Synthetic strategies to achieve further-functionalised monoaryl phosphate primary building units: crystal structures and solid-state aggregation behavior

Abstract

New 4-halo functionalized 2,6-diisopropyl phenyl phosphates, X-dippH₂ [(RO)P(O)(OH)₂] (R = 4-X-2,6-ⁱPr₂C₆H₃; X = Cl 1, Br 2, I 3) have been synthesized in two steps starting from the corresponding 4-halophenols and characterized by analytical, spectroscopic, and single crystal X-ray diffraction studies. Isomorphous organophosphates 1–3 form a tubular structure in the solid state through extensive hydrogen bonding interactions between adjacent –PO₃H₂ groups, an aggregation previously unknown among organophosphates and phosphonic acids. The methyl ester of 2, [(RO)P(O)(OMe)₂] (R = 4-Br-2,6-ⁱPr₂C₆H₃) (4), was reacted with a series of boronic acids under Suzuki coupling conditions to yield the corresponding C–C bond coupled products, 3,5-diisopropylbiphenyl-4-yl dimethyl phosphate (5), 4′-formyl-3,5-diisopropyl-biphenyl-4-yl dimethyl phosphate (6) and 4′-(diphenylmethyleneamino)-3,3′,5,5′-tetraisopropyl-biphenyl-4-yl dimethyl phosphate (7). The possible reaction conditions for the selective deprotection of phosphate triesters have been established, under which 6 yields 4′-formyl-3,5-diisopropyl-biphenyl-4-yl dihydrogenphosphate (8). Compound 8 is a formyl group functionalized phosphate and shows hydrogen bonding similar to 1–3 forming tubular channels surrounded by peripheral organic groups. The dangling formyl groups in phosphates 6 and 8 undergo intermolecular tail-to-tail hydrogen bonding forming 1-dimensional assemblies in the former and 3-dimensional supramolecules in the latter. Amino and formyl functionalized phosphates may serve as ideal primary building units for building suitably functionalized metal phosphate secondary building units.