of T(N-py-4-CH2(CH3)NSO2Ar)P. Consequently, in 7 the deshielding of the methyl signals, even the axial Co−CH3 signal, is attributed to anisotropy of the porphyrin core. The methyl signals for [CH3Co(DH)2]4T(N-py-4-CH2(CH3)NSO2Ar)P (6) have normal shifts. The absence of an anisotropic effect is attributable to the large distance of the CH3Co(DH)2 moieties from the porphyrin core caused by the intervening linker in 6. Indeed, the separation led to only a slightly reduced (25%) fluorescence emission of 6 compared to 5, whereas that of 7 is considerably reduced (90%) compared to TpyP(4). The X-ray structures of 5, its Cu(II) complex, and [CH3Co(DH)2]4TpyP(4) (7) (all of which have C i symmetry) support the spectroscopy. For example, the Co−Nax bond lengths of [CH3Co(DH)2]4TpyP(4) (2.055(4) and 2.079(4) Å) are comparable to that of CH3Co(DH)2py (2.068(3) Å), consistent with the normal coordinating ability of TpyP(4). In an accompanying study, the new pyridylporphyrins have been converted to DNA-binding, water-soluble cationic porphyrins.