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

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