Facile, high-yield functionalization of germanium and tin by oxidative insertion of tetrelenes into the E-H bonds of inorganic acids (E = C, N, O, F): Arene elimination versus oxidative addition and formation of a germanium cation-water complex

Article abstract of DOI:10.1021/om301121x

Reaction of the diarylgermylene Ge(ArMe₆)₂ [ArMe ₆ = C₆H₃-2,6-(C₆H ₂-2,4,6-(CH₃)₃)₂] with various inorganic acids (HCN, HN₃, and HBF₄) led to the facile oxidation of the germanium atom to yield the corresponding Ge(IV) products (ArMe₆)₂Ge(H)X (X = CN (1), N₃ (2), F (3)). The cationic germanium-water complex [(ArMe₆)₂GeH(OH ₂)][SO₃CF₃] (4) was prepared by treating Ge(ArMe₆)₂ with triflic acid in the presence of trace amounts of moisture. The reactions provide an efficient method of installing a variety of functional groups at a germanium atom and can be used in the preparation of germanium complexes that are analogous to lighter carbon species. The tin species Sn(Ar6)₂ was also oxidized to the Sn(IV) analogue of 3. In all reactions, no evidence of arene elimination was observed, which was in contrast to the reaction of the stannylene (or bulkier germylenes) with hydrogen or ammonia, which yielded H(ArMe₆), [(ArMe₆)Sn(μ-H)]₂, and [(ArMe₆)Sn(μ- NH₂)]₂.

Full text of DOI:10.1021/om301121x

Article
pubs.acs.org/Organometallics
Facile, High-Yield Functionalization of Germanium and Tin by
Oxidative Insertion of Tetrelenes into the E−H Bonds of Inorganic
Acids (E = C, N, O, F): Arene Elimination versus Oxidative Addition
and Formation of a Germanium Cation−Water Complex
Zachary D. Brown, Jeremy D. Erickson, James C. Fettinger, and Philip P. Power*
Department of Chemistry, University of California, 1 Shields Avenue, Davis, California 95616, United States
S
* Supporting Information
ABSTRACT: Reaction of the diarylgermylene Ge(ArMe
)
2
[ArMe = C6H3-2,6-
6
6
(C6H2-2,4,6-(CH3)3)2] with various inorganic acids (HCN, HN3, and HBF4) led to
the facile oxidation of the germanium atom to yield the corresponding Ge(IV)
products (ArMe )2Ge(H)X (X = CN (1), N3 (2), F (3)). The cationic germanium−
6
water complex [(ArMe )2GeH(OH2)][SO3CF3] (4) was prepared by treating
6
Ge(ArMe )2 with triflic acid in the presence of trace amounts of moisture. The
6
reactions provide an efficient method of installing a variety of functional groups at a germanium atom and can be used in the
preparation of germanium complexes that are analogous to lighter carbon species. The tin species Sn(ArMe )2 was also oxidized to
6
the Sn(IV) analogue of 3. In all reactions, no evidence of arene elimination was observed, which was in contrast to the reaction of
Me6
the stannylene (or bulkier germylenes) with hydrogen or ammonia, which yielded H(ArMe ), [(Ar )Sn(μ-H)]2, and
6
[(ArMe )Sn(μ-NH2)]2.
6
(bulkier germanium diaryls can also afford arene elimination).20
INTRODUCTION
■
Herein, we describe our further explorations into the insertion
chemistry of germylenes and stannylenes by treating them with
various Brønsted acids.
The reaction chemistry of carbenes,1,2 electron-rich olefins
(EROs),3 and their heavier group 14 element analogues4 is of
major current interest in main group chemistry. Their ability to
replicate the reactivity found in transition metal complexes or
to mirror common reactions in traditional synthetic organic
chemistry is one of the major themes of that work.5 In addition,
the synthesis of heavier group 14 element analogues of
alkenes,6 alkynes,7−10 and other analogues of their lighter
carbon congeners has been explored to compare their reactivity
with the corresponding carbon species.11 A primary focus of the
reactivity studies of the low-valent group 14 species is the
oxidative addition chemistry of these main group complexes
with small molecules and unsaturated organic substrates, e.g.,
H2,12−16 NH3,16−20 P4,21−24 and C2H4.25−27
The reaction of Ge(ArMe )2 with the inorganic acids HN3,
6
HCN, HBF4, and H(SO3CF3) affords oxidized products in
which germanium has been inserted into an E−H bond. The
28a
reaction of Ge(ArMe )2 with HN3 (pKa = 4.69) and HCN
6
(pKa = 9.21)28b led to the formation of the corresponding
29
insertion products, (ArMe )2Ge(H)X (X = CN (1), N3 (2)).
6
The diarylgermylene was very resistant to arene elimination, as
demonstrated by the reaction with HBF4 (pKa = −0.44),30
which yields the Ge(IV) product (ArMe )2Ge(H)F (3) with BF3
6
elimination. The reaction with H(SO3CF3) (pKa = −14.1)31
oxidizes the germanium atom, but the triflate anion does not
coordinate to the metal. However, the cationic germanium
atom becomes complexed to an adventitious molecule of water
Recently, we have shown that when treated with NH3 (pKa =
10.5), diarylgermylenes and -stannylenes E(ArMe )2 or E(Ar
)
=
iPr4
to form [(ArMe )2GeH(OH2)](SO3CF3) (4). Unexpectedly,
6
6
2
[E = Ge, Sn; ArMe = C6H3-2,6-(C6H2-2,4,6-(CH3)3)2; AriPr
Sn(ArMe )2 does not undergo arene elimination upon treatment
6
4
6
C6H3-2,6-(C6H3-2,6-Pri2)2] undergo insertion into the N−H
bond to form Ge(IV) amido hydrides or result in arene
elimination to yield aryl Sn(II) amide dimers (Scheme 1)
with HBF4 and instead forms the Sn(IV) species (ArMe )2Sn-
6
(H)F (5), analogous to 3.
EXPERIMENTAL SECTION
■
Scheme 1. Reactivity of Diarylgermylenes or -stannylenes
with Ammonia
General Experimental Procedures. Standard Schlenk techniques
were used for all syntheses, and all manipulations were carried out
under anaerobic and anhydrous conditions. All solvents were dried
over NaK prior to use. Ge(ArMe
) was synthesized by published
6
2
methods.32 Trimethylsilyl cyanide (Aldrich, 98%), azidotrimethylsilane
Received: November 21, 2012
© XXXX American Chemical Society
A
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Scheme 2. Reactivity of Ge(ArMe )2 with HCN, HN3, HBF4, and H(SO3CF3)
Article
6
(Aldrich, 95%), and tetrafluoroboric acid diethyl ether complex
(Aldrich) were used as received. Trifluoromethanesulfonic acid
(Aldrich, >99%) was received in a glass ampule and was opened just
prior to use. Methanol was vacuum distilled from magnesium metal
and degassed (freeze, pump, thaw) prior to use. Melting points were
measured in glass capillaries sealed under N2 by using a Mel-Temp II
g). 1H NMR (400 MHz, C6D6): δ 1.86 (24H, d, JHH = 11.3 Hz, o-Me),
2.25 (12H, s, p-Me), 6.21 (1H, d, JHF = 41.0 Hz, Ge−H), 6.66 (4H, d,
JHH = 7.6 Hz, m-C6H3), 6.83 (8H, d, JHH = 9.8 Hz, m-Mes), 6.97 (2H,
t, JHH = 7.6 Hz, p-C6H3). 13C NMR (400 MHz, C6D6, 25 °C): δ 21.7
(p-Me), 22.2 (o-Me), 128.7, 129.0, 130.5, 130.8, 136.7, 137.0, 137.6,
140.6 (Ar). 19F NMR (300 MHz, C6D6, 25 °C): δ −186.5 (d, JHF = 45
Hz). IR (ATR, cm−1): ν(2146) (br, Ge−H).
1
apparatus and are uncorrected. H and 13C NMR spectroscopy were
[(ArMe )2GeH(OH2)](SO3CF3)(HSO3CF3) (4). HSO3CF3 (0.17 g, 1.1
6
carried out on a Varian 400 MHz spectrometer and referenced to
residual solvent peaks. 19F NMR spectroscopy was carried out on a
Varian 300 MHz spectrometer and referenced to known standards.
FT-IR spectroscopy was carried out on a Bruker Tensor 27 FT-IR
spectrometer using attenuated total reflectance.
mmol) was added to a stirred solution of Ge(ArMe )2 (0.35 g, 0.5
6
mmol) in toluene (ca. 20 mL) at ca. 0 °C, and the color of the solution
immediately became pale yellow. The mixture was allowed to stir for
ca. 1 h, and the volume of the solution was reduced to ca. 5 mL.
Hexane (ca. 5 mL) was added to the flask, and the mixture was slowly
cooled to ca. −20 °C overnight to afford 4 as colorless blocks suitable
for single-crystal X-ray diffraction. Yield: 83% (0.42 g). 1H NMR (400
MHz, C6D6): δ 1.74 (24H, d, JHH = 10.8 Hz, o-Me), 2.25 (12H, s, p-
Me), 6.49 (4H, d, JHH = 7.6 Hz, m-C6H3), 6.75 (4H, s, m-Mes), 6.79
(1H, s, Ge−H), 6.84 (4H, s, m-Mes) 6.90 (2H, t, JHH = 7.6 Hz, p-
C6H3). 13C NMR (400 MHz, C6D6, 25 °C): δ 21.6 (p-Me), 21.9 (o-
Me), 22.1 (o-Me), 129.7, 130.0, 131.4, 132.3, 134.3, 137.2, 137.4,
138.4, 139.0 (Ar). 19F NMR (300 MHz, C6D6, 25 °C): δ −78.38. IR
(ATR, cm−1): ν(2143) (br, Ge−H), ν(3334) (br, HOSO2CF3).
Synthesis of 1−5. (ArMe )2Ge(H)CN (1). An ethereal solution of
6
hydrogen cyanide was prepared by adding methanol (0.16 g, 0.5
mmol) to a solution of (Me3Si)CN (0.10 g, 1.0 mmol) in diethyl ether
(15 mL). The colorless solution was allowed to stir for 30 min, after
which it was added to a stirred solution of Ge(ArMe )2 (0.35 g, 0.5
6
mmol) in toluene (20 mL) at room temperature. The mixture was
stirred overnight, and the purple solution became colorless. All volatile
materials were removed under reduced pressure, and the resulting
white solid was washed with a small amount of pentane (10 mL) and
dried under reduced pressure. FT-IR and 1H and 13C NMR
(ArMe )2Sn(H)F (5). In a manner similar to the synthesis of 3,
6
spectroscopy confirmed the presence of 1, which we have previously
t
reported via the rearrangement of (ArMe )2Ge(CNBu ) to give 1 with
HBF4(OEt2) (0.16 g, 1.0 mmol) was added to a stirred solution of
6
isobutene elimination. Yield: 95% (0.34 g). Mp: 185−190 °C. 1H
NMR (400 MHz, C6D6, 25 °C): δ 1.84 (12H, s, o-Me), 1.87 (12H, s,
o-Me), 2.22 (12H, s, p-Me), 5.42 (1H, s, Ge−H), 6.62 (4H, d, m-
C6H3), 6.78 (4H, s, m-Mes), 6.81 (4H, s, m-Mes), 6.91 (2H, t, p-
C6H3). 13C NMR (400 MHz, C6D6, 25 °C): δ 21.4 (p-Me), 21.9 (o-
Me), 129.4, 131.1, 136.7, 137.1, 139.3 (Ar) 148.7 (CN). IR (ATR,
cm−1): ν(Ge−H) 2117 (br), ν(C−N) 2177 (w).
Sn(ArMe )2 (0.38 g, 0.5 mmol) in toluene (20 mL) at 0 °C. The ice
6
bath was removed after the addition, and the mixture warmed to room
temperature. The solution was allowed to stir for 2 h, and the intense
purple color of the solution faded to colorless. All volatile materials
were removed under reduced pressure, and the colorless powder was
washed with a small amount of hexane (10 mL) and dried under
reduced pressure to afford 5 as a white powder. Yield: 40% (0.15 g).
1H NMR (400 MHz, C6D6): δ 1.87 (12H, s, o-Me), 1.93 (12H, s, o-
(ArMe )2Ge(H)N3 (2). An ethereal solution of hydrazoic acid was
6
prepared by adding methanol (0.16 g, 0.5 mmol) to a solution of
(Me3Si)N3 (0.08 g, 0.7 mmol) in diethyl ether (15 mL). The colorless
solution was allowed to stir for 5 min, after which it was added to a
Me), 2.23 (12H, s, p-Me), 6.72 (4H, d, JHH = 7.5 Hz, m-C6H3), 6.84
(8H, d, JHH = 9.7 Hz, m-Mes), 7.01 (2H, t, JHH = 7.3 Hz, p-C6H3), 7.64
(1H, JHF = 39.7 Hz, Sn−H). 13C NMR (400 MHz, C6D6, 25 °C): δ
21.7 (p-Me), 22.0 (o-Me), 22.2 (o-Me), 128.8, 129.1, 129.6, 130.8,
136.9, 137.4, 137.7, 140.9 (Ar). 19F NMR (282.23 MHz, C6D6, 25
°C): δ −207.3 (m, JHF = 39.5 Hz, JFSn = 1140 Hz). 119Sn NMR
(223.63 MHz, C6D6): δ −121.9. IR (ATR, cm−1): ν(1880) (m, Sn−
H).
X-ray Crystallographic Data and Collection Parameters for
2, 3, and 4. All crystallographic calculations were performed on a
personal computer with a Pentium 3.20 GHz processor and 4 GB of
extended memory. Data were collected based upon a single
component, processed with SAINT,34 and corrected for Lorentz and
polarization effects and absorption using Blessing’s method as
incorporated into the program SADABS.35,36
The structures were determined by direct methods using the
program XS.37 Refinement of the structure was achieved using the
program XL.37 All of the non-hydrogen atoms were located initially or
from one difference-Fourier map least-squares cycle, and convergence
proceeded quickly with all of the hydrogen atoms located from a
subsequent difference-Fourier map. Crystals of 2−4 suitable for single-
crystal X-ray diffractometry were removed from a Schlenk flask under a
stream of N2 and immediately covered with a layer of hydrocarbon oil.
A single crystal was selected, attached to a glass fiber on a copper pin,
and placed in the cold N2 stream of the diffractometer. Crystallo-
stirred solution of Ge(ArMe )2 (0.35 g, 0.5 mmol) in toluene (20 mL)
6
at room temperature. The mixture was stirred overnight, and the
purple solution became colorless. All volatile materials were removed
under reduced pressure, the resulting white solid was washed with a
small amount of pentane (10 mL), and the powder was taken up in
hot hexane (20 mL). Slow cooling of the solution to ca. 6 °C overnight
resulted in colorless blocks of 2 suitable for single-crystal X-ray
1
diffraction. Yield: 79% (0.29 g). Mp: 177−183 °C (red oil). H NMR
(400 MHz, C6D6): δ 1.86 (24H, d, JHH = 5.9 Hz, o-Me), 2.24 (12H, s,
p-Me), 5.86 (1H, s, Ge−H), 6.63 (4H, d, JHH = 7.6 Hz, m-C6H3), 6.84
(4H, s, m-Mes), 6.86 (4H, s, m-Mes), 6.95 (2H, t, JHH = 7.6 Hz, p-
C6H3). 13C NMR (400 MHz, C6D6, 25 °C): δ 21.6 (p-Me), 22.2 (o-
Me) 22.6 (o-Me), 106.6, 129.2, 130.9, 136.7, 137.2, 137.5, 140.5 (Ar).
IR (ATR, cm−1): ν(NNN) 2104 (s), 2078 (m).
(ArMe )2Ge(H)F (3). HBF4(OEt2) (0.16 g, 1.0 mmol) was added to a
6
stirred solution of Ge(ArMe )2 (0.35 g, 0.5 mmol) in toluene (20 mL)
6
at 0 °C. The mixture was allowed to warm to room temperature
overnight, and the purple solution became colorless. All volatile
materials were removed under reduced pressure, and the colorless oil
was washed with a small amount of pentane (5 mL) to afford a white
powder. Slow cooling (ca. −20 °C) of a 1:1 toluene/diethyl ether
solution (ca. 15 mL) afforded colorless needles of 3. Yield: 96% (0.34
B
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graphic information for complex 1 was previously reported. See below
for more details.
RESULTS AND DISCUSSION
■
Complex 1 was prepared at room temperature by treating the
free germylene Ge(ArMe )2 with hydrogen cyanide. This highly
6
toxic reagent (Caution) was prepared in situ by treating an
excess of Me3SiCN with methanol in diethyl ether. The
ethereal HCN solution was then added to a stirred solution of
Ge(ArMe )2 at ca. 0 °C in toluene. The reaction mixture was
6
allowed to warm to room temperature overnight, after which
time the volatile materials were removed under reduced
pressure. The resulting colorless powder was washed with a
small amount of pentane (ca. 5 mL) and was redissolved in a
1:2 mixture of toluene and pentane to afford colorless crystals
upon overnight storage at ca. −20 °C. As we showed recently,
compound 1 can also be obtained by a different route involving
the thermolysis of a germanium isocyanide adduct,
37
Figure 1. Thermal ellipsoid (30%) drawing of 2. Carbon-bound
hydrogen atoms are not shown for clarity. Selected bond lengths (Å)
and angles (deg): Ge(1)−N(1) 1.909(4), Ge(1)−C(1) 2.031(3),
Ge(1)−H(1) 1.51(1), N(1)−N(2) 1.231(6), N(2)−N(3) 1.200(5)
C(1A)−Ge(1)−C(1) 116.0(1), C(1)−Ge(1)−N(1) 110.6(2),
Ge(1)−N(1)−N(2) 117.3(4), N(1)−N(2)−N(3) 177.0(5).
t
(ArMe )2GeCNBu , which eliminates isobutene to form 1.
6
Similar to the synthesis of 1, the germanium(IV) hydride/
azide complex 2 was formed by adding an ethereal solution of
freshly prepared hydrazoic acid to a stirred solution of
Ge(ArMe )2 in toluene at ca. 0 °C. The characteristic deep
6
purple color of the germylene faded overnight, after which time
all the volatile materials were removed under reduced pressure.
The colorless oil was washed with a small amount of pentane
(ca. 5 mL) to afford a colorless powder, which was taken up in
hot hexane and allowed to slowly cool to ca. 6 °C overnight to
afford colorless blocks of 2 in high yield (90%). The use of
hydrazoic acid as a reagent in synthetic inorganic chemistry is
solution of HBF4 at 0 °C in toluene led to immediate bleaching
of the purple color. Removal of all the volatile materials under
reduced pressure produced a colorless powder, which upon
dissolving in a 1:1 ether/toluene mixture (ca. 10 mL) and
storage overnight at ca. −18 °C led to the crystalline formation
of 3 in nearly quantitative yield.
Complex 3 is the first structurally characterized germanium
hydride/fluoride complex and possesses the same distorted
tetragonal geometry as in 1 and 2. It crystallized in the
orthorhombic Fdd2 space group with the fluorine atom
disordered between two positions. The Ge(1)−H(1) and
Ge(1)−F(1) distances are 1.46(1) and 1.629(3) Å, respectively,
and the C(1)−Ge(1)−C(25) angle is 132.0(1)°. The 1H NMR
rare. Moran and Gayoso reported the oxidative addition
́
reactions of dicyclopentadienylvanadium and -chromium with
an excess of HN3 almost three decades ago,38 and, more
recently, Weidenbruch and co-workers found that hydrazoic
acid cleanly adds across the Ge−Ge double bond of
tetrakis(2,4,6-triisopropylphenyl)digermene to produce the
corresponding asymmetric digermane.39 Complex 2 crystallized
in the centrosymmetric, monoclinic space group C2/c with the
azide group disordered over two positions.
The structure of 2 (Figure 1) displays a four-coordinate
germanium atom with distorted tetrahedral geometry, with a
C(1)−Ge(1)−C(25) angle near 116°. The Ge(1)−N(1)
distance of 1.909(4) Å is similar to other reported examples
of Ge(IV) azides (cf. 1.895(9) Å for Mes3GeN3)40 and shorter
than the 2.264(2) Å for the Ge(II) azide HB(3,5-Me2pz)-
GeN3.41 The N(1)−N(2) and N(2)−N(3) bonds are nearly
equal (1.231(6) and 1.201(5) Å, respectively), but the small
difference in N−N bond length has been noted in both
germanium40 and silicon(IV) azides.42 West and co-workers
noted that the bonding in these complexes more closely
resembled ionic azides, which could be rationalized on the basis
of the high degree of polarity of the Ge−N bond.42 The
Ge(1)−N(1)−N(2) bond angle of 117.3(4)° is similar to the
angle reported for Mes3GeN3 (119.0°).34 The germanium
hydride was freely refined from the X-ray data (Ge(1)−H(1) =
1
1.51(2) Å), and its presence was further confirmed in the H
NMR spectrum (5.86 ppm). In the infrared spectrum, the Ge−
H stretching band is masked by the intense azide stretching
band in the same region; there is an intense stretching band at
2104 cm−1 with a small shoulder at 2078 cm−1.
Figure 2. Thermal ellipsoid (30%) drawing of 3. Carbon-bound
hydrogen atoms are not shown for clarity. Selected bond lengths (Å)
and angles (deg): Ge(1)−C(1) 1.966(2), Ge(1)−H(1) 1.46(1),
Ge(1)−F(1) 1.629(3), C(1)−Ge(1)−F(1) 110.7(1), C(1)−Ge(1)−
H(1) 111(2).
Significantly increasing the acidity of the reactant does not
appear to increase the likelihood of arene elimination by
Ge(ArMe )2. Treatment of the germylene with an ethereal
6
C
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spectrum of 3 showed the germanium hydride signal is shifted
significantly downfield (6.21 ppm) in comparison to those of 1
or 2 (cf. 5.42 and 5.86 ppm, respectively) due to the increased
effective positive charge on the germanium atom, which leads
to a decrease in shielding at the hydride. The Ge−H signal
displays coupling to fluorine and is observed as a doublet with
JHF = 40.9 Hz, a value that is comparable to the JHF = 53.3 Hz
observed for Mes2Si(H)F.42 Ethereal solutions of tetrafluor-
oboric acid have recently gained interest as effective
nucleophilic fluorinating reagents in organic synthesis.43
Germanium and silicon(IV)−aryl bonds have been shown to
be cleaved by hydrohalic acids;44−46 their low-valent counter-
parts prefer oxidative reaction pathways.47 However, these
reactions tend to be dependent upon the nature of the
connectivity between the tetrel and the aryl ligand. Tokitoh and
co-workers have similarly shown that a base-stabilized silylene
can oxidatively add hydrochloric acid.48 Conversely, Jutzi and
co-workers have shown that π-bound cyclopentadienyl ligands
can be readily protonated by ethereal solutions of HBF4.49 Our
Figure 3. Thermal ellipsoid (30%) drawing of 4. Methyl groups on
flaking mesityl rings, carbon-bound hydrogen atoms, and cocrystallized
molecule of triflic acid not shown for clarity.47 Selected bond lengths
(Å) and angles (deg): Ge(1)−C(1) 1.966(3), Ge(1)−C(25) 1.950(3),
Ge(1)−H(1) 1.30(4), Ge(1)−O(1) 1.911(2) H(1B)---O(51) 1.73(1),
O(1)---O(51) 2.570(3), C(1)−Ge(1)−C(25) 136.7(1), C(1)−
Ge(1)−O(1) 104.9(1), C(25)−Ge(1)−O(1) 90.7(1).
objective for the reaction of Ge(ArMe )2 and HBF4 was the
6
isolation of a cationic germanium complex with a hydride
+
−
bound to the germanium, [(ArMe )2GeH] [BF4] . We believe
that the initial step of this reaction involves the protonation of
the germanium to form the intended complex; however, the
increased electrophilicity induced at the cationic germanium
6
−
atom is sufficient to abstract a fluoride from the BF4 anion.
This phenomenon has also been reported during attempts of
forming analogous cationic silicon complexes.45,50 Although the
tetrafluoroborate anion is considered to be a less coordinating
anion than triflate, we postulated that both its increased size
and decreased lability might make it a more suitable
counteranion for the preparation of a cationic germanium
species.51
of the coordinated water molecule were freely refined from the
X-ray data, and the Ge(1)−O(1) distance was measured to be
1.911(2) Å. A second molecule of triflic acid was cocrystallized
with 4; however, it can be removed by repeated trituration of
toluene at room temperature.55 The proton H(55) located
from the X-ray data is bound to O(55) in the second molecule
of triflate and is hydrogen bound to O(52) of the same triflate
anion, which is coordinated to the water molecule (H(55)--
O(52) = 1.66 Å).
When treated with a slight excess of triflic acid at ca. 0 °C,
the purple toluene solution of Ge(ArMe )2 immediately became
6
colorless. This solution was concentrated, and a small portion
of hexane was added to facilitate crystallization. The water-
complexed, cationic germanium species, 4, was structurally
Due to its facile loss of an arene ligand for the reactions with
hydrogen or ammonia,20 we expected to see arene elimination
1
upon treatment of the diarylstannylene Sn(ArMe )2 with HBF4.
6
characterized by single-crystal X-ray diffractometry, and H
NMR spectra of both the crystalline material and bulk solid
confirmed it to be the only major product obtained. Complex 4
(Figure 3)52 possesses a distorted tetrahedral geometry at the
germanium atom and is related to the cationic bis(8-
methoxynapthyl)hydridogermanium complex isolated by Riv-
However, spectroscopic study of the reaction products shows
that the Sn(IV) species 5 is the only major product from the
1
reaction. The tin hydride signal in the H NMR spectrum is
shifted significantly downfield (7.64 ppm), and JHF = 39.7 Hz,
almost identical to that of 3. Additionally, the Sn−H stretching
band in the IR spectrum was located at 1880 cm−1. The 119Sn
NMR signal was found at −207 ppm, providing further support
for a Sn(IV) species. The divergence of reactivity for the
stannylene in comparison to the results obtained for the
reaction with hydrogen or ammonia can be easily rationalized
by differing reaction pathways (Scheme 3).
̀
iere and co-workers, [(8-OMe-C10H6)2GeH(OH2)](SO3CF3)
(5), which was obtained as a dimeric species in which the two
germanium hydride water-complexed centers are bridged by
triflate ions that interact, through two oxygens, with the
complexed waters.53
The Ge(1)−C(Ar) distances of 1.965(3) and 1.950(3) Å in
4 are in good agreement with those of complexes 1−3.
Nevertheless, the C(1)−Ge(1)−C(25) angle is very wide
(136.7(1)°) and is increased in comparison to the other four-
coordinate germanium products (124.9(1)°, 115.9(2)°, and
132.0(1)° for 1−3, respectively). The C−Ge−C angle in
[CH3GeHCH3]+ was predicted by ab initio studies to be
126.4°,54 and the increased angle for 4 is presumably due to the
increased steric bulk provided by the m-terphenyl ligands. The
germanium hydrogen, H(1), was freely refined from the X-ray
We reported that the initial intermediate for the reaction of
Sn(ArMe )2 with ammonia was the formation of a Lewis adduct
6
species with a high degree of electron density located on the
metal atom. The resulting effective negative charge, coupled
with the enhanced stability of the Sn lone pair, is sufficient to
cleave the Sn−C bond to form the dimeric amido speces.
Conversely, we believe the initial intermediate for the reactions
of the germylenes and stannylenes with the acids mentioned
here is the formal oxidation of the metal by protonation. This is
followed by subsequent attack by the conjugate base. The
pseudocationic intermediate in the preparation of 5 prevents
the loss of the arene, and the Sn(IV) species is the main
product in the reaction.
1
data. Its H NMR signal was shifted significantly downfield to
6.79 ppm, almost 0.6 ppm further downfield than that observed
for the germanium hydride in 3, and the Ge(1)−H(1) distance
is contracted to 1.30(4) Å in comparison to 1−3. Both protons
D
dx.doi.org/10.1021/om301121x | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Scheme 3. Comparison of the Reactivity of Sn(ArMe )2 with HBF4 and NH3
Article
6
(12) Spikes, G. H.; Fettinger, J. C.; Power, P. P. J. Am. Chem. Soc.
2005, 127, 12232−12233.
CONCLUSION
■
In conclusion, and in contrast to previous reactions with H2 and
(13) Welch, G. C.; San Juan, R. R.; Masuda, J. D.; Stephan, D. W.
Science 2006, 314, 1124−1126.
NH3, both Ge(ArMe )2 and Sn(Ar )2 are resistant to arene
Me6
6
elimination upon treatment with a variety of inorganic acids
and instead form the oxidized products 1−5. These reactions
are initiated by the oxidative protonation of the metal, followed
by facile nucleophilic attack by the conjugate base. These high-
yield reactions provide an efficient method of installing a variety
of functional groups at a germanium or tin center and could be
utilized in the preparation of heavy group 14 complexes that are
analogous to the lighter carbon species. Further explorations
into the insertion capabilities of the tetrelenes, as well as
subsequent reactivity studies of the reported products, are
under way and will be reported in future publications.
(14) Geier, S. J.; Gilbert, T. M.; Stephan, D. W. J. Am. Chem. Soc.
2008, 130, 12632−12633.
(15) Ullrich, M.; Lough, A. J.; Stephan, D. W. J. Am. Chem. Soc. 2009,
131, 52−53.
(16) Frey, G. D.; Lavallo, V.; Donnadieu, B.; Schoeller, W. W.;
Bertrand, G. Science 2007, 316, 439−441.
(17) Jana, A.; Schulzke, C.; Roesky, H. W. J. Am. Chem. Soc. 2009,
131, 4600−4601.
(18) Xiong, Y.; Yao, S.; Muller, R.; Kaupp, M.; Driess, M. J. Am.
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(19) Zhu, Z. L.; Wang, X. P.; Peng, Y.; Lei, H.; Fettinger, J. C.;
Power, P. P. Angew. Chem., Int. Ed. 2009, 48, 2031−2034.
(20) Peng, Y.; Guo, J. D.; Ellis, B. D.; Zhu, Z. L.; Fettinger, J. C.;
Power, P. P. J. Am. Chem. Soc. 2009, 131, 16272−16282.
(21) Khan, S.; Michel, R.; Sen, S. S.; Roesky, H. W.; Stalke, D. Angew.
Chem., Int. Ed. 2011, 50, 11786−11789.
ASSOCIATED CONTENT
■
S
* Supporting Information
NMR spectra for 2−5 and X-ray crystallographic data in CIF
format for 3−5. This material is available free of charge via the
Internet at http://pubs.acs.org.
(22) Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G. J.
Am. Chem. Soc. 2007, 129, 14180−14181.
(23) Masuda, J. D.; Schoeller, W. W.; Donnadieu, B.; Bertrand, G.
Angew. Chem., Int. Ed. 2007, 46, 7052−7055.
AUTHOR INFORMATION
(24) Xiong, Y.; Yao, S.; Brym, M.; Driess, M. Angew. Chem., Int. Ed.
2007, 46, 4511−4513.
■
Notes
(25) Caputo, C. A.; Zhu, Z. L.; Brown, Z. D.; Fettinger, J. C.; Power,
P. P. Chem. Commun. 2011, 47, 7506−7508.
The authors declare no competing financial interest.
(26) Peng, Y.; Ellis, B. D.; Wang, X. P.; Fettinger, J. C.; Power, P. P.
Science 2009, 325, 1668−1670.
ACKNOWLEDGMENTS
■
We thank the U.S. Department of Energy (DE-FG02-
07ER46475) for support of this work.
(27) McCahill, J. S. J.; Welch, G. C.; Stephan, D. W. Angew. Chem.,
Int. Ed. 2007, 46, 4968−4971.
(28) (a) Breton, G. W.; Kropp, P. J. e-Encyclopedia of Reagents for
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(b) Romeder, G. e-Encyclopedia of Reagents for Organic Synthesis;
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(29) Although the pKa values quoted are for aqueous solutions, the
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solvent is not as effective at supporting the charges that develop upon
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(30) Friestand, G. K.; Branchaud, B. P. e-Encyclopedia of Reagents for
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(31) Subramanian, L. R.; Martinex, A. G.; Hanack, M. e-Encyclopedia
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(32) Simons, R. S.; Pu, L. H.; Olmstead, M. M.; Power, P. P.
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(34) SMART (Version 5.054) and SAINT (Version 7.46a); Bruker
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1
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1
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F
dx.doi.org/10.1021/om301121x | Organometallics XXXX, XXX, XXX−XXX