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Gas-Chromatographic Enantiomer Separation of Unfunctionalized Cycloalkanes on Permethylated -Cyclodextrin.

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141 H. Schumann, C . Janiak, J. Pickardt. U . Borner, Angew. Chem. YY (1987)
788: Angew Chem. I n / . Ed. Engl. 26 (1987) 789.
[5] H. Schumann, C. Janiak, M. A. Khan, J. J. Zuckermann. J. Orgunomer.
Cbem. 354 (1988) 7.
[6] C . Schade, P. von R. Schleyer. Adv. Orgunumer. C h m . 27 (1987) 169.
[7] E. Weiss, T. Lambertsen, B. Schubert, J. K. Cockcraft. J. OrgunonwV.
Chem. 358 (1 988) 1 .
[XI P. Jutzi. W Leffers, B. Hampel, S. Pohl, W. Saak, Angew. Cbem. 99 (1987)
563; Angew. Cbem. lnr. Ed. Engl. 26 (1987) 583.
[9]1 crystallizes in the space group P2,jn; Z = 4; u = 1198.2(7),
h = 1530.6(2), c = 2458.7(13) pm, I( = 102.07(3) . 3875 observed reflections with 6 > 3cr(F,) were measured on a four-circle diffractometer
(CAD4, Enraf-Nonius) with Cu,, radiation at 193 K ; n o absorption correction (hi = 1 2 c m - ‘ ) . The structure was solved by direct methods. All
heavy atoms were refined with anisotropic temperature factors; the H
atoms were included a t calculated positions with groupwise common
isotropic temperature factors (509 parameters). The use of weighting
factors ~ t =
. l/o*(&) and inclusion
of an extinction correction
[F,(corr.) = F,(1 - &F:/sin 0 ) with i:= 1.8 x lo-’] resulted in residual indices of R = 0.070 and R , = 0.055 [16]. Further details of the crystal
structure investigation may be obtained from the Fachinforrnationszentrum Karlsruhe, Gesellschaft fur wissenschaftllch-technische Information mbH, D-7514 Eggenstein-Leopoldshafen 2 (FRG). on quoting the
depository number CSD-53777. the names of the authors, and the journal
citation.
[lo] J W. Chambers, A. J. Baskar, S. G. Bolt. J. L. Atwood. M. D . Rausch.
OrganomeruNrcs 5 (1 986) 1635
[I I ] E. Weiss, G. Sauermann. Cberrr. Ber. 103 (1970) 265; Angew. Chem. NO
(1968) 123; Angew. Chem. In!. Ed. Engl. 7 (1968) 133.
[12] Y. Otaka. F. Marumo. Y Saito, Acru Cryslullugr. Secr. BZX (1972) 1590.
[13] M. 1. Bruce, J. K. Walton, M. L. Williams, S . R.Hall, B. W. Skelton. A. H
White, J. Cbem. Soc. Dulron Trans. 1982, 2209.
(141 G. Liebling, R. E. Marsh, Arra Crjstullogr. 19 (1965) 202.
I151 E. Keller, SCHAKAL-X6 B (A FORTRAN Program for the Graphic Representation of Molecular and Crystallographic Models), Freiburg 1986.
1161 G. M. Sheldrick, SHELX-76 (Program for Crystal Structure Determination), Cambridge 1976; SHELXS-86 (Program for Crystal Structure Solution), Gottingen 1986.
Gas-Chromatographic Enantiomer Separation
of Unfunctionalized Cycloalkanes
on Permethylated P-Cyclodextrin **
By Voiker Schurig,* Huns-Peter Nowotny,
and Dieter Schmalzing
The enantiomer separation of simple, unfunctionalized,
saturated hydrocarbons is a challenge,[’] since no procedure
based on the formation of diastereomers o r on chemical,
diastereomeric interaction with chiral auxiliaries (NMR,
GC)”] can be used. Even the determination of optical purity
is often difficult owing to unknown maximum specific rotations. In 1981, we began experiments on the gas-chromatographic separation of the enantiomers of tetraalkylmethanes, R’RZR3R4C (R = alkyl), on glass capillary columns
coated with permethylated 0-cyclodextrins in polysiloxane
solution.[31 Although these experiments have been unsuccessful so far, it has recently been shown that peralkylated
cyclodextrins are suitable for the enantiomer separation of
unfunctionalized 01efins.I~- Packed columns coated with
a-cyclodextrin in formamide were also successfully used, despite their poor efficiency, to separate the enantiomers of
trans-pinane (semiquantitatively) and cis-pinane[‘] as well as
the diastereomers of cis/frans-dimethylcycloalkanes.In the
latter case, the chiral isomers were not resolved into enantiomers. “1
The quantitative separation of a series of alkylcyclohexanes by gas chromatography has now been achieved on per-
~
b)
i
1
10
20
30
*
LO
10
20
30min *
Fig. 1. a) Separation of the enantiomers of rruns- and c;.~-l-ethyl-2-methylcyclohexane and /runs- and cD-1-methyl-2-propylcyclohexane
o n a glass capillary
column (25-m x 0.25-mm inner diameter) coated with 10% heptakis(2,3.6-tri0-methyl)-P-cyclodextrinin OV-1701 (0.08 m). Oven temperature 50 “C; carrier gas pressure 0.7 bar helium. b) Separation of the enantiomers and diastereomers of 1.1,3-trimethylcyclohexane and cci- and /runs-1.1.3.5-tetramethylcyclohexane: conditions same as in a) except for the oven temperature (45 “C).
Table 1. Gas-chromatographic data for enantiomer separation on permethylP-cyclodextrin in OV-1701.
Compound
rruns- 1.2-dimethylcyclohexane
trunr-l,3-dimethylcyclohexane
ci.7-1-ethyl-2-methylcyclohexane
/runs- 1-ethy1-2-methylcyclohexane
cis- 1-methyl-2-propylcyclohexane
frunr- 1 -methyl-2-propylcyclohexane
1.1.3-trimethylcyclohexane
rruns-1 .I .3.5-tetramethyicyclohexane
crs-pinane
rruru-pinane
T
[‘C]
p
Separation
[bar] factor 1
R,
23
23
60
60
60
60
60
60
40
40
1.0
1.0
0.7
0.7
1.0
1.0
0.7
0.7
1.0
1.0
0.85
1.28
1.40
1.oo
1.60
1.69
1.41
2.00
2.28
0.89
1.06
1.07
1.04
1.03
1.03
1-04
1.05
1.05
1.10
1.03
Resolution
methylated !3-cyclodextrin in OV-I 701 on glass capillaries
between 23 and 60 “C (cf. Fig. 1 and Table 1).
Since the enantiomers of both cis-1-ethyl-2-methylcyclohexane and cis-I -methyl-2-propylcyclohexane are separated,
the cyclodextrin phase should, in principle, discriminate between the enantiomers of the homologous cis-I ,2-dimethylcyclohexane, the chair conformation of which is chiral.
Rapid inversion of the chair Conformation, however, leads
(without change in configuration at the chiral centers) to
formation of the enantiomeric conformer.[*] The appearance
of only one peak is therefore interpreted as an interesting
example of an extremely rapid enantiomerization (“peak coalescence of the first kind”191).
Hitherto, the investigation of the separation of enantiomers o n cyclodextrin phases has not allowed a clear distinction to be made between the contributions from the nonpolar interactions in the interior of the cavity (inclusion) and
[*] Prof. Dr. V. Schung, Dip].-Chcm. H:P.
[**I
736
Nowotny,
DipLChem. D. Schmalzing
lnstitut fur Organische Chemie der Universitit
Auf der Morgenstelle 18, D-7400 Tubingen (FRG)
This work was supported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie.
(0 VCH Ver/ugsjie.sell.rchu/rmhH. 0.6940 Weinherm, f Y8Y
057(J-fJ#33/89/0606-0736$07.5O/fJ
Angrw. Chepn. inr. Ed. EngI. 28 (lYX9)Nu.6
the polar interactions with the alkoxy groups on the outside
of the torus. Our results on unfunctionalized, saturated hydrocarbons, for which polar interactions can be excluded,
indicate that inclusion represents the decisive contribution,
whereby the methoxy groups shield the cavity only slightly
and, moreover, increase the flexibility of the cyclodextrin
ring (“induced fit”).[”’ Heptakis(2,6-di-O-methyl-3-O-trifluoroacety1)-(3-cyclodextrin does not separate the enantiomers of the cycloalkanes discussed here.
The direct separation of the enantiomers of unfunctionalized cycloalkanes described here allows a simple investigation of enantioselective synthesis (e.g., asymmetric hydrogenation of aromatic or olefinic compounds) or of enzymatic
or chemical transformations (kinetic resolution of enantiomers). The method is also suitable for extrapolation and
quantification of chiroptic data.
Received: January 23, 1989 [Z 3137 IE]
German version: Angew. C/iern. 101 (1989) 785
M
Q
Triple-Decker Complexes as Intermediates
in Ring-Ligand Transfers **
Fe
5
[(q 5-C4H4BPh)R~H(CO),] 7
The neutral cobalt complex 8[’] undergoes a similar electrophilic stacking reaction with 9aL9Iin acetone to afford the
reddish-brown triple-decker salt 10a, which is isolable in
pure form and undergoes degradation with NaI in acetone[*]
to give the known (boro1e)ruthenium complex 1 1
The
labile triple-decker salt l o b was observed in the analogous
reaction with the iridium complex 9b’”’ in an N M R tube;
in this case, however, the degradation product 1 1 b appears
in the reaction mixture before the cobalt complex 8 is completely consumed. Again, the preparative degradation is carried out with NaI.
+
The principle and the preparative value of ring-ligand
transfer[’I was first shown by Maitlis et al. for (cyclobutadiene)metal complexes.[31 They found, for example, that
[(q‘-C,Ph,)PdBr,],
reacts with Fe(CO), to give
[(q4-C,Ph4)Fe(CO),], Pd metal, CO, and FeBr,
They
suggested a mechanism in which the transferred ligand is
never free but, instead, changes its metallic center via i n t e r
mediates of type 1 with a monofacially bridging ligand.‘3b1
This hypothesis is supported by the identification of compounds with monofacially bridging l i g a n d ~ . However,
[~~
the
Maitlis mechanism has not yet been proved and several
mechanistic alternatives are conceivable. We show here that,
for I H-borole complexes, ring-ligand transfer can also occur
via triple-decker intermediates 2 with bifacially bridging ring
1iga nds.
[(p-qs-C,H,BPh) (CoCp) (ML)] (BF,),
IOa, b
Triple-Decker Complexes, Part 7. This work was supported by the
Deutsche Forschungsgemeinsctiaf[ and the Fonds der Chemischen Indurtrie. Part 6: [ t ] .
a B - P
4
3
[CpCo(q’-C,H,BPh)]
8
[**I
2
+
By Gerhard E. Herberich,* Barry J. Dunne,
and Bernd Hejner
[*] Prof. Dr. G. E. Herberich, B. J. Dunne, B. Sc., Dr. B. HeBncr
Institut fur Anorganische Chemie der Technischen Hochschule
Professor-Pirlet-Strasse 1, D-5100 Aachen (FRG)
M*
1
The sodium borataferrocene Na-315] reacts with
[ReBr(NCMe),(CO),][hl as electrophile in ether to give the
stable, wine-red triple-decker complex 4. The triple-decker
structure of 4 is confirmed by the typical small coupling
constant N = 3J23 4J24of 4.1 Hz for the bridging borole
ligands.[’] Nucleophilic degradation with KCN transforms 4
into the rhenate 5,[*l which can be isolated as NMey salt 6
( N = 5.9 Hz) or. after protonation, as hydride 7
( N = 6.2 Hz). The overall result of the electrophilic stacking
reaction and nucleophilic degradation is the transfer of the
Iff-borole ligand from iron to rhenium.
CAS Registry numbers:
~run.s-1.2-dirnethylcyclohexane. 6876-23.9; /runs-1,3-diinethyIcyclol~ex~i~e.
2207-03-6: cis-I-ethyl-2-methylcyclohexane. 4923-77-7: 1run.s-l-ethyl-2methylcyclohexane. 4923-78-8; ci.7-I -methyl-2-propylcyclohexane.
4926-71-0:
trun~-l-methyl-2-propylcyclohexane,
42806-77-9; 1,1,3-trin~ethylcyclohexane.
5-tetramethylcyclohexane. 50876-31-8; cis-p~nane.687613-7; /runs-pinane. 33626-25-4: permethyl-26-cyclodextrin, 5521 6-1 1-0.
[ I ] V. Schurig. A n g c w Chmi. Y6 (1984) 733; Angew. Chem. Inl. Ed. Engl. 23
(1984)747.
[2] V. Schurig. Kuntukle (Durmstadt), / 9 H S ( I ) . 54; 1YH5(2), 22; IY86(1). 3.
[ 3 ] Ref. 16 in [4].
[4] V. Schurig. H.-P. Nowotny, J. Clzromurogr. 441 (1988) 155.
[5] J. Ehlers, W. A. Konig, S. Lutz. G. Wenz, H. tom Dieck. Angeii,. C/iem. I00
(lY88) 1614; Anpir.. Chem. In( Ed. En$. 27(1988) 1556.
161 T. Koscielski. D. Sybilska. S. Belniak, J. Jurczak, Chromutogruphiu 19
( 19x4) 292.
[7] T. Koscielski, D. Sybilska. 1 Chromutogr. 349 (1985) 3.
181 E L. Eliel; Sr(,reochenii.s/r~of’ Curhon Coriipound~,McGraw-Hill, New
York 1962, p. 212.
191 V. Schurig, W. Biirkle. J. Am. C/icm. Soc. 104 (1982) 7573.
[lo] K . Harata, K . Uekarna, M. Otagiri, F. Hirdyama, J. Inclusion Phmoni. 2
(1984) 583.
M-M’
[LM(OCMe,),l (BF,), --*
9a; L M = Ru(q‘-C,Me,)
9b: L M = Ir(q5-C,Me,)
”’+
[LM(q’-C,H,BPh)]
Ila, b
The transfer of the borole hgands affords the first borole
complexes of rhenium (4-7) and iridium (lob, I1 b) and, at
the same time, the first triple-decker complexes of these
metals. The direct observation of triple-decker intermediates
was made possible by the way in which the reaction was
performed.
Even when no intermediates are observed in ring-ligand
transfers, it is possible, in principle, to distinguish between
the different mechanisms. According to the Maitlis mechanism, the transferred ligand is coordinated to the sunw side
in the starting material and the product. By contrast, the
transferred ligand is bound to ciif’&wzt sides in the starting
material and product when the reaction proceeds via tripledecker intermediates. If the reaction involves a free ligand,
on the other hand, the stereochemical information is lost.
Chiral complexes should allow one to distinguish between
these cases.
737
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