Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts

Article abstract of DOI:10.1002/anie.201612548

The replacement of noble metal technologies and the realization of new reactivities with earth-abundant metals is at the heart of sustainable synthesis. Alkene hydrogenations have so far been most effectively performed by noble metal catalysts. This study reports an iron-catalyzed hydrogenation protocol for tri- and tetra-substituted alkenes of unprecedented activity and scope under mild conditions (1–4 bar H₂, 20 °C). Instructive snapshots at the interface of homogeneous and heterogeneous iron catalysis were recorded by the isolation of novel Fe nanocluster architectures that act as catalyst reservoirs and soluble seeds of particle growth.

Full text of DOI:10.1002/anie.201612548

Angewandte
Communications
Chemie
International Edition: DOI: 10.1002/anie.201612548
German Edition: DOI: 10.1002/ange.201612548
Iron Cluster Catalysis
Alkene Hydrogenations by Soluble Iron Nanocluster Catalysts
Tim N. Gieshoff, Uttam Chakraborty, Matteo Villa, and Axel Jacobi von Wangelin*
Abstract: The replacement of noble metal technologies and the
realization of new reactivities with earth-abundant metals is at
the heart of sustainable synthesis. Alkene hydrogenations have
so far been most effectively performed by noble metal catalysts.
This study reports an iron-catalyzed hydrogenation protocol
for tri- and tetra-substituted alkenes of unprecedented activity
and scope under mild conditions (1–4 bar H2, 208C). Instruc-
tive snapshots at the interface of homogeneous and heteroge-
neous iron catalysis were recorded by the isolation of novel Fe
nanocluster architectures that act as catalyst reservoirs and
soluble seeds of particle growth.
=
C
atalytic hydrogenations of unsaturated C C bond systems
are pivotal to modern chemical transformations and mostly
performed with nickel or platinum group catalysts.[1] While
some of the largest technical processes are iron-catalyzed
hydrogenations (Haber–Bosch, Fischer–Tropsch), the poten-
tial of iron as abundant, non-toxic, and cheap transition metal
Scheme 1. Soluble Fe catalysts for hydrogenations of alkenes.
iron in various low oxidation states, and prevent unwanted
aggregation to larger, catalytically inactive particles; 3) the
ligands create a lipophilic periphery that enhances solubiliza-
tion under the non-polar conditions of alkene hydrogena-
tions; and iv) the catalytic hydrogenation operates under mild
conditions without sophisticated additives in common organic
solvents. With these framework conditions, we investigated
combinations of iron(II) bis(1,1,1,3,3,3-hexamethyl-disilazan-
2-ide), Fe(hmds)2,[7] and various reductants. Documented
herein are the benefits of using this simple catalytic system
that presents tangible advances over the current state-of-the-
art that could not have been predicted: Clean hydrogenations
of challenging alkenes (for exqmple, tetra-substituted) pro-
ceed under very mild conditions. A most user-friendly
protocol can be adopted by simple mixing of the ferrous
salt, reductant, and ligand. The isolation of novel soluble Fe
nanocluster topologies provides new insight into reductive
catalyst formation and cluster aggregation (Scheme 1,
bottom).
There are several reports of the coordination chemistry of
Fe(hmds)2 in the presence of various ligands, but only very
few applications to catalytic reactions have been demon-
strated.[8] The displacement of hmds ligands from Fe(hmds)2
by formal hydride donors has not received significant
attention despite its relevance to the preparation of simple
hydridoiron species[9] and hydrogenase model compounds.[10]
In the context of alkene hydrogenations, Chaudret et al.
prepared catalytically active Fe nanoparticles by thermal
decomposition of Fe(hmds)2 at 1508C in the presence of H2.[11]
We studied the generation of active hydrogenation catalysts
from Fe(hmds)2 and various simple and commercial hydride
donors and reductants under mild conditions (Table 1).
Ethylmagnesium chloride or zinc afforded poor hydrogena-
tion catalysts (entries 1, 2). Similar low activity was observed
when following Chaudretꢀs protocol of thermal decomposi-
=
catalyst for C C hydrogenations has only very recently been
tapped.[2] Significant progress in the design of molecular Fe
catalysts was made by the introduction of tridentate bis-
(imino)pyridine ligands (PDI) by Budzelaar et al.[3] and
Chirik et al.[4] The (PDI)Fe(N2)2 pre-catalysts cleanly hydro-
genate mono- and di-substituted alkenes under mild condi-
tions and exceed the productivity of some precious metal
catalysts.[4] Further improved activities were observed with
the related bis(carbene)–pyridine iron(0) complexes
(Scheme 1, top).[4] On the other hand, ill-defined or nano-
particulate Fe catalysts were prepared by decompositions of
iron carbonyls or by reductions of iron salts with organome-
tallic or hydride reagents but exhibited only moderate
hydrogenation activities.[5] While providing an operationally
simple access to Fe-based hydrogenation catalysts, the latter
approaches provided limited mechanistic insight, often
involved precipitation of heterogeneous species especially in
the absence of suitable ligands, and generally displayed high
catalyst sensitivity and limited scope. From our recent studies
into the development of low-valent iron catalysts for hydro-
genations,[6] we reasoned that an effective yet operationally
simple protocol would fulfill the following criteria: 1) The
active catalyst is prepared in situ by the reduction of iron(II)
precursors with commercial reductants; 2) the catalyst con-
tains bulky ligands that are cheap, easily available, coordinate
[*] Dr. T. N. Gieshoff, Dr. U. Chakraborty, M. Villa,
Prof. Dr. A. Jacobi von Wangelin
Institute of Organic Chemistry, University of Regensburg
Universitꢀtsstrasse 31, 93040 Regensburg (Germany)
E-mail: axel.jacobi@ur.de
Supporting information and the ORCID identification number(s) for
the author(s) of this article can be found under:
http://dx.doi.org/10.1002/anie.201612548.
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Table 1: Selected optimization experiments.[a]
Table 2: Robustness of the Fe(hmds)2/Dibal-H catalyst.
Entry Reductant Catalyst treatment
TOF
[hÀ1
Entry
Reductant (mol%)
Conditions
Yield [%][b]
]
1
2
3
4
5
6
7
8
EtMgCl (10)
Zn (10)
–
5 bar H2, 408C, 18 h
as entry 1
5 bar H2, 1508C, 18 h
as entry 1
1.3 bar H2, 208C, 3 h
as entry 4
1.3 bar H2, 208C, 0.5 h
as entry 7
5 (9)
<1 (1)
1 (1)
99 (99)
1 (2)
99 (99)
90 (98)
93 (99)
100 (100)
98 (99)
<1 (1)
<1 (1)
1
2
3
4
Dibal-H
Dibal-H
Dibal-H
Dibal-H
freshly prepared
41
37
30
27
storage for 5 d in solution
solvent removal, then dissolution
solvent removal, storage for 5 d, then
dissolution
NaBH4 (5)
NaBH4 (5)
LiAlH4 (5)
Me3Al (10)
iBu3Al (10)
iBu2AlH (10)
iBu2AlH (10)
–
5
6
7
Me3Al
Me3Al
Dibal-H
freshly prepared
storage for 1 d in solution
from FeCl2·1.5thf, HN(TMS)2, n-BuLi
13
<1
27
9
as entry 7
10
11
12
FeCl2, HN(TMS)2, nBuLi[d]
as entry 7
tetra-substituted alkenes (1–4 bar H2, 208C).[4] The harsher
conditions required for complete hydrogenation of 1,2-
dimethylindene might be a consequence of the low isomer-
ization activity of the Fe(hmds)2/Dibal-H catalyst.[13] Notably,
no ring-opening of a-cyclopropyl styrene was observed.[14]
With reduced catalyst loadings of 0.5 mol% Fe(hmds)2 and
1 mol% Dibal-H, turnover frequencies (TOF in hÀ1) of 660
and 280 were recorded in the hydrogenations of 1-octene and
a-methylstyrene, respectively (2 bar H2, PhMe, 208C, 5 min).
Under the same conditions, conversion of 1-phenyl-1-cyclo-
hexene required 3 mol% catalyst loading which resulted in
a TOF of 60 hÀ1. Alkynes were cleanly reacted to alkanes
under identical conditions (Scheme 3).
Kinetic poisoning studies were performed to ascertain the
topicity of the operating catalyst species.[15] The addition of
sub-catalytic amounts of trimethylphosphine (PMe3) led to
catalyst inhibition already at a catalyst/poison ratio of 10:1
(Scheme 4, top).[16]
Contrary to this, the selective homogeneous catalyst
poison dibenzo-[a,e]cyclooctatetraene[17] (dct, 4 equiv per
Fe) showed no significant inhibition but was merely a com-
peting substrate for hydrogenation (Scheme 4, bottom). We
thus postulate the operation of a heterotopic mechanism by
polynuclear low-valent Fe catalysts.
In an effort to identify potential catalytically active
species, we investigated the reaction of Fe[N(SiMe3)2]2 with
Dibal-H under the conditions of the hydrogenation reactions
(toluene or hexane, 208C). The reaction of Fe[N(SiMe3)2]2
and Dibal-H in a toluene/hexane mixture underwent rapid
color change from green to brown–black. Filtration, removal
of the solvents, and crystallization from n-hexane afforded the
dark crystalline Fe4 nanocluster Fe3(hmds)4Fe(toluene) in
38% yield (Scheme 5, Figure 1).[18] Single crystal structure
analysis showed a planar Fe4 core which is peripherally
decorated with four hmds ligands of which two hmds adopt
a bridging m2-coordination mode. One Fe atom bears an h6-
toluene. The paramagnetic complex had a melting point of
[c]
iBu2AlH (10)
as entry 7, FeCl2
[a] Conditions: 0.2 mmol alkene, 0.5m in toluene, 5 mol% Fe[N-
(SiMe3)2]2, reductant, H2. [b] Yields determined by quantitative GC-FID
vs. internal n-pentadecane. [c] 5 mol% FeCl2 instead of Fe(hmds)2.
[d] 5 mol% FeCl2, 10 mol% HN(SiMe3)2, 10 mol% n-butyl lithium (1.6m
in PhMe) instead of Fe(hmds)2.
tion of Fe(hmds)2 to nanoparticles (entry 3).[11] Extremely
high hydrogenation activity was achieved in the presence of
aluminium hydrides and organoaluminium reagents
(entries 6–9).[12] The most active catalyst was formed with
diiso-butylaluminium hydride (Dibal-H) which afforded
quantitative conversion of 1-phenyl-1-cyclohexene at 1.3 bar
H2 and 208C after 30 min. The operationally most convenient
in situ catalyst formation from FeCl2, HN(SiMe3)2, and n-
butyl lithium gave nearly identical yields (entry 10). Com-
plete inhibition was observed in the absence of Dibal-H or the
amido ligand N(TMS)2, respectively (entries 11, 12). Further
tests of the catalyst mixtures revealed high chemoselectivity
and robustness when employing Dibal-H (Scheme 2, Table 2).
This catalyst could be stored in solution for several days or
dried in vacuum without significant loss of activity (entries 1–
4, Table 2, turnover frequency (TOF) recorded after 7 min
reaction at about 0% conversion).
The optimized set of conditions was applied to the
hydrogenation of various alkenes (Scheme 3). Mono-, di-,
and tri-substituted alkenes were cleanly reacted under 2 bar
H2 pressure at room temperature.
The mild conditions tolerated fluoride, chloride, bromide,
silylenol ether, amine, imide, ester, thioether, and benzyl
ether functions. The hydrogenations of some challenging
substrates required elevated temperature and/or pressure.
Remarkably mild conditions enabled the hydrogenation of
1238C and exhibited an effective magnetic moment meff
=
2.0 mB (in C6D6). Two structurally related nanoclusters were
isolated by slow solvent evaporation from the reaction of
Fe[N(SiMe3)2]2 and Dibal-H in n-hexane. Crystal structure
analysis established the dark-red oligohydridoiron clusters
Fe5(hmds)6FeH5 and Fe6(hmds)6FeH6 (35% yield, 4/1,
Scheme 2. Chemoselectivity of the Fe(hmds)2/Dibal-H catalyst.
2
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Scheme 3. Substrate scope of iron-catalyzed hydrogenations of alkenes and alkynes. Bonds in blue indicate the site of complete p-bond
hydrogenation. Standard conditions: 0.2 mmol alkene/alkyne, 0.5m in toluene, 5 mol% Fe[N(SiMe3)2]2, 10 mol% Dibal-H, 2 bar H2, 208C, 3 h. If
not otherwise noted, yields were determined by quantitative GC-FID vs. n-pentadecane. Conversions are given in parentheses if <90%.
[a] 0.5 mol% Fe[N(SiMe3)2]2, 1 mol% Dibal-H.
Scheme 5. Synthesis of novel planar Fe4, Fe6, and Fe7 nanoclusters.
LIFDI-MS (m/z 1301.2287, 1358.1793). The Fe4, Fe6, and Fe7
nanocluster architectures contain multiple iron centers in low
oxidation states (formally Fe0, FeI, FeII) and constitute
Scheme 4. Poisoning studies with trimethylphosphine (PMe3, top) and
dibenzo[a,e]cyclooctatetraene (dct, bottom).
a distinct class of metallic cluster complexes[20] that adopt
rare planar Fen geometries and are void of the common
Scheme 5, Figure 1). The Fe6 cluster is a truncated derivative
of the Fe7 cluster and bears one m2-H and four m3-H atoms
coordinated to iron. The highly symmetrical Fe7 cluster, a low-
valent “Fe wheel”, contains six peripheral m2-hmds ligands
and six m3-H ligands.[19] The composition of the cluster mixture
was further verified by X-ray analysis, elemental analysis, and
carbonyl, nitrido, oxo and carbido ligands.[21] Generally,
discrete metallic clusters with direct interactions between
the redox centers are considered as materials for optical,
magnetic, and catalytic applications.[22] Detailed studies of
spectroscopic and coordination properties of the Fe nano-
clusters are beyond the scope of this catalytic method
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Figure 1. Crystal structures (50% probability level, peripheral H atoms omitted) of Fe3(hmds)4Fe(toluene), Fe5(hmds)6FeH4, Fe6(hmds)6FeH6 (left
to right).
Keywords: amides · hydrides · hydrogenations · iron ·
nanoclusters
development but will be reported soon. Preliminary studies
proved that the Fe4 nanocluster is a competent hydrogenation
pre-catalyst in the presence of Dibal-H and HN(TMS)2
(Scheme 6).
[1] a) The Handbook of Homogeneous Hydrogenation (Eds.: J. G.
de Vries, C. J. Elsevier), Wiley-VCH, Weinheim, 2007; b) S.
Nishimura, Handbook of Heterogeneous Catalytic Hydrogena-
tion for Organic Synthesis, Wiley, New York, 2001.
[2] a) Catalysis without Precious Metals (Ed.: R. M. Bullock),
Wiley-VCH, Weinheim, 2010; b) P. J. Chirik, Acc. Chem. Res.
2015, 48, 1687; c) K. Junge, K. Schrçder, M. Beller, Chem.
Commun. 2011, 47, 4849; d) B. A. F. Le Bailly, S. P. Thomas, RSC
Adv. 2011, 1, 1435.
Scheme 6. Catalytic hydrogenation with the isolated Fe4 nanocluster.
[3] Q. Knijnenburg, A. D. Horton, H. van der Heijden, A. W. Gal,
P. H. M. Budzelaar, WO2003042131 A1 20030522, 2003.
[4] a) S. C. Bart, E. Lobkovsky, P. J. Chirik, J. Am. Chem. Soc. 2004,
126, 13794; b) R. J. Trovitch, E. Lobkovsky, E. Bill, P. J. Chirik,
Organometallics 2008, 27, 1470; c) J. M. Hoyt, M. Shevlin, G. W.
Margulieux, S. W. Krska, M. T. Tudge, P. J. Chirik, Organo-
metallics 2014, 33, 5781; d) R. P. Yu, J. M. Darmon, J. M. Hoyt,
G. W. Margulieux, Z. R. Turner, P. J. Chirik, ACS Catal. 2012, 2,
1760.
[5] a) P. H. Phua, L. Lefort, J. A. F. Boogers, M. Tristany, J. G.
de Vries, Chem. Commun. 2009, 3747; b) C. Rangheard, C.
de Julian Fernandez, P.-H. Phua, J. Hoorn, L. Lefort, J. G.
de Vries, Dalton Trans. 2010, 39, 8464; c) M. Stein, J. Wieland,
P. Steurer, F. Tçlle, R. Mꢁlhaupt, B. Breit, Adv. Synth. Catal.
2011, 353, 523; d) R. Hudson, A. Riviꢂre, C. M. Cirtiu, K. L.
Luska, A. Moores, Chem. Commun. 2012, 48, 3360; e) A.
Welther, A. Jacobi von Wangelin, Curr. Org. Chem. 2013, 17,
326; f) T. S. Carter, L. Guiet, D. J. Frank, J. West, S. P. Thomas,
Adv. Synth. Catal. 2013, 355, 880; g) D. J. Frank, L. Guiet, A.
Kaslin, E. Murphy, S. P. Thomas, RSC Adv. 2013, 3, 25698; h) R.
Hudson, G. Hamasaka, T. Osako, Y. M. A. Yamada, C.-J. Li, Y.
Uozumi, A. Moores, Green Chem. 2013, 15, 2141; i) A. J.
MacNair, M.-M. Tran, J. E. Nelson, G. U. Sloan, A. Ironmonger,
S. P. Thomas, Org. Biomol. Chem. 2014, 12, 5082.
In summary, we have developed an iron-catalyzed hydro-
genation protocol that displays unprecedented activity for
challenging tri- and tetra-substituted alkenes under very mild
reaction conditions. The catalyst is prepared by reaction of
Fe[N(SiMe3)2]2 with diisobutylaluminum hydride or by a most
user-friendly in situ method from FeCl2. The isolation of novel
low-valent nanoclusters with planar Fe4, Fe6, and Fe7 geo-
metries under such conditions provides new insight into the
interface of homogeneous/heterogeneous catalysis and the
growth of metallic nanoparticle materials. Further studies of
the spectroscopic and chemical properties of these and
related planar [(amido)Fe]n nanoclusters are currently being
executed.
Acknowledgements
We thank the Evonik Foundation (T.N.G.) and the Fonds der
Chemischen Industrie (M.V.) This work was funded by the
European Research Council (ERC) through a Consolidator
grant (683150).
[6] a) D. Gꢃrtner, A. Welther, B. R. Rad, R. Wolf, A. Jacobi von
Wangelin, Angew. Chem. Int. Ed. 2014, 53, 3722; Angew. Chem.
2014, 126, 3796; b) T. N. Gieshoff, M. Villa, A. Welther, M. Plois,
U. Chakraborty, R. Wolf, A. Jacobi von Wangelin, Green Chem.
2015, 17, 1408; c) A. Welther, M. Bauer, M. Mayer, A.
Jacobi von Wangelin, ChemCatChem 2012, 4, 1088.
Conflict of interest
The authors declare no conflict of interest.
[7] R. A. Andersen, K. Faegri, J. C. Green, A. Haaland, M. F.
Lappert, W.-P. Leung, Inorg. Chem. 1988, 27, 1782.
4
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[8] Selected recent examples: a) M. I. Lipschutz, T. Chantarojsiri, Y.
2002, 41, 1529; Angew. Chem. 2002, 114, 1600; b) A related
Dong, T. D. Tilley, J. Am. Chem. Soc. 2015, 137, 6366; b) L. C. H.
Maddock, T. Cadenbach, A. R. Kennedy, I. Borilovic, G. Aromꢄ,
E. Hevia, Inorg. Chem. 2015, 54, 9201; c) T. Hatakeyama, R.
Imayoshi, Y. Yoshimoto, S. K. Ghorai, M. Jin, H. Takaya, K.
Norisuye, Y. Sohrin, M. Nakamura, J. Am. Chem. Soc. 2012, 134,
20262; d) J. Yang, T. D. Tilley, Angew. Chem. Int. Ed. 2010, 49,
10186; Angew. Chem. 2010, 122, 10384; e) J. Yang, M. Fasulo,
T. D. Tilley, New J. Chem. 2010, 34, 2528.
synthesis of an (h6-toluene)FeI diamide complex: T. Janes, J. M.
Rawson, D. Song, Dalton Trans. 2013, 42, 10640.
[19] Y. Lee, K. J. Anderton, F. T. Sloane, D. M. Ermert, K. A.
Abboud, R. Garcꢄa-Serres, L. J. Murray, J. Am. Chem. Soc.
2015, 137, 10610.
[20] Non-planar nitrido/imido/amido Fe clusters: a) R. Hernꢅn-
dez Sꢅnchez, T. A. Betley, J. Am. Chem. Soc. 2015, 137, 13949;
b) D. A. Iovan, T. A. Betley, J. Am. Chem. Soc. 2016, 138, 1983;
c) R. Hernꢅndez Sꢅnchez, A. K. Bartholomew, T. M. Powers, G.
Mꢆnard, T. A. Betley, J. Am. Chem. Soc. 2016, 138, 2235; d) R.
Hernꢅndez Sꢅnchez, S.-L. Zheng, T. A. Betley, J. Am. Chem.
Soc. 2015, 137, 11126; e) R. Hernꢅndez Sꢅnchez, A. M. Willis, S.-
L. Zheng, T. A. Betley, Angew. Chem. Int. Ed. 2015, 54, 12009;
Angew. Chem. 2015, 127, 12177; f) T. M. Powers, T. A. Betley, J.
Am. Chem. Soc. 2013, 135, 12289; g) E. T. Hennessy, T. A.
Betley, Science 2013, 340, 591; h) Q. Zhao, T. A. Betley, Angew.
Chem. Int. Ed. 2011, 50, 709; Angew. Chem. 2011, 123, 735;
i) E. R. King, E. T. Hennessy, T. A. Betley, J. Am. Chem. Soc.
2011, 133, 4917; j) “Kochi-type” [Fe8Me12]À double decker: S. B.
MuÇoz, S. L. Daifuku, W. W. Brennessel, M. L. Neidig, J. Am.
Chem. Soc. 2016, 138, 7492; k) Related Co6 and Co7 clusters: Y.
Ohki, Y. Shimizu, R. Araake, M. Tada, W. M. C. Sameera, J.-I.
Ito, H. Nishiyama, Angew. Chem. Int. Ed. 2016, 55, 15821;
Angew. Chem. 2016, 128, 16053.
[21] a) M. Akita in Comprehensive Organometallic Chemistry III,
Vol. 6, 1st ed. (Eds.: R. H. Crabtree, D. M. P. Mingos), Elsevier,
Amsterdam, 2007, p. 259; b) K. H. Whitmire, Adv. Organomet.
Chem. 1998, 42, 1. Anionic (CO)xFe3 triangles or non-planar
(CO)yFe4 envelopes with bridging amido/imido/nitrido ligands:
c) P. Zanello, F. Laschi, A. Cinquantini, R. Della Pergola, L.
Garlaschelli, M. Cucco, F. Demartin, T. R. Spalding, Inorg.
Chim. Acta 1994, 226, 1; d) R. D. Pergola, C. Bandini, F.
Demartin, E. Diana, L. Garlaschelli, P. L. Stanghellini, P.
Zanello, J. Chem. Soc. Dalton Trans. 1996, 747; e) H. Bantel, P.
Suter, H. Vahrenkamp, Organometallics 1995, 14, 4424.
[22] a) Metal Clusters in Chemistry (Eds.: P. Braunstein, L. A. Oro,
P. R. Raithby), Wiley-VCH, Weinheim, 1999; b) D. Gatteschi, R.
Sessoli, J. Villain, Molecular Nanomagnets, Oxford University
Press, Oxford, 2006; c) E. de Smit, B. M. Weckhuysen, Chem.
Soc. Rev. 2008, 37, 2758.
[9] H. Nakazawa, M. Itazaki, Top. Organomet. Chem. 2011, 33, 27.
[10] a) W. Lubitz, H. Ogata, O. Rꢁdiger, E. Reijerse, Chem. Rev.
2014, 114, 4081; b) S. Tschierlei, S. Ott, R. Lomoth, Energy
Environ. Sci. 2011, 4, 2340; c) P. Du, R. Eisenberg, Energy
Environ. Sci. 2012, 5, 6012.
[11] V. Kelsen, B. Wendt, S. Werkmeister, K. Junge, M. Beller, B.
Chaudret, Chem. Commun. 2013, 49, 3416.
[12] Ziegler-type Fe/Al catalysts in hydrogenations: a) M. F. Sloan,
A. S. Matlack, D. S. Breslow, J. Am. Chem. Soc. 1963, 85, 4014;
b) Y. Takegami, T. Ueno, T. Fujii, Bull. Chem. Soc. Jpn. 1965, 38,
1279; c) N. F. Noskova, A. Zh. Kazimova, K. K. Kambarova,
S. R. Savelev, N. L. Melamud, Zh. Org. Khim. 1992, 28, 1352.
[13] a) Isomerization of allylbenzene (to b-methylstyrene) and 1-
octene (to 2-,3-,4-octenes) with 5 mol% Fe(hmds)2/10 mol%
Dibal-H proceeded sluggishly under otherwise identical con-
ditions (no H2). b) M. Mayer, A. Welther, A. Jacobi von Wan-
gelin, ChemCatChem 2011, 3, 1567.
[14] M. Newcomb in Encyclopedia of Radicals in Chemistry, Biology
and Materials (Eds.: C. Chatgilialoglu, A. Studer), Wiley,
Chichester, 2012.
[15] a) J. A. Widegren, R. G. Finke, J. Mol. Catal. A 2003, 198, 317;
b) D. Astruc, F. Lu, J. Ruiz Aranzaes, Angew. Chem. Int. Ed.
2005, 44, 7852; Angew. Chem. 2005, 117, 8062; c) R. H. Crabtree,
Chem. Rev. 2012, 112, 1536.
[16] a) K.-N. T. Tseng, J. W. Kampf, N. K. Szymczak, ACS Catal.
2015, 5, 411; b) Y. Li, S. Yu, X. Wu, J. Xiao, W. Shen, Z. Dong, J.
Gao, J. Am. Chem. Soc. 2014, 136, 4031; c) E. Alberico, P.
Sponholz, C. Cordes, M. Nielsen, H.-J. Drexler, W. Baumann, H.
Junge, M. Beller, Angew. Chem. Int. Ed. 2013, 52, 14162; Angew.
Chem. 2013, 125, 14412.
[17] a) D. R. Anton, R. H. Crabtree, Organometallics 1983, 2, 855;
b) G. Franck, M. Brill, G. Helmchen, J. Org. Chem. 2012, 89, 55;
c) J. F. Sonnenberg, R. H. Morris, Catal. Sci. Technol. 2014, 4,
3426; d) D. Gꢃrtner, A. L. Stein, S. Grupe, J. Arp, A. Jacobi
von Wangelin, Angew. Chem. Int. Ed. 2015, 54, 10545; Angew.
Chem. 2015, 127, 10691.
[18] a) A structurally similar tetraborane motif: A. Maier, M.
Hofmann, H. Pritzkow, W. Siebert, Angew. Chem. Int. Ed.
Manuscript received: December 28, 2016
Final Article published: && &&, &&&&
Angew. Chem. Int. Ed. 2017, 56, 1 – 7
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
5
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Iron Cluster Catalysis
T. N. Gieshoff, U. Chakraborty, M. Villa,
A. Jacobi von Wangelin*
&&&& — &&&&
Alkene Hydrogenations by Soluble Iron
Nanocluster Catalysts
An iron-catalyzed hydrogenation has
been developed based on the simple
ternary catalyst system Fe[N(SiMe3)2]2/
iBu2AlH. Clean hydrogenations of chal-
lenging alkenes proceeded under very
mild conditions (1–4 bar H2, 208C). The
simple mixing of the ferrous salt, reduc-
tant, and ligand is particularly user-
friendly. Isolation of soluble Fe nano-
clusters provides insight into reductive
catalyst formation and nanoparticle
aggregation.
Eisencluster-Katalyse
T. N. Gieshoff, U. Chakraborty, M. Villa,
A. Jacobi von Wangelin*
&&&& — &&&&
Alkene Hydrogenations by Soluble Iron
Nanocluster Catalysts
Eine eisenkatalysierte Hydrierung mit
dem ternꢀren System Fe[N(SiMe3)2]2/
iBu2AlH fꢁhrt auch mit schwierigen
Alkensubstraten unter sehr milden
Bedingungen (1–4 bar H2, 208C) zum
Erfolg. Fꢁr die Reaktionen kann das
Eisen(II)-Salz einfach mit dem Reduk-
tionsmittel und dem Liganden gemischt
werden. Die Isolierung lçslicher Fe-
Nanocluster gibt Einblicke in die reduk-
tive Katalysatorbildung und die Nano-
partikelaggregation.
6
www.angewandte.org
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2017, 56, 1 – 7
These are not the final page numbers!

Angewandte
Communications
Chemie
Communications
Iron Cluster Catalysis
T. N. Gieshoff, U. Chakraborty, M. Villa,
A. Jacobi von Wangelin*
&&&& — &&&&
Alkene Hydrogenations by Soluble Iron
Nanocluster Catalysts
An iron-catalyzed hydrogenation has
been developed based on the simple
ternary catalyst system Fe[N(SiMe3)2]2/
iBu2AlH. Clean hydrogenations of chal-
lenging alkenes proceeded under very
mild conditions (1–4 bar H2, 208C). The
simple mixing of the ferrous salt, reduc-
tant, and ligand is particularly user-
friendly. Isolation of soluble Fe nano-
clusters provides insight into reductive
catalyst formation and nanoparticle
aggregation.
Angew. Chem. Int. Ed. 2017, 56, 1 – 7
ꢀ 2017 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
7
These are not the final page numbers!