Tetraarylstannagermene: A molecule with a Ge=Sn double bond

Article abstract of DOI:10.1021/om020855f

A study was conducted on a molecule with a Ge=Sn double bond. The treatment of R₂Ge=SnR₂ with dry oxygen yielded a 3,4-germastannadioxetane with a stretched O-O bond length. It was found that the four-membered heterocyclic ring was folded from the torsion angle Ge-O-O-Sn of 31.4°.

Full text of DOI:10.1021/om020855f

© Copyright 2003
Volume 22, Number 2, January 20, 2003
American Chemical Society
Communications
Tetr a a r ylsta n n a ger m en e: A Molecu le w ith a GedSn
Dou ble Bon d 1
Annemarie Scha¨fer, Wolfgang Saak, and Manfred Weidenbruch*
Fachbereich Chemie, Universita¨t Oldenburg, Carl-von-Ossietzky-Strasse 9-11,
D-26111 Oldenburg, Germany
Received October 15, 2002
Ch a r t 1
Summary: The reaction of the Grignard compound
RMgBr, R ) 2,4,6-iPr3C6H2, with GeCl2‚(dioxane) and
SnCl2 furnishes the stannagermene R2GedSnR2 (4) with
a short Ge-Sn double bond length of 2.5065(5) Å.
Treatment of 4 with dry oxygen at low temperature yields
a 3,4-germastannadioxetane with a stretched O-O bond
length.
Since the isolation of the first distannene by Lappert
et al. more than 25 years ago,2 the synthesis and
characterization of compounds with multiple bonds
between the heavier elements of group 14 have been
subjects of intensive research. Thus, not only have
molecules of the type 1 (Chart 1) containing homo-
nuclear double bonds between all elements of this group
been prepared,3 but also just recently the first examples
of alkyne analogues 2 of germanium, tin, and lead were
described. While the short bond lengths and the rather
small trans-bent angles in the digermanium4 and ditin5
compounds support the existence of multiple bonds, the
dilead compound must rather be considered as a diplum-
bylene with a Pb-Pb single bond on the basis of
experimental findings and theoretical calculations.6
In contrast, stable molecules with heteronuclear
multiple bonds between the heavier elements of group
14 were unknown until recently, due to their ready
isomerization. For example, calculations on the parent
compound of the germasilenes, H2SidGeH2, revealed
that the silylgermylene H3Si(H)Ge: is appreciably more
stable than the molecule with a heteronuclear double
bond.7 Even so, Sekiguchi et al. were recently able to
isolate thermally stable germasilenes of the type 3.8 We
now report on the formation and structural character-
ization of the first rather stable stannagermene 4, which
is formed surprisingly simply by the reaction of (2,4,6-
(1) Compounds of Germanium, Tin, and Lead. 40. Part 39: Meiners,
F.; Saak, W.; Weidenbruch, M. Z. Anorg. Allg. Chem., in press.
(2) (a) Goldberg, D. E.; Harris, D. H.; Lappert, M. F.; Thomas, K.
M. J . Chem. Soc., Chem. Commun. 1976, 261. (b) Goldberg, D. E.;
Hitchcock, P. B.; Lappert, M. F.; Thomas, K. M.; Thorne, A. J .;
Fjeldberg, T.; Haaland, A.; Schilling, B. E. R. J . Chem. Soc., Dalton
Trans. 1986, 2387.
(6) (a) Pu, L.; Twamley, B.; Power, P. P. J . Am. Chem. Soc. 2000,
122, 3524. (b) Chen, Y.; Hartmann, M.; Diedenhofen, M.; Frenking,
G. Angew. Chem. 2001, 113, 2108; Angew. Chem., Int. Ed. 2001, 40,
2052.
(3) For recent reviews see: (a) Power, P. P. Chem. Rev. 1999, 99,
3463. (b) Weidenbruch, M. J . Organomet. Chem. 2002, 646, 39.
(4) Stender, M.; Phillips, A. D.; Wright, R. J .; Power, P. P. Angew.
Chem. 2002, 114, 1963; Angew. Chem., Int. Ed. 2002, 41, 1785.
(5) Phillips, A. D.; Wright, R. J .; Olmstead, M. M.; Power, P. P. J .
Am. Chem. Soc. 2002, 124, 5930.
(7) Grev, R. S.; Schaefer, H. F.; Baines, K. M. J . Am. Chem. Soc.
1990, 112, 9458.
(8) (a) Lee, V. Y.; Ichinohe, M.; Sekiguchi, A.; Tagaki, N.; Nagase,
S. J . Am. Chem. Soc. 2000, 122, 9034. (b) Lee, V. Y.; Sekiguchi, A. J .
Am. Chem. Soc. 2000, 122, 12604. (c) Ichinohe, M.; Arai, Y.; Sekiguchi,
A.; Tagaki, N.; Nagase, S. Organometallics 2001, 20, 4141.
10.1021/om020855f CCC: $25.00 © 2003 American Chemical Society
Publication on Web 12/17/2002

216 Organometallics, Vol. 22, No. 2, 2003
Communications
Sch em e 1
triisopropylphenyl)magnesium bromide with GeCl2‚
(dioxane) and SnCl2 at low temperature (Scheme 1).9
The 119Sn-NMR spectrum, showing a typical signal
for such compounds in the low-field region at 268 ppm,
provided the first indication for the existence of a double
bond. An X-ray crystallographic analysis10 of the red
crystals confirmed not only the structure of 4 but also
revealed some interesting features (Figure 1). With a
length of 2.5065 Å the Ge-Sn double bond is about 0.12
Å shorter than the average value for Ge-Sn single
bonds12 and, despite the bulky aryl groups, is even
shorter than the value of 2.555 Å calculated for the
parent compound H2GedSnH2.13 As expected, the trans-
bent angle between the R2Sn plane and the SndGe
vector of 43.3° is larger than the corresponding angle
of 30.2° at the germanium atom.
F igu r e 1. Molecule of 4 in the crystal state (hydrogen
atoms omitted). Ellipsoids are drawn at 50% probability.
Selected bond lengths (Å) and angles (deg): Ge-Sn )
2.5065(5), Ge-C(31) ) 2.056(4), Ge-C(46) ) 2.051(4), Sn-
C(1) ) 2.150(4), Sn-C(16) ) 2.158(4); C(1)-Sn-C(16) )
104.92(14), C(31)-Ge-C(46) ) 108.13(17), C(1)-Sn-Ge )
111.50(11), C(16)-Sn-Ge ) 120.90(11), C(31)-Ge-Sn )
123.49(12), C(46)-Ge-Sn ) 117.45(10).
Compound 4 is relatively stable in the solid state. It
decomposes slowly in solution with formation of the
cyclotristannane 514 and the digermene 6,15 as detected
by their 1H NMR spectra and, in the case of 5, 119Sn
NMR spectrum. Even after 4 weeks in toluene solution
4 can still be detected together with 5 and 6. Thus, 4
behaves differently from the stannagermene, in which
merely the triisopropylphenyl groups at germanium
have been replaced by mesityl groups. Although the
latter compound can be characterized by trapping
(9) To a suspension of GeCl2‚(dioxane) (0.55 g, 2.37 mmol) and SnCl2
(0.45 g, 2.37 mmol) in THF (35 mL) and dioxane (5 mL) was added at
-78 °C dropwise a solution of the Grignard compound, prepared from
1-bromo-2,4,6-triisopropylbenzene (3.0 g, 10.6 mmol) and magnesium
turnings in THF (30 mL). The mixture was allowed to come to -10
°C. At -40 °C the color changed from light yellow to red. After the
mixture was stirred for 30 min at -10 °C, the solvents were distilled
off, the residue was redissolved in cooled n-pentane (80 mL), and the
precipitated salts were filtered off. Concentration of the solution to a
minimum amount at -20 °C afforded 0.90 g (37% yield) of red crystals
of 4. Because of the low stability of 4 no reliable spectral and analytical
data could be obtained.
F igu r e 2. Molecule of 7 in the crystal state (hydrogen
atoms omitted). Ellipsoids are drawn at 50% probability.
Selected bond lengths (Å): Ge-Sn ) 2.6347(7), O(1)-O(2)
) 1.521(3).
reactions and its 119Sn NMR signal at 360 ppm, it has
not yet been isolated.16
(10) Crystal data for 4: (C60H92GeSn)2, fw ) 2009.23, monoclinic,
space group P21/n, a ) 14.4059(6) Å, b ) 37.5545(14) Å, c ) 21.6693-
(11) Å, â ) 95.804(6)°, Z ) 4, V ) 11663.1(9) Å3, Dcalcd ) 1.144 g cm-3
,
One of the most interesting reactions of compounds
of type 1 is their oxidation in air, which, in the case of
digermenes, leads to stable 3,4-digermadioxetanes.17 We
thus addressed the question of whether compound 4
would react analogously, despite the greater GedSn
bond length, or whether other reaction pathways would
dominate. Passage of dry air through a solution of 4 in
n-hexane at 0 °C gave the compound 7 in quantitative
yield (Scheme 2). This product was characterized by its
119Sn NMR spectrum (δ 128 ppm) and an X-ray crystal-
lographic analysis (Figure 2).18
µ ) 0.977 mm-1, T ) 193(2) K, crystal size 0.80 × 0.38 × 0.27 mm3,
Stoe-IPDS area detector, structure solution by direct methods, refine-
ment on F2 (2θmax ) 52°), 22 569 unique reflections, R1 ) 0.0500, wR2
(all data) ) 0.1502, GOF (F2) ) 1.031.11
(11) The data have been deposited with the Cambridge Crystal-
lographic Data Centre: CCDC-192 690 (4) and CCDC-192 691 (7).
(12) (a) Pannell, K. H.; Parkanyi, L.; Sharma, H.; Cervantes-Lee,
F. Inorg. Chem. 1992, 31, 522. (b) Leue, C.; Reau, R.; Neumann, B.;
Stammler, H.-G.; J utzi, P.; Bertrand, G. Organometallics 1994, 13, 436.
(c) Kawachi, A.; Tanak, Y.; Tamao, K. J . Organomet. Chem. 1999, 590,
15.
(13) (a) Windus, T. L.; Gordon, M. S. J . Am. Chem. Soc. 1992, 114,
9559. (b) Karni, M.; Apeloig, Y.; Kapp, J .; Schleyer, P. v. R. In The
Chemistry of Organic Silicon Compounds; Rappoport, Z., Apeloig, Y.,
Eds.; Wiley: Chichester, U.K., 2001; Vol. 3, p 1.
(14) Masamune, S.; Sita, L. R. J . Am. Chem. Soc. 1985, 107, 6390
and Supporting Information.
(15) Scha¨fer, H.; Saak, W.; Weidenbruch, M. Organometallics 1999,
18, 3159 and literature cited therein.
(16) Chaubon, M.-A.; Escudie´, J .; Ranaivonjatovo, H.; Satge´, J .
Chem. Commun. 1996, 2621.
(17) Masamune, S.; Batcheller, S. A.; Park, J .; Davies, W. A.;
Yamashita, O.; Ohta, Y.; Kabe, Y. J . Am. Chem. Soc. 1989, 111, 1888.

Communications
Organometallics, Vol. 22, No. 2, 2003 217
Sch em e 2
7 is relatively stable in the solid state, whereas in
solution at room temperature the formation of subse-
quent products occurs. According to the 119Sn NMR
signals at -92.4, -102.5, -111.7, and -122.1 ppm these
products are in the typical region of oligostannoxanes14
and probably -germoxanes, which cannot be character-
ized by NMR data.
While the Ge-Sn bond length of 2.6347(7) Å is in the
same range as other single bonds of this type,12 the O-O
bond length of 1.521(3) Å is markedly stretched. In
addition, the four-membered heterocyclic ring is ap-
preciably folded, as can be seen from the torsion angle
Ge-O-O-Sn of 31.4°. Similar to compound 4, product
Ack n ow led gm en t. Financial support of our work
by the Deutsche Forschungsgemeinschaft and the Fonds
der Chemischen Industrie is gratefully acknowledged.
(18) Crystal data for 7: C60H92GeO2Sn, fw ) 1036.62, monoclinic,
space group P21/n, a ) 12.465(3) Å, b ) 28.216(7) Å, c ) 17.473(3) Å,
â ) 104.43(2)°, Z ) 4, V ) 5951(2) Å3, Dcalcd ) 1.157 g cm-3, T ) 193-
(2) K, crystal size 0.55 × 0.26 × 0.16 mm3, Stoe-IPDS area detector,
structure solution by direct methods, refinement on F2 (2θmax ) 52°),
10 904 unique reflections, R1 ) 0.0350, wR2 ) 0.0912 (all data), GOF
(F2) ) 1.018. The Ge and Sn atoms are disordered and were refined
on two positions with an occupancy factor of 0.5 each.11
Su p p or tin g In for m a tion Ava ila ble: Lists of atomic
coordinates, anisotropic displacement parameters, and bond
lengths and angles for 4 and 7. This material is available free
of charge via the Internet at http://pubs.acs.org.
OM020855F