DOI: 10.1039/C4CC09239B
Page 3 of 4
Journal Name
ChemComm
COMMUNICATION
internal standard. TON and TOF are given in reference to the number of
Fax: (+)33 (0)5 6155 8204. E-mail: mezailles@chimie.ups-tlse.fr
a
b
c
hydride transferred. Additional BH
Reactions are done in a Schlenk tube to increase the volume of CO
Hexamethylbenzene is used as an internal standard. 2 times 1 bar CO
3 2 2
.SMe and CO was added after 2h.
b
Division of Chemistry and Biological Chemistry, School of Physical
2
.
2
.
and Mathematical Sciences, Nanyang Technological University, 637371
Singapore.
Satisfyingly, 4 alone reacted with CO2 (1 bar, 80°C) to from
c
Institut de Chimie de Toulouse ICT-FR2599, Université Paul Sabatier ,
methanol derivatives, showing that the BH had indeed the expected
2
3
1062 Toulouse Cedex, France.
hydridic character. Secondly, in the presence of BH , 4 was a
3
†
Electronic Supplementary Information (ESI) available: Synthetic
catalyst for the transformation (entry 1), which showed that the final
products are not trapped by the carbenoid fragment. Since the
reaction to form 4 from 2 and BH .SMe is facile at room
procedures, solution NMR data, crystallographic information and
computational details. CCDC-1034939 (2) and CCDC-1034940 (4)
3
2
temperature, carbenoid 2 was subsequently used as pre-catalyst. As contain the supplementary crystallographic data for this paper. These data
shown by entry 2, 2 is slightly less competent than 4 in the catalytic
process. Lowering of the catalytic amount to 5% provided similar
results (entry 3 vs 2). Carrying the reaction at room temperature was
possible, yet required 40h instead of 2h at 80°C (entries 3 and 4).
crystallographic data, see DOI: 10.1039/c000000x/
Entry 5 showed that after a first catalytic run, addition of BH .SMe2
and CO2 allowed further reduction, proving that little or no
decomposition of catalyst occurred. When the catalyst loading was
3
‡
Synthesis of compound 2. To 1 (0.133 g, 0.2 mmol) in ether (10
o
ml), hexachloroethane (0.0474 g, 0.2 mmol) was added at -78 C.
reduced to 1% (NMR tube scale reaction), the reaction became The reaction was warmed up to room temperature and stirred for 30
sluggish likely because solid formed during the reaction, which mins. The colour changed from bright orange to dark brown. After
prevented efficient mixing of the reagents. Nevertheless, it reached
3
0 mins, the mixture was filtered and the filtrate was concentrated to
similar yield (83%) after 24h (entry 6). On the other hand, when the
same reaction was carried out in a Schlenk flask with efficient
stirring, the reaction was again complete within 2h at 80°C (entry 7).
For comparison, starting from 4 (1%, entry 8) provided quantitative
1
afford crystals of 2 (0.122 g, 73 %). H NMR (C D , 298 K): δ 0.712
6
6
3
(t, J
= 7.11 Hz, 6H, Ether-CH ), 2.10 (s, 6H, Mes p-CH ), 2.24
H-H 3 3
3
(s, 12H, Mes o-CH ), 2.82 (q, J = 7.11 Hz, 4H, Ether-CH ), 6.68
3
H-H
2
yield of methanol derivative, with a better selectivity in compound 6 (s, 4H, Mes CH), 7.12 (m, 12H, m,p-Ph CH), 7.92 (m, 8H, o-Ph
96 to 3). The TON reached 313 within 2h. Using the same CH). Li NMR (C D , 298 K): δ 1.7 (s). C{ H} NMR (C D , 298
7
13
1
(
6
6
6
6
conditions (Schlenk flask rather than NMR tube) allowed further
lowering of the catalyst loading down to 0.1%, with a slightly
increased reaction time (entry 9, 4h). Overall, these conditions
K): δ 14.5 (s, ether CH ), 20.8 (s, Mes p-CH ), 21.2 (s, Mes o-CH ),
3
3
3
6
4.9 (s, ether CH ), 127.4 (t, J = 5.69 Hz, Ph o-C), 133.4 (t, JP-C =
2 P-C
-
1
4.41 Hz, Mes ipso-C), 129.1 (s, Mes o-C), 129.3 (t, JP-C = 2.20 Hz,
Ph p-C), 129.8 (s, Ph m-C), 134.9 (t, JP-C = 3.32 Hz, Mes m-C),
provide comparable TOF and TON (661 h and 2646 respectively) to
3
a
the best known results for the reduction of CO by BH .SMe .
2
3
2
1
35.3 (d, J = 96.6 Hz, Ph ipso-C), 146.2 (t, JP-C = 3.72 Hz, Mes o-
P-C
3
1
1
C). P{ H} NMR (C D , 298 K): δ 27.2 (s). Anal. Calc for
6
6
Conclusions
C H ClLiN OP : C, 73.77; H, 6.85; N, 3.66 %. Found: C, 73.77;
4
7
52
2
2
In conclusion, we have synthesized a novel example of
stable Li/Cl carbenoid compound, 2, based on the controlled
oxidation of bis iminophosphorane geminal dianion. Reaction of this
H, 6.67; N, 3.56 %.
1
(a) Müller, M. Marsch, K. Harms, J. C. W. Lohrenz and G.
Boche, Angew. Chem. Int. Ed. 1996, 35, 1518; (b) G. Boche and
J. C. W. Lohrenz, Chem. Rev. 2001, 101, 697; (c) T. Cantat, X.
Jacques, L. Ricard, X. F. Le Goff, N. Mézailles and P. Le Floch,
Angew. Chem. Int. Ed. 2007, 46, 5947; (d) H. Heuclin, S. Y. F.
Ho, X. F. Le Goff, C.-W. So and N. Mézailles, J. Am. Chem.
Soc. 2013, 135, 8774.
carbenoid
species
toward
BH .SMe
resulted in
its
3
2
-
+
disproportionation into BH4 and BH2 fragments. The driving force
for this reaction is the strong stabilization of the BH2 by the C-
+
chloro bis-iminophosphoranyl methanide moiety. This easily
synthesized stable zwitterionic boronium compound 4 was fully
characterized. DFT analysis on this compound pointed strongly
negative charges at N, positive charge at B and a hydridic character
2
3
(a) V. H. Gessner, Organometallics 2011, 30, 4228; (b) C.
Kupper, S. Molitor and V. H. Gessner, Organometallics 2013,
-
for the H, similar to BH . As a consequence, using the carbenoid
4
compound 2, two equivalents of BH3 are transformed into two
borohydride species. Most interestingly, both are capable of reducing
CO2 selectively to form methanol derivatives. Overall, the new
3
1
4
2
3, 347; (c) S. Molitor and V. H. Gessner, Chem.-Eur. J. 2013,
9, 11858 (d) J. Becker and V. H. Gessner, Dalton Trans. 2014,
3, 4320; (e) K.-S. Feichtner and V. H. Gessner, Dalton Trans.
014, 43, 14399.
carbenoids
2 and 4, readily generated from a stable bis-
iminophosphorane methanediide, are to date among the best
catalysts for the CO reduction by BH .SMe .
(a) M.-A. Courtemanche, M.-A. Légaré, L. Maron and F.-G.
Fontaine, J. Am. Chem. Soc. 2013, 135, 9326; (b) M.-A.
Courtemanche, M.-A. Légaré, L. Maron and F.-G. Fontaine, J.
Am. Chem. Soc. 2014, 136, 10708; (c) C. Das Neves Gomes, E.
Blondiaux, P. Thuéry and T. Cantat, Chem.-Eur. J. 2014, 20,
2
3
2
The authors gratefully acknowledge the financial support
of CNRS, Université P. Sabatier and Nanyang Technological
University. S. H. thanks NTU for a “Ecole Polytechnique/NTU”
joint Ph.D. fellowship and N. M. is grateful for a generous grant
from the “Région Midi-Pyrénées”. The authors are grateful to
CalMip (CNRS, Toulouse, France) for calculation facilities.
7
098.
4
5
T. Wang and D. W. Stephan, Chem.-Eur. J. 2014, 20, 3036.
(a) E. Blondiaux, J. Pouessel and T. Cantat, Angew. Chem. Int.
Ed. 2014, 53, 12186; (b) T. Wang and D. W. Stephan, Chem.
Commun. 2014, 50, 7007.
Notes and references
Laboratoire Hétérochimie Fondamentale et Appliquée, Université Paul
6
7
M.-A. Legare, M.-A. Courtemanche and F.-G. Fontaine, Chem.
Commun. 2014, 50, 11362.
O. J. Cooper, J. McMaster, W. Lewis, A. J. Blake and S. T.
Liddle, Dalton Trans. 2010, 39, 5074.
a
Sabatier, CNRS, 118 Route de Narbonne, 31062 Toulouse (France).
This journal is © The Royal Society of Chemistry 2012
J. Name., 2012, 00, 1-3 | 3