Skip to main page content
U.S. flag

An official website of the United States government

Dot gov

The .gov means it’s official.
Federal government websites often end in .gov or .mil. Before sharing sensitive information, make sure you’re on a federal government site.

Https

The site is secure.
The https:// ensures that you are connecting to the official website and that any information you provide is encrypted and transmitted securely.

Access keys NCBI Homepage MyNCBI Homepage Main Content Main Navigation
. 2015 May 26;20(6):9575-90.
doi: 10.3390/molecules20069575.

Reactivity of Amine/E(C6F5)3 (E = B, Al) Lewis Pairs toward Linear and Cyclic Acrylic Monomers: Hydrogenation vs. Polymerization

Jiawei Chen  1 , Eugene X-Y Chen  2
Affiliations

Reactivity of Amine/E(C6F5)3 (E = B, Al) Lewis Pairs toward Linear and Cyclic Acrylic Monomers: Hydrogenation vs. Polymerization

Jiawei Chen et al. Molecules. .

Abstract

This work reveals the contrasting reactivity of amine/E(C6F5)3 (E = B, Al) Lewis pairs toward linear and cyclic acrylic monomers, methyl methacrylate (MMA) and biorenewable γ-methyl-α-methylene-γ-butyrolactone (γMMBL). While mixing of 2,2,6,6-tetramethylpiperidine (TMP) and B(C6F5)3 leads to a frustrated Lewis pair (FLP), Et3N reacts with B(C6F5)3 to form disproportionation products, ammonium hydridoborate ionic pair and iminium zwitterion. On the other hand, the stoichiometric reaction of either TMP or Et3N with Al(C6F5)3 leads to clean formation of a classic Lewis adduct (CLA). Neither TMP nor Et3N, when paired with E(C6F5)3, polymerizes MMA, but the Et3N/2B(C6F5)3 pair promotes transfer hydrogenation of MMA to form methyl isobutyrate. In contrast, the amine/E(C6F5)3 pairs promote rapid polymerization of γMMBL carrying the more reactive exocyclic methylene moiety, achieving full conversion in less than 3 min even at a low catalyst loading of 0.0625 mol %. TMP is more effective than Et3N for the polymerization when paired with either the borane or the alane, while the alane exhibits higher polymerization activity than the borane when paired with Et3N. Overall, the TMP/Al(C6F5)3 system exhibits the highest polymerization activity, achieving a maximum turn-over frequency of 96,000 h-1 at 0.125 mol % of catalyst loading, producing high molecular weight PγMMBL with Mn = 1.29 × 105 g∙mol-1.

Keywords: Lewis pair polymerization; alane; amine; borane; frustrated Lewis pair.

PubMed Disclaimer

Conflict of interest statement

The authors declare no conflict of interest.

Figures

Scheme 1
Scheme 1
Generalized chain initiation and propagation mechanism for polymerization of conjugated polar alkenes carrying a functional group (FG) by Lewis pairs through zwitterionic active species or intermediates [56], and the structure of LAs, LBs and monomers examined in this study.
Scheme 2
Scheme 2
Different amine/E(C6F5)3 (E = B or Al) systems employed for this LPP study and their corresponding reactivity in the absence of monomer.
Figure 1
Figure 1
1H- and 19F- (inset) spectra (C6D6) of adduct Et3N·Al(C6F5)3.
Figure 2
Figure 2
1H- and 19F- (inset) spectra (C6D6) of adduct TMP·Al(C6F5)3.
Figure 3
Figure 3
1H-NMR spectra (CD2Cl2) of a mixture of Et3N/B(C6F5)3/MMA in the ratio of 1:1:1 (top), 1:1.5:1 (middle) and 1:2:1 (bottom, some amount of Et3N-H···H-B(C6F5)3 remains due to a slight deficiency of MMA).
Scheme 3
Scheme 3
Stoichiometric hydrogenation of MMA to methyl isobutyrate by Et3N/B(C6F5)3.
See this image and copyright information in PMC

References

    1. Stephan D.W. Frustrated Lewis pairs: From concept to catalysis. Acc. Chem. Res. 2015;48:306–316. doi: 10.1021/ar500375j. - DOI - PubMed
    1. Stephan D.W., Erker G. Frustrated Lewis pair chemistry of carbon, nitrogen and sulfur oxides. Chem. Sci. 2014;5:2625–2641. doi: 10.1039/c4sc00395k. - DOI
    1. Erker G., Stephan D.W., editors. Frustrated Lewis Pairs I & II. Springer-Verlag; Berlin, Germany: 2013.
    1. Stephan D.W. “Frustrated Lewis pair” hydrogenations. Org. Biomol. Chem. 2012;10:5740–5746. doi: 10.1039/c2ob25339a. - DOI - PubMed
    1. Erker G. Frustrated Lewis pairs: Some recent developments. Pure Appl. Chem. 2012;84:2203–2217. doi: 10.1351/PAC-CON-12-04-07. - DOI

Publication types

LinkOut - more resources