Halogen Bonds of Halotetrafluoropyridines in Crystals and Co-crystals with Benzene and Pyridine

Article abstract of DOI:10.1002/chem.201900334

The structures of the three para-substituted halotetrafluoropyridines with chlorine, bromine, and iodine have been determined in the solid state (X-ray diffraction). The structures of these compounds and that of pentafluoropyridine were also determined in the gas phase (electron diffraction). Structures in the solid state of the bromine and iodine derivatives exhibit halogen bonding as a structure-determining motif. On the way to an investigation of halogen bond formation of halotetrafluoropyridines in the solid state with the stronger Lewis base pyridine, co-crystals of benzene adducts were investigated to gain an understanding of the influence of aryl–aryl interactions. These co-crystals showed halogen bonding only for the two heavier halotetrafluoropyridines. In the pyridine co-crystals halogen bonding was observed for all three para-halotetrafluoropyridines. The formation of homodimers and heterodimers with pyridine is also supported by quantum-chemical calculations of electron density topologies and natural bond orbitals.

Full text of DOI:10.1002/chem.201900334

A Journal of
Accepted Article
Title: Halogen Bonds of Halotetrafluoropyridines in Crystals and Co-
crystals with Benzene and Pyridine
Authors: Norbert Werner Mitzel, Pia Trapp, Hans-Georg Stammler,
Beate Neumann, Jan-Hendrik Lamm, Yury Vishnevskiy, and
Leif Körte
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
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to ensure accuracy of information. The authors are responsible for the
content of this Accepted Article.
To be cited as: Chem. Eur. J. 10.1002/chem.201900334
Link to VoR: http://dx.doi.org/10.1002/chem.201900334
Supported by

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A Neutral Germanium/Phosphorus Frustrated Lewis Pair and its
Contrasting Reactivity Compared to its Silicon Analogue
Timo A. Kinder,a René Pior,a Sebastian Blomeyer, Beate Neumann,a Hans-Georg Stammler,a and
Norbert W. Mitzela*
Abstract. The chlorogermane (C2F5)3GeCl with very electronegative
pentafluoroethyl groups was converted with LiCH2PtBu2 to obtain the
intramolecular frustrated Lewis pair (FLP) (C2F5)3GeCH2PtBu2 – a
neutral germanium-based FLP. Its reactivity was compared to its
silicon homologue (C2F5)3SiCH2PtBu2. Both FLP cleave NO but give
cyclic (Si) and open-chain oxides (Ge). In reactions with HCl both FLP
give the same adduct type in the solid state, while the proton seems
more mobile in solution in the germanium case. Reactions with
PhCNO and Me3SiCHN2 result in ring-type adducts. The structures of
(C2F5)3GeCH2PtBu2 and of five adducts with substrates were
elucidated by X-ray diffraction. The study clearly features the germa-
nium compound to have a more moderate Lewis acidity compared to
the silicon analogue.
their chlorogermane (C2F5)3GeCl[14b] we were now able to prepare
a neutral germanium-containing FLP, (C2F5)3SiCH2P(tBu)2 (2), by
reacting it in a nucleophilic substitution reaction with the lithiated
phosphane LiCH2P(tBu)2.[15] This enables us now exploring its
chemistry in comparison to the silicon analogue 1.[7d]
Compound 2 was obtained as a colourless liquid. Its 1H NMR
spectrum contains two doublets, one at 1.78 ppm with a coupling
constant of 1 Hz for the methylene unit and at 0.85 ppm with a
coupling constant of 12 Hz for the tert-butyl group. The 19F NMR
shows the typical pattern for pentafluoroethyl groups.[14] A 31P{1H}
NMR signal is observed at 14.9 ppm, similar to the shift of 1
(18.5 ppm).[7d] This indicates three-coordinate phosphorus atoms
and thus the presence of a FLP system without direct PGe
interaction. This is not naturally so, because the geminal system
1 comprises an electronegatively substituted germanium atom
and a potent donor function in close proximity. It is thus related to
Ge/N systems such as Ge(ONMe2)4 H3GeONMe2 or
Frustrated Lewis pair (FLP) chemistry is investigated since
only slightly more than a decade but already has a tremendous
impact as powerful chemical concept. It explains the concerted
activity of Lewis acids and bases in activation of small molecu-
les.[1] Besides reversible hydrogen binding and transfer,[2] the re-
actions with several other small substrate molecules have been
investigated. Activation of CO2 is still a major aspect.[3] With the
hydroboration of diazomethane derivatives, Stephan et al. have
recently opened a new field to FLP-chemistry and interpret this as
potential prelude to FLP-N2 chemistry in the sense of metal-free
activation of dinitrogen-species.[4]
Most FLP are based on combinations of boron Lewis acids
and phosphorus Lewis bases, either in two independent molecu-
les or as two functions within one intramolecular FLP system.
Nitrogen bases are also frequently employed. Far less common
are systems containing Al,[5] C,[6] Si,[7] Ge,[8] Sn,[8,9] rare-earth[10] or
transition elements (e.g. Zr,[11] Zn,[12] Sc[13]) as acid functions.
We have recently reported the synthesis of the first neutral
silicon/phosphorus FLP, (C2F5)3SiCH2P(tBu)2 (1).[7d] Its activity in
H2 splitting, and addition of CO2 and SO2 is due to the highly elec-
tron-withdrawing pentafluoroethyl groups, which turn the silane
function into a strong Lewis acid. Hoge et al. explored the
foundations of pentafluoroethyl element chemistry in detail and
made a range of new Lewis acidic functions accessible.[14] With
[16]
Cl3GeONMe2 or related Si/N systems[17] with direct Ge···N or
Si···N interactions. The absence of a PGe bond is confirmed by
a PGe distance of 3.266(1) Å in the crystalline state (Figure 1).
This was determined by X-ray diffraction of a single crystal
generated in situ from the liquid compound 2 (details see Suppor-
ting Information). The angle Ge-C-P is wide at 117.8(1)°, but 2.7°
narrower than the corresponding angle Si-C-P in FLP 1
(120.4(1)°). The coordination sphere of germanium is only slightly
distorted from tetrahedral.
[a]
T. A. Kinder, M.Sc., R. Prior. B.Sc., Dr. S. Blomeyer, B. Neumann,
Dr. H.-G. Stammler, Prof. Dr. N. W. Mitzel
Lehrstuhl für Anorganische Chemie und Strukturchemie und
Centrum für Molekulare Materialien CM2, Fakultät für Chemie,
Universität Bielefeld; Lehrstuhl für Anorganische Chemie und
Strukturchemie, Fakultät für Chemie, Universität Bielefeld,
Universitätsstraße 25, 33615 Bielefeld, Germany
E-mail: mitzel@uni-bielefeld.de
CCDC 1892520-1892525. Supporting information for this article is
given via a link at the end of the document.
Figure 1. Molecular structure of compound 2 in the solid state. Ellipsoids are
set at 50% probability; hydrogen atoms are omitted for clarity. Selected bond
lengths [Å] and angles [°]: P1Ge1 3.266(1), P1–C1 1.876(1), Ge1–C1
1.939(1), Ge1-C1-P1 117.8(1), C1-P1-C8 99.4(1), C1-P1-C12 101.6(1), C12-
P1-C8 110.9(1).
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While compound 1 was earlier shown to cleave dihydrogen, 2
turned out to be inactive in this respect. 1 also gave isolable
adducts with CO2 and SO2, while solutions of 2 showed no
changes in NMR shifts when exposed to these reactants. How-
ever, 1 and 2 both react with nitrogen oxide, but afford rather
different products. Both reactions lead to the cleavage of NO and
only the oxygen atom is found in the products – unlike the reaction
of a boron-based FLP with NO reported by Sajid et al., in which
the entire NO unit is captured in the product.[18]
The 31P NMR resonance of 4, an oxidation product of 2 with
NO, at 61.5 ppm is at higher field than that of 3, but still at much
lower field than that of 2. This is consistent with the absence of a
bond between the Lewis acid function (Ge) and oxygen in this
case – in contrast to 3. This fact from solution finds confirmation
in the molecular structure determined in the crystalline state (Fi-
gure 3). The two molecules in the asymmetric unit (denoted a and
b) vary drastically in their non-bonding GeO distances (a:
3.204(2), b: 2.860(2) Å) and Ge-C7-P angles (a: 116.8(1)°, b:
108.0(1)°). Their torsion angles O-P-C7-Ge are similar (a: 5.7(2)°,
b: 4.1(1)°). The Ge1-C7-P1 angle of 4a is similar to the corres-
ponding angle in 2 at 116.8(1)°. The P–O bond in 4 at 1.491(2) Å
is significantly shorter than that in 3, and closer to the standard
value of a phosphane oxide (Me3PO: 1.489(6) Å).[20]
The structures in the solid state (Figures 2 and 3) show that
FLP 1 reacts with NO to afford a formal phosphane oxide; its
oxygen atom –also a Lewis base site– is coordinated to the silicon
atom. So, product 3 is not a frustrated Lewis pair, but one where
acid and base functions joined to form a Si–O bond. The two
molecules in the asymmetric unit of 3 differ only marginally in the
t
structure of their four-membered rings; only the C2F5 and Bu
groups are arranged slightly differently.
Figure 3. Molecular structure of compound 4 in the solid state. Ellipsoids are
set at 50% probability; hydrogen atoms and second molecule are omitted for
clarity. Selected bond lengths [Å] and angles [°] (given for molecules a/b if
markedly different, otherwise only for a): P1Ge1 3.056(1)/3.223(1), P1–O1
1.491(2), Ge1O1 3.240(1)/2.860(2), P1–C7 1.832(2), Ge1–C7 1.951(2), Ge1–
C1 2.027(2), Ge1–C5 2.029(2), Ge1–C3 2.014(2), Ge1-O1-P1 76.0(1)/82.7(1),
Ge1-C7-P1 116.8(1), C7-Ge1-C1 103.3(1), C7-Ge1-C3 112.6(1), C7-Ge1-C5
114.9(1), O1-P1-C7-Ge1 5.7(2)/ 4.1(1).
Figure 2. Molecular structure of compound 3 in the solid state. Ellipsoids are
set at 50% probability; hydrogen atoms and second molecule are omitted for
clarity. Selected bond lengths [Å] and angles [°]: P1Si1 2.620(1), P1–O1
1.574(2), Si1–O1 1.869(2), P1–C7 1.779(2), Si1–C7 1.942(2), Si1–C1 1.964(2),
Si1–C5 1.968(2), Si1–C3 2.049(2), Si1-O1-P1 98.8(1), Si1-C7-P1 89.4(1), O1-
Si1-C3 164.0(1), C3-Si1-C1 92.4(1), C3-Si1-C5 96.2(1), C3-Si1-C7 88.6(1).
The silicon atom in 3 is trigonal bipyramidally coordinate with
oxygen and C3 atoms adopting the axial positions (angle O-Si-C3
164.0(1)°). Si–C distances including carbon atoms C1/C5/C7 are
almost 0.1 Å shorter than the axial bond Si–C3. Penta-coor-
dination of silicon is conserved in solution as is proven by a 29Si
NMR chemical shift of −91.5 ppm. The 31P NMR resonance at
89.9 ppm is at lower field than that of 1 (18.5 ppm) The non-bon-
ded SiP distance within the four-membered ring at 2.620(1) Å is
much shorter than that in 1 (3.248(1) Å). The Si–O distance at
1.869(2) Å is longer than standard Si–O bonds (e.g. 1.632(5) Å
for (Me3Si)2O).[19] The Si-O-P angle is 98.8(1)°.
Figure 4. Relaxed potential energy profiles along the E–O distances for
compounds 3 (E = Si) and 4 (E = Ge), calculated at the B97-3c level of theory.
Quantum-chemical investigations for the reasons of the differ-
ent structures of products 3 and 4 were undertaken by calculating
the potential of a series of optimized structures with increasing
fixed E–O distances (E = Si, Ge, Figure 4, details see Supporting
Information). Surprisingly, 3 shows a double-minimum potential;
that means the structure found in the crystalline state represents
the absolute minimum, with a slightly longer calculated Si–O
distance of 1.962 Å (B97-3c, compare solid state: 1.869(2) Å),
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while a structure with a Si–O distance of 3.207 Å represents a
second minimum, but is 4.6 kJ mol–1 higher in energy. Germanium
compound 4, in contrast, shows a single minimum at a Ge–O
distance of 3.132 Å, in the range of experimental values in the
solid state (3.240(1)/2.860(2) Å).
Expectedly both FLPs, 1 and 2, react with hydrogen chloride
gas: in the products the chloride is linked to the silicon and ger-
manium sites, respectively, but the protons are found at different
positions in solution.
Figure 6. Molecular structure of one molecule in compound 6 in the solid state.
Hydrogen atoms, disordered atoms and second molecule are omitted for clarity.
Ellipsoids are set at 50% probability. Selected bond lengths [Å] and angles [°]
(given for molecules a/b if markedly different, otherwise only for a): P1–Ge1
3.343(1)/ 3.296(1), P1–Cl1 3.292(2)/ 3.426(2), Ge1–Cl1 2.510(2)/2.442(1), P1–
C7 1.805(4), Ge1–C7 1.988(4), Ge1–C1 2.054(4), Ge1–C5 2.028(5), Ge1–C3
2.132(5), Ge1-C7-P1 123.5(2)/120.4(2), Cl1-Ge1-C3 177.5(2)/179.5(1), C7-
Ge1-C1 123.1(2)/123.4(2), C12-P1-C8 117.4(2), C7-P1-C8 111.2(2), C7-P1-
C12 107.4(2), Cl1-Ge1-C7-P1 39.0(3)/ 52.6(3).
Crystals of 5 contain three molecules in the asymmetric unit;
they slightly differ in their P–Cl distances. Compound 6 contains
two molecules (a and b) in the asymmetric unit; they differ in their
torsion angles Cl-Ge-C7-P (a: 52.6(3)°, b: 39.0(3)°) and subse-
quently in their PCl distances (a: 3.292(2), b: 3.426(2) Å).
The complexed Lewis acid functions adopt trigonal bipyrami-
dal coordination, indicated by their τ parameters:[21] it is 0.91 –0.94
for 5 and 0.92/0.94 for 6. The averaged Si–Cl bond at 2.260 Å and
the averaged Ge–Cl bond at 2.476 Å are longer than in the related
five-coordinate silicate [PNP][(C2F5)4SiCl] 2.218(1) Å[22] and
germanate [PNP][(C2F5)3GeCl2] 2.322(1) Å),[23] respectively.
Hydrogen chloride can be removed from both adducts by reacting
them with a hydride source such as tBu3SnH, whereby elemental
dihydrogen is released.
NMR spectra for product 5 are consistent with expectation of
a P–H bonded system. One of three observed H NMR signals
1
can be assigned to a P–H unit (doublet of triplets at 5.97 ppm;
=
3
=
1JPH 482.9 Hz, JHH 4.7 Hz). The other two resonances, a
doublet of doublets at 1.89 ppm (2JPH = 16.5 Hz and 3JHH = 4.7 Hz),
and a doublet at 0.91 ppm, belong to the CH2 and tert-butyl
groups, respectively. Consistently, the 31P NMR resonance at
47.5 ppm shows a characteristic doublet splitting of 482.9 Hz and
nonet splitting of 16.5 Hz; the 2JHH coupling to the CH2 protons is
– as frequently observed for such compounds– not observed.
By contrast, product 6, resulting from the reaction of FLP 2
with HCl, has different NMR characteristics. Its 1H NMR spectrum
contains two doublets at 2.19 and 1.52 ppm and a broad signal at
7.07 ppm (low-temperature experiments did not markedly impro-
ve the line-width). This indicates that the proton is not directly
bound to the phosphorus atom. Consistently, 31P and 31P{1H}
NMR spectra feature broadened resonances, but no doublet sig-
nal indicating a P–H bond. However, a hydrogen atom at phos-
phorus was located in the molecular structures of both, 5 and 6,
in the solid state by low-temperature X-ray diffraction (Figures 5
and 6).
In contrast to nitrogen oxide and hydrogen chloride, both FLP
react with phenylisocyanate under formation of the same type of
adducts, 7 and 8: here the oxygen atoms coordinate to the Lewis
acid functions and the carbon atom to the phosphane unit. This
binding pattern has also been observed for other FLP systems.[24]
This leads to five-membered rings. Low-field NMR shifts of the 31
P
nuclei of 7 (40.9 ppm) and 8 (31.2 ppm) were observed relative to
1
the free FLPs 1 and 2, respectively. The H NMR spectra show
CH2 resonances at 1.80 (7) and 2.07 ppm (8) split into doublets –
characteristic for adduct formation of the FLP. Adequate crystals
for X-ray diffraction were not obtained.
FLP 1 reacts –in contrast to its germanium analogue 2– with
trimethylsilyldiazomethane (Me3SiCHNN) under 1,1-addition. Its
terminal nitrogen atom becomes coordinated between the silicon
and phosphorus atoms of 1. This binding type is the same as for
Uhl’s FLP tBu2AlC(CHPh)PMes2 in its Me3SiCHNN adduct[25] and
related to the potential metal-free activation of dinitrogen de-
Figure 5. Molecular structure of compound 5 in the solid state. Hydrogen atoms,
disordered atoms and second molecule are omitted for clarity. Ellipsoids are
set at 50% probability. Selected bond lengths [Å] and angles [°] (given for
molecules a/b/c if markedly different, otherwise only for a): P1–Cl1 3.294(1)/
3.307(1)/3.375(1), P1–Si1 3.249(1), Si1–Cl1 2.268(1), Si1-C7-P1 122.8(1)/ -
121.0(1)/ 121.3(1), C3-Si1-Cl1 178.4(1)/178.5(1)/179.3(1), C5-Si1-C1
123.7(1)/122.9(1)/ 124.0(1), C8-P1-C7 109.7(1), C8-P1-C12 116.2(1), C7-P1-
C12 112.7(1).
1
scribed by Stephan and Melen.[4] The four H NMR signals of 9
include a singlet at 0.05 ppm for the TMS group, two doublets at
0.87 ppm for the tert-butyl groups, a doublet at 2.07 ppm for the
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methylene and a singlet at 7.91 ppm for the N2CH group. Penta-
coordination at the silicon atom follows from a 29Si resonance at
−88.6 ppm.
Acknowledgments
We gratefully acknowledge financial support from Deutsche
Forschungsgemeinschaft (DFG, grant MI477/31-1 and core faci-
lity GED@BI grant MI477/35-1) and Solvay GmbH (Hannover,
Germany) for providing pentafluoroethane.
Conflict of interest
Final proof for the formation of a four-membered ring (similar
to the product of the reaction with NO: 3) stems from X-ray crys-
tallography (Figure 7). The ring angle Si1-N1-P is 99.0(1)° while
Si1-C7-P is 94.5(1)°. The Si1P distance at 2.736(1) Å is 0.11 Å
longer compared to compound 3.
The authors declare no conflict of interest.
Keywords: Frustrated Lewis Pairs • Germanium • Silicon •
Phosphorus • Fluoroalkyl groups
[1]
a) G. C. Welch, R. R. San Juan, J. D. Masuda, D. W. Stephan, Science
2006, 314, 1121–1124; b) D. W. Stephan, Acc. Chem. Res. 2015, 48,
306–316; c) P. Spies, G. Erker, G. Kehr, K. Bergander, R. Fröhlich, S.
Grimme, D. W. Stephan, Chem. Commun. 2007, 5072–5074; d) G. C.
Welch, D. W. Stephan, J. Am. Chem. Soc. 2007, 129, 1880–1881; e) D.
W. Stephan, Dalton Trans. 2009, 3129–3136; f) C. M. Mömming, E.
Otten, G. Kehr, R. Fröhlich, S. Grimme, D. W. Stephan, G. Erker, Angew.
Chem. Int. Ed. 2009, 48, 6643–6646; g) D. W. Stephan, G. Erker, Angew.
Chem. Int. Ed. 2010, 49, 46–76; h) D. W. Stephan, G. Erker, Chem. Sci.
2014, 5, 2625–2641; i) D. W. Stephan, G. Erker, Angew. Chem. Int. Ed.
2015, 54, 6400–6441; j) L. A. Körte, S. Blomeyer, S. Heidemeyer, A. Mix,
B. Neumann, N. W. Mitzel, Chem. Commun. 2016, 52, 9949–9952.
a) P. A. Chase, G. C. Welch, T. Jurca, D. W. Stephan, Angew. Chem.
2007, 119, 8196–8199; b) H. Wang, R. Fröhlich, G. Kehr, G. Erker, Chem.
Commun. 2008, 5966–5968; c) K. Chernichenko, M. Nieger, M. Leskelä,
T. Repo, Dalton Trans. 2012, 41, 9029–9032; d) D. J. Scott, M. J. Fuchter,
A. E. Ashley, Chem. Soc. Rev. 2017, 46, 5689–5700.
[2]
[3]
a) C. M. Mömming, E. Otten, G. Kehr, R. Fröhlich, S. Grimme, D. W.
Stephan, G. Erker, Angew. Chem. Int. Ed. 2009, 48, 6643–6646. b) B.
Chen, R. Neumann, Eur. J. Inorg. Chem. 2018, 6, 791–794. c) M. Pieper,
J.-H. Lamm, B. Neumann, H.-G. Stammler, N. W. Mitzel, Dalton Trans.
2017, 46, 5326–5336.
Figure 7. Molecular structure of compound 9 in the solid state. Ellipsoids are
set at 50% probability; only hydrogen atom at C16 is shown for clarity. Selected
bond lengths [Å] and angles [°]: P1–Si1 2.736(1), P1–N1 1.655(2), Si1–N1
1.933(2), P1–C7 1.785(2), Si1–C7 1.939(2), Si1–C1 2.012(3), Si1–C5 1.999(2),
Si1–C3 2.054(2), C16–N2 1.290(3), N1–N2 1.398(3), Si1-N1-P1 99.0(1), Si1-
C7-P1 94.5(1), C16-N2-N1 119.2(2), Si2-C16-N2 116.5(2).
[4]
[5]
[6]
[7]
a) R. L. Melen, Angew. Chem. Int. Ed. 2018, 57, 880–882; b) C. Tang,
Q. Liang, A. R. Jupp, T. C. Johnstone, R. C. Neu, D. Song, S. Grimme,
D. W. Stephan, Angew. Chem. Int. Ed. 2017, 56, 16588–16592.
C. Appelt, H. Westenberg, F. Bertini, A. W. Ehlers, J. C. Slootweg, K.
Lammertsma, W. Uhl, Angew. Chem. Int. Ed. 2011, 50, 3925–3928; b)
G. Menard, D. W. Stephan, Angew. Chem. Int. Ed. 2012, 51, 4409.
E. J. Lawrence, E. R. Clark, L. D. Curless, J. M. Courtney, R. J. Blagg,
M. J. Ingleson G. G. Wildgoose, Chem. Sci. 2016, 7, 2537–2543; b) E.
R. Clark, M. J. Ingleson, Angew. Chem. Int. Ed. 2014, 53, 11306–11309.
a) S. A. Weicker, D. W. Stephan, Chem. Eur. J. 2015, 21, 13027–13034;
b) A. Schäfer, M. Reißmann, A. Schäfer, W. Saak, D. Haase, T. Müller,
Angew. Chem. Int. Ed. 2011, 50, 12636–12638; c) T. J. Herrington, B. J.
Ward, L. R. Doyle, J. McDermott, A. J. P. White, P. A. Hunt, A. E. Ashley,
Chem. Commun. 2014, 50, 12753–12756; d) B. Waerder, M. Pieper, L.
A. Körte, T. A. Kinder, A. Mix, B. Neumann, H.-G. Stammler, N. W. Mitzel,
Angew. Chem. Int. Ed. 2015, 54, 13416–13419.
Herein we demonstrated the neutral Ge/P FLP-system
(C2F5)3GeCH2P(tBu)2 (2) to be capable of cleaving NO and HCl,
as well as to bind Ph-NCO, the same applies to the silicon
analogue (C2F5)3SiCH2P(tBu)2 (1). However, unlike the latter, 2
does not react with H2, CO2 or SO2 under comparable conditions.
There are a number of facts that demonstrate clearly that the
germanium function is the reason for the weaker Lewis acidity in
comparison to the silicon analogue: a) the different structures of
the NO oxidation products, b) the predicted double-minimum
potential for the SiCPO ring-type oxidation product 3 (E = Si) while
4 (E = Ge) has a single minimum and open-chain structure, c) the
fact that only 1 but not 2 is able to split Me3Si-CHN2. In addition,
we calculated free enthalpies for the addition of HCl (ΔGHCl) and
the fluoride ion affinities (FIA) for 1 and 2 (ΔGHCl [kJ mol–1] = –77
(1), –63 (2); FIA [kJ mol–1] = 378 (1), 308 (2)) which fully confirm
this trend (details see Supporting Information). This feature can
allow a fine tuning of Lewis acidity in future applications.
[8]
[9]
Y. Yu, J. Li, W. Liu, Q. Ye, H. Zhu, Dalton Trans. 2016, 45, 6259–6268.
a) S. Freitag, J. Henning, H. Schubert, L. Wesemann, Angew. Chem. Int.
Ed. 2013, 52, 5640–5643; b) S. Freitag, K. M. Krebs, J. Henning, J.
Hirdler, H. Schubert, L. Wesemann, Organometallics 2013, 32, 6785–
6791; c) D. J. Scott, N. A. Phillips, J. S. Sapsford, A. C. Deacy, M. J.
Fuchter, A. E. Ashley, Angew. Chem. 2016, 128, 14958–14962; d) R. C.
Turnell-Ritson, J. S. Sapsford, R. T. Cooper, S. S. Lee, T. Földes, P. A.
Hunt, I. Pápai, A. E. Ashley, Chem. Sci. 2018, 9, 8716–8722; e) D. A.
Dickie, E. N. Coker, R. A. Kemp, Inorg. Chem. 2011, 50, 11288–11290.
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[10] M. Pieper, J.-H. Lamm, B. Neumann, H.-G. Stammler, N. W. Mitzel,
Dalton Trans. 2017, 46, 5326–5336.
[11] a) A. M. Chapman, M. F. Haddow, D. F. Wass, J. Am. Chem. Soc. 2011,
133, 18463–18478; b) A. M. Chapman, M. F. Haddow, D. F. Wass, J.
Am. Chem. Soc. 2011, 133, 8826–8829; c) X. Xu, G. Kehr, C. G. Daniliuc,
G. Erker, J. Am. Chem. Soc. 2013, 135, 6465–6476; d) M. Pieper, P.
Auer, S. Schwarzbich, F. Kühn, B. Neumann, H.-G. Stammler, N. W.
Mitzel, Z. Anorg. Allg. Chem. 2017, 643, 909–915;
[12] a) R. Dobrovetsky, D. W. Stephan, Isr. J. Chem. 2015, 55, 206–209; b)
R. Dobrovetsky, D. W. Stephan, Angew. Chem. Int. Ed. 2013, 52, 2516–
2519; c) P. Jochmann, D. W. Stephan, Angew. Chem. Int. Ed. 2013, 52,
9831–9835.
[13] K. Chang, X. Wang, Z. Fan, X. Xu, Inorg. Chem. 2018, 57, 8568–8580.
[14] a) S. Steinhauer, T. Böttcher, N. Schwarze, B. Neumann, H.-G. Stam-
mler, B. Hoge, Angew. Chem. Int. Ed. 2014, 53, 13269–13272. b) S.
Pelzer, B. Neumann, H.-G. Stammler, N. Ignat’ev, B. Hoge, Chem. Eur.
J. 2016, 22, 3327–3332.
[15] a) F. Eisenträger, A. Göthlich, I. Gruber, H. Heiss, C. A. Kiener, C. Krüger,
J. Ulrich Notheis, F. Rominger, G. Scherhag, M. Schultz, B. F. Straub, M.
A. O. Volland, P. Hofmann, New J. Chem. 2003, 27, 540–550; b) H. H.
Karsch, H. Schmidbaur, Z. Naturforsch. 1977, 32 b, 762–767.
[16] a) N. W. Mitzel, K. Vojinović, J. Chem. Soc., Dalton Trans. 2002, 2341–
2343; b) N. W. Mitzel, U. Losehand, S. L. Hinchley, D. W. H. Rankin,
Inorg. Chem. 2001, 40, 661–666; c) N. W. Mitzel, U. Losehand, D. W. H.
Rankin, J. Chem. Soc. Dalton Trans. 1999, 4291 – 4297.
[17] a) N. W. Mitzel, U. Losehand, A. Wu, D. Cremer, D. W. H. Rankin, J. Am.
Chem. Soc. 2000, 122, 4471–4482; b) N. W. Mitzel, K. Vojinović, R.
Fröhlich, T. Foerster, D. W. H. Rankin, J. Am. Chem. Soc. 2005, 127,
13705–13713.
[18] M. Sajid, A. Stute, A. J. P. Cardenas, B. J. Culotta, J. A. M. Hepperle, T.
H. Warren, B. Schirmer, S. Grimme, A. Studer, C. G. Daniliuc, R. Fröhlich,
J. L. Petersen, G. Kehr, G. Erker, J. Am. Chem. Soc. 2012, 134, 10156–
10168.
[19] M. J. Barrow, E. A. V. Ebsworth, M. M. Harding, Acta Crystallogr. 1979,
35, 2093–2099.
[20] L. E. Engelhardt, C. L. Raston, C. R. Whitaker, A. H. White, Aust. J.
Chem. 1986, 39, 2151–2154.
[21] A. W. Addison, T. Nageswara Rao, J. Reedijk, J. van Rijn, G. C. Ver-
schoor, Dalton Trans. 1984, 3, 1349–1984.
[22] S. Steinhauer, T. Bötcher, N. Schwarze, B. Neumann, H.-G. Stammler,
B. Hoge, Angew. Chem. Int. Ed. 2014, 53, 13269–13272.
[23] S. Pelzer, B. Neumann, H.-G. Stammler, N. Ignat'ev, B. Hoge, Chem.
Eur. J. 2016, 22, 16460–16466.
[24] a) K. Chang, X. Wang, Z. Fan, X. Xu, Inorg. Chem. 2018, 57, 8568–8580;
B.-H. Xu, G. Kehr, R. Fröhlich, B. Wibbeling, B. Schrimer, S. Grimme, G.
Erker, Angew. Chem. Int. Ed. 2011,50, 7183–2186.
[25] W. Uhl, J. Backs, A. Hepp, L. Keweloh, M. Layh, D. Pleschka, J. Possart,
A. Wollschläger, Z. Naturforsch. 2017, 72b, 821–838.
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10.1002/chem.201900334
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Entry for the Table of Contents
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Frustrated as well is the germanium
Lewis Pair (C2F5)3GeCH2P(tBu)2, but
compared to its silicon homologue it
shows contrasting behaviour in its
reactivity to certain substrates as HCl
and NO featuring the germanium
function to be less Lewis acidic.
T. A. Kinder, R. Pior, S. Blomeyer, B.
Neumann, H.-G. Stammler and N. W.
Mitzel*
XXX – XXX
A
Neutral Germanium/Phosphorus
Frustrated Lewis Pair and its Con-
trasting Reactivity Compared to its
Silicon Analogue
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