To assess the effects of a more electron-donating aryl ring on the properties of the pyrazolyl-phosphine oxides, azophosphine-borane p-OMe(C6H4)N2P( i Pr)2.BH3 (4, Scheme 2) was synthesised according to our general synthetic procedure. The spectroscopic data for this new compound are consistent with our previously reported azophosphine-boranes, and the single-crystal X-ray diffraction (SXRD) structure is shown in Figure (see ESI for details). 4 could be converted to the corresponding pyrazolyl-phosphine oxide 5 via the one-pot procedure in 56% yield (Scheme 2). In the 1 H NMR spectra of both 3 and 5, the -OH protons possess very downfield chemical shifts (both 11.1 ppm), consistent with the enol tautomers of the pyrazole unit, rather than the keto form. In the IR spectra for both compounds, only one C=O peak (from the ester moiety) is observed for each, also consistent with the enol form.