Angewandte
Chemie
hydrogen (2 bar), the pressure was released, the vial removed, and the
tors which are present in large excess (arenes, olefins).
Cobalt-catalyzed hydrogenations of styrene and 1,3-diphenyl-
acetone followed by work-up with D2O afforded no deuter-
reaction quenched with saturated aqueous NaHCO3 (1 mL). The
mixture was extracted (diethyl ether) and the organic phases dried
(Na2SO4). For quantitative GC-FID analysis, n-pentadecane was
added as an internal standard. For preparative work-up, the solvents
were removed in vacuum and the residue was purified by flash-
chromatography (SiO2, pentane/ethyl acetate). 2-Methoxy-6-ethyl-
2
ated products (1H, H NMR). The reaction of styrene under
2 bar D2 gave a,b-[D2]-ethylbenzene. Treatment of 1 with
alcohols (ethanol, 1,3-diphenylpropan-2-ol) at room temper-
ature resulted in oxidation of the catalyst to another catalytic
species, a color change (dark red to dark green), and H2
evolution.[24] Transfer hydrogenation between 1,3-diphenyl-
propan-2-ol (4 equiv) and 4-methylstyrene in the presence of
1 indeed afforded 1-ethyl-4-methylbenzene with 100% selec-
tivity (18% yield) in the absence of an H2 atmosphere
(Scheme 7). NMR studies confirmed the exchange of anthra-
1
naphthalene: H NMR (400 MHz, CDCl3): d = 7.63 (m, 3H), 7.56 (s,
1H), 7.32 (m, 1H), 7.10 (m, 2H), 3.91 (s, 3H), 2.78 (q, 7.6 Hz, 2H),
1.31 ppm (t, 7.6 Hz, 3H). 13C{1H} NMR (101 MHz, CDCl3): d = 157.1,
139.47, 132.9, 129.2, 128.9, 127.6, 126.7, 125.4, 118.6, 105.7, 55.3, 28.8,
15.6 ppm. MS (EI, 70 eV, m/z): 186 [M+].
Representative procedure for the hydrogenation of ketones/
imines: In an argon-filled glove box, a dry 5 mL vial with a screw cap
and PTFE septum was charged with a magnetic stir bar and a solution
of catalyst
1 (15.1 mg, 0.025 mmol) and 1-phenylpropan-2-one
(67.1 mg, 0.5 mmol) in toluene (2 mL). The vial was placed into
a high-pressure reactor (Parr Instr.) and the septum punctured with
a short needle (Braun). The reactor was sealed, removed from the
glove box, placed on a magnetic stirrer plate, and purged with
hydrogen. After 20 h at 608C under an atmosphere of hydrogen
(10 bar), the pressure was released, the vial removed, and the reaction
quenched with saturated aqueous NaHCO3 (1 mL). The mixture was
extracted (diethyl ether) and the organic phases dried (Na2SO4). For
quantitative GC-FID analysis, n-pentadecane was added as an
internal standard. For preparative work-up, the solvents were
removed in vacuum and the residue was purified by flash-chroma-
tography (SiO2, pentane/ethyl acetate). 1-Phenylpropan-2-ol:
1H NMR (300 MHz, CDCl3): d = 7.33–7.19 (m, 4H), 4.00 (m, 1H),
2.80–2.64 (m, 2H), 1.70 (m, 1H), 1.23 ppm (d, 6.1 Hz, 3H).
13C{1H} NMR (75 MHz, CDCl3): d = 138.6, 129.4, 128.6, 126.5, 68.9,
45.8 ppm, 22.8. MS (EI, 70 eV, m/z): 121 [MÀO]+.
Scheme 7. Initial result of a transfer hydrogenation with secondary
alcohols.
cene ligands with ketones in the coordination sphere of 1 (see
Figure S5 in the Supporting Information). No direct reduction
of diphenylacetone by an equimolar amount of 1 was
observed. We thus postulate the initiation of carbonyl hydro-
genation by cobaltate 1 and the operation of a cobalt(I)
catalyst after the first turnover at elevated temperature and
H2 pressure.[24,25]
Received: October 14, 2013
Published online: February 24, 2014
For the first time, homoleptic arene complexes were
applied to catalytic hydrogenations. Catalysts 1 and 2 are
readily accessible by reduction of metal halides with potas-
sium-anthracene.[10] Bis(anthracene)cobaltate 1 was highly
active in the hydrogenation of alkenes, ketones, and imines
(1–5 mol% cat., 1–10 bar H2, 20–608C). It displays compara-
ble activity to Hansonꢀs ternary catalyst system PNP ligand/
cobalt/HB(ArF)4,[7] but does not require sophisticated ligands
or further additives (e.g. Brookhartꢀs acid). Olefin hydro-
genation catalysis with 1 is initiated by anthracene dissocia-
tion to release an active species which is homogeneous and
stable in the presence of suitable p acceptors. Consecutive
reactions were performed without loss of activity. Current
studies aim at the spectroscopic characterization of the
intermediate cobalt species with labile p-acceptor ligands
and applications of this new catalyst concept to other
transformations with alkenes, carbonyl compounds, and
arenes, including transfer hydrogenation.[26]
Keywords: arene complexes · cobalt · homogeneous catalysis ·
hydrogenations · iron
.
[1] a) Catalytic Hydrogenation (Ed.: L. Cerveny), Elsevier, Amster-
dam, 1986; b) The Handbook of Homogeneous Hydrogenation
(Eds.: J. G. de Vries, C. J. Elsevier), Wiley-VCH, Weinheim,
2007.
[2] a) P. N. Rylander, Catalytic Hydrogenation over Platinum
Metals, Academic Press, New York, 1967; b) A. Molnꢂr, A.
[3] a) Catalysis without Precious Metals (Ed.: R. M. Bullock),
Wiley-VCH, Weinheim, 2010; b) M. S. Holzwarth, B. Plietker,
[5] a) L. H. Slaugh, R. D. Mullineaux, US Patent 3239569, 1966;
b) J. L. van Winkle, R. C. Morris, R. F. Mason, US Patent
3420898, 1969; c) G. F. Pregaglia, A. Andreetta, G. F. Ferrari,
[6] Selected examples: a) M. R. Thompson, V. W. Day, K. D. Tau,
burg, A. D. Horton, H. v. d. Heijden, T. M. Kooistra, D. G. H.
Hetterscheid, J. M. M. Smits, B. de Bruin, P. H. M. Budzelaar,
Experimental Section
Representative procedure for the hydrogenation of styrenes: In an
argon-filled glove box, a dry 5 mL vial with a screw cap and PTFE
septum was charged with a magnetic stir bar and a solution of catalyst
1
(0.005 mmol, 3.2 mg) and 2-methoxy-6-vinylnaphthalene
(0.5 mmol, 92.1 mg) in toluene (2 mL). The vial was placed into
a high-pressure reactor (Parr Instr.) and the septum punctured with
a short needle (Braun). The reactor was sealed, removed from the
glove box, placed on a magnetic stirrer plate, and purged with
hydrogen. After 3 h at room temperature under an atmosphere of
Angew. Chem. Int. Ed. 2014, 53, 3722 –3726
ꢀ 2014 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
3725