Bis-NHC Aluminium and Gallium Dihydride Cations [(NHC)2EH2]+ (E = Al, Ga)

Article abstract of DOI:10.1002/ejic.202000720

The NHC alane and gallane adducts (NHC)·AlH₂I (NHC = Me₂Im^Me 7, iPr₂Im 8, iPr₂Im^Me 9) and (NHC)·GaH₂I (NHC = Me₂Im^Me 10, iPr₂Im^Me 11,

Full text of DOI:10.1002/ejic.202000720

European Journal of Inorganic Chemistry
Accepted Article
Title: Bis-NHC Aluminium and Gallium dihydride cations
[(NHC)2EH2]+ (E = Al, Ga)
Authors: Andreas Hock, Luis Werner, Melanie Riethmann, and Udo
Radius
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.202000720
Link to VoR: https://doi.org/10.1002/ejic.202000720
01/2020

10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
Bis-NHC Aluminium and Gallium Dihydride Cations [(NHC)2EH2]+
(E = Al, Ga)
Andreas Hock[a], Luis Werner[a], Melanie Riethmann[a] and Udo Radius[a]*
[a] A. Hock, L. Werner, M. Riethmann, Prof. Dr. U. Radius,
Institut für Anorganische Chemie
Julius-Maximilians-Universität Würzburg
Am Hubland, 97074 Würzburg (Germany)
u.radius@uni-wuerzburg.de;
http://www.ak-radius.de
Electronic Supplementary Information (ESI) available: NMR and IR spectroscopic data. See DOI: 10.1039/x0xx00000x
Abstract: The NHC alane and gallane adducts (NHC)∙AlH2I (NHC =
Me2ImMe 7, iPr2Im 8, iPr2ImMe 9) and (NHC)∙GaH2I (NHC = Me2ImMe
c.n. = 2
c.n. = 3
10, iPr2ImMe 11, Dipp2Im 12; R2Im = 1,3-di-organyl-imidazolin-2-
ylidene; Dipp = 2,6 diisopropylphenyl; iPr = isopropyl; Me2ImMe
+
Dipp
N
2+
=
Ph
Ph
N
N
Dipp
N
Ga
N
1,3,4,5-tetra-methyl-imidazolin-2-ylidene) were prepared either by the
simple yet efficient reaction of the NHC adduct (NHC)∙AlH3 with
elemental iodine or by the treatment of (NHC)∙GaH3 with an excess of
methyl iodide at room temperature. The reaction of one equivalent of
the group 13 NHC complexes with an additional equivalent of the
corresponding NHC afforded cationic aluminium and gallium hydrides
[(NHC)2∙AlH2]I (NHC = Me2ImMe 13, iPr2Im 14, iPr2ImMe 15) and
[(NHC)2∙GaH2]I (NHC = Me2ImMe 16, iPr2ImMe 17) and the normal and
abnormal NHC coordinated compound [(Dipp2Im)∙GaH2(aDipp2Im)]I
18. Compounds 7-18 were isolated and characterized by means of
elemental analysis, IR and multinuclear NMR spectroscopy and by X-
ray diffraction of the compounds 7, 9, 10, 15, 16 and 18.
Al
Dipp
N
N
HPh
Ph
II
N
I
Dipp
c.n. = 4
+
2+
Dipp
+
+
N
N
Dipp
NHtBu
NMe3
Al
Dipp
H
Dipp
Al
N
Al
H
H
Al
H
N
N
Ga
H
H
Dipp
N
N
H
BuH2N
H
Dipp
Me3N
N
R
H
Dipp
H
Dipp
III
IV
V
H
VI
c.n. = 5
c.n. = 6
+
+
Me
+
N
N
iPr
H
Me
N
iPr
iPr
iPr
N
Al
N
Me
N
N
N
Al
Me
2N Al NMe2
N
N
N
H
N
H
Me
iPr
iPr
N
H
H
iPr
iPr
Me
VIII
VII
IX
Introduction
Scheme 1. Lewis-base stabilized aluminium and gallium cations.
Aluminum and gallium hydrides are important reagents in organic
and inorganic synthesis, e.g. for reductions and hydride
transfer,1,2 as well as important materials, in particular for hydride
storage.3 The majority of aluminum and gallium hydride species
are either neutral or anionic, whereas cationic Lewis-base
stabilized aluminium and especially gallium hydrides are rather
scarce in the literature. Atwood and co-worker synthesized and
fully characterized the six- and five-coordinated aluminium
hydride cations [(MeNCH2CH2N(Me)CH2CH2CH2)2)∙AlH2]+ VIII
and [(MeN(CH2CH2NMe2)∙AlH2]+ VII as their aluminium hydride
[AlH4]- salts (see Scheme 1, VII & VIII).4 The first four-coordinated
aluminium hydride cation [(NMe3)2∙AlH2]+ III was reported by
Roesky et al., synthesized from a rather unforeseeable reaction.
A mixture of (NMe3)∙AlH2Cl, (NMe3)∙AlH3 and tBuC≡CLi leads to
Aluminium or gallium hydride cations stabilized by N-heterocyclic
carbenes (NHCs) are less common. Recently we reported the
synthesis of a six-coordinated aluminium cation [(iPr2Im)4∙AlH2]+
IX as a side product of the reaction of lithium aluminium hydride
with an excess of iPr2Im (iPr2Im = 1,3-di-iso-propyl-imidazolin-2-
ylidene, see Scheme 1, IX).7 Stephan et al. presented recently a
dinuclear dicationic aluminium hydride [(Dipp2Im)∙AlH(µ-H)]22+ VI
in [(Dipp2Im)∙AlH(µ-H)]2[B(C6F5)4]2 (Dipp2Im
diisopropyl-phenyl)imidazolin-2-ylidene) and a three-coordinated
mononuclear dication [(Bn2Im)2∙AlH]2+ (Bn2Im
1,3-
=
1,3-bis(2,6-
=
dibenzylimidazolin-2-ylidene) in [(Bn2Im)2∙AlH]2[B(C6F5)4] II (see
Scheme 1, VI & II).8 Jones and Stasch et al. reported the
monocationic aluminium hydride [(Dipp2Im)∙AlH2(aDipp2Im)]+ VI
(“a” denotes “abnormal coordination”) which is stabilized by one
normal and one abnormal coordinated NHC (see Scheme 1, VI).9
Furthermore, Krossing and Jones et al. disclosed recently the
synthesis of a “naked” Ga(I) cation [(Dipp2Im)2Ga]+ I stabilized by
a sterically demanding NHC and a non-coordinating anion as
counterion in [(Dipp2Im)2Ga][Al(OC(CF3)3)4] (see Scheme 1, I).10
Thus, NHC stabilized cationic aluminium hydrides are rather
scarce and NHC stabilized cationic gallium hydrides are currently
unknown.
t
formation of [(NMe3)2∙AlH2]2[(AlH)8(CCH2 Bu)6], in which the
[AlH2]+ cation is stabilized by two Lewis-bases NMe3 (see Figure
1,
III)
and
the
carbaalanate
cluster
counter-ion
[(AlH)8(CCH2 Bu)6]2-, formed in course of the reaction, serves as
a bulky, non-coordinating anion.5 The first authenticated cationic
gallium hydrides were presented by Parsons and co-workers.6
Treatment of lithium gallium hydride with [NtBuH3]Cl or
[NsecBuH3]Cl leads to the formation of the salts [(NtBuH2)2GaH2]+
and [(NsecBuH2)2GaH2] + (see Figure 1, IV) as their chloride salts.6
t
We7,11 and others12 investigate currently group 13 metal
compounds (M = Al, Ga, In) which are stabilized with strong σ-
1
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
donating NHC-ligands. The coordination of NHCs, for example, to
alanes and gallanes leads to the synthesis of stable NHC metal
hydride adducts.7,11,12 Thermally stable examples such as
(Dipp2Im)∙MH3 (M = Al, Ga, In) have been prepared particularly
for sterically demanding NHCs. Moreover, the syntheses of some
low-valent, NHC-stabilized dinuclear hydrodialane and
hydrodigallene compounds were presented,13 for example the
dialanes [(Dipp2Im)∙AlH2]2 which were reported by Jones et al.12,14
However, the formation of cationic aluminium and gallium
dihydrides is rare and stabilization of [EH2]+ with two strong σ-
donating NHC-ligands should lead to accessible hydroalane and
hydrogallane cations. Herein we present the formation of such
cationic bis-NHC aluminium and gallium hydrides from the
reaction of (NHC)∙AlH2I and (NHC)∙GaH2I with additional NHC for
the carbenes Me2ImMe, iPr2Im, iPr2ImMe and Dipp2Im.
(NHC)∙GaH3 with an excess of methyl iodide at room temperature.
Results and Discussion
Scheme 2. Synthesis of (NHC)∙AlH2I (NHC= Me2ImMe 7, iPr2Im 8, iPr2ImMe 9)
and (NHC)∙GaH2I (NHC= Me2ImMe 10, iPr2ImMe 11, Dipp2Im 12).
Cationic bis-NHC stabilized aluminium and gallium hydrides
[(NHC)2EH2]+ (E = Al, Ga) should be electronically and sterically
saturated. Thus, our strategy was to synthesize adducts of the
type (NHC)∙EH2I (E = Al, Ga) with a good leaving group iodide as
precursor. Syntheses of NHC stabilized aluminium and gallium
hydride chlorides are well known in literature. NHC stabilized
mono- and dichloroalanes and gallanes (NHC)∙EH2Cl and
(NHC)∙EHCl2 (E = Al, Ga) are either accessible by the reaction of
the NHCs with in situ generated “EH2Cl” and “EHCl2” or by
dismutation between (NHC)∙EH3 and (NHC)∙ECl3 (E = Al, Ga).9,
Table 1. Selected NMR (ppm) and IR (cm-1) shifts of the compounds
(Me2ImMe)∙AlH3 1, (iPr2Im)∙AlH3 2, (iPr2ImMe)∙AlH3 3, (Me2ImMe)∙GaH3 4,
(iPr2ImMe)∙GaH3 5, (Dipp2Im)∙GaH3 6, (Me2ImMe)∙AlH2I 7, (iPr2Im)∙AlH2I 8,
(iPr2ImMe)∙AlH2I 9, (Me2ImMe)∙GaH2I 10, (iPr2ImMe)∙GaH2I 11 and
(Dipp2Im)∙GaH2I 12.
Al-H
1H{27Al}-
NMR
Ga-H
1H-
NMR
NCN
13C{1H}-
NMR
27Al{1H}-
NMR
nAl/Ga-
H
12d, 15
For the synthesis of NHC-stabilized iodoalanes only a few
examples are available in the literature,9,16 e.g. a report by Jones
and Stasch et al. on synthesis of (NHC)∙AlH2I adducts (NHC =
Mes2Im, Dipp2Im) by dismutation between two equivalents of
(NHC)∙AlH3 and one equivalent (NHC)∙AlI3. For the synthesis of
(Me2ImMe)·AlH3
(1)
4.48
-
168.7
170.3
170.0
172.2
172.7
172.7
161.4
162.7
162.3
162.1
163.4
170.3
106.4
17277
(iPr2Im)·AlH3 (2)
4.53
-
106.3
1719,
17767
diiodoalanes (NHC)∙AlHI2 (NHC
= Mes2Im, Dipp2Im) the
corresponding NHC stabilized aluminium hydrides were treated
with an excess of methyl iodide. However, for the heavier gallium
analogues only one example of NHC stabilized iodogallane was
presented in the literature so far, i.e. (Mes2Im)∙GaH2I, which was
prepared from the reaction of metastable “Ga(I)I” with
(Mes2Im)∙GaH3.16
We were interested to develop a simple synthetic route to obtain
the NHC adducts (NHC = Me2ImMe, iPr2Im, iPr2ImMe) of iodoalane
and iodogallane (NHC)∙MH2I (M = Al, Ga) of sterically less
demanding NHCs in a way that may be transferred to large
quantity synthesis. Therefore, we reacted the compounds
(NHC)∙AlH3 (NHC = Me2ImMe 1, iPr2Im 2, iPr2ImMe 3) with
0.5 equivalents of elemental iodine I2 in toluene at room
temperature. Straight after addition of iodine, dissolved in
minimum amounts of toluene, to a toluene solution of 1 - 3,
respectively, the solution discoloured. After 15 min stirring at
room temperature all volatiles were removed in vacuo and the
compounds (NHC)∙AlH2I (NHC = Me2ImMe 7, iPr2Im 8, iPr2ImMe 9)
were isolated as colourless powders in excellent yields (7: 88 %,
8: 97 %, 9: 86 %) and purity (see Scheme 2).
(iPr2ImMe)·AlH3
(3)
4.60
-
107.8
1718,
17717
(Me2ImMe)·GaH3
(4)
-
4.51
4.66
3.73
-
-
1767
(iPr2ImMe)·GaH3
(5)
-
-
177312d
179912d
(Dipp2Im)·GaH3
(6)
-
-
(Me2ImMe)·AlH2I
(7)
4.54
107.8
1796,
1827
(iPr2Im)·AlH2I (8)
4.63
-
109.6
1792,
1809
(iPr2ImMe)·AlH2I
(9)
4.70
-
109.0
1779,
1825
(Me2ImMe)·GaH2I
(10)
-
-
-
4.81
5.00
4.13
-
-
-
1895
(iPr2ImMe)·GaH2I
(11)
1839,
1889
For the reaction of (NHC)∙GaH3 with elemental iodine, however,
consistently the formation of small amounts of (NHC)∙GaI3 was
observed, independent on the stoichiometry used and even after
short reaction times. Therefore, the gallane compounds
(NHC)∙GaH2I (NHC = Me2ImMe 10, iPr2ImMe 11, Dipp2Im 12) were
synthesized by the reaction of the NHC gallane adduct
(Dipp2Im)·GaH2I
(12)
1886
2
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
Al1–I1 108.7(12), H2–Al1–I1 106.5(14), C1–Al1–H1 114.3(14), C1–Al1–H2
106.5(14), C1–Al1–I1 105.88(7); 9: C1–Al1 2.039(3), Al1–H1 1.58(5), Al1–H2
1.60(4), Al1–I1 2.5960(10); H1–Al1–H2 104 (2), H1–Al1–I1 110.5(17), H2–Al1–
I1 111.1(14), C1–Al1–H1 106.7(18), C1–Al1–H2 120.2(14), C1–Al1–I1
103.77(9); 10: Ga–C1 2.036(4), Ga–H1 1.52 (6), Ga–H2 1.44(7), Ga–I
2.6415(6). C1-Ga-H1 109(2), C1-Ga-H2 108(2), C1-Ga-I 100.07(13), H1-Ga-H2
122(3), H1-Ga-I 110(2), H2-Ga-I 105(2).
This reaction affords selectively the colourless compounds
(NHC)∙GaH2I (NHC= Me2ImMe 10, iPr2ImMe 11, Dipp2Im 12) within
30 min at room temperature in very good (10: 88 %, 11: 76 %) to
quantitative (12: 99 %) yield (see Scheme 2). The compounds 7–
12 were characterized by NMR spectroscopy, IR spectroscopy,
and elemental analysis. All new compounds show NHC
resonances in their 1H- and 13C{1H}-NMR-spectra similar as
observed for the corresponding alane and gallane adducts. The
most important NMR and IR data of 7 – 12 are summarized in
Table 1 and compared to their parent compounds 1 – 6. The
27Al{1H} NMR resonances of the compounds 7- 9 in solution were
found at δ = 107.8 (7) ppm, 109.6 (8) ppm and 109.0 (9) ppm. The
signals are in good accordance to the literature-known
resonances of NHC stabilized tetrahedral coordinated alanes,
which lead to signals in the range of δ = 100 and 120 ppm.[11] The
1H or 1H{27Al} NMR resonances of the hydride substituents bound
to the central metal atom for the compounds 7 - 12 were detected
at δ = 4.54 (7) ppm, 4.63 ppm (8), 4.70 (9) ppm, 4.81 (10) ppm,
5.00 (11) ppm and 4.13 (12) ppm, which are only slightly shifted
compared to their corresponding metal hydride compounds
(1: 4.48 ppm, 2: 4.53 ppm, 3: 4.60 ppm, 4: 4.51 ppm, 5: 4.66 ppm,
6: 3.73 ppm).[7,12d] The characteristic E-H (E = Al, Ga) stretching
vibrations of 7 – 12 were observed in the range between 1779 –
1889 cm-1 (see Table 1). The values compare well with Al-H
respectively Ga-H stretches for related compounds such as
molecules adopt a tetrahedral structure at the metal centre,
spanned by the NHC, two hydrogen atoms and the iodine. The M-
CNHC (M = Al, Ga) bond length of 2.025(2) Å (7), 2.039(3) Å (9)
and 2.036(4) (10) differ only marginally from the bond lengths
observed in the NHC aluminum(III)- and gallium(III)hydride
adducts.[17]
The alane adducts 7 - 9 are stable in solution at least up to the
boiling point of toluene and show no decomposition or change in
1
the H NMR spectra. Heating the gallium compounds 10 – 12 in
benzene to 80°C leads to irreversible decomposition, which
afforded elemental gallium as dark grey precipitate and NHC-H2
according to 1H NMR spectroscopy.
We reported earlier on NHC ring expansion and NHC ring opening
by treating (iPr2Im)∙AlH3 2 with an additional equivalent of the
small NHC iPr2Im or the sterically demanding NHC Dipp2Im.[7b]
Thus, we were interested in the reactivity of the NHC stabilized
iodo alanes and gallanes with respect to their behaviour upon
addition of further NHC. The reaction of the alane compounds
(Me2ImMe)∙AlH2I 7, (iPr2Im)∙AlH2I 8 and (iPr2ImMe)∙AlH2I 9 with an
additional equivalent of the corresponding NHC in benzene or
(Dipp2Im)∙AlH2I at 1830 cm-1 and (Mes2Im)∙GaH2I at 1863 cm-1.9,
16
Single crystals of the compounds (Me2ImMe)∙AlH2I 7,
(iPr2ImMe)∙AlH2I 9 and (Me2ImMe)∙GaH2I 10 were grown by slow
toluene led immediately to the formation of
a colourless
precipitate. The 1H NMR spectrum of the mixture shows only one
broadened set of signals for the NHC ligands in solution. Heating
the solution to 80°C does not lead to any change in the 1H NMR
spectra of the compounds and no formation of either ring
expansion or ring opening products was observed. These
colourless precipitates were isolated and identified as the cationic
bis-NHC adducts [(Me2ImMe)2∙AlH2]I 13, [(iPr2Im)2∙AlH2]I 14 and
[(iPr2ImMe)2∙AlH2]I 15 (see Scheme 2). Similarly, the reaction of
(Me2ImMe)∙GaH2I 10 and (iPr2ImMe)∙GaH2I 11 with an additional
equivalent of the NHC in toluene leads to the cationic bis-NHC
adducts [(Me2ImMe)2∙GaH2]I 16 and [(iPr2ImMe)2∙GaH2]I 17 as
colourless solids in good yield and purity (Scheme 2). These
compounds are the first examples of NHC stabilized cationic
gallium dihydrides.
evaporation of
saturated solutions in benzene at room
temperature. The molecular structures of 7, 9 and 10 reveal the
expected four coordinated NHC adducts (see Figure 1).
(Me2ImMe)∙AlH2I
7 crystallizes in the space group C2/c,
(iPr2ImMe)∙AlH2I 9 in the orthorhombic space group Pbca and
(Me2ImMe)∙GaH2I 10 in the monoclinic space group P 21/n. These
Scheme 3. Synthesis of [(Me2ImMe)2∙AlH2]I 13, [(iPr2Im)2∙AlH2]I 14,
[(iPr2ImMe)2∙AlH2]I 15, [(Me2ImMe)2∙GaH2]I 16 and [(iPr2ImMe)2∙GaH2]I 17.
The compounds 13 - 17 are nearly insoluble in aromatic solvents
such as benzene and toluene, only sparingly soluble and
sufficiently stable in more polar solvents such as thf, acetonitrile
and acetone. Solutions of 13 - 15 in acetone show good solubility
Figure 1. Molecular structure of (Me2ImMe)∙AlH2I 7 (left), (iPr2ImMe)∙AlH2I 9 (right)
and (Me2ImMe)∙GaH2I 10 (down) in the solid state (ellipsoids set at the 50%
probability level). Selected bond lengths [Å] and angles [°]: 7: C1–Al1 2.025(2),
Al1–H1 1.61(4), Al1–H2 1.66(4), Al1–I1 2.586(8); H1–Al1–H2 109.4(18), H1–
3
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
and to our surprise only slow decomposition to the corresponding
imidazolium salts [NHCH]+I- (NHC = Me2ImMe, iPr2Im, iPr2ImMe
)
after hours. Samples dissolved in d6-acetone do not exchange the
hydrogen atoms attached to the metal. These samples still reveal
the characteristic Al-H bands in the IR spectrum after evaporation
to dryness and thus some spectroscopic evidence is provided that
the Al-H fragments of the cationic species are retained in d6-
acetone, at least for the time of collecting the NMR spectra.
The compounds 16 and 17 have similar solubilities as the alane
analogues, but they are less stable in acetonitrile and acetone and
decompose readily to the imidazolium salts [Me2ImMeH]I and
[iPr2ImMeH]I after a few hours at room temperature. Whereas the
aluminium complexes 13 - 15 are stable up to the boiling point of
benzene, the gallium complexes decompose to give considerable
amounts of the corresponding imidazolium salts and other
unidentified species at this temperature.
Figure 2. Molecular structure of [(iPr2ImMe)2∙AlH2]I 15 (left) and
[(Me2ImMe)2∙GaH2]I 16 (right) in the solid state (ellipsoids set at the 50%
probability level). Selected bond lengths [Å] and angles [°]: 15: C1–Al1 2.048(4),
C11–Al1 2.050(3), Al1–H1 1.47(4), Al1–H2 1.49(5); H1–Al1–H2 122.(3), C1–
Al1–H1 107.0(17), C1–Al1–H2 108.0(2), C1–Al1–C11 102.20(12), C11–Al1–H1
107.5(16), C11–Al1–H2 108.7(19); 16: C1–Ga1 2.027(4), C11–Ga1 2.025(4),
Ga1–H1 1.38(7), Ga1–H2 1.29(4); H1–Ga1–H2 129.(4), C1–Ga1–H1 109.(3),
C1–Ga1–H2 105.(3), C1–Ga1–C11 104.32(14), C11–Ga1–H1 104(3), C11–
Ga1–H2 102(3).
The compounds 13
- 17 were characterized by NMR
spectroscopy, IR spectroscopy and elemental analysis. The most
1
important NMR and IR data are summarized in Table 2. The H
and 13C{1H} NMR spectra show one set of resonances for the
NHC ligands due to free rotation of the carbenes along the Al-C-
bonds in solution. The 27Al{1H} NMR resonances of the
compounds 13 and 14 in solution were not observed, whereas for
15 the resonance in thf solution was found at 108.7 (15) ppm. This
signal is in good accordance to the literature known resonances
of NHC stabilized tetrahedral coordinated alanes, which lie in the
range between δ = 100 and 120 ppm.7,11 The 1H{27Al} NMR
resonances of the hydrides of 13 to 15 were not observed, but the
hydrides of the gallium compounds were detected at δ = 4.17
(16) ppm and δ = 4.37 (17) ppm in the 1H NMR spectra. The
characteristic metal hydride stretching vibrations were located at
1772, 1791 cm-1 (13), 1820, 1825 cm-1 (14), 1799, 1819 cm-1 (15)
as well as at 1826, 1839 cm-1 (16) and 1857, 1877 cm-1 (17) (see
Table 2) and compare well with literature known cationic
Table 2. Selected NMR (ppm) and IR (cm-1) shifts of the compounds
[(Me2ImMe)2∙AlH2]I
13,
[(iPr2Im)2∙AlH2]I
14
[(iPr2ImMe)2∙AlH2]I
15,
[(Me2ImMe)2∙GaH2]I 16, [(iPr2ImMe)2∙GaH2]I 17 and [(Dipp2Im)∙GaH2(aDipp2Im)]I
18.
Ga-H
1H-NMR
NCN
13C{1H}-
NMR
27Al{1H}-
NMR
nAl/Ga-H
[(Me2ImMe)2∙AlH2]I (13)
[(iPr2Im)2∙AlH2]I (14)
-
-
-
1772,
1791
-
-
-
1820,
1825
[(iPr2ImMe)2∙AlH2]I (15)
[(Me2ImMe)2∙GaH2]I (16)
[(iPr2ImMe)2∙GaH2]I (17)
-
-
108.7
1799,181
9
aluminium
hydrides
[(Dipp2Im)∙AlH2(aDipp2Im)]+I-
and
or the amine stabilized gallium
8-9
[(Bn2Im)2∙AlH]2[B(C6F5)4]2
hydride [(NH2 Bu)2∙GaH2]Cl at 1927 cm-1.6
t
4.17
4.37
3.23
-
-
-
-
1826,
1839
Single crystals of the compounds [(iPr2ImMe)2∙AlH2]I 15 and
[(Me2ImMe)2∙GaH2]I 16 were grown by slow evaporation of a
saturated solution in benzene respectively acetonitrile at room
temperature (see Figure 2). [(iPr2ImMe)2∙AlH2]I 15 crystallizes in
the triclinic space group P1¯ and [(Me2ImMe)2∙GaH2]I 16 in the
monoclinic space group P21/n. The molecules adopt a tetrahedral
structure each, spanned by the two NHC ligands and two
hydrogen atoms. The M-CNHC (M = Al, Ga) bond lengths of
2.048(3) Å and 2.050(3) Å (15) and 2.027(4) Å and 2.025(4) Å
(16) differ only marginally from the bond lengths observed in the
aluminum(III) and gallium(III) hydride adducts. Compared to the
mixed hydride iodide complexes 7 and 9 the bond lengths M-H1
and M-H2 (M = Al, Ga) of the salts 15 and 16 are slightly
shortened. Due to the lower steric demand of the
162.8
171.6
1857,
1877
[(Dipp2Im)∙GaH2(aDipp2
Im)]I (18)
1858,187
6
NHCs compared to Dipp2Im all NHCs are coordinated in a normal
mode. The angles between the two NHCs and the metal centre
(C1-Al-C11) and (C1-Ga-C11) of 102.20(12)° (15) and
104.32(14)° (16) are much smaller compared to those found for
[(Dipp2Im)∙AlH2(aDipp2Im)]I (114.24(8)°).9 Interestingly the angle
between the two hydrides and the metal centre H1-Al-H2 of
122(3)° (15) and H1-Ga-H2 of 129(4)° (16) are quite large
compared to C1-Al1-C11 of 102.20(12) (15) and C1-Ga1-C11 of
104.32(14) (16), which accounts for more metal p-character in the
corresponding M-C (M = Al, Ga) bond according to Bent’s rule.
We propose that the reaction follows an associative substitution
pathway, in which the NHC coordinates to (NHC)∙AlH2I to form a
neutral five coordinated intermediate bis-NHC adduct
(NHC)2∙EH2I (E = Al, Ga; Scheme 4, i). We detected earlier for the
NHC ring expansion or ring opening of (NHC)∙AlH3 in the
presence of NHC such a bis-NHC aluminium hydride adduct
(iPr2Im)2∙AlH3 which was the reactive intermediate for ring
4
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
expansion.7 Calculations have shown that the five coordinated
bis-NHC adducts of group 13 hydrides are higher in energy and
less stable than the four coordinated tetrahedral mono NHC
adducts and are often intermediates of further reactions.18 Instead
of NHC ring expansion we observe in the case of (NHC)2∙EH2I
stabilization by an elimination of the good leaving group iodide to
give the four-coordinated tetrahedral aluminium or gallium cation,
respectively (see Scheme 4, ii). The strong σ-donating alkyl
substituted NHCs stabilize the cationic electron deficient metal
centre in its 8VE count.
abnormal coordinated NHC. The hydrides were detected at δ =
3.23 ppm in the 1H NMR spectrum. In the 13C NMR spectrum the
carbene carbon atom of the normal coordinating NHC was
detected at 171.6 ppm in good accordance to the compound
(Dipp2Im)∙GaH2I 12 at δ = 170.3 ppm. The characteristic metal
hydride stretching vibrations were observed at 1858 and 1876 cm-
1
(see Table 2) and compare well with literature known cationic
aluminium hydrides [(Dipp2Im)∙AlH2(aDipp2Im)]+I- at 1811 and
1827 cm-1.6
Single crystals of the compound [(Dipp2Im)∙GaH2(aDipp2Im)]I 18
were grown by slow evaporation of a saturated solution in
acetonitrile
at
room
temperature
(see
Figure
3).
[(Dipp2Im)∙GaH2(aDipp2Im)]I 18 crystallizes in the monoclinic
space group P21/n. The molecule adopts a tetrahedral structure
spanned by one normal and one abnormal NHC ligand and the
two hydrogen atoms. The Ga-CNHC bond length is slightly shorter
for the abnormal coordinated NHC (Ga-CaNHC = 2.0164(22) Å)
compared with the normal coordinated NHC (Ga-CNHC
=
2.0570(23) Å) as expected due to less steric demand and better
σ-donating properties of the abnormal NHC. These results are in
good accordance with the aluminium analogue cation
[(Dipp2Im)∙AlH2(aDipp2Im)]I presented earlier by Jones and
Stasch et al. (Al-CaNHC = 2.012(2) Å and Ga-CNHC = 2.051(2) Å).9
Scheme 4. Proposed mechanism of the formation of bis NHC aluminium- and
gallium hydride cations.
To further evaluate the influence of the sterics of the NHC on the
reaction and to compare the reactivity with aluminium and gallium
hydrides, we additionally reacted the iodogalane adduct
(Dipp2Im)∙GaH2I 12 with an additional equivalent of the NHC. For
aluminium, Jones and Stasch et al. isolated earlier
[(Dipp2Im)∙AlH2(aDipp2Im)]I, in which the NHCs coordinate the
cation in a normal and an abnormal NHC fashion.9 The reaction
of (Dipp2Im)∙GaH2I 10 with Dipp2Im in benzene at room
temperature afforded a soluble product which shows only one
broadened set of signals for the NHC ligands in the 1H NMR
spectrum. We assume that for this large NHC an equilibrium
exists in solution between free Dipp2Im and coordinated NHC in
(Dipp2Im)∙GaH2I. Heating the mixture up to the boiling point of
Figure 3. Molecular structure of [(Dipp2Im)∙GaH2(aDipp2Im)]I 18 in the solid
state (ellipsoids set at the 50% probability level). Selected bond lengths [Å] and
angles [°]: C1–Ga1 2.057(2), C11–Ga1 2.016(2), Ga1–H1 1.46(4), Ga1–H2
1.58(4); H1–Ga1–H2 116.(2), C1–Ga1–H1 101.4(14), C1–Ga1–H2 102.6(15),
C1–Ga1–C11 113.55(9), C11–Ga1–H1 111.6(14), C11–Ga1–H2 111.1(16);
toluene affords
a
colourless precipitate of the cation
[(Dipp2Im)∙GaH2(aDipp2Im)]I 18 (see Scheme 5), which is
stabilized with a normal and abnormal coordinated NHC. The
compound [(Dipp2Im)∙GaH2(aDipp2Im)]I 18 was isolated from
toluene as colourless powder in good yield (18: 54 %) and
excellent purity.
We propose that the formation of the compound 18 follows a
similar mechanism postulated by Jones and Stasch et al. for the
aluminium analogue compound and the earlier discussed cationic
bis NHC alanes and gallanes. We also observe an equilibrium in
solution via a reactive five-coordinated bis NHC stabilized
intermediate (Dipp2Im)2∙AlH2I. Due to steric demand of both NHCs,
stabilization of the compound was reached by steric relief, i.e. (ii)
switching one of the NHCs into an abnormal coordination mode
and (iii) abstraction of the good iodide leaving group, to yield the
four-coordinated gallium cation (see Scheme 4 & 5).
Scheme 5. Synthesis of [(Dipp2Im)∙GaH2(aDipp2Im)]I 18.
The compound 18 was characterized by NMR spectroscopy, IR
Conclusion
spectroscopy and elemental analysis. The most important NMR
1
and IR data are summarized in Table 2. The H NMR spectrum
The synthesis of the NHC-stabilized cationic aluminium- and
gallium hydrides [(NHC)2∙AlH2]I (NHC = Me2ImMe 13, iPr2Im 14,
shows one set of signals for the normal and one set for the
5
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
[%]: C, 34.67 (35.08); H, 5.96 (5.89); N, 8.99 (9.09). IR (ATR[cm-1]): 3151
(w), 3124 (w), 2976 (m), 2932 (w), 1860 (m), 1837 (m, nAl–H, str.), 1809 (m),
1792 (m, nAl–H, str.), 1460 (m), 1430 (m), 1398 (m), 1371 (w), 1207 (s), 1174
(w), 1126 (m), 766 (s), 747 (s), 703 (m), 661 (s), 627 (s), 578 (s), 525 (m),
455 (m). 1H{27Al}-NMR (400.1 MHz, C6D6, 298 K): d [ppm] = 0.93 (d, 12 H,
3JHH = 6.7 Hz, iPr-CH3), 4.63 (sbr, 2 H, Al-H), 5.17 (sept, 2 H, 3JHH = 6.7 Hz,
iPr-CH), 6.15 (s, 2 H, NCHCHN). 13C{1H}-NMR (100.6 MHz, C6D6, 298 K):
d [ppm] = 22.9 (iPr-CH3), 51.8 (iPr-CH), 117.5 (NCCN), 162.7 (NCN).
27Al{1H}-NMR (104.3 MHz, C6D6, 298 K): d [ppm] = 109.6.
iPr2ImMe 15) and [(NHC)2∙GaH2]I (NHC = Me2ImMe 16, iPr2ImMe
17), balanced by an iodide counter anion, is reported. These
cations are accessible in good yields and high purity via the direct
reaction of the free carbenes (Me2ImMe, iPr2Im, iPr2ImMe) with the
corresponding group 13 NHC hydride iodide complexes
(NHC)∙AlH2I (NHC = Me2ImMe 7, iPr2Im 8, iPr2ImMe 9) and
(NHC)∙GaH2I (NHC = Me2ImMe 10, iPr2ImMe 11), respectively. The
NHC iodo alanes and iodo gallanes 7 - 12 were prepared via a
simple yet efficient synthesis starting from (NHC)∙EH3 (NHC =
Me2ImMe, iPr2ImMe; E = Al, Ga) and either elemental iodine or
(iPr2ImMe)∙AlH2I 9: Elemental solid iodine (453 mg, 1.78 mmol) was added
at room temperature to a solution of (iPr2ImMe)∙AlH3 (750 mg, 3.57 mmol)
3 dissolved in 15 mL of toluene and the resulting solution was stirred for
45 minutes. The solvent was evaporated to dryness which gave 9 as
colourless powder. Yield: 1.06 g (88 %). Crystals suitable for X-ray
diffraction of the compounds 9 were grown by slow evaporation of a
saturated solution in benzene. C11H22N2AlI [336.20 g/mol] found
(calculated) [%]: C, 39.05 (39.30); H, 6.50 (6.60); N, 8.11 (8.33). IR
(ATR[cm-1]): 2977 (w), 2933 (vw), 1825 (m, nAl–H, str.), 1779 (s, nAl–H, str.),
1624 (vw), 1455 (w), 1372 (m), 1337 (w), 1223 (m), 1168 (w), 1135 (w),
1115 (w), 1082 (w), 888 (w), 783 (s), 7058 (s), 666 (vs), 565 (m), 471 (m).
methyl
iodide.
The
compounds
[(NHC)2∙GaH2]I
(NHC = Me2ImMe 16, iPr2ImMe 17) are the first examples of NHC
stabilized gallium hydride cations reported. Additionally we
investigated the influence of the steric demand of the NHC used
and synthesized [(Dipp2Im)∙GaH2(aDipp2Im)]I 18, in which
normal and abnormal coordination of the NHC is observed.
Experimental Section
1H{27Al}-NMR (400.1 MHz, C6D6, 298 K): d [ppm] = 1.11 (d, 12 H, 3JHH
=
i
7.1 Hz, Pr-CH3), 1.44 (s, 6 H, NCCH3CCH3N), 4.70 (sbr, 2 H, Al-H), 5.39
(sept, 2 H, 3JHH = 7.1 Hz, iPr-CH). 13C{1H}-NMR (100.6 MHz, C6D6, 298 K):
d [ppm] = 9.7 (NCCH3CCH3N), 21.4 (iPr-CH3), 52.6 (iPr-CH), 126.5
(NCCN), 162.3 (NCN). 27Al{1H}-NMR (104.3 MHz, C6D6, 298 K): d [ppm]
= 109.0.
All reactions and subsequent manipulations involving organometallic
reagents were carried out under an inert atmosphere of argon by using
standard Schlenk-line and glovebox techniques as reported previously.[1]
All reactions were performed in oven-dried glassware. Toluene and n-
hexane were obtained from a solvent purification system (Innovative
Technology). C6D6, thf-d8, CD3CN and d6-acetone were purchased from
(Me2ImMe)∙GaH2I 10: Methyliodide (1.20 mL) was added to a solution of
(Me2ImMe)∙GaH3 4 (400 mg, 2.03 mmol) in 10 mL of toluene at room
temperature via a syringe and stirred for 30 minutes. The solvent was
evaporated which gave compound 10 as colourless powder. Yield: 590 mg
(88 %). Crystals of compound 10 suitable for X-ray diffraction were grown
by slow evaporation of a saturated solution of the compound in benzene.
C7H14N2GaI [322.83 g/mol] found (calculated) [%]: C, 25.66 (26.04); H,
4.21 (4.37); N, 8.03 (8.68). IR (ATR[cm-1]): 2921 (m), 1895 (s, nGa–H, str.),
1650 (m), 1577 (m), 1435 (m), 1391 (w), 1371 (m), 848 (m), 755 (s), 743
(s), 677 (s), 633 (s), 456 (s). 1H-NMR (400.1 MHz, C6D6, 298 K): d [ppm]
= 1.07 (s, 6 H, NCCH3CCH3N), 3.06 (s, 6 H, CH3), 4.81 (sbr, 2 H, Ga-H).
13C{1H}-NMR (100.6 MHz, C6D6, 298 K): d [ppm] = 7.8 (CH3), 33.7
(NCCH3CCH3N), 125.7 (NCCN), 162.1 (NCN).
Sigma-Aldrich and stored over molecular sieve. The carbenes Me2ImMe 19
iPr2Im,19 iPr2ImMe 19 Dipp2Im20 and the compounds (Me2ImMe)∙AlH3 1,7
,
,
(iPr2Im)∙AlH3 2,7 (iPr2ImMe)∙AlH3 3,7 (Me2ImMe)∙GaH3 4,12 (iPr2ImMe)∙GaH3
5,12 (Dipp2Im)∙GaH3 612 were synthesized according to reported
procedures. Elemental iodine and methyl iodide were purchased from
Sigma-Aldrich and used as received. Elemental analyses were performed
in the micro-analytical laboratory of the University of Würzburg with an
Elementar vario micro cube. Infrared spectra were recorded on a Bruker
alpha spectrometer as solids using an ATR unit. 1H, 27Al and 13C{1H} NMR
spectra were recorded at 298 K on a Bruker Avance 400 spectrometer (1H,
400.4 MHz; 13C{1H}, 100.7 MHz; 27Al, 104.3 MHz). 1H NMR chemical shifts
are listed in parts per million (ppm), are reported relative to TMS and were
referenced via residual proton resonances of the deuterated solvent
(C6D5H: 7.16 ppm, d8-thf: 1.73, 3.58 ppm, CD3CN: 1.94 ppm, d6-acetone:
2.05). 13C{1H} NMR resonances are reported relative to TMS using the
natural-abundance carbon resonances of C6D6 (128.06 ppm), d8-thf (25.37,
67.57 ppm), CD3CN (1.39, 118.7 ppm) and d6-acetone (29.92,
206.68 ppm).[21]
(iPr2ImMe)∙GaH2I 11: Methyliodide (245 µL) was added to a solution of
(iPr2ImMe)∙GaH3 5 (100 mg, 395 µmol) in 10 mL of toluene at room
temperature via a syringe and stirred for 30 minutes. The solvent was
evaporated which gave compound 11 as colourless powder. Yield: 111 mg
(75 %). C7H14N2GaI [322.83 g/mol] found (calculated) [%]: C, 34.75
(34.87); H, 5.65 (5.85); N, 7.37 (7.39). IR (ATR[cm-1]): 2962 (m), 1889
(snGa–H, str.), 1839 (s,nGa–H, str.), 1488 (m), 1457 (m), 1385 (m), 1368 (m),
1272 (m), 1262 (m), 805 (s), 761 (s), 648 (s). 1H-NMR (400.1 MHz, C6D6,
(Me2ImMe)∙AlH2I 7: Elemental solid iodine (370 mg, 1.46 mmol) was added
at room temperature to a solution of (Me2ImMe)∙AlH3 (450 mg, 2.92 mmol)
1 dissolved in 15 mL of toluene and the resulting solution was stirred for
45 minutes. The solvent was evaporated to dryness which gave 7 as
colourless powder. Yield: 706 mg (86 %). Crystals suitable for X-ray
diffraction of the compounds 7 were grown by slow evaporation of a
saturated solution in benzene. C7H14N2AlI [280.09 g/mol] found
(calculated) [%]: C, 30.21 (30.02); H, 5.05 (5.04); N, 10.08 (10.00). IR
(ATR[cm-1]): 2949 (vw), 2922 (vw), 1827 (s, nAl–H, str.), 1796 (s, nAl–H, str.),
1646 (w), 1435 (m), 1403 (w), 1385 (w), 1370 (m), 1231 (vw), 1175 (vw),
846 (m), 768 (vs), 685 (vs), 633 (vs), 601 (s), 471 (s). 1H{27Al}-NMR (400.1
MHz, C6D6, 298 K): d [ppm] = 1.14 (s, 6 H, NCCH3CCH3N), 3.15 (s, 6 H,
CH3), 4.54 (sbr, 2 H, Al-H). 13C{1H}-NMR (100.6 MHz, C6D6, 298 K): d
[ppm] = 7.6 (CH3), 33.6 (NCCH3CCH3N), 125.8 (NCCN), 161.4 (NCN).
27Al{1H}-NMR (104.3 MHz, C6D6, 298 K): d [ppm] = 107.8.
3
i
298 K): d [ppm] = 1.09 (d, 12 H, JHH = 7.1 Hz, Pr-CH3), 1.42 (s, 6 H,
NCCH3CCH3N), 5.00 (sbr, 2 H, Ga-H), 5.32 (septbr, 2 H, iPr-CH). 13C{1H}-
NMR (100.6 MHz, C6D6, 298 K): d [ppm] = 9.7 (NCCH3CCH3N), 21.4 (iPr-
CH3), 52.6 (iPr-CH), 126.2 (NCCN), 163.4 (NCN).
(Dipp2Im)∙GaH2I 12: Methyliodide (500 µL) was added to a solution of
(Dipp2Im)∙GaH3 6 (400 mg, 867 µmol) in 10 mL of toluene at room
temperature via a syringe and stirred for 30 minutes. The solvent was
evaporated which gave compound 9 as colourless powder. Yield: 509 mg
(99 %). Elemental analysis C27H38N2GaI [587.24 g/mol] found
(calculated) [%]: C, 55.35 (55.22); H, 6.82 (6.52); N, 4.75 (4.77). IR
(ATR[cm-1]): 2962 (s), 1886 (snGa–H, str.), 1456 (s), 1299 (m), 1270 (m), 1257
(m), 1108 (m), 801 (s), 757 (s), 725 (s), 707 (m), 661 (s). 1H-NMR (400.1
MHz, C6D6, 298 K): d [ppm] = 0.98 (d, 12 H, 3JHH = 7.1 Hz, iPr-CH3), 1.42
(d, 12 H, 3JHH = 7.1 Hz, iPr-CH3), 2.69 (sept, 4 H, 3JHH = 7.1 Hz, iPr-CH),
4.13 (sbr, 2 H, Ga-H), 6.45 (s, 2 H, NCHCHN), 7.09 (m, 4 H, aryl-CmetaH),
7.22 (m, 2 H, aryl-CparaH). 13C{1H}-NMR (100.6 MHz, C6D6, 298 K): d [ppm]
(iPr2Im)∙AlH2I 8: Elemental solid iodine (557 mg, 2.19 mmol) was added
at room temperature to a solution of (iPr2Im)∙AlH3 (800 mg, 4.39 mmol) 2
dissolved in 10 mL of toluene and the resulting solution was stirred for 2
hours. The solvent was evaporated to dryness which gave 8 as colourless
powder. Yield: 1.31 g (97 %). C9H18N2AlI [308.14 g/mol] found (calculated)
6
This article is protected by copyright. All rights reserved.

10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
= 23.3 (iPr-CH3), 25.6 (iPr-CH3), 29.1 (iPr-CH), 124.5 (aryl-CmetaH), 131.2
(aryl-CparaH), 134.2 (aryl-Cipso), 145.6 (aryl-Cortho), 170.3 (NCN).
(100.6 MHz, CD3CN, 298 K): d [ppm] = 8.9 (CH3), 35.0 (NCCH3CCH3N),
128.5 (NCCN). NCN not observed.
[(Me2ImMe)2∙AlH2]I 13: Toluene (15 mL) was added to a mixture of
(Me2ImMe)∙AlH2I 7 (200 mg, 714 µmol) and Me2ImMe (88.7 mg, 714 µmol)
in a Schlenk flask. The reaction mixture was stirred for 16 hours at room
temperature, then the solvent was evaporated. N-hexane (10 mL) was
added to the residue and the white precipitate was filtered off and washed
with n-hexane. The white solid was dried in vacuo to afford compound 13.
Yield: 260 mg (90 %). C14H26N4AlI [404.28 g/mol] found (calculated) [%]:
C, 41.12 (41.59); H, 6.47 (6.48); N, 13.36 (13.86). IR (ATR[cm-1]): 2976
(w), 1791 (s, nAl–H, str.), 1772 (s, nAl–H, str.), 1644 (m), 1575 (m), 1440 (w),
1388 (w), 851 (m), 767 (s), 753 (m), 708 (s), 650 (s), 576 (m), 474 (m). 1H-
NMR (400.1 MHz, Acetone-d6, 298 K): d [ppm] = 2.35 (s, 12 H,
NCCH3CCH3N), 3.93 (s, 12 H, CH3). Al-H not observed. 13C{1H}-NMR
(100.6 MHz, Acetone-d6, 298 K): d [ppm] = 8.3 (CH3), 34.1 (NCCH3CCH3N),
127.9 (NCCN). NCN not observed.27Al{1H}-NMR (104.3 MHz, Acetone-d6,
298 K): No signal observed.
[(iPr2ImMe)2∙GaH2]I 17: Toluene (15 mL) was added to a mixture of
(iPr2ImMe)∙GaH2I 11 (75 mg, 198 µmol) and iPr2ImMe (39 mg, 198 µmol) in
a Schlenk flask. The reaction mixture was stirred for 16 hours at room
temperature, then the solvent was evaporated. N-hexane (10 mL) was
added to the residue and the white precipitate was filtered off and washed
with n-hexane. The white solid was dried in vacuo to afford compound 17.
Yield: 56 mg (51 %). C22H42N4GaI [559.23 g/mol] found (calculated) [%]:
C, 45.98 (47.25); H, 7.45 (7.57); N, 9.51 (10.02). IR (ATR[cm-1]): 2972 (m),
1877 (m, nGa–H, str.), 1857 (m, nGa–H, str.), 1626 (m), 1555 (s), 1446 (m), 1376
(m), 1365 (m), 1231 (s), 1190 (s), 1110 (s), 764 (m), 678 (m), 659 (m), 521
(m).1H-NMR (400.1 MHz, thf-d8, 298 K): d [ppm] = 1.52 (d, 24 H, 3JHH = 6.9
i
Hz, Pr-CH3), 2.40 (s, 12 H, NCCH3CCH3N), 4.37 (sbr, 2 H, Ga-H), 4.98
i
(sept, 4 H, Pr-CH). 13C{1H}-NMR (100.6 MHz, thf-d8, 298 K): d [ppm] =
11.3 (NCCH3CCH3N), 22.1 (iPr-CH3), 54.1 (iPr-CH), 129.3 (NCCN), 162.8
(NCN).
[(iPr2Im)2∙AlH2]I 14: Toluene (15 mL) was added to a mixture of
(iPr2Im)∙AlH2I 7 (100 mg, 325 µmol) and iPr2Im (49.4 mg, 325 µmol) in a
Schlenk flask. The reaction mixture was stirred for 16 hours at room
temperature, then the solvent was evaporated. N-hexane (10 mL) was
added to the residue and the white precipitate was filtered off and washed
with n-hexane. The white solid was dried in vacuo to afford compound 14.
Yield: 92 mg (62 %). C18H34N4AlI [460.38 g/mol] found (calculated) [%]: C,
46.49 (46.96); H, 7.35 (7.44); N, 11.74 (12.17). IR (ATR[cm-1]): 3068 (m),
2976 (m), 1825 (mnAl–H, str.), 1820 (m, nAl–H, str.), 1403 (m), 1215 (s), 1134
(m), 792 (m), 769 (s), 717 (s), 678 (s), 664 (s), 576 (m), 480 (m). 1H-NMR
(400.1 MHz, Acetone-d6, 298 K): d [ppm] = 1.64 (d, 24 H, 3JHH = 6.9 Hz,
iPr-CH3), 4.96 (sept, 4 H, iPr-CH), 7.93 (4 H, NCHCHN). Al-H not observed.
13C{1H}-NMR (100.6 MHz, Acetone-d6, 298 K): d [ppm] = 23.1 (iPr-CH3),
53.8 (iPr-CH), 121.3 (NCCN). NCN not observed. 27Al{1H}-NMR (104.3
MHz, Acetone-d6, 298 K): No signal observed.
[(Dipp2Im)∙GaH2(aDipp2Im)]I 18: Toluene (10 mL) was added to a mixture
of (Dipp2Im)∙GaH2I 12 (200 mg, 341 µmol) and Dipp2Im (133 mg,
341 µmol) in a Schlenk flask. The reaction mixture was stirred for 16 hours
at 110 °C, then the solvent was evaporated. N-hexane (10 mL) was added
to the residue and the white precipitate was filtered off and washed with n-
hexane. The white solid was dried in vacuo to afford compound 18. Yield:
180 mg (54 %). C54H74N4GaI [975.79 g/mol] found (calculated) [%]: C,
66.06 (66.40); H, 7.78 (7.74); N, 5.64 (5.74). IR (ATR[cm-1]): 2961 (s), 1876
(m, nGa–H, str.), 1858 (m, nGa–H, str.), 1540 (m), 1466 (m), 1329 (m), 1212 (w),
1188 (w), 805 (s), 755 (s), 742 (s), 690 (s), 464 (m). 1H-NMR (400.1 MHz,
CD3CN, 298 K): d [ppm] = 0.96 (d, 6 H, 3JHH = 7.1 Hz, aNHC-iPr-CH3), 1.03
(d, 6 H, 3JHH = 7.1 Hz, aNHC-iPr-CH3), 1.13 (d, 6 H, 3JHH = 7.1 Hz, aNHC-
iPr-CH3), 1.14 (d, 12 H, 3JHH = 7.1 Hz, NHC-iPr-CH3), 1.17 (d, 12 H, 3JHH
=
3
7.1 Hz, NHC-iPr-CH3), 1.33 (d, 6 H, JHH = 7.1 Hz, aNHC-iPr-CH3), 2.12
(d-sept, 4 H, 3JHH = 7.1 Hz, aNHC-iPr-CH), 2.50 (sept, 4 H, 3JHH = 7.1 Hz,
4
NHC-iPr-CH), 3.22 (sbr, 2 H, Ga-H), 4.26 (d, 1 H, JHH = 1.44 Hz, aNHC-
[(iPr2ImMe)2∙AlH2]I 15: Toluene (15 mL) was added to a mixture of
(iPr2ImMe)∙AlH2I 8 (200 mg, 595 µmol) and iPr2ImMe (107.3 mg, 595 µmol)
in a Schlenk flask. The reaction mixture was stirred for 16 hours at room
temperature, then the solvent was evaporated. N-hexane (10 mL) was
added to the residue and the white precipitate was filtered off and washed
with n-hexane. The white solid was dried in vacuo to afford compound 15.
Yield: 270 mg (88 %). Suitable crystals of compounds 15 for X-ray
diffraction were grown by slow evaporation of a saturated solution in
benzene. C22H42N4AlI [516.49 g/mol] found (calculated) [%]: C, 41.12
(41.59); H, 6.47 (6.48); N, 13.36 (13.86). IR (ATR[cm-1]): 2971 (m), 2932
(m), 1819 (m, nAl–H, str.), 1799 (m, nAl–H, str.), 1657 (m), 1627 (m), 1555 (m),
1446 (m), 1313 (m), 1190 (m), 1110 (m), 770 (s), 720 (s), 661 (s), 540 (m).
1H-NMR (400.1 MHz, thf-d8, 298 K): d [ppm] = 1.53 (d, 24 H, 3JHH = 6.9 Hz,
iPr-CH3), 2.35 (s, 12 H, NCCH3CCH3N), 4.94 (sept, 4 H, iPr-CH). Al-H not
observed. 13C{1H}-NMR (100.6 MHz, thf-d8, 298 K): d [ppm] = 11.2
(NCCH3CCH3N), 22.7 (iPr-CH3), 53.9 (iPr-CH), 129.1 (NCCN), NCN not
observed. 27Al{1H}-NMR (104.3 MHz, thf-d8, 298 K): d [ppm] = 108.7.
NCCHN), 7.29 (s, 2 H, NHC- NCHCHN) 7.26-7.65 (m, 12 H, aryl-CH), 7.22
(m, 2 H, aryl-CparaH), 8.71 (d, 1 H, 4JHH = 1.44 Hz, aNHC-NCHN). 13C{1H}-
NMR (100.6 MHz, CD3CN, 298 K): d [ppm] = 22.6 (aNHC -iPr-CH3), 23.3
(NHC-iPr-CH3), 23.7 (aNHC-iPr-CH3), 24.8 (NHC-iPr-CH3), 25.6 (aNHC-
iPr-CH3), 25.9 (aNHC-iPr-CH3), 29.4 (aNHC-iPr-CH), 29.5 (aNHC-iPr-
CH), 29.8 (NHC-iPr-CH), 125.2 (arylCH), 125.4 (arylCH), 125.5 (arylCH),
125.8 (arylCH), 127.1 (arylCH), 130.4 (arylCH), 131.8 (arylCH), 132.3
(arylCH), 132.6 (arylCH), 134.9 (arylCH), 139.5 (aNHC-NCHN) 146.1
(aNHC-NCCHN), 146.4 (aNHC-NCCHN), 147.3 (NHC-NCHCHN), 171.7
(NCN).
CRYSTALLOGRAPHIC DETAILS
Crystals were immersed in a film of perfluoropolyether oil on a glass fiber
MicroMountTM (MiTeGen) and transferred to a Rigaku XtaLAB Synergy-
DW diffractometer with Hy-Pix-6000HE detector and monochromated Cu-
Kα equipped with an Oxford Cryo 800 cooling unit. Data were collected at
100 K. The images were processed with Crysalis software packages and
equivalent reflections were merged. Corrections for Lorentz-polarization
effects and absorption were performed if necessary and the structures
were solved by direct methods. Subsequent difference Fourier syntheses
revealed the positions of all other non-hydrogen atoms. The structures
were solved by using the ShelXTL software package.22 All non-hydrogen
atoms were refined anisotropically. Hydrogen atoms were usually
assigned to idealized positions and were included in structure factors
calculations.
[(Me2ImMe)2∙GaH2]I 16: Toluene (15 mL) was added to a mixture of
(Me2ImMe)∙GaH2I 9 (50 mg, 155 µmol) and Me2ImMe (19.2 mg, 155 µmol)
in a Schlenk flask. The reaction mixture was stirred for 16 hours at room
temperature, then the solvent was evaporated. N-hexane (10 mL) was
added to the residue and the white precipitate was filtered off and washed
with n-hexane. The white solid was dried in vacuo to afford compound 16.
Yield: 38 mg (55 %). Suitable crystals of compounds 16 for X-ray
diffraction were grown by slow evaporation of a saturated solution in
benzene. C14H26N4GaI [447.02 g/mol] found (calculated) [%]: C, 37.45
(37.62); H, 5.78 (5.86); N, 11.87 (12.53). IR (ATR[cm-1]): 3019 (w), 1839
(m, nGa–H, str.), 1826 (m, nGa–H, str.), 1646 (m), 1577 (m), 1440 (m), 1391 (m),
1209 (w), 851 (s), 764 (s), 744 (m), 695 (s), 642 (s), 572 (m), 452 (m). 1H-
NMR (400.1 MHz, CD3CN, 298 K): d [ppm] = 2.15 (s, 12 H, NCCH3CCH3N),
3.61 (s, 12 H, CH3), 4.17 (sbr, 2 H, Ga-H), (sbr, 4 H, iPr-CH). 13C{1H}-NMR
Crystallographic data (excluding structure factors) for the structures in this
paper have been deposited with the Cambridge Crystallographic Data
Centre, CCDC, 12 Union Road, Cambridge CB21EZ, UK. Copies of the
data can be obtained free of charge on quoting the depository numbers
CCDC-1993675 (7), CCDC-1993679 (9), CCDC-1993676 (10), CCDC-
1993677 (15), CCDC-1993678 (16) and CCDC-2013190 (18) (Fax: +44-
7
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
1223-336-033;
http://www.ccdc.cam.ac.uk).
E-Mail:
deposit@ccdc.cam.ac.uk,
Acknowledgements
This work was supported by the Julius-Maximilians-Universität
Würzburg and the Deutsche Forschungsgemeinschaft (Ra
720/13).
Crystal Data of (Me2ImMe)∙AlH2I 7 C13H20AlIN2, Mr = 358.19, colorless
block, 0.20 x 0.17 x 0.14 mm, orthorhombic group Pbca, a = 24.6229(3) Å,
b = 8.35440(10) Å, c = 15.6920(2) Å, α = 90°, b = 64.043(5)°, γ = 101.
37770(10)°, V = 3164.57(7) Å3, T = 100(10) K, Z = 8, ρcalcd. = 1.504 g·cm–
3, μ = 16.292, F(000) = 1424, 15990 reflections, in h(–30/31), k(-10/10), l(-
19/19) measured in the range 3.6850 ° < θ < 76.9390°, completeness
98.0 %, 3012 independent reflections, 2946 observed reflections (I > 2σ(I)),
168 parameters, 0 restraints; all data: R1 = 0.0297 and wR2 = 0.0758, I >
2σ(I): R1 = 0.0301 and wR2 = 0.00761, Goof 1.097, largest difference
Keywords: N-Heterocyclic Carbenes • Aluminium • Gallium •
Cations • Main Group Element Hydrides
[1]
(a) R. Brückner, Chapter 14: Oxidations and Reductions. In Advanced
Organic Chemistry, Elsevier 2002, pp 545-612; (b) J. March, M. B. Smith,
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peak/hole 1.379 /-0.697 e·Å–3
.
Crystal Data of (iPr2ImMe)∙AlH2I 9 C11H22AlIN2, Mr = 336.18, colorless
block, 0.22 x 0.22 x 0.12 mm, monoclinic group C2/c, a = 15.7664(3) Å, b
= 10.9910(2) Å, c = 17.1308(4) Å, α = 90°, b = 90°, b = 90°, V = 3164.57(7)
Å3, T = 99.99(10) K, Z = 8, ρcalcd. = 1.504 g·cm–3, μ = 17.320, F(000) =
1344, 15340 reflections, in h(-13/19), k(-13/13), l(-21/21) measured in the
range 5.5540 ° < θ < 76.4870°, completeness 98.0 %, 2714 independent
reflections, 2434 observed reflections (I > 2σ(I)), 150 parameters, 0
restraints; all data: R1 = 0.0355 and wR2 = 0.0939, I > 2σ(I): R1 = 0.0392
and wR2 = 0.0967, Goof 1.070, largest difference peak/hole 1.735 /-0.892
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(a) W. G. Brown, Org. React. 1951, 6, 469-510; (b) H. C. Brown, A.
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43, 7284-7293; (f) R. J. Wehmschulte, P. P. Power, Polyhedron 2000,
19, 1649-1661.
e·Å–3
.
Crystal Data of (Me2ImMe)∙GaH2I 10 C7H14N2GaI, Mr = 322.83, colorless
block, 0.17 x 0.13 x 0.06 mm, monoclinic group P21/n, a = 9.1674(3) Å, b
= 9.9889(2) Å, c = 12.4319(3) Å, α = 90°, b = 108.739(3)°, γ = 90°, V =
1078.07(5) Å3, T = 100.0(5) K, Z = 4, ρcalcd. = 1.989 g·cm–3, μ = 25.555,
F(000) = 616, 5683 reflections, in h(–8/11), k(-12/11), l(-15/11) measured
in the range 3.270 ° < θ < 70.075°, completeness 100.0 %, 2049
independent reflections, 1968 observed reflections (I > 2σ(I)), 112
parameters, 0 restraints; all data: R1 = 0.0444 and wR2 = 0.0456, I > 2σ(I):
R1 = 0.1148 and wR2 = 0.1161, Goof 1.030, largest difference peak/hole
[3]
A. Schneemann, J. L. White, S. Kang, S. Jeong, L. F. Wan, E. S. Cho, T.
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2.28 /-1.62 e·Å–3
.
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Crystal Data of [(iPr2ImMe)2∙AlH2]I 15 C14H26N4AlI, Mr = 404.28, colorless
block, 0.17 x 0.01 x 0.06 mm, triclinic group P¯1, a = 10.1308(3) Å, b =
13.0257(4) Å, c = 13.5023(5) Å, α = 76.396(3)°, b = 82.890(3)°, b =
79.406(3)°, V = 1696.21(1) Å3, T = 100.01(1) K, Z = 2, ρcalcd. = 1.241 g·cm–
3, μ = 7.833, F(000) = 662, 14143 reflections, in h(-12/12), k(-15/19), l(-
16/16) measured in the range 3.380 ° < θ < 72.101°, completeness 99.7 %,
6674 independent reflections, 6226 observed reflections (I > 2σ(I)), 354
parameters, 0 restraints; all data: R1 = 0.0377 and wR2 = 0.0400, I > 2σ(I):
R1 = 0.0994 and wR2 = 0.1007, Goof 1.090, largest difference peak/hole
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1.40 /-1.08 e·Å–3
.
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2014, 275, 63-86; (b) V. Nesterov, D. Reiter, P. Bag, P. Frisch, R. Holzner,
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14384-14387.
Crystal Data of [(Me2ImMe)2∙GaH2]I 16 C14H26N4GaI, Mr = 447.02,
colorless block, 0.15 x 0.09 x 0.06 mm, monoclinic group P21/n, a =
11.8570(4) Å, b = 11.7644(3) Å, c = 13.5361(5) Å, α = 90°, b = 90.219(3)°,
b = 90°, V = 1888.14(11) Å3, T = 99.99(10) K, Z = 4, ρcalcd. = 1.572 g·cm–3
,
μ = 14.799, F(000) = 888, 4267 reflections, in h(-11/14), k(-16/6), l(-16/16)
measured in the range 4.968 ° < θ < 68.230°, completeness 95.9 %, 3314
independent reflections, 2923 observed reflections (I > 2σ(I)), 197
parameters, 0 restraints; all data: R1 = 0.0381 and wR2 = 0.0428, I > 2σ(I):
R1 = 0.0994 and wR2 = 0.1031, Goof 1.029, largest difference peak/hole
1.60 /-0.60 e·Å–3
.
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Crystal Data of [(Dipp2Im)∙GaH2(aDipp2Im)]I 18 C54H74N4GaI, Mr
=
975.79, colorless block, 0.24 x 0.15 x 0.13 mm, monoclinic group P21/n, a
= 10.86080(10) Å, b = 22.4035(3) Å, c = 21.5667(2) Å, α = 90°, b =
92.6500(10)°, b = 90°, V = 5242.00(10) Å3, T = 100.00(10) K, Z = 4, ρcalcd.
= 1.236 g·cm–3, μ = 5.607, F(000) = 2040, 27454 reflections, in h(-12/13),
k(-28/27), l(--26/23) measured in the range 2.846 ° < θ < 77.506°,
completeness 97.6 %, 10888 independent reflections, 10009 observed
reflections (I > 2σ(I)), 565 parameters, 0 restraints; all data: R1 = 0.0383
and wR2 = 0.0417, I > 2σ(I): R1 = 0.1017 and wR2 = 0.1036, Goof 1.059,
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largest difference peak/hole 1.19 /-1.68 e·Å–3
.
8
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
Inorg. Chem. 2019, 58, 12441-12445; (f) S. G. Alexander, M. L. Cole,
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9
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10.1002/ejic.202000720
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
FULL PAPER
-
+
NHC alane and gallane adducts
(NHC)∙AH2I and (NHC)∙GaH2I were
prepared either by reaction of the
NHC adduct (NHC)∙AlH3 with
elemental iodine or by the treatment of
(NHC)∙GaH3 with an excess of methyl
iodide at room temperature. The
reaction of one equivalent of the group
13 NHC complexes with an additional
equivalent of the corresponding NHC
afforded cationic aluminium and
gallium hydrides [(NHC)2∙EH2]I (E =
Al, Ga).
Aluminium and Gallium Cations
I
N
N
N
R
R
R
R
N
N
Andreas Hock, Luis Werner,
Melanie Riethman] and Udo Radius*
R
R
M
H
R
M
I
H
H
N
H
Page No. – Page No.
N
R
N
Bis-NHC Aluminium and Gallium
Dihydride Cations [(NHC)2EH2]+ (E
= Al, Ga)
M = Al, Ga
10
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