Preparation of stable low-oxidation-state group 14 element amidohydrides and hydride-mediated ring-expansion chemistry of N-heterocyclic carbenes

Article abstract of DOI:10.1002/chem.201202195

Various low oxidation state (+2) group 14 element amidohydride adducts, IPr·EH(BH₃)NHDipp (E=Si or Ge; IPr=[(HCNDipp)₂C:], Dipp=2,6-iPr₂C₆H₃), were synthesized. Thermolysis of the reported adducts was investigated as a potential route to Si- and Ge-based clusters; however, unexpected transmetallation chemistry occurred to yield the carbene-borane adduct, IPr·BH₂NHDipp. When a solution of IPr·BH₂NHDipp in toluene was heated to 100 °C, a rare Ci￡N bond-activation/ring-expansion reaction involving the bound N-heterocyclic carbene donor (IPr) transpired. Copyright

Full text of DOI:10.1002/chem.201202195

FULL PAPER
DOI: 10.1002/chem.201202195
Preparation of Stable Low Oxidation State Group 14 Element
Amidohydrides and Hydride-Mediated Ring-Expansion Chemistry of N-
Heterocyclic Carbenes
S. M. Ibrahim Al-Rafia, Robert McDonald, Michael J. Ferguson, and Eric Rivard*[a]
Abstract: Various low oxidation state (+2) group 14 element amidohydride ad-
ducts, IPr·EHACHTUNGTRENNUNG(BH3)NHDipp (E=Si or Ge; IPr=[(HCNDipp)2CD], Dipp=2,6-
iPr2C6H3), were synthesized. Thermolysis of the reported adducts was investigated
as a potential route to Si- and Ge-based clusters; however, unexpected transmetal-
lation chemistry occurred to yield the carbene–borane adduct, IPr·BH2NHDipp.
Keywords: amides
hydrides · main-group elements ·
ring expansion
·
carbenes
·
ꢀ
When a solution of IPr·BH2NHDipp in toluene was heated to 1008C, a rare C N
bond-activation/ring-expansion reaction involving the bound N-heterocyclic car-
bene donor (IPr) transpired.
Introduction
tures, while concurrently serving as models for the chemical
transformations that occur at or near the surface of bulk
materials.[8] In addition, group 14 (tetrel) element particles
of nanometer dimensionality have been shown to display
useful electronic properties, such as tunable luminescence.[9]
Over the years, a number of tetrel element clusters have
been reported, and their syntheses have generally involved
the reduction of RECl (R=aryl or amide group) precursors
with alkali-metal-based reagents (e.g., KC8).[10] Power, Lap-
pert, and co-workers have devised an alternate route to
novel Sn17 or Sn7 clusters by the thermolysis of either in situ
generated or isolable SnII hydrides, such as the metastable
amide [(Me3Si)NDipp]SnH or the room-temperature-stable
The use of electron-donating N-heterocyclic carbenes
(NHCs) to stabilize reactive main-group species is a rapidly
expanding area of inorganic chemistry.[1] In many instances,
the resulting coordinative NHC–element interactions are of
sufficient strength to enable the isolation of complexes fea-
turing molecular entities that only exist as fleeting inter-
mediates or were previously unknown altogether. For exam-
ple, the recent isolation of stable molecular adducts of the
parent compounds borylene (DBH)[2] and disilylene (DSi=SiD)[3]
represents a synthetic breakthrough made possible by car-
bene coordination chemistry. In addition, NHC–BH3 ad-
ducts have recently been shown to be versatile precatalysts
for the photoinduced radical polymerization of methacry-
lates.[4] It is therefore important to uncover new decomposi-
tion or activation pathways involving N-heterocyclic carbene
ligands due to their increasing supporting role in catalysis.
Recently, our group has prepared donor–acceptor adducts
of the low-valent group 14 methylene and ethylene ana-
logues IPr·EH2·LA and IPr·H2EEH2·LA (E=Si, Ge, and
Sn; IPr=[HCNDipp)2CD]; Dipp=2,6-iPr2C6H3; LA=Lewis
acid, such as BH3 or W(CO)5).[5,6] These hydride complexes
are promising precursors for the controlled synthesis of clus-
ters and nanoparticles, as demonstrated by the clean forma-
tion of Ge metal from the solution-phase thermolysis of the
germanium(II) dihydride adduct, IPr·GeH2·BH3.[5a,7] The
synthesis of Group 14 element clusters is highly desirable
because they often contain new structural and bonding fea-
species, [Ar’SnACTHNUTRGNEUNG
(m-H)]2 (Ar’=(2,6-Dipp)2C6H2).[11a,b] In addi-
tion, Klinkhammer et al. have generated Pb clusters from
the decomposition of putative PbII hydride intermediates.[11c]
Drawing inspiration from this chemistry, we explored the
preparation of N-heterocyclic carbene stabilized amidohy-
dride complexes of the general form IPr·EHNHDipp (E=
Si, Ge, or Sn) in order to access new clusters by mild and
controllable thermolytic reaction pathways. In pursuit of this
goal, we uncovered a new decomposition pathway involving
the carbene–borane adduct IPr·BH2NHDipp, which led to
ꢀ
C N bond activation and ring expansion of the generally
inert donor, IPr. This discovery has widespread implications
because IPr and related NHCs are often used as supporting
ligands in catalysis.
Results and Discussion
[a] S. M. I. Al-Rafia, Dr. R. McDonald, Dr. M. J. Ferguson,
Prof. Dr. E. Rivard
Low-valent group 14 element hydrides, REH (R=aryl or
amide group) are often unstable and can readily decompose
to give clusters.[11] With this in mind, we targeted the prepa-
ration of the amidohydride–carbene adducts IPr·E(H)NH-
Dipp (E=Si, Ge, and Sn) in order to access new cluster ar-
Department of Chemistry, University of Alberta
11227 Saskatchewan Drive, Edmonton
Alberta, T6G 2G2 (Canada)
Fax : (+1)780-492-8231
E-mail: erivard@ualberta.ca
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chetypes (e.g., IPrx·Ey; x<y) upon controlled thermolysis.
As an entry point for our studies, we synthesized the requi-
site EII amidohalide precursors IPr·E(Cl)NHDipp (E=Si,
Ge, or Sn; 1–3, respectively) by treating the known adducts,
IPr·ECl2, with one equivalent of LiACTHUNTRGNEU[GN NHDipp] in Et2O
[Equation (1)].
Although examples of GeII and SnII amides are common
in the literature,[12] compound 1 represents a rare example
of a silicon(II) amide that is stable at ambient tempera-
ture.[13] In the absence of sterically encumbered groups at
the nitrogen atom, the free, heavy group 14 chloroamines
E(Cl)N(H)R (E=Ge or Sn) have a tendency to spontane-
ously oligomerize and/or participate in further condensation
chemistry.[14] However, the presence of s-donating carbenes
in compounds 1–3 results in occupation of the initially
vacant p orbitals at the group 14 centers, thereby suppress-
ing oligomerization of the target E(Cl)N(H)R units.
Compounds 1–3 (IPr·E(Cl)NHDipp; E=Si, Ge, or Sn)
were isolated as air- and moisture-sensitive yellow solids in
45, 98, and 85% yields, respectively. The formation of ad-
ducts 1–3 was confirmed by elemental analysis and NMR
and IR spectroscopy. The H NMR data of these complexes
exhibit similar spectral features, with well-resolved singlet
Figure 1. Molecular structures of IPr·E(Cl)NHDipp (E=Si, Ge, or Sn; 1–
3) with thermal ellipsoids presented at the 30% probability level. All
carbon-bound hydrogen atoms and solvate molecules have been omitted
for clarity. For compound 2 only one of the two molecules in the asym-
metric unit is shown; parameters for the second molecule are listed in
square brackets. Selected bond lengths [ꢁ] and angles [8]: Compound 1:
1
ꢀ
resonances belonging to the N H groups at d=4.14, 4.11,
and 3.82 ppm for 1–3, respectively. Moreover, each of the
six -CH3 groups in compounds 1–3 exists in a magnetically
distinct environment, reflecting the presence of a high
degree of intramolecular crowding in these chloroamide
complexes. Compound 1 yields a 29Si NMR signal at d=
ꢀ6.0 ppm, which is positioned upfield relative to the
29Si NMR resonance of the SiII precursor, IPr·SiCl2 (d=
19.1 ppm).[15] The tin(II) amide IPr·Sn(Cl)NHDipp 3 dis-
plays a similar 119Sn NMR resonance (d=ꢀ96.2 ppm) to the
related, three-coordinate SnII adduct IPr·SnCl2 (d=
ꢀ68.7 ppm).[5a] The IR spectra for 1–3 corroborate the
abovementioned NMR assignments; stretching frequencies
ꢀ
ꢀ
ꢀ
ꢀ
Si C(1) 1.980(3), Si N(3) 1.765(2), Si Cl 2.2463(11), N(3) C(51)
1.433(3); N(1)-C(1)-N(2) 103.7(2), Cl-Si-N(3) 101.87(9), Cl-Si-C(1)
89.88(8), N(3)-Si-C(1) 98.49(11), Si-N(3)-C(51) 118.64(18). Compound 2:
ꢀ
ꢀ
Ge(1A) C(1A) 2.103(3) [2.093(3)], Ge(1A) N(3A) 1.903(3) [1.897(2)],
ꢀ
ꢀ
Ge(1A) Cl(1A) 2.3548(9) [2.3632(9)], N(3A) CACTHNURTGNEU(GN 51A) 1.419(4)
ꢀ
[1.420(4)]; Cl(1A) Ge(1A)-N(3A) 99.05(8) [98.23(8)], Cl(1A)-Ge(1A)-
C(1A) 88.96(8) [90.14(8)], N(3A)-Ge(1A)-C(1A) 96.14(11) [96.81(11)],
ꢀ
ꢀ
Ge(1A)-N(3A)-CACTHUNTGRNEUNG(51 A) 117.9(2). Compound 3: Sn C(1) 2.3220(19), Sn
ꢀ
ꢀ
N(3) 2.1142(16), Sn Cl(1) 2.4898(6), N(3) C(51) 1.403(2); Cl-Sn-N(3)
95.21(5), Cl-Sn-C(1) 89.59(5), N(3)-Sn-C(1) 94.83(6), Sn-N(3)-C(51)
116.53(12).
ꢀ
belonging to the N H residues are found in the narrow
interactions in the Robinson adducts IPr·(Cl)Si=Si(Cl)·IPr
(1.934(6) ꢁ) and IPr·SiCl4 (1.928(2) ꢁ).[3] In the heavier-ele-
range of 3357 to 3371 cmꢀ1. Conclusive evidence for the for-
mation of IPr·E(Cl)NHDipp (E=Si, Ge, or Sn; 1–3) was
obtained by single-crystal X-ray crystallography, and the re-
fined structures are collectively shown in Figure 1.
ꢀ
ment congeners 2 and 3, the respective CIPr Ge (2.098(4) ꢁ
ꢀ
average) and CIPr Sn (2.3220(19) ꢁ) bond lengths are very
similar to values found in the progenitor GeII and SnII com-
ꢀ
ꢀ
Compounds 1–3 are isostructural with distorted trigonal-
pyramidal geometries at each of the three-coordinate E cen-
ters (E=Si, Ge, or Sn). This is consistent with the presence
of a stereochemically active lone pair at the tetrel element
pounds, IPr·GeCl2 and IPr·SnCl2 (CIPr Ge=2.112(2), CIPr
Sn=2.341(8) ꢁ).[5a] The Si N bond length in 1 (1.765(2) ꢁ)
ꢀ
ꢀ
is marginally longer than the Si N bond lengths present in
the
Roesky
dimeric
silaisonitrile,
{[(2,4,6-
ꢀ
centers. Furthermore, each of the E Cl bonds in 1–3 is ori-
iPr3C6H2)2C6H3]NSiD}2 (1.756(1) ꢁ average).[16] Similarly, the
ꢀ
ented towards the steric cradle that is created by the flank-
E N (E=Ge or Sn) bond lengths in 2 and 3 are 1.900(3) ꢁ
(average) and 2.1142(16) ꢁ, respectively, and are within the
range that is expected for single bonds. For comparison, the
Ge N bonds in the acyclic Ge bisamide (Ar’’NH)2GeD
ꢀ
ing Dipp groups of the IPr donors. The CIPr Si bond length
in 1 (1.980(3) ꢁ) is identical within experimental error to
the corresponding distance in the SiII adduct IPr·SiCl2
II
ꢀ
(1.985(4) ꢁ),[15] but is significantly longer than the CIPr Si
(Ar’’=2,6-(2,4,6-Me3C6H2)2C6H3) are 1.896(2) ꢁ, whereas
ꢀ
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Preparation of Stable Low Oxidation State Amidohydrides
FULL PAPER
ꢀ1
ꢀ
ꢀ
an average Sn N separation of 2.101(3) ꢁ exists in the tin
at 2096 cm . The frequency of the Si H vibration is identi-
congener (Ar’’NH)2SnD.[17] As expected, the CIPr-E-N angles
in 1–3 become narrower as the group 14 element becomes
heavier, decreasing from a value of 98.49(1)8 in 1 to
94.83(6)8 in 3.
cal within experimental error to the n˜
A
ꢀ
in IPr·SiH2·BH3.[5e]
Similarly, when the GeII chloroamide IPr·Ge(Cl)NHDipp
(2) was reacted with Li
ACHTUNGTNER[NUGN BH4], the formation of a new prod-
We have recently shown that the halide substituents in
the carbene-bound EII dihalides, IPr·ECl2 (E=Si, Ge, or Sn)
can undergo clean chloride/hydride metathesis chemistry
ꢀ
uct, IPr·GeH(BH3)NHDipp (5), was observed as a compo-
ACHTUNGTRENNUNG
nent of the product mixture that also contained
IPr·BH2NHDipp (6), IPr·BH3, and IPrH2 (as identified by
1H, 13C{1H}, and 11B NMR spectroscopy). The borane-
with LiACHTUNGTRENNUNG[BH4] or LiACHTUNGTRENNUNG[AlH4] to yield stable adducts with E H
bonds.[5] Inspired by these previous studies, we anticipated
that the reactions of complexes 1–3 with hydride sources
could provide access to the desired carbene-bound amidohy-
drides IPr·EHNHDipp. These could then be thermolyzed to
afford low-valent group 14 element clusters [IPrxEy] by the
loss of H2NDipp.[11a]
capped GeII hydride adduct IPr·GeH
ACTHNGUTREN(NUG BH3)NHDipp (5) was
isolated as an analytically pure solid by following a proce-
dure similar to that used to obtain the silicon congener 4.
The GeH unit in 5 appears as a broad singlet at d=
1
5.66 ppm in the H NMR spectrum, and the amide proton of
the -NHDipp group shows a doublet resonance at d=
The reaction of IPr·Si(Cl)NHDipp (1) with one equivalent
1.97 ppm as a result of discernable coupling to a proximal
of Li
the new compounds IPr·SiH
IPr·BH2NHDipp (6; see below), and the known compounds
T
GeH residue (3JHH =6.5 Hz). As in IPr·SiH
ACTHNGUTREN(NUG BH3)NHDipp
E
(4), the BH3 unit in 5 can be located by using 11B NMR
spectroscopy (d=ꢀ39.1 ppm). Similarly, the IR spectrum of
[18]
and IPrH2,[5b] as summarized in Scheme 1. The
5 displays a characteristic N H stretching vibration at n˜ =
ꢀ
IPr·BH3
10/11
3346 cmꢀ1, with expected
B H and Ge H stretching vi-
ꢀ
ꢀ
brations at n˜ =2371–2253 and 1997 cmꢀ1, respectively. The n˜-
(Ge H) band in 5 is in the range expected for Ge com-
II
ꢀ
G
[5,20]
ꢀ
pounds with terminal Ge H bonds.
Additional evidence
for the formation of the silylene and germylene borane ad-
ducts (4 and 5) was obtained by X-ray crystallography, and
the molecular structures of these adducts are shown in
Figure 2.
Scheme 1. Synthesis of the silicon(II) and germanium(II) amidohydride
complexes IPr·EH(BH3)NHDipp (E=Si or Ge; 4 and 5).
ACHTUNGTRENNUNG
silicon(II) hydride complex 4 was isolated in pure form
(34% yield) by cooling a saturated solution of the crude
product mixture in Et2O/hexanes to ꢀ358C. Initial evidence
for the formation of IPr·SiHACHTNUTRGNENG(U BH3)NHDipp (4) was obtained
1
by H NMR spectroscopy, in which a broad SiH resonance
with resolvable flanking 29Si satellites (1JSiH =160.3 Hz) was
located at d=5.13 ppm. The proximal amide proton in the
-NHDipp group was detected as a doublet resonance at d=
1.94 ppm (3JHH =5.5 Hz), with the observed pattern resulting
from the coupling of an NH hydrogen atom with the adja-
cent silicon-bound hydride. The presence of coordinated
BH3 in 4 was confirmed by 11B NMR spectroscopy, which
gave a quartet resonance at d=ꢀ44.1 ppm with an expected
Figure 2. Molecular structures of IPr·SiH
AHCTUNGTRENNUNG
ACHTUNGRTEN(NUNG BH3)NHDipp (4) and IPr·GeH-
bility level. All carbon-bound hydrogen atoms and solvate molecules
have been omitted for clarity. Selected bond lengths [ꢁ] and angles [8]:
ꢀ
ꢀ
ꢀ
ꢀ
Compound 4: Si C(1) 1.9431(15), Si B 1.9760(19), Si H 1.400(16), Si
ꢀ
N(3) 1.7680(14), N(3) C(51) 1.422(2); N(3)-Si-C(1) 103.00(7), N(3)-Si-B
119.27(8), C(1)-Si-B 110.04(8), Si-N(3)-C(51) 120.63(13). Compound 5:
1
coupling constant of JBH =89.5 Hz.[5e,19] For comparison, the
ꢀ
ꢀ
ꢀ
ꢀ
Ge C(1) 2.020(2), Ge B 2.032(3), Ge H 1.53(2), Ge N(3) 1.883(2),
previously reported SiII dihydride adduct IPr·SiH2·BH3 has a
SiH2 resonance at d=3.76 ppm in the 1H NMR spectrum,
ꢀ
N(3) C(51) 1.416(3); N(3)-Ge-C(1) 100.90(10), N(3)-Ge-B 119.36(12),
C(1)-Ge-B 110.57(11), Ge-N(3)-C(51) 117.27(18).
and a 11B NMR quartet resonance at d=ꢀ46.2 ppm (1JBH
=
93.0 Hz) due to the silylene-bound BH3 group.[5e] Consistent
with the NMR data, the IR spectrum of 4 shows an absorp-
IPr·SiHACTHUNGTRENNU(G BH3)NHDipp (4) and IPr·GeHACHTUGNRTEN(NUNG BH3)NHDipp (5)
tion band at 3559 cmꢀ1 belonging to an N H stretching vi-
each represent formal donor–acceptor complexes of encap-
sulated, heavy group 14 amidohydride units, E(H)NHDipp,
with the four-coordinated Si and Ge centers in 4 and 5 locat-
ꢀ
10/11
ꢀ
bration, along with broadened
B H stretching modes
ꢀ1
ꢀ
from 2326 to 2237 cm , and a sharp Si H stretching band
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E. Rivard et al.
ed within slightly canted transoid CIPr-E-N-CDipp bonding ar-
rangements (torsion angles=177.58(13) and 177.98(19)8, re-
1H NMR spectrum of 6 shows a broad singlet at d=
2.55 ppm that is due to the boron-bound hydrogen atoms
within the -BH2NHDipp unit, and the -NH proton appears
at d=1.64 ppm. The -BH2NHDipp residue in 6 gives a
broad signal at d=ꢀ16 ppm in the proton-coupled 11B NMR
spectrum, with no resolvable coupling to hydrogen. The re-
ꢀ
spectively). The dative CIPr Si bond length in
1.9431(15) ꢁ, which is considerably longer than the CIPr Si
4 is
ꢀ
separation reported in the donor–acceptor adduct
IPr·SiH2·BH3 (1.9284(15) ꢁ).[5e] Similar CIPr Si bond lengths
ꢀ
1
to those of
4
are found in the formal SiH2 adduct
maining IPr donor in 6 has H and 13C{1H} NMR spectro-
IPr·SiH2·BH2 SiH
(B3H7)·IPr (1.934(4) and 1.944(4) ꢁ).[19b]
scopic features that are in line with a coordinated N-hetero-
ꢀ
ꢀ
ꢀ
The adjacent Si B bond length in 4 is 1.9760(19) ꢁ and is in
the range previously reported for silicon(II)–borane adducts
that involve pseudotetrahedral geometries at silicon
cyclic carbene. An N H stretching band centered at
3402 cmꢀ1 is present in the IR spectrum of 6, and lower fre-
ꢀ
quency n˜
N
(1.965(2) to 1.996(4) ꢁ).[19,21] IPr·GeH
C
ꢀ
ꢀ
constituent CIPr Ge and Ge B bond lengths in 5 are
2.020(2) and 2.032(3) ꢁ, respectively, and are comparable to
ꢀ
ꢀ
the CIPr Ge (2.0148(13) ꢁ) and Ge B (2.0567(18) ꢁ) inter-
actions in IPr·GeH2·BH3,[5a] which suggests the presence of
similar dative bonding interactions in 5.
Motivated by the above chemistry, we treated the tin(II)
amide IPr·Sn(Cl)NHDipp (3) with one equivalent of Li-
ACHTUNGTRENNUNG[BH4] in Et2O, and observed the rapid evolution of gas ac-
companied by the precipitation of metallic Sn. Analysis of
the soluble fraction of the product mixture by 1H NMR
spectroscopy revealed the formation of IPr·BH2NHDipp (6,
[17]
50% yield; see below), IPr·BH3
(37% yield), and
[5b]
IPrH2 (13% yield), with no sign of the target hydridostan-
nylene adduct IPr·SnH(BH3)NHDipp (Scheme 2). Despite
AHCTUNGTRENNUNG
Figure 3. Molecular structure of IPr·BH2NHDipp (6) with thermal ellip-
soids presented at the 30% probability level. All carbon-bound hydrogen
atoms and solvate (Et2O) molecules have been omitted for clarity. Only
one molecule in the asymmetric unit is presented (molecule B), and pa-
rameters for a disordered BH2NHDipp unit in molecule A are listed in
square brackets. Selected bond lengths [ꢁ] and angles [8]: molecule A:
ꢀ
ꢀ
ꢀ
C(1) B(1) 1.627(4) [1.627(4)], N(3) B(1) 1.542(8) [1.541(8)], N(3)
C(51) 1.427(4) [1.427(4)]; N(3)-B(1)-C(1) 109.2(3) [108.7(5)], B(1)-N(3)-
ꢀ
ꢀ
C(51) 118.1(6) [132.6(7)]. molecule B: C(1) B(1) 1.626(3), N(3) B(1)
ꢀ
1.534(3), N(3) C(51) 1.426(3); N(3)-B(1)-C(1) 112.07(17), B(1)-N(3)-
C(51) 116.70(17).
pare compound 6 in higher yields from the reaction of the
haloborane adducts IPr·BH2X (X=Cl or I)[22] with Li-
AHCTUNGTREG[NNNU NHDipp] were unsuccessful, and led only to the recovery
Scheme 2. The formation of IPr·BH2NHDipp (6) from the reaction of
IPr·Sn(Cl)NHDipp (3) with Li[BH4].
AHCTUNGTRENNUNG
of the starting materials.
the absence of a stable tin hydride product, the remaining
species that were generated from the reaction were also
IPr·BH2NHDipp (6) adopts a transoid CIPr-B-N-CDipp core
ꢀ
in the solid state with an average CIPr B bond length of
formed during the synthesis of IPr·EH
or Ge; 4 and 5). The formation of similar products from the
reaction of 3 with Li[BH4] can be rationalized by the de-
composition of a putative IPr·SnH(BH3)NHDipp intermedi-
A
1.627(5) ꢁ between two crystallographically independent
molecules. These interactions are longer than that in the di-
[18]
ꢀ
N
borane bisadduct IPr·H2B BH2·IPr (1.577(2) ꢁ), suggest-
ꢀ
N
ing that a weaker CIPr B donor–acceptor interaction is pres-
ent in 6. However, a similar CIPr B bond length exists in the
ꢀ
ate; although thus far, our attempts to identify this inter-
mediate at low temperatures (e.g., ꢀ78 to 08C) by NMR
spectroscopy have been unsuccessful.
structurally related four-coordinate azido–borane adduct
IPr·BH2N3 (1.614(2) ꢁ).[22] The central B N bond length in
ꢀ
The soluble products formed from the reaction of
6 is 1.538(8) ꢁ (average), which is also comparable to the
[22]
ꢀ
IPr·Sn(Cl)NHDipp (3) with Li
N
B N separation found in IPr·BH2N3 (1.573(2) ꢁ).
NMR spectroscopy, and the new amino-borane adduct
IPr·BH2NHDipp (6) was isolated as a pure, colorless solid
by fractional crystallization from Et2O (55% yield). The
Occasionally, during the synthesis of IPr·BH2NHDipp (6)
from the reaction of the stannyl chloride adduct
IPr·Sn(Cl)NHDipp (3) with LiACHTNUGTRENUNG[BH4], we noted the forma-
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Preparation of Stable Low Oxidation State Amidohydrides
FULL PAPER
1
tion of trace quantities (<2% by H NMR spectroscopy) of
py), with no sign of soluble carbene-encapsulated clusters.
Notably, a similar product mixture arose from the reaction
a new carbene-containing product. Given the existence of a
lone pair on the nitrogen center in 6, and the likely presence
of free borane in the reaction mixture, we posited that the
of IPr·Sn(Cl)NHDipp with Li
ACHTUNGRTEN[NUNG BH4], thus lending support to
the proposal that IPr·SnH(BH3)NHDipp is a plausible inter-
AHCTUNGTRENNUNG
amine–borane adduct IPr·BH2NHDipp
G
mediate in this reaction. In line with these results, carbene-
bound SnII–hydride complexes are generally much less ther-
mally stable than their Si and Ge counterparts.[5] Although
both 4 and 5 are stable at ambient temperature in the solid
state, they both decompose slowly in THF (ca. 20% decom-
position in 10 days at room temperature). The exact mecha-
unknown species that was formed. Therefore, we subse-
quently treated IPr·BH2NHDipp (6) with a stoichiometric
quantity of H3B·THF to give the new complex
IPr·BH2NHDippACHTUNGTRENNUNG(BH3) (7) as a moisture-sensitive, colorless
solid in 81% isolated yield. Importantly, the H NMR spec-
trum of 7 matched that of the minor product that was pro-
nism by which IPr·EHACTHUNGTERUNN(G BH3)NHDipp (E=Si or Ge; 4 and
duced from the reaction of 3 with Li
[BH4], thus confirming
5) decomposes to give IPr·BH2NHDipp (6) is unclear; how-
ever, the related isotopologue IPr·BD2NHDipp ([D2]-6) can
be isolated as a spectroscopically pure product from the re-
our original postulate. In addition to resonances belonging
to the IPr and NHDipp groups in 7, two broad resonances
due to the -BH2 and -BH3 groups were observed at d=3.14
action of 3 with Li
ACHTUNGTRENNUNG
1
and 2.34 ppm in the H NMR spectrum, and the correspond-
units are generated directly from Li
N
ACHTUNGTRENNUNG
ing 11B NMR resonances for these units were located as
broad resonances at d=ꢀ14.4 and ꢀ16.5 ppm, respectively.
The molecular structure of 7 was determined by single-crys-
spectively. One possible pathway for the formation of 6 (and
[D2]-6) involves transmetallation between a BH3 unit and
the Si- or Ge-bound amide group -NHDipp, to yield the
ꢀ
ꢀ
tal X-ray crystallography (Figure 4), and the observed CIPr
transient amino–borane H2B NHDipp, which is later inter-
cepted by free IPr to form 6 (or [D2]-6). Although we do
not have direct evidence at this time, the decomposition of
[IPr·SnH2·W(CO)5] yields both the free carbene IPr and
IPrH2 as soluble products,[5b] implying that any IPr·SnH2
formed by transmetallation could undergo a similar decom-
position process to yield free IPr and the IPrH2 byproduct
observed during the formation of 6. It should be mentioned
that related transmetallation chemistry was used by Power
and co-workers to generate the aryltin(II) hydride dimer
ꢀ
[Ar’SnACTHNUGRTNEUNG(m-H)]2 from the reaction of (Ar’Sn NMe2)2 with
H3B·THF, yielding volatile (Me2NBH2)x as a coproduct.[11b]
Due to the presence of both acidic (N Hd+) and hydridic
ꢀ
(B Hdꢀ) functional groups in IPr·BH2NHDipp (6), we inves-
ꢀ
Figure 4. Molecular structure of IPr·BH2NHDippACTHUNGRTNEUNG(BH3) (7) with thermal
ellipsoids presented at the 30% probability level. All carbon-bound hy-
drogen atoms and solvate (hexane) molecules have been omitted for
tigated whether the liberation of H2 from 6 could transpire
to yield
a
carbene-stabilized iminoborane, IPr·HB=
NDipp.[24] To explore this possibility, 6 was combined with
ꢀ
clarity. Selected bond lengths [ꢁ] and angles [8]: C(1) B(1) 1.607(3),
ꢀ
ꢀ
ꢀ
N(3) B(1) 1.585(3), N(3) B(2) 1.604(3), N(3) C(51) 1.477(2); N(3)-
B(1)-C(1) 113.73(15), N(3)-B(2)-B(1) 124.76(16), C(51)-N(3)-B(1)
109.05(14), C(51)-N(3)-B(2) 115.64(16).
the known dehydrogenation catalyst [{RhACTHNUTRGENUG(N cod)Cl}2] (cod=
1,5-cyclooctadiene);[24a] however, no sign of hydrogen loss
was observed at ambient temperature when a 5 mol% cata-
lyst loading was used. When the reaction mixture was
heated to 1008C in toluene in the presence of [{Rh-
B bond length in this complex (1.607(3) ꢁ) was determined
ꢀ
to be slightly shorter than the CIPr B separation in 6
(1.627(5) ꢁ).
ACHTUNGTRNE(NGNU cod)Cl}2], the quantitative formation of a new product was
observed. A similar product with a new 11B NMR resonance
at d=28.6 ppm was also observed when 6 was heated to
1008C in the absence of the Rh complex. This new product
was isolated as a colorless, crystalline solid and was identi-
fied by X-ray crystallography (Figure 5) as the new, ring-ex-
panded product [(HCNDipp)2CH2BNHDipp] [8; Equa-
tion (2)].
As mentioned previously, it was expected that hydridoa-
mide complexes containing the E(H)NHDipp structural unit
(as found within the isolated complexes IPr·EH-
ACHTUNGTRENNUNG(BH3)NHDipp; E=Si or Ge; 4 and 5) might undergo the
thermally induced elimination of H2NDipp to form new,
group 14 element clusters with potentially unique structural
and electronic properties. To investigate this possibility,
complexes 4 and 5 were each heated at 708C in toluene.
However, rather than the formation of products with cluster
motifs, the formation of a colorless solution and a bright-
orange precipitate was observed in both instances.[23] The
soluble products from the thermal decomposition of 4 and 5
1
were identified as
a
mixture of IPr·BH2NHDipp (6),
The H NMR spectrum of 8 is consistent with the X-ray
IPr·BH3, and IPrH2 (by using H and 11B NMR spectrosco-
crystallographic data; a singlet resonance at d=3.17 ppm
1
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E. Rivard et al.
cies [(HCNDipp)2CD2BNHDipp] ([D2]-8). For example,
2H{1H} NMR spectroscopy revealed the presence of deuteri-
um at the intraring methylene carbon (CD2) at d=3.17 ppm,
whereas the corresponding proton resonance was absent in
the 1H NMR spectrum. The clean formation of
[(HCNDipp)2CD2BNHDipp] ([D2]-8) indicates that the
direct transfer of two boron-bound deuterium atoms from
the BD2 unit in [D2]-6 to the carbene-carbon center of the
IPr group occurred. As no H/D exchange was observed for
the pendant -NHDipp group, it can be concluded that the
ꢀ
N H bond is not directly involved in the deuterium migra-
tion process [see Equation (2)].
Figure 5. Molecular structure of [(HCNDipp)2CH2BNHDipp] (8) with
thermal ellipsoids presented at the 30% probability level. All carbon-
bound hydrogen atoms except those bonded to C(1) have been omitted
for clarity. Only one of the two crystallographically independent mole-
cules is shown; parameters for the second molecule are listed in square
ꢀ
The observation of C N bond insertion chemistry involv-
ing
the
N-heterocyclic
carbene–borane
adduct
IPr·BH2NHDipp (6) is significant given the role NHC–
borane adducts have recently had in advancing catalytic
transformations.[4] In general, the C H bond activation of a
ꢀ
ꢀ
brackets. Selected bond lengths [ꢁ] and angles [8]: N(1A) B(1A)
ꢀ
ꢀ
1.4213(18) [1.4183(19)], B(1A) C(1A) 1.5889(19) [1.583(2)], N(2A)
ring-backbone-positioned hydrogen atom is a more com-
monly observed reaction pathway amongst N-heterocyclic
carbenes, such as IPr.[28] Notably, Hill and co-workers uncov-
ered a Be H-mediated C N bond-activation/ring-expansion
reaction that is mechanistically related to the formation of
8. Moreover, these authors provided compelling evidence
for the migration of hydrides directly from the main-group
element, beryllium, to the carbenic carbon of IPr.[29] There-
fore, our combined research efforts indicate that main-
ꢀ
C(1A) 1.4601(18) [1.4591(18)], N(3A) B(1A) 1.4148(19) [1.4103(19)];
N(2A)-C(1A)-B(1A) 111.60(11) [111.07(11)], N(1A)-B(1A)-N(3A)
121.62(12) [121.77(13)], N(1A)-B(1A)-C(1A) 117.30(12) [117.51(12)],
N(3A)-B(1A)-C(1A) 121.08(12) [120.72(12)].
ꢀ
ꢀ
that corresponds to a CH2 moiety is present, and the back-
bone CH groups of the newly formed boracycle appear as
two distinct doublet resonances at d=4.95 and 5.31 ppm
(3JHH =6.0 Hz). The intraring methylene group is found at
d=40.2 ppm in the 13C{1H} NMR spectrum, and the reso-
nance due to the carbenic carbon in 6, which is initially pres-
ent, is absent in the spectrum of 8. As mentioned, the
11B NMR spectrum of 8 shows a signal at d=28.6 ppm,
which is in the typical range for three-coordinate boron
compounds, commensurate with the assigned structure of
8.[25]
ꢀ
group-element hydrides have the potential to undergo C N
bond-activation/ring-expansion reactions with typically inert
NHCs, thus leading to possible catalyst deactivation path-
ways when NHC-based catalysts (or precatalysts) are ex-
posed to elevated temperatures. We are currently exploring
the generality of this ring-expansion reaction in our labora-
tory.
As shown in Figure 5, compound 8 consists of a six-mem-
bered boron-containing heterocycle in which the intraring
CH2 group is buckled above the BN2C2 plane to give a pseu-
Conclusion
A series of low oxidation state group 14 element chloroa-
mines, IPr·E(Cl)NHDipp (1–3; E=Si, Ge, or Sn), that are
stabilized by N-heterocyclic carbenes have been prepared.
ꢀ
doenvelope conformation. The C(1) B(1) interatomic sepa-
ration in 8 was determined to be 1.586(3) ꢁ (an average of
two crystallographically independent molecules) and is typi-
Compounds 1 and 2 react with Li
valent hydrido–amide adducts IPr·EH
5; E=Si or Ge). The tin congener IPr·Sn(Cl)NHDipp (3) in-
teracts with Li[BH4] to give the amino–borane adduct
IPr·BH2NHDipp (6) as the major product, with no evidence
for the formation of IPr·SnH(BH3)NHDipp as a stable spe-
ACHTUNGTRENNUNG
ꢀ
cal for B C bonds in three-coordinate boranes (e.g.,
ACHTUNGTRENNUNG
1.589(5) ꢁ
in
Ph3B
and
1.574(4) ꢁ
in
[2,6-
(MeO)2C6H3]3B).[26] The average endocyclic B N(1)
(1.420(3) ꢁ), and exocyclic B N(3) (1.413(3) ꢁ) bond
AHCTUNGTRENNUNG
ꢀ
ꢀ
lengths in 8 are the same within experimental error, and are
ACHTUNGTRENNUNG
ꢀ
slightly shorter than the B N bond lengths in N-triphenyl-
cies. Thermolysis of 4 and 5 was also investigated as a poten-
tial route to Si- and Ge-based clusters; however, in each
case the formation of IPr·BH2NHDipp (6) occurred. Upon
further heating, IPr·BH2NHDipp (6) participated in a rare
borazine ([PhNBH]3; 1.429(2) to 1.431(2) ꢁ),[27] suggesting
the presence of partial B=N bond character between the
boron atom and nitrogen centers in 8.
ꢀ
To gain some mechanistic insight into the thermal conver-
sion of IPr·BH2NHDipp (6) into the carbene-activated prod-
uct 8, the ring-expansion reaction was repeated with the use
of the deuterium isotopologue IPr·BD2NHDipp ([D2]-6).
Heating a sample of [D2]-6 to 1008C for 12 h generated a
product with NMR and IR spectroscopic data that were
consistent with the formation of the isotopically labeled spe-
ring-expansion reaction involving C N bond activation of
the coordinated N-heterocyclic carbene IPr, and which was
mediated by BH-hydride transfer chemistry. This ring-ex-
pansion reaction shows that N-heterocyclic carbenes are
prone to ring-activation processes in the presence of main-
group hydrides at elevated temperatures, and thus highlights
a potential deactivation pathway in NHC-based catalysis.
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Preparation of Stable Low Oxidation State Amidohydrides
FULL PAPER
CCDC-881533 (1), CCDC-881534 (2·Et2O), CCDC-881535 (3·THF),
CCDC-881536 (4), CCDC-881537 (5), CCDC-881538 (6·0.4Et2O),
CCDC-881539 (7·hexane), and CCDC-881540 (8) contain the supplemen-
tary crystallographic data for this paper. These data can be obtained free
of charge from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif
Experimental Section
General methods: All of the reactions were performed by using standard
Schlenk-line techniques under an atmosphere of nitrogen or in an inert-
atmosphere glovebox (Innovative Technology, Inc.). Solvents were dried
by using a Grubbs-type solvent-purification system[30] (Innovative Tech-
nology, Inc.), degassed (freeze–pump–thaw method), and stored under an
Special refinement conditions:
Compound 2: The following distance restraints were applied to the disor-
atmosphere of nitrogen prior to use. LiACTHNURGTNNEUG[BH4] and LiACHUTNGTNER[NUNG BD4] were pur-
ꢀ
ꢀ
dered solvent (diethyl ether) molecules: C C 1.530(2) ꢁ, C O
1.430(2) ꢁ, CꢀC 2.340(4) ꢁ, CꢀO 2.420(4) ꢁ.
chased from Aldrich and used as received. 1,3-Bis(2,6-diisopropylpheny-
l)imidazol-2-ylidene (IPr),[31] IPr·SiCl2,[15] IPr·GeCl2,[5a] IPr·SnCl2,[5a] and
LiACHTUNGTRENNUNG
[NHDipp][32] (Dipp=2,6-iPr2C6H3) were synthesized by following liter-
Compound 3: Attempts to refine peaks of residual electron density locat-
ed about the inversion center (1= , 1= , 0) as disordered, half-occupancy
ature procedures. 1H, 13C{1H}, 29Si, 11B, and 119Sn NMR spectra were re-
corded on Varian iNova-400 or iNova-500 spectrometers and were refer-
enced externally to SiMe4 (1H, 13C{1H} and 29Si), Et2O·BF3 (11B), and
2
2
tetrahydrofuran-solvent oxygen or carbon atoms were unsuccessful. The
data were corrected for disordered electron density through use of the
SQUEEZE procedure[38] as implemented in PLATON.[39] A total solvent-
accessible void volume of 790.6 ꢁ3 with a total electron count of 177
(consistent with 4 molecules of solvent (tetrahydrofuran), or 0.5 mole-
cules per formula unit of the tin complex) was found in the unit cell in
addition to the inversion-disordered solvent tetrahydrofuran molecule lo-
cated near the inversion center (1= ,1= , 0) that had been successfully mod-
SnMe4 (
119Sn). The Analytical and Instrumentation Laboratory at the
University of Alberta performed elemental analyses. Infrared spectra
were recorded on a Nicolet IR100 FTIR spectrometer as Nujol mull sam-
ples between NaCl plates. Melting points were measured in sealed glass
capillaries by using a MelTemp melting-point apparatus under a nitrogen
atmosphere and are uncorrected.
4
4
eled.
X-ray Crystallography: Crystals of suitable quality for X-ray diffraction
studies were removed from a vial (in a glovebox) and immediately cov-
ered with thin layer of hydrocarbon oil (Paratone-N). A suitable crystal
was selected, mounted on a glass fiber, and quickly placed in a low-tem-
perature stream of nitrogen on an X-ray diffractometer.[33] All data were
collected by using MoKa or CuKa radiation (Bruker APEX II CCD detec-
tor/D8 diffractometer), with the crystals cooled to ꢀ1008C. The data
were corrected for absorption by Gaussian integration from the indexing
of the crystal faces.[34] Structures were solved by using the direct-methods
programs SHELX-97[35] (compound 5) and SIR97[36] (compounds 2 and
6), or by using the Patterson search/structure expansion facilities within
the DIRDIF-2008[37] (compounds 1 and 3) and SHELXD[38] program
suites (compounds 4 and 7); structure refinement was accomplished by
using SHELXL-97.[35] Hydrogen atoms were assigned positions 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. See Tables 1 and 2 for a list of crystallographic data.
Compound 4: Attempts to refine peaks of residual electron density as
disordered or partial-occupancy n-hexane-solvent carbon atoms were un-
successful. The data were corrected for disordered electron density
through use of the SQUEEZE procedure[39] as implemented in
PLATON.[40] A total solvent-accessible void volume of 2346.5 ꢁ3 with a
total electron count of 439 (consistent with 8 molecules of solvent (n-
hexane), or 1 molecule per formula unit of the {1,3-bis(2,6-diisopropyl-
phenyl)-1,3-dihydro-2H-imidazol-2-ylidene}SiHACHTNUTGRNEUNG(BH3)NH(2,6-diisopropyl-
phenyl) molecule) was found in the unit cell.
Compound 5: Attempts to refine peaks of residual electron density as
disordered or partial-occupancy n-hexane-solvent carbon atoms were un-
successful. The data were corrected for disordered electron density
through use of the SQUEEZE procedure[39] as implemented in
PLATON.[40] A total solvent-accessible void volume of 2392.7 ꢁ3 with a
total electron count of 511 (consistent with 8 molecules of solvent
(hexane), or 1 molecule per formula unit of 5) was found in the unit cell.
ꢀ
ꢀ
ꢀ
Compound 6: Pairs of distances for atoms C1 B1, B1 N3, and N3 C51
within the disordered BH2NH-
(C6H3iPr2) fragment of molecule A
AHCTUNGTRENNUNG
were restrained to have the same bond
lengths by use of the SHELXL SAME
instruction. Additionally, the phenyl
rings within this disordered fragment
were constrained to be idealized hexa-
gons. The minor (20%) orientation of
Table 1. Summary of crystallographic data for 1, 2·Et2O, 3·THF, and 4.
1
2·Et2O
3·THF
4
empirical formula
C39H54ClN3Si
628.39
C43H64ClGeN3O
747.01
C43H62ClN3OSn
791.10
C45H72BN3Si
693.96
Mr
crystal size [mm3]
crystal system
space group
a [ꢁ]
0.36ꢂ0.18ꢂ0.08
monoclinic
P21/n (No. 14)
19.8052 (17)
12.3167 (11)
15.8436 (14)
90
0.41ꢂ0.36ꢂ0.18
monoclinic
P21/n (No. 14)
19.4351 (11)
23.3885 (14)
20.1177 (12)
90
0.56ꢂ0.50ꢂ0.46
monoclinic
C2/c (No. 15)
43.642 (3)
12.0988 (8)
16.7555 (11)
90
104.3880 (8)
90
8569.8 (10)
8
1.226
0.692
173(1)
54.98
37306
9835 (0.0143)
9255
444
0.0309
0.40ꢂ0.37ꢂ0.15
monoclinic
I2/a (No. 15)
23.8535 (4)
14.3021 (2)
27.0924 (4)
90
95.4166 (9)
90
9201.4 (2)
8
1.002
0.663
173(1)
139.82
30372
8496 (0.0204)
7276
417
0.0530
the
disordered
diisopropylphenyl
group in molecule B was restrained to
have the same geometry as that of the
major orientation by use of the
SHELXL SAME instruction. The dis-
ordered solvent (diethyl ether) mole-
cule had the following restraints ap-
b [ꢁ]
c [ꢁ]
a [8]
b [8]
98.8045 (12)
90
3819.3 (6)
4
1.093
0.160
104.8410 (10)
90
8839.6 (9)
8
1.123
0.786
g [8]
ꢀ
ꢀ
plied: C C 1.53(1) ꢁ; C O 1.43(1) ꢁ;
V [ꢁ3]
ꢀ
ꢀ
C O 2.42(1) ꢁ; C C 2.34(1) ꢁ. Final-
ly, the following pairs of atoms were
restrained to have equivalent aniso-
Z
1 [gcmꢀ3
]
]
m [mmꢀ1
T [K]
tropic
displacement
parameters:
173(1)
173(1)
C51A/C, C52A/C, C53A/C, C54A/C,
C55A/C, C56A/C, C62A/C, B1A/C,
and O1S/O2S.
2qmax [8]
51.40
50.50
total data
27859
17242
unique data (Rint
)
7257 (0.0946)
4223
401
0.0527
0.1378
17242 (0.0428)
14046
857
0.0483
0.1527
Compound 7: Attempts to refine
peaks of residual electron density as
disordered or partial-occupancy n-
hexane-solvent carbon atoms were un-
successful. The data were corrected
obs data [I>2s(I)]
params
R1 [I>2s(I)][a]
wR2 [all data][a]
max/min D1 [eꢀ ꢁꢀ3
0.0786
0.677/ꢀ0.627
0.1669
0.280/ꢀ0.263
]
0.256/ꢀ0.304
0.843/ꢀ0.598
for
disordered electron
density
1
2
4
2
[a] R1 =Sj jFo jꢀjFc j j/SjFo j ; wR2 =[S w
(Fo ꢀFc2)2/S w
N
.
through use of the SQUEEZE proce-
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
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E. Rivard et al.
Table 2. Summary of crystallographic data for 5, 6·0.4Et2O, 7·Hexane and 8.
of 2 in Et2O layered with hexanes to
ꢀ358C. M.p. 152–1548C; 1H NMR
5
6·0.4Et2O
7·Hexane
8
3
(500 MHz, C6D6): d=0.96 (d, JHH
=
empirical formula
C45H72BGeN3
738.46
C40.6H60BN3O0.4
607.33
C45H73B2N3
677.68
C39H56BN3
577.68
7.0 Hz, 6H; CHCAHTUNGTRENNNUG
3JHH =7.0 Hz, 6H; CH
3JHH =7.0 Hz, 6H; CH
3JHH =7.0 Hz, 6H; CH
3JHH =7.0 Hz, 6H; CH
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
Mr
crystal size [mm3]
crystal system
space group
a [ꢁ]
0.45ꢂ0.42ꢂ0.05
monoclinic
I2/a (No. 15)
23.8622 (12)
14.3819 (7)
27.3526 (14)
90
0.45ꢂ0.36ꢂ0.18
monoclinic
C2/c (No. 15)
47.114 (3)
12.1840 (7)
29.0791 (17)
90
0.41ꢂ0.33ꢂ0.21
monoclinic
C2/c (No. 15)
22.5387 (11)
14.7074 (7)
25.9542 (13)
90
0.34ꢂ 0.25ꢂ0.17
monoclinic
P21/n (No. 14)
10.5312 (1)
18.7236 (3)
36.5391 (5)
90
90.1432 (6)
90
7204.83 (17)
8
1.065
0.456
173(1)
141.48
48851
13784 (0.0197)
12394
775
0.0532
AHCTUNGTRENNUNG
AHCTUNGTRENNUNG
3JHH =7.0 Hz, 6H; CH
ACHTUNGTRENNUNG
b [ꢁ]
c [ꢁ]
a [8]
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
3
b [8]
95.6700 (10)
90
9341.0 (8)
8
1.050
0.686
110.5450 (7)
90
15630.6 (16)
16
1.032
0.060
90.5331 (8)
90
8603.1 (7)
8
1.065
0.059
2H; NCH-), 6.88 (t, JHH =7.5 Hz, 1H;
ArH), 7.01–7.20 ppm (m, 8H; ArH);
13C{1H} NMR (125 MHz, C6D6): d=
g [8]
V [ꢁ3]
Z
23.1 (CH
25.2 (CH
C
ACHTUNGTRENNUNG
1 [gcmꢀ3
]
]
ACHTUNGTRENNUNG
m [mmꢀ1
T [K]
25.86 (CH
27.6 (CH
29.4 (CH
A
ACHTUNGTRENNUNG
173(1)
173(1)
173(1)
A
ACHTUNGTRENNUNG
2qmax [8]
50.50
50.50
50.80
AHCTUNGTRENNUNG
total data
32964
52431
30770
(ArC), 124.43 (ArC), 124.46 (ArC),
124.51 (-NCH-), 131.4 (ArC), 133.6
(ArC), 139.1 (ArC), 144.3 (ArC),
145.9 (ArC), 146.7 (ArC), 177.1 ppm
(NCN); IR (Nujol): n˜ =3371 cmꢀ1 (br,
unique data (Rint
)
8477 (0.0699)
5797
408
0.0439
0.0998
14167 (0.0460)
9171
856
0.0666
0.2212
7934 (0.0422)
4747
421
0.0574
0.1751
obs data [I>2s(I)]
params
R1 [I>2s(I)][a]
wR2 [all data][a]
max/min D1 [eꢀ ꢁꢀ3
0.1463
0.775/ꢀ0.450
ꢀ
N H); elemental analysis calcd (%)
]
0.397/ꢀ0.313
0.246/ꢀ0.243
0.246/ꢀ0.243
for C39H54ClN3Ge: C 69.50, H 8.23, N
6.23; found: C 69.20, H 8.22, N 5.73.
1
2
4
2
[a] R1 =Sj jFo jꢀjFc j j/SjFo j ; wR2 =[S w
(Fo ꢀFc2)2/S w
N
.
Synthesis of IPr·Sn(Cl)NHDipp (3): A
dure[39] as implemented in PLATON.[40] A total solvent-accessible void
volume of 1670.0 ꢁ3 with a total electron count of 370 (consistent
with 8 molecules of solvent (n-hexane), or one molecule per formula
unit of the {1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-
cold (ꢀ358C) solution of Li
ACHTUNGTRENNUNG
(0.23 g, 1.2 mmol) in Et2O (12 mL) was added dropwise to
a
(ꢀ358C) slurry of IPr·SnCl2 (0.71 g, 1.2 mmol) in Et2O (5 mL). The re-
sulting mixture was warmed slowly to room temperature and stirred for
2 h to give a beige solution over a white precipitate (LiCl). The reaction
mixture was then filtered through Celite and the volatiles were removed
in vacuo to yield 3 as a pale-brown powder (0.83 g, 85% yield). Crystals
of 3 suitable for X-ray crystallography were grown by cooling a solution
of 3 in THF layered with hexanes to ꢀ358C. M.p. 180–1828C; 1H NMR
ylidene}BH2NH
unit cell.
ACHTUNGTRENNUNG(BH3)(2,6-diisopropylphenyl) molecule) was found in the
Synthetic procedures:
IPr·Si(Cl)NHDipp (1): A solution of LiACTHUNRGTNE[NUG NHDipp] (0.031 g, 0.17 mmol) in
(500 MHz, C6D6): d=0.96 (d, 3JHH =7.0 Hz, 6H; CH
ACHTUNGTRENNUNG
of cold Et2O (10 mL, ꢀ358C) was added dropwise to a cold (ꢀ358C)
slurry of IPr·SiCl2 (0.081 g, 0.17 mmol) in Et2O (3 mL). The resulting
mixture was warmed slowly to room temperature and stirred for 20 min
to give an orange solution over a white precipitate (LiCl). The reaction
mixture was filtered through Celite and the volatiles were removed in
vacuo to yield 1 as a yellow powder. Crystals of 1 suitable for X-ray crys-
tallography were grown by cooling a solution of 1 in THF/hexanes to
ꢀ358C for 7 days (0.047 g, 45% yield). M.p. 179–1818C; 1H NMR
3JHH =7.0 Hz, 6H; CH
G
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
3
A
G
=
N
ACHTUNGTRENNUNG
3
(s, 1H, -NH), 6.46 (s, 2H; NCH-), 6.83 (t, JHH =7.5 Hz, 1H; ArH), 7.03–
7.22 ppm (m, 8H; ArH); 13C{1H} NMR (125 MHz, C6D6): d=23.1 (CH-
A
U
A
ACHTUNGTRENNUNG
(500 MHz, C6D6): d=0.96 (d, 3JHH =7.0 Hz, 6H; CH
ACHTUNGTRENNUNG
(CH
A
G
A
ACHTUNGTRENNUNG
3JHH =7.0 Hz, 6H; CH
N
ACHTUNGTRENNUNG
(CHACHTGNUTRENNUNG
AHCTUNGTRENNUNG
(-NCH-), 133.9 (ArC), 137.1 (ArC), 146.1 (ArC), 146.2 (ArC), 146.6
3
(ArC), 147.2 (ArC), 184.8 ppm (NCN); 119Sn{1H} NMR (149 MHz, C6D6):
A
U
=
d=ꢀ93.2 ppm; IR (Nujol): n˜ =3358 cmꢀ1 (m, N H); elemental analysis
A
ACHTUNGTRENNUNG
ꢀ
3
(s, 1H; -NH), 6.36 (s, 2H; NCH-), 6.94 (t, JHH =7.5 Hz, 1H; ArH), 6.99–
7.19 ppm (m, 8H; ArH); 13C{1H} NMR (125 MHz, C6D6): d=22.9 (CH-
calcd (%) for C39H54ClN3Sn: C 65.15, H 7.57, N 5.84; found: C 64.67, H
7.93, N 5.82.
A
G
N
ACHTUNGTRENNUNG
Reaction of 1 with Li
Et2O (ꢀ358C, 10 mL) was added to a mixture of 1 (77 mg, 0.12 mmol)
and Li[BH4] (2.9 mg, 0.13 mmol). The reaction mixture was then warmed
ACHTUNGTERNNUG[BH4] to form IPr·SiHACHTUNGTREN(NNGU BH3)NHDipp (4): Cold
E
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
(-NCH-), 131.4 (ArC), 133.7 (ArC), 140.5 (ArC), 141.9 (ArC), 145.8
(ArC), 146.3 (ArC), 171.7 ppm (NCN); 29Si NMR (80 MHz, C6D6): d=
to room temperature and stirred overnight to give a yellow solution over
a white precipitate (LiCl). The precipitate was allowed to settle and the
resulting supernatant was filtered through Celite to obtain a bright-
yellow solution. Removal of the volatiles from the filtrate yielded a pale-
ꢀ6.0 ppm; IR (Nujol): n˜ =3360 cmꢀ1 (s, N H); elemental analysis calcd
ꢀ
(%) for C39H54ClN3Si: C 74.54, H 8.66, N 6.69; found: C 74.54, H 8.49, N
6.58.
1
yellow solid that was identified by H NMR spectroscopy as a mixture of
IPr·Ge(Cl)NHDipp (2): A solution of LiACTHUNTGRNEUNG[NHDipp] (0.18 g, 0.98 mmol) in
4 (ca. 47%), 6 (ca. 3%), IPr·BH3 (ca. 31%), and IPrH2 (ca. 10%). Spec-
troscopically pure 4 was isolated by fractional crystallization (cooling a
saturated solution of the crude material in Et2O layered with hexanes to
ꢀ358C). Crystals of 4 suitable for X-ray crystallography were grown by
cooling a solution of 4 in Et2O layered with hexanes to ꢀ358C for 3 days
cold Et2O (12 mL, ꢀ358C) was added dropwise to a cold (ꢀ358C) slurry
of IPr·GeCl2 (0.51 g, 0.96 mmol) in Et2O (5 mL). The resulting mixture
was warmed slowly to room temperature and stirred overnight to form a
pale-yellow solution over a white precipitate (LiCl). The reaction mixture
was then filtered through Celite and the volatiles were removed in vacuo
to yield 2 as a pale-yellow powder (0.63 g, 98% yield). Crystals of 2 suita-
ble for X-ray crystallography were grown by cooling a saturated solution
1
(25 mg, 34%). M.p. 182–1848C; H NMR (300 MHz, C6D6): d=0.01–0.62
(brq, 1JBH =89.5 Hz, 3H; BH3), 0.93 (d, 3JHH =6.9 Hz, 6H; CH
ACHTUNGTRENNUNG
0.97 (d, 3JHH =6.9 Hz, 6H; CH
ACHTUNGTRENNUNG
&
8
&
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ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 0000, 00, 0 – 0
ÝÝ
These are not the final page numbers!

Preparation of Stable Low Oxidation State Amidohydrides
FULL PAPER
(CH3)2), 1.27 (d, 3JHH =6.9 Hz, 6H; CH
6H; CH
(CH3)2), 1.47 (d, 3JHH =6.9 Hz, 6H; CH
5.5 Hz, 1H; -NH), 2.88 (septet, 3JHH =6.9 Hz, 4H; CH
(septet, 3JHH =6.9 Hz, 2H; CH
(CH3)2), 5.12 (s, 1H; -SiH-; satellites:
1JHSi =163.0 Hz), 6.39 (s, 2H; NCH-), 7.01–7.19 ppm (m, 9H; ArH);
13C{1H} NMR (125 MHz, C6D6): d=22.7 (CH
(CH3)2), 22.9 (CH(CH3)2),
24.7 (CH(CH3)2), 25.5 (CH(CH3)2), 25.9 (CH(CH3)2), 26.1 (CH(CH3)2),
27.5 (CH(CH3)2), 29.3 (CH(CH3)2), 29.4 (CH(CH3)2), 123.1 (ArC), 123.6
E
ꢀ16.5 ppm (brt); IR (Nujol): n˜ =3373 (br, N H), 2393 (sh, B H),
ꢀ
ꢀ
3
2310 cmꢀ1 (br, B H); elemental analysis calcd (%) for C39H56BN3: C
ꢀ
G
81.08, H 9.77, N 7.27; found: C 81.05, H 9.92, N 7.36.
AHCTUNGTRENNUNG
Synthesis of IPr·BD2NHDipp ([D2]-6): Et2O (12 mL) was added to a
mixture of 3 (430 mg, 0.51 mmol) and LiACHTUNRGTNEUNG[BD4] (15.5 mg, 0.60 mmol). The
reaction mixture was stirred for 2 h at ambient temperature to give a
clear solution over a black precipitate. The precipitate was then allowed
to settle and the mother liquor was filtered through Celite to give a color-
less filtrate. Removal of the volatiles from the filtrate yielded a white
solid from which spectroscopically pure [D2]-6 was isolated (188 mg,
54% yield) by fractional crystallization following the same procedure as
E
G
E
G
(ArC), 124.6 (ArC), 125.2 (ArC), 131.7 (-N-CH-), 133.6 (ArC), 139.9
(ArC), 143.4 (ArC), 145.7 (ArC), 146.2 (ArC), 166.4 ppm (NCN);
11B{1H} NMR (159 MHz, C6D6): d=ꢀ44.1 ppm (s); 11B NMR (159 MHz,
1
ꢀ
C6D6): d=ꢀ44.1 ppm (q, JBH =89.5 Hz); IR (Nujol): n˜ =3359 (m, N H),
1
ꢀ
6. H NMR (500 MHz, C6D6): essentially the same as 6 except the N H
ꢀ1
ꢀ
ꢀ
ꢀ
resonance at d=1.64 ppm was observed as
a
singlet; 11B{1H} NMR
2326 (br, B H), 2237 (m, B H), 2096 cm (m, Si H); elemental analysis
calcd (%) for C39H58BN3Si: C 77.07, H 9.62, N 6.91; found: C 77.07, H
9.02, N 6.30.
(128 MHz, C6D6): same as compound 6; 2H{1H} NMR (61 MHz, C6D6):
d=2.53 ppm (brs; -BD2-); IR (Nujol): similar to 6 except for the absence
Reaction of 2 with Li
Et2O (ꢀ358C, 10 mL) was added to a mixture of compound 2 (88 mg,
0.13 mmol) and Li[BH4] (2.8 mg, 0.13 mmol). The reaction mixture was
ACHTUNGTRENNUNG[BH4] to form IPr·GeHACHTUNGTREN(NNGU BH3)NHDipp (5): Cold
ꢀ
ꢀ
of B H stretches; the B D stretching frequencies were observed at n˜ =
ꢀ1
ꢀ
ꢀ
1724 (sh, B D) and 1630 cm (br, B D).
ACHTUNGTRENNUNG
Reaction of
6 with H3B·THF to form IPr·BH2NHDippACHTUNTGERNUN(G BH3) (7):
stirred overnight at ambient temperature to give an orange solution with
a yellow precipitate. The resulting mixture was then filtered through
Celite to give an orange filtrate. Removal of the volatiles from the fil-
trate yielded an orange solid that was identified by 1H NMR spectrosco-
py as a mixture of 5 (ca. 55% yield), 6 (ca. 30% yield), IPr·BH3 (ca. 5%
yield), and IPrH2 (ca. 7% yield). Spectroscopically pure 5 was isolated
by fractional crystallization (cooling a saturated solution of the crude ma-
terial in Et2O layered with hexanes to ꢀ358C). Crystals of 5 suitable for
X-ray crystallography were grown by cooling a solution of 5 in Et2O lay-
ered with hexanes to ꢀ358C for 3 days (43 mg, 50%). M.p. 151–1538C
(decomposed, turned red), 159–1618C (melted); 1H NMR (500 MHz,
H3B·THF (0.16 mL, 1.0m solution in THF) was added dropwise to a solu-
tion of 6 (86 mg, 0.15 mmol) in Et2O (10 mL). The reaction mixture was
stirred overnight at room temperature to give a colorless solution and
the volatiles were then removed in vacuo to yield a white powder. The
powder was washed with hexanes (4 mL) and dried to afford spectroscop-
ically pure 7. Crystals of 7 suitable for X-ray crystallography were grown
by cooling a saturated solution of 7 in Et2O layered with hexanes to
ꢀ358C for 4 days (71 mg, 81% yield). M.p. 156–1588C; 1H NMR
(500 MHz, C6D6): d=0.93 (d, 3JHH =6.5 Hz, 3H; CH
ACHTUNGTRENNUNG
3JHH =6.5 Hz, 9H; CH
N
ACHTUNGTRENNUNG
3
1.06 (d, JHH =6.5 Hz, 9H; CH
N
C6D6): d=0.93 (d, 3JHH =6.5 Hz, 6H; CH
6H; CH
(CH3)2), 1.01 (d, 3JHH =7.0 Hz, 6H; CH
6.5 Hz, 6H; CH
(CH3)2), 1.41 (d, 3JHH =7.0 Hz, 6H; CH
3JHH =6.5 Hz, 6H; CH(CH3)2), 1.97 (d, 3JHH =6.5 Hz, 1H; -NH), 2.84
(septet, 3JHH =7.0 Hz, 2H; CH(CH3)2), 2.85 (septet, 3JHH =6.5 Hz, 2H;
CH (CH3)2), 5.67 (brs, 1H;
(CH3)2), 3.20 (septet, 3JHH =7.0 Hz, 2H; CH
-GeH), 6.41 (s, 2H; NCH-), 6.95–7.21 ppm (m, 9H; ArH); the -BH3 unit
was not located; 13C{1H} NMR (125 MHz, C6D6): d=22.7 (CH
(CH3)2),
(CH3)2),
(CH3)2),
(CH3)2), 0.97 (d, 3JHH =7.0 Hz,
ACHTUNGTRENNUNG
blets, 3JHH =6.5 Hz, 9H; CH
ACHTUNGTRENNUNG
3
N
N
=
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
3
-BH3), 2.90 (septet, JHH =6.5 Hz, 2H; CH
4.15 (septet, 3JHH =6.5 Hz, 1H; CH
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
U
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
A
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
23.9 (CH
25.7 (CH
N
G
U
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
ACHTUNGTRENNUNG
22.9 (CH
25.9 (CH
N
G
U
ACHTUNGTRENNUNG
28.2 (CH
N
N
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
(-NCH-), 124.4 (ArC), 124.5 (ArC), 124.7 (ArC), 126.8 (ArC), 130.7
(ArC), 134.1 (ArC), 138.6 (ArC), 144.3 (-NCH-), 145.5 (ArC), 146.5 ppm
(NCN); 11B{1H} NMR (128 MHz, C6D6): d=ꢀ14.4 (-BH2-), ꢀ16.5 ppm
121.9 (ArC), 123.5 (ArC), 124.6 (ArC), 125.2 (ArC), 131.7 (-NCH-),
133.5 (ArC), 141.2 (ArC), 143.2 (ArC), 145.7 (ArC), 146.3 (ArC),
169.7 ppm (NCN); 11B{1H} NMR (128 MHz, C6D6): d=ꢀ39.0 ppm; IR
ꢀ
ꢀ
ꢀ
(-BH3); IR (Nujol): n˜ =3321 (m, N H), 2484 (m, B H), 2388 (sh, B H),
ꢀ1
ꢀ
ꢀ
ꢀ
(Nujol): n˜ =3346 (m, N H), 2371 (brs, B H), 2253 (sh, B H), 1997 cm
ꢀ1
ꢀ
ꢀ
2308 (s, B H), 2266 cm (s, B H); elemental analysis calcd (%) for
C39H59B2N3: C 79.19, H 10.05, N 7.10; found: C 78.99, H 10.13, N 6.98.
ꢀ
(m, Ge H); elemental analysis calcd (%) for C39H58BN3Ge: C 71.80, H
8.96, N 6.44; found: C 71.57, H 9.11, N 5.87.
Thermolysis
of
IPr·BH2NHDipp
(6)
to
form
Reaction of 3 with Li
(ꢀ358C, 12 mL) was added to a mixture of 3 (366 mg, 0.51 mmol) and Li-
ACHTUNGTRENNUNG[BH4] (11.1 mg, 0.51 mmol). The reaction mixture was stirred for 2 h at
ACHTUNGTRENNUNG[BH4] to form IPr·BH2NHDipp (6): Cold Et2O
[(HCNDipp)2CH2BNHDipp] (8): A solution of 6 (142 mg, 0.25 mmol) in
toluene (10 mL) was heated at 1008C for 12 h to form a pale-yellow solu-
tion. The reaction mixture was then filtered through Celite and the vola-
tiles were removed in vacuo to yield crude 8 as a bright-yellow oil. Crys-
tals of 8 suitable for X-ray crystallography were grown by cooling a satu-
rated solution of 8 in hexanes layered with (Me3Si)2O to ꢀ358C for
ambient temperature to give a clear solution along with an insoluble
black precipitate. The precipitate was then allowed to settle and the
mother liquor was filtered through Celite. Removal of the volatiles from
the filtrate yielded 6 as a white solid that was identified by 1H NMR
spectroscopy as a mixture of 6 (ca. 58% yield), IPr·BH3 (ca. 30% yield),
and IPrH2 (ca. 12% yield). Spectroscopically pure 6 was isolated by frac-
tional crystallization (cooling a saturated solution of the crude materials
in Et2O to ꢀ358C). Crystals of 6 suitable for X-ray crystallography were
1
4 days (113 mg, 80% yield). M.p. 124–1268C; H NMR (500 MHz, C6D6):
d=1.14 (d, 3JHH =7.0 Hz, 9H; CH
G
3
3
CH
N
9H; CH
G
ACHUTNGRENNUG CAHTUNGTRENNUNG
(CH3)2) 3.58 (septet, 3JHH =7.0 Hz, 2H; CH
grown by cooling a solution of 6 in Et2O to ꢀ358C for 2 days (163 mg,
3
3.85 (septet, 3JHH =7.0 Hz, 2H; CH
55%). M.p. 145–1478C; 1H NMR (500 MHz, C6D6): d=1.03 (d, JHH
=
NCH-), 5.31 (d, JHH =6.0 Hz, 1H; NCH-), 6.95–7.22 ppm (m, 9H; ArH);
7.0 Hz, 12H; CH
(d, 3JHH =7.0 Hz, 12H; CH
(s, 2H; -BH2; located in the 1H
7.0 Hz, 4H; CHACHTUNGTRENNUNG ACHTUGNTRENUN(GN CH3)2), 6.35
(CH3)2), 3.01 (septet, 3JHH =7.0 Hz, 2H; CH
G
ACHTUGNTRNEN(UNG CH3)2), 1.36
13C{1H} NMR (125 MHz, C6D6): d=23.4 (CH
24.9 (CH(CH3)2), 25.7 (CH(CH3)2), 27.8 (CH
29.4 (CH(CH3)2), 40.2 (-CH2-), 109.5 (-NCH-), 118.7 (-NCH-), 122.9
AHCTUNGTRENNUNG
3
AHCTUNGTERNNUNG =
{11B} NMR spectrum), 2.74 (septet, JHH
(s, 2H; NCH-), 6.98 (t, 3JHH =7.5 Hz, 2H; ArH), 7.08 (d, 3JHH =7.5 Hz,
1H; ArH), 7.10 (d, 3JHH =7.5 Hz, 2H; ArH), 7.23 ppm (t, 3JHH =7.5 Hz,
(ArC), 124.1 (ArC), 124.2 (ArC), 126.2 (ArC), 135.9 (ArC), 140.1 (ArC),
145.3 (ArC), 145.7 (ArC), 147.2 (ArC), 147.9 ppm (NCN); 11B{1H} NMR
(128 MHz, C6D6): d=28.6 ppm; IR (Nujol/cmꢀ1): n˜ =3391 cmꢀ1 (br, N
H); elemental analysis calcd (%) for C39H56BN3: C 81.08, H 9.77, N 7.27;
found: C 81.17, H 9.74, N 7.23.
ꢀ
4H; ArH); 13C{1H} NMR (125 MHz, C6D6): d=22.9 (CH
ACHTUNGTRENNUNG
(CHACHTUNGTRENNUNG(CH3)2), 25.4 (CHACHTUNGTRENNUNG(CH3)2), 27.1 (CHAHCTUNGTREN(GNUN CH3)2), 29.2 (CHCAHTUNGTRENNNUG
(ArC), 122.3 (ArC), 123.3 (ArC), 124.2 (ArC), 130.6 (-NCH-), 134.5
(ArC), 140.9 (ArC), 145.9 (ArC), 150.3 ppm (NCN); 11B{1H} NMR
(128 MHz, C6D6): d=ꢀ16.5 ppm (s); 11B NMR (C6D6, 128 MHz): d=
Thermolysis
of
IPr·BD2NHDipp
([D2]-6)
to
form
[(HCNDipp)2CD2BNHDipp] ([D2]-8):
A
solution of [D2]-6 (85 mg,
Chem. Eur. J. 2012, 00, 0 – 0
ꢀ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
&
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ÞÞ
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E. Rivard et al.
0.15 mmol) in toluene (10 mL) was heated at 1008C for 12 h to give a
pale-yellow solution. The reaction was then filtered through Celite and
the volatiles were removed in vacuo to yield [D2]-8 as a bright-yellow oil
(57 mg, 79% yield). 1H NMR (500 MHz, C6D6): essentially the same as
compound 8 except for the absence of a resonance for the -CH2- group
Mangolini, S. A. Campbell, Pure Appl. Chem. 2008, 80, 1901; d) X.
Li, Y. He, S. S. Talukdar, M. T. Swihart, Langmuir 2003, 19, 8490.
[8] a) A. Schnepf, Chem. Soc. Rev. 2007, 36, 745; b) A. Pacher, C.
Schrenk, A. Schnepf, J. Organomet. Chem. 2010, 695, 941; c) N.
Wiberg, P. P. Power, Molecular Clusters of the Main Group Elements
(Eds.: M. Driess, H. Nçth), Wiley-VCH, Weineim, 2004, Chapter 25,
pp. 188–208.
2
at d=3.17 ppm; H{1H} NMR (61 MHz, C6H6): d=3.16 ppm (-CD2-).
[9] J. A. Kelly, E. J. Henderson, J. G. C. Veinot, Chem. Commun. 2010,
46, 8704.
[10] a) H. Matsumoto, K. Higuchi, Y. Hoshino, H. Koike, Y. Naoi, Y.
Nagai, J. Chem. Soc. Chem. Commun. 1988, 1083; b) A. F. Richards,
M. Brynda, M. M. Olmstead, P. P. Power, Organometallics 2004, 23,
2841; c) A. F. Richards, H. Hope, P. P. Power, Angew. Chem. 2003,
115, 4205; Angew. Chem. Int. Ed. 2003, 42, 4071; d) B. E. Eichler,
P. P. Power, Angew. Chem. 2001, 113, 818; Angew. Chem. Int. Ed.
2001, 40, 796; e) A. F. Richards, B. E. Eichler, M. Brynda, M. M.
Olmstead, P. P. Power, Angew. Chem. 2005, 117, 2602; Angew.
Chem. Int. Ed. 2005, 44, 2546.
Acknowledgements
This work was supported by the Natural Sciences and Engineering Re-
search Council (NSERC) of Canada, the Canada Foundation of Innova-
tion (CFI), Alberta Innovates—Technology Futures (New Faculty Award
to E.R. and a graduate fellowship to S.M.I.A) and Suncor Energy, Inc.
(Petro–Canada Young Innovator Award for E.R.).
[11] a) M. Brynda, R. Herber, P. B. Hitchcock, M. F. Lappert, I. Nowik,
[1] For reviews, see: a) N. Kuhn, A. Al-Sheikh, Coord. Chem. Rev.
2005, 249, 829; b) R. Wolf, W. Uhl, Angew. Chem. 2009, 121, 6905;
Angew. Chem. Int. Ed. 2009, 48, 6774; c) Y. Wang, G. H. Robinson,
Inorg. Chem. 2011, 50, 12326; d) K. O. Feldmann, J. J. Weigand,
Angew. Chem. 2012, 124, 6670; Angew. Chem. Int. Ed. 2012, 51,
6566; for recent examples highlighting this concept, see: e) H.
Braunschweig, R. D. Dewhurst, K. Hammond, J. Mies, K. Radacki,
A. Vargas, Science 2012, 336, 1420; f) H. Tanaka, M. Ichinohe, A.
Sekiguchi, J. Am. Chem. Soc. 2012, 134, 5540; g) N. Katir, D. Mat-
ioszek, S. Ladeira, J. Escudiꢃ, A. Castel, Angew. Chem. 2011, 123,
5464; Angew. Chem. Int. Ed. 2011, 50, 5352; h) S. M. I. Al-Rafia,
M. J. Ferguson, E. Rivard, Inorg. Chem. 2011, 50, 10543.
˚
ˇ
ˇ
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Preparation of Stable Low Oxidation State Amidohydrides
FULL PAPER
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Received: June 20, 2012
Published online: && &&, 0000
Chem. Eur. J. 2012, 00, 0 – 0
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www.chemeurj.org
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These are not the final page numbers!

E. Rivard et al.
Breaking the ring that binds: A series
of low oxidation state group 14 ele-
ment hydridoamides, NHC·EH-
Ring Expansion
S. M. I. Al-Rafia, R. McDonald,
M. J. Ferguson, E. Rivard* . &&&& — &&&&
AHCTUNTGREG(NNNU BH3)NHDipp (E=Si or Ge;
NHC=N-heterocyclic carbene;
Dipp=2,6-iPr2C6H3), is reported.
These hydrides underwent transmetal-
lation upon heating to give
Preparation of Stable Low Oxidation
State Group 14 Element Amidohy-
drides and Hydride-Mediated Ring-
Expansion Chemistry of N-Heterocy-
clic Carbenes
IPr·H2BNHDipp; this borane partici-
ꢀ
pates in C N bond-activation reactions
involving a carbene donor at 1008C.
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Chem. Eur. J. 0000, 00, 0 – 0
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These are not the final page numbers!