Versatile 1,2- and 1,3-dipole behavior of the 1-arsa-3-germaallene Tip(t -Bu)Ge=C=AsMes*: Formation of a heterocyclic arsa(germa)carbene (AsGeHC)

Article abstract of DOI:10.1021/om200968x

The 1-arsa-3-germaallene Tip(t-Bu)Ge=C=AsMes* (1; Tip = 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) reacts with selenium, fluorenone, N-tert-butylphenylnitrone, and 9,10-phenanthrenequinone as a 1,2-dipole by the Ge=C double bond, to give the corresponding three-, four-, five-, and six-membered-ring derivatives 2-5, respectively. Both [2 + 2] and [2 + 4] cycloadditions involving the Ge=C double bond are observed between 1 and benzil, leading to the four- and six-membered-ring derivatives 6 and 7. In great contrast, 1 reacts with diphenylketene as a 1,3-dipole by the whole Ge=C=As unit to afford the transient heterocyclic arsa(germa)carbene 12 according to a [3 + 2] cycloaddition. DFT calculations were carried out to understand this particular behavior. This first heavier analogue of an NHC with an arsenic atom rearranges to the tricyclic compound 11.

Full text of DOI:10.1021/om200968x

Article
pubs.acs.org/Organometallics
Versatile 1,2- and 1,3-Dipole Behavior of the 1-Arsa-3-Germaallene
Tip(t-Bu)GeCAsMes*: Formation of a Heterocyclic
Arsa(germa)carbene (AsGeHC)
Dumitru Ghereg,† Jean-Marc Sotiropoulos,*,‡ Jean Escudie,*,† Karinne Miqueu,‡ Dimitri Matioszek,†
́
Sonia Ladeira,§ and Nathalie Saffon-Merceron§
†Universite
Toulouse cedex 09, France
‡Institut Pluridisciplinaire de Recherche sur l’Environnement et les Mater
́
de Toulouse, UPS, LHFA, 118 route de Narbonne, F-31062 Toulouse, France, and CNRS, LHFA, UMR 5069, F-31062
́
iaux, UMR-CNRS, 5254, Universite
́ ́
l’Adour, Helioparc, 2 Avenue du President Angot, 64053 Pau cedex 09, France
́
de Pau et des Pays de
§Institut de Chimie de Toulouse, ICT-FR 2599, Universite
́
Paul Sabatier, 118 route de Narbonne, 31062 Toulouse cedex 09, France
S
* Supporting Information
ABSTRACT: The 1-arsa-3-germaallene Tip(t-Bu)GeCAsMes* (1; Tip
= 2,4,6-triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) reacts with
selenium, fluorenone, N-tert-butylphenylnitrone, and 9,10-phenanthrenequi-
none as a 1,2-dipole by the GeC double bond, to give the corresponding
three-, four-, five-, and six-membered-ring derivatives 2−5, respectively. Both
[2 + 2] and [2 + 4] cycloadditions involving the GeC double bond are
observed between 1 and benzil, leading to the four- and six-membered-ring
derivatives 6 and 7. In great contrast, 1 reacts with diphenylketene as a 1,3-
dipole by the whole GeCAs unit to afford the transient heterocyclic arsa(germa)carbene 12 according to a [3 + 2]
cycloaddition. DFT calculations were carried out to understand this particular behavior. This first heavier analogue of an NHC
with an arsenic atom rearranges to the tricyclic compound 11.
known: [2 + 2], [2 + 3], and [2 + 4] cycloadditions with
various unsaturated derivatives involving the sole GeC
double bond are generally observed, this heteroallene behaving
as a 1,2-dipole12b,13 (see for example Scheme 1 for the [2 + 2]
cycloaddition with fluorenone). However, an unexpected, new,
and very interesting type of reaction has been reported
recently: with dimethyl acetylenedicarboxylate,13a benzonitri-
le,13b and diphenylketene13c this phosphagermaallene surpris-
ingly behaves as a 1,3-dipole, reacting by the whole GeCP
skeleton to lead to phospha(germa)carbenes A−C, respectively
(Scheme 1), which constitute a novel class of heterocyclic
carbenes; the latter are heavier analogues of the N-heterocyclic
carbene (NHC) D14,15 (Chart 1) with germanium and
phosphorus atoms on the carbenic carbon center. It is the
only case reported to date in which an heteroallene leads to a
carbene.
These N-heterocyclic push−push carbenes D have many
applications in the field of coordination chemistry, replacing
phosphines on transition metals for catalysis,16 but are also used
in nanoscience,17 medical chemistry,18 the synthesis of
luminescent derivatives,19 etc. The replacement of one or two
nitrogen atoms by other heteroelements, which modifies the
steric and electronic properties of the carbene, should increase
its synthetic potential and thus offer new important
1. INTRODUCTION
Low-coordinate derivatives such as alkenes, allenes, and
carbenes are among the most important compounds in organic
chemistry, since they are the precursors of many new
derivatives and organic functions by the addition of various
reagents on the CC double bond or on the carbenic
unsaturation.
The heavier analogues of alkenes and allenes, EE′ and E
CE′, whose one or two carbon atoms have been replaced by
heteroelements E and/or E′ (E, E′ = group 14 and 15
elements), are of great importance in heterochemistry, in order
to introduce into a structure a heavier heteroelement.
Heteroallenes,1−6 due to the presence of two double bonds,
are interesting potential building blocks, particularly the case of
those containing two different heavy elements of groups 14 and
15 in a low coordination state, E14CE15 (E14 = Si, Ge, Sn;
E15 = N, P, As) which have been recently obtained.6−12 They
are of great interest because of their multiple possibilities of
reactions: addition or cycloaddition on the E14C or E15C
double bond or on both double bonds and reaction of the
whole E14CE15 unit, the lone pair of E15, or a heavier
carbene >E14 if there is a cleavage of the E14C double bond.
However, there are still very few compounds of this type which
have been reported; owing to a large steric hindrance, the
phosphagermaallene Tip(t-Bu)GeCPMes* (Tip = 2,4,6-
triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl) has been
stabilized and isolated.12 Its reactivity has begun to be well-
Received: October 14, 2011
Published: February 1, 2012
© 2012 American Chemical Society
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Scheme 1. Reactivity of Phosphagermaallene as a 1,2- or a 1,3-Dipole
Chart 1. N-Heterocyclic Carbene (NHC) D and Its
Phosphorus Analogue
The formation, in one case, of the first heterocyclic carbene of
the type AsGeHC, substituted on the carbenic carbon atom by
a germanium and an arsenic atom will be discussed; this
compound constitutes a heavier analogue of an NHC.
Theoretical calculations have been performed to understand
the peculiar [3 + 2] dipole behavior of arsagermaallene 1 and to
describe the electronic properties of the arsa(germa)carbene.
potentialities in organic and organometallic chemistry. For
example, a new, heavier analogue of NHC substituted on the
carbenic carbon atom by two phosphorus atoms has been
described recently (E, Chart 1).20
From our previous work showing that phospha(germa)-
carbenes (PGeHC) A−C could be obtained from the
phosphagermaallene Tip(t-Bu)GeCPMes*, it appeared
that heavier analogues of NHC substituted on the carbenic
carbon atom by heteroelements other than germanium and
phosphorus could possibly be synthesized from new types of
heteroallenes.
We have very recently reported the synthesis of the 1-arsa-3-
germaallene Tip(t-Bu)GeCAsMes* (1; Tip = 2,4,6-
triisopropylphenyl, Mes* = 2,4,6-tri-tert-butylphenyl),21 the
heaviest mixed group 14 and 15 heteroallenic compound, which
has been obtained by debromofluorination of the correspond-
ing 1-arsa-3-fluorogermapropene by t-BuLi at low temperature
(Scheme 2).21
2. RESULTS AND DISCUSSION
(a). 1,2-Dipole Behavior of Arsagermaallene 1. One
molar equivalent of the reactants (selenium, fluorenone, N-tert-
butylphenylnitrone, 9,10-phenanthrenequinone) was added to
a crude solution of arsagermaallene 1 (in Et2O) containing LiF,
1
cooled to −80 °C. H and 13C NMR analysis of the reaction
mixture immediately after warming to room temperature
showed the complete disappearance of the reactants and the
presence in each case of a signal around 200−225 ppm in the
13C NMR spectra. These signals were assigned to a carbon
atom doubly bonded to an arsenic atom, proving the presence
of a >CAsMes* unit. Such chemical shifts are among the
most deshielded for a >CAs− derivative.22 Thus, this means
that the reaction occurred only by the GeC double bond,
according to [2 + 1], [2 + 2], [2 + 3], and [2 + 4]
cycloadditions for selenium, fluorenone, nitrone, and quinone,
respectively, leading to derivatives 2−5 (Scheme 3). These
cycloadducts were isolated after crystallization from pentane;
they are soluble in classical organic solvents and present a good
air and moisture stability, despite the presence of the AsC
double bond. Only one isomer was found in the case of 1-
selena-2-germacyclopropane 2 (δ(13CAs) 205.03 ppm), 1-
oxa-2-germacyclobutane 3 (δ(13CAs) 209.91 ppm), and 1,4-
dioxa-2-germacyclohex-5-ene 5 (δ(13CAs) 223.38 ppm),
whereas two diastereoisomers in the ratio 55/45 were obtained
for the 1-oxa-2-aza-5-germacyclopentane 4 (δ(13CAs) 205.34
and 211.90 ppm, respectively), due to the presence, in addition
to the chiral germanium atom, of the chiral carbon of the CHPh
unit. 1H and 13C NMR spectra display two signals for the o-t-Bu
groups, indicating a hindered rotation of the Mes* group on
the NMR time scale, due to the large steric congestion.
Whereas a hindered rotation of the Tip group is also observed
for 3 (two different o-i-Pr groups), a free rotation occurs in the
case of 5, the steric congestion being less important in the six-
membered ring dioxagermacyclohexene. In 3 and 5, the two
methyl groups on every i-Pr are diastereotopic. In the case of 2
Scheme 2. Synthesis of Arsagermaallene 1
It appeared very important to study the reactivity of such a
derivative and particularly to see if it can lead to a new class of
heavier NHC potential building blocks in As chemistry.
We present in this paper the versatile reactivity of the
arsagermaallene 1 toward selenium and various representatives
of organic functions such as fluorenone, N-tert-butylphenylni-
trone, 9,10-phenanthrenequinone, benzil, and diphenylketene.
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Scheme 3. Reaction of Arsagermaallene 1 with Various Reagents
1
and 4, broad signals are observed in the H NMR spectra for
reactions of the GeC double bond with benzil must be
emphasized, since with the closely related phosphagermaallene
8, the sole [2 + 4] cycloaddition was observed,25 whereas with
germene Mes2GeCR2 9 an unexpected epoxidation reaction
occurred26 (Scheme 5); in contrast, the GeC double bond of
the o-i-Pr groups, probably due to a coalescence phenomenon
involving a slow rotation of the Tip group. In all cases the
oxygen is bonded to the germanium atom, as expected from the
polarity Ge+−C− of the GeC double bond. The nucleophilic
attack of the oxygen at the germanium is probably the first step
of the reaction.
In the reaction of 1 with selenium, the three-membered ring
species 2 was obtained by a [2 + 1] cycloaddition involving the
exclusive GeC double bond. There was no reaction of
selenium with the CAs double bond or with the arsenic lone
pair. However, an X-ray structure determination showed the
presence of disorder, the crystal being about an 89/11 mixture
of the three-membered ring species 2 and of a central four-
membered ring compound with a Ge−C−Se−Se skeleton (see
the Supporting Information). Despite many attempts, it has not
been possible to obtain crystals of pure 2. Addition of an excess
of Se to 2 led to a complex mixture with unidentified derivatives
and did not allow the isolation of the four-membered ring
derivative.
Scheme 5. Reaction of Germene and Phosphagermaallene
with Benzil
the transient germavinylidene [Me3SiNP(Ph2)]2CGe does
not react with benzil, only a [1 + 4] cycloaddition with the
germylene function occurring.27
Two concurrent reactions occurred between 1 and benzil,
with the simultaneous formation of four- and six-membered
ring derivatives 6 and 7 (ratio 60/40) by [2 + 2] and [2 + 4]
cycloadditions, respectively, between the GeC double bond
and one CO or the OC−CO unit (Scheme 4).
X-ray determinations from single crystals obtained by slow
crystallization from pentane unambiguously confirmed the
structures of 2 (Figure 1), 3 (Figure 2), 4 (Figure 3), 5 (Figure
4), and 7 (Figure 5). In the case of heterocycle 6, an X-ray
structure determination proved unambiguously the presence of
the central four-membered ring Ge−C−C−O; however, due to
the very poor quality of the crystals, a good refinement could
not be obtained and the structural parameters of this derivative
will not be discussed. In heterocycles 3−5 and 7, the AsC
double bond presents a Z configuration (Mes* and Ge in a cis
disposition); in contrast, in the case of 2, the reverse
stereochemistry is observed, the Mes* group being in a trans
disposition in relation to the germanium atom. A reverse
stereochemistry has been reported for the reaction of
phosphagermaallene 8 with Se.28
Scheme 4. Reaction of Arsagermaallene 1 with Benzil
Note that [2 + 4] cycloadditions are generally observed
between benzil and doubly bonded main group elements: for
example, the silene (Me3Si)2SiC(OSiMe3)R (R = t-Bu, Ad)23
or phosphagermene Mes2GePMes*.24 The great variety of
In 3, the four-membered ring is slightly distorted (torsion
angles around the ring between 11 and 15°). Greater torsion
angles, up to 23°, have been reported in other 1-oxa-3-
germacyclobutanes,12a,29 but smaller ones (from 4 to 10°) are
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Figure 1. Molecular structure of 2. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms and disorder (see the
Supporting Information) are omitted, and i-Pr and t-Bu on aromatic
groups are simplified for clarity. Relevant bond lengths (Å) and angles
(deg): Ge1−C1 = 1.918(3), Ge1−C2 = 1.977(3), Ge1−C6 =
1.960(3), Ge1−Se1 = 2.3740(5), C1−Se1 = 1.889(3), C1−As1 =
1.775(3), As1−C21 = 1.991(3); Ge1−C1−Se1 = 77.13(12), C1−
Se1−Ge1 = 51.98(9), Se1−Ge1−C1 = 50.89(9), C2−Ge1−C6 =
117.47(13), C1−Ge1−C2 = 117.18(13), C1−Ge1−C6 = 119.81(13),
Ge1−C1−As1 = 144.11(18), C1−As1−C21 = 98.86(13), Se1−C1−
As1 = 138.68(18), C6−Ge1−Se1 = 119.47(9).
Figure 3. Molecular structure of 4. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms and solvent molecules are
omitted, and i-Pr and t-Bu on aromatic groups are simplified for clarity.
Relevant bond lengths (Å), angles (deg), and torsion angles (deg):
Ge1−C1 = 1.983(2), Ge1−C7 = 2.005(2), Ge1−C3 = 2.038(2),
Ge1−O1 = 1.8250(16), O1−N1 = 1.470(2), N1−C2 = 1.482(3), C1−
C2 = 1.564(3), C1−As1 = 1.801(2), As1−C22 = 1.985(2); Ge1−C1−
As1 = 144.54(14), C2−C1−As1 = 110.47(15), C1−As1−C22 =
114.47(10), Ge1−C1−C2 = 104.24(13), C1−C2−N1 = 107.99(17),
C2−N1−O1 = 104.14(16), N1−O1−Ge1 = 106.57(11), O1−Ge1−
C1 = 87.89(8), C2−C1−Ge1−O1 = −6.31(14), Ge1−C1−C2−N1 =
−23.82(19), C1−Ge1−O1−N1 = 35.38(13).
Figure 2. Molecular structure of 3. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms and solvent molecules are
omitted, and i-Pr and t-Bu on aromatic groups are simplified for clarity.
Relevant bond lengths (Å), angles (deg) and torsion angles (deg):
Ge1−C1 = 1.970(2), Ge1−C16 = 1.976(2), Ge1−O1 = 1.831(2),
O1−C21 = 1.433(3), C21−C20 = 1.545(3), C20−Ge1 = 1.997(2),
C20−As1 = 1.794(2), As1−C34 = 1.974(2); Ge1−O1−C21 =
96.17(12), O1−C21−C20 = 100.94(18), C21−C20−Ge1 =
Figure 4. Molecular structure of 5. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms and solvent molecules are
omitted, and i-Pr and t-Bu on aromatic groups are simplified for clarity.
Relevant bond lengths (Å) and angles (deg): Ge1−C1 = 1.981(4),
Ge1−C16 = 1.980(3), Ge1−O1 = 1.824(2), O1−C20 = 1.362(4),
C20−C33 = 1.362(5), C33−O2 = 1.398(4), O2−C34 = 1.433(4),
C34−Ge1 = 1.977(3), C34−As1 = 1.804(4), C35−As1 = 1.987(4);
Ge1−O1−C20 = 120.8(2), O1−Ge1−C34 = 90.87(12), O2−C34−
As1 = 107.6(2), O2−C34−Ge1 = 101.3(2), C33−O2−C34 =
113.1(2), O2−C33−C20 = 122.3(3), C33−C20−O1 = 124.5(3),
C34−As1−C35 = 107.51(15), Ge1−C34−As1 = 149.7(2).
86.22(14), C20−Ge1−O1
= 73.66(8), Ge1−C20−As1 =
152.88(13), C21−C20−As1 = 117.93(16), C20−As1−C34 =
103.98(10); C20−C21−O1−Ge1 = −15.40(15), C21−O1−Ge1−
C20 = 12.13(12), O1−Ge1−C20−C21 = −11.20(11), Ge1−C20−
C21−O1 = 14.03(13). Angle between Ge1−O1−C21−C20 mean
plane and fluorenylidene ring: 84.78°.
being 0.958 Å out of this mean plane. In 7, the five atoms Ge1,
O2, C22, C21, and O1 are almost coplanar, the C20 atom
being 0.96 Å out of this mean plane. Short AsC double
bonds (1.794(2)−1.804(4) Å) are determined for 3−5 and 7 at
the lower limit of the range (1.79−1.90 Å).30 The AsC
double bond in 2 (1.775(3) Å) is the shortest As−C distance
ever reported.
observed in the closely related oxagermacyclobutanes with an
exocyclic CP double bond.12b
In the case of 4, the four atoms O1, Ge1, C1, and C2 are
nearly in the same plane, the N1 atom being 0.713 Å out of this
plane. In the six-membered ring dioxagermacyclohexene of 5,
the five atoms Ge1, O1, C20, C33, and O2 are nearly exactly in
the same plane as the fluorenylidene group, the C34 atom
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membered heterocycle)28 and benzil (sole formation of a [2 +
4] cycloadduct)25 slightly different reactions were reported.
(b). 1,3-Dipole Behavior of Arsagermaallene 1:
Formation of the First Arsa(germa)carbene. Whereas [2
+ 2] and [2 + 4] cycloadditions were observed between the sole
GeC unsaturation of arsagermaallene 1 and the CO
double bond of a ketone, an α-diketone, and a quinone, a
completely different reaction occurred with the CO of
diphenylketene. Addition of 1 equiv of the latter to a cooled
solution of 1 was performed in Et2O, as previously described
for the other reactants. The 13C NMR analysis of the crude
reaction mixture displayed no signal at low field, excluding in
this case the presence of a >CAsMes* unit. There were only
two tert-butyl groups on the former Mes* group, one of the o-t-
Bu groups being transformed into a CH2CMe2 unit which is
bonded to the central carbon atom between germanium and
arsenic. This carbon is also substituted by an hydrogen. These
data prove that the surprising formation of the tricyclic
derivative 11 (Scheme 6) can only be understood by the
intermediate formation of the transient arsa(germa)carbene 12,
which inserts into the C−H bond of an o-t-Bu group of the
Mes* group. This carbene should be formed by a surprising [3
+ 2] cycloaddition between the GeCAs unit of the
arsagermaallene 1 and the CO double bond, the heteroallene
behaving, unexpectedly, as a 1,3-dipole. As mentioned
previously, such a very surprising 1,3-dipole behavior for an
heteroallene has only been reported up to now for the closely
related phosphagermaallene Tip(t-Bu)GeCPMes*, which
gives similar [3 + 2] cycloadditions with dimethyl acetylene-
dicarboxylate,13a benzonitrile,13b and diphenylketene13c with
the formation of the carbene analogue bearing a phosphorus
instead of an arsenic atom.
Figure 5. Molecular structure of one independent molecule of 7
present in the asymmetric unit. Thermal ellipsoids are drawn at the
50% probability level. All hydrogen atoms are omitted, and i-Pr and t-
Bu on aromatic groups are simplified for clarity. Relevant bond lengths
(Å) and angles (deg): Ge1−O2 = 1.822(7), O2−C22 = 1.384(11),
C22−C21 = 1.367(14), C21−O1 = 1.400(13), C20−Ge1 =
1.968(10), C20−As1 = 1.803(11), As1−C35 = 1.978(12), Ge1−C1
= 1.992(12), Ge1−C16 = 1.972(12); Ge1−C20−O1 = 101.4(7),
C20−O1−C21 = 113.6(8), O1−C21−C22 = 122.0(8), C21−C22−
O2 = 121.1(9), C22−O2−Ge1 = 123.0(6), O2−Ge1−C20 = 89.4(4),
C20−As1−C35 = 106.5(5), Ge1−C20−As1 = 148.0(7), O1−C20−
As1 = 108.9(7).
Rather long intracyclic Ge−C bond lengths are determined
(1.997(2) Å in 3, 1.983(2) Å in 4, 1.977(3) Å in 5, and
1.968(10) Å in 7) at the upper limit of the classical range
(1.95−1.98 Å).31 In contrast, the intracyclic Ge1−C1 distance
in 2 (1.918(3) Å) is very short and the sum of angles on the
germanium atom, excluding Se (354.44°), is relatively close to
360°, showing that the germanium center displays some sp2
character. Thus, it seems from this partially planar geometry
that 2 presents a structure intermediate between a normal
three-membered ring and a π complex. Similar structures have
been reported in other three-membered ring derivatives
containing one germanium atom and a pnictogen such as
GePS,32a GeCSe,28 and GeCTe28,32b or two germanium atoms
such as GeGeX (X = C,33a N,33a S,33b Te33c). These results can
be interpreted in terms of the Dewar−Chatt−Duncanson
model of metal−olefin bonding.
Monitoring the reaction by dynamic 1H and 13C NMR
between −80 °C and room temperature did not allow us to
characterize the carbene 12, which inserts into the C−H bond
of an o-t-Bu group very rapidly at low temperature. Such
insertion reactions into C−H bonds are well-known and are
characteristic of carbenes.14
In order to be sure that the presence of LiF was not a key
factor in the course of the reaction, addition of diphenylketene
was also performed with Et2O solutions of pure arsagermaal-
lene previously crystallized in pentane. The same result was
observed, excluding the influence of LiF.
Carbene 12 is a new type of heterocyclic carbene, which can
be called AsGeHC, by analogy with its well-known lighter
analogue NHC. It is the first time that a carbene bearing an
arsenic atom has been evidenced as reaction intermediate.
Using density functional theory (DFT) at the B3LYP/6-
31G** level,34,35 we considered in the reaction of the parent
arsagermaallene H2GeCAsH (1H) with diphenylketene
two reaction pathways, a [2 + 2] and a [3 + 2] cycloadditions
(Figure 6). The two barriers, lying at around 23 kcal mol−1 over
the reactant energy, are found close (calculated energy
difference of 5 kcal mol−1), and we can observe that a [2 +
In all these reactions, the arsagermaallene 1 behaves as a 1,2-
dipole with the GeC double bond much more reactive than
the AsC bond, in agreement with the nature of the HOMO
mainly localized on the πGeC orbital. Even with an excess of
fluorenone, nitrone, benzil, or 9,10-phenanthrenequinone, the
AsC unsaturation appeared to be unreactive. No reaction was
observed in the case of selenium with the lone pair on arsenic.
Similar results have been obtained between the related
phosphagermaallene Tip(t-Bu)GeCPMes* and fluoreno-
ne,12a 9,10-phenanthrenequinone,25 and nitrone,13b whereas
with selenium (exclusive formation of the corresponding three-
Scheme 6. Reaction of Arsagermaallene 1 with Diphenylketene
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Figure 6. [2 + 2] and [3 + 2] reaction pathways in the reaction between 1H and diphenylketene.
2] adduct is found highly thermodynamically favored (−44 kcal
mol−1) compared with the [3 + 2] one. The geometry
parameters calculated for TS[2+2] indicate a weak interaction
between the oxygen atom and the germanium atom (2.310 Å
with a planar environment of the germanium atom), the As−
C1 having not been formed (2.445 Å). The AsC bond length
(1.756 Å) and the GeC length (1.811 Å) remain in the range
of double bonds but the GeCAs bond angle decreases (−16°)
compared with 1H. TS[3+2], which corresponds to a
nucleophilic attack from the 1H πGeC-nAs orbital to the
ketene π*CO orbital (see in Figure 7 the corresponding orbital
Å) in contrast to 12H (1.953/1.905 Å). The geometry structure
is, in fact, intermediate between those of the reactants and the
final carbene. The important point is that, even if the carbene is
a minimum on the PES, the insertion compound in a CH of a t-
Buthe only possibility considering the real moleculemust
be the driving force of this reaction and, as observed
experimentally, its formation remains the only product.
Consequently, this reaction seems both kinetically (smaller
activation barrier) and thermodynamically controlled (for-
mation of the insertion product).
To gain more insight into this new carbene, we have
calculated the structural and electronic properties of the real
carbenic molecule 12 (see the Supporting Information). On
comparison with the previously studied phosphorus analogue-
s,13a we found the same trends. In fact, the Ge−C bond is in the
range of a single bond (1.931 Å) and the As−C bond
corresponds to a double bond (1.745 Å). The GeCAs bond
angle is calculated at 101°. Calculation also found a planar
geometry around the arsenic atomprobably favored by the
steric effect provided by the substituentsallowing a strong
donation of the arsenic lone pair into the 2pπ vacant orbital of
the carbene. Considering the heterocyclic pnictogen GeE15HC
compounds (arsenic and phosphorus derivatives), it seems
reasonable to describe them as λ4-pnictavinylylide species.36
Figure 7. HOMO-1 of TS[3+2]
.
The molecular orbital and particularly the HOMO-4 (πAsC
)
HOMO-1), is found slightly more accessible than the
previously described TS[2+2]. This pathway reaction is
connected with the heavy carbene derivative 12H, which is
predicted to be a minimum on the potential surface energy
(PES). The energy of this [3 + 2] adduct is found at the same
magnitude as the reactant energy. In this case, the syn approach
between the ketene and the allene leads to a transition state
with a planar structure and a smaller GeCAs bond angle (125°)
in comparison to the starting allene 1H. This TS[3+2] shows a
As−C1 distance smaller than the Ge−O distance (2.532/2.818
and the LUMO (π*AsC) drawing (Figure 8) illustrate very
well this observation.
The reason for this heterocarbene stability can be due to
electronic factors, which can be rationalized by the help of
NBO analysis.37 In addition to the stabilizing interaction
involving the carbenic σ lone pair (nσ ) and the vicinal σ*AsC
C
orbitals (13 kcal mol−1), we found an antiperiplanar interaction
between the πAsC and the extracyclic π*CC (6 kcal mol−1).
The latter seems to play an important role, since if we consider
the case of the [3 + 2] adduct obtained in the reaction of 1 with
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Figure 8. Plots of the MO involving the πAsC system (HOMO-4 and LUMO).
the “Service de Microanalyse de l’Ecole de Chimie de Toulouse”. C,C-
Dibromo(2,4,6-tri-tert-butylphenyl)arsaalkene (Mes*AsCBr2)38 and
difluoro(tert-butyl)(2,4,6-triisopropylphenyl)germane (Tip(t-Bu)-
GeF2)12 were prepared according to previously reported procedures.
Synthesis of 1-Arsa-3-germapropene Tip(t-Bu)Ge(F)-C(Br)
AsMes*. This derivative was synthesized according to the procedure
previously described.21 To a diethyl ether solution (50 mL) of C,C-
dibromo(2,4,6-tri-tert-butylphenyl)arsaalkene (Mes*AsCBr2)38
(2.46 g, 5 mmol) cooled to −100 °C was added n-butyllithium (1.6
M in hexane; 3.2 mL, 5.10 mmol) dropwise. After the mixture was
stirred at the same temperature for 1 h, a solution of difluoro(tert-
butyl)(2,4,6-triisopropylphenyl)germane (1.86 g, 5 mmol) in diethyl
ether (20 mL) was slowly added over a period of 30 min. The reaction
mixture was stirred for 30 min at −100 °C and then warmed to room
temperature. The solvents were evaporated under reduced pressure
and replaced by 100 mL of pentane. The resulting suspension was
filtered through Celite to remove the lithium salts, and the filtrate was
concentrated to generate a saturated solution. Storage of the solution
at −30 °C afforded colorless crystals of Tip(t-Bu)Ge(F)-C(Br)
AsMes* (2.48 g, 65%, mp 136 °C).
fluorenone (see the Supporting Information), no such
interaction occurs: thus, the carbene adduct formed in this
case lies 10 kcal mol−1 over the energy of the reactants.
Moreover, in the phospha(germa)cyclocarbene analogue,13a we
have previously shown the importance of such interactions
involving the πPC and the π*CC orbitals on the carbene
stabilization.
3. CONCLUSION
Arsagermaallene 1 generally behaves as a 1,2-dipole, reacting by
the GeC double bond, which appears much more reactive
than the AsC bond. However with diphenylketene
arsagermaallene 1 surprisingly behaves as a 1,3-dipole, leading
by a [3 + 2] cycloaddition to the unprecedented heterocyclic
carbene AsGeHC, a heavier analogue of the well-known NHC,
bearing germanium and arsenic atoms on the carbenic center.
DFT calculations point out that this latter species is a minimum
on the PES and is quasi-isoenergetic with the starting
compounds. The reaction is in a first step kinetically controlled
(low barrier compared to the [2 + 2] cycloadduct). In a second
step, the presence of the tert-butyl group leads to the insertion
product 11, thermodynamically controlled, this process being
the driving force of the reaction. The chemical behavior of 1 is
similar to that of the closely related phosphagermaallene Tip(t-
Bu)GeCPMes*, showing a great resemblance between
phosphorus and arsenic in this type of heteroallene, and very
different from that of other E14CE15 derivatives such as
azasilaallene (SiCN) and azastannaallene (SnCN), in which the
E14C bond is easily cleaved.
Note: some signals have not been observed by 1H NMR (o-CHMe2)
and 13C NMR (m-CH, o-C, and o-CHMe2 of Tip) due to a
coalescence effect caused by the slow rotation of the Tip group around
the Cipso−Ge bond on the NMR time scale.
3
1H NMR (CDCl3): δ 1.23 (d, JHH = 6.6 Hz, 12H) and 1.25 (d,
3JHH = 6.9 Hz, 6H) (o- and p-CHMe2), 1.33 (s, 9H, p-CMe3), 1.35 (d,
4JHF = 1.2 Hz, 9H, GeCMe3), 1.44 and 1.48 (2s, 2 × 9H, o-CMe3),
2.88 (sept, 3JHH = 6.9 Hz, 1H, p-CHMe2), 7.05 (broad s, 2H, m-CH of
Tip), 7.43 (s, 2H, m-CH of Mes*). 13C NMR (CDCl3): δ 23.75 and
23.80 (p-CHMe2), 26.17 (o-CHMe2), 28.24 (GeCMe3), 31.37 (p-
CMe3), 32.34 (d, 2JCF = 10.3 Hz, GeCMe3), 33.08 and 33.30 (o-CMe3),
34.00 (p-CHMe2), 34.99 (p-CMe3), 38.05 and 38.09 (o-CMe3), 122.23
and 122.51 (m-CH of Mes*), 128.75 (d, 2JCF = 7.6 Hz, ipso-C of Tip),
145.00 (ipso-C of Mes*), 150.21 (p-C of Mes*), 150.52 (p-C of Tip),
The synthetic potential of 1 in heterocyclic and organo-
metallic chemistry (particularly its use as a ligand in
coordination chemistry) and the search for the stable
heterocyclic carbene AsGeHC are now under active inves-
tigation.
2
152.95 and 153.33 (o-C of Mes*), 176.18 (d, JCF = 7.2 Hz, CAs).
19F NMR (CDCl3): δ −175.04. MS (m/z, %): 765 (M + H, 1), 746
(M − F + H, 5), 708 (M − t-Bu + H, 3), 690 (M − F − t-Bu + 2H, 3),
666 (M − F − Br, 2), 610 (M − F − Br − t-Bu + H, 7), 519 (M −
Mes*, 7), 499 (M − Mes* − F − H, 10), 413 (M − Tip(t-Bu)GeF, 5),
319 (Mes*As − H, 15), 275 (TipGe − 2H, 12), 57 (t-Bu, 100). Anal.
Calcd for C38H61AsBrFGe (764.31): C, 59.72; H, 8.04. Found: C,
59.52; H, 8.26.
4. EXPERIMENTAL SECTION
General Procedure. All experiments were performed in flame-
dried glassware under an inert atmosphere of argon using high-
vacuum-line techniques. Solvents were dried using an MBraun solvent
purification system and degassed through successive freeze−pump−
thaw cycles prior to use. Deuterated solvents (C6D6 and CDCl3) were
dried and stored over 4 Å molecular sieves. NMR spectra were
reported in parts per million (ppm) and recorded on a Bruker Avance
300 spectrometer at the following frequencies: 1H, 300.13 MHz;
13C{1H}, 75.47 MHz (reference Me4Si); 19F, 282.38 MHz (reference
CFCl3). 1H and 13C{1H} NMR assignments were confirmed by COSY
(1H), HSQC (1H−13C), and HMBC (1H−13C) experiments. Melting
points were determined on a Stuart Automatic Melting Point SMP40
instrument. Mass spectra were obtained on a Hewlett-Packard 5989A
spectrometer by EI at 70 eV. Elemental analyses were performed by
Synthesis of 1-Arsa-3-germaallene 1. To a solution of the 1-
arsa-3-germapropene previously prepared (1.14 g, 1.50 mmol) in
diethyl ether (15 mL) was added 1 equiv of tert-butyllithium (1.7 M in
pentane; 0.3 mL, 0.5 mmol) at −100 °C. The reaction mixture turned
immediately from colorless to orange-pink. After the mixture was
warmed to room temperature, a 1H NMR analysis showed the almost
quantitative formation of 1-arsa-3-germaallene 1. Lithium salts were
then filtered off, giving a brown solution. After removal of solvents
under reduced pressure, the resulting residue was recrystallized from
diethyl ether to give orange crystals of 1 (0.90 g, 91%, mp 118 °C).
However, as 1 is obtained nearly quantitatively, it is not necessary to
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crystallize it and reactions were generally performed with the crude
(arom H of phenanthrene unit). 13C NMR (C6D6): δ 23.63 and 23.74
(p-CHMeMe′), 24.69 and 25.80 (o-CHMeMe′), 27.93 (GeCMe3),
29.30 (GeCMe3), 31.49 (p-CMe3), 33.86 (p-CHMeMe′), 33.96 and
34.22 (o-CMe3), 34.50 (broad s, o-CHMeMe′), 38.64 and 38.86 (o-
CMe3), 121.50, 122.05, 122.21, 122.44, 122.88, 123.52, 124.78, 125.87,
and 126.27 (arom CH), 125.88, 127.76, 128.13, and 129.80 (arom C
of phenanthrene unit), 129.58 (ipso-C of Tip), 135.21 (ipso-C of
Mes*), 138.37 and 140.23 (OCCO), 149.72 and 149.87 (p-C of
Tip and Mes*), 154.76 (broad s, o-C of Tip), 155.31 and 156.03 (o-C
of Mes*), 223.38 (CAs). Anal. Calcd for C52H69AsGeO2 (873.63):
C, 71.49; H, 7.96. Found: C, 71.81; H, 8.09.
solution containing LiF.
3
1H NMR (C6D6): δ 0.97, 1.20, 1.33, and 1.42 (4 broad d, JHH
=
3
5.1−5.7 Hz, 4 × 3H, o-CHMeMe′), 1.14 (d, JHH = 6.9 Hz, 6H, p-
CHMe2), 1.27 (s, 9H, GeCMe3), 1.32 (s, 9H, p-CMe3), 1.65 (s, 18H,
3
o-CMe3), 2.73 (sept, JHH = 6.9 Hz, 1H, p-CHMe2), 2.86 and 3.43 (2
broad signals, 2 × 1H, o-CHMeMe′), 7.04 and 7.07 (2s, 2 × 1H, m-CH
of Tip), 7.53 (s, 2H, m-CH of Mes*). 13C NMR (C6D6): δ 23.75,
24.29, 25.41, and 26.01 (o-CHMeMe′), 24.16 (p-CHMe2), 30.58
(GeCMe3), 31.73 (p-CMe3), 34.13 (GeCMe3), 34.58 (o-CMe3), 34.72
(p-CHMe2), 34.99 (p-CMe3), 38.98 (o-CMe3), 40.77 and 41.61 (o-
CHMeMe′), 121.50 (m-CH of Tip), 122.24 (m-CH of Mes*), 133.41
(ipso-C of Tip), 148.44 (p-C of Mes*), 151.39 (p-C of Tip), 152.30
(ipso-C of Mes*), 152.97 (o-C of Mes*), 153.29 and 153.50 (o-C of
Tip), 305.23 (GeCAs). MS (m/z, %): 667 (M + H, 5), 609 (M − t-Bu,
5), 553 (M − 2t-Bu + H, 10), 495 (M − 3t-Bu, 3), 463 (M − Tip, 5),
421 (M − Mes*, 7), 349 (M − 2t-Bu − Tip, 10), 319 (Mes*As − H,
8), 275 (TipGe − 2H, 15), 57 (t-Bu, 100). Anal. Calcd for
C38H61AsGe (665.41): C, 68.59; H, 9.24. Found: C, 68.81; H, 9.36.
General Procedure for the Reaction of 1 with Fluorenone,
9,10-Phenanthrenequinone, and Diphenylketene. To a solution
of arsagermaallene 1 (1.47 mmol) in Et2O (15 mL) cooled to −80 °C
was added 0.26 g (1.47 mmol) of fluorenone (or 0.29 g (1.47 mmol)
of 9,10-phenanthrenequinone or 0.26 g (1.47 mmol) of diphenylke-
tene) in solution in 2 mL of Et2O. A brown coloration appeared
immediately. After 15 min of stirring at −80 °C, the reaction mixture
was warmed to room temperature; solvent was eliminated under
vacuum and replaced by pentane (20 mL), and the lithium salts were
removed by filtration. After concentration of a part of the pentane,
crystallization at −20 °C afforded white crystals of derivatives 3 (1.01
g, 81%), 5 (0.94 g 75%), and 6 (0.96 g, 76%).
1
Carbene Insertion Product 11 from Diphenylketene. H NMR
3
(C6D6): δ 0.31, 0.96, 1.31, and 1.47 (4d, JHH = 6.6 Hz, 4 × 3H, o-
3
CHMeMe′), 1.28 (d, JHH = 6.6 Hz, 6H, p-CHMeMe′), 1.26 and 1.41
(2s, 2 × 3H, CH2CMeMe′), 1.17 and 1.43 (2s, 2 × 9H, t-Bu on Mes*),
1.37 (t-Bu on Ge), 1.87−1.94 (m, 1H, CHH′), 2.31−2.36 (m, 2H,
3
CHH′ and GeCH), 2.86 and 3.39 (2sept, JHH = 6.6 Hz, 2 × 1H, o-
3
CHMeMe′), 2.89 (sept, JHH = 6.6 Hz, 1H, p-CHMeMe′), 6.49 (d,
3JHH = 7.2 Hz, 2H, o-CH of Ph), 6.63 (t, 3JHH = 7.5 Hz, 2H, m-CH of
Ph), 6.82 (tt, 3JHH = 7.5 Hz, 4JHH = 1.2 Hz, 1H, p-CH of Ph), 6.90 and
4
3
7.03 (2d, JHH = 1.5 Hz, 2 × 1H, m-CH of Tip), 7.09 (tt, JHH = 7.2
4
4
Hz, JHH = 1.5 Hz, 1H, p-CH of Ph), 7.15 (d, JHH = 1.8 Hz, 1H, m-
CH of Mes*), 7.20 (t, 3JHH = 7.5 Hz, 2H, m-CH of Ph), 7.29 (d, 3JHH
4
= 7.2 Hz, 2H, o-CH of Ph), 7.52 (d, JHH = 1.8 Hz, 1H, m-CH of
Mes*). 13C NMR (C6D6): δ 23.82 and 23.89 (p-CHMeMe′), 24.32,
24.63, 25.82, and 27.11 (o-CHMeMe′), 29.27, 31.56, and 32.98
(CMe3), 31.30 and 34.27 (CH2CMeMe′), 32.98 and 33.59 (o- and p-
CHMeMe′), 29.22, 35.03, 38.00, 38.79, and 39.53 (CMe3 and
CH2CMe2), 120.67 and 122.65 (m-CH of Tip), 121.17 and 122.27
(m-CH of Mes*), 124.72 and 124.76 (p-CH of Ph), 126.02 (OCC),
126.77 and 127.10 (m-CH of Ph), 128.21 (ipso-C of Tip), 130.65 and
132.07 (o-CH of Ph), 131.70 (CAs of Mes*), 141.49 and 144.60 (ipso-
C of Ph), 150.15, 150.22, and 150.68 (p-C of Tip, p-C of Mes* and C
of Mes* bonded to CMeMe′), 152.66 and 156.65 (o-C of Tip), 153.84
(o-C of Mes*), 159.87 (OCCPh2). Anal. Calcd for C52H71AsGeO
(859.64): C, 72.65; H, 8.32. Found: C, 72.51; H, 8.24.
Fluorenone Adduct 3. The carbon atoms of the fluorenyl unit are
numbered as follows:
Reaction of 1 with Selenium: Formation of 2. The reaction of
arsagermaallene 1 with selenium was performed as previously
described for other reactants from 1.47 mmol of 1 in Et2O (15 mL)
cooled to −80 °C and 0.11 g (1.47 mmol) of selenium, which was
slowly added by portions. After it was warmed to room temperature,
the reaction mixture was stirred for an additional 1 h. Diethyl ether
was eliminated and replaced by 20 mL of pentane. The lithium salts
were removed by filtration. After concentration of a part of the
pentane, crystallization at −20 °C afforded 0.48 g of derivative 2.
However, the X-ray structural study showed the presence of a disorder
due to a four-membered ring derivative with a Ge−C−Se−Se skeleton
(see the Supporting Information). In NMR only one type of signal can
be observed.
1H NMR (C6D6): δ 0.74, 0.94, 1.06, and 1.13 (4d, 3JHH = 6.6 Hz, 4
3
× 3H, o-CHMeMe′), 1.34 (d, JHH = 6.6 Hz, 6H, p-CHMeMe′), 1.10
and 1.57 (2s, 2 × 9H, o-t-Bu of Mes*), 1.37 and 1.38 (2s, 2 × 9H, t-Bu
3
of Ge and p-t-Bu of Mes*), 2.26 and 3.34 (2sept, JHH = 6.6 Hz, 2 ×
1H, o-CHMeMe′), 2.94 (sept, 3JHH = 6.6 Hz, 1H, p-CHMeMe′), 6.85−
6.91 (m, 2H, H of C7 and C8), 6.94 and 7.10 (2 broad s, 2 × 1H, m-
CH of Tip), 7.18 (td, 3JHH = 7.2 Hz, 4JHH = 0.9 Hz, 1H, H of C6), 7.32
and 7.45 (2 broad s, 2 × 1H, m-CH of Mes*), 7.34−7.42 (m, 2H, H of
C2 and C3), 7.58 (d, 3JHH = 7.5 Hz, 1H, H of C5), 7.65−7.67 (m, 1H,
H of C4), 7.93−7.96 (m, 1H, H of C1). 13C NMR (C6D6): δ 23.88
and 23.91 (p-CHMeMe′), 24.97, 25.39, 25.57, and 25.97 (o-
CHMeMe′), 28.27 and 31.45 (GeCMe3 and p-CMe3), 32.49 and
36.83 (o-CHMeMe′), 34.12 (p-CHMeMe′), 34.86 and 35.30 (o-CMe3),
38.36 and 39.30 (o-CMe3), 101.23 (GeOC), 119.40, 119.57 (C4 and
C5 of CR2), 120.51 and 123.01 (m-CH of Tip), 121.54 and 122.27 (m-
CH of Mes*), 125.59, 125.89, 127.09, 127.49, 128.24, and 128.78
(other arom CH of CR2), 131.71 (ipso-C of Tip), 137.13, 140.41,
152.40, and 152.70 (arom C of CR2), 141.51 (ipso-C of Mes*), 149.08
(p-C of Mes*), 150.58 (p-C of Tip), 153.13 and 155.89 (o-C of Tip),
153.98 and 154.47 (o-C of Mes*), 209.91 (CAs). MS (m/z, %): 845
(M − H, 5), 789 (M − t-Bu, 15), 601 (M − Mes*, 20), 351 (Tip(t-
Bu)GeO + H, 35), 275 (TipGe − 2H, 30), 57 (t-Bu, 100). Anal. Calcd
for C51H69AsGeO (845.61): C, 72.44; H, 8.22. Found: C, 72.55; H,
8.34.
1H NMR (C6D6; due to slow rotation of the Tip and Mes* groups,
some of the signals are broad and appear as multiplets): δ 1.05−1.54
(m, 54H, o-and p-CHMeMe′, o- and p-CHMeMe′, t-Bu on Ge, N and
Mes*), 2.74 (sept, 3JHH = 6.6 Hz, 1H, o-CHMeMe′), 2.79 (sept, 3JHH
6.9 Hz, 1H, p-CHMeMe′), 3.47 (broad sept, JHH = 6.6 Hz, 1H, o-
CHMeMe′), 6.98 (s, 2H, m-CH of Tip), 7.41 (s, 2H, m-CH of Mes*).
13C NMR (C6D6): δ 22.58, 24.33, 27.21, 31.36, 31.70, 32.50, 33.28,
=
3
34.42, and 34.66 (o-and p-CHMeMe′, o- and p-CHMeMe′, CMe3),
30.06, 34.99, 38.61, and 40.17 (CMe3), 119.54 (m-CH of Mes*),
122.25 (m-CH of Tip), 148.94, 150.04, 150.19, 153.85, and 153.99
(arom-C of Tip and Mes*), 205.03 (CAs). MS (m/z, %): 824 (M +
Se, 5), 767 (M + Se − t-Bu, 2), 745 (M + H, 5), 711 (M + Se − 2t-Bu
+ H, 7), 687 (M − t-Bu, 8), 579 (M + Se − Mes*, 6), 499 (M −
Mes*, 10), 275 (TipGe − 2H, 20), 57 (t-Bu, 100). Anal. Found: C,
60.73; H, 8.18 (corresponding to a mixture of three- and four-
membered ring derivatives, 90/10). Calcd for 2: C, 61.32; H, 8.26.
Calcd for the four-membered ring compound: C, 55.44; H, 7.47.
Reaction of 1 with N-tert-Butylphenylnitrone: Formation of
4. The reaction of arsagermaallene 1 with N-tert-butylphenylnitrone
was performed as previously described for other reactants from 1.47
mmol of 1 in Et2O (15 mL) cooled to −80 °C and 0.26 g (1.47 mmol)
1
9,10-Phenanthrenequinone Adduct 5. H NMR (C6D6): δ 0.83
(broad s, 6H, o-CHMeMe′), 0.89 (s, 9H, t-Bu on Ge), 1.17 (s, 9H, o-t-
3
Bu on Mes*), 1.19 (d, JHH = 6.6 Hz, 6H, p-CHMeMe′), 1.31−1.33
(broad s, 6H, o-CHMeMe′), 1.39 (s, 9H p-t-Bu on Mes*), 1.68 (s, 9H,
3
o-t-Bu on Mes*), 2.28 (sept, JHH = 6.6 Hz, 1H, p-CHMeMe′), 3.23
(very broad s, 2H, o-CHMeMe′), 6.92 (broad s, 2H, m-CH of Tip),
7.42 and 7.49 (2 broad s, 2 × 1H, m-CH of Mes*), 7.50 (t, 3JHH = 7.2
3
Hz, 1H), 7.56−7.59 (m, 2H), 7.61 (t, JHH = 7.2 Hz, 1H), 8.32−8.39
(m, 1H), 8.46 (d, 3JHH = 9.0 Hz, 1H) and 8.60 (d, 3JHH = 8.1 Hz, 2H)
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1
of N-tert-butylphenylnitrone in solution in 2 mL of Et2O. H and 13C
NMR analysis of the crude reaction mixture showed the formation of
two diastereoisomers. After concentration of a part of the pentane,
crystallization at −20 °C afforded 0.90 g (73%) of a 55/45 mixture of
the two isomers 4a/4b. As they present the same solubility in various
solvents, their separation has been impossible.
(M − t-Bu, 10), 631 (M − Mes*, 6), 557 (M − Mes*As − 1, 5), 499
(M − Mes*As − t-Bu − 2, 10), 349 (Tip(t-Bu)GeO − 1, 10), 333
(Tip(t-Bu)Ge − 1, 2), 319 (Mes*As, 50), 275 (TipGe − 2H, 27), 57
(t-Bu, 100).
X-ray Structure Determinations for 2−5 and 7. The data of
the structures for compounds 2−5 and 7 were collected on a Bruker-
AXS SMART APEX II diffractometer (4 and 5) and on a Bruker-AXS
kappa APEX II Quazar diffractometer (2, 3, and 7) at a temperature of
193(2) K using an oil-coated shock-cooled crystal with Mo Kα
radiation (wavelength 0.710 73 Å) by using ψ and ω scans. The data
were integrated with SAINT, and an empirical absorption correction
with SADABS was applied.39,40 The structures were solved by direct
methods (SHELXS-97)41 and refined against all data by full-matrix
least-squares methods on F2 (SHELXL-97).42 For 2−5 and 7, all non-
hydrogen atoms were refined with anisotropic displacement
parameters. The hydrogen atoms were refined isotropically on
calculated positions using a riding model with their Uiso values
constrained to 1.5 times the Ueq of their pivot atoms for terminal sp3
carbon atoms and 1.2 times that value for all other carbon atoms.
For 7, the asymmetric unit contains two independent molecules
with identical structural arrangements; thus, the data of only one
molecule of the asymmetric unit are discussed.
1H NMR (C6D6; due to slow rotation of the Tip and Mes* groups,
most of the signals are broad and appear as multiplets): δ 0.65−0.72
(m) and 0.85−1.60 (m) (54H, o-and p-CHMeMe′, o- and p-
CHMeMe′, t-Bu on Ge, N and Mes*), 2.75−2.93 (m), 3.15−3.31
(m), 3.38−3.60 (m) and 3.64−3.80 (m) (3H, o- and p-CHMeMe′),
4.47 (4a) and 5.12 (4b) (2s, 2H, CHPh), 6.36 (d, 3JHH = 7.0 Hz, o-CH
of Ph), 6.55−6.75 (m), 6.81−7.91 (m) and 8.25 (broad s) (totally 9H,
arom H of Ph, Tip and Mes*). 13C NMR (C6D6): δ 22.36, 23.85,
25.76, 26.21, 27.28, 27.55, 27.81, 28.45, 29.06, 29.41, 29.82, 30.12,
30.73, 31.28, 31.62, 32.54, 33.21, 33.54, 33.92, 33.98, 34.00, and 34.14
(o-and p-CHMeMe′, o- and p-CHMeMe′, CMe3 on Ge, N and Mes*),
30.31, 34.94, 36.65, 36.98, 37.50, 38.29, 38.51, and 38.62 (CMe3),
60.07 (4a) and 60.62 (4b) (NCMe3), 76.13 (4a) and 78.32 (4b)
(CHPh), 119.48, 119.96, 121.32, 121.81, 122.05, 122.30, 122.60, and
122.85 (m-CH of Tip and Mes*), 127.19, 127.71, 128.67, 128.77,
129.89, and 130.35 (CH of Ph), 142.18, 143.19, 147.15, 148.85,
149.21, 149.35, 149.38, 149.51, 149.94, 152.87, 153.16, 153.51, 154.37,
155.09, 155.83, 157.01, and 157.39 (ipso-, o-, and p-C of Tip and
Mes*, ipso-C of Ph), 205.34 (4a) and 211.90 (4b) (CAs). Anal.
Calcd for C49H76AsGeNO (842.66): C, 69.84; H, 9.09. Found: C,
70.11; H, 9.24.
Reaction of 1 with Benzil: Formation of 6 and 7. Reaction of 1
with benzil was performed under the same conditions as for
fluorenone or diphenylketene from 1.47 mmol of 1 in Et2O (15
mL) and 1 equiv of benzil. After the usual workup, a mixture of both
yellow and yellow-orange crystals was obtained from pentane (0.84 g,
65%). Both present about the same solubility in common organic
solvents and cannot be separated by crystallization. However, crystals
can be manually separated, owing to their different colors, yellow (6)
and yellow-orange (7), but in rather low yield.
Selenium Adduct 2: the crystal is made up of a mixture of about
89% of the three-membered ring species 2 and 11% of a four-
membered ring derivative with
a Ge−C−Se−Se moiety;
C38H61AsGeSe1.11, Mr = 752.83; crystal size 0.22 × 0.20 × 0.14
mm3; monoclinic; space group P21/c; a = 10.3723(8) Å, b =
16.4418(15) Å, c = 23.513(2) Å, α = γ = 90°, β = 99.872(3)°; V =
3950.4(6) Å3; Z = 4; 71 406 reflections collected; 6667 unique
reflections (Rint = 0.0347); R1 = 0.0308, wR2 = 0.0724 (I > 2σ(I)); R1
= 0.0413, wR2 = 0.0779 (all data); largest difference peak and hole
1.185 and −0.720 e Å−3.
Fluorenone Adduct 3: C51H69AsGeO·C4H10O, Mr = 919.71; crystal
size 0.12 × 0.08 × 0.02 mm3; triclinic; space group P1; a =
̅
10.1766(10) Å, b = 12.5486(12) Å, c = 20.381(2) Å, α = 77.202(4)°, β
= 85.813(4)°, γ = 82.062(4)°; V = 2511.3(4) Å3; Z = 2; 33 681
reflections collected; 10 088 unique reflections (Rint = 0.0429); R1 =
0.0365, wR2 = 0.0784 (I > 2σ(I)); R1 = 0.0585, wR2 = 0.0866 (all
data); largest difference peak and hole 0.546 and −0.311 e Å−3.
Nitrone Adduct 4: C49H77AsGeNO·1/2C5H12, Mr = 879.70; crystal
1
Data for 6 are as follows. H NMR (C6D6): δ 0.58, 1.01, 1.34, and
1.80 (4d, 3JHH = 6.6 Hz, 4 × 3H, o-CHMeMe′), 1.18 (d, 3JHH = 6.6 Hz,
6H, p-CHMeMe′), 0.30, 1.15, 1.35, and 1.43 (4s, 4 × 9H, t-Bu), 2.36
and 4.13 (2sept, 3JHH = 6.6 Hz, 2 × 1H, o-CHMeMe′), 2.74 (sept, 3JHH
= 6.6 Hz, 1H, p-CHMeMe′), 6.80−7.20 (m, 6H, m- and p-CH of Ph),
7.01 and 7.29 (2 broad d, 4JHH = 1.2 Hz, 2 × 1H, m-CH of Tip), 7.47
size 0.70 × 0.25 × 0.22 mm3; triclinic; space group P1; a = 11.0351(5)
̅
and 7.58 (2d, 4JHH = 2.1 Hz, 2 × 1H, m-CH of Mes*), 7.93 (dd, 3JHH
=
Å, b = 12.2305(6) Å, c = 20.1455(10) Å, α = 98.1380(10)°, β =
100.0020(10)°, γ = 105.7760(10)°; V = 2525.1(2) Å3; Z = 2; 34 967
reflections collected; 12 438 unique reflections (Rint = 0.0419); R1 =
0.0413, wR2 = 0.0931 (I > 2σ(I)); R1 = 0.0738, wR2 = 0.1056 (all
data); largest difference peak and hole 0.462 and −0.680 e Å−3.
9,10-Phenanthrenequinone Adduct 5: C52H69AsGeO2·CHCl3, Mr
= 992.97; crystal size 0.40 × 0.28 × 0.16 mm3; monoclinic; space
group P21/c; a = 10.0231(5) Å, b = 31.4407(17) Å, c = 18.7805(9) Å,
α = γ = 90°, β = 118.019(3)°; V = 5224.7(5) Å3; Z = 4; 39 234
reflections collected; 9485 unique reflections (Rint = 0.0368); R1 =
0.0486, wR2 = 0.1229 (I > 2σ(I)); R1 = 0.0654, wR2 = 0.1334 (all
data); largest difference peak and hole 0.716 and −0.820 e Å−3.
Benzil Adduct 7: C52H71AsGeO2, Mr = 875.62; crystal size 0.24 ×
0.06 × 0.04 mm3; monoclinic; space group P21; a = 9.9250(6) Å, b =
23.8454(15) Å, c = 22.0595(13) Å, α = γ = 90°, β = 99.647(3)°; V =
5146.9(5) Å3; Z = 4; 38 494 reflections collected; 19 545 unique
reflections (Rint = 0.1122); R1 = 0.0966, wR2 = 0.2415 (I > 2σ(I)); R1
= 0.1283, wR2 = 0.2627 (all data); largest difference peak and hole
2.475 and −0.701 e Å−3.
8.1 Hz, 4JHH = 1.2 Hz, 2H, o-CH of Ph on CO), 8.58 (dd, 3JHH = 8.4
Hz, JHH = 1.2 Hz, 2H, o-CH of Ph on C−O). 13C NMR (C6D6): δ
4
23.61 and 23.68 (p-CHMeMe′), 25.10, 25.14, 25.20, and 25.27 (o-
CHMeMe′), 27.97, 31.22, 33.81, and 34.52 (CMe3), 32.13 and 37.38
(p-CHMeMe′), 34.17 (o-CHMeMe′), 34.20, 34.72, 37.97, and 39.04
(CMe3), 102.68 (C−O), 120.88 and 122.89 (m-CH of Tip), 122.18
and 122.89 (m-CH of Mes*), 125.35 (o-CH of Ph on CO), 126.76,
128.22, 128.72, and 129.68 (m- and p-CH of Ph), 131.55 (o-CH of Ph
on C−O), 131.59 (ipso-C of Tip), 135.74 (ipso-C of Ph), 143.56 (ipso-
C of Mes*), 148.24 (ipso-C of Ph), 148.24, 149.20, 150.72, 153.78,
153.82, 154.53, and 155.64 (o- and p-C of Tip and Mes* and CAs),
197.98 (CO). MS (m/z, %): 876 (M, 5), 819 (M − t-Bu, 2), 771
(M − PhCO, 10), 631 (M − Mes*, 6), 557 (M − Mes*As − 1, 5),
542 (M − Tip(t-Bu)Ge, 38), 349 (Tip(t-Bu)GeO − 1, 10), 333
(Tip(t-Bu)Ge − 1, 15) 319 (Mes*As, 20), 275 (TipGe − 2H, 17), 57
(t-Bu, 100).
1
Data for 7 are as follows. H NMR (C6D6): δ 0.84, 1.30, 1.45, and
1.62 (4s, 4 × 9H, t-Bu), 1.10−115 (m, 18H, o- and p-CHMeMe′), 2.71
(sept, JHH = 6.6 Hz, 1H, p-CHMeMe′), 3.60 (very broad s, 2H, o-
3
CHMeMe′), 6.84−7.10 (m, m-CH of Tip (2H) and 6H of Ph), 7.46
and 7.51 (2d, 4JHH = 2.1 Hz, 2 × 1H, m-CH of Mes*), 7.69−7.80 (m,
4H, CH of Ph). 13C NMR (C6D6): δ 23.65, 23.72, 23.80, 27.74, 28.06,
29.25, 31.34, 33.92, 34.14, 34.27, 34.44, 34.62, 34.69, 38.08, 38.71, and
39.06 (CHMe2 and CMe3), 122.19, 122.29, 122.54, 123.01, 125.46,
126.88, 127.03, 127.14, 128.84, 129.80, 129.94, 130.17, 131.71, 135.37,
136.45, 138.03, 138.87, 143.16, 149.78, 150.14, 155.66, and 156.37
(arom C and CH, CAs, OCCO). MS (m/z, %): 876 (M, 5), 819
ASSOCIATED CONTENT
■
S
* Supporting Information
CIF files giving crystallographic data for 2−5 and 7 and tables
and figures giving theoretical results and the structure of 2,
showing the disorder. This material is available free of charge
via the Internet at http://pubs.acs.org.
938
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Organometallics
Article
(11) Ramdane, H.; Ranaivonjatovo, H.; Escudie,
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ACKNOWLEDGMENTS
■
We are grateful to the CNRS and to the Agence Nationale pour
la Recherche (contract ANR-08-BLAN-0105-01) for financial
support of this work. The theoretical work was granted access
to the HPC resources of Idris under allocation 2011
(i2011080045) made by the GENCI (Grand Equipement
National de Calcul Intensif).
́
́
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Gornitzka, H.; Saffon, N.; Miqueu, K.; Lazraq, M. Organometallics
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J.; Ladeira, S. Inorg. Chem.
́
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DEDICATION
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Escudie, J.; Gornitzka, H. Angew. Chem., Int. Ed. 2011, 50, 5352−5355.
Dedicated to the memory of Dumitru Ghereg, a brilliant young
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