Cycloadditions of diarylgermylenes to a diazabutadiene

Article abstract of DOI:10.1002/zaac.200400527

The reaction of tetrakis(2-tert-butyl-4,5,6-trimethylphenyl)digermene, which dissociates into the germylene molecules 2 in solution, with 1,4-diisopropyl-1,4-diazabuta-1,3-diene (3) furnishes the [4+1] cycloaddition product of 2 to the nitrogen atoms of 3. Under drastic conditions tetrakis(2,4,6-triisopropylphenyl)digermene also forms the germylene molecules 6 which react with 3 in a similar fashion to afford the corresponding [4+1] cycloadduct.

Full text of DOI:10.1002/zaac.200400527

Kurze Mitteilungen
Cycloadditions of Diarylgermylenes to a Diazabutadiene [1]
Annika Arndt, Helmut Schäfer, Wolfgang Saak, and Manfred Weidenbruch*
Oldenburg, Institut für Reine und Angewandte Chemie der Universität
Received December 2nd, 2004.
Dedicated to Professor Gerd Becker on the Occasion of his 65th Birthday
Abstract. The reaction of tetrakis(2-tert-butyl-4,5,6-trimethylphe-
nyl)digermene, which dissociates into the germylene molecules 2 in
solution, with 1,4-diisopropyl-1,4-diazabuta-1,3-diene (3) furnishes
the [4ϩ1] cycloaddition product of 2 to the nitrogen atoms of 3.
Under drastic conditions tetrakis(2,4,6-triisopropylphenyl)diger-
mene also forms the germylene molecules 6 which react with 3 in
a similar fashion to afford the corresponding [4ϩ1] cycloadduct.
Keywords: Germanium; Germylene; Cycloaddition
Although compounds containing SiϭSi double bonds are stable
towards dissociation into silylene molecules :SiR2, in the solid state
and, mostly, in solution, the behaviour of digermenes R2GeϭGeR2
is less uniform. For example, the digermene 1 exists in solution
almost completely as the germylenes 2 [2, 3]. Reaction of the or-
ange solution of 2 with the 1,4-diazabutadiene 3 at room tempera-
ture yielded pale yellow crystals of the [4ϩ1] cycloaddition product
4 in 90 % yield.
The failure of 3 to react with the digermene 5 is in opposition to
the behaviour of disilenes which, when the spatial demands of the
substituents on the nitrogen atoms are not too great, can undergo
smooth [4ϩ2] cycloadditions [5]. In comparison to the SiϭSi
double bond the greater length of the GeϭGe double bond appar-
ently hinders the formation of a [4ϩ2] adduct.
First indications for the existence of the cycloadduct 4 were pro-
vided by the olefinic protons in the 1H-NMR spectrum in which
the signal of 3 at 7.94 ppm has disappeared and been replaced by
a new singlet at 6.01 ppm. The structure of 4 was confirmed by
an X-ray crystal structure analysis (Figure 1) which revealed some
unusual features. The five-membered ring has an angular sum of
539.7° and is therefore almost planar. Worthy of note are the en-
vironments of the nitrogen atoms which, with angular sums of
358.5° and 355.7° are also practically planar with their substituents.
In contrast to 1 the structurally related digermene 5 retains its
structural integrity in solution and undergoes cleavage into the ger-
mylene molecules 6 only under drastic reaction conditions [4].
Treatment of 3 with 5 at room temperature does not result in any
detectable reaction. Only after heating for 200 hours in boiling di-
methoxyethane (DME) does the colour of the orange solution be-
come lighter and the light yellow crystals of the cycloadduct 7 can
be isolated in 33 % yield. A [4ϩ2] adduct of 3 and 5 could not
be detected.
Fig. 1 Molecule of 4 in the crystal (hydrogen atoms omitted; ellip-
soids are drawn at 50 % probability). Selected bond lengths/pm and
angles/°: C1ϪC2 132.2(3), C1ϪN1 140.4(3), C2ϪN2 141.1(3),
N1ϪGe 186.8(2), N2ϪGe 185.5(2), N1ϪGeϪN2 88.20(8),
C1ϪN1ϪGe 109.4(2), C2ϪN2ϪGe 108.62(14), C2ϪC1ϪN1
116.2(2), C1ϪC2ϪN2 117.3(2).
* Prof. Dr. M. Weidenbruch
Institut für Reine und Angewandte Chemie
Universität Oldenburg
Carl-von-Ossietzky-Straße 9Ϫ11
D-26111 Oldenburg/Germany
E-mail: manfred.weidenbruch@uni-oldenburg.de
Z. Anorg. Allg. Chem. 2005, 631, 1341Ϫ1342
DOI: 10.1002/zaac.200400527
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
1341

A. Arndt, H. Schäfer, W. Saak, M. Weidenbruch
to primary, secondary, tertiary, and quaternary carbon atoms. Ϫ MS (CI,
isobutene) 564 (Mϩ, 100 %).
2,2-Bis(2,4,6-triisopropylphenyl-)1,3-diisopropyl-1,3-diaza-2-
germacyclopent-4-ene (7): Compound 3 (0.23 g, 1.64 mmol) was ad-
ded to a solution of 5 (0.90 g, 0.94 mmol) in 10 mL of DME and
the mixture was heated for 200 h under reflux. During this time the
colour of the solution changed from orange to yellow. The volume
of the solution was concentrated to 2 mL and cooled at Ϫ22 °C.
After 12 h 0.40 g (33 % yield) of pale yellow crystals of 7 were iso-
lated, mp 158 Ϫ 161 °C.
Elemental analysis: Calcd: C 73.76, H 10.08, N 4.52. Found: C
73.32, H 9.97, N 4.33 %.
Spectroscopic data: 1H NMR: δ 0.41 (d, 6H, 3J ϭ 6.4 Hz), 0.92 (d, 6H, 3J ϭ
6.4 Hz), 1.15 Ϫ 1.18 (m, 12H), 1.25 (d, 6H, 3J ϭ 6.4 Hz), 1.31 (d, 6H, 3J ϭ
6.4 Hz), 1.38 Ϫ 1.45 (m, 12H), 2.73 (sept, 2H), 2.87 (sept, 2H), 3.71 (sept,
2H), 4.57 (sept, 2H), 6.04 (s, 2H), 6.34 (s, 2H), 7.19 (s, 2H). Ϫ 13C NMR: δ
22.72, 23.41, 23.66, 24.06, 24.16, 25.52, 26.83, 31.59, 34.54, 36.85, 47.15,
112.75, 121.96, 122.53, 137.57, 150.38, 151.95, 153.79.
Crystallographic analyses: In each case, the crystal was mounted in
an inert oil. Data collection was performed with a STOE IPDS
area detector using graphite monochromated Mo Kα radiation
(71.073 pm). The structures were solved by direct phase determi-
nation and refined by full-matrix least-squares techniques against
F2 with the SHELXL-97 program package [7]. Hydrogen atoms
were placed in the calculated positions, and all other atoms were
refined anisotropically. 4: C34H54GeN2 (563.38), crystal dimensions
0.35 ϫ 0.08 ϫ 0.06 mm3, temperature 153(2) K, triclinic, space
Fig. 2 Molecule of 7 in the crystal (hydrogen atoms omitted; ellip-
soids are drawn at 50 % probability).
1
The H- and 13C-NMR spectra of 7 show major similarities with
those of compound 4. In addition, the X-ray crystal structure
analysis of 7 (Figure 2) shows differences only in the orientation of
the two aryl groups. The five-membered ring has an angular sum
of 539.8° and is thus almost planar like that of 4. The environments
of the two nitrogen atoms with angular sums of 355.9° und 355.7°
are somewhat more pyramidalized as those of the corresponding
atoms in 4.
Compounds 4 and 7 are the first structurally characterized hetero-
cyclic compounds of this type. Although the formation of anal-
ogous ring systems by cycloaddition of thermally generated di-
methylgermylene to 1,4-diazabutadienes has been reported, the
molecules thus obtained were unstable and were characterized
merely by their spectroscopic data [6].
¯
groups P1, a ϭ 964.24(7), b ϭ 966.61(6), c ϭ 1739.53(12) pm, Ͱ ϭ
99.107(8)°, β ϭ 90.187(8)°, γ ϭ 100.803(8)°, V ϭ 1571.60(19) ·
106 pm3, dcalcd ϭ 1.191 g/cm3, Z ϭ 2, 2θmax ϭ 52°; collected reflec-
tions 5759, observed reflections 4667; μ ϭ 0.998 mmϪ1. R1 ϭ
0.0310, wR2 (all data) ϭ 0.0731 for 334 parameters, GOF ϭ 0.936.
7: C38H62GeN2 (619.49), crystal dimensions 0.38 ϫ 0.26 ϫ
0.25 mm3, temperature 193(2) K, orthorhombic, space group
Pna21, a ϭ 2065.47(5), b ϭ 1352.84(4), c ϭ 1313.20(6) pm, V ϭ
3669.4(2) · 106 pm3, dcalcd ϭ 1.121 g/cm3, Z ϭ 4, 2θmax ϭ 52°; col-
lected reflections 27990, observed reflections 5340;
μ ϭ
0.861 mmϪ1. Flack-x ϭ 0.004(10). R1 ϭ 0.0295, wR2 (all data) ϭ
0.0681 for 370 parameters; GOF ϭ 0.905 [8].
Financial support of our work by the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie is gratefully
acknowledged.
Experimental Section
General Procedure. All reactions were carried out in oven-dried
glassware under an atmosphere of dry argon.
[1] Compounds of Germanium, Tin, and Lead. Part 44; Part 43:
G. Ramaker, W. Saak, D. Haase, M. Weidenbruch, Organomet-
allics 2003, 22, 5112.
[2] M. Weidenbruch, M. Stürmann, H. Kilian, S. Pohl, W. Saak,
Chem. Ber./Recueil 1997, 130, 735; see also, ref. [1].
[3] For recent reviews, see: N. Tokitoh, R. Okazaki, Coord. Chem.
Rev. 2000, 210, 251; M. Weidenbruch, J. Organomet. Chem.
2002, 646, 39; M. Weidenbruch, Organometallics 2003, 22, 1570.
[4] H. Schäfer, W. Saak, M. Weidenbruch, Organometallics 1999,
16, 3159.
1H and 13C NMR spectra: Bruker AM 300; mass spectra: Finnigan
MAT 212 or MAT 95; elemental analyses: Analytische Laborator-
ien, D-51789 Lindlar.
2,2-Bis(2-tert-butyl-4,5,6-trimethylphenyl)-1,3-diisopropyl-1,3-
diaza-2-germacyclopent-4-ene (4): At room temperature a solution
of 3 (66 mg, 0.47 mmol) in 20 mL of THF was added dropwise to
a solution of 1 (200 mg, 0.238 mmol) in 40 mL of THF and the
mixture stirred for 2 d. During this time the colour of the solution
changed from orange to pale yellow. The solvent was removed in
vacuo and the residue redissolved in 10 mL of n-hexane. Cooling
to Ϫ30 °C afforded 240 mg (90 % yield) of a pale yellow solid.
Recrystallisation from n-pentane furnished pale yellow crystals of
4, mp 155 °C.
Elemental analysis: Calcd: C 72.48, H 9.66, N 4.97. Found: C
72.36, H 9.34, N 4.72 %.
Spectroscopic data: 1H NMR: δ 0.76 (d, 6H, 3J ϭ 6.4 Hz), 1.23 (d, 6H, 3J ϭ
6.8 Hz), 1.63 (s, 18H), 1.81 (s, 6H), 2.13 (s, 6H), 2.30 (s, 6H), 3.55 (m, 2H),
6.01 (s, 2H), 7.39 (s, 2H). Ϫ 13C NMR: δ 15.85 (Cp), 21.13 (Cp), 23.03 (Cp),
24.48 (Cp), 24.97 (Cp), 33.40 (Cp), 33.75 (Cp), 37.24 (Ct), 48.06 (Cq), 112.18
(Cs), 128.98, 132.99, 136.03, 138.84, 144.09, 150.42. Cp, Cs, Ct, and Cq refer
[5] M. Weidenbruch, A. Lesch, K. Peters, J. Organomet. Chem.
1991, 407, 31.
[6] K. Bootz, W. P. Neumann, Tetrahedron Lett. 1989, 30, 6669.
[7] G. M. Sheldrick. SHELXL-97, Program for crystal structure
refinement. University Göttingen, Germany, 1997.
[8] CCDC-256943 (4) and CCDC-256944 (7) contain the sup-
plementary crystallographic data for this paper. These data can
be obtained free of charge via www.ccdc.cam.ac.uk/conts/retriev-
ing.httm (or from the Cambridge Crystallographic Centre, 12,
Union Road, Cambridge CB2 1EZ, UK); fax: (ϩ44)1223-336-
033; or deposit@ccdc.cam.ac.uk.
1342
© 2005 WILEY-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim
zaac.wiley-vch.de
Z. Anorg. Allg. Chem. 2005, 631, 1341Ϫ1342