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ChemComm
DOI: 10.1039/C6CC05228B
COMMUNICATION
Journal Name
results, a mixture of
4
and
6
also shows catalytic activity to-
B. Wibbeling, R. Fröhlich and G. Erker, Dalton Trans., 2009,
534–1541; d) P. Spies, G. Erker, G. Kehr, K. Bergander, R.
Fröhlich, S. Grimme and D. W. Stephan, Chem. Commun.,
007, 5072–5074; e) T. Özgun, K-Y. Ye, C. Daniliuc, B. Wibbe-
ling, L. Liu, S. Grimme, G. Kehr and G. Erker, Chem. Eur. J.,
2016, 22, 5988-5995.
1
wards reduction of imine 10. Consequently, imine system 10 is
not suitable to distinguish between a catalytic activity of due
5
2
to (a) cooperative hydride complexation, as observed in H/D-
scrambling experiments, and (b) due to an effect of the sole
dangling acid of
important as the sole Lewis acid
of silylenol ether 11 (Table 1, line 2), probably due to its poor
basicity. The catalytic activity of catalyst towards reduction
of 11 has therefore to be addressed to a cooperativity of both
Lewis acids. Interestingly, a mixture of is active in the
hydrogenation of silylenol ether 11, although its activity is
somewhat less than that of . This observation possibly indi-
5
. Anyhow, the latter point is clarified as un-
6
a) G. D. Frey, V. Lavallo, B. Donnadieu, W. W. Schoeller and
G. Bertrand, Science, 2007, 316, 439–441; b) P. A. Chase and
D. W. Stephan, Angew. Chem. Int. Ed., 2008, 47, 7433–7437.
S. J. Geier, T. M. Gilbert and D. W. Stephan, J. Am. Chem.
Soc., 2008, 130, 12632–12633.
6
is inactive in hydrogenation
7
8
5
a) C. M. Mömming, E. Otten, G. Kehr, R. Fröhlich, S. Grimme,
D. W. Stephan and G. Erker, Angew. Chem. Int. Ed., 2009, 48,
643–6646, b) M. Sajid, A. Klose, B. Birkmann, L. Liang, B.
4+
6
6
Schirmer, T. Wiegand, H. Eckert, A. J. Lough, R. Fröhlich, C.
Daniliuc, S. Grimme, D. W. Stephan, G. Kehr and G. Erker,
5
cates a more complex intermolecular cooperative mechanism
in the reduction experiments of the silylenol ether.
Chem. Sci., 2013,
a) G. Ménard, J. A. Hatnean, H. J. Cowley, A. J. Lough, J. M.
Rawson and D. W. Stephan, J. Am. Chem. Soc., 2013, 135
446–6449; b) C. Appelt, J. C. Slootweg, K. Lammertsma and
4, 213-219.
9
In essence, the above facts show, that the presence of two
,
6
B(C
H/D-scrambling as well as in hydrogenation experiments,
whereas the singly acid-functionalised compound is much
6 5 2
F ) acid groups in catalyst 5 leads to catalytic activity in
W. Uhl, Angew. Chem. Int. Ed., 2013, 52, 4256–4259; c) L.
Keweloh, H. Klöcker, E.-U. Würthwein and W. Uhl, Angew.
Chem. Int. Ed., 2016, 55, 3212–3215.
4
less active. Quantum-chemical investigations revealed that the 10 a) A. Schäfer, M. Reißmann, A. Schäfer, M. Schmidtmann and
hydrogen-splitting product of FLP
5
is stabilised by a chelate-
T. Müller, Chem. Eur. J., 2014, 20, 9381–9386; b) M. Reiß-
mann, A. Schäfer, S. Jung and T. Müller, Organometallics,
type hydride binding by both boron Lewis-acid functions. As a
result, this concept decreases the hydrogen splitting reaction
energy without increasing the Lewis acidity. The latter would
counterproductively increase the barrier to thermal activation
of B–N cleavage. In this way the described cooperative effect
can be used to tune the activity of FLP systems.
2
013, 32, 6736–6744.
1 a) S. A. Weicker and D. W. Stephan, Chem. Eur. J., 2015, 21
3027–13034; b) B. Waerder, M. Pieper, L. A. Körte, T. A.
1
,
1
Kinder, A. Mix, B. Neumann, H.-G. Stammler and N. W.
Mitzel, Angew. Chem. Int. Ed., 2015, 54, 13416–13419.
1
1
2 a) R. Dobrovetsky and D. W. Stephan, Isr. J. Chem., 2015, 55
06–209; b) P. Jochmann and D. W. Stephan, Angew. Chem.
Int. Ed., 2013, 52, 9831–9835.
,
2
3 a) A. M. Chapman, M. F. Haddow and D. F. Wass, J. Am.
Chem. Soc., 2011, 133, 8826-8829; b) A. M. Chapman, M. F.
Acknowledgements
Haddow and D. F. Wass, J. Am. Chem. Soc., 2011, 133
8463-18478; c) O. J. Metters, S. J. K. Forrest, H. A. Sparks, I.
Manners and D. F. Wass, J. Am. Chem. Soc., 2016, 138, 1994-
003.
,
We thank Klaus-Peter Mester and Gerd Lipinski for recording
NMR spectra, Brigitte Michel for performing elemental analy-
ses, Dr. Jens Sproß, Heinz-Werner Patruck and Sandra Heit-
1
2
kamp for recording mass spectra and ”Regionales Rechenzen- 14 C. Jiang, O. Blacque and H. Berke, Chem. Commun., 2009,
5
518-5520.
5 P. A. Chase, T. Jurca and D. W. Stephan, Chem. Commun.,
008, 1701–1703; b) T. Rokob, A. Hamza, A. Stirling and I. J.
Pápai, J. Am. Chem. Soc., 2009, 131, 2029-2036;
6 L. J. Hounjet, C. Bannwarth, C. N. Garon, C. B. Caputo, S.
trum, Universität zu Köln” (RRZK) for computational resources.
1
1
2
Notes and references
1
a) G. C. Welch, R. R. San Juan, J. D. Masuda and D. W.
Stephan, Science, 2006, 314, 1124–1126. b) P. A. Chase, G. C.
Grimme and D. W. Stephan, Angew. Chem. Int. Ed., 2013, 52,
7492–7495.
Welch, T. Jurca and D. W. Stephan, Angew. Chem. Int. Ed., 17 B. Schmidt, S. Krehl and E. Jablowski, Org. Biomol. Chem.,
007, 46, 8050–8053.
2012, 10, 5119–5130.
For a detailed overview, see the following reviews: a) D. W. 18 a) D. J. Parks, W. E. Piers and G. P. A. Yap, Organometallics,
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2
Stephan, Dalton Trans., 2009, 3129–3136; b) D. W. Stephan
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,
6
1
400–6441; d) D. W. Stephan, J. Am. Chem. Soc., 2015, 137
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,
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4
G. C. Welch and D. W. Stephan, J. Am. Chem. Soc., 2007, 129
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ger, M. Leskelä, T. Repo, P. Pyykkö and B. Rieger, J. Am.
Chem. Soc., 2008, 130, 14117–14119.
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2
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5
and G. Erker, Angew. Chem. Int. Ed., 2008, 47, 7543–7546. b)
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| J. Name., 2012, 00, 1-3
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