Simple Access to the Heaviest Alkaline Earth Metal Hydride: A Strongly Reducing Hydrocarbon-Soluble Barium Hydride Cluster

Article abstract of DOI:10.1002/anie.201709771

Reaction of Ba[N(SiMe₃)₂]₂ with PhSiH₃ in toluene gave simple access to the unique Ba hydride cluster Ba₇H₇[N(SiMe₃)₂]₇ that can be described as a square pyramid spanned by five Ba²⁺ ions with two flanking BaH[N(SiMe₃)₂] units. This heptanuclear cluster is well soluble in aromatic solvents, and the hydride ¹H NMR signals and coupling pattern suggests that the structure is stable in solution. At 95 °C, no coalescence of hydride signals is observed but the cluster slowly decomposes to undefined barium hydride species. The complex Ba₇H₇[N(SiMe₃)₂]₇ is a very strong reducing agent that already at room temperature reacts with Me₃SiCH=CH₂, norbornadiene, and ethylene. The highly reactive alkyl barium intermediates cannot be observed and deprotonate the (Me₃Si)₂N^? ion, as confirmed by the crystal structure of Ba₁₄H₁₂[N(SiMe₃)₂]₁₂[(Me₃Si)(Me₂SiCH₂)N]₄.

Full text of DOI:10.1002/anie.201709771

A Journal of the Gesellschaft Deutscher Chemiker
Angewandte
International Edition Chemie
www.angewandte.org
Accepted Article
Title: Simple Access to the Heaviest Alkaline-Earth Metal Hydride: A
Strongly Reducing Hydrocarbon-Soluble Barium Hydride Cluster
Authors: Sjoerd Harder, Brant Maitland, Michael Wiesinger, Christian
Färber, Gerd Ballmann, Holger Elsen, and Christian Fischer
This manuscript has been accepted after peer review and appears as an
Accepted Article online prior to editing, proofing, and formal publication
of the final Version of Record (VoR). This work is currently citable by
using the Digital Object Identifier (DOI) given below. The VoR will be
published online in Early View as soon as possible and may be different
to this Accepted Article as a result of editing. Readers should obtain
the VoR from the journal website shown below when it is published
to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Angew. Chem. Int. Ed. 10.1002/anie.201709771
Angew. Chem. 10.1002/ange.201709771
Link to VoR: http://dx.doi.org/10.1002/anie.201709771
http://dx.doi.org/10.1002/ange.201709771

Angewandte Chemie International Edition
10.1002/anie.201709771
Table of Contents
The first barium hydride cluster has been prepared by the surprisingly simple reaction of
Ba[N(SiMe ) ] with PhSiH3 in toluene. Despite lack of additional Lewis bases,
3
2 2
Ba H [N(SiMe ) ] is remarkably soluble in aromatic solvents and is in its crystal structure
7
7
3 2 7
capped with two benzene ligands. The cluster is retained in solution (C D ) and even at 95 °C
6
6
(decomposition temperature) no coalescence of hydride signals is observed. This solubilized
Ba hydride cluster is strongly reducing and reacts at room temperature with isolated
alkenes, including ethylene.
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
2
Simple Access to the Heaviest Alkaline-Earth Metal Hydride:
A Strongly Reducing Hydrocarbon-Soluble Barium Hydride Cluster **
Michael Wiesinger, Brant Maitland, Christian Färber, Gerd Ballmann, Christian Fischer,
Holger Elsen, Sjoerd Harder*
[
a] Prof. Dr. S. Harder, M. Wiesinger, Dr. B. Maitland, Dr. C. Färber, G. Ballmann, C. A.
Fischer, H. Elsen
Inorganic and Organometallic Chemistry, Universität Erlangen-Nürnberg,
Egerlandstrasse 1, 91058 Erlangen, Germany
Fax: (+49) 9131-8527387
E-mail: sjoerd.harder@fau.de
Supporting information for this article is available on the WWW under
http//:www.angewandte.chemie.org or from the author.
Keywords: Barium – Hydrides – Reductant – Alkaline-earth metals – Self-assembly
Abstract: Reaction of Ba[N(SiMe ) ] with PhSiH in toluene gave simple access to the unique Ba hydride cluster
3
2 2
3
2+
Ba H [N(SiMe ) ] that can be described as a square pyramid spanned by five Ba ions with two flanking
7
7
3 2 7
1
BaH[N(SiMe ) ] units. This heptanuclear cluster is well soluble in aromatic solvents and the hydride H NMR
3
2
signals and coupling pattern suggests that the structure is stable in solution. At 95 °C, no coalescence of
hydride signals is observed but the cluster slowly decomposes to undefined Ba hydride species. Complex
Ba H [N(SiMe ) ] is a very strong reducing agent that already at room temperature reacts with Me SiCH=CH ,
7
7
3 2 7
3
2
norbornadiene and ethylene. The highly reactive alkylbarium intermediates cannot be observed and
deprotonate the (Me Si) Nˉ ion, as confirmed by the crystal structure of
Ba H [N(SiMe ) ] [(Me Si)(Me SiCH )N] .
3
2
14
12
3 2 12
3
2
2
4
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
3
Organometallic compounds of the least electronegative group 1 and 2 metals are renowned
for extremely high reactivity. Consequently, their hydrides are expected to possess superb
reducing abilities. Despite their insolubility, KH, and to a certain degree also NaH, are indeed
[1]
highly reactive salts, commonly used in synthesis. This stands in strong contrast to the poor
reactivity of the lightest hydride, LiH. The very high lattice energy of insoluble (LiH) (920
∞
[
3]
kJ/mol) impedes heterogeneous surface reactions and LiH is essentially inert in reaction
[
2]
with oxygen, chlorine or hydrogen chloride. Combining LiH with AlH , however, gives the
3
+
[4]
highly reactive, ether-soluble, aluminate [Li (Et O) ][AlH ˉ]. Although this solubilized
2
x
4
reagent was already discovered in the 40’s, its strongly reducing powers can even today
hardly be surpassed thus explaining its small-scale industrial use and high commercial value.
Solubilization as a strategy to increase reactivity has also been documented for NaH which in
[
5]
combination with LiI or NaI shows a potent hydride reduction chemistry.
On a similar note, the lighter alkaline-earth metal (Ae) hydrides, BeH and MgH , are hardly
2
2
[
6]
[7]
reactive. Whereas MgH reacts slowly with water, BeH is practically inert to hydrolysis.
2
2
The heavier CaH reacts vigorously with water but is inert to a large variety of functional
2
groups like C-X (X = halogenide), C=O, C=N, C≡N, C=C and epoxides. This explains its popular
use as a drying agent for various solvents. Being aware of the enormous importance of
solubilisation for reactivity, we demonstrated that a hydrocarbon-soluble Ca hydride
[
8]
complex (1) smoothly reacts with the same functional groups but the reduction of alkenes
[9]
was limited to activated (conjugated) C=C bonds.
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
4
The key to stabilization of the Ca hydride complex 1 has been kinetic stabilization by the
bulky bidentate ß-diketiminate ligand. Using large multi-dentate ligands, further examples of
[10]
[11]
neutral (e.g. 2) and cationic (e.g. 3-5) Ca hydride complexes have been reported. As Ae-
ligand bond energies decrease down group 2, syntheses of the heavier, even more reducing,
Sr and Ba hydride complexes is increasingly challenging (ligand exchange by the Schlenk
equilibrium gives insoluble AeH salts). Very recently, we reported the first Sr hydride cluster
2
that simply could be obtained without use of large stabilizing ligands. In agreement with our
[
10b]
earlier observation that the neutral THF ligand in 1 is also crucial to its stability,
reaction
of the well-known precursors AeN’’ (Ae = Ca or Sr, N’’ = N(SiMe ) ) with PhSiH in the
2
3 2
3
presence of a stabilizing neutral tridentate ligand PMDTA gave self-assembly to
[
12]
Ae H N’’ ∙(PMDTA) (6 and 7, Scheme 1); (PMDTA = MeN(CH CH NMe ) ). Prior to this
6
9
3
3
2
2
2 2
work, it had been shown that this strategy is also valid for isolation of a lighter, less dynamic,
Mg hydride cluster: reaction of MgN’’ with PhSiH and a strongly coordinating NHC ligand
2
3
[13]
gave Mg H N’’ ∙(NHC) (8; Scheme 1).
4
6
2
2
Scheme 1. Syntheses of Ae metal hydride
clusters from AeN’’2 and PhSiH ; N’’ =
3
N(SiMe ) .
3
2
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
5
The synthetic procedure for the heavier Ca and Sr hydride clusters (6-7), however, did not
allow for access to the heaviest Ba hydride cluster. Assuming that the presence of neutral,
strongly coordinating, ligands is crucial to stabilize Ae hydride clusters, we started our
investigations on this last remaining challenge. To our surprise, however, we found that not
only large multidentate anionic ligands but also strongly coordinating neutral ligands are
superfluous. The reaction of BaN’’ with PhSiH in toluene at -90 °C gave after slowly
2
3
warming to room temperature a complex of formula BaHN’’ as a white powder in a
reproducible yield of 51% (9). Considering the generally very poor solubility of Ba
[
14]
complexes, BaHN’’ is surprisingly well soluble in benzene and crystallized from this solvent
as Ba H N’’ ∙(C H ) (Figure 1).
7
7
7
6 6 2
Figure 1. (a) Crystal structure of Ba H N’’ ∙(C H ) ; C and H atoms (except for the hydrides) omitted for clarity.
7
7
7
6 6 2
Selected bond distances: Ba1∙∙∙H1 3.21(3), Ba1-H2 2.57(2), Ba1-H3 2.77(3), Ba2-H1 2.91(1), Ba2-H2’ 2.58(2),
Ba2-H3 2.77(3), Ba2-H4 2.63(3), Ba3-H3 2.67(3), Ba3-H4 2.67(3), Ba4-H1 2.79(1), Ba4-H2 2.59(2), Ba4-H3
2
.82(3), Ba4-H4 2.67(2). (b) Schematic representation of Ae H N’’ ∙(PMDTA) (left) and Ba H N’’ ∙(C H ) (right).
6 9 3 3 7 7 7 6 6 2
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
6
The structure is of very good quality and despite the vicinity of heavy Ba cations, all hydride
anions could be located in the difference Fourier map and were refined isotropically. The
structure of Ba H N’’ ∙(C H ) is related to those of Ae H N’’ ∙(PMDTA) (Ae = Ca, Sr); Figure
7
7
7
6
6 2
6
9
3
3
2
+
1
b. While the latter can be described as an octahedron of Ae ions with hydride anions at
the octahedron center and at each of the eight faces, the Ba hydride cluster could be seen as
an opened octahedron, i.e. a square pyramid (basal plane Ba2-Ba4-Ba2’-Ba4 and top Ba1)
with two flanking BaHN’’ units (Ba3 and Ba3’). The Ba-H bonding arrangements show close
[
15]
similarities with fragments found in crystalline BaH2. The Ba-H bonds vary from 2.55(3) to
[
15a]
3
.21(3) Å (average 2.73 Å); cf. BaH : 2.570(11)-2.979(8) Å (average: 2.720 Å).
The longest
Ba-H bond, Ba1-H1 3.21(3) Å, is significantly longer than the other Ba-H bonds (2.55(3)-
.91(1) Å) and shown as a dashed line. Bridging N’’ ligands show Ba-N’’ distances in the
2
2
range 2.750(1)-2.951(2) Å (average: 2.820 Å) whereas the bond to the terminal N’’ is shorter:
Ba1-N’’ 2.614(2) Å. Both are in agreement with bridging (2.798(3)-2.846(4) Å) and terminal
[
16]
(
2.576(3) Å) bonds in (BaN’’ ) . Ba3 has a short contact to the center of a cocrystallized
2
2
benzene molecule (3.634(1) Å). This weakly bound ligand is lost under high vacuum and also
in solution facile fast exchange is to be expected.
Complex Ba H N’’ (9) dissolves remarkably well in C D (this is likely due to solubilizing N’’
7
7
7
6 6
1
groups). The H NMR spectrum shows an overlapping set of sharp and broader signals for
the N’’ ligands that decorate the outside of the cluster. More important, the four different
hydride ligands in Ba H N’’ can clearly be found in the low-field region of the spectrum:
7
7
7
signals in the correct 1/2/2/2 ratio at 7.92, 8.37, 8.75 and 9.88 ppm are tentatively assigned
to H1, H3, H4 and H2, respectively. This assignment is based on hydride∙∙∙hydride coupling
1
1
constants and a phase-selective 2D H, H-COSY spectrum (Figure 2). There is strong coupling
between H3 and H4 (3.6 Hz) but no coupling between H2 and H3. H1 shows weak coupling to
H2 (2.4 Hz) and even weaker coupling to H3 (0.6 Hz) which is not visible in the COSY
spectrum but would explain the double doublet pattern observed for H3. As observed
previously, the value of hydride∙∙∙hydride coupling constants seems to correlate with H∙∙∙H
separation.
Additional support for the correct assignment of the hydride signals comes from the
1
observation that these signals are missing in a H NMR spectrum of the deuteride cluster
2
Ba D N’’ (prepared by using PhSiD ) and observed in the D NMR spectrum; Figure S1. The
7
7
7
3
rather high chemical shifts for the hydrides are in agreement with the chemical shift for solid
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
7
[
17]
BaH (8.9 ppm) and follow the expected trend for increased deshielding down the group
2
[
12]
[18]
Be to Ba.
This has been explained with spin-orbit-induced-heavy-atom effects
that
strongly increase with the atom number of the heavy atom and is in line with the extreme
[
19]
chemical shift of 35.6 ppm for the hydride in a recently reported ArPbH species.
Heating a solution of Ba H N’’ in toluene-d gives at 75 °C broadening of the four hydride
7
7
7
8
signals but further heating to 95 °C does not lead to coalescence. Instead, decomposition
into larger undefined Ba hydride clusters is observed (Figure S9). This is evident from the
appearance of a very broad hydride signal at 9.5 ppm which is accompanied by a very broad
resonance in the N’’ region and a sharper N’’ signal that can be assigned to BaN’’ (all signals
2
1
remain after cooling). In the solid, Ba H N’’ decomposes at 175 °C. H NMR shows only trace
7
7
7
quantities of H and a major signal for BaN’’ .
2
2
Figure 2. Phase-selective 2D COSY spectrum of Ba H N’’ dissolved in C D .
7
7
7
6 6
Theoretical calculations on a model system in which the N(SiMe ) anions have been
3
2
replaced by NMe anions (B3LYP/def2tzvp using core potentials at Ba) simulate the crystal
2
2
+
structure surprisingly well (Table S3). The NPA charges on Ba vary from +1.680 to +1.767
average: +1.721) and on Hˉ from -0.826 to -0.862 (average: -0.839), indicating highly ionic
(
bonds (Table S4). The electron densities in the bond-critical-points (BCP in Table S6)
3
correlate well with the Ba-H distances: the value for the Ba1-H1 bond (0.044 e∙Åˉ ) is much
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
8
3
lower than that for the other Ba-H bonds (average: 0.135 e∙Åˉ ), indicating only partial
bonding. Whereas the Ca hydride cluster Ca H N’’ ∙(PMDTA) featured eight BCP’s between
6
9
3
3
3
the central Hˉ and the outer hydrides of considerable electron density (BCP = 0.102 e∙Åˉ ), in
Ba H N’’ there are only two hydride-hydride BCP’s (H1-H2/H1-H2’) of low electron density
7
7
7
3
(
BCP = 0.052 e∙Åˉ ).
Having at hand a route to the heaviest and most reactive Ae metal hydride, we investigated
the strongly reducing properties of Ba H N’’ . We specifically focussed on reactions that are
7
7
7
not feasible for Ca hydride complexes. Neutral Ca hydride complexes (e.g. 1 and 2) showed
fast addition to carbon-heteroatom unsaturated bonds but the reduction of C=C bonds is
[
9]
limited to conjugated double bonds. This selectivity is based on product stability: addition
of the Ca-H bond to C=C bonds in styrene or cyclohexadiene yield benzylic or allylic
carbanions that are stabilized by resonance. This reactivity has been the key to its use as the
[
20]
the first non-transition metal catalyst for hydrogenation of activated alkenes. Okuda et al.
very recently reported that cationic Ca hydride complexes (e.g. 4 and 5) are able to
[
11d]
hydrogenate isolated alkenes.
Consequently, these cationic Ca hydride complexes should
show addition to unactivated alkenes but discrete Ca alkyl could not be isolated: addition
and ß-hydride elimination seemed to be reversible. It was concluded that the cationic nature
2
+
of 4 and 5 imparts high electrophilicity to the Ca center and is crucial to this reactivity.
Would the more polar neutral Ba hydride complexes be able to reduce unactivated C=C
bonds?
Reaction of Ba H N’’ with Me SiCH=CH in C D gave at room temperature already a notable
7
7
7
3
2
6 6
conversion of the alkene (Scheme 2). After six days full conversion to Me SiCH CH was
3
2
3
established. Similar, Ba H N’’ reacts already at room temperature slowly with
7
7
7
norbornadiene (full conversion after 6 days) and at 60 °C essential full conversion is found
overnight (15 h). The hydrogenation products can be explained by Ba hydride addition to
give highly reactive Ba-alkyl intermediates that are protonated. In case of norbornadiene,
hydride addition is followed by an internal addition of the Ba-alkyl intermediate to the
[
21]
remaining C=C bond giving the unusually stable nortricyclene. The origin of the proton in
the last protonation step is not the C D solvent which would have introduced deuterium in
6
6
the final product for which we did not find evidence. Instead, we found evidence for
deprotonation of the N(SiMe ) anion by the intermediate Ba-alkyl, an unusual reaction that
3
2
is sometimes observed in transition metal chemistry or for complexes with more Lewis-
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
9
[22]
acidic metal centers (U, Sc, Zr but also Mg). In the reduction of norbornadiene we isolated
in one case a highly insoluble side-product in the form of large single crystals. X-ray
diffraction revealed a very large tetradecanuclear Ba hydride cluster (10) containing a
deprotonated N’’ ligand (Figure 3).
2
+
The centrosymmetric cluster consists of 14 Ba ions, 12 hydride anions (all refined
isotropically), 12 N’’ anions and 4 dianionic ligands (Me Si)(Me SiCH ˉ)Nˉ. Although it is hard
3
2
2
to describe the geometry of 10, it contains structural elements reminiscent of Ba H N’’ . The
7
7
7
asymmetric unit in complex 10 contains a somewhat deformed square pyramid (basal plane
2+
Ba2-Ba4-Ba5-Ba6 and top Ba1) and flanking BaHN’’ unit (Ba3). There are seven different Ba
ions (from 4- to 7-coordinate) and six different Hˉ ions (from 3- to 5-coordinate). The Ba-H
bonds range from 2.78(4) to 3.06(3) Å (average: 2.75 Å). There are two different types of Ba-
2
+
alkyl bonds: C1 bridges three Ba ions with Ba-C bonds varying from 2.938(3) to 3.046(3) Å
2
+
(
average: 2.998 Å) and C2 bridges two Ba ions with shorter Ba-C bonds of 2.852(3) and
2
.897(3) Å.
Scheme 2. Reaction of Ba H N’’ (9) with alkenes.
7
7
7
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
1
0
Figure 3. Crystal structure of Ba H N’’ [(Me Si)(Me SiCH )N] (10); C and H atoms (except hydrides and CH
2
14
12
12
3
2
2
4
groups) have been omitted for clarity.
Although the C=C bonds in Me SiCH=CH and norbornadiene are formally isolated double
3
2
bonds, they should be considered to be partially activated. Hydride addition to Me SiCH=CH2
3
gives an -Si-stabilized carbanion whereas double bonds in norbornadiene show some
[23]
degree of through-space homoconjugation. Therefore, we investigated the reactivity of
Ba H N’’ with a truly isolated alkene. Reaction with the simplest alkene, ethylene (1 bar),
7
7
7
gave at room temperature within 24 hours full consumption of Ba H N’’ with concomittant
7
7
7
ethene to ethane conversion (Figure S23). This reaction must proceed through a highly
reactive ethylbarium species that forms ethane by deprotonation of the N’’ ligand.
In summary, starting from the simple precursor BaN’’ , we developed an easy synthetic
2
route to a well-defined, hydrocarbon-soluble, Ba hydride cluster. The neutral complex
Ba H N’’ ∙(C H ) does not contain any stabilizing ether or amine ligands but in the crystal
7
7
7
6 6 2
2
+
structure two Ba ions interact with a soft benzene ligand. As relatively Brønsted acidic
ether or amine ligands often form a weak spot for the stability of strongly basic reagents,
hydrocarbon-soluble Ba H N’’ is an attractive reducing reagent, especially since it is stable
7
7
7
up to 95 °C. Since the fourties, LiAlH has been among the most potent reducing agents.
4
Although it reduces ketones and imines, it generally shows no reactivity to simple alkenes or
styrenes. Preliminary investigations demonstrated that Ba H N’’ ∙(C H ) smoothly reduces
7
7
7
6 6 2
isolated and unactivated C=C double bonds (e.g. ethylene) under mild conditions (20 °C, 1
bar). The unobserved, highly reactive, ethylbarium intermediate presumably deprotonates
This article is protected by copyright. All rights reserved.

Angewandte Chemie International Edition
10.1002/anie.201709771
1
1
N’’ to form ethane and (Me Si)(Me SiCH ˉ)Nˉ. Modifications of the N’’ ligand could prevent
3
2
2
its deprotonation and enable isolation of the extremely reactive alkylbarium intermediates
that may be highly active catalysts for anionic alkene polymerization or hydrogenation. We
are currently investigating scope and applications of these heaviest Ba hydride clusters.
References
[1]
[2]
[3]
C. A. Brown, J. Am. Chem. Soc. 1973, 95, 982-983.
T. Ohkuma, S. Hashiguchi, R. Noyori, J. Org. Chem. 1994, 59, 217-221 and references cited therein.
In CRC Handbook of Chemistry and Physics, 63rd ed.; Weast, R. C., Ed., Astle, M. J., Associate Ed.; CRC
Press: Boca Raton, FL, 1982; Section D, p. 109.
[4]
[5]
[6]
A. E. Finholt, A. C. Bond, H. I. Schlesinger, J. Am. Chem. Soc. 1947, 95, 1199-1203.
P. C. Too, G. H. Chan, Y. L. Tnay, H. Hirao, S. Chiba, Angew. Chem. Int. Ed. 2016, 55, 3719-3723.
In Lehrbuch der Anorganischen Chemie; A. F. Holleman, N. Wiberg; Walter de Gruyter: Berlin, 2007.
1
02nd Edition, p. 1128.
[7]
R. W. Baker, G. J. Grendel, B. R. Lowrance, J. R. Mangham, E. M. Marlett, L. H. Shepherd, Jr. J.
Organomet. Chem. 1978, 159, 123-130.
S. Harder, J. Brettar, Angew. Chem. Int. Ed. 2006, 45, 3474-3478.
J. Spielmann, S. Harder, Chem. Eur. J. 2007, 13, 8928-8938.
(a) A. Causero, G. Ballmann, J. Pahl, H. S. Zijlstra, C. Färber, S. Harder, Organometallics 2016, 35,
[
[
[
8]
9]
10]
3350−3360; (b) A. Causero, G. Ballmann, J. Pahl, C. Färber, J. Intemann, S. Harder, Dalton Trans. 2017,
46, 1822-1831.
[11]
(a) P. Jochmann, J. P. Davin, T. P. Spaniol, L. Maron, J. Okuda, Angew. Chem. Int. Ed. 2012, 51, 4452 –
455; (b) V. Leich, T. P. Spaniol, J. Okuda, Inorg. Chem. 2015, 54, 4927-4933; (c) V. Leich, T. P. Spaniol,
4
L. Maron, J. Okuda, Angew. Chem. Int. Ed. 2016, 55, 4794-4797; (d) D. Shuhknecht, C. Lhotzky, T. P.
Spaniol, L. Maron, J. Okuda, Angew. Chem. Int. Ed. 2017, 55, accepted.
[12]
B. Maitland, M. Wiesinger, J. Langer, G. Ballmann, J. Pahl, H. Elsen, C. Färber, S. Harder, Angew. Chem.
Int. Ed. 2017, accepted.
[
[
13]
14]
M. Arrowsmith, M. S. Hill, D. J. MacDougall, M. F. Mahon, Angew. Chem. Int. Ed. 2009, 48, 4013–4016.
(a) K. Izod, P. G. Waddell, Organometallics 2015, 34, 2726-2730; (b) M. Arrowsmith, M. S. Hill, G.
Kociok-Köhn, Organometallics 2010, 29, 4203–4206; (c) M. Westerhausen, C. Gückel, H. Piotrowski, P.
Mayer, M. Warchhold, H. Nöth, Z. Anorg. Allg. Chem. 2001, 627, 1741-1750; (d) S. Harder, M. Lutz,
Organometallics 1997, 16, 225−230.
[15]
Neutron diffraction: (a) W. Bronger, S. Chi-Chien, P. Müller, Z. Anorg. Allg. Chem. 1987, 545, 69-74; X-
ray: (b) G. J. Snyder, H. Borrmann, A. Simon, Z. Kristallogr. 1994, 209, 458. Calculations: (c) W. Luo, R.
Ahuja, J. Alloys Compd. 2007, 446-447, 405-408.
[16]
[17]
[18]
B. A. Vaartstra, J. C. Huffman, W. E. Streib, K. G. Caulton, Inorg. Chem. 1991, 30, 121-125.
A. T. Nicol, R. W. Vaughan, J. Chem. Phys. 1978, 69, 5211-5213.
(a) M. Kaupp, O. L. Malkina, V. G. Malkin, P. Pyykkö, Chem. Eur. J. 1998, 4, 118-126. (b) ) M. Kaupp, O.
L. Malkina, J. Chem. Phys. 1998, 108, 3648-3658.
[19]
J. Schneider, C. P. Sindlinger, K. Eichele, H. Schubert, L. Wesemann, J. Am. Chem. Soc. 2017, 139, 6542-
6
545.
[20]
[21]
[22]
J. Spielmann, F. Buch, S. Harder, Angew. Chem. Int. Ed. 2008, 47, 9434–9438.
P. v. R. Schleyer, J. Am. Chem. Soc. 1958, 80, 1700-1704.
(a) L. Barr, A. R. Kennedy, J. G. MacLellan, J. H. Moir, R. E. Mulvey, P. J. A. Roger, Chem. Commun. 2000,
1
757-1758; (b) I. Korobkov, S. Gambarotta, Inorg. Chem. 2010, 49, 3409–3418; (c) X. Yu, S. Bi, I. A.
Guzei, Z. Lin, Z.-L. Xue Inorg. Chem. 2004, 43, 7111–7119; (d) R. Messere, M.-R. Spirlet, D. Jan, A.
Demonceau, A. F. Noels, Eur. J. Inorg. Chem. 2000, 1151-1153.
[23]
E. Heilbronner, A. Schmelzer, Helv. Chim. Acta 1975, 58, 936-967.
This article is protected by copyright. All rights reserved.