Multiple Reactivity of SnIIComplexes Bearing Catecholate and o-Amidophenolate Ligands

Article abstract of DOI:10.1002/ejic.201600501

The reactivity of tin(II) catecholate complex CatSn (1) (where Cat = 3,6-di-tert-butylcatecholate dianion) and two o-amidophenolate complexes^DippAPSn (2) and^PhAPSn (3) [where^DippAP = 4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)amidophenolate;^PhAP = 4,6-di-tert-butyl-N-(phenyl)amidophenolate dianions] towards different reagents is reported. Products of the insertion of 1 and 2 into the S–S bond of tetramethylthiuram disulfide were obtained and characterised by X-ray diffraction analyses. The low temperature oxidation of complexes 1 and 2 with 2-ethoxy-3,6-di-tert-butylphenoxy radical enabled us to detect formation of paramagnetic tin(II) derivatives containing the radical-anion form of the redox-active ligand. The reaction of tin derivative 3 with Ni(CO)₄leads to substitution of one of the CO groups in the latter with the formation of a new bimetallic product.

Full text of DOI:10.1002/ejic.201600501

DOI: 10.1002/ejic.201600501
Full Paper
Stannylenes
Multiple Reactivity of SnII Complexes Bearing Catecholate and
o-Amidophenolate Ligands
Maxim G. Chegerev,[a] Alexander V. Piskunov*[a] Aryna V. Maleeva,[a] Georgy K. Fukin,[a] and
Gleb A. Abakumov[a]
Dedicated to Professor Vladimir K. Cherkasov on the occasion on his 70th birthday
Abstract: The reactivity of tin(II) catecholate complex CatSn (1) analyses. The low temperature oxidation of complexes 1 and
(where Cat = 3,6-di-tert-butylcatecholate dianion) and two o-
2 with 2-ethoxy-3,6-di-tert-butylphenoxy radical enabled us to
detect formation of paramagnetic tin(II) derivatives containing
the radical-anion form of the redox-active ligand. The reaction
of tin derivative 3 with Ni(CO)4 leads to substitution of one of
the CO groups in the latter with the formation of a new bimetal-
lic product.
amidophenolate complexes DippAPSn (2) and PhAPSn (3) [where
DippAP
=
4,6-di-tert-butyl-N-(2,6-diisopropylphenyl)amido-
phenolate; PhAP = 4,6-di-tert-butyl-N-(phenyl)amidophenolate
dianions] towards different reagents is reported. Products of the
insertion of 1 and 2 into the S–S bond of tetramethylthiuram
disulfide were obtained and characterised by X-ray diffraction
Introduction
Considerable interest in the chemistry of heavier carbene ana-
logues[1a–1c] developed following the isolation of the first stable
N-heterocyclic carbene in 1991 by Arduengo III.[1d] At present
many stable silylenes,[2] germylenes,[3] stannylenes[3f,4] and
plumbylenes[5] derived from different heterocycles have been
prepared. Interest in these compounds arises from their elec-
tronic structures, chemical properties and their ability to act in
catalytically active metal complexes as N-heterocyclic carb-
enes.[6]
The variation of heteroatoms in the chelating fragment of
various metallenes provides a useful means for tuning their re-
activity. Replacement of nitrogen atoms in the metallocycle
with O-atoms leads to the formation of chelate O,N-(o-amido-
phenolate) and O,O-(catecholate) complexes (Scheme 1). More-
over, as mentioned above, N,N, O,N and O,O ligands are poten-
tially redox-active, which significantly expands their scope of
reactivity.
Redox ligands can be used as reservoirs of electrons for
bond-making and bond-breaking reactions. They also can sup-
port multi-electron transformations required to promote atom-
and group-transfer reactions.[7] The ability of o-quinones and o-
iminoquinones to exist in three different redox states provides
the foundation for their rich coordination chemistries.[7f,8] Such
complexes are interesting as potential reagents in organic syn-
thesis, especially for addition, activation or transfer reactions of
Scheme 1. Stable heavier analogues of carbenes.
small molecules. In particular, these species have proven to be
very convenient objects for EPR investigations.[9]
The complexes under consideration possess four possible
and useful aspects of reactivity (Scheme 2): a) low valence SnII
atom, which can be involved in oxidative addition reactions
with the following formation of SnIV species, b) the ability to
donate a lone pair of electrons to Lewis acids, such as transition
metals, giving bimetallic derivatives, c) a vacant p-orbital by
which the compound can react with Lewis bases, and d) a
redox-active ligand enabling participation in redox processes
independent of metal oxidation state.
[a] G. A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of
Sciences, Laboratory of Organoelement Compounds,
Tropinina Street 49, 603950 Nizhny Novgorod, Russian Federation
E-mail: pial@iomc.ras.ru
http://www.iomc.ras.ru
Scheme 2. Possible reactivity centres of stannylenes.
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The present work reports investigation of multiple reactivity into the S–S bond and consequent formation of new hexacoor-
modes of some stannylenes bearing catecholate and o-amido- dinate tin(IV) complexes 3 and 4 containing Sn–S bonds
phenolate ligands.
(Scheme 4).
Results and Discussion
We previously reported the synthesis of stannylene derivatives
based on 3,6-di-tert-butyl-o-benzoquinone CatSn (1) and 4,6-
di-tert-butyl-N-(2,6-diisopropylphenyl)-o-iminobenzoquinone
DippAPSn (2). White trimeric complex 1 was obtained earlier as
a minor product (21 % yield) of the reduction of 3,6-di-tert-
butyl-o-benzoquinone by tin amalgam.[10a] Herein we used the
Scheme 4. Oxidative addition of TMTD to stannylenes.
[10b]
salt metathesis reaction between CatNa2
and the dioxane
complex of tin dichloride in THF solution. This pathway is more
efficient and complex 1 was obtained with high yield (84 %)
(Scheme 3). Dimeric o-amidophenolate supported stannylene
complex 2 was obtained as a result of salt metathesis reaction
between DippAPLi2 and SnCl2·diox in THF solution as a yellow
material soluble in most organic solvents.[4c] The compounds
obtained were found to be stable in both the solid state and in
solutions under anaerobic conditions.
The molecular structures of 3 and 4 were determined by X-
ray diffraction analysis and are shown in Figure 1. Selected met-
rical parameters can be found in Table 1. Single crystals suitable
for X-ray diffraction analysis were obtained from the chilled
mixture of CH2Cl2/n-hexane. Crystals of 3 contain one solvated
dichloromethane molecule. The geometry of coordination poly-
hedra in 3 and 4 can be described as a distorted trigonal prism
or octahedron. The univocal choice of the coordination polyhe-
dron type is unclear. The authors[13] propose the use of the
torsion angle α between coordination centres of bidentate li-
Scheme 3. Synthesis of complexes 1 and 2.
The (a) Pathway: Oxidative Addition
Bond homolysis is a very useful reaction for probing accessible
ligand-based reactivity and disulfides were found to be versatile
reagents for examining reduction reactivity of metal complexes
with redox-active ligands.[10b,11a–11c] On the other hand, it is
known that stannylenes undergo oxidative addition with disulf-
ides.[4f,11d] We have found that complexes 1 and 2 react readily
with equimolar amounts of tetramethylthiuram disulfide
(TMTD) to give dark-red crystalline diamagnetic products 3 and
4 with high yields. The reaction is complete within a few hours
at the room temperature. These conditions do not induce ho-
molytic dissociation of TMTD which proceeds at T = 130–
150 °C.[12] The reaction involves the insertion of low valence tin
Figure 1. Crystal structures of 3 (top) and 4 (bottom) with 30 % thermal
probability ellipsoids. The H atoms are omitted for clarity.
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gands for the definition of coordination geometry in hexacoor- resonances are located at δSn = –658 ppm and δSn = –661 ppm
dinate complexes. The α value is equal to zero for a perfect in the 119Sn NMR spectra. This region of δSn = –500 to
trigonal prism, whereas it becomes 60° for a pure octahedral –750 ppm is characteristic for hexacoordinate bis(dithiocarb-
geometry. In the case of 3 and 4 (αav. = 43.3° and 44.4°, respec- amato)tin(IV) derivatives.[17a,18]
tively) the coordination geometry is intermediate between the
two edge structures. The Sn(1)–O(1) [2.0479(9) Å] and Sn(1)–
The (b) Pathway: Reaction with Lewis Acid
O(2) [2.0223(9) Å] distances for 3 and Sn(1)–O(1) [2.0439(13) Å]
and Sn(1)–N(1) [2.0640(17) Å] bond lengths for 4 are less than
the sum of the covalent radii of the corresponding elements
(2.09 Å for Sn–O,[14] 2.1 Å for Sn–N[14]) and are quite close to
those observed in tin(IV) catecholate complexes (1.995–
2.080 Å)[10] and known o-amidophenolate tin compounds.[15]
Some adducts of stannylenes with Lewis-acids like boron com-
pounds or AlCl3 are known.[19] Regarding the complexes of
stannylenes with transition metals, it should be mentioned that
stannylenes act in these cases as Lewis bases; they may be
stabilized by coordination of one or two solvent molecules.[20]
In an effort to obtain a new bimetallic product, catecholate
complex 1 was treated with Ni(CO)4 in a molar ratio of 1:1.
Unfortunately, all attempts to yield a Ni0 compound coordi-
nated with stannylene failed. Most likely this compound is un-
stable and decomposes in solution to afford unidentified prod-
ucts.
With the aim of obtaining the amidophenolate-supported
bimetallic compound, we decided to prepare less sterically-hin-
dered stannylene complex 5 containing a phenyl group at the
nitrogen atom. Preparation of the N-phenyl-substituted stannyl-
ene 5 was achieved by an amine elimination reaction between
bis[bis(trimethylsilyl)amido]tin(II)[21] and PhAPH2 [where
PhAPH2 = 4,6-di-tert-butyl-N-(phenyl)-o-aminophenol][22] in Et2O
solution (Scheme 5).
Table 1. Selected bond lengths [Å] and angles [°] of 3·CH2Cl2, 4, 5 and 7.
Bond [Å]
3·CH2Cl2
4
5
7
Sn(1)–O(1)
Sn(1)–O(2)
Sn(1)–N(1)
Sn(1)–N(2)
Sn(1)–S(1)
Sn(1)–S(2)
Sn(1)–S(3)
Sn(1)–S(4)
C(1)–O(1)
C(2)–O(2)
C(2)–N(1)
C(1)–C(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(6)–C(1)
2.0479(9)
2.0223(9)
–
2.0439(13)
–
2.0640(17)
–
2.0438(11)
–
2.2583(12)
–
–
–
–
–
2.0411(7)
–
2.0892(8)
2.4090(9)
–
–
–
–
–
2.5269(4)
2.5417(4)
2.5339(4)
2.5211(4)
1.3667(17)
1.3630(16)
–
1.4164(19)
1.401(2)
1.395(2)
1.388(2)
1.392(2)
1.403(2)
2.5598(9)
2.5400(9)
2.5407(9)
2.5714(11)
1.367(2)
–
1.397(2)
1.420(3)
1.395(3)
1.391(3)
1.395(3)
1.403(3)
1.400(3)
1.3546(18)
–
1.3642(12)
–
1.451(2)
1.404(2)
1.397(2)
1.382(2)
1.405(2)
1.393(2)
1.410(2)
1.4027(12)
1.4215(13)
1.3951(13)
1.4031(13)
1.3933(14)
1.4103(14)
1.4001(14)
Angles [°]
O(1)–Sn(1)–N(1)
O(1)–Sn(1)–N(2)
O(1)–Sn(1)–O(2)
N(1)–Sn(1)–N(2)
S(1)–Sn(1)–S(2)
S(3)–Sn(1)–S(4)
–
–
80.78(6)
–
–
–
71.30(3)
70.764(19)
78.65(4)
79.84(3)
84.84(3)
–
99.74(3)
–
–
–
–
–
–
–
80.88(4)
–
71.650(12)
71.727(12)
Scheme 5. Preparation of complex 5.
The molecular structure of 5 was determined by single crys-
tal X-ray diffraction analysis and is shown in Figure 2. Selected
bond lengths and angles are reported in Table 1. Single crystals
suitable for X-ray diffraction analysis were obtained from a satu-
rated toluene solution. It was found that stannylene 5 dimerizes
in the solid state via two strong intermolecular Sn···N (2.351 Å)
donor-acceptor interactions (sum of covalent radii of Sn and
N = 2.21 Å[14]).
The geometric parameters of redox-active ligands [C(1)–O(1)
1.3667(17) Å, C(2)–O(2) 1.3630(16) Å and C(1)–O(1) 1.367(2) Å
and C(2)–N(1) 1.397(2) Å distances for 3 and 4 respectively] are
in the range typical for the dianion form of the o-quinonate or
o-iminobenzoquinonate ligands.[16] The C–C distances in the
six-membered carbon rings {C(1)–C(6) ring [1.388(2)–1.4164(19)]
for 3 and 1.391–1.420 Å for 4} are close to the typical aromatic
bonds. All these data support the dianionic nature of redox-
active ligands in 3 and 4. Each thiocarbamate ligand adopts a
The empty p-orbital of this tin centre normally acts as a
bidentate mode of chelatation to the tin centre thus forming strong Lewis-acid towards the unshared pair of electrons on
four-membered {CS2Sn} rings. The S–Sn–S angles are close to the N-atom of a neighbouring molecule. Notably, this property
72°. The Sn(1)–S(1,2,3,4) bonds are practically equivalent and influences the aggregation behaviour of stannylenes.[4]
have middle lengths equal to 2.531 0.010 Å for 3 and lie in
the range from 2.540 Å to 2.571 Å for 4. The carbon–sulfur
bond lengths of the chelate rings lie in the range from 1.724 Å
to 1.736 Å, which are intermediate between single and double
bond lengths and suggest considerable delocalization of
charge.[17]
Also, there is a short metal–metal contact Sn···Sn (3.548 Å)
which is longer than double the tin covalent radii (2.94 Å) but
significantly shorter than double van-der-Waals radii (4.4 Å).[14]
However, at present we are not able to confirm the existence
of a bonding interaction between these two tin atoms. This
pursuit requires additional research and will be the subject of
The methyl protons of two thiocarbamate ligands are equiv- further investigations. Furthermore it should be noted that 5
alent in the [D6]benzene 1H NMR spectra and appear as singlets shows a weak Sn···η6-C6 intermolecular p–π contact (3.373 Å)
at δ = 2.10 and 2.25 ppm for 3 and 4 respectively. The tin between tin atoms and the aromatic six-membered rings lo-
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at room temperature in toluene (Scheme 6). The interaction is
accompanied by gas evolution without any colour change of
the reaction mixture. In contrast to N-heterocyclic stannyl-
enes[24a,24c] the reaction of 5 with Ni(CO)4 leads to the forma-
tion of new monosubstituted diamagnetic bimetallic product 6
[
PhAPSnNi(CO)3], which was identified on the basis of multinu-
clear NMR and IR spectroscopy. Unfortunately, all attempts to
obtain single crystals suitable for X-ray diffraction analysis
failed. The constitution of 6 was therefore confirmed by analyti-
cal and spectroscopic data. In the case of the 1H NMR spectrum
of 6 in [D6]benzene, all resonances mentioned above (complex
5) are slightly shifted. The 13C NMR spectrum revealed new sig-
nals belonging to the carbonyl groups bonded to the nickel
atom at δC = 191.4 and 195.2 ppm. The tin resonance is down-
shifted (relative to that in compound 5) and is located at δSn
=
–201 ppm in the 119Sn NMR spectrum of 6. Additionally, the
vibrations of the carbonyl CO bonds in 6 are present in the IR
spectrum as strong absorption bands in the range 1970–
2080 cm–1.
Figure 2. Crystal structure of 5 (top) with 30 % thermal probability ellipsoids.
One-dimensional motif in crystal packing of 5 (bottom). The H atoms are
omitted for clarity.
cated at nearby dimers. These kinds of weak Sn···aryl interac-
tions are known in the literature.[23a] However, the distances
observed in 5 are much greater than those seen in the well-
established examples of Sn···η6-aryl interactions,[23b–23d] where
distances as small as 2.53 Å have been observed.[23d]
Scheme 6. Reactivity of stannylene 5 towards Ni(CO)4.
It is necessary to note that reactivity similar to that of the
stannylene species towards tetracarbonylnickel(0) with the for-
mation of monosubstituted derivatives of the type R2Sn-Ni(CO)3
was observed for dialkoxytin(II)[25a] and dialkyltin(II)[25b] deriva-
tives and triamidostannate anion.[25c]
The tin atom in 5 has a distorted trigonal pyramidal ligand
environment. The O(1), N(1) and N(1A) atoms of PhAP ligands
form the base of the pyramid. The lone pair of electrons is
located at the vertex of a pyramid. The C(1)–O(1) 1.354 Å and
C(2)–N(1) 1.451 Å distances lie in the range typical of the di-
anion form of the o-iminobenzoquinone ligand.[16] The C–C dis-
tances in the six-membered carbon ring (1.382–1.410 Å) of the
o-amidophenolate ligand are close to the typical aromatic bond
values. The Sn(1)–N(1) and Sn(1)–O(1) bond lengths are compa-
rable with known amidophenolate tin complexes.[4c] The skele-
tons of the amidophenolate ligands are planar and are practi-
cally parallel to each other.
The (c) Pathway: Reaction with Lewis Base
The presence of a vacant p-orbital at the tin atom endows stan-
nylenes with Lewis-acid properties and makes it possible for
these species to react with different reagents containing un-
shared electron pairs. Such reactivity towards Lewis-bases was
partly addressed above. Notably, the tin(II) derivatives are
known to dimerize in the solid state through intermolecular
donor–acceptor Sn–O or Sn–N interactions.[4]
We were interested in the synthesis of a monomeric stannyl-
ene complex with strong Lewis bases such as pyridine. Freshly
prepared yellow microcrystalline amidophenolate complex 2
was dissolved in pyridine to give an orange solution. Single
crystals of new complex 7 suitable for X-ray diffraction analysis
1
The [D6]benzene H NMR spectrum of 5 shows two singlets
at δ = 1.35 and 1.66 ppm representative of protons for two tert-
butyl groups. Aromatic protons of the amidophenolate frag-
ment appear as singlets at δ = 7.20 and 7.27 ppm and the
protons of the N-phenyl substituent are represented as multi-
plets in the range from 6.76–7.07 ppm. The tin resonance is
located at δSn = –212 ppm in the 119Sn NMR spectrum.
The first homoleptic nickel(0) complex of an N-heterocyclic were obtained from saturated toluene solution. The geometry
stannylene – a stannylene analogue of nickel tetracarbonyl – of the coordination polyhedron in 7 is best described as a dis-
was prepared in 1990.[24a] Homoleptic complexes with dialkyl torted trigonal pyramidal (Figure 3). The C(1)–O(1) (1.364 Å),
stannylene ligands were first isolated in 1999.[24b] The benzan- C(2)–N(1) (1.403 Å) and Sn(1)–O(1) (2.041 Å) and Sn(1)–N(1)
nulated bis-stannylenes react with Ni(cod)2 to give intensely (2.089 Å) bond lengths are comparable with amidophenolate
colored homoleptic Ni0 complexes.[24c] It was found that yellow tin complexes 2,[4c] 4 and 5. The value of the Sn(1)–N(2) dis-
stannylene 5 reacts readily with equimolar amounts of Ni(CO)4 tance (2.409 Å) is more than the sum of the covalent (2.21 Å)[14]
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but less than the sum of the van-der-Waals radii (3.8 Å)[14] of
the corresponding elements, indicating the donor–acceptor na-
ture of this moiety.
Scheme 7. Oxidation of 1 and 2 by RO· (top). Coordination-decoordination
equilibrium of complex 9 in solution (bottom).
Figure 3. Crystal structure of 7 with 30 % thermal probability ellipsoids. The
H atoms are omitted for clarity.
The chelating o-amidophenolate ligand has nearly a planar
geometry. The coordinated molecule of pyridine is practically
orthogonal to the dianion ligand plane (93.64°). The sum of
angles around the tin atom in 7 is 264.4° with a narrow endocy-
clic O(1)–Sn(1)–N(1) angle of 79.8°. These data are indicative of
p3 geometry with a noninteracting stereochemically active lone
pair of electrons.
The (d) Pathway: Oxidation of the Redox-Active Ligand
Stannylenes 1 and 2 were found to react with TMTD through
the (a)-pathway (Scheme 2) involving oxidation of a low-valence
metal atom giving tin(IV) derivatives. During the reaction the
redox-active ligand retained its oxidation state.
It has been previously shown that catecholate and diimine
complexes of non-transition metals react with different radicals
and subsequent oxidation of the redox-active ligand giving par-
amagnetic derivatives observable by EPR spectroscopy.[9,10b,26]
In order to obtain paramagnetic stannylene derivatives, com-
plexes 1 and 2 were treated with a THF solution of stable 2-
ethoxy-3,6-di-tert-butylphenoxy radical (RO·).[27] The latter was
found to be a versatile radical source; it is a dimeric diamagnetic
compound in the solid state which dissociates reversibly in so-
lution to give two phenoxy radicals at 200–350 K.[27] Stannyl-
enes 1 and 2 were found to interact readily with RO· to produce
radical derivatives 8 and 9, respectively (Scheme 7). Reactions
were realized in an EPR-cell with equimolar amounts of RO·. It
is notable that paramagnetic adducts 8 and 9 were identified
by EPR-spectroscopy only at low temperature (Figure 4 and Fig-
ure 5).
Figure 4. X-band EPR spectra of complex 8 in THF at 235 K.
hyperfine coupling constant (HFC) values (ai117,119Sn
≥
90 G).[26a,28] In the case of SnIV derivatives, HFC values are usu-
ally decreased and located in the range from 20–50 G.[29] This
is known both for tin derivatives[28] as well as for other non-
transition metal compounds.[30]
In the case of complex 8, the hyperfine structure of the EPR
spectrum arises from the HFC of an unpaired electron with two
equivalent magnetic nuclei of 1H (99.98 %, I = 1/2, μN = 2.7928)
as well as satellite splitting on 117Sn (7.68 %, I = 1/2, μN = 1.000)
and 119Sn (8.58 %, I = 1/2, μN = 1.046).[31] The splitting parame-
ters are as follows: ai(21H) = 3.73 G, ai(117Sn) = 94.3 G, ai(119Sn) =
98.6 G, gi = 2.0031. The observation of HFCs with two equiva-
lent hydrogens and large values of ai(117,119Sn) indicates the
Metal complexes with paramagnetic organic ligands contain- formation in the reaction system of a derivative containing a
ing SnII or SnIV centres can be easily distinguished. Compounds one-electron oxidized Cat ligand – o-semiquinone (SQ) with the
containing low-valence tin are usually characterized by large SnII centre.
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and bis-amidophenolate AP2Sn·THF[4c] species, respectively. Bis-
phenoxy complex of divalent tin (RO)2Sn was also formed as
the result of these reactions. The presence of these compounds
in the reaction mixture can be explained by symmetrisation of
complexes 8 and 9 in solution with the subsequent formation
of (RO)2Sn and diradical species of low-valence tin – com-
pounds 10 and 11. Species 10 and 11 undergo intramolecular
redox transformations[10,32] (Scheme 8) to produce diamagnetic
Cat2Sn(THF)2 and AP2Sn·THF.
Scheme 8. Transformations of complexes 8 and 9. The benzene part of the
ligands is omitted for clarity.
Conclusions
In summary, the multiple modes of reactivity for new stannyl-
enes supported by redox-active ligands were investigated. Re-
action with TMTD invokes oxidation of the tin(II) centre and
leads to formation of new hexacoordinate tin(IV) derivatives. In
the reaction with Ni(CO)4 stannylene acts as a Lewis-base giving
new bimetallic product 6. Through a vacant p-orbital, metallene
compound can react with Lewis-bases such as pyridine. Addi-
tionally, oxidation of the redox-active ligand at tin leads to for-
mation of paramagnetic derivatives of divalent tin, which un-
dergo intramolecular redox transformation giving derivatives of
tin(IV).
Figure 5. X-band EPR spectra of the reaction mixture of complex 2 and (RO·)
in THF at 235 K. (a – spectra of the complex 9′, b – 9 and exp – experimental
spectra).
It should be noted that the EPR spectrum of compound 9 is
a superposition of two signals (Figure 5, lines a and b) with
different g-factors and 117,119Sn satellite splitting. It can be ex-
plained by the existence of two forms of the radical complex in
solution – three-coordinate 9′ in which ethoxy group is not
coordinated by metal centre and four-coordinate compound 9,
where this bonding does, in fact, take place. The splitting pa-
rameters are as follows: for 9 –ai(1H) = 4.69 G, ai(14N) = 6.69 G,
ai(117Sn) = 167.3 G, ai(119Sn) = 175 G, gi = 2.0018 and for 9′ –
ai(1H) = 4.69 G, ai(14N) = 6.69 G, ai(117Sn) = 100.9 G, ai(119Sn) =
105.6 G, gi = 2.0009. The fact that we observe both isomers can
be tentatively explained by the slow (on the EPR time scale)
equilibrium between 9 and 9′. In the case of complex 8, we do
not observe a three-coordinate derivative due to the reduced
steric hindrance presented by the redox-active ligand, relative
to 9. Analysis of the EPR data clearly indicates formation of
compounds containing radical-anion redox-active ligands and
the SnII centre.
Experimental Section
General Considerations: All reactants were purchased from Aldrich
[Caution!!! Ni(CO)4 is an exceedingly toxic material and requires
careful handling]. Solvents were purified by standard methods.[33]
o-Amidophenolate complex 2[4c] and dimeric 2-ethoxy-3,6-di-tert-
butylphenoxy radical[27] were prepared according to known proce-
dures. All manipulations on complexes were performed in vacuo
under conditions in which oxygen and moisture were excluded. EPR
spectra were recorded 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.[34] The
infrared spectra of complexes in the 4000–400 cm–1 range were
recorded with a FSM 1201 Fourier-IR spectrometer in nujol. NMR
spectra were recorded in C6D6 solution 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. Elemental analyses were performed with an Elemental
Analyzer Euro EA 3000 instrument. Metal atom percentages were
estimated by pyrolysis of the investigated samples and subsequent
weighing of the obtained metal oxide.
Unfortunately, all attempts to isolate paramagnetic com-
pounds 8 and 9 failed. It was established that increasing the
temperature to 290 K led to disappearance of the EPR spectra
for reaction mixtures and changed solution colours from blue
(8) or green (9) to yellow. Complexes 8 and 9 were found to be
labile in solution and to undergo transformations giving rise to
diamagnetic products, which were identified on the basis of
[10]
NMR as previously noted SnIV bis-catecholate Cat2Sn(THF)2
Eur. J. Inorg. Chem. 0000, 0–0
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Synthesis of [CatSn]3 (1): The straw-coloured solution of sodium
catecholate[10b] (1.57 g, 2.5 mmol) in THF (25 mL) was added to the
THF (15 mL) solution of SnCl2·diox (0.695 g, 2.5 mmol). The reaction
mixture became cloudy and colourless in a few minutes. THF was
removed under reduced pressure and the residue was dissolved in
hexane (25 mL). The NaCl precipitate was removed by filtration.
Trimeric complex 1 was obtained as a fine crystalline nearly colour-
less product. IR and NMR spectra of product obtained were identical
to those previously reported[10b] for 1, yield 0.71 g (84 %).
not change. During the reaction CO gas evolution was observed.
The residue was recrystallized from the n-hexane. Complex 6 was
obtained as a fine crystalline yellow product, yield 0.41 g (73 %).
C23H25NNiO4Sn (556.85): calcd. C 49.61, H 4.53; found C 49.66, H
1
4.50. H NMR (C6D6, 20 °C): δ = 7.26 (s, 1 H, HAP); 7.21 (s, 1 H, HAP);
7.07–6.76 (m, 5 H, Haryl); 1.67 [s, 9 H, (tBu)]; 1.34 [s, 9 H, (tBu)] ppm.
13C NMR (C6D6, 20 °C): δ = 195.2, 191.4, 156.9, 147.4, 140.7, 139.7,
138.3, 129.5, 122.0, 120.7, 118.1, 117.3, 35.5, 34.4, 31.6, 29.8 ppm.
119Sn NMR (C6D6, 20 °C): δ = –201. 6 ppm. IR (Nujol): ν = 2073 (m),
˜
2006 (m), 1988 (m), 1593 (m), 1482 (s), 1411 (s), 1296 (s), 1254 (s),
1236 (s), 1211 (s), 1180 (m), 1154 (m), 1120 (w), 1080 (w), 1030 (w),
963 (w), 915 (w), 873 (m), 840 (m), 820 (m), 766 (s), 756 (s), 694
The Interaction of Complex 1 with TMTD: The solution of TMTD
(0.3 g, 1.25 mmol) in CH2Cl2 (20 mL) was added to the suspension
of complex 1 (0.425 g, 1.25 mmol) in the same solvent (20 mL). The
reaction mixture was kept for a few hours at room temperature.
The colour of reaction mixture became intense orange-red. The resi-
due was recrystallized from the mixture CH2Cl2/n-hexane (1:1). The
obtained crystals lose solvated dichloromethane molecule under
drying on vacuum conditions. Complex 3 was obtained as a red
crystalline product, yield 0.57 g (78 %). C20H32N2O2S4Sn (579.41):
calcd. C 41.46, H 5.57, S 22.13, Sn 20.49; found C 41.50, H 5.60, S
22.09, Sn 20.43. 1H NMR (C6D6, 20 °C): δ = 6.97 (s, 2 H, HCat); 2.10
(s, 12 H, Me); 1.84 [s, 18 H, (tBu)] ppm. 13C NMR (C6D6, 20 °C): δ =
197.3, 149.1, 132.9, 114.1, 64.4, 52.8, 45.0, 34.8, 30.0, 15.1 ppm. 119Sn
(m) cm–1
.
Synthesis of Complex DippAPSnPy (7): Freshly prepared complex
2 (0.5 g, 1.0 mmol) was dissolved in excess pyridine (15 mL). The
colour of reaction mixture became intense orange. Pyridine was
removed under reduced pressure and the residue was recrystallized
from hot toluene. Complex 7 was obtained as a crystalline orange
product, yield 0.53 g (91 %). C31H42N2OSn (577.38): calcd. C 64.49,
1
H 7.33, Sn 20.56; found C 64.52, H 7.30, Sn 20.51. H NMR (C6D6, J/
Hz, 20 °C): δ = 8.10 (m, 3 H, HPy), 7.29–7.20 (m, 3 H, Hanyl), 7.13–
7.08 [m, 2 H, H(C-H)]; 6.36 (m, 2 H, HPy), 3.06 [sept, JH,H = 7.1 Hz, 2
H, CH(iPr)]; 1.91 [s, 9 H, CH3(tBu)]; 1.35 [s, 9 H, CH3(tBu)]; 1.10 [d,
NMR (C6D6, 20 °C): δ = –657.5 ppm. IR (Nujol): ν = 1550 (s) , 1475
˜
(s), 1400 (s), 1275 (s), 1250 (s), 1205 (m), 1170 (m), 1150 (m), 975 (s),
JH,H = 7.1 Hz, 6 H, CH3(iPr)]; 0.83 [d, JH,H = 7.1 Hz, 6 H, CH3(iPr)] ppm.
945 (w), 925 (m), 800 (w), 745 (w), 700 (m) cm–1
.
13C NMR (C6D6, 20 °C): δ = 156.9, 153.1, 147.9, 147.1, 146.1, 141.6,
139.4, 139.1, 138.1, 137.3, 134.1, 123.9, 123.6, 121.5, 120.1, 110.1,
41.1, 35.3, 31.9, 31.4, 29.6, 28.8, 28.7, 27.7, 26.14, 25.8, 25.5, 25.3,
25.0, 24.5, 24.3, 23.5, 22.7, 22.6, 22.5 ppm. 119Sn NMR (C6D6, 20 °C):
δ = –80.4 ppm.
The Interaction of Complex 2 with TMTD: The solution of TMTD
(0.24 g, 1.0 mmol) in CH2Cl2 (20 mL) was added to the solution of
complex 2 (0.5 g, 1.0 mmol) in the same solvent (20 mL). The reac-
tion mixture was kept for a few hours at room temperature. The
colour of the reaction mixture became intense crimson-red. The
residue was recrystallized from the mixture CH2Cl2/n-hexane (1:1).
Complex 4 was obtained as a crystalline product, yield 0.61 g
(82 %). C32H49N3OS4Sn (738.69): calcd. C 52.03, H 6.69, S 17.36, Sn
The EPR-Experiment: Interactions of Complexes 1 and 2 with
3,6-di-tert-Butyl-2-ethoxyphenoxy Radical: The solution of 3,6-
di-tert-butyl-2-ethoxyphenoxy radical (0.05 g, 0.1 mmol) in THF
(2 mL) was placed in an EPR-cell. The solution was frozen at 77 K.
The solution of complex 1 (0.03 g, 0.1 mmol) or complex 2 (0.05 g,
0.1 mmol) in toluene (2 mL) was added into this EPR-cell and the
reaction mixture was frozen again. Generating radical complexes
were registered by EPR-spectroscopy upon thawing without isola-
tion. Paramagnetic compounds are unstable and undergo transfor-
mations giving diamagnetic products, which were identified by us-
1
16.07; found C 52.1, H 6.63, S 17.40, Sn 16.10. H NMR (C6D6, J/Hz,
20 °C): δ = 7.34–7.24 (m, 3 H, Haryl); 7.05 [s, JH,H = 2.6 Hz, 1 H, HAP];
6.33 (s, JH,H = 2.6 Hz, 1 H, HAP); 3.72 [sept, JH,H = 6.8 Hz, 2 H, CH(iPr)];
2.25 (s, 12 H, Me); 1.91 [s, 9 H, (tBu)]; 1.40 [s, 9 H, (tBu)]; 1.33 [d,
J
H,H = 6.8 Hz, 6 H, CH3(iPr)]; 1.20 [d, JH,H = 6.8 Hz, 6 H, CH3(iPr)] ppm.
13C NMR (C6D6, 20 °C): δ = 198.8, 149.9, 147.1, 144.1, 140.8, 137.6,
132.8, 126.0, 123.9, 110.0, 107.8, 65.4, 52.8, 45.0, 35.3, 34.3, 31.9,
31.3, 30.2, 29.7, 28.0, 25.9, 24.7, 22.5, 15.1, 13.9 ppm. 119Sn NMR
ing NMR spectroscopy as previously obtained bis-catecholate
[10]
Cat2Sn(THF)2
and bis-amidophenolate AP2Sn·THF[4c] complexes.
(C6D6, 20 °C): δ = –660.6 ppm. IR (Nujol): ν = 1582 (s), 1414 (s), 1359
˜
(m), 1329 (s), 1286 (m), 1266 (m), 1256 (m), 1232 (m), 1211 (s), 1111
(w), 1101 (w), 1051 (w), 1026 (m), 994 (s), 914 (w), 870 (s), 797 (s),
X-ray Crystallographic Study of 3·CH2Cl2, 4, 5 and 7: The single
crystals suitable for X-ray diffraction analysis were obtained from
the mixture of CH2Cl2/hexane (3·CH2Cl2 and 4) and toluene (5 and
7). Intensity data were collected at 100 K on a Smart Apex I (3) and
Xcalibur Eos (4, 5 and 7) diffractometers with graphite monochro-
mated Mo-Kα radiation (λ = 0.71073 Å). The intensity data were
integrated by the SAINT[35] (for 3) and CrysAlisPro[36] (for 4, 5 and
7) programs. SADABS[37] and SCALE3 ABSPACK[36] were used to per-
form area-detector scaling and absorption corrections. The struc-
tures 3·CH2Cl2, 4, 5 and 7 were solved by direct methods and were
refined on F2 using all reflections with SHELXTL package.[38] All non-
hydrogen atoms were refined anisotropically. The hydrogen atoms
were placed in calculated positions and refined in the “riding-
model”. Selected bond lengths and angles of complexes obtained
are given in Table 1. Table 2 summarizes the crystal data and some
details of the data collection and refinement.
775 (w), 693 (w), 656 (m), 609 (m), 534 (w), 446 (w) cm–1
.
Synthesis of PhAPSn (5): The solution of Sn[N(SiMe3)2]2[21] (0.444 g,
1 mmol) in Et2O (25 mL) was added to the solution of 4,6-di-tert-
butyl-N-(phenyl)-o-aminophenol[22] (0.3 g, 1 mmol) in the same sol-
vent (15 mL). The reaction mixture became pale yellow in a few
minutes. Et2O was removed under reduced pressure and the residue
was recrystallized from the hot toluene. Complex 5 was obtained
as a fine crystalline yellow product, yield 0.33 g (80 %). C20H25NOSn
(414.11): calcd. C 58.00, H 6.08, N 3.38, Sn 28.67; found C 58.06, H
1
6.04, N 3.40, Sn 28.62. H NMR (C6D6, 20 °C): δ = 7.27 (s, 1 H, HAP);
7.20 (s, 1 H, HAP); 7.07–6.76 (m, 5 H, Haryl); 1.66 [s, 9 H, (tBu)]; 1.35
[s, 9 H, (tBu)] ppm. 13C NMR (C6D6, 20 °C): δ = 156.8, 147.5, 140.8,
139.7, 138.3, 129.4, 121.9, 120.9, 118.3, 117.1, 35.4, 34.3, 31.7,
29.7 ppm. 119Sn NMR (C6D6, 20 °C): δ = –212.1 ppm.
The Interaction of Complex 5 with Ni(CO)4: The Ni(CO)4 (0.17 g,
CCDC 1470507 (for 3·CH2Cl2), 1470508 (for 4), 1470509 (for 5) and
1.0 mmol) was added to the frozen solution of complex 5 (0.42 g, 1470510 (for 7) contain the supplementary crystallographic data for
1.0 mmol) in toluene (25 mL). The reaction mixture was kept for a
this paper. These data can be obtained free of charge from The
few days at room temperature. The colour of reaction mixture did
Cambridge Crystallographic Data Centre.
Eur. J. Inorg. Chem. 0000, 0–0
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7
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Table 2. Summary of crystal and refinement data for complexes 3·CH2Cl2, 4, 5 and 7.
3·CH2Cl2
4
5
7
Empirical formula
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system
C21H34Cl2N2O2S4Sn
664.33
100(2)
0.71073
monoclinic
P21/n
a = 11.3701(6) Å
b = 16.4553(9) Å
c = 15.4319(8) Å
α = 90°
ꢀ = 96.8940(10)°
γ = 90°
2866.4(3)
4
1.539
1.390
0.21 × 0.16 × 0.09
1352
C32H49N3OS4Sn
738.67
150(2)
0.71069
triclinic
C40H50N2O2Sn2
828.20
100(2)
0.71073
monoclinic
C2/c
a = 30.2314(4) Å
b = 6.28481(8) Å
c = 20.0063(3) Å
α = 90°
ꢀ = 94.9298(11)°
γ = 90°
3787.12(8)
4
1.453
C31H42N2OSn
577.36
100(2)
0.71073
monoclinic
P21/c
a = 15.72609(14) Å
b = 9.99875(8) Å
c = 19.03126(17) Å
α = 90°
ꢀ = 105.5279(9)°
γ = 90°
2883.27(4)
4
1.330
Space group
Unit cell dimensions
P1
¯
a = 11.674(5) Å
b = 12.470(5) Å
c = 13.199(5) Å
α = 98.756(5)°
ꢀ = 100.105(5)°
γ = 102.285(5)°
1812.1(13)
2
Volume [Å3]
Z
Density (calculated) [g cm–3
]
1.354
0.963
0.40 × 0.24 × 0.18
768
Absorption coefficient [mm–1
Crystal size [mm3]
F(000)
]
1.354
0.20 × 0.10 × 0.10
1680
0.911
0.40 × 0.40 × 0.20
1200
Theta range for data collection,
Reflections collected
1.82 to 24.00
14232
3.20 to 28.88
18740
3.25 to 27.00
29734
3.05 to 30.00
55278
Independent reflections (Rint
Absorption correction
)
4461 (0.0183)
8209 (0.0208)
4108 (0.0359)
8340 (0.0251)
semi-empirical from equivalents
Max. and min. transmission
Refinement method
0.8851 and 0.7590
0.8457 and 0.6992
0.8765 and 0.7735
0.8388 and 0.7121
full-matrix, least-squares on F2
Data/restraints/parameters
Final R indices [I > 2σ(I)]
4461/0/423
R1 = 0.0203,
wR2 = 0.0498
R1 = 0.0233,
wR2 = 0.0507
1.056
8209/0/384
R1 = 0.0248,
wR2 = 0.0596
R1 = 0.0337,
wR2 = 0.0621
1.050
4108/0/214
R1 = 0.0216,
wR2 = 0.0449
R1 = 0.0314,
wR2 = 0.0473
1.050
8340/0/326
R1 = 0.0183,
wR2 = 0.0440
R1 = 0.0214,
wR2 = 0.0453
1.039
R indices (all data)
Goodness-of-fit on F2
Largest diff.
peak and hole (e Å–3
)
0.523 and –0.289
0.646 and –0.367
0.553 and –0.361
0.412 and –0.274
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Acknowledgments
The authors are grateful to the Russian Foundation for Basic
Research (grant 15-43-02351-r_povolzh'e_a) and Russian Presi-
dent Grants (NSh-7916.2016.3) for financial support of this
work.
Keywords: Tin · Carbene analogues · Chelates ·
Quinones · N,O ligands
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Received: April 29, 2016
Published Online: ■
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© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Full Paper
Stannylenes
Multiple modes of reactivity for se-
lected stannylenes bearing redox-ac-
tive catecholate and o-amidophenol-
ate ligands towards different reagents
are reported.
M. G. Chegerev, A. V. Piskunov,*
A. V. Maleeva, G. K. Fukin,
G. A. Abakumov .............................. 1–10
Multiple Reactivity of SnII Com-
plexes Bearing Catecholate and o-
Amidophenolate Ligands
DOI: 10.1002/ejic.201600501
Eur. J. Inorg. Chem. 0000, 0–0
www.eurjic.org
10
© 0000 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim