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One-Dimensional Semiconducting Chains of the Quaternary Zintl Anion in (Et4N)4[Au(Ag1-xAux)2Te9].

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[I41 P. von R. Schleyer, C. Maerker. A. Dransfeld. H. Jiao. N . J R. van
Eikcrna Honinies, .I A i l 7 Chciir S o c 1996. 118. 6317 .
[ I S ] Mcaii of the carbon coordinates. The C, ring in 10 is not planar. and [he NlCS
changes depending on the point iit which the value is computed The NlCS
value at the midpoint between the bridgehead cai bon atoms i\ - 11 8 and that
a t the center oi'rectanglc formed by tlie other four aromatic cai-bons is -7 8 .
[I61 T. A. Keith. R . F W. Bader, Clieni. P/ij..s.Lett. 1992. 194. 1 : rhid. 1993.110. 223
[17] D. V. Siinion, T. S Sorensen, J. Ail?. C'ho??. Soi. 1996, 118, 7345.
[ I X ] Thc A valiie wiis calciilatcd following the protocol used in U. Fleischer.
W. Kutrelnigg. P. La~7eretti.V. Muhlenkanip. .I ,4171. Clioii. Soc. lYY4. 116,
529X; see also ref. [I71
[lO] A detailed theoretical study on the siructui-e. strain energy, and magnetic
susceptibility of [4]paracyclophane recently appcarcd. B. Ma. H M . Sulrhacli.
R. B. Reiniiigton, H F. Scliaefcr Ill.J .4i!r. C / i m So(. 1995. 117. 8392.
One-Dimensional Semiconducting Chains of the
Quaternary Zintl Anion in
(Et,N),IAu(Ag, - xA~,),Sn*Te,l**
Sandeep S. Dhingra, Dong-Kyun Seo,
Glen R. Kowach, Reinhard K. Kremer,
Julie L. Shreeve-Keyer, Robert C. Haushalter.* and
Myung-Hwan Whangbo*
One particularly desirable type of 1-D conducting solid,
which is analogous to a macroscopic copper wire surrounded by
an organic polymer insulator, would be composed of chains of
covalently bonded metals surrounded by insulating organic regions that hinder electronic coupling between the moleculgr
wires. We report here the preparation of ii semiconductive 8 Awide, 1-D chain composed of four different elements surrounded by insulating organic material. The synthesis, crystal stl-ucture, physical properties, and electronic structure of the first
quaternary Zintl-anion material (Et,N),[Au(Ag, -xAux)2Sn,Te,] (.Y = 0.32), which exhibits a delocalized 1-D band structure, are discussed.
The title compound is prepared by ethylenediamine (en) extraction of a pentanary alloy of composition K,AuAg,Sn,Te, .
Other compositions were attempted, including K,AuAg,Sn,Te,, but they gave either no products or significantly lower
yields. After the alloy is extracted, and Et,N ' cations are added
to the filtrate, it generally takes several months for the first
crystals to appear. This is followed by a period of more rapid
crystal growth. The crystal quality, and to a lesser extent the
yield, vary from reaction to reaction, but no other products are
detected and all crystals examined contain Au, Ag, Sn, and Te.
Crystals of (Et,N),[Au(Ag, -,Au,),Sn,Te,] contain unprecedented, linear, 1-D chains of cornposition Au(Ag, -xAu,)2Sn,Te:- (Figure 1) separated by Et,N+ cations.[51The closest
Dedicated to Hans Georg V O I ZSclinerir7g
on tlic. occasion of his 65th birthday
Several chemical approaches have been
developed over the last two decades for
preparing one-dimensional conducting materials such as platinum chain compounds,
the salts of organic donor molecules, and
transition metal chalcogenides.['I We recently initiated a study designed to determine the possibility of introducing unpaired
electrons into closed-shell, low-dimensional
Figure 1. Structure of the I-D Au(Ag,. ,Au,),Sn,Tct- chaiii drawn with tlicriniil ellipsoids at the 50%
Zintl-phase materials, by suitable structural
probability level. I n t h i s iiiitiiil model Tc2 was relined as il single. fully occupied position, and the Agl and
modifications or elemental substitutions,
Ag? positions were refined with Ag occupancy only. Selcctcd bond lengths [A]: Aul -Te2 2 970(6),Te?-TeS
hence increasing their electrical conductivi3.187(6). and angle[ ] Te2-TeS-Te2 1S4.7(4)
ty. In several cases the structures achieve a
closed-shell electronic configuration by uninterchain Te ' . Te contact is 7.0 A. The Au atom has distorted
dergoing site specific elemental substitutions (for example
square-planar coordination, whereas the Sn and mixed Ag/Au
K,GeIn,Sb,,)r21 or forming exceedingly complex structures (for
site show tetrahedral and trigonal-planar coordination, respecexample K,In,Ge,As,, or K,In,Ge5A~,,).[31Likewise, several
tively. Structure refinement (by fixing the thermal parameter of
binary and ternary I-D Zintl anions such as InGeTe,,
the site and allowing the Au:Ag ratio to refine) gives 3 2 %
Hg2Te:-, Hg3Te;-. Hg2Tei-, As,Te:-,
substitution of Au onto the Agl and Ag2 sites; a small stoichioInTe,
possess structures consistent with closed-shell electronic configurations
metric range is apparent from refinements of other crystals.
Substitution is possible since Au-Te and Ag-Te bond distances in trigonal-planar coordination are very similar.r61From
[*I Dr. R C . Haushaltcr. Dr. S. S Dhingra. G R. Kowach,
an initial refinement with a single Te2 position (see below), each
Dr. J. L. S h r e w - K e y c r
atom is twofold coordinated if only bonds shorter than 3
NEC Keseoirh I nst i t LI te
4 lndcpeiidrnce Way
are considered. The prominent structural feature of the polyPrinceton. N J 08540 (USA)
anion is the {-Au-Te-Te-Te-) strand composed of Au atoms
Far: lnt code +(609)951-?4X?
approximately linear Te2-TeS-Te2 units (4:Te-Te-Te =
e-inail haush,ilr.u i-cscarcli uj.n
The two symmetry-equivalent Te2-Te5 distances are
Prof. M -H Whaiigho. D:K. Seo
3.187(6) A, which is longer than a typical Te-Te single bond
(2.75 A) but much shorter than the vim der Waals Te . . . Te
contact (4.0 A). This suggests a bonding interaction of the type
observed in tellurides such as Te:;.
HgTef ~, Cu,SbTe:;,
Dr R K. Kreiiicr
,['I as well its some othtr solid-state tellurides.[''
Max-Planck-ln\littit Kii- Fcjihijrpeil'oi scliung. Stuttgai-1 (Gerniany)
The Au-Te2 distance of 2.970(6) A is much longer than
[**I The work at North Carolina State I ei-sit! n.a\ supportcd by the U. S
contacts (about 2.65 A) found for Au,Te:;.
iices. Di\i\ion of Materials Scieiiccs
Dep;irtincnt of Eiicrgy. Oflice o f 13;i~ic
KAu,Te$-, K,Au,Te: ~, and Au2Te:-.r41 However, the Te2
(grant 110. DE-FG05-XhFRJ5259)
atoms have very large anisotropic displacements along the chain
running parallel to the [OIO] direction (Figure 1). This observation is essential to understanding the electronic structure of
(Et,N),[Au(Ag, -,Au,),Sn,Te,] discussed below.
Given the oxidation states I for Ag and Au, I V for Sn, and - 11
for Te, the charge on Au(Ag, -xAu,),Sn,Te, is - 7, which is in
disagreement with the charge of - 4 inferred from the crystal
structure and elemental analysis. (One may consider Au atoms
in square planar units such as Aul, and AuTe, to be A u 3 + , but
theoretical and experimental studies show that they are
Au' .[''I) In this simplified analysis, the close Te2-Te5 contacts
(3.19 A) within each linear Te, trimer were neglected. There is
one Te, trimer per formula unit Au(Agt -xAu,),Sn,Tey, so the
charge is balanced if each Te, trirner is considered to possess a
charge of -3. In -general the forinal charge of -2 is associated
with an oligomeric chain Tel with T e - k T e bond angles of
about 90". A linear Te,
trimer has three o orbitals
made up of p orbitals, that
is, bonding (5),nonbonding ( n ) , and antibonding
(5*)levels (Figure 2). Both
n the bonding and nonbonding levels can accommodate
electrons, so the maximum
charge associated with a
Figure 2. Three o orbitals derived from
linear Te, trimer is -4.
the p orbit& of a linear Tc, trimei-.
Since the Te:- units in the
Au(Ag, -,Au,),Sn,Te$
chain have half-filled nonbonding levels, the Au(Ag, -,Au,),Sn,Te$- chain should possess a half-filled band largely composed of the nonbonding levels. This is confirmed by the electronic band structure of a n isolated Au(Ag, -xAu,),Sn,Te<chain (Figure 3a) calculated by the tight-binding extended
be metallic. However, since it is a I-D band (Et,N),[Au(Ag, -.vA~.,)2SnrTes]
should be susceptible to a Peierls distortion that would open a band gab at the Fermi
The magnetic susceptibility of (Et,N),[Au(Ag, -,ALI,),S~,T~,]
indicates that the chain is diamagnetic and is nearly independent of temperature down to 4 K ; the gram-susceptibility of
approximately -2 x lo-' emug-' is similar to that of other
chalcogenide semiconductors (Figure 4a). Single crystals of
(Et,N),[Au(Ag, -,Au,),Sn,Te,]
grow to a maximum size
of about 30 x 30x 80 pm3 and form mostly as clusters of
crystals, thereby precluding conventional four-probe electrical resistivity measurements. Resistivity data obtained by
the microwave cavity perturbation technique" 31 (though confined to a small range of temperatures due to sample decomposition above about S O T ) show, by extrapolating to 0 K
and assuming that the activated conductivity is purely intrinsic, that (Et,N),[Au(Ag, - ~yAux),Sn,Te,] is a semiconductor with a band gap of 0.45(5) eV (Figure 4b). However,
I : : : 01
2.5 04
Figure 3. Dispersion relations of the electronic energy bands of an isolated
Au(Ag, .tAu,J,Sii,Te$ chain calculated for a) the average structure in which the
Te2 position is not split and b) the structure with a Peierls distortion coiistructed
with the split positions of Te2 (see Figure 6). The horizontal. broken line refers to
the Fermi level. = 0 and Y = P 2 .
Huckel method.["] The repeat unit cell of the Au(Ag, -,AuJZSn,Te:- chain has two formula units (hence two Te:- units), so
the half-filled band is folded, and the Fermi level occurs at the
zone edge. This band is largely composed of the G nonbonding
orbitals of the linear Te, trimers and the d+,, orbitals of the Au
atoms. Since the Au(Ag, . x Au,),Sn,Te;- chain has a partially
filled band. one might expect (Et,N,)[Au(Ag, .xA~,)2Sn2Ter]
Figure 4. Physical properties of (Et,N),[Au(Ag, -lAu,),Sn,Te,]. a ) Tcmperaturedependence of the magnetic susceptibility b) Temperature-dependent resistivity /J
measured by the microwave cavity perturbation technique. Three experiments were
carried out with different quartz tube diameters [2mni ( + 1, 1 min ( x ) . and
0.5min (.)I.
A band gap of 0.45(5) eV is extracted from the In p - T
b) Optical diffuse rellectance R versus wavelength 7. of incident light illustrating the
absorption band edge.
microwave absorption measures the total conductivity including extrinsic conductivity from defect-generated charge carriers.
Optical diffuse reflectance measurements show a band gap of
0.95(5) eV (Figure 4c). To explain this semiconducting character, one must conclude that the Au(Ag, -,Au,),Sn,Te;chains
of (Et,N),[Au(Ag, -,Au,),Sn,Te,]
have undergone a Peierls
distortion above room temperature.
A Peierls distortion that is appropriate for the half filled band
of the Au(Ag, -xAu,),Sn,Te;chain makes two formula units
of its repeat unit cell (Figure 1) nonequivalent, thus opening a
band gap at the Fermi level. This distortion should involve
primarily the displacement of the Te2 atoms, because their thermal parameter U,, (along the I-D chain direction) is unusually
large. Such an elongated thermal ellipsoid occurs when the real
position of the Te2 atom is not at the center but close to either
end of the ellipsoid.[’41 In fact, the residual electron density
around Te2 suggests that it is appropriate to refine Te2 as two
half Te atoms (that is, Te2A and Te2B) on two independent sites
along the chain. Half the electron density expected for a Te atom
was placed on the two electron density peaks from the difference
Fourier map (Figure 5a). Unconstrained refinements lower the
residual R value, and the two independent Te positions display
nearly spherical thermal ellipsoids of very similar magnitude
(Figure 5b). As a result, the structure is better described by the
two Te positions that are separated by 0.65 8, and occupied to
50%. In reality, either Te2A or Te2B should be 100% occupied,
and the 50% occupation of both positions is a result of equal
probability of populating them. The Te2A and Te2B positions
give bond lengths of Aul -Te2A = 2.666(4) 8, and Te5-Te2B =
2.855(4) A, which agrees well with the values expected for
Au-Te and Te-Te single bonds.
Since a superstructure was not observed, we must assume a
distortion model that is consistent with the lattice parameters
and symmetry. We searched for a noncommensurate lattice
change with transmission electron microscopy (TEM), but the
sample decomposed rapidly in the electron beam. One would
not expect any change in the X-ray data corresponding to a
doubling of the cell concomitant with distortion of the AuTe,
unit, because the other atoms in the I-D chain not involved in
the delocalized states (for example Ag, Sn, and two-coordinate
Te atoms) are arranged such that the actual cell is twice as long
as each individual AuTe, unit. No changes in unit cell parameters were observed at -160°C. We were also unable to observe
loss of the Peierls distorted state below the sample decomposition temperature of about 80 “C. On the basis of the split positions of the Te2 atoms, we consider a Peierls distortion relevant
for the Au(Ag, -xAu,),Sn,Te:chain. The two formula units of
its repeat unit cell can be made nonequivalent when the split
positions are chosen as depicted in Figure 6. The small arrow at
each Te2 indicates the choice of the split position on the lefthand side (LHS) or right-hand side (RHS) of the average position. Therefore, in Figure 6a the coordination of the LHS Au
atom becomes more square planar, and that of the RHS Au
atom more linear (distortion pattern A); this is reversed in Figure 6b (distortion pattern B). Except for the sense of the displacement vectors, the two patterns are equivalent.
Figure 6. Two ways of using the split positions of Te2 to introduce a Peierls distortion in the Au(Ag, .,Au,),Sn2Te:chain. The filled and empty circles represent the
Auand Te atoms ofthe {-Au-Te-Te-Te-}, strand. The small arrow at each Te2 atom
indicates which of its two split positions (that is, the LHS and RHS positions of the
average site) is chosen in the distortion patterns a) A and b) B.
Figure 5. a) Contoured electron density difference map after refining a single, fully
occupied Te2 positron demonstrating peaks on either side of Te2. b) ORTEP depicting the half-occupied Te2A and Te2B positions and thermal parameters at the 50%
probability level. Bond lengths [A] within the chain: Aul-Tel 2.599(3),
Aul-Te2A 2.666(4), Te?A-Te2B 0.648(5), Te2B-Te5 2.854(4), Snl-Te2A
2.760(10), Snl-Te2B 2.741(10), Snl-Te3 2.707(4), Snl-Te4 2.716(4), Agl-Te4
2.621(3), Ag2-Te3 2.610(3), Agl-Te5 2.724(5), Ag2-Te5 2.725(5), Agl-Ag2
3.1028(2), Te3-Te4 4.467(5). Selected bond angle [“I. Te2B-Te5-Te2B 153.4(4).
AnZen.. Chem. Inr. Ed En,?/ 1997. 36, N o . I 0
Figure 3b shows the band dispersion relations calculated for
the Au(Ag, -,Au,),Sn,Te;chain with the Peierls distortion
defined in Figure 6a or 6b with the split Te2A and Te2B positions. As expected, the distorted Au(Ag, -IAux),Sn,Te:- chain
has a band gap. (The calculated band gap is 2.5 eV and larger
than those estimated from resistivity and optical measurements
(0.45 and 0.95 eV, respectively). However, this is not surprising
due to the semi-empirical nature of the calculation.) In the extreme case, this distortion would result in some Te . . ’ Te nonbonding contacts, as well as alternating two- and four-coordinate Au centers (from which one may suppose an average
formal Au oxidation state of 11 from equal amounts of Au‘ and
Au“‘) along the chain, but we d o not think this extreme distortion is a n important contribution to the actual electronic structure; the resulting “ionic” structure would not be expected to
show the narrow bandgap and low resistivity experimentally
The synthesis and characterization of the first quaternary
Zintl anion, Au(Ag, -xAu,),Sn,Te:-,
demonstrates that polymerization of anionic subunits by extraction of alkali/transition/main group alloys is a viable route to novel, low-dimensional conductive materials. Both the physical property mea-
VCH Verlagsgesellsrhafr mbH, 0-69451 Weinheim.1997
0570-0833/Y713610-1089$17.50+ .SOW
surements and electronic structure calculations are consistent
with the formation of delocalized, I-D electronic states derived
from what is formally an unpaired electron in the nonbonding
orbital on a Te:- unit through intervening Au centers. Magnetic
susceptibility, conductivity, and optical measurments show that
this I-D Zintl anion exists in a Peierls distorted state exhibiting
semiconducting, diamagnetic behavior. This concept of an organic-insulated conductive wire, combined with the rich structural diversity of the Zintl materials, suggest that many more
materials of this type could be prepared.
Experimental Section
All manipulations were performed under helium, and en was distilled from a red
solution of K,Sn,. An alloy of composition K,AglSn,Te, was prepared by fusing
(about 800-C) K,Te (2.000 g, 9.72 mmol), Au (0.638 g, 3.24 mmol). Ag (0.698 g,
6.48 mmol), Sn (0.770 g, 6.48 mmol), and Te (2.894 g. 22.7 mmol) in a quartz tube
under argon (1 atm) for I min with swirling. This homogeneous melt was crushed
toafinepowder,extracted withen(1 galloyper 10 mLen)for 12-24 hr,and filtered
to remove undissolved solid. The dark red-brown extract was added to a vial containing a saturated solution of tetraethylammonium iodide (TEA I, 0.600 g,
2.33 mmoi) in en (9-10 mL). The first crystals of (Et,N),[Au(Ag, _,Au,),Sn,Te,],
which form as tiny, radially protruding intergrowths of black blades, appear after
approximately 2-3 months and continue to form for several months thereafter.
Yields are typically 1 - 5 % by weight based on alloy; it is noteworthy that there are
no other solid products Elemental analysis cakd for (Et,N),Au(Ag, -xAux)2Sn,Te,: C 16 17, H 3.39, N 2.36, Au 13.59, Ag 6.17, Sn 9.99, Te 48.32, found- C
16.35, H 3 57. N 2.59. Au 9.25, Ag 5.26, Sn 10.42, Te 50.49.
Received November 4. 1996 [Z9725IE]
German version Angett . C/wm 1991, 109. 1 127 - 1 130
Keywords: semiconductors solid-state chemistry
elucidation tellurium - Zintl anions
- structure
[I] Crystal Chemi.srry and Properties o / A4ateriul.i with Qua~i-One-Dimensi(jn~1
Structures (Ed.: J. Rouxel), Reidel, Dordrecht, 1986, Strucrure Phase Trunsrrions in Layered TransitionMetal Compounds(Ed : K . Motizuki), Reidel, DorBronzes
drecht, 1986; Low-Dimensional Electronic Properties of Molj~bde17um
and Oxides (Ed.: C.Schlenker), Kluwer. Dordrecht, 1989, S. Kagoshima, H.
Nagasawa, T. Sambongi, One-DimensionalConductors, Springer, Heidelberg,
1988; J. M. Williams, J. R. Ferraro, R. J. Thorn, K. D. Carlson, U. Geiser,
H. H . Wang, A. M. Kini, M.-H. Whangbo, Organic Superconducrors,Prentice
Hall, New York, 1992.
[2] J. L. Shreeve-Keyer, R. C. Haushalter, D.-K. Seo, M.-H. Whangbo, J Solid
State Chem. 1996, 122, 239.
[3] J. L. Shreeve-Keyer. Y. S. Lee. S. Li, C. J. O'Connor, R. C. Haushalter. D. K.
Seo, M.-H. Whangbo, J Solid State Chem., in press.
141 S. s. Dhingra. R C. Haushalter, Chem. Mater. 1994, 6 , 2376; R. C.Haushalter, Angew. Chem. 1985, 97,414; Angeir. Chem. Int. Ed. Engl. 1985,24,433;
S . S . Dhingra, C.J. Warren, R. C. Haushalter. A. B. Bocarsly, Chem. Muter.
1994, 6, 2382; C.J. Warren, R. C.Haushalter. A. B. BoCdrsfy, ihid. 1994, 6,
780; C. J. Warren, S. S. Dhingra, R. C. Haushalter. A. B. Bocarsly, J. Solid
S a t e Chem. 1994, 112, 340.
[ S ] Crystal structure data for [N(CH,CH,),],Au, ,,Ag,,,,Sn,Te,: orthorhombic,
a = 20.448(4). b = 24.315(7). c = 11.540(3) A, V = 5737(2) A'. space group
Pnma, Z = 4, pcnlcd
= 2.752 gcm-3. M , = 2376.52 gmol- approximate crystal dimensions= 5 O x 5 0 x 1 0 0 m m . p(MoK1) =100.18cm-'. ;.(MoK.)=
0.71073~,20,,, = 45", T = 291(3) K Thetotaldatasetconsistsof4219reflections collected in the ro-scan mode; of 4218 independent reflections 1462 with
I,> 3o(I)were used for calculations. The data were corrected for Lorentzian,
polarization. decompostion (13.5 YO),and absorption effects (empirical I+scans, transmission factors 0.75- 1.00). The structure was determined by direct
methods (SAPJ91) followed by least-squares refinement on Fwith the texsan
software package. All heavy atoms were refined anisotropically, C and N
atoms isotropically, and H atoms not included. Au substitution on the Ag site
was accomplished by constraining both atoms to the same site in addition to
constraining the anisotropic thermal parameters. The Te2 atom was split into
two positions at half occupancy, but the positional and thermal parameters
were allowed to freely refine. The 166 parameters were refined to R(F) = 0.056
and R,(F) = 0.057 based on a o weighting scheme; minimum and maximum
details of the crystal
residual electron density: - 1.41 and 1.54 e - k 3Further
structure investigation may be obtained from the Fachinformationszentrum
Karlsruhe, D-76344 Eggenstein-Leopoldshafen (Germany), on quoting the
depository number CSD-406 539
[6] W. Bronger, H. U Kathage. J Less Common Mer. 1990. 160, 181; M . A
Ansari. J. C Bollinger, J. A. Jbers. Inorg. Chem. 1993.32. 1746.
VCH VerlagsgeseilschafrnibH, 0-69451 Weinheim, 1997
[71 C. J. Warren, R. C. Haushalter, A. B Bocarsly, J. Alloys Compd. 1996,223.23;
J. M . McConnachie, M. A. Ansari, J. C. Bollinger, R. J. Salm, J. A Ibers, Inorg.
Chem. 1993, 32, 3201; U. Myller, C. Grebe, B. Neumyeller, B. Schreiner, K.
Dehnicke, 2. Anorg. Allg. Chem. 1993,619,500; S . S. Dhingra, R C. Haushalter, J Am. Chem. Soc. 1994, 116.3651 ;S. S. Dhingra, R. C. Haushalter, h o g .
Chem. 1994,33,2735.
181 P BSttcher. Angen. Chem. 1988. 100,781; Angeiv. Chem. Int. Ed. Engl. 1988,
27, 759.
[9] R. C.Haushalter, Angew. Clirm. 1985, 97, 412; Angew Chem. Int. Ed. Engl.
1985, 24. 432; R. C. Haushalter, Inorg. Chim. Acta 1985, 102. L37.
[lo] J. A. Pdradis, M.-H. Whangbo, R. V. Kasowski, New J. Chem. 1993, 17, 525;
A. van Triest, W. Folkerts, C. Haas. J. Phys. Condens. Matter 1990, 2, 8733
[ l l ] M:H. Whangbo, R. Hoffmann. J Am. Chem. Soc. 1978, 100.6093,
1121 M:H. Whangbo, Acc. Chem. Res. 1983, 16, 95.
[13] W. Bauhofer. J Phjr. ESci. Insrrum. 1981,14,934, R. K. Kremer, unpublished
[14] M:H. Whangbo, E. Canadell, Solid State Commun 1992, 81, 895.
Diastereo- and Enantioselective Synthesis of
1,2,3-Substituted Cyclopropanes with
Zinc Carbenoids""
Andre B. Charette* and Jacinthe Lemay
A significant number of natural products containing 1,2,3substituted cyclopropanes have been isolated in the last few
decades.". '1 Traditionally, these cyclopropane units have been
prepared by a nucleophilic addition-elimination sequence on
o$-unsaturated carbonyl derivatives (Scheme 1, A)[31 or by a
R2,R3 = EWG
R ' C H N ~ ,ML,
Scheme 1. Different strategies for the cyclopropanation of olefins (EWG =
electron-withdrawing group).
cyclopropanation reaction involving the transition metal catalyzed decomposition of diazoesters (B).[4,51 It is clear that the
diastereo- and enantiocontrol is a serious limitation in some of
these methods. The use of the Simmons-Smith cyclopropanation reactionE6I to generate 1,2,3-substituted cyclopropanes is
very rare, and so far no method has provided good diastereoand enantiomeric levels (C).['.*I In this communication, we report a new method to generate 1,2,3-substituted cyclopropanes
with excellent diastereo- and enantiocontrol by using substituted zinc carbenoids, and we show for the first time that functionalized zinc carbenoids['] can be prepared and are effective cyclopropanating reagents.
[*] Prof. A. B. Charette, J. Lemay
Departement de Chimie
Universite de Montreal
P. 0 Box 6128, Station Downtown, Montreal H3C 3J7 (Canada)
Fax' Jnt. code +(514)343-5900
e-mail: charetta(a
[**I This research was supported by the NSERC (Canada), the Petroleum Research
Fund administrered by the ACS, the Alfred P. Sloan Foundation. Merck
Frosst Canada, F. C. A. R. (Qubec), Eli Lilly, and the Universite de Montreal.
0570-0833197!3610-10~1)$ 17.50i- .5010
Angen.. Chem. Inr. Ed. Engl. 1997, 36. No. 1 0
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