Synthesis of some di- and tetraphosphonic acids by Suzuki cross-coupling

Five diphosphonic acids, namely, benzene-1,4-bis-p-phenylphosphonic acid (1), anthracene-9,10-bis-p-phenylphosphonic acid (2), benzene-1,2-bis-p-phenylphosphonic acid (3), benzene-1,3-bis-p-phenylphosphonic acid (4), and biphenyl-4,4′-bis-p-phenylphosphonic acid (5) as well as three tetraphosphonic acids, namely, benzene-1,2,4,5-tetrakis-p-phenylphosphonic acid (6), tetrabiphenylsilane tetrakis-4-phosphonic acid (7), and pyrene-1,3,6,8-tetrakis-p-phenylphosphonic acid (8) and their dimethyl esters 1a–8a were prepared via Suzuki cross-coupling reactions involving p-dimethylphosphonatophenylboronic acid and brominated aromatics. The Suzuki cross-coupling occurs under milder conditions than the transition metal catalyzed Arbuzov reaction usually applied for the preparation of dialkyl phosphonates. For the same starting material both reactions are complementary and yield phosphonic acids with different spacer lengths, which was exemplified for tetrakis(4-bromophenyl)silane. Suzuki cross-coupling gives rise to 7, whereas the Arbuzov reaction produces tetraphenylsilane tetrakis-4-phosphonic acid.