1,3,5-benzene-tri-p-phenylphosphonic acid.: A new building block in supramolecular chemistry

Benzene-1,3,5-tri-p-phenylphosphonic acid, 1,3,5-[p-C6H4P(O)(OH)(2)](3)C6H3, (8), a novel building block for applications in supramolecular chemistry, was prepared in two steps with an overall yield of 82%. The [Pd(PPh3)(4)]-catalyzed Arbuzov reaction of 1,3,5-tris(p-bromophenyl)benzene with P(Oi-Pr)(3) afforded benzene-1,3,5-tri-p-phenylphosphonic diisopropyl ester, 1,3,5-[p-C6H4P(O)(Oi-Pr)(2)](3)C6H3 (9). The hydrochloric acid-catalyzed hydrolysis of 9 produced 8, which forms a crystalline salt with p-dimethylaminopyridine (DMAP) in a ratio of 2:3 (as methanol solvate) that was characterized by X-ray crystallography. The supramolecular structure features organic domains of stapled 1,3,5-triphenylbenzene units associated by PO-H center dot center dot center dot OP hydrogen bonds and pi-stacking. These staples are horizontally cross-linked by PO-H... OP hydrogen bonds. The protonated DMAP molecules fill the voids between the staples and participate in the stabilization of the framework by formation of N-H center dot center dot center dot OP hydrogen bonds. The melting point of the adduct (381 degrees C) confirms the high thermal stability of the supramolecular framework.