Insight into the Decomposition Mechanism of Donor-Acceptor Complexes of EH2(E = Ge and Sn) and Access to Germanium Thin Films from Solution

Article abstract of DOI:10.1021/acs.inorgchem.0c01492

Electron-donating N-heterocyclic carbenes (Lewis bases, LB) and electron-accepting Lewis acids (LA) have been used in tandem to yield donor-acceptor complexes of inorganic tetrelenes LB·EH2·LA (E = Si, Ge, and Sn). Herein, we introduce the new germanium (II) dihydride adducts ImMe2·GeH2·BH3 (ImMe2 = (HCNMe)2C:) and ImiPr2Me2·GeH2·BH3 (ImiPr2Me2 = (MeCNiPr)2C:), with the former complex containing nearly 40 wt % germanium. The thermal release of bulk germanium from ImMe2·GeH2·BH3 (and its deuterated isotopologue ImMe2·GeD2·BD3) was examined in solution, and a combined kinetic and computational investigation was undertaken to probe the mechanism by which Ge is liberated. Moreover, the thermolysis of ImMe2·GeH2·BH3 in solution cleanly affords conformal nanodimensional layers of germanium as thin films of variable thicknesses (20-70 nm) on silicon wafers. We also conducted a computational investigation into potential decomposition pathways for the germanium(II)- and tin(II)-dihydride complexes NHC·EH2·BH3 (NHC = [(HCNR)2C:]; R = 2,6-iPr2C6H3 (Dipp), Me, and H; and E = Ge and Sn). Overall, this study introduces a mild and convenient solution-only protocol for the deposition of thin films of Ge, a widely used semiconductor in materials research and industry.

Full text of DOI:10.1021/acs.inorgchem.0c01492

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Article
Insight into the Decomposition Mechanism of Donor−Acceptor
Complexes of EH2 (E = Ge and Sn) and Access to Germanium Thin
Films from Solution
Jocelyn Sinclair, Guoliang Dai, Robert McDonald, Michael J. Ferguson, Alex Brown,* and Eric Rivard*
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ABSTRACT: Electron-donating N-heterocyclic carbenes (Lewis bases, LB) and electron-
accepting Lewis acids (LA) have been used in tandem to yield donor−acceptor complexes
of inorganic tetrelenes LB·EH2·LA (E = Si, Ge, and Sn). Herein, we introduce the new
germanium (II) dihydride adducts ImMe2·GeH2·BH3 (ImMe2 = (HCNMe)2C:) and
ImiPr2Me2·GeH2·BH3 (ImiPr2Me2 = (MeCNiPr)2C:), with the former complex containing
nearly 40 wt % germanium. The thermal release of bulk germanium from ImMe2·GeH2·
BH3 (and its deuterated isotopologue ImMe2·GeD2·BD3) was examined in solution, and a
combined kinetic and computational investigation was undertaken to probe the mechanism
by which Ge is liberated. Moreover, the thermolysis of ImMe2·GeH2·BH3 in solution
cleanly affords conformal nanodimensional layers of germanium as thin films of variable
thicknesses (20−70 nm) on silicon wafers. We also conducted a computational
investigation into potential decomposition pathways for the germanium(II)- and tin(II)-
dihydride complexes NHC·EH2·BH3 (NHC = [(HCNR)2C:]; R = 2,6-iPr2C6H3 (Dipp),
Me, and H; and E = Ge and Sn). Overall, this study introduces a mild and convenient
solution-only protocol for the deposition of thin films of Ge, a widely used semiconductor in materials research and industry.
and Dipp = 2,6-iPr2C6H3).7 This donor−acceptor stabilization
INTRODUCTION
■
approach involves coordinating reactive main group fragments
Inorganic tetrelenes EH2 (E = Si, Ge, Sn, and Pb) are highly
(such as GeH2) between Lewis basic (LB) and Lewis acidic
reactive species that can be generated and trapped with
(LA) entities (Chart 1).8,9 Subsequently, this general donor−
sophisticated low-temperature matrix techniques (often <−200
°C).1 As shown in Chart 1, these main group species adopt
acceptor protocol provided access to various isolable
complexes of inorganic tetrelenes EH2 and ethylenes
H2EEH2 (E = Si, Ge, and Sn).10 Of added note, LB·GeH2·
Chart 1. Depiction of the Frontier Orbitals in Inorganic
Tetrelenes (EH2; E = Si, Ge, Sn, and Pb) and their
Stabilization via Donor−Acceptor (Lewis Base or Acid, LB
or LA) Coordination
LA complexes were shown to be precursors to luminescent Ge
nanoparticles upon microwave heating of the complexes to 190
°C in organic solvents.11 For comparison, this element
deposition procedure is much milder than the widely used
gas phase decomposition of toxic GeH4 (>450 °C) to
elemental Ge and dihydrogen.3c
Herein, new germanium-rich NHC·GeH2·BH3 adducts
(NHC = N-heterocyclic carbene) are introduced with nearly
a 40 wt % of Ge. A number of different NHCs were
investigated experimentally and computationally (Chart 2) en
singlet electronic ground states, leading to a dual electron-
route to the isolation of the new reported complexes.
accepting and electron-donating character. Group 14 element
Moreover, we show that ImMe2·GeH2·BH3 (ImMe2
=
dihydrides are of considerable fundamental interest,2 due in
part to the role of SiH2 and GeH2 as key intermediates in the
chemical vapor deposition (CVD) of bulk Si and Ge from
gaseous tetrelanes EH4.3 While methylene-type (CH2)
reactivity can be coaxed from both metal (LnMCH2)4 and
nonmetal (H2CN2)5 precursors, compounds bearing heavier
element EH2 reactivity are much scarcer.6 In 2009, the Rivard
group prepared the first isolable complex of GeH2 in the form
of the Ge(II) adduct IPr·GeH2·BH3 (IPr = [(HCNDipp)2C:]
(HCNMe)2C:) can cleanly deposit germanium as 20 to 70
Received: May 22, 2020
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Ge(II) reduction and Ge−Cl to Ge−H metathesis procedure
was used in our group to generate IPr·GeH2·BH3.20 Unlike its
bulkier IPr congener IPr·GeH2·BH3, the less-hindered adduct
ImiPr2Me2·GeH2·BH3 (2) is prone to decomposition in
solution, resulting in the formation of byproducts containing
the imidazolium cation [ImiPr2Me2-H]+. As these charged
byproducts possess very similar solubilities to the GeH2
complex 2, samples of ImiPr2Me2·GeH2·BH3 (2) could only
be obtained with a bulk purity of ca. 80%.19 From a crude
sample of 2 we were able to select crystals suitable for single-
crystal X-ray crystallographic analysis. The quality of the
resulting crystallographic data was sufficient to allow for the
full refinement of all boron- and germanium-bound hydrides
(Figure 1a), leading to Ge−H bond lengths (1.43(2) and
1.48(2) Å) that are within the same range as those reported for
IPr·GeH2·BH3.7 The Ge−B distance (2.073(2) Å) in 2 is
similar in length to that of the corresponding distance in IPr·
GeH2·BH3 (2.053(3) Å).7 The adjacent CNHC−Ge bond
length in ImiPr2Me2·GeH2·BH3 (2) is 2.013(2) Å and is
shorter than the CNHC−Ge interaction found in Baines’ Ge(II)
dichloride adduct ImiPr2Me2·GeCl2 (2.106(3) Å).21
Chart 2. N-Heterocyclic Carbenes Investigated in This
Study
nm thick films onto various substrates.12,13 While ImMe2·
GeH2·BH3 does not have the required volatility to enable its
use in CVD, the use of this complex to yield nanometer-thick
Ge coatings via an entirely solution-phase and low-temperature
approach has distinct advantages over pre-existing routes to Ge
films, including the ability to deposit Ge onto thermally
sensitive and nonconducting substrates without the need for
high vacuum chambers or electrochemical apparatuses.13d−f In
addition to these promising new results, an important question
remained unanswered: what is the mechanism of EH2 release
from our donor−acceptor complexes? Does the first step
involve LB-E or E-LA bond cleavage, or does a competing
process, such as a 1,2-hydrogen shift from the tetrel element
(E) to an N-heterocyclic carbene carbon center,14 occur en
route to element deposition? Due to the transient nature of the
EH2 species,15 a combined experimental (kinetics) and
computational approach was used to evaluate possible
decomposition pathways available to ImMe2·GeH2·BH3. We
also used computations to evaluate the decomposition
energetics associated with the E(II) dihydride adducts NHC·
EH2·BH3 (NHC = IPr, ImMe2, or [(HCNH)2C:] (Im) and E
= Ge or Sn).
Given the challenges in obtaining pure ImiPr2Me2·GeH2·
BH3 (2), we prepared the known saturated NHC complex
sImMe2·GeCl4 (3)22 [sImMe2 = (H2CNMe)2C:] from a C−Cl
insertion reaction involving Cl2Ge·dioxane and then explored
the reactivity of 3 with Li[BH4] (Scheme 2). Despite careful
control of the reaction temperature (from −35 °C to room
temperature), the main product isolated was invariably the
known trans isomer23 of the dihydroaminal-bis(borane) adduct
{[H2CNMe(BH3)]2CH2} (4) (Scheme 2). The formation of 4
was accompanied by gray and white solids on the walls of the
reaction vessel, which is consistent with the formation of bulk
germanium and lithium chloride. Compound 4 was also
isolated directly from the reaction between 2-chloro-1,3-
dimethylimidazolinium chloride and Li[BH4] (Scheme 2).
Our search for a new, stable, and low-weight germanium-rich
NHC·GeH2·BH3 complex successfully ended with the high
RESULTS AND DISCUSSION
■
NHC·GeH2·BH3 Adducts with Increased Germanium
Content. Given the successful preparation of IPr·GeH2·BH3,7
and the subsequent application of similar donor−acceptor LB·
GeH2·BH3 compounds for the deposition of bulk and
nanodimensional germanium,11 we leveraged the functional
group tunability of NHCs to pursue higher germanium weight-
content precursors. The first carbene donor explored in this
study, ImiPr2Me2 ([(MeCNiPr)2C:]), made an early debut in
N-heterocyclic carbene chemistry16 and is a ligand commonly
employed for Group 14 element halides and alkoxides.17 It also
has half the molecular weight of IPr. Moreover, ImiPr2Me2 is a
useful supporting ligand for copper atomic layer deposition
(ALD) as it helps impart good thermal stability and high
volatility to the Cu complexes involved.18
yield preparation of ImMe2·GeH2·BH3 (ImMe2
=
[(HCNMe)2C:]). Our route to this Ge(II) dihydride complex
(Scheme 3) involved generation of the free carbene ImMe2 in
situ,24 followed by the addition of a THF solution of this
carbene to Cl2Ge·dioxane to afford the new adduct ImMe2·
GeCl2 (5); notably, prior computational studies indicated that
the precursor complex 5 should be stable.25 Crystals of ImMe2·
GeCl2 (5) suitable for X-ray crystallography (Figure S43)19
were obtained by cooling a THF solution of this Ge(II) adduct
to −35 °C. ImMe2·GeH2·BH3 (6) was then prepared by
combining slurries of ImMe2·GeCl2 and Li[BH4] in Et2O,
followed by vigorously stirring the reaction mixture at room
temperature for 2 h (Scheme 3). After exchanging the solvent
for fluorobenzene, X-ray quality crystals were subsequently
grown at −35 °C, which conclusively identified the product as
ImMe2·GeH2·BH3 (6). As for the ImiPr2Me2 analogue 2, the
quality of the data allowed for the full refinement of the
hydrogen atoms within the −GeH2BH3 unit (Figure 1b). The
observed Ge−B distance in ImMe2·GeH2·BH3 (6) (2.054(4)
Å) is similar in length to that in the temperature-sensitive
complex ImiPr2Me2·GeH2·BH3 (2) (2.073(2) Å), while the
adjacent Ge−CNHC bond length in 6 (1.996(2) Å) is shorter
than those of the Ge−CNHC linkages found in both IPr·GeH2·
BH3 (2.053(3) Å)7 and the precursor Ge(II) complex ImMe2·
GeCl2 (2.069(4)−2.085(3) Å; the range from three different
molecules in the asymmetric unit).19
The target Ge(II) dihydride complex ImiPr2Me2·GeH2·BH3
(2) was prepared by combining the new Ge(IV) halide adduct
ImiPr2Me2·GeCl4 (1, made from free ImiPr2Me2 and GeCl4)19
with excess Li[BH4] (Scheme 1). A related in situ Ge(IV) to
Scheme 1. Synthesis of ImiPr2Me2·GeH2·BH3 (2)
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Figure 1. Crystal structures of (a) ImiPr2Me2·GeH2·BH3 (2, left) and (b) ImMe2·GeH2·BH3 (6, right). Thermal ellipsoids are plotted at the 30%
probability level with all carbene-based hydrogen atoms omitted for clarity. Selected bond lengths (Å) and angles (°) for 2 are as follows: C1−Ge
2.013(2), Ge−B 2.073(2), Ge−H1 1.43(2), Ge−H2 1.48(2), N1−C1−N2 106.6(1), C1−Ge−B 110.21(7), and H−Ge−H 101(1). Selected bond
lengths (Å) and angles (°) for 6 are as follows: C1−Ge 1.996(2), Ge−B 2.054(4), Ge−H1 1.46(3), Ge−H2 1.62(2), N1−C1−N2 106.0(2), C1−
Ge−B 113.5(1), and H−Ge−H: 101(1).
Scheme 2. Preparation of sImMe2·GeCl4 (3) and Subsequent Reactions with Li[BH4] to Form 1,3-Dimethyl-1,3-diazolidine
Bis(borane) (4)
Scheme 3. Synthesis of ImMe2·GeH2·BH3 (6)
Controlled Release of Elemental Germanium from
ImMe2·GeH2·BH3 (6). We were then eager to see if ImMe2·
GeH2·BH3 (6) could yield bulk Ge after being heated in
solution, and wanted to identify the nature of the byproducts
formed to gain insight into the mechanism of decomposition.
To start, a sample of ImMe2·GeH2·BH3 (6) was heated to 100
°C (2 h) or 125 °C (3 days) under a static vacuum (ca. 2 ×
10−2 mbar), and the products were examined by Raman
spectroscopy (Figure 2). Analysis of the products formed after
heating 6 to 100 °C (Figure 2, left) showed the appearance of
the expected Ge−Ge peak26 at 280 cm−1 for amorphous Ge
coupled with a collective decrease in the intensity of the
Raman peaks associated with 6. The consumption of 6 was
accompanied by the formation of the carbene−borane adduct
ImMe2·BH3. The photograph shown at the right of Figure 2
depicts the remaining sample after the thermolysis of 6 at 125
°C under N2 (for 18 h) and illustrates the volatility of the
decomposition byproduct ImMe2·BH3, which crystallized on
the walls of the upper (cooler) portion of the glass NMR tube;
elemental Ge can be seen at the bottom of the tube. If the
decomposition of 6 is repeated at 125 °C under a static
vacuum of ca. 2 × 10−2 mbar for 3 days, the only nonvolatile
species that remains (according to Raman spectroscopy) is
amorphous Ge (Figure 2, left). The clean conversion of
ImMe2·GeH2·BH3 (6) to Ge and volatile ImMe2·BH3 is
promising, as the organic byproducts formed can be removed
either by sublimation or washing with an organic solvent.
Consistent with the Raman data in Figure 2, the deposited
germanium from the solid state thermolysis of 6 was confirmed
to be amorphous by powder X-ray diffraction (Figure S44).19
C
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to a residual mass of 49.6 wt % according to TGA. ImMe2·BH3
was independently subjected to TGA (Figure 3, right) and the
onset of its sublimation can be seen at 150 °C, aligning with
features in the TGA trace of ImMe2·GeH2·BH3 (6); for
ImMe2·BH3, sublimation reaches completion (100 wt % loss)
at 290 °C. Given that ImMe2·GeH2·BH3 (6) initially contains
39 wt % Ge, there is unaccounted mass left in the residue after
TGA. At this stage, we are unsure as to the reason for the mass
difference; however, we cannot rule out oxidation of the
deposited Ge by traces of atmospheric oxygen. It may be
posited also that some ImMe2 or organic contaminants remain
adhered to the surface of the deposited germanium, leading to
the higher final mass yield. Energy dispersive X-ray (EDX)
analyses of the residual samples of Ge after the decomposition
of 6 in solution (vide infra) do not indicate the presence of
nitrogen (Figure S48);19 however, the sensitivity of this
technique to nitrogen is low.
The solution-phase deposition of Ge films was also carried
out by the immersion of various substrates into solutions of
ImMe2·GeH2·BH3 (6) in toluene, followed by controlled
heating. The samples were heated at 100 °C for either 3 or 10
h, after which time the substrates were washed with benzene to
remove the ImMe2·BH3 byproduct. Gratifyingly, 6 was
consistently able to deposit thin layers of elemental Ge onto
a variety of substrates, including Si wafers (Figure 4) and glass
wool (Figure S52).19 Deposition of thin films of germanium
onto Si wafers yielded the best surface coverage, allowing for a
reliable determination of the thickness of the deposited Ge by
scratching the surface (post deposition, Figure 4a) and imaging
of the exposed Ge film edges at an angle of 54° (Figure 4b).28
EDX analysis (Figure 4c) illustrates the Ge deposited on the
surface and the lower Ge signal where the deposited layer had
been removed. The thicknesses of the deposited layers after
heating for 10 h did not correlate with the concentration of 6
in solution (from 0.5 to 1.2 × 10−2 M); however, all samples
that were heated for this time period gave films with average
thicknesses in the range of 17(2)−29(4) nm (Table 1) with a
similar morphology of overlapping hemispheroids. After
samples of 6 were heated to 100 °C for a shorter period of
3 h, the deposition of Ge still transpired to yield thicker layers
(up to 70 nm).
Figure 2. (left) Raman spectra associated with the decomposition of
ImMe2·GeH2·BH3 (6). Trials were conducted in the solid state under
static vacuum. (right) Photograph of a sealed glass NMR tube under
N2 after the thermal decomposition of 6 at 125 °C (18 h). Elemental
Ge and crystalline ImMe2·BH3 (also confirmed by 1H NMR
analysis)19 can be seen in the lower and upper portions of the tube,
respectively.
To characterize the organic byproducts from the above-
mentioned decomposition of ImMe2·GeH2·BH3 (6), a sample
of this adduct was then heated to reflux in C6D6 (external bath
1
temperature of 100 °C; caution, closed system). H and 11B
NMR spectroscopy after 48 h indicated the clean conversion of
27
6 into the known compound ImMe2·BH3 (Figures S27 and
S28).19 ImMe2·BH3 was also independently synthesized to
confirm its identity and to determine its thermal properties
(vide infra).
The thermal properties of ImMe2·GeH2·BH3 (6) were
analyzed by differential scanning calorimetry (DSC) and
thermogravimetric analysis (TGA), both of which were
conducted at heating rates of 10 °C/min under N2. A
representative DSC trace is shown at the left in Figure 3 and
reveals the onset of an endothermic event at 108 °C, agreeing
well with the visually determined melting point of 6 (103−105
°C). The subsequent exothermic event beginning at 118 °C
appears to be linked to the onset of Ge deposition, as thermal
gravimetric analysis of ImMe2·GeH2·BH3 (6) (Figure 3,
middle) shows mass loss beginning at ca. 110 °C. TGA
recorded another dip in mass near 150 °C, which corresponds
with the tail end of the exothermic feature in the DSC of 6.
Continued heating of 6 up to 600 °C results in the sublimation
of the decomposition product ImMe2·BH3 (vide infra), leading
One possible explanation for the formation of thin films at
longer deposition times (Table 1) is an Ostwald ripening-type
growth of the remaining suspended Ge nanoparticles in
toluene at the expense of the surface-bound Ge.29 Dynamic
light scattering experiments revealed that the Ge particles in
solution exhibited steady growth over time from a 187(28) nm
solvodynamic radius after 30 min to 773(21) nm after 3 h
Figure 3. (left) DSC of ImMe2·GeH2·BH3 (6) under a flow of N2, with a heating rate of 10 °C/min. TGA of (middle) ImMe2·GeH2·BH3 (6) and
(right) ImMe2·BH3 conducted under a gentle flow of N2 at a heating rate of 10 °C/min.
D
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XPS measurements; however, it should also be stated that XPS
has a depth sensitivity of ∼10 nm. Thus, it is likely that the
bulk sample contains a higher ratio of Ge than is detected on
the surface by XPS. An extremely low (0.48 atom %) amount
of nitrogen was detected by the survey XPS on the substrates
after deposition, supporting the earlier supposition that very
little carbene (ImMe2) remains bound to the surface of the
deposited germanium even with the low deposition temper-
atures involved (Figure S49).19
Computed Structures for NHC·EH2·BH3 Complexes (E
= Ge and Sn). To probe the electronic and steric effects
associated with the decomposition of our Ge(II) dihydride
complexes, we first optimized the structures of the following
three adducts: NHC·GeH2·BH3, where NHC = [(HCNR)2C:]
and R = Dipp (IPr), Me (ImMe2), or H (Im) (Chart 3). The
Chart 3. NHC·EH2·BH3(E = Ge and Sn) Donor−Acceptor
Adducts Examined Computationally in This Study
Figure 4. Ge layer deposited onto a Si wafer via the decomposition of
ImMe2·GeH2·BH3 (6) in toluene (at a concentration of 6.3 × 10−3
M
for 10 h at 100 °C). (a) Secondary electron SEM image of a Si wafer
with the Ge layer scratched off in a pattern using a stainless-steel
needle. (b) Micrograph taken at a 54° angle with respect to the
electron beam to determine the layer thickness (17(2) Å) at the edge
of the scratch. (c) EDX mapping of the imaged section in Figure 4a
showing a higher Ge signal in the unscratched areas along with a
strong background of Si; some background C was also detected.
Micrographs and EDX measurements were collected at 5 kV. Dotted
lines on the Ge EDX map in Figure 4c are provided as guides for the
eye.
7
two most hindered complexes in the series, IPr·GeH2·BH3
and ImMe2·GeH2·BH3 (6), have been synthesized in the
laboratory, while the parent system Im·GeH2·BH3 represents
an experimentally unknown model complex. For comparison,
the corresponding (unknown) Sn(II) dihydride complexes
NHC·SnH2·BH3 were also studied computationally (Chart 3).
Unless specified, all energies and geometrical parameters refer
to those determined computationally with a THF polarizable
continuum model (PCM); geometries for all structures are
available in the Supporting Information.19 For all structures
determined computationally in this work, the geometry
optimizations were performed via density functional theory
(DFT) calculations, using default convergence criteria, with
the M06-2X functional.30 In most computations, the cc-pVDZ
basis set31 was used for all atoms except Sn, where the cc-
pVDZ-PP basis set and a corresponding effective core potential
were used.31 For Sn-containing compounds, this combination
of basis sets will be referred to as cc-pVDZ-(PP). For the
largest IPr·GeH2·BH3 complex, the 6-311+G(d) basis set31 was
used.
Our computations show that NHC substitution has only a
modest impact on the proximal CNHC−Ge bond length, with a
ca. 0.04 Å bond elongation noted when the less hindered
complex Im·GeH2·BH3 is compared to the Dipp-containing
complex IPr·GeH2·BH3 (2.039 vs 2.074 Å). Notably, the
CNHC−Ge−B bond angle widens from 100.0° (NHC = Im) to
116.3° (ImMe2) to 125.5° (IPr) as the steric bulk of the NHC
is increased. Within the NHC·SnH2·BH3 series,19 the
computed CNHC−Sn bond length in IPr·SnH2·BH3 (2.369 Å)
is significantly longer than that in Im·SnH2·BH3 (2.312 Å).
The CNHC−Sn−B bond angles also increase from 91.5° to
109.6° to 123.9° when the NHC is altered from Im to ImMe2
to IPr, respectively. Lastly, the nature of the N-bound
substituents has a minimal impact on the coordinative E−B
bond lengths, with all values within 0.01 Å of each other
Table 1. Layer Thickness Measurements of Amorphous Ge
Deposited from 6 onto Si Wafers at 100 °C in Toluene
deposition time (h)
[ImMe2·GeH2·BH3] (M)
layer thickness (nm)
10
10
10
10
3
1.2 × 10−2
1.0 × 10−2
6.3 × 10−3
5.0 × 10−3
1.0 × 10−2
5.1 × 10−3
20(4)
22(4)
17(2)
29(4)
73(12)
40(7)
3
(Table S5),19 which provides support for the growth of Ge
nanoparticles in solution over time. However, no direct
evidence of a surface to nanoparticle germanium transfer was
observed, which would have supported our Ostwald ripening
postulate mentioned above. The walls of the reaction vessel
were coated with an orange and red precipitate after Ge film
deposition onto Si, indicating that Ge deposition is not
exclusive to the Si substrate. Although a number of equilibria
are possible between the solution, the precipitate, and the Ge
film deposited on the substrate, it should be noted that the
diameter of the hemispheroids deposited onto the Si wafer do
not exceed ∼150 nm (Figure S47),19 suggesting that larger
particles of Ge are unstable on the Si surface and may be rinsed
off during substrate processing. The Raman spectra of the
deposited films consistently yield a characteristic broad peak
for amorphous Ge, centered at 280 cm−1 (Figure S51).19,26
XPS identified the major deposited species to be elemental Ge
(61%), with GeO and GeO2 also present, likely due to the
unavoidable exposure of the sample to oxygen before
measurements were taken. Surface oxidation is to be expected
due to the intermittent exposure of the sample to air prior to
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a
Scheme 4. Computationally Investigated Pathways for NHC·EH2·BH3 Decomposition
a
Paths A and B represent heterolytic CNHC−E and E−B bond cleavage, while paths C and D follow an initial common 1,2-hydride shift to generate
a putative (NHCH)E(H)·BH3 intermediate (IM1).
among the GeH2 and SnH2 adduct series.19 Natural bond
orbital (NBO) analysis showed that the CNHC−E linkages in
the NHC·EH2·BH3 adducts are substantially polarized toward
the ligating NHC carbon (CNHC). For example, the CNHC−Ge
bond in IPr·GeH2·BH3 has a single bond character with 76.3%
of the electron density toward carbon while the Ge−B bond in
IPr·GeH2·BH3 shows a slight polarization of electron density
toward the Ge atom (53.5%).19
Computational Evaluation of Possible Decomposi-
tion Mechanisms for NHC·GeH2·BH3 Adducts. Given the
above-mentioned ability of ImMe2·GeH2·BH2 to yield
elemental germanium upon mild thermolysis in either THF
or toluene, the mechanism by which this process happens is of
significant interest. Herein, two possible decomposition routes
were examined for the NHC·EH2·BH3 adducts (E = Ge or
Sn): (a) the stepwise dissociation of E−B and CNHC−E bonds
(or in the reverse order) to liberate EH2 and eventually afford
bulk Ge (or Sn), NHC·BH3, and H2 gas (paths A and B in
Scheme 4) and (b) 1,2-hydride transfer (migration) routes that
either involve carbene-ring expansion14 and the reductive
elimination of Ge or Sn (path C in Scheme 4) or the direct
formation of a dihydroaminal (NHC)H2 by sequential Ge (or
Sn) to C hydride transfers (path D). We also computed the
Gibbs free energies associated with various intermediates and
transition states along paths A−D, both in the gas phase and
with a THF polarizable continuum model (PCM). For the
final E(g) to E(s) steps, we used the experimentally known
ΔfG for the gaseous elements,32 which are 335.9 and 267.3 kJ/
mol for Ge(g) and Sn(g), respectively. The results determined
at 298.15 K for paths A/B and C/D for ImMe2·GeH2·BH3(6)
are summarized in Figures 5 and 6, respectively; corresponding
results at 373.15 K (100 °C) in THF can be found as Figures
S72 and S73 in the Supporting Information and demonstrate
that all the reported free energy differences are modestly
reduced. The corresponding energy profiles for the decom-
position of the structurally related Im·GeH2·BH3 and IPr·
GeH2·BH3 adducts can be found as Figures S57−S61 in the
Supporting Information.19
Paths A and B: Direct Adduct Cleavage. The most
direct route by which NHC·GeH2·BH3 adducts might
decompose is via the initial heterolytic cleavage of a polar
covalent (dative) CNHC−Ge or Ge−B bond with the eventual
formation of NHC·BH3, elemental Ge, and H2. Path A
(Scheme 4) involves an initial CNHC−Ge bond breakage,
followed by Ge−B bond dissociation; path B (Scheme 4)
begins with Ge−B bond dissociation, followed by CNHC−Ge
bond breakage. Both of these pathways then proceed by the
coordination of BH3 to NHC (yielding NHC·BH3) and the
concomitant decomposition of GeH2 into Ge and H2. As
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occurs with a free energy change of 143.9 kJ/mol (in THF);
thus, CNHC−Ge bond cleavage becomes slightly more
endoergic in ImMe2·GeH2·BH3 versus that in ImMe2·GeH2,
which partially explains our inability to isolate NHC·GeH2
complexes thus far in our laboratory. As outlined in Figures
S57−S61 in the Supporting Information,19 similar energy
trends for the decomposition of IPr·GeH2·BH3 and Im·GeH2·
BH3 were found, and a preference for path B was noted.
Alternate Decomposition Routes for NHC·GeH2·BH3
Adducts: Ring Expansion (Path C) and Direct Hydrogen
Transfer (Path D) Mechanisms. Path C is outlined in
Scheme 4 and starts with a 1,2-hydride shift from germanium
to the carbene carbon (CNHC) to give (NHCH)GeH·BH3
(IM1), followed by a carbene ring expansion to eventually give
intermediate IM3. Path C ends with the formal reductive
elimination of the dihydroaminal (NHC)H2 from the ring-
expanded intermediate IM3, releasing “Ge·BH3” to later form
elemental Ge and BH3 as coproducts (PC/D, Scheme 4). For
ImMe2·GeH2·BH3 (Figure 6), the first step in path C, hydride
migration from Ge to CNHC involves a relatively high Gibbs
free energy of activation of 218.8 kJ/mol; therefore, path C is
already more energetically unfavorable at this stage for the
decomposition of ImMe2·GeH2·BH3 in relation to paths A and
B by ca. 70−100 kJ/mol. The next step in path C involves
carbene ring expansion,14 where a Ge atom inserts into a C−N
bond to yield a GeN2C2 six-membered ring intermediate IM2
(Scheme 4 and Figure 6). This ring expansion process is
Figure 5. Computed Gibbs free energies (kJ/mol) associated with the
intermediates formed in the decomposition of ImMe2·GeH2·BH3 via
path A (e.g. IMA and PA/B) and path B (e.g., IMB and PA/B) with a
THF PCM; values in parentheses refer to gas-phase computations.
Lowest energy states are plotted; in this case, IMC contains H2Ge in
the singlet state, and IMD is plotted containing Ge(g) (triplet) (Table
S6).19 The Gibbs free energy of formation (ΔfG) for Ge(g) was taken
as 335.9 kJ/mol.32
before, each mechanism was examined in the gas phase and
THF using a PCM.19
accompanied by a modest free energy of activation (via TS1−2
)
Path A involves the endoergic cleavage of a CNHC−Ge bond
in ImMe2·GeH2·BH3 (Figure 5) at a Gibbs free energy penalty
of 168.2 kJ/mol in THF, which is slightly less favorable in
comparison to the free energy cost of 149.6 kJ/mol in the gas
phase. Next, Ge−B cleavage in the putative intermediate
H2Ge-BH3 is predicted to occur at a lower free energy change
of 98.4 kJ/mol. Overall, the first step associated with path B is
slightly more energetically favorable, given the lower free
energy associated with the initial heterolytic Ge−B bond
cleavage (ΔG = 122.7 kJ/mol) in THF compared to that of the
initial CNHC−B bond scission in path A (168.2 kJ/mol). Once
the BH3 group is liberated, scission of the remaining
coordinative CNHC−Ge bond in the adduct ImMe2·GeH2
of ΔG‡ = 39.4 kJ/mol, which is energetically more favorable by
about 180 kJ/mol compared to that of the initial 1,2-hydride
shift. From IM2, another 1,2-hydrogen shift (via TS2−3) was
modeled to yield the cyclic intermediate IM3 (ΔG‡ = 106.8 kJ/
mol). The last computed step in this mechanism involves the
direct reductive elimination of the dihydroaminal (ImMe2)H2
from IM3, producing the putative species “Ge·BH3”; this step is
the least favorable of path C, with a large free energy of
activation of 230.3 kJ/mol (via TS3−4).
We also probed a direct hydrogen transfer mechanism (path
D) in which two direct Ge to CNHC hydride transfer processes
occur to release the dihydroaminal (ImMe2)H2 without a
Figure 6. Computed Gibbs free energies in kJ/mol associated with the intermediates formed in the decomposition of ImMe2·GeH2·BH3 via path C
(stepwise via IM1−IM4) and path D (via TS1−4) with a THF PCM; values in parentheses refer to gas phase computations. Lowest energy states are
plotted; in this case, IM5 is plotted as containing Ge(g) (triplet) (see Table S6).19 The Gibbs free energy of formation (ΔGformation) for Ge(g) was
taken as 335.9 kJ/mol.32
G
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carbene ligand ring expansion. The first step in path D is
exactly the same as in path C, with a 1,2-H shift from Ge to
CNHC to form (ImMe2H)GeH·BH3 (IM1, Figure 6); to recap,
this step has a large free energy of activation (in THF) of 218.8
kJ/mol. As summarized in Figure 6, path D then involves a
second direct 1,2-hydrogen migration between Ge and CNHC in
IM1 to form (ImMe2)H2 and “Ge·BH3” (IM4); this second 1,2-
H shift has a computed free energy of activation of 78.4 kJ/mol
(via TS1−4). Once at the intermediate IM4, path D follows a
similar route as path C to eventually give the final
decomposition products (ImMe2)H2, Ge(s) and BH3 (PC/D
in Figure 6).
When rate-determining steps (RDSs) for paths A−D (note:
the initial bond dissociations in paths A and B are barrierless,
Figure S57) were calculated,19 the decomposition of ImMe2·
GeH2·BH3 was predicted to proceed via path B (with a free
energy of activation for the RDS of 143.9 kJ/mol, Figure 5),
with an associated barrier in the RDS for path A of 168.2 kJ/
mol (Figure 5). The initial cleavage of the Ge−B bond in path
B is the most energetically feasible initial step of the paths
explored (A−D), with a free energy penalty of 122.7 kJ/mol in
THF; the RDSs for paths C (230.3 kJ/mol) and D (218.8 kJ/
mol) are energetically the highest of the series. In line with our
computations, the thermal decomposition of ImMe2·GeH2·
BH3 does not yield any dihydroaminal (ImMe2)H2; thus, the
decomposition of the Ge(II) dihydride adducts via either path
A or B appears to be the most plausible.
SnH2·BH3 → ImMe2·BH3 + Sn(s) + H2, was estimated to have
a ΔdecompG value of −241.1 kJ/mol in THF (vs one of −242.9
in the absence of solvent); as for the germanium analogues,
similar overall trends were found in the computed Sn(II)
dihydride complexes Im·SnH2·BH3 and IPr·SnH2·BH3.19
Kinetic Analysis of the Decomposition of ImMe2·
GeH2·BH3 (6) and Link to Computations. Based our
computational work (vide supra), paths A and B are viable
routes by which the elemental germanium is extruded from
NHC·GeH2·BH3 adducts. Because we used THF as our
solvent model, the decomposition of the Ge(II) hydride
adduct ImMe2·GeH2·BH3 (6) in refluxing THF-D8 (18 h) was
explored to see if the dominant product was an NHC·BH3
complex (arising from path A or B, Scheme 4) or a
dihydroaminal [(HCNMe)2CH2] (arising from path C or D,
Scheme 4). After the thermolysis of 6 in THF-D8, ImMe2·BH3
1
was detected as a product by H NMR spectroscopy (20%,
determined relative to 4,4′-difluorobiphenyl as an internal
standard, Figure S31);19 however, other unidentified products
were also present. Interestingly, THF·BH3 was also detected by
11B NMR analysis of the end products (Figure S32),19
indicating that the coordinating solvent (THF) plays an
added role in the thermal degradation of 6 by trapping some of
the BH3 that is liberated.
To recap, when ImMe2·GeH2·BH3 (6) was heated at 100 °C
in either toluene-D8 or C6D6, ImMe2·BH3 was found to be the
only soluble decomposition product. Thus, at this point, either
path A or B was likely responsible for the decomposition of 6
in weakly coordinating solvents due to the absence of the
dihydroaminal degradation product [(HCNMe)2CH2]. To
further investigate the mechanism by which ImMe2·GeH2·BH3
(6) decomposes, a solution of 634 in toluene-D8 was heated in
a sealed J-Young NMR tube to 100 °C, and the progress of the
We also estimated the overall free energies associated with
the formation of the ImMe2·GeH2·BH3 decomposition
products from paths A/B: ImMe2·BH3, Ge(s), and H2 (PA/B
in Scheme 4 and Figure 5). After taking the Gibbs free energy
of formation for Ge(g) into consideration,32 an overall
ΔdecompG of −175.4 kJ/mol was estimated (−182.5 kJ/mol
in the absence of solvent). For comparison, the free energy
associated with ImMe2·GeH2·BH3 decomposition via paths C/
D to give (ImMe2)H2, Ge(s), and BH3 was found to be
unfavorable in THF, with an estimated ΔdecompG of +26.7 kJ/
mol (−4.1 kJ/mol in the absence of solvent, Figure 6). Thus
far, our computational and experimental data suggest that
NHC·GeH2·BH3 adducts likely decompose via either path A or
B.
1
decomposition was monitored in situ using H NMR (in the
presence of 4,4′-difluorobiphenyl as an internal standard). As
expected for unimolecular decomposition, a linear relationship
of ln[6] with time was found (Figure 7), leading to a first-order
rate constant (kH) of 1.9(2) × 10−4 s−1. It should be stated that
the observed first-order decay in 6 could fit any of the
computationally investigated paths (A−D) in Scheme 4, as all
Computed Mechanisms for NHC·SnH2·BH3 Decom-
position. We also computed the Gibbs free energies
associated with the decomposition of the model Sn(II)
dihydride complexes NHC·SnH2·BH3 (NHC = IPr, ImMe2,
and Im; Chart 2). It should be stated that our attempts to
prepare IPr·SnH2·BH3 afforded exclusively Sn metal, H2, and
7
IPr·BH3 while the isolation of stable Sn(II) dihydride
complexes required the presence of strongly Lewis acidic
metal carbonyls, e.g., IPr·SnH2·M(CO)5 (M = Cr and W).10a,33
Overall, similar trends were found with respect to the
energetics of decomposition in our NHC·SnH2·BH3 models
(Figures S65−S69)19 as in the above-mentioned GeH2
donor−acceptor complexes. When examining ImMe2·SnH2·
BH3, the biggest difference is the more facile and favorable
cleavage of the Sn−B linkage in path B (90.3 kJ/mol in THF,
80.1 kJ/mol in the gas phase)19 compared to the Ge−C bond
breakage in ImMe2·GeH2·BH3 (122.7 kJ/mol in THF). For
ImMe2·SnH2·BH3, the common Sn to CNHC 1,2-hydride shift
in paths C and D (to give (ImMe2H)SnH·BH3) is substantially
uphill energetically, with a free energy of activation of 192.8
kJ/mol in THF (Figure S69).19 In addition, the overall
decomposition reaction associated with paths A and B, ImMe2·
Figure 7. Decomposition rates of ImMe2·GeH2·BH3(6, black squares)
and ImMe2·GeD2·BD3 (6D, red circles). Each thermolysis run was
conducted at 100 °C in toluene-D8 with spectral integration relative
to an internal standard of 4,4′-difluorobiphenyl. Average data points
from three trials are plotted.
H
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paths are unimolecular-based decompositions. However, one
might see different kinetic isotope effects (KIEs) among the
proposed decomposition pathways, as paths C and D start with
a common Ge−H bond breaking event as a rate-determining
step (i.e., 1,2-hydrogen shift). As a result, the deuterium
isotopologue ImMe2·GeD2·BD3 (6D) was prepared from
ImMe2·GeCl2 and Li[BD4], and its decomposition in
toluene-D8 was examined.
angles and bond lengths in the molecule were optimized.
Figure 8 shows the changes in the Raman resonance frequency
The thermolysis of 6D in toluene-D8 (100 °C) was carried
out in triplicate, leading to a rate of decomposition of 2.2(2) ×
10−4 s−1 (Figure 7) and a kinetic isotope effect (KIE = kH/kD)
of 0.86(11). Rate-determining hydride-transfer in path C or D
would be expected to follow a normal primary KIE (kH/kD ≫
1); thus, the observed kinetic data supports that decom-
position of 6 (and 6D) via either path A or B.35 Moreover,
both paths A and B might yield a small inverse KIE (kH/kD <
1), as the H and D atoms are located in secondary positions in
relation to the rate determining bond cleavage (C−Ge or Ge−
B) involved in the decomposition.
Curious about further differentiating between paths A and B,
we decided to computationally investigate the KIE associated
with each path. Specifically, we aimed to determine whether an
inverse KIE would be expected for these pathways due to
secondary bond breakage effects. Before outlining our
computational work, we would like to highlight eq 1, which
links the dependence of the KIE value to changes in the kinetic
energy during secondary bond breakage events36
1
2
kH/kD = exp{− × Σ[uH‡ − uD‡ − (uH0 − uD0)]}
(1)
Given that u represents the hν/kT of the transition state (‡)
and the initial condition (0), and that the relationship between
the vibrational frequencies of E−H and E−D bonds can be
approximated as νE−D = νE−H/1.35, this expression can be
simplified to eq 2, wherein the direct association of KIE to the
sum of the E−H vibrational frequency changes becomes
evident. When the overall change in E−H bond frequencies
(ΣΔν, in cm−1) becomes greater than zero (ΣΔν > 0) during
complex dissociation, an inverse kinetic isotope can be
expected (i.e., kH/kD< 1)36
Figure 8. Deviations from the initial calculated Raman frequencies
(B3-LYP/cc-pVDZ) of the BH3 and GeH2 resonance frequencies with
increasing C−Ge (path A, starting bond length 2.010 Å) and Ge−B
(path B, starting bond length 2.060 Å) bond lengths.
kH/kD = exp{(−0.1865/T) × ΣΔν}
(2)
Going back to the assumption that either path A or B (Ge−
C or Ge−B bond cleavage, respectively) is the most likely
mechanism for the decomposition of ImMe2·GeH2·BH3 (6)
(vide supra), a computational study (B3LYP/cc-pVDZ) was
carried out to investigate the change in Raman frequencies of
the Ge−H and B−H bonds during adduct dissociation and
bond cleavage.37 As the simplified expression in eq 2 relies only
on the change in the vibrational frequency and already
accounts for the change in mass between H and D, calculations
were carried out only on the hydrogen isotopologue ImMe2·
GeH2·BH3 (6). Although the default temperature for the
computed vibrational frequencies was 298 K19 and exper-
imental decomposition occurred at 373 K, Raman frequencies
do not shift drastically with temperature;38 therefore, a
comparison can be made between the computed and
experimental KIE values.
of the BH3 and GeH2 symmetric and asymmetric stretches
during the ImMe2 dissociation from IMe2·GeH2·BH3 (6).
According to eq 2, the Raman frequencies should be modeled
at the transition state of the bond breaking step. However, the
energies associated with this dissociation confirmed the earlier
assumption that the bond is broken without an energy barrier
in the form of a transition state (Figure S57); therefore, the
highest energy species (longest bond length) was examined for
comparative purposes. The longest tested bond length had a
C−Ge bond length of 3.062 Å. The sum changes in E−H
frequencies at this C−Ge distance have values of −35 and +99
cm−1 for the B−H and Ge−H stretches, respectively. Of
particular note is the strong negative contribution of the BH3
symmetric stretching frequency, which comprises the entirety
of the negative frequency contributions.37 Applying eq 2 to this
system (kH = 1.9 × 10−4 s−1, ΣΔν = +64 cm−1, and T = 373
K), a kD of 2.0 × 10−4 s−1 was expected (KIE = 0.93).
For the calculations related to path A, sequential C−Ge
bond extensions in 0.1 Å increments were applied starting from
an optimized C−Ge bond length of 2.062 Å to a final distance
of 3.062 Å (B3LYP/cc-pVDZ).19 After each bond elongation
event, the new bond length was then frozen, and all other
Path B was modeled in a similar fashion with sequential Ge−
B bond extensions in 0.1 Å increments from a starting bond
length of 2.010 Å to a final distance of 3.010 Å. As the BH3
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center in this model begins to rehybridize from its starting 4-
coordinate sp3 environment in 6 to an approximately planar sp2
arrangement as the B−Ge bond lengthens, the resulting
increase in s-orbital character in the B−H bonds should lead to
higher B−H stretching frequencies. Accordingly, the total
change in B−H stretching frequencies from the initial to final
geometry was computed to be +451 cm−1. In contrast, the
overall change in Ge−H asymmetric and symmetric stretches
decreased by 136 cm−1; thus, the change in the B−H
stretching frequency is the dominant term (by a factor of 3).
The summary large positive change in the vibrational
frequencies for path B leads to an expected kD of 2.7 × 10−4
s−1 (by eq 2, ΣΔν = +314 cm−1 and KIE = 0.82). It should be
taken into consideration that the experimental values do have
an inherent error and that the rates predicted by the
computational analysis fall within 3σ of the experimental
values for both paths A and B. Thus, our computational
analysis of the KIE is in line with the experimental data and
supports the decomposition of 6 via an initial bond
dissociation process, with a slight preference for path B
(starting with the Ge−B bond breaking) on the basis of the
computed free energies involved.
tional data can be downloaded free of charge from FigShare:
10.6084/m9.figshare.11962752
AUTHOR INFORMATION
■
Corresponding Authors
Alex Brown − Department of Chemistry, University of Alberta,
Edmonton, Alberta, Canada T6G 2G2; orcid.org/0000-
0002-5384-9222; Email: alex.brown@ualberta.ca
Eric Rivard − Department of Chemistry, University of Alberta,
Edmonton, Alberta, Canada T6G 2G2; orcid.org/0000-
0002-0360-0090; Email: erivard@ualberta.ca
Authors
Jocelyn Sinclair − Department of Chemistry, University of
Alberta, Edmonton, Alberta, Canada T6G 2G2; orcid.org/
0000-0001-5835-4344
Guoliang Dai − School of Chemistry, Biology and Materials
Engineering, Suzhou University of Science and Technology,
2215009 Suzhou, P. R. China
Robert McDonald − Department of Chemistry, University of
Alberta, Edmonton, Alberta, Canada T6G 2G2; orcid.org/
0000-0002-4065-6181
Michael J. Ferguson − Department of Chemistry, University of
Alberta, Edmonton, Alberta, Canada T6G 2G2; orcid.org/
0000-0002-5221-4401
CONCLUSIONS
■
This work introduces new NHC·GeH2·BH3 donor−acceptor
complexes featuring an unprecedented high Ge atom content
(approaching 40 wt %). We also show that ImMe2·GeH2·BH3
can deposit nanodimensional films of Ge onto silicon wafers
and unusual substrates, such as glass wool, from solution via a
convenient and mild (100 °C) procedure.19 Our procedure
requires only standard Schlenk techniques and glassware, and
any byproducts formed during Ge film deposition can be easily
removed by washing with an organic solvent. This is in
contrast to pre-existing routes to Ge films that require very
high temperatures or sophisticated CVD set-ups.13 Addition-
ally, we examined four different decomposition pathways for
various NHC·EH2·BH3 (E = Ge and Sn) complexes, and an
analysis of the computed Gibbs free energies and kinetic
studies points toward the initial E−B bond cleavage as the
most likely decomposition route to eventually yield NHC·BH3,
Ge or Sn, and H2. Future work will involve the application of
our mild Ge deposition strategy to nanochemistry (i.e., core−
shell nanoparticle synthesis) and the modification of our
donor−acceptor approach to enable more atom efficient
element deposition cycles.
Complete contact information is available at:
https://pubs.acs.org/10.1021/acs.inorgchem.0c01492
Author Contributions
The manuscript was written through contributions of all
authors. J.S. contributed all experimental work, simulated
Raman and kinetic studies, and contributed to the manuscript.
G.D. contributed computational investigations of decomposi-
tion and rearrangement pathways. M.J.F. and R.M. provided X-
ray crystallographic structure refinements. A.B. and E.R. are the
principle investigators, contributing to the manuscript and the
interpretation of data. All authors have given approval to the
final version of the manuscript.
Funding
This work was supported by the NSERC of Canada (Discovery
grants to E.R. and A.B.), NSERC CREATE funding to E.R.
and J.M.S., and the National Natural Science Foundation of
China (No. 21203135) for supporting G.D. J.M.S. also thanks
NSERC for a CGS-M scholarship and the University of Alberta
for a QE II Scholarship.
ASSOCIATED CONTENT
Notes
■
The authors declare no competing financial interest.
sı
* Supporting Information
The Supporting Information is available free of charge at
https://pubs.acs.org/doi/10.1021/acs.inorgchem.0c01492.
ACKNOWLEDGMENTS
■
The computational studies in this work were made possible by
the Compute/Calcul Canada (www.computecanada.ca) facili-
ties. We also thank Haoyang Yu for the SEM images, Mark
Miskolzie for the high-temperature NMR data collection and
discussions, Christoph Wallach and Dr. Mustafa Supur for the
collection of the Raman data, Dr. Emanuel Hupf for the
computational assistance with the modeling of the Raman
spectra, Ian Watson for helpful suggestions, and Lorenzo
Garcia for the initial work on ImiPr2Me2·GeH2·BH3. A.B. and
G.D. thank Tyler Ries and Hanseul Kim for carrying out the
exploratory computational studies on the decomposition of
IPr·GeH2·BH3.
Experimental details, NMR characterization, crystallo-
graphic data, characterization of the deposited Ge,
computational details, and a link to output (.log) files for
all computations that were conducted (PDF)
Accession Codes
CCDC 1986302−1986305 contain the supplementary crys-
tallographic data for this paper. These data can be obtained
free of charge via www.ccdc.cam.ac.uk/data_request/cif, or by
emailing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: + 44 1223 336033. Computa-
J
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