Reactions of m-Terphenyl-Stabilized Germylene and Stannylene with Water and Methanol: Oxidative Addition versus Arene Elimination and Different Reaction Pathways for Alkyl- and Aryl-Substituted Species

Article abstract of DOI:10.1021/acs.organomet.5b00884

Reactions of the divalent germylene Ge(Ar^Me₆)₂ (Ar^Me₆ = C₆H₃-2,6-{C₆H₂-2,4,6-(CH₃)₃}₂) with water or methanol gave the Ge(I

Full text of DOI:10.1021/acs.organomet.5b00884

Article
pubs.acs.org/Organometallics
Reactions of m‑Terphenyl-Stabilized Germylene and Stannylene with
Water and Methanol: Oxidative Addition versus Arene Elimination
and Different Reaction Pathways for Alkyl- and Aryl-Substituted
Species
Jeremy D. Erickson,† Petra Vasko,‡ Ryan D. Riparetti,† James C. Fettinger,† Heikki M. Tuononen,*,‡
and Philip P. Power*,†
†Department of Chemistry, University of California, One Shields Avenue, Davis, California 95616, United States
‡Department of Chemistry, Nanoscience Center, University of Jyvaskyla, P.O. Box 35, FI-40014 Jyvaskyla, Finland
̈
̈
̈
̈
S
* Supporting Information
ABSTRACT: Reactions of the divalent germylene Ge(ArMe
)
2
6
(ArMe = C6H3-2,6-{C6H2-2,4,6-(CH3)3}2) with water or
6
methanol gave the Ge(IV) insertion product (ArMe )2Ge(H)-
6
OH (1) or (ArMe )2Ge(H)OMe (2), respectively. In contrast,
6
its stannylene congener Sn(ArMe
) reacted with water or
2
6
6
methanol to produce the Sn(II) species {ArMe Sn(μ-OH)}2
(3) or {ArMe Sn(μ-OMe)}2 (4), respectively, with elimination
6
of ArMe H. Compounds 1−4 were characterized by IR and
6
NMR spectroscopy as well as by X-ray crystallography. Density
functional theory calculations yielded mechanistic insight into
Me6
the formation of (ArMe )2Ge(H)OH and {Ar Sn(μ-OH)}2. The insertion of an m-terphenyl-stabilized germylene into the O−H
bond was found to be catalytic, aided by a second molecule of water. The lowest energy pathway for the elimination of arene
from the corresponding stannylene involved sigma-bond metathesis rather than separate oxidative addition and reductive
6
elimination steps. The reactivity of Sn(ArMe )2 with water or methanol contrasts with that of Sn{(CH(SiMe3)2}2, which affords
6
the Sn(IV) insertion products {(Me3Si)2CH}2Sn(H)OH and {(Me3Si)2CH}2Sn(H)OMe. The differences were tentatively
ascribed to the Lewis basicity of the employed solvent (Et2O vs THF) and the use of molar vs millimolar concentrations of the
substrate.
16
SO3CF3 , and BF4 ), and AlMe3 and GaMe3.17 A logical
−
−
INTRODUCTION
■
extension of this chemistry is the investigation of the reactions
Stable divalent group 14 carbene analogues (tetrylenes) have
attracted much interest over the last four decades.1 Some of the
more recent advances in this area include the synthesis of two-
coordinate acyclic silylenes,2 the donor−acceptor stabilization
of heavy group 14 hydrides GeH2 and SnH2,3 and the
characterization of two-coordinate 1,2-bis-metallylenes,4 heavier
analogues of 1,2-dicarbenes. The interest in stable tetrylenes is
in part due to their facile and in some cases reversible reactivity
with fundamentally important small molecules such as CO,5
of E(ArMe
) with hydroxyl compounds and of water and
6
2
methanol in particular. Although the insertion of transient
tetrylenes such as EH2, EMe2, or EPh2 (E = Si, Ge, or Sn) into
O−H bonds has been studied both experimentally and
theoretically,18 there are only a few examples of similar
reactions involving stable acyclic tetrylenes that yield
structurally characterized products. Most notably, Lappert et
al. have reported the crystallographic characterization of
{(Me3Si)2CH}2Ge(H)OEt from the reaction of Ge{CH-
H2,2a,4,6 NH3,6a,7 and C2H4 under mild conditions. Of
8
(SiMe3)2}2 with ethanol,19 while Porschke et al. obtained
̈
particular significance have been insertion reactions of which
topical examples include the insertion of a silylene into a P−P
bond of P4,9 the insertion of a cationic metallogermylene into
X−H bonds (X = H, B, or Si),10 and the insertion of a boryl-
substituted stannylene into the CC bond in alkynes.11
In recent years, we have carried out detailed investigations of
the reactivity of m-terphenyl-stabilized heavier tetrylenes with
{(Me3Si)2CH}2Sn(H)OH by reacting Sn{CH(SiMe3)2}2 with
excess water.20 A related species, {L(H)2GeGe(H)(OH)L}·
(OEt2) (L = C6H2-4-Me-2,6-{C(H)Ph2}2), was recently
described by Jones et al. as a minor side product from the
reaction of LGeGeL with H2 in the presence of adventitious
moisture.4 In addition, insertion reactions of Ge{CH(SiMe3)2}2
into the O−H bond of the enolic forms of several ketones have
small molecules.12 In this context, we have reported the
reactions of E(ArMe )2 (E = Ge, Sn; Ar = C6H3-2,6-{C6H2-
Me6
6
2,4,6-(CH3)3}2)13 with H2,6 NH3,6a CO,5 isocyanides,14
Received: October 20, 2015
hydrazines,15 inorganic acids HX (X = CN−, N3 , F−,
−
© XXXX American Chemical Society
A
DOI: 10.1021/acs.organomet.5b00884
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Organometallics
Article
been reported, although none of the products have been
structurally characterized.21
We now describe the reaction of E(ArMe )2 (E = Ge, Sn) with
6
water or methanol, which gives the insertion products
(ArMe )2Ge(H)OR (1, R = H; 2, R = Me) or the dimers
6
{ArMe Sn(μ-OR)}2 (3, R = H; 4, R = Me) depending on the
6
group 14 element E (Scheme 1). The products 1−4 were
Scheme 1. Reaction of E(ArMe )2 (E = Ge, Sn) with Water or
6
Methanol to Form 1−4
Figure 1. Thermal ellipsoid plot (30% probability) of 1. Structural
disorder and carbon-bound hydrogen atoms are not shown for clarity.
characterized by spectroscopic methods and single-crystal X-ray
crystallography. The observed reactivity is similar to that seen
for E(ArMe )2 with NH36a and alkyl-amino tetrylenes [LEEt] (L
6
22
i
= N(C6H2-4-SiiPr3-2,6-{C(H)Ph2}2 Pr)) with protic reagents,
but differs from that of E(ArMe )2 with HBF4, which resulted in
6
the formation of the insertion product (ArMe )2E(H)F
6
irrespective of the element E.15 To shed light on the
mechanistic details of the observed transformations, the
reactions of stable germylenes and stannylenes with water
were also probed computationally. The acquired experimental
and computational results were compared with those reported
for E{CH(SiMe3)2}2 as well as with the data available for
transient tetrylenes EMe2 and EPh2.
Figure 2. Thermal ellipsoid plot (30% probability) of 2. Structural
disorder and carbon-bound hydrogen atoms are not shown for clarity.
RESULTS AND DISCUSSION
■
The reaction of Ge(ArMe )2 with water or methanol resulted in
6
formal insertion of the germylene into the O−H bond to afford
The structure of 1 can be compared to that of the related
23
tetravalent (ArMe )2Ge(H)OH (1) or (Ar )2Ge(H)OMe (2),
dihydroxy species (ArMe )2Ge(OH)2, synthesized by us, and
Me6
6
6
respectively. In contrast, the reaction of Sn(ArMe )2 with water
to (Eind)2Ge(H)OH (Eind = 1,1,3,3,5,5,7,7-octaethyl-s-hydri-
dacen-4-yl) reported by Tamao, Matsuo, and co-workers
through the reaction of the germanone (Eind)2GeO with
6
or methanol gave the divalent dimers {ArMe Sn(μ-OH)}2 (3)
6
and{ArMe Sn(μ-OMe)}2 (4), respectively, with elimination of
6
ArMe H.
LiAlH4.24 The Ge−O bond lengths in (ArMe )2Ge(OH)2
6
6
Structures. Single-crystal X-ray diffraction studies revealed a
similar structural arrangement in 1 and 2 (Figures 1 and 2;
selected structural data are given in Table 1). Compound 1
crystallizes in the orthorhombic Fdd2 space group, while the
space group of the methoxy derivative 2 is monoclinic P21/c. In
1, the germanium atom and the hydrogen and hydroxide
groups bound to it are disordered over two sites each with 50%
occupancy. A similar distortion is seen in the structure of 2, in
which case the crystals were also found to contain cocrystallized
1 (18%) due to the presence of adventitious water in the
reaction mixture.
(1.782(3) and 1.803(3) Å) and in (Eind)2Ge(H)OH
(1.757(2) Å) are equal to that in 1 (within 3σ), but the
interligand C−Ge−C angles between organic substituents
(123.04(6)° and 122.5(3)°) are slightly narrower. The
interligand C−Ge−C angle in 1 is also wider than that in the
12
germylene precursor Ge(ArMe )2 (114.2(2)°). A comparison
6
of the structure of 2 to that of {(Me3Si)2CH}2Ge(H)OEt
shows their Ge−O bond lengths to be equal (1.797(5) Å in
{(Me3Si)2CH}2Ge(H)OEt).18 However, the C−Ge−C inter-
ligand angles are significantly different (114.5(3)° in
{(Me3Si)2CH}2Ge(H)OEt versus 136.33(7)° in 2), most likely
due to difference in the steric bulk of the ArMe and
6
In both 1 and 2, the germanium atom has distorted
tetrahedral coordination due to bonding to two terphenyl
ligands, an oxygen atom from the hydroxyl/methoxy group, and
a hydrogen atom. The germanium-bound hydrogen atom could
not be clearly identified from the electron density difference
map for either 1 or 2, but its presence in the structures was
(Me3Si)2CH groups.
Compounds 3 and 4 crystallize in monoclinic space groups
C2/m and P21/n, respectively. Their structures revealed a
dimeric arrangement with two SnArMe moieties bridged by two
6
hydroxide (3) or methoxide (4) groups (Figures 3 and 4;
selected structural data are given in Table 1). In contrast to
1
confirmed with IR and H NMR spectroscopies.
B
DOI: 10.1021/acs.organomet.5b00884
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Table 1. Selected Bond Lengths (Å) and Angles (deg) in Products 1−4
1
2
3
4
Ge1−O1
1.77(1)
Ge1−O1
C1−O1
C26−Ge1−O1
C2−Ge1−O1
Ge1−O1−C1
C26−Ge1−C2
1.797(2)
1.358(6)
98.81(8)
101.88(8)
123.9(3)
136.33(7)
Sn1−O1
2.1345(14)
Sn1−O1
C1−O1
Sn1−C2
C2−Sn1−O1
Sn1−O1−Sn1′
O1−Sn1−O1′
Sn1···Sn1′
2.168(1)
1.430(2)
2.256(2)
92.53(5)
107.67(5)
72.33(4)
3.4801(7)
C1−Ge1−O1
C1′−Ge1−O1
109.1(5)
101.7(5)
Sn1−C1
2.208(3)
C1−Sn1−O1
Sn1−O1−Sn1′
O1−Sn1−O1′
Sn1···Sn1′
92.69(7)
108.42(11)
71.58(11)
3.4627(5)
C1−Ge1−C1′
129.5(5)
1
Spectroscopy. The H NMR spectra of 1−4 display the
characteristic signals of the ArMe group with methyl and
6
aromatic proton resonances appearing from 1.8 to 2.3 ppm and
from 6.6 to 7.1 ppm, respectively (see Supporting Information).
The methoxy protons in 2 appear as a singlet at 2.74 ppm in
1
the H NMR spectrum, whereas the germanium-bound proton
in 1 and 2 shows a resonance at 6.06 and 6.05 ppm,
respectively. The Ge−OH proton chemical shift (0.47 ppm)
was confirmed by COSY NMR spectroscopy. It is further
upfield than that reported for the O−H proton in (Eind)2Ge-
(H)OH (5.21 ppm),24 possibly as a result of shielding by the
flanking rings. The Ge−H proton resonance was found to be a
doublet with a coupling constant to the O−H proton of 1.4 Hz,
confirming, albeit indirectly, the existence of the hydroxyl
proton in the structure. The presence of the O−H proton is
also supported by IR spectroscopy and the synthesis of the
deuterium analogue of 1, (ArMe )2Ge(D)OD (1′), via reaction
6
Figure 3. Thermal ellipsoid plot (30% probability) of 3. Carbon-
bound hydrogen atoms are not shown for clarity.
of Ge(ArMe )2 with D2O (see Supporting Information). IR
6
spectroscopy of 1′ showed the appearance of an O−D stretch
at 2660 cm−1, while the O−H stretch of 1 could be identified at
3600 cm−1.
Products 3 and 4 could not be readily separated from the
ArMe H byproduct to provide completely clean NMR spectra.
6
This is due to the low solubility of 3 and 4 and the relatively
high solubility of ArMe H to common solvents. Because of this,
6
the NMR spectra of 3 and 4 were deconvoluted through
comparison of the data to a spectrum of pure ArMe H (see
6
Supporting Information). The methoxy proton in 4 appears as
a singlet at 2.74 ppm in the 1H NMR spectrum, while the O−H
proton of 3 shows a resonance at 0.00 ppm. The latter
assignment could be confirmed via synthesis of {ArMe Sn(μ-
6
OD)}2 (3′), the deuterium analogue of 3 (see Supporting
Information). Even though the O−H stretch of 3 could not be
seen in the IR spectrum at the expected region (ca. 3500
cm−1),24 the O−D stretch of 3′ is clearly visible at 2620 cm−1.
While 1 and 2 are both colorless, products 3 and 4 are pale
yellow and absorb in the near-UV and violet region with λmax of
365 and 337 nm for 3 and 4 (see Supporting Information).
Discussion. The observation of the dimeric products 3 and
Figure 4. Thermal ellipsoid plot (30% probability) of 4. Hydrogen
atoms are not shown for clarity.
compounds 1 and 2, no structural disorder was observed for
25
either 3 or 4. However, crystals of the arene ArMe H, a side
6
4 parallels the reactivity of Sn(ArMe )2 with NH3.6a However, it
6
product in the synthesis of both 3 and 4, were obtained
together with 3 and 4 in all crystallizations.
differs from the results obtained by Porschke and co-workers,
̈
who found that the tin species Sn{CH(SiMe3)2}2 undergoes
simple insertion into both water and methanol,20 forming
{(Me3Si)2CH}2Sn(H)OH and {(Me3Si)2CH}2Sn(H)OMe,
respectively. The germanium congener Ge{C(H)(SiMe3)2}2 is
also known to form insertion products {(Me3Si)2CH}2Ge(H)R
(R = H, Me) analogous to 1 and 2.19 Hence, in order to
The structures of 3 and 4 are similar to comparable structural
parameters. Notable differences are observed only in the
orientation of the ArMe ligands in relation to the four-
6
membered Sn2O2 ring that is influenced by the steric
requirements of the bridging hydroxide/methoxide group. In
both 3 and 4, the coordination around tin atoms is trigonal
pyramidal with near 90° interligand C−Sn−O angles. We note
that the structure of 3 is very similar to that of the related dimer
understand the reactivity observed for E(ArMe )2 with water or
6
methanol, mechanistic investigations of possible reaction
pathways were conducted computationally using density
{AriPr Sn(μ-OH)}2 (AriPr = C6H3-2,6-{C6H2-2,4-[CH-
(CH3)2]2}2), which was synthesized previously by us via
reaction of a distannyne with TEMPO or pyridine-N-oxide.26
4
4
functional theory (DFT). The calculations were performed
Me4
for model compounds E(ArMe )2 (Ar = C6H3-2,6-{C6H3-2,6-
4
C
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Figure 5. Energy diagrams (ΔG, kJ mol−1) for the reactions of (ArMe )2E (E = Ge or Sn) with water leading to insertion into the O−H bond and
4
Me4
Me4
formation of (ArMe )2E(H)OH (left) or arene elimination and formation of {Ar E(μ-OH)}2 + Ar H (right).
4
(CH3)2}2), as the p-methyl substituent in ArMe is not expected
to influence the reaction mechanism and can therefore be
omitted to lower the computational cost.
addition pathway. However, the energy barrier for elimination
4
6
Me4
of ArMe H from (Ar )2E(H)OH was found to be considerably
higher than that calculated for the σ bond metathesis.
Computational Results. Insertion into O−H bonds is one
of the most studied reactions of transient silylenes and
germylenes.18 It has been shown both experimentally and
theoretically that the reaction proceeds by formation of a Lewis
acid−base complex, R′2E′-OHR (E′ = Si, Ge; R′ = H, Me, Ph),
followed by a proton transfer from oxygen to the group 14
element to give the O−H insertion product R′2E′(H)OR. The
latter step in the mechanism is not unimolecular but rather
involves catalytic proton transfer by a second molecule of water
or alcohol. An alternative reaction channel involving elimi-
nation of H2 from water/alcohol complexes of parent
tetrylenes, H2E′-OHR, to yield HE′OR has also been identified
computationally and experimentally verified by Leigh et al.18a
Calculations (PBE1PBE-D3BJ/def-TZVP) performed for the
A comparison of the two energy diagrams in Figure 5 shows
that the oxidative insertion pathway has a lower barrier when E
= Ge, whereas for E = Sn, the arene elimination pathway is
kinetically favored. However, the dimer {ArMe E(μ-OH)}2 is the
4
thermodynamically preferred product independent of the
identity of the group 14 element. As a whole, the computational
results predict different reactivity for Ge(ArMe
) and Sn-
4
2
(ArMe
)
with water, which is in good agreement with
4
2
experimental observations. The lower energy barrier for
Ge(ArMe )2 in oxidative insertion can be rationalized with its
4
greater Lewis basicity as compared to Sn(ArMe )2. In a similar
4
fashion, the barriers for reductive elimination parallel the
strength of the E−C bond, with the weaker bond
corresponding to a lower barrier.
reaction of E(ArMe )2 with water show that the formation of
The computational results allow a straightforward ration-
4
complexes (ArMe )2E-OH2 is slightly endergonic or energy
alization as to why Sn(ArMe )2 reacts with HBF4 by simple
4
6
insertion.15 The elimination of ArMe H from (Ar )2Sn(H)F
Me6
6
neutral for E = Ge and Sn, respectively. The insertion into the
O−H bond was found to take place catalytically, aided by a
second molecule of water (Figure 5, left). This parallels the
reactivity of transient tetrylenes with water/alcohols18 or
amines28 as well as the mechanism calculated for the insertion
would most likely proceed via a high-energy transition state,
rendering such transformation unlikely. It is, however, less
obvious why Sn{CH(SiMe3)2}2 reacts with water or alcohol by
oxidative insertion,19 while Sn(ArMe
)
undergoes arene
2
4
6
of Ge(ArMe )2 into the N−H bond in NH3.6a The Gibbs energy
elimination and subsequent dimerization to yield {ArMe Sn(μ-
OR)}2. For this reason, we also examined the reaction of
E{CH(SiMe3)2}2 with water using computational methods.
The results from DFT calculations (PBE1PBE-D3BJ/def-
TZVP) suggested that the reaction of E{CH(SiMe3)2}2 with
water proceeds qualitatively similarly to that observed for
6
of activation for the formation of (ArMe )2E(H)OH was found
4
to be 46 and 73 kJ mol−1 for E = Ge and Sn, respectively. We
note that the mechanism for a unimolecular proton transfer was
found to have a considerably greater barrier, well above 100 kJ
mol−1, representing an improbable reaction pathway on the
potential energy surface.
E(ArMe )2 (see Supporting Information). Specifically, Ge{CH-
4
The arene elimination pathway (Figure 5, right) was
calculated to proceed via one-step σ bond metathesis27 that
has a Gibbs energy of activation of 64 and 40 kJ mol−1 for E =
Ge and Sn, respectively. The reaction was found to proceed via
a cyclic transition state in which a hydrogen from the
(SiMe3)2}2 was predicted to react via oxidative insertion,
whereas Sn{CH(SiMe3)2}2 should eliminate CH2(SiMe3)2 to
give {(Me3Si)2HC}SnOH, which would readily dimerize to
[{(Me3Si)2HC}Sn(μ-OR)]2. The dimer [{(Me3Si)2HC}Sn(μ-
OR)]2 was found to be both the thermodynamically and
kinetically favored product, with a difference of 16 kJ mol−1 in
activation energy for the two investigated pathways. We note
that the energy barriers for the elimination of the alkane
CH2(SiMe3)2 were calculated to be approximately twice as high
coordinated water molecule in (ArMe )2E-OH2 is transferred
4
Me4
to the aryl substituent, yielding ArMe EOH and Ar H. This is
4
reminiscent of the mechanism calculated for the reaction of
6a
Me6
Sn(ArMe )2 with NH3 to give Ar SnNH2. The hydroxyte-
6
trylene ArMe EOH can undergo a subsequent barrierless
as those determined for the arene ArMe H, as expected based on
4
4
dimerization to form the hydroxide-bridged dimer {ArMe E(μ-
the differences in their electronic structures.
4
OH)}2 as the final product. We also tested the possibility that
arene elimination would involve the product of the oxidative
At this point we can only speculate as to why the
experimental and computational results for the reactivity of
D
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Methanol was dried with CaH2 and distilled onto 3 Å molecular sieves.
1H and 13C{1H} spectra were recorded on a Bruker 500 MHz
spectrometer and referenced to solvent signals. No 119Sn signals could
be observed in the region between +2400 and −1000 ppm. Melting
points were determined on a Mel-Temp II apparatus using capillary
tubes sealed with vacuum grease under an inert atmosphere. IR spectra
were recorded as Nujol mulls between CsI plates on a PerkinElmer
1430 ratio recording infrared spectrometer. UV−visible spectra were
recorded from dilute solutions in toluene using a 3 mL quartz cuvette
and an Olis 17 modernized Cary 14 UV/vis/NIR spectrophotometer.
Sn{CH(SiMe3)2}2 with water differ. We note that the reactions
of Sn{CH(SiMe3)2}2 have used an excess (14 equiv) of water at
molar concentrations,20 whereas strict 1:1 stoichiometry and
only millimolar concentrations of substrate have been
employed in all other instances, including this work. Thus,
the reaction conditions of the present study favor elimination,
while those of Porschke et al. are set up to favor insertion.
̈
It should also be pointed out that the experiments reported
by Porschke et al. employ THF as the solvent,20 while the
̈
analogous reactions with Ge{CH(SiMe3)2}2,19 as well as those
(ArMe )2Ge(H)OH (1). H2O (11.2 μL, 0.621 mmol) was dissolved in
6
involving E(ArMe )2, were performed in Et2O. The properties of
6
Et2O (20 mL), and this solution was added dropwise to a slurry of
Ge(ArMe )2 (0.4343 g 0.621 mmol) in Et2O (35 mL) at ca. −78 °C.
6
strong electron pair donor solvents are known to have
significant influence on the reactivity of GeH2 and SiMe2, as
the reacting species in such cases is not the free tetrylene but its
Lewis acid−base adduct.18a,29 In a similar fashion, the product
distribution from the reaction of GePh2 with CCl4 has been
observed to depend on the solvent employed, with the
insertion product Ph2Ge(Cl)CCl3 being favored in neat THF
solutions or in hexanes containing catalytic amounts of THF;30
with an even stronger donor, NEt3, the insertion product was
obtained exclusively. These data strongly suggest that the
reactivity of Sn{CH(SiMe3)2}2 with water or methanol could
be different if the reactions were carried out in Et2O and in the
presence of millimolar quantities of the substrate. Solvent-
modified reactivities of stable acyclic tetrylenes are currently
under further computational and experimental investigations in
The resulting mixture was stirred and allowed to warm to room
temperature overnight, which resulted in a colorless solution. The
solution was concentrated to ca. 5 mL and stored at ca. −28 °C to
produce a colorless crystalline solid, 1. Yield: 84% (0.373 g). Mp:
147−150 °C. 1H NMR (500 MHz, C6D6, 25 °C, ppm): 0.47 (br s, 1H,
O-H) 1.89 (s, 6H, o-Me), 1.94 (s, 6H, o-Me), 2.22 (s, 6H, p-Me), 6.06
(d, JHH = 1.4 Hz, 1H, Ge-H), 6.65, (d, JHH = 7.5 Hz, 4H, C6H3), 6.80
(s, 4H, C6H2), 6.81 (s, 4H, C6H2), 6.99 (t, JHH = 7.5 Hz, 2H, C6H3).
13C{1H} NMR (151 MHz, C6D6, 25 °C, ppm): 21.27 (p-CH3), 22.05
(o-CH3), 22.16 (o-CH3), 128.35, 128.75, 129.65, 130.25, 136.72,
136.99, 137.05, 138.74, 140.69, 148.27. IR (cm−1): 3600 (w), 3000 (s),
2820 (m), 2500 (w), 2150 (w), 1500 (s), 1420 (s), 1300 (s), 1050
(br), 980 (w), 890 (w), 850 (m), 765 (w), 720 (w).
(ArMe )2Ge(H)OMe (2). MeOH (15.9 μL, 0.3924 mmol) was
6
dissolved in Et2O (20 mL), and this solution was added dropwise to a
slurry of Ge(ArMe )2 (0.2745 g 0.3924 mmol) in Et2O (35 mL) at −78
6
our laboratories. The reaction of Sn(ArMe )2 with 10-fold excess
6
°C. The resulting mixture was stirred and allowed to warm slowly to
room temperature overnight, giving a pale purple solution. After 48 h
of stirring, a pale yellow solution was obtained. Reduction of the
solvent to ca. 4 mL gave colorless X-ray quality crystals that contained
2 (82%) cocrystallized with 1 (18%). The formation of 1 presumably
occurs due to the presence of adventitious water. Adjusted mass yield:
of water in Et2O or THF led to decomposition to several
products, which included 3.
CONCLUSION
■
The m-terphenyl-stabilized tetrylenes Ge(ArMe
) and Sn-
2
6
1
53%, 0.161 g. Mp: 189−194 °C. H NMR (500 MHz, C6D6, 25 °C,
(ArMe )2 were found to have differing reactivity toward both
6
ppm): 1.85 (s, 12H, o-Me), 1.86 (s, 12H, o-Me), 2.24 (s, 12H, p-Me),
2.74 (s, 3H, OMe), 5.83 (s, 1H, GeH), 6.69 (d, JHH = 7.5 Hz, 4H,
C6H3) 6.81 (s, 8H, C6H2), 7.00 (t, JHH = 7.5 Hz, 2H, C6H3). 13C{1H}
NMR (151 MHz, C6D6, 25 °C, ppm): 21.20 (p-CH3), 22.11 (o-CH3),
22.17 (o-CH3), 128.58, 128.70, 129.67, 130.37, 136.28, 136.64, 137.16,
139.03, 141.41, 148.99. IR (cm−1): 2920 (s), 2830 (s), 1450 (m), 1370
(w), 1255 (w), 1050 (br), 800 (m).
water and methanol. While the germylene Ge(ArMe )2 inserts
6
into the O−H bond to form the Ge(IV) products (ArMe )2Ge-
6
(H)OH (1) and (ArMe )2Ge(H)OMe (2), the corresponding
6
stannylene Sn(ArMe )2 undergoes arene elimination followed by
6
dimerization to yield the Sn(II) species {ArMe Sn(μ-OH)}2 (3)
6
and {ArMe Sn(μ-OMe)}2 (4). Computational analyses at the
6
{ArMe Sn(μ-OH)}2 (3). H2O (3.13 μL, 0.174 mmol) was dissolved in
6
DFT level reproduced the experimental results and gave
Et2O (15 mL), and this solution was added dropwise to a slurry of
mechanistic insight into the formation of (ArMe )2Ge(H)OH
6
Sn(ArMe )2 (0.1300 g, 0.174 mmol) in Et2O (40 mL) at −78 °C. The
6
Me4
and {ArMe Sn(μ-OH)}2. The insertion of an Ar -stabilized
6
resulting mixture was stirred and allowed to warm slowly to room
temperature overnight, which resulted in a slightly cloudy pale yellow
solution. The solvent volume was reduced to ca. 5 mL, after which the
solution was decanted. The resulting solid was dried under reduced
pressure, giving a yellow powder. X-ray quality single crystals of both 3
germylene into the O−H bond was found to be catalytic, aided
by a second molecule of water. The lowest energy pathway for
the elimination of arene from the corresponding stannylene
involved sigma-bond metathesis rather than separate oxidative
and ArMe H were grown from a saturated Et2O solution. Total mass
6
addition and reductive elimination steps. DFT calculations
yield: 90% (0.1175 g). Upon heating, crystals of 3 become visibly
orange at ca. 160 °C, but no melting is observed at <250 °C. 1H NMR
(500 MHz, C6D6, 25 °C, ppm): 0.00 (s, 2H, OH), 2.14 (s, 24H, o-
Me), 2.29 (s, 12H, p-Me) 6.83 (s, 8H, C6H2), 6.96 (d, JHH = 7.5 Hz,
4H, C6H3), 7.23 (t, JHH = 7.5 Hz, 2H, C6H3). 13C{1H} NMR (151
MHz, C6D6, 25 °C, ppm): 21.46 (p-Me), 21.62 (o-Me), 128.79,
136.38, 136.50, 139.81, 146.92. IR (cm−1): 2910 (s), 2855 (s), 1600
(w), 1450 (m), 1370 (m), 1255 (m), 1190 (m), 1015 (m), 840 (m),
795 (s), 730 (m), 395 (m). λmax (nm, ε): 362 (700).
found no difference in the preferred reactivity of Sn(ArMe
)
4
2
and Sn{CH(SiMe3)2}2 even though the latter is known to
undergo oxidative insertion into O−H bonds. A plausible
explanation for the experimental behavior of the alkyl
stannylene is the use of reaction conditions that favour
insertion (molar concentrations of water and THF as the
solvent).
{ArMe Sn(μ-OMe)}2 (4). MeOH (13.2 μL, 0.327 mmol) was
6
EXPERIMENTAL SECTION
General Procedures. All manipulations were carried out either in
dissolved in Et2O (15 mL), and this solution was added dropwise to
■
a slurry of Sn(ArMe )2 (0.2438 g, 0.327 mmol) in Et2O (40 mL) at ca.
6
an inert atmosphere glovebox or by using modified Schlenk techniques
−78 °C. The resulting mixture was stirred and allowed to warm to
room temperature overnight, which afforded a yellow solution.
Filtration via cannula and evaporation of the solvent gave a mixture
to maintain strictly anaerobic and anhydrous conditions. Ge(ArMe
)
6
2
and Sn(ArMe
)
were prepared by literature procedures.13 Solvents
2
6
were dried using a Grubbs-style purification system31 and stored over
NaK. Water was collected from a Thermo Scientific Barnstead
Nanopure and degassed under reduced pressure (<1 Torr) for 2 h.
of 4 and ArMe H as a yellow powder. Single crystals of 4 suitable for X-
6
ray diffraction were grown from a saturated Et2O solution. Total mass
yield: 93.3% (0.2373 g). Mp: 127−129 °C. 1H NMR (500 MHz, C6D6,
E
DOI: 10.1021/acs.organomet.5b00884
Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
25 °C, ppm): 2.16 (s, 24H, o-Me), 2.22 (s, 12H, p-Me), 2.37 (s, 6H,
OMe), 6.79 (s, 8H, C6H2), 6.94 (d, JHH = 7.5 Hz, 4H, C6H3), 7.19 (t,
2H, C6H3). 13C{1H} NMR (151 MHz, C6D6, 25 °C, ppm): 21.20 (p-
Me), 22.03 (o-Me), 51.81 (OMe), 128.95, 129.32, 136.16, 136.18,
140.79, 147.91, 178.24. IR (cm−1): 2890 (s), 2700 (w), 1590 (w),
1440 (s), 1360 (s), 1240 (m), 1100 (br), 830 (w), 780 (m), 700 (m),
360 (w). λmax (nm, ε): 337 (1600).
Computational Details. All calculations were performed with
Gaussian09.32 The structures of the studied systems were optimized
using the PBE1PBE hybrid exchange−correlation functional33 in
conjunction with the def-TZVP basis sets.34 For tin, a def2-TZVP basis
with an effective core potential (ECP) was used to treat scalar
relativistic effects.35 Dispersion interactions were modeled by applying
Grimme’s empirical dispersion correction with Becke−Johnson
damping (D3BJ).36 The choice of a particular functional−basis set
combination was motivated by our recent theoretical−experimental
studies of the chemistry of metallylenes as well as computational
efficiency.2a,8,14 The correction for dispersion effects was considered
crucial in order to obtain accurate energetics for systems employing
bulky terphenyl substituents.
P. P. J. Am. Chem. Soc. 2000, 122, 3524−3525. (c) Peng, Y.; Fischer, R.
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Calculations were performed only for the reactions of heavier
tetrylenes with water. Model compounds based on the ArMe ligand
4
(ArMe = C6H3-2,6-{C6H3-2,6-(CH3)2}2) were used to reduce the
4
(13) Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P.
Organometallics 1997, 16, 1920−1925.
computational cost. The nature of stationary points found (minimum
or transition state) was assessed with calculation of full Hessian
matrices using analytic or numerical gradients.
(14) (a) Brown, Z. D.; Vasko, P.; Erickson, J. D.; Fettinger, J. C.;
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ASSOCIATED CONTENT
* Supporting Information
■
S
(15) Brown, Z. D.; Guo, J. D.; Nagase, S.; Power, P. P.
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The Supporting Information is available free of charge on the
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met.5b00884.
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Synthetic details of deuterium analogues 1′ and 3′ and
additional spectroscopic (NMR, IR, and UV/vis) and
computational data (PDF)
Optimized structures (XYZ)
Crystallographic information files for 1−4 (CIF)
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AUTHOR INFORMATION
Corresponding Authors
*E-mail: heikki.m.tuononen@jyu.fi.
*E-mail: pppower@ucdavis.edu.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
We are grateful to the U.S. Department of Energy (DE-FG02-
07ER46475; P.P.P.) and the Academy of Finland (136929,
253907, and 272900; H.M.T.) for funding. P.V. thanks the
Fulbright Center for a personal scholarship.
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NOTE ADDED IN PROOF
■
Initial computational investigations suggest that the reactivity of
Sn{CH(SiMe3)2}2 is more dictated by the amount of substrate
used rather than the choice of solvent (Et2O vs THF).
G
DOI: 10.1021/acs.organomet.5b00884
Organometallics XXXX, XXX, XXX−XXX