Application of the donor-acceptor concept to intercept low oxidation state group 14 element hydrides using a Wittig reagent as a lewis base

Article abstract of DOI:10.1021/ic501265k

This article outlines our attempts to stabilize the Group 14 element dihydrides, GeH₂ and SnH₂, using commonly employed phosphine and pyridine donors; in each case, elemental Ge and Sn extrusion was noted. However, when these phosphorus and nitrogen donors were replaced with the ylidic Wittig ligand Ph₃P=CMe₂, stable inorganic methylene complexes (EH₂) were obtained, demonstrating the utility of this under-explored ligand class in advancing main group element coordination chemistry.

Full text of DOI:10.1021/ic501265k

Article
pubs.acs.org/IC
Application of the Donor−Acceptor Concept to Intercept Low
Oxidation State Group 14 Element Hydrides using a Wittig Reagent
as a Lewis Base
Anindya K. Swarnakar, Sean M. McDonald, Kelsey C. Deutsch, Paul Choi, Michael J. Ferguson,
Robert McDonald, and Eric Rivard*
Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta, Canada T6G 2G2
S
* Supporting Information
ABSTRACT: This article outlines our attempts to stabilize the Group 14
element dihydrides, GeH2 and SnH2, using commonly employed
phosphine and pyridine donors; in each case, elemental Ge and Sn
extrusion was noted. However, when these phosphorus and nitrogen
donors were replaced with the ylidic Wittig ligand Ph3PCMe2, stable
inorganic methylene complexes (EH2) were obtained, demonstrating the
utility of this under-explored ligand class in advancing main group
element coordination chemistry.
Scheme 1. Representative Resonance Forms for Ph3PCR2
INTRODUCTION
■
The use of electron-donating ligands to intercept/stabilize
reactive inorganic element centers is a widely explored concept
in inorganic chemistry. Recently, N-heterocyclic carbenes
(NHCs) have received considerable attention in this regard
due to their ease of synthesis and ability to tune the steric bulk
about the ligating carbon centers.1 A commonly employed
NHC in formally low oxidation state main group element
chemistry is IPr (IPr = [(HCNDipp)2C:], Dipp =
2,6-iPr2C6H3), which has been used to access stable complexes
of E2 (E = B, Si, Ge, Sn, P, and As)2 and related species with
unusual/novel bonding environments.3 Our group has also
employed IPr in conjunction with suitable Lewis acidic
acceptors (BH3 and W(CO)5) to prepare various inorganic
Group 14 element methylene EH2 and ethylene H2EE′H2
complexes (E and E′ = Si, Ge, and/or Sn) via a general
donor−acceptor protocol.4 In addition, we have shown that
many of these parent main group hydrides can be accessed
using the ylidic N-heterocyclic olefin (NHO) donor, IPrCH2
[IPrCH2 = (HCNDipp)2CCH2] in place of IPr.4e,f,5
Added interest from this work stems from the implication of
EH2 species, such as the silylene :SiH2, as key intermediates in
the growth of semiconducting films from gas phase precursors
(e.g., SiH4).6
known N-heterocyclic carbene-based donors. It should be
mentioned that, while the use of related Wittig reagents8 as
ligands is known for transition metals and actinides,9 well-
defined coordination chemistry involving R′3PCR2 donors
within the main group remains a largely untouched area.10
RESULTS AND DISCUSSION
■
While carbon-based donors are known to bind/stabilize main
group element polyhydrides,3a,4,5a,11 we desired to test the
scope of the donor−acceptor protocol by including phosphine-
and pyridine-based Lewis bases (LB) to yield new adducts of
the general form LB·EH2·LA (LA = Lewis acid). A motivation
for such studies would be to later study the controlled
thermolysis of these complexes to generate Group 14 metal
coatings and/or nanoparticles.4g It should be mentioned that
nanomaterials are often capped with phosphorus- or nitrogen-
containing ligands to engender solubility and to prevent
quenching of luminescence by surface reactive sites.12 More-
over the use of amines and phosphines within the context of
low oxidation state Group 14 coordination chemistry has
precedence.13
In this article we detail our attempts to prepare low oxidation
state Group 14 element hydride complexes with the aid of
common phosphine- and pyridine-based donors. In addition we
7
demonstrate that the Wittig reagent Ph3PCMe2 is an
excellent ligand for molecular main group chemistry by virtue
of the nucleophilic character of the terminal carbon atom
(Scheme 1). Furthermore, the ability to rapidly prepare
structural variants of this Wittig reagent from inexpensive
reagents makes this system advantageous over many well-
Received: May 30, 2014
Published: July 30, 2014
© 2014 American Chemical Society
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We began this study by preparing Ge(II) dihalide adducts of
the widely explored donors, 4-dimethylaminopyridine (DMAP)
and tricyclohexylphosphine (Cy3P). Specifically, these adducts
were obtained by combining either DMAP or Cy3P with Cl2Ge·
dioxane in toluene to afford the respective Ge(II) dichloride
complexes DMAP·GeCl2 (1) and Cy3P·GeCl2 (2)14 as air-
sensitive (yet thermally stable) colorless solids (Scheme 2).
Lewis bases.10 This study was motivated by the structural
parallels that exist between Wittig reagents and N-heterocyclic
olefins (such as IPrCH2) due to the mutual presence of ylidic
bonding, leading to significant electron density being
positioned at a terminal carbon atom (Scheme 1).5 Prior
studies with the donor Ph3PCH2 revealed a potential ligand
degradation pathway wherein deprotonation of a terminal
methylene unit occurs in the presence of electron-deficient
main group compounds to yield RxE-CHPPh3 species.16
Accordingly, we focused on the phosphorus ylide, Ph3P
CMe2 (3),7 which does not contain acidic hydrogen atoms
adjacent to the carbon ligation site. Fortunately the methylated
donor Ph3PCMe2 (3) is conveniently prepared in high yield
as a moisture-sensitive red solid by treating the commercially
Scheme 2. Synthesis of DMAP and Cy3P Adducts of GeCl2
(1 and 2) and Interaction of These Species with Excess
Li[BH4]
n
available phosphonium salt [Ph3PiPr]I with BuLi in toluene,
followed by removal of the LiI byproduct by filtration. Crystals
of 3 were also analyzed by single-crystal X-ray crystallography,
and the resulting molecular structure can be found in the
Supporting Information (Figure S1).17
The formation of the stable Ge(II) dihalide adduct
Ph3PCMe2·GeCl2 (4) was accomplished by combining
equimolar amounts of Ph3PCMe2 (3) and Cl2Ge·dioxane
in toluene solvent (eq 1). Compound 4 can be obtained in
While the synthesis of the DMAP adduct 1 proceeded in a
quantitative fashion, the synthesis of Cy3P·GeCl2 (2) routinely
yielded a [Cy3PH]+-containing byproduct (presumably as a
GeCl3 salt)15 which necessitated further purification by
−
fractional crystallization from toluene/hexanes to afford pure
2. Both compounds 1 and 2 have been structurally
authenticated by X-ray crystallography (Figure 1), and as
expected, pyramidalized Ge centers are present with an angle
sum at Ge (∑Ge) for compound 1 of 280.83(7)° [∑Ge for
compound 2 = 284.33(4)°].
analytically pure form via recrystallization from CH2Cl2/
hexanes, and the crystallographically determined structure of
this species is presented as Figure 2. The binding of the Wittig
Figure 1. Molecular structures of DMAP·GeCl2 (1) (left) and Cy3P·
GeCl2 (2) (right) with thermal ellipsoids at the 30% probably level. All
hydrogen atoms have been omitted for clarity. Selected bond lengths
[Å] and angles [deg]: Compound 1: Ge−N(1) 2.028(2), Ge−Cl(1)
2.2881(8), Ge−Cl(2) 2.2907(9); N−Ge−Cl(1) 93.03(7), N−Ge−
Cl(2) 92.49(7), Cl(1)−Ge−Cl(2) 95.31(3). Compound 2: Ge−P
2.5087(7), Ge−Cl(1) 2.2782(7), Ge−Cl(2) 2.2723(7); P−Ge−Cl(1)
93.96(3), P−Ge−Cl(2) 93.21(2), Cl(1)−Ge−Cl(2) 97.16(2).
Figure 2. Molecular structure of Ph3PCMe2·GeCl2 (4) with thermal
ellipsoids at the 30% probability level. All hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg): Ge−
Cl(1) 2.2735(6), Ge−Cl(2) 2.3106(6), Ge−C(1) 2.1535(19),
P−C(1) 1.6785(18); C(1)−Ge−Cl(1) 99.07(6), C(1)−Ge−Cl(2)
93.25(5), Cl(1)−Ge−Cl(2) 95.10(2).
When DMAP·GeCl2 (1) and Cy3P·GeCl2 (2) were each
treated with the soluble hydride source, lithium borohydride
Li[BH4], the only spectroscopically identifiable products were
the known adducts, DMAP·BH3 and Cy3P·BH3, respectively;
these reactions also afforded copious amounts of gray
precipitate which is assumed to be elemental germanium
(Scheme 2). These observations are in contrast to what is
found with the strongly donating N-heterocyclic carbene IPr,
which yields IPr·GeH2·BH3 under similar reaction conditions as
an isolable colorless solid.4a
reagent 3 to a GeCl2 unit (to form 4) is accompanied by a
significant 31P NMR shift from 9.8 to 37.0 ppm. The methyl
substituents within the Ph3PCMe2 donor in 4 appear as a
1
doublet resonance at 1.77 ppm in the H NMR spectrum, and
this signal is shifted upfield in comparison to the methyl
resonance within the free ligand 3 (2.17 ppm). Ph3PCMe2·
GeCl2 exhibits a pyramidal geometry about germanium [∑Ge
= 287.42(8)°] consistent with the presence of a lone pair at Ge.
As will be seen in all complexes of Ph3PCMe2 in this study, the
binding of the nucleophilic carbon center in Ph3PCMe2 to a
With the goal of expanding the range of suitable donors for
stabilizing low oxidation state main group hydrides, our
attention shifted to exploring Wittig reagents R′3PCR2 as
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GeCl2 unit results in elongation of the intraligand P−C bond
from 1.6785(18) Å in free Ph3PCMe2 (3) to 1.807(2) Å in
Ph3PCMe2·GeCl2; this effect can be rationalized by a reduction
in C(p) → P−C(σ*) hyperconjugative interactions once 3
participates in adduct formation. The formally dative C−Ge
bond length in Ph3PCMe2·GeCl2 (4) [2.1535(19) Å] is slightly
elongated with respect to the corresponding distance in IPr·
GeCl2 [2.112(2) Å];4a direct structural comparison of 4 with
the ylide adduct IPrCH2·GeCl2 is not possible at the moment
due to a lack of suitable X-ray crystallographic data for IPrCH2·
GeCl2.5a
2.053(3) Å; Ge−C = 2.011(2) Å]. Therefore, the metrical
data suggest that Ph3PCMe2 is a weaker donor than the N-
heterocyclic carbene, IPr (vide infra).
The Wittig reagent-appended germanium(II) dihydride
complex Ph3PCMe2·GeH2·BH3 (5) showed similar thermal
stability in solution in relation to IPr·GeH2·BH3. For example,
we heated a toluene-d8 solution of Ph3PCMe2·GeH2·BH3 (5) in
a J-Young NMR tube at 100 °C for 24 h which led to the
18
decomposition of 5 to afford Ph3P·BH3 (>95% conversion
according to 31P NMR spectroscopy; δ = 21.7); for comparison,
IPr·GeH2·BH3 decomposes in hot toluene to yield IPr·BH3.4a
11B{1H} NMR spectroscopy on the product mixture formed
when 5 is heated also confirmed the presence of Ph3P·BH3 (d,
δ = 42.1, 1JBP = 43.7 Hz) with the accompanying formation of a
volatile product at ∼80 ppm which is tentatively assigned as
When Ph3PCMe2·GeCl2 (4) was treated with 2 equiv of
Li[BH4] in diethyl ether, clean Cl/H exchange transpired to
yield the isolable germanium dihydride−borane adduct
Ph3PCMe2·GeH2·BH3 (5) (eq 2). The successful installation
i
being the triorganoborane Pr3B (literature 11B NMR shift =
83.7 ppm in C6D6).19 One possible route for this decom-
position process is hydride transfer20 from an E−H group (E =
Ge or B) to a CMe2 carbon atom of the Wittig donor, leading
to population of a C−P σ* orbital and release of PPh3, which is
later trapped by liberated BH3 to form Ph3P·BH3. The insoluble
precipitate which formed during the thermolysis of Ph3PCMe2·
GeH2·BH3 (5) in toluene was identified as elemental
germanium according to EDX analysis (Figure S3 in SI);17 in
addition this solid was imaged by SEM which revealed the
formation of a bulk material with a globular morphology
(Figure S4 in SI).17
It appears that Ph3PCMe2 is a weaker electron pair donor
than the carbene IPr, as Ph3PCMe2·GeH2·BH3 (5) rapidly
reacts with a stoichiometric amount of IPr to afford IPr·GeH2·
BH3 and free Ph3PCMe2 as major products via a Lewis base
exchange reaction, as determined by NMR spectroscopy. We
also attempted to prepare the Ge(II) hydride complex
Ph3PCMe2·GeH2 by treating the GeCl2 adduct Ph3PCMe2·
GeCl2 (4) with the milder hydride source K[HBsBu3]. It was
hoped that hydride delivery would occur to yield the less
reactive and more hindered borane, sBu3B, as a byproduct, thus
suppressing decomplexation of the Lewis base from Ge via LB−
borane adduct formation.4a However, Ph3PCMe2·GeCl2 (4)
reacts with 2 equiv of K[HBsBu3] to yield free PPh3 and
sBu3B21 according to 31P and 11B NMR spectroscopy, along
with the formation of gray precipitate (presumably elemental
Ge).
Of note, our previous attempts to form IPrCH2·GeH2·BH3
led to loss of germanium metal and the isolation of IPrCH2·
BH3 as the sole donor-containing product.5a Thus, Ph3PCMe2
is likely a stronger donor than the N-heterocyclic olefin IPrCH2
and the previously discussed Lewis bases Cy3P and DMAP. The
mechanism by which LB·GeH2·BH3 complexes (LB = Lewis
base) degrade to yield the boranes LB·BH3 is unknown at this
time. Either LB−Ge or Ge−B bond scission (or even hydride
transfer from Ge or B20) could be involved as the key step in
the decomposition process; we are currently exploring possible
LB·GeH2·BH3 degradation pathways by computational meth-
ods.
of hydride functionality at germanium in 5 was evidenced by 1H
NMR spectroscopy, which revealed the presence of a new
broad resonance at 4.63 ppm. In addition, IR spectroscopy
clearly displayed a Ge−H stretching band at 1975 cm−1 which
is similar in value to the vibration at 1987 cm−1 belonging to a
GeH2 moiety in IPr·GeH2·BH3.4a Compound 5 gave a 11B
NMR spectrum with a quartet resonance at −39.4 ppm (in
1
C6D6; JBH = 95.4 Hz) that was assigned to the terminal BH3
unit, which is comparable with the 11B NMR resonance
1
observed previously for IPr·GeH2·BH3 (−40.0 ppm; JBH = 99
Hz).4a The deutero analogue of 5, Ph3CMe2·GeD2·BD3 (5D)
was also synthesized by combining 2 equiv of Li[BD4] with 4 in
Et2O. As expected, the 2H{1H} NMR spectrum of 5D consisted
of broad peaks positioned at 4.63 and 1.56 ppm, corresponding
to GeD2 and BD3 units, respectively.
As shown in Figure 3, Ph3PCMe2·GeH2·BH3 (5) exhibits a
tetrahedral coordination environment at Ge with crystallo-
graphically determined Ge−H bond distances of 1.477(18) and
1.46(2) Å. The adjacent Ge−B and Ge−C bond lengths are
2.0786(17) and 2.0460(13) Å, respectively, which are elongated
by ∼0.3 Å in comparison to the related distances found in the
N-heterocyclic carbene adduct IPr·GeH2·BH3 [Ge−B =
Analogous coordination and hydride transfer chemistry was
explored between the Wittig reagent Ph3PCMe2 and Sn(II)
halides. As a start, we prepared the Sn(II) halide adduct
Ph3PCMe2·SnCl2 (6) from the direct reaction of Ph3PCMe2
and SnCl2 in toluene. This reaction proceeds to high yield if
conducted over a short time frame of 3 h. If this reaction is
allowed to proceed for longer periods (>24 h), then increasing
amounts of the phosphonium salt [Ph3PCHMe2]SnCl3
Figure 3. Molecular structure of Ph3PCMe2·GeH2·BH3 (5) with
thermal ellipsoids at the 30% probability level. All carbon-bound
hydrogen atoms and THF solvate have been omitted for clarity.
Selected bond lengths (Å) and angles (deg): Ge−B 2.0786(17), Ge−
C (1) 2.0460(13), Ge−H(1A) 1.477(18), Ge−H(1B) 1.46(2); C(1)−
Ge−B 111.26(6), C(1)−Ge−H(1A) 103.5(7), C(1)−Ge−H(1B)
100.8(8), H(1A)−Ge−H(1B) 103.4(11), H−B−H 109.1(16) to
113.6(18).
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occurs17 as evidenced by the emergence of a new 31P signal at
30.9 ppm. Ph3PCMe2·SnCl2 (6) was also characterized by
single-crystal X-ray crystallography, and the molecular structure
of this adduct is found in Figure 4. The most salient metrical
Figure 5. Molecular structure of Ph3PCMe2·GeCl2·W(CO)5 (8) with
thermal ellipsoids presented at a 30% probability level. All hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): C(6)−Ge 2.0826(15), P−C(6) 1.8315(16), Ge−Cl(1)
2.2588(4), Ge−Cl(2) 2.2369(4), Ge−W 2.59459(17), W−C(1)
1.982(3), W−C(2−5) 2.019(3) to 2.043(3); C(6)−Ge−W
124.17(4), Cl(1)−Ge−Cl(2) 94.679(17), Ge−W−C(1) 175.25(5),
Ge−W−C(2−5) 82.75(6) to 99.11(5).
Figure 4. Molecular structure of Ph3PCMe2·SnCl2 (6) with thermal
ellipsoids at the 30% probability level. All hydrogen atoms have been
omitted for clarity. Selected bond lengths (Å) and angles (deg): Sn−
C(1) 2.3518(14), Sn−Cl(1) 2.4854(4), Sn−Cl(2) 2.4852(4), P−C(1)
1.8036(15); Cl(1)−Sn−Cl(2) 87.828(15), C(1)−Sn−Cl(1) 94.87(4),
C(1)−Sn−Cl(2) 90.91(4).
approach worked well for the isolation of the formal Sn(II)
dihydride adducts, IPr·SnH2·W(CO)5 and IPrCH2·SnH2·W-
(CO)5.4b,5a The requisite SnCl2 precursor to a tin hydride−
Wittig reagent complex, Ph3PCMe2·SnCl2·W(CO)5 (9), was
prepared in nearly quantitative yield as a colorless solid by a
THF solvent displacement reaction between the known tin
chloride tungsten pentacarbonyl adduct (THF)2·SnCl2·W-
(CO)5 and the two-electron Wittig donor Ph3PCMe2 (3) (eq
4). The formation of Ph3PCMe2·SnCl2·W(CO)5 (9) was
parameters of 6 include a Sn−C bond length of 2.3518(14) Å
and a sum of the bond angles at Sn of 273.61(6)°; this latter
value is substantially smaller than in the Ge congener 4
[287.42(8)°] as is expected for an increase in s-character within
the sterochemically active Sn lone pair in Ph3PCMe2·SnCl2 (6).
When Ph3PCMe2·SnCl2 (6) was treated with 2 equiv of
Li[BH4] in Et2O, the formation of Ph3PCMe2·BH3 (7) along
with a black precipitate (presumably metallic tin) was observed.
Compound 7 was reported previously by Bestmann and co-
workers,10a and we independently prepared this species from
Ph3PCMe2 and THF·BH3 in order to obtain structural
characterization by X-ray crystallography (Figure S2 in SI).17
We also attempted to prepare the germastannene adduct
Ph3PCMe2·Cl2Ge-SnCl2·W(CO)5 by combining the nucleo-
philic Ge(II) adduct Ph3PCMe2·GeCl2 (4) with the known
stannylene complex, (THF)2·SnCl2·W(CO)5.22 However, as
noted previously within the IPr adduct series,4f SnCl2/GeCl2
exchange at tungsten transpired to afford the thermally stable
germylene complex, Ph3PCMe2·GeCl2·W(CO)5 (8) (eq 3).
accompanied by a large change in chemical shift in the 31P
NMR spectrum relative to free Ph3PCMe2 (9.8 ppm) to
yield a singlet resonance at 38.2 ppm with flanking tin satellites
(3JPSn = 44.5 Hz). The IR spectrum of 9 shows two resolvable
stretching bands at 1930 and 2060 cm−1 consistent with a LB·
W(CO)5 environment (LB = Lewis base), while a 119Sn NMR
resonance at 131.3 ppm in C6D6 was located which is similar to
the resonance observed for Ph3PCMe2·SnCl2 (6) (113.3 ppm),
despite the change in coordination number at tin. The related
N-heterocyclic carbene adduct IPr·SnCl2·W(CO)5 has a 119Sn
resonance positioned at −71.3 ppm,4b while the ylidic N-
heterocyclic olefin complex IPrCH2·SnCl2·W(CO)5 yields a
resonance at −96 ppm.5a
The molecular structure of Ph3PCMe2·SnCl2·W(CO)5 (9) is
presented in Figure 6. As discussed earlier for related adducts,
binding of the Ph3PCMe2 ligand to a SnCl2·W(CO)5 unit
leads to considerable elongation of the Ph3P-CMe2 P−C bond
length from 1.6785(18) Å in the free ligand to 1.8174(18) Å in
9. The adjacent C−Sn bond length in 9 is 2.2660(18) Å and is
similar in value as the C−Sn interaction in the N-heterocyclic
olefin bound Sn(II) complex IPrCH2·SnCl2·W(CO)5
[2.2435(5) Å avg.].5a The Sn−W distance in 9 is
2.73047(15) Å and is slightly shorter than the corresponding
distances in the structurally authenticated adducts Cy3P·SnCl2·
W(CO)5 [2.7438(2) Å]4e and IPrCH2·SnCl2·W(CO)5
[2.758(4) Å avg.].5a As expected, a localized C4v coordination
environment exists about the tungsten center in 9 with a nearly
colinear Sn−W−C(1) array [177.02(7)°] and Sn−W−C(2−5)
bond angles involving the remaining CO groups that approach
orthogonal geometries [83.98(7) to 96.07(6)°]; a related
Compound 8 was also characterized by a single-crystal X-ray
diffraction study (Figure 5), and the geometric parameters
about the Ge center in 8 are similar to those found in the NHO
adduct IPrCH2·GeCl2·W(CO)5, with a slightly elongated Ge−
C dative linkage in 8 [2.0826(15) Å] observed relative to the
IPrCH2 adduct [2.053(2) Å].5a
It is known from our prior studies, and confirmed above, that
the synthesis of Sn(II) dihydride (SnH2) complexes is a more
challenging endeavor than for GeH2 adducts as a result of
decreased Lewis acidic and basic character at Sn, leading to
weaker coordinative interactions.4g In order to increase the
eventual Lewis acidity of a coordinated SnH2 unit, we decided
to use a highly electron-deficient W(CO)5 group as the
acceptor moiety within our donor−acceptor protocol; a related
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Figure 6. Molecular structure of Ph3PCMe2·SnCl2·W(CO)5 (9) with
thermal ellipsoids presented at a 30% probability level. All hydrogen
atoms have been omitted for clarity. Selected bond lengths (Å) and
angles (deg): C(6)−Sn 2.2660(18), P−C(6) 1.8174(18), Sn−Cl(1)
2.4217(5), Sn−Cl(2) 2.4018(5), Sn−W 2.73047(15), W−C(1)
2.002(2), W−C(2−5) 2.025(2) to 2.038(2); C(6)−Sn−W
123.82(5), Cl(1)−Sn−Cl(2) 93.901(18), Sn−W−C(1) 177.02(7),
Sn−W−C(2−5) 83.98(7) to 96.07(6).
Figure 7. Molecular structure of Ph3PCMe2·SnH2·W(CO)5 (10) with
thermal ellipsoids at a 30% probability level. All carbon-bound
hydrogen atoms and diethyl ether solvate have been omitted for
clarity. Selected bond lengths (Å) and angles (deg): C(6)−Sn
2.269(2), P−C(6) 1.808(2), Sn−H(1) 1.73(4), Sn−H(2) 1.71(3),
Sn−W 2.7833(2), W−C(1) 2.019(3), W−C(2−5) 2.026(3) to
2.043(3); C(6)−Sn−W 117.03(6), H(1)−Sn−H(2) 100.3(17), Sn−
W−C(1) 174.66(8), Sn−W−C(2−5) 82.77(10) to 92.66(8).
coordination environment exists about the W center in
Ph3PCMe2·GeCl2·W(CO)5 (8) (Figure 5).
With the successful installation of a Lewis acidic W(CO)5
group and a Wittig electron pair donor at Sn to give
Ph3PCMe2·SnCl2·W(CO)5 (9), this compound was then
combined with Li[BH4] in Et2O (eq 5). In line with prior
enhanced electron density and X-ray scattering), these atoms
could be located in the electron difference map. Accordingly,
Sn−H distances of 1.73(4) and 1.71(3) Å in 10 were
determined. The Sn−W distance in Ph3PCMe2·SnH2·W(CO)5
(10) [2.7833(2) Å] is elongated in relation to the Sn−W bond
length within the SnCl2 adduct Ph3PCMe2·SnCl2·W(CO)5 (9)
[2.73407(15) Å], despite the anticipated increase of electron
density at the SnH2 center in relation to SnCl2 (which bears
electron-withdrawing Cl atoms). The Wittig carbon−tin
interaction in Ph3PCMe2·SnH2·W(CO)5 (10) is the same
within experimental error [2.269(2) Å] as the C−Sn bond
length in the halogenated congener 9 [2.2660(18) Å]. The
intraligand P−C distance involving the CMe2 unit in 10 is
1.808(2) Å and matches well the adjacent P−C bond distances
within the Ph3P array [1.802(2) to 1.807(2) Å], indicating the
presence of single bonds in each case.
Our investigations into the thermal stability of Ph3PCMe2·
SnH2·W(CO)5 (10) show that this Wittig complex is less stable
than the corresponding carbene-supported adduct IPr·SnH2·
W(CO)5 reported by our group in 2011.4b Compound 10
melts with decomposition to generate black insoluble materials
upon heating to 80−81 °C under an atmosphere of nitrogen. In
addition, compound 10 is stable for a few hours in C6D6
solution at room temperature; however, if solutions of 10 are
allowed to stand for greater than 24 h, the complete
decomposition of 10 into a black metallic precipitate
(containing either Sn metal, Sn/W clusters or both) and free
Ph3P occurs, as determined by 31P NMR spectroscopy; notably,
IPr·SnH2·W(CO)5 is stable under similar conditions. In order
to further evaluate the relative binding affinity of Ph3PCMe2,
IPrCH2 and IPr, the Wittig analogue Ph3PCMe2·SnH2·
W(CO)5 (10) was combined with stoichiometric amounts of
IPr or IPrCH2 in toluene at room temperature. These reactions
led to the full decomposition of Ph3PCMe2·SnH2·W(CO)5
before any discernible reactivity (Lewis base exchange) with
either IPr or IPrCH2 was detected.
research from our group, the resulting reaction mixture
contained the target Sn(II) dihydride adduct Ph3PCMe2·
SnH2·W(CO)5 (10) which could be isolated as a brown
crystalline solid after crystallization from a diethyl ether/
hexanes mixture at −35 °C. Compound 10 was readily
identified by the emergence of a new characteristic singlet
resonance at 6.66 ppm in the 1H NMR spectrum which
displayed a set of resolvable tin satellites (1JH−119Sn = 1030 Hz,
1JH−117Sn = 991 Hz) as expected for the formation of a tin(II)
hydride with terminally positioned hydrogen atoms.3a,4b,5a,23
Moreover, a triplet resonance at −49.8 ppm was noted in the
1
119Sn NMR spectrum of 10 with a JSn−H coupling constant
1
which mirrored the value obtained from H NMR spectrosco-
py; further coupling to phosphorus could not be resolved due
to the gradual decomposition of 10 during the acquisition of
the 119Sn NMR data (vide infra). Sn−H IR vibrations in 10
were also located at 1740 cm−1 with proximal bands from 1891
to 2040 cm−1 due to ν(CO) stretches within the W(CO)5 unit.
1
The A1 ν(CO) stretching band at 2040 cm−1 in Ph3PCMe2·
SnH2·W(CO)5 (10) is positioned at a lower wavenumber in
relation to the SnCl2 adduct Ph3PCMe2·SnCl2·W(CO)5 (9)
(2060 cm−1) consistent with a higher degree of electron
donation to W(CO)5 from the electron-rich SnH2 unit in 10.
The analogous complex IPrCH2·SnH2·W(CO)5 affords a
ν(Sn−H) band in the IR spectrum at 1758 cm−1 with a high
frequency CO stretching band at 2043 cm−1, each of which are
close in value as the corresponding vibrations in Ph3PCMe2·
SnH2·W(CO)5 (10), reflecting the similar donating ability of
the Wittig and NHO donors in this system.5a
The molecular structure of Ph3PCMe2·SnH2·W(CO)5 (10)
is presented in Figure 7 and confirms the successful isolation of
a new member of the SnH2 adduct series. By virtue of the
hydridic character of the hydrogen atoms at tin (leading to
CONCLUSIONS
■
In this paper we highlight the donating ability of the C-
methylated Wittig reagent Ph3PCMe2 (3) within the context
of supporting low oxidation state Group 14 element hydride
chemistry. It is shown that reactive targets such as GeH2 and
SnH2 could be generated/intercepted with the aid of this
readily available Wittig donor, while parallel chemistry with the
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Inorganic Chemistry
Article
Table 1. Crystallographic Data for Compounds 1−5
1
2
3
4
5·THF
formula
C7H10Cl2GeN2
256.66
C18H33Cl2GeP
423.90
C21H21P
304.35
C21H21Cl2GeP
447.84
C25H34BGeOP
464.89
formula fw
cryst. dimens. (mm3)
cryst. syst.
space group
unit cell
a (Å)
0.33 × 0.08 × 0.05
monoclinic
P21/n
0.42 × 0.31 × 0.28
orthorhombic
Pca21
0.20 × 0.16 × 0.15
triclinic
0.32 × 0.21 × 0.15
orthorhombic
Pna21
0.19 × 0.17 × 0.12
monoclinic
C2/c
P1
̅
7.3784(2)
10.6075(3)
13.2845(3)
90
15.158(5)
9.974(3)
13.629(11)
90
10.0042(2)
10.1516(2)
18.8977(4)
104.8757(15)
93.2352(13)
112.6166(12)
1686.16(6)
4
12.0720(3)
9.3272(3)
17.8199(5)
90
34.2302(9)
7.9115(2)
23.0344(6)
90
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
90.1560(10)
90
90
90
128.5873(3)
90
90
90
V (Å3)
1039.73(5)
4
2060.5(11)
4
2006.48(10)
4
4876.0(2)
8
Z
ρ (g cm−3
)
1.697
1.366
1.199
1.482
1.267
μ (mm−1
)
8.330
1.820
1.372
1.874
1.335
T (K)
173(1)
137.42
173(1)
54.98
173(1)
173(1)
55.02
173(1)
56.49
2θmax (deg)
142.50
total data
6480
16583
11431
16975
22028
unique data (Rint)
obs data [I > 2σ(I)]
params.
1889 (0.0366)
1664
4664 (0.0204)
4527
6200 (0.0173)
5443
4572 (0.0159)
4472
5986 (0.0188)
5317
111
199
401
226
284
a
R1 [I > 2σ(I)]
0.0313
0.0189
0.0510
0.530/−0.254
0.0379
0.0164
0.0435
0.287/−0.185
0.0264
a
wR2 [all data]
0.0850
0.1020
0.0735
max/min Δρ (e− Å−3
)
0.497/−0.412
0.423/−0.207
0.858/−0.394
0.018(2)
Flack param.
0.015(6)
a
2
4
R1 = ∑||F0| − |Fc||/∑|F0|; wR2 = [∑w(F0 − Fc2)2/∑w(F0 )]1/2
.
Microscope, JEOL 6301F: each sample was dispersed in toluene and
then deposited on an ethanol-cleaned Si(100) wafer (purchased from
University Wafer) which was attached to aluminum stubs using
double-sided carbon tape. A conductive coating of chrome was then
applied to each sample using a Xenosput XE200 sputter coater before
the sample was loaded into the SEM holder. Images were recorded
using secondary electron imaging with an accelerating voltage of 5.0
kV. Energy dispersive X-ray (EDX) spectra were recorded via a PGT
X-ray analysis system on a JEOL 6301F SEM; the samples were placed
on carbon tape (purchased from Ted Pella) for EDX analysis.
commonly used ligands Cy3P and DMAP was unsuccessful
(presumably due to their weaker donating ability in relation to
carbon-based ligands). Given the ability to access a wide scope
of Wittig donors of the general form R3PCR′2 in a rapid fashion
from inexpensive precursors, it is anticipated that these Lewis
bases will be used more actively in the domain of synthetic
inorganic main group chemistry in the future. Thus, one can
view Wittig reagents as viable synthetic analogues to ubiquitous
N-heterocyclic carbene donors, with their potential use to
access new bonding inorganic bonding motifs via coordination
chemistry and to advance inorganic element-mediated catalysis.
X-ray Crystallography. Crystals of suitable quality for X-ray
diffraction studies were removed from a vial in a glovebox and
immediately covered with a thin layer of hydrocarbon oil (Paratone-
N). A suitable crystal was selected, mounted on a glass fiber, and
quickly placed in a low temperature stream of nitrogen on an X-ray
diffractometer.25 All data were collected at the University of Alberta
using a Bruker APEX II CCD detector/D8 diffractometer using Mo
Kα (Cy3P·GeCl2 (2), Ph3PCMe2·GeCl2 (4), Ph3PCMe2·GeH2·BH3
(5), Ph3PCMe2·SnCl2 (6), Ph3PCMe2·BH3 (7), Ph3PCMe2·GeCl2·
W(CO)5 (8), Ph3PCMe2·SnCl2·W(CO)5 (9), Ph3PCMe2·SnH2·W-
(CO)5 (10)) or Cu Kα (DMAP·GeCl2 (1), Ph3PCMe2 (3)) radiation
with the crystals cooled to −100 °C. The data were corrected for
absorption through Gaussian integration from the indexing of the
crystal faces.26 Structures were solved using the direct methods
program SHELXS-9727 (compounds 1, 3−6), Patterson search/
structure expansion facilities within the DIRDIF-2008 program suite28
(compounds 2, 6, 8 and 9), or intrinsic phasing SHELXT27
(compounds 7 and 10); structure refinement was accomplished
using either SHELXL-97 or SHELXL-2013.27 All carbon-bound
hydrogen atoms were assigned positions on the basis of the sp2 or
sp3 hybridization geometries of their attached carbon atoms, and were
given thermal parameters 20% greater than those of their parent
atoms. For compounds 5, 7, and 10, all hydrogen atoms attached to
heteroatoms (B, Ge, and Sn) were located from difference Fourier
maps, and their coordinates and isotropic displacement parameters
EXPERIMENTAL SECTION
■
Materials and Instrumentation. All reactions were performed
using standard Schlenk line techniques under an atmosphere of
nitrogen or in an inert atmosphere glovebox (Innovative Technology,
Inc.). Solvents were dried using a Grubbs-type solvent purification
system24 manufactured by Innovative Technology, Inc., degassed
(freeze−pump−thaw method), and stored under an atmosphere of
n
nitrogen prior to use. Li[BH4], Li[BD4], BuLi (2.5 M solution in
hexanes), H3B·THF (1.0 M solution in THF), K[HBsBu3] (1.0 M
solution in THF), [Ph3PiPr]I, Cl2Ge·dioxane, DMAP, and Cy3P were
purchased from Aldrich and used as received. (THF)2SnCl2·W(CO)5
was prepared according to a literature procedure.22 1H, H{1H}, 11B,
2
13C{1H}, and 119Sn NMR spectra were recorded on a Varian iNova-
400 spectrometer and referenced externally to SiMe4 (1H and
13C{1H}), Si(CD3)4 (2H{1H}), F3B·OEt2 (11B), and SnMe4 (119Sn),
respectively. Elemental analyses were performed by the Analytical and
Instrumentation Laboratory at the University of Alberta. Infrared
spectra were recorded on a Nicolet IR100 FTIR spectrometer as Nujol
mulls between NaCl plates. Melting points were measured in sealed
glass capillaries under nitrogen using a MelTemp melting point
apparatus and are uncorrected. Scanning electron microscopy (SEM)
images were recorded with a Field Emission Scanning Electron
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Inorganic Chemistry
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Table 2. Crystallographic Data for Compounds 6−10
6
7
8
9
10·0.5 Et2O
formula
C21H21Cl2PSn
493.94
C21H24BP
318.18
C26H21Cl2GeO5PW
771.74
C26H21Cl2O5PSnW
817.84
C28H28O5.5PSnW
786.01
formula fw
cryst. dimens. (mm)
cryst. syst.
space group
unit cell
a (Å)
0.28 × 0.26 × 0.03
monoclinic
C2/c
0.28 × 0.14 × 0.10
triclinic
0.32 × 0.32 × 0.10
monoclinic
0.32 × 0.32 × 0.07
monoclinic
0.45 × 0.32 × 0.28
triclinic
P1
I2/a
I2/a
P1
̅
̅
12.9507(4)
14.5477(4)
22.1627(6)
90
9.7208(4)
9.9807(4)
10.0913(4)
99.4355(4)
92.3567(5)
113.1114(4)
882.28(6)
2
14.2653(4)
12.4535(3)
31.0261(3)
90
14.4711(6)
12.6086(5)
31.0557(13)
90
10.7586(6)
11.9138(7)
12.7748(8)
79.1297(6)
89.4825(7)
64.8919(6)
1451.45(15)
2
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
103.1066(3)
90
97.2299(2)
90
96.8451(4)
90
V (Å3)
4066.7(2)
8
5468.1(2)
8
5626.0(4)
8
Z
ρ (g cm−3
)
1.613
1.198
1.875
1.931
1.798
μ (mm−1
)
1.599
0.153
5.592
5.254
4.911
T (K)
173(1)
54.93
173(1)
173(1)
55.11
173(1)
56.66
173(1)
2θmax (deg)
57.87
52.79
total data
17697
8248
24150
25310
30449
unique data (Rint)
obs data [I > 2σ(I)]
params
4658 (0.0144)
4367
4297 (0.0128)
3890
6334 (0.0122)
6063
6879 (0.0151)
6540
5932 (0.0168)
5850
228
222
325
326
335
a
R1 [I > 2σ(I)]
0.0180
0.0466
0.0348
0.0129
0.0154
0.0167
a
wR2 [all data]
0.0928
0.0311
0.0387
0.0425
max/min Δρ (e− Å−3
)
0.438/−0.198
0.426/−0.235
0.518/−0.391
0.876/−0.359
1.019/−0.738
a
R1 = ∑||F0| − |Fc||/∑|F0|; wR2 = [∑w(F0 − Fc2)2/∑w(F0 )]1/2
.
2
4
were allowed to refine freely. A tabular listing of the crystallographic
data for compounds 1−10 can be found in Tables 1 and 2.
isopropyltriphenylphosphonium iodide (1.01 g, 2.3 mmol), and the
mixture was stirred for overnight to yield a dark-red slurry. The
reaction mixture was filtered, and the solvent was then removed from
the filtrate under vacuum to give 3 as a red powder (0.58 g, 84%).
Crystals suitable for single-crystal X-ray diffraction were grown from a
concentrated hexanes solution at −35 °C. 1H NMR (400 MHz,
C6D6): δ = 2.17 (d, 3JHP = 16.4 Hz, 6H, C(CH3)2), 7.03−7.15 (m, 9H,
ArH), 7.60−7.66 (m, 6H, ArH). 13C{1H} NMR (100.5 MHz, C6D6): δ
= 9.2 (d, JPC = 123.0 Hz, C(CH3)2), 20.9 (d, JCP = 13.6 Hz, CH3),
130.5 (s, ArC), 133.2 (s, ArC), 133.9 (d, JCP = 8.8 Hz, ArC); the ipso
C atoms on the Ph rings could not be located. 31P{1H} NMR (161.8
MHz, C6D6): δ = 9.8 (s). Anal. Calcd for C21H21Cl2GeP: C, 82.87; H,
6.95. Found: C, 82.00; H, 6.84. Mp (°C): 115−118.
Special Refinement Conditions. Compound 10. The O−C and
C−C distances within the disordered Et2O solvent molecule were
restrained to be 1.43(1) and 1.50(1) Å, respectively.
Synthetic Details. Synthesis of DMAP·GeCl2 (1). To a mixture of
DMAP (0.069 g, 0.56 mmol) and Cl2Ge·dioxane (0.130 g, 0.56 mmol)
was added 12 mL of toluene. The reaction mixture was stirred
overnight to give a clear, colorless solution. The volatiles were then
removed under vacuum to give 1 as a white solid (0.147 g, 98%).
Crystals of suitable quality for X-ray crystallography were grown from
1
a toluene/hexanes mixture at −35 °C. H NMR (500 MHz, C6D6): δ
3
= 1.85 (s, 6H, N(CH3)2), 5.46 (d, JHH = 7.5 Hz, 2H, ArH), 8.05 (d,
3JHH = 7.0 Hz, 2H, ArH). 13C{1H} NMR (126 MHz, C6D6): δ = 38.2
(N(CH3)2), 106.6 (ArC), 143.9 (ArC), 155.6 (ArC). Anal. Calcd for
C7H10Cl2GeN2: C, 31.64; H, 3.79; N, 10.54. Found: C, 31.90; H, 3.80;
N. 10.26. Mp (°C): 132−136.
Synthesis of Ph3PCMe2·GeCl2 (4). To a mixture of Ph3PCMe2
(0.42 g, 1.4 mmol) and GeCl2·dioxane (0.32 g, 1.4 mmol) was added 5
mL of toluene, and the mixture was stirred for 1 h at room
temperature to give an orange slurry. The resulting precipitate was
separated from the mother liquor and dried under vacuum. The
precipitate was then purified by crystallization from CH2Cl2/hexanes
Preparation of Cy3P·GeCl2 (2).14 Cy3P (83 mg, 0.29 mmol) and
Cl2Ge·dioxane (69 mg, 0.29 mmol) were combined in 12 mL of
toluene. The reaction mixture was stirred overnight to give a white
slurry. The mixture was filtered, and the resulting filtrate was
concentrated to 7 mL, and 2.5 mL of hexanes was carefully layered
on top. This mixture was cooled to −35 °C for 12 h to yield a white
microcrystalline solid, containing 2 and a coproduct tentatively
identified as a [Cy3PH]GeCl3,15 which was separated from the
mother liquor. The solvent was removed from the mother liquor to
yield 2 as a white powder (70 mg, 55%). Crystals of suitable quality for
X-ray crystallography were subsequently grown from a toluene/
1
at −35 °C to give X-ray quality crystals of 4 (0.29 g, 46%). H NMR
(500 MHz, C6D6): δ = 1.88 (d, 3JHP = 20.9 Hz, 6H, C(CH3)2), 6.88−
6.92 (m, 6H, ArH), 6.98−7.02 (m, 3H, ArH), 7.41−7.46 (m, 6H,
ArH). 31P{1H} NMR (161.8 MHz, C6D6): δ = 37.5 (s). 1H NMR (500
MHz, CD2Cl2): δ = 1.77 (d, 3JHP = 20.4 Hz, 6H, C(CH3)2), 7.58−7.63
(m, 6H, ArH), 7.68−7.77 (m, 9H, ArH). 13C{1H} NMR (125.3 MHz,
CD2Cl2): δ = 22.1 (s, CH3), 29.9 (d, JPC = 24.1, C(CH3)2), 120.9 (d,
JCP = 80.5 Hz, ArC), 129.9 (d, JCP = 11.3 Hz, ArC), 134.2 (s, ArC),
135.1 (d, JCP = 8.8 Hz, ArC). 31P{1H} NMR (161.8 MHz, CD2Cl2): δ
= 37.4 (s). Anal. Calcd for C21H21Cl2GeP: C, 56.31; H, 4.73. Found:
C, 55.85; H, 4.63. Mp (°C): 103−105.
1
hexanes mixture at −35 °C. H NMR (500 MHz, C6D6): δ = 0.91−
1.05 (m, 9H, CyH), 1.37−1.60 (m, 15H, CyH), 1.93−1.96 (m, 6H,
CyH), 2.25−2.30 (m, 3H, CyH). 13C{1H) NMR (126 MHz, C6D6): δ
= 26.3 (s, CyC), 27.4 (d, JCP = 10.0 Hz, CyC), 29.7 (s, CyC), 31.9 (d,
JCP = 3.8 Hz, CyC). 31P{1H) NMR (162 MHz, C6D6): δ = 1.8 (s).
Anal. Calcd for C18H33Cl2GeP: C, 50.99; H, 7.85. Found: C, 51.03; H,
7.99. Mp (°C): 177−180.
Synthesis of Ph3PCMe2·GeH2·BH3 (5). To a mixture of Ph3PCMe2·
GeCl2 (62 mg, 0.14 mmol) and Li[BH4] (6 mg, 0.3 mmol) was added
5 mL of Et2O, followed by stirring for 3 h at room temperature to give
a white slurry. The volatiles were then removed under vacuum, and the
crude product was dissolved in 10 mL of CH2Cl2, and the mixture was
filtered. The solvent was removed from the filtrate to yield 5 as a white
powder (43 mg, 80%). Crystals of X-ray quality were grown from a
Synthesis of Ph3PCMe2 (3). n-BuLi (0.96 mL, 2.5 M solution in
hexanes, 2.4 mmol) was added to a 10 mL toluene solution of
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Inorganic Chemistry
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1
saturated THF solution at −35 °C. H NMR (500 MHz, C6D6): δ =
Synthesis of Ph3PCMe2·SnCl2·W(CO)5 (9). Ph3PCMe2 (49 mg,
0.17 mmol) and (THF)2SnCl2·W(CO)5 (110 mg, 0.167 mmol) were
combined in 10 mL of toluene and stirred for 3 h at room temperature
to give a yellow slurry. The volatiles were removed under vacuum to
afford 9 as a pale-yellow powder (130 mg, 94%). Crystals of X-ray
1
3
1.73 (br quartet, JBH = 3H, 94.8 Hz, BH3), 1.66 (d, JHP = 20.4 Hz,
6H, C(CH3)2), 4.64 (br, 2H, GeH2), 6.86−6.93 (m, 6H, ArH), 6.97−
7.16 (m, 3H, ArH), 7.48−7.51 (m, 6H, ArH). 13C{1H} NMR (125.3
1
MHz, C6D6): δ = 17.4 (d, JCP = 23.3 Hz, C(CH3)2), 26.5 (s, CH3),
1
121.9 (d, JCP = 81.0 Hz, ArC), 129.3 (d, JCP = 11.4 Hz, ArC), 133.4 (s,
ArC), 134.8 (d, JCP = 8.3 Hz, ArC). 31P{1H} NMR (161.8 MHz,
C6D6): δ = 38.8 (s). 11B NMR (159.8 MHz, C6D6): δ = −39.4
(quartet, 1JBH = 95.4 Hz, BH3). IR (cm−1): 1975 (m, υGe−H) and 2343
(w, υB−H). Anal. Calcd for C21H26BGeP: C, 64.20; H, 6.67. Found: C,
64.63; H, 6.81. Mp (°C): 110−113.
Synthesis of Ph3PCMe2·GeD2·BD3 (5D). To a mixture of
Ph3PCMe2·GeCl2 (68 mg, 0.15 mmol) and Li[BD4] (9 mg, 0.3
mmol) was added 5 mL of Et2O, followed by stirring for 3 h at room
temperature to give a white slurry. The volatiles were then removed
under vacuum, and the crude product was dissolved in 10 mL of
CH2Cl2, and the mixture was filtered. The solvent was removed from
quality were grown from CH2Cl2/hexanes at −35 °C. H NMR (400
3
MHz, C6D6): δ = 1.61 (d, JHP = 20.4 Hz, 6H, C(CH3)2; satellites:
4
3JHSn and/or JHW = ∼66 Hz), 6.92−7.08 (m, 9H, ArH), 7.32−7.37
(m, 6H, ArH). 13C{1H} NMR (125.3 MHz, C6D6): δ = 24.6 (s, CH3),
32.3 (d, JCP = 27.5 Hz, C(CH3)2), 120.1 (d, JCP = 82.7 Hz, ArC), 129.8
(d, JCP = 11.6 Hz, ArC), 134.2 (s, ArC), 134.8 (d, JCP = 8.8 Hz, ArC),
1
198.8 (s, satellites: JCW = 123.4 Hz, eq CO), 201.2 (s, ax. CO).
31P{1H} NMR (161.8 MHz, C6D6): δ = 38.2 (s, satellites: 2JP−Sn = 44.5
Hz). 119Sn{1H} NMR (149.1 MHz, C6D6): δ = 131.3 (d, 2JSn−P = 48.5
Hz). IR (Nujol, cm−1): 1930 (br, υCO) and 2060 (m, υCO). Anal. Calcd
for C26H21Cl2O5PSnW: C, 38.18; H, 2.59. Found: C, 38.35; H, 2.65.
Mp (°C): 178−180.
1
the filtrate to yield 5D as a white powder (52 mg, 87%). H NMR
Synthesis of Ph3PCMe2·SnH2·W(CO)5 (10). To a mixture of
Ph3PCMe2·SnCl2·W(CO)5 (78 mg, 0.095 mmol) and Li[BH4] (4.5
mg, 0.21 mmol) was added 5 mL of Et2O, followed by stirring for 4 h
at room temperature to yield a brown slurry. The volatiles were
removed under vacuum, and the product was extracted with 10 mL of
toluene, and the resulting mixture was filtered. The solvent was then
removed under vacuum from the filtrate to yield 10 as a red-brown
powder (72 mg, 76%). Crystals of X-ray quality were grown from
(500 MHz, C6D6): Similar to that of Ph3PCMe2·GeH2·BH3 with very
low intensity peaks due to residual GeHD and GeH2 isotopologues
(<8%). 2H{1H} NMR (61.39 MHz, C6H6) δ = 1.56 (br, BD3), 4.63 (s,
GeD2). 11B NMR (159.8 MHz, C6D6): δ = −39.4 (br). IR (cm−1):
1377 (m, υGe−D), 1754 (w, υB−D) and low intensity peaks for Ge−H
and B−H vibrations at 1975 and 2330, respectively.
Synthesis of Ph3PCMe2·SnCl2 (6). Ph3PCMe2 (113 mg, 0.37
mmol) and SnCl2 (70 mg, 0.37 mmol) were combined in a 5 mL
toluene/1 mL THF mixture, followed by stirring for 3 h. The solvent
was removed under vacuum to yield 6 as a white powder (153 mg,
83%). Crystals of X-ray quality were grown from CH2Cl2/hexanes
1
Et2O/hexanes at −35 °C. H NMR (500 MHz, C6D6): δ = 1.61 (d,
3JHP = 20.4 Hz, 6H, C(CH3)2; satellites: 3JHSn and/or 4JHW = ∼60 Hz),
1
1
6.66 (s, 2H, SnH2; satellites: JH‑119Sn = 1030 Hz, JH‑117Sn = 991 Hz),
6.87−7.06 (m, 9H, ArH), 7.29−7.36 (m, 6H, ArH). 13C{1H} NMR
(125.3 MHz, C6D6): δ = 12.9 (d, JCP = 27.5 Hz, C(CH3)2), 27.8 (s,
CH3), 121.7 (d, JCP = 81.6 Hz, ArC), 129.4 (d, JCP = 11.5 Hz, ArC),
133.6 (s, ArC), 134.5 (d, JCP = 8.3 Hz, ArC), 202.8 (s, eq CO), 205.1
(s, ax. CO). 31P{1H} NMR (161.8 MHz, C6D6): δ = 38.3 (s; satellites:
2JP−Sn = 36.3 Hz). 119Sn{1H} NMR (149.1 MHz, C6D6): δ = −49.8 (d,
2JSn−P = 37.4 Hz). 119Sn NMR (149.1 MHz, C6D6): δ = −49.8 (t,
1JSn−H = ∼1075 Hz; the expected t of d pattern was not resolvable due
to decomposition of 10 during prolonged time periods in solution). IR
(Nujol, cm−1): 1740 (s, υSn−H) and 1891 (w, υCO), 1959 (s, υCO), 2040
(m, υCO). Anal. Calcd for C26H23O5PSnW: C, 41.69; H, 3.10. Found:
C, 42.72; H, 3.63. Mp (°C): 80−82 (turns black 70−75 °C).
Synthesis of Ph3PCMe2·SnD2·W(CO)5 (10D). To a mixture of
Ph3PCMe2·SnCl2·W(CO)5 (130 mg, 0.16 mmol) and Li[BD4] (9 mg,
0.3 mmol) was added 5 mL of Et2O, followed by stirring for 4 h at
room temperature to yield a brown slurry. The volatiles were removed
under vacuum, and the product was extracted with 10 mL of toluene,
and the resulting mixture was filtered. The solvent was then removed
under vacuum from the filtrate to yield 10D as a red-brown powder
(73 mg, 61%). 1H NMR (500 MHz, C6D6): same as Ph3PCMe2·SnH2·
W(CO)5 with very low intensity peaks due to residual SnHD and
SnH2 isotopomers (<9%). 2H{1H} NMR (61.39 MHz, C6H6) δ = 6.66
(s, SnD2). IR (cm−1): 1975 (m, υCO) and 2343 (w, υCO), 1254
(υSn−D); very low intensity υSn−H peak at 1746 cm−1.
solution at −35 °C. 1H NMR (400 MHz, CD2Cl2): δ = 1.87 (d, 3JHP
=
21.2 Hz, 6H, C(CH3)2), 7.61−7.76 (m, 15H, ArH). 13C{1H} NMR
1
(125.3 MHz, CD2Cl2): δ = 21.6 (s, CH3), 32.3 (d, JCP = 24.8 Hz,
C(CH3)2), 121.8 (d, JCP = 81.0 Hz, ArC), 130.1 (d, JCP = 11.4 Hz,
ArC), 134.2 (s, ArC), 134.7 (d, JCP = 8.5 Hz, ArC). 31P{1H} NMR
2
(161.8 MHz, CD2Cl2): δ = 36.9 (s, satellites: JP−Sn = ∼89 Hz).
119Sn{1H} NMR (149 MHz, CD2Cl2): δ = 113.3 (br). Anal. Calcd for
C21H21Cl2PSn: C, 51.06; H, 4.28. Found: C, 49.86; H, 4.28. Mp (°C):
165−167 (turns black 155−157).
Synthesis of Ph3PCMe2·BH3 (7).10a To a solution of Ph3PCMe2
(213 mg, 0.70 mmol) in 5 mL of Et2O was added a solution of THF·
BH3 (701 μL, 1.0 M solution in THF, 0.70 mmol) dropwise. The
reaction mixture was then stirred overnight at room temperature, and
the solvent was then removed under vacuum. The resulting solid was
washed with hexanes (3 × 5 mL) and dried to afford 7 as a white solid
(0.154 g, 69%). Crystals suitable for X-ray crystallography were grown
1
from hexanes/CH2Cl2 at −35 °C. H NMR (400 MHz, C6D6): δ =
3
1
1.74 (d, 6H, JPH = 21.2 Hz, C(CH3)), 2.33 (q, 3H, JBH = 90 Hz,
BH3), 6.89−7.01 (m, 9H, ArH), 7.81−7.85 (m, 6H, ArH). 13C{1H}
NMR (125 MHz, C6D6): δ = 30.5 (s, CH3), 124.7 (d, JCP = 77.0, ArC),
128.7 (d, JCP = 10.8, ArC), 132.4 (d, JCP = 2.3, ArC), 135.4 (d, JCP
=
7.8, ArC); the ylidic CMe2 carbon could not be located. 11B NMR
(128 MHz, C6D6): δ = −19.4 (q, 1JBH = 85.7 Hz, BH3). 31P{1H} NMR
(161 MHz, C6D6): δ = 39.4 (s).
Reaction of DMAP·GeCl2 (1) with Li[BH4]. To a mixture of the
DMAP·GeCl2 (126 mg, 0.47 mmol) and Li[BH4] (22 mg, 0.99 mmol)
was added 5 mL of diethyl ether. Upon addition of the solvent a rapid
reaction ensued as evidenced by the formation of (presumably)
elemental Ge. Analysis of the soluble fraction after 12 h of stirring
revealed the clean presence of DMAP·BH3,27 which was identified by
comparison of the 11B NMR spectroscopic data with those found in
the literature.27 In order to isolate DMAP·BH3, the solvent was
removed from the reaction mixture, and 6 mL of CH2Cl2 was added.
The resulting mixture was filtered, and the volatiles were removed
from the filtrate to yield DMAP·BH3 as a white powder as DMAP·BH3
(51 mg, 79%).
Synthesis of Ph3PCMe2·GeCl2·W(CO)5 (8). Ph3PCMe2·GeCl2 (43
mg, 0.096 mmol) and (THF)2·SnCl2·W(CO)5 (63 mg, 0.096 mmol)
were combined in 10 mL of toluene and stirred for 24 h at room
temperature to give a pale-yellow slurry. The volatiles were removed
from the reaction mixture, and 15 mL of CH2Cl2 was added. The
resulting solution was filtered, and the solvent was removed from the
filtrate to give 8 as a white powder (73 mg, 94%). Crystals of suitable
quality for X-ray analysis were grown from CH2Cl2/hexanes at −35
°C. H NMR (500 MHz, C6D6): δ = 1.49 (d, JHP = 19.9 Hz, 6H,
C(CH3)2), 6.89−6.94 (m, 6H, ArH), 6.97−7.03 (m, 3H, ArH), 7.38−
7.44 (m, 6H, ArH). 13C{1H} NMR (125.3 MHz, C6D6): δ = 26.2 (s,
CH3), 32.4 (d, JCP = 25.5 Hz, C(CH3)2), 120.4 (d, JCP = 82.1 Hz,
ArC), 129.3 (d, JCP = 6.5 Hz, ArC), 133.8 (s, ArC), 135.5 (d, JCP = 8.8
Hz, ArC), 199.5 (s, eq CO), 202.0 (s, ax. CO). 31P{1H} NMR (161.8
MHz, C6D6): δ = 38.8 (s). IR (Nujol, cm−1): 1924 (br, υCO) and 2063
(m, υCO). Anal. Calcd for C26H21Cl2O5PGeW: C, 40.46; H, 2.74.
Found: C, 40.44; H, 2.72. Mp (°C): 188−192.
1
3
Reaction of Cy3P·GeCl2 (2) with Li[BH4]. Following an identical
procedure as listed for the reaction of DMAP·GeCl2 with Li[BH4], a
mixture of the Cy3P·GeCl2 (38 mg, 0.089 mmol) and Li[BH4] (5 mg,
0.2 mmol) were combined in 5 mL of Et2O. The resulting mixture
28
containing (presumably) elemental Ge and Cy3P·BH3 was purified
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dx.doi.org/10.1021/ic501265k | Inorg. Chem. 2014, 53, 8662−8671

Inorganic Chemistry
Article
by removing the voltailes, followed by extraction of Cy3P·BH3 with 6
mL of CH2Cl2. The isolated white solid from the soluble extract (23
mg, 87%) was identified as Cy3P·BH3 by comparison of the 11B and
31P NMR spectroscopic data with those found in the literature.28
Reaction of Ph3PCMe2·SnCl2 (6) with Li[BH4]. To a mixture of the
Ph3PCMe2·SnCl2 (99 mg, 0.20 mmol) and Li[BH4] (10 mg, 0.44
mmol) was added 5 mL of diethyl ether. The resulting slurry was
stirred for 2 h to form a shiny black precipitate (presumably metallic
tin) with the formation of Ph3PCMe2·BH3 (7) as the sole soluble
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Reaction of Ph3PCMe2·GeH2·BH3 (5) with IPr. To a mixture of
Ph3PCMe2·GeH2·BH3 (5) (63 mg, 0.16 mmol) and IPr (62 mg, 0.16
mmol) was added 10 mL of toluene, and the reaction mixture was
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1
yield a brown powder that was directly analyzed by H, 11B, and 31P
NMR spectroscopy. These data revealed the formation of IPr·GeH2·
BH3 (32%),4a Ph3PCMe2 (3) (24%), PPh3 (11%), an unidentified
product at 31.7 ppm (22%), and unreacted starting material
Ph3PCMe2·GeH2·BH3 (5) (11%) according to 1H, 11B, and 31P
NMR spectroscopy.
(3) For recent examples with IPr and related NHC donors, see:
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Thermolysis of Ph3PCMe2·GeH2·BH3 (5). Compound 5 (40 mg,
0.10 mmol) was dissolved in 10 mL of toluene, and the solution was
heated to reflux. Within 4 h a gray suspension was noted, and
continued heating for a total of 24 h afforded a dark-gray slurry. The
reaction mixture was filtered, and the solvent was removed from the
filtrate to yield a white solid that was identified as Ph3P·BH318 (>95%
yield) by 1H, 11B, and 31P NMR spectroscopy. When the same
thermolysis was repeated in a closed system in d8-toluene and the
resulting product mixture analyzed in situ by 11B NMR spectroscopy,
another peak was observed at 80 ppm (16% in relation to 84% of
H. W.; Stuckl, A. C.; Niepotter, B.; Carl, E.; Wolf, H.; Herbst-Irmer,
̈
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R.; Stalke, D. Inorg. Chem. 2013, 52, 4736. (f) Al-Rafia, S. M. I.;
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C.-T.; Liu, Y.-H.; Peng, S.-M.; Chiu, C.-W. Angew. Chem., Int. Ed.
2013, 52, 13293.
i
Ph3P·BH3) that was tentatively assigned as the triorganoborane Pr3B;
21
i
literature 11B NMR shift for Pr3B = 83.7 ppm in C6D6. The dark-
gray insoluble product formed in the above-mentioned thermolysis
was analyzed by EDX spectroscopy and determined to be elemental
germanium (Figure S3 in SI).17
Decomposition of Ph3PCMe2·SnH2·W(CO)5 (10). Compound 10
(45 mg, 0.060 mmol) was dissolved in 10 mL of toluene and stirred at
room temperature for 24 h to yield a brown solution over a black
precipitate. The volatiles were removed under vacuum, and 31P NMR
spectroscopy identified the presence of PPh3 as the only phosphorus-
containing product.
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ASSOCIATED CONTENT
* Supporting Information
■
S
Full crystallographic details and the molecular structures of
Ph3PCMe2 (3), Ph3PCMe2·BH3 (7), and [Ph3PCHMe2]-
SnCl3. EDX spectrum and SEM image of the precipitate (Ge)
formed during the thermolysis of Ph3PCMe2·GeH2·BH3 (5).
This material is available free of charge via the Internet at
http://pubs.acs.org.
J.; Blaser, D.; Boese, R. J. Chem. Soc., Chem. Commun. 1993, 1136.
̈
(c) Furstner, A.; Alcarazo, M.; Goddard, R.; Lehmann, C. W. Angew.
̈
AUTHOR INFORMATION
Corresponding Author
*E-mail: erivard@ualberta.ca
Chem., Int. Ed. 2008, 47, 3210. (d) Dumrath, A.; Wu, X.-F.; Neumann,
H.; Spannenberg, A.; Jackstell, R.; Beller, M. Angew. Chem., Int. Ed.
2010, 49, 8988. (e) Malcolm, A. C.; Sabourin, K. J.; McDonald, R.;
Ferguson, M. J.; Rivard, E. Inorg. Chem. 2012, 51, 12905. (f) Wang, Y.;
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H. Organometallics 2013, 32, 6639. (g) Berger, C. J.; He, G.; Merten,
C.; McDonald, R.; Ferguson, M. J.; Rivard, E. Inorg. Chem. 2014, 53,
1475.
■
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
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This work was supported by the Natural Sciences and
Engineering Research Council (NSERC) of Canada (Discovery
Grant for E.R.; Undergraduate Research Award for S.M.M. and
K.C.D.), the Canada Foundation for Innovation (CFI), and
Alberta Innovates Technology Futures (New Faculty Award to
E.R.). The authors acknowledge Kevin Haggerty and Dr. Tapas
Purkait for experimental assistance, and Dr. Gang He for his
help in making the TOC graphic associated with this paper.
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1
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1
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