Chiral discrimination in dimers of diphosphines PH₂-PH₂ and PH₂-PHF.

A theoretical study of the conformational profile of two diphosphines, PH2-PH2 and PH2-PHF, is carried using second-order Møller-Plesset perturbation theory (MP2) computational methods. The chiral minima found are used to build homo- and heterochiral dimers. Six minima are found for the (PH2-PH2 )2 dimers and 27 for the (PH2-PHF)2 dimers. Pnicogen and hydrogen bonds, the non-covalent forces that stabilize the complexes, are characterized by Atoms in Molecules (AIM) and Natural Bond Orbital (NBO) methodologies. Those with several pnicogen bonds are more stable than those with hydrogen bonds. The chirodiastaltic energies amount to a total of 1.77 kJ mol(-1) for the Ra:Ra versus Ra:Sa (PH2-PH2 )2 dimers, 0.81 kJ mol(-1) for the RSa:RSa versus RSa:SRa (PH2-PHF)2 dimers, and 2.93 kJ mol(-1) for the RRa:RRa versus RRa:SSa (PH2-PHF)2 dimers. In the first and second cases, the heterochiral complex is favored whereas in the third case, the homochiral complex is favored.