Synthesis and characterization of rigid ditopic N-heterocyclic benzobisgermylenes and -stannylenes

Article abstract of DOI:10.1021/om3000604

A rigid ditopic benzobisgermylene, 4a, was prepared by the reaction of the 1,2,4,5-tetra(alkylamine)benzene 3a and Ge[N(SiMe₃)₂] ₂. The analogous reaction of two 1,2,4,5-tetra(alkylamine)benzenes, 3b,c, with Sn[N(SiMe

Full text of DOI:10.1021/om3000604

Article
pubs.acs.org/Organometallics
Synthesis and Characterization of Rigid Ditopic N-Heterocyclic
Benzobisgermylenes and -stannylenes
Sergei Krupski, Julia V. Dickschat, Alexander Hepp, Tania Pape, and F. Ekkehardt Hahn*
Institut fur Anorganische und Analytische Chemie, Westfalische Wilhelms-Universitat Munster, Corrensstraße 30, D-48149 Munster,
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Germany
S
* Supporting Information
ABSTRACT: A rigid ditopic benzobisgermylene, 4a, was prepared
by the reaction of the 1,2,4,5-tetra(alkylamine)benzene 3a and
Ge[N(SiMe3)2]2. The analogous reaction of two 1,2,4,5-tetra-
(alkylamine)benzenes, 3b,c, with Sn[N(SiMe3)2]2 led to the oxidation
of the tetramine ligand and formation of N-alkyl-2-(alkylamine)-
N′-alkyl-5-(alkylamine)-1,4-benzoquinonediimines (5b,c) and tin(0).
The p-benzoquinonediimines 5b,c subsequently react with remaining
Sn[N(SiMe3)2]2 to yield distannylene complexes of type [N-alkyl-2-
(alkylamino)-N′-alkyl-5-(alkylamino)-1,4-benzoquinonediimine]di[bis-
(trimethylsilyl)aminotin(II)] (6b,c). The 2,5-di(alkylamine)-1,4-ben-
zoquinonediimines 5b,c can also be obtained directly by aerial
oxidation of the 1,2,4,5-tetrakis(alkylamine)benzenes 3b,c. They react
with two equivalents of Sn[N(SiMe3)2]2 also under transmetalation
and formation of [N-alkyl-2-(alkylamino)-N′-alkyl-5-(alkylamino)-1,4-benzoquinonediimine]di[bis(trimethylsilyl)aminotin(II)]
(6b,c). The molecular structures of 3b, 4a, 6b, and 6c have been established by X-ray diffraction.
1. INTRODUCTION
Germylenes (R2Ge:)1a,b and stannylenes (R2Sn:)1a,c are di-
valent species of germanium and tin, which in spite of some
differences in their electronic properties and reactivity can be
considered as the heavier analogues of carbenes.1 Particularly
N-heterocyclic carbenes have been studied in detail since the
first stable derivative of this type was isolated by Arduengo in
1991.2 Various applications for these compounds as spectator
ligands in organometallic chemistry and catalysis,3 material
science,4 biologically relevant complexes,5 and most recently
even metallosupramolecular chemistry6 have been reported.
Stable N-heterocyclic germylenes and stannylenes1f,g,7 received
Figure 1. N-Heterocyclic carbenes, germylenes, and stannylenes.
less attention, although the first derivatives of this type were
known some years before the first N-heterocyclic carbenes had
been isolated.
The first representative of an N-heterocyclic germylene (A1)8
was prepared in 1982 by Veith et al. (Figure 1). Its heavier
analogue, the stannylene A2 was also prepared by Veith et al.
in 1975.9 Both compounds have been known more than 10 years
before the first stable N-heterocyclic carbene (B1) was described.
Shortly after the preparation of the Arduengo-carbene B1,2
the analogous germanium(II) compound (B2) was synthesized
and characterized by Herrmann et al.10 The synthesis of the
corresponding stannylene (B3) has also been reported.11
N-heterocyclic germylenes1,7,15 and stannylenes,1,7,16 including
some chiral derivatives,16c are known.
A number of polydentate germylenes and stannylenes have
been described.17 We prepared bidentate bisgermylenes18 and
bisstannylenes19 of type D, which are capable of forming
chelate complexes E with selected transition metals. In analogy
to the known rigid dicarbene ligands of type F1 (Figure 2),4,20
we have now studied the preparation of rigid ditopic
digermylenes (F2) and distannylenes (F3). Like the dicarbenes
F1,6e−g the rigid ditopic digermylenes and distannylenes are
The isolation and complete characterization of the first benz-
annulated germylene of type C2 was reported in 1989,12
10 years before the synthesis of benzannulated carbene C1.13
Stannylenes of type C3 were first prepared and completely
characterized in 1994.14 Today, various types of benzannulated
Received: January 25, 2012
Published: February 29, 2012
© 2012 American Chemical Society
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potential building blocks for tetranuclear molecular squares and
additional metallosupramolecular structures.
Scheme 2. Transamination Reactions of the 1,2,3,4-
Tetra(alkylamine)benzenes 3a−c with Ge[N(SiMe3)2]2 and
Sn[N(SiMe3)2]2
Figure 2. Linear rigid dicarbenes and their heavier analogues.
2. RESULTS AND DISCUSSION
Benzannulated N-heterocyclic germylenes and stannylenes
are conveniently obtained by transamination of suitable N,N′-
dialkylated o-phenylenediamines with M[N(SiMe3)2]2 (M =
Ge, Sn).18,19 The same protocol can be applied for the
synthesis of benzobisgermylenes and benzobisstannylenes of
types F2 and F3 provided suitable 1,2,3,4-tetra(alkylamine)-
benzenes are available. We have prepared the asymmetrically
substituted 1,2,3,4-tetra(alkylamine)benzene 3a (Scheme 1) by
Scheme 1. Synthesis of the Asymmetrical 1,2,3,4-
Tetra(alkylamine)benzene 3a
Figure 3. Molecular structure of 3b (50% displacement ellipsoids,
hydrogen atoms have been omitted, the molecule resides on a
crystallographic inversion center). Selected bond lengths (Å) and
angles (deg): N1−C3 1.406(2), N1−C4 1.449(2), N2−C1 1.419(2),
N2−C9 1.449(2), C1−C2 1.391(2), C1−C3* 1.405(2), C2−C3
1.400(2); C3−N1−C4 119.99(14), C1−N2−C9 121.21(14).
The 1,2,3,4-tetra(alkylamine)benzene 3a was reacted with
Ge[N(SiMe3)2]223 to yield via transmetalation the rigid ditopic
benzobisgermylene 4a, featuring two differently substituted
N-heterocyclic diaminogermylene subunits (Scheme 2). Benzo-
bisgermylene 4a was isolated as a yellow air-sensitive solid that
is soluble in THF, benzene, and toluene but almost insoluble in
aliphatic hydrocarbons such as n-hexane.
reaction of the known compound 121 with acetyl chloride to
give the 1,2,3,4-tetraamidobenzene 2. Subsequent reduction of
the amido groups with AlH3 (generated in situ18a) gave 3a in
good yield.
The symmetrically substituted 1,2,4,5-tetra(alkylamine)-
benzenes 3b,c20,22 (Scheme 2) were prepared following
described procedures. As previously noticed,22 the tetra-
(alkylamine)benzenes 3a−c are very sensitive toward oxidation,
and exposure of them to aerial oxygen leads to the formation of
N-alkyl-2-(alkylamine)-N′-alkyl-5-(alkylamine)-1,4-benzoquino-
nediimines. We have, however, isolated 1,2,4,5-tetra(neopentyl-
amine)benzene 3b and crystallized the compound at ambient
temperature from a toluene solution.
The benzobisgermylene 4a was characterized by NMR
1
spectroscopy and mass spectrometry. The H NMR spectrum
shows the resonances for the aromatic protons at δ 6.86 ppm
and for the methylene protons of the N-substituents at δ 3.84−
4.08 ppm. Compared to the free tetramine (δ 6.45 ppm and
2.89−3.01 ppm), equivalent resonances are shifted down-
field in the benzobisgermylene, reflecting a decrease of the
electron density in the organic scaffold upon formation of
the germanium(II) compound.
The X-ray diffraction analysis confirms the formation of the
tetramine 3b (Figure 3). Bond parameters of 3b fall in the
expected range. The aromatic ring is undisturbed, with C−C
bond lengths in the range 1.391(2)−1.405(2) Å.
Compound 4a was crystallized from a THF/n-hexane
solution at −18 °C. The X-ray diffraction structure analysis
confirmed the formation of the benzobisgermylene (Figure 4,
top). The two diaminogermylene subunits feature essentially
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molecules, leaving one secondary amine at each side of the
molecule unchanged for the subsequent reaction with Sn[N-
(SiMe3)2]2. The reasons for this partial oxidation of 1,2,3,4-
tetra(alkylamine)benzenes to p-benzoquinonediimines have been
discussed on the basis of DFT calculations.22 A two-electron
oxidation of 1,2-di(alkylamine)benzenes would lead to 1,2-
benzoquinonediimines, which subsequently cannot undergo
any transamination reaction with Sn[N(SiMe3)2]2.
To test this hypothesis, we have carried out the aerial
oxidation of the 1,2,3,4-tetra(alkylamine)benzenes 3b,c in THF
and obtained the expected N-alkyl-2-(alkylamino)-N′-alkyl-
5-(alkylamino)-1,4-benzoquinonediimines 5b,c as yellow,
air-stable solids in essentially quantitative yield (Scheme 3).
Scheme 3. Oxidation of the 1,2,4,5-
Tetra(alkylamine)benzenes 3b,c with Aerial Oxygen and
Subsequent Transamination with Sn[N(SiMe3)2]2
Figure 4. Molecular structure of 4a (top, 50% displacement ellipsoids)
and plot of the intermolecular interaction between the benzobisger-
mylenes (bottom). Selected bond lengths (Å) and angles (deg): Ge1−
N1 1.862(3), Ge1−N2 1.877(3), Ge2−N3 1.856(3), Ge2−N4
1.865(3), N1−C1 1.393(4), N1−C7 1.450(4), N2−C2 1.386(4),
N2−C9 1.454(4), N3−C5 1.391(4), N3−C11 1.471(4), N4−C4
1.393(4), N4−C16 1.456(4); N1−Ge1−N2 84.41(11), N3−Ge2−N4
84.77(11).
identical metric parameters in spite of the differences in the
N-substituents. The Ge−N and N−C bond distances as well as
the N−Ge−N bond angles fall in the range previously reported
for benzannulated N-heterocyclic germylenes.12a,18 The five-
membered heterocycles are planar, with each containing two
trigonal-planar nitrogen atoms (range for the sum of angles at
the nitrogen atoms N1−N4 359.8−360.0°).
In the solid state the benzobisgermylene 4a forms infinite
polymeric chains via interactions of the germanium atoms of
one molecule with the aromatic rings of neighboring molecules
(Figure 4, bottom). The shortest intermolecular Ge···C dis-
tances measure 3.441−3.663 Å. Similar interactions have been
observed in the solid-state structures of related benzannulated
N-heterocyclic germylenes, confirming the electrophilic nature
of the empty p-orbital at the germylene germanium atom.24
The reaction of the 1,2,3,4-tetra(alkylamine)benzenes 3b,c
with Sn[N(SiMe3)2]223a yielded unexpected results (Scheme 2).
Instead of the expected benzobisstannylenes analogous to 4a,
the noncyclic diimine-stabilized distannylenes 6b,c featuring
a p-benzoquinonediimine backbone and elemental tin were
obtained. The distannylenes 6b,c have been identified by NMR
spectroscopy. The spectra show the characteristic resonances
for the SiMe3 groups, while the signal for the aromatic protons
of the backbone has been replaced by resonances of the
p-benzoquinonediimine moiety, which appear in the range δ
5.13−5.52 ppm.
The formation of 6b,c was surprising since it has been shown
multiple times that 1,2-di(alkylamine)benzenes react smoothly
with Sn[N(SiMe3)2]2 to yield the benzannulated N-heterocyclic
stannylenes,14,16 and no oxidation of the 1,2-di(alkylamine)-
benzene precursors was observed in these reactions. We attribute
the different reactivity of the 1,2,4,5-tetra(alkyamine)benzenes
3b,c to the possibility of two one-electron oxidations proceeding
at each of the two o-phenylenediamine sites of the tetramine
The oxidation of 1,2,3,4-tetra(alkylamine)benzenes with loss of
the aromatic character in favor of the 1,4-quinoid structure has
been reported previously.21
Reaction of the compounds 5b,c with Sn[N(SiMe3)2]2
proceeds under mono-transamination at each side of the mole-
cule and formation of the distannylenes 6b,c in yields of
67% and 57%, respectively. The 1H NMR spectra of the
distannylenes 6b,c feature a characteristic resonance for the
quinoid CH group21 at δ 5.52 ppm (5b) and δ 5.14 ppm (5c)
and at around δ 0 ppm for the SiMe3 groups. The 29Si{1H}, the
1
119Sn{1H}, and in part the H and 13C{1H} NMR spectra
exhibit a doubling of all signals (for example 119Sn{1H} NMR: δ
−21.8, −33.0 ppm for 6b; δ −31.0, −42.4 ppm for 6c). We
assume that two isomers (syn and anti, Scheme 3) exist in solu-
tion. At ambient temperature, these isomers do not inter-
convert due to the steric crowding at the tin atoms.
Red to purple crystals of the air-sensitive anti isomers of 6b
and 6c were obtained from THF solutions of the compounds
after slow evaporation of the solvent over one week at ambient
temperature. Both distannylenes (Figure 5) feature an essen-
tially planar structure. The Sn−N bond lengths within the
heterocycles of 6b,c differ only marginally and fall in the range
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Sn[N(SiMe3)2]2 to yield the stannylenes 6b,c. Like its lighter
benzobiscarbene analogues,6 benzobisgermylene 4a is a poten-
tial building block for larger metallosupramolecular structures.
4. EXPERIMENTAL SECTION
General Procedures. If not noted otherwise, all reactions were
carried out under an argon atmosphere using conventional Schlenk
techniques or in a glovebox. Solvents were dried and freshly distilled
by standard procedures prior to use. NMR spectra were recorded on
Bruker AC 200, Bruker AVANCE I 400, or Bruker AVANCE III
400 spectrometers. Chemical shifts (δ) are expressed in ppm down-
field from tetramethylsilane using the residual protonated solvent (1H
NMR), Me4Si (29Si NMR), or Me4Sn as an internal standard. EI mass
spectra were obtained with a Finnigan MAT 95 spectrometer. Di[bis-
(trimethylsilyl)amino]tin(II), di[bis(trimethylsilyl)amino]germanium-
(II),23 and compound 121 were prepared by published procedures.
Compound 3b·2HCl, but not the free tetramine 3b, was previously
isolated.22 We prepared 3b,c by AlH3 reduction of the corresponding
tetramides in analogy with the procedure used for the synthesis of 3a.
The tetramines (related compounds are used as oxygen sensors) as well
as the germylens and stannylenes are highly sensitive toward oxygen.
Satisfactory microanalytical data could not be obtained. Instead, MS data
are given in the Experimental Section, and detailed NMR spectra have
been deposited as Supporting Information.
Figure 5. Molecular structures of 6b (top, 50% displacement
ellipsoids) and 6c (bottom, 50% displacement ellipsoids). Both
molecules reside on crystallographic inversion centers located at the
midpoint of the p-benzochinonediimine ring. Selected bond lengths
(Å) and angles (deg) for 6b [6c]: Sn−N1 2.2056(14) [2.206(2)], Sn−
N2 2.1917(13) [2.170(2)], Sn−N3 2.1340(14) [2.124(2)], Si1−N3
1.7315(15) [1.730(2)], Si2−N3 2.7370(14) [1.734(2)], N1−C3
1.321(2) [1.328(2)], N1−C4/C8 1.469(2) [1.471(3)], N2−C2
1.329(2) [1.325(2)], N2−C9/C4 1.466(2) [1.468(3)], C1−C2
1.397(2) [1.401(3)], C2−C3 1.507(2) [1.491(3)], C3−C1*
1.394(2) [1.397(3)]; N1−Sn−N2 73.96(5) [74.35(6)], N1−Sn−N3
92.06(5) [104.58(7)], N2−Sn−N3 102.88(5) [93.44(7)], sum of
angles at nitrogen atoms 358.12−359.92°.
1,2-Bis(2,2-dimethylpropanamido)-4,5-di(ethylamido)-
benzene (2). Compound 121 (0.75 g, 2.5 mmol) was dissolved in
THF (50 mL) at 0 °C under an argon atmosphere. To this solution
was added dropwise under an argon atmosphere 0.7 g (8.9 mmol) of
acetyl chloride. The reaction mixture was stirred for 3 d at ambient
temperature. Over the reaction time the tetramide 2 precipitated from
the solution. It was isolated by filtration and recrystallized from
previously found for benzannulated N-heterocyclic stannylenes.16
This observation indicates electron delocalization within the five-
membered stannylene heterocycles. The quinone structure of the
central six-membered ring manifests itself with short C1*−C3 and
C1−C2 bond lengths (range 1.394(2)−1.401(3) Å) and elon-
gated C2−C3 bonds (range 1.491(3)−1.507(2) Å). These
features are consistent with experimental data and DFT calcula-
tions on the free [N-neopentyl-2-(neopentylamino)-N′-neopentyl-
5-(neopentylamino)-1,4-benzoquinonediimine (5b) which had
been previously characterized by X-ray crystallography.22
1
methanol. Yield: 0.81 g (2.07 mmol, 85%) of colorless crystals. H
NMR (400 MHz, [D6]DMSO): δ 9.34 (s, br, 2H, H8), 9.02 (s, br, 2H,
H4), 7.64 (s, 2H, H6), 2.06 (s, 6H, H10), 1.21 ppm (s, 18H, H1).
13C{1H} NMR (101 MHz, [D6]DMSO): δ 176.7 (C9), 168.6 (C3),
127.7 (C7), 127.5 (C5), 121.1 (C6), 39.4 (C2), 27.2 (C10), 23.6 ppm
(C1). MS (EI): m/z (%) = 390 (100) [M]+. C20H30N4O4, M = 390.48.
3. CONCLUSIONS
1,2-Di(ethylamine)-4,5-di(neopentylamine)benzene (3a).
Concentrated sulfuric acid (0.82 mL, 15.4 mmol) was cautiously and
dropwise added at 0 °C to a suspension of 1.17 g (30.8 mmol) of
lithium aluminum hydride in 100 mL of argon-saturated THF. After
the initial development of hydrogen gas ceased the resulting white
suspension was stirred for 1 h at ambient temperature. Subsequently,
0.4 g (1.02 mmol) of tetramide 2 was slowly added. The resulting
orange suspension was stirred for 3 d at ambient temperature. Excess
lithium aluminum hydrides and AlH3 was then destroyed with
degassed water at 0 °C. The aqueous suspension was extracted with
diethyl ether (5 × 15 mL). The combined ether extracts were dried
over magnesium sulfate, and the solvent was removed in vacuo, leaving
We have prepared symmetrically and unsymmetrically substi-
tuted 1,2,3,4-tetra(alkylamine)benzenes. The unsymmetrically
tetramine 3a reacts with Ge[N(SiMe3)2]2 to yield the ditopic
digermylene 4a featuring two differently N,N′-substituted
N-heterocyclic germylene moieties. Reaction of the symmetrically
substituted tetramines 3b,c with Sn[N(SiMe3)2]2 did not yield
the expected distannylene but elemental tin and distannylenes
6b,c, featuring an N-alkyl-2-(alkylamino)-N′-alkyl-5-(alkylamino)-
1,4-benzoquinonediimine backbone and an additional N(SiMe3)2
ligand per tin(II) center. The reasons for the differences in the
reactivity of the 1,2,3,4-tetra(alkylamine)benzenes with the GeII
and SnII precursors and particularly for the facile oxidation of
the tetramines by SnII is not yet known. Aerial oxidation of
the tetramines 3b,c yields the free N-alkyl-2-(alkylamino)-N′-
alkyl-5-(alkylamino)-1,4-benzoquinonediimes, which react with
1
compound 3a as an orange solid. Yield: 0.33 g (0.98 mmol, 95%). H
NMR (400 MHz, C6D6): δ 6.45 (s, 2H, H6), 3.16 (s, br, 4H, H4 and
3
3
H8), 3.01 (s, 4H, H3), 2.89 (q, J = 7.0 Hz, 4H, H9), 1.09 (t, J =
7.0 Hz, 6H, H10), 1.01 ppm (s, 18H, H1). 13C{1H} NMR (100 MHz,
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C6D6): δ 132.6 (C7), 132.1 (C5), 103.9 (C6), 58.8 (C3), 40.4 (C9),
31.8 (C2), 28.0 (C1), 15.5 ppm (C10). MS (EI): m/z (%) = 334
(100), [M]+. C20H38N4, M = 334.55.
H3), 1.97 (m, 4H, H4), 0.99 ppm (d, 3J = 6.7 Hz, 24H, H5). 13C{1H}
NMR (100 MHz, CDCl3): δ 135.8 (C1), 84.5 (C2), 34.2 (C3), 30.3
(C4), 20.7 ppm (C5).
1,2,4,5-Tetra(neopentylamine)benzene (3b) and 1,2,4,5-
Tetra(isobutylamine)benzene (3c). Compounds 3b,c were
prepared as described for 3a by reduction of the corresponding tetra-
1
mides. Selected analytic date for 3b: Yield 46%. H NMR (400 MHz,
[D8]toluene): δ 6.22 (s, 2H, H2), 3.40 (s, 4H, NH), 2.73 (s, 8H, H3),
1.01 ppm (s, 36H, H5). 13C{1H} NMR (100 MHz, [D8]toluene): δ
137.5 (C1), 133.0 (C2), 58.9 (C3), 31.8 (C4), 28.0 ppm (C5). MS
(EI): m/z (%) = 418.0 (100) [M+]. C26H50N4, M = 418.71. The
tetramine 3c could not be isolated in pure form. The p-benzoquino-
nediimine 5c obtained by oxidation of 3c, however, was fully charac-
terized. Crystals of 3b have been obtained from a toluene solution at
ambient temperature.
[N-Neopentyl-2-(neopentylamino)-N′-neopentyl-5-(neopen-
tylamino)-1,4-benzoquinonediimine]di[bis(trimethylsilyl)-
aminotin(II)] (6b). An oven-dried Schlenk flask was cooled under
argon and charged with p-benzoquinonediimine 5b (100 mg, 0.24 mmol)
and THF (20.0 mL). To this was added Sn[N(SiMe3)2]2 (210 mg,
0.48 mmol). The reaction mixture was stirred for 24 h at ambient temper-
ature. Subsequently the solvent and the volatile byproduct HNSiMe3
were removed in vacuo. The resulting solid residue was taken up in
n-hexane, and the slurry was filtered. Removal of the solvent from
the filtrate gave compound 6b as a purple solid. Yield: 156 mg
(0.16 mmol, 67%). Crystals of 6b were obtained from a THF solution
of the compound by slow evaporation of the solvent at ambient
temperature over 1 week. Most resonances in the NMR spectra are
doubled due to the presence of two isomers (syn and anti) of compound
6b, which are present in a 1:1 ratio in solution. 1H NMR (400.0 MHz,
[D8]THF): δ 5.52 (s, 2H, H2), 5.51 (s, 2H, H2), 3.52−3.31 (m, 16H,
H3, both isomers), 1.10 (s, 36H, H5), 1.09 (s, 36H, H5), 0.06 (s, 18H,
H6), 0.05 ppm (s, 18H, H6). 13C{1H} NMR (100 MHz, [D8]THF): δ
163.7 (C1), 163.5 (C1), 90.6 (C2), 90.3 (C2), 60.0 (C3), 35.6 (C3),
35.5 (C4), 34.1 (C4), 30.3 (C5), 30.2 (C5), 6.6 (C6), 6.5 ppm (C6).
29Si{1H} NMR (79.5 MHz, [D8]THF): δ 0.09, −0.27 ppm. 119Sn{1H}
1,2-Di(ethylamino)-4,5-di(neopentylamino)digermanium(II)
(4a). A dried Schlenk flask was charged in the glovebox with 64 mg
(0.192 mmol) of tetramine 3a and 3 mL of dry THF. To the resulting
23
solution was added 0.159 g (0.403 mmol) of Ge[N(SiMe3)3]2 at
ambient temperature. The reaction mixture was stirred at 65 °C for
36 h. Subsequently the solvent and volatile products were removed
in vacuo. A yellow solid was obtained, which was dissolved in THF (as
little as possible), and the solution was layered with n-hexane. After
cooling to −18 °C for 3 d red-orange crystals of the benzobisgermylene
4a were obtained. Yield: 82 mg (0.173 mmol, 90%). 1H NMR (200 MHz,
C6D6): δ 6.86 (s, 2H, H5), 4.08−3.84 (m, 8H, H3, H7), 1.49 (t, 6H, H8),
1.03 ppm (s, 18H, H1). 13C{1H} NMR (50 MHz, C6D6): δ 138.1 (C6),
137.1 (C4), 91.0 (C5), 57.4 (C3), 41.6 (C7), 33.3 (C2), 29.0 (C1),
18.2 ppm(C8). MS (EI): m/z (%) = 476 (100) [M+] (correct isotope
pattern). C20H34N4Ge2, M = 475.70.
NMR (149.2 MHz, [D8]THF): δ −21.8, −33.0 ppm. MS (EI): m/z
(%): 972 (1) [M]+, 812 (11) [M − N(SiMe3)2]+. C38H82N6Si4Sn2 M =
972.82.
[N-Isobutyl-2-(isobutylamino)-N′-isobutyl-5-(isobutylami-
no)-1,4-benzoquinonediimine]di[bis(trimethylsilyl)aminotin-
(II)] (6c). Compound 6c was prepared as described for 6b from
p-benzoquinonediimine 5c (80 mg, 0.25 mmol) and Sn[N(SiMe3)2]2
(220 mg, 0.50 mmol) in THF (20.0 mL). Yield: 130 mg (0.14 mmol,
57%) of a red solid. Crystals of 6c were obtained from a THF solution
of the compound by slow evaporation of the solvent at ambient tem-
perature over 1 week. Most resonances in the NMR spectra are
doubled due to the presence of two isomers (syn and anti) of com-
N-Neopentyl-2-(neopentylamino)-N′-neopentyl-5-(neopen-
tylamino)-1,4-benzoquinonediimine (5b). Tetramine 3b 0.80 g
(1.92 mmol) was dissolved in THF (20.0 mL), and the solution was
stirred in air for 12 h. Subsequently the solvent was removed in vacuo,
giving 5b as a yellow solid. Yield: 780 mg (1.88 mmol, 98%). 1H NMR
(400.0 MHz, CDCl3): δ 6.75 (s, 2H, NH), 5.17 (s, 2H, H2), 2.96
(s, 8H, H3), 1.01 ppm (s, 36H, H5). 13C{1H} NMR (100 MHz, CDCl3):
δ 135.8 (C1), 84.0 (C2), 32.2 (C3), 30.3 (C4), 27.9 ppm (C5). MS
(MALDI): m/z (%) = 418 (100) [M + 2H]+. C26H48N4, M = 416.69.
N-Isobutyl-2-(isobutylamino)-N′-isobutyl-5-(isobutylamino)-
1,4-benzoquinonediimine (5c). Compound 5c was synthesized as
described for 5b from 0.60 g (1.67 mmol) of tetramine 3c. Yield:
1
pound 6c, which are present in a 0.6:0.4 ratio in solution. H NMR
(400.0 MHz, [D8]THF): δ 5.14 (s, 2H, H2), 5.13 (s, 2H, H2), 3.40−
3.18 (m, 16H, H3, both isomers), 2.26−2.13 (m, 8H, H4, both
isomers), 1.07 (d, 24H, H5), 1.05 (d, 24H, H5), 0.07 (s, 18H, H6),
0.04 ppm (s, 18H, H6). 13C{1H} NMR (100.6 MHz, THF-d8): δ
161.8 (C1), 161.7 (C1), 88.7 (C2), 88.1 (C2), 57.1 (C3), 56.6 (C3),
1
590 mg (1.64 mmol, 98%) of a red solid. H NMR (400.0 MHz,
CDCl3): δ 6.53 (s, 2H, NH), 5.19 (s, 2H, H2), 3.29−2.66 (m, 8H,
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Organometallics
Article
32.0 (C4), 31.8 (C4), 29.8 (C5), 29.7 (C5), 6.4 (C6), 6.3 ppm (C6).
29Si{1H} NMR (79.5 MHz, [D8]THF): δ 0.33, 0.00 ppm. 119Sn{1H}
NMR (149.2 MHz, [D8]THF): δ −31.0, −42.4 ppm. MS (EI): m/z
(%): 596 (9) [M − N(SiMe3)2]+. C34H74N6Si4Sn2 M = 916.72.
X-ray Diffraction Studies. X-ray diffraction data for 3b, 4a, 6b,
and 6c were collected at T = 153(2) K with a Bruker AXS APEX CCD
diffractometer equipped with a rotating anode using monochromated
Mo Kα radiation (λ = 0.71073 Å). Diffraction data were collected over
the full sphere and were corrected for absorption. Structure solutions
were found with the SHELXS-9725 package using direct methods
and were refined with SHELXL-9725 against |F2| using first isotropic
and later anisotropic thermal parameters for all non-hydrogen atoms.
Hydrogen atoms were added to the structure models in calculated
positions.
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: fehahn@uni-muenster.de.
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
The authors thank the Deutsche Forschungsgemeinschaft (SFB
858, IRTG 1444) for financial support.
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