New fused bicyclic cyclotrigermanes from cycloaddition reactions of cyclotrigermene

Article abstract of DOI:10.1002/1521-3773(20001103)39:21<3881::AID-ANIE3881>3.0.CO;2-3

The mesityl-substituted cyclotrigermene 1 underwent [2+4] cycloaddition with isoprene and 2,3-dimethyl-1,3-butadiene to yield 1,6,7-trigerma-7-mesitylbicyclo[4.1.0]hept-3-ene derivatives 2, and [2+2] cycloaddition with phenylacetylene to yield 1,4,5-trige

Full text of DOI:10.1002/1521-3773(20001103)39:21<3881::AID-ANIE3881>3.0.CO;2-3

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reaction mixture was stirred for 1 hbefore it was allowed to warm to
ambient temperature. After the mixture had been stirred for a further 24 h,
a cloudy yellow/brown solution was produced. The mixture was filtered
through Celite, cooled to À208C, and left to stand for 12 h, resulting in the
precipitation of small, colorless crystals of 1. Yield 60.5%; m.p. >3008C; IR
Crystallographic Data Centre as supplementary publication no.
CCDC-142922. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK >fax:
>‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
[10] a) D. A. Atwood, D. Rutherford, Organometallics 1996, 15, 436;
b) D. A. Atwood, D. Rutherford, J. Am. Chem. Soc. 1996, 118, 11535.
[11] Gaussian 94, revision E. 2. No constraints were used in any of the
calculations. M. J. Frisch, G. W. Trucks, H. B. Schlegel, P. M. W. Gill,
B. G. Johnson, M. A. Robb, J. R. Cheeseman, T. Keith, G. A.
Petersson, J. A. Montgomery, K. Raghavachari, M. A. Al-Laham,
V. G. Zakrzewski, J. V. Ortiz, J. B. Foresman, J. Cioslowski, B. B.
Stefanov, A. Nanayakkara, M. Challacombe, C. Y. Peng, P. Y. Ayala,
W. Chen, M. W. Wong, J. L. Andres, E. S. Replogle, R. Gomperts,
R. L. Martin, D. J. Fox, J. S. Binkley, D. J. Defrees, J. Baker, J. P.
Stewart, M. Head-Gordon, C. Gonzalez, J. A. Pople, Gaussian Inc.,
PittsburghPA, 1995.
>Nujol): nĈ 1775 cmÀ1 >Al H); elemental analysis calcd for C60H94Al4Li4-
À
N6O6 >%): C 63.72, H 8.32, N 7.43; found: C 63.45, H 7.55, N 8.70; 1HNMR
>variable-temperature studies showed only one set of resonances >with
broadening) in the range 300 ± 193 K; 400.13 MHz, C6D6, 300 K): d ˆ 7.76
>d, 2H; o-H, Ph), 7.16 >t, 2H; m-H, Ph), 6.74 >t, 1H; p-H, Ph), 5.40 >v br.,
1H; AlH), 2.88 >q, 4H; OCH2), 0.60 >t, 6H; CH3); 13CNMR >100.62 MHz,
C6D6, 300 K): d ˆ 156.70 >i-C; Ph), 129.21 >m-C; Ph), 124.88 >o-C; Ph),
7
117.58 >p-C; Ph), 65.33 >OCH2), 13.66 >CH3); Li NMR >variable-temper-
ature studies showed only a single resonance in the range 300 ± 213 K but
the appearance of a second resonance at 193 K; 155.51 MHz, referenced to
LiCl in D2O, [D8]toluene, 193 K): d ˆ 6.75, d 6.58; 27Al NMR >C6D6, 298 K,
52.12 MHz, referenced to AlCl3 in D2O): d ˆ 131.30, 69.91.
Received: April 25, 2000 [Z15042]
[1] A. C. Jones, Chem. Soc. Rev. 1997, 101.
[2] a) H. Yamomoto in Organometallics in Synthesis >Ed.: M. Schlosser),
Wiley, Chichester, UK, 1994, chap. 7; b) Y. Koide, S. G. Bott, A. R.
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[3] M. A. Petrie, S. C. Shoner, H. V. R. Dias, P. P. Power, Angew. Chem.
1990, 102, 1061; Angew. Chem. Int. Ed. Engl. 1990, 29, 1033.
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1628; b) R. E. Allan, M. A. Beswick, P. R. Raithby, A. Steiner, D. S.
Wright, J. Chem. Soc. Dalton Trans. 1996, 4153; c) R. E. Allan, M. A.
Beswick, N. L. Cromhout, M. A. Paver, P. R. Raithby, A. Steiner, M.
Trevithick, D. S. Wright, Chem. Commun. 1996, 1501.
[5] a) A. J. Edwards, M. A. Paver, P. R. Raithby, M.-A. Rennie, C. A.
Russell, D. S. Wright, Angew. Chem. 1994, 106, 1334; Angew. Chem.
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A. D. Hopkins, M. McPartlin, M. A. Paver, P. R. Raithby, A. Steiner,
M. Tombul, D. S. Wright, Inorg. Chem. 1998, 37, 2177; c) M. A.
Beswick, J. M. Goodman, C. N. Harmer, A. D. Hopkins, M. A. Paver,
P. R. Raithby, A. E. H. Wheatley, D. S. Wright, Chem. Commun. 1997,
1879.
New Fused Bicyclic Cyclotrigermanes from
Cycloaddition Reactions of Cyclotrigermene**
Norihisa Fukaya, Masaaki Ichinohe, and
Akira Sekiguchi*
The chemistry of three- and four-membered ring systems
consisting of Group 14 elements heavier than carbon is a
subject of considerable interest.[1] The thermal and photo-
chemical conversion of cyclotrigermanes into digermenes and
germylenes is well established and has been used for the
synthesis of a variety of novel germanium compounds.[2]
However, cyclotrigermane derivatives incorporating a bicyclic
system are completely unknown for synthetic reasons.[3, 4]
Most of the cyclotrigermane derivatives were synthesized by
the simple reductive coupling reaction of the corresponding
diorganodihalogermane with the appropriate reducing
agents.[1, 2] Recently, we succeeded in synthesizing a variety
of cyclotrigermene analogues of cyclopropene by reaction of
the cyclotrigermenium ion with nucleophiles.[5] The reactivity
of the cyclotrigermenes is of special interest, since cyclo-
[6] L. Zsolnai, G. Huttner, M. Driess, Angew. Chem. 1993, 105, 1549;
Angew. Chem. Int. Ed. Engl. 1993, 32, 1439.
[7] a) P. Kosse, E. Popowski, M. Veith, V. Huch, Chem. Ber. 1994, 127,
2103; b) D. J. Brauer, H. Bürger, G. R. Liewald, J. Wilke, J. Organo-
met. Chem. 1985, 287, 305; c) D. J. Brauer, H. Bürger, G. R. Liewald, J.
Organomet. Chem. 1986, 308, 119; d) G. Huber, A. Jockisch, H.
Schmidbaur, Z. Naturforsch. B 1999 54, 8; e) M. Veith, A. Spaniol, J.
Pöhlmann, F. Gross, V. Huch, Chem. Ber. 1993, 126, 2625; f) M. Driess,
G. Huttner, N. Knopf, H. Pritzkow, L. Zsolnai, Angew. Chem. 1995,
107, 354; Angew. Chem. Int. Ed. Engl. 1995, 34, 316.
ˆ
addition to the endocyclic Ge Ge bond could provide access
[8] J. L. Atwood, F. R. Bennett, F. M. Elms, C. Jones, C. L. Raston, K. D.
Robinson, J. Am. Chem. Soc. 1991, 113, 8183.
to new bicyclic compounds. We now report the synthesis of the
first bicyclic cyclotrigermane derivatives by the reaction of a
mesityl-substituted cyclotrigermene withisoprene, 2,3-di-
methyl-1,3-butadiene, and phenylacetylene.
[9] Crystal structure data for 1: C60H94Al4Li4N6O6, Mr ˆ 1131.1, colorless
plates, cut to approximately 0.60 Â 0.40 Â 0.20 mm. MoKa graphite-
monochromated radiation >l ˆ 0.71069 Š), Tˆ 123 K; monoclinic,
space group C2/c; a ˆ 22.035>6), b ˆ 12.818>3), c ˆ 46.487>6) Š; b ˆ
After the successful synthesis of tetrakis>tri-tert-butylsilyl)-
cyclotrigermene >tBu3Si)4Ge3 >1a)[6] and tetrakis>tri-tert-bu-
tylgermyl)cyclotrigermene >tBu3Ge)4Ge3 >1b)[6] by reaction
of GeCl2>dioxane) with tBu3SiNa or tBu3GeLi, we presumed
that the cyclotrigermenes should be suitable as precursors of
90.581>15)8; Vˆ 13129>5) Š3, Z ˆ 8, m ˆ 0.121 mmÀ1
,
1calcd
ˆ
1.144 MgmÀ3, 2qmax ˆ 468, 8786 reflections collected, 8509 unique
used >Rm ˆ 0.0650). The structure was solved and refined on F2 using
published programs and techniques >a) A. Altomare, M. C. Burla, M.
Camalli, G. Cascarano, C. Giacovazzo, A. Guagliardi, G. Polidori, J.
Appl. Crystallogr. 1994, 27, 435; b) G. M. Sheldrick, SHELXL-97.
University of Gottingen, Germany, 1997) to convergence at R1 ˆ
0.0917 >for 4592 reflections with I > 2s>I)), wR2 ˆ 0.2271 and S ˆ
1.064 for 777 parameters. Maximum residual electron density
0.505 eŠÀ3. Several factors combined to adversely affect the quality
of the solution. The crystals reacted with the oil used to mount them
and the large c axis gave overlapping reflections. Additionally the
ether groups of the cation were severely disordered over two sites
each. There was also some movement in the phenyl ring bonded to N6.
Crystallographic data >excluding structure factors) for the structure
reported in this paper have been deposited with the Cambridge
[*] Prof. Dr. A. Sekiguchi, Dipl.-Chem. N. Fukaya, Dr. M. Ichinohe
Department of Chemistry, University of Tsukuba
Tsukuba, Ibaraki 305-8571 >Japan)
Fax : >‡81)298-53-4314
E-mail: sekiguch@staff.chem.tsukuba.ac.jp
[**] This work was supported by a Grant-in-Aid for Scientific Research
>Nos. 10304051, 12020209, 12042213) from the Ministry of Education,
Science and Culture of Japan, and TARA >Tsukuba Advanced
ResearchAlliance) Fund.
Angew. Chem. Int. Ed. 2000, 39, No. 21
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bicyclic cyclotrigermanes. Nevertheless, all attempted reac-
tions of 1a,b withvarious dienes or acetylenes failed due to
the steric overcrowding of 1a,b. However, we found that
1,2,3-tris>tri-tert-butylsilyl)-3-mesitylcyclotrigermene
>2)[5]
ˆ
shows relatively high reactivity at the Ge Ge bond due to
the decrease in steric crowding on replacing one tBu3Si group
at the saturated germanium atom with a mesityl group. The
reaction of 2 with2,3-dimethyl-1,3-butadiene in hexane at
room temperature produced the Diels ± Alder adduct 3a as a
yellow, air-stable crystalline compound in 63% yield
>Scheme 1). The reaction of 2 withisoprene gave 3b in 78%
yield. These [2‡4] cycloadducts were isolated by chromatog-
raphy on silica gel without any decomposition. The NMR
spectral data and X-ray crystal structure suggest the formation
of just one of the two possible stereoisomers.
SitBu3
Ge
Figure 1. Structure of 3b >ORTEP plot; hydrogen atoms omitted for
R
Me
Ge
R
Ge
Me
tBu3Si
SitBu3
À
clarity). Selected bond lengths [Š] and angles [8]: Ge1 Ge2 2.5938>3),
hexane, RT
À
À
À
À
Ge1 Ge3 2.6068>3), Ge2 Ge3 2.4705>3), Ge1 Si1 2.5529>7), Ge2 Si2
SitBu3
À
À
À
2.4873>6), Ge3 Si3 2.5314>7), Ge1 C37 2.029>2), Ge2 C46 2.048>2),
Ge
À
3a: R = Me
3b: R = H
Ge3 C49 2.050>2); Ge2-Ge1-Ge3 56.724>9), Ge3-Ge2-Ge1 61.903>9),
Ge2-Ge3-Ge1 61.374>9).
Ge
Ge
tBu3Si
SitBu3
SitBu3
>typically 2.460 ± 2.590 Š).[1, 2] In contrast, the Ge2 Ge3 bond
is appreciably shorter >2.4705>3) Š), probably due to the
effect of the fused ring system.
À
Ge
2
Ph
H
Ge Ge
tBu3Si
SitBu3
C6D6, 70 °C
Ph
The [2‡2] cycloaddition of 2 withphenylacetylene at 70 8C
smoothly proceeded to give the more strained molecule 4
>Scheme 1), which was isolated as orange crystals of the two
isomers 4a >57%) and 4b >22% yield).
The molecular structure of the favored isomer 4a was
determined by X-ray crystallography >Figure 2).[7] The three
4a
+
SitBu3
Ge
Ge Ge
Ph
tBu3Si
SitBu3
4b
Scheme 1. Synthesis of 3 and 4.
The molecular structure of 3b was determined by X-ray
diffraction >Figure 1).[7] It reveals that isoprene attacked the
ˆ
Ge Ge bond from the mesityl side of the three-membered
ring to give only one stereoisomer. The difference in the steric
bulk of the substituents on the sp3 Ge atom of 2 >Mes <
tBu3Si) apparently can control the facial selectivity in the
[2‡4] cycloaddition. The three tBu3Si groups in 3b are
arranged in the same direction relative to the three-mem-
bered cyclotrigermane skeleton. Due to the large steric bulk
of the tBu3Si group, the three tBu3Si groups occupy the less
hindered pseudoequatorial positions, whereas the mesityl
ˆ
group and the CH2C>Me) CHCH2 moiety occupy the pseu-
doaxial positions, as determined by the angles between the
Figure 2. Structure of 4a >ORTEP plot; hydrogen atoms omitted for
À
À
clarity). Selected bond lengths [Š] and angles [8]: Ge1 Ge2 2.5958>5),
three-membered ring plane and the Ge R bond >R ˆ tBu3Si,
À
À
À
À
Ge1 Ge3 2.5592>4), Ge2 Ge3 2.4857>4), Ge1 Si1 2.5248>9), Ge2 Si2
ˆ
CH2C>Me) CHCH2, and Mes): 29.68 for tBu3Si, 100.88 for
À
À
À
2.4780>9), Ge3 Si3 2.4797>9), Ge1 C37 2.032>3), Ge2 C46 1.963>3),
ˆ
À
CH2C>Me) CHCH2, and 106.68 for Mes. The Ge1 Ge2
>2.5938>3) Š) and Ge1 Ge3 >2.6068>3) Š) bond lengths lie
in the upper range of known values for cyclotrigermanes
À
À
Ge3 C47 2.021>3), C46 C47 1.357>4); Ge3-Ge1-Ge2 57.65>1), Ge3-Ge2-
Ge1 60.44>1), Ge2-Ge3-Ge1 61.91>1), C46-Ge2-Ge3 73.36>9), C47-Ge3-
Ge2 73.66>9), C47-C46-Ge2 109.1>2), C46-C47-Ge3 103.8>2).
À
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were removed in vacuo, and the resulting residue was separated by column
chromatography on silica gel with hexane as eluent to give 4a >57 mg, 57%)
and 4b >22 mg, 22%). 4a: orange crystals; m.p. 178 ± 1808C; 1H NMR
>[D6]benzene, TMS): d ˆ 1.30 >s, 27H), 1.37 >s, 27H), 1.40 >s, 27H), 1.89 >s,
3H), 2.67 >s, 3H), 3.11 >s, 3H), 6.59 >s, 1H), 6.61 >s, 1H), 6.82 ± 6.99 >m,
5H), 7.24 >s, 1H); 13C{1H} NMR >[D6]benzene, TMS): d ˆ 20.9, 25.5, 26.0,
26.4, 29.3, 30.8, 32.3, 32.7, 33.2, 125.7, 126.1, 127.3, 128.5, 128.7, 129.8, 130.0,
136.1, 143.1, 143.5, 144.7, 145.5, 155.9, 170.8; 29Si{1H} NMR >[D6]benzene,
TMS): d ˆ 38.5, 44.7, 50.0; UV/Vis >n-hexane): lmax >e) ˆ 250 >46700), 303
>21930), 410 nm >2410); 4b: orange crystals; m.p. 90 ± 93 C; 1H NMR
>[D6]benzene, TMS): d ˆ 1.19 >s, 27H), 1.27 >s, 27H), 1.38 >s, 27H), 2.11 >s,
3H), 2.99 >s, 3H), 3.18 >s, 3H), 6.81 >s, 2H), 7.06 >t, J ˆ 7.8 Hz, 1H), 7.22 >t,
J ˆ 7.8 Hz, 2H), 7.45 >d, J ˆ 7.8 Hz, 2H), 7.52 >s, 1H); 13C{1H} NMR
>[D6]benzene, TMS): d ˆ 21.2, 25.8, 26.0, 26.5, 30.3, 31.0, 32.3, 32.4, 33.6,
126.5, 127.2, 128.0, 128.1, 129.1, 137.3, 140.7, 143.6 >2C), 145.7, 153.0, 167.4;
29Si{1H} NMR >[D6]benzene, TMS): d ˆ 39.6, 45.5, 49.4; UV/Vis >n-
hexane): lmax >e) ˆ 240 >41200), 302 >20900), 400 nm >2500).
tBu3Si groups are situated in cis,cis positions, as in 3b, and the
bicyclo[2.1.0] skeleton is highly folded to relieve steric
repulsion, as shown by the dihedral angle between the planes
of the three- and four-membered rings >97.48).
It is noteworthy that 3 is a good precursor of germylene and
digermene under mild conditions. Thermolysis of cyclotriger-
mane 3a at 708C in dry C6D6 for 3 hin the presence of an
excess of 2,3-dimethyl-1,3-butadiene cleanly yielded germa-
cyclopent-3-ene 7 >80%) and digermabicyclo[4.4.0]deca-3,8-
diene 8 >86%), clear evidence for the trapping of the
germylene 5 and the digermene 6, respectively >Scheme 2).
However, heating of 3 in the solid state at 1808C in vacuo led
to the quantitative formation of 2 by retro-Diels ± Alder
reaction.
Received: May 16, 2000 [Z15130]
Mes
SitBu3
Mes
SitBu3
Ge
Ge
[1] For general reviews on the chemistry of Si, Ge, Sn,
Me
Me
Me
5
+
and Pb, see: a) The Chemistry of Organic Germa-
7
nium, Tin and Lead Compounds >Ed.: S. Patai),
Wiley, Chichester, 1995; b) The Chemistry of Or-
ganic Silicon Compounds, Vol. 2 >Eds.: Z. Rappo-
port, Y. Apeloig), Wiley, New York, 1998.
70 °C
C6D6
Me
Me
SitBu3
tBu3Si
3a
Ge Ge
Me
[2] Reviews: a) T. Tsumuraya, S. A. Batcheller, S.
Masamune, Angew. Chem. 1991, 103, 916; Angew.
Me
Me
tBu3Si Ge Ge
SitBu3
6
Â
Chem. Int. Ed. Engl. 1991, 30, 902; b) J. Escudie, C.
Me
Me
Â
Couret, H. Ranaivonjatovo, J. Satge, Coord. Chem.
8
Rev. 1994, 130, 427; c) M. Weidenbruch, Chem. Rev.
1995, 95, 1479; d) M. Driess, H. Grützmacher,
Angew. Chem. 1996, 108, 900; Angew. Chem. Int.
Ed. Engl. 1996, 35, 828; e) K. M. Baines, W. G.
Scheme 2. Thermolysis of 3a and trapping of the thermolysis products.
The present [2‡4] and [2‡2] cycloaddition reactions of
cyclotrigermenes cleanly afford fused bicyclic cyclotriger-
mane derivatives and thus provide a new route to small ring
systems of Group 14 elements heavier than carbon.
Stibbs, Adv. Organomet. Chem. 1996, 39, 275; f) M. Weidenbruch, Eur.
J. Inorg. Chem. 1999, 373.
[3] Related three- and four-membered ring systyems of Si, Ge, and Sn:
Cyclotrisilenes: a) T. Iwamoto, C. Kabuto, M. Kira, J. Am. Chem. Soc.
1999, 121, 886; b) M. Ichinohe, T. Matsuno, A. Sekiguchi, Angew.
Chem. 1999, 111, 2331; Angew. Chem. Int. Ed. 1999, 38, 2194;
cyclotrigermenes: see refs. [5] and [6]; Cyclotrigermenium ions: c) A.
Sekiguchi, M. Tsukamoto, M. Ichinohe, Science 1997, 275, 60; d) M.
Ichinohe, N. Fukaya, A. Sekiguchi, Chem. Lett. 1998, 1045; e) A.
Sekiguchi, N. Fukaya, M. Ichinohe, Y. Ishida, Eur. J. Inorg. Chem. 2000,
1155; cyclotrigermenyl radical: f) M. M. Olmsted, L. Pu, R. S. Simons,
P. P. Power, Chem. Commun. 1997, 1595; cyclotristannene: g) N.
Wiberg, H.-W. Lerner, S.-K. Vasisht, S. Wagner, K. Karaghiosoff, H.
Nöth, W. Ponikwar, Eur. J. Inorg. Chem. 1999, 1211; cyclotetrasilenes:
h) M. Kira, T. Iwamoto, C. Kabuto, J. Am. Chem. Soc. 1996, 118, 10303;
i) T. Iwamoto, M. Kira, Chem. Lett. 1998, 277; j) N. Wiberg, H. Auer, H.
Nöth, J. Knizek, K. Polborn, Angew. Chem. 1998, 110, 3030; Angew.
Chem. Int. Ed. 1998, 36, 2869.
[4] For polyhedral germanium compounds containing three-membered
rings, see: a) A. Sekiguchi, C. Kabuto, H. Sakurai, Angew. Chem. 1989,
101, 97; Angew. Chem. Int. Ed. Engl. 1989, 28, 55; b) A. Sekiguchi, T.
Yatabe, C. Kabuto, H. Sakurai, J. Am. Chem. Soc. 1993, 115, 5853; c) N.
Wiberg, W. Hochmuth, H. Nöth, A. Appel, M. Schmidt-Amelunxen,
Angew. Chem. 1996, 108, 1437; Angew. Chem. Int. Ed. Engl. 1996, 35,
1333.
Experimental Section
3a: Orange crystals of 2 >60 mg, 0.064 mmol) were placed in a reaction
vessel witha magnetic stirrer. Dry, degassed hexane >1.5 mL) and 2,3-
dimethyl-1,3-butadiene >70 mg, 0.85 mmol) were introduced by vacuum
transfer, and the mixture was stirred for 6 h at room temperature. The
solvent and excess 2,3-dimethyl-1,3-butadiene were removed in vacuo, and
the resulting residue was separated by column chromatography on silica gel
withhexane as eluent to give 3a >41 mg, 63%) as yellow crystals; m.p. 123 ±
1268C >decomp); 1H NMR >[D6]benzene, TMS): d ˆ 1.30 >s, 27H), 1.37 >s,
54H), 1.70 >s, 6H), 1.90 >s, 3H), 2.60 >s, 2H), 2.64 >s, 2H), 2.80 >s, 6H),
6.78>s, 2H); 13C{1H} NMR >[D6]benzene, TMS): d ˆ 14.3, 23.0, 25.6, 26.8,
28.4, 29.9, 32.9, 33.5, 126.6, 128.8, 129.1, 137.0, 144.8; 29Si{1H} NMR
>[D6]benzene, TMS): d ˆ 45.9, 49.4; UV/Vis >n-hexane): lmax >e) ˆ 277
>18950), 388 nm >1740); elemental analysis calcd for C51H102Ge3Si3 >%): C
60.21, H 10.10; found: C 60.14, H 10.17.
3b: Compound 3b was prepared in 78% yield as yellow crystals; m.p. 130 ±
1328C >decomp); 1H NMR >[D6]benzene, TMS): d ˆ 1.30 >s, 27H), 1.35 >s,
27H), 1.37 >s, 27H), 1.84 >s, 3H), 1.97 >s, 3H), 2.57 ± 2.61 >m, 2H), 2.70 ±
2.73 >m, 1H), 2.79 >s, 3H), 2.80 >s, 3H), 2.95 ± 3.00 >m, 1H), 5.51 ± 5.53 >m,
1H), 6.78 >s, 2H); 13C{1H} NMR >[D6]benzene, TMS): d ˆ 20.9, 22.7, 25.6,
25.8, 26.8, 26.9, 27.0, 28.0, 28.6, 32.8, 32.9, 33.4, 123.3, 129.0, 129.1, 132.0,
137.0, 143.7, 144.5, 144.8; 29Si{1H} NMR >[D6]benzene, TMS): d ˆ 45.3, 45.4,
47.9; UV/Vis >n-hexane): lmax >e) ˆ 277 >16860), 388 nm >1520); elemental
analysis calcd for C50H100Ge3Si3 >%): C 59.85, H 10.04; found: C 59.74, H
10.06.
[5] A. Sekiguchi, N. Fukaya, M. Ichinohe, N. Takagi, S. Nagase, J. Am.
Chem. Soc. 1999, 121, 11587.
[6] A. Sekiguchi, H. Yamazaki, C. Kabuto, H. Sakurai, S. Nagase, J. Am.
Chem. Soc. 1995, 117, 8025.
[7] Diffraction data were collected at 120 K for 3b and 150 K for 4a on a
Mac Science DIP2030 Image Plate Diffractometer witha rotating
anode >50 kV, 90 mA) and graphite-monochromated MoKa radiation
>l ˆ 0.71070 Š). The structures were solved by direct methods and
refined by full-matrix least-squares method with the SHELXL-97
program. Crystal data for 3b ´ C7H8: C57H108Ge3Si3, Mr ˆ 1095.47,
monoclinic, space group P21/n, a ˆ 15.2160>3), b ˆ 13.6410>3), c ˆ
4a and 4b: Orange crystals of 2 >60 mg, 0.064 mmol) were placed in a
reaction tube. Dry, degassed benzene >0.5 mL) and phenylacetylene
>90 mg, 0.88 mmol) were introduced by vacuum transfer, and the mixture
was heated for 6 h at 708C. The solvent and the excess phenylacetylene
29.2430>5) Š, b ˆ 99.810>1)8, Vˆ 5981.0>2) Š3, Z ˆ 4, 1calcd
ˆ
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1.217 gcmÀ3. The final R factor was 0.0461 >Rw ˆ 0.1328) for 12902
and the structure of the resulting unique polyoxometalate
withmultiple terminal halide ligands.
reflections with I > 2s>I). Crystal data for 4a ´ 0.5C6H14: C56H105Ge3Si3,
Å
Mr ˆ 1080.47, triclinic, space group ˆ P1, a ˆ 13.7810>7), b ˆ 14.485>1),
The bromoanion [PW9O28Br6]3À >1) was initially obtained as
one of the products from the reaction between >nBu4N)6-
[NaPW11O39][5] and C2O2Br2 in an attempt to attachoxalate
groups to the surface of the PW11 Keggin fragment. The
acetonitrile solvate of >nBu4N)3-1 crystallized as yellow
crystals along withcolorless crystals of > nBu4N)2[W2O4-
Br4>m-C2O4)] and bothcompounds were structurally charac-
terized by single-crystal X-ray diffraction.[6] The bromoanion
1 has the b,A-PW9 structure >Figure 1), and is formally
c ˆ 15.339>1) Š, a ˆ 100.917>3), b ˆ 91.953>4), g ˆ 95.408>4)8, Vˆ
2988.9>3) Š3, Z ˆ 2, 1calcd ˆ 1.201 gcmÀ3. The final R factor was 0.0496
>Rw ˆ 0.1408) for 10780 reflections with I > 2s>I). Crystallographic
data >excluding structure factors) for the structures reported in this
paper have been deposited with the Cambridge Crystallographic Data
Centre as supplementary publication nos. CCDC-144512 and CCDC-
144513. Copies of the data can be obtained free of charge on
application to CCDC, 12 Union Road, Cambridge CB21EZ, UK
>fax: >‡44)1223-336-033; e-mail: deposit@ccdc.cam.ac.uk).
Direct Bromination of Keggin Fragments To
Give [PW9O28Br6]3À: A Polyoxotungstate with a
Hexabrominated Face**
R. John Errington,* Richard L. Wingad, William Clegg,
and Mark R. J. Elsegood
The design and synthesis of polyoxometalates with specific
structures and properties requires synthetic methodologies
that enable framework morphology and surface functionality
to be manipulated in a rational fashion and, although some
progress has been made in recent years, there is still enormous
scope for new, systematic chemistry in this area. Since the
initial work by Knoth,[1] a particularly fruitful approachhas
been the attachment of organometal or organometalloid
groups to lacunary species suchas teh tungstate Keggin
fragments [PW11O39]7À, [SiW11O39]8À, [SiW10O36]8À, [PW9O34]9À,
and [SiW9O34]10À, and derivatives resulting from this strategy
have been reviewed recently.[2] However, reactions involving
the metathesis of labile halides, a ubiquitous method for
ligand manipulation in synthetic organometallic and metal-
organic chemistry, are not generally available for the surface
functionalization of polyoxometalates because of the paucity
of suitable halogenated derivatives. Although several fluo-
ropolyoxoanions have been characterized,[2] and polyoxo-
metalates containing heterometal ± halide bonds have been
prepared from reactions between lacunary anions and hetero-
metal halides,[3] previously reported attempts to halogenate a
polyoxometalate surface to produce reactive M ± X sites
resulted instead in degradation of the polyoxometalate
framework and the production of low-nuclearity oxohalide
complexes.[4] Herein we report the first successful halogen-
ation of Keggin derivatives [PW9O34]9À and [NaPW11O39]6À
Figure 1. Structure of 1 showing also the position of the acetonitrile solvate
molecule. Selected bond lengths [Š] and angles [8] >mean values within W6
ring, values in parentheses are ranges of esds for individual measurements):
W-Br 2.500>2 ± 3), W-Oterm 1.698>10 ± 13), W-O>P) 2.399>10 ± 11), W-O>W)
>edge-sharing) 1.902>11 ± 12), W-O>W) >corner-sharing) 1.881>10 ± 12),
W-O-W >edge-sharing) 125.3>5 ± 6), W-O-W >corner-sharing) 159.9>6-7).
Mean values between W6 and W3 rings: >Br)W-O>W) 1.875>11 ± 13),
>BrW)O-W 1.928>11 ± 14), W-O-W 147.8>6).
derived from the triply vacant lacunary Keggin anion b,
A-[PW9O34]9À by replacement of six terminal oxo ligands with
six bromo ligands, giving a molecular oxide witha fully
brominated face. The structure of the dinuclear anion
[W2O4Br4>m-C2O4)]2À >2) is analogous to that of the molyb-
denum chloro analogue [Mo2O4Cl4>m-C2O4)]2À[7] and will be
reported separately.
À
The mean W Br bond lengthof 2.50 Š in 1 is similar to that
in 2 >2.52 Š) and, although no discrete b,A-[PW9O28X6]
À
structures have previously been reported, W O bond lengths
in 1 are similar to those in a,A-[PW9O34{Si>tBu)OH}3]3À[8] and
in [>PhSnOH)3>b,A-PW9O34)2]12À [9]
.
Another feature of this crystal structure also shown in
Figure 1 is the acetonitrile solvate molecule situated with the
N atom 1.19 Š above the mean plane of the six bromo ligands,
withN ´´´ Br distances of 3.773 ± 4.053 Š. Partial occupancy of
a second acetonitrile molecule position is correlated with
disorder in some cation alkyl chains. The formation of 1 from
[NaPW11O39]6À and C2O2Br2 is consistent witha degradation
process in which initial electrophilic attack at the basic oxide
surface is followed by excision of two WO2Br2 fragments as
the oxalato-bridged dinuclear complex 2.
[*] Dr. R. J. Errington, R. L. Wingad, Prof. Dr. W. Clegg,
Dr. M. R. J. Elsegood
Department of Chemistry
Bedson Building
University of Newcastle upon Tyne
NE1 7RU >UK)
À
ˆ
Bands for n>P O), n>W O), and n>W-O-W) in the IR
spectrum of >nBu4N)3-1 are at higher wavenumbers than those
for Na8H[PW9O34], as previously observed for a,A-
[PW9O34>RPO)2]5À ions.[10] A band at 928 cmÀ1 is low for
Fax : >‡44)191-222-6929
E-mail: John.Errington@ncl.ac.uk
[**] This work was supported by the UK Engineering and Physical
Sciences ResearchCouncil.
ˆ
terminal W O, and may reflect stronger bonding in the
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