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DOI: 10.1039/C7CC04613H
Journal Name
COMMUNICATION
provides another dialkylated example. Catalytic results are in catalyst loading equates to a higher relative concentration
presented in Table 3.
2
of H , and therefore a higher activity.
In conclusion, we have developed a new homogeneous
catalytic approach to carbon dioxide hydrogenation to
methanol using ruthenium catalysts and amine auxiliaries, the
nature of both the catalyst but crucially the amine being
essential for good performance. The figures of merit for this
system are unprecedented, surpassing previous homogeneous
catalysts for this transformation in terms of turnover number
and frequency by at least an order of magnitude. Further
mechanistic study and a wider screen of catalysts are
underway.
Table 3. Catalysis Results Comparing Complexes 3-6.
Ph
P
Ph
P
Ph
P
Ph
P
Ph
P
Ph
P
Ph
H
Cl
Ru
Cl
Ph Ph
H
Cl
Ru
Cl
Ph Ph
Cl
Ru
Cl
Ph
N
N
N
N
N
N
4
5
6
[
M], R NH
2
CO2 + nH2
HC(O)NR2 + CH OH + H O
3 2
NaOEt, toluene
Run
Precat.
Amine Amide mmol
MeOH mmol
[b]
[b]
(
TON) [TOF/h]
1.6 (320) [16]
1.7 (330) [17]
2.2 (430) [22]
(TON) [TOF/h]
1.2 (240) [22]
9.1 (1800) [90]
0.0 (0) [0]
Notes and references
1
2
2
2
2
9
0
1
2
3
3
4
5
6
3
4
5
6
3
4
Me
Me
Me
2
2
2
2
NH
NH
NH
NH
The EPSRC Bristol Chemical Synthesis Centre for Doctoral
Training is thanked for funding.
Me
i
0.39 (77) [3.9]
0.0 (0) [0]
0.0 (0) [0]
0.0 (0) [0]
0.0 (0) [0]
0.0 (0) [0]
0.0 (0) [0]
0.0 (0) [0]
Pr
Pr
Pr
Pr
Pr
Pr
2
NH
NH
NH
NH
NH
NH
12 (2300) [120]
21 (4000) [2000]
0.0 (0) [0]
[a]
i
i
i
i
i
(1)
M. Peters, B. Köhler, W. Kuckshinrichs, W. Leitner, P. Markewitz, T. E.
Müller, ChemSusChem 2011, 4, 1216–1240; Carbon Dioxide as
Chemical Feedstock (Ed.: M. Aresta), Wiley-VCH, Weinheim, 2010; D. M.
D'Alessandro, B. Smit, and J. R. Long, Jeffrey R. Angew. Chem. Int. Ed.,
2
4
2
2
2
2
2
2
2
5
6
0.0 (0) [0]
[
b]
2
7
[
0.25 (5100) [260]
0.44 (8900) [4500]
2
010, 49, 6058–6082.
a,b]
2
8
(2)
Shamsul, N. S.; Kamarudin, S. K.; Rahman, N. A.; Kofli, N. T. Renew.
Sustain. Energy Rev. 2014, 33, 578–588.
Conditions: precatalyst (5 µmol), NaOEt (0.15 mmol), amine (2 mL), toluene
10 mL), CO (10 bar), H (30 bar), 100 °C, 20 h. [a] 2 h. [b] 50 nmol
(
3)
4)
Tominaga, K.; Sasaki, Y.; Kawai, M.; Watanabe, T.; Saito, M. J. Chem.
Soc. Chem. Commun. 1993, 7, 629.
(
2
2
precatalyst used. [c] Turnover Number with respect to catalyst.
(
Balaraman, E.; Ben-David, Y.; Milstein, D. Angew. Chemie - Int. Ed.
2
011, 50, 11702–11705; Balaraman, E.; Gunanathan, C.; Zhang, J.;
Shimon, L. J. W.; Milstein, D. Nat. Chem. 2011, 3, 609–614.
J. Schneidewind, R. Adam, W. Baumann, R. Jackstell, M. Beller, Angew.
Chem. Int. Ed. 2017, 56, 1890-1893; X. Chen , H. Ge and X. Yang
Catal. Sci. Technol., 2017, 7, 348-355.
The difference in performance between ligands having primary
or secondary amine groups, and tertiary amines is clear. Whilst
(
5)
3
and
runs 19 and 20),
2). The mono-N-methylated ligand complex
4
produce both DMF and methanol with dimethylamine
and produce the amide only (runs 21 and
demonstrates
(
6)
7)
Han, Z.; Rong, L.; Wu, J.; Zhang, L.; Wang, Z.; Ding, K. Angew. Chem.,
Int. Ed. 2012, 51, 13041–13045.
(
5
6
2
4
(
Leitner, W.; Klankermayer, J. J.; Wesselbaum, S.; Moha, V.; Meuresch,
M.; Brosinski, S.; Thenert, K. M.; Kothe, J.; et al. Chem. Sci. 2015, 6,
693–704.
advantages in terms of higher overall turnover numbers and
selectivity to methanol (run 24). This trend is continued with
(
(
(
8)
Wesselbaum, S.; Vom Stein, T.; Klankermayer, J.; Leitner, W. Angew.
Chem. Int. Ed. Engl. 2012, 51, 7499–7502.
di-iso-propylamine,
complex giving the best performance seen to date, highly
selective and with turnover number of 4000. This
5 and 6 being inactive in this case but
4
9)
Klankermayer, J.; Leitner, W. Phil. Trans. R. Soc.
0150315.
A 2016, 374,
a
2
-1
corresponds to a TOF of 2000 h .
10) Markewitz, P.; Kuckshinrichs, W.; Leitner, W.; Linssen, J.; Zapp, P.;
These data are strong evidence for an outer sphere type
mechanism, in which amine ligand deprotonation leads to an
Bongartz, R.; Schreiber, A.; Müller, T. E. Energy Environ. Sci. 2012, 5,
7
281.
2
2,23
(11) Klankermayer, J.; Wesselbaum, S.; Beydoun, K.; Leitner, W. Angew.
Chem., Int. Ed. June 20, 2016, pp 7296–7343.
intermediate metal amide complex.
significant increase in activity from
Intriguingly, the
to 4 is also consistent
3
(
12) Rohmann, K.; Kothe, J.; Haenel, M. W.; Englert, U.; Hölscher, M.; Leitner,
with the very recent mechanism suggested by Gordon et al.,
W. Angew. Chemie., Int. Ed. 2016, 55, 8966–8969.
with the amine acting as a “cooperative and chemically (13) Huff, C.; Sanford, M. J. Am. Chem. Soc. 2011, 134, 18122–18125.
2
4
(
(
(
14) Rezayee, N. M.; Huff, C. A.; Sanford, M. S. J. Am. Chem. Soc. 2015,
innocent ligand.”
The excellent performance of
1
37, 1028–1031.
4
with the di-iso-propylamine
15) Kothandaraman, J.; Goeppert, A.; Czaun, M.; Olah, G. A.; Prakash, G. K.
S. J. Am. Chem. Soc. 2016, 138, 778–781.
auxiliary led us to speculate that we might now be in the
regime where catalytic performance is limited by mass
transport effects. Indeed, a catalyst run with lower catalyst
loading (50 nmol) over 2 h, and otherwise identical conditions,
gives an unprecedented TON of 8900 with an impressive TOF
16) Jessop, P.; Hsiao, Y.; Ikariya, T.; Noyori, R. J. Am. Chem. Soc. 1994,
116, 8851–8852.
(
17) Kröcher, O.; Köppel, R.; Baiker, A. Chem. Commun. 1997, 2, 453–454.
18) Breman, B. B.; Beenackers, A. A. C. M.; Rietjens, E. W. J.; Stege, R. J.
H. J. Chem. Eng. Data 1994, 39, 647–666.
(
-1
of 4500 h . The increase in reaction rate is attributed to the
rate limiting low solubility of the H , meaning that a reduction
(
19) Brunner, E. J. Chem. Eng. Data 1985, 30, 269–273.
20) Simnick, J. J.; Sebastian, H. M.; Lin, H.-M.; Chao, K.-C. J. Chem. Eng.
Data 1978, 23, 339–340.
2
(
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