Conformational Landscapes of Metal(II) Porphyrinato, Chlorinato, and Morpholinochlorinato Complexes

The macrocycle conformation of [meso-tetraarylporphyrinato]metal complexes is metal-dependent. Furthermore, hydroporphyrins and some of their analogues are known to be more conformationally flexible than the parent porphyrins, but the extent to which this is reflected in their metal-dependent conformations was much less studied. meso-Tetraarylmorpholinochlorins are intrinsically nonplanar chlorin analogues in which the five-membered pyrroline moiety was replaced by a six-membered morpholine moiety. The metal complexes (M = Ni2+, Cu2+, Zn2+, Pd2+, Ag2+) of meso-aryl-2,3-dimethoxychlorins and meso-arylmorpholinochlorins were prepared. Their conformations were determined using X-ray crystal structure diffractometry and compared against those of their free bases, as well as against the conformations of the corresponding metalloporphyrins. Out-of-plane displacement plots visualized and quantified the conformational changes upon stepwise conversion of a pyrrole moiety to a dimethoxypyrroline moiety and to a dia...