Ligand Exchange Reaction for Controlling the Conformation of Platinum-Containing Polymers

Control of the conformation of polymers can be achieved by the <i>ligand exchange reaction</i> of optically active poly­(phenylene­ethynylene) <b>1′</b> containing −Pt­(PPh₃)₂– moieties in the main chain. Polymer <b>1′</b> was reacted with 1,2-bis­(diphenyl­phosphino)­ethane (dppe), 1,3-bis­(diphenyl­phosphino)­propane (dppp), and 1,4-bis­(diphenyl­phosphino)­butane (dppb) to give the corresponding polymers <b>2′</b>, <b>3′</b>, and <b>4′</b> containing −Pt­(dppe)–, −Pt­(dppp)– , and −Pt­(dppb)– moieties in the main chain, respectively. Polymers <b>1′</b> and <b>2′</b> exhibited negligibly small circular dichroism (CD) signals in THF, indicating the absence of regulated chiral structures, while polymers <b>3′</b> and <b>4′</b> exhibited strong CD signals in THF. The dynamic light scattering (DLS) analysis of the polymer solutions indicated that polymer <b>3′</b> formed a chirally regulated one-handed helix intramolecularly bridged with dppp, and polymer <b>4′</b> formed aggregates intramolecularly and/or intermolecularly bridged with dppb