Synthesis of phenanthroline derivative by Suzuki coupling reaction and the use of its ruthenium complex as an optical pH sensor

A phenanthroline derivative, which has an aniline group, was synthesized by palladium catalyzed Suzuki cross coupling reactions. The aryl phosphine ligand, PPh3, showed higher activity than the alkyl phosphines, P(tBu)3 and PCy3, in the Suzuki couplings and provided the coupled product, 4-phenyl-7-(4′-amino-biphenyl-4-yl)-[1,10]phenanthroline (5), with 73% yield. Its ruthenium complex, bis(4,7-diphenyl-[1,10]phenanthroline){4-phenyl-7-(4′-amino-biphenyl-4-yl)-[1,10]phenanthroline} ruthenium(II) bis(hexafluorophosphate) (8), was synthesized under mild conditions. This complex showed a linear fluorescence intensity response between pH 3.5 and pH 8.5.