Synthesis of optically active P-chiral and optically inactive oligophosphines.

A series of optically active P-chiral oligophosphines (S,R,R,S)-2, (S,R,S,S,R,S)-3, (S,R,S,R,R,S,R,S)-4, and (S,R,S,R,S,R,R,S,R,S,R,S)-5 with four, six, eight, and 12 chiral phosphorus atoms, respectively, were successfully synthesized by a step-by-step oxidative-coupling reaction from (S,S)-1. The corresponding optically inactive oligophosphines 1'-5' were also prepared. Their properties were characterized by DSC, XRD, and optical-rotation analyses. While optically active bisphosphine (S,S)-1 and tetraphosphine (S,R,R,S)-2 behaved as small molecules, octaphosphine (S,R,S,R,R,S,R,S)-4 and dodecaphosphine (S,R,S,R,S,R,R,S,R,S,R,S)-5 exhibited the features of a polymer. Furthermore, DSC and XRD analyses showed that hexaphosphine (S,R,S,S,R,S)-3 is an intermediate between a small molecule and a polymer. Comparison of optically active oligophosphines 1-5 with the corresponding optically inactive oligophosphines 1'-5' revealed that the optically active phosphines have higher crystallinity than the optically inactive counterparts. It is considered that the properties of oligophosphines depend on the enantiomeric purity as well as the oligomer chain length.