Redox Isomerism in Main-Group Chemistry: Tin Complex with o-Iminoquinone Ligands

Article abstract of DOI:10.1002/ejic.201701361

The bis-chelate tin complex 1, based on the 4,6-di-tert-butyl-N-(tert-butyl)-ortho-aminophenol ligand and representing the first example of a redox-isomeric compound in main-group chemistry, is synthesized and characterized by X-ray diffraction analysis.

Full text of DOI:10.1002/ejic.201701361

A Journal of
Accepted Article
Title: Redox-isomerism in main group chemistry: tin complex with o-
iminoquinone ligands
Authors: Maxim Chegerev, Alexandr Vladimirovich Piskunov,
Alyona Starikova, Stanislav Kubrin, Georgy Fukin, Vladimir
Cherkasov, and Gleb Abakumov
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To be cited as: Eur. J. Inorg. Chem. 10.1002/ejic.201701361
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
FULL PAPER
Redox-isomerism in main group chemistry: tin complex with
o-iminoquinone ligands
Maxim G. Chegerev[a], Alexander V. Piskunov[a]*, Alyona A. Starikova[b], Stanislav P. Kubrin[c], Georgy
K. Fukin[a], Vladimir K. Cherkasov[a], and Gleb A. Abakumov[a]
Abstract: Bis-chelate tin complex 1 on the basis of 4,6-di-tert-butyl-
N-(tert-butyl)-ortho-aminophenol ligand representing the first
example of redox-isomeric compound in main group chemistry was
synthesized and characterized by X-ray analysis. It was found that 1
exists in two electromeric forms in non-polar solvents: diamagnetic
pseudotetrahedral (AP)2SnIV (1a) and paramagnetic tetragonal-
pyramidal structure of low-valence tin (imSQ)2SnII (1b) (where AP
The search for a unique phenomenon of redox-isomerism
in non-transition metal complexes represents a challenge. To
the best of our knowledge, reversible valence-tautomeric
rearrangement, involving a main group metal centre and redox-
active ligands, was not observed. An example of the solvent-
induced metal–metal bond dissociation supported by electron
transfer to the organic ligands was found in gallium complex
bearing diiminoacenaphthene.[5] It should be noted that this
process is irreversible and accompanied with chemical
transformation.
Ligand-based redox-isomerism in zinc compound Zn(L)2
bearing tridentate o-iminoquinone ligands has been reported by
Wieghardt et al.[6] However further theoretical investigations
have shown that it is neither metal-to-ligand nor ligand-to-ligand
electron transfer and most likely this transformation is caused by
singlet-triplet transition of one of the redox-active ligands.[7]
Recently, we reported a quantum chemical investigation of
the possibility of the occurrence of VT in group 14 (E = Si, Ge,
Sn, Pb) element derivatives with redox-active o-indophenols and
o-aminophenols.[8] It was shown that bis-chelate tin complex 1
and imSQ
– dianion and radical-anion forms of the ligand,
respectively). The reversible redox-isomeric rearrangement between
1a and 1b was investigated in solution by means of
magnetochemistry, EPR, UV-Vis and 119Sn Mössbauer spectroscopy.
This interconversion can be quenched by an addition of strong donor
ligand such as pyridine (Py), resulting in an octahedral complex
(AP)2SnIV(Py)2 (2) which does not undergo redox-isomerism.
Introduction
Transition metal complexes may exhibit thermally or light-
induced reversible intramolecular electron transfer between a
metal centre and a redox-active ligand (or ligands) giving rise to
two isomers. This effect is called redox-isomerism (or valence
tautomerism) and was firstly reported by Pierpont and Buchanan
in 1980 for substituted o-benzoquinone complex of cobalt.[1]
Since rearrangements of this type are usually accompanied by a
change in the systems spin state, complexes capable of valence
tautomerism (VT) represent promising candidates for the design
of molecular switches with magnetic responses.[2] To date, the
synthesis and VT behaviour of transition metal (V, Mn, Fe, Co,
Ni, Cu and Ru) coordination compounds with a variety of redox-
active ligand types including o-quinones, o-iminoquinones and
α-diimines have been extensively studied and amply reviewed.[3]
Rare examples of redox-isomerism in lanthanide (Yb)
complexes of diiminoacenaphthene ligand were reported
recently.[4]
on
the
basis
of
4,6-di-tert-butyl-N-(tert-butyl)-
narrow energy gap
o-aminophenol is characterized by
a
(7.0 kcal·mol-1) between the pseudotetrahedral 1a and
tetragonal-pyramidal 1b electromeric[9] forms and a low energy
barrier for their interconversion (11.7 kcal·mol-1). Noteworthy that
according to the calculations diradical tin(II) structure 1b is a
ground state with respect to the pseudotetrahedral diamagnetic
1b. Thus, data obtained allow us to consider compound 1 as a
promising candidate for the observation of thermally driven
redox-isomeric rearrangement (Scheme 1).
[a]
M.G. Chegerev, A.V. Piskunov, G.K. Fukin, V.K. Cherkasov,
G.A. Abakumov
Scheme 1. Reversible redox-isomeric rearrangement.
G.A. Razuvaev Institute of Organometallic Chemistry
603950, Tropinina str. 49, Nizhny Novgorod, Russia. Fax: +7 8314
627497; Tel: +7 8314 627682
E-mail: pial@iomc.ras.ru
https://www.researchgate.net/profile/Alexandr_Piskunov
A.A. Starikova
Institute of Physical and Organic Chemistry at Southern Federal
University
344090, Stachka Avenue 194/2, Rostov-on-Don, Russia.
S.P. Kubrin
Research Institute of Physics, Southern Federal University
344090, Stachka Avenue 194, Rostov-on-Don, Russia.
It should be noted that solid state intramolecular electron
transfer in transition metal complexes does not require
significant change of the geometry of coordination polyhedron.[3]
In contrast to mentioned above, predicted VT in compound 1 is
accompanied by the significant change of coordination geometry
(tetragonal pyramidal vs tetrahedral). Such structural
reconstructions in bis-chelate tin complex 1 can be realized in
solution only. Similar considerable transformations of geometry
[b]
[c]
of
copper (square planar vs tetrahedral)[10a-c] and rhodium
(tetragonal pyramidal vs trigonal
bipyramidal)[10d]
o-semiquinonates.
VT
complexes
in
solutions
are
known
for
Supporting information, including spectral data, magnetic
susceptibility measurements and computational details is given via a
link at the end of the document.
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
FULL PAPER
Herein we report the synthesis, characterization and
investigation of redox-isomeric properties of bis-chelate tin
complex 1 bearing redox-active 4,6-di-tert-butyl-N-(tert-butyl)-o-
aminophenol ligand.
for Sn–N12) and are comparable with those in known o-
amidophenolate tin compounds.[13] The C(1)–O(1) 1.3670(15) Å,
C(2)–N(1) 1.4111(16) Å and C–C distances in the six-membered
carbon ring (1.3901(17)–1.4149(17) Å) lie in the range typical for
the dianion form of the o-iminobenzoquinone ligand. We have
performed the analysis of bond lengths for redox-active ligands
in 1a using utility of “metric oxidation state” (MOS) values for
assessing bonding in catecholate and amidophenolate
ligands.[14] The MOS value obtained for complex 1a is consistent
with the dianion nature of the ligands and amounts to -1.98(6).
Measurements of magnetic susceptibility of crystals of 1a
show no paramagnetism in the range from 300K to 2K that
confirms its diamagnetic nature. However, it was found that
dissolution of diamagnetic orange crystals of 1a in non-polar
solvents such as toluene (or hexane) leads to intense yellow-
green colouring immediately. UV-Vis spectrum of the solution of
1 in toluene displays the intense band at 415 nm and broadened
signal in the region of 600-900 nm at room temperature (Figure
2). The presence of wide band at 600-900 nm is characteristic
Results and Discussion
[11]
The tert-butyl substituted aminophenol APH2
was
prepared as white air-stable solid in high 94% overall yield
through the modified one-step solvent-free procedure from 3,5-
di-tert-butylcatechol and tert-butyl amine in presence of catalytic
amount of iodine.
The bis-chelate complex 1 was prepared by the addition of
SnCl4 to a cold hexane solution of (AP)Li2. The latter was
prepared from APH2 and 2 eq. of n-BuLi and used in situ. The tin
ion readily bind 2 eq. of the chelating dianionic ligand (AP)2-
giving four-coordinated complex (Scheme 2). The colour of
reaction mixture became yellow-green immediately. Compound
1 was isolated in diamagnetic form 1a as a yellow-orange
crystalline solid in 70% yield from the concentrated hexane
solution.
According to the single crystal X-ray diffraction analysis,
the geometry of coordination polyhedron in 1a is best described
as feebly distorted tetrahedron (Figure 1). The O and N atoms of
both AP ligands occupy the tetrahedron vertices. Chelating
o-amidophenolate ligands have nearly planar geometry. The
dihedral angle between two planes of redox-active ligands
amounts to 89.94°.
for
the
metal
complexes
containing
radical-anion
o-iminosemiquinonato (imSQ) ligands[15,16] and specifies the
formation of diradical isomer 1b (Scheme 1). The results of time-
dependent density functional theory (TD-DFT B3LYP/6-
311++G(d,p)/SDD) calculations of electron transitions performed
by using the Gaussian 09 program package[17] are in accordance
with experimental data. The molecular orbital (MO) shapes in 1b
indicate that the long wavelength transitions correspond to
intraligand charge transfer (ILCT) combined with a significant
metal to ligand charge transfer (MLCT) character, in which the
SOMOs and LUMO β-MOs are involved (Figures S1-S2 in
Supporting information).
t-Bu
t-Bu
t-Bu
N
O
O
OLi
t-Bu
+SnCl4
Sn
2
-4LiCl
hexane
t-Bu
t-Bu
N
NLi
t-Bu
t-Bu
1a
t-Bu
Scheme 2. Synthesis of complex 1.
Figure 1. Solid-state structure of the isomer 1a with 50% thermal probability
ellipsoids. The H atoms are omitted for clarity.
Figure 2. Temperature dependence of the absorption spectrum of 1 in toluene
(1 – 293 K, 2 – 323 K, 3 – 343 K, 4 – 363 K). Line 5 is absorption spectrum of
compound 2 in pyridine at 293 K (C = 2.0x10-3 M, L = 1 cm). Insets: isosbestic
points at 430 and 520 nm.
The values of Sn(1)–O(1) 1.9697(8) Å and Sn(1)–N(1)
1.9938(9) Å bond lengths are less than the sum of the covalent
radii of the corresponding elements (2.09 Å for Sn–O[12], 2.1 Å
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
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The elevation of temperature from 293 K to 363 K is
accompanied by decreasing the intensity of these bands and is
caused, apparently, by lowering the equilibrium concentration of
diradical isomer 1b in mixture.
quadrupole splitting of ∆EQ = 1.83(2) mm·s-1. The isomer shift
lies in the typical range for tetravalent tin.[19]
The determination of the magnetic susceptibility of 1 in
toluene solution using Evans method revealed a value of
effective magnetic moment (μeff) 0.25 μB at 313 K. Decreasing
the temperature to 223K leads to rising magnetic moment up to
0.87 μB. Observed process is completely reversible (Figure S4
in Supporting information).
The X-band EPR spectrum of the solution of complex 1 in
toluene demonstrates the presence of broadened signal at room
temperature. In glassy toluene matrix at 150 K EPR spectrum
shows features indicative of triplet diradical species (gav
=
2.0026) with characteristic half-field (∆ms = 2) signal (Figure 3).
The zero-field splitting parameters are following: D = 22.7x10-3
cm-1 and E = 4.7x10-3 cm-1. These values obtained are
comparable with D and E found for tin diradical derivatives.[15]
The sharp signal (marked by asterisk), which corresponds to
doublet particles, can be explained by association of diradicals
1b
in
solution
giving
rise
S = 1/2 species. Such clusterization behavior is well known for
such type diradical metal bis-o-semiquinolates in non-polar
solvents.[18]
Figure 4. Experimental and simulated 119Sn Mössbauer spectra of the isomer
1a at various temperatures.
Figure 3. EPR spectra of compound 1 in glassy toluene matrix at 150K (a -
experimental, b – simulation; asterisk denotes a doublet species). Inset: half-
field region.
The presence of tin ions in different oxidation states (+2
and +4) in toluene solution of compound 1 was unequivocally
proved by 119Sn Mössbauer spectroscopy. For the comparison,
investigations were carried out both for the crystals of 1a and for
frozen toluene solution of 1. The Mössbauer spectra at different
temperatures are presented in Figure 4 and Figure 5 together
with transmission integral fits. The corresponding fitting
parameters are listed in Table 1. At 300 K the spectrum of
crystals 1a (Figure 4) could be well reproduced with a single
signal at an isomer shift of δ = 0.79(2) mm·s-1, subjected to
Figure 5. Experimental and simulated 119Sn Mössbauer spectra of frozen
toluene solution of 1 at various temperatures.
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
FULL PAPER
Observed asymmetry of the corresponding spectrum
disappears with decreasing the temperature that is caused by
Goldanskii-Karyagin effect.[20] It should be noted, that we did not
observe any new signals belonging to tin ions. On the other
hand, the spectra of frozen solution of 1 at 13K and 100K
(Figure 5) were best reproduced by a superposition of two
signals (D1 and D2) with different isomer shifts and quadrupole
splitting parameters (Table 1). The D1 (δ1 = 0.74(2) mm·s-1) is
quite close to signal obtained for crystalline 1a and is
which leads to association of diradicals with subsequent
lowering of the entropy of the system. It shifts the equilibrium
(Scheme 1) to the diamagnetic form 1a. The fact of association
of related diradical metal complexes in non-polar solvents is well
known in the literature[18]
.
Moreover, mentioned above
observation of signals from S=1/2 species in EPR spectra can
indirectly confirm this hypothesis.
We can assume two possible mechanisms for this
interconversion of paramagnetic 1b into diamagnetic 1a. The
repulsion of two sterically hindered o-iminosemiquinonate
ligands and a lone pair of tin(II) leads to the distortion of the
initial pyramidal geometry to the pseudotetrahedral one (through
characteristic for Sn+4, while D2 (δ2
=
2.07(2) mm·s-1)
corresponds to divalent tin derivative.[19] The quadrupole splitting
in both cases, as expected, arises from the low site symmetry of
the tin ions in 1a and 1b.
predicted
by
calculations[8]
MECP
geometry).
Such
The relative intensities of the various peaks in Mössbauer
spectra reflect the relative concentrations of compounds in a
sample and can be used for quantitative analysis. In case of
spectra of frozen toluene solution of complex 1, concentration of
the divalent species amounts to 11 %. This value is in a good
agreement with results of the magnetic susceptibility
measurements using Evans method. The experimental moment
can be compared with the spin-only value of 2.45 μB for two
uncoupled spins. The share N of available diradicals can be
tentatively estimated from equation: 0.87 = 2.45•(N)1/2, which
yields 13% of paramagnetic molecules (at 223K).
rearrangement causes the electron transfer from the divalent
metal to radical-anion ligands. The alternative route includes
oxidation of the low valent tin center by two iminosemiquinone
ligands in 1b which leads to the formation of tin(IV) compound.
The last stabilizes as a tetrahedron. It has to be mentioned that
the unequivocal choice of the mechanism of this redox-isomeric
interconversion needs the additional investigations.
It was found that dissolution of 1 in pyridine leads to
conversion of the solution colour from yellow-green to intense
orange and the subsequent full disappearance of any radical
signal in EPR spectrum. The UV-Vis spectrum does not
demonstrate characteristic broadened signal at 600-900 nm
(Line 5 in Figure 2). All these alterations are caused by the
formation of new octahedral diamagnetic tin complex 2 (Scheme
3). According to the computational results, absorption in the area
of 500 nm corresponds to the band of charge transfer from o-
amidophenolate ligand to pyridines (LLCT) (Figure S3 in
Supporting information).
Table 1. Fitting parameters of 119Sn Mössbauer spectroscopic measurements
of 1 at different temperatures (δ – isomer shift, ∆EQ – electric quadrupole
splitting, G – line weight).
δ±0.02,
∆EQ ±0.02,
G±0.02,
mm/s
Phase
T, K
component
mm/s
mm/s
Single crystals of complex 2 suitable for X-ray diffraction
analysis were obtained from saturated pyridine solution. In solid
state, compound 2 shows a distorted octahedral coordination
geometry composed of the O and N atoms of two AP ligands
and N(3) and N(4) atoms of coordinated pyridine molecules
(Figure 6). The dihedral angle between two redox-active ligands
amounts to 72.14°. The C-O, C-N, Sn-O and Sn-N bond lengths
in chelating fragments are comparable with o-amidophenolate
tin structure 1a and confirm its dianionic nature.[13] Two pyridine
molecules have cis-spatial arrangement in the complex 2. The
values of Sn(1)–N(3) 2.3385(11) Å and Sn(1)–N(4) 2.3624(11) Å
distances are larger than the sum of the covalent (2.12 Å)[12] but
significantly less than the sum of the van-der-Waals (3.8 Å)[12]
radii of corresponding elements. It indicates its donor–acceptor
bonding character.
300
200
100
13
D1
D1
D1
D1
D1
D2
D1
D2
0.79
0.79
0.80
0.81
0.69
2.04
0.74
2.07
0.81
0.80
0.94
1.25
1.83
0.92
1.88
1.36
1.83
1.87
1.87
1.85
1.39
4.38
1.47
4.37
Crystals
of 1a
100
13
Frozen
solution
of 1
Data obtained indicate that dissolution of diamagnetic
compound 1a in toluene is accompanied by occurrence of
redox-isomeric rearrangement with the formation of 1b
comprising tin ion in oxidation state +2 and ligands in o-
iminosemiquinonate form (Scheme 1). Noteworthy that previous
quantum-chemical calculations[8] suggested that the diradical 1b
should be more preferable than the pseudotetrahedral
diamagnetic 1a. However, as we can see, in a frozen matrix the
distribution of the diradical structure amounts to only 11%. We
suppose that the formation of diradicals is not favored
entropically due to intermolecular interaction between them
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
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Experimental Section
General considerations: All reactants were purchased from
Aldrich. Solvents were purified by standard methods.[22] All
manipulations on complexes were performed under vacuum
conditions, in which oxygen and moisture were excluded. EPR
spectra were recorded by using a Bruker EMX spectrometer
(working frequency ≈ 9.75 GHz). The gi values were determined
using 2,2-diphenyl-1-picrylhydrazyl (DPPH) as the reference (gi
= 2.0037). EPR spectra were simulated using Easyspin toolbox
for Matlab.[23] NMR spectra were recorded by using a Bruker
Avance III 400 MHz instrument with TMS as an internal standard.
The signals in the NMR spectra were assigned using 2D ge-
COSY and ge-HSQC procedures. Solution magnetic
susceptibility for complex 1 was determined by Evans method[24]
using Bruker Avance III 400 NMR spectrometer. UV-VIS spectra
were obtained on a Perkin Elmer λ 25 spectrometer. 119Sn
Mössbauer spectra were recorded at MS1104Em spectrometer
by using Ca119mSnO3 as a source. The measurements were
conducted in the usual transmission geometry in the
temperature range from 13 to 300 K with a total counting time of
up to 1 day per spectrum. The magnetic susceptibility of the
polycrystalline complex 1a was measured with a Quantum
Design MPMSXL SQUID magnetometer in the temperature
Figure 6. Solid-state structure of complex 2 with 50% thermal probability
ellipsoids. The H atoms and lattice solvent molecules are omitted for clarity.
Selected bond lengths [Å]: C(1)-O(1) 1.3649(15), C(19)-O(2) 1.3620(15), C(2)-
N(1) 1.3991(16), C(20)-N(2) 1.3943(16), Sn(1)-O(1) 2.0182(9), Sn(1)-O(2)
2.0251(9), Sn(1)-N(1) 2.0769(10), Sn(1)-N(2) 2.0790(11).
toluene
Py
II
IV
IV
(imSQ) Sn
(AP) Sn
(AP) Sn (Py)
2 2
2
2
1b
1a
2
Scheme 3. Transformations of complex 1 in different solvents.
range 2-300
K with magnetic field of up to 5 kOe.
Crystallographic data for the structural analysis have been
deposited with the Cambridge Crystallographic Data Centre,
CCDC no. 1472088 and 1472089 for compounds 1a and 2•2Py
respectively.
Complex 2, which does not undergo redox-isomeric
transformations, is the only product of the interaction of
electromers 1a and 1b with pyridine (Scheme 3). It should be
noted that the formation of compound 2 is irreversible: a heating
of the solution up to 353 K does not result in dissociation of this
complex into initial components. It is confirmed by the results of
calculations (DFT B3LYP/6-311++G(d,p)/SDD)) pointing to the
energy preference of 2 by 17 kcal·mol-1 as compared to the sum
of energies of isolated tetrahedral isomer 1а and two pyridine
molecules (Table S1 in Supporting information). Compound 2
can be recrystallized from toluene without losing solvated
pyridine molecules. It should be noted that the effect of added
donor ligands on the distribution of redox states between ligand
and metal center is known in the literature.[21]
Synthesis of 4,6-di-tert-butyl-N-(tert-butyl)-o-aminophenol
(APH2): Ampoule was charged with 3,5-di-tert-butylcatechol (5 g,
22.5 mmol) and 2,5 ml of tert-butyl amine was added. 0.28 g
(5% mol) of I2 was entered into the reaction. Reaction mixture
was kept for a 4 hours at 120°C (melting point of 3,5-di-tert-
butylcatechol). The colour of reaction mixture became brown.
The residue was twice recrystallized from hot acetonitrile. APH2
was obtained as a white crystalline product. Yield: 5.9 g (94%).
Synthesis of bis-(4,6-di-tert-butyl-N-(tert-butyl)-o-amido-
phenolato)tin(IV) (1a): A frozen hexane solution (20 ml) of
APLi2, generated from 0.34 g of APH2 (1.2 mmol) and 2 equiv of
n-BuLi in hexanes, was thawed and SnCl4 (0.156 g, 0.6 mmol)
was added. The reaction mixture was allowed to warm to room
temperature and then was kept for 1 h. Reaction mixture
became intense yellow-green. A white precipitate of LiCl
byproduct was removed by filtration. Solution was concentrated
twice (10 ml). Complex 1 was isolated in diamagnetic 1a form as
a yellow-orange crystalline solid in 70% yield from hexane
solution. Yield: 0.28 g (70%). C36H58N2O2Sn. Calculated C 64.58,
Conclusions
In summary, bis-chelate tin complex 1 bearing 4,6-di-tert-
butyl-N-(tert-butyl)-o-aminophenol ligands is the first non-
transition metal compound, which demonstrates the redox-
isomerism phenomenon. This compound exists in non-polar
solvents as an equilibrium mixture of two different isomers –
diamagnetic pseudotetrahedral (AP)2SnIV and paramagnetic
tetragonal-pyramidal structure of low-valence tin (imSQ)2SnII.
This process can be quenched by an addition of strong donor
ligand resulting in an octahedral complex 2 which does not
undergo reversible intramolecular electron transfer. This work
can be regarded as a starting point in investigations of
unexplored field of redox-isomerism in main group chemistry.
H 8.73, N 4.18, Sn 17.73; found C 64.54, H 8.78, N 4.23, Sn
1
17.78. H NMR (toluene-d8, J/Hz, 20°C): δ = 7.14 (d, 2H, JH,H
=
2.1, HAP); 7.06 (d, 2H, JH,H = 2.1, HAP); 1.67 (s, 18H, t-Bu); 1.42
(s, 18H, t-Bu); 1.37 (s, 18H, N-(t-Bu)) ppm. 13C NMR (toluene-d8,
20°C): δ = 144.7, 140.2 (C-(t-Bu)); 135.9 (C-O); 135.6 (C-N);
112.2, 109.5 (Caryl); 54.1 (N-Cquat); 35.2, 34.4 (Cquat); 31.7, 31.4,
29.7 (CH3(t-Bu)) ppm.
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
FULL PAPER
2001, 40, 5653-5659; d) G. A. Abakumov, G. A. Razuvaev, V. I.
Nevodchikov, J. Organomet. Chem. 1988, 341, 485-494.
Synthesis of bis-(4,6-di-tert-butyl-N-(tert-butyl)-o-amido-
phenolato)tin(IV) bis-pyridinate (2): Complex 1a (0.28g 0.42
mmol) was dissolved in an excess of pyridine (20 ml). The
reaction mixture became intense orange. Solution was
concentrated twice (10 ml). Complex 2 was isolated as orange
crystals in 85% yield. Yield: 0.29 g (85%). C46H68N4O2Sn.
Calculated C 66.74, H 8.28, N 6.77, Sn 14.34; found C 66.71, H
[11] K. J. Blackmore, J. W. Ziller, A. F. Heyduk, Inorg. Chem. 2005, 44,
5559-5561.
[12] S. S. Batsanov, Russ. J. Inorg. Chem. 1991, 36, 1694-1706.
[13] a) R. Contreras, V.M. Jimenez-Perez, C. Camacho-Camacho, M.
Güizado-Rodrigues, B. Wrackmeyer, J. Organomet. Chem. 2000, 604,
229-233; b) I. A. Aiva’zyan, A. V. Piskunov, G. K. Fukin, E. V. Baranov,
A. S. Shavyrin, V. K. Cherkasov, G. A. Abakumov, Inorg. Chem.
Commun. 2006, 9, 612-615; c) A. V. Piskunov, I. A. Aivaz’yan, G. A.
Abakumov, V. K. Cherkasov, O. V. Kuznetsova, G. K. Fukin, E. V.
Baranov, Russ. Chem. Bull. 2007, 56, 261-266; d) A. V. Piskunov, M. G.
Chegerev, G. K. Fukin, J. Organomet. Chem. 2016, 803, 51-57.
1
8.25, N 6.81, Sn 14.38. H NMR (C6D6, J/Hz, 20 °C): δ = 8.69
(dd, 4H, JH,H = 1.5, JH,H = 4.6, Hpy); 7.22 (d, 2H, JH,H = 2.1, HAP);
6.96 (d, 2H, JH,H = 2.1, HAP); 6.65 (tt, 2H, JH,H = 1.5, JH,H = 7.7,
Hpy); 6.35 (m, 4H, Hpy); 1.77 (s, 18H, t-Bu); 1.67 (s, 18H, t-Bu);
1.44 (s, 18H, N-(t-Bu)) ppm. 13C NMR (C6D6, 20 °C): δ = 148.5
(CPy); 145.5, 139.7 (C-(t-Bu)); 138.0 (CPy); 137.6 (C-O); 132.2
(CPy); 123.5 (C-N); 110.6, 108.4 (Caryl); 53.9 (N-Cquat); 34.9, 34.4
(Cquat); 32.0 (CH3(t-Bu)); 31.0, 30.5 (CH3(t-Bu)) ppm. 119Sn NMR
(C6D6, 20 °C): δ = -451.4 ppm.
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We are grateful to the Russian Science Foundation
(grant 17-13-01428) for financial support of this work.
Keywords: redox-isomerism • redox-active ligand •
iminoquinone • tin complex• Mössbauer spectroscopy
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European Journal of Inorganic Chemistry
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10.1002/ejic.201701361
European Journal of Inorganic Chemistry
FULL PAPER
Entry for the Table of Contents
FULL PAPER
M.G. Chegerev, A.A. Starikova, S.P.
Kubrin, G.K. Fukin, V.K. Cherkasov,
G.A. Abakumov, A.V. Piskunov*
Page No. – Page No.
Redox-isomerism in main group
chemistry: tin complex with
o-iminoquinone ligands
Bis-chelate tin complex bearing redox-active o-aminophenol ligand representing the
first example of redox-isomeric compound in main group chemistry was synthesized
and investigated. This complex exists in non-polar solvents as an equilibrium
mixture of two different isomers – diamagnetic pseudotetrahedral tin(IV) compound
and paramagnetic tetragonal-pyramidal structure of tin(II).
This article is protected by copyright. All rights reserved.