Triethylantimony(V) complexes with bidentate O,N-, O,O- and tridentate O,N,O′-coordinating o-iminoquinonato/o-quinonato ligands: Synthesis, structure and some properties

Article abstract of DOI:10.1016/j.jorganchem.2009.06.027

The novel triethylantimony(v) o-amidophenolato (AP-R)SbEt₃ (R = i-Pr, 1; R = Me, 2) and catecholato (3,6-DBCat)SbEt₃ (3) complexes have been synthesized and characterized by IR, NMR spectroscopy (AP-R is 4,6-di-tert-butyl-N-(2,6-dial

Full text of DOI:10.1016/j.jorganchem.2009.06.027

Journal of Organometallic Chemistry 694 (2009) 3462–3469
Contents lists available at ScienceDirect
Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
Triethylantimony(V) complexes with bidentate O,N-, O,O- and tridentate
O,N,O0-coordinating o-iminoquinonato/o-quinonato ligands:
Synthesis, structure and some properties
a
b
a
a
Andrey I. Poddel’sky a, , Nina N. Vavilina , Nikolay V. Somov , Vladimir K. Cherkasov , Gleb A. Abakumov
*
a G.A. Razuvaev Institute of Organometallic Chemistry, Russian Academy of Sciences, Tropinina 49, 603950 Nizhniy Novgorod, GSP-445, Russia
b Nizhniy Novgorod State University, Physical Faculty, Building 3, Gagarina Av. 23, 603950 Nizhniy Novgorod, Russia
a r t i c l e i n f o
a b s t r a c t
Article history:
The novel triethylantimony(v) o-amidophenolato (AP-R)SbEt3 (R = i-Pr, 1; R = Me, 2) and catecholato (3,6-
DBCat)SbEt3 (3) complexes have been synthesized and characterized by IR, NMR spectroscopy (AP-R is
4,6-di-tert-butyl-N-(2,6-dialkylphenyl)-o-amidophenolate, alkyl = isopropyl (1) or methyl (2); 3,6-DBCat
is 3,6-di-tert-butyl-catecholate). Complexes 1–3 have been obtained by the oxidative addition of corre-
sponding o-iminobenzoquinones or o-benzoquinones to Et3Sb. The addition of 4,6-di-tert-butyl-N-(3,5-
di-tert-butyl-2-hydroxyphenyl)-o-iminobenzoquinone to Et3Sb at low temperature gives hexacoordinate
[(AP-AP)H]SbEt3 (4) which decomposes slowly in vacuum with the liberation of ethane yielding pentaco-
ordinate complex [(AP-AP)]SbEt2 (5). [(AP-AP)H]2ꢀ is O,N,O0-tridentate amino-bis-(3,5-di-tert-butyl-phe-
nolate-2-yl) dianion and [(AP-AP)]3ꢀ is amido-bis-(3,5-di-tert-butyl-phenolate-2-yl) trianion. The
decomposition of 4–5 accelerates in the presence of air. o-Amidophenolates 1 and 2 bind molecular oxy-
gen to give spiroendoperoxides Et3Sb[L-iPr]O2 (6) or Et3Sb[L-Me]O2 (7) containing trioxastibolane rings.
This reaction proceeds slowly and reaches the equilibrium at 15–20% conversion five times more than for
(AP-R)SbPh3 analogues. Molecular structures of 1 and 5 were determined by X-ray analysis.
Ó 2009 Elsevier B.V. All rights reserved.
Received 25 March 2009
Received in revised form 8 June 2009
Accepted 19 June 2009
Available online 26 June 2009
Keywords:
Antimony
N,O-ligands
O,O-ligands
Dioxygen
NMR spectroscopy
X-ray diffraction
1. Introduction
amidophenolato complexes, (AP)SbPh3, where o-amidophenolato
is dianion of o-iminobenzoquinone, and some catecholates
The coordination chemistry of redox-active o-benzoquinonato
and o-iminobenzoquinonato ligands attracts the scientist’s atten-
tion during 30 years at the least. Unusual and interesting phenom-
ena have been observed on o-quinonato/o-iminoquinonato
complexes. Among them are ‘‘photo/thermomechanical effect”
[1–3], valence tautomerism [4–13], ‘‘wandering valence”, elemen-
totropy [14] etc. Transition metal o-semiquinonato/o-imi-
nosemiquinonato (SQ/ISQ) complexes demonstrate a versatility
of structural types, different types of magnetic exchange depend-
ing on complex structure as well as the nature of central atom
and ligands [7,15–20], etc. Non-transition metal complexes also re-
veal interesting magnetic properties depending on metal nature
and complex geometry [21–25], they can serve as model objects
for the investigation of ligand-to-ligand magnetic exchange [21–
25], as the spin traps [26–28]. Four years earlier, we have found
that complexes of non-transition metals with redox-active ligands
are able to demonstrate chemical behavior typical for transition
metal complexes. We have found that triphenylantimony(V) o-
(Cat)SbPh3, can bind molecular oxygen in a reversible manner
[29–31]. This unique ability is caused by the combination of re-
dox-active dianionic AP/Cat ligand (which is oxidized by molecular
oxygen to radical-anion) and heavy antimony atom, which has a
large spin–orbit constant (this feature of antimony facilitates an in-
ter-spin conversion) and a vacant site to coordinate superoxide
radical-anion (Scheme 1) according to the proposed mechanism
[29,31].
The complex ability to bind dioxygen depends on the redox-po-
tential of AP or Cat ligand. We have shown that a number of triph-
enylantimony(V) catecholates with an acceptor substituents (such
as Cl, Br, F, NO2) at Cat ligand are inactive in reaction with dioxygen
[32,33] while donor groups (for example, methoxy-groups) in Cat
ligand allow the complex derived to be dioxygen-active [30,31].
On the other hand, the tridentate O,N,O0-ligand o-iminobenzoqui-
none with hydroxyl-group at N-aryl forms amino-bis-phenolate
triphenylantimony(V) complex which is air-stable due to its struc-
tural features: it cannot form stable o-iminobenzosemiquinonato
radical-anion upon oxidation [34]. What about chemical properties
of Cat and AP complexes of antimony(V) with ethyl groups instead
of phenyls? In this paper, we report the synthesis of new o-amido-
phenolato triethylantimony(V) complexes with bidentate O,N- and
* Corresponding author. Fax: +7 831 462 74 97.
E-mail address: aip@iomc.ras.ru (A.I. Poddel’sky).
0022-328X/$ - see front matter Ó 2009 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2009.06.027

A.I. Poddel’sky et al. / Journal of Organometallic Chemistry 694 (2009) 3462–3469
3463
3
3
1
O
O
O
O
O
O
tBu
R
tBu
R
tBu
R
tBu
R
tBu
R
O
O
O
N
O
N
O
N
O
N
O
N
3O2
SbPh3
SbPh3
SbPh3
SbPh3
SbPh3
tBu
tBu
tBu
tBu
tBu
R
R
R
R
R
[(ISQ)SbPh3]+(O2)-
(AP)SbPh3
triplet diradical complex
singlet diradical complex
spiroendoperoxide
interspin
conversion
Scheme 1.
tridentate O,N,O0-ligands, its 3,6-di-tert-butyl-catecholate ana-
logue, and the investigation of the dioxygen activity of complexes.
that the samples of complexes 1 and 2 prepared by the first meth-
od demanding the coordinating solvent (THF) do not contain THF
as the ligand on central antimony atom.
The crystal structure of 1 was determined by X-ray analysis and
a PLATON diagram is shown in Fig. 1; selected bond distances and
angles are collected in Table 1.
2. Results and discussion
o-Amidophenolato triethylantimony(V) complexes may be pre-
pared by two different methods (Scheme 2). The first is a classic ex-
change reaction of o-amidophenolato alkali salts (AP-R)M2
(M = Na, K) with Et3SbBr2 [18,35]. The second way is an oxidative
addition of neutral o-iminobenzoquinones (IBQ-R) to low-valent
antimony compounds. Noteworthy, the reaction of Et3Sb with o-
iminobenzoquinones proceeds as the two-electron oxidation but
not as the 1,2- or 1,4-nucleophylic addition usual for reactions of
o-quinones with dialkyl alkali-earth metals (Et2Zn, Et2Cd, etc.)
[36]. The yield of (AP-R)SbEt3 (R = iPr, 1; R = Me, 2) in reaction is
close to quantitative (ꢁ98%).
Compound 1 has a slightly distorted trigonal bipyramidal envi-
ronment at Sb(1) with the base formed by N(1), C(27) and C(29)
atoms (the bond angle sum is 356.2(3)°). The apical positions are
occupied by oxygen atom O(1) and carbon atom C(31); the angle
C(31)–Sb(1)–O(1) is 169.81(7)°. The chelate ring is almost planar:
the torsion angle O(1)–C(1)–C(2)–N(1) is 0.82(6)°, and the bent an-
gle along O(1)ꢃ ꢃ ꢃN(1) line is 0.4°. The geometrical characteristics of
AP ligand are completely consistent with its dianionic nature [18],
O(1)–C(1) and N(1)–C(2) bonds of 1.350(2) and 1.396(3) Å are
close to the corresponding bonds in triphenylantimony(V) ana-
logue (AP-iPr)SbPh3 (1.351(4) and 1.408(4) Å, correspondingly)
[29]. The average carbon-carbon bond length in six-membered ring
of AP ligand (1.395 0.014 Å) is indicative of its aromaticity. The
plane of this ring C(1–6) is nearly orthogonal to the plane of N-aryl
group with the angle of 86.92°. The unit cell of 1 contains two
enantiomers of complex with different rotating sense of three ethyl
groups. Noteworthy is that antimony(V)-heteroatom bond lengths
in 1 and its triphenylantimony(V) analogue (AP-iPr)SbPh3 are suf-
ficiently close: the O(1)–C(1) and N(1)–C(2) bonds are 2.0843(15)
and 2.0418(16) Å in 1 while in (AP-iPr)SbPh3 they are 2.074(2)
Complexes 1 and 2 were isolated as bright-yellow crystalline
powders stable in solutions as well as in solid under oxygen-free
conditions. Compounds were characterized by 1H, 13C NMR, IR
spectroscopy. The crystal structure of (AP-iPr)SbEt3 (1) was deter-
mined using single-crystal X-ray studies. The spectral characteris-
tics of complexes prepared by different method are identical.
The NMR spectroscopy of 1 and 2 shows that alkyl groups at 2
and 6 positions of N-aryl fragment are equal. For instance, methyne
protons in 1 appears in 1H NMR spectrum as one septet at
4
3.16 ppm with spin-spin coupling constant JHH = 6.86 Hz and
methyl protons of isopropyls give two doublets at 1.03 and
1.18 ppm (3JHH = 6.9 Hz). Ethyl groups of SbEt3 moiety are nearly
equal in NMR time scale: they give rise to two quartets (1:2) with
nearly identical chemical shift at d ꢂ 1.61 ppm with
D
d < 0.005 ppm from six methylene protons, and triplet at
1.29 ppm from nine methyl protons (3JHH = 7.5 Hz). It is interesting
tBu
R
tBu
R
O
N
ONa
NNa
tBu
tBu
R
R
(AP-R)Na2
IBQ-R
R = iPr, Me
R = iPr, Me
Et3SbBr2
- 2 NaBr
Et3Sb
tBu
O
N
SbEt3
tBu
R
R
(AP-R)SbEt3
1 (R = iPr), 2 (R = Me)
Fig. 1. X-ray structure of (AP-iPr)SbEt3 (1) (PLATON presentation [37]). Hydrogen
Scheme 2.
atoms are omitted for clarity.

3464
A.I. Poddel’sky et al. / Journal of Organometallic Chemistry 694 (2009) 3462–3469
Table 1
ever, chemical behavior of complexes is rather different. If triphe-
nylantimony complex [(AP-AP)H]SbPh3 is stable on the exposition
to air, and it does not undergo any decomposition at ambient tem-
perature, its triethylantimony analogue 4 decomposes slowly in
vacuo with the liberation of ethane yielding pentacoordinate com-
plex [(AP-AP)]SbEt2 (5) (Scheme 4). Fig. 2 shows the changes in 1H
NMR spectrum upon transformation of 4 to 5. Worthy of note is the
symmetry plane of molecule remains in 5 like as in 4 that is clearly
obvious from the NMR spectrum. NMR spectroscopy shows the
disappearance of amino proton signal (singlet at d = 4.96 ppm) in
5, and this fact is corroborated by the absence of stretch vibration
band of NH-group in IR spectrum of 5.
The decomposition accelerates in the presence of oxygen. How-
ever in this case, in the addition to complex 5, we have found
among decomposition products diethyl ether and ethanol using
NMR spectroscopy. Apparently, they are formed from ethyl groups
of SbEt3 fragment. Complex 5 was found to be air-stable; it was iso-
lated as X-ray suitable pale yellow crystals (Fig. 3).
Selected bond distances (Å) and bond angles (°) in 1.
Bond (Å)
Angle (°)
Sb(1)–N(1)
Sb(1)–O(1)
Sb(1)–C(27)
Sb(1)–C(29)
Sb(1)–C(31)
O(1)–C(1)
N(1)–C(2)
N(1)–C(15)
C(29)–C(30)
C(27)–C(28)
C(31)–C(32)
C(1)–C(2)
2.0418(16)
2.0843(15)
2.129(3)
2.142(3)
2.161(2)
1.350(2)
1.396(3)
1.439(3)
1.487(4)
1.354(5)
1.509(3)
1.409(3)
1.385(3)
1.392(3)
1.390(3)
1.401(3)
1.390(3)
N(1)Sb(1)O(1)
N(1)Sb(1)C(27)
O(1)Sb(1)C(27)
N(1)Sb(1)C(29)
O(1)Sb(1)C(29)
C(27)Sb(1)C(29)
N(1)Sb(1)C(31)
O(1)Sb(1)C(31)
C(27)Sb(1)C(31)
C(29)Sb(1)C(31)
C(2)N(1)C(15)
C(2)N(1)Sb(1)
77.40(6)
125.66(13)
85.13(11)
119.12(10)
88.91(9)
111.40(14)
92.73(8)
169.81(7)
98.91(12)
98.21(11)
120.00(16)
116.20(12)
123.79(14)
115.1(2)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(15)N(1)Sb(1)
C(30)C(29)Sb(1)
C(28)C(27)Sb(1)
C(32)C(31)Sb(1)
117.1(3)
112.14(17)
C(6)–C(1)
The antimony atom Sb(1) possesses trigonal bipyramidal geom-
etry where the byramid base is formed by atoms N(1), C(29) and
C(31) (the angle sum is 360.0(1)°), The bond angle between apical
oxygen substituents O(1)–Sb(1)–O(2) is 159.30(4)° reflecting the
bipyramid distortion. Both six-membered carbon rings have aro-
matic character with average C-C distance of 1.396 0.012 Å that
is very close to value for o-amidophenolate 1. The O(1)–C(1) and
O(2)–C(7) as well as N(1)–C(2) and N(1)–C(8) bonds are equal
within the experimental error (see Table 2). They are close to val-
ues of single O-C and O-N bonds in complexes of O,N-bidentate o-
amidophenolato ligands [18,29] and, at the same time, remarkably
longer than those bonds in transition metal complexes with
O,N,O0-ligand in oxidation levels ꢀ1, ꢀ2 (for example, O–C,
1.267(5) Å, N–C, 1.344(5) Å in NiII(AP-IBQ)2 [38]; O–C, 1.297(3) Å,
N–C, 1.357(3) Å in FeIII(AP-ISQ)(AP-IBQ) [39]; O–C, av. 1.305(7) Å,
N–C, av. 1.362(6) Å in CoIII(AP-ISQ)(AP-IBQ) [40]; O–C, av.
1.326(7) Å, N–C, av. 1.379(7) Å in VIV(AP-ISQ)2 [41], O–C, av.
1.325(9) Å, N–C, av. 1.381(9) Å in MnIV(AP-ISQ)2 [40], where AP-
IBQ is monoanion, AP-ISQ is dianion-radical). The nitrogen atom
N(1) is planar and sp2-hybridized pointing to its amido-nature.
So, the geometric characteristics of this O,N,O0-bis-chelate ligand
reflect its clear trianionic nature. Noteworthy, [(AP-AP)]3ꢀ ligand
in 5 is not planar (Fig. 4). The angle between the planes of phenyl
rings is 25.8(1)° being significantly larger than those angles in tran-
sition metal complexes with this type O,N,O0-ligand (what about
transition metal complexes, the highest value of this twist angle
is 13.4° for MnIV(AP-ISQ)2 complex [40], in other complexes it is
5–12°). The deviation of the phenyl rings in O,N,O0-ligand from
coplanarity can be attributed to the sterical repulsion between
tert-butyl substituents of rings; the same situation is described
for tin complex SnIV(AP-ISQ)2 (the corresponding angles are
30.4(7)° and 28.7(7)° for two ligands, [42]).
Triethylantimony(V) complex 4 was also prepared by the oxida-
tive addition of 4,6-di-tert-butyl-N-(3,5-di-tert-butyl-2-hydroxy-
phenyl)-o-iminobenzoquinone (IBQ-AP)H to triethylstibine
(Scheme 5). Remarkably, the reagent addition order determines
the final reaction product. Complex 4 is formed when the ligand
(IBQ-AP)H is added dropwise to a solution of triethylstibine. If
the order is inversed, the main product is diethylantimony(V)
derivative 5. Apparently, in the second case complex 4 formed is
attacked by the neutral (IBQ-AP)H ligand which plays role of dehy-
drogenating agent yielding complex 5.
In previous papers we have reported the reversible binding of
molecular oxygen by triphenylantimony(V) o-amidophenolates
with the formation of spiroendoperoxide species [29–31]. The
change of phenyl groups with ethyl substituents at antimony (com-
plexes 1, 2) results in a change of complexes reactivity: o-amido-
phenolates 1 and 2 react with molecular oxygen (Scheme 6) to
and 2.041(3) Å, correspondingly. This observation indicates a neg-
ligible dependence of these distances on the nature of alkyl/aryl
substituents at Sb(V) atom.
As mentioned above, zinc and cadmium alkyl organometallics
(Et2Zn, Et2Cd, etc.) react with 3,6-di-tert-butyl-o-benzoquinone
through the 1,2- or 1,4-nucleophylic addition mechanism [36].
We have treated triethylstibine with one equivalent of 3,6-DBBQ
(Scheme 3). Surprisingly, in this case the single product of reaction
was triethylantimony(V) catecholate (3,6-DBCat)SbEt3 (3) but not
3,6-di-tert-butyl-2-(diethylstibinooxy)-2-ethylcyclohexa-3,5-die-
none or 3,6-di-tert-butyl-2-(diethylstibino-oxy)-4-ethylcyclohexa-
2,5-dienone – the possible products of 1,2- and 1,4-nucleophilic
addition [36].
Catecholate 3 was isolated with the yield of 95%; it is a pale yel-
low crystalline solid which is easily soluble in different non-polar
solvents such as pentane, hexane, benzene, toluene and even more
in diethyl ether, THF etc. Complex may be stored for a long time in
solid state under air-free conditions.
The third common way to o-quinonato and o-iminobenzoqui-
nonato complexes is an exchange reaction of metal salts with the
corresponding catechol or o-aminophenol in the presence of base
[18,35]. This method being applied to Et3SbBr2 gave the hexacoor-
dinate compound [(AP-AP)H]SbEt3 (4) with O,N,O0-tridentate ami-
no-bis-phenolate ligand [(AP-AP)H]2ꢀ (Scheme 4). This complex
was isolated as nearly colorless microcrystalline solid which
should be stored in vacuo under low temperature because of its
quite easy decomposition at room temperature and on air (see be-
low). The structures of compounds 3 and 4 were determined by 1H,
13C and IR spectroscopy. Compound 4 is related to triphenylanti-
mony(V) complex [(AP-AP)H]SbPh3 [34]. Both complexes have a
symmetry plane dividing complex to two symmetrical parts. How-
tBu
tBu
O
O
or
H
OSbEt2
Et
tBu
tBu
OSbEt2
Et
O
O
tBu
tBu
Et3Sb
tBu
tBu
O
O
3,6-DBBQ
SbEt3
(3,6-DBCat)SbEt3
3
Scheme 3.

A.I. Poddel’sky et al. / Journal of Organometallic Chemistry 694 (2009) 3462–3469
3465
Et
Et
Et
tBu
tBu
Et
O
Et
O
Sb
Sb
N
OH
NH
Et3SbBr2
2 NEt3
- 2 [NEt3H]Br
O
O
t, τ
tBu
tBu
5
tBu
tBu
HN
tBu
- C2H6
OH
tBu
tBu
[(AP-AP)]SbEt2
tBu
tBu
tBu
(AP-AP)H3
[(AP-AP)H]SbEt3
4
Scheme 4.
Fig. 2. 1H NMR spectra: (a) clear [(AP-AP)H]SbEt3 (4), (b, c) the reaction mixtures during the conversion of 4 to 5; and (d) resulting [(AP-AP)]SbEt2 (5) (conditions: CDCl3,
298 K).
Table 2
Selected bond distances (Å) and bond angles (°) in 5.
Bond (Å)
Angle (°)
Sb(1)–O(1)
Sb(1)–O(2)
Sb(1)–N(1)
Sb(1)–C(31)
Sb(1)–C(29)
O(1)–C(1)
O(2)–C(7)
N(1)–C(2)
N(1)–C(8)
C(1)–C(2)
C(1)–C(6)
C(2)–C(3)
C(3)–C(4)
C(4)–C(5)
C(5)–C(6)
C(7)–C(8)
C(7)–C(12)
C(8)–C(9)
C(9)–C(10)
C(10)–C(11)
C(11)–C(12)
2.0338(10)
2.0310(10)
2.0011(12)
2.1157(16)
2.1173(16)
1.3633(17)
1.3644(17)
1.3992(18)
1.3994(18)
1.4075(18)
1.4019(19)
1.3865(19)
1.3897(19)
1.3947(19)
1.3948(19)
1.4085(19)
1.3972(19)
1.3890(20)
1.3859(19)
1.3960(20)
1.3980(20)
O(1)Sb(1)O(2)
N(1)Sb(1)O(1)
N(1)Sb(1)O(2)
N(1)Sb(1)C(31)
N(1)Sb(1)C(29)
O(1)Sb(1)C(31)
O(1)Sb(1)C(29)
O(2)Sb(1)C(31)
O(2)Sb(1)C(29)
C(31)Sb(1)C(29)
C(1)O(1)Sb(1)
C(7)O(2)Sb(1)
C(2)N(1)C(8)
159.29(4)
79.61(4)
79.69(5)
121.90(6)
122.01(6)
93.26(6)
96.81(6)
97.62(5)
94.15(6)
116.08(7)
113.51(8)
113.49(8)
130.30(12)
115.00(9)
114.69(9)
113.61(12)
112.21(11)
C(2)N(1)Sb(1)
C(8)N(1)Sb(1)
C(30)C(29)Sb(1)
C(32)C(31)Sb(1)
Fig. 3. X-ray structure of [(AP-AP)]SbEt2 (5). The H atoms are omitted for clarity.

3466
A.I. Poddel’sky et al. / Journal of Organometallic Chemistry 694 (2009) 3462–3469
proposed [29,31]. The first stage (one-electron oxidation of dian-
ionic AP ligand to radical-anion by molecular oxygen) is followed
by the coordination of superoxide anion to antimony(V) to form
a triplet diradical complex containing o-iminobenzosemiquinonato
and end-on bound peroxo-ligands. The initial coordination of
molecular oxygen to antimony (which should forego the first
stage) depends on the sensitivity to the electrophylic attack. The
latter can be controlled by the positive charge on antimony which
decreases in Et3Sb compared with Ph3Sb. In the former case, ethyl
groups donate the electronic density to antimony decreasing its
positive charge, and it makes dioxygen-binding ability to be less
pronounced.
3. Experimental
3.1. General considerations
All manipulations were carried out under an air-free atmo-
sphere. All solvents were purified using standard technique
[43]. Diethyl ether was distilled from sodium benzophenone ke-
tyl and degassed immediately prior to use. Hexane and toluene
were distilled from CaH2 and degassed immediately prior to
use. Deuterated chloroform was dried with phosphorus(V) oxide
and vacuum-transferred. Anhydrous SbCl3, SbPh3 and EtBr were
purchased. Et3SbBr2 and Et3Sb [44,45], 4,6-di-tert-butyl-N-(2,6-
di-isopropylphenyl)-o-iminobenzoquinone IBQ-iPr, 4,6-di-tert-
butyl-N-(2,6-dimethylphenyl)-o-iminobenzoquinone IBQ-Me
[46].
Fig. 4. Views on complex 5 molecule. Hydrogen atoms are omitted for clarity.
tBu
O
N
The reagent
The reagent
tBu
addition order
addition order
OH
tBu
tBu
The synthesis of 4,6-di-tert-butyl-N-(3,5-di-tert-butyl-2-
hydroxyphenyl)-o-iminobenzoquinone (IBQ-AP)H: the methanol
solution (30 ml) of 4,6-di-tert-butyl-o-aminophenol [47] (1 g,
4.5 mmol) was added to a methanol solution (30 ml) of 3,5-di-
tert-butyl-o-benzoquinone (1 g, 4.5 mmol) at ambient tempera-
ture. The mixture color turned deep violet. The reaction solution
was kept for 0.5 h at RT and then it was stored at ꢀ18 °C for a night.
The dark violet precipitate was filtered and dried on air. Yield is
1.6 g (83.9%). 1H NMR (200 MHz, CDCl3, 20 °C, TMS, d, ppm): 1.25
(s, 18H, 2 t-Bu); 1.37 (s, 18H, t-Bu); 4.88 (v.br.s, 1H, OH); 6.88
(br.s, 2H, C6H2); 7.16 (br.s, 2H, C6H2). The synthesis of amino-bis-
(3,5-di-tert-butyl-2-hydroxyphenyl) ligand (AP-AP)H3: the mix-
ture of 4,6-di-tert-butyl-o-aminophenol [47] (1 g, 4.5 mmol) and
3,5-di-tert-butyl-o-benzoquinone (1 g, 4.5 mmol) in 50 ml of
methanol was stirred at RT for 15 min and then 0.5 ml of hydrazine
hydrate was added to this solution. After vigorous boiling was
complete, bright-yellow solution was diluted with 5 ml of water
and allowed to stay at ꢀ18 °C for a night. Yield is 1.55 g (80.4%).
1H NMR (200 MHz, CDCl3, 20 °C, TMS, d, ppm): 1.22 (s, 18H, 2 t-
Bu); 1.46 (s, 18H, t-Bu); 5.33 (br.s, 1H, NH); 5.46 (br.s, 2H, 2 OH);
6.73 (br.s, 2H, C6H2); 7.01 (br.s, 2H, C6H2).
(IBQ-AP)H
Et3Sb
Et
Et3Sb
-C2H6
Et
Sb
Et Et
Sb
Et
O
O
O
O
tBu
5
tBu
tBu
tBu
N
HN
tBu
tBu
[(AP-AP)]SbEt2
tBu
[(AP-AP)H]SbEt3
tBu
4
Scheme 5.
t
Bu
R
t
Bu
R
O
O
O
N
O
N
O2
SbEt3
R
SbEt3
t
Bu
tBu
R
Bruker AVANCE DPX-200 spectrometer was used for recording
the 1H, 13C, 13C DEPT NMR spectra. Chemical shifts for 1H and 13C
spectra were referenced internally according to the residual sol-
vent resonances and reported relative to TMS; CDCl3 was used as
solvent. Infrared spectra were recorded on a Perkin–Elmer FT-IR
1 (R = iPr),2 (R = Me)
Scheme 6.
6 (R = iPr), 7 (R = Me)
spectrometer in Nujol mulls and reported in cmꢀ1
.
give spiroendoperoxides 6 and 7, correspondingly, slower than
their triphenylantimony analogues. The reaction reaches an equi-
librium five times slower than for (AP-R)SbPh3 and amounts
to 15–20% of conversion compared with 94–98% conversion of
(AP-R)SbPh3.
3.2. X-ray diffraction studies
X-ray diffraction data for 1 and 5 were collected using Oxford
Diffraction (Gemini S) diffractometer with graphite monochromat-
The removal of oxygen leads to the shift of this equilibrium with
the formation of initial o-amidophenolates 1, 2. At the same time,
the prolonged exposition of these complexes to air allows deeper
subsequent oxidation of spiroendoperoxides 6 and 7.
The decrease of o-amidophenolates conversion to spiroendoper-
oxides can be rationalized from the viewpoint of the mechanism
ed Mo K
a
radiation (k = 0.71073 Å) and with CCD detector Sapphire
III in the
x
-scan mode (hemisphere with max 2h = 61° resolution,
exposure 10 sec on each frame). X-ray data on samples 1 and 5
were collected at temperatures 298 and 100 K, correspondingly.
The crystal structure was solved by direct methods (SHELX97) [48]

A.I. Poddel’sky et al. / Journal of Organometallic Chemistry 694 (2009) 3462–3469
3467
Table 3
(AP-iPr)SbEt3 (1): IR (Nujol, KBr,
m
, cmꢀ1): 1566 m, 1464 m, 1440
Crystallographic data of 1 and 5.
s, 1419 s, 1356 w, 1338 m, 1316 m, 1287 s, 1252 vs, 1239 m,
1200 m, 1180 w, 1103 m, 1080 w, 1050 w, 1040 w, 1027 m, 992
s, 935 w, 920 w, 901 m, 850 m, 826 w, 803 s, 772 m, 760 w, 712
w, 688 w, 670 w, 666 w, 654 w, 606 w, 585 w, 543 w, 531 w,
518 w, 506 m, 478 m, 452 w, 425w. 1H NMR (200 MHz, CDCl3,
Compound 1
Compound 5
Empirical formula
Formula weight
Temperature (K)
Wavelength (Å)
Crystal system
Space group
C32H52NOSb
588.50
298(2)
0.71073
monoclinic
C2/c
C32H50NO2Sb
602.48
100(2)
0.71073
monoclinic
P21/c
3
20 °C, TMS, d, ppm): 1.03 (d, JHH = 6.9 Hz, 6H, 2 CH(CH3)2); 1.09
3
(s, 9H, t-Bu); 1.18 (d, JHH = 6.9 Hz, 6H, 2 CH(CH3)2); 1.29 (t,
3JHH = 7.6 Hz, 9H,
3 CH2CH3); 1.45 (s, 9H, t-Bu); 1.61 (q,
Unit cell dimensions
a = 27.7750(9) Å
a = 11.4101(2) Å
a = 90.00°
b = 13.7573(2) Å
b = 91.7856(13)°
c = 19.9503(3) Å
c = 90.00°
3130.12(9)
4
1.278
0.908
1264
0.3 ꢄ 0.25 ꢄ 0.1
3.13–30.51°
99.3%
9499
8299 [Rint = 0.0173]
SADABS
Full-matrix least-
squares on F2
9499/0/526
R1 = 0.0257,
wR2 = 0.0565
R1 = 0.0336,
wR2 = 0.0583
1.090
3
3JHH = 7.6 Hz, 6H, 3 CH2CH3); 3.16 (sept., JHH = 6.9 Hz, 2H, 2
a
= 90.00°
4
4
CH(CH3)2); 5.72 (d, JHH = 2.3 Hz, 1H, C6H2); 6.55 (d, JHH = 2.3 Hz,
1H, C6H2); 7.16–7.33 (m, 3H, C6H3). 13C NMR (50 MHz, CDCl3,
20 °C, d, ppm): 9.28, 18.88, 23.90, 25.69, 27.61, 29.66, 31.77,
34.18, 34.64, 107.18, 111.06, 123.92, 127.06, 130.27, 135.80,
136.69, 139.05, 146.40, 149.09. 13C{1H} NMR (50 MHz, CDCl3,
20 °C, d, ppm): 9.28 (s, 3 CH2CH3), 18.88 (s, 3 CH2CH3), 23.90 and
25.69 (both s, both 2 CH(CH3)2), 27.61 (s, 2 CH(CH3)2), 29.67 and
31.77 (both s, both 3 C(CH3)3), 107.18 (s, Ar), 111.06 (s, Ar),
123.92 (s, Ar), 127.06 (s, Ar). Anal. Calc. (%) for C32H52NOSb
(588.52): C, 65.31; H, 8.91; N, 2.38; Sb, 20.69. Found: C, 65.47; H,
8.99; N, 2.04; Sb, 20.97%.
b = 11.6703(3) Å
b = 96.688(3)°
c = 19.6418(5) Å
c
= 90.00°
Volume (Å3)
Z
6323.4(3)
8
1.236
0.895
Dcalc (mg/m3)
Absorption coefficient (mmꢀ1
F(0 0 0)
)
2480
Crystal size (mm3)
0.4 ꢄ 0.25 ꢄ 0.1
3.35–30.51°
99.8%
9645
6459 [Rint = 0.0547]
SADABS
Full-matrix least-
squares on F2
9645/0/319
R1 = 0.0407,
wR2 = 0.0640
R1 = 0.0873,
wR2 = 0.0725
0.965
h Range for data collection
Completeness to
Reflections collected
Independent reflections
Absorption correction
Refinement method
H = 30.51
(AP-Me)SbEt3 (2): IR (Nujol, KBr, m
, cmꢀ1): 1563 m, 1443 s, 1416
s, 1356 w, 1331 m, 1288 s, 1246 vs, 1202 m, 1163 w, 1119 w, 1096
w, 1026 w, 991 s, 975 w, 920 w, 897 m, 849 m, 827 w, 770 m, 760
w, 742 w, 708w, 695 w, 667 w, 651 w, 605 w, 540 w, 532 w, 514 w,
505 m, 475 m, 448 w. 1H NMR (200 MHz, CDCl3, 20 °C, TMS, d,
Data/restraints/parameters
Final R indices [I > 2
r(I)]
3
ppm): 1.11 (s, 9H, t-Bu); 1.27 (t, JHH = 7.8 Hz, 9H, 3 CH2CH3);
R indices (all data)
3
1.45 (s, 9H, t-Bu); 1.64 (q, JHH = 7.8 Hz, 6H, 3 CH2CH3); 2.18 (s,
4
4
Goodness-of-fit (GOF) on F2
Largest difference in peak and
hole (e Åꢀ3
6H, 2 CH3); 5.74 (d, JHH = 2.3 Hz, 1H, C6H2); 6.62 (d, JHH = 2.3 Hz,
1H, C6H2); 7.10–7.14 (m, 3H, C6H3). 13C NMR (50 MHz, CDCl3,
20 °C, d, ppm): 9.35, 18.54, 19.09, 29.62, 31.79, 34.12, 34.65,
105.09, 111.46, 126.20, 128.53, 130.48, 134.66, 136.29, 138.81,
141.94, 146.83. 13C{1H} NMR (50 MHz, CDCl3, 20 °C, d, ppm): 9.35
(s, 3 CH2CH3), 18.54 (s, 2 CH3), 19.09 (s, 3 CH2CH3), 29.62 and
31.79 (both s, both 3 C(CH3)3), 105.09 (s, Ar), 111.46 (s, Ar),
126.20 (s, Ar), 128.53 (s, Ar). Anal. Calc. (%) for C28H44NOSb
(532.41): C, 63.16; H, 8.33; N, 2.63; Sb, 22.87. Found: C, 63.01; H,
8.09; N, 2.77; Sb, 22.28%.
0.683; ꢀ0.683
0.580; ꢀ0.475
)
and refined by full matrix method (WINGX and SHELX97) [49]. The
reflection data were processed using the analytical absorption
correction algorithm [50]. All non-hydrogen atoms were refined
with anisotropic correction. The some part of H atoms were placed
in calculated positions and refined in the ‘‘riding-model”
(Uiso(H) = 1.2 Ueq(carbon) Å2 for aromatic hydrogen and 1.5
Ueq(carbon) Å2 for alkyl hydrogen), and the another part was
located from Fourier synthesis and refined isotropically [48]. The
follow minimal R1-factors obtained for 1 and 5 correspond to
R1 = 0.0407 and R1 = 0.0257.
Method 2: The sample of Et3Sb (0.1 M toluene solution) was
added with stirring to a solution of IBQ-iPr (0.250 g, 0.66 mmol)
or IBQ-Me (0.220 g, 0.68 mmol) in toluene (15–20 ml) till color
change from cherry-red to yellow was complete. Toluene was
evaporated under vacuum, and the solid residue was dissolved in
pentane (15 ml). After the slow evaporation of pentane followed
by cooling of solution to ꢀ12 °C and storing at this temperature
for 1 day allowed to isolate complex 1 or 2, correspondingly, as
an yellow crystalline solids (0.372 g, 95.8% for 1 and 0.341 g,
94.2% for 2). The spectroscopic characteristics of the products pre-
pared by methods 1 and 2 are identical.
There are no solvent molecules in crystals of 1 and 5 were
found. Table 3 summarizes the crystal data and some details of
the data collection and refinement for 1 and 5. Selected bond dis-
tances and angles are given in Tables 1 and 2, respectively.
3.3. Preparation of complexes
3.3.2. (3,6-Di-tert-butyl-catecholato)triethylantimony(V) (3)
The sample of complex 3 was synthesized by procedure similar
to method 2 for 1 and 2; complex was isolated as the viscous pale
yellow oil which crystallizes with time. It can be easily stored at
room temperature under inert atmosphere. Yield was 93%. IR (Nu-
3.3.1. (4,6-Di-tert-butyl-N-(2,6-di-iso-propylphenyl)-o-
amidophenolato)triethylantimony (1) and (4,6-di-tert-butyl-N-(2,6-
dimethylphenyl)-o-amidophenolato)triethylantimony (2)
jol, KBr, m
, cmꢀ1): 1586 w, 1572 w, 1534 w, 1484 m, 1451 m, 1403
Method 1: The THF solution of sodium o-amidophenolate (pre-
pared from 0.379 g (1 mmol) of IBQ-iPr (for 1) or 0.323 g (1 mmol)
of IBQ-Me (for 2) and an excessing Na in 20 ml THF) was added
slowly with an extensive stirring to a THF solution of Et3SbBr2
(0.369 g, 1 mmol). After addition was complete, the reaction mix-
ture was heated at 50–60 °C for 30 min. Then THF was replaced
with pentane (ꢁ25 ml), filtered to remove NaBr residue and con-
centrated to half initial volume. The storing of solution at ꢀ18 °C
for 1–2 day allowed to obtain the yellow microcrystalline products
which were recrystallized from pentane to give X-ray suitable yel-
low crystals of 1 (0.520 g, 88.4%) or 2 (0.490 g, 92.1%).
s, 1352 m, 1282 s, 1258 s, 1241 s, 1203 s, 1145 m, 1026 m, 976 s,
941 s, 925 m, 810 m, 787 s, 710 m, 689 s, 651 s, 589 m, 541 w,
515 m, 496 w, 465 m, 444 m. 1H NMR (200 MHz, CDCl3, 20 °C,
3
TMS, d, ppm): 1.39 (s, 18H, 2 t-Bu), 1.41 (t, JHH = 7.9 Hz, 9H, 3
3
CH2CH3), 1.90 (q, JHH = 7.9 Hz, 6H, 3 CH2CH3), 6.54 (s, 2H, C6H2).
13C NMR (50 MHz, CDCl3, 20 °C, d, ppm): 9.10, 20.06, 29.34,
34.08, 113.38, 131.35, 140.06. 13C{1H} NMR (50 MHz, CDCl3,
20 °C, d, ppm): 9.10 (s, 3 CH2CH3), 20.06 (s, 3 CH2CH3), 29.34 (s, 2
C(CH3)3), 113.38 (s, Ar). Anal. Calc. (%) for C20H35O2Sb (429.25):
C, 55.96; H, 8.22; Sb, 28.37. Found: C, 56.07; H, 8.39; Sb, 28.65%.

3468
A.I. Poddel’sky et al. / Journal of Organometallic Chemistry 694 (2009) 3462–3469
3.3.3. Amino-bis-(3,5-di-tert-butyl-phenolate-2-
yl)triethylantimony(V) (4)
34.63, 34.93, 107.98, 113.68, 132.03, 133.66, 139.30, 145.71.
13C{1H} NMR (50 MHz, CDCl3, 20 °C, d, ppm): 8.13 (2 CH2CH3),
23.38 (2 CH2CH3), 29.56 (2 C(CH3)3), 31.86 (2 C(CH3)3), 107.98 (s,
Ar), 113.68 (s, Ar). Anal. Calc. (%) for C32H50NO2Sb (602.463): C,
63.79; H, 8.36; N, 2.32; Sb, 20.21. Found: C, 64.06; H, 8.12; N,
2.23; Sb, 20.51%.
Method 1: The solution of amino-bis-phenol (AP-AP)H3 (0.212 g,
0.5 mmol, toluene 30 ml) was added dropwise to a solution of
Et3SbBr2 (0.185 g, 0.5 mmol) and Et3N (0.14 ml, 1 mmol) in toluene
(20 ml) at ꢁ0 °C. After the addition was complete, reaction mixture
was filtered to remove colorless precipitate of [Et3NH]Br. The
change of the solvent with hexane and storing this solution at
ꢀ18 °C for 1 day allowed colorless microcrystalline solid product.
Yield is 0.197 g (62.4%). This complex should be stored in vacuo un-
3.3.5. Reaction of 1 and 2 with molecular oxygen
The solution of 1 or 2 in CDCl3 (0.015 M) was exposed to air in
NMR tube and a steam of fresh air was passed through solution. 1H
NMR spectra were recorded each hour during 8 h. Then tube was
degassed by the five time repeating cycle ‘‘freeze-pump-warm”
to remove air and then 1H NMR spectra were recorded again to
show the formation of initial complexes 1 or 2, correspondingly.
[(L-iPr)O2]SbEt3 (6): 1H NMR (200 MHz, CDCl3, 20 °C, TMS, d,
der low temperature. IR (Nujol, KBr, m
, cmꢀ1): 3158 s, 1603 w, 1563
w, 1482 s, 1454 s, 1445 s, 1415 m, 1377 m, 1360 m, 1302 s, 1284 s,
1269 w, 1240 m, 1202 s, 1164 w, 1129 m, 1034 w, 1020 m, 980 m,
936 w, 914 m, 878 m, 857 w, 834 s, 810 w, 785 m, 751 s, 707 s, 667
w, 645 w, 584 w, 541 w, 519 s, 510 w, 487 m, 475 m, 439 w, 405 w.
1H NMR (200 MHz, CDCl3, 20 °C, TMS, d, ppm): 1.16 (t,
3JHH = 7.9 Hz, 6H, 2 CH2CH3), 1.26 and 1.35 (s, both 18 H, t-Bu),
3
ppm): 0.99 (s, 9H, t-Bu); 1.36 (s, 9H, t-Bu); 1.28 (t, JHH = 7.9 Hz,
3
9H, 3 CH2CH3); 2.47 (q, JHH = 7.9 Hz, 6H, 3 CH2CH3); 2.83 (sept.,
3
3
3
1.42 (q, JHH = 7.9 Hz, 4H, 2 CH2CH3), 1.61 (t, JHH = 7.8 Hz, 3H,
3JHH = 6.8 Hz, 1H, CH(CH3)2); 3.45 (sept., JHH = 6.8 Hz, 1H,
3
4
4
CH2CH3), 1.90 (q, JHH = 7.8 Hz, 2H, CH2CH3), 4.96 (br.s, 1H, NH),
CH(CH3)2); 6.36 (d, JHH = 1.7 Hz, 1H, C6H2); 6.42 (d, JHH = 1.7 Hz,
1H, C6H2); 6.97–7.30 (m, 3H, C6H3). Methyl groups of iPr were dif-
ficult to determine.
4
7.08 and 7.21 (both d, JHH = 2.4 Hz, both 2H, 2 C6H2). 1H NMR
3
(400 MHz, benzene-d, 20 °C, TMS, d, ppm): 1.06 (t, JHH = 7.9 Hz,
3
6H, 2 CH2CH3); 1.21 (q, 4H, JHH = 7.9 Hz, 2 CH2CH3); 1.32 (s, 18H,
[(L-Me)O2]SbEt3 (7): 1H NMR (200 MHz, CDCl3, 20 °C, TMS, d,
ppm): 1.01 (s, 9H, t-Bu); 1.29 (t, JHH = 7.9 Hz, 9H, 3 CH2CH3);
1.35 (s, 9H, t-Bu); 2.46 (q, JHH = 7.9 Hz, 6H, 3 CH2CH3); 2.08 and
2.21 (both s, both 3H, 2 CH3); 5.37 (d, JHH = 1.6 Hz, 1H, C6H2);
3
2 t-Bu); 1.56 (s, 18H, 2 t-Bu); 1.69 (t, J = 7.9 Hz, 3H, CH2CH3);
3
3
1.89 (q, 2H, JHH = 7.9 Hz, CH2CH3), 4.38 (s, 1H, NH); 7.09 (d,
4
4
4JHH = 2.0 Hz, 2H, C6H2); 7.32 (d, JHH = 2.0 Hz, 2H, C6H2). 13C NMR
4
(101 MHz, benzene-d, 20 °C, d, ppm): 9.03, 9.18, 9.72, 10.18,
16.69, 22.86, 29.41, 29.94, 31.69, 34.11, 35.33, 118.60, 122.87,
129.78, 137.53, 137.64, 151.86. 13C{1H} NMR (50 MHz, CDCl3,
20 °C, d, ppm): 8.16 (3 CH2CH3), 23.41 (3 CH2CH3), 29.56 and
31.87 (both 2C(CH3)3), 107.99 (Ar), 13.70 (Ar). Anal. Calc. (%) for
C34H56NO2Sb (632.57): C, 64.56; H, 8.92; N, 2.21; Sb, 19.25. Found:
C, 63.91; H, 8.79; N, 2.07; Sb, 18.98%.
Method 2: The solution of 4,6-di-tert-butyl-N-(3,5-di-tert-butyl-
2-hydroxyphenyl)-o-iminobenzoquinone (IBQ-AP)H (254 mg,
0.6 mmol, toluene 30 ml) was slowly added to a toluene solution
of SbEt3 (125 g, 0.6 mmol, toluene 20 ml) at low temperature
(ꢁ0 °C) with the extensive stirring. After the complete disappear-
ance of violet color of the solution, the solvent was removed off
by evaporation, and the pale yellow residue was dissolved in hex-
ane. This solution was allowed to stay at ꢀ18 °C for a night after
that the pale yellow crystalline powder was collected by filtration.
Yield is 0.25 g (65.9%).
6.35 (d, JHH = 1.6 Hz, 1H, C6H2); 6.9–7.1 (m, 3H, C6H3).
Acknowledgements
We are grateful to the Russian Foundation for Basic Research
(Grants 07-03-00819 and 07-03-00711), Russian President Grant
(Grants NSh-4182.2008.3 and MK-1286.2009.3), Russian Science
Support Foundation (A.I. Poddel’sky) for financial support of this
work.
Appendix A. Supplementary data
CCDC 716050 and 716049 contains the supplementary crystal-
lographic data for complexes 1 and 5. These data can be obtained
free of charge from The Cambridge Crystallographic Data Centre
via www.ccdc.cam.ac.uk/data_request/cif.
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.jorganchem.2009.06.027.
3.3.4. Amido-bis-(3,5-di-tert-butyl-phenolate-2-
yl)diethylantimony(V) (5)
References
Method 1: The exposure of the solution of 4 to air for a 1 h leads
to yellow complex 5 with a nearly quantitative yield (ꢁ98%).
Method 2: The solution of SbEt3 (105 g, 0.5 mmol, toluene
20 ml) was added dropwise to a solution of 4,6-di-tert-butyl-N-
(3,5-di-tert-butyl-2-hydroxyphenyl)-o-iminobenzoquinone (IBQ-
AP)H (212 mg, 0.5 mmol, toluene 25 ml). The violet color was dis-
appeared and toluene was changed with hexane. The yellow resi-
due precipitated after solution cooling was recrystallized from
another hexane portion. The storage of this solution at ꢀ18 °C for
3 days gave white X-ray quality crystals which were collected by
filtration and dried in vacuo. Yield is 0.265 g (88.0%). IR (Nujol,
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KBr, m
, cmꢀ1): 1726 w, 1713 w, 1587 m, 1568 s, 1480 s, 1445 s,
1416 m, 1391 m, 1377 m, 1346 s, 1313 m, 1282 s, 1260 w, 1243
s, 1218 m, 1204 s, 1162 w, 1130 m, 1052 s, 1022 m, 1012 s, 959
s, 931 w, 913 w, 861 s, 841 s, 822 w, 754 m, 739 w, 703 w, 688
w, 679 w, 642 s, 601 w, 548 s, 529 m, 504 w, 451 w, 423 w, 414
w, 403 w. 1H NMR (200 MHz, CDCl3, 20 °C, TMS, d, ppm): 1.38 (s,
3
18 H, 2 t-Bu); 1.43 (s, 18 H, 2 t-Bu); 1.46 (t, JHH = 7.90 Hz, 6H, 2
3
CH2CH3); 2.30 (q, JHH = 7.9 Hz, 4H,
2 CH2CH3); 6.84 (d,
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