Addition of alkynes to a gallium bis-amido complex: Imitation of transition-metal-based catalytic systems

Article abstract of DOI:10.1002/chem.201102243

Acetylene, phenylacetylene, and alkylbutynoates add reversibly to (dpp-bian)Ga-Ga(dpp-bian) (dpp-bian=1,2-bis[(2,6-diisopropylphenyl)-imino] acenaphthene) to give addition products [dpp-bian(R¹C=CR ²)]Ga-Ga[(R²C=CR¹

Full text of DOI:10.1002/chem.201102243

FULL PAPER
DOI: 10.1002/chem.201102243
Addition of Alkynes to a Gallium Bis-Amido Complex: Imitation of
Transition-Metal-Based Catalytic Systems
Igor L. Fedushkin,* Alexander S. Nikipelov, Alexander G. Morozov,
Alexandra A. Skatova, Anton V. Cherkasov, and Gleb A. Abakumov*[a]
Abstract: Acetylene, phenylacetylene,
and alkylbutynoates add reversibly to
metal–metal bond by approximately
0.13 ꢀ. The adducts undergo a facile
alkynes elimination at elevated temper-
atures. The equilibrium between [dpp-
bianACTHNGUTREN(UNG PhC=CH)]Ga–GaACHTUNGTRENUN[NG (HC=CPh)dpp-
bian] and [(dpp-bian)Ga–GaACTHNGUTERNNU(G dpp-bian)
146.0 JKꢀ1molꢀ1). The reactivity of
(dpp-bian)Ga–Ga(dpp-bian) towards
ACHTUNGTRENNUNG
(dpp-bian)Ga–Ga
G
(dpp-
alkynes permits use as a catalyst for
carbon–nitrogen and carbon–carbon
bond-forming reactions. The bisgallium
complex was found to be a highly ef-
fective catalyst for the hydroamination
of phenylacetylene with anilines. For
bian=1,2-bis[(2,6-diisopropylphenyl)-
imino]acenaphthene) to give addition
products [dpp-bian
G
G
[(R2C=CR1)dpp-bian]. The alkyne adds
+ 2 PhC CH] in toluene solution was
studied by H NMR spectroscopy. The
ꢁ
1
ꢀ ꢀ
across the Ga N C section, which re-
sults in new carbon–carbon and
carbon–gallium bonds. The adducts
were characterized by electron absorp-
tion, IR, and 1H NMR spectroscopy
and their molecular structures have
been determined by single-crystal X-
ray analysis. According to the X-ray
data, a change in the coordination
number of gallium from three [in (dpp-
equilibrium constants at various tem-
peratures (298ꢂTꢂ323 K) were deter-
mined, from which the thermodynamic
parameters for the phenylacetylene
elimination were calculated (DG8=
2.4 kJmolꢀ1, DH8=46.0 kJmolꢀ1, DS8=
instance, with [(dpp-bian)Ga–GaACHTUNGTRENNUNG(dpp-
bian)] (2 mol%) in benzene more than
ꢁ
99% conversion of PhNH2 and PhC
CH into PhN=C(Ph)CH3 was achieved
in 16 h at 908C. Under similar condi-
tions, the reaction of 1-aminoanthra-
ꢁ
cene with PhC CH catalyzed by (dpp-
bian)Ga–Ga
A
formed
a
Keywords: alkynes · gallium · hy-
droamination · hydroarylation · re-
dox-active ligands
carbon–carbon bond to afford 1-amino-
2-(1-phenylvinyl)anthracene in 99%
yield.
bian)Ga–GaACHTUNGTRENNUNG(dpp-bian)] to four (in the
adducts) results in elongation of the
Introduction
pecially the polymerization of olefins and dienes.[2h–l] In
2003, the unique ability of bians to act as an electron sponge
was illustrated by a four-step reduction of the most useful
representative in the series—1,2-bis[(2,6-diisopropyl-
1,2-Bis(arylimino)acenaphthene (bian) ligands have attract-
ed rising attention in recent years.[1–3] Their transition-metal
complexes were first reported by Elsevier and van Asselt in
the early 1990s.[1] More than 1200 d-block-metal complexes
with neutral bians have been reported to date, and approxi-
mately 90 of them have been studied by X-ray analysis. Nu-
merous articles that discussed bian complexes of transition
metals were published in 2010.[2] The combination of s-
donor and p-acceptor character with conformational rigidity
in the bians allows preparation of transition-metal com-
plexes that serve as catalysts in various organic reactions, es-
AHCTUNGTRENNUNG
phenyl)imino]acenaphthene (dpp-bian)—with sodium.[4]
However, transition-metal complexes with anionic bian li-
gands are limited to the recently reported chromium(II)/
dpp-bian radical anion complexes.[5] In comparison with
other chelating p-acceptor ligands (for example, o-quinones
are widely used in transition-metal chemistry), the bians
have a more negative reduction potential (bians E<ꢀ1.0 V;
quinones E>ꢀ0.6 V vs. the saturated calomel electrode).
Therefore, transition metals in their positive oxidation states
are not stable to the reducing power of coordinated anionic
bian ligands. In contrast, Group 1, 2, 13, and 14 metals,[6a] as
well as the lanthanides,[6b] form thermodynamically stable
complexes with radical-anionic and dianionic bian ligands.
The main research motive in the field of main-group-metal
complexes of bians is to generate redox-active complexes of
redox-inactive metals, such as magnesium(II) or aluminum-
[a] Prof. Dr. I. L. Fedushkin, A. S. Nikipelov, Dr. A. G. Morozov,
Dr. A. A. Skatova, A. V. Cherkasov, Prof. Dr. G. A. Abakumov
Institute of Organometallic Chemistry
Russian Academy of Sciences
Tropinina 49
AHCTUNGTREG(NNUN III), by using redox-active bian ligands. It is expected that
603950 Nizhny Novgorod (Russia)
Fax : (+7)831-2627-497
E-mail: igorfed@iomc.ras.ru
this type of complex may demonstrate new types of catalytic
activity or emulate the catalytic behavior of known transi-
tion-metal complexes. The concept of ligands that can store
and release electrons during catalytic processes has begun to
Supporting information for this article is available on the WWW
under http://dx.doi.org/10.1002/chem.201102243.
Chem. Eur. J. 2012, 18, 255 – 266
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
255

be exploited in transition-metal chemistry. The development
of this approach has just been highlighted by Dzik et al.[7]
Applications of transition-metal complexes with “stan-
dard” spectator ligands in homogeneous catalysis are en-
sured by two distinct features of transition-metal ions: 1) the
ability to coordinate unsaturated organic molecules; 2) the
ability to exist in several, easily interchangeable oxidation
states. The latter makes oxidative addition and reductive
elimination possible at a single transition-metal center. A
lack of these features was always one of the limiting factors
for the use of main-group metals in catalyses that were suc-
cessfully performed with transition metals. Nevertheless, s-,
p-, and f-block-metal complexes that can emulate the reac-
tivity of transition-metal complexes have been produced. In
this context, a complex of the dpp-bian dianion with magne-
tronic lability of the ligand on the molecular structure and
chemical properties of the complex. Due to steric reasons,
the phenyl rings at the nitrogen atoms in the dpp-bian dia-
nion are orientated perpendicular to the metallacycle, the
nitrogen atoms are forced to adopt sp2 hybridization, and
the isopropyl groups shield the nitrogen lone pairs. The
three-coordinate gallium species represents a typical Lewis
acid and 1 can be isolated as solvent-free complex, even
from strongly coordinating solvents, such as diethyl ether or
THF. Thus, a three-coordinate gallium atom in compound 1
can be considered an unsaturated center, which, in theory,
could bind compact electron-rich moieties (e.g., carbon–
carbon multiple bonds). This concept has been realized[9]
and the data obtained are presented in this paper. We dem-
onstrate the possibility of the binding and activation of
alkyne triple bonds by gallium complex 1, which contains a
redox-active diimine ligand. We further show that alkynes
bound to complex 1 become reactive towards electron-rich
reagents, similar to olefins or arenes when coordinated to
transition metals.
sium, [(dpp-bian)MgACHTNUTRGNE(NUG thf)3], is an illustrative example. The
complex exhibits diverse reactivity towards various sub-
strates. In the course of the reactions of [(dpp-bian)Mg-
ACHTUNGTRENNUNG(thf)3] dramatic changes are noted in the electronic configu-
ration, atomic arrangements, and functionality (bis-amido,
amido-imino, amido-amino) of the dpp-bian ligand
(Scheme 1).[8]
Results and Discussion
Reactions of alkynes with (dpp-bian)Ga–Ga
ACHTUNGTRENUN(NG dpp-bian)
Characterization of complexes 2–5: Treatment of a solution
ꢁ
ꢁ
ꢁ
of 1 in toluene with HC CH, PhC CH, MeC CCO2Me, or
ꢁ
MeC CCO2Et at ambient temperature caused an instant
color change of the solution from deep-blue to red. All four
reactions proceed as [3+2] cycloadditions and afforded com-
pounds 2–5, respectively (Scheme 2). Digallane 1 is selective
toward alkynes and does not react with other substances
that contain multiple bonds, for example, H2C=
ꢁ
C(Me)CO2Me, Me2C=O, RC N (R=Me, Ph), and PhNC.
Among the possible mechanisms of alkyne addition to com-
plex 1, a concerted process—interaction of the LUMO (p*)
of the alkyne with the HOMO (p) of 1—seems to be the
most plausible. Products 2–5 were isolated as red crystals by
room temperature crystallization from diethyl ether (2), 1,2-
dimethoxyethane (3), or benzene (4, 5). Compounds 2–5
Scheme 1. Reactivity of [(dpp-bian)MgACHTNUGTRENUNG(thf)3]; coordinated solvent mole-
cules are omitted. TEMPO=2,2,6,6-tetramethylpiperidine N-oxide.
Because the reactivity of transition-metal complexes can
be fine-tuned by changing the nature of the spectator li-
gands, variation of the metal ion at the dpp-bian dianion
may change the reaction course. Switching from [(dpp-
bian)MgACHTUNGTRENNUNG(thf)3] to [(dpp-bian)Ga–GaHCATUNGTRENN(UGN dpp-bian)] (1) the
pathway for reaction with phenylacetylene changes from
acid–base interaction (Scheme 1) to 1,3-dipolar cycloaddi-
tions.[9] From a structural point of view, digallene 1 illus-
trates the influence of the conformational rigidity and elec-
Scheme 2. Reaction of 1 with alkynes.
256
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 255 – 266

Addition of Alkynes to a Gallium Bis-Amido Complex
FULL PAPER
have been characterized by elemental analysis, IR and
1H NMR spectroscopy, and X-ray crystallography.
In transition-metal chemistry there is a sole example of a
related isolable compound produced from the reaction of a
tion of R,R- and S,S-enantiomers, plus the R,S-diastereo-
mers for every addition. The 1H NMR spectrum of com-
1
pound 2 is depicted in Figure 1 (for the H NMR spectrum
ꢁ
very strong p-acceptor alkyne (MeO2CC CCO2Me) with a
zero-valent iron complex with N,O-chelating ligand [(tBuN=
ꢀ
C(H) C(Ph)=O)Fe(CO)
(dppe)]
(dppe=1,2-bis(diphenyl-
phosphino)ethane).[10] Frꢂhauf and co-workers established
the formation of kinetically unstable [3+2] cycloadducts in
the reactions of Fe-, Ru-, and Mn complexes of 1,4-diaza-
1,3-dienes (dads) with reagents that contained p-acceptor
multiple carbon–carbon and carbon–element bonds.[11] The
dad complexes of the transition metals are inert towards
ꢁ
ꢁ
less-reactive substrates, for example, PhC CH and HC CH.
Cycloaddition products related to compounds 2–5 have been
isolated from the reaction of aromatic ketones with dad
complexes of zirconium[12a] and samarium.[12b] In the same
manner, iridium[13a] and rhodium[13b] catecholates add dioxy-
gen across the metal–oxygen–carbon atom 1,3-dipole to give
isolable endoperoxides. In main-group-metal chemistry the
only example of a cycloaddition with reversible binding of
dioxygen was found to be mediated by triphenylstibiumcate-
cholate and -amidophenolate complexes.[14] Note that the re-
ꢀ
Figure 1. 1H NMR spectrum of complex 2 (293 K, 400 MHz, [D8]toluene).
of compound 3 see the Supporting Information). Both spec-
tra confirm the presence of only one isomer in toluene solu-
1
tion. The H NMR spectroscopic data obtained for 4 and 5
in [D8]toluene (see the Supporting Information) suggest the
presence of homochiral enantiomers (R,R and S,S) in solu-
tion, together with the R,S-diastereomers. These data are
consistent with the results of X-ray crystallography of com-
pounds 2–5 (see Figures 6–9 below). The asymmetry of the
ligands in 2–5 causes non-equivalence of the four methine
protons and eight methyl groups of the four isopropyl sub-
stituents. In complex 2, the methine protons give rise to four
septets (d=3.78, 3.60, 3.48, and 2.87 ppm) and the methyl
groups appear as eight doublet signals (d=1.64, 1.25, 1.24,
1.06, 0.83, 0.54, 0.47, and ꢀ0.03 ppm). The low-field singlet
actions of [(dpp-bian)MgACHTNUTRGENNG(U thf)3] with R X (Scheme 1) also
proceed by addition across the metal–ligand 1,3-dipole and
result in new carbon–carbon and magnesium–halide
bonds.[15] In the context of activation of carbon–carbon mul-
tiple bonds in main-group-metal complexes, the recently re-
ported addition of H2C=CH2 to the metal–metal triple bond
[16a]
ꢁ
in ArSn SnAr is remarkable.
Further, terminal alkynes
can be activated by systems comprised of Lewis pairs
(Scheme 3).[16b–d]
1
(d=7.93 ppm) in the H NMR spectrum of complex 3 is as-
signed to the proton at the C=C double bond, which origi-
ꢁ
nates from the C C triple bond of phenylacetylene.
The IR spectra of crystalline adducts 2–5 were recorded
in paraffin oil. The IR spectra of 2-ethylbutynoate and the
product of its addition to digallane 1 are presented in the
Supporting Information. The spectra of 2–5 reveal a strong
absorption at n˜ =1635ꢃ5 cmꢀ1, which corresponds to the
stretching vibrations of the carbon–nitrogen double bond. In
the IR spectrum of free dpp-bian, the corresponding C=N
vibrations appear in the range n˜ =1642–1670 cmꢀ1.[17] Fur-
ther, in the IR spectra of 2–5 the absorptions related to the
ꢁ
C C bond are absent. For instance, the carbon–carbon
triple bond of 2-ethylbutynoate gives rise to a very strong
absorption at n˜ =2242 cmꢀ1. The absorption arising from the
ester group in 5 is shifted by 15 cmꢀ1 to a lower wavenumber
relative to free 2-ethylbutynoate (n˜ =1711 cmꢀ1). In the IR
spectra of compounds 2–5 the carbon–carbon double bonds
that result from the cleavage of one of the p bonds of the al-
kynes cause absorptions of medium intensity at 1585ꢃ
2 cmꢀ1.
Scheme 3. Activation of phenylacetylene with Lewis pairs (A,[16b] B,[16c]
and C[16d]).
ꢀ ꢀ
Cycloaddition of alkynes across the Ga N C fragment in
1 makes one carbon atom in each metallacycle and both gal-
lium atoms chiral, thus there are four asymmetric centers in
dinuclear complexes 2–5. Hence, one may expect the forma-
Elimination of alkynes from complexes 2–5: Compounds 2
and 3 eliminate the corresponding alkyne in toluene solution
at elevated temperatures. The temperature-dependent equi-
Chem. Eur. J. 2012, 18, 255 – 266
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
257

G. A. Abakumov, I. L. Fedushkin et al.
ꢁ
librium in the systems [2] Ð [1 + 2 HC CH] and [3] Ð [1
ꢁ
+ 2 PhC CH] has been monitored by electron absorption
spectroscopy. The absorption spectrum of complex 2 in tolu-
ene at different temperatures is depicted in Figure 2; the
spectrum of compound 3 is provided in the Supporting In-
formation.
Figure 3. Temperature dependence of the absorption spectrum of com-
plex 4 in toluene.
Figure 2. Temperature dependence of the absorption spectrum of com-
plex 2 in toluene.
At 293 K the absorption maxima for 2 and 3 are located
at approximately 350 nm, which corresponds to the red
color of their toluene solutions. Upon raising the tempera-
ture, the intensity of this absorption gradually decreases
with a concurrent increase of the absorption at 585 nm,
which clearly indicates the formation of digallane 1.[18] For
the solutions of 2 and 3, the spectral pictures remain un-
changed at temperatures above 363 and 343 K, respectively,
indicative of full conversion of 2 and 3 into the correspond-
ing starting materials at those temperatures. The elimination
processes are reversible; lowering the temperature to 293 K
leads to restoration of the initial spectral image. However,
extended heating of solutions of 2 or 3 in toluene at reflux
or standing at ambient temperatures for more than one
month led to conversion of the alkynes to unidentified prod-
ucts and the regeneration of digallane 1, which is stable in
solution for an indefinite period of time. The heating of sol-
utions of 4 and 5 in toluene up to 373 K does not result in
any visible color change of the solution. However, the elec-
tron absorption spectroscopy allows detection of weak spec-
tral changes for a solution of 4 in toluene in the range of
293–373 K (Figure 3). In the case of 4, the alterations of the
absorption intensities are similar to those observed for solu-
tions of 2 and 3 at ambient temperature. In all three cases,
at the initial stages of the elimination processes intermediate
absorption at l=488 nm could be detected. We assign this
absorption to a species in which the alkyne has added to
only one of the two metal fragments.
Figure 4. The upfield region of the 1H NMR spectra of complex 3 in
[D8]toluene at a) 293 and b) 353 K.
of the eight doublets (each 3H) of the methyl groups in the
1H NMR spectrum of complex 3 by a broadened signal
(24H) centered at d=0.99 ppm (Figure 4b). The latter is a
result of coalescence of two methyl group doublets of the di-
gallane 1.
In the 1H NMR spectrum of compound 1 at 293 K in
C6D6 the analogous doublets (each 12H) appeared at d=
1.01 and 0.97 ppm.[18] The intensity of the four septets (each
1H) of the methine protons of the four isopropyl groups de-
creased with rising temperature. In parallel, a broad signal
(4H) at d=3.42 ppm grew (dꢄ3.47 ppm for 1 in C6D6 at
293 K). At each temperature chosen in the range 298–323 K,
an equilibrium constant (Keq) could be calculated from the
relative amounts of 1 and 3 at that given temperature, deter-
mined from the integrals of the methine and methyl proton
resonances in the 1H NMR spectra. The measured data
points give a straight line when plotting the reciprocal tem-
perature values against the natural logarithm of the equilib-
rium constants (see the Supporting Information). Assuming
that DH and DS are constant across the temperature range
298–323 K, the thermodynamic standard parameters for the
Because calculation of reliable equilibrium constants from
the UV/Vis data obtained for 2 and 3 is difficult we decided
to use 1H NMR spectroscopy for determination of these
1
constants. The upfield region of the H NMR spectrum of
complex 3 at 293 K is depicted in Figure 4a. Raising the
temperature from 293 to 353 K leads to gradual replacement
258
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 255 – 266

Addition of Alkynes to a Gallium Bis-Amido Complex
FULL PAPER
ꢁ
elimination of two PhC CH moieties from 3 are: DG8=
2.4 kJmolꢀ1, DH8=46.0 kJmolꢀ1, DS8=146.0 JKꢀ1 molꢀ1).
The positive value of DG indicates that complex 3 is ther-
modynamically more stable than digallane 1. The enthalpy
of the alkyne elimination for dinuclear complex 3 in toluene
(DH8=46.0 kJmolꢀ1) is rather small if a cleavage of two
carbon–carbon and two carbon–gallium bonds is assumed.
To gain more insight into the alkyne elimination we investi-
gated the solid-state behavior of complex 3. In a sealed glass
capillary, red crystals of complex 3 became dark blue when
heated to 373 K. As shown by thermal gravimetric analysis
(TGA), elimination of the alkyne from solid 3 begins at T>
373 K (Figure 5).
Figure 6. The molecular structure of complex 2. Selected bond lengths
ꢀ
ꢀ
ꢀ
[ꢀ]: Ga(1) Ga(2) 2.4067(4), Ga(1) N(1) 1.929(2), Ga(1) N(2) 2.190(2),
ꢀ
ꢀ
ꢀ
ꢀ
Ga(1) C(37) 1.994(3), N(1) C(1) 1.481(3), N(2) C(2) 1.280(3), C(1)
ꢀ
ꢀ
C(2) 1.550(3), C(1) C(38) 1.551(3), C(37) C(38) 1.316(3).
Figure 7. The molecular structure of complex 3. Selected bond lengths
Figure 5. TGA and DSC curves for complex 3 curve.
ꢀ
ꢀ
[ꢀ]: Ga(1)>C->Ga(2) 2.4052(3), Ga(1) N(1) 1.926(1), Ga(1) N(2)
ꢀ
ꢀ
ꢀ
2.173(1), Ga(1) C(37) 1.988(1), N(1) C(1) 1.476(2), N(2) C(2) 1.280(2),
ꢀ
ꢀ
ꢀ
C(1) C(2) 1.554(2), C(1) C(38) 1.575(2), C(37) C(38) 1.336(2).
In the temperature range 373–410 K, the crystals of 3 lose
approximately 16% of their mass, which corresponds to lib-
eration of two phenylacetylene molecules per dimeric com-
plex 3. Note, the temperature interval for elimination of the
alkyne unit from solid 3 is much narrower (ꢄ35 K) relative
to the interval in toluene solution (ꢄ70 K). We explain this
by the different conditions of the UV-VIS experiment
versus the TGA experiment. The spectroscopic measure-
ments were carried out in a sealed glass cell, whereas the
TGA experiment was conducted in a nitrogen flow that
purged the eliminated alkyne. Also, according to the differ-
ential scanning calorimetry (DSC) measurements, the heat
absorbed when the alkyne is eliminated from 3 in the solid
state (DH8=131.8 kJmolꢀ1, Figure 5) is about 30% higher
than in solution (DH8=94.8 kJmolꢀ1). This difference re-
flects the influence of the crystal-lattice energy on the elimi-
nation process.
ꢀ ꢀ
case, the alkyne adds across the Ga N C fragment to result
in carbon–carbon and carbon–gallium bond formation.
Increase in the coordination number of the gallium atoms
from three (1) to four (2–5) causes elongation of the Ga–Ga
bond by approximately 0.05 ꢀ relative to 1 (2.3598(3) ꢀ).[18]
The atoms C(1) and Ga(1), and their analogues in the
second part of the dimer, become chiral upon the cycloaddi-
tion of alkynes. The result is four asymmetric centers in the
dinuclear complexes 2–5. In the crystals, complexes 2 and 3
are represented as C-homochiral dimers (two pairs of R,R-
and S,S-enantiomers). In the case of compound 5, the unit
cell only includes a heterochiral dimer. Complex 4 repre-
sents the third case: the unit cell simultaneously consists of
two pairs of R,R- and S,S-enantiomers (C-homochiral
dimers) as well as the R,S diastereomer. The regioselectivity
of addition of alkynes to digallane 1 is controlled by elec-
tronic rather than steric factors. Thus, in complex 3, the
Crystal structures of complexes 2–5: The molecular struc-
tures of compounds 2–5 were determined by X-ray crystal-
lography at 100 K and are depicted in Figures 6–9. The crys-
tal data and structure-refinement details are collected in
Table 1. The crystal structures of 2–5 prove that, in each
ꢁ
bulkier Ph substituent at the C C triple bond is orientated
away from the metal (Figure 7), whereas in the case of 4
and 5 the bulkier ester group is orientated towards the
metal (Figures 8 and 9). The carbon–carbon triple bonds in
Chem. Eur. J. 2012, 18, 255 – 266
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
259

G. A. Abakumov, I. L. Fedushkin et al.
Table 1. Crystal data and structure refinement details for compounds 2–5.
Compound
2
3
4
5
Formula
Mr [gmolꢀ1
T [K]
C76H84Ga2N4
1192.91
100
C88H92Ga2N4·1.075 C4H10O2
1441.98
100
C82H92Ga2N4O4·C6H6
1415.14
100
C84H96Ga2N4O4·3C6H6
1599.47
100
]
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
monoclinic
P21/c
17.741(2)
26.137(3)
13.6513(17)
90
89.915(3)
90
6330.1(13)
4
1.252
0.898
2520
0.32ꢃ0.10ꢃ0.08
1.39/28
monoclinic
P21/n
17.3786(19)
26.579(3)
17.903(2)
90
108.121(2)
90
7859.1(15)
4
1.219
0.737
3055
0.34ꢃ0.25ꢃ0.22
1.43/29
monoclinic
C2/c
29.176(4)
12.985(2)
39.497(6)
90
100.678
90
14704(4)
8
1.279
triclinic
P1
¯
15.546(6)
15.791(6)
21.274(8)
70.086(7)
76.781(8)
61.731(6)
4310(3)
a [8]
b [8]
g [8]
V [ꢀ3]
Z
2
1calc, [gmꢀ3
]
1.232
0.680
1696
0.15ꢃ0.10ꢃ0.08
1.02/27.50
ꢀ19ꢂhꢂ20
ꢀ19ꢂkꢂ20
0ꢂlꢂ27
29553
m [mmꢀ1
(000)
]
0.788
5984
F
A
crystal size, [mm3]
qmin/qmax
0.12ꢃ0.10ꢃ0.10
1.42/27
ꢀ33ꢂhꢂ37
ꢀ16ꢂkꢂ16
ꢀ50ꢂlꢂ50
58589
index ranges
ꢀ23ꢂhꢂ23
ꢀ34ꢂkꢂ34
ꢀ17ꢂlꢂ18
50835
15272
0.0812
ꢀ23ꢂhꢂ23
ꢀ36ꢂkꢂ30
ꢀ24ꢂlꢂ24
73068
20873
0.0383
reflections collected
independent reflections
Rint
16047
0.0903
19808
0.0000
max/min transmission
data/restraints/parameters
GOF on F2
0.932/0.762
15272/0/755
1.006
0.855/0.788
20873/3/943
1.012
0.925/0.911
16047/0/879
0.956
0.948/0.905
29554/4/1028
0.993
final R indices [I>2s (I)]
R1 =0.0465
wR2 =0.0908
R1 =0.0898
wR2 =0.1059
0.539/ꢀ0.494
R1 =0.0388
wR2 =0.0890
R1 =0.0593
wR2 =0.0987
0.926/ꢀ0.511
R1 =0.0616
wR2 =0.1061
R1 =0.1475
wR2 =0.1355
0.648/ꢀ0.689
R1 =0.0883
wR2 =0.1518
R1 =0.2192
wR2 =0.2026
0.962/ꢀ0.843
R indices (all data)
largest diff. peak/hole [eꢀꢀ3
]
Figure 8. The molecular structure of complex 4. Selected bond lengths
ꢀ
ꢀ
ꢀ
[ꢀ]: Ga(1) Ga(2) 2.416(1), Ga(1) N(1) 1.904(3), Ga(1) N(2) 2.203(3),
ꢀ
ꢀ
ꢀ
ꢀ
Ga(1) C(37) 2.015(4), N(1) C(1) 1.465(5), N(2) C(2) 1.272(5), C(1)
ꢀ
ꢀ
C(2) 1.556(6), C(1) C(38) 1.574(6), C(37) C(38) 1.333(6).
Figure 9. The molecular structure of complex 5. Selected bond lengths
ꢀ
ꢀ
ꢀ
[ꢀ]: Ga(1) Ga(2) 2.419(1), Ga(1) N(1) 1.913(5), Ga(1) N(2) 2.193(5),
ꢀ
ꢀ
ꢀ
ꢀ
Ga(1) C(37) 2.020(6), N(1) C(1) 1.463(7), N(2) C(2) 1.282(7), C(1)
ꢀ
ꢀ
C(2) 1.556(8), C(1) C(38) 1.568(8), C(37) C(38) 1.335(7).
ꢁ
ꢁ
alkynes PhC CH and MeC CCO2R (R=Me, Et) are polar-
ized as shown in Figure 10. Interaction of the opposite
ꢀ ꢀ
charges of the alkynes with the Ga N C 1,3-dipole defines
the formation of the regioisomers that are observed.
slightly distorted trigonal planar environments of atoms
C(37) and C(38) are credited to their sp2 nature and the
C(37)=C(38) bond lengths (1.316(3)–1.336(2) ꢀ) correspond
ꢀ
A marked difference in the Ga N bond lengths within
ꢀ
each metallacycle in compounds 2–5 (Figures 6–9) reflects
perfectly to double bonds. The newly formed C(1) C(38)
the amido-imino character of the N-chelating fragment. The
bonds (1.551(3)–1.575(2) ꢀ) are longer than a typical single
260
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 255 – 266

Addition of Alkynes to a Gallium Bis-Amido Complex
FULL PAPER
responding imines 6b, 7b, and 9b–11b were obtained in
high yields (Table 2, entries 1, 2, and 4–6). However, 1 does
not catalyze the hydroamination of phenylacetylene with
anilines that possess alkyl substituents on the aromatic ring,
for example, 2,6-diisopropylphenylamine and 2,5-di-tert-bu-
tylphenylamine. Furthermore, the reaction rates of anilines
with a substituent ortho to the amino group (9a, 10a, and
12a) are remarkably low relative to the rates with meta- or
para-substituted anilines. These data indicate that ortho sub-
stituents effectively shield the aniline amino group, thus
making phenylacetylene unreactive towards these anilines,
even in the presence of 1. The difference in reactivity be-
tween closely related anilines 7a and 8a in the reaction with
phenylacetylene in the presence of catalytic 1 (Table 2,
entry 2 versus 3) seemed unusual at first glance. However, a
low yield of the hydroamination product 8b can be ex-
plained by the reaction of 8a with 1, which proceeds
ꢀ
Figure 10. Regioselectivity of the alkyne addition.
ꢀ
ꢀ
C C bond (1.54 ꢀ). The Ga(1) C(37) bond lengths
(1.988(1)–2.020(6) ꢀ) are comparable with those reported in
gallium–vinyl
(1.95(2) and 1.96(2) ꢀ)[19a] and 1,4-C6H
(tBu)2]2 (1.974(4) ꢀ).[19b] Considering the lengths of the
derivatives
[(CH2=CH)2Ga
G
ACHTUNGTRNE(NUNG tBu)2)]2
4A[HC=C
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
ꢀ
ꢀ
newly formed C C and C Ga bonds, the facile elimination
of alkynes from 2–5 observed at elevated temperatures is
very surprising.
Reactions of phenylacetylene with anilines catalyzed by
complex 1: New carbon–nitrogen bond-forming reactions
are of special interest, in both organic synthesis and industri-
al chemistry, because amines and their derivatives are im-
portant industrial chemicals.[20] The hydroamination of al-
kynes—addition of an NH unit to a carbon–carbon triple
bond—is a useful method to produce new nitrogen-contain-
ing organic compounds. Among other advantages, this syn-
thetic approach is attractive in terms of atom economy be-
cause the alkyne and amine combine to give a single prod-
uct without waste. Transition-metal complexes are the most
efficient catalysts for hydroamination of unsaturated sub-
strates, such as alkenes, alkynes, allenes, and dienes.[21] Ob-
taining a high regioselectivity of the addition with terminal
and internal asymmetric alkynes remains a problem. Chiral
lanthanide complexes display high activity in enantioselec-
tive intramolecular hydroamination.[22] Also, application of
non-transition-metal complexes as catalysts of hydroamina-
tion reactions has been reported. Thus, the a-diketiminate
derivatives of magnesium and calcium serve well as precata-
lysts for the hydroamination/cyclization of aminoalkenes.[23]
Roesky and co-workers have demonstrated the catalytic effi-
ciency of pyrrolyl and aminotroponiminate calcium and zinc
complexes in the intramolecular hydroamination of aminoal-
kenes.[24] Hydroamination reactions catalyzed by aluminum
or gallium complexes have not yet been reported but their
use as catalysts is attractive because these metals are readily
available and nontoxic. Taking the unique reactivity of di-
gallane 1 towards alkynes into account, assessment of the
catalytic activity of 1 in hydroamination of alkynes seemed
very reasonable. Catalyst complex 1 was tested in the reac-
through cleavage of the Br CACTHNGUTRENNU(G aryl) bond and oxidation of
the dpp-bian dianion to the radical anion. Finally, the reac-
tion results in destruction of the catalyst.
The reaction of 1-aminonaphthalene (13a) with phenyla-
cetylene catalyzed by digallane 1 gives two products in
nearly equimolar quantities. The first is the Markovnikov
hydroamination product 13b, the second is the hydroaryla-
tion product 13c, also formed according to Markovnikovꢄs
1
rule (Table 2, entry 8). The H NMR spectra of the mixture
of 13a and phenylacetylene before addition of digallane 1
and of the mixture after a full conversion of the reagents in
the presence of 1 are provided in the Supporting Informa-
tion. In the 1H NMR spectrum of the initial mixture, the
amino protons in the aniline unit and the proton at the
carbon–carbon triple bond of the alkyne give rise to singlet
signals at d=3.38 and 2.76 ppm, respectively. The methyl
1
group in 13b is represented in the H NMR spectrum by a
resonance at d=1.78 ppm. The protons of the H2N group in
13c appear in the 1H NMR spectrum at d=3.79 ppm and
two signals at d=5.30 and 5.74 ppm correspond to the two
diastereotopic protons at the carbon–carbon double bond.
The course of the reaction of 1-aminoanthracene (14a),
with phenylacetylene catalyzed by digallane 1 changes to
give exclusive formation of the hydroarylation product 14b,
which has been isolated and characterized (including by
single-crystal X-ray analysis). Note, insertions of acetylenes
into aromatic carbon–hydrogen bonds catalyzed by Rh and
Ru complexes have been reported.[25] The crystal data and
structure refinement details for compounds 7b and 14b are
reported in Table 3, their molecular structures are depicted
in Figures 11 and 12, respectively. The crystal data confirm
the formation of the Markovnikov hydroamination product
ꢁ
tions of PhC CH with a series of anilines. All of the reac-
ꢀ
ꢀ
tions were performed with 1 (2 mol%) in C6D6 in an NMR
tube. The results are summarized in Table 2. The reactions
presented in Table 2, entries 2 and 9, were also carried out
on a preparative scale and products 7b and 14b were isolat-
ed and characterized (including by X-ray crystallography).
We have found that 1 serves well as a Markovnikov-selec-
7b. The C C and C N bond lengths in 7b are in the range
expected for an organic compound. Restricted rotation
ꢀ
around the C(14) C(15) bond in 14b causes the existence of
two enantiomers.
Notably, the hydroamination of alkynes with anilines de-
scribed above is relevant in Kutcherovꢄs hydration of acety-
lenes.[26] We suggest that, similar to alkyne hydration,[27] the
amination of alkynes proceeds by nucleophile attack of
ꢁ
tive catalyst for the hydroamination of PhC CH by various
anilines. Starting from anilines 6a, 7a, and 9a–11a, the cor-
Chem. Eur. J. 2012, 18, 255 – 266
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
261

G. A. Abakumov, I. L. Fedushkin et al.
Table 2. Reaction of phenylacetylene with anilines, catalyzed by complex 1.
quite interesting. In the pres-
ence of Et3Ga (50 mol%), phe-
nylacetylene reacts with 4-
chloroaniline (7a) to give hy-
droamination product 7b in
99% yield within 30 h. Compa-
ratively,
with
catalyst
1
(2 mol%), compound 7b can
be obtained in quantitative
yield after 6 h. Note, in the
presence of Et3Ga (10 mol%)
ꢁ
no reaction between PhC CH
Entry
1
Aniline
Product
t [h]
T [8C]
Yield [%]
and 7a could be observed over
50 h at 1108C. For the phenyla-
cetylene/14a system two differ-
ent reaction routes were ob-
served, dependent on whether
digallane 1 or GaCl3 was em-
6a
6b
16
90
>99
2
3
7a
8a
7b
8b
6
110
110
>99
ployed
(Scheme 4). Under equivalent
reaction conditions (C6D6,
as
the
catalyst
90
19
908C, 18 h), the amine 14a and
4
5
6
9a
9b
50
200
18
110
110
110
98
95
92
ꢁ
PhC CH react catalyzed by 1
(2 mol%) to afford the hydro-
arylation product 14b in nearly
quantitative yield, whereas
these reagents interact under
GaCl3 (5.2 mol%) catalysis to
give the hydroamination prod-
uct 14c in only 55% yield
(Scheme 4).
10a
11a
10b
11b
The difference in activity be-
tween 1, Et3Ga, and GaCl3 as
catalysts in the reactions of
7
12a
12b
13b
66
90
13
48
ꢁ
PhC CH with anilines suggests
that the kinetically active spe-
cies generated from these galli-
um compounds have a different
nature and catalyze the reac-
tions by different mechanisms.
The most important observa-
tion is that a combination of
8
9
13a
14a
12
18
90
90
13c
14b
52
>99
the
redox-active
dpp-bian
ligand with gallium resulted in
catalytic systems with much
higher efficiency than that of
ArNH2 on the activated/coordinated alkyne. A change of
the reaction course from hydroamination (for 6a<Pr>6b)
to hydroarylation of phenylacetylene (13a<Pr>13c and
14a<Pr>14b) leads to the conclusion that, in the series
considered, the nucleophilic character of the carbon atom
ortho to the amino group increases with extension of the p
system. Additionally, the nucleophilic character of the
ortho-carbon atom becomes comparable, or even stronger,
than that of the nitrogen atom of the amino group.
typical Lewis acids. Further, the activity of 1 as a catalyst is
comparable to catalysts based on transition metals, for ex-
ample, [Ir(bispyrazolylemethane)(CO)2]
bis(trifluoromethyl)phenyl),[28]
[(3-iminophosphine)Pd-
(allyl)] (NMe2)4 (Table 4).
[OSO2CF3],[29] and Ti
We suggest that hydroamination of PhC CH with anilines
ACHTUNGRTEN[NUNG BArF4] (Ar=3,5-
[30]
N
N
ACHTUNGTRENNUNG
ꢁ
catalyzed by 1 proceeds through attack of the carbon atom
at the double bond of the stable intermediate 3 by aniline
(Scheme 5), similar to Kutcherovꢄs hydration reaction.
The resulting intermediate I undergoes proton transfer to
afford intermediate II, which is unstable due to its constrain-
Comparison of the catalytic activity of complex 1 with
simple gallium compounds, such as Et3Ga and GaCl3, is
262
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 255 – 266

Addition of Alkynes to a Gallium Bis-Amido Complex
FULL PAPER
Table 3. Crystal data and structure refinement details for compounds 7b
and 14b.
Compound
7b
14b
Formula
Mr [gmolꢀ1
T [K]
C14H12ClN
229.70
150
C22H17N
295.37
100
]
crystal system
space group
a [ꢀ]
b [ꢀ]
c [ꢀ]
monoclinic
P21/n
14.0214(12)
13.8297(12)
18.1938(15)
90
monoclinic
P2/1
6.2024(3)
13.0085(6)
9.3124(5)
90
a [8]
b [8]
98.143(2)
90
3492.4(5)
12
1.311
0.298
92.6940(10)
90
750.53(6)
2
1.307
0.075
g [8]
V [ꢀ3]
Z
Scheme 4. Comparison of the catalytic activity of digallane 1 and GaCl3
in the reaction of 1-aminoanthracene with phenylacetylene.
1calc, [gmꢀ3
]
m [mmꢀ1
(000)
]
F
A
1440
312
crystal size [mm3]
qmin/qmax
0.37ꢃ0.35ꢃ0.33
2.08/26.00
ꢀ17ꢂhꢂ17
ꢀ12ꢂkꢂ17
ꢀ22ꢂlꢂ22
19551
0.38ꢃ0.18ꢃ0.18
2.19/25.98
ꢀ7ꢂhꢂ7
ꢀ16ꢂkꢂ15
ꢀ11ꢂlꢂ8
4548
Table 4. Comparison of the catalytic activity of digallane 1 with transi-
ꢁ
tion-metal complexes in the reaction of PhC CH with phenylamine.
index ranges
Entry Catalyst
mol% t [h] T [8C] Yield [%]
1
2
3
4
1
[Ir
G
2
5
5
16
22
22
2
90
60
70
75
100
57
75
N
[BArF4][a]
[OTf][b]
reflections collected
independent reflections
Rint
6855
0.0489
2535
0.0229
E
N
A
10
49
max/min transmission
data/restraints/parameters
GOF on F2
0.9082/0.8979
6855/0/436
0.946
0.9865/0.9719
2535/1/224
1.040
[a] bpm=bispyrazolylmethane,
[b] 3-IP=3-iminophosphine, Tf=trifluoromethanesulfonyl.
ArF=3,5-bis(trifluoromethyl)phenyl;
final R indices [I>2s(I)]
R1 =0.0499
wR2 =0.0975
R1 =0.1064
wR2 =0.1116
0.358/ꢀ0.220
R1 =0.0363
wR2 =0.0948
R1 =0.0376
wR2 =0.0960
0.210/ꢀ0.149
R indices (all data)
largest diff. peak/hole [eꢀꢀ3
]
Figure 11. The molecular structure of complex 7b. Selected bond lengths
ꢀ
ꢀ
ꢀ
ꢀ
[ꢀ]: N(1) C(7) 1.279(3), N(1) C(9) 1.422(3), C(6) C(7) 1.491(3), C(7)
C(8) 1.509(3).
Scheme 5. Hydroamination of phenylacetylene with anilines catalyzed by
1.
ꢀ
ꢀ
ed structure and weakened C C and C Ga bonds. Structure
II represents the case in which an olefin is added across the
ꢀ ꢀ
Ga N C 1,3-dipole but, as discussed above, complex 1 is
inert towards olefins and non-alkyne organic substances that
contain multiple carbon–carbon and carbon–element bonds.
Elimination of the a-aminoolefin regenerates catalyst 1. The
a-aminoolefin isomerizes to afford the final imine product
(Scheme 5).
Figure 12. The molecular structure of complex 14b. Selected bond lengths
ꢀ
ꢀ
ꢀ
[ꢀ]: N(1) C(1) 1.396(2), C(1) C(14) 1.380(2), C(14) C(15) 1.501(2),
ꢀ
ꢀ
C(15) C(16) 1.335(2), C(15) C(17) 1.491(2).
Chem. Eur. J. 2012, 18, 255 – 266
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
263

G. A. Abakumov, I. L. Fedushkin et al.
An immediate color change from deep-blue to red was observed. Toluene
was removed under vacuum and the residue was dissolved in Et2O. Crys-
tallization from Et2O afforded complex 2 as red crystals (0.43 g, 72%).
M.p. >1008C (dec); 1H NMR (400 MHz, [D8]toluene, 258C, TMS): d=
7.96 (d, 3J=9.2 Hz, 1H; arom.), 7.33 (d, 3J=8.2 Hz, 1H; arom.), 7.24 (d,
3J=8.2 Hz, 1H; arom.), 7.22–7.20 (m, 3H; arom.), 7.10–7.08 (m, 3H;
arom.), 6.94 (pst, 3J=7.6 Hz, 1H; arom.), 6.91 (dd, 3J=9.2, 3.1 Hz, 1H;
arom.), 6.80 (pst, 3J=7.6 Hz, 1H; arom.), 6.61 (d, 3J=7.0 Hz, 1H;
arom.), 6.45 (d, 3J=7.0 Hz, 1H; arom.), 3.78 (sept, 3J=6.8 Hz, 1H; CH-
Conclusion
Combining main-group metals with redox-active ligands
allows the design of metal complexes with reactivity that re-
sembles that of redox-active transition-metal complexes
with redox-inactive spectator ligands. As shown by the reac-
tions of bis-amide gallium complex 1 with a series of alkynes
the coordination of p bonds becomes possible by a molecu-
lar assembly that comprises of a main-group metal and
redox-active ligand. The system (dpp-bian)/gallium is exclu-
sively selective towards alkynes. We believe that addition of
an alkyne to complex 1 proceeds as a concerted process that
involves the LUMO (p*) of the alkyne and the HOMO (p)
of the digallane 1. However, it is still inexplicable why al-
kenes, nitriles, ketones, and isonitriles do not react with 1.
We believe the situation can be altered by replacement of
the substituents at the nitrogen atoms with stronger elec-
tron-donating groups. Variation of the metal may also dra-
matically influence the reactivity of the dpp-bian dianion.
We have already demonstrated that reaction of diallane
ꢁ
ACHUTNGRENNUG CAHTUNGTRENNUNG
(CH3)2), 3.60 (sept, 3J=6.8 Hz, 1H; CH
1H; CH
G
ACHTUNGTRENNUNG
3
3
6.8 Hz, 3H; CH
6.8 Hz, 3H; CH
6.8 Hz, 3H; CHACHTUNTRGENNUG(CH3)2), 0.54 (d, J=6.8 Hz, 3H; CHACHTUGNTRENNNUG
ACHTUTGNRENNGU(CH3)2), 1.25 (d, J=6.8 Hz, 3H; CHAHCUTNGTREN(NUGN CH3)2), 1.24 (d, J=
ACHUTNGRENU(NG CH3)2), 1.06 (d, J=6.8 Hz, 3H; CHACHTUNGTERN(NUGN CH3)2), 0.83 (d, J=
3
3
3
3
6.8 Hz, 3H; CH
N
ACHTUNGTRENNUNG
(nujol): n˜ =1640 (vs), 1586 (m), 1360 (s), 1324 (m), 1310 (m), 1274 (m),
1254 (s), 1207 (w), 1187 (m), 1157 (w), 1100 (m), 1058 (w), 1040 (s), 1004
(w), 977 (w), 934 (s), 903 (w), 861 (m), 832 (m), 799 (s), 781 (vs), 754 (s),
715 (s), 644 (w), 617 (w), 603 (w), 578 (w), 545 (w), 521 (w), 497 (w),
462 cmꢀ1 (m); elemental analysis calcd (%) for C76H84Ga2N4 (1192.91): C
76.52, H 7.10; found: C 76.41, H 6.98.
Compound 3: Phenylacetylene (0.1 g, 1.0 mmol) was added to a solution
of complex
1 [generated in situ from dpp-bian (0.5 g)] in toluene
(30 mL). The mixture turned red immediately. Toluene was removed
under vacuum and the residual solid was crystallized from 1,2-dimethoxy-
ethane. Complex 3 was isolated as red crystals (0.52 g, 78%). M.p.
(dpp-bian)Al–AlACHTUNGTRENNUNG(dpp-bian) with PhC CH proceeds as 1,3-
dipolar cycloaddition but affords a thermally stable regioiso-
mer, in which the phenyl ring is oriented towards the metal.
The results of hydroamination/hydroarylation of PhC CH
1
>1008C (dec); H NMR (400 MHz, [D8]toluene, 258C, TMS): d=7.93 (s,
1H; H(Ga)C=C(C)Ph), 7.38 (d, 3J=8.0 Hz, 1H; arom.), 7.24–7.18 (m,
2H; arom.), 7.13 (d, 3J=8.0 Hz, 1H; arom.), 7.10–7.06 (m, 3H; arom.),
6.90 (dd, 3J=6.5, 2.0 Hz, 1H; arom.), 6.84 (pst, 3J=7.8 Hz, 1H; arom.),
6.66 (pst, 3J=7.8 Hz, 1H; arom.), 6.61 (pst, 3J=7.3 Hz, 1H; arom.), 6.57
(m, 3H; arom.), 6.49 (m, 2H; arom.), 6.38 (d, 3J=6.8 Hz, 1H; arom.),
ꢁ
with anilines catalyzed by complex 1 are promising. The re-
action rates are comparable with other catalytic systems,
which include those based on transition metals. We believe
that use of co-catalysts or additives can optimize the process.
Kinetic experiments will give more insight into the mecha-
nisms of the reactions of alkynes with anilines. We intend to
involve other electron-rich substrates, for instance, disul-
fides, thiols, and phosphines, in the reactions with alkynes in
the presence of 1.
4.28 (sept, 3J=6.8 Hz, 1H; CH
(CH3)2), 3.44 (sept, 3J=6.8 Hz, 1H; CH
ACHTUNGTRENNUNG
ACHTUNGTRENNUNG
G
3
3
1H; CH
3H; CH
3H; CH
G
(CH3)2), 1.39 (d, J=6.8 Hz,
3
3
ACHTUGNTRENUN(GN CH3)2), 1.10 (d, J=6.8 Hz,
3
(CH3)2), 0.61 (d, J=6.8 Hz,
3
3H; CH
A
(CH3)2), ꢀ0.12 ppm (d, J=
6.8 Hz, 3H; CHCAHTUNGTRENNNUG
1485 (m), 1418 (m), 1362 (m), 1323 (w), 1309 (w), 1256 (m), 1208 (w),
1188 (m), 1157 (w), 1143 (w), 1107 (m), 1078 (w), 1041 (m), 1032 (m),
1003 (w), 968 (w), 938 (w), 895 (w), 861 (m), 833 (m), 816 (w), 802 (m),
783 (s), 752 (s), 698 (s), 676 (m), 658 (m), 612 (w), 589 (w), 557 (w), 481
(w), 463 cmꢀ1 (w); elemental analysis calcd (%) for C88H92Ga2N4·C4H10O2
(1435.27): C 76.99, H 7.16; found: C 76.81, H 7.07.
Experimental Section
General remarks: All manipulations were carried out under vacuum by
using Schlenk techniques. Diethyl ether, 1,2-dimethoxyethane, THF, ben-
zene, and toluene were condensed into the reaction flask from sodium/
benzophenone prior to use. Deuterated solvents [D8]THF, [D6]benzene,
and [D8]toluene (Aldrich) were distilled at ambient temperature over
sodium/benzophenone and, just prior to use, condensed under vacuum
into NMR tubes that contained the compound to be analyzed. NMR
spectra were obtained on Bruker DPX 200 and Bruker Avance III spec-
trometers; arom.=aromatic, d=doublet, m=multiplet, t=triplet, pst=
pseudotriplet, s=singlet, sept=septet. UV spectra were recorded on a
Perkin–Elmer l 25 spectrometer. IR spectra (4000–400 cmꢀ1) were ob-
tained on Specord M-80 in Nujol; (vs) very strong, (s) strong, (m)
medium, (w) weak. Diimine dpp-bian was prepared according to a litera-
ture procedure.[17] Differential scanning calorimetry (DSC) was carried
out on a DSC 200 PC (NETZSCH) under nitrogen. Thermal gravimetric
analysis (TGA) was carried out on a Pyris 6 TGA under nitrogen at a
heating rate of 58C minꢀ1. Melting points were determined in sealed ca-
pillaries: dec=decomposition. Complex 1 was prepared by reaction of
dpp-bian (0.5 g, 1.0 mmol) with gallium metal (4 g, 57 mmol) in toluene
(30 mL) at reflux temperature, then used in situ. The yields of 2–5 are
calculated based on the amount of dpp-bian used for the preparation of
1.
Compound 4: Methyl-2-butynoate (0.1 g, 1.0 mmol) was added to a solu-
tion of 1 (generated in situ from dpp-bian (0.5 g)] in toluene (30 mL). An
instant color change from deep-blue to red was observed. The solvent
was evaporated under vacuum. Crystallization from benzene afforded
complex 4 as red crystals (0.46 g, 65%). M.p. >1508C (dec); 1H NMR
(200 MHz, [D8]THF, 258C, TMS): d=7.97 (d, 3J=8.3 Hz, 1H; arom.),
7.71 (d, 3J=8.3 Hz, 1H; arom.), 7.40–7.18 (m, 5H; arom.), 7.11 (dd, 3J=
6.8, 2.0 Hz, 1H; arom.), 6.98 (pst, 3J=7.5 Hz, 1H; arom.), 6.71 (d, 3J=
7.3 Hz, 1H; arom.), 6.18 (d, 3J=7.3 Hz, 1H; arom.), 6.14 (d, 3J=7.3 Hz,
1H; arom.), 4.69 (sept, 3J=6.8 Hz, 1H; CH
ACHTUNGTRENNUNG
(CH3)2), 2.83 (sept, 3J=6.8 Hz, 1H; CH
CHACTHNUGTRENNGNU ACHTUNGTRENNUNG
CH3C(C)=C(Ga)CO2CH3), 1.15 (d, 3J=6.8 Hz, 6H; CH
G
3
3J=6.8 Hz, 3H; CH
(CH3)2), 0.68 (d, J=6.8 Hz, 3H; CH
N
G
Compound 5: Ethyl-2-butynoate (0.11 g, 1 mmol) was added to a solution
of complex 1 [generated in situ from dpp-bian (0.5 g)]. The color of the
reaction mixture changed rapidly from deep-blue to red. Toluene was re-
Compound 2: Acetylene (24 mL, 1.1 mmol) was added to a solution of
complex 1 [generated in situ from dpp-bian (0.5 g)] in toluene (30 mL).
264
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 255 – 266

Addition of Alkynes to a Gallium Bis-Amido Complex
FULL PAPER
moved under vacuum and the residue was dissolved in benzene. Slow
evaporation of the solvent under vacuum gave 5 as red crystals (0.54 g,
73%). M.p. >1508C (dec); 1H NMR (200 MHz, [D8]THF, 258C, TMS):
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.
3
3
d=7.94 (d, J=8.3 Hz, 1H; arom.), 7.68 (d, J=8.3 Hz, 1H; arom.), 7.38–
7.26 (m, 3H; arom.), 7.21 (d, 3J=6.6 Hz, 1H; arom.), 7.13 (dd, 3J=6.3,
2.7 Hz, 1H; arom.), 7.00–6.88 (m, 2H; arom.), 6.68 (pst, 3J=4.8 Hz, 1H;
arom.), 6.26 (d, 3J=7.0 Hz, 1H; arom.), 6.15 (d, 3J=7.3 Hz, 1H; arom.),
4.37 (m, 1H; CH3C(C)=C(Ga)CO2CH2CH3), 4.20 (m, 1H; CH3C(C)=
Acknowledgements
C(Ga)CO2CH2CH3), 3.82 (sept, 3J=6.8 Hz, 1H; CH
3J=6.8 Hz, 1H; CH(CH3)2), 3.16 (sept, 3J=6.8 Hz, 1H; CH
(sept, 3J=6.8 Hz, 1H; CH(CH3)2), 1.27 (d, 3J=6.8 Hz, 6H; CH
1.25 (d, 3J=6.8 Hz, 3H; CH
(CH3)2), 1.25 (s, 3H; CH3C(C)=C(Ga)-
CO2CH2CH3), 1.17 (m, 3H; CH3C(C)=C(Ga)CO2CH2CH3), 1.09 (d, 3J=
ACHTUNGTRENNUNG
This work was supported by the Russian Ministry of Education and Sci-
ence (contract no. 14.740.11.0613), the Russian Foundation for Basic Re-
search (grant no. 11–03–01184), and the Alexander von Humboldt foun-
dation (partnership project between G.A. Razuvaev, Institute of Organo-
metallic Chemistry, and the Technical University of Berlin). The authors
thank Prof. K. A. Lyssenko, Dr. A. S. Shavyrin, Mrs. T. I. Lopatina, and
Dr. A. V. Arapova for assistance with X-ray analysis, NMR spectroscopy,
TGA, and DSC experiments, respectively. We thank Dr. E. C. E. Rosen-
thal for fruitful discussions.
U
ACHTUNGTRENNUNG
A
ACHTUNGTRENNUNG
AHCTUNGTRENNUNG
3
3
6.8 Hz, 3H; CH
6.8 Hz, 3H; CHACHTUNGTRENNUNG(CH3)2), 0.64 (d, J=6.8 Hz, 3H; CHACHTUGNTRENNNUG
ACHTUNGTRENNUNG(CH3)2), 0.84 (d, J=6.8 Hz, 3H; CHAHCUTNGTREN(NUGN CH3)2), 0.77 (d, J=
3
3
6.8 Hz, 3H; CH
N
ACHTUNGTRENNUNG
(nujol): n˜ =1698 (s), 1635 (s), 1585 (m), 1314 (m), 1251 (s), 1227 (s), 1188
(m), 1138 (m), 1108 (w), 1099 (w), 1036 (s), 968 (w), 935 (w), 902 (w),
858 (m), 831 (m), 798 (m), 780 (s), 758 (s), 675 (vs), 592 (w), 547 (m), 525
(w), 489 (m), 463 cmꢀ1 (w); elemental analysis calcd (%) for
C84H96Ga2N4O4·3C6H6 (1599.47): C 76.59, H 7.18; found: C 75.15, H 7.22.
[1] a) R. van Asselt, E. E. C. G. Gielens, R. E. Rulke, C. J. Elsevier, J.
Chem. Soc. Chem. Commun. 1993, 1203–1205; b) R. van Asselt, K.
Vrieze, C. J. Elsevier, J. Organomet. Chem. 1994, 480, 27–40; c) R.
van Asselt, C. J. Elsevier, W. J. J. Smeets, A. L. Spek, R. Benedix,
Recl. Trav. Chim. Pays-Bas 1994, 113, 88–98; d) R. van Asselt, C. J.
Elsevier, Organometallics 1994, 13, 1972–1980; e) R. van Asselt,
C. J. Elsevier, W. J. J. Smeets, A. L. Spek, Inorg. Chem. 1994, 33,
1521–1531; f) R. van Asselt, E. Rijnberg, C. J. Elsevier, Organome-
tallics 1994, 13, 706–720; g) R. van Asselt, E. E. C. G. Gielens, R. E.
Rulke, K. Vrieze, C. J. Elsevier, J. Am. Chem. Soc. 1994, 116, 977–
985.
[2] a) V. Rosa, C. I. M. Santos, R. Welter, G. Aullon, C. Lodeiro, T.
Aviles, Inorg. Chem. 2010, 49, 8699–8708; b) M. J. Sgro, D. W. Ste-
phan, Dalton Trans. 2010, 39, 5786–5794; c) S. I. Pascu, G. Balazs,
J. C. Green, M. L. H. Green, I. C. Vei, J. E. Warren, C. Windsor,
Inorg. Chim. Acta 2010, 363, 1157–1172; d) J. Parmene, A. Krivo-
kapic, M. Tilset, Eur. J. Inorg. Chem. 2010, 1381–1394; e) C. Zuc-
caccia, G. Bellachioma, G. Ciancaleoni, A. Macchioni, D. Zuccaccia,
Inorg. Chim. Acta 2010, 363, 595–600; f) K. M. Clark, J. W. Ziller,
A. F. Heyduk, Inorg. Chem. 2010, 49, 2222–2231; g) T. Kern, U.
Monkowius, M. Zabel, G. Knoer, Eur. J. Inorg. Chem. 2010, 4148–
4156; h) B. L. Small, R. Rios, E. R. Fernandez, D. L. Gerlach; J. A.
Halfen, M. J. Carney, Organometallics 2010, 29, 6723–6731; J. A.
Halfen, M. J. Carney, Organometallics 2010, 29, 6723–6731; i) S.
Park, T. Okada, D. Takeuchi, K. Osakada, Chem. Eur. J. 2010, 16,
8662–8678; j) C. Chen, R. F. Jordan, J. Am. Chem. Soc. 2010, 132,
10254–10255; k) C. Chen, S. Luo, R. F. Jordan, J. Am. Chem. Soc.
2010, 132, 5273–5284; l) Y. Miyamura, K. Kinbara, Y. Yamamoto,
V. K. Praveen, K. Kato, M. Takata, A. Takano, Y. Matsushita, E.
Lee, M. Lee, T. Aida, J. Am. Chem. Soc. 2010, 132, 3292–3294.
[3] For a review article on main-group metal complexes of bian ligands,
see: N. J. Hill, I. Vargas-Baca, A. H. Cowley, Dalton Trans. 2009,
240–253.
Reaction of anilines with phenylacetylene: Phenylacetylene and amines
were purchased from Aldrich. 2,4-Dimethoxyaniline was purified by re-
crystallization from hexane. Liquid amines were distilled from CaH2.
Phenylacetylene was degassed and stored over molecular sieves (4 ꢀ).
Samples were prepared in NMR tubes under vacuum by dissolving the
catalyst
(1.0 mmol) in [D6]benzene (0.5 mL). The NMR tubes were sealed under
vacuum and then placed in temperature-controlled oil bath (90–
1
(0.02 mmol), phenylacetylene (1.0 mmol), and amine
a
1
1108C). Conversion of the reagents was monitored by H NMR spectros-
copy. The ratio between the reagents and the product was calculated
from the integral intensities of the corresponding signals.
Compound 7b: Complex 1 (0.22 g, 0.2 mmol) was added to a solution of
phenylacetylene (1.0 g, 10 mmol) and 4-chloroaniline (1.28 g, 10 mmol) in
benzene (30 mL). The color of the solution turned red. The reaction mix-
ture was heated at reflux temperature (1108C) for 6 h and the solution
changed color from red to dark-brown. Benzene was removed under
vacuum and the residue was dissolved in n-hexane. Slow evaporation of
the solvent afforded complex 7b as colorless crystals. 1H NMR
(200 MHz, CDCl3, 258C, TMS): d=7.96 (m, 2H; arom.), 7.46 (m, 3H;
arom.), 7.32 (d, 3J=8.5 Hz, 2H; arom.), 6.74 (d, 3J=8.5 Hz, 2H; arom.),
2.24 ppm (s, 3H; N=CACTHNUTRGNE(UNG CH3)Ph); elemental analysis calcd (%) for
C14H12ClN (229.70): C 85.33, H 5.22; found: C 84.96, H 5.07.
Compound 14b: Complex 1 (0.22 g, 0.2 mmol) was added to a solution of
phenylacetylene (1.0 g, 10 mmol) and 1-aminoanthracene (2.95 g,
10 mmol) in benzene (30 mL). The mixture turned red immediately. The
reaction mixture was heated at reflux temperature (908C) for 18 h and
the solution changed color from red to dark-brown. Benzene was re-
moved under vacuum and the residual solid was crystallized from n-
hexane. Complex 14b was isolated as colorless crystals. 1H NMR
(400 MHz, CDCl3, 258C, TMS): d=8.42 (d, 3J=4.5 Hz, 2H; arom.), 8.02
(dd, 3J=7.0 Hz, 2H; arom.), 7.50 (m, 5H; arom.), 7.37 (m, 3H; arom.),
7.27 (d, 3J=8.5 Hz, 1H; arom.), 6.03 (d, 3J=1.26 Hz, 1H; HC=C(Ph)),
5.55 (d, 3J=1.26 Hz, 1H; HC=C(Ph)), 4.42 ppm (s, 2H; NH2); elemental
analysis calcd (%) for C22H17N (295.37): C 89.38, H 5.76; found: C 89.47,
H 5.63.
[4] I. L. Fedushkin, A. A. Skatova, V. A. Chudakova, G. K. Fukin,
Angew. Chem. 2003, 115, 3416–3420; Angew. Chem. Int. Ed. 2003,
42, 3294–3298.
[5] I. L. Fedushkin, V. M. Makarov, V. G. Sokolov, G. K. Fukin, Dalton
Trans. 2009, 8047–8053.
Single-crystal X-ray structure determination of 2–5, 7b, and 14b: The
data were collected on a Bruker APEX II CCD diffractometer (2–5) or a
Bruker SMART APEX diffractometer (7b, 14b). In both diffractometers,
graphite monochromated MoKa radiation (w-scan technique, l=
0.71073 ꢀ) was used. The structures were solved by direct methods by
using SHELXS-97[31] and were refined on F2 with SHELXL-97.[32]
SADABS[33] was used to perform area-detector scaling and absorption
corrections. All non-hydrogen atoms were refined anisotropically. The
hydrogen atoms were placed in calculated positions and assigned to an
isotropic displacement parameter of 0.08 ꢀ2. CCDC-770785 (2), CCDC-
770786 (3), CCDC-770787 (4), CCDC-770788 (5), CCDC-836606 (7b),
and CCDC-836607 (14b) contain the supplementary crystallographic
[6] a) 120 complexes of bians with Group 1, 2, 13, and 14 metals are re-
ported; b) 22 complexes of bians with lanthanides are reported. For
full lists of references see the Supporting Information.
[7] W. I. Dzik, J. I. van der Vlugt, J. N. H. Reek, B. de Bruin, Angew.
Chem. 2011, 123, 3416–3418; Angew. Chem. Int. Ed. 2011, 50, 3356–
3358.
[8] a) I. L. Fedushkin, N. M. Khvoinova, A. A. Skatova, G. K. Fukin,
Angew. Chem. 2003, 115, 5381–5384; Angew. Chem. Int. Ed. 2003,
42, 5223–5226; b) I. L. Fedushkin, A. A. Skatova, V. K. Cherkasov,
V. A. Chudakova, S. Dechert, M. Hummert, H. Schumann, Chem.
Eur. J. 2003, 9, 5778–5783; c) I. L. Fedushkin, A. A. Skatova, A. N.
Lukoyanov, V. A. Chudakova, S. Dechert, M. Hummert, H. Schu-
Chem. Eur. J. 2012, 18, 255 – 266
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.chemeurj.org
265

G. A. Abakumov, I. L. Fedushkin et al.
mann, Russ. Chem. Bull. 2004, 53, 2751–2762; d) I. L. Fedushkin,
A. A. Skatova, M. Hummert, H. Schumann, Eur. J. Inorg. Chem.
2005, 1601–1608; e) I. L. Fedushkin, A. G. Morozov, O. V. Rassadin,
G. K. Fukin, Chem. Eur. J. 2005, 11, 5749–5757; f) I. L. Fedushkin,
A. A. Skatova, G. K. Fukin, M. Hummert, H. Schumann, Eur. J.
Inorg. Chem. 2005, 2332–2338; g) I. L. Fedushkin, A. G. Morozov,
V. A. Chudakova, G. K. Fukin, V. K. Cherkasov, Eur. J. Inorg.
Chem. 2009, 4995–5003; h) I. L. Fedushkin, A. S. Nikipelov, A. A.
Skatova, O. V. Maslova, A. N. Lukoyanov, G. K. Fukin, A. V. Cher-
kasov, Eur. J. Inorg. Chem. 2009, 3742–3749.
Angew. Chem. 2011, 123, 4011–4014; Angew. Chem. Int. Ed. 2011,
50, 3925–3928.
[17] A. A. Paulovicova, U. El-Ayaan, K. Shibayama, T. Morita, Y.
Fukuda, Eur. J. Inorg. Chem. 2001, 2641–2646.
[18] I. L. Fedushkin, A. N. Lukoyanov, S. Y. Ketkov, M. Hummert, H.
Schumann, Chem. Eur. J. 2007, 13, 7050–7056.
[19] a) R. D. Culp, A. H. Cowley, A. Decken, R. A. Jones, M. R. Bond,
L. M. Mokry, C. J. Carrano, Inorg. Chem. 1997, 36, 5165–5172;
b) W. Uhl, H. R. Bock, F. Breher, M. Claesener, S. Haddadpour, B.
Jasper, A. Hepp, Organometallics 2007, 26, 2363–2369.
[20] Catalytic Heterofunctionalization (Eds.: A. Togni, H. Grꢂtzmacher),
Wiley-VCH; Weinheim, 2001, pp. 91–133.
[9] I. L. Fedushkin, A. S. Nikipelov, K. A. Lyssenko, J. Am. Chem. Soc.
2010, 132, 7874–7875.
[10] R. Siebenlist, H.-W. Frꢂhauf, K. Vrieze, W. J. J. Smeets, A. L. Spek,
Organometallics 2002, 21, 5628–5641.
[21] T. E. Mꢂller, K. C. HultzscH; M. Yus, F. Foubelo, M. Tada, Chem.
Rev. 2008, 108, 3795–3892.
[11] a) M. van Wijnkoop, P. P. M. de Lange, H.-W. Frꢂhauf, K. Vrieze,
W. J. J. Smeets, A. L. Spek, Organometallics 1995, 14, 4781–4791;
b) P. P. M. de Lange, R. P. de Boer, M. van Wijnkoop, J. M. Ernsting,
H.-W. Frꢂhauf, K. Vrieze, W. J. J. Smeets, A. L. Spek, K. Goubitz,
Organometallics 1993, 12, 440–453; c) P. P. M. de Lange, E. Alberts,
M. van Wijnkoop, H.-W. Frꢂhauf, K. Vrieze, H. Kooijman, A. L.
Spek, J. Organomet. Chem. 1994, 465, 241–249; d) N. Feiken, H.-W.
Frꢂhauf, K. Vrieze, J. Fraanje, K. Goubitz, Organometallics 1994, 13,
2825–2832.
[12] a) J. Scholz, H. Goerls, Inorg. Chem. 1996, 35, 4378–4382; b) J.
Scholz, H. Goerls, H. Schumann, R. Weimann, Organometallics
2001, 20, 4394–4402.
[13] a) P. Barbaro, C. Bianchini, C. Mealli, A. Meli, J. Am. Chem. Soc.
1991, 113, 3181–3183; b) S. Dutta, S.-M. Peng, S. Bhattacharya,
Inorg. Chem. 2000, 39, 2231–2234.
[14] a) G. A. Abakumov, A. I. Poddelꢄsky, E. V. Grunova, V. K. Cherka-
sov, G. K. Fukin, Y. A. Kurskii, L. G. Abakumova, Angew. Chem.
2005, 117, 2827–2831; Angew. Chem. Int. Ed. 2005, 44, 2767–2771;
b) G. A. Abakumov, V. K. Cherkasov, E. V. Grunova, A. I. Poddelꢄ-
skii, L. G. Abakumova, Yu. A. Kurskii, G. K. Fukin, E. V. Baranov,
Dokl. Chem. 2005, 405, 222–225; c) V. K. Cherkasov, G. A. Abaku-
mov, E. V. Grunova, A. I. Poddelꢄsky, G. K. Fukin, E. V. Baranov,
Y. V. Kurskii, L. G. Abakumova, Chem. Eur. J. 2006, 12, 3916–3927.
[15] I. L. Fedushkin, V. M. Makarov, E. C. E. Rosenthal, G. K. Fukin,
Eur. J. Inorg. Chem. 2006, 827–832.
[16] a) Y. Peng, B. D. Ellis, X. Wang, J. C. Fettinger, P. P. Power, Science
2009, 325, 1668–1670; b) M. A. Dureen, D. W. Stephan, J. Am.
Chem. Soc. 2009, 131, 8396–8397; c) C. Jiang, O. Blacque, H. Berke,
Organometallics 2010, 29, 125–133; d) C. Appelt, H. Westenberg, F.
Bertini, A. W. Ehlers, J. C. Slootweg, K. Lammertsma, W. Uhl,
[22] a) I. Aillaud, J. Collin, C. Duhayon, R. Guillot, D. Lyubov, E.
Schulz, A. Trifonov, Chem. Eur. J. 2008, 14, 2189–2200; b) G. Zi, L.
Xiang, H. Song, Organometallics 2008, 27, 1242–1246.
[23] M. R. Crimmin, M. ArrowsmitH; A. G. M. Barrett, I. J. Casely, M. S.
Hill, P. A. Procopiou, J. Am. Chem. Soc. 2009, 131, 9670–9685;
A. G. M. Barrett, I. J. Casely, M. S. Hill, P. A. Procopiou, J. Am.
Chem. Soc. 2009, 131, 9670–9685.
[24] a) J. Jenter, R. Kçppe, P. W. Roesky, Organometallics 2011, 30,
1404–1413; b) S. Datta, P. W. Roesky, S. Blechert, Organometallics
2007, 26, 4392–4394.
[25] a) W. T. Boese, A. S. Goldman, Organometallics 1991, 10, 782–786;
b) U. R. Aulwurm, J. U. Melchinger, H. Kisch; Organometallics
1995, 14, 3385–3395.
[26] M. G. Kutscheroff, Ber. Dtsch. Chem. Ges. 1881, 14, 1540–1542.
[27] Marchꢁs Advanced Organic Chemistry, 5th ed. (Eds.: M. B. Smith; J.
March), Wiley-VCH; New York, 2001, p. 995.
[28] S. L. Dabb, B. A. Messerle, Dalton Trans. 2008, 6368–6371.
[29] A. R. Shaffer, J. A. R. Schmidt, Organometallics 2008, 27, 1259–
1266.
[30] Y. Shi, J. T. Ciszewski, A. L. Odom, Organometallics 2002, 21, 5148.
[31] G. M. Sheldrick, SHELXS-97 Program for the Solution of Crystal
Structures, Universitꢅt Gçttingen, Gçttingen (Germany), 1990.
[32] G. M. Sheldrick, SHELXL-97 Program for the Refinement of Crystal
Structures, Universitꢅt Gçttingen, Gçttingen (Germany), 1997.
[33] G. M. Sheldrick, SADABS Bruker/Siemens Area Detector Absorp-
tion Correction Program, Madison, WI (USA), 1998.
Received: July 21, 2011
Published online: December 2, 2011
266
www.chemeurj.org
ꢁ 2012 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Chem. Eur. J. 2012, 18, 255 – 266