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FLPs for N-Functionalized Vinyl Polymer Synthesis
1537
generated in the same fashion, which was found to behave
similarly to zwitterion 2 in the above mechanistic probing
reaction sequences. Overall, these results showed that an
excess amount of the LA is required, in addition to the
zwitterionic intermediate, to generate an effective polym-
erization, which is consistent with the bimolecular, acti-
vated monomer propagation mechanism previously
proposed for the conjugate-addition polymerization by
LPs.4 In this specific case, a propagating step is proposed
to involve nucleophilic attack of the activated monomer
(i.e., adduct 1) by zwitterion 2 and its homologues; the LA
attached to the antepenultimate monomer unit after each
addition step is recaptured by the incoming monomer, and
the repeated conjugate addition in such a propagating cy-
cle produces the high molecular-weight polymer (Scheme
2).
References and Notes
(1) For selected reviews, see: (a) Frustrated Lewis Pairs I & II,
In Topics in Current Chemistry; Vols. 332 & 334; Stephan,
D. W.; Erker, G., Eds.; Springer: New York, 2013. (b) Erker,
G. Pure Appl. Chem. 2012, 84, 2203. (c) Stephan, D. W.
Org. Biomol. Chem. 2012, 10, 5740. (d) Erker, G. Dalton
Trans. 2011, 40, 7475. (e) Stephan, D. W.; Erker, G. Angew.
Chem. Int. Ed. 2010, 49, 46. (f) Stephan, D. W. Dalton
Trans. 2009, 3129. (g) Stephan, D. W. Org. Biomol. Chem.
2008, 6, 1535.
(2) For selected recent examples, see: (a) Hounjet, L. J.;
Bannwarth, C.; Garon, C. N.; Caputo, C. B.; Grimme, S.;
Stephan, D. W. Angew. Chem. Int. Ed. 2013, 52, 7492.
(b) Ménard, G.; Hatnean, J. A.; Cowley, H. J.; Lough, A. J.;
Rawson, J. M.; Stephan, D. W. J. Am. Chem. Soc. 2013, 135,
6446. (c) Dobrovetsky, R.; Stephan, D. W. J. Am. Chem.
Soc. 2013, 135, 4974. (d) Chernichenko, K.; Madarász, A.;
Pápai, I.; Nieger, M.; Leskelä, M.; Repo, T. Nat. Chem.
2013, 5, 718. (e) Sajid, M.; Elmer, L.-M.; Rosorius, C.;
Daniliuc, C. G.; Grimme, S.; Kehr, G.; Erker, G. Angew.
Chem. Int. Ed. 2013, 52, 2243. (f) Sajid, M.; Kehr, G.;
Wiegand, T.; Eckert, H.; Schwickert, C.; Pöttgen, R.;
Cardenas, A. J. P.; Warren, T. H.; Fröhlich, R.; Daniliuc, C.
G.; Erker, G. J. Am. Chem. Soc. 2013, 135, 8882. (g) Appelt,
C.; Slootweg, J. C.; Lammertsma, K.; Uhl, W. Angew.
Chem. Int. Ed. 2013, 52, 4256.
N
N
LB
LA
Al(C6F5)3 (LA)
N
N
LA
It-Bu (LB)
N
(3) Chen, E. Y.-X. Top. Curr. Chem. 2013, 334, 239.
(4) (a) Zhang, Y.; Miyake, G. M.; John, M. G.; Falivene, L.;
Caporaso, L.; Cavallo, L.; Chen, E. Y.-X. Dalton Trans.
2012, 41, 9119. (b) Zhang, Y.; Miyake, G. M.; Chen, E.
Y.-X. Angew. Chem. Int. Ed. 2010, 49, 10158.
2
N
N
N
2-VP
n
LA
LA
N
LA
(5) Piedra-Arroni, E.; Ladavière, C.; Amgoune, A.; Bourissou,
D. J. Am. Chem. Soc. 2013, 135, 13306.
N
N
N
N
(6) Sajid, M.; Stute, A.; Cardenas, A. J. P.; Culotta, B. J.;
Hepperle, J. A. M.; Warren, T. H.; Schirmer, B.; Grimme, S.;
Studer, A.; Daniliuc, C. G.; Fröhlich, R.; Petersen, J. L.;
Kehr, G.; Erker, G. J. Am. Chem. Soc. 2012, 134, 10156.
(7) Xu, T.; Chen, E. Y.-X. J. Am. Chem. Soc. 2014, 136, 1774.
(8) (a) Barz, M.; Luxenhofer, R.; Zentel, R.; Vicent, M. J.
Polym. Chem. 2011, 2, 1900. (b) Luxenhofer, R.; Sahay, G.;
Schulz, A.; Alakhova, D.; Bronich, T. K.; Jordan, R.;
Kabanov, A. V. J. Controlled Release 2011, 153, 73.
(c) Viegas, T. X.; Bentley, M. D.; Harris, J. M.; Fang, Z.;
Yoon, K.; Dizman, B.; Weimer, R.; Mero, A.; Pasut, G.;
Veronese, F. M. Bioconjugate Chem. 2011, 22, 976.
(d) Knop, K.; Hoogenboom, R.; Fischer, D.; Schubert, U. S.
Angew. Chem. Int. Ed. 2010, 49, 6288. (e) Luxenhofer, R.;
Schulz, A.; Roques, C.; Li, S.; Bronich, T. K.; Batrakova, E.
V.; Jordan, R.; Kabanov, A. V. Biomaterials 2010, 31, 4972.
(f) Schlaad, H.; Diehl, C.; Gress, A.; Meyer, M.; Demirel, A.
L.; Nur, Y.; Bertin, A. Macromol. Rapid Commun. 2010, 31,
511. (g) Hoogenboom, R. Angew. Chem. Int. Ed. 2009, 48,
7978. (h) Adams, N.; Schubert, U. S. Adv. Drug Delivery
Rev. 2007, 59, 1504. (i) Tomalia, D. A.; Thill, B. P.; Fazio,
M. J. Polym. J. 1980, 12, 661.
1
2
Scheme 2 Proposed bimolecular, activated monomer propagation
mechanism for the polymerization of 2-VP by the Al(C6F5)3-based
FLP
In summary, FLPs based on Al(C6F5)3 and NHCs have
been found to effectively polymerize 2-VP and iPOx to
medium to high molecular-weight, N-functionalized vinyl
polymers, representing the first example of Lewis pair po-
lymerization of conjugated polar vinyl monomers carry-
ing the C=C–C=N functionality. Preliminary mechanistic
efforts have isolated and structurally characterized the ac-
tivated monomer-LA adduct 1 and the initiated zwitter-
ionic intermediate 2, and the results obtained to date point
to a bimolecular, activated monomer polymerization
mechanism.
Acknowledgment
(9) (a) Weber, C.; Neuwirth, T.; Kempe, K.; Ozkahraman, B.;
Tamahkar, E.; Mert, H.; Becer, C. R.; Schubert, U. S.
Macromolecules 2012, 45, 20. (b) Zhang, N.; Huber, S.;
Schulz, A.; Luxenhofer, R.; Jordan, R. Macromolecules
2009, 42, 2215.
This work was supported by the US National Science Foundation
(CHE-1150792). We thank Boulder Scientific Co. for the generous
donation of B(C6F5)3 for research.
(10) Tomalia, D. A.; Thill, B. P.; Fazio, M. J. Polym. J. 1980, 12,
661.
(11) Zhang, N.; Salzinger, S.; Soller, B. S.; Rieger, B. J. Am.
Chem. Soc. 2013, 135, 8810.
(12) Kaneko, H.; Nagae, H.; Tsurugi, H.; Mashima, K. J. Am.
Chem. Soc. 2011, 133, 19626.
Supporting Information for this article is available online
at
10.1055/s-00000083.SunpfgIpi
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o
nr
i
© Georg Thieme Verlag Stuttgart · New York
Synlett 2014, 25, 1534–1538