Carbon-Halogen Bond Activation with Powerful Heavy Alkaline Earth Metal Hydrides

Article abstract of DOI:10.1002/ejic.202100529

Reaction of [(^DIPePBDI)SrH]₂ with C₆H₅X (X=Cl, Br, I) led to hydride-halogenide exchange (^DIPePBDI=HC[(Me)CN-2,6-(3-pentyl)phenyl]₂). Conversion rates increase with increasing halogen size (FDIPePBDI)SrH]₂ with C₆H₅F was slow and ill-defined but addition of C₆H₄F₂ gave smooth hydride-fluoride exchange. After addition of THF the full range of Sr halogenides was structurally characterized: [(^DIPePBDI)SrX ? THF]₂ (X=F, Cl, Br, I). Mixtures of AeN“₂ and PhSiH₃ in situ formed less defined but more robust Ae metal hydride clusters (Ae_xN”_yH_z, Ae=Ca, Sr, Ba and N“=N(SiMe₃)₂) which are able to hydrodefluorinate C₆H₅F. Conversion rates increase with increasing metal size (Ca2/PhSiH₃ mixtures also converted SF₆ at room temperature to give undefined decomposition products. Addition of Me₆Tren to a SrN“₂/PhSiH₃ led to crystallization of [Sr₆N”₂H₉ ? (Me₆Tren)₃⁺][SrN“₃^?]; Me₆Tren=tris[2-(dimethylamino)ethyl]amine). After hydrodefluorination, Sr₆N”₄F₈ ? (Me₆Tren)₂ was formed and structurally characterized. Dissolution in THF led to cluster growth and the larger cluster Sr₁₆N“₈F₂₄ ? (THF)₁₂ is structurally characterized. DFT calculations support that hydrodehalogenation of halobenzenes follows a concerted nucleophilic aromatic substitution mechanism (cS_NAr).

Full text of DOI:10.1002/ejic.202100529

European Journal of Inorganic Chemistry
Accepted Article
Title: Carbon-Halogen Bond Activation with Powerful Heavy Alkaline
Earth Metal Hydrides
Authors: Michael Wiesinger, Bastian Rösch, Christian Knüpfer,
Jonathan Mai, Jens Langer, and Sjoerd Harder
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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
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202100529
Link to VoR: https://doi.org/10.1002/ejic.202100529
0
1/2020

European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Carbon-Halogen Bond Activation with Powerful
Heavy Alkaline Earth Metal Hydrides
Michael Wiesinger, Bastian Rösch, Christian Knüpfer, Jonathan Mai, Jens Langer, Sjoerd Harder*
Inorganic and Organometallic Chemistry, Universität Erlangen-Nürnberg, Egerlandstraße 1, 91058
Erlangen, Germany
Mr. M. Wiesinger, Mr. B. Rösch, Mr. C. Knüpfer, Mr. J. Mai, Dr. J. Langer, Prof. Dr. S. Harder
E-mail: sjoerd.harder@fau.de Twitter: @harder_research
Homepage: https://www.harder-research.com
Abstract Reaction of [(DIPePBDI)SrH]
HC[(Me)CN-2,6-(3-pentyl)phenyl] ). Conversion rates increase with increasing halogen size (F < Cl < Br < I).
Reaction of [(DIPePBDI)SrH]
with C F was slow and ill-defined but addition of C gave smooth hydride-
fluoride exchange. After addition of THF the full range of Sr halogenides was structurally characterized:
(DIPePBDI)SrX·THF]
(X = F, Cl, Br, I). Mixtures of AeN" and PhSiH in situ formed less defined but more robust Ae
metal hydride clusters (Ae N" , Ae = Ca, Sr, Ba and N" = N(SiMe ) which are able to hydrodefluorinate C F.
Conversion rates increase with increasing metal size (Ca < Sr < Ba). Also alkylfluorides (1-F-hexane, F-cyclohexane,
-F-adamantane) could be converted but, due to solubility problems of the Ba species, the fastest conversion
was found for Sr. These AeN" /PhSiH mixtures also converted SF at room temperature to give undefined
decomposition products. Addition of Me Tren to SrN" /PhSiH led to crystallization of
Sr N" ·(Me ][SrN" ˉ]; Me Tren = tris[2-(dimethylamino)ethyl]amine). After hydrodefluorination,
Tren) +
Sr N" ·(Me Tren) was formed and structurally characterized. Dissolution in THF led to cluster growth and the
larger cluster Sr16N" 24·(THF)12 is structurally characterized. DFT calculations support that hydrodehalogenation
with C
H
X (X = Cl, Br, I) led to hydride-halogenide exchange (DIPePBDI =
2
6
5
2
2
6
H
5
6
H
F
4 2
[
2
2
3
x
y
H
z
)
3 2
H
6 5
1
2
3
6
6
a
2
3
[
6
2
H
9
6
3
3
6
6
4
F
8
6
2
8
F
of halobenzenes follows a concerted nucleophilic aromatic substitution mechanism (cS Ar).
N
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Introduction
Halogenated hydrocarbons are widely used as solvents and raw materials for pesticides, polymers, fire
retardants, refrigerants and surfactants. While being highly useful in their intended purpose,
halogenated materials may pose an environmental hazard due to accumulation within the food chain
or cause ozone-depleting effects in the stratosphere.[1–5] Therefore, the development of sustainable
degradation methods to safely dispose such substances is of industrial and academic interest.
Compared to C-X bonds with the heavier halogens, the activation of the C-F bond is particularly
-
1
challenging. Bond dissociation energies rapidly increase along the series (kcal·mol ): H
3 3
C-I 58 < H C-Br
7
2 < H C-Cl 84 < H
3
3
C-F 115).[6] Several heterogeneous and homogeneous catalysts have been
established for hydrodehalogenation, including Pt black, Raney metal alloys, transition metal salts and
complexes of Pd, Pt, Ti, Ru, Ni and Rh.[1,7] While these all involve transition metals, examples of defined
main group metal complexes capable to activate the C-F bond are scarce and, in some cases, are
assisted by a transition metal. Generally these involve highly reactive low-valent main group metal
species like AlI [8–10] and MgI [11–14] complexes that are capable to undergo oxidative addition to the C-F
bond.
-
1
The C–F bond in fluorobenzene (126 kcal·mol ) is arguably one of the strongest single bonds that
carbon can form.[15] Dimeric Mg complexes of the form (BDI)MgMg(BDI) can only cleave activated C-F
bonds in polyfluorinated aromatics with electron-poor -systems (BDI = -diketiminate ligand; Scheme
I
1
a). At least four F-substituents in the ring are needed and the presence of an ortho-F atom lowers the
energy barrier for the transition state.[11,12] Low-valent (BDI)Al complexes can cleave the C-F bond in a
ring with at least three F-substituents (Scheme 1b), requiring long reaction times and high
temperatures, however, addition of catalytic quantities of Pd(PCy
and C
F under mild conditions.[16–18] The mildest conditions (-30 °C) for C-F bond cleavage in C
have been reported for a heterobimetallic Al -Rh complex.
3
)
2
also allowed conversion of C
6
H
4 2
F
H
6 5
6
H F
5
I
I
[19]
We reported C-F bond cleavage in fluorobenzene using a Mg complex with a strongly reducing, anti-
2
-
anion, but conditions were harsh (5 days, 100 °C); Scheme 1c.[14] A mild, room
aromatic C
temperature protocol was recently presented relying on a photoactivated (DIPPBDI)MgMg(DIPPBDI)
complex inducing a radical process with fluorobenzene to yield [(DIPPBDI)MgF]
and biphenyl (Scheme
d); (DIPPBDI = HC[(Me)CN-2,6-(isopropyl)phenyl] ).[20] Most recently, we reported that the combination
of (BDI)Al and a “naked” cationic -diketiminate Zn complex cleaves the C-F bond in C F instantly at
0 °C following an unusual dearomatization/aromatization mechanism (Scheme 1e).[21] This
H
6 6
2
1
2
H
6 5
2
heterobimetallic system also allowed immediate scission of the even more electron-rich p-
fluorotoluene.
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Scheme 1. Activation of C–F bonds using low-valent main group metal complexes.
Alternatively, hydrodehalogenation goes via nucleophilic aromatic substitution (S
nucleophilic metal hydride reagents. Combinations of nano-sized NaH and LiAlH with transition metal
or lanthanide salts were found highly potent reagents for converting monofluoroarenes to arenes.[22–
N
Ar) with
4
24]
Relying exclusively on main group (semi)metals, few systems have been identified that allow direct
substitution of the C-X bond. Ogoshi and coworkers reported the silicate mediated
hydrodefluorination of fluoroarenes with silanes and although this reaction is catalytic, it only works
for polyfluorinated arenes (Scheme 2a).[25] At an early stage the Pierre group demonstrated that KH
converts C
conversion was found).[26] The reaction was proposed to follow a concerted nucleophilic aromatic
substitution mechanism (cS Ar, Scheme 2b) but depending on solvent also a single-electron-transfer
mechanism is possible.[27] The commonly used drying agent CaH
was indentified to be capable of
complete hydrodechlorination of C Cl and C Cl to benzene and CaCl in a mechanochemical
approach.[28] While authors believe this technology could be transferred to fluorinated substrates,
evidence is currently not reported. Since the low solubility of CaH limits its reactivity, hydrocarbon-
6 5
H X into benzene but this method only worked for X = Cl, Br and I (for C
6 5
H F ca. 5%
N
2
6
6
H
6 5
2
2
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
soluble Ca hydride complexes would be highly advantageous. In solution, the first defined Ca hydride
complex [(DIPPBDI)CaH·THF] has shown astonishing reactivities.[29,30]
2
Scheme 2. Activation of C–F bonds using main group (semi)metal hydrides.
The THF-free analogue [(DIPPBDI)CaH]
groups demonstrated that it is able to substitute the halogen in C
(DIPPBDI)CaX] or (DIPPBDI)CaH/(DIPPBDI)CaX complexes (Scheme 2c), however, the reaction with C
led to ill-defined products.[32] The Okuda and Maron groups recently reported a dicationic dimeric Ca
hydride complex that also cleaved the C-F bond in unactivated C F but full F-H substitution needed
two days at 60 °C (Scheme 2d).[33] These reactions are proposed to follow the mechanism for
was found to be even more reactive.[31] The Hill and Maron
2
6 5
H X (X = Cl, Br, I) giving benzene and
[
2
6
H F
5
H
6 5
2+
nucleophilic aromatic substitution in which the cation Ca has recently been shown to play a unique
role. Being a large, soft cation it prefers bonding to the arene -system, activating the ring for
substituent exchange.[31,34] The larger cations Sr and Ba are even much more efficient in activating
arenes for nucleophilic aromatic substitution. We recently introduced the first Ae metal catalysts for
Hydrogen-Isotope-Exchange in arenes and reported a catalytic scenario for benzene deuteration by
2+
2+
D
2
.[35,36] The catalysts can either be well-defined complexes (e.g. [(BDI)SrH]
2
)[35] or ill-defined in situ
generated HAeN(SiR
)
3 2
aggregates (Ae = Ca, Sr, Ba);[36] examples of such mixed Ae metal hydride-amide
aggregates have been characterized.[37,38] The latter are also highly active catalysts in the
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
hydrogenation of alkenes and the more challenging arenes, also following a nucleophilic aromatic
substitution mechanism.[39] In addition, while Hill reported stoichiometric benzene alkylation with
[
(DIPPBDI)Ca(alkyl)]
Sr hydride dimer following the steps: [(BDI)SrH]
(BDI)SrH] + C Et, a reaction which is competing with ethylene polymerization and the formation of
2
,[31] we published the first example for catalytic benzene alkylation with the heavier
2
+ 2 H C=CH → [(BDI)SrEt] and [(BDI)SrEt] + C
2
2
2
2
6 6
H →
[
2
H
6 5
higher alkylbenzenes.[35] We now report initial studies on C-X bond activation in non-activated C
H X
6
5
substrates (X = F, Cl, Br, I) with heavier Ae metal hydrides.
Results and Discussion
Hydrodehalogenation with defined Ae metal hydride complexes
Since solvent-effects in heteroleptic -diketiminate Ca hydride complexes can play an important
role,[40] we investigated hydrodehalogenation with the THF adduct [(DIPPBDI)CaH·THF]
. Like the THF-
free complex, [(DIPPBDI)CaH·THF]
reacted instantaneously with iodobenzene at room temperature to
give benzene and [(DIPPBDI)CaI·THF]
(Figure S30). Minor quantities of the homoleptic complex
(DIPPBDI)
Ca have been detected with full conversion to homoleptic complexes at 60 °C. With
2
2
2
2
fluorobenzene no reaction was observed but heating 42 h at 60 °C gave full conversion of the Ca
hydride complex. Larger quantities of literature-known [(DIPPBDI)CaF·THF] [41]
could be detected by H
1
2
and 19F NMR (Figure S31 - 32) but the reaction is not clean. These experimental observations
demonstrate that nucleophilic substitution of halides in halobenzenes are also possible with the THF
adduct [(DIPPBDI)CaH·THF]
. Much higher reactivities are expected for the heavier Sr hydride complexes.
2
We recently introduced a superbulky -diketiminate ligand, abbreviated as DIPePBDI (Scheme 3), that is
able to control detrimental Schlenk equilibria for heteroleptic complexes of Ca, Sr and Ba (DIPePBDI =
HC[(Me)CN-2,6-(3-pentyl)phenyl]
complex [(DIPePBDI)SrH]
that is also in aromatic solvents stable towards ligand exchange until at least
0 °C.[35] Dissolution of [(DIPePBDI)SrH]
in halobenzene C X (X = I, Br, Cl) led in all cases to hydride-
halide exchange. With increasing size of X, the reaction conditions steadily become less harsh: C Cl
60°C, 12h), C Br (20°C, 14h), C I (20°C, < 1h). After removal of excess halobenzene and
crystallization from a hexane-THF mixture the dimeric Sr halide complexes [(DIPePBDI)SrX·THF]
could be
isolated as colorless crystals in yields of 53% (X = Cl), 72% (X = Br) or 43% (X = I); Scheme 3. Twofold H-
X exchange could also be achieved in benzene solutions containing only two equivalent of C X per
2
).[42] This very bulky ligand enabled synthesis of the Sr hydride
2
7
2
H
6 5
H
6 5
(
H
6 5
H
6 5
2
H
6 5
Sr hydride dimer but is clearly slower. In contrast to observations by Hill on the reactivity of Ca
hydrides, in none of the case could we isolate the intermediate single exchange product, i.e. the mixed
halide-hydride dimer. This is due to the much higher reactivity of Sr hydrides compared to Ca hydrides
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
but also may be related to the solubilizing effect of the DIPeP substituents which prevent crystallization
of poorly soluble mixed halide-hydride intermediates. Reaction of [(DIPePBDI)SrH]
with C F was found
2
H
6 5
to be slower and needed more forcing conditions (60 °C, 3 days) which led to ill-defined products.
However, reaction with 1,2-difluorobenzene, which is slightly activated to C-F bond cleavage, was
found to be much faster (60 °C, 4 h) and, after work-up and recrystallization from hexane/THF, crystals
of [(DIPePBDI)SrF·THF]
were isolated in 56% yield.
2
Scheme 3. Reaction of [(DIPePBDI)SrH]
with C
H
F .
2
6 5
H X (X = I, Br, Cl) or C
6
4
2
Dissolved in toluene, all halide complexes proved to be stable towards ligand exchange reactions even
under reflux conditions. Reaction with the silanes PhSiH , Et SiH, Ph SiH, or (EtO) SiH did not form the
3
3
3
3
initial Sr hydride complex which disables a possible catalytic hydrodehalogenation scenario using
silanes as a H-source.
Figure 1. Solid state structure of [(DIPePBDI)SrF·(THF)]
; H atoms not shown (50 % probability).
2
All Ae metal halide complexes crystallize as centrosymmetric dimers of constitution [(DIPePBDI)SrX·THF]
the fluoride complex is exemplary shown in Figure 1) but despite their similar architecture they do
2
(
not crystallize isomorphous. Although each complex crystallizes in a different crystal lattice with a
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
different packing, their structures compare well to each other. In all cases, the halide anions bridge the
two strontium metal atoms in µ -fashion. The coordination sphere of each Sr metal was further
2
saturated by an N,N-chelating DIPePBDI ligand and a THF ligand [Sr-O: 2.493(2)-2.594(2) Å], giving the Sr
metal centers a coordination number of five. In all cases metal coordination is completed by anagostic
3
Sr···CH CH
2
interactions which range from Sr···C = 3.302 Å to 3.413 Å. While Sr-N [2.492(2)-2.553(3) Å]
and Sr-O [2.493(2)-2.594(2) Å] bond distances are in a narrow range, the Sr-X bond lengths increase
with halogen size. They are, however, closely comparable to Sr-X bonds in similar [(DIPPBDI)SrX]
complexes (Table 1).[43,44]
·(THF)
2
n
Table 1. Comparison of the Sr-X distances in [(DIPePBDI)SrX·THF]
(DIPPBDI)SrX] .[43,44] Bold values represent mean averages.
·(THF)
with values reported for
2
[
2
n
[
(DIPePBDI)SrX·THF]
2.318(1) - 2.376(1)
.347
Sr–Cl 2.825(2) - 2.900(1)
.860
2
[(DIPPBDI)SrX]
2
·(THF)
n
Sr–F
2.317(1) - 2.333(1) a
2.325
2
2.821(1) - 2.890 a
2.856
2
Sr–Br 2.9774(5) - 3.1043(6) unknown
.0282
3.2054(7) - 3.3272(7) 3.2284(4) - 3.3100(3) b
.2649 3.2567
a) n = 3: One of the Sr metals is coordinated with one THF ligand while the other is bound to two THF ligands.
The listed bond distances are those for the metal atom with a comparable coordination number of five. (b) n =
3
Sr–I
3
(
2.
Attempts to extend the scope of fluorinated substrates to fluoroalkanes like 1-fluorohexane, fluoro-
cyclohexane or 1-fluoroadamantane were not successful. Contrary to expectations, [(DIPePBDI)SrH]
2
reacted only sparingly with these substrates, even at elevated temperatures just below its
decomposition temperature of 70 °C.[35] This may be due to considerable steric shielding of the
reaction center by the bulky DIPePBDI ligands. We were therefore interested in more open and robust
Ae metal hydride systems which are also at higher temperatures stable.
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European Journal of Inorganic Chemistry
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Hydrodefluorination with undefined Ae metal hydride complexes
It has been shown that the sterically moderately encumbered Ae metal bis-amide complexes
Ae[N(SiMe , abbreviated as AeN" (Ae = Ca, Sr, Ba), react in situ with H or PhSiH to large hydride
3
)
]
2 2
2
2
3
clusters[37,38] that are efficient catalysts for imine or alkene hydrogenation[45–47] or hydrosilylation.[48]
These studies also showed that, although these systems are less defined, they are highly robust and
tolerate higher temperatures. Encouraged by the hydrodehalogenation capability of the well-defined
strontium hydride complex [(DIPePBDI)SrH]
2
, we wondered whether simple amides could also be
effective in the activation of the most challenging C-F bond.
The amides AeN"
of PhSiH under forcing conditions (120 °C, 6-24 h, toluene-d
and GC-MS. The SrN" /PhSiH
4% (or 78% after 12 h); (Table 2, entries 1-2). The temperature could be lowered to 60 °C but this
elongated the reaction time significantly (entry 3). The lighter CaN" is clearly less reactive than SrN"
entry 4) and not only gave F-H exchange but also F-N" exchange was observed and traces of C N"
was found to be most reactive, reaching a conversion of up to 85%
, the PhSiH content was increased to 10
equivalents but this had clearly a detrimental effect (entry 6). This is attributed to the formation of
insoluble (BaH or to formation of less reactive silanates like Ba[PhSiH . The silanes (MeO) SiH,
EtO) SiH, Et SiH or Ph SiH were not effective. Using AeN" /PhSiH combinations, we also were able to
hydrodefluorinate most challenging substrates like 2,6-dimethyl-fluorobenzene with a sterically
2
(Ae = Ca, Sr, Ba) were reacted with two equivalents of C
6 5
H F and three equivalents
1
3
8
) and conversion was checked by H NMR
2
3
combination gave after 6 h a fluorobenzene-to-benzene conversion of
5
2
2
(
H
6 5
were detected. The heavier BaN"
2
after 6 h (entries 5-6). Using the most active reagent BaN"
2
3
2
)
∞
]
4 2
3
(
3
3
3
2
3
protected C-F bond and an electron-rich arylring (entries 7-9). While CaN"
conversion of 58% (12 h) could be reached.
2
failed, with BaN" a
2
Following success in the activation of aromatic C-F bonds, the AeN"
2
/PhSiH combinations were
3
investigated in the hydrodefluorination of alkyl C-F bonds. 1-Fluorohexane was converted to hexane
following the reactivity order Ca < Ba < Sr (entries 10-12). Since Ba amides and hydrides are generally
more reactive than their Sr congeners, this reactivity order is unexpected. It may partially be explained
by the observation that in reactions with the BaN"
2
/PhSiH combination a considerable quantity of a
3
precipitate was formed. The assumption that these are likely insoluble Ba-N"-H clusters was supported
by the fact that a CD OD quench of the insoluble material led to vigorous gas evolution and detection
3
1
of H-D and N"D by H NMR. The formation of a precipitate is explained by the fact that alkylfluorides
are poorer solvents than fluorobenzene. Also for 1-fluorohexane partial F-N" exchange was observed
with the CaN"
hexane could not be detected. For the secondary alkylfluoride fluoro-cyclohexane (entries 13-15),
hydrodefluorination with BaN" is also slower than with SrN" . In this case not only cyclohexane but
2
/PhSiH
3
combination but using the heavier amides SrN"
2
and BaN" the product 1-N"-
2
2
2
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
also cyclohexene is formed. This side-reaction, which presumably follows a deprotonation-elimination
pathway, strongly depends on metal size and becomes more important with decreasing metal size: Ba
<
Sr < Ca. Also for the tertiary 1-fluoro-adamantane SrN"
2
performed better than BaN" (entries 16-17)
2
and in this case no elimination side-products were observed. The general reactivity trend is that
conversion slows down in the order: primary > secondary > tertiary fluoroalkanes.
The efficiency of AeN"
reaction with SF , a highly stable fluorine compound. Sulfur hexafluoride, which finds application as an
insulator in high voltage electrical equipment, is one of the most potent greenhouse gases, surpassing
CO with LiAlH at room temperature has been
by a factor of 23.900.[49] Chemical breakdown of SF
previously reported,[50] but is extremely slow (4-7 days). Reaction of SF
with SrN" or BaN" in the
at room temperature is fast. Monitoring with F-NMR showed a gradual decrease
2
/PhSiH
3
mixtures as a hydrodefluorination reagent was further investigated by
6
2
6
4
6
2
2
19
presence of PhSiH
3
19
of the SF signal at -58.3 ppm and complete disappearance within 1 h, but no new F signal set was
6
observed. This is explained by formation of considerable quantities of an insoluble yellow precipitate
containing 1.77 w% S but also organic matter (C 24.14 w%, H 3.77 w%, N 1.64 w%). Its complete
insolubility complicated any further analyses. We propose precipitation of larger metal clusters
2
[51]
containing a variety of anions like N"ˉ, Hˉ, Fˉ but also SF
temperature destruction of SF by in situ formed Sr or Ba hydrides demonstrates the very high
reactivity of the heavier Ae metal hydrides.
5
ˉ or S ˉ could be expected. Room
6
Although the AeN"
able to isolate well-defined Ae-fluoride complexes from reaction mixtures. Since the addition of
PMDTA (pentamethyldiethylenetriamine) to AeN" /PhSiH mixtures led to isolation of well-defined Ae
metal hydride clusters of formula Ae N" ·(PMDTA)
(Ae = Ca or Sr),[37] we attempted to isolate
defined Ae metal fluoride clusters by hydrodefluorination with AeN" /PhSiH /PMDTA mixtures. As
these experiments were unsuccessful, we replaced PMDTA by the tetradentate ligand Me Tren (tris[2-
dimethylamino)ethyl]amine).
2
/PhSiH
3
combination is an effective hydrodefluorination reagent, we have not been
2
3
6
H
3 9
3
2
3
6
(
Heating
Sr N"
a
SrN"
2
/PhSiH
3
/Me
6
Tren mixture alone led to crystallization of the salt
[
6
2
H
9
·(Me
6
Tren) +
3
][SrN"
3
ˉ] which was characterized by X-ray diffraction (Figure 2a) but could not
be obtained pure in larger quantities. Its crystal structure is strikingly similar to that of the previously
2+
reported Sr
corners of an octahedron, one interstitial 
octahedron. The cluster is further stabilized by two terminal N"ˉ ligands and three neutral,
tetradentate Me Tren ligands. Its positive charge is balanced by the SrN" ˉ anion. The bond distances
in the cation Sr N" ·(Me (Sr–Hcenter avg. 2.70 Å; Sr–Houter avg. 2.47 Å) are close to identical with
Tren) +
those in the neutral cluster Sr N" ·(PMDTA) (Sr–Hcenter avg. 2.69 Å; Sr–Houter avg. 2.43 Å) (Table S2).
6
N"
3 9
H ·(PMDTA)
3
cluster in which the core of the cluster consists of six Sr cations at the
6
-Hˉ and eight  -Hˉ anions that cap the Sr -faces of the
3
3
6
3
6
H
2 9
6
3
6
3
H
9
3
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Heating SrN"
2 3
/PhSiH /Me
6
Tren in a mixture of fluorobenzene and 1-fluorohexane led to immediate
conversion of 1-fluorohexane, supporting the more facile hydrodefluorination of alkylfluorides vs.
arylfluorides, and crystallization of centrosymmetric Sr N" ·(Me Tren) . This complex could be
isolated in crystalline purity (yield: 10%) and its crystal structure could be determined unequivocally
6
4
F
8
6
2
2+
(
Figure 2b). The core of the cluster is formed by six Sr cations in an octahedral arrangement with an
average Sr···Sr distance of 3.9343 Å which is slightly larger than that in the Sr hydride cluster
Sr
6
N"
-faces of the octahedron and span a cube (Figure 2c). The Sr
fluorit crystal lattice, i.e. a face-centered-cubic packing of Sr cations with Fˉ in the eight
tetrahedral holes (coordination numbers: Sr = 8, F = 4). The neutral cluster is stabilized by four terminal
N"ˉ ligands and two neutral, tetradentate Me Tren ligands which prevent further growth to (SrF
The average Sr–(µ -F) bond length of 2.434 Å compares well to that in Sr10 (2,4,6-
trimethylphenolate)12·(dme) (dme = dimethoxyethane) cluster (avg. Sr–F 2.44 Å), which to the best of
our knowledge is the only other reported Sr–F cluster to date.[52]
2
H
9
·(Me
6
Tren) +
3
(3.8135 Å). Although there is no interstitial Fˉ anion, eight 
3
-Fˉ anions cap the
Sr
3
6 9
H -core can be regarded as a sub-unit
2+
of the SrF
2
6
2 ∞
) .
3
F
8
4
Figure 2. (a) Crystal structure of [Sr
6
N"
2 9
H ·(Me
6
Tren) +
3
][SrN"
3
ˉ]; methyl groups, SiMe groups, and the
3
–
anion SrN"
3
have been omitted for clarity. All hydride atoms have been identified in the difference
N" ·(Me Tren) . Methyl groups
] core. Fluoride anions (green) describe
Fourier map and were refined isotropically. (b) Crystal structure of Sr
6
F
4 8
6
2
4+
and SiMe
3
groups have been omitted for clarity. (c) The [Sr
F
6 8
a cube in an octahedron spanned by strontium cations (red). All ellipsoids are shown with 50 %
probability.
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European Journal of Inorganic Chemistry
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The most striking difference between the two hexanuclear Sr hydride and fluoride clusters is found in
3+
4+
their core structures. Compared to the hydride cluster with a Sr
H
6 9
core, the Sr
F
6 8
core lacks an
interstitial µ -Fˉ anion. This may originate from size differences. Based on ionic bond radii in alkali
6
metal salts (coordination number = 6) the fluoride ion radius of 1.547 Å is larger than that for the
hydride estimated at 1.399 Å.[53] However, argumentation with ionic radii should be taken with caution
since effective ionic radii in the literature vary significantly.[54–56] DFT calculations (B3PW91/def2tzvp)
3+
on a Sr F
6 9
core indicated that an interstitial µ
6
-Fˉ anion would fit. Calculating the energy of Xˉ anion
4+
capture in a Sr
6 8
X
cage showed that this process, which due to electrostatic attraction is highly
exergonic, is even more exergonic for Xˉ = Fˉ (G = -485.3 kcal/mol) than for Xˉ = Hˉ (G = -358.7
kcal/mol) (Table S5). Atoms-In-Molecules (AIM) analysis showed for the hydride cluster unusual Hˉ···Hˉ
bond paths between the interstitial hydride and the eight outer hydrides with electrons densities in
3
3+
the bond-critical-points (bcp’s) of 0.094 e·Å . For Sr
F
6 9
similar weakly bonding Fˉ···Fˉ interactions
3
were found with electron densities in bcp’s that are even higher (0.113 e·Å ) which means that there
3+
is a priori no reason why a Sr
F
6 9
core could not be formed.
6
Complex Sr N"
4 8
F ·(Me
6
Tren)
2
displays poor solubility but dissolved in a mixture of C
6
D
6
6
and C D
5
Br (1:1)
1
19
19
H NMR and F NMR spectra could be obtained (Figures S26-27). Observation of only one sharp F
signal implies a higher symmetry than in the crystal structure in which two different types of F atoms
are present (Figure S27). The higher symmetry in solution is likely due to dynamic coordination of the
Me
6
Tren ligand giving rise to an average structure with four equal equatorial Sr-N" units and two equal
axial Sr···Me
6
Tren units. The complex is stable in solution and can even be recrystallized from the
benzene/bromobenzene mixture. Its rather poor solubility precludes the recording of a 13C{ H}
1
13
spectrum but the C chemical shifts could be obtained by HSQC (Figure S29). Improved solubility of
Sr N" ·(Me Tren) was obtained upon heating in a mixture of C and a small quantity of THF-d
6
4
F
8
6
2
6
D
6
8
,
19
however, rapid complex degradation was observed, indicated by numerous new F NMR signals. The
isolation of a colorless crystal from this solution shed some light on the decomposition process.
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Figure 3. (a) The crystal structure of Sr16N"
8
F24·(THF)12 (Me
3
Si units and CH
2
fragments have been
8+
omitted for clarity). (b) The Sr16
F
24 core described as four fused Sr -octahedra. All ellipsoids are shown
6
with 50 % probability.
A larger neutral aggregate of formula Sr16N"
which all tetradentate Me Tren ligands have been replaced by THF ligands (Figure 3a). This large
aggregate can be seen as four fused Sr -octahedra (Figure 3b) and, similar to the smaller Sr fluoride
cluster Sr N" ·(Me Tren) , it can be regarded a sub-unit of the SrF fluorit crystal lattice. The large
24 core is protected for further growth by eight shielding N"ˉ anions and twelve THF ligands. The
Sr···Sr distances in the Sr16-cluster (avg. 3.9863 Å) are slightly larger than in the Sr -cluster (avg. 3.9343
Å). The Sr - and Sr16-cluster show equal average Sr–(µ -F) bond distances of ≈2.433 Å but the average
Sr–(µ -F) bond distance in the Sr16-cluster is somewhat larger: 2.499 Å (Table S2).
8
F24·(THF)12 crystallized as a centrosymmetric entity in
6
6
6
F
4 8
6
2
2
8+
Sr16F
6
6
3
4
Proposed mechanism for hydrodehalogenation of aromatic halobenzenes
While the hydrodehalogenation of alkyl halogenides with metal hydride reagents follows standard
nucleophilic substitution or elimination routes, there has been some discussion on the
hydrodehalogenation of halobenzenes. For the hydrodehalogenation of C
6
H X with KH, Pierre
5
observed a reactivity order: X = Cl < Br < I.[26] For an S
N
Ar mechanism via a Meisenheimer anion the
opposite order would be expected: I < Br < Cl < F. The fast reaction for fluorobenzene may seem
counterintuitive due to the strong C-F bond, however, cleavage of the strong C-F bond is in this case
not rate-determining. The rate-determining step in this two-step reaction is formation of the
Meisenheimer anion, an intermediate in which ring aromaticity is lost (Figure 4a) and which is
stabilized by electronegative substituents like F. The barrier for the second step in which C-F bond
cleavage takes place is much lower due to rearomatization. In order to explain the observed reactivity
order, Pierre proposed a one-step concerted nucleophilic aromatic substitution (cS Ar), a mechanism
N
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
which is currently in focus of modern organic chemistry.[57] The energy barrier for this reaction
mechanism is determined by C-X bond strengths (Figure 4a). Calculations by Murphy and coworkers
confirmed this mechanism for the hydrodeiodination of C
groups reported this mechanism for hydrodehalogenation (X = Cl or Br) with a Ca hydride complex. We
here report DFT mechanisms for the hydrodehalogenation of C X (X = Br or I) with Sr hydride
H
6 5
I with KH.[27] Also the Hill and Maron
H
6 5
reagents (B3PW91/def2tzvp//B3PW91/def2svp). The complete energy profile for reaction of
monomeric (DIPePBDI)SrH with PhI can be found in the Supporting Information (Figure S64). This also
Ph
contains the full profile for a dimeric model system [( BDI)SrH]
2
in which for simplicity the DIPeP
substituents in the ligand have been replaced by smaller Ph groups; Figure S65. For comparison with
an earlier reported pathway, we calculated the hydrodebromination of C
6 5
H Br with the model system
[
(DIPPBDI)SrH]
2
in which the DIPeP substituents have been replaced by somewhat smaller DIPP groups
-
1
(
Figure 4b). The activation barrier for Br-H exchange is H = 30.3 kcal·mol . Hill and Maron reported
for the same reaction with [(DIPPBDI)CaH]
a slightly higher barrier of H = 31.6 kcal·mol . Since these
-1 [32]
2
calculations were done at a different level (B3PW91/6-311+G*), we repeated these calculations using
-
1
our level of theory and found a considerably higher barrier of 34.5 kcal·mol . This demonstrates that
-
1
the barrier for the Sr hydride reagent is circa 4 kcal·mol lower than for the comparable Ca hydride
reagent, supporting the experimentally observed higher reactivity of Sr complexes. The transition
states clearly show a concerted process with concomitant hydride attack and C-Br bond cleavage
(Figure 4c). The transition state for the Sr hydride dimer is not only significantly lower in energy but
than that for the ananlogue Ca hydride complex but also slightly earlier in respect of bond breaking
and bondmaking.
We therefore propose a cS Ar mechanism but have indications for competing mechanisms. Especially
N
for the heavier halobenzenes (Br and I), some gas development was observed during reaction with
(DIPePBDI)SrH]
in the H NMR confirmed this observation. This points to a competing
1
[
2
. Traces of H
2
mechanism in which ortho-deprotonation and concomitant H production is followed by Ae-X
2
elimination and benzyne formation. Traces of biphenyl and terphenyl, detected by GC-MS analysis,
support that this mechanism could play a minor role. We note that this may also be the case in
hydrodehalogenation with [(DIPPBDI)CaH]
for which Wilson and Hill likewise report effervescence.[58]
A
2
strong argument in favor of a cS Ar mechanism (and precluding a benzyne mechanism) is the
N
observation that 2,6-dimethyl-fluorobenzene, in which the ortho-positions are protected, could also
be converted to meta-xylene (Table 1, entries 7-9). At this stage, however, we also do not rule out
contributions of a SET mechanism as observed by Murphy.[27]
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Figure 4. (a) Reaction of metal hydride (MH) with halobenzene (C
6
H
5
X) via a S
Br with [(DIPPBDI)SrH]
(red); B3PW91/def2tzvp//B3PW91/def2svp. (c) Calculated transition states for the
N
Ar or cS
N
Ar mechanism.
(
b) Energy profile (H in kcal/mol) for the hydrodebromination of C
(DIPPBDI)CaH]
6
H
5
2
(black) or
[
2
hydrodebromination of C
H
6 5
Br with [(DIPPBDI)SrH]
2
(left) or [(DIPPBDI)CaH]
(right).
2
Conclusion
Hydrodehalogenation of aromatic halides with [(DIPePBDI)SrH]
gave after crystallization from THF well
2
defined dimers [(DIPePBDI)SrX·THF]
(X = F, Cl, Br, I). These could not be regenerated back to the Sr
2
hydride starting material by reaction with silanes which precludes a catalytic protocol. The bulky
DIPePBDI ligand, which is needed to stabilize the Sr hydride complex, hinders the hydrodehalogenation
reaction and therefore more open Ae metal hydride systems have been tested. Mixtures of AeN"
2
and
PhSiH
3
gave less defined but more robust Ae metal hydride clusters of formula Ae
x
N"
H
y z
(y + z = 2x)
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
which in solution are also stable at the higher temperature of 120 °C. The conversion rate increases
with increasing metal size (Ca < Sr < Ba) and increasing halogen size (F < Cl < Br < I). At this temperature,
the BaN"
difficult substrates like C
methylated ortho-positions which could be converted to m-xylene. Although the in situ generated Ae
metal hydride reagents are not as defined as [(DIPePBDI)SrH]
, it was possible to isolate and structurally
2
/PhSiH
3
combination was found to be especially effective for the hydrodefluorination of
6 5
H F and even 2,6-dimethyl-fluorobenzene, an electron-rich substrate with
2
characterize distinct Sr fluoride clusters. Hydrodefluorination of primary, secondary and tertiary
alkylfluorides was also achieved. In this case the following order of reactivity was found: Ca < Sr > Ba.
This exceptional reactivity order can be explained by the poor solubility of the Ba amide-hydride
clusters, corroborated by the precipitation of considerable quantities of an insoluble Ba species. These
AeN"
undefined decomposition products.
In agreement with earlier work, hydride-halogenide exchange in aromatic substrates like C
proposed to proceed through direct nucleophilic aromatic substitution. The reactivity order for
hydrodehalogenation of C X (F < Cl < Br <I) rules out a two-step nucleophilic aromatic substitution
mechanism with a Meisenheimer intermediate. Instead, a concerted mechanism is proposed (cS Ar).
DFT calculations on the hydrodeiodination of C I with a dimeric -diketiminate Sr hydride complex
2
/PhSiH
3
combinations (Ae = Sr, Ba) could even fully convert SF at room temperature to give
6
6
H X is
5
H
6 5
N
H
6 5
support this conclusion, however, smaller contributions from benzyne or radical formation as
alternative mechanisms cannot be fully ruled out.
The most important conclusion of this work is that either defined or undefined Ae metal hydride
clusters are highly effective in the hydrodehalogenation of aromatic halobenzenes or alkylfluorides.
Their reactivity increases with metal size (Ca < Sr < Ba) but the larger Ba reagents may suffer from
solubility problems. Especially for the most reactive Sr and Ba hydride complexes, we continue to
explore further applications.
Experimental Section
General Experimental Procedures
All experiments were conducted in dry glassware under an inert nitrogen atmosphere by applying
standard Schlenk techniques or gloveboxes (MBraun) using freshly dried and degassed solvents.
Benzene, toluene, pentane and hexane were degassed with nitrogen, dried over activated aluminum
oxide (Innovative Technology, Pure Solv 400-4-MD, Solvent Purification System) and then stored under
inert atmosphere. THF was dried over molecular sieves (3 Å) and distilled from sodium afterwards.
Deuterated benzene (C
and Euriso-top, degassed and dried over molecular sieves (3 Å). Following reagents were obtained
commercially and used without further purification: PhSiH (Alfa Aesar, 97 %). 1-fluoradamantane (TCI)
6
D
6
; 99.6+%D) and toluene-d
8
(99.6+%D) were purchased from Deutero GmbH
3
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
and SF (3.0, Westfalen). Fluorohexane (abcr, 99 %), fluorocyclohexane (Acros Organics, 97 %), 2-
6
fluoro-m-xylene (Alfa Aesar, 98 %), iodobenzene (PhI, Alfa Aesar 98 %), bromobenzene (PhBr, Sigma
Aldrich, 99 %), chlorobenzene (PhCl, Alfa Aesar, 99 %), fluorobenzene (PhF, Fluorochem, 98 %) and 1,2-
difluorobenzene (PhF
2
, Fluorochem, 98 %) were distilled from CaH
3 Å). The following compounds were synthesized according to literature procedures:
(DIPePBDI)SrH] ,[35] Ca[N(SiMe ).[59] NMR
(CaN" ), Sr[N(SiMe (SrN" ) and Ba[N(SiMe (BaN"
2
and stored over molecular sieves
(
[
2
3
)
]
2 2
2
3
)
2
]
2
2
3
)
]
2 2
2
spectra were measured on Bruker Avance III HD 400 MHz and Bruker Avance III HD 600 MHz
spectrometers. Chemical shifts (δ) are denoted in ppm (parts per million), coupling constants in Hz
(
Hertz). For describing signal multiplicities common abbreviations are used: s (singlet), d (doublet), t
triplet), q (quartet), quin (quintet), m (multiplet) and br (broad). Spectra were referenced to the
(
solvent residual signal. Elemental analysis was performed with an Hekatech Eurovector EA3000
analyzer. GC-MS measurements were performed on a Thermo Scientific™ Trace™ 1310 gas
chromatography system (carrier gas Helium) with detection by a Thermo Scientific™ ISQ™ LT Single
Quadrupole mass spectrometer. A Phenomenex® ZebronTM ZB-5 GC column of the dimensions
0
.25 mm x 30 m with a film thickness of 0.25 μm was used. The samples (1 μL) were injected with an
Instant Connect-SSL Module in the split mode (injector temperature: 280 °C). Temperature programs
were started at 40 °C followed by heating ramps, optimized for the separation problem, until 280°.
Baseline separation of each analyte was achieved by choosing the different temperature programs.
The molecular identities were confirmed by comparison with entries in the NIST/EPA/NIH mass
spectral library (v2.2, built June 10 2014). All crystal structures have been measured on a SuperNova
(
Agilent) diffractometer with dual Cu and Mo microfocus sources and an Atlas S2 detector.
Crystallographic data have been deposited with the Cambridge Crystallographic Data Centre as
supplementary publication numbers: CCDC 2091324 [(DIPePBDI)SrI(THF)] , 2091325 [(DIPePBDI)SrBr(thf)]
, 2091328 [Sr N" ·(Me ][SrN" ˉ],
Tren) +
2
2
,
2
2
091326 [(DIPePBDI)SrCl(thf)]
091329 Sr N" ·(Me Tren)
2
, 2091327 [(DIPePBDI)SrF(thf)]
and 2091330 Sr16N"
: In a J-Young NMR tube [(DIPePBDI)SrH]
(102.6 mg, 165.9 µmol) was
2
6
2
H
9
6
3
3
6
F
4 8
6
2
8
F24·(THF)12
Synthesis of [(DIPePBDI)SrI·THF]
2
2
dissolved in PhI (520 µL). The solution was stirred at ambient temperature for 1 h and the solvent
removed subsequently in vacuo. The oily residue was dissolved in a mixture of hexane (400 µL) and
THF (30 µL), filtered and stored at room temperature overnight, affording colorless crystals suitable
for X-ray diffraction analysis. The supernatant was decanted, the product washed with cold pentane
(
-20 °C, 2 x 0.5 ml) and dried under high vacuum. [(DIPePBDI)SrI·THF]
2
was obtained as colorless
1
3
crystalline blocks (58.2 mg, 71.3 µmol, 43 %). H NMR (600.13 MHz, C
6
D
6
, 298K): δ = 0.90 (t, J = 7.4 Hz,
3
1
6
3
2H, CH
H, CH
.66-3.68 (m, 4H, OCH
3
), 1.01 (t, J = 7.4 Hz, 12H, CH
3
), 1.29-1.31 (m, 4H, OCH
2
CH
2
), 1.65-1.72 (m, 8H, CH ), 1.70 (s,
2
3
3
-backbone), 1.71-1.76 (m, 4H, CH
2
), 1.82-1.89 (m, 4H, CH
2
), 2.91 (quint, J = 6.3 Hz, 4H, CH),
13
2 2
CH ), 4.83 (s, 1H, CH-backbone), 7.10-7.14 (m, 6H, CH-arom) ppm. C NMR
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
(
150.92 MHz, C
8.1 (CH ), 41.2 (CH), 69.2 (OCH
arom), 149.1 (C-arom), 165.0 (CN-backbone) ppm. Elemental analysis calculated for C82
M = 1633.02 g/mol): C 60.31, H 8.02, N 3.43; Found: C 60.16, H 8.06, N 3.46.
6
D
6
, 298K): δ = 11.5 (CH
CH ), 93.0 (CH-backbone), 123.3 (C-arom), 125.8 (C-arom), 138.2 (C-
Sr
3
), 12.3 (CH
3
), 25.4 (CH
3
-backbone), 25.4 (OCH
2
CH
2
), 26.4 (CH
2
),
2
2
2
2
H
130
I
2
2
N
4
O
2
(
Synthesis of [(DIPePBDI)SrBr·THF]
: In a J-Young NMR tube [(DIPePBDI)SrH]
(92.2 mg, 149.1 µmol) was
2
2
dissolved in PhBr (520 µL, gas evolution observed) and the solution was stirred at ambient temperature
overnight (14 h). Subsequently the solvent was removed and the oily residue dried under high vacuum.
Crystals of [(DIPePBDI)SrBr·THF]
suitable for X-ray diffraction analysis were obtained by slow diffusion
2
of THF to a diluted hexane solution (500 µL) at ambient temperature overnight (18 h). The crystals
were isolated by decantation, washed with cold pentane (-20 °C, 2 x 0.5 ml) and dried under high
vacuum. [(DIPePBDI)SrBr·THF]
was obtained as pale orange colored small crystalline blocks (82.6 mg,
2
1
3
3
1
07.3 µmol, 72 %). H NMR (600.13 MHz, C
6
D
6
, 298K): δ = 0.89 (t, J = 7.4 Hz, 12H, CH
), 1.62-1.64 (m, 6H, CH ), 1.68 (s, 6H, CH -backbone), 1.69-
CH ), 4.76 (s, 1H, CH-
, 298K): δ = 11.5 (CH ), 12.2
), 41.2 (CH), 69.0 (OCH CH ), 93.2 (CH-
backbone), 123.2 (C-arom), 125.7 (C-arom), 138.7 (C-arom), 148.9 (C-arom), 164.9 (CN-backbone)
3
), 0.97 (t, J = 7.3
Hz, 12H, CH
3
), 1.36-1.38 (m, 4H, OCH
2
CH
2
2
3
3
1
.77 (m, 10H, CH
2
), 2.86 (quint, J = 6.3 Hz, 4H, CH), 3.69-3.71 (m, 4H, OCH
2
2
13
backbone), 7.08-7.13 (m, 6H, CH-arom) ppm. C NMR (150.92 MHz, C
CH ), 25.2 (CH -backbone), 25.5 (OCH CH ), 26.4 (CH ), 27.9 (CH
6
D
6
3
(
3
3
2
2
2
2
2
2
ppm. Elemental analysis calculated for C82
2
H130Br Sr
2
N
4
2
O (M = 1539.02 g/mol): C 64.00, H 8.51, N 3.64;
Found: C 63.96, H 8.71, N 3.63.
Synthesis of [(DIPePBDI)SrCl·THF]
In a J-Young NMR tube [(DIPePBDI)SrH]
2
:
2
(104.4 mg, 168.8 µmol) was dissolved in PhCl (520 µL). The
solution was heated to 60 °C and stirred at this temperature for 20 h. The solvent was pumped off and
the sticky semi solid dried under high vacuum. The residue was dissolved in hexane (300 µL), filtered
and covered with a mixture of hexane (200 µL) and THF (30 µL). Leaving it standing overnight at room
temperature gave yellowish crystalline blocks of [(DIPePBDI)SrCl·THF]
suitable for X-ray diffraction
2
analysis. The supernatant was decanted, the crystals washed with cold pentane (-20 °C, 2 x 0.5 ml) and
1
, 298K): δ = 0.89 (t, 3J
dried under high vacuum (64.9 mg, 89.5 µmol, 53 %). H NMR (600.13 MHz, C
D
6 6
3
=
1
7.4 Hz, 12H, CH
.64-1.70 (m, 10H, CH
CH
98K): δ = 11.6 (CH
8.8 (OCH CH ), 93.3 (CH-backbone), 123.1 (C-arom), 125.6 (C-arom), 138.9 (C-arom), 148.8 (C-arom),
3
), 0.92 (t, J = 7.3 Hz, 12H, CH
3
), 1.40-1.43 (m, 4H, OCH
2
CH
2
), 1.62-1.64 (m, 6H, CH ),
2
3
2
), 1.68 (s, 6H, CH
3
-backbone), 2.83 (quint, J = 6.4 Hz, 4H, CH), 3.67-3.69 (m, 4H,
13
OCH
2
2
), 4.74 (s, 1H, CH-backbone), 7.07-7.12 (m, 6H, CH-arom) ppm. C NMR (150.92 MHz, C
6
D
6
,
2
6
1
6
3
), 12.1 (CH ), 25.1 (CH -backbone), 25.6 (OCH CH ), 26.6 (CH ), 27.9 (CH ), 41.3 (CH),
3
3
2
2
2
2
2
2
64.7 (CN-backbone) ppm. Elemental analysis calculated for C82
H130Cl
Sr
2 2
4
N O (M = 1450.11 g/mol): C
2
7.92, H 9.04, N 3.86; Found: C 68.09, H 9.34, N 3.65.
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Synthesis of [(DIPePBDI)SrF·THF]
: In a J-Young NMR tube [(DIPePBDI)SrH]
(95.7 mg, 154.7 µmol) was
2
2
dissolved in PhF
removed in vacuo. The powdery residue was dissolved in hexane (400 µL), filtered and THF (30 µL,
diluted with hexane (100 µL) was added slowly. Small, pale yellow, crystals of [(DIPePBDI)SrF·THF]
2
(520 µL). The solution was stirred at 60 °C for 4 h and the solvent subsequently
2
suitable for X-ray diffraction analysis formed overnight at ambient temperature. The supernatant was
decanted, the crystals washed with cold pentane (-20 °C, 2 x 0.5 ml) and dried under high vacuum
1
3
(
61.4 mg, 86.6 µmol, 56 %). H NMR (600.13 MHz, C
6
D
6
, 298K): δ = 0.73 (t, J = 7.3 Hz, 12H, CH
), 1.49-1.55 (m, 4H, CH ), 1.55-1.61 (m, 4H, CH
-backbone), 2.78 (quint, J = 6.7 Hz, 4H, CH), 3.66-3.69 (m, 4H,
), 4.73 (s, 1H, CH-backbone), 7.03-7.05 (m, 4H, CH-arom), 7.08-7.11 (m, 2H, CH-arom) ppm.
13C NMR (150.92 MHz, C
, 298K): δ = 12.2 (CH ), 12.3 (CH ), 24.9 (CH -backbone), 25.3 (OCH CH ),
), 41.7 (CH), 68.3 (OCH CH ), 93.1 (CH-backbone), 123.2 (C-arom), 125.1 (C-arom),
39.1 (C-arom), 149.3 (C-arom), 164.0 (CN-backbone) ppm. F NMR (564.63 MHz, C
3
), 0.90
3
(t, J = 7.4 Hz, 12H, CH
3
), 1.43-1.45 (m, 4H, OCH
2
CH
2
2
2
),
3
1
.61-1.66 (m, 8H, CH
2
), 1.69 (s, 6H, CH
3
OCH CH
2
2
D
6 6
3
3
3
2
2
2
1
5
9
7.8 (CH
2
), 28.3 (CH
2
2
2
1
9
6
D
6
, 298K): δ = -
1.5 (Sr-F) ppm. Elemental analysis Calculated for C82
H
130
F
2
Sr
2
N
4
O
2
(M = 1417.20 g/mol): C 69.50, H
.25, N 3.95; Found: C 69.41, H 9.37, N 3.88.
Synthesis of [Sr
6
N"
2
H
9
·(Me
6
Tren) +
3
][SrN"
3
ˉ]: SrN"
2
(100 mg, 0.245 mmol, 2.33 eq) and Me
(38.8 µL, 34.1 mg,
.315 mmol, 3 eq) was added to the stirring mixture. The suspension was stirred untill all solid material
6
Tren
(28.1 µL, 24.1 mg, 0.105 mmol, 1 eq) were suspended in 3 mL of benzene. PhSiH
3
0
dissolved and the formation of a two-phase system (brown oil and colorless solution) was observed. A
colorless crystal was isolated from the reaction mixture after resting at room temperature for 27 days
and identified by X-ray diffraction as [Sr
6
N"
2 9
H ·(Me
6
Tren) +
3
][SrN"
3
ˉ]. Larger quantities could not be
obtained.
Synthesis of Sr
6 4 8 6
N" F ·(Me Tren)
2
: To a stirred solution of SrN"
2
(500 mg, 1.22 mmol, 2.33 eq) in
toluene (5 mL) was added in sequence: fluorobenzene (833 µL), 1-fluorohexane (333 µL, 267 mg,
2
1
.56 mmol, 2.1 eq) and Me
6
Tren (333 µL, 287 mg, 1.24 mmol, 1.02 eq). Phenylsilane (227 µL, 199 mg,
.84 mmol, 1.5 eq.) was added slowly to the stirring reaction mixture and the resulting dark orange
solution was stirred at 80°C for 2.5 h. All volatiles were removed under reduced pressure, and the
brown oily residue was dried in vacuo at room temperature. The oil was washed with pentane (3 x
4
mL, sonification) to obtain a brownish powder. All liquids were removed under reduced pressure and
the residue recrystallized from a toluene (1 mL), fluorobenzene (1 mL) mixture to obtain clear,
colorless crystals overnight. The crystals (36 mg, 0.020 mmol, 9.9 % based on SrN" ) were washed with
toluene (1.5 mL) and pentane (3 x 2 mL) and dried at room temperature in a glovebox under N
atmosphere. The solid material was dried under vacuum to remove crystal solvent prior to NMR
2
2
-
investigations. Yield was calculated on the basis that six eq of SrN"
Sr N" ·(Me Tren) / BrC
. 1H NMR (600.13 MHz, C
2
are needed to form one eq of
3
6
4
F
8
6
2
6
D
6
6
D
5
ratio 1:1, 298K): δ = 2.63 (t, J=6.8, 4H, CH
2
),
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
2
7
.37 (d, J=7.0, 4H, CH
2
), 2.15 (s, 24H, N(CH
3
)
2
), 2.12 (s, 12H, N(CH
3
)
2
), 2.03 – 1.97 (m, 8H, CH ), 0.30 (s,
2
19
2H, Si[CH ]
3 3
) ppm. F NMR (564.63 MHz, C
6
D
6
/BrC ratio 1:1, 298K): δ = -70.47 ppm. Poor solubility
6 5
D
13
1
1
13
did not allow for C{ H} NMR analysis. HSQC (Heteronuclear Single Quantum Coherence) H- C NMR
(600.13, 150.92) MHz, C ): δ = (2.63 / 53.96, CH ), (2.37 / 58.49, CH ), (2.15 / 45.39, N(CH ), (2.11
), (2.00 / 56.20, CH ), (0.31 / 7.55, Si[CH ) ppm. Elemental analysis calculated for
Sr (M = 1872.20 g/mol): C: 35.29; H: 7.54; N: 8.98. Found: C 35.12, H 7.39, N 8.68.
(
D
6 6
2
2
)
3 2
/
51.29, N(CH
3
)
2
2
]
3 3
55
C H
140
F
8
N12Si
8
6
8
Synthesis of Sr16N" F24·(THF)12: In a J-Young NMR tube, Sr
6
N"
4
F
8
·(Me
6
Tren) (20 mg) was suspended in
2
5
00 µL C followed by 50 µL THF-d
6
D
6
8
. The suspension was quickly heated to 60 °C to obtain a clear
solution. The solution was filtered and few, very small crystals suitable for single crystal X-ray
diffraction were observed after one week at room temperature. Larger quantities could not be
obtained.
Hydrodefluorination with AeN"
AeN" (Ca: 16 mg, 0.044 mmol; Sr: 20 mg, 0.049 mmol, Ba: 20 mg, 0.044 mmol), followed by addition
of toluene-d (550 µL) and two equivalent of the organofluorine compound. Phenylsilane (3 or 10 eq.)
was added to the solution. In case BaN" was used, this was followed by rapid formation of precipitate.
2
/PhSiH
3
(Ae = Ca, Sr, Ba): A J-Young NMR tube was charged with
2
8
2
The mixture was heated to 120 °C (for 6 or 12 h) or to 60 °C (for 24 h). The product mixture was
quenched with diethylether (500 µL) and distilled water (20 µL), filtered and analyzed by GC/MS
and/or NMR.
Preparation of a SF
bottom Schlenk flask. Rapidly stirring the solution, a gentle vacuum was applied which led to cooling.
The cold solution was saturated with SF gas and stirred under SF atmosphere (1.06 bar) for one hour.
The solution was subsequently exposed a second time to 1.06 bar of SF pressure. The presence of SF
/C , 298 K): δ = -58.3 (S-
6
solution in toluene: Degassed toluene (10 mL) was placed in a 50 mL round-
6
6
6
6
19
19
was checked prior to each reaction by F NMR. F NMR (564.63 MHz, C
H
7 8
D
6 6
F) ppm.
Reactions of AeN"
2
/PhSiH
3
(Ae = Sr, Ba) with SF
6
: A J-Young NMR tube was charged with AeN"
solution in toluene (300 µL)
(550 µL). Four equivalents of phenylsilane (Sr: 24.2 µL, 0.196 mmol; Ba: 21.7 µL,
2
(Sr:
2
0 mg, 0.049 mmol; Ba: 20 mg, 0.044 mmol), followed by the saturated SF
6
and benzene-d
6
0
.176 mmol) were added to the solution. This was in both cases followed by immediate formation of
a yellowish precipitate. This suspension was stirred for 12 h at room temperature, during which time
additional precipitate was formed. The supernatant was decanted and the yellow powder dried in
vacuo and characterized by elemental analysis. In reaction with BaN"
2
/PhSiH following values were
3
found: C 24.14%, H 3.77%, N 1.64%, S 1.77%.
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European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Supporting Information
1
H, Si, F, 13C NMR spectra, crystallographic details including ORTEP plots, details for the DFT
29
19
calculations including XYZ-files.
Author Information
Corresponding author: sjoerd.harder@fau.de
The authors declare no competing financial interest.
Acknowledgement
We acknowledge C. Wronna and A. Roth for CHN analyses and Dr. C. Färber and J. Schmidt for
assistance with NMR analyses. We thank the Deutsche Forschungsgemeinschaft for funding (HA
3
218/9-1).
Key words
Alkaline-earth metal; DFT calculation; Hydride; Hydrodehalogenation;
Key topic
Hydrodehalogenation with heavy alkaline earth metals
References
[1]
[2]
[3]
[4]
[5]
H. Amii, K. Uneyama, Chem. Rev. 2009, 109, 2119–2183.
F. J. Urbano, J. M. Marinas, J. Mol. Catal. A Chem. 2001, 173, 329–345.
Z. Ainbinder, L. E. Manzer, M. J. Nappa, in Environ. Catal., Wiley, 1999, pp. 197–212.
M. Hudlicky, J. Fluor. Chem. 1989, 44, 345–359.
D. Schrenk, M. Bignami, L. Bodin, J. K. Chipman, J. del Mazo, B. Grasl-Kraupp, C. Hogstrand, L.
Hoogenboom, J. C. Leblanc, C. S. Nebbia, E. Ntzani, A. Petersen, S. Sand, T. Schwerdtle, C. Vleminckx, H.
Wallace, B. Brüschweiler, P. Leonards, M. Rose, M. Binaglia, Z. Horváth, L. Ramos Bordajandi, E. Nielsen,
EFSA J. 2020, 18, 1–220.
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202100529
[
[
[
[
[
[
[
[
6]
S. J. Blanksby, G. B. Ellison, Acc. Chem. Res. 2003, 36, 255–263.
7]
Q. Shen, Y. G. Huang, C. Liu, J. C. Xiao, Q. Y. Chen, Y. Guo, J. Fluor. Chem. 2015, 179, 14–22.
C. Bakewell, A. J. P. White, M. R. Crimmin, Angew. Chemie - Int. Ed. 2018, 57, 6638–6642.
M. R. Crimmin, M. J. Butler, A. J. P. White, Chem. Commun. 2015, 51, 15994–15996.
T. Chu, Y. Boyko, I. Korobkov, G. I. Nikonov, Organometallics 2015, 34, 5363–5365.
C. Bakewell, A. J. P. White, M. R. Crimmin, J. Am. Chem. Soc. 2016, 138, 12763–12766.
C. Bakewell, B. J. Ward, A. J. P. White, M. R. Crimmin, Chem. Sci. 2018, 9, 2348–2356.
G. Coates, B. J. Ward, C. Bakewell, A. J. P. White, M. R. Crimmin, Chem. - A Eur. J. 2018, 24, 16282–
8]
9]
10]
11]
12]
13]
16286.
[14]
T. X. Gentner, B. Rösch, G. Ballmann, J. Langer, H. Elsen, S. Harder, Angew. Chemie Int. Ed. 2019, 58,
07–611.
6
[15]
[16]
[17]
B. Cui, S. Jia, E. Tokunaga, N. Shibata, Nat. Commun. 2018, 9, 1–8.
M. Batuecas, N. Gorgas, M. R. Crimmin, Chem. Sci. 2021, 12, 1993–2000.
W. Chen, T. N. Hooper, J. Ng, A. J. P. White, M. R. Crimmin, Angew. Chemie - Int. Ed. 2017, 56, 12687–
12691.
[18]
[19]
[20]
[21]
[22]
[23]
[24]
[25]
[26]
[27]
F. Rekhroukh, W. Chen, R. K. Brown, A. J. P. White, M. R. Crimmin, Chem. Sci. 2020, 11, 7842–7849.
I. Fujii, K. Semba, Q. Z. Li, S. Sakaki, Y. Nakao, J. Am. Chem. Soc. 2020, 142, 11647–11652.
D. D. L. Jones, I. Douair, L. Maron, C. Jones, Angew. Chemie Int. Ed. 2021, 60, 7087–7092.
A. Friedrich, J. Eyselein, J. Langer, C. Färber, S. Harder, Angew. Chemie Int. Ed. 2021, anie.202103250.
H. Li, S. Liao, Y. Xu, Chem. Lett. 1996, 25, 1059–1060.
K. Fuchibe, T. Akiyama, Synlett 2004, 1282–1284.
Y. Zhang, S. Liao, Y. Xu, D. Yu, Q. Shen, Synth. Commun. 1997, 27, 4327–4334.
K. Kikushima, M. Grellier, M. Ohashi, S. Ogoshi, Angew. Chemie Int. Ed. 2017, 56, 16191–16196.
H. Handel, M. A. Pasquini, J. L. Pierre, Tetrahedron 1980, 36, 3205–3208.
J. P. Barham, S. E. Dalton, M. Allison, G. Nocera, A. Young, M. P. John, T. McGuire, S. Campos, T. Tuttle,
J. A. Murphy, J. Am. Chem. Soc. 2018, 140, 11510–11518.
[
28]
29]
S. Loiselle, M. Branca, G. Mulas, G. Cocco, Environ. Sci. Technol. 1997, 31, 261–265.
S. Harder, J. Brettar, Angew. Chemie Int. Ed. 2006, 45, 3474–3478.
[
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202100529
[30]
[31]
[32]
[33]
[34]
[35]
J. Spielmann, S. Harder, Chem. - A Eur. J. 2007, 13, 8928–8938.
A. S. S. Wilson, M. S. Hill, M. F. Mahon, C. Dinoi, L. Maron, Science 2017, 358, 1168–1171.
A. S. S. Wilson, M. S. Hill, M. F. Mahon, C. Dinoi, L. Maron, Tetrahedron 2021, 131931.
D. Schuhknecht, T. P. Spaniol, Y. Yang, L. Maron, J. Okuda, Inorg. Chem. 2020, 59, 9406–9415.
S. Brand, H. Elsen, J. Langer, S. Grams, S. Harder, Angew. Chemie Int. Ed. 2019, 58, 15496–15503.
B. Rösch, T. X. Gentner, H. Elsen, C. A. Fischer, J. Langer, M. Wiesinger, S. Harder, Angew. Chemie Int.
Ed. 2019, 58, 5396–5401.
[
36]
37]
J. Martin, J. Eyselein, S. Grams, S. Harder, ACS Catal. 2020, 10, 7792–7799.
[
B. Maitland, M. Wiesinger, J. Langer, G. Ballmann, J. Pahl, H. Elsen, C. Färber, S. Harder, Angew. Chemie
-
Int. Ed. 2017, 56, 11880.
[
38]
39]
M. Wiesinger, B. Maitland, C. Färber, G. Ballmann, C. Fischer, H. Elsen, S. Harder, Angew. Chemie Int.
Ed. 2017, 56, 16654–16659.
[
J. Martin, C. Knüpfer, J. Eyselein, C. Färber, S. Grams, J. Langer, K. Thum, M. Wiesinger, S. Harder,
Angew. Chemie Int. Ed. 2020, 59, 9102–9112.
[
40]
41]
A. Causero, G. Ballmann, J. Pahl, C. Färber, J. Intemann, S. Harder, Dalt. Trans. 2017, 46, 1822–1831.
[
S. Nembenna, H. W. Roesky, S. Nagendran, A. Hofmeister, J. Magull, P. J. Wilbrandt, M. Hahn, Angew.
Chemie - Int. Ed. 2007, 46, 2512–2514.
[42]
T. X. Gentner, B. Rösch, K. Thum, J. Langer, G. Ballmann, J. Pahl, W. A. Donaubauer, F. Hampel, S.
Harder, Organometallics 2019, 38, 2485–2493.
[43]
[44]
[45]
S. P. Sarish, H. W. Roesky, M. John, A. Ringe, J. Magull, Chem. Commun. 2009, 3, 2390.
S. Pillai Sarish, A. Jana, H. W. Roesky, T. Schulz, M. John, D. Stalke, Inorg. Chem. 2010, 49, 3816–3820.
H. Bauer, M. Alonso, C. Fischer, B. Rösch, H. Elsen, S. Harder, Angew. Chemie Int. Ed. 2018, 57, 15177–
15182.
[46]
H. Bauer, M. Alonso, C. Färber, H. Elsen, J. Pahl, A. Causero, G. Ballmann, F. De Proft, S. Harder, Nat.
Catal. 2018, 1, 40–47.
[47]
[48]
[49]
H. Bauer, K. Thum, M. Alonso, C. Fischer, S. Harder, Angew. Chemie - Int. Ed. 2019, 58, 4248–4253.
H. Elsen, C. Fischer, C. Knüpfer, A. Escalona, S. Harder, Chem. - A Eur. J. 2019, 25, 16141–16147.
M. Rigby, J. Mühle, B. R. Miller, R. G. Prinn, P. B. Krummel, L. P. Steele, P. J. Fraser, P. K. Salameh, C. M.
Harth, R. F. Weiss, B. R. Greally, S. O’Doherty, P. G. Simmonds, M. K. Vollmer, S. Reimann, J. Kim, K.-R.
Kim, H. J. Wang, J. G. J. Olivier, E. J. Dlugokencky, G. S. Dutton, B. D. Hall, J. W. Elkins, Atmos. Chem.
Phys. 2010, 10, 10305–10320.
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202100529
[50]
[51]
[52]
[53]
[54]
[55]
D. K. Padma, A. R. Vasudeva Murthy, W. Becher, J. Massonne, J. Fluor. Chem. 1972, 2, 113–114.
M. Rueping, P. Nikolaienko, Y. Lebedev, A. Adams, Green Chem. 2017, 19, 2571–2575.
G. B. Deacon, P. C. Junk, G. J. Moxey, Dalt. Trans. 2010, 39, 5620.
P. F. Lang, B. C. Smith, Dalt. Trans. 2010, 39, 7786.
C. E. Messer, J. Solid State Chem. 1970, 2, 144–155.
R. D. Shannon, C. T. Prewitt, Acta Crystallogr. Sect. B Struct. Crystallogr. Cryst. Chem. 1969, 25, 925–
946.
[56]
[57]
[58]
[59]
R. D. Shannon, Acta Crystallogr. Sect. A 1976, 32, 751–767.
E. E. Kwan, Y. Zeng, H. A. Besser, E. N. Jacobsen, Nat. Chem. 2018, 10, 917–923.
A. Wilson, Frontiers of Organo- and Hydridocalcium Chemistry, University of Bath, 2018.
M. Westerhausen, Inorg. Chem. 1991, 30, 96–101.
This article is protected by copyright. All rights reserved.

European Journal of Inorganic Chemistry
10.1002/ejic.202100529
Table 2. Hydrodefluorination with AeN" /PhSiH
3
8
combinations in toluene-d ; F-substrate
2
concentration: 0.16-0.18 M (conversion determined by GC-MS).
Substrate
2 eq]
PhSiH
3
T
t
Conv.
Entry
AeN"
2
Product(s)
[
[eq]
[°C]
[h]
[%]
SrN"2
SrN"2
SrN"2
CaN"2
BaN"2
BaN"2
CaN"2
SrN"2
BaN"2
CaN"2
SrN"2
BaN"2
CaN"2
SrN"2
BaN"2
SrN"2
1
2
3
4
5
6
7
8
9
3
3
3
3
3
10
3
3
3
3
3
3
3
3
3
3
120
120
60
6
54
78
50
11a
85
21
1
12
24
6
120
120
120
120
120
120
120
120
120
120
120
120
120
6
12
12
12
12
12
12
12
12
12
12
12
51
58
61b
100
82
1
1
1
1
1
1
1
0
1
2
3
4
5
6
/86c
7
28/65
55/13
73/24
BaN"2
1
7
3
120
12
57/53
a) additional 6 % of N"C
c) additional 7 % of N"C
6
H
5
were identified by GC-MS, b) additional 39 % of N"C
6
H13 were identified by GC-MS,
6
H11 were identified by GC-MS.
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European Journal of Inorganic Chemistry
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Table of Contents:
A well-defined dimeric strontium hydride complex or undefined in-situ generated strontium
hydride clusters are highly active reagents for the hydrodehalogenation of C X (X = F, Cl, Br,
H
6 5
I). Even the C-F bond in electron-rich arenes like 2,6-dimethyl-fluorobenzene was cleaved. DFT
calculations support a concerted nucleophilic aromatic substitution.
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