CD-113 SHIELDING TENSORS OF THE CADMIUM COMPLEX OF TEXAPHYRIN, A NOVEL EXPANDED PORPHYRIN, AND ITS PYRIDINE AND BENZIMIDAZOLE ADDUCTS

The cadmium complex of an expanded five-coordinate porphyrin known as “texaphyrin” (Sessler et al. J. Am. Chem. Soc. 1988, 110, 5586) and its complexes with pyridine and benzimidazole have been investigated by solution- and solid-state 113Cd NMR spectroscopy. In chloroform solution at 25 °C, the spectrum of unligated, five-coordinate Cd-texaphyrin is observed as a single resonane at 163 ppm. Similarly, a deuterated pyridine solution at 25 °C of cadmium texaphyrin produces a single resonanee at 160 ppm. At −40° C in deuterated pyridine, three resonances, corresponding to a mixture of free Cd-texaphyrin (150 ppm) and six-coordinate (140 ppm) and seven-coordinate (210 ppm) pyridine complexes, are observed in slow exchange. The benzimidazole complex of Cd-texaphyrin in chloroform was observed as a single resonance at 158 ppm. From solid-state MAS results, a single tensor was observed for the five-coordinate complex with a corresponding isotropic chemical shift of 194 ppm. The MAS spectrum of the sample collected after preparation of the pyridine complex of Cd-texaphyrin revealed two tensors presumed to be due to a mixture of six- and seven-coordinate species. Based upon the isotropic chemical shifts and the symmetry of the tensors the six-coordinate species was assigned to the isotropic shift of 188 ppm and the seven-coordinate species as assigned to the isotropic shift of 221 ppm. The MAS spectrum of the benzimidazole complex of Cd-texaphyrin consisted of a single tensor, assumed to represent the six-coordinate species, with an isotropic chemical shift of 188 ppm. The principle shielding tensor elements were determined for each complex and are discussed in terms of reported crystal studies of Cd-texaphyrin and in comparison to cadmium complexes with other porphyrin and similar macrocycle ligands. © 1990, American Chemical Society. All rights reserved.