Forschungsgemeinschaft (DFG) for financial support. L.R.
thanks the Alexander-von-Humboldt Foundation for a post-
doctoral fellowship. We also thank Prof. Dr Thorsten Bach and
his group for their great support.
Fig. 2 Imidazolium- and pyridinium-based multidentate XB donors.
Notes and references
1 Halogen Bonding: Fundamentals and Applications, ed. P. Metrangolo
and G. Resnati, Springer, Berlin, 2008.
2 Selected recent reviews: (a) P. Metrangolo, F. Meyer, T. Pilati,
G. Resnati and G. Terraneo, Angew. Chem., Int. Ed., 2008,
47, 6114; (b) M. Fourmigue, Curr. Opin. Solid State Mater. Sci.,
2009, 13, 36; (c) A. C. Legon, Phys. Chem. Chem. Phys., 2010,
12, 7736; (d) G. Cavallo, P. Metrangolo, T. Pilati, G. Resnati,
M. Sansotera and G. Terraneo, Chem. Soc. Rev., 2010, 39, 3772.
3 See, for example: (a) N. Kuhn, T. Kratz and G. Henkel, J. Chem.
Soc., Chem. Commun., 1993, 1778; (b) R. Weiss, M. Rechinger and
F. Hampel, Angew. Chem., Int. Ed. Engl., 1994, 33, 893;
(c) A. J. Arduengo III, M. Tamm and C. J. Calabrese, J. Am.
Chem. Soc., 1994, 116, 3625.
4 Selected reviews: (a) P. Metrangolo and G. Resnati, Chem.–Eur. J.,
2001, 7, 2511; (b) K. Rissanen, CrystEngComm, 2008, 10, 1107;
(c) L. Brammer, G. M. Espallargas and S. Libri, CrystEngComm,
2008, 10, 1712; (d) R. Bertani, P. Sgarbossa, A. Venzo, F. Lelj,
M. Amati, G. Resnati, T. Pilati, P. Metrangolo and G. Terraneo,
Coord. Chem. Rev., 2010, 254, 677.
Fig. 3 Yield-versus-time profile of selected reactions from Table 1
(numbers for individual lines correspond to entries in Table 1). Y-axis:
1
yield of 2 according to H-NMR spectroscopy.
the iodinated equivalent 1,3,5-IBn/OTf (entry 8), which gave a
quantitative yield of 2 even after 48 hours. This also constitutes
a marked increase compared to the bidentate analogue
1,3-IBn/OTf, indicating that there might indeed be a tridentate
binding to the bromine substituent in 1 and/or to the liberated
bromide.15 Strangely, the corresponding hexafluorophosphate
salt 1,3,5-IBn/PF6 (entry 9) was slightly less active than the
triflate salt, opposite to the coordinating ability of the counterions.
The same is true for the non-iodinated compound 1,3,5-HBn/PF6
(compared to 1,3,5-HBn/OTf, see the ESIw).
5 M. Erdelyi, Chem. Soc. Rev., 2012, 41, 3547.
6 See, for example: (a) A. Mele, P. Metrangolo, H. Neukirch, T. Pilati
and G. Resnati, J. Am. Chem. Soc., 2005, 127, 14972;
(b) M. G. Sarwar, B. Dragisic, S. Sagoo and M. S. Taylor, Angew.
Chem., Int. Ed., 2010, 49, 1674; (c) E. Dimitrijevic, P. Kvak and
M. S. Taylor, Chem. Commun., 2010, 46, 9025; (d) C. J. Serpell,
N. L. Kilah, P. J. Costa, V. Felix and P. D. Beer, Angew. Chem., Int.
Ed., 2010, 49, 5322; (e) A. Caballero, N. G. White and P. D. Beer,
Angew. Chem., Int. Ed., 2011, 50, 1845; (f) A. V. Jentzsch, D. Emery,
J. Mareda, P. Metrangolo, G. Resnati and S. Matile, Angew. Chem.,
Int. Ed., 2011, 50, 11675; (g) A. Caballero, F. Zapata, N. G. White,
P. J. Costa, V. Felix and P. D. Beer, Angew. Chem., Int. Ed., 2012,
51, 1876; (h) M. Cametti, K. Raatikainen, P. Metrangolo, T. Pilati,
G. Terraneo and G. Resnati, Org. Biomol. Chem., 2012, 10, 1329.
7 (a) S. M. Walter, F. Kniep, E. Herdtweck and S. M. Huber,
Angew. Chem., Int. Ed., 2011, 50, 7181; (b) F. Kniep, S. M. Walter,
E. Herdtweck and S. M. Huber, Chem.–Eur. J., 2012, 18, 1306.
8 J. E. Hein, J. C. Tripp, L. B. Krasnova, K. B. Sharpless and
V. V. Fokin, Angew. Chem., Int. Ed., 2009, 48, 8018.
Finally, a comparison of 1,3-IBn/OTf with the previously
reported XB donors 37a and 47b (Fig. 2) was conducted. It
became apparent that the topologically related imidazolium- and
triazolium-based XB donors (i.e. 1,3-IBn/OTf and 3) possess a very
similar activation potential (see entry 10). The tetra-iodinated
(yet bidentate) azo compound 4 (entry 11), however, equaled the
tridentate triazolium compound 1,3,5-IBn/OTf in its carbon–
bromine activation strength. This is further illustrated in the
yield-versus-time profiles in Fig. 3.
9 (a) N. L. Kilah, M. D. Wise, C. J. Serpell, A. L. Thompson,
N. G. White, K. E. Christensen and P. D. Beer, J. Am. Chem. Soc.,
2010, 132, 11893; (b) N. L. Kilah, M. D. Wise and P. D. Beer,
Cryst. Growth Des., 2011, 11, 4565.
10 S. M. Walter, F. Kniep, L. Rout, F. P. Schmidtchen, E. Herdtweck
and S. M. Huber, J. Am. Chem. Soc., 2012, 134, 8507.
In summary, we have synthesized 5-iodo-1,2,3-triazolium-
based multidentate XB donors and tested their carbon–bromine
activation potential in a benchmark reaction.16 The presented
synthetic route via dipolar cycloaddition reactions allows access
to variously substituted derivatives, which was exemplified by
the preparation of one of the first chiral XB donors as well as
the synthesis of a tricationic one. While all new XB donors act
as activators, we found little effect of the counterion, yet a
noticeable influence of the N-substituent (in the N-octyl versus
the N-benzyl variant). The bidentate XB donors equal our
previously reported imidazolium-based compounds in their
carbon–bromine activation potential, whereas the markedly
stronger trifunctionalized compounds are analogous in activation
strength to the recently introduced bidentate pyridinium-based
XB donors.
11 K. M. Mullen, J. Mercurio, C. J. Serpell and P. D. Beer, Angew.
Chem., Int. Ed., 2009, 48, 4781.
12 For the resolution of 1,2-dibromohexafluoropropane, see:
A. Farina, S. V. Meille, M. T. Messina, P. Metrangolo,
G. Resnati and G. Vecchio, Angew. Chem., Int. Ed., 1999, 38, 2433.
13 ORTEP plot: cf. L. J. Farrugia, J. Appl. Crystallogr., 1997, 30, 565
Thermal ellipsoids are drawn at the 50% probability level. For
more information see the ESIw and CCDC 886241.
14 A. Bondi, J. Phys. Chem., 1964, 68, 441.
15 Orientating DFT calculations indicate that tridentate coordination
of compounds like 1,3,5-IBn/OTf to bromide is feasible (see the
ESIw).
16 In order to get a first idea on the difference in potency between our
novel tridentate activator 1,3,5-IBn/OTf versus our bidentate
activators 1,3-IBn/OTf and 3 for more challenging substrates, we
also tested their respective activation potential on a further test
substrate: (1-bromoethyl)benzene (‘‘a-methylbenzyl bromide’’).
Under identical reaction conditions, after four days at room
temperature in CD3CN we obtained yields of the corresponding
amide of 35% (3), 25% (1,3-IBn/OTf), and 43% (1,3,5-IBn/OTf).
Further investigations on the substrate scope are in progress.
The authors are grateful to the Fonds der Chemischen
Industrie (Liebig Fellowship to S.M.H.) and the Deutsche
c
This journal is The Royal Society of Chemistry 2012
Chem. Commun., 2012, 48, 9299–9301 9301