A zwitterionic carbene-stannylene adduct via cleavage of a dibenzotetraazafulvalene by a stannylene

Article abstract of DOI:10.1016/S0022-328X(00)00700-2

Reaction of the tetraamine 1,2-C₆H₄-[NHCH₂CH₂N(CH ₃)₂]₂ (8) with bis(bis(trimethylsilyl)amido)tin(II) yields the N-heterocyclic stannylene 1,2-C₆H₄-[NCH

Full text of DOI:10.1016/S0022-328X(00)00700-2

www.elsevier.nl/locate/jorganchem
Journal of Organometallic Chemistry 617–618 (2001) 629–634
A zwitterionic carbene–stannylene adduct via cleavage of a
dibenzotetraazafulvalene by a stannylene
F. Ekkehardt Hahn a,*, Lars Wittenbecher a, Michaela Ku¨hn a, Thomas Lu¨gger a,
Roland Fro¨hlich b
a Anorganisch-Chemisches Institut der Westfa¨lischen, Wilhelms-Uni6ersita¨t Mu¨nster, Wilhelm Klemm-Straße 8, D-48149 Mu¨nster, Germany
b Organisch-Chemisches Institut der Westfa¨lischen Wilhelms-Uni6ersita¨t Mu¨nster, Corrensstraße 40, D-48149 Mu¨nster, Germany
Received 1 September 2000; accepted 18 September 2000
Abstract
Reaction of the tetraamine 1,2-C6H4-[NHCH2CH2N(CH3)2]2 (8) with bis(bis(trimethylsilyl)amido)tin(II) yields the N-hetero-
cyclic stannylene 1,2-C6H4-[NCH2CH2N(CH3)2]2Sn (9) which contains additional 2-(dimethylamino)ethyl groups at the nitrogen
atoms of the five-membered ring. These additional donor groups provide for an intramolecular stabilization of the electron
deficient tin center. The X-ray structure analysis with crystals of 9 shows two three-coordinated tin atoms with different
coordination environments in a dinuclear complex. Reaction of the stannylene 9 with the N,N%N%%N%%%-tetramethyldibenzotetraaza-
fulvalene 4 leads via CꢀC bond cleavage in the dibenzotetraazafulvalene to the yellow carbene–stannylene adduct 10. The X-ray
structure analysis of 10 reveals bond parameters consistent with a zwitterionic species made up from a partially cationic carbene
subunit and a partially anionic stannylene unit. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Dibenzotetraazafulvalene; CꢁC cleavage; Carbene; Stannylene; Adduct
tyl, stabilize the free carbene 3 [3,4], while the N-methyl
substituted thione yields upon reduction the dibenzo-
tetraazafulvalene 4 [4,9] with a N2CꢀCN2 double bond.
Dimerization and CꢀCꢁbond formation was never
observed with unsaturated carbenes of type 1 but can
be enforced by bridging the carbenes together over the
ring nitrogen atoms [10]. On the other hand, enetetra-
amine formation is not untypical for derivatives of type
2, which depending on the steric bulk of the N-sub-
stituents can exist as monomeric carbenes or as enete-
traamines [2b].
We have shown recently, that an equilibrium between
the carbene and the enetetraamine exists at room tem-
perature in the presence of KH for the i-butyl substi-
tuted derivative 5 [11]. This behavior was proposed
almost 40 years ago [12] but was never demonstrated
conclusively [13–15] for carbenes of type 2. For the
sterically less demanding methyl substituted dibenzo-
tetraazafulvalene 4, the carbene–enetetraamine equi-
librium can only be established in the presence of a
catalyst, presumably a trace of electrophile, and it
becomes impracticably slow in the presence of KH [16]
(see Scheme 1).
1. Introduction
Some years after the synthesis of the first stable
carbene of the imidazolin-2-ylidene type 1 [1] the prepa-
ration of saturated imidazolidin-2-ylidenes 2 [2] and of
N,N%-bis(2,2-dimethylpropyl)benzimidazolin-2-ylidene 3
[3,4] as well as triazol derived [5] and acyclic N,N%-sta-
bilized carbenes [6] were reported [7]. The N-hetero-
cyclic carbene
3
exhibits, with respect to the
five-membered ring, the topology of an unsaturated
carbene of type 1. However, spectroscopic and struc-
tural properties of 3 are similar to those observed for
saturated derivatives of type 2 [4].
Not only spectroscopically, but also chemically N,N%-
dialkylated benzimidazolin-2-ylidenes are similar to sat-
urated carbenes of type 2 [2]. During their preparation
from the corresponding thiones according to Kuhns
method [8], different products are obtained depending
on the N-substituents. Larger substituents, like neopen-
* Corresponding author: Tel.: +49-251-8333111; fax: +49-251-
8333108.
E-mail address: fehahn@uni-muenster.de (F. Ekkehardt Hahn).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(00)00700-2

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F. Ekkehardt Hahn et al. / Journal of Organometallic Chemistry 617–618 (2001) 629–634
While the carbene–enetetraamine equilibrium ob-
In contrast to heteroatom stabilized carbenes, which
react normally as strong nucleophiles [7], the isoelec-
tronic diazastannylenes show both nucleophilic and
electrophilic properties [18]. The nucleophilic character
of stannylenes is apparent from the multitude of metal
complexes with stannylene ligands [18]. Braunschweig
et al. reported the molecular structures of N,N%-disub-
stituted o-phenylenediamido tin(II) compounds [19].
These stannylenes possess an electrophilic p-orbital,
which lead to the formation of stable adducts with a
tertiary amine.
Free stable carbenes like 2 or 3 react with bivalent
Group 14 compounds like plumbylenes [20] or silylenes
[3] to yield zwitterionic carbene adducts in which car-
bene coordination occurs in the empty p-orbital of the
Group 14 atom. We report here the reaction of the
dibenzotetraazafulvalene 4 with the diazastannylene 9
which leads to CꢀCꢁbond cleavage and formation of a
zwitterionic carbene–stannylene adduct.
served for 5 at room temperature is unique [11], the
cleavage of enetetraamines including 4 under catalysis
by an electrophile is not. In fact, reaction of an ene-
tetraamine with a coordinatively unsaturated metal
complex is a standard method for the preparation of
complexes with N-heterocyclic carbene ligands and
Lappert and coworkers have reported numerous exam-
ples for such carbene complexes [17]. In the light of
these results, we became interested in searching for the
weakest Lewis acids which would still be able to induce
cleavage of dibenzotetraazafulvalene 4 and to form a
carbene complex. Cyclic diazastannylenes were selected
as promising weak Lewis acids for such a study (see
Scheme 2).
2. Results and discussion
The tetraamine 8 (Scheme 2) was obtained according
to methods described previously [4] by double acylation
of o-phenylenediamine followed by substitution of the
chloro groups for tertiary amines and finally reduction
with lithium aluminum hydride. The tetraamine 8 reacts
with Sn[N(SiMe3)2]2 in THF to yield the orange, air
sensitive diazastannylene 9, which can be recrystallized
from toluene.
Scheme 1.
The resonance of the tin atom in the 119Sn-NMR
spectrum of 9 is strongly shifted upfield from that
observed for similar N-heterocyclic diazastannylenes
(e.g. 1,2-C6H4[N(CHt2Bu)]2Sn in C6D6 l=269.03 ppm
[19]). In addition, the 119Sn resonance of 9 does not
depend on the solvent used (in C6D6 l=49.0 ppm, in
THF-d8 l=50.6 ppm). We take the upfield shift and
the independence of the 119Sn resonance from the sol-
vent as an indication of either intermolecular or in-
tramolecular donor stabilization. An intermolecular
stabilization can, for example, result from an interac-
tion of the ring amido groups of one stannylene with
the tin atom of another stannylene molecule, leading to
a dimer with three-coordinated tin atoms. Such dimer-
ization has been reported by Veith [21]. Alternatively,
the ethylamine arms at the ring nitrogen atoms allow
an intermolecular or intramolecular donor stabilization
of the tin atom. A similar stabilization of a cyclic
diazastannylene with free tmeda has been reported by
Lappert [19]. The 1H- and 13C-NMR spectroscopic data
in solution indicate, that 9 is a highly symmetric and
probably monomeric. The N-bonded residues are found
to be equivalent by NMR spectroscopy and only three
13C resonances are observed in the aromatic region.
However, solid state NMR measurements of 9 shows
Scheme 2. Preparation of stannylene 9 and of the carbene–stannylene
adduct 10.

F. Ekkehardt Hahn et al. / Journal of Organometallic Chemistry 617–618 (2001) 629–634
631
,
length (2.202(2) A) compared to the Sn2ꢁN6 distance
,
(2.105(2) A), where the Sn2ꢁN6 distance is in the range
observed for the Sn1ꢁN(sp2) distances. Atom Sn2 com-
pletes its coordination sphere by interaction with nitro-
,
gen atoms N7 (Sn2ꢁN7 2.497(2) A). It is interesting to
note, that the intermolecular Sn1ꢁN5 bond is almost of
the same length as the intramolecular Sn2ꢁN7 bond
although different donors (amido N5 or amine N7) are
involved.
The coordination geometry at the tin atoms differs
significantly. The Sn1ꢁN5 vector resides almost perpen-
dicular on the N1ꢁSn1ꢁN2 plane (angles N1ꢁSn1ꢁN5
89.69(8)°, N2ꢁSn1ꢁN5 90.78(8)°), as would be expected
for a donor atom coordination into the p-orbital at
Sn1. The Sn2ꢁN7 bond, on the other hand, is strongly
tilted towards N5 (N5ꢁSn2ꢁN7 74.82(8)°, N6ꢁSn2ꢁN7
104.31(8)°) which is due to the steric limitations of the
short ethylamine ligand arm (see Fig. 1).
The yellow, crystalline stannylene–carbene adduct 10
was obtained by slow evaporation of the toluene sol-
vent from a solution of 9 and dibenzotetraazafulvalene
4. The yield of crystalline 10 was about 67%. However,
the product is extremely unstable. A very likely reason
for the rapid decomposition is the interaction with
visible light during purification attempts. Therefore all
experiments to isolate a pure sample from the solution
failed. Similar behavior has been reported for a car-
bene–plumbylene adduct [20], while a carbene–silylene
adduct which is very similar to 10 appears to be more
stable [3]. NMR investigations with 10 could not be
carried out. However, it was possible to isolate and
prepare for X-ray analysis a crystal from the reaction
mixture.
,
Fig. 1. Molecular structure of 9. Selected bond lengths [A] and bond
angles [°]: Sn1ꢁN1 2.101(2), Sn1ꢁN2 2.131(2), Sn1ꢁN5 2.541(2),
N1ꢁC1 1.386(3), N1ꢁC11 1.454(3), N2ꢁC6 1.378(3), N2ꢁC7 1.448(3),
Sn2ꢁN5 2.202(2), Sn2ꢁN6 2.105(2), Sn2ꢁN7 2.497(2), N5ꢁC15
1.420(4), N5ꢁC21 1.471(4), N6ꢁC20 1.386(3), N6ꢁC25 1.443(3);
N1ꢁSn1ꢁN2 76.75(8), N1ꢁSn1ꢁN5 89.69(8), N2ꢁSn1ꢁN5 90.78(8),
Sn1ꢁN1ꢁC1 116.2(2), Sn1ꢁN1ꢁC11 127.4(2), C1ꢁN1ꢁC11 116.2(2),
Sn1ꢁN2ꢁC6 115.5(2), Sn1ꢁN2ꢁC7 126.8(2), C6ꢁN2ꢁC7 117.4(2),
N5ꢁSn2ꢁN6 76.74(8), N5ꢁSn2ꢁN7 74.82(8), N6ꢁSn2ꢁN7 104.31(8),
Sn1ꢁN5ꢁSn2 106.00(8), Sn2ꢁN5ꢁC15 112.5(2), Sn2ꢁN5ꢁC21 111.2(2),
C15ꢁN5ꢁC21 114.0(2), Sn2ꢁN6ꢁC20 117.5(2), Sn2ꢁN6ꢁC25 125.5(2),
C20ꢁN6ꢁC25 117.0(2).
three to four different signals for some atoms, indicat-
ing a more complex structure of 9 in the solid state.
The molecular structure of 9 (Fig. 1) was established
by single crystal X-ray diffraction and shows, that both
an intermolecular and an intramolecular mode of nitro-
gen donor coordination is operative in 9. The asymmet-
ric unit contains a dinuclear complex made up from
two molecules of 9. The tin atoms in the distannylene
are both three-coordinated. Atom Sn1 is coordinated
by two amido nitrogen atoms from its N-heterocyclic
ring (N1, N2) and one amido group (N5) from the
second stannylene of the dinuclear complex. As ex-
pected, nitrogen atoms N1 and N2 are planar (sum of
angles are 359.8 and 359.7°, respectively) as is the whole
five-membered ring. The bond distances Sn1ꢁN1
Compound 10 crystallizes with two independent
molecules in the asymmetric unit. The results of the
X-ray structure analysis of 10 are presented in Fig. 2.
Only one of the two essentially identical molecules is
shown. Complex 10 possesses a long SnꢁCcarbene bond
,
(SnꢁC30 2.399(4) for molecule A, 2.382(4) A for
molecule B). The essentially planar carbene is oriented
in a perpendicular fashion to the planar stannylene
unit. The bond lengths found for the N(sp2)ꢁSn con-
,
,
(2.101(2) A) and Sn1ꢁN2 (2.131(2) A) are similar and
are much shorter than the Sn1ꢁN5 bond (2.541(2) A).
,
tacts (SnꢁN1 2.142(3), SnꢁN2 2.162(4) A for molecule
,
,
A; 2.160(4) and 2.133(4) A for molecule B) are slightly
The bond angle N1ꢁSn1ꢁN2 76.75(8)° is typical for
cyclic diazastannylenes and corresponds well with the
values reported for similar molecules [19]. Atom Sn2 is
also coordinated by two ring amido atoms. However,
atoms N5 and N6 show different geometries. While
atom N6 is planar (sum of angles 360°) like atoms N1
and N2, this does not hold for N5 which deviates
significantly from planarity (sum of angles 337.7°) ow-
ing to its simultaneous intramolecular coordination to
Sn2 and intermolecular coordination to Sn1. The sp3-
character and the reduced electronegativity of atom N5
are also expressed in an elongation of the Sn2ꢁN5 bond
longer than those found in the dinuclear stannylene 9
,
(range 2.101(2)–2.131(2) A), indicating a partial nega-
tive charge at the tin atom. Compared to the free
benzimidazolin-2-ylidene 3 [4], the coordinated carbene
in 10 experiences a widening of the NꢁCꢁN angle
(N31ꢁC30ꢁN32 106.1(3) and 105.4(3)° vs. 103.5(1) and
104.3(1)° in 3) and a shortening of the NꢁCcarbene bond
,
lengths (N31ꢁC30 1.346(5) and 1.356(5) A, N32ꢁC30
,
1.347(5) and 1.348(5) vs. average 1.365 A in 3). The
bond parameters observed for the carbene subunit in 10
are comparable to those of the dication of 4 (NꢁCꢁN
,
109.0(7), 111.5(7)° and NꢁC 1.333(7), 1.328(7) A) [9],

632
F. Ekkehardt Hahn et al. / Journal of Organometallic Chemistry 617–618 (2001) 629–634
tain a nucleophilic carbene coordinated to a subvalent
Group 14 atom where the carbene plane and the ER2
plane (E=subvalent Group 14 element) are oriented in
an almost perpendicular fashion. This differs, obviously
due to the different size of the involved orbitals, from
the bonding situation in dimers of benzimidazolin-2-
ylides, where the two singlet carbenes combine to form
a non-planar double bond [9,11].
indicating that the carbene subunit in 10 possesses a
partial positive charge.
The tertiary amine groups (N13, N23) which were at
least partially coordinated to the tin atom in 9 are no
longer in the vicinity of the tin atom in 10. One of them
(N23) is now positioned over the empty p-orbital of the
partially positive charged carbene carbon atom C30 at
,
a distance of 3.208(6) (molecule A) or 3.230(6) A
Meanwhile carbene–stannylene adducts have been
reported for cyclopropenylidene [23], imidazolin-2-yli-
dene [24], and benzimidazolin-2-ylidene [25], where the
latter two N-heterocyclic carbenes, in contrast to the
benzimidazolin-2-ylidenen in 10, can also be isolated in
the free state. None of these adducts exhibits properties
consistent with a SnꢀC double bond. However, the
SnꢁC distances vary in the carbene–stannylene adducts
(molecule B) which is slightly shorter than the sum of
,
the corresponding van der Waals radii (NꢁC 3.25 A
[22]). This might be due to packing effects but could
also result from a weak interaction between the partial
positive carbene carbon atom C30 and the electron rich
tertiary amine nitrogen atom N23. The direction of the
C30ꢁN23 vector is not exactly perpendicular to the
carbene plane, apparently due to the limited lengths of
the ethylamine arm (see Fig. 2).
,
from 2.472(5) [25] to 2.303(9) A [23] which appears to
be caused by the steric demand of the carbene or
stannylene, respectively.
The bond parameters determined for 10 allow the
conclusion that the labile carbene–stannylene adduct
has zwitterionic character and is made up from a
partially cationic carbene and a partially anionic stan-
nylene subunit. The molecular structure of 10 is similar
to those of the carbene–silylene adduct reported by
Lappert [3] or the carbene–plumbylene adduct de-
scribed by Weidenbruch [20]. All three molecules con-
The carbene–stannylene adduct 10 is part of a wider
study to explore the reactivity of nucleophilic N-hetero-
cyclic carbenes with main group compounds. The car-
benes used for this will be either of type 3, as in
carbene–stannylene adduct reported by Lappert [25] or
can be generated in situ by cleavage of suitably substi-
tuted dibenzotetraazafulvalenes by quite weak Lewis
acids like stannylene 9.
3. Experimental
3.1. General procedures
1H- and 13C-NMR spectra were recorded on a
Bruker AC 200 or Bruker AM 250 spectrometer. Ele-
mental analyses were obtained with a Vario EL elemen-
tal analyzer at the Freie Universita¨t Berlin. Mass
spectra (EI, 70 eV) were taken on a Finnigan MAT 112
spectrometer. Air sensitive compounds were prepared
and handled under argon by Schlenk techniques. All
solvents used were dried rigorously (typically over Na
or Na/K and benzophenone) and freshly distilled prior
to use. X-ray data sets were collected on a CAD-4
counter diffractometer for 9 or on a Nonius Kap-
paCCD diffractometer for 10. Sn[N(SiMe3)2]2 was pur-
chased from Aldrich.
Fig. 2. Molecular structure of 10. Only one of the two molecules in
,
the asymmetric unit is shown. Selected bond lengths [A] and angles [°]
for molecule A [molecule B]: SnꢁN1 2.142(3) [2.160(4)], SnꢁN2
2.162(4) [2.133(3)], SnꢁC30 2.399(4) [2.382(4)], N1ꢁC3 1.381(5)
[1.383(6)], N1ꢁC11 1.447(5) [1.422(7)], N2ꢁC8 1.382(6) [1.379(6)],
N2ꢁC21 1.441(6) [1.444(7)], N31ꢁC30 1.346(5) [1.356(5)], N31ꢁC31
1.457(5) [1.460(6)], N31ꢁC33 1.393(5) [1.392(5)], N32ꢁC30 1.347(5)
[1.348(5)], N32ꢁC32 1.456(6) [1.464(5)], N32ꢁC38 1.392(5) [1.398(5)],
N23···C30 3.208(6) [3.230(6)]; N1ꢁSnꢁN2 74.85(14) [75.10(15)],
N1ꢁSnꢁC30 98.93(13) [93.69(14)], N2ꢁSnꢁC30 92.87(14) [97.94(15)],
SnꢁC30ꢁN31 130.9(3) [122.0(3)], SnꢁC30ꢁN32 122.5(3) [132.5(3)],
N31ꢁC30ꢁN32 106.1(3) [105.4(3)].
3.2. N,N%-Bis(2-chloroethyl)-1,2-diamidobenzene (6)
Yield 90% of a red solid. 1H-NMR (250 MHz,
DMSO-d6): 9.61 (s, 2H, NHC(O)), 7.50 (m, 2H, ArH),
7.18 (m, 2H, ArH), 4.42 (s, 4H, CH2C(O)). 13C-NMR
(62.9 MHz, DMSO-d6): 165.2 (NHC(O)), 130.2, (i-
ArC), 125.7 (m-ArC), 125.1 (o-ArC), 43.3 (CH2Cl).

F. Ekkehardt Hahn et al. / Journal of Organometallic Chemistry 617–618 (2001) 629–634
633
3.3. N,N%-Bis(2-dimethylaminoethyl)-1,2-
diamidobenzene (7)
3.7. Synthesis of the (N,N%-dimethyl-benzimidazolin-
2-ylidene)-[N,N%-bis(2-dimethylamino-ethyl)-1,2-
diamidobenzene tin(II)] adduct (10)
Yield 84% of a brown oil. 1H-NMR (250 MHz,
DMSO-d6): 9.2 (s, br, 2H, NHC(O)), 7.43 (m, 2H,
ArH), 6.71 (m, 2H, ArH), 2.96 (s, 4H, CH2C(O)), 2.06
(s, 12H, CH3). 13C-NMR (62.9 MHz, DMSO-d6): 168.6
(NHC(O)), 129.2 (i-ArC), 125.2 (m-ArC), 123.9 (o-
ArC), 62.2 (CH2N), 45.1 (CH3).
Stannylene 9 (0.22 g, 0.6 mmol) was dissolved in 20
ml of toluene. To this solution was added a solution of
dibenzotetraazafulvalene 4 (0.09 g, 0.3 mmol) in 10 ml
of toluene. The resulting solution was stirred for 24 h.
Slow evaporation of the toluene solvent yielded yellow,
air sensitive crystals of 10. Yield 0.21 g (0.4 mmol,
66.7%). Upon isolation the crystals decompose rapidly.
NMR spectroscopic investigations showed only the res-
onances for the starting materials 4 and 9. The crystals
can be stored under toluene for some weeks without
decomposition.
3.4. N,N%-Bis(2-dimethylaminoethyl)-1,2-
diaminobenzene (8)
Yield 85% of an air-sensitive brown oil. 1H-NMR
(250 MHz, C6D6): 6.98 (m, 2H, ArH), 6.76 (m, 2H,
ArH), 4.20 (s, br, 2H, NHCH2), 2.96 (t, 4H, NHCH2),
2.38 (t, 4H, CH2N(CH3)2), 1.97 (s, 12H, CH3). 13C-
NMR (62.9 MHz, C6D6): 138.2 (i-ArC), 119.3 (m-ArC),
111.6 (o-ArC), 58.2 (NHCH2), 45.1 (CH3), 41.9
(CH2N(CH3)2).
3.8. Selected crystallographic details for 9
Orange crystals of 9 were obtained from a toluene
solution at r.t. Selected crystallographic details for 9:
size of data crystal 0.15×0.5×0.8 mm, formula
C28H48N8Sn2, M=734.12 amu, monoclinic, space
3.5. Synthesis of N,N%-bis(2-dimethylaminoethyl)-1,2-
diamidobenzene tin(II) (9)
group P21/n (no. 14), a=12.2857(12), b=16.8231(8),
3
,
,
c=15.5989(14) A, i=97.828(8)°, V=3194.0(5) A ,
To a stirred solution of 8 (0.30 g, 1.2 mmol) in 30 ml
of THF was added 0.53 g (1.2 mmol) of Sn[N(SiMe3)2]2.
The solution was stirred for 36 h at room temperature
(r.t.) and then evaporated to dryness. The orange
residue was recrystallized from toluene to yield 0.37 g
(83%) of orange, air-sensitive crystals of 9. M.p. 163°C.
1H-NMR (400 MHz, THF-d8): 6.48 (m, 2H, ArH), 6.41
(m, 2H, ArH), 3.51 (t, 4H, HNCH2), 2.43 (t, 4H,
CH2N(CH3)2), 2.12 (s, 12H, CH3). 13C-NMR (100
MHz, THF-d8): 147.8 (i-ArC), 116.6 (m-ArC), 109.3
(o-ArC), 59.6 (SnNCH2), 47.1 (CH2N(CH3)2), 44.7
(CH3). 13C-NMR (75.5 MHz, MAS, solid state): 150.9
(i-ArC), 147.4 (i-ArC), 146.3 (i-ArC), 143.4 (i-ArC),
120.1 (m-ArC), 115.5 (m-ArC), 115.1 (m-ArC), 114.6
(m-ArC), 108.4 (o-ArC), 106.9 (o-ArC), 60.7
(SnNCH2), 58.7 (SnNCH2), 55.4 (SnNCH2), 50.3
Z=4, zcalc=1.527 g cm−3, Mo–Ka radiation, (u=
,
0.71073 A, graphite monochromator), v(Mo−Ka)=
1.594 mm−1. 9265 symmetry independent diffraction
data were measured at −120(2)°C in the 2[-range
5–60°. Structure solution with Patterson and refinement
with Fourier methods, refinement (on F2) of positional
parameters of all non-hydrogen atoms with anisotropic
thermal parameters. Hydrogen atoms on calculated po-
,
sitions (d(CꢁH)=0.95 A) with Ueq(H)=1.3Ueq(C). R=
0.034, wR2=0.092 for 8310 structure factors I]2|(I)
and 343 refined parameters. Neutral atomic scattering
factors were used and all scattering factors were
corrected for anomalous dispersion. All calculations
were carried out with the SHELX program package
[26,27].
(CH2N(CH3)2),
46.8
(CH2N(CH3)2),
45.2
(CH2N(CH3)2), 43.3 (CH3). 119Sn-NMR (149 MHz,
C6D6): 49.0. 119Sn-NMR (149 MHz, THF-d8): 50.6. MS
(EI, relative intensity %) m/e: 368 (3.8, M+), 310 (8.6,
M+−CH2N(CH3)2), 58 (100, (CH2N(CH3)2)+).
3.9. Selected crystallographic details for 10
Air sensitive crystals of 10 were obtained at r.t.
Formula C23H34N6Sn*C7H8, M=605.39 amu, yellow
crystal 0.35×0.20×0.05 mm, a=11.112(1), b=
3.6. Synthesis of N,N%,N%%,N%%%-tetramethyl-
dibenzotetraazaful6alene (4)
,
16.302(1), c=16.631(1) A, h=68.97(1), i=77.91(1),
3
k=84.43(1)°, V=2748.8(3) A , zcalc=1.463 g.cm−3
,
,
v(Mo–Ka)=0.960 mm−1, empirical absorption correc-
tion via SORTAV (0.7305T50.954), Z=4, triclinic,
We have synthesized compound 4 according to the
method described in Ref. [4]. An alternative synthesis is
described by Lappert et al. in Ref. [9]. H-NMR (400
MHz, C6D6): 6.82 (m, 4H, ArH), 6.40 (m, 4H, ArH),
2.69 (s, 12H, CH3). 13C-NMR (100 MHz, C6D6): 136.4
(i-ArC), 124.4 (N2C=CN2), 120.8 (m-ArC), 110.8 (o-
ArC), 36.0 (CH3).
1
(
,
space group P1 (no. 2), u=0.71073 A, T=198 K, ꢀ
and € scans, 36 786 reflections collected (9h, 9k, 9l)
in the 2[-range 3.8–55.0°, 12 594 independent (Rint
=0.039) and 10 062 observed reflections [I]2|(I)],
575 refined parameters, R=0.050, wR2=0.161, max

634
F. Ekkehardt Hahn et al. / Journal of Organometallic Chemistry 617–618 (2001) 629–634
−3
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,
residual electron density 1.39 (−1.62) e A
in the
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region of the disordered solvate molecules toluene
(refined with geometrical constrains), two almost identi-
cal independent molecules in the asymmetric unit, hy-
drogen atoms reside on calculated positions and were
refined as riding atoms. Data set was collected with a
Nonius KappaCCD diffractometer, equipped with a
rotating anode generator Nonius FR591. Programs
used: data collection [28], data reduction [29], absorp-
tion correction [30], structure solution [26], structure
refinement [27], graphics [31].
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4. Supplementary material available
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Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC no. 149333 for compound 9 and
CCDC no. 149 334 for compound 10. Copies of this
information can be obtained free of charge from the
Director, CCDC, 12 Union Road, Cambridge CB2
1EZ, UK (fax: +44-1223-336033; e-mail: deposit@
ccdc.cam.ac.uk or www: http://www.ccdc.cam.ac.uk).
Acknowledgements
The Fonds der Chemischen Industrie and the
Deutsche Forschungsgemeinschaft supported our work
financially. We thank Professor Dr. Hellmut Eckert,
Universita¨t Mu¨nster for recording the MAS spectra
1
and Dr. D. Le Van for recording the H-, 13C-, and
119Sn-NMR spectra.
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