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Two-Step Transformation of Aliphatic Polyketones into π-Conjugated Polyimines
Yumehiro Manabe1, Mitsuharu Uesaka1, Tomoki Yoneda1
1Division of Applied Chemistry, Faculty of Engineering , Hokkaido University , Kita 13, Nishi 8 , Kita-ku, Sapporo , Hokkaido 060-8628 , Japan.
Abstract:
The chemo- and stereo-selective two-step transformation of aliphatic polyketones composed of 3,3-dimethylpentane-2,4-dione units was achieved to generate π-conjugated polyimines. Upon treatment with hydrazine, discrete oligoketones with 4-8 carbonyl groups afforded ethylene-bridged oligoisopyrazoles in 80-89% yields. These oligoisopyrazoles underwent stereoselective oxidation at the ethylene bridge to give fully π-conjugated oligo(isopyrazole-3,5-diyl-trans-vinylene)s in 73-87% yields. Oxidation of the oligoimines drastically changed their absorption and metal-coordination behaviors. Finally, this two-step transformation was applied to polydisperse polymers. Imine formation proceeded almost quantitatively, even for longer polyketones, including docosamer. Subsequent oxidation of the polyimines furnished a virtually insoluble material that showed broad and red-shifted solid-state absorption over the whole visible region resulting from extended π-conjugation.
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