Use of MoO2Cl2(DMF)2 as a precursor for molybdate promoted hydrolysis of phosphoester bonds

Abstract

Phosphoester bond cleavage of para-nitrophenylphosphate (pNPP), a commonly used model substrate, is accelerated by using the complex MoO₂Cl₂(DMF)₂ (1) (DMF = dimethylformamide) as a hydrolysis promoting agent, even when catalytic amounts of 1 (10 mol% relative to pNPP) are used. The reactions were performed under mild conditions (37–75 °C) and followed by ¹H NMR spectroscopy. For assays performed with high amounts of 1 (1000 mol% relative to pNPP), a white solid (2) precipitates during the initial stages of the reaction, which subsequently dissolves, leading eventually to the precipitation of a less soluble yellow solid (3). Taken together, the characterization data for 2 (FT-IR spectroscopy, elemental analysis, ¹H and ¹³C NMR, and electrospray ionization mass spectrometry) indicate that it is a polymeric material with the formula Mo₂O₆(DMF)_n and a structure comprising infinite isopolyoxomolybdate chains built up from edge-shared {MoO₆} octahedra. Compound 3 was identified as the Keggin-type phosphomolybdate [(CH₃)₂NH₂]₃PMo₁₂O₄₀. The formation of 3 is explained by the reaction of inorganic phosphate ions with isopolymolybdate species derived from 2, with dimethylammonium ions arising from the degradation of DMF. Both 2 and 3 are active for phosphoester bond hydrolysis with conversion profiles comparable to the ones obtained with the precursor 1.