Dual-mode coupling copolymerization of aryl dialdehyde and alkynylaldehyde monomers via Concurrent McMurry olefination and alkyne [2+2+2] cycloaddition trimerization reactions mediated by a low-valent titanium reagent
Introduction
The McMurry coupling/olefination polymerization [1] of aryl dialdehydes is a useful method for the preparation of poly(arylene−vinylene)s, which have attracted much interest as materials for electronic devices such as OLEDs and semiconductors [2,3]. To promote the McMurry olefination reaction, the combination of TiCl3 or TiCl4 with a reductant such as Zn powder or LiAlH4 is normally used [4], and the low-valent titanium reagent can be prepared in refluxing tetrahydrofuran (THF) prior to the reaction with substrate(s), followed by heating the mixture with the substrate(s) to reflux. The system is heterogeneous slurry, and a large excess of reagent is often required.
We have recently developed a low-valent titanium (LVT) reagent, Ti(O-i-Pr)4/Me3SiCl/Mg, which is active for the McMurry coupling olefination of aromatic aldehydes, which provides the corresponding diarylethenes with a high E-selectivity (>95% E). This reagent can be readily prepared by mixing Ti(O-i-Pr)4, Mg powder, and Me3SiCl in THF at low temperature (room temperature to 55 °C) in the presence of substrate aldehyde(s) [5,6]. The reaction mixture is nearly homogenous except for the Mg powder, and the coupling/olefination proceeds with a small excess amount of the reagent. Herein, we report a Ti(O-i-Pr)4/Me3SiCl/Mg-mediated McMurry olefination polymerization of aromatic dicarbonyl compounds 1 (Equation 1, Scheme 1). In addition, we found that the Ti(O-i-Pr)4/Me3SiCl/Mg reagent enables the [2 + 2 + 2] cyclotrimerization of aromatic and aliphatic terminal alkynes to the corresponding trisubstituted benzenes [7,8], and the application of the reaction to the [2 + 2 + 2] cycloaddition polymerization of diyne monomers 2, which generates highly branched polymers, was also studied (Equation 2). Furthermore, the combination of these reactions led to the development of a novel dual-mode copolymerization of dialdehyde monomer 1 and alkynyl aldehyde monomer 3 via concurrent McMurry olefination and alkyne [2 + 2 + 2] cyclotrimerization reactions (Equation 3).
Section snippets
General
Nuclear magnetic resonance (NMR) spectra were recorded in CDCl3 at 600 and 500 MHz for 1H and 150 and 125 MHz for 13C on JEOL JNM-ECA600 and -ECA500 instruments, respectively. Chemical shifts are reported in parts per million (ppm, δ) relative to Me4Si (δ 0.00) or residual CHCl3 (δ 7.26 for 1H NMR) and CDCl3 (δ 77.0 for 13C NMR). Infrared (IR) spectra were recorded on a JASCO IR FT/IR 4100 spectrometer. High-resolution mass spectra (HR-MS) were measured on a JEOL Accu TOF T-100 equipped with an
McMurry olefination polymerization of aromatic dialdehyde
We have previously reported preliminary results of the McMurry olefination polymerization of aryl dialdehydes mediated by the LVT reagent Ti(O-i-Pr)4/Me3SiCl/Et3N/Mg [5,6]. Model reactions of aryl aldehydes revealed that the 1,2-diaryl-1,2-ethanediols with the coupled 1,2-diarylethene was obtained as by-product in the absence of Et3N. It was found that addition of Et3N diminished the production of diol coproducts.
Similarly, the amine additive was found to be effective in the application of the
Conclusions
Facile McMurry coupling polymerization of aryl dicarbonyl compounds and [2 + 2 + 2] cycloaddition polymerization of diyne monomers have been developed, which are mediated by a LVT reagent, Ti(O-i-Pr)4/Me3SiCl/Mg. From the results of these reactions, a novel dual-mode coupling copolymerization of aryl dialdehyde and alkynyl aldehyde monomers via concurrent McMurry olefination and alkyne cyclotrimerization reactions mediated by the LVT reagent has been developed, which afforded
Declaration of competing interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgements
This work was partly supported by the Ministry of Education, Culture, Sports, Science, and Technology (MEXT), Japan [grant# 22550103, 25288057, and 17K05869]. We thank Yousuke Yasuda, Youtaro Kitamura, Ryouhei Shigematsu, and Shoya Takano for their contributions at the early stage of this study. The authors would like to thank MARUZEN-YUSHODO Co., Ltd. (https://kw.maruzen.co. jp/kousei-honyaku/) for the English language editing.
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