Synthetic access to a hydrocarbon-soluble trifluorinated Ge(II) compound and its Sn(II) congener

Article abstract of DOI:10.1021/ja412151e

Trifluorinated germanium anions attracted attention of theoretical chemists already in the late 1990s to predict their physical and chemical properties. However these species were not synthesized in the laboratory, although substantial evidence for their existence was obtained from the mass spectrometry of GeF₄. The present study shows that controlled fluorination of LMNMe₂ (L = PhC(N^tBu)₂, M = Ge, Sn) using HF·pyridine in toluene leads to the formation of [LH₂] ⁺[MF₃]^- under elimination of HNMe₂. The products contain the trifluorinated Ge(II) and Sn(II) anionic species which are stabilized by interionic H···F bonds. The new compounds were characterized by single crystal X-ray structural analysis, NMR spectroscopy, and elemental analysis.

Full text of DOI:10.1021/ja412151e

Communication
pubs.acs.org/JACS
Synthetic Access to a Hydrocarbon-Soluble Trifluorinated Ge(II)
Compound and its Sn(II) Congener
Prinson P. Samuel,† Yan Li,‡ Herbert W. Roesky,*,† Veniamin Chevelkov,§ Adam Lange,§
Anja Burkhardt,∥ and Birger Dittrich*,⊥
†Institut fur Anorganische Chemie, Georg-August-Universitat, Tammannstrasse 4, D-37077, Gottingen, Germany
̈
̈
̈
‡State Key Laboratory of Physical Chemistry of Solid Surfaces, College of Chemistry and Chemical Engineering, Xiamen University,
Xiamen, Fujian, 361005, China
§Research Group Solid-State NMR Spectroscopy, Max Planck Institute for Biophysical Chemistry, Am Fassberg 11, D-37077,
Gottingen, Germany
̈
∥Deutsches Elektronen-Synchrotron, Notkestrasse 85, D-22607, Hamburg, Germany
⊥Institut fur Anorganische und Angewandte Chemie, Universitat Hamburg, Martin-Luther-King-Platz 6, D-20146, Hamburg,
̈
̈
Germany
S
* Supporting Information
center.4d In this respect our continuous interest in the
chemistry of fluorides of low-valent group 14 elements
prompted us to utilize dimethyl amino Ge(II) and Sn(II)
compounds to access the trifluorinated anions of these
elements in the +2 oxidation state.
ABSTRACT: Trifluorinated germanium anions attracted
attention of theoretical chemists already in the late 1990s
to predict their physical and chemical properties. However
these species were not synthesized in the laboratory,
although substantial evidence for their existence was
obtained from the mass spectrometry of GeF4. The
present study shows that controlled fluorination of
LMNMe2 (L = PhC(NtBu)2, M = Ge, Sn) using HF·
pyridine in toluene leads to the formation of
[LH2]+[MF3]− under elimination of HNMe2. The
products contain the trifluorinated Ge(II) and Sn(II)
anionic species which are stabilized by interionic H···F
bonds. The new compounds were characterized by single
crystal X-ray structural analysis, NMR spectroscopy, and
elemental analysis.
The behavior of different coordinate germanium fluorides
has been experimentally and theoretically studied by many
chemists. The broad interest in such compounds is mainly due
to their utility in the fine processing of semiconductors. Even
though the structure of GeF3 is still unknown, geometries of
GeF, GeF2, and GeF4 in their ground states have been studied
by experimental methods.6 However, the experimental data
−
revealing the properties or structures of GeFn species are
scarce in the literature even though such ions had been
detected in the mass spectrum of GeF4 already in 1972.7 In this
context, theoretical chemists were interested in finding the
optimized structures of such monoanionic species since 1990s.8
Very recently, Bjarnason et al. described the dissociative
electron attachment to GeF4 in which the molecular ion
ne of the widely studied class of compounds in chemistry
Oconsists of silylenes, germylenes, and stanylenes which
are in fact heavier carbene analogues of silicon, germanium, and
tin, respectively. Silicon, germanium, and tin centers in these
compounds exhibit an oxidation state of +2. A number of room
temperature stable silylenes,1a−g germylenes,1h,i−n and stanyle-
nes1i,o are known, and the advent of these compounds opened a
fertile research field of group 14 chemistry. Much effort has
been devoted to the synthesis of compounds with low-valent
centers bearing hydrides, hydroxyl groups, or halides. Among
them the fluorides of group 14 elements are important due to
their synthetic utility in the laboratory as well as in industry.2 In
the literature, the known group 14 fluoro compounds are
preferentially in the +4 oxidation state. Only a few examples of
organo germanium(II) and tin(II) fluorides are known.3,4 In
two recent communications we reported on the synthesis of
lead(II)monofluoride5 from dimethylamino lead(II) and tin-
(II)monofluoride4d from dimethylamino tin(II) using penta-
fluoropyridine as a fluorinating reagent. A similar reaction using
diisopropylamino germanium(II) however led to the oxidative
addition of a C−F bond of pentafluoropyridine at the Ge(II)
−
−
−
GeF4 and the fragments GeF3 , GeF2 , GeF−, and F− were
observed with appreciable intensities.9 However, no synthetic
route has been outlined so far for obtaining stable complexes
with GeF3− anions, and the synthetic methodology described in
this communication fills that niche. In contrast to this, several
−
compounds with SnF3 anions are known including the
inorganic salts like KSnF3 and NH4SnF3 and complex inorganic
structures like [Ni(H2O)6](SnF3)2.10a−e The disadvantage of
these salts is their insolubility in organic solvents. In addition,
compounds like (naphthalene-1,5-diammonim)(SnF3)2 are also
known for which the cationic part is organic.10f,g
−
−
Our initial attempts to prepare GeF3 and SnF3 anionic
−
−
species by the fluorination of GeCl3 and SnCl3 anions
present in our previously reported [(LB)MCl][MCl3] com-
plexes11 (LB = 2,6-diacetylpyridinebis(2,6-diisopropylanil), M
= Ge, Sn) were not successful. Inspired by our recent success in
using dimethylamino lead(II) and tin(II) as precursors for
Received: November 28, 2013
Published: January 7, 2014
© 2014 American Chemical Society
1292
dx.doi.org/10.1021/ja412151e | J. Am. Chem. Soc. 2014, 136, 1292−1295

Journal of the American Chemical Society
Communication
obtaining the corresponding monofluorides, we used LGeNMe2
BP86, 96.4° BLYP) by Schaefer et al.8 The average Ge−F bond
distance is 1.807 Å. The C−N bond distances are 1.325(3) and
1.322(3) Å which lie in between single- and double-bond
distances, indicating the delocalization of the positive charge
between the two nitrogen atoms.
−
(1) and LSnNMe2 (2) as starting materials for GeF3 and
−
SnF3 anions, respectively. In a controlled reaction with HF·
pyridine, 1 and 2 afford (LH2)+(GeF3)− (3) and
(LH2)+(SnF3)− (4) in good yields.
Compound 4 crystallizes in the monoclinic space group P21/
c. 4 is not isostructural with 3 as the former shows a dimeric
arrangement in the crystal structure (Figure 2). Two Sn atoms
To a precooled solution (−78 °C) of 1 (2), 3 equiv of HF·
pyridine were added very slowly under strict inert atmosphere,
and the stirring was continued for 30 min allowing the
temperature to rise gradually. One proton of HF reacts with
NMe2 to form HNMe2. The remaining two protons react with
the anionic amidinate (L−) ligand to form the LH2+ species, the
cation of 3 (4). The 3 equiv of fluoride ions react with the
M(II) center (M = Ge, Sn) to form the MF3− species, the anion
of 3 (4). (Scheme 1).
Scheme 1. Syntheses of Compounds 3 and 4
Figure 2. Dimeric molecular structure of 4. Hydrogen atoms (except
of NH) are omitted for clarity. Anisotropic displacement parameters
are depicted at the 50% probability level. Selected bond lengths [Å]
and bond angles [o]: C1−N1, 1.323(3); C1−N2, 1.319(4); Sn1−F1,
2.017(3); Sn1−F2, 2.035(3); Sn1−F3, 2.043(5); Sn1−F3′, 2.217; N1−
C1−N2, 117.6(2), F1−Sn1−F2, 84.61(11), F1−Sn1−F3, 90.89(18),
F2−Sn1−F3, 85.12(16); F3−Sn1−F3′, 69.96(17); Sn1−F3−Sn1′,
110.04(17).
are bridged through two fluorine atoms of the SnF3− units, and
the remaining fluorine atoms are connected to the NH groups
of the corresponding cationic ligands through hydrogen bonds.
Single crystals of 3 and 4 suitable for X-ray diffraction were
obtained from their toluene solutions. Compound 3 crystallizes
in the orthorhombic space group P212121. The molecular
structure of 3 shows that GeF3 has a trigonal pyramidal
structure with the F atoms at the base and Ge atom at the apex
(Figure 1). Two of the three F atoms of GeF3− interact with the
−
The SnF3 anions present in the dimer represent two trigonal
pyramids with fluorine atoms constituting the bases and Sn
atoms occupying the apex positions. The arrangements of the
two units are in such a way that the vectors passing through the
centers of the triangular bases to the corresponding apexes are
parallel but in opposite directions. The Sn−F bond distances
are 2.017(3) (Sn1−F1), 2.035(3) (Sn1−F2), and 2.043(5) Å
(Sn1−F3). The Sn1−F3′ bond distance is 2.217 Å, which is
longer than the Sn1−F3 bond length (2.043(5) Å). This
indicates that the bridging fluorine atoms are not equally
arranged between the two tin atoms and the tin−fluorine core
structure can be better regarded as [(SnF3)−]2 rather than
Sn2F62−. The Sn1F3Sn1′F3′ core constitutes a parallelogram
with the angles 69.96(17)o (F3−Sn1−F3′) and 110.04(17)o
(Sn1−F3−Sn1′), the center of which acts as an inversion
center in the dimeric structure, [(LH2)+(SnF3)−]2.
The NH protons in the cation of 3 show the resonance at
1
9.22 ppm in the H NMR spectrum. The 19F NMR spectrum
Figure 1. Molecular structure of 3. Hydrogen atoms (except of NH)
are omitted for clarity. Anisotropic displacement parameters are
depicted at the 50% probability level. Selected bond lengths [Å] and
bond angles [o]: C1−N1, 1.325(3); C1−N2, 1.322(3); Ge1−F1,
1.825(2); Ge1−F2, 1.800(2); Ge1−F3, 1.796(2); N1−C1−N2,
118.2(2), F1−Ge1−F2, 90.31(10), F1−Ge1−F3, 90.10(12), F2−
Ge1−F3, 91.07(11).
exhibits a single resonance at −62.98 ppm corresponding to the
three fluorine atoms in the GeF3 anion. A difference between
the hydrogen-bonded fluorine atoms and the terminal fluorine
atom was not observed in the NMR spectrum probably due to
the fast exchange of the fluorine atoms. This shows that the
hydrogen bonds involving the NH and F atoms are very weak
−
−
and thereby allow the GeF3 unit to rapidly exchange the
positions of the fluorine atoms. The H NMR spectrum of 4
1
H atoms of the NH groups present in the cationic part. The
average F−Ge−F bond angle is 90.49° which is significantly
smaller than the standard tetrahedral angle (109°28′), and this
is attributed to the large repulsion experienced by the Ge−F
bond pairs from the lone pair present in the germanium atom.
Moreover, the H···F interactions associated with two fluorine
atoms also play a significant role in the size of the bond angle.
The F−Ge−F bond angle (av 90.49°) experimentally found in
the present study is close to the corresponding value predicted
at different levels of theory (95.1° BHLYP, 95.7° B3LYP, 96.2°
shows the NH resonance at 9.81 ppm. The corresponding 19F
NMR spectrum in solution exhibits the resonance at −81.41
ppm. The 119Sn NMR spectrum shows a broad resonance at
−531.67 ppm. The Sn−F coupling was not observed at room
temperature, but in the 19F NMR spectrum measured at −80
°C, the fluorine resonance is flanked by two 119Sn satellites with
a coupling constant of J(119Sn−19F) = 2959 Hz.
Even though several compounds containing SnF3− anions are
known so far,10 NMR spectra of these compounds were seldom
1293
dx.doi.org/10.1021/ja412151e | J. Am. Chem. Soc. 2014, 136, 1292−1295

Journal of the American Chemical Society
Communication
reported. The main obstacle for utilizing NMR spectroscopy for
the characterization of trifluorinated stannate compounds is
their limited solubility in common organic solvents. However,
the 19F NMR spectrum of 4 shows a relatively broad (105 Hz
half width) single resonance, and the fluorine atoms involved in
the H···F and Sn···F contacts were not differentiable.
Nevertheless, at −60 °C the chemical shift position slightly
shifts to −82.20 ppm with a half width of 210 Hz. However,
recording the 19F NMR spectrum of 3 at −60 °C also did not
result in the splitting of the peak except that the chemical shift
position was slightly shifted from −62.98 ppm (25 °C) to
−63.27 ppm (−60 °C). It should be noted that the 19F NMR
spectra not reflecting the nonequivalent fluorine atoms as
evident from the molecular structures have been reported for
other fluorides too. For example, the 19F NMR spectrum of
[SbF3(phen)]2 (phen = 1,10-phenanthroline) shows only one
resonance at −95.8 ppm (−83 °C) even though the molecular
structure of this compound is a dimer with four terminal and
two bridging fluorine atoms.12 The 19F NMR of the tin
fluorides recently reported by Gurnani et al. and others also
exhibited a smaller number of fluorine resonances in the NMR
spectra than the number of nonequivalent fluorine atoms found
in the molecular structure.10g,12 As a representative example,
the molecular structure of [Sn2F4(dmso)2] shows two types of
fluorine atoms (terminal and bridging) but gives rise to only
one resonance at −86.4 ppm (20 °C) in the 19F NMR
spectrum.10g In line with the reported spectra and on the basis
of the single resonance positions observed in the 19F NMR
spectra of 3 and 4, it can be assumed that random
NMR (THF-d8, 200 MHz, 25 °C): δ 1.06 (s, 18H, tBu), 7.51−
7.57 (m, 5H, Ar), 9.22 (br, 2H, NH) ppm; 19F NMR (THF-d8,
282.38 MHz, 25 °C): δ −62.98 (s, 3F, GeF3) ppm; elemental
analysis (%) calcd for C15H25F3GeN2 (363.01): C, 49.63, H,
6.94, N, 7.72 Found: C, 49.75, H, 6.96, N, 7.49.
To a cooled (−78 °C) solution of 2 (500 mg, 1.27 mmol),
HF·pyridine (0.10 mL, 3.81 mmol, 70% HF) was added very
slowly, and the stirring was continued for 30 min while allowing
the temperature to rise slowly. After reaching 0 °C, the solution
was subjected to vacuum for a few minutes to remove any
amount of unreacted HF, and the solution was warmed to
room temperature. Followed by filtration, the solution was
stored at −5 °C to afford 4 as a colorless crystalline product
which was separated by decantation. Storing a saturated
solution of 4 in toluene at 0 °C afforded single crystals suitable
1
for X-ray diffraction. (Yield: 68%, 0.35g). H NMR (THF-d8,
200 MHz, 25 °C): δ 1.05 (s, 18H, tBu), 7.41−7.60 (m, 5H, Ar),
9.81 (br, 2H, NH) ppm; 19F NMR (THF-d8, 282.38 MHz, 25
°C): δ −81.41 (s, 3F, SnF3) ppm; 119Sn NMR (THF-d8, 111
MHz, 25 °C): δ −531.67 ppm. Elemental analysis (%) calcd for
C15H25F3N2Sn (409.08): C, 44.04, H, 6.16, N, 6.85 Found: C,
44.26, H, 6.24, N, 6.78.
Molecular structures of compounds 3 and 4 were established
by single-crystal X-ray crystallographic studies. X-ray intensity
data sets for 3 were collected on a Bruker D8 goniometer with
Apex2 detector and an Incoatec Mo microsource with mirror
optics. Data reduction was carried out with SAINT.13 Data for
4 were collected at beamline P11 of the new PETRA-III storage
ring at DESY in Hamburg. The crystallography endstation at
P11 is equipped with a high-precision one-axis goniometer and
Pilatus 6 M single photon counting detector. The beam size
was adjusted to 200 μm. Data were collected at a temperature
of 120 K and an X-ray energy of 20 keV (λ = 0.6199 Å). In total
540 frames were collected in rotation increments of 0.5° and an
exposure time of 0.25 s per frame. Data were processed using
the XDS program package.14 Intensity data for both
compounds were corrected for absorption and scaled with
SADABS.15 Structures were solved by direct methods and
refined by full-matrix least-squares methods on F2 with the
program SHELXL-2013,16 utilizing anisotropic displacement
parameters for nonhydrogen atoms. Visualization and modeling
was done using SHELXLE.17
−
intermolecular exchange of the MF3 (M = Ge, Sn) species
and rapid exchange of the positions of fluorine atoms play an
important role which in turn imply the weakness of H···F and
Sn···F contacts.
In summary, we have prepared hydrocarbon soluble
−
−
compounds containing the GeF3 and SnF3 species. While
the former shows a monomeric structure, the latter exists as a
dimer [(SnF3)−]2. Weak hydrogen bonds exist between the two
fluorine atoms of each MF3− anion and the NH protons of the
cationic part. Compound 3 represents the first oganometallic
−
compound containing a GeF3 moiety.
Syntheses were carried out under inert gas atmosphere of
dinitrogen in oven-dried glassware using standard Schlenk
techniques. Other manipulations were accomplished in a
dinitrogen filled glovebox. Solvents were purified by MBRAUN
solvent purification system MB SPS-800. All chemicals were
purchased from Aldrich and used without further purification.
Compounds 1 and 2 were prepared as reported in the
literature.4d 1H, 19F, and 119Sn NMR spectra in solution were
recorded with a Bruker Avance DPX 200 or a Bruker Avance
DRX 300 spectrometer, using THF-d8 as solvent. Elemental
analyses were carried out in the Analytische Labor der
ASSOCIATED CONTENT
* Supporting Information
■
S
Cif files of 3 and 4, a table containing crystal structure
refinement parameters, and the details of 19F solid state NMR.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Authors
hroesky@gwdg.de
■
Anorganischen Chemie der Universitat Gottingen.
̈
̈
To a cooled (−78 °C) solution of 1 (500 mg, 1.44 mmol),
HF·pyridine (0.11 mL, 4.31 mmol, 70% HF) was added very
slowly, and the stirring was continued for 30 min while allowing
the temperature to rise gradually. After reaching 0 °C, the
solution was subjected to vacuum for a few minutes to remove
any amount of unreacted HF, and the solution was warmed to
room temperature. Followed by filtration, the solution was
partially evaporated and kept at −5 °C to yield 3 as a crystalline
compound which was separated by decanting the solvent.
Storing a solution of 3 in toluene at 0 °C afforded colorless
birger.dittrich@chemie.uni-hamburg.de
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
H.W.R. thanks the Deutsche Forschungsgemeinschaft for
financial support (RO 224/60-1). Portions of this research
were carried out at the PETRA light source at DESY, a member
of the Helmholtz Association (HGF). B.D. thanks J. Matussek
1
crystals suitable for X-ray diffraction. (Yield: 74%, 0.38g). H
1294
dx.doi.org/10.1021/ja412151e | J. Am. Chem. Soc. 2014, 136, 1292−1295

Journal of the American Chemical Society
Communication
(17) Hubschle, C.; Sheldrick, G. M.; Dittrich, B. J. Appl. Crystallogr.
2011, 44, 1281.
̈
for providing alternative X-ray data for compound 3 and for
helpful discussions. We thank Dr. M. John for fruitful
suggestions and discussions on NMR spectroscopy.
REFERENCES
■
(1) For reviews on silylenes: (a) Haaf, M.; Schmedake, T.; West, R.
Acc. Chem. Res. 2000, 33, 704. (b) Hill, N. J.; West, R. J. Organomet.
Chem. 2004, 689, 4165. (c) Ottosson, H.; Steel, P. G. Chem.Eur. J.
2006, 12, 1576. (d) Kira, M. Chem. Commun. 2010, 46, 2893. (e) Asay,
M.; Jones, C.; Driess, M. Chem. Rev. 2011, 111, 354. (f) Yao, S.; Xiong,
Y.; Driess, M. Organometallics 2011, 30, 1748. (g) Sen, S. S.; Khan, S.;
Samuel, P. P.; Roesky, H. W. Chem. Sci. 2012, 3, 659. For reviews on
germylenes and stannylenes: (h) Veith, M. Angew. Chem. 1987, 99, 1;
Angew. Chem., Int. Ed. Engl. 1987, 26, 1. (i) Neumann, W. P. Chem.
Rev. 1991, 91, 311. (j) Dias, H. V. R.; Wang, Z.; Jin, W. Coord. Chem.
Rev. 1998, 176, 67−86. (k) Kuhl, O. Coord. Chem. Rev. 2004, 248, 411.
̈
(l) Saur, I.; Alonso, S. G.; Barrau, J. Appl. Organomet. Chem. 2005, 19,
414. (m) Leung, W.-P.; Kan, K.-W.; Chong, K.-H. Coord. Chem. Rev.
2007, 251, 2253. (n) Nagendran, S.; Roesky, H. W. Organometallics
2008, 27, 457. (o) Tokitoh, N.; Okazaki, R. Coord. Chem. Rev. 2000,
210, 251.
(2) Murphy, E. F.; Murugavel, R.; Roesky, H. W. Chem. Rev. 1997,
97, 3425.
(3) (a) Riviere, P.; Satge, J.; Castel, A.; Normant, H. C. R. Acad. Sci.
̀ ́
Paris. 1976, 282, 971. (b) Ding, Y.; Hao, H.; Roesky, H. W.;
Noltemeyer, M.; Schmidt, H.-G. Organometallics 2001, 20, 4806.
(4) (a) Chorley, R. W.; Ellis, D.; Hitchcock, P. B.; Lappert, M. F. Bull.
Soc. Chim. Fr. 1993, 129, 599. (b) Jana, A.; Roesky, H. W.; Schulzke,
C.; Doring, A.; Beck, T.; Pal, A.; Herbst-Irmer, R. Inorg. Chem. 2009,
̈
48, 193. (c) Jana, A.; Roesky, H. W.; Schulzke, C.; Samuel, P. P.
Organometallics 2010, 29, 4837. (d) Samuel, P. P.; Singh, A. P.; Sarish,
S. P.; Matussek, J.; Objartel, I.; Roesky, H. W.; Stalke, D. Inorg. Chem.
2013, 52, 1544.
(5) Jana, A.; Sarish, S. P.; Roesky, H. W.; Leusser, D.; Objartel, I.;
Stalke, D. Chem. Commun. 2011, 47, 5434.
(6) (a) Martin, R. W.; Merer, A. J. Can. J. Phys. 1973, 51, 125. (b) van
der Kerk, S. M. Polyhedron 1983, 2, 509. (c) Takeo, H.; Curl, R. F.;
Wilson, P. W. J. Mol. Spectrosc. 1971, 38, 464. (d) Caunt, A. D.;
Mackle, H.; Sutton, L. E. Trans. Faraday Soc. 1951, 47, 943.
(7) Harland, P. W.; Cradock, S.; Thynne, J. C. J. Int. J. Mass Spectrom.
Ion Phys. 1972/73, 10, 169.
(8) Li, Q.; Li, G.; Xu, W.; Xie, Y.; Schaefer, H. F., III J. Chem. Phys.
1999, 111, 7945.
(9) Bjarnason, E. H.; Omarsson, F. H.; Hoshino, M.; Tanaka, H.;
Brunger, M. J.; Limao-Vieira, P.; Ingolfsson, O. Int. J. Mass Spectrom.
2013, 339, 45.
(10) (a) Bergerhoff, G.; Goost, L.; Schultke-Rhonhof, E. Acta
Crystallogr. 1968, B24, 803. (b) Bergerhoff, G.; Goost, L. Acta
̌ ̌ ̌ ̌ ̌
Crystallogr. 1973, B29, 632. (c) Kaucic, V.; Leban, I.; Gaspersic-
̌
Skander, S.; Gantar, D.; Rahten, A. Acta Crystallogr. 1988, C44, 1329.
(d) Abrahams, I. Acta Crystallogr. 1995, C51, 345. (e) Kokunov, Y. V.;
Gorbunova, Y. E.; Petrov, V. N.; Gustyakova, M. P.; Buslaev, Y. A.
Dokl. Akad. Nauk SSSR 1989, 307, 1126. (f) Boufas, S.; Merazig, H.;
Moliterni, A. G.; Altomare, A. Acta Crystallogr. 2007, C63, m315.
(g) Gurnani, C.; Hector, A. L.; Jager, E.; Levason, W.; Pugh, D.; Reid,
G. Dalton Trans. 2013, 42, 8364.
(11) Singh, A. P.; Roesky, H. W.; Carl, E.; Stalke, D.; Demers, J. −P.;
Lange, A. J. Am. Chem. Soc. 2012, 134, 4998.
(12) (a) Benjamin, S. L.; Burt, J.; Levason, W.; Reid, G.; Webster, M.
J. Fluor. Chem. 2012, 135, 108. (b) Levason, W.; Light, M. E.;
Maheshwari, S.; Reid, G.; Zhang, W. Dalton Trans. 2011, 40, 5291.
(13) SAINT, version 7.68A; Bruker APEX, version 2011.9; Bruker
AXS: Madison, WI, 2011.
(14) Kabsch, W. Acta Crystallogr. 2010, D66, 125.
(15) Sheldrick, G. M. SADABS; University of Gottingen: Gottingen,
̈
̈
Germany, 2009.
(16) Sheldrick, G. M. Acta Crystallogr. 2008, A64, 112.
1295
dx.doi.org/10.1021/ja412151e | J. Am. Chem. Soc. 2014, 136, 1292−1295