Linking Low-Coordinate Ge(II) Centers via Bridging Anionic N-Heterocyclic Olefin Ligands

Article abstract of DOI:10.1021/acs.inorgchem.9b01449

We introduce a large-scale synthesis of a sterically encumbered N-heterocyclic olefin (NHO) and illustrate the ability of its deprotonated form to act as an anionic four-electron bridging ligand. The resulting multicenter donating ability has been used to link two low oxidation state Ge(II) centers in close proximity, leading to bridging Ge-Cl-Ge and Ge-H-Ge bonding environments supported by Ge₂C₂ heterocyclic manifolds. Reduction of a dimeric [RGeCl]₂ species (R = anionic NHO, [(MeCNDipp)₂C=CH]^- Dipp = 2,6-ⁱPr₂C₆H₃) did not give the expected acyclic RGeGeR analogue of an alkyne, but rather ligand migration/disproportionation transpired to yield the known diorganogermylene R₂Ge and Ge metal. This process was examined computationally, and the ability of the reported anionic NHO to undergo atom migration chemistry contrasts with what is typically found with bulky monoanionic ligands (such as terphenyl ligands).

Full text of DOI:10.1021/acs.inorgchem.9b01449

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX−XXX
Linking Low-Coordinate Ge(II) Centers via Bridging Anionic
N‑Heterocyclic Olefin Ligands
Emanuel Hupf,†,§ Felix Kaiser,‡,§ Paul A. Lummis,†,§ Matthew M. D. Roy,† Robert McDonald,†
‡
Michael J. Ferguson,† Fritz E. Kuhn, and Eric Rivard*,†
̈
†Department of Chemistry, University of Alberta, 11227 Saskatchewan Drive, Edmonton, Alberta T6G 2G2, Canada
‡
̈
̈
Catalysis Research Center and Department of Chemistry, Technische Universitat Munchen, Lichtenbergstraβe 4, 85748 Garching
nchen, Germany
bei Mu
̈
S
* Supporting Information
ABSTRACT: We introduce a large-scale synthesis of a sterically
encumbered N-heterocyclic olefin (NHO) and illustrate the ability
of its deprotonated form to act as an anionic four-electron bridging
ligand. The resulting multicenter donating ability has been used to
link two low oxidation state Ge(II) centers in close proximity,
leading to bridging Ge−Cl−Ge and Ge−H−Ge bonding environ-
ments supported by Ge2C2 heterocyclic manifolds. Reduction of a
dimeric [RGeCl]2 species (R = anionic NHO, [(MeCNDipp)2C
CH]−; Dipp = 2,6-iPr2C6H3) did not give the expected acyclic
RGeGeR analogue of an alkyne, but rather ligand migration/disproportionation transpired to yield the known
diorganogermylene R2Ge and Ge metal. This process was examined computationally, and the ability of the reported anionic
NHO to undergo atom migration chemistry contrasts with what is typically found with bulky monoanionic ligands (such as
terphenyl ligands).
Chart 1. Selected Examples of Sterically Hindered Bridging
INTRODUCTION
■
Ligands and Their Use to Link Electron-Deficient Main
Ligand design remains a lynchpin of modern inorganic
chemistry, with the use of bulky ligands to access reactive
low coordinate bonding environments being a particularly
active field of study.1 Recently, main group compounds have
been shown to exhibit “transition-metal like” reactivity, and
this concept relies on the presence of low coordination
numbers for small molecule activation2 leading to nonmetal
mediated catalysis.3 The development of bridging ligands that
retain a high degree of steric bulk4,5 adds a new dimension of
reactivity, including the cooperative binding of substrates (cf.
H− and F− encapsulation by bis(boranes)).6 Chart 1 outlines
recently prepared low valent main group species supported by
bulky bridging ligands,4,5 wherein heterocycle formation allows
the placement of two electron-deficient/reactive centers in
close proximity.
a
Group Centers
a
Mes = 2,4,6-Me3C6H2; Trip = 2,4,6-iPr3C6H2.
In this article, we demonstrate the ability of a sterically
hindered vinylic ligand (R) [MeIPrCH]− (MeIPr = [(MeCN-
Dipp)2C; Dipp = 2,6-iPr2C6H3)],7,8 to link two low oxidation
state Ge(II) centers via a terminal carbon atom acting as a
four-electron donor (Scheme 1). Computational studies also
explain our inability to access an inorganic alkyne RGeGeR
upon reduction of the Ge(II) chloride precursor [(MeIPrCH)-
GeCl]2; this observation can be linked to the high propensity
of the reported anionic NHO ligand to form bridging isomers
leading to the eventual extrusion of Ge via the isomer
R2GeGe.9 While the bridging of two Ge(II) centers via
anionic heteroatom-based ligands to yield dimeric [(μ-
R′)GeCl]2 species (e.g., R′ = -NR2, -PR2, -OR, or -SR) is
known,10 herein we show that added interactions between the
linked Ge(II) centers in the form of bridging Ge−Cl−Ge and
Ge−H−Ge interactions are possible, opening the door for
possible cooperative activation of substrates in catalysis.
RESULTS AND DISCUSSION
■
This study arose from our exploration of the ligating properties
of a recently reported diorganogermylene (MeIPrCH)2Ge:
(1).7f Motivated by our past syntheses of Ge(II) chains, such
Received: May 17, 2019
© XXXX American Chemical Society
A
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two-coordinate diorganogermylene (MeIPrCH)2Ge: (1)
[1.364(3) Å].7f Furthermore, the computed gas-phase
dissociation of 2 into two monomeric MeIPrCH-GeCl
Scheme 1. Nature of the Bridging (4-Electron) Donor
a
Ligand [MeIPrCH]−
units has been predicted to be slightly exothermic (ΔHDiss
−1.11 kcal mol−1).
=
Given that two reactive Ge(II)-halide environments are held
in close proximity within 2, we attempted to promote Ge−Ge
bond formation via reduction. Combining 2 with the common
reducing agents, Na, K, Na/K, KC8, Rieke Zn or Mg, or the
milder reductant Na[C10H8], consistently afforded the known
germylene (MeIPrCH)2Ge: (1) (Scheme 2; bottom-left
reaction). Given that 1 was originally prepared by the
reduction of (MeIPrCH)GeCl3 with 3 equiv of KC8,7f it is
plausible that [(MeIPrCH)GeCl]2 2 is an intermediate in this
process. All attempts to isolate 2 by directly reducing
(MeIPrCH)GeCl3 were unsuccessful, and in each case over-
reduction to yield the germylene 1 and Ge metal transpired;
thus, the reduction of 2 is fast. The ease at which the
[MeIPrCH]− ligand can bridge two Ge centers and eventually
yield the observed disproportionation products will be revisited
later.
a
Herein multiple ligand-element (E) interactions are possible, as
shown in red.
as IPr·GeCl2GeCl2 (IPr = [(HCNDipp)2C:]),11a we combined
1 with GeCl2·dioxane in tetrahydrofuran (THF). The resulting
highly moisture-sensitive dark yellow-orange solid was shown
by X-ray crystallography (Figure 1) to be the halide/ligand
Motivated by the presence of long Ge−Cl bonds in
[(MeIPrCH)GeCl]2 (2) [2.3191(5) Å], this complex was
combined with Na[BArF ] in Et2O (ArF = 3,5-(F3C)2C6H3).
4
The resulting orange-red solid was identified by single-crystal
X-ray diffraction as [{(MeIPrCH)Ge}2(μ-Cl)][BArF ] ([3]-
4
[BArF ]); [3]+ contains a butterfly-shaped Ge2C2 ring (Figure
4
2) capped by a bridging chloride to form a propellane
structure14 with Ge−Cl distances of 2.457(1) and 2.507(1) Å.
Attempts to synthesize a dicationic species [Ge{μ-
(MeIPrCH)2}Ge]2+ by reacting [(MeIPrCH)GeCl]2 (2) with
2 equiv of AlCl3 gave the monocationic [3]+ as major product
1
in ca. 70% spectroscopic yield, according to H NMR analysis
of the crude reaction mixture. However, the intended dication
[Ge{μ-(MeIPrCH)2}Ge]2+ was examined computationally and
was found to be a minimum structure on the potential energy
surface. Notably, the computed Ge−Ge separation of the
dication is predicted to be 2.9466 Å (Figure S24)13 and no
sign of Ge−Ge bonding was found, either by Natural Bond
Order (NBO)15 or Atoms-in-Molecules (AIM)16 analyses
(Figure S36c in the Supporting Information).13 Moreover, this
bonding scenario was complemented by our Non-Covalent
Index (NCI)17 study, which revealed weakly repulsive Ge···Ge
interactions (Figure S37c in the Supporting Information).13
As Ge(II) hydrides have played important roles in main
group catalysis3a,d and as precursors to Ge nanomaterials,18 we
attempted the synthesis of the hydride dimer [(MeIPrCH)-
GeH]2. Addition of 2 equiv of Li[HBEt3] to 2 in THF
eventually gave X-ray quality single crystals of the hydride-
bridged salt [{(MeIPrCH)Ge}2(μ-H)][BEt4] [4][BEt4]
(Scheme 2 and Figure 3). The Ge···Ge separation of
2.584(1) Å in [4][BEt4] is in the range expected for a single
bond, and is significantly shorter than the Ge···Ge distance of
Figure 1. Molecular structure of [(MeIPrCH)GeCl]2 (2) with thermal
ellipsoids presented at a 50% probability level. The hydrogen atoms
H4 and H4′ are shown with an arbitrary radius, and the Dipp groups
are depicted in wireframe. Selected bond lengths (Å) and angles
(deg): Ge1−Ge2 2.8941(7), Ge−Cl 2.3191(5), Ge−C4 2.0745(14),
Ge−C4′ 2.1117(15), C1−C4 1.415(2); C4−Ge−C4′ 80.78(7), Ge−
C4−Ge′ 87.47(6), C4−Ge−Cl 95.36(4).
exchange product [(MeIPrCH)GeCl]2 (2) (eq 1). The key
structural feature in 2 is the presence of a puckered Ge2C2 ring
supported by bridging (MeIPrCH)− ligands; this ring is capped
by syn-arranged Ge−Cl bonds. The core Ge−C distances
[2.0745(14)−2.1117(17) Å] are similar in length as the long
Ge−C dative bond in IPr·GeCl2 [2.112(2) Å],12 suggesting a
lack of Ge−C π-bonding in 2. The transannular Ge···Ge
separation in 2 [2.8941(7) Å] is consistent with an absence of
Ge−Ge bonding, a finding that has been corroborated by our
density functional theory (DFT) computations.13 As expected,
the presence of bridging interactions involving the (MeIPrCH)−
ligands in 2 leads to substantially longer “vinylic” C−C lengths
[C1−C4 = 1.415(2) Å] in comparison to those found in the
2.8247(8) Å in Fassler’s [Ph2ZrGe4(μ-H)]3− cluster,19 which is
̈
the only other reported species with a structurally
authenticated Ge−H−Ge unit. The Ge−H distances in
[4][BEt4] of 1.71(4) and 1.70(5) Å were the same within
error as those [1.74(3) Å average (avg)] found in
[Ph2ZrGe4(μ-H)]3−.19 Intrigued by the short Ge···Ge distance
in [4][BEt4], we performed a series of DFT computations on
the cation [4]+.13 The geometrical parameters of the computed
optimized structure of [4]+ were in good agreement with the
crystallographically determined molecular structure. The
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Scheme 2. Formation of the Cationic Halide- and Hydride-Bridged Ge(II) Cations [3]+ and [4]+, as well as the Low-
Coordinate Germylenes 1 and 5 from the Ge(II) Precursor 2
Figure 3. Molecular structure of [{(MeIPrCH)Ge}2(μ-H)][BEt4]
([4][BEt4]) with thermal ellipsoids presented at a 50% probability
level. The hydrogen atoms H1, H4, and H54 are shown with an
arbitrary radius, and the Dipp groups are depicted in wireframe; the
[BEt4]− anion was omitted for clarity. Selected bond lengths (Å) and
angles (deg): Ge1−Ge2 2.584(1), Ge1−H1 1.71(4), Ge2−H
1.70(5), Ge1−C4 2.088(4), Ge2−C34 2.077(4), C1−C4 1.425(6),
C31−C34 1.422(6); H1−Ge1−C4 79(2), H1−Ge1−C34 81(3),
H1−Ge2−C4 80(3), H1−Ge2−C34 80(2), C4−Ge1−C34 78.1(2),
C4−Ge2−C34 78.3(2), Ge1−H1−Ge2 98(3).
Figure 2. Molecular structure of [{(MeIPrCH)Ge}2(μ-Cl)][BArF ]
4
([3][BArF ]) with thermal ellipsoids presented at a 50% probability
4
level. The hydrogen atoms H4 and H54 are shown with an arbitrary
radius, and the Dipp groups are depicted in wireframe; the [BArF ]−
4
anion was omitted for clarity. Selected bond lengths (Å) and angles
(deg): Ge1−Ge2 2.7547(6), Ge1−Cl 2.457(1), Ge2−Cl 2.507(1),
Ge1−C4 2.087(3), Ge2−C54 2.068(4), C1−C4 1.434(4), C51−C54
1.436(4); Cl−Ge1−C4 88.44(8), Cl−Ge1−C54 88.19(8), Cl−Ge2−
C4 87.54(8), Cl−Ge2−C54 87.15(8), C4−Ge1−C54 78.3(1), C4−
Ge2−C54 79.0(1), Ge1−Cl−Ge2 67.41(3).
schemes on the basis of short interatomic distances alone,
especially when the elements are hydride-bridged. The central
Ge−H−Ge unit in [4]+ can best be described as a 3-center-2-
electron bond with an average computed Ge−H Wiberg Bond
Index (WBI) of 0.45.20 Pronounced hydridic character was
also found by both Natural Population Analysis (NPA) and
AIM (computed charges of −0.19 and −0.45 e, respectively).
Despite numerous attempts, we were only able to obtain bulk
quantities of [4]+ as its analytically pure [BEt4]− salt a single
computed Ge···Ge separation was 2.620 Å, and interestingly, as
was also found for the dicationic [Ge{μ-(MeIPrCH)2}Ge]2+, no
sign of Ge−Ge bonding could be located by either NBO or
AIM16 analyses (Figure S36b in the Supporting Information)
despite the significantly shorter Ge−Ge distance in [4]+.13
Moreover, a weakly repulsive Ge···Ge interaction was located
by a NCI study (Figure S37b in the Supporting Informa-
tion).13 Thus, one needs to be careful in assigning bonding
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1
time. In all other attempts, [4][BEt4] was obtained with
various quantities of cocrystallized mixed hydridoalkylborate
salts [4][BHxEty].
(prepared from Li[DBEt3] and 2) yielded a triplet H NMR
resonance at −1.28 ppm due to coupling of the ligand CH
proton with the deuterium atom in the Ge-D-Ge bridge (3JHD
= 1.9 Hz; Figure 4), while a Ge-D-Ge resonance was located at
The formation of the perethylated [BEt4]− anion likely
proceeds via a known H/Et scrambling reaction between BEt3
(a byproduct in the synthesis of [4]+) and [HBEt3]−.21
Fortunately in each preparation, the cationic portion of the
cocrystallized salts remained as [4]+. While a pure sample of
[4][BEt4] was stable at room temperature in THF, the mixed
salts [4][BHxEty] slowly decomposed in THF to give the N-
heterocyclic olefin MeIPrCH2,22 (MeIPrCH)2Ge: (1),7f and
various unidentified products, likely via anion (B−H hydride)
mediated decomposition of [4]+.23
13
−1.08 ppm in the H{1H} spectrum for [4D]+ (Figure 4).
2
Our synthetic investigations of [(MeIPrCH)GeCl]2 (2)
concluded with an attempt to induce HCl loss by treatment
with Li(THF)4[CPh3] as a possible Brønsted base. However,
direct Cl/CPh3 exchange transpired to yield the monomeric
germylene (MeIPrCH)Ge(CPh3) (5) (Scheme 2) as an orange-
red solid (see Figure S1 in the Supporting Information for the
X-ray structure).13 The metrical parameters of 5 were in line
with what is expected for an anionic NHO-supported
diorganogermylene.7f
The hydrogen-bridged cation [4]+ affords two shielded
1
second-order multiplet H NMR resonances spanning from
To gain a better understanding of the reduction pathway
from [(MeIPrCH)GeCl]2 (2) to (MeIPrCH)2Ge: (1) and bulk
Ge metal, we investigated possible intermediates by DFT
computations at the B3LYP/cc-pVDZ level.13 We started with
the assumption that reduction of 2 would initially yield the
cyclic Ge(I) dimer cyclic-Ge(μ-R)2Ge [R = (MeIPrCH)−]
(Figure 5); as expected this species features a Ge−Ge single
bond [2.4538 Å]. Moreover, cyclic-Ge(μ-R)2Ge is a local
minimum on the potential energy surface and is isostructural
to Ge(μ-H)2Ge, which has been predicted to be the most
stable isomer within the parent Ge2H2 structural series.24
Interestingly, the Ge−Ge bond in cyclic-Ge(μ-R)2Ge is derived
from the canted overlap of Ge(p) orbitals to yield a “bent” σ-
bond (Figure 5) as determined by real-space bonding analysis
according to the AIM and Electron-Localizability Indicator
(ELI-D) space-partitioning schemes (Figures 5, S35, S36d, and
S38d).13 This Ge−Ge unit in cyclic-Ge(μ-R)2Ge has been
computed to readily accept a proton [ΔH = −296.4 kcal
mol−1; Eqn 2] to yield the hydrogen-bridged cation [4]+. For
reference, a similar proton affinity has been computed for the
N-heterocyclic carbene ITr (ITr = [(HCNCPh3)2C:).25
A plausible isomer of cyclic-Ge(μ-R)2Ge would be the open
digermylene form, acyclic-RGeGeR, which was computed to be
only +3.8 kcal mol−1 higher in energy (Figure 5). Thus, one
sees a minimal energy difference between doubly bridging and
nonbridging [MeIPrCH]− coordination. acyclic-RGeGeR con-
tains a typical Ge−Ge single bond (Figures S35 and S36e in
−1.13 to −1.27 ppm (d8-THF), assigned to ligand −CH-Ge
and bridging hydride Ge-H-Ge environments, respectively
(Figure 4). As anticipated, the deuterium analogue [4D]+
Figure 4. Superposition of ligand −CH-Ge and Ge-H-Ge/Ge-D-Ge
1
resonances in the H NMR spectra (d8-THF) of [4][BEt4] (blue),
[4D][BHxEty] (red), and the 2H{1H} NMR spectrum of [4D]-
[BHxEty] (black).
Figure 5. Computed relative enthalpies for the formation of the diorganogermylene 1 from the cyclic-Ge(μ-R)2Ge. The enthalpy of sublimation of
germanium is included in the final step, decomposition of R2Ge=Ge into R2Ge and Ge(s) (ΔsubH = 89.5 kcal mol−1).27 (inset) The highest
occupied molecular orbital of the cyclic-LGe(μ-R)2Ge representing the overlap of the Ge(p) orbitals and the geometry of the monobridged RGe(μ-
R)Ge intermediate.
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in THF) were purchased from Aldrich and used as received.
Germanium tetrachloride was obtained from Gelest and used as
received. Sodium tetrakis[3,5-bis(trifluoromethyl)phenyl]borate (Na-
[BArF ]) was purchased from Ark Pharmaceuticals and heated under
4
vacuum at 110 °C for 48 h prior to use, after which it was stored
inside a glovebox at room temperature. (MeIPrCH)2Ge (MeIPr =
[(MeCNDipp)2C; Dipp = 2,6-iPr2C6H3),7f [Li(THF)4][CPh3],32
KC8,33 and (DippNCMe)2 were prepared according to literature
34
the Supporting Information)13 and is structurally similar to
related 1,2-diaminodigermylenes reported by Jones and co-
workers.26
1
procedures. H, 13C{1H}, 11B{1H}, and 19F{1H} NMR spectra were
recorded on a Varian Inova-400, Varian Inova-500, Bruker AVHD500
cryo, Bruker AV400, or Varian Inova-700 spectrometer and
referenced externally to SiMe4 (1H, 13C{1H}), F3B·OEt2 (11B), and
CFCl3 (19F{1H}), respectively. 2H{1H} NMR was referenced
internally to THF (1.73 ppm downfield shifted to SiMe4). Because
all NMR samples were prepared in a glovebox containing solvent,
minor contamination of NMR solvent is sometimes observed. Where
applicable, these minor impurities are noted on the spectra provided
in the Supporting Information. Liquid Injection Field Desorption
Ionization Mass Spectrometry (LIFDI MS) measurements were
conducted on a Waters LCT, liquid injection field desorption
ionization special ionization cell obtained from Linden CMS GmbH.
Elemental analyses and UV−visible spectroscopic measurements were
performed by the Analytical and Instrumentation Laboratory at the
University of Alberta or the Mikroanalytisches Labor der Technischen
Both the cyclic-Ge(μ-R)2Ge and acyclic-RGeGeR isomers
can potentially yield the digermavinylidene R2Ge=Ge: via 1,2-
ligand migration (Figure 5).28 A monobridged intermediate for
this process, RGe(μ-R)Ge, was also located and found to be
similar in relative energy as R2Ge=Ge; notably RGe(μ-R)Ge
has considerable GeGe multiple bond character (short Ge−
Ge distance 2.294 Å), which is slightly shorter than the
corresponding distance of 2.391 Å in R2Ge=Ge. The latter
B
species is similar to Aldridge’s digermavinylidene R2Ge=Ge
(BR = (HCNDipp)2B-).9 Conversion of either cyclic-Ge(μ-
R)2Ge or acyclic-RGeGeR into RGe(μ-R)Ge and R2Ge=Ge
was computed to be thermodynamically feasible [ΔH = +14.3
to 18.1 kcal mol−1], while decomposition of R2Ge=Ge into
R2Ge (1) and Ge(s) was predicted to be an exothermic process
[ΔH = −33.9 kcal mol−1], once the energetics associated with
the formation of bulk germanium metal were considered
(Figure 5).9 Comparative Non-Covalent Index (NCI) analyses
were performed to gain insight into the different stabilities of
R2Ge=Ge and the isolable boryl-stabilized digermavinyldene
BR2Ge=Ge (Figure S39).13 This study revealed additional
dispersive interactions between the terminal Ge=Ge unit and
the flanking boryl ligands BR2Ge=Ge,29 leading to a more
enclosed Ge=Ge vicinity when compared to its anionic-NHO
counterpart R2Ge=Ge. Thus, BR2Ge=Ge represents another
example of how ligand-derived dispersion forces can stabilize
unusual bonding environments.30
̈
̈
Universitat Munchen. Infrared spectra were recorded using a Nic-Plan
FTIR microscope. Melting points were obtained in sealed glass
capillaries under nitrogen using a MelTemp apparatus.
Synthesis of Li[DBEt3]. SuperDeuteride was prepared by a
slightly modified procedure as described by Brown and co-workers,35
adding BEt3 (7.0 mmol, 1.0 M solution in hexanes) to a suspension of
LiD (126 mg, 14.0 mmol) in 6 mL of THF. The resulting reaction
mixture was stirred at room temperature for 12 h and filtered to give a
clear solution of Li[DBEt3] (0.53 M in THF/hexanes).
Large-Scale Synthesis of [MeIPrH]Cl. N,N′-Bis-(2,6-diisopropyl-
phenyl)-butane-2,3-diimine (72.4 g, 179 mmol) was dissolved in 1.2 L
of THF in an oven-dried Schlenk flask and cooled in an ice bath.
Paraformaldehyde (8.06 g, 268 mmol) was suspended in a 4.0 M
solution of HCl in 1,4-dioxane (80.5 mL, 320 mmol), and this
suspension was added to the yellow solution of diamine via cannula
over a period of 20 min. The resulting suspension was warmed to
room temperature and stirred for 18 h. The solvent was removed to
final residual volume of ca. 200 mL, 600 mL of Et2O was added, and
the mixture was stored at −18 °C for 2 h. The crude product was then
isolated by vacuum filtration and recrystallized from a mixture of 120
mL of MeOH and 700 mL of Et2O. [MeIPrH]Cl was isolated as a
CONCLUSION
■
The synthesis of the dimeric Ge(II) species [(MeIPrCH)-
GeCl]2 (2) is reported, wherein with two Ge centers are linked
by a bulky anionic N-heterocyclic olefin ligand. In addition, the
ability of related Ge2C2 cyclic scaffolds to support bridging μ-
chloride and μ-hydride units between low-valent Ge(II)
centers was shown. Accompanying computational studies
revealed the ease at which the [MeIPrCH]− ligand can form
bridged species en route to final 1,2-migration. We hope that
the ligand binding mode introduced in this study will
encourage the future construction of linked bimetallic species
for use in cooperative catalysis.
1
colorless crystalline solid (40.5 g, 50%). H NMR analysis revealed
the formation of pure [MeIPrH]Cl with resonances that matched
literature values.36
Large-Scale Synthesis of MeIPrCH2.37 MeIPrH]Cl (35.5 g, 78.4
[
mmol) was suspended in 1 L of THF in an oven-dried Schlenk flask.
KOtBu (17.2 g, 154 mmol) was quickly added, and the slightly turbid
mixture was stirred for 40 min. MeI (4.78 mL, 10.9 g, 76.8 mmol) was
added, and the resulting yellow slurry was stirred for 40 h. The slurry
was suction filtered through diatomaceous earth, the remaining filter
cake was washed with 200 mL of THF, and the filtrate was evaporated
to dryness. MeIPrCH2 was isolated from the filtrate as a colorless solid
EXPERIMENTAL SECTION
■
22
1
(24.3 g, 72%) with H NMR data consistent with the literature.
General. All reactions were performed using standard Schlenk
techniques under an atmosphere of nitrogen or argon or in a
nitrogen/argon-filled glovebox (Innovative Technology, Inc./
MBraun). Solvents were dried using a Grubbs-type solvent
purification system manufactured by Innovative Technology, Inc. or
MBraun, degassed, and stored under an atmosphere of nitrogen or
argon prior to use.31 Fluorobenzene was dried by refluxing over
calcium hydride, followed by distillation, degassing (freeze−pump−
thaw method), and storage over molecular sieves prior to use. 1,4-
Diazabicyclo[2.2.2]octane (DABCO), germanium(II) chloride−diox-
ane (1:1 complex), paraformaldehyde, methyl iodide, potassium tert-
butoxide, HCl (4.0 M in dioxane), LiD, triethylborane (1.0 M
solution in hexanes), and SuperHydride (1.0 M solution of Li[HBEt3]
Large-Scale Synthesis of (MeIPrCH)GeCl3. MeIPrCH2 (24.3 g,
56.5 mmol) and 1,4-diazabicyclo[2.2.2]octane (6.39 g, 56.5 mmol)
were dissolved in 500 mL of toluene. GeCl4 (6.44 mL, 12.1 g, 56.5
mmol) was added, and the suspension was stirred for 18 h. The
suspension was filtered, the remaining filter cake was washed with 500
mL of THF, and the volatiles were removed from the filtrate in vacuo
leaving a thick slurry behind. Addition of 300 mL of pentane caused
further precipitation of the product that was isolated by filtration,
washed with pentane (2 × 50 mL), and dried in vacuo. This
procedure afforded (MeIPrCH)GeCl3 as a colorless solid (31.0 g,
91%) with spectroscopic data that matched those found in the
literature.7f
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Article
Large-Scale Synthesis of (MeIPrCH)2Ge (1). (MeIPrCH)GeCl3
(22.1 g, 36.3 mmol) and KC8 (14.7 g, 109 mmol) were placed in an
oven-dried Schlenk flask and cooled in an ice-bath, and 350 mL of
Et2O was quickly added. The resulting suspension was stirred for 18 h
and filtered through diatomaceous earth, and the filter cake was
washed with Et2O (2 × 100 mL). The filtrate was then evaporated to
dryness, and 100 mL of pentane was added, followed by stirring for 1
h. The resulting suspension was then stored at −30 °C for 18 h, and
the red precipitate was isolated by filtration and washed with 5 mL of
cold (−30 °C) pentane. The solid was dried in vacuo to give 1 as a
5.17, N 2.91%. mp (°C): 136−140. UV−Vis (THF): λmax = 317 nm
(ε = 5520 L mol−1 cm−1).
Synthesis of [{(MeIPrCH)Ge}2(μ-H)]+ ([4]+). To a dark yellow
solution of 2 (387 μmol), prepared in situ from 1 and GeCl2·dioxane
in THF (10 mL), was added a 1.0 M solution of Li[HBEt3] in THF
(773 μL, 773 μmol), which resulted in an immediate color change to
orange. The reaction mixture was allowed to stir for 1 h, filtered
through a glass fiber filter, and then stored at −30 °C for 2 d, upon
which large, light-yellow crystals formed. The crystals were isolated,
washed with pentane (2 mL) and benzene (6 mL), and dried in vacuo
giving of a pale yellow solid (34.4−164 mg, depending on the
effectiveness of crystallization) containing the [{(MeIPrCH)Ge}2(μ-
H)]+ cation (see Figure S8). Note that the cationic fragment [4]+ is
formed reproducibly; however, despite multiple attempts the nature of
1
red solid (8.75 g, 52%). The H NMR spectrum of 1 is identical to
that reported in the literature.7f
Synthesis of [(MeIPrCH)GeCl]2 (2). (MeIPrCH)2Ge (0.251 g,
0.269 mmol) was dissolved in 10 mL of THF in a 20 mL scintillation
vial to afford a deep red solution. To this solution was added Cl2Ge·
dioxane (0.062 g, 0.27 mmol) as a powder, and the resulting mixture
was allowed to stir for 1 h, leading to an immediate color change to
yellow. Removal of the volatiles in vacuo afforded a dark yellow-
orange solid that was washed with 2 × 3 mL of cold (−30 °C)
hexanes to yield the desired product 2 (0.235 g, 81%). Crystals
suitable for X-ray crystallographic analysis were obtained by adding 2
mL of toluene to the product, filtering this solution through a 1 cm
plug of diatomaceous earth, and layering the filtered solution with an
equal volume of hexanes. This mixture was then stored at −30 °C for
48 h, yielding yellow-orange crystals of 2. 1H NMR (C6D6, 700
−
−
the anion varies with different runs of the reaction (HBEt3 , BEt4 ,
and other ill-defined anions). The resulting yellow solid is unstable in
THF at room temperature with decomposition occurring within a few
hours under inert atmosphere (formation of 1 is observed), whereas
the solid as well as the THF solutions can be stored at −30 °C for 10
d without sign of degradation by 1H NMR analysis. 1H NMR (THF-
2
3
d8, 400 MHz): δ −1.27 (dd, 2H, JHH = 13.2 Hz, JHH = 2.0 Hz,
2
−CH-Ge2), −1.13 (dd, 1H, JHH = 14.5 Hz, 11.9 Hz, Ge−H−Ge),
0.44−0.48 (m, 5H, Anion), 0.77−0.78 (m, 7H, anion), 1.09 (d, 24H,
3JHH = 6.8 Hz, CH(CH3)2), 1.20 (d, 24H, 3JHH = 6.8 Hz, CH(CH3)2),
3
1.87 (s, 12H, ImCH3), 2.32 (sept, 8H, JHH = 6.9 Hz, CH(CH3)2),
7.29 (d, 8H, JHH = 7.8 Hz, Dipp-m-H), 7.55 (t, 4H, JHH = 7.8 Hz,
Dipp-p-H).
3
3
3
MHz): δ 1.01 (d, 12H, JHH = 7.0 Hz, CH(CH3)2), 1.06 (d, 12H,
3JHH = 7.0 Hz, CH(CH3)2), 1.30 (d, 12H, 3JHH = 7.0 Hz, CH(CH3)2),
From multiple recrystallization attempts it was only once possible
to obtain single crystals suitable for X-ray diffraction measurements
with a well-defined [BEt4]− anion. This sample was obtained by
dissolving the crude mixture of [4][BHxEty] (164 mg, see above) in 1
mL of CH2Cl2, layering with 5 mL of benzene, and storing the
mixture at room temperature for one week, during which light yellow
needle-shaped crystals of [4][BEt4] formed. The crystals were
isolated, washed with benzene (1 mL) and pentane (2 × 1 mL),
and dried in vacuo to give [4][BEt4] as light yellow crystals (80.1 mg,
18% yield based on starting amount of 2 used in the synthesis). In
sharp contrast to the crude mixture, the isolated crystals with the well-
defined [BEt4]− anion are stable at room temperature, both in THF
1.39 (s, 6H, ImCH3), 1.45 (s, 6H, ImCH3), 1.49 (d, 12H, 3JHH = 7.0
3
Hz, CH(CH3)2), 2.78 (br, 4H, CH(CH3)2), 3.02 (sept, 4H, JHH
=
=
7.0 Hz, CH(CH3)2), 3.03 (s, 2H, MeIPrCHGe), 7.12 (br d, 4H, 3JHH
3
7.7 Hz, Dipp-m-H), 7.15 (d, 4H, JHH = 7.7 Hz, Dipp-m-H), 7.21 (t,
2H, 3JHH = 7.7 Hz, Dipp-p-H), 7.25 (t, 2H, 3JHH = 7.7 Hz, Dipp-p-H).
13C{1H} NMR (C6D6, 176 MHz): δ 9.1 (ImCH3), 10.2 (ImCH3),
24.0 (CH(CH3)2), 24.8 (CH(CH3)2), 24.9 (CH(CH3)2), 25.1
(CH(CH3)2), 28.9 (CH(CH3)2), 29.1 (CH(CH3)2), 49.4
(
MeIPrCHGe), 122.8 (ArC), 124.8 (ArC), 128.4 (ArC), 130.5
(ArC), 132.0 (ArC), 140.2 (ArC), 147.4 (ArC), 158.8 (ArC), 162.3
(NCN). Anal. Calcd for C60H82Cl2Ge2N4: C 67.01, H 7.69, N 5.21.
Found: C 64.10, H 7.66, N 5.06%; despite repeated attempts, an
acceptable value for C could not be obtained; please see Figures S2
and S3 for the 1H and 13C{1H} NMR spectra of 2 as an indication of
purity.13 mp (°C): 215 (dec). UV−Vis (THF): λmax = 424 nm (ε =
4010 L mol−1 cm−1).
solution and in the solid state (under inert atmosphere). Data for
3
[4][BEt4]:1H NMR (THF-d8, 400 MHz): δ −1.26 (dd, 2H, JHH
=
4
3
13.2 Hz, JHH = 1.7 Hz, −CH-Ge2), −1.13 (dd, 1H, JHH = 14.8 Hz,
11.5 Hz, Ge−H−Ge), −0.20 to −0.05 (m, 8H, BCH2CH3), 0.56−
0.77 (m, 12H, BCH2CH3), 1.08 (d, 24H, 3JHH = 6.8 Hz, CH(CH3)2),
1.20 (d, 24H, 3JHH = 6.8 Hz, CH(CH3)2), 1.86 (s, 12H, ImCH3), 2.31
(sept, 3JHH = 6.8, 8H, CH(CH3)2), 7.29 (d, 8H, 3JHH = 7.8 Hz, Dipp-
Synthesis of [{(MeIPrCH)Ge}2(μ-Cl)][BArF ] (3). To an orange-
4
yellow solution of 2 in 4 mL of Et2O (0.112 g, 0.104 mmol) was
m-H), 7.52 (t, 4H, JHH = 7.8 Hz, Dipp-p-H). 13C{1H} NMR (THF-
3
added Na[BArF ] (0.093 g, 0.10 mmol), which resulted in an
4
2
d8, 101 MHz): δ 9.9 (ImCH3), 12.5 (q, JCB = 1.2 Hz, BCH2CH3),
18.1 (q, JBC = 40.8 Hz, BCH2CH3), 24.7 (CH(CH3)2), 24.8
immediate color change to red-orange. This mixture was stirred for 2
h and then filtered through a 2 cm plug of diatomaceous earth.
Removal of all volatiles from the filtrate in vacuo yielded 3 as a
spectroscopically pure orange solid (0.198 g, 95%). This compound
was recrystallized from a concentrated fluorobenzene solution that
was layered with an equal volume of hexanes and stored at −30 °C for
48 h, yielding orange-yellow crystals of 3 suitable for single-crystal X-
1
(CH(CH3)2), 29.8 (CH(CH3)2), 31.1 (−CH−Ge2), 124.6 (N(CH3)
CC), 126.0 (Dipp-m-C), 130.3 (Dipp-ipso-C), 132.3 (Dipp-p-C),
147.8 (Dipp-o-C), 157.4 (N2CCH). 11B NMR (THF-d8, 128 MHz):
δ −16.4 (s, [BEt4]−). High-resolution mass spectrometry (HRMS)
−
(LIFDI, CH2Cl2): m/z = 1005.4635 [(4 − BEt4 )+] Anal. Calcd for
C68H103BGe2N4: C 72.11, H 9.17, N 4.95. Found: C 72.20, H 9.15, N
4.97%.
1
ray diffraction. H NMR (CD2Cl2, 700 MHz): δ 0.08 (s, 2H, −CH-
Ge2), 1.04 (d, 24H, 3JHH = 6.9 Hz, CH(CH3)2), 1.12 (d, 24H, 3JHH
=
=
Synthesis of [{(MeIPrCH)Ge}2(μ-D)]+ ([4D]+). A dark yellow
solution of 2 (387 μmol) in THF (10 mL) was prepared in situ from
1 and GeCl2·diox. A 0.53 M solution of Li[DBEt3] in THF/hexanes
(1.46 mL, 773 μmol) was then added, which resulted in an immediate
color change to orange. The reaction mixture was allowed to stir for 1
h, filtered through a glass fiber filter, and then stored at −30 °C for 2
d, upon which large, light yellow crystals formed. The crystals were
isolated, washed with pentane (2 mL) and benzene (6 mL), and dried
in vacuo giving 45.2 mg of a pale yellow solid containing the
[{(MeIPrCH)Ge}2(μ-D)]+ cation (see Figure S12). Note that the
cation can be formed reproducibly, which is analogous to
[{(MeIPrCH)Ge}2(μ-H)]+; however, despite multiple attempts, the
nature of the anion varies with different runs of the reaction. The
crude yellow solid is unstable in THF solutions at room temperature
3
6.8 Hz, CH(CH3)2), 1.86 (s, 12H, ImCH3), 2.54 (sept, 8H, JHH
6.8, CH(CH3)2), 7.21 (d, 8H, 3JHH = 7.8 Hz, Dipp-m-H), 7.45 (t, 4H,
3JHH = 7.8 Hz, Dipp-p-H), 7.56 (s, 4H, [BArF ]− p-H), 7.72 (m, 8H,
4
[BArF ]− m-H). 13C{1H} NMR (CD2Cl2, 176 MHz): δ 10.3
4
(ImCH3), 24.4 (CH(CH3)2), 24.6 (CH(CH3)2), 29.3 (CH(CH3)2),
3
50.8 (−CH−Ge2), 118.0 (t, JFC = 3.8 Hz, [BArF ]− p-C), 125.2 (q,
4
1JFC = 272.4 Hz, [BArF ]− CF3), 125.3 (N(CH3)CC), 125.7 (Dipp-
4
m-C), 129.4 (qq, 2JFC = 31.5 Hz, 4JFC = 2.8 Hz, [BArF ]− m-C), 130.5
4
(Dipp-ipso-C), 131.4 (Dipp-p-C), 135.4 ([BArF ]− o-C), 146.5 (Dipp-
4
o-C), 157.1 (N2CCH), 162.3 (q, 1JBC = 49.8 Hz, [BArF ]− ipso-C). 19F
4
NMR (CD2Cl2, 469 MHz): δ −62.9 (s, [BArF ]− CF3). 11B{1H}
4
NMR (CD2Cl2, 160 MHz): δ −6.6 (s, [BArF ]−). Anal. Calcd for
4
C92H94BClF24Ge2N4: C 58.06, H 4.98, N 2.94. Found: C 57.47, H
F
DOI: 10.1021/acs.inorgchem.9b01449
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
and decomposes within a few hours under an inert atmosphere,
mission was 0.899. The calculated minimum and maximum
transmission coefficients (based on crystal size) are 0.8260 and
0.8760. The final anisotropic full-matrix least-squares refinement on
F2 with 1430 variables converged at R1 = 5.57% for the observed data
and at wR2 = 15.77% for all data. The goodness-of-fit was 1.044. The
largest peak in the final difference electron density synthesis was 1.174
e−/Å3, and the largest hole was −0.780 e−/Å3 with a root-mean-
square (RMS) deviation of 0.075 e−/Å3. On the basis of the final
model, the calculated density was 1.136 g/cm3 and F(000), 2432 e−.
Computational Methodology. Geometry optimizations of the
gas-phase structures were performed using DFT with the B3LYP41
functional and the cc-pVDZ42 basis set for compounds 2, 3, 4 (only
the cations were considered, referred to as [3]+ and [4]+ hereafter,
respectively), and 5. In addition, the non-hydrogen bridged cyclic
digermylene Ge(μ-R)2Ge as well as the dicationic analogue [Ge(μ-
R)2Ge]2+ were modeled at the same level of theory. The initial
structures were taken from the experimental obtained X-ray structures
of the respective compounds. For [Ge(μ-R)2Ge]2+ and Ge(μ-R)2Ge
the structure of [4]+ of was taken as a starting geometry for
optimization with the bridging H atom removed manually. To
investigate if the cyclic-Ge(μ-R)2Ge or acyclic-RGeGeR form of the
digermylene is energetically favored, the acyclic isomer of RGeGeR
was optimized at the B3LYP/cc-pVDZ level of theory starting from
the cis and trans-arrangement of the N-heterocyclic vinyl ligands
about the Ge2 core. Notably, both starting geometries (cis/trans) led
to an optimized geometry being basically identical (trans arrange-
ment) with a total energy difference of only ΔE = 0.0133 kcal mol−1.
The initial structures of R2Ge7f and BR2Ge=Ge9 were taken from the
respective cif files deposited at the CCSD. Initial starting geometry of
R2Ge=Ge was obtained by manually placing a Ge atom to the
optimized R2Ge structure. RGeCl was obtained by manually
removing one RGeCl unit from the optimized structure of 2.
RGe(μ-R)Ge was obtained by modeling a transition state of the
smaller anionic NHO ligand ([(HCNMe)2CCH]−) and taking the
obtained structure for the more bulkier MeIPrCH-ligand. Subsequent
frequency analysis of all investigated compounds confirmed the
obtained structures to be local minima on their respective potential
energy surfaces. All calculations were performed with the Gaussian16
software.43 The geometries of all optimized structures are available as
a separate .xyz file.13 The wave function files were used for a
topological analysis of the electron density according to the AIM
space-partitioning scheme16 using AIM2000,44 whereas DGRID45 was
used to generate and analyze the ELI-D related real-space bonding
descriptors46 applying a grid step size of 0.05 au. The NCI17 grids
were computed with NCIplot.47 Bond paths are displayed with
AIM2000,44 and ELI-D and NCI figures are displayed with MolIso48
and VMD,49 respectively. The molecular orbitals (MOs) were
extracted from the Gaussian16 checkpoint files, and the final
molecular geometries were used to compute the NBOs using the
NBO6 program.50 The MOs and NBOs are visualized with VMD.49
whereas the solid as well as the THF solutions can be stored at −30
1
°C for 10 d without sign of degradation by H NMR analysis. Data
for [4D]+:1H NMR (THF-d8, 498 MHz): δ −1.28 (t, 2H, 3JHD = 1.9
Hz, −CH-Ge2), 0.52−0.61 (m, 12H, anion), 0.78−0.81 (m, 20H,
anion), 1.09 (d, 24H, 3JHH = 6.8 Hz, CH(CH3)2), 1.20 (d, 24H, 3JHH
= 6.8 Hz, CH(CH3)2), 1.86 (s, 12H, ImCH3), 2.31 (sept, 8H, 3JHH
=
6.8 Hz, CH(CH3)2), 7.29 (d, 8H, 3JHH = 7.8 Hz, Dipp-m-H), 7.53 (t,
3
2
4H, JHH = 7.8 Hz, Dipp-p-H). H{1H} NMR (THF, 61 MHz): δ
−1.08 (s), −2.71 (s, anion). 13C{1H} NMR (THF-d8, 176 MHz): δ
9.6 (ImCH3), 24.5 (CH(CH3)2), 24.6 (CH(CH3)2), 29.6 (CH-
(CH3)2), 124.4 (N(CH3)CC), 125.8 (Dipp-m-C), 130.1 (Dipp-
ipso-C), 132.1 (Dipp-p-C), 147.6 (Dipp-o-C), 157.2 (N2CCH). 11B
NMR (THF-d8, 128 MHz): No peaks were observed, possibly due to the
asymmetric boron environment.
Synthesis of (MeIPrCH)Ge(CPh3) (5). To a dark yellow
suspension of 2 (0.118 g, 0.110 mmol) in 5 mL of Et2O was added
[Li(THF)4][CPh3] (0.118 g, 0.219 mmol) in 8 mL of Et2O. Upon
addition, the solution changed slightly to orange-red, and the reaction
mixture was stirred for 1 h. At this point, the mixture was filtered, and
the filtrate was dried in vacuo to afford the product as a dark orange
solid (0.142 g, 87%). Crystals of 5 suitable for single-crystal X-ray
diffraction were obtained by dissolving the product in 1 mL of Et2O,
layering with 3 mL of hexanes, and storing at −30 °C for 2 d, yielding
1
3
orange crystals. H NMR (C6D6, 700 MHz): δ 1.08 (d, 12H, JHH
=
3
7.0 Hz, CH(CH3)2), 1.23 (d, 12H, JHH = 7.0 Hz, CH(CH3)2), 1.45
(s, 6H, ImCH3), 2.81 (sept, 4H, CH(CH3)2), 5.70 (s, 1H,
MeIPrCHGe), 6.85 (t, 3H, JHH = 7.7 Hz, Trityl-p-H), 7.02 (t, 6H,
3
3JHH = 7.7 Hz, Trityl-m-H), 7.08 (d, 4H, JHH = 7.7 Hz, Dipp-m-H),
3
3
3
7.23 (t, 2H, JHH = 7.7 Hz, Dipp-p-H), 7.34 (d, 6H, JHH = 7.7 Hz,
Trityl-o-H). 13C{1H} NMR (C6D6, 176 MHz): δ 9.4 (NCCH3), 24.0
(CH(CH3)2), 24.5 (CH(CH3)2), 29.0 (CH(CH3)2), 71.9
(
MeIPrCHGe), 120.6 (ArC), 123.9 (ArC), 124.5 (ArC), 125.4
(ArC), 128.6 (ArC), 130.6 (ArC), 131.2 (ArC), 146.6 (ArC), 149.6
(ArC), 159.8 (NCN). Anal. Calcd for C49H56GeN2: C 78.93, H 7.57,
N 3.76. Found: C 77.83, H 7.63, N 3.63%; despite repeated attempts,
an acceptable value for C could not be obtained, presumably due to
the high moisture sensitivity of this product; please see Figures S16
and S17 for the 1H and 13C{1H} NMR spectra of 5 as an indication of
purity.13 mp (°C): 157−159 UV−Vis (THF): λmax = 514 nm (ε =
5940 L mol−1 cm−1), 339 nm (ε = 36 600 L mol−1 cm−1).
X-ray Crystallography. Crystals of appropriate quality for X-ray
diffraction studies were removed from a vial (glovebox) and
immediately covered with a thin layer of hydrocarbon oil (Para-
tone-N) or perfluorinated ether (Fomblin Y). A suitable crystal was
then selected, attached to a glass fiber or a microsampler, and quickly
placed in a low-temperature stream of nitrogen.38 Data for 2, 3, and 5
were collected using a Bruker APEX II CCD detector/D8
diffractometer using Cu Kα radiation, with the crystal cooled to
−100 °C. Crystal structures were solved using intrinsic phasing
(SHELXT)39 and refined using SHELXL-2014.40 The assignment of
hydrogen atom positions were based on the sp2- or sp3-hybridization
geometries of their attached carbon atoms and were given thermal
parameters 20% greater than those of their parent atoms. X-ray
intensity data for [4]BEt4 were measured on a Bruker D8 Venture
system equipped with a Helios optic monochromator and a Mo TXS
rotating anode (λ = 0.710 73 Å) at −173.15 °C. A total of 2074
frames was collected. The total exposure time was 11.52 h. The
frames were integrated with the Bruker SAINT software package
using a narrow-frame algorithm. The integration of the data using a
triclinic unit cell yielded a total of 179 372 reflections to a maximum θ
angle of 25.030° (0.84 Å resolution), of which 23 352 were
ASSOCIATED CONTENT
* Supporting Information
■
S
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.9b01449.
Optimized molecular structures (XYZ)
Full crystallographic and computational details, along
with copies of all NMR spectra for all newly reported
compounds (PDF)
independent (average redundancy 7.681, Rint = 10.53%, Rsig
=
Accession Codes
6.00%), and 17 764 (76.07%) were greater than 2σ(F2). The final cell
constants of a = 12.637(6) Å, b = 24.400(11) Å, c = 24.565(11) Å, α
= 118.704(11)°, β = 91.502(15)°, γ = 93.284(15)°, and volume =
6620.(5) Å3 are based upon the refinement of the XYZ-centroids of
8904 reflections above 20σ(I), with 4.410° < 2θ < 50.56°. Data were
corrected for absorption effects using the Multi-Scan method
(SADABS). The ratio of minimum to maximum apparent trans-
CCDC 1816455−1816458 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.
G
DOI: 10.1021/acs.inorgchem.9b01449
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
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AUTHOR INFORMATION
Corresponding Author
*E-mail: erivard@ualberta.ca.
ORCID
Emanuel Hupf: 0000-0003-0121-7554
Robert McDonald: 0000-0002-4065-6181
Michael J. Ferguson: 0000-0002-5221-4401
Fritz E. Kuhn: 0000-0002-4156-780X
̈
Eric Rivard: 0000-0002-0360-0090
■
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Author Contributions
The manuscript was written through contributions of all
authors. All authors have given approval to the final version of
the manuscript.
Author Contributions
§These authors contributed equally. Experimental design was
performed by E.R., P.A.L., and F.K., with synthetic
investigations by P.A.L., F.K., E.H., and M.M.D.R. Crystallog-
raphy data collection and refinement for compounds 2, 3, and
5 was performed by R.M. and M.J.F., with collection and data
refinement for 4 by F.K. All computational investigations were
performed by E.H. The manuscript was written with the help
of all coauthors.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
E.R. thanks the NSERC of Canada for Discovery, Discovery
Accelerator, and CREATE funding, the Canada Foundation for
Innovation, the donors of the American Chemical Society
Petroleum Research Fund, and the Univ. of Alberta, Faculty of
Science (Research Award) for funding. E.H. thanks the
German Research Foundation (Deutsche Forschungsgemein-
schaft DFG) for a research fellowship (HU 2512/1-1). F.K.
acknowledges the “Fonds der Chemischen Industrie” for his
fellowship and the IRTG 2022 “ATUMS” (DFG) for financial
support. The computational studies in this work were made
possible by the facilities of the Shared Hierarchical Academic
Computing Network (SHARCNET: www.sharcnet.ca), West-
Grid (www.westgrid.ca), and Compute/Calcul Canada (www.
computecanada.ca). E.R. is also grateful to the Alexander von
Humboldt Foundation for a visiting professorship. We also
gratefully acknowledge M. Miskolzie at the Univ. of Alberta for
(4) (a) Hitchcock, P. B.; Lappert, M. F.; Thorne, A. J. Novel two-
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the measurement of the H{1H} NMR spectrum.
2
DEDICATION
■
This article is dedicated to the memory of Prof. Håkon Hope.
̈
Propper, K.; Dittrich, B.; Klein, S.; Frenking, G. A Dimer of
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