Synthesis and structure of semi(tetrahydrofuran-O)bispotassium bis(2,3,4,5-tetraethylstibolide)

Article abstract of DOI:10.1021/om000161b

The reaction of bis(cyclopentadienyl)zircona-2,3,4,5- tetraethylcyclopentadiene (1) with antimony trichloride yields 1-chloro-2,3,4,5-tetraethyl-1-stibole (2). The reduction with potassium gives semi(tetrahydrofuran-O)bispotassium bis(2,3,4,5- tetraethylstibolide) (3). The potassium stibolide columns are linked via K-Sb contacts of 3.618 angstrom, thus forming a wavelike layer structure. The molecular structure shows three crystallographically different metal cations. One potassium atom is located between two stibolide anions, whereas the other ones show additional K-O and K-Sb contacts of 2.681 and 3.618 angstrom, respectively.

Full text of DOI:10.1021/om000161b

Organometallics 2000, 19, 2393-2396
2393
Syn th esis a n d Str u ctu r e of
Sem i(tetr a h yd r ofu r a n -O)bisp ota ssiu m
Bis(2,3,4,5-tetr a eth ylstibolid e)
Matthias Westerhausen,* Christian Gu¨ckel, Marcus Warchhold, and
Heinrich No¨th
Department Chemie, Ludwig-Maximilians-Universita¨t Mu¨nchen, Butenandtstrasse 9
(House D), D-81377 Munich, Germany
Received February 18, 2000
Summary: The reaction of bis(cyclopentadienyl)zircona-
2,3,4,5-tetraethylcyclopentadiene (1) with antimony
trichloride yields 1-chloro-2,3,4,5-tetraethyl-1-stibole (2).
The reduction with potassium gives semi(tetrahydrofu-
ran-O)bispotassium bis(2,3,4,5-tetraethylstibolide) (3).
The potassium stibolide columns are linked via K-Sb
contacts of 3.618 Å, thus forming a wavelike layer
structure. The molecular structure shows three crystal-
lographically different metal cations. One potassium
atom is located between two stibolide anions, whereas
the other ones show additional K-O and K-Sb contacts
of 2.681 and 3.618 Å, respectively.
we report on the synthesis and structure of an alkylated
potassium stibolide that exhibits both η5- as well as η1-
coordination to a potassium cation.
Cyclopentadienides of the heavier alkali metals are
of interest not only due to their application as cyclo-
pentadienyl transfer reagents but also due to their
structural and physical properties. Very recently, Cloke
et al.10 published the synthesis of (tetrahydrofuran-O)-
potassium 2,4,5-tri(tert-butyl)-1,3-diphosphacyclopen-
tadienide with its columnar structure. Whereas unsub-
stituted cyclopentadienyllithium, -sodium, and -potassium
are polymeric in the solid state,11 demanding groups and
coordination of neutral coligands lead to the formation
of monomeric or oligomeric molecules.1 On the other
hand, addition of bases such as THF and the use of
substituted cyclopentadienyl groups is necessary to
obtain substances soluble in common organic solvents.
In tr od u ction
Cyclopentadienides of the alkali metals are widely
used synthons for the preparation of metallocenes of the
d-block elements. Their synthesis is straightforward,
and an isolation of these reactive species usually is
unnecessary to perform ligand transfer reactions.1,2 The
formal substitution of a CH unit by a phosphorus atom
gives the well-known phospholides,3 which show proper-
ties similar to those of the hydrocarbon analogues. The
aromaticity within the five-membered cycle based on
NMR data and theoretical investigations lies in the
same order of magnitude,4 and also the structures of
the metallocenes and the phospha-substituted deriva-
tives are often alike.3 However, in addition to the η5-
coordination phospholides can act as η1-ligands prefer-
ably to 16-electron species of d-block metals. For the
alkaline earth metal phospholides, metallocenes5 (η5-
coordination) and 1-phosphacyclopenta-2,4-dien-1-ides6
(η1-coordination) were observed. There are only a few
examples of structurally characterized pentelacyclopen-
tadienides of the heavier penteles (pnictogenes). To our
knowledge for antimony only the molecular structures
of 1,1′-distibaferrocenes have been published.7-9 Here
Resu lts a n d Discu ssion
The reaction of zirconocene dichloride with butyl-
lithium and hex-3-yne at -78 °C in THF yields nearly
quantitatively red 1,1-bis(cyclopentadienyl)-2,3,4,5-tet-
raethyl-1-zirconacyclopenta-2,4-diene (1).12 The trans-
metalation with antimony trichloride gives the corre-
sponding 1-chloro-2,3,4,5-tetraethyl-1-stibole (2) as a
yellow oil according to Scheme 1. The reduction of 2 with
potassium metal in THF and recrystallization from
heptane yields slightly yellow crystals of semi(tetrahy-
drofuran-O)bispotassium bis(2,3,4,5-tetraethyl-1-sti-
bolide) (3).
The molecular structure and the numbering scheme
of 3 are represented in Figure 1. The unit shown in
Figure 1 is part of a column in which potassium cations
and stibolide anions alternate. However, there are three
crystallographically and chemically different metal
centers: K1 lies between two parallel stibolide anions,
and at K3 a THF ligand is bonded (K3-O3 2.68(1) Å)
and enforces a nonparallel orientation of the neighbor-
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1999, 99, 969.
(2) Burkey, D. J .; Hanusa, T. P. Comments Inorg. Chem. 1995, 17,
41.
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Mathey, F. Chem. Rev. 1988, 88, 429. Mathey, F. Coord. Chem. Rev.
1994, 137, 1.
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Organometallics 1991, 10, 2068.
(8) Ashe, A. J ., III; Kampf, J . W.; Al-Taweel, S. Organometallics
1992, 11, 1491.
(4) Malar, E. J . P. J . Org. Chem. 1992, 57, 3694. Dransfeld, A.;
Nyula´szi, L.; Schleyer, P. v. R. Inorg. Chem. 1998, 37, 4413. Nyula´szi,
L.; Bergstra¨sser, U.; Regitz, M.; Schleyer, P. v. R. New J . Chem. 1998,
651.
(5) Westerhausen, M.; Digeser, M. H.; Gu¨ckel, C.; No¨th, H.; Knizek,
J .; Ponikwar, W. Organometallics 1999, 18, 2491.
(6) Westerhausen, M.; Digeser, M. H.; No¨th, H.; Ponikwar, W.;
Seifert, T.; Polborn, K. Inorg. Chem. 1999, 38, 3207.
(9) Ashe, A. J ., III; Kampf, J . W.; Pilotek, S.; Rousseau, R. Orga-
nometallics 1994, 13, 4067.
(10) Cloke, F. G. N.; Hitchcock, P. B.; Nixon, J . F.; Wilson, D. J .
Organometallics 2000, 19, 219.
(11) Dinnebier, R. E.; Behrens, U.; Olbrich, F. Organometallics 1997,
16, 3855.
(12) Xi, C.; Huo, S.; Afifi, T. H.; Hara, R.; Takahashi, T. Tetrahedron
Lett. 1997, 38, 4099, and references therein.
10.1021/om000161b CCC: $19.00 © 2000 American Chemical Society
Publication on Web 05/11/2000

2394 Organometallics, Vol. 19, No. 12, 2000
Notes
F igu r e 1. Molecular structure and numbering scheme of
3. The ellipsoids represent a probability of 40%. The
hydrogen atoms are omitted for clarity reasons. The carbon
atoms of the THF ligand are shown with arbitrary radii.
Atoms marked with one prime are generated by an inver-
sion center (-x, -y, -z); those marked with two primes
are generated by C2 symmetry (-x+1, y, -z-0.5).
F igu r e 2. Linkage of two columns in the crystal structure
of 3. All hydrogen atoms are omitted for clarity reasons;
all carbon atoms are represented with arbitrary radii. The
ellipsoids represent a probability of 40%. Linking of the
columns occurs via a K1 and Sb1′′′ of the stibolide gener-
ated by -x+1, -y, -z. The centers of the stibolide anions
are symbolized by Z(n) with n the same number as the
corresponding Sb(n). Environment of the potassium cen-
ters: distances (Å) K1-Z1 2.839, K2-Z1 2.901, K2-Z2
2.893, K3-Z2 2.922; angles (deg) Z1-K1-Z1′ 180.0, Z1-
K2-Z2 139.5, Z1-K2-Sb1′′′ 111.8, Z2-K2-Sb1′′′ 108.6,
Z2-K3-Z2′′ 138.2, O3-K3-Z2 110.9, O3-K3-Z2′′ 110.9.
Sch em e 1. Syn th esis of Stibole 2 a n d Its
Red u ction w ith P ota ssiu m to Stibolid e 3
As expected, the shortening of the Sb-C bond lengths
compared to single bonds is less pronounced. On the
other hand these bonds are clearly longer than observed
for a SbdC double bond (2.06 Å),13 calculated for
stibaethene H-SbdCH2 (2.01 Å)14 or found for stiba-
benzene (stibinine, 2.05 Å).15 Surprisingly, the Sb1-C11
and Sb1-C14 bond lengths of 2.085(8) and 2.087(7) Å
are smaller than the values for Sb2-C21 (2.115(8) Å)
and Sb2-C24 (2.100(7) Å), although the linkage be-
tween the columns leads to a higher coordination
number at Sb1. In 2,2′,5,5′-tetramethyl-7 and octameth-
yl-1,1′-distibaferrocene9 mean endocyclic Sb-C bond
lengths of 2.11 Å were reported.
Another point of interest concerns the delocalization
of the anionic charge within the stibolide anions. Taking
the bond length difference between the endocyclic C-C
bonds as shown in Table 1 as a criterion, the delocal-
ization should be disturbed since the C(n1)-C(n2) and
C(n3)-C(n4) bonds with a mean value of 1.39 Å are
shorter than the C(n2)-C(n3) bonds at approximately
1.44 Å. In contrast to this observation the corresponding
endocyclic C-C bonds in 2,2′,5,5′-tetrakis(trimethylsi-
lyl)-3,3′,4,4′-tetramethyl-1,1′-distibaferrocene8 are alike
(mean value 1.43 Å). For octamethyl-1,1′-distibafer-
ing stibolide substituents, whereas K2 displays close
contacts to the neighboring column, as shown in Figure
2. As a consequence of the lower coordination number
of K1, the distances of K1 to the centers of the neighbor-
ing stibolide cycles with values of 2.839 Å are smaller
than the corresponding contacts between K2 and K3 to
their neighboring anions. The parallel orientation of the
anions bonded to K1 is crystallographically enforced by
an inversion center. The stibolide anions at K2 and K3
show strong deviations from parallelism, and the angles
between the centers of the stibolide cycles show values
of 139.5° and 138.2° at K2 and K3, respectively. Along
with this bending increasing distances between the
stibolide centers and the cations of approximately 290.5
Å are observed. The columns are linked via K2-Sb1′′′
contacts of 3.618 Å, thus forming a wavelike layer
structure rather than a chain structure.
(13) Hitchcock, P. B.; J ones, C.; Nixon, J . F. Angew. Chem. 1995,
107, 522; Angew. Chem., Int. Ed. Engl. 1995, 34, 492.
(14) Dobbs, K. D.; Boggs, J . E.; Cowley, A. H. Chem. Phys. Lett. 1987,
141, 372.
(15) Fong, G. D.; Kuczkowski, R. L.; Ashe, A. J ., III. J . Mol.
Spectrosc. 1978, 70, 197.

Notes
Organometallics, Vol. 19, No. 12, 2000 2395
Ta ble 1. Selected Bon d Len gth s (Å) a n d An gles
(d eg) of 3
Ta ble 3. Cr ysta llogr a p h ic Da ta of 3 a s Well a s
Deta ils of th e Str u ctu r e Solu tion a n d Refin em en t
P r oced u r es
n
empirical formula
C26H44K2O0.5Sb2
686.31
1
2
fw (g mol-1
)
K1-Sb(n)
3.4861(6)
3.555(2)
temp T (K)
193(2)
C2/c (No. 15)
space group18
unit cell dimens
a (Å)
K2-Sb(n)
3.487(2)
3.501(2)
2.115(8)
2.100(7)
1.38(1)
K3-Sb(n)
Sb(n)-C(n1)
Sb(n)-C(n4)
C(n1)-C(n2)
C(n2)-C(n3)
C(n3)-C(n4)
2.085(8)
2.087(7)
1.40(1)
1.45(1)
1.38(1)
11.4558(8)
18.331(1)
30.601(2)
100.078(2)
6326.8(8)
8
1.441
0.71073
1.983
5197 (Rint ) 0.0463)
0.1355
0.0985
3250
b (Å)
c (Å)
1.44(1)
1.40(1)
â (deg)
V (Å3)
Z
C(n4)-Sb(n)-C(n1)
Sb(n)-C(n1)-C(n2)
C(n1)-C(n2)-C(n3)
C(n2)-C(n3)-C(n4)
C(n3)-C(n4)-Sb(n)
81.1(3)
81.1(3)
Fcalcd (g cm3)
λ (Å)
112.5(5)
116.2(7)
118.0(6)
112.0(5)
111.6(5)
118.0(6)
117.7(7)
111.6(5)
µ (cm-1
)
R indices (all data)
wR2a
R1a
Ta ble 2. NMR Sp ectr oscop ic Da ta of 1, 2, a n d 3
R indices with I > 2σ(I) (data)
([D6]ben zen e, 25˚C)
a
R1
0.0536
1.011
1.277/-0.943
goodness-of-fit sbon F2
1
2
3
residual density (e Å-3
)
1H:
δ(CH3)
0.87
2.19
7.6
0.97
2.31
7.2
0.87
1.98
7.2
1.13
2.38
7.2
1.01
2.22
broad
1.01
2.43/2.83
broad
performed by using standard Schlenk techniques and dried
with thoroughly deoxygenated solvents. NMR spectra were
recorded on J EOL spectrometers GSX270 and EX400, and the
NMR data are listed in Table 2. A Nicolet 520 FT-IR spectro-
photometer was used to record the IR spectra; solid substances
were measured in Nujol between KBr plates (vs very strong,
s strong, m medium strong, w weak, vw very weak, sh
shoulder). The low carbon value of 1 at the elemental analysis
results from carbide and carbonate formation during handling
and combustion of the compound.
δ(CH2)
3J (H,H)
δ(CH3)
δ(CH2)
3J (H,H)
δ
5.91 (Cp)
1.41 (THF)
3.52 (THF)
13C{1H}:
δ(CH3)
δ(CH3)
δ(CH2)
δ(CH2)
δ(C2, C5)
δ(C3, C4)
δ
14.31
15.96
21.19
29.41
133.65
190.67
109.60 (Cp)
14.26
16.95
22.47
24.92
157.59
153.54
15.15/16.05
18.91/21.22
23.11/23.74
26.50/29.05
153.34
150.24
25.50 (THF)
67.65 (THF)
Syn th esis of 1,1-Bis(cyclop en ta d ien yl)-2,3,4,5-tetr a -
eth yl-1-zir con a cyclop en ta -2,4-d ien e (1).12 A 2.5 M butyl-
lithium solution in hexane (28.43 mL, 71.08 mmol) was
dropped slowly into a solution of 10.39 g of zirconocene
dichloride (35.54 mmol) and 5.84 g of hex-3-yne (71.08 mmol)
in 40 mL of THF at -78 °C. After complete addition and an
additional 15 min at this temperature this reddish brown
solution was warmed to room temperature. All volatile materi-
als were removed in vacuo, and the residue was dissolved in
40 mL of toluene. All solids were filtered off, and the removal
of toluene left 11.51 g of red and analytically pure powder of
1 (29.85 mmol, 84%), mp 57 °C. IR [cm-1]: 1672 s, 1620 s,
1613 s, 1604 s, 1580 s, 1463 s, 1453 s, 1415 m, 1375 s, 1340
m, 1323 m, 1262 m, 1232 m, 1192 m, 1134 s, 1098 s, 1063 s,
1016 vs, 901 m, 893 w, 846 m, 795 vs, 740 s, 676 s, 668 s, 601
m, 540 m, 531 m, 510 m, 493 m, 476 m, 331 w. Anal. Calcd for
rocene9 similar results were reported; however, due to
less steric strain the bond lengths are in general slightly
smaller. All these stibolide anions have a very narrow
C-Sb-C angle of approximately 80° in common.
Table 2 summarizes the NMR spectroscopic data. The
ethyl groups of 3 are split; we were not able to
distinguish whether this splitting arises from two
chemically different stibolide anions or from the ethyl
substituents of one anion. There is no temperature
dependency observed. Therefore, hindered rotation can
be ruled out as the reason for this observation.
C
22H30Zr, 385.68 g mol-1: C, 68.51; H, 7.84. Found: C, 68.26;
H, 7.68.
Syn th esis of 1-Ch lor o-2,3,4,5-tetr a eth yl-1-stibole (2).
Con clu sion
Antimony trichloride (1.13 g, 4.95 mmol) was added to a
solution of 1.91 g of 1 (4.95 mmol) in 25 mL of THF. After 24
h of stirring ar room temperature all volatile materials were
removed under vacuum. The yellow residue was extracted with
30 mL of pentane. Removal of the solvent left 1.27 g of an
analytically pure yellow oil of 2 (3.95 mmol, 80%). IR [cm-1]:
2967 vs, 2931 vs, 2872 s, 1766 vw, 1735 vw, 1710 vw, 1670
vw, 1721 vw, 1584 vw, 1559 vw, 1550 vw, 1506 vw, 1456 s,
1376 m, 1311 w, 1284 vw, 1259 vw, 1223 vw, 1179 vw, 1156
vw, 1105 vw, 1090 vw, 1063 w, 1050 w, 962 vw, 943 vw, 922
vw, 884 vw, 866 vw, 817 vw, 784 vw, 729 vw, 698 vw, 578 vw,
529 vw, 443 vw, 403 vw, 331 m, 316 m, 281 vw. Anal. Calcd
for C12H20ClSb, 321.53 g mol-1: C, 44.83; H, 6.27. Found: C,
44.81; H, 6.09.
Interactions between soft cations and heavier p-block
elements are of general interest.16 In the crystal struc-
ture of 3 η5-coordination of the stibolide anions to the
potassium cations leads to the formation of columns.
These structural motifs are linked by metal centers
which are η1-bonded to the antimony atoms of the
neighboring column. The K-Sb distances within a
column vary between 3.49 and 3.56 Å, whereas the
linkage between the columns shows K-Sb σ-bond
lengths of 3.62 Å.
Exp er im en ta l Section
Syn th esis of Sem i(tetr a h yd r ofu r a n -O)bisp ota ssiu m
bis(2,3,4,5-tetr a eth yl-1-stibolid e) (3). Potassium (0.33 g,
8.44 mmol) was added to a solution of 1.65 g of 2 (5.13 mmol)
in 25 mL of THF. After 2 days of stirring at room temperature
all volatiles were removed under reduced pressure. Extraction
Gen er a l P r oced u r es. All experiments and manipulations
were carried out under an atmosphere of argon. Reactions were
(16) Paver, M. A.; Russell, C. A.; Wright, D. S. Angew. Chem. 1995,
107, 1679; Angew., Int. Ed. Engl. 1995, 34, 1545.

2396 Organometallics, Vol. 19, No. 12, 2000
Notes
of the residue with 30 mL of heptane and recrystallization from
benzene gave 3.69 g of yellow crystals of 3 (5.47 mmol, 72%),
dec above 165 °C. IR [cm-1]: 1688 vw, 1641 vw, 1579 w, 1559
w, 1472 vs, 1447 vs, 1402 s, 1372 vs, 1342 w, 1309 s, 1259 vs,
1174 vw, 1144 w, 1078 vs, 1061 vs, 1050 vs, 1024 vs, 996 s,
925 m, 912 m, 900 m, 861 m, 847 m, 810 vs, 756 s, 721 m, 696
m, 664 m, 644 w, 612 w, 531 vw, 521 vw, 482 vw, 438 vw, 388
m, 366 m. Anal. Calcd for C26H44K2O0.5Sb2, 686.31 g mol-1: C,
45.50; H, 6.46. Found: C, 45.21; H, 6.50.
from Cromer and Mann20 and for the hydrogen atoms from
Stewart et al.21 The non-hydrogen atoms were refined aniso-
tropically. The H-atoms were considered with a riding model
under restriction of ideal symmetry at the corresponding
carbon atoms. One of the methyl groups is disordered on two
positions with a population ratio C112/C113 of 0.52(2)/0.48-
(2). This disorder is not represented in Figure 1 due to clarity
reasons. We were not able to adopt a split model for the carbon
atoms of the THF ligand (C31, C32) with high thermal motion.
Cr ysta llogr a p h ic An a lysis of 3. Data were collected on
a Siemens P4 diffractometer with a Siemens SMART-CCD
area detector with graphite-monochromated Mo KR radiation
(λ ) 0.71073 Å) at -80 °C using oil-coated rapidly cooled single
crystals.17 A total of 11 180 reflections were collected in the
range 2.7° < 2θ < 55.5°. A semiempirical absorption correction
was applied (Tmin/Tmax 0.755/0.826). Crystallographic param-
eters, details of data collection, and refinement procedures are
summarized in Table 3.
Ack n ow led gm en t. This work was financially sup-
ported by the Deutsche Forschungsgemeinschaft and
the Fonds der Chemischen Industrie. C.G. wishes to
express his gratitude to the State of Bavaria/Germany
for a Ph.D. scholarship granted.
Su p p or tin g In for m a tion Ava ila ble: An X-ray crystal-
lographic file for the structure determination of 3. This
material is available free of charge via the Internet at
http://pubs.acs.org.
The structure was solved by direct methods, and 288
parameters were refined with the software packages SHELXL-
93 and SHELXL-97.19 Neutral scattering factors were taken
OM000161B
(19) Sheldrick, G. M. SHELXL-93, Universita¨t Go¨ttingen, 1993;
SHELXL-97, Universita¨t Go¨ttingen, 1997.
(20) Cromer, D. T.; Mann, J . B. Acta Crystallogr. 1968, 24, 321.
(21) Stewart, R. F.; Davidson, E. R.; Simpson, W. T. J . Chem. Phys.
1965, 42, 3175.
(17) Kottke, T.; Stalke, D. J . Appl. Crystallogr. 1993, 26, 615. Stalke,
D. Chem. Soc. Rev. 1998, 27, 171.
(18) Hahn, T., Ed. International Tables for Crystallography, Vol. A,
Space Group Symmetry, 2nd ed.; D. Reidel: Dordrecht, 1984.