2,6-Dimethylphenol derived H-phosphonate and α-hydroxyphosphonate: facile synthesis, crystal chemistry, supramolecular association and metal complexation

Abstract

Facile synthesis of a H-phosphonate [(ArO)P(O)H(OH)] (2) and an α-hydroxyarylphosphonate [(ArO)P(O)(OH)(CMe₂OH)] (3) has been achieved through the hydrolysis of [(ArO)PCl₂] (1) with toluene and acetone as the solvent, respectively. The dichloride (1) itself was synthesized from the reaction of ArOH (Ar = 2,6-Me₂C₆H₃O) with phosphorous trichloride. The unstable H-phosphonate (2) and the three different crystalline modifications of the α-hydroxyarylphosphonate (3) (viz., ansolvate, solvate and hydrate) have been crystallized under different crystallization conditions and their molecular structures have been determined by single crystal X-ray diffraction studies. These four crystalline forms exhibit either two-dimensional sheet-like polymeric structures or tubular structures with water channels, assisted by supramolecular interactions such as H-bonding, CH–π, etc. Crystallisation of the α-hydroxyarylphosphonate (3) from a warm dimethylformamide solution leads to the ready decomposition of the solvent to the dimethylammonium cation, giving the salt of 3, [Me₂NH₂][(ArO)(CMe₂OH)POO] (6). The reactivity of the α-hydroxyarylphosphonate 3 with metal acetates has been investigated and its copper and zinc complexes [M(HL)₂(2,2′-bpy)(H₂O)](H₂O) (M = Cu (7); Zn (8) (HL = [(ArO)P(O)(O)(CMe₂OH)]⁻) have been isolated and structurally characterized. Mononuclear 7 and 8 form linear polymeric chains assisted by intermolecular H-bonding interactions involving a large number of proton donor and acceptor sites present in these complexes.