Proton‐Catalysed Cleavage of Enol Phosphates and Phosphonates

Abstract

Reduction of an ethereal solution of chloropentakis(trifluoro-ph0sphine)rhenium [21 (0.12 niole/l) with an excess of about 1 7; potassium amalgam at 20 "C affords potassium pentakis-(trifluorophosphine)rhenate, which on treatment with 88 % phosphoric acid forms HRe(PF&, thc first hydrido-trifluorophosphine complex of a group VIIA metal. Use of D3P04 affords the analogous deuterido compound. CHI C2Hs C2H5 CH3 CH3 CH3 CH3 CHI HRe(PF3)5 is, however, also directly accessible, in 40 % yield, by reduction of ReCIs with Cu powder (molar ratio ca. 1 : 40) at 300 OC with a PF3 pressure of 250 atm and a H2 pressure of 100 atm. It is purified by sublimation. Hydridopentakis(trifluorophosphine)rhenium resembles the monohydrido compounds HM(PF3)4 of cobalt and iridium [31 in its high thermal and chemical stability. The colorless, centimeter-long needles of this hydrophobic compound (m.p. 42OC, decomp. from 160°C) sublime at 2O0C/1O mm and are stable for several days in dry air. The covalent nature of the Re-H bond is confirmed by an intense Re-H stretching vibration at 1882 (m) cm-1[41 [GR~-D = 1346 (m) cm-11 and the strong chemical shift to high field of its broad 1H-NMR signal (no fine structure)[sl (8 = 8.2 ppm; TMS as internal standard). The P-F vibrations are at 971(w), 918 (vs), 877 (s), 869 (s), and 860 (m-s) cm-1.