PROTON MAGNETIC RESONANCE LINE BROADENING OF METHANOL AND TRICHLORO- AND TRIFLUOROETHANOL BY VANADYL COMPLEXES

The line broadening of the methyl and hydroxy protons of solvent methanol caused by VO(CH3OH)52+ shows typical chemical exchange control above 0° with the OH protons exchanging faster than the CH3 protons. The results are interpreted in terms of proton dissociation from the coordinated hydroxy group (ΔH‡ = 10.9 kcal mol-1, ΔS‡ = -5.3 cal mol-1 deg-1) and solvent methanol molecule exchange (ΔH‡ = 9.46 kcal mol-1, ΔS‡ = -14.2 cal mol-1 deg-1). Bis (acetylacetonato )-vanadyl (VO(acac)2) causes chemical exchange control of the hydroxy proton line broadening only in methanol (ΔH‡ = 11.79 kcal mol-1, ΔS‡ = 3.1 cal mol-1 deg-1) and trichloroethanol (ΔH‡ = 6.41 kcal mol-1, ΔS‡ = -11.5 cal mol-1 deg-1). This complex in trifluoroethanol shows no chemical exchange behavior. The hydroxy proton exchange rate is obtained for bis(trifluoroacetylacetonato)vanadyl (VO(tfac)2) in methanol (ΔH‡ = 11.1 kcal mol-1, ΔS‡ = -2.6 cal mol-1 deg-1). The mechanism for proton exchange is discussed. The kinetic results and the interpretation of the dipole-dipole interaction line broadening observed at low temperatures show that the vanadyl complexes are six-coordinate in these alcohol solvents. © 1969, American Chemical Society. All rights reserved.