Digallane with redox-active diimine ligand: Dualism of electron-transfer reactions

Article abstract of DOI:10.1021/ic500259k

The reactivity of digallane (dpp-Bian)Ga-Ga(dpp-Bian) (1), which consists of redox-active ligand 1,2-bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-Bian), has been studied. The reaction of 1 with I₂ proceeds via one-electron oxidation of each of two dpp-Bian ligands to a radical-anionic state and affords complex (dpp-Bian)IGa-GaI(dpp-Bian) (2). Dissolution of complex 2 in pyridine (Py) gives monomeric compound (dpp-Bian)GaI(Py) (3) as a result of a solvent-induced intramolecular electron transfer from the metal-metal bond to the dpp-Bian ligands. Treatment of compound 3 with B(C ₆F₅)₃ leads to removal of pyridine and restores compound 2. The reaction of compound 1 with 3,6-di-tert-butyl-ortho- benzoquinone (3,6-Q) proceeds with oxidation of all the redox-active centers in 1 (the Ga-Ga bond and two dpp-Bian dianions) and results in mononuclear catecholate (dpp-Bian)Ga(Cat) (4) (Cat = [3,6-Q]^2-). Treatment of 4 with AgBF₄ gives a mixture of [(dpp-Bian)₂Ag][BF ₄] (5) and (dpp-Bian)GaF(Cat) (6), which both consist of neutral dpp-Bian ligands. The reduction of benzylideneacetone (BA) with 1 generates the BA radical-anions, which dimerize, affording (dpp-Bian)Ga-(BA-BA)-Ga(dpp-Bian) (7). In this case the Ga-Ga bond remains unchanged. Within 10 min at 95°C in solution compound 7 undergoes transformation to paramagnetic complex (dpp-Bian)Ga(BA-BA) (8) and metal-free compound C₃₆H ₄₀N₂ (9). The latter is a product of intramolecular addition of the C-H bond of one of the iPr groups to the C=N bond in dpp-Bian. Diamagnetic compounds 3, 5, 6, and 9 have been characterized by NMR spectroscopy, and paramagnetic complexes 2, 4, 7, and 8 by ESR spectroscopy. Molecular structures of 2-7 and 9 have been established by single-crystal X-ray analysis.

Full text of DOI:10.1021/ic500259k

Article
pubs.acs.org/IC
Digallane with Redox-Active Diimine Ligand: Dualism of Electron-
Transfer Reactions
Igor L. Fedushkin,*,†,‡ Alexandra A. Skatova,† Vladimir A. Dodonov,† Valentina A. Chudakova,†
Natalia L. Bazyakina,† Alexander V. Piskunov,†,‡ Serhiy V. Demeshko,§ and Georgy K. Fukin†,‡
†G. A. Razuvaev Institute of Organometallic Chemistry of Russian Academy of Sciences, Tropinina 49, Nizhny Novgorod 603950,
Russian Federation
‡Nizhny Novgorod State University, Prospect Gagarina 23, Nizhny Novgorod 603950, Russian Federation
§Institut fur Anorganische Chemie, Georg-August-Universitat, Tammannstrasse 4, Gottingen 37077, Germany
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S
* Supporting Information
ABSTRACT: The reactivity of digallane (dpp-Bian)Ga−
Ga(dpp-Bian) (1), which consists of redox-active ligand 1,2-
bis[(2,6-diisopropylphenyl)imino]acenaphthene (dpp-Bian),
has been studied. The reaction of 1 with I2 proceeds via
one-electron oxidation of each of two dpp-Bian ligands to a
radical-anionic state and affords complex (dpp-Bian)IGa−
GaI(dpp-Bian) (2). Dissolution of complex 2 in pyridine (Py) gives monomeric compound (dpp-Bian)GaI(Py) (3) as a result of
a solvent-induced intramolecular electron transfer from the metal−metal bond to the dpp-Bian ligands. Treatment of compound
3 with B(C6F5)3 leads to removal of pyridine and restores compound 2. The reaction of compound 1 with 3,6-di-tert-butyl-ortho-
benzoquinone (3,6-Q) proceeds with oxidation of all the redox-active centers in 1 (the Ga−Ga bond and two dpp-Bian dianions)
and results in mononuclear catecholate (dpp-Bian)Ga(Cat) (4) (Cat = [3,6-Q]2−). Treatment of 4 with AgBF4 gives a mixture of
[(dpp-Bian)2Ag][BF4] (5) and (dpp-Bian)GaF(Cat) (6), which both consist of neutral dpp-Bian ligands. The reduction of
benzylideneacetone (BA) with 1 generates the BA radical-anions, which dimerize, affording (dpp-Bian)Ga−(BA−BA)−Ga(dpp-
Bian) (7). In this case the Ga−Ga bond remains unchanged. Within 10 min at 95 °C in solution compound 7 undergoes
transformation to paramagnetic complex (dpp-Bian)Ga(BA−BA) (8) and metal-free compound C36H40N2 (9). The latter is a
product of intramolecular addition of the C−H bond of one of the iPr groups to the CN bond in dpp-Bian. Diamagnetic
compounds 3, 5, 6, and 9 have been characterized by NMR spectroscopy, and paramagnetic complexes 2, 4, 7, and 8 by ESR
spectroscopy. Molecular structures of 2−7 and 9 have been established by single-crystal X-ray analysis.
feature of the dpp-Bian ligand in main-group metal complexes
is correlated to the ability of transition metals to change their
oxidation state within catalytic processes. However, realization
of two-electron oxidative addition on the main-group metal
complexes of dpp-Bian is difficult. For example, the dianion of
dpp-Bian in the complex (dpp-Bian)Mg(thf)3 can give up two
electrons when reacting with oxidants. However, this leads to
formation of neutral dpp-Bian, which, unfortunately, is not able
to retain coordination to magnesium. In part this problem can
be solved using metals that possess of two oxidation states
differing in a unit of charge, e.g., a Sm2+/Sm3+ couple. But, the
release of two electrons by complex (dpp-Bian)2−Sm2+(dme)3
in the course of its reactions with oxidizing reagents occurs in
fact as two independent one-electron processes. Thus, the
reaction of (dpp-Bian)2−Sm2+(dme)3 with 1 molar equiv of
P h ( B r ) C H C H ( B r ) P h a ffo r d s c om p le x [ ( d pp -
Bian)−Sm3+Br2(dme)3]2, in which both redox-active centers
are oxidized in comparison with the starting complex. On the
other hand the reaction of (dpp-Bian)2−Sm2+(dme)3 with 0.5
INTRODUCTION
■
One of the modern concepts in the field of catalysis concerns
the use of metal complexes of redox-active ligands for activation
of organic molecules, thus allowing their further chemical
transformation.1 According to the concept, redox-active ligands
should store and release electrons during catalytic processes as
transition metal ions do in classical catalytic systems, e.g., Pd,
Rh, and Ru.2 However, all the catalysts of this new generation
are still limited to the derivatives of transition metals, namely,
Ir,3 Rh,4 Fe,5 Re,6 Zr,7 Ta,8 Ti,9 and Cu.10
Since 2003 we have been interested in the preparation of
main-group metal complexes, which may emulate specific
reactivity of coordination and organometallic compounds of
transition metals. At the beginning we have found that the
magnesium complex (dpp-Bian)Mg(thf)3,11 which contains the
redox-active chelating ligand 1,2-bis[(2,6-diisopropylphenyl)-
imino]acenaphthene (dpp-Bian), is highly reactive toward
some organic compounds.12 In contrast to transition metals,13
in complexes of group 1, 2, 13, and 14 elements dpp-Bian may
act as a radical-anionic (dpp-Bian) or dianionic ligand (dpp-
Bian)11,14,15 and can undergo one-electron reduction or
oxidation processes while still coordinated to the metal. This
Received: February 1, 2014
Published: May 8, 2014
© 2014 American Chemical Society
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molar equiv of Ph(Br)CHCH(Br)Ph produces stable com-
pound (dpp-Bian)2−Sm3+Br(dme)3, in which the oxidation
state of the only metal center is altered.16
substrate by complex 1 are recruited from the metal, while the
electrons are provided by the ligand.
A remarkable reactivity has been observed for (dpp-
Bian)Ga−Ga(dpp-Bian) (1).17 Since a formal oxidation state
of the metal atoms in 1 is +2, this compound behaves to some
extent similar to complex (dpp-Bian)2−Sm2+(dme)3. The
reaction of 1 with 2 molar equiv of PhCH2S−SCH2Ph
produces (dpp-Bian)−Ga3+(SCH2Ph)2, while the reaction of 1
with 1 molar equiv of Me2N(S)CS−SC(S)NMe2 gives (dpp-
Bian)2−Ga3+(S2CNMe2) (Scheme 1).18 In the reactions of
RESULTS AND DISCUSSION
■
Reactions of Compound 1 with Oxidizing Reagents.
Formation and Spectroscopic Characterization of (dpp-
Bian)IGa−GaI(dpp-Bian) (2), (dpp-Bian)GaI(Py) (3), (dpp-
Bian)Ga(Cat) (4), [(dpp-Bian)2Ag][BF4] (5), (dpp-Bian)-
GaF(Cat) (6), (dpp-Bian)Ga−(BA−BA)−Ga(dpp-Bian) (7),
(dpp-Bian)Ga(BA−BA) (8), and C36H40N2 (9). Treatment of
compound 1 with 1 molar equiv of I2 in toluene results in an
immediate color change from deep blue, which is typical for
dpp-Bian2−, to red, which is indicative for the formation of dpp-
Bian−. The product (dpp-Bian)IGa−GaI(dpp-Bian) (2) is
poorly soluble in toluene and precipitates from the reaction
mixture as a red crystalline powder (Scheme 3).
Scheme 1. Reactivity of Compound 1 toward Disulfides
Scheme 3. Syntheses of Compounds 2 and 3
(dpp-Bian)Ga−Ga(dpp-Bian) (1) with alkynes no electron
transfer from compound 1 to the substrate takes place, but the
ligand exhibits a marvelous lability with the ligand being directly
involved in bonding of the substrate (Scheme 2).19 Amazingly,
Scheme 2. Reactivity of compound 1 towards alkynes
Crystallization of the crude product from hot 1,2-dimethoxy-
ethane resulted in compound 2 (47%) as deep red, prismatic
crystals. Addition of 2 molar equiv of I2 to the toluene solution
of 1 results in a clear red solution, from which compound (dpp-
Bian)GaI2 was isolated. The latter has been previously obtained
by reacting dpp-Bian with “GaI”.22 Dissolution of complex 2 in
pyridine resulted in a color change from red to deep blue.
Crystallization from toluene gives (dpp-Bian)GaI(Py) (3)
(Scheme 3) as deep blue, nearly black crystals in 63% yield.
It is worth mentioning that compound 3 is formed in the
course of a solvent-induced intramolecular electron transfer
from the Ga−Ga bond to two dpp-Bian ligands in complex 2.
One may expect that removing pyridine from complex 3 should
restore binuclear compound 2. In fact we have found that
addition of 1 molar equiv of B(C6F5)3 to a solution of complex
3 in toluene results in the formation of dinuclear compound 2,
isolated in 28% yield after crystallization from 1,2-dimethoxy-
ethane. This process is a sort of redox-isomerism that is well
established in 3d-metal complexes23 and recently also in f-
element series, e.g., ytterbium complexes of the dpp-Bian
ligand, [(dpp-Bian)YbX(dme)]2 (X = Cl,24a Br24b). However,
in the main-group metal complexes such a phenomenon is
difficult to realize because of the lack of existence of at least two
the addition of alkynes by complex 1 is reversible. The ability of
complex 1 to coordinate phenylacetylene allows its catalytic
functionalization including hydroamination and hydroarylation
with anilines.19b It is worth mentioning that catalytic activity of
compound 1 in hydroamination of PhCCH with aromatic
amines is comparable with the activity of transition metal-based
systems.20 The extensive study on reactions of group 13 metal−
metal bond-containing compounds is reported.21
Here we report a new type of reactivity of compound 1. We
demonstrate that in the reactions with some substrates
oxidation of the dianionic dpp-Bian ligands in 1 can take
place before oxidation of the metal−metal bond. In fact, we
were able to perform concerted two-electron oxidative addition
to the Ga−Ga center in the complex (dpp-Bian)Ga−Ga(dpp-
Bian). In this process the empty orbitals for the binding of the
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stable oxidation states and facile shuttling between them in s-
and p-metal series.
Temperature-independent paramagnetism (TIP) and a
Curie-behaved paramagnetic impurity (PI) with spin S = 1/2
were included according to χcalc = (1 − PI)χ + PIχmono + TIP.
The obtained fit parameters are J = −38 cm−1, g = 1.92, PI =
9.5%, and TIP = 2.4 × 10−4 cm3 mol−1. The relatively high
coupling constant indicates an effective mediation of the
digallane bridge in the exchange interaction. Since an
inspection of the crystal packing in 2 (vide infra) has revealed
a π stacking between the naphthalene rings of the neighboring
molecules, an intermolecular antiferromagnetic exchange
probably takes place. This intermolecular interaction provides
for the formation of indefinite 1D polymeric chains in the
crystals of compound 2 and makes complex 2 poorly soluble.
An example of an extreme form of such coupling resulted in a
C−C bond, reported recently for related indium diimine
complexes.26
Despite the presence of the ligands bearing an unpaired
electron compound 2 does not reveal well resolved ESR signal:
only a broad signal could be detected in the solid state as well
as in solution (toluene or 2-Me-THF) in a temperature range
360−120 K. This observation allows making two conclusions.
First, compound 2 does not disproportionate in solution into
mononuclear radical species as in the case of related gallium
complexes25 (Scheme 4). Second, unpaired electrons of dpp-
Bian radicals are antiferromagnetically coupled.
Scheme 4. Two Pathways of Disproportionation of
Diazadiene Digallanes
Compound 3 is diamagnetic, its 1H NMR spectrum in C6D6
reveals an expected signal set for the dpp-Bian dianion. In free
dpp-Bian as well as in the coordinated dpp-Bian ligand a
rotation of the Ph rings (N−Cipso) as well as the iPr
substituents (C(H)−Cipso) is not possible due to steric reasons.
In contrast to free dpp-Bian, which consists of two mirror
planes, only one plane of symmetry (defined with atoms I, Ga,
and N) is present in the molecule of complex 3. Therefore, its
1H NMR spectrum consists of four doublets of methyl groups
(δ 1.57, 1.23, 1.13, 0.33 ppm) and two septets of the methine
protons (δ 3.95, 3.27 ppm).
In contrast to the reaction with iodine, the oxidation of
complex 1 with 3,6-di-tert-butyl-ortho-benzoquinone (3,6-Q)
proceeds only at elevated temperatures. At 95 °C the reaction is
accompanied by a color change from deep blue to green within
1 h. At the molar ratio 1 to 2 (complex 1 to 3,6-Q) catecholate
(dpp-Bian)Ga(Cat) (4) (Cat = [3,6-Q]2−) was isolated in 80%
yield (Scheme 5). Complex 4 resulted from oxidation of all the
The existence of an antiferromagnetic exchange between
unpaired electrons in the molecule of complex 2 has been
further confirmed by the measurements of the magnetic
susceptibility of the crystalline sample. A temperature depend-
ence of the magnetic moment of compound 2 is shown in
Figure 1.
Scheme 5. Oxidation of Compound 1 with 3,6-Di-tert-butyl-
ortho-benzoquinone (3,6-Q)
Figure 1. Temperature dependence of the magnetic moment of
compound 2. The solid line shows the best fit curve (see text).
At ambient temperature the magnetic moment of compound
2 is close to the value calculated for two noninteracting ligand-
localized unpaired electrons (μeff = [(1.73)2 + (1.73)2]1/2 = 2.45
μB). Lowering the temperature from 400 K to 150 K results in a
monotonic decrease of the magnetic moment. Below 150 K the
value of μeff starts to decrease more rapidly, and at 2 K the
sample behaves nearly as diamagnetic. The exchange coupling
constant between spin carriers in 2 was determinated by using a
fitting procedure to the Heisenberg−Dirac−van-Vleck (HDvV)
spin Hamiltonian for isotropic exchange coupling and Zeeman
splitting, eq 1.
redox-active centers in 1: the Ga−Ga bond and two dpp-Bian
dianions. Due to the presence of the dpp-Bian radical-anion,
complex 4 reveals a well-resolved ESR signal (Figure 2). The
hyperfine structure of the signal is caused by the coupling of an
unpaired electron to two pairs of protons (99.98%, I = 1/2, μN
= 2.7928),25 to two equivalent 14N nuclei (99.63%, I = 1, μN =
0.4037),27 and to gallium magnetic isotopes 69Ga (60.11%, I =
3/2, μN = 1.8507) and 71Ga (39.89%, I = 3/2, μN = 2.56227).25
The ESR spectroscopy unequivocally indicates the presence in
̂
̂
̂
⃗
⃗
⃗
H = −2JS1·S2 + gμB(S1 + S2)B
(1)
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Scheme 6. Oxidation of Complex 4 with AgBF4
1
coincides with the diimine plane. Therefore, the H NMR
spectrum of compound 6 consists of two septets (δ 3.66 and
2.64 ppm) and four doublets (δ 1.47, 1.18, 1.0 (overlap with
tBu signal), and 0.69 ppm).
Benzylideneacetone (BA) was chosen as a substrate for
investigation of the reactivity of complex 1 because several
reaction pathways may be expected. First, the reaction between
1 and BA can proceed as a 2+4 cycloaddition similar to that
observed in the reactions of complex 1 with alkynes (Scheme
2). Such 2+4 cycloaddition of vinylacetone to aluminum
complex (dpp-Bian)AlEt(Et2O) has been recently observed.29
Second, one may expect formation of ketyl radicals under
electron transfer from complex 1 to BA. In this case the
electrons can be provided either by the ligand or by the metal−
metal bond. The BA ketyl radicals, in turn, may further
dimerize to give a gallium pinacolate. In fact it has been found
that reaction between compound 1 and BA in toluene easily
proceeds at room temperature. Within a few minutes after
mixing the reagents the toluene solution turned from deep blue
to red-brown, thus indicating the formation of dpp-Bian radical-
anionic species. Crystallization from the reaction mixture
afforded dark brown crystals of compound (dpp-Bian)Ga−
(BA−BA)−Ga(dpp-Bian) (7) in 26% yield (Scheme 7).
Investigation of compound 7 by spectroscopic and crystallo-
graphic methods has shown that the compound consists of two
radical-anionc dpp-Bian ligands, a gallium−gallium bond, and a
Figure 2. ESR spectrum of 4 (toluene, 293 K): (a) experimental; (b)
simulated (ai(2 14N) = 0.427 mT, ai(69Ga) = 1.420 mT, ai(71Ga) =
1.805 mT, ai(2 H) = 0.107 mT, ai(2 H) = 0.115 mT, g = 2.0025).
1
1
complex 4 of a radical-anion of the dpp-Bian. The catecholate
nature of the quinone ligand in compound 4 is supported by its
IR spectrum; the C−O stretching vibrations of neutral 3,6-BQ
(1680 and 1640 cm−1)28 as well as its semiquinonic form (1485
and 1450 cm−1)26 are absent.
Looking for another example of oxidative addition to the
Ga−Ga center in compound 1, we carried out the reaction
between 1 and acenaphthenequinone (AQ). Despite a more
negative reduction potential of AQ compared to 3,6-Q, the
reaction between 1 and AQ proceeds easily and results in the
desired product. Detailed characterization of this product will
be published elsewhere together with other related complexes.
In order to prepare a gallium complex containing two
different radical-anionic ligands, namely, dpp-Bian and 3,6-SQ,
we have studied oxidation of the 3,6-Cat ligand in complex 4
with AgBF4. To the best of our knowledge heteroligand
biradicals have not been reported so far. The reaction between
4 and AgBF4 proceeds at ambient temperature. One of the
products of this reaction, [(dpp-Bian)2Ag][BF4] (5), starts to
crystallize as orange crystals from the reaction mixture when
evaporation of the solvent begins. Separation of crude product
5 and continued evaporation of the solvent from the mother
liquor afforded deep green crystals of a second product, (dpp-
Bian)GaF(Cat) (6) (Scheme 6). Both compounds 5 and 6
consist of neutral dpp-Bian ligands. Thus, oxidation of the dpp-
Bian radical-anion to neutral dpp-Bian takes place before
oxidation of catecholate ligand to its semiquinonic state. It
should be also noted that product 6 consists of fluorine as the
anionic ligand, not the BF4 anion. Compound 5 can be
prepared also in good yield just by reacting dpp-Bian with
AgBF4.
Scheme 7. Oxidation of Complex 1 with Benzylideneacetone
Both compounds 5 and 6 are diamagnetic; they have been
1
characterized by IR and H NMR spectroscopy. Similar to
complex 3, in compound 6 there is no mirror plane that
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4,5-diphenylocta-2,6-diene-2,7-diolate fragment. The latter is
formed in the course of dimerization of two BA radical-anions.
Surprisingly, dimerization of two BA radical-anions occurred
not at the α position to the oxygen atom but at the γ position.
We believe that dimerization at the α position would not be
optimal because of the stronger tensions in the six-membered
metallacycle compared to the 10-membered metallacycle, which
is observed in fact in the product 7. On the other hand in this
case radical stability considerations also may play a role. Thus,
stabilization of the putative radical at the γ-position to the
oxygen atom may be provided by both phenylic and olefinic
substituents. Compound 7 is paramagnetic due to the presence
of two dpp-Bian radical-anions. However, no ESR signal could
be observed in solution at ambient temperature. Only at 150 K
in a toluene matrix does compound 7 give rise to an ESR signal,
which clearly indicates the presence of the biradical species.
The distance between centers of localization of unpaired
electrons in molecule 7 has been estimated using zero field
splitting parameters (|D| = 10 mT, |E| = 0.8 mT). The
calculated value is 6.52 Å. For comparison, according to the X-
ray data, the distance between the middle points of the bonds
C(1)−C(2) and C(1a)−C(2a) is 7.15 Å, whereas the distance
between the geometrical centers defined with atoms N(1)−
C(1)−C(2)−N(2) and N(1a)−C(1a)−C(2a)−N(2a) is 6.03
Å. A half-field ESR signal, which corresponds to a forbidden
transition (Δms = 2), has also been observed (inset in Figure
3). Although this signal is broadened, its hyperfine structure
Figure 4. ESR signal of 8 (toluene, 297 K): (a) experimental (ai(2
14N) = 0.48 mT, ai(69Ga) = 1.125 mT, ai(71Ga) = 1.430 mT, gi =
2.0026); (b) simulated.
Scheme 8. Thermal Decomposition of 7 and Formation of
Compounds 8 and 9
Figure 3. ESR signal of 7 (toluene, 150 K): (a) experimental; (b)
simulated.
two equivalent 14N nuclei and magnetic isotopes of gallium
69Ga and 71Ga.
(septet) can be distinguished. This structure is caused by the
presence in the molecule of 7 of two atoms of Ga, whose
isotopes (69Ga and 71Ga) possess nuclear spin IN = 3/2.
In solution complex 7 is unstable. Heating a toluene solution
of complex 7 at 95 °C for 10 min gives rise to a well-resolved
ESR signal (Figure 4), whose parameters allow suggesting the
formation of mononuclear gallium complex (dpp-Bian)Ga-
(BA−BA) (8) (Scheme 8).
Workup of the reaction mixture allows isolation of
compound 9 in the form of yellow (Et2O) or red crystals
(hexane). Compound 9 represents a tautomeric form of dpp-
Bian. It is formed in the course of the intramolecular addition
of the C−H bond of one of the iPr groups to the CN bond
in dpp-Bian. The hyperfine structure of the ESR signal of
complex 8 is caused by the coupling of the unpaired electron to
Diamagnetic compound 9 has been characterized by IR and
1H NMR spectroscopy. In contrast to dpp-Bian, which
possesses two mirror planes, the molecule of compound 9 is
asymmetric. Moreover, one of the carbon atoms of the newly
formed C−C bond in compound 9 is chiral. The asymmetry of
molecule 9 causes nonequivalence of all the carbon atoms as
well as of all protons except the protons in the CH3 groups.
Molecular Structures of 2−7 and 9. The molecular
structures of compounds 2, 3, 4, 5, 6, 7, and 9 were determined
by single-crystal X-ray diffraction and are depicted in Figures 5,
7, 8, 9, 10, 11, 12, correspondingly. The packing of molecules in
the crystal of compound 2 is shown in Figure 6. The crystal
data collections and structure refinement details are listed in
Table 1.
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Figure 7. Molecular structure of 3. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted. Selected bond
lengths (Å) and angles (deg): Ga(1)−N(1) 1.906(2), Ga(1)−N(2)
1.887(2), Ga(1)−N(3) 2.042(2), Ga(1)−I(1) 2.4931(3), N(1)−C(1)
1.404(3), N(2)−C(2) 1.400(3), C(1)−C(2) 1.376(3), N(2)−Ga(1)−
N(1) 92.03(8), N(2)−Ga(1)−N(3) 103.85(8), N(1)−Ga(1)−N(3)
104.01(8), N(2)−Ga(1)−I(1) 121.91(6), N(1)−Ga(1)−I(1)
128.29(6), N(3)−Ga(1)−I(1) 103.76(6).
Figure 5. Molecular structure of 2. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted. Selected bond
lengths (Å) and angles (deg): Ga(1)−N(1) 1.997(2), Ga(1)−N(2)
1.999(2), Ga(1)−Ga(1a) 2.4655(5), Ga(1)−I(1) 2.5910(3), N(1)−
C(1) 1.352(3), N(2)−C(2) 1.338(3), C(1)−C(2) 1.425(3), N(1)−
Ga(1)−N(2) 84.95(8), N(1)−Ga(1)−Ga(1a) 119.38(6), N(2)−
Ga(1)−Ga(1a) 120.14(6), N(1)−Ga(1)−I(1) 109.55(6), N(2)−
Ga(1)−I(1) 109.48(6), Ga(1a)−Ga(1)−I(1) 110.781(17), C(1)−
N(1)−Ga(1) 108.83(15), C(2)−N(2)−Ga(1) 109.40(16).
(Ar-dad)IGa−GaI(Ar-dad) (2.5755(16) Å).31b The equality of
the Ga−N bonds in 2 (1.997(2) and 1.999(2) Å) indicates an
effective delocalization of the electron density within the
diimine fragment. In the crystal molecules of compound 2 are
arranged in such a way that the acenaphthene rings are lying in
planes that are entirely parallel to each other (Figure 6). The
shortest distance between these planes is 3.40 Å. This value is
close to the distance between the layers in graphite (3.35 Å).32
It is worth noting that earlier we have observed the formation
of infinite 1D quasi-polymeric structures through the
intermolecular π interaction between the ligands in the crystals
of samarium and europium 2,2′-bipyridyl complexes Ln(bipy)4
(Ln = Sm, Eu).33 The distances between the planes of the 2,2′-
bipyridyl ligands in these lanthanide complexes (Sm, 3.25 Å;
The molecule of compound 2 (Figure 5) is situated on the
crystallographic inversion center, which is located at the middle
of the gallium−gallium bond. Coordination tetrahedrons of
both metal atoms are slightly distorted.
The acenaphthene-1,2-diimine planes are parallel to each
other, with gallium atoms lying almost perfectly within the
planes, estimated with atoms N(1)−C(1)−C(2)−N(2) and
their symmetry equivalent counterparts. The Ga−Ga distance
in compound 2 (2.4655(5) Å) corresponds to a covalent
metal−metal bond. This distance is remarkably longer than that
in complex 1 (2.3598(3) Å),30 but it matches well the Ga−Ga
distances in (tBu-dad)IGa−GaI(tBu-dad) (2.4232(7) Å)31a and
Figure 6. Crystal packing of compound 2. The lattice DME molecules are omitted for clarity.
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Figure 8. Molecular structure of 4. Thermal ellipsoids are drawn at the
50% probability level. Hydrogen atoms are omitted. Selected bond
lengths (Å) and angles (deg): Ga(1)−O(1) 1.8255(13), Ga(1)−O(2)
1.8269(13), Ga(1)−N(1) 1.9432(13), Ga(1)−N(2) 1.9335(16),
O(1)−C(37) 1.380(2), O(2)−C(38) 1.372(2), C(37)−C(38)
1.414(3), N(1)−C(1) 1.336(2), N(2)−C(2) 1.343(2), C(1)−C(2)
1.431(2), O(1)−Ga(1)−O(2) 92.16(6), N(2)−Ga(1)−N(1)
87.54(6), O(1)−Ga(1)−N(2) 124.15(6), O(1)−Ga(1)−N(1)
118.24(6).
Figure 10. Molecular structure of 6. Thermal ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted. Selected bond
lenghts (Å) and angles (deg): Ga(1)−F(1) 1.795(7), Ga(1)−O(1)
1.859(0), Ga(1)−O(2) 1.854(8), Ga(1)−N(1) 2.087(7), Ga(1)−
N(2) 2.120(1), N(1)−C(1) 1.278(2), N(2)−C(2) 1.284(2), C(1)−
C(2) 1.517(2), O(1)−C(37) 1.355(2), O(2)−C(38) 1.361(2),
C(37)−C(38) 1.418(2), F(1)−Ga(1)−O(2) 112.80(5), F(1)−
Ga(1)−O(1) 110.09(5), F(1)−Ga(1)−N(1) 96.18(5), O(2)−
Ga(1)−N(1) 149.33(6), O(2)−Ga(1)−O(1) 88.72(5), N(1)−
Ga(1)−N(2) 78.98(6).
Figure 9. Molecular structure of the cation [(dpp-Bian)2Ag] in 5.
Thermal ellipsoids are drawn at the 50% probability level. Hydrogen
atoms are omitted. Selected bond lengths (Å) and angles (deg):
Ag(1)−N(1) 2.334(3), Ag(1)−N(2) 2.374(3), Ag(1)−N(3)
2.378(3), Ag(1)−N(4) 2.311(3), N(1)−C(1) 1.260(4), N(2)−C(2)
1.271(4), C(1)−C(2) 1.528(4), N(3)−C(37) 1.281(4), N(4)−C(38)
1.276(4), C(37)−C(38) 1.529(5), N(1)−Ag(1)−N(2) 73.40(9).
Figure 11. Molecular structure of 7. Thermal ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted. Selected bond
lengths (Å) and angles (deg): Ga(1)−N(1) 2.0075(12), Ga(1)−N(2)
2.0258(12), Ga(1)−O(1) 1.8456(10), Ga(1)−Ga(1A) 2.4871(3),
O(1)−C(37) 1.3646(18), N(1)−C(1) 1.3369(19), N(2)−C(2)
1.3370(19), C(1)−C(2) 1.441(2), C(37)−C(39) 1.331(2), C(39)−
C(40) 1.508(2), C(40)−C(40A) 1.594(3), O(1)−Ga(1)−N(1)
98.91(5), O(1)−Ga(1)−N(2) 108.26(5), N(1)−Ga(1)−N(2)
84.30(5), O(1)−Ga(1)−Ga(1A) 117.11(3), N(1)−Ga(1)−Ga(1A)
123.77(4), N(2)−Ga(1)−Ga(1A) 118.83(4), C(37)−O(1)−Ga(1)
125.01(9).
Eu, 3.31 Å) are even shorter than interlayer distances in
graphite. Accordingly, compounds are absolutely insoluble in
organic media. We believe that intermolecular interaction in
compound 2 is rather strong and responsible for the low
solubility of the compound. Also, this interaction may provide
an opportunity for the unpaired electrons to couple
antiferromagnetically.
Compound 3 is a mononuclear four-coordinate complex
(Figure 7). Due to the stronger interaction between Ga and the
dpp-Bian dianion, the Ga−N bonds (Ga(1)−N(1) 1.906(2)
and Ga(1)−N(2) 1.887(2) Å) in complex 3 are ca. 0.1 Å
shorter than corresponding bonds in compound 2, which
consists of a dpp-Bian radical-anion. The Ga−I bond
(2.4931(3) Å) in 3 is also remarkably shorter than the Ga−I
bond in 2 (2.5910(3) Å). Probably, a shortening of the Ga−I
distance in 3 compared to that distance in 2 is caused by a
higher formal oxidation state of the gallium atom in complex 3
(+3) compared to compound 2 (+2).
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only 0.14 Å. Deviation of the gallium atom from the basal plane
toward the axially positioned fluorine ligand is 0.47 Å. The Ga−
N distances (2.087(7) and 2.120(1) Å) in 6 are remarkably
longer compared to those distances in related compound 4
(1.9432(13) and 1.9335(16) Å), whereas the Ga−O bonds in 4
and 6 (average values: 1.826 and 1.857 Å, correspondingly) are
very much alike. Further, the N(1)−C(1) and N(2)−C(2)
distances in complex 6 are quite close to those values in
compound 5, which consists of neutral dpp-Bian. The C−O
distances in 6 (O(1)−C(37) 1.355(2) and O(2)−C(38)
1.361(2) Å) compare well with those in compound 4
(O(1)−C(37) 1.380(2) and O(2)−C(38) 1.372(2) Å) as
well as in catecholates of Ga(III),37a Sn(IV),37b−d and
Ge(IV).37e Thus, according to the X-ray data, compound 6
consists of neutral dpp-Bian and dianionic 3,6-di-tert-butyl-
ortho-benzoquinone.
Compound 7 (Figure 11) is situated on the crystallographic
2-fold rotation axis that runs through the centers of the Ga−Ga
and C(40)−C(40A) bonds. Reduction of benzylideneacetone
with digallane results in radical-anions that recombine to give a
4,5-diphenylocta-2,6-diene-2,7-diolate dianion. In contrast to
complex 2, in which the iodine atoms are trans-positioned, the
diolate ligand shows a cis-coordination to the metallacenter in
complex 7. Due to this chelating effect, the diimine planes are
not parallel to each other within a single molecule or between
the molecules in the unit cell as in complex 2. Note, in contrast
to compound 2, complex 7 is well soluble in different organic
media, e.g., ethers or aromatic hydrocarbons.
The Ga−Ga bond as well as the Ga−N distances in complex
7 (Ga−Ga, 2.4871(3) Å; Ga−N 2.0075(12) and 2.0258(12) Å)
are only slightly longer than corresponding values in compound
2 (Ga−Ga 2.4655(5) Å; Ga−N 1.997(2) and 1.999(2) Å). The
newly formed Ga−O bonds (both 1.8456(10) Å) compare well
with Ga−O distances in compounds 4 and 6 (average 1.826
and 1.856 Å, correspondingly). The newly formed bond
C(40)−C(40A) (1.594(3) Å) is significantly longer than
ordinary C−C bonds in alkanes (1.54 Å). However, the
C(40)−C(40A) bond in compound 7 is almost the same as a
central C−C bond, 1.605(7) Å, in the benzpinacolate ligand
formed in the course of recombination of diphenylketyl
radicals. The latter were generated from Ph2CO under
reduction with a magnesium complex of the dpp-Bian dianion
(dpp-Bian)Mg(thf)3.12a The bonds O(1)−C(37), C(39)−
C(40), and C(37)−C(39) in compound 7 are altered
compared to the free BA.38 The latter bond is shortened to a
double bond, while two former bonds became single bonds.
Formation of the C(40)−C(40A) bond makes the carbon
atoms involved in the bond formation chiral. It is worth
mentioning that in a crystal of compound 7 that was used for
the single-crystal X-ray analysis equal quantities of the R,R and
S,S diastereomeric forms were present. A radical-anionic nature
of both dpp-Bian ligands in complex 7 is evident from the bond
distances within the diimine moiety: the C−N distances are
longer than in free dpp-Bian (vide supra) but shorter than in the
dpp-Bian dianion, for instance in complex 3.
Figure 12. Molecular structure of 9. Thermal ellipsoids are drawn at
the 50% probability level. Hydrogen atoms are omitted. Selected bond
lengths (Å) and angles (deg): N(1)−C(1) 1.2731(13), C(1)−C(2)
1.5671(14), C(2)−N(2) 1.4704(13), C(2)−C(31) 1.5863(14),
N(2)−C(25) 1.4153(13), C(26)−C(31) 1.5203(14), N(1)−C(1)−
C(2) 120.43(9), N(2)−C(2)−C(1) 112.89(8), N(2)−C(2)−C(31)
101.57(8), C(1)−C(2)−C(31) 111.07(8), C(25)−N(2)−C(2)
106.83(8).
Compound 4 is a mononuclear four-coordinate complex
(Figure 8), which consists of two different redox-active ligands.
The Ga−N and Ga−O distances are very close in the pairs. The
Ga−N distances (1.9432(13) and 1.9335(16) Å) are ca. 0.6 Å
shorter than corresponding distances in compound 2, which
consists of a radical-anionic dpp-Bian ligand. On the other
hand, the Ga−N bonds in 4 are ca. 0.5 Å longer compared with
those bonds in compound 3. One can expect the existence of
two redox isomers of compound 4: (dpp-Bian)−Ga(3,6-Q)−2 or
(dpp-Bian)−2Ga(3,6-Q)−. To make the decision whether the
dpp-Bian ligand in 4 acts as a radical-anion or dianion, an
inspection of the bond distances within the diimine section is
useful.
Thus, the C−N distances within the metallacycle in complex
4 (1.336(2) and 1.343(2) Å) are very close to those in
compound 2 (1.352(3) and 1.338(3) Å), but remarkably
shorter than in compound 3 (1.404(3) and 1.400(3) Å).
Hence, the present structural data are in agreement with
spectroscopic data (vide supra), which indicate the presence of
the dpp-Bian radical-anion in compound 4. Accordingly, 3,6-Q
is present in 4 as a catecholate. For comparison, in neutral 3,6-
Q the CO distances are 1.207(2) and 1.214(2) Å.34 The
dihedral angle between the planes of the dpp-Bian and 3,6-Cat
ligands is 87°.
Compound 5 consists of separated ions, [(dpp-Bian)2Ag]+
(Figure 9) and [BF4]−. In the cation dpp-Bians act as neutral
chelating ligands. Thus, the C−N distances within both
metallacycles in compound 5 (1.260(4), 1.271(4), 1.281(4),
1.276(4) Å) are very close to those bonds in free dpp-Bian
(1.282(4) Å)35 as well as in compound (dpp-Bian)SbCl3,36
which also consists of a neutral dpp-Bian ligand. Due to steric
reasons, the dpp-Bians in compound 5 are twisted from each
other at 47°. Probably in this geometry the steric repulsion
between the isopropyl groups of the dpp-Bian ligands is
minimal.
Compound 6 represents a five-coordinate gallium complex
(Figure 10). Its coordination polyhedron can be described as a
distorted tetragonal pyramid with a basal plane defined by the
atoms N(1), N(2), O(1), and O(2). Deviation of the latter
from the plane formed with atoms N(1), N(2), and O(1) is
Organic compound 9 (Figure 12) is a result of the
intramolecular addition of the C−H bond of one of the iPr
groups to the CN bond in dpp-Bian. The N(1)−C(1) bond
(1.2731(13) Å) is almost the same as the C−N distances in
dpp-Bian (1.282(4) Å), while the C(2)−N(2) bond
(1.4704(13) Å) corresponds to a single carbon−nitrogen
bond. Addition across the CN bond makes atom C(2) chiral.
In the unit cell of compound 9 both enantiomers are present.
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Table 1. Crystal Data and Structure Refinement Details for Compounds 2, 3, 4, 5, 6, 7, and 9
2·C4H10O2
3·C7H8
4·C7H8
5·3C4H8O
6
7
9
formula
Mr [g mol−1
cryst syst
space group
a [Å]
C76H90Ga2I2N4O2
1484.76
C48H53GaIN3
868.55
C57H68GaN2O2
882.85
C84H104AgBF4N4O3 C50H60FGaN2O2
C106H116Ga2N4O2
1617.47
C36H40N2
]
1412.39
monoclinic
P21/c
809.72
500.70
triclinic
monoclinic
P21/n
monoclinic
C2/c
orthorhombic
Pbca
orthorhombic
Pnna
monoclinic
P21/c
P1
̅
10.7776(6)
12.9040(7)
14.3443(8)
77.3430(10)
70.4290(10)
66.6210(10)
1716.76(16)
1
12.2025(4)
19.4990(7)
17.6340(6)
90.00
26.9451(8)
20.7134(6)
21.8637(6)
90.00
12.8321(9)
26.0947(17)
23.6182(16)
90.00
14.9694(10)
19.7485(14)
29.977(2)
90.00
24.1618(3)
24.3348(3)
14.65391(18)
90.00
14.6726(5)
10.2442(3)
18.9211(6)
90.00
b [Å]
c [Å]
α [deg]
β [deg]
γ [deg]
V [Å3]
Z
90.7170(10)
90.00
124.4690(10)
90.00
105.682(2)
90.00
90.00
90.00
92.961(3)
90.00
90.00
90.00
4195.4(2)
4
10060.3(5)
8
7614.2(9)
4
8862.0(11)
8
8616.13(18)
4
2840.20(16)
4
ρcalc
,
1.436
1.375
1.166
1.232
1.214
1.247
1.171
[g cm−3
]
μ [mm−1
F(000)
]
1.732
758
1.428
1784
0.589
3768
0.325
2992
0.665
3440
0.679
3432
0.067
1080
crystal size,
[mm3]
0.35 × 0.28 × 0.15 0.15 × 0.10 ×
0.24 × 0.18 ×
0.16
0.24 × 0.13 × 0.12 0.23 × 0.20 × 0.03 0.20 × 0.15 × 0.10 0.20 × 0.18 ×
0.08
0.05
θmin/θmax
[deg]
2.14/26.00
2.04/26.00
2.27/25.00
2.22/26.00
1.84/26.00
2.99/28.00
3.20/25.00
index ranges −13 ≤ h ≤ 7
−15 ≤ k ≤ 12
−13 ≤ h ≤ 15
−24 ≤ k ≤ 24
−21 ≤ l ≤ 20
25 227
−32 ≤ h ≤ 23
−22 ≤ k ≤ 24
−23 ≤ l ≤ 26
27 495
−15 ≤ h ≤ 14
−30 ≤ k ≤ 32
−29 ≤ l ≤ 29
45 500
−18 ≤ h ≤ 18
−24 ≤ k ≤ 24
−36 ≤ l ≤ 36
73 311
−31 ≤ h ≤ 31
−32 ≤ k ≤ 32
−19 ≤ l ≤ 19
146 847
−17 ≤ h ≤ 17
−12 ≤ k ≤ 12
−22 ≤ l ≤ 22
38 582
−17 ≤ l ≤ 17
reflns
collected
10 513
independ
reflns
6724
8242
8760
14 876
8699
10 387
4990
Rint
0.0299
0.0293
0.0328
0.1121
0.1103
0.1218
0.0402
max/min
transmn
0.7812/0.5824
0.8943/0.8144
0.9117/0.8716
0.9621/0.9262
0.9803/0.8621
0.9352/0.8761
0.9966/0.9867
data/
6724/0/397
8242/0/487
8760/0/574
14 876/80/884
8699/2/536
10 387/128/595
4990/20/407
restraints/
params
GOF on F2
1.023
1.065
1.051
1.000
0.992
1.012
1.043
final R
0.0424/0.1091
0.0337/0.0810
0.0487/0.1299
0.0695/0.1369
0.0445/0.0902
0.0418/0.0825
0.0425/0.1050
indices [I >
2σ(I)]
R indices (all 0.0508/0.1143
data)
0.0447/0.0854
0.0654/0.1400
0.1510/0.1569
0.0857/0.1004
0.0737/0.0898
0.0520/0.1097
largest diff
1.860/0.720
1.601/−0.377
1.231/−0.361
1.137/−0.978
0.454/−0.240
0.365/−0.321
0.651/−0.592
peak/hole
[e Å−3
]
most of the reactions would be preferable compared to the
metal-centered oxidation of compound 1. This supposition may
be rationalized in terms of the bulkiness of the dpp-Bian ligand
itself. The latter consists of 2,6-iPr2C6H3 groups that may
conflict with ligands that coordinate to the metal in the course
of the addition reaction. Repulsion between the dpp-Bian and
these ligands can be released to some extent when the dpp-Bian
ligand is oxidizing from the dianion to the radical-anion. This
causes a ca. 0.1 Å elongation of the Ga−N distances.
We believe that the ability of complex 1 to add the substrates
in a two-electron oxidative addition manner provides a chance
to use complexes like 1 in catalytic reactions of organic
synthesis. Another aspect of the chemistry reported here is the
redox-isomerism phenomenon in the main-group metal
complexes. This phenomenon is well established for transition
metal systems. Redox-isomerism is reversible intramolecular
metal-to-ligand electron transfer induced thermally or by
irradiation. Sometimes metal-to-ligand electron transfer may
be induced by solvent. Complex 2 is exactly the latter case.
Thus, coordination of pyridine to gallium in complex 2 results
in its dissociation to mononuclear species with simultaneous
CONCLUSION
■
In an extension of our research we have studied the reactivity of
complex (dpp-Bian)Ga−Ga(dpp-Bian) (1) toward iodine, 3,6-
di-tert-butyl-ortho-benzoquinone, and benzylideneacetone. In
the course of this study a new type of reactivity of compound 1
has been disclosed. We have demonstrated that in the reactions
with iodine and benzylideneacetone an oxidation of the
dianionic dpp-Bian ligands in complex 1 to radical-anionic
state takes place before oxidation of the metal−metal bond. In
contrast, the reaction of compound 1 with Me2N(S)CS−
SC(S)NMe2 proceeds with cleavage of the Ga−Ga bond to give
gallium(III) derivative (dpp-Bian)Ga(S2CNMe2) (Scheme 1).
In this reaction the oxidation state of the ligand is preserved.
The dualism of the reactivity of compound 1 is caused by the
presence in the molecule of two different redox-active centers.
Obviously, the course of reactions of compound 1 is dependent
on several factors, mainly the nature of the substrate involved.
The bulkiness and coordinative features of the substrate
(monodentate, chelating, etc.) are of primary importance.
Intuitively, we feel that the ligand-centerd oxidation process in
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products were calculated from the amount of the dpp-Bian used (0.5 g,
1.0 mmol) in the syntheses.
transfer of an electron from the gallium to the dpp-Bian ligand,
resulting in compound 3. To the best of our knowledge, this is
the first observation of such behavior in main-group metal
complex. Also complexes 4 and 6 are unique examples, as they
consist of two different redox-active ligands. In such systems a
redox-isomerism that involves only the ligands can be expected.
In the case of compound 6 the two most probable redox-
isomers should have the following charge distribution: (dpp-
Bian)−Ga(F)(3,6-Q)− and (dpp-Bian)0Ga(F)(3,6-Q)2−. The
latter has been in fact observed. The stability of the redox-
isomers with some degree of probability can be deduced from
the reduction potentials of the ligands involved. Thus, the
existence of isomer (dpp-Bian)−Ga(F)(3,6-Q)− of complex 6
cannot be excluded since the first reduction potential of dpp-
Bian and the second reduction potential of 3,6-Q are close
(both −1.0 V).39 However, in such a situation the redox-
isomers as unique species might not exist at all: an electron can
be delocalized between two radical-anionic ligands via shuttle
transfer from one ligand to another and back, causing no
geometrical changes in the molecules, as usually observed in
redox-isomers.
In the reaction of compound 1 with BA the formation of a
2+4 cycloadduct may happen. But, one can expect that this
cycloadduct is thermodynamically less stable compared to
compound 7, which was isolated, although with only 26% yield.
Transformation of the cycloadduct to a more stable product
with dpp-Bian radicals has been recently observed in the
reaction of (dpp-Bian)Ga−Ga(dpp-Bian) with PhCCH.40
Unexpected coupling of the BA radical-anions at the γ position
to the oxygen atom is driven probably by the binuclear
character of the metal coordination center in compound 1: with
a fixed Ga−Ga bond distance the formation of a C−C bond at
the α position would cause tension in the six-membered
metallacycle.
Reaction of Compound 1 with Iodine. Preparation of (dpp-
Bian)IGa−GaI(dpp-Bian) (2) and (dpp-Bian)GaI(Py) (3). Addition
of iodine (0.13 g, 0.5 mmol) to a deep blue solution of 1 caused an
immediate red-brown coloring of the reaction mixture. After removal
of the solvent under vacuum 1,2-dimethoxyethane (50 mL) was added
to a residual brick-red solid. The ampule was sealed off under vacuum,
and the mixture was heated at 110 °C for 5 h. In 48 h after cooling of
the mixture to ambient temperature compound 2 (0.35 g, 47%) was
isolated as brown crystals. Mp: >280 °C. IR (Nujol): 1534 vs, 1339 w,
1318 m, 1255 m, 1216 w, 1187 s, 1147 w, 1120 s, 1045 w, 934 m, 895
w, 870 m, 820 s, 802 s, 762 vs, 699 w, 591 w, 549 m, 453 w cm−1. Anal.
Calcd for C72H80Ga2I2N4 × C4H10O2 (1484.76): C, 60.85; H, 5.89.
Found: C, 60.48; H, 6.11. In a separate synthesis the crude product 2
left after evaporation of 1,2-dimethoxyethane was dissolved in pyridine
(20 mL). All the volatiles were removed from the blue solution, and
the residue was crystallized from toluene. Compound 3 was isolated as
deep blue crystals (0.55 g, 63%) from toluene. Mp: 253 °C. Anal.
Calcd for C41H45GaIN3 × C7H8 (868.55): C, 66.25; H, 5.89. Found:
C, 66.38; H, 6.15. IR (Nujol): 1601 m, 1589 w, 1512 s, 1461 s, 1435 s,
1358 w, 1331 m, 1317 m, 1260 m, 1213 m, 1180 w, 1136 w, 1106 w,
1068 m, 1044 m, 1017 w, 938 w, 926 m, 902 m, 813 s, 766 vs, 695 s,
645 m, 618 w cm−1. 1H NMR (400 MHz, C6D6): δ 8.61 ppm (d, 2 H,
Py, J = 5.0 Hz); 7.30−7.26 (m, 4 H, Ar); 7.20−7.15 (m, 2 H, Ar); 7.11
(d, 2 H, Ar, J = 7.5 Hz); 7.08 (d, 2 H, Ar, J = 8.0 Hz); 7.04 (d, 1 H,
Ar); 7.00 (d, 2 H, Py, J = 7.5 Hz), 6.90−6.87 (dd, 2 H, Ar, J1 = 7.0 Hz,
J2 = 7.0); 6.67−6.60 (pst, 1 H, Py); 6.37 (d, 2 H, Ar, J = 6.8 Hz);
6.26−6.21 (pst, 2 H, Ar); 3.95 (sept, 2 H, CH(CH3)2, J = 6.8 Hz);
3.27 (sept, 2 H, CH(CH3)2, J = 6.8 Hz); 2.1 (s, 3 H, CH3C6H5), 1.57
(d, 6 H, CH(CH3)2, J = 6.8 Hz); 1.23 (d, 6 H, CH(CH3)2, J = 6.8 Hz);
1.13 (d, 6 C, CH(CH3)2, J = 6.8 Hz); 0.33 (d, 6 H, CH(CH3)2, J = 6.8
Hz).
Reaction of Compound 1 with 3,6-Di-tert-butyl-ortho-
benzoquinone. Synthesis of (dpp-Bian)Ga(Cat) (4). To a solution
of 1 in toluene (50 mL) was added 3,6-di-tert-butyl-ortho-
benzoquinone (0.22 g, 1.0 mmol). At 95 °C within 1 h the solution
changed color from deep blue to green. Green crystals of complex 4
(80%, 0.71 g) were separated from a concentrated toluene solution.
Mp: 265−268 °C. Anal. Calcd for C57H68GaN2O2 (882.85): C, 76.64;
H, 7.55. Found: C, 77.55; H, 7.76. IR (Nujol): 1593 m, 1536 vs, 1397
s, 1356 w, 1324 m, 1281 w, 1256 s, 1234 vs, 1215 m, 1200 m, 1147 vs,
1114 w, 1082 w, 1060 w, 1041 w, 1025 w, 971 vs, 952 m, 937 m, 920
m, 897 s, 881 m, 836 w, 824 s, 806 s, 793 s, 766 vs, 695 m, 671 w, 649
s, 627 w, 590 w, 550 w, 507 w cm−1. ESR (toluene, 293 K): ai(2 14N) =
0.43, ai(69Ga) = 1.42, ai(71Ga) = 1.81, ai(2 1H) = 0.11, ai(2 1H) = 0.12
mT, g = 2.0025.
EXPERIMENTAL SECTION
■
General Remarks. All manipulations were carried out under
vacuum using glass ampules. The solvents toluene, diethyl ether, DME,
and THF were dried over sodium/benzophenone and pyridine, over
sodium. Benzene-d6 (Aldrich) was dried over sodium/benzophenone
at ambient temperature and, just prior to use, condensed under
vacuum into the NMR tubes already containing the respective
compound. The IR spectra were recorded on a FSM-1201
Reaction of Compound 4 with AgBF4. Formation of [(dpp-
Bian)2Ag][BF4] (5) and (dpp-Bian)GaF(Cat) (6). To a solution of
compound 4 in toluene (50 mL), obtained in situ as described above,
AgBF4 (0.19 g, 1.0 mmol) was added. The color of the solution turned
from green to brown. Concentration of the solution under vacuum
gave orange crystals of compound 5, which were recrystallized from
THF (0.4 g, 57%). Complex 5 was also obtained by the reaction of
AgBF4 (0.1 g, 0.5 mmol) with dpp-Bian (0.5 g, 1 mmol) in THF.
Yield: 0.5 g (71%). Mp: 223 °C. Anal. Calcd for C84H104AgBF4N4O3
(1412.39): C, 72.26; H, 6.81. Found: C, 71.43; H, 7.42. IR (Nujol):
1653 m, 1617 m, 1584 m, 1363 m, 1316 w, 1281 m, 1250 w, 1228 w,
1189 m, 1057 s, 938 w, 836 s, 800 m, 784 m, 759 m, 610 w, 541 m,
521 w cm−1. 1H NMR of the crude product 5 precipitated from
toluene (200 MHz, C6D6): δ 7.5−6.5 ppm (m, 24 H, arom.); 3.35
(sept, 8 H, CH(CH3)2, J = 6.8 Hz); 1.42 (d, 24 H, CH(CH3)2, J = 6.8
Hz); 1.16 (d, 12 H, CH(CH3)2, J = 6.8 Hz). Concentration of the
toluene solution left after separation of crude 5 gave complex 6 (0.1 g,
25%) as dark green crystals. Mp: 187 °C. Anal. Calcd for
C50H60FGaN2O2 (809.72): C, 74.17; H, 7.47. Found: C, 73.55; H,
7.76. IR (Nujol): 1665 m, 1630 s, 1583 s, 1411 s, 1366 s, 1326 m, 1294
s, 1254 w, 1226 w, 1208 w, 1182 m, 1134 m, 1090 s, 1056 s, 970 m,
955 s, 850 m, 838 s, 806 s, 797 m, 782 s, 764 m, 757 m, 731 m, 695 m,
1
spectrometer in a Nujol; the H NMR spectra, on a Bruker DPX-
200 (200 MHz) and Bruker Avance III (400 MHz) NMR
spectrometer. The ESR spectra were obtained using a Bruker EMX
spectrometer (9.75 GHz); the signals were referenced to the signal of
diphenylpicrylhydrazyl (g = 2.0037). The magnetic susceptibilities in
the solid state were determined using a SQUID MPMS-XL-5
(Quantum Design) at 5 kOe in the range from 2 to 400 K. The
powdered sample was placed in a Teflon bucket and fixed in a
nonmagnetic sample holder. Each raw data file for the measured
magnetic moment was corrected for the diamagnetic contribution of
the sample holder and the Teflon bucket. The molar susceptibility data
were corrected for the diamagnetic contribution. Simulation of the
experimental magnetic data was performed with the julX program (E.
Bill, Max-Planck Institute for Chemical Energy Conversion, Mulheim/
̈
Ruhr, Germany). Melting points were measured in sealed capillaries.
The dpp-Bian was prepared by the condensation of acenaphthene-
quinone with 2,6-diisopropylaniline (both from Aldrich) in acetonitrile
under reflux. 3,6-Di-tert-butyl-o-benzoquinone was prepared according
to the literature procedure.41 AgBF4 was purchased from Aldrich.
Starting compound 1 has been prepared by reflux of dpp-Bian (0.5 g,
1.0 mmol) with an excess of gallium metal in toluene (50 mL) and
used in situ in the reactions described below. The yields of the
1
681 s, 654 s, 617 w, 583 m, 546 m, 516 w, 502 m, 405 w cm−1. H
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Inorganic Chemistry
Article
NMR (200 MHz, CDCl3): δ 8.20 ppm (d, 2 H, Ar, J = 8.3 Hz); 7.66
(t, 2 H, Ar, J = 7.5 Hz); 7.51 (s, 2 H, CH Cat); 7.07 (d, 2 H, Ar, J = 7.3
Hz); 3.66 (sept, 2 H, CH(CH3)2, J = 6.8 Hz); 2.64 (sept, 2 H,
CH(CH3)2, J = 6.8 Hz); 1.47 (d, 6 H, CH(CH3)2, J = 6.8 Hz), 1.18 (d,
6 H, CH(CH3)2, J = 6.8 Hz); 1.05 (m, 24 H, C(CH3)3, CH(CH3)2),
0.69 (d, 6 H, CH(CH3)2, J = 6.8 Hz).
DEDICATION
■
Dedicated to Professor Mikhail N. Bochkarev on the occasion
of his 75th birthday.
REFERENCES
■
Reaction of Compound 1 with Benzylideneacetone. For-
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Mp: 143 °C. Anal. Calcd for C106H116Ga2N4O2 (1617.47): C, 78.71;
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1
m, 830 m, 786 s, 753 s, 679 w, 610 m, 516 m cm−1. H NMR (400
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Single-Crystal X-ray Structure Determination of 2−7 and 9.
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■
S
* Supporting Information
This material is available free of charge via the Internet at
http://pubs.acs.org.
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AUTHOR INFORMATION
■
Corresponding Author
*E-mail: igorfed@iomc.ras.ru.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
This work was supported by the Russian Science Foundation
(grant 14-13-01063).
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