Synthesis of oligomers including eight P-chiral centers and the construction of the 12-phosphacrown-4 skeleton

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.

Synthesis of a Stimuli-Responsive P-Chiral Polymer with Chiral Phosphorus Atoms and Azobenzene Moieties in the Main Chain

A reaction of the P-chiral compound (S,S)-1,2-bis(boranato(tert-butyl)methylphosphino)ethane with an azobenzene derivative gave stimuli-responsive polymers with P-chiral phosphines in the main chain. This is the first example of a stimuli-responsive P-chiral polymer. The polymer isomerized from the trans to the cis form upon UV irradiation and reverted to the trans form reversibly. The polymer was able to coordinate to platinum, and the resulting polymer complex exhibited the Cotton effect owing to the chirality of the phosphorus atoms. The structure of the P-chiral polymer obtained could be changed reversibly by light and thermal stimuli, and the polymer chain was induced to rotate helically when complexed with transition metals through the chiral phosphorus atoms.