A.V. Piskunov et al. / Journal of Organometallic Chemistry 691 (2006) 1531–1534
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Irradiation of toluene solution containing 1 and
Co2(CO)8 at 220 K results in a weak broad singlet in
EPR spectrum, which disappears under further irradiation
or increase temperature. When Mn2(CO)10 and Re2(CO)10
were used as radical sources, we were unable to detect any
EPR signals both under ambient temperature and when
cooled.
Available data on the structures of the b-diketoiminate
three-coordinate tin(II) complexes [12] and the EPR
parameters for compounds 2 and 3 allow us to assume a
similar geometry of a distorted trigonal pyramid with
nitrogen, tin, and halide atoms at apical sites. This is also
supported by large HFC constants on magnetic isotopes
of chlorine and bromine. The position of the Sn–Hal bond
being close to perpendicular to the chelate ring plane will
be favorable for a larger contribution of the r(r*) orbital
of M–Hal to the p-MO occupied by unpaired electron.
2-Phenyl-4,4,5,5-tetramethyl-4,5-dihydro-1H-imidazole-
1-oxy-3-oxide and TEMPO radicals add to stannylene 1
giving rise to EPR spectra, indicating the formation of
derivatives 6 and 7 (Scheme 1), respectively. In these spec-
1
tra, HFC of unpaired electron to magnetic nuclei H, 14N,
3. Experimental
117Sn and 119Sn (Table 1) can be observed.
We have found no sign of interaction between the tin
complex and carbon-centered trityl radical. Thus, the tolu-
ene solution containing 1 and trityl radical does not change
for several days, showing neither initial EPR spectrum
decrease, nor new spectra appearance.
EPR spectra were recorded on Bruker ER 200 D-SRC
(working frequency ꢀ9.5 GHz) spectrometer with ER041
MR microwave bridge, ER 4105 DR double resonator
and ER 4111 VT variable temperature unite. The irradia-
tion of samples was made with focused light of incandescent
lamp (250 W) in resonator of EPR spectrometer. The gi val-
ues were determined using diphenylpicrylhydrazyl as the
reference (gi = 2.0037). HFC constants were obtained by
simulation with the WinEPR SimFonia Software (Bruker).
Treatment of 1 with mercury or silver halides and free
radicals was made by addition of stannylene (15 mg,
0.03 mmol) solution in toluene (2 ml) to solid reagents
under EPR conditions. Tin complex was taken in approx-
imately tenfold excess to radical sources or metal halides.
When transition metals carbonyls were used, the reaction
mixture was cooled to about 220 K and irradiated in
EPR resonator to produce corresponding metal-centered
radicals.
As we have reported recently, addition of 3,6-di-tert-
butyl-2-ethoxyphenoxy radical to N,N0-substituted 1,2,3-
diazagermole-2-ylidenes yields the radical germylene
adducts. The enhanced stability of the latter was explained
by the following: a weak ancillary coordination bond
between germanium and ethoxy group causes considerable
steric hindrances in the coordination sphere of germanium,
and thus prevents addition of the second radical [6b]. Tak-
ing into account the fact, that the tetracoordinate state is
more usual for tin(II) than for germanium(II) derivatives
[8], we proposed, that the product of above mentioned phe-
noxyl addition to stannylene 1 would show even higher
stability.
Actually, interaction between 1 and 3,6-di-tert-butyl-2-
ethoxyphenoxy radical in toluene leads to paramagnetic
products and EPR spectrum appearance. The latter is
caused by the HFC of unpaired electron to magnetic nuclei
1H, 14N, 117Sn and 119Sn (Table 1). The spectrum can be
explained by the formation of product 8 (Scheme 1).
Paramagnetic stannylene 8 is stable in toluene solution
at ambient temperature for about two months. Com-
pounds 2, 3, 6, 7 are significantly less stable: their solutions
keep EPR-activity for no more than two weeks at 290 K.
The HFC constants on two equivalent protons and two
equivalent nitrogen nuclei (Ai(1H) and Ai(14N)) for deriva-
tives 2–8 are analogous to the values obtained for para-
magnetic stannylene [5], germylene and silylene [6]
complexes. The HFC constants due to magnetic isotopes
of tin Ai(117Sn) and Ai(119Sn) are in the same range as those
for the short-living (s1/2 ꢀ 2 min) radical-anion stannylene
Ar2SnÅꢁ (Ai(Sn) = 151 G; Ar = 2,6-diethylphenyl) [9] and
substantially exceed the HFC constants for paramagnetic
tin(IV) complexes (5–20 G) [10]. On the other hand,
Ai(117Sn) and Ai(119Sn) constants for 2–8 are approxi-
mately tenfold lower than the corresponding values for
the known tin-centered radicals (1700–3300 G) [11]. This
fact indicates that spin density in 2–8 is delocalized over
the entire chelate ring as in germanium and silicon [6]
derivatives.
All reagents were grade. Solvents were purified follow-
ing standard methods [13]. 3,6-Di-tert-butyl-2-ethoxyphen-
oxy radical [14] and 2-phenyl-4,4,5,5-tetramethyl-4,
5-dihydro-1H-imidazole-1-oxy-3-oxide [15] were prepared
according to known procedures.
3.1. Synthesis of N,N0-bis[(2,6-di-iso-propylphenyl)-1,2,3-
diazastannole-2-ylidene
Stannylene 1 was synthesized as follows: the THF solu-
tion of dilithium derivative [16] of corresponding diazabut-
adiene (1.88 g, 5 mmol), was added dropwise to cooled at
ꢁ20 °C THF solution, containing SnCl2Ædiox [17] complex
(1.39 g, 5 mmol). After mixing, THF was evaporated and
the residue was dissolved in hexane. The solution was sep-
arated from lithium chloride deposit by filtration. After
partial evaporation, 1 precipitated from hexane solution
as needle orange crystals (Yield: 0.68 g, 1.38 mmol,
27.5%. m.p. 206 °C (decomp.) 1H NMR (toluene-d8): d
i
1.22 (d, 6 H, 6.8 Hz, CH3, Pr), 1.24 (d, 6 H, 6.8 Hz,
i
i
CH3, Pr), 3.31 (septet, 4 H, 7.0 Hz, CH, Pr), 7.03 (s, 2
H, NCH, J(119Sn–H) = 9.0 Hz), 7.15–7.22 (br, 6 H, CH,
3
Ar). Anal. Calc. for C26H36N2Sn (495.29): C, 63.05; H,
7.33; Sn, 23.97. Found: C, 63.39; H, 7.37; Sn, 23.76%.).
All manipulations on complexes were carried out under
conditions excluding air oxygen and moisture.
Piskunov, Alexander V.
