Phosphine–Imidazolyl Ligands for Ruthenium Catalysis
FULL PAPER
of esters is presented. The combination of [{Ru-
ACHTUNGTRENNUNG
[1] a) P. N. Rylander, Catalytic Hydrogenation in Organic Syntheses,
Academic Press, New York, 1979; b) Handbook of Heterogeneous
hydrogenation for Organic Synthesis (Ed.: S. Nishimura), Wiley,
New York, 2001; c) Handbook of Homogeneous Hydrogenation
(Eds.: J. G. de Vries, C. J. Elsevier), Wiley-VCH, Weinheim, 2007;
d) P. G. Andersson, I. J. Munslow, Modern Reduction Methods,
Wiley, New York, 2008.
[2] a) L. Saudan in Applied Homogeneous Catalysis with Organometal-
lic Compounds: A Comprehensive Handbook in Three Volumes
(Eds.: B. Cornils, W. A. Herrmann, M. Beller, R. Paciello), Wiley-
VCH, Weinheim, 2012, in press; b) M. L. Clarke, G. J. Roff, The
Handbook of Homogeneous Hydrogenation (Eds.: J. G. de Vries,
C. J. Elsevier), Wiley-VCH, Weinheim, 2007, pp. 313–454; c) M. Ito,
AHCTUNGTRENNUNG
1c gave especially good results for the hydrogenation of ali-
phatic lactones or carboxylic esters. The scope of these in
situ catalyst systems was demonstrated in the reduction of
23 esters, which generally proceeded in good yields. Further-
more, a series of ruthenium complexes with phosphine–imi-
dazolyl ligands [RuACHTUNGTRENNUNG(C6H6)Cl2(1)] were synthesized and fully
characterized to investigate the active catalyst. These com-
plexes should also be useful in other reductions reactions,
such as the reduction of nitriles,[14] amides, etc.
[3] For the catalytic reduction of carboxylic acids, see: a) M. Bianchi, G.
Menchi, F. Francalanci, F. Piacenti, U. Matteoli, P. Frediani, C.
AHCTUNGTRENNUNG
Experimental Section
AHCTUNGTRENNUNG
[4] For the catalytic reduction of amide derivatives, see: a) A. A. NfflÇez
Magro, G. R. Eastham, D. J. Cole-Hamilton, Chem. Commun. 2007,
3154–3156; b) E. Balaraman, B. Gnanaprakasam, L. J. W. Shimon,
Ootsuka, R. Watari, A. Shiibashi, A. Himizu, T. Ikariya, J. Am.
see: f) R. Aoun, J.-L. Renaud, P. H. Dixneuf, C. Bruneau, Angew.
2023; g) M. Ito, A. Sakaguchi, C. Kobayashi, T. Ikariya, J. Am.
General procedure for the catalytic hydrogenation of esters: A mixture
of [{RuACHTUNGTRENNUNG(benzene)Cl2}2] (0.5 mol% Ru) and ligand 1 (1 mol%) in THF
(5 mL) was purged with argon in a Schlenk tube and stirred for 15 min at
RT. To the in-situ-generated catalyst were added KOtBu (0.1 mmol),
hexaACHTUNGTRENNUNGdecane (as a standard, 1 mL), and a liquid ester (10 mmol) and the
mixture was stirred for a further 5 min. (If a solid ester was used, it was
added directly into the autoclave.) The reaction mixture was transferred
via a syringe into the autoclave (25 mL Parr autoclave), the autoclave
was flushed twice with hydrogen, filled with hydrogen (50 bar), and the
mixture was stirred at the required temperature (80–1208C) for the pre-
determined time (4.5–16 h). The autoclave was allowed to cool to RT, the
hydrogen was released, and the reaction mixture was passed through
a short plug of silica gel. The yield was determined by GC (30 m HP 5
Agilent Technologies 50–3008C).
Computational details: Structure optimizations were carried out at the
BP86[15] density functional level of theory with the SVP basis set for non-
metal elements (C, H, P, N, Cl)[16] and with the LANL2DZ basis set for
Ru[17] with the Gaussian03 program package.[18] The optimized geome-
tries were characterized as energy minima at the potential energy surface
from frequency calculations at the same level of theory (BP86/SVP), that
is, the energy-minimum structure had only real frequencies. For compari-
son with the X-ray structural parameters, the structures were refined
with the TZVP basis set for the non-metal elements;[19] the computed en-
ergies were used for the relative-energy discussion.
[5] a) R. A. Grey, G. P. Pez, A. Wallo, J. Corsi, Chem. Commun. 1980,
AHCTUNGERTGPNNUN rediani, F. Piacenti, J. Mol. Catal. 1984, 22, 353–362; d) U. Matteo-
233–238; e) U. Matteoli, G. Menchi, M. Bianchi, F. Piacenti, J. Mol.
Catal. 1988, 44, 347–355; f) U. Matteoli, G. Mechi, M. Bianchi, F.
177–186; g) J. Zhang, G. Leitus, Y. Ben-David, D. Milstein, Angew.
1115; h) L. A. Saudan, C. M. Saudan, C. Debieux, P. Wyss, Angew.
7476; i) M. L. Clarke, M. B. Dıaz-Valenzuela, A. M. Z. Slawin, Orga-
X-ray crystal-structure analysis: Diffraction data for 1a·2HBr and
1c·HBr were collected on a STOE IPDS II diffractometer, whilst diffrac-
tion data for [Ru
N
ACHTUNGTNRE(NUGN 1b)]Cl, [RuCAHUTNGTREN(NGU C6H6)ClACHTUNGETRG(NNUN 1c)]Cl, [RuACHTNUGTRENN(GUN C6H6)Cl-
A
U
Duo; graphite-monochromated Mo Ka radiation was used in all cases.
The structures were solved by direct methods and refined by full-matrix
least-squares procedures on F2 with the SHELXTL software package;
XP (Bruker AXS) was used for graphical representations.[20]
Fogler, E. Balaraman, Y. Ben-David, G. Leitus, L. J. W. Shimon, D.
CCDC-865729 (1a·2HBr), CCDC-865728 (1c·HBr), CCDC-865726 ([Ru-
[6] For the in situ formation of a [RuACTHUNGRETNNU(G acac)3]/phosphine catalyst, see:
A
E
N
ACHTUNGTRENNUNG
A
E
U
CHTUNGTRENNUNG
supplementary crystallographic data for this paper. These data can be ob-
tained free of charge from The Cambridge Crystallographic Data Centre
Acknowledgements
[7] a) S. Zhou, K. Junge, D. Addis, S. Das, M. Beller, Angew. Chem.
Das, S. Zhou, D. Addis, S. Enthaler, K. Junge, M. Beller, Top. Catal.
We thank Dr. C. Fischer, S. Buchholz, S. Schareina, and S. Rossmeisl (all
at the Leibniz-Institut fꢀr Katalyse e.V.) for their excellent analytical and
technical support. Special thanks go to Dr. W. Baumann and A. Koch for
the variable-temperature NMR spectroscopy measurements.
Chem. Eur. J. 2012, 00, 0 – 0
ꢂ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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