Benzimidazolin-2-stannylenes with N,N′-alkyl (Me and Et) and Lewis base functional groups

Article abstract of DOI:10.1021/ic701064z

Symmetrically and unsymmetrically N,N′-substituted benzimidazolin-2-stannylenes with sterically nondemanding alkyl (Me and Et) and Lewis base functional groups (-(CH₂)_nOMe, -(CH ₂)_nNMe₂; n = 2, 3) have been synthesized by the transamination reaction between suitably substituted o-phenylenediamines and Sn[N(SiMe₃)₂]₂. The N,N′-dimethyl- substituted stannylene 3 exists in the solid state as a bimolecular aggregate which is held together by strong intermolecular Sn...N interactions leading to three-coordinated tin atoms. The benzimidazolin-2-stannylenes with N,N′-(CH₂)_nOMe substituents (5, n = 2; 6, n = 3) exhibit weak intramolecular Sn...O interactions in solution. Benzannulated stannylenes with N,N′-(CH₂)_nNMe₂ substituents (7, n = 2; 8, n = 3) are again dimers which exhibit both intramolecular Sn...NMe₂ and intermolecular Sn...N interactions, which leads to tri- or tetracoordinated tin atoms. Some unsymmetrically N,N′-substituted benzimidazolin-2-stannylenes have also been synthesized. The molecular structures of 3, 5, and 8 and the relation between the chemical shift recorded for the tin atoms and the solvent (C ₆D₆ or THF-d₈) used for recording ¹¹⁹Sn NMR spectra will be discussed.

Full text of DOI:10.1021/ic701064z

Inorg. Chem. 2007, 46, 7662−7667
Benzimidazolin-2-stannylenes with N,N′-Alkyl (Me and Et) and Lewis
Base Functional Groups
F. Ekkehardt Hahn,*,† Lars Wittenbecher,† Duc Le Van,† and Alexander V. Zabula†,‡
Institut fu¨r Anorganische und Analytische Chemie der Westfa¨lischen Wilhelms-UniVersita¨t Mu¨nster
and NRW Graduate School of Chemistry, Corrensstrasse 36, D-48149 Mu¨nster, Germany
Received May 31, 2007
Symmetrically and unsymmetrically N,N
alkyl (Me and Et) and Lewis base functional groups (
by the transamination reaction between suitably substituted o-phenylenediamines and Sn[N(SiMe3)2]2. The N,N
′
-substituted benzimidazolin-2-stannylenes with sterically nondemanding
−
(CH2)nOMe, (CH2)nNMe2; n 2, 3) have been synthesized
−
)
′
-
dimethyl-substituted stannylene 3 exists in the solid state as a bimolecular aggregate which is held together by
strong intermolecular Sn‚‚‚N interactions leading to three-coordinated tin atoms. The benzimidazolin-2-stannylenes
with N,N
Benzannulated stannylenes with N,N
both intramolecular Sn‚‚‚NMe2 and intermolecular Sn‚‚‚N interactions, which leads to tri- or tetracoordinated tin
atoms. Some unsymmetrically N,N -substituted benzimidazolin-2-stannylenes have also been synthesized. The
′
-(CH2)nOMe substituents (5, n
)
2; 6, n
)
3) exhibit weak intramolecular Sn‚‚‚O interactions in solution.
′
-(CH2)nNMe2 substituents (7, n
)
2; 8, n 3) are again dimers which exhibit
)
′
molecular structures of 3, 5, and 8 and the relation between the chemical shift recorded for the tin atoms and the
solvent (C6D6 or THF-d8) used for recording 119Sn NMR spectra will be discussed.
Scheme 1. Different Types of Diaminostannylenes
Introduction
Stannylenes are diamagnetic derivatives of divalent tin
which possess an unshared electron pair and a vacant
p-orbital at the tin atom in the ground state.1 Due to their
electronic structure they are potential Lewis base ligands for
transition metals2 and can act in such complexes as σ-donor
and weak π-acceptor ligands.3 The longest known stable tin-
(II) organyl s bis(cyclopentadienyl)tin or stannocene s was
synthesized by Fischer and Gruber in 1956.4 The first stable
dialkyl-5 and diaminostannylenes A6 (Scheme 1) were
* To whom correspondence should be addressed. E-mail: fehahn@uni-
muenster.de.
† Institut fu¨r Anorganizche and Analytische Chemie der WWU.
‡ NRW Graduate School of Chemistry.
synthesized by Lappert et al. in 1973 and 1974, respectively.
The reactive tin(II) atom in the monomeric diaminostan-
nylene A is stabilized not only by the sterically demanding
N(SiMe3)2 groups but also by the interaction of the vacant
p-orbital at the tin atom with the free electron pairs of the
trigonal-planar nitrogen atoms. The first N-heterocyclic
(1) (a) Neumann, W. P. Chem. ReV. 1991, 91, 311. (b) Takeda, N.;
Tokitoh, N.; Okazaki, R. Sci. Synth. 2003, 5, 311. (c) Tokitoh, N.;
Okazaki, R. Coord. Chem. ReV. 2000, 210, 251.
(2) (a) Lappert, M. F.; Rowe, R. S. Coord. Chem. ReV. 1990, 100, 267.
(b) Lappert, M. F.; Power, P. P. J. Chem. Soc., Dalton Trans. 1985,
51.
(3) Veith, M.; Rectenwald, O. Top. Curr. Chem. 1982, 104, 1.
(4) (a) Fischer, E. O.; Grubert, H. Z. Naturforsch. 1956, 11b, 423. (b)
Atwood, J. L.; Hunter, W. E.; Cowley, A. H.; Jones R. A.; Stewart,
C. A. J. Chem. Soc., Chem. Commun. 1981, 925.
(5) (a) Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Chem. Commun.
1973, 317. (b) Fjeldberg, T.; Haaland, A.; Schilling, B. E. R.; Lappert,
M. F.; Thorne, A. J. J. Chem. Soc., Dalton Trans. 1986, 1551. (c)
Davidson, P. J.; Harris, D. H.; Lappert, M. F. J. Chem. Soc., Dalton
Trans. 1976, 2268.
(6) (a) Davidson, P. J.; Lappert, M. F. J. Chem. Soc., Chem. Commun.
1974, 895. (b) Lappert, M. F.; Power, P. P.; Slade, M. J. J. Chem.
Soc., Chem. Commun. 1979, 369. (c) Braunschweig, H.; Hitchcock,
P. B.; Lappert, M. F.; Pierssen, L. J.-M. Angew. Chem., Int. Ed. Engl.
1994, 33, 1156.
7662 Inorganic Chemistry, Vol. 46, No. 18, 2007
10.1021/ic701064z CCC: $37.00
© 2007 American Chemical Society
Published on Web 08/01/2007

Benzimidazolin-2-stannylenes
stannylenes of type B were reported by Veith.7 They are
monomeric or dimeric, depending on the N-substituent R.
Some years thereafter, the first representatives of a new type
of cyclic diaminostannylenes C-G, which contain the tin
atom as part of aromatic system, were described. The
benzimidazolin-2-stannylene C was synthesized and char-
acterized in 1995,8 4 years before its carbene analogue was
reported.9 The benzimidazolin-2-stannylenes of type C
contain bulky N,N′-substituents (R ) neopentyl or trimeth-
ylsilyl), which leads an efficient steric shielding of the tin-
(II) center. A different type of benzannulated stannylene D
with a pyridoannulated five-membered ring was prepared by
Heinecke et al.10 The diaminostannylene E which is an
analogue of Arduengo’s carbene was isolated recently.11
Finally, stannylenes derived from diaminonaphtalene F12 and
cationic stannylenes G13 containing a 10-π-electron ring
system have been prepared. We have previously described
a benzannulated stannylene of type C with donor-function-
alized N-substituents (R ) CH2CH2NMe2). This stannylene
exists as a bimolecular aggregate in the solid state and
exhibits strong intramolecular and intermolecular Sn‚‚‚N
interactions.14 Here we describe a series of benzannulated
stannylenes of type C (R ) alkyl, donor-functionalized
group). Their molecular structures and 119Sn NMR spectra,
which show a relation between the chemical shift observed
for the tin atom and the solvent used for recording the
spectra, are discussed.
was added to a solution of an N,N’-dialkyl-1,2-diaminobenzene
(2a-d,g-i,m-o) (4 mmol) in toluene (40 mL). After stirring of
the reaction mixture for 36 h at ambient remperature, the solvent
and volatile products were removed in vacuo. The residue was
recrystallized from toluene or THF. Stannylenes 4, 6, and 9-12
were isolated as brown or red oils.
N,N′-Dimethylbenzimidazolin-2-stannylene (3). Recrystalli-
zation from toluene gave orange crystals (mp 169 °C). Yield: 98%.
1H NMR (400 MHz, C6D6): δ 7.07 (m, 2H, Ar-H), 6.79 (m, 2H,
Ar-H), 3.28 (s, 6H, CH3). 13C NMR (100 MHz, C6D6): δ 147.6
(Ar-Cipso), 117.9 (Ar-Cmeta), 109.8 (Ar-Cortho), 34.0 (CH3). 119Sn
NMR (149 MHz, C6D6): δ 225.3. 119Sn NMR (149 MHz, THF-
d8): δ 106.5. MS (EI, 70 eV) [m/z (%)]: 254 (21.3) [M]+, 239
(4.3) [M - CH3]+, 224 (3.0) [M - 2CH3]+.
N,N′-Diethylbenzimidazolin-2-stannylene (4): brown oil.
1
Yield: 97%. H NMR (400 MHz, C6D6): δ 6.99 (m, 2H, Ar-H),
6.83 (m, 2H, Ar-H), 3.76 (q, 4H, NCH2), 1.36 (t, 6H, CH3). 13C
NMR (100 MHz, C6D6): δ 147.1 (Ar-Cipso), 117.9 (Ar-Cmeta), 109.8
(Ar-Cortho), 43.4 (NCH2), 19.2 (CH3). 119Sn NMR (149 MHz,
C6D6): δ 236.6. 119Sn NMR (149 MHz, THF-d8): δ 174.5. MS
(EI, 70 eV) [m/z (%)]: 282 (19.4) [M]+, 253 (6.8) [M - CH2-
CH3]+.
N,N′-Bis(2-methoxyethyl)benzimidazolin-2-stannylene (5). Com-
pound 5 was recrystallized from THF to give yellow crystals (mp
156 °C). Yield: 99%. 1H NMR (400 MHz, C6D6): δ 7.02 (m, 2H,
Ar-H), 6.76 (m, 2H, Ar-H), 3.69 (t, 4H, NCH2), 3.32 (t, 4H, CH2O),
2.96 (s, 6H, OCH3). 13C NMR (100 MHz, C6D6): δ 146.8 (Ar-
Cipso), 117.6 (Ar-Cmeta), 110.4 (Ar-Cortho), 72.2 (CH2O), 57.6
(NCH2), 48.0 (OCH3). 119Sn NMR (149 MHz, C6D6): δ 147.8.
119Sn NMR (149 MHz, THF-d8): δ 89.4. MS (EI, 70 eV) [m/z
(%)]: 342 (4.1) [M]+.
Experimental Section
N,N′-Bis(3-methoxypropyl)benzimidazolin-2-stannylene (6):
brown oil. Yield: 95%. 1H NMR (400 MHz, THF-d8): δ 6.58 (m,
2H, Ar-H), 6.55 (m, 2H, Ar-H), 3.94 (t, 4H, NCH2), 3.41 (t, 4H,
CH2O), 3.22 (s, 6H, OCH3), 2.02 (quint, 4H, CH2CH2CH2). 13C
NMR (100 MHz, THF-d8): δ 147.3 (Ar-Cipso), 116.9 (Ar-Cmeta),
109.2 (Ar-Cortho), 71.9 (CH2O), 58.8 (NCH2), 45.8 (OCH3), 33.1
(CH2CH2CH2). 119Sn NMR (149 MHz, C6D6): δ 226.4. 119Sn NMR
(149 MHz, THF-d8): δ 171.0. MS (EI, 70 eV) [m/z (%)]: 370
(3.6) [M]+.
General Comments. All manipulations were carried out under
an argon atmosphere using standard Schlenk techniques. Solvents
were dried over sodium/benzophenone under argon and were
freshly distilled prior to use. 1H and 13C NMR spectra were
measured on Bruker AC 200, AM 270, and AM 250 spectrometers.
Tetramethylstannane (δ ) 0) was used as an internal or external
standard for 119Sn NMR spectra. Sn[N(SiMe3)2]2 was purchased
from Aldrich. Spectroscopic data for the starting materials of types
1 and 2 can be found in the Supporting Information. Microanalytical
data for the stannylenes were difficult to obtain. Multiple attempts
gave different results due to the sensitivity of these compounds
toward moisture and air. However, all stannylenes were character-
ized by mass spectroscopy (all molecular ions were detected) and
1H, 13C, and 119Sn NMR spectroscopy, and three derivatives, by
X-ray diffraction.
N,N′-Bis(2-(dimethylamino)ethyl)benzimidazolin-2-stan-
nylene (7). The spectroscopic data for stannylene 7 are identical
with those previously reported by us.14
N,N′-Bis(3-(dimethylamino)propyl)benzimidazolin-2-stan-
nylene (8). Compound 8 was recrystallized from toluene as yellow
crystals (mp 163 °C). Yield: 98%. 1H NMR (400 MHz, C6D6): δ
6.92 (m, 2H, Ar-H), 6.75 (m, 2H, Ar-H), 3.75 (t, 4H, NCH2), 2.12
(t, 4H, CH2N(CH3)2), 1.79 (s, 12H, N(CH3)2), 1.62 (quint, 4H,
CH2CH2CH2). 13C NMR (100 MHz, C6D6): δ 147.4 (Ar-Cipso),
116.4 (Ar-Cmeta), 109.2 (Ar-Cortho), 59.2 (NCH2), 46.2 (CH2N-
(CH3)2), 45.3 (NCH3), 27.6 (CH2CH2CH2). 119Sn NMR (149 MHz,
C6D6): δ 51.7. 119Sn NMR (149 MHz, THF-d8): δ 51.4. MS (EI,
70 eV) [m/z (%)]: 396 (25.3) [M]+, 338 (4.6) [M - CH2N-
(CH3)2)]+, 58 (100) [CH2N(CH3)2]+.
Preparation of N,N′-Dialkylbenzimidazolin-2-stannylene De-
rivatives 3-12. A sample of Sn[N(SiMe3)2]2 (1.66 mL, 4.3 mmol)
(7) (a) Veith, M. Z. Naturforsch. 1978, 33b, 7. (b) Veith, M. Z.
Naturforsch. 1978, 33b, 1.
(8) Braunschweig, H.; Gehrhus, B.; Hitchcock, P. B.; Lappert, M. F. Z.
Anorg. Allg. Chem. 1995, 621, 1922.
(9) Hahn, F. E.; Wittenbecher, L.; Boese, R.; Bla¨ser, D. Chem.sEur. J.
1999, 5, 1931.
(10) Heinicke, J.; Oprea, A.; Kindermann, M. K.; Karpati, T.; Nyula´szi,
L.; Veszpre´mi, T. Chem.sEur. J. 1998, 4, 541.
(11) Gans-Eichler, T.; Gudat, D.; Nieger, M. Angew. Chem., Int. Ed. 2002,
41, 1888.
(12) (a) Drost, C.; Hitchcock, P. B.; Lappert, M. F. Angew. Chem., Int.
Ed. 1999, 38, 1113. (b) Bazinet, P.; Yap, G. P. A; DiLabio, G. A.;
Richenson, D. S. Inorg. Chem. 2005, 44, 4616.
(13) (a) Dias, R. H. V.; Jin, W. J. Am. Chem. Soc. 1996, 118, 9123. (b)
Ayaers, A. E.; Dias, H. V. R. Inorg. Chem. 2002, 41, 3259.
(14) Hahn, F. E.; Wittenbecher, L.; Ku¨hn, M.; Lu¨gger, T.; Fro¨hlich, R. J.
Organomet. Chem. 2001, 617-618, 629.
N-(2-Methoxyethyl)-N′-ethylbenzimidazolin-2-stannylene (9):
1
brown oil. Yield: 98%. H NMR (400 MHz, C6D6): δ 7.05 (m,
2H, Ar-H), 6.84 (m, 1H, Ar-H), 6.78 (m, 1H, Ar-H), 3.75 (m, 4H,
NCH2), 3.29 (t, 2H, CH2O), 2.94 (s, 3H, OCH3), 1.32 (t, 3H, CH3).
13C NMR (100 MHz, C6D6): δ 147.3, 146.6 (Ar-Cipso), 117.7, 117.6
(Ar-Cmeta), 110.0, 109.9 (Ar-Cortho), 72.3 (CH2O), 57.4 (NCH2CH2),
48.1 (NCH2CH3), 43.1 (OCH3); 16.0 (NCH2CH3). 119Sn NMR
(149 MHz, C6D6): δ 173.6. 119Sn NMR (149 MHz, THF-d8): δ
124.6. MS (EI, 70 eV) [m/z (%)]: 312 (2.38) [M]+.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7663

Hahn et al.
Table 1. Crystallographic Data for 3, 5, and 8
param
3
5
8
formula
Mr
C8H10N2Sn
252.87
C12H18N2O2Sn
340.97
C16H28N4Sn
395.11
a (Å)
b (Å)
c (Å)
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
6.8230(10)
7.8730(10)
15.404(2)
90.0
96.0100(10)
90.0
7.4890(10)
17.5030(10)
20.286(2)
90.0
90.0
90.0
8.5390(10)
11.1540(10)
11.097(2)
59.550(2)
78.7500(10)
72.970(2)
869.8(2)
2
821.4(2)
4
2659.1(5)
8
space group
P21/c
2.045
3.042
5.3-54.9
1941
Pbca
1.703
3.048
6.1-49.9
4039
P1h
F
calcd (g cm-3
)
1.509
µ(Mo KR) (mm-1
2θ range (deg)
data collcd
)
1.469
5.0-59.9
5262
no. of unique data, Rint
no. obsd data [I g 2σ(I)]
R (all data)
1875, 0.0136
1622
0.0268
2322, 0.0365
1867
0.0415
5032, 0.0089
4934
0.0354
wR (all data)
0.0463
0.0742
0.0970
no. of variables
140
0.541/-0.443
226
1.232/-0.911
302
2.459/-2.771
peak/hole (e Å-3
)
Scheme 2. Preparation of Symmetric Amines 2a-d,g,h
N-(2-(Dimethylamino)ethyl)-N′-ethylbenzimidazolin-2- stan-
nylene (10): red oil. Yield: 98%. H NMR (400 MHz, C6D6): δ
1
6.96 (t, 1H, Ar-H), 6.88 (t, 1H, Ar-H), 6.75 (d, 1H, Ar-H), 6.69 (d,
1H, Ar-H), 3.73 (q, 2H, NCH2CH3), 3.40 (t, 2H, NCH2CH2), 2.07
(t, 2H, CH2N(CH3)2), 1.69 (s, 6H, NCH3), 1.44 (t, 3H, NCH2CH3).
13C NMR (100 MHz, C6D6): δ 148.3, 146.2 (Ar-Cipso), 118.7, 116.1
(Ar-Cmeta), 111.9, 109.0 (Ar-Cortho), 57.9 (NCH2CH2), 46.9 (CH2N-
(CH3)2), 43.5 (N(CH3)2), 42.8 (NCH2CH3), 18.9 (NCH2CH3).
119Sn NMR (149 MHz, C6D6): δ 95.9. 119Sn NMR (149 MHz, THF-
d8): δ 102.4. MS (EI, 70 eV) [m/z (%)]: 325 (51.4) [M]+, 267
(57.5) [M - CH2N(CH3)2)]+, 58 (100) [CH2N(CH3)2]+.
N-(3-(Dimethylamino)propyl)-N′-ethylbenzimidazoline-2-stan-
1
nylene (11): red oil. Yield: 96%. H NMR (400 MHz, C6D6): δ
6.93 (t, 1H, Ar-H), 6.89 (t, 1H, Ar-H), 6.63 (d, 1H, Ar-H), 6.61 (d,
1H, Ar-H), 3.65 (t, 2H, NCH2CH2), 3.52 (q, 2H, NCH2CH3), 1.93
(t, 2H, CH2N(CH3)2), 1.48 (s, 6H, NCH3), 1.36 (quint, 2H, CH2CH2-
CH2), 1.34 (q, 3H, NCH2CH3). 13C NMR (100 MHz, C6D6): δ
149.2, 145.7 (Ar-Cipso), 117.5, 116.0 (Ar-Cmeta), 110.4, 108.8 (Ar-
crystal and data collection details, see Table 1. Structure solutions
were found with the SHELXS-9716 package using the heavy-atom
method and were refined with SHELXL-9717 against F2 using first
isotropic and later anisotropic thermal parameters for all non-
hydrogen atoms. Hydrogen atom positions were identified in
subsequent Fourier maps and were added to the structure model.
Their positional parameters were refined with isotropic thermal
parameters.
C
ortho), 59.7 (NCH2CH2), 46.3 (CH2N(CH3)2), 45.0 (N(CH3)2), 43.0
(NCH2CH3), 24.8 (CH2CH2CH2), 19.6 (NCH2CH3). 119Sn NMR
(149 MHz, C6D6): δ 41.7. 119Sn NMR (149 MHz, THF-d8): δ
51.1. MS (EI, 70 eV) [m/z (%)]: 339 (22.7) [M]+, 281 (3.4) [M -
CH2N(CH3)2]+, 266 (8.8) [M - CH2CH3 - N(CH3)2)]+, 252 (5.7)
[M - CH2CH3 - CH2N(CH3)2]+.
N-(3-(Dimethylamino)propyl)-N′-(2-(dimethylamino)ethyl)-
benzimidazolin-2-stannylene (12): red oil. Yield: 97%. 1H NMR
(400 MHz, C6D6): 6.96 (m, 2H, Ar-H), 6.62 (m, 2H, Ar-H), 3.84,
3.35 (t, 2H, NCH2), 2.24, 2.10 (t, 2H, CH2N(CH3)2), 1.86, 1.57 (s,
6H, N(CH3)2), 1.52 (quint, 2H, CH2CH2CH2). 13C NMR (100 MHz,
C6D6): δ 148.8, 145.6 (Ar-Cipso), 115.9, 115.8 (Ar-Cmeta), 108.2,
107.9 (Ar-Cortho), 60.8, 59.4 (NCH2), 46.1, 45.8 (CH2N(CH3)2), 44.9,
44.4 (N(CH3)2), 25.0 (CH2CH2CH2). 119Sn NMR (149 MHz,
C6D6): δ -5.0. 119Sn NMR (149 MHz, THF-d8): δ -5.1. MS (EI,
70 eV) [m/z (%)]: 382 (5.4) [M]+, 324 (7.2) [M - CH2N(CH3)2)]+.
X-ray Diffraction Studies. Diffraction data for 3, 5, and 8 were
collected with a Enraf Nonius CAD-4 diffractometer using graphite
monochromated Mo KR radiation (λ ) 0.71073 Å). Diffraction
data were collected at 143(2) K for 3 and at 293(2) K for 5 and 8
and were corrected for absorption. The data reduction was
performed with the Bruker SMART15 program package. For further
Results and Discussion
The symmetrically substituted o-phenylene diamines 2a-d
were obtained by LiAlH4 reduction of the carbonyl groups
of the amides 1a-d (Scheme 2). The derivatives with amino-
substituted side chains 2g,h were synthesized by reaction of
the chloro-substituted diamides 1e,f with HNMe2 and
subsequent reduction of the carbonyl groups with LiAlH4.
The preparation of the unsymmetric o-phenylene diamines
2i,m-o was started from o-nitroaniline which was initially
acylated. The remaining nitro group was subsequently
reduced using Raney-Ni/N2H4 (Scheme 3). A second acy-
(16) SHELXS-97: Sheldrick, G. M. Acta Crystallogr. 1990, A46, 467.
(17) Sheldrick, G. M. SHELXL-97; Universita¨t Go¨ttingen: Go¨ttingen,
Germany, 1997.
(15) SMART; Bruker AXS: Madison, WI, 2000.
7664 Inorganic Chemistry, Vol. 46, No. 18, 2007

Benzimidazolin-2-stannylenes
Scheme 3. Preparation of Unsymmetric Amines 2i,m-o
Scheme 5. 119Sn Chemical Shifts for Stannylenes 3-12 in C6D6 and
THF-d8 (in Parentheses)a
Scheme 4. Preparation of Symmetric and Unsymmetric Stannylenes
3-12
lation gave the unsymmetric diamides 1i-l. One of these
(1i) was directly converted by reduction of the carbonyl
groups into the unsymmetric o-phenylene diamine 2i. The
o-phenylenediamides with chloro-substituted side chains 1j-l
were reacted with dimethylamine to give the unsymmetric
diamides 1m-o which upon reduction of the carbonyl
function yielded the unsymmetric o-phenylene diamines
2m-o (Scheme 3).
The reaction between the symmetric (2a-d,g,h) or un-
symmetric (2i,2m-o) o-phenylenediamines and Sn-
[N(SiMe3)2]2 gave the symmetric and unsymmetric stan-
nylenes 3-12 as dark orange to brown solids or oils in good
yield (95-99%) (Scheme 4). The stannylenes are sensitive
to air and moisture. They are only sparingly soluble in
hydrocarbons but dissolve well in ethers or aromatic solvents.
13C NMR spectra of the stannylenes 3-12 show the
characteristic downfield shift for the resonances of the ipso-
carbon atoms of the aromatic ring (δ ≈ 147 ppm) compared
to the corresponding o-phenylene diamines (δ ≈ 137 ppm).
The 119Sn NMR resonances fall in a broad range between δ
) 237 and δ ) -5 ppm (Scheme 5). A value comparable
to these has been reported for N,N’-dineopentylbenzimida-
zolin-2-stannylene at 269 ppm.8 It is obvious that chemical
shift reflects the amount of electron density at the tin atom
and a highfield shift would indicate a gain of electron density
at the tin center.
a Asterisk indicates a value reported for a C6D6 solution reported in ref
8.
(δ ) 222 ppm). Coordination of THF molecules to the
electron deficient stannylene center explains the observed
highfield shift for the tin resonance of 3 in THF compared
to the lowfield value observed in benzene. The dependence
of the chemical shift for the tin resonance from the solvent
used can thus serve as a probe for the presence of additional
donor interactions with the stannylene tin atom. For example,
the dependence of the 119Sn chemical shift from the solvent
can be used to evaluate intramolecular interactions in
stannylenes with donor-functionalized N,N′-substituents like
5-12. The stronger the intramolecular or intermolecular
Lewis-acid-Lewis-base interaction between the tin center
and the donor groups of the N,N′-side chains is, the smaller
will be the difference in the chemical shift of the 119Sn
resonance in THF and benzene. This effect is clearly visible
with the stannylenes bearing amine-substituted side chains
(7, 8, 10-12), which are strong donors.
The stannylenes with two amine-substituted side chains
(7, 8, 12) exhibit almost identical 119Sn chemical shifts in
benzene and THF. The side-chain donors coordinate to the
stannylene center in both solvents, and thus, no solvent
dependence of the 119Sn resonance was found. The presence
of only one amine-substituted side chain like in 10 and 11
causes a slight dependence of the 119Sn resonance from the
solvent (∆δ ) 6 ppm for 10; ∆δ ) 9 ppm for 11) indicating
The sterically least demanding substituted stannylene 3
shows a strong dependence of the 119Sn NMR resonance for
the stannylene tin atom from the solvent used (Scheme 5).
The resonance in THF-d8 (δ ) 107 ppm) is shifted highfield
by 115 ppm compared to the resonance in nonpolar C6D6
Inorganic Chemistry, Vol. 46, No. 18, 2007 7665

Hahn et al.
Figure 1. Molecular structure of stannylene 3. Selected bond lengths (Å)
and angles (deg): Sn-N1 2.092(2), Sn-N2 2.189(2), Sn‚‚‚N2* 2.361(2),
N1-C2 1.378(3), N1-C7 1.451(3), N2-C1 1.424(3), N2-C8 1.478(3),
C1-C2 1.425(3); N1-Sn-N2 77.12(7), N1-Sn‚‚‚N2* 90.69(7), N2-
Sn‚‚‚N2* 84.17(8), Sn-N1-C2 115.90(15), Sn-N1-C7 124.5(2), C2-
N1-C7 118.3(2), Sn-N2-C1 110.67(14), Sn-N2-C8 118.83(15), C1-
N2-C8 115.0(2).
Figure 2. Molecular structure of stannylene 5. Selected bond lengths (Å)
and angles (deg): Sn-N1 2.079(3), Sn-N2 2.085(3), Sn‚‚‚O1 3.060(3),
Sn‚‚‚O2 3.120(3), N1-C2 1.370(4), N1-C7 1.460(4), N2-C1 1.365(4),
N2-C10 1.465(4), C1-C2 1.451(4); N1-Sn-N2 77.59(10), Sn-N1-C2
116.2(2), Sn-N1-C7 126.6(2), C2-N1-C7 117.2(3), Sn-N2-C1 116.1-
(2), Sn-N2-C10 126.8(2), C1-N2-C10 117.1(2).
that the tin center still acts as a Lewis acid in THF solution
even after N-coordination of the amine group of the side
chain.
tin atom. The equivalence of the methyl groups of 3 in
benzene solution could be the result of a fast intermolecular
interchange of the nitrogen atoms coordinated to the tin atom.
Alternatively, and more likely, the dimer simply breaks up
in benzene solution into two monomers with two-coordinated
tin atoms. Such a behavior is indicated by the significant
highfield shift of the 119Sn resonance of 3 in benzene
compared to the same resonance in THF.
Stannylene 5 exists in the solid state as a monomer
(Figure 2). The heterocycle as well as the annulated ring
are essentially planar. The nitrogen atoms are surrounded in
a trigonal-planar fashion (sum of angles at N1 and N2 360°).
The Sn-N bond lengths are identical within experimental
error. Their values as well as the N-Sn-N bond angle
compare well with with reported equivalent values for N,N′-
dineopentylbenzimidazolin-2-stannylene.8 The intramolecular
Sn‚‚‚O distances measure 3.060(3) and 3.120(3) Å and are
only slightly shorter that the sum of the van der Waals radii
for these atoms.19 They are much longer than the Sn-O
bonds on complex SnCl2‚1,4-dioxane, where the coordinative
Sn-O bond lengths measures 2.527(5) Å.20
As predicted by the strong variation of the chemical shift
for the stannylene tin atom in the 119Sn NMR spectra (∆δ )
59 ppm, Scheme 5), the molecular structure analysis
confirmed the existence of only weak intramolecular Sn‚‚‚
O interactions in 5. In THF solution this solvent will
coordinate to the tin center substituting any other weak
intramolecular Sn‚‚‚O interaction and thereby causing the
observed upfield shift of the 119Sn resonance. While the
chemical shift for the tin atoms is significantly different in
5 and 6, the ∆δ calculated for 119Sn spectra recorded in C6D6
and THF-d8 are almost identical, which we take as an
indication that similar intramolecular interactions exist in
those two stannylenes.
The stannylenes 5, 6, and 9 with ether-functionalized side
chains exhibit a strong dependence of the 119Sn chemical
shift from the solvent (∆δ ) 59 ppm for 5; ∆δ ) 55 ppm
for 6; ∆δ ) 49 ppm for 9) indicating a weak interaction of
the tin center with the oxygen atoms of the side chain. In
THF, the solvent molecules apparently displace the ether
donors from the side chains. The stongest dependence of
the 119Sn chemical shift from the solvent used is, as expected,
found for the N,N′-alkyl-substituted stannylenes 3 (∆δ )
115 ppm) and 4 (∆δ ) 62 ppm).
The conclusions drawn from the NMR spectra have been
confirmed by the molecular structures of the stannylenes 3,
5, and 8 which we determined by X-ray diffraction. In the
solid state, stannylene 3 is a bimolecular aggregate with
three-coordinated tin atoms (Figure 1). The centrosymmetric
aggregate is held together by strong intermolecular Sn‚‚‚N
interactions (Sn‚‚‚N2* 2.361(2) Å). This contrasts the
dimerization behavior of the stannylene with the sterically
demanding N,N′-CH2t-Bu groups which exists in the solid
state as a dimer with contacts between the tin atom of one
stannylene and the phenyl ring of an adjacent stannylene
molecule. The free electron pair of one of the ring nitrogen
atoms (N2) interacts with the formally empty p-orbital of a
tin atoms from an adjacent stannylene (Sn*). This leads to
a significant pyramidalization of the nitrogen atoms involved
in intermolecular coordination (sum of angles at N2 344.5°)
compared to the other ring nitrogen atom (sum of angles at
N1 358.7°). A similar but weaker interaction was observed
in bridged benzannulated bisgermylenes.18 As a consequence
of the intermolecular interaction the Sn-N2 bond distance
is significantly longer than the Sn-N1 distance due to the
less effective π-bonding between N2 and Sn.
The N,N′-methyl groups in the crystal structure of 3 are
nonequivalent. Only equivalent N-methyl groups have been
We have previosly described the molecular structure of
the stannylene 7, which is substituted at the nitrogen atoms
with CH2CH2NMe2 groups.14 The structure analysis revealed
the existence of both intermolecular Sn-N interactions like
1
detected in H NMR and 13C NMR spectra of 3. This is
obvious for a THF solution of 3, as the dimer breaks up
giving the monomer presumably of formula 3‚2THF with
the THF donors coordinating into the empty p-orbital at the
(19) (a) Bondi, A. J. Chem. Phys. 1964, 68, 441. (b) Batsanov, S. S. Inorg.
Mater. 2001, 37, 871.
(20) Hough, E; Nicholson, D. G. J. Chem. Soc., Dalton Trans. 1976, 1782.
(18) Zabula, A. V.; Hahn, F. E.; Pape, T.; Hepp, A. Organometallics 2007,
26, 1972.
7666 Inorganic Chemistry, Vol. 46, No. 18, 2007

Benzimidazolin-2-stannylenes
Consequently, atom N2 is pyramidalized (sum of angles
346.9°) while atoms N1 is surrounded in a trigonal-planar
fashion (sum of angles 358.4°). The intermolecular distance
Sn-N2* (2.611(2) Å) and the intramolecular Sn-N4
distance (2.612(2) Å) are about equally long. They are,
however, much longer than the endocyclic Sn-N1(N2)
distances. The Sn-N4 and Sn-N2* bonds are oriented
almost perpendicular to the plane of the stannylene ring,
indicating that the tin p-orbital interacts with these donor
functions. The bimolecular aggregate appears to be stable
in the solid state. However, since no dependence of the
119Sn resonance from the solvent was observed, the dimer 8
appears to break up in solution as the NMR spectra indicate
only one set of resonances for the NMe2 donor groups.
Figure 3. Molecular structure of stannylene 8. Selected bond lengths (Å)
and angles (deg): Sn-N1 2.111(2), Sn-N2 2.149(2), Sn-N2* 2.611(2),
Sn-N4 2.612(2), N1-C2 1.380(2), N1-C7 1.456(2), N2-C1 1.411(2),
N2-C12 1.468(2), C1-C2 1.427(3); N1-Sn-N2 77.90(6), N1-Sn-N2*
91.15(6), N1-Sn-N4 90.63(8), N2-Sn-N2* 80.36(6), Sn-N1-C2
114.82(12), Sn-N1-C7 126.81(13), C2-N1-C7 116.8(2), Sn-N2-C1
112.68(12), Sn-N2-C12 116.70(13), C1-N2-C12 117.5(2).
Conclusions
Benzimidazolin-2-stannylenes with alkyl and donor-func-
tionalized N,N′-substituents have been prepared and were
characterized by 119Sn NMR spectroscopy and X-ray analysis.
Substitution of the ring nitrogen atoms with -(CH2)nNMe2
(n ) 2, 3) donor groups leads to stannylenes with tetraco-
ordinated tin atoms by intermolecular or intramolecular
nitrogen coordination showing the Lewis-acidic character of
the tin atom in these derivatives. 119Sn NMR spectroscopy
indicates that these stannylenes are stabilized in solution by
intramolecular coordination of donor-functionalized N-sub-
stituents and/or solvent molecules.
in 3 and intramolecular coordination of the Me2N group of
the side chains to the tin atoms. The intramolecular interac-
tion appeared to be hampered by the topology of the ethylene
side chain which is too short to allow for a strain-free
interaction of the Me2N donor with the p-orbital at the tin
atom.
Stannylene 8 possesses longer -CH2CH2CH2NMe2 sub-
stituents at the ring nitrogen atoms, and this might allow for
a strain-free intramolecular coordination of the Me2N donor
group. The molecular structure of 8 was established by X-ray
diffraction (Figure 3). The unit cell of 8 contains a cen-
trosymmetric bimolecular aggregate where each tin atom
maintains four Sn-N contacts. Two Sn-N1(N2) bonds are
formed within the stannylene heterocycle. In addition, one
intermolecular Sn-N2* and one intramolecular Sn-N4
bonds are formed. As observed for 3, the intramolecular Sn-
N2 bond distance involving the nitrogen atoms engaged in
intermolecular contacts is elongated (Sn-N2 2.149(2) Å)
compared to the Sn-N1 bond distance of 2.111(3) Å.
Acknowledgment. We thank the Deutsche Forschungs-
gemeinschaft and the Fonds der Chemischen Industrie for
financial support. A.V.Z. thanks the NRW Graduate School
of Chemistry Mu¨nster for a predoctoral grant.
Supporting Information Available: X-ray crystallographic files
for compounds 3, 5, and 8 in CIF format and the spectroscopic
data for the amides 1a-o and amines 2a-d,g-i,m-o. This material
is available free of charge via the Internet at http://pubs.acs.org.
IC701064Z
Inorganic Chemistry, Vol. 46, No. 18, 2007 7667