1,2-Disila-3-germacyclopenta-2,4-dienes: Cyclopentadiene analogs based on heavier group 14 elements

Full text of DOI:10.1007/s11172-011-0376-4

Russian Chemical Bulletin, International Edition, Vol. 60, No. 11, pp. 2434—2435, November, 2011
2434
Letters to the Editor
1,2ꢀDisilaꢀ3ꢀgermacyclopentaꢀ2,4ꢀdienes: cyclopentadiene analogs
based on heavier group 14 elements*
V. Ya. Lee, R. Kato, Sh. Aoki, and A. Sekiguchi
Department of Chemistry, Graduate School of Pure and Applied Sciences, University of Tsukuba,
Tsukuba, Ibaraki 305ꢀ8571, Japan.
Fax: +81 (29) 853 4314. Eꢀmail: leevya@chem.tsukuba.ac.jpu, sekiguch@chem.tsukuba.ac.jp
Multiple bonding between the heavier main group eleꢀ
lated and characterized by spectroscopic and crystalloꢀ
graphic (for 3a) analyses (see Experimental, the synthesis
of 3b and its spectral data will be reported elsewhere)
(Scheme 1).
ments is one of the mainstream fields of contemporary
organometallic chemistry.1 To date, many room temperaꢀ
ture stable alkene analogs of the heavier group 14 elements
have been isolated and structurally characterized.2 As for
silagermenes >Si=Ge<, the first metastable tetramesitylꢀ
silagermene was prepared in 1991 (see Ref. 3), whereas
the first isolable representatives were synthesized by us in
2000 (see Ref. 4). The first (and still the only) cyclic silaꢀ
germene, incorporating a Si=Ge bond into the 1,3ꢀdiene
fragment and representing a novel class of cyclic metallaꢀ
dienes, was reported by us some time ago.4b In the present
study, we report the synthesis of novel members of the
metalladiene family.
Scheme 1
R3Si = SiMeBut2
We found that the scope of the reaction of 1Hꢀdisilaꢀ
germirene 1 (see Ref. 4a) with arylacetylenes Ar—C≡C—H 2
can be expanded by varying the aryl substituents. Thus,
compound 1 readily reacts with both 1ꢀethynylꢀ4ꢀmethylꢀ
benzene (2a) (Ar = 4ꢀMe—C6H4) and 1ꢀethynylꢀ4ꢀtriꢀ
fluoromethylbenzene (2b) (Ar = 4ꢀCF3—C6H4) forming
1,1,2,3ꢀtetrakis[diꢀtertꢀbutyl(methyl)silyl]ꢀ4ꢀ(4´ꢀAr)ꢀ1,2ꢀ
disilaꢀ3ꢀgermacyclopentaꢀ2,4ꢀdienes 3a,b, which were isoꢀ
Ar = 4ꢀMe—C6H4 (a), 4ꢀCF3—C6H4 (b)
For the reaction between 1 and 2, one can suggest
a primary π(Si=Ge)—π*(C≡C) frontier orbital interaction
indicated by the contrast between the remarkable ease and
high rate of the reaction in the case of 2b (which is characꢀ
terized by a strongly electronꢀwithdrawing CF3 group on
the aryl substituent that lowers the π*(C≡C) energy level)
and the case of 2a (with its electronꢀreleasing CH3 group
on the aryl substituent) where the reaction was several
times longer.
* Dedicated to Academician of the Russian Academy of Sciences
O. M. Nefedov on the occasion of his 80th birthday.
Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2387—2388, November, 2011.
1066ꢀ5285/11/6011ꢀ2434 © 2011 Springer Science+Business Media, Inc.

1,2ꢀDisilaꢀ3ꢀgermacyclopentaꢀ2,4ꢀdienes
Russ.Chem.Bull., Int.Ed., Vol. 60, No. 11, November, 2011 2435
Table 1. Selected bond lengths (d) and bond angles (ω) in moꢀ
lecule 3a
Si(4)
Bond
d/Å
Angle
ω/deg
Si(1)—Ge(1) 2.2439(6)
Si(1)—Ge(1)—C(37) 101.66(6)
Si(1)—Si(2) 2.3746(8)
Ge(1)—Si(1)—Si(2)
Si(1)—Si(2)—C(38)
Si(2)—C(38)—C(37) 126.18(17)
C(38)—C(37)—Ge(1) 118.26(16)
95.29(3)
98.48(7)
Si(1)
Ge(1)—C(37) 1.986(2)
Si(2)—C(38) 1.885(2)
C(37)—C(38) 1.351(3)
Ge(1)
Si(2)
Si(3)
Si(6)
Si(5)
C(37)
C(38)
2 Me); 0.43 (s, 3 H, Me); 0.59 (s, 3 H, Me); 1.01 (s, 18 H, But);
1.16 (s, 18 H, But); 1.20 (s, 18 H, But); 1.32 (s, 18 H, But); 2.16
(s, 3 H, CH3 (tolyl)); 7.06 (d, 2 H, Harom, J = 8.0 Hz); 7.36 (d, 2 H,
Harom, J = 8.0 Hz); 7.33 (s, 1 H, C=CH). 13C NMR (100.6
MHz, C6D6), δ: –3.1, –2.4 (3 C); 21.1, 22.0, 22.4, 23.0, 23.5,
29.8, 30.8, 31.0, 31.3, 127.6, 128.8, 135.4, 148.7, 149.5
(ArC=CH), 173.2 (ArC=CH). 29Si NMR (79.5 MHz, C6D6), δ:
–46.0 (ring sp3ꢀSi); 19.2, 26.5, 29.9, 123.6 (ring sp2ꢀSi). UV,
Fig. 1. Molecular structure of compound 3a (ORTEP, hydrogen
max/nm (ε/L mol–1 cm–1, hexane): 313 (8300), 471 (8300).
atoms are not shown).
λ
Crystal data for 3a at 120 K: C48H99GeSi6, М = 917.40, triꢀ
clinic, space group P1–, a = 12.1270(8), b = 12.4810(7),
c = 21.1020(11) Å, α =96.964(3)°, β = 94.473(3)°, γ = 116.768(3)°,
V = 2798.8(3) Å3, Z = 2, dcalc = 1.089 g cm–3, R = 0.0427 for
9751 reflections with I0 > 2σ(I0) (Rw = 0.1191 for all data, 12 310
reflections), GOOF = 1.050.
The most peculiar NMR spectra feature of both comꢀ
pounds 3a and 3b is the lowꢀfield resonance of their sp2ꢀSi
atoms observed at 123.6 ppm for 3a and 127.3 ppm for 3b.
The Si2GeC2 fiveꢀmembered ring in 3a is nearly planar
(the sum of the interior bond angles is 539.9°) with a twistꢀ
ed (the twist angle between the planes formed by the Si or
Ge atoms and their substituents is 20.8°) Si=Ge bond,
whose length of 2.2439(6) Å is between those of typical
Si=Si and Ge=Ge bonds (Fig. 1). Both UV spectra (the
absence of a notable bathochromic shift) and structural
(the absence of shortening of the single bonds and stretchꢀ
ing of the double bonds) features of 3a give evidence for
the lack of any observable conjugation between the Si=Ge
and C=C bonds.
References
1. (a) P. P. Power, Chem. Rev., 1999, 99, 3463; (b) R. C. Fisꢀ
cher, P. P. Power, Chem. Rev., 2010, 110, 3877.
2. V. Ya. Lee, A. Sekiguchi, Organometallic Compounds of Lowꢀ
Coordinate Si, Ge, Sn and Pb: From Phantom Species to Stable
Compounds, Wiley, Chichester, 2010, Chapter 5.
3. K. M. Baines, J. A. Cooke, Organometallics, 1991, 10, 3419.
4. (a) V. Ya. Lee, M. Ichinohe, A. Sekiguchi, N. Takagi,
S. Nagase, J. Am. Chem. Soc., 2000, 122, 9034; (b) V. Ya. Lee,
M. Ichinohe, A. Sekiguchi, J. Am. Chem. Soc., 2000,
122, 12604.
1HꢀDisilagermirene 1 (1.03 g, 1.36 mmol) was reacted with
eightfold excess of arylacetylene 2a (1.25 g, 10.8 mmol) in anꢀ
hydrous O2ꢀfree benzene (4 mL) in a sealed evacuated tube at
room temperature. Pure 3a was isolated by the recrystallization
from anhydrous hexane as bright orange crystals (0.34 g, 29%),
1
m.p. 166—168 °C. H NMR (400 MHz, C6D6), δ: 0.38 (s, 6 H,
Received June 10, 2011