1,2-Bis(2,6-diisopropylphenyl)diphosphane: a structural, spectroscopic, and computational investigation

The title compound Dipp(H) P-P(H)Dipp where Dipp = 2,6-diisopropylyphenyl has been prepared starting from DippPH(2) via DippPHLi reacting 2:1 with BrCH2CH2Br. A high-resolution single-crystal X-ray diffraction study at 153 +/- 2 K provides an accurate description of the structure in the solid state, only the fourth dihydro diorganophosphane to have been so characterized. The Raman spectrum of the solid shows an intense, broad peak for P-H stretching at 2314 cm(-1) and two peaks at 460 and 450 cm(-1) for P-P stretching, assignments confirmed by RHF/6-31G+(3d,2p) frequency calculations undertaken on the anti conformers. P-31, P-31{H-1}, H-1{P-31}, and C-13{H-1} solution NMR spectra in CDCl3 are consistent with the presence of 58% meso and 42% rac diastereomers. Analysis of their AA'XX' spin systems enabled calculation of (1)J(PP') values of (-)189 and (-)205 Hz, respectively. A B3LYP/6-31G(d,p) computational analysis of the energetics of rotation about the P-P bond in both diastereomers shows that the anti and two gauche conformers are likely to be populated approximately equally in each. The resulting average phi angles (torsions of the phosphorus lone pairs) are 110 degrees for meso and 103 degrees for rac; the smaller phi angle fits with the larger (1)J(PP') value for the rac isomer.