The solution conformation and rotational dynamics of tetramesityldiphosphane studied by 2-D NMR spectroscopy

Detailed proton and C-13 dynamic NMR and 2-D EXSY studies of tetramesityldi phosphane at a field of 11.8 T over the temperature range 193-313 K showed that rotations about the P-P bond and two types of P-C-ipso bond are associ ated with three different barriers. This supports a gauche conformation of this molecule in solution at low temperature rather than trans as found in the solid state, and is consistent with the pattern of coupling constants o bserved in the low temperature proton and C-13 spectra. It can be attribute d to favoured electron lone pair/lone pair interactions allied to a propell er twist of the mesityl groups which minimises their effective steric requi rements.