1,10-Phenanthroline Carboxylic Acids for Preparation of Functionalized Metal-Organic Frameworks

Synthetic approaches to 1,10-phenanthroline-3-carboxylic acid (2), 1,10-phenanthroline-3,8-dicarboxylic acid (3) and their functionalized derivatives were investigated. Acids 2 and 3 were prepared in good yields from bromophenanthrolines via palladium-catalyzed alkoxycarbonylation. Moreover, butyl 8-bromo-1,10-phenanthroline-3-carboxylate was obtained in acceptable yield (25-35%) by ceasing the carbonylation of the dibromide 5 after 30-70% consumption of the starting compound. To prepare functionalized derivatives of acids 2 and 3, the reactions of butyl 8-bromo-1,10-phenanthroline-3-carboxylate and diethyl 4,7-dichloro-1,10-phenanthroline-3,8-dicarboxylate with various nucleophiles were investigated. SNAr reactions are suitable for the synthesis of 4,7-diazido-, dimethoxy- and diamino-substituted 3,8-bis(ethoxycarbonyl)phenanthrolines, including the macrocyclic derivatives. The bromine atom at position 8 of the phenanthroline ring reacts with nucleophiles only in the presence of the palladium catalysts. The scope of these reactions was briefly investigated conducting Sonogashira, Suzuki-Miyaura and Hirao reactions. Hydrolysis of the functionalized esters of phenanthroline leads to corresponding acids in good yields.