MULTI-NUCLEAR NUCLEAR MAGNETIC-RESONANCE STUDY OF B4H8PF2N(CH3)2 - GEOMETRICAL AND ROTATIONAL ISOMERS AND THEIR DYNAMIC BEHAVIOR

The 1H, 11B, 19F, and 31P NMR spectra of B4H8PF2N(CH3)2 indicate that the compound exists as two isomers in solution. Low-temperature 19F NMR spectra demonstrate that these isomers are geometrical in nature. At low temperatures (-125 °C) rotation about the P-B bond in one isomer becomes slow on the experimental time scale, while this rotation remains rapid in the second isomer. Spectral simulations yield a ΔG* value of 7.8 kcal/mol for the barrier to rotation about the P-B bond in one of the geometrical isomers. At high temperature (80 °C) the two geometrical isomers interconvert rapidly on the 19F NMR time scale. Simulations of the high-temperature spectra yield a ΔG* value of 19 kcal/mol for the barrier to interconversion of these isomers. This value and other data including isotopic labeling studies are discussed in terms of the mechanism by which the geometrical isomers interconvert at high temperature. © 1979, American Chemical Society. All rights reserved.