NHC-Stabilized Organotin(II) Cation
COMMUNICATION
[RSnPh2]+ (2.241(3) and 2.249(2) ꢃ).[22] The Sn(1) N(1) dis-
Sn(1) N(1) distance of 2.297(2) ꢃ is elongated in compari-
À
À
À
À
tance of 2.234(2) ꢃ in compound 2 is shorter than the Sn N
son to compound 2, whereas the Sn O distances are short-
distance reported for compound F (2.286(6) ꢃ; Scheme 1).
One phenyl ring (C61–C66) of the tetraphenylborate anion
shows a p-type interaction with the Sn(1) cation at a dis-
tance of 3.6955(2) ꢃ. This interaction, although much
weaker, resembles the situation reported for the Sn···Ph in-
ened to 2.250(1) and 2.227(1) ꢃ.
The 31P and 119Sn NMR spectra showed a singlet at d=
31
22.9 ppm (J( P 117/119Sn)=105/110 Hz) and a triplet reso-
À
nance at d=À423 ppm (J(119Sn 31P)=108 Hz, 2J(119Sn
À
À
117Sn)=341 Hz), respectively, that resemble the data report-
teraction at
a
distance of 3.110(2) ꢃ reported for
ed for [R’(Cl)SnS]2 [119Sn NMR: d=À439 ppm (t, J(119Sn
À
Cp*SnBPh4 (Cp*=C5Me5).[5]
31P)=84 Hz); P NMR: d=26.7 ppm (J( P 119/117Sn)=86/
31
31
À
119
The 119Sn NMR spectra in CD2Cl2 of compounds 1 and 2
displayed sharp triplet resonances at d=À169 and
À170 ppm, respectively, showing that the tin atoms in both
compounds are in similar electronic environments, as con-
firmed by natural charge calculations (+1.11 for 1 and
82 Hz)].[20b]
for [Sn
[L’(Ph)Sn
A
2A
Sn 117Sn coupling larger than that observed
À
(ArN2)
(m-S)]2 (277 Hz, ArN2 =2,6-(Me2N)2C6H3)[26] or
(m-S)]2
(226 Hz,
L’=2,6-(tBuOCH2)2C6H3)[27]
shows that the four-membered ring is retained in solution.
1
The H NMR spectrum of compound 3 showed two broad
+1.21 for 2). The 31P NMR spectra showed resonances shift-
unresolved signals (n = ca. 250 Hz) for the CH
and a broad unresolved signal for the CHACTHUNGTRENNUNG
A
1
2
31
ed to lower frequency with larger J( P 117/119Sn) coupling
À
31
constants [1, d=30.0 ppm (s, J( P 117/119Sn)=137/141 Hz);
Lowering the temperature to À848C resulted in sharpening
À
31
2, d=35.6 ppm (s, J( P 117/119Sn)=129/135 Hz] than those
of the two CH signals and resolution into four doublets for
À
À
observed for the organostannylene RSnCl (d=37.8 ppm,
the CH
N
31
J( P 117/119Sn)=113/118 Hz)[20c]. The 1H and the 13C NMR
ation has become slow on the 1H NMR time scale. The
15N NMR spectrum showed two higher frequency resonan-
ces, with respect to 2, at d=À152 and À309 ppm. An elec-
trospray ionization mass spectrum of compound 3 (positive
ion mode) in CH3CN showed a mass cluster centered at
m/z=612.2 corresponding to a dicationic structure resulting
from loss of both dmap ligands.
À
spectrum of compound 1 showed two sets of signals for the
isopropyl groups, whereas the spectra of compound 2
showed only one set of signals. A 1H NMR spectrum of
compound 2 at À848C failed to resolve the isopropyl group.
À
This is attributed to a fast Sn N dissociation–association
À
process in compound 2, whereas no Sn C dissociation is ob-
served for carbene complex 1 as evidenced by the 13C NMR
The reaction of the carbene-stabilized compound 1 with
sulfur appeared to be more complex than that of 2 and no
reaction product could be identified unambiguously.
The calculation of the electronic structures of compounds
1 and 2 revealed the natural bond orbitals (NBOs) depicted
13
spectrum of 1. This spectrum showed J( C 117/119Sn) cou-
À
3
13
À
plings for the imidazole CH carbon (d=126.6 ppm, J( C
117/119Sn)=23.0 Hz) and a triplet resonance for the carbene
13
carbon atom at d=183.2 ppm (J
( C 31P)=1.5 Hz). The
À
À
chemical shift of the latter is comparable to the value re-
in Figure 4. In both 1 and 2 the Sn(1) C(1) bond is the only
covalent bond, whereas all other interactions involving the
ported for (IPr)SnCl2 (d=184.2 ppm).[25] The 15N NMR
spectrum of compound
2
showed two resonances at d=
À166 (HCNCH) and À307 ppm
(NMe2), which are shifted in
comparison to free DMAP (d=
À107 and À327 ppm).
The reaction of compound 2
with elemental sulfur provided
the novel four-membered-ring
species [R(L)SnS]2ACHTUNGTRENNUNG[BPh4]2 (3:
L=DMAP) containing a dinu-
clear dication. Its molecular
structure, determined from
single crystals of its acetonitrile
solvate 3·3CH3CN, is shown in
Figure 3. In compound 3 the tin
atom adopts a distorted octahe-
dral geometry. The structure of
3 strongly resembles that of the
chlorido-substituted analogue
[R’(Cl)SnS]2
{P(O)
(R’=4-tBu-2,6-
(OEt)2}2C6H2).[20b]
The
Figure 3. Molecular structure of compound 3 with thermal ellipsoids showing 30% probability and the hydro-
gen atoms, the methyl groups, the acetontrile solvate molecule and the tetraphenylborate anions omitted for
À
Sn(1) S(1)/S(1A) bond lengths
are 2.3472(5)/2.5515(5) ꢃ. The clarity.
Chem. Eur. J. 2013, 19, 9463 – 9467
ꢂ 2013 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
9465