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

2009, Inorganic Chemistry

New pyridyl meso-tetraarylporphyrins (TArP, Ar = -C 6 H 4 -) of the general formula, T(R 1 R 2 NSO 2 Ar)P (R 1 = N-py-n-CH 2 (n = 2 or 4) and R 2 = CH 3 ), have been synthesized by the versatile approach of utilizing meso-tetra(4chlorosulfonylphenyl)porphyrin. After characterization by mass spectrometry and by visible absorption and 1 H NMR spectroscopy, the porphyrins were converted to various metalloderivatives, including Cu(II) and Zn(II). Treatment of T (N-py-4-CH 2 (CH 3 )NSO 2 Ar)P (5) or TpyP(4) (meso-tetra(4-pyridyl)porphyrin) with CH 3 Co(DH) 2 H 2 O (DH = monoanion of dimethylglyoxime) afforded [CH 3 Co(DH) 2 ] 4 T(N-py-4-CH 2 (CH 3 )NSO 2 Ar)P (6) and [CH 3 Co(DH) 2 ] 4 TpyP(4) (7). Typically, basic pyridines shift the axial methyl 1 H NMR signal of CH 3 Co(DH) 2 L upfield but leave the equatorial methyl signal unshifted. However, both signals for [CH 3 Co(DH) 2 ] 4 TpyP(4) are ∼0.2 ppm more downfield than normal, suggesting perhaps an extremely non-basic pyridyl group. However, TpyP(4) forms CH 3 Co(DH) 2 py adducts with binding ability comparable to that of other pyridine ligands with normal basicity and to that of T(N-py-4-CH 2 (CH 3 ) NSO 2 Ar)P. Consequently, in 7 the deshielding of the methyl signals, even the axial Co-CH 3 signal, is attributed to anisotropy of the porphyrin core. The methyl signals for [CH 3 Co(DH) 2 ] 4 T(N-py-4-CH 2 (CH 3 )NSO 2 Ar)P (6) have normal shifts. The absence of an anisotropic effect is attributable to the large distance of the CH 3 Co(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 [CH 3 Co(DH) 2 ] 4 TpyP(4) (7) (all of which have C i symmetry) support the spectroscopy. For example, the Co-N ax bond lengths of [CH 3 Co(DH) 2 ] 4 TpyP(4) (2.055(4) and 2.079(4) Å ) are comparable to that of CH 3 Co(DH) 2 py (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.