Reaction of [tris(trimethylsilyl)methyl]tribromogermane with magnesium: Generation of a bromogermylene

Article abstract of DOI:10.1021/om970371x

The reaction of [tris(trimethylsilyl)methyl]tribromogermane with magnesium in the presence of olefins and acetylenes has been investigated. 1,4-Digermabicyclo[2.2.0]hexanes and bromogermacyclopent-3-ene are obtained in the reactions of [tris(trimethylsilyl)-methyl]bromogermylene with olefins and 1,3-butadiene, respectively. In the presence of diphenylacetylene a 1,2-dihydro-1,2-digermacyclobutene was formed, which can be explained in terms of an electron-transfer reaction of the bromogermylene intermediate.

Full text of DOI:10.1021/om970371x

4956
Organometallics 1997, 16, 4956-4958
Rea ction of [Tr is(tr im eth ylsilyl)m eth yl]tr ibr om oger m a n e
w ith Ma gn esiu m : Gen er a tion of a Br om oger m ylen e
Harunobu Ohgaki, Norihisa Fukaya, and Wataru Ando*
Department of Chemistry, University of Tsukuba, Tsukuba, Ibaraki 305, J apan
Received May 5, 1997X
Sch em e 1
Summary: The reaction of [tris(trimethylsilyl)methyl]-
tribromogermane with magnesium in the presence of
olefins and acetylenes has been investigated. 1,4-
Digermabicyclo[2.2.0]hexanes and bromogermacyclopent-
3-ene are obtained in the reactions of [tris(trimethylsilyl)-
methyl]bromogermylene with olefins and 1,3-butadiene,
respectively. In the presence of diphenylacetylene a 1,2-
dihydro-1,2-digermacyclobutene was formed, which can
be explained in terms of an electron-transfer reaction of
the bromogermylene intermediate.
Despite extensive studies of reactions of trihaloger-
manes that contain a bulky substituent with alkali
metals,1 no attempt has been made to find the reactive
intermediate involved in such reactions. On the other
hand, the chemistry of germylenes has been studied
over the last two decades, and several organohaloger-
mylenes (R-Ge-X) were identified as synthetic inter-
mediates;2 a few stable ones (Cp*-Ge-Cl, Mes*-Ge-
Cl) even could be isolated.3 Very recently, we reported
a stable chlorogermylene which reacts with ethylene to
form a 1,2-dichloro-1,2-digermacyclobutane and a 1,4-
digermabicyclo[2.2.0]hexane.4 In this communication
we report that the halogermylene and, possibly, its
radical anion are important intermediates in the reac-
tion of (trisyl)trihalogermanes (trisyl ) tris(trimethyl-
silyl)methyl) with magnesium.
Treatment of (trisyl)tribromogermane5 (1; 200 mg,
0.38 mmol) with Mg6 (48 mg, 2.0 mmol) in THF (5 mL)
containning 2-methyl-1,3-butadiene (780 mg, 11 mmol)
at room temperature for 10 h produced a [1 + 4]
cycloadduct, the bromogermacyclopent-3-ene compound
3 in 45% yield7 (77 mg) (Scheme 1). Moreover, 1 was
reduced by Mg in the absence of a germylene trapping
reagent over 10 h. After removal of unreacted magne-
sium, addition of 2-methyl-1,3-butadiene to the remain-
ing solution resulted in formation of 3 in 40% yield. This
result shows that (trisyl)bromogermylene (2) formed in
the 1/Mg reaction is a stable species in THF and that it
has the characteristic reactivity of a germylene. Reac-
tions of 1 with magnesium in the presence of olefins
gave 1,4-digermabicyclo[2.2.0]hexanes. Thus, the 1 (200
mg, 0.38 mmol)/Mg reaction in the presence of gaseous
ethylene gave 4a (5 mg, 8% yield),8a while 4b (21 mg,
28% yield) was produced in the presence of an excess of
styrene8b (Scheme 2).
Although (trisyl)trichlorogermane was not reduced by
magnesium alone, (trisyl)chlorogermylene could be gen-
erated by the action of the magnesium/magnesium
dibromide system on this germane. Thus, reaction of
(trisyl)trichlorogermane (200 mg, 0.49 mmol) with
magnesium (60 mg) and magnesium dibromide (120 mg)
in the presence of 2-methyl-1,3-butadiene (170 mg, 2.5
mmol) yielded the [1 + 4] cycloadduct chlorogermacy-
X Abstract published in Advance ACS Abstracts, November 1, 1997.
(1) (a) Sekiguchi, A.; Kabuto, C.; Sakurai, H. Angew. Chem., Int.
Ed. Engl. 1989, 28, 55. (b) Sekiguchi, A.; Yatabe, T.; Kamatani, H.;
Kabuto, C.; Sakurai, H. J . Am. Chem. Soc. 1992, 114, 6260.
(2) (a) Wiberg, N.; Hochmuth, W.; No¨th, H.; Appel, A.; Schmidt-
Amelunxen, M. Angew. Chem., Int. Ed. Engl. 1996, 35, 1333. (b) J utzi,
P.; Hampel, B.; Hursthouse, M. B.; Howes, A. J . Organometallics 1986,
5, 1994. (c) J utzi, P.; Becker, A.; Stammer, H. G.; Neumann, B.
Organometallics 1991, 10, 1647. (d) J utzi, P.; Becker, A.; Leue, C.;
Stammer, H. G.; Neumann, B. Organometallics 1991, 10, 3838. (e)
Kobayashi, S.; Cao, S. Chem. Lett. 1994, 941. (f) Braunschweig, H.;
Hitchcock, P. B.; Lappert, M.; Pierssens, L. J . Angew. Chem., Int. Ed.
Engl. 1994, 33, 1156. (g) Tokitoh, N.; Suzuki, H.; Matsumoto, T.;
Matsuhashi, Y.; Okazaki, R. J . Am. Chem. Soc. 1991, 113, 7047. (h)
Simons, R. S.; Pu, L.; Olmstead, M. M.; Power, P. P. Organometallics
1997, 16, 1920.
(7) 3: colorless crystals; decomp. >300 °C; 1H NMR (C6D6, 300 MHz)
δ 0.33 (s, 27H, SiCH3), 1.72 (s, 3H, CCH3), 2.07-2.23 (m, 4H, GeCH2C),
5.63 (m, 1H, CH2CH); 13C NMR (C6D6, 75 MHz) δ 4.5 (SiCH3), 8.0
(GeCSi), 22.6 (CCH3), 31.0 (GeCH2C), 33.6 (GeCH2CH), 123.8
(GeCH2CH), 138.3 (GeCH2C); MS (EI) m/z 437 (M+ - Me). Anal. Calcd
for C15H35BrSi3Ge: C, 39.84; H, 7.80. Found: C, 39.94; H, 7.23.
(8) (a) Reaction of (trisyl)tribromogermane (1; 200 mg, 0.38 mmol)
with Mg (48 mg, 2.0 mmol) in the presence of gaseous ethylene at room
temperature gave the 1,4-digermabicyclo[2.2.0]hexane 4a in 8% yield
(5 mg). 4a : colorless crystals; decomp 202 °C; 1H NMR (C6D6, 300 MHz)
δ 0.50 (s, 54H, SiCH3), 2.43 (m, 4H, GeCH2); 13C NMR (C6D6, 75 MHz)
δ 5.7 (SiCH3), 26.8 (GeCSi), 34.8 (GeCH2).4 (b) Reaction of 1 (200 mg,
0.38 mmol) with Mg (48 mg, 2.0 mmol) in the presence of an excess of
styrene (100 mg, 0.96 mmol) gave the 1,4-digerma-2,5-diphenylbicyclo-
[2.2.0]-hexane 4b in 28% yield (21 mg). 4b: colorless waxy solid; 1H
NMR (C6D6, 300 MHz) δ 0.20 (br, 27H, SiCH3), 0.40 (s, 27H, SiCH3),
2.72 (dd, J ) 7.7, 14.5 Hz, 1H, GeCH2), 2.96 (dd, J ) 11.2, 13.2 Hz,
1H, GeCH2), 3.06 (dd, J ) 7.7, 13.2 Hz, 1H, GeCH2), 3.11 (dd, J )
11.2, 14.5 Hz, 1H, GeCH2), 4.10 (dd, J ) 7.7, 11.2 Hz, 1H, GeCHC6H5),
4.85 (dd, J ) 7.7, 11.2 Hz, 1H, GeCHC6H5), 6.85-7.66 (m, 10H, C6H5);
13C NMR (C6D6, 75 MHz) δ 5.2 (SiCH3), 5.5 (SiCH3), 12.2 (GeCSi), 20.8
(GeCSi), 38.4 (GeCH2), 41.7 (GeCH2), 48.1 (GeCH), 53.0 (GeCH), 125.1
(C6H5), 124.5 (C6H5), 128.1 (C6H5), 128.4 (C6H5), 129.2 (C6H5), 129.4
(C6H5), 146.8 (CHC6H5), 147.3 (CHC6H5); MS (EI) m/z 710 (M+ - C6H5-
CHCH2), 606 (M+ - (C6H5CHCH2)2).
(3) (a) J utzi, P.; Leue, C. Organometallics 1994, 13, 2898. (b) Lange,
L.; Meyer, B.; du Mont, W. W. J . Organomet. Chem. 1987, 329, C17.
(c) Kohl, F. X.; J utzi, P. J . Organomet. Chem. 1983, 243, 31. (d) J utzi,
P. J . Organomet. Chem. 1990, 400, 1.
(4) Ohtaki, T.; Ando, W. Organometallics 1996, 15, 3103.
(5) 1 was prepared by bromination of (trisyl)trihydrogermane in 74%
yield: white solid; decomp >300 °C; 1H NMR (CDCl3, 300 MHz) δ 0.46
(s, 27H, SiCH3); 13C NMR (CDCl3, 75 MHz) δ 5.4 (SiCH3), 30.5 (GeCSi);
MS (EI) m/z 529 (M+ - Me). Anal. Calcd for C10H27Br3Si3Ge: C, 22.08;
H, 5.00. Found C, 22.30; H, 4.90.
(6) These reductions require 99.98% pure magnesium (Aldrich).
S0276-7333(97)00371-3 CCC: $14.00 © 1997 American Chemical Society

Communications
Organometallics, Vol. 16, No. 23, 1997 4957
Sch em e 3
Sch em e 4
F igu r e 1. Ortep drawing of 5. Selected bond lengths (Å)
and angles (deg): Ge(1)-Ge(2), 2.514(2); Ge(1)-C(1), 1.95-
(1); Ge(2)-C(2), 2.00(1); C(1)-C(2), 1.33(2); C(1)-C(101),
1.52(2); C(2)-C(201), 1.50(2); Ge(2)-Ge(1)-C(1), 72.7(4);
Ge(1)-Ge(2)-C(2), 72.5(4); Ge(1)-C(1)-C(2), 109.6(9); Ge-
(2)-C(2)-C(1), 105.3(9); Ge(1)-C(1)-C(101), 130(1); C(2)-
C(1)-C(101), 120(1); Ge(2)-C(2)-C(201), 129.1(9); C(1)-
C(2)-C(201), 125(1).
Sch em e 5
Sch em e 2
clopent-3-ene (32 mg) in 20% yield and the halogen-
exchange product 3 in 40% yield (64 mg).9
The reduction of 1 (100 mg, 0.19 mmol) with Mg in
the presence of an excess of diphenylacetylene (320 mg,
1.8 mmol) gave the unexpected 1,2-dihydro-1,2-diger-
macyclobutene 5 in 36% yield (27 mg).10,11 The struc-
ture of 5, determined by single-crystal X-ray diffraction,
is shown in Figure 1.12 The Ge2C2 trapezoidal core has
planarity (torsional angle 1.08°). The bulky substitu-
ents inhibit free rotation of the two phenyl groups and
spread the angle Ge(1)-C(1)-C(101) to 130(1)° and Ge-
(2)-C(2)-C(201) to 129.1(9)°; also, the C(1)-C(101) and
C(2)-C(201) bond lengths are 1.52(2) and 1.50(2) Å,
which are near the length of a carbon-carbon single
bond. Interestingly, although an isolated (trisyl)chlo-
rogermylene-LiCl complex (6; 120 mg, 0.2 mmol)4 did
not react with diphenylacetylene,13 5 was formed in the
presence of magnesium (35 mg) in 16% yield (13 mg)14
(Scheme 3). These results would suggest that in the
present case a reactive intermediate is generated by
single-electron transfer from magnesium to the halog-
ermylene. Electron-transfer reactions of a stable ger-
mylene have been reported15 to produce germylene
anion radicals. Such electron transfer from magnesium
to the halogermylene might be expected to result in
dimerization of anion radical 7 to form the 1,2-dihalo
digerma 1,2-dianion (Scheme 4). The latter then could
(9) Chlorogermacyclopent-3-ene: colorless crystals; decomp >300 °C;
1H NMR (C6D6, 300 MHz) δ 0.32 (s, 27H, SiCH3), 1.72 (s, 3H, CCH3),
2.07-2.23 (m, 4H, GeCH2), 5.63 (m, 1H, CH2CH); 13C NMR (C6D6, 75
MHz) δ 4.5 (SiCH3), 8.0 (GeCSi), 22.6 (CCH3), 31.0 (GeCH2C), 33.6
(GeCH2CH), 123.8 (GeCH2CH), 138.3 (GeCH2C); MS (EI) m/z 393 (M+
- Me).
(10) 5: colorless crystals: decomp >300 °C; 1H NMR (C6D6, 300
MHz) δ 0.33 (s, 54H, SiCH3), 6.03 (s, 2H, GeH), 6.90-7.10 (m, 10H,
C6H5); 13C NMR (C6D6, 75 MHz) δ 5.1 (SiCH3), 30.1 (GeCSi), 127.5
(C6H5), 127.8 (C6H5), 129.4 (C6H5), 141.7 (CC6H5), 166.6 (GeCC6H5);
MS (EI) m/z 788 (M+). Anal. Calcd for C34H66Si6Ge: C, 51.78; H, 8.44.
Found: C, 51.04; H, 7.73.
(11) When 1 was reacted with magnesium/magnesium dibromide
in the absence of diphenylacetylene, tetrahedro-tetragermane2a was
not formed. Only an oligogermane and tris(trimethylsilyl)methane were
obtained.
(12) Crystal data for 5: fw 788.60, triclinic, with a ) 13.668(5) Å, b
(13) An isolated (trisyl)chlorogermylene-LiCl complex (6; 120 mg,
0.2 mmol) was stirred in THF containing an excess of diphenylacety-
lene (250 mg, 1.5 mmol) for 24 h, and then 2-methyl-1,3-butadiene
was added to the reaction mixture; only the [1 + 4] adduct chlorog-
ermacyclopent-3-ene was obtained in 45% yield (36 mg). No dipheny-
lacetylene adduct was obtained.
(14) Reaction of 6 (120 mg, 0.2 mmol) with Mg (35 mg) in the
presence of an excess of diphenylacetylene (320 mg, 1.8 mmol) gave 5
(13 mg) in 16% yield.
) 16.182(10) Å, c ) 20.095(17) Å, R ) 90.11(7)°, â ) 79.70(6)°, γ )
90.09(4)°, V ) 4372.9 Å3, space group P21/a, Z ) 4, µ(Mo KR) 15.4 cm-1
,
F(calcd) 1.20 g/cm3. A total of 2695 independent reflections (2θ e 50°;
2
2
|Fo| g 3σ|Fo| ) were measured on an Enraf-Nonius CAD4 diffracto-
meter using Mo KR irradiation and ω-2θ scan. An empirical absorption
correction based on a series of ψ scans were applied to the data 0.86/
1.00. The structure was solved by direct methods, and hydrogen atoms
were located and added to the structure factor calculations, but their
positions were not refined. All non-hydrogen atoms were refined
anisotropically to R ) 0.049 (Rw ) 0.056).
(15) Egorov, M. P.; Nefedov, O. M.; Lin, T.; Gaspar, P. P. Organo-
metallics 1995, 14, 1539.

4958 Organometallics, Vol. 16, No. 23, 1997
Communications
undergo the elimination of halogen to form the diger-
maacetylene (digermyne) 9, the [2 + 2] cycloaddition of
which with diphenylacetylene then would form 1,2-
digermacyclobutadiene 10, which would need to abstract
two hydrogen atoms from the solvent to give the isolated
product 5. Due to the steric hindrance of the bulky
trisyl groups, the 1,4-digerma Dewar benzene species
11 could not be formed by addition of 2 mol of diphe-
nylacetylene. That 5 might be formed from 1,2-diger-
macyclobutadiene 10 is suggested by the formation of
the 1,2-dihydro-1,2-digermacyclobutene compound 14
(89% yield) in the reaction of 1,2-dichloro-1,2-digerma-
cyclobutene 12 with magnesium/ magnesium dibro-
mide16 and also the formation of 1,4-digermabicyclo-
[2.2.0]hexene 15 (64% yield) in the presence of an excess
of styrene17 (Scheme 5). A disilyne intermediate, the
silicon analog of a digermyne, has been suggested to be
involved in the formation of 1,2-dihydro-1,2-disilacy-
clobutene in the reduction of a tetrabromodisilane, RBr2-
SiSiBr2R (R ) tri-tert-butylsilyl).18 However, we point
out that there is no firm evidence for such a reduction-
course. While the intermediacy of digermyne is an
intriguing possibility, the reaction course above is,
admittedly, speculative.
Ack n ow led gm en t. We are grateful to Asai Germa-
nium Institute and Shin-Etsu Co. Ltd. for their gifts of
trichlorogermane and chlorosilanes. This work was
supported by Research Fellowships of the J apan Society
for the Promotion of Science for Young Scientists and a
Grant-in-Aid for Scientific Research on Priority Area
(Grant No. 09239101) from the Ministry of Education,
Science and Culture of J apan.
Su p p or tin g In for m a tion Ava ila ble: Text giving details
of the X-ray crystal structure study and tables of crystal
structure determination data, atomic coordinates, anisotropic
thermal parameters, and bond lengths and angles for com-
pound 5 and text giving details of experimental procedures
(23 pages). Ordering information is given on any current
masthead page.
OM970371X
(17) In the presence of an excess of styrene the reaction of 12 (60
mg, 0.077 mmol) with Mg (35 mg)/MgBr2 (120 mg) gave 1,4-digerma-
2,5-diphenylbicyclo[2.2.0]hex-2-ene 15 in 64% yield (40 mg) and 14 in
36% yield (14 mg). 15: colorless crystals; decomp 185 °C; 1H NMR
(C6D6, 300 MHz) δ 0.25 (bs, 27H, SiCH3), 0.40 (s, 27H, SiCH3), 2.49
(dd, J ) 5.2, 13.0 Hz, 1H, GeCH2CH(C6H5)Ge), 2.98 (dd, J ) 11.7, 13.0
(16) The reaction of 6 with phenylacetylene gave the 1,2-dichloro-
1,2-digermacyclobutene 12.4 Dehalogenation of 12 (70 mg, 0.090 mmol)
with magnesium (35 mg)/magnesium dibromide (120 mg) gave the 1,2-
dihydro-1,2-digermacyclobutene 14 in 89% yield (56 mg). 14: white
powder; decomp 203-204 °C; 1H NMR (C6D6, 300 MHz) δ 0.31 (s, 27H,
SiCH3), 0.40 (s, 27H, SiCH3), 5.58 (d, J ) 2.1 Hz, 1H, C6H5CGeHGeH),
6.02 (dd, J ) 2.1, 5.8 Hz, 1H, GeHGeHCH), 7.02-7.08 (m, 1H, C6H5),
7.11-7.18 (m, 2H, C6H5), 7.27-7.32 (m, 2H, C6H5), 7.41 (d, J ) 5.8
Hz, 1H, GeHCHC6H5); 13C NMR (C6D6, 75 MHz) δ 4.4 (SiCH3), 4.7
(SiCH3), 13.4 (GeCSi), 14.0 (GeCSi), 127.2 (C6H5), 127.4 (C6H5), 128.1
(C6H5), 145.1 (CC6H5), 156.8 (GeCHCC6H5), 174.0 (GeCPhCH); MS (EI)
m/z 712 (M+). Anal. Calcd for C28H62Si6Ge2: C, 47.23; H, 8.78. Found:
C, 46.92; H, 7.73.
Hz, 1H, GeCH2sCH(C6H5)Ge), 4.05 (dd,
J ) 5.2, 13.0 Hz, 1H,
GeCH2sCH(C6H5)Ge), 7.00-7.19 (m, 6H, C6H5), 7.52 (s, 1H, GeCHdC-
(C6H5)Ge), 7.53-7.70 (m, 4H, C6H5); 13C NMR (C6D6, 75 MHz) δ 5.1
(SiCH3), 5.4 (SiCH3), 10.3 (GeCSi), 17.2 (GeCSi), 39.4 (GeCH2sCH-
(C6H5)Ge), 48.3 (GeCH2sCH(C6H5)Ge), 125.1 (C6H5), 126.3 (C6H5),
127.9 (C6H5), 128.1 (C6H5), 128.5 (C6H5), 129.3 (C6H5), 146.4
(GeCH2sCH(C6H5)Ge), 148.4 (GeC(C6H5)dCHGe), 153.8 (GeC-
(C6H5)dCHGe), 170.2 (GeC(C6H5)dCHGe); MS (EI) m/z 710 (M+
CH2dCH(C6H5)). Anal. Calcd for C36H68Si6Ge2: C, 53.08; H, 8.41.
Found: C, 52.87; H, 8.27.
-
(18) Wiberg, N.; Finger, C. M. M.; Auner, H.; Polborn, K. J .
Organomet. Chem. 1996, 521, 377.