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Reactions of Hexa-tert-butylcyclotrigermane Isolation of an Enantiomerically Pure 1 3-Diiodotrigermane.

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Reactions of Hexa-tert-butylcyclotrigermane:
Isolation of an Enantiomerically Pure
Manfred Weidenbruch,* Annette Hagedorn,
Karl Peters, and H a n s Georg von Schnering
Whereas the Si analogue of 4 crystallizes as a racemate," 4
forms a conglomerate of enantiomerically pure crystals on slow
cooling to -25°C. The absolute configuration of the single
crystal that was selected and investigated was determined by the
anomalous scattering of X-rays and is shown in Figure 1.
The hexaarylcyclotrigermanes 1, which have been known since
1982, can be photochemically and thermally converted to tetraaryldigermenes(tetraaryldigermaethenes)2.[11These, in turn, undergo a large variety of addition and cycloaddition reactions,[71
for example with chalcogens,[2-61alkynes,14. 6] and a ~ i d e s . ' ~ .
Hexa-ferf-butylcyclotrigermane 3,[*] the or--; known hexas
to date, behaves rather differently, reacting
with the heavier chalcogens by cleavage of just one Ge-Ge
bond to give the ring-expanded thia-, ~elena-,'~]
and telluratrigermetanes.'l0] We have now found that the reaction with
iodine also occurs with the cleavage of one Ge-Ge bond and
results in the formation of the strained open-chain hexa-tertbutyl-I ,3-diiodotrigermane 4.
According to the crystal structure analysis," 4 assumes the
gauche-trans conformation. The Ge-Ge bonds are of different
lengths (266.0 and 262.2 pm) and considerably stretched in comparison to the normal bond length of 244 pm.["] This length is
only exceeded by the Ge-Ge bond in hexa-tert-butyldigermane
(d = 271 .O pm).['] Trigermane 4 is thus analogous to the strucwhich also
turally related hexa-tert-butyl-l,3-diiodotri~ilane,(~~~
contains extended Si-Si bonds of different lengths.
Prof. Dr. M. Weidenbruch. A. Hagedorn
Fachbereich Chemie der Universitiit
Carl-von-Ossietzky-Strasse 9- 11. D-26111 Oldenburg (Germany)
Telefax: Int. code + (441)798-3329
Dr. K. Peters, Prof. Dr. H. G. von Schnering
Max-Planck-lnstitut fur Festkorperforschung, Stuttgart (Germany)
Compounds of Germanium and Tin, Part 15. This work was supported by the
Deutsche Forschungsgemeinschaft and the Fonds der Chemischen Industrie.
Part 14: M. Weidenbruch, A. Stilter, J. Schlaefke, K . Peters, H. G. von Schnering. J. Orgonomei. Chem. in press.
Fig. 1. Molecular structure of P-4 in the crystal ( H atoms not shown). Selected
bond lengths [pm] and angles I"]: Gel-Ge2 266.0(1), GeI-Ge3 262.2(1), Ce2-I2
261 . O ( l ) , Ge3-I3 260.5(1); Ge2-Gel-Ge3 1 1S.4(1).
Although several hundred conglomerates have been described since their initial discovery by Pasteur," 31 the enantiomers isolated from these almost all owe their chirality to the
presence of stereogenic
In contrast. the chirality in 4
is based on a helical arrangement of the germanium and iodine
atoms, in which the conformers form either a right-handed or a
left-handed helix. This is the first case known to us in which a
simple molecular compound made from heavier elements of
Group 14 (fourth main group) undergoes spontaneous enantiomeric resolution on crystallizing. Intermolecular contacts
that could be significant for the formation of the conglomerate
are not observed, since the I . . . I and I . . . G e distances of
>45O pm are too long for bonding interactions.
Further proof of the presence of a conglomerate is provided
by the melting points of 4; the melting point of the racemate is
21 K lower than that of the pure enantiomers. In solution, 4 may
have a symmetrical structure with unhindered rotation around
the Ge-Ge bonds, as the very simple 'H and I3C NMR spectra
do not reflect the different Ge-Ge bond lengths nor the different orientations of the tert-butyl groups observed in the crystal.
Whereas 3 reacts differently in the absence of light than the
cyclotrigermanes 1, it undergoes photochemically induced bond
cleavage to give tetra-ter~-butyldigermene.This can be trapped,
for example, by [2 21 cycloaddition with phenylacetylene leading to 1,2-digermacyclobutene 5. the constitution of which has
been confirmed by the X-ray structure analysis (Fig. 2) .[I '1
This manner of reaction is not self-evident, since the only
tetraalkyldigermene R,Ge=GeR, (R = CH(SiMe,),) known to
date, although stable in the crystal, reacts in solution exclusively
as singlet germylene (germanediyl) .[I '1
c2 7
[ I l l 4: C,,H,,Ge,l,.
M , = 814.27. orthorhombic, space group P2,2,2,, u =
1794.3(6). h =1982.3(5), L' = 903.5(3) pm, V = 3214(2) x lo6 pm3, Z = 4.
= 1.683 gcm-.3. Mo,. r;idiation, graphite monochroniatol-, 20,,, = 55".
Wyckoff scan. 73x2 independent reflections. 6649 observed independent reflections ( F > 3 g ( F ) ) ,&pai-ametcr ratio = 25.2. Solved using direct methods and
relined using the Siemens SHELXTL-Plus Program system. R = 0.048. R, =
0.044. Due to the systematic evaluation of the reflections hkl and F U a n d the
heavy atoms in 4. it was possible to determine the absolute configuration using
"Hamilton's Ratio Test [16]. 5 : C,,H,,Ge,. M , = 475.78. trichnic. spacegroup
Pi, ~ = 1 1 6 6 ( 2 ) .h = l 3 5 5 ( 3 ) , (.=826(2)pm. a = 9 3 . 1 ( 2 ) , /i=Y1.3(2). ;'=
= 1.258 gcm-'. Mo,, radia105.4(2)', V = 1256(5) x 10' pm3. Z = 2, pLalrd
tion, graphite monochromator, 20,,, = 55 , Wyckoff scan, 5763 independent
reflections. 4546 observed independent reflections ( F > 3u(F)). FJparameter
ratio = I 9 3 Solved using direct methods and relined using the Siemens
SHELXTL-Plus Program system. R = 0.077, R, = 0.063. Further details of
the crystal structure investigations may be obtained from the Fachinformationszenlrum Karlsruhe. D-76344 Eggenstein-Leopoldshafen (Germany) on
quoting the depository numbers CSD-401472 (5) and CSD-401473 (4).
[12] M. Weidenbruch, 9. Flintjer. K . Peters. H. G. von Schnering. Angrn.. C h m .
1986, 98. 1090; Angew. Chem. Inr. Ed. Engl. 1986, 25. 1129.
[I31 L. Pasteur, C . R. Hehd. Seunces Acud. Sci. 1848, 26, 535.
[I41 Reviews: A. Collet, M.-J. Brienne. J. Jacques, Chem. Rev. 1980, SO, 215; J.
Jacques. A. Collet. S. H. Wilen. Enantiomcrs. Rucemutrs. ond Resohrtrons, Wiley. New York, 1981: E. L. Eliel. S. H. Wilen. L. N. Mander, Stercoc/~em;,str~
of'Orgonic Comporrnds, Wiley. New York. 1994.
[15] P. B. Hitchcock, M. F. Lappert, S. J. Miles. A. J. Thorne, J. Chem. Soc. Clirm.
Commrm. 1984. 480
[I61 D. Rogers. Acto CrjrroNogr. Swr. A 1981, 37. 734.
[17] Average value for the Ge-Ge bonds with sterically undemanding substituents
on the germanium atoms. The value corresponds to twice the covalent radius.
Fig. 2. Molecular structure o f 5 in the crystal (H atoms not shown). Selected bond
lengths [pm] and angles [.I: Gel-Ge2 253.1(6); Gel-Ge2-C3 73.0(3). Ge2-C3-C4
107.0(6). C3-C4-Gel 107.8(6). C4-Gel -Ge2 72.2(3).
E-xperimerital Procedure
Complexation of IN,"-Bis(salicy1idene)ethylenediiminato]cobalt(~~~)by Anilines in
4: A solution of 3 (I00 mg. 0.18 mmol) in n-hexane (50 mL) was cooled to -78 'C
and a solution of iodine (46 mg. 0.18 mmol) in n-hexane (30 mL) added dropwise.
The mixture was allowed to warm to room temperature and solvent removed under
reduced pressure to give 30 mL of solution. After cooling to -25 C , colorless
needles of 4 (120 mg. 83% yield) were obtained. M.p. (enantiomers) 322 C. m.p.
(racematej 101 C. ' H N M R ( 3 0 0 M H z . C 6 D , j . d =1.44(s,36H. 1.57(s. 18H): '.'C
N M R (75.44 MHz. CDCI,): ii = 33.13 ( C o ) ,34.46 (CJ, 37.02 (C,,).37.34 ( C J ; MS
(CI. isobutane). n ; : ( O h ) : 687 (54. M' - I). Correct C . H, I elemental analyses.
5 : A solution of 3 (150 mg. 0.27 mmol) and phenylacetylene (73 mg, 0.71 mmol) in
n-hexane (70 mL) was irradiated at -25 "C with a high-pressure mercury lamp
(Herdeus TQl50) until 3 was no longer detectable by TLC (about 4 h). After exchanging 17-hexane with toluene and cooling to - 25 C , yellow crystals of 5 (36 mg,
27%) were obtained. M.p. 96 ' C . ' H N M R (300MHz. CDCI,). ii =1.30 (s, IX),
1.33(s. 18H),7.27(m.SH).7.X2(s. I H ) ; 17CNMR(75.44MHz,CDCli):6= 29.99
(CJ> 30.07 (CJ. 32.18 (CJ. 32.25 (CJ. 126.78. 126.99, 128.16. 142.46, 152.29.
476 (28. M - tBu). Correct C, H elemental
173.43: MS (CI, isobutane): q / : (YO):
Bernd Speiser* and Hartmut Stahl
1, binds oxygen reversibly and is employed as an oxygenation
catalyst for the transfer of one or two 0 atoms to organic substrates.[2-51It is assumed that a hypothetical ternary complex of
1, O,, and a substrate molecule is formed. In investigations of
the catalyst in solvent mixturesr6] we have shown that axial
ligands in neutral Co" as well as in Co"' complexes (having a
single positive charge) and with 2 as the central unit can be
Received: January 20. 1995 [Z76491E]
German version: Angrw. C h i . 1995. 107, 11 87
Keywords: germanium compounds - enantiomeric resolution .
[l] Reviews: T. TSUmUrdya, S. A. Batcheller. S. Masamune. Angcw. C h m . 1991.
103. 916; Angrw. Chcnr. h r . Ed. Engl. 1991. 30. 902: T. Tsumuraya. Y. Kabe.
W. Ando, J Orgonomet. C h e m 1994. 482. 131.
[2] S. Masamune. S. A. Batcheller. J. Park. W. M. Davis, J. A m C h w f .Soc. 1989.
l J J . 1888.
131 T. Tsumuraya. S. Sato, W. Ando. Org~monrcmllic~
1988, 7. 2015.
[4] S. A. Batcheller, S. Masamune, E,trakrdron Lerr. 1988, 27, 3383.
[5] T. Tsumuraya. Y. Kabe. W. Ando. J. Chcm. SOC. Chem.Commim. 1990. 1159.
[6] W. Ando, T. Tsumuraya. Or~ononrerallics1988. 7. 1882; T. Tsumuraya. S. Sato,
W. Ando, ;bid. 1990, 9. 2061
[7] Review. Y. Kabe. W. Ando. A r h . Struin Orx. C h m 1993, 3. 59.
(81 M. Weidenbruch. F,-T. Grimm. M. Herrndorf. A. Schifer. K. Peters, H. G. von
Chein. 1988, 341, 335.
Schnering, J Or,~rmomrf.
191 M. Weidenbruch. A. Ritschl. K . Peters. H. G. von Schnering, J. Orgunmiic,r.
Chcni. 1992. 43X. 39.
[lo] M. Weidenhruch, A. Ritschl. K. Peters. H. G. von Schnering. J. Orgommi~t.
Chrfn. 1992. 437. C25.
exchanged in two steps. A total of six redox-active species are
linked together by three electron transfer and four ligand exchange equilibria ("ladder scheme", Scheme 1 ) . We report here
that this not only applies when both ligands are solvent molecules, but also that solvent molecules (L') can be exchanged by
[*] Priv.-Doz. Dr. B. Speiser, DipLChem. H. Stahl
Institut fur Organische Chemie der Universitit
Auf der Morgenstelle 18, D-72076 Tubingen (Germany)
Telefax: Int. code + (7071)29-6205
Electrochemistry of Oxygenation Catalysts, Part 5. This work was supported
by the Votkswagen-Stiftung and the Fonds der Chemischen Industrie. B. S.
would like to thank the Deutsche Forschungsgemeinschaft for a Heisenberg
fellowship Part 4. [ I ] .
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enantiomerically, reaction, isolation, hexa, tert, butylcyclotrigermane, diiodotrigermane, pure
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