| |
[摘要]：To study the electrochem. properties of purpurinimide dyads and electron transfer sites for their redn. and oxidn., dimers with variable C-C linkages were synthesized. For the prepn. of these novel structures, the formyl and 2-formylvinyl substituents were regioselectively introduced at positions 3 and 20 of Ni(II) purpurinimides by the Vilsmeier reaction. The Ni(II) complexes were then subjected to the McMurry reaction under two different conditions with unexpected results. For example, the reaction of formyl purpurinimides with TiCl3(DME)1.5 failed to produce the desired C-C dimers, and the starting compds. were recovered almost quant. Under similar reaction conditions, the 20-(2-formylvinyl)purpurinimide also did not dimerize but produced instead unexpected benzoisobacteriochlorins via an intramol. cyclization. However, treatment of the 3-formyl- and 20-formylpurpurinimides with TiCl4/Zn produced corresponding dimers linked with one double bond (trans) in modest yields. Under similar conditions, Ni(II) purpurinimides contg. a 2-formylvinyl substituent either at position 3 or at position 20 afforded the resp. C-C dimers, where the purpurinimide moieties were joined with a trans-trans-trans hexatriene linker. Mol. modeling data suggest that the nature of the conformational energy difference found in all trans vs. trans-cis-trans conformers of the dimers connected by a hexatriene linker at the meso- or b-position of the macrocycle is not because of the intrinsic conformational energy difference of the linker region, which is identical for both dimers. |
|
