Bis(trifluoromethyl)phosphinous Acid(CF_3)_2P-O-H:An Example of a Thermally Stable Phosphinous Acid-Synthesis,Gas-Phase Structure,and Rotational Isomers

摘要

The bis(trifluoromethyl)-phosphinous acid,(CF_3)_2P-O-H,is the only known example of a thermally stable phosphinous acid.Although this compound has been known since 1960,little is known about the chemistry of this extraordinary compound;this might be due to the tedious,and in some part risky,synthesis that was originally published.An improved,simple,and safe synthesis that is based on the treatment of the easily accessible(CF_3)_2PNEt_2,with at least three equivalents of p-toluene sulfonic acid,is presented.The reaction results in a complete conversion to the phosphinous acid,which is isolated in almost 90% yield.The compound exists in an equilibrium of two P- OH rotational iso-mers,a fact which is supported by quantum chemical calculations.The relative enthalpy difference of 6.4kJmol~(-1),calculated at the B3PW91/ 6-311G(3d,p)level,is in excellent agreement with the experimental value of 5.9 kJ mol~(-1),which was determined from the temperature dependence of the v(OH)bands of the two rotational isomers.The complete experimental vi-brational spectra of both rotamers,their predicted vibrational spectra obtained by using quantum chemical calculations,and an attempt at photoin-duced isomerization of matrix-isolated(CF_3)_2POH is presented.The experimental structure,obtained from an electron-diffraction study in the gas phase,is reproduced very well by ab initio and density functional theory(DFT)methods.