Synthesis and structures of an unusual germanium(II) calix[4]arene complex and the first germanium(II) calix[8]arene complex and their reactivity with diiron nonacarbonyl

Article abstract of DOI:10.1021/ic700969m

The protonolysis reaction of the germanium(II) amide Ge[N(SiMe ₃)₂]₂ with calix[4]arene and calix[8]arene furnishes the two germanium(II) calixarene complexes {calix[4]}Ge₂ and {calix[8]}Ge₄, respectively, which have been crystallographically characterized. The calix[4]arene complex contains a Ge₂O₂ rhombus at the center of the molecule and is one of the only four germanium(II) calix[4]arenes that have been structurally characterized. The calix[8]arene species is the first reported germanium calix[8]arene complex, and it exhibits an overall bowl-shaped structure which contains two Ge₂O₂ fragments. The latter complex reacts with Fe₂(CO)₉ to yield an octairon compound, which has also been structurally characterized and contains four GeFe₂ triangles arranged around the macrocyclic ring. The germanium(II) centers are oxidized to germanium(IV) in this process, with concomitant reduction of the neutral diiron species to Fe₂(CO) ₈^2- anions.

Full text of DOI:10.1021/ic700969m

Inorg. Chem. 2007, 46, 7579−7586
Synthesis and Structures of an Unusual Germanium(II) Calix[4]arene
Complex and the First Germanium(II) Calix[8]arene Complex and Their
Reactivity with Diiron Nonacarbonyl
Anthony E. Wetherby, Jr.,† Lindy R. Goeller,† Antonio G. DiPasquale,‡ Arnold L. Rheingold,‡ and
Charles S. Weinert*,†
Department of Chemistry, Oklahoma State UniVersity, Stillwater, Oklahoma 74078, and
Department of Chemistry and Biochemistry, UniVersity of California, San Diego, La Jolla,
California 92093-0303
Received May 18, 2007
The protonolysis reaction of the germanium(II) amide Ge[N(SiMe
the two germanium(II) calixarene complexes calix[4] Ge and
crystallographically characterized. The calix[4]arene complex contains a Ge
3
)
2
]
{
2
with calix[4]arene and calix[8]arene furnishes
calix[8] Ge , respectively, which have been
rhombus at the center of the molecule
{
}
2
}
O
2
4
2
and is one of the only four germanium(II) calix[4]arenes that have been structurally characterized. The calix[8]-
arene species is the first reported germanium calix[8]arene complex, and it exhibits an overall bowl-shaped structure
which contains two Ge
2
O
2
2 9
fragments. The latter complex reacts with Fe (CO) to yield an octairon compound,
which has also been structurally characterized and contains four GeFe
2
triangles arranged around the macrocyclic
ring. The germanium(II) centers are oxidized to germanium(IV) in this process, with concomitant reduction of the
(CO) 2
-
anions.
neutral diiron species to Fe
2
8
Introduction
few examples only three materials having germanium bound
directly to the calixarene oxygen atoms have been synthe-
Calixarenes are highly useful macrocyclic compounds
which have a variable cavity size and have a variety of
applications in the areas of molecular self-assembly, ionic
and molecular recognition, and catalysis.1-7 A number of
3
3,34
sized and structurally characterized.
calix[4]arene complexes [Bu calix]Ge
These include the
and the two struc-
t
33
2
(
8) Redshaw, C.; Rowan, M. A.; Warford, L.; Homden, D. M.; Arbaoui,
A.; Elsegood, M. R. J.; Dale, S. H.; Yamato, T.; Casas, C. P.; Matsui,
S.; Matsuura, S. Chem.sEur. J. 2007, 13, 1090-1107.
transition-metal and main-group complexes using these
species as ligands have been prepared,8
-28
but calixarene
and of these
complexes containing germanium are rare2
9-35
(9) Marcos, P. M.; Mellah, B.; Ascenso, J. R.; Michel, S.; Hubscher-
Bruder, V.; Arnaud-Neu, F. New J. Chem. 2006, 30, 1655-1661.
10) Coquiere, D.; Marrot, J.; Reinaud, O. Chem. Commun. 2006, 3924-
3926.
(
*
Author to whom correspondence should be addressed. E-mail:
weinert@chem.okstate.edu.
(11) Duerr, S.; Bechlars, B.; Radius, U. Inorg. Chim. Acta 2006, 359, 4215-
†
Oklahoma State University.
University of California, San Diego.
4226.
‡
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(
1) Gutsche, C. D. Calixarenes ReVisited; Royal Society of Chemistry:
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(
(
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1
0.1021/ic700969m CCC: $37.00
© 2007 American Chemical Society
Inorganic Chemistry, Vol. 46, No. 18, 2007 7579
Published on Web 08/11/2007

Wetherby et al.
Table 1. Selected Bond Distances (Å) and Angles (deg) for Compound
1
Ge(1)-O(1)
Ge(1)-O(2)
Ge(1)-O(2′)
C(1)-O(1)
C(13)-O(2)
1.845(1)
1.989(1)
1.987(1)
1.373(3)
1.385(2)
Ge(1)-O(2)-Ge(1′)
O(1)-Ge(1)-O(2)
O(2)-Ge(1)-O(2′)
Ge(1)-O(1)-C(1)
Ge(1)-O(2)-C(13)
107.89(6)
91.72(6)
72.11(6)
117.9(1)
126.5(1)
Ge(II)-O bonds.3
6-39
The germanium centers in 1 are
formally in the +2 oxidation state, and the lone pairs of
electrons present point out and away from the central Ge O
2
2
rhombus. The Oterm-Ge-Obr and bond angles in 1 are close
to the expected value of 90°, while the angles inside the
central rhombus are 107.89(6)° for Ge(1)-O(2)-Ge(1′) and
7
2.11(6)° for O(2)-Ge(1)-O(2′). The aromatic ring attached
to the O(1) atom is bent back such that they lie above Ge-
1′) on the opposite side of the Ge rhombus, and the
Figure 1. ORTEP diagram of 1. Thermal ellipsoids are drawn at 50%
(
2 2
O
probability.
closest contact between the ring carbons and the germanium
atoms is 3.28 Å indicating the absence of any Ge-C π-type
interactions.
tural isomers of [Butcalix(TMS)2]Ge.34 We have prepared the
related unsubstituted germanium(II) calix[4]arene complex
and also the first germanium calix[8]arene complex and have
determined the X-ray crystal structures of each. All of the
germanium(II) centers in both of these complexes have a
lone pair of electrons available for donation to other metal
centers, and thus these species could be useful platforms for
the support of multiple main-group or transition-metal
fragments. We have investigated the reaction of both
2 2
The bonding environment in the Ge O rhombus closely
resembles that of the germanium(II) aryloxide compounds
i
[
6 3 2 2 2 6 2 3 2 2
Ge(OC H (Pr ) -2,6) ] and [Ge(OC H (Me) -2,4,6) ] , both
3
8
of which contain bridging aryloxide groups. Furthermore,
the structures of 1 and the tert-butyl calix[4]arene [Bu calix]-
Ge (2) are nearly identical with these two species having
2
t
3
3
the same Ge-O bond distances and O-Ge-O bond angles
within the measured estimated standard deviation values. The
structures of the two possible isomers of the only other
crystallographically characterized germanium(II) calixarene
2 9
complexes with Fe (CO) , resulting in the formation of a
germanium iron macrocycle containing eight iron atoms in
the case of the germanium calix[8]arene compound.
t
(TMS)2
[
Bu calix
]Ge (3) differ considerably from 1 and 2 in
Results and Discussion
that 3 contains only one germanium atom and can adopt
3
4
either an exo or an endo isomeric form. In the exo isomer,
the germanium atom is formally bound to the two unsub-
stituted oxygen atoms with Ge-O distances of 1.765(6) and
Reaction of calix[4]arene with 2 equiv of Ge[N(SiMe
furnishes the chealted complex {calix[4]}Ge (1) in 56%
3 2 2
) ]
2
yield. The structure of 1 has been determined and an ORTEP
diagram is shown in Figure 1 while selected bond distances
and angles are collected in Table 1. The two germanium
centers are related by a center of inversion, and each is bound
to three different oxygen atoms. The shorter Ge(1)-O(1)
distance is representative of a typical germanium(II)-
phenolic oxygen bond whereas the elongated Ge(1)-O(2)
and Ge(1)-O(2′) distances can be regarded as two dative
1
.842(6) Å and also exhibits long dative interactions with
the oxygen atoms of the two -OSiMe groups measuring
.421(5) and 2.486(5) Å. In the endo isomer, the Ge-O
3
2
distances are 1.841(5) and 1.853(5) Å and there are no dative
interactions with the oxygen atoms of the trimethylsiloxy
groups. The formal Ge-O single bonds in the endo isomer
are similar to those of 1, while the elongated dative
interactions are a result of the steric crowing of the -OSiMe
3
(
(
(
(
(
21) Sliwa, W. Croat. Chem. Acta 2002, 75, 131-153.
groups which point outward from the center of the macro-
cycle.
22) Seitz, J.; Maas, G. Chem. Commun. 2002, 338-339.
23) Brown, M.; Jablonski, C. Can. J. Chem. 2001, 79, 463-471.
24) Loffler, F.; Luning, U.; Gohar, G. New J. Chem. 2000, 24, 935-938.
25) Pellet-Rostaing, S.; Regnouf-de-Vains, J.-B.; Lamartine, R.; Fenet, B.
Inorg. Chem. Commun. 1999, 2, 44-47.
While free calix[4]arene undergoes a rapid exchange
between a cone and inverted cone configuration in solution,40
the presence of the bridging oxygen atoms attached to the
two germanium centers enforces structural rigidity in 1. The
(
(
26) Xie, D.; Gutsche, C. D. J. Org. Chem. 1998, 63, 9270-9278.
27) Khasnis, D. V.; Burton, J. M.; Lattman, M.; Zhang, H. J. Chem. Soc.,
Chem. Commun. 1991, 562-563.
1
H NMR spectrum obtained for 1 correlates with its solid-
(28) Khasnis, D. V.; Lattman, M.; Gutsche, C. D. J. Am. Chem. Soc. 1990,
1
12, 9422-9423.
29) Sakurai, T.; Takeuchi, Y. Appl. Organomet. Chem. 2005, 19, 372-
76.
state structure, where resonances for protons directed toward
(
3
(
(
(
(
(
36) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. J. Chem. Soc., Dalton
(30) Sakurai, T.; Takeuchi, Y. Appl. Organomet. Chem. 2004, 18, 23-27.
(31) Sakurai, T.; Takeuchi, Y. Heteroat. Chem. 2003, 14, 365-373.
(32) Takeuchi, Y.; Sakurai, T.; Tanaka, K. Main Group Met. Chem. 2000,
Trans. 2002, 2948-2950.
37) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. Acta Crystallogr. 2002,
E58, m718-m720.
23, 311-316.
38) Weinert, C. S.; Fenwick, A. E.; Fanwick, P. E.; Rothwell, I. P. J.
Chem. Soc., Dalton Trans. 2003, 532-539.
(
(
33) McBurnett, B. G.; Cowley, A. H. Chem. Commun. 1999, 17-18.
34) Hascall, T.; Rheingold, A. L.; Guzei, I.; Parkin, G. Chem. Commun.
39) Weinert, C. S.; Fanwick, P. E.; Rothwell, I. P. Inorg. Chem. 2003,
1998, 101-102.
4
2, 6089-6094.
40) Lang, J.; Deckerov a´ , V.; Czernek, J.; Lhot a´ k, P. J. Chem. Phys. 2005,
22, 0445061-04405611.
(35) Hockeymeyer, J.; Valentin, B.; Castel, A.; Riviere, P.; Satge, J.; Cardin,
C. J.; Teixeira, S. Main Group Met. Chem. 1997, 20, 775-781.
1
7580 Inorganic Chemistry, Vol. 46, No. 18, 2007

Unusual Germanium(II) Calixarene Complexes
Scheme 1
the central Ge
2
O
2
rhombus are shifted downfield versus those
macrocyclic ring system from a cone to an inverted cone
4
0
pointing away from this moiety, which are observed for both
the meta and para protons of the aromatic rings. The two
sets of bridging methylene units of the calix[4]arene ligand
system are also diasterotopic, where the protons attached to
C(7) and C(14) directed toward the Ge O rhombus give rise
2 2
to a doublet at δ 4.41 ppm (J ) 12.9 Hz) whereas those
configuration and correspond to the axial and equatorial
-CH - groups, respectively.
3 2 2 6 6
Addition of 1 equiv of Ge[N(SiMe ) ] to a C D solution
2
of calix[4]arene results in the formation of two intermediate
species as well as the final product 1 (Scheme 1). Two
singlets for the nonequivalent -OH groups of 4 were visible
at δ 9.50 and 9.18 ppm (intensity ratio 1:2), while a third
singlet at δ 7.74 ppm arises from the two equivalent -OH
groups of 5. The integrated intensity of the feature for 5 was
approximately half of that of the two resonances for 4. The
feature at δ 10.21 ppm for the calix[4]arene starting material
was also still present. The formation of 4 and 5 was also
reflected in the signals for the methylene groups of the calix-
[4]arene system as there were six sets of doublets visible in
attached to these two carbon atoms and directed away from
the Ge
2.9 Hz).
The pathway for the formation of 1 was determined to
2 2
O fragment appear as a doublet at δ 3.23 ppm (J )
1
1
occur in a stepwise manner and was monitored using H
NMR spectroscopy by the introduction of sequential aliquots
of Ge[N(SiMe ) ] to a solution of calix[4]arene in C D .
3 2 2 6 6
The diagnostic resonances for this investigation were those
of the bridging methylene units as well as the hydroxyl
resonances of the calix[4]arene system. Calix[4]arene exhibits
1
the H NMR spectrum at this time. The signals at δ 4.41
and 3.23 ppm correspond to 1, those at δ 4.38 (J )
12.9 Hz) and 3.26 (J ) 13.8 Hz) ppm correspond to 4, and
those at δ 4.33 (J ) 13.8 Hz) and 3.18 (J ) 13.5 Hz) ppm
correspond to 5, wherein the assignments for 4 and 5 are
based on the integrated intensities of the respective peaks.
A singlet at δ 0.90 ppm was also visible due to the formation
6 6
a singlet at δ 10.21 ppm in C D arising from the four
equivalent hydroxyl protons, and the methylene resonances
for this compound appear as two broad features centered at
δ 4.12 and 3.28 ppm due to the rapid interconversion of the
Scheme 2
Inorganic Chemistry, Vol. 46, No. 18, 2007 7581

Wetherby et al.
Figure 3. Wireframe drawing of 6. The germanium atoms are drawn in
blue, the oxygen atoms in red, and the carbon atoms in gray.
1
.833(4) Å, which is considerably shorter than the corre-
sponding distances in 1.
Both of the Ge rhombi in 6 have essentially the same
2
O
2
Figure 2. ORTEP diagram of 6‚C6H6. The benzene molecule is not shown,
geometry wherein the individual fragments are skewed such
that one Ge-Obr distance is shorter than the other for each
of the four germanium atoms (Table 2). The Oterm-Ge-Obr
bond angles deviate significantly from 90° with an average
value of 93.1(2)° while the Obr-Ge-Obr angles within the
and thermal ellipsoids are drawn at 50% probability.
Table 2. Selected Bond Distances (Å) and Angles (deg) for Compound
6
‚C6H6
Ge(1)-O(1)
Ge(1)-O(2)
Ge(1)-O(4)
Ge(2)-O(2)
Ge(2)-O(3)
Ge(2)-O(4)
Ge(3)-O(5)
Ge(3)-O(7)
Ge(3)-O(8)
Ge(4)-O(6)
Ge(4)-O(7)
Ge(4)-O(8)
1.834(4)
2.036(3)
2.012(3)
1.970(3)
1.833(4)
2.000(3)
1.837(4)
2.019(3)
2.030(3)
1.828(4)
1.980(3)
1.953(4)
O(1)-Ge(1)-O(2)
O(1)-Ge(1)-O(4)
O(2)-Ge(1)-O(4)
O(2)-Ge(2)-O(3)
O(3)-Ge(2)-O(4)
O(2)-Ge(2)-O(4)
O(5)-Ge(3)-O(7)
O(5)-Ge(3)-O(8)
O(7)-Ge(3)-O(8)
O(6)-Ge(4)-O(7)
O(6)-Ge(4)-O(8)
O(7)-Ge(4)-O(8)
Ge(1)-O(2)-Ge(2)
Ge(1)-O(4)-Ge(2)
Ge(3)-O(7)-Ge(4)
Ge(3)-O(8)-Ge(4)
93.7(2)
90.7(1)
72.0(1)
94.4(2)
92.3(2)
73.6(1)
93.0(2)
92.1(2)
71.7(1)
95.2(2)
93.1(2)
74.2(1)
106.5(1)
106.3(1)
106.1(1)
106.7(1)
Ge
2
O
2
rhombi have an average value of 72.9(2)°, and the
average Ge-Obr-Ge bond angle within the Ge
O
2 2
fragments
is 106.4(1) °. The Ge(1)-O(2)-Ge(2)-O(4) rhombus is
puckered by 8.2° while the other fragment containing Ge-
(3)-O(7)-Ge(4)-O(8) is puckered by 7.3 °. This contrasts
with the structure of 1 where the Ge moiety is completely
2 2
O
planar. The overall shape of the molecule resembles a deep
U-shaped bowl with two of the aromatic rings, which contain
C(31)-C(36) and C(71)-C(76), bent inward toward the
center of the molecule. A wireframe diagram illustrating the
structure of the molecule is shown in Figure 3.
As found for 1, the individual protons of the eight
methylene groups in the calix[8]arene macrocycle are
magnetically nonequivalent and the presence of an ap-
proximate center of symmetry in the molecule results in the
of HN(SiMe
to the trimethylsilyl groups of 4. Addition of a further
.5 equiv of Ge[N(SiMe to the NMR tube resulted in
an increase in intensity of the hydroxyl resonance at δ
.74 ppm for 5, while the hydroxyl resonances for 4 and
calix[4]arene were very weak. The methylene resonances for
had also diminished, while those for 1 and 5 had increased
in intensity. Increasing the amount of Ge[N(SiMe to a
3 2
) , and a singlet at δ 0.28 ppm can be attributed
0
3 2 2
) ]
1
appearance of eight doublets for these protons in the H NMR
spectrum of 6. One resonance appears far downfield at δ
7
5.83 ppm (J ) 16.8 Hz) that can be attributed to the hydrogen
atoms H(4a) and H(8a) bound to C(4) and C(8), which are
located at the bottom of the bowl-shaped geometry of the
molecule and point inward toward each of the two Ge O
2 2
4
3 2 2
) ]
slight excess of 2 equiv resulted in the consumption of the
remaining calix[4]arene starting material and complete
conversion of 4 and 5 to compound 1.
rhombi. In the solid-state structure of 6, H(8a) has two close
contacts with O(1) and O(5) measuring 2.32(1) and 2.52(1)
Å, respectively, while H(4a) has two similar close contacts
with O(1) and O(4) measuring 2.32(1) and 2.46(1) Å,
respectively, all of which are within the sum of the van der
The reaction of calix[8]arene with 4 equiv of Ge-
[
N(SiMe
ium species {calix[8]}Ge
6 6
Scheme 2). The structure of 6‚C H
3
)
2
]
2
resulted in the formation of the tetragerman-
(6) in excellent (89%) yield
was determined and
4
41
Waals radii of hydrogen and oxygen (2.60 Å). There are
(
two additional close contacts between H(4a)-O(5) and
H(8a)-O(1) measuring 2.67(1) and 2.60(1) Å, respectively.
The hydrogen atom H(1b) has two close contacts with O(1)
an ORTEP diagram is shown in Figure 2, while selected bond
distances and angles are collected in Table 2. The four
germanium atoms in 6 are assembled in pairs on opposite
sides of the molecule, and each germanium is bound to three
oxygen atoms to form rhombi in a similar fashion to 1. The
Ge-O bonds to the terminal oxygen atoms are all shorter
than those to the bridging oxygens with an average value of
(2.48(1) Å) and O(2) (2.47(1) Å), and H(5b) has close
contacts with O(5) and O(8) measuring 2.52(1) and 2.50(1)
Å, respectively. These two protons, which are directed inward
(41) Emsley, J. The Elements, 2nd ed.; Clarendon Press: Oxford, 1991.
7582 Inorganic Chemistry, Vol. 46, No. 18, 2007

Unusual Germanium(II) Calixarene Complexes
Scheme 3
Table 3. Selected Bond Distances (Å) and Angles (deg) for Compound
7‚C6H6
Ge(1)-O(1)
Ge(1)-O(2)
Ge(1)-Fe(1)
Ge(1)-Fe(2)
Fe(1)-Fe(2)
Fe(1)-C(16)
Fe(1)-C(17)
Fe(1)-C(18)
Fe(1)-C(22)
Fe(2)-C(15)
Fe(2)-C(19)
Fe(2)-C(20)
Fe(2)-C(21)
C(15)-O(6)
C(16)-O(3)
C(17)-O(4)
C(18)-O(5)
C(19)-O(8)
C(20)-O(10)
C(21)-O(9)
C(22)-O(7)
1.788(2)
1.772(2)
2.3543(5)
2.3244(6)
2.8407(6)
1.812(3)
1.810(4)
1.778(4)
1.826(4)
1.837(4)
1.791(4)
1.808(4)
1.806(4)
1.120(5)
1.131(4)
1.129(5)
1.150(4)
1.125(5)
1.140(5)
1.139(5)
1.121(4)
O(1)-Ge(1)-O(2)
O(1)-Ge(1)-Fe(1)
O(1)-Ge(1)-Fe(2)
O(2)-Ge(1)-Fe(1)
O(2)-Ge(1)-Fe(2)
Fe(1)-Ge(1)-Fe(2)
Ge(1)-Fe(1)-Fe(2)
Ge(1)-Fe(2)-Fe(1)
Ge(1)-Fe(1)-C(16)
Ge(1)-Fe(1)-C(17)
Ge(1)-Fe(1)-C(18)
Ge(1)-Fe(1)-C(22)
Ge(1)-Fe(2)-C(15)
Ge(1)-Fe(2)-C(19)
Ge(1)-Fe(2)-C(20)
Ge(1)-Fe(2)-C(21)
103.7(1)
116.77(7)
119.70(7)
115.91(7)
124.55(8)
74.77(2)
52.14(2)
53.10(2)
90.6(1)
90.0(1)
96.3(1)
154.5(1)
140.5(1)
108.0(1)
85.9(1)
2 2
toward the Ge O rhombi, result in the appearance of a
1
doublet at δ 4.77 ppm (J ) 12.6 Hz) in the H NMR
spectrum of 6, and a second set of closely spaced doublets
at δ 4.60 (J ) 15.8 Hz) and 4.57 (J ) 15.0 Hz) ppm can be
attributed to the four protons attached to C(2) and C(3) and
C(6) and C(7), respectively, which are directed inward
87.6(1)
toward the two Ge
atoms on each of the methylene groups are directed outward
from the two Ge rhombi and have chemical shifts in the
2 2
O rhombi. The remaining eight hydrogen
2 2
O
range of δ 3.48-3.22 ppm. One feature appears upfield at
δ 3.24 ppm (J ) 12.6 Hz) arising from the two protons
attached to C(1) and C(5) which are located at distances of
generated from the asymmetric unit which consists of a
germanium atom, a Fe (CO) moiety, two phenyl rings, and
two methylene groups. The structure of this fragment is
shown in Figure 5.
4.46 and 4.47 Å, respectively, from the centroids of the two
2
8
Ge rhombi in 6.
2
O
2
The presence of four lone pairs of electrons on the
germanium(II) atoms in 6 renders this molecule a potentially
useful platform for the support of multiple coordinatively
unsaturated transition-metal centers. In order to investigate
Initially, we expected the reaction of 6 with Fe
result in cleavage of the Fe-Fe bond leading to the
coordination of a Fe(CO) unit to each of the germanium
centers with concomitant formation of free Fe(CO) , which
O) Ge
. Instead, reductive decarbonylation involving
extrusion of one bridging CO group in Fe (CO) and
formation of four triangular GeFe three-membered rings was
2 9
(CO) to
4
2
this postulate, compound 6 was reacted with 4 equiv of Fe -
5
(CO)
9
resulting in the isolation of a ruby-red solid in good
t
was observed in the reaction of (Bu
2
-2,6-Me-4-C
H
6 2
2
(73%) yield (Scheme 3). The product was isolated and
4
2
2 9
with Fe (CO)
identified to be the octairon complex 7 upon obtaining its
X-ray crystal structure. Compound 7 crystallizes with one
molecule of benzene in the unit cell and an ORTEP diagram
of 7 is shown in Figure 4, while selected bond distances
and angles are collected in Table 3. The overall complex
has fourfold symmetry, and the entire structure can be
2
9
2
observed. This reaction involves formal oxidation of the Ge
atoms from the +2 to the +4 oxidation state as the diiron
2-
fragments are regarded as Fe
in the reactivity between 6 and germylene complex with Fe
CO) likely stems from the electronic attributes of the Ge
moieties versus a discrete germanium(II) atom in (Bu
Me-4-C O) Ge. The oxidation state of germanium is
clearly indicated by the Ge-O distances in 7, which measure
.772(2) and 1.788(2) Å and are representative of Ge(IV)-O
2
(CO)
8
anions. The difference
2
-
(
9
2 2
O
-2,6-
t
2
6
H
2
2
1
single bonds. Each germanium center is, thus, formally bound
to two oxygen atoms and any dative-type interactions are
absent, which is expected since germanium(IV) does not have
the vacant p-orbital that can accommodate electron density
from donor atoms or molecules; the p-orbital is available
when it is in the +2 oxidation state.
Formation of 7 also results in the reduction of each of the
iron atoms of Fe
oxidation state with loss of one carbonyl ligand. Thus, the
reaction of Fe (CO) with the germanium atoms of the calix-
8]arene complex can be regarded as a two-electron transfer
from each of the four germanium centers to a bonded pair
of iron atoms to generate the di-ferrate moiety. The GeFe
triangles are planar, and each of the iron atoms in these
groups has approximate C symmetry. The iron-iron bond
2 9
(CO) from the neutral to the -1 formal
2
9
[
2
s
Figure 4. ORTEP diagram of the complete molecule of 7‚C6H6. The
benzene molecule is not shown, and thermal ellipsoids are drawn at 50%
probability.
(42) Hitchcock, P. B.; Lappert, M. F.; Thomas, S. A.; Thorne, A. J.; Carty,
A. J.; Taylor, N. J. J. Organomet. Chem. 1986, 315, 27-44.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7583

Wetherby et al.
2
-
oxygen atoms versus a second Fe
2
(CO)
8
moiety in 8. The
average Fe-Ge-Fe bond angle in 8 (among the two
structure reports) is 71.9(1)° while the average Ge-Fe-Fe
4
4,45
bond angle is 54.0(1)°,
both of which are more acute
than the corresponding angles in 7 due to the spirocyclic
geometry in 8.
The geometries at the iron atoms in 7 and 8 are identical
but the C-O bond lengths in 7 are shorter than the
4
4
corresponding distances in 8, again resulting from the
germanium atoms in 7 being bound to electron-withdrawing
phenolic oxygen atoms. The average of the bond distances
for the C-O groups pointing outward from the GeFe
2
triangle (C(15)-O(6) and C(22)-O(7)) in 7 is 1.120(4) Å
while the corresponding C-O groups for 8 have an average
4
4
distance of 1.134(7) Å. The three sets of C-O distances
remaining in 7 average 1.135(4), 1.140(4), and 1.132(4) Å
while the corresponding average distances in 8 are 1.140-
(7), 1.138(7), and 1.148(7) Å.
These differences are manifested in the infrared spectrum
Figure 5. ORTEP diagram of the asymmetric unit of 7‚C6H6. Thermal
ellipsoids are drawn at 50% probability.
4
4
length in 7 is 2.8407(6) Å while the two Ge-Fe distances
measure 2.3543(5) and 2.3244(6) Å. The Fe-Fe distance in
the dianion of [(Ph
3
P)
Å, which like 7 has no bridging carbonyl ligands. The
introduction of a µ -bridging germanium(IV) atom results
in an elongation of the Fe-Fe bond due to electron donation
2
N]
2
[Fe
2
(CO)
8
]‚2CH
3
CN is 2.787(2)
of 7 in CH Cl , which contains four carbonyl stretching bands
2
2
4
3
-1
at 2109, 2059, 2044, and 2020 cm as a result of the Cs
symmetry at each of the iron atoms. Each of these bands
appear at higher energy than the corresponding IR features
2
2
-
-1 45
from the Fe
2
(CO)
8
anion to the germanium(IV) metal
for 8 in CH Cl (2076, 2050, 2033, and 2011 cm ). These
2
2
center.
structural and spectroscopic differences indicate that the
The germanium atoms of 7 are in a highly distorted
tetrahedral environment enforced by the presence of the
C-O bonds in 7 are stronger than those in 8 since the
2
-
Fe (CO)
2
8
groups in 7 are more strongly bound to the
GeFe
2
moieties. The O(1)-Ge(1)-O(2) angle is compressed
germanium atom than those in 8, which results in less
to 103.7(1)° from the ideal value of 109.5°, and the two
O-Ge-Fe angles are widened to 119.70(7)° and 124.55-
electron density for Fe-CO backbonding to the carbonyl
groups.
1
(8)°. The Fe(1)-Ge(1)-Fe(2) angle is highly distorted from
The H NMR spectrum of 7 recorded in CD
3
CN indicates
the ideal value measuring 74.77(2)°. The geometry at the
germanium centers is a result of the presence of the strained
that the molecule retains its rigid structure in solution. There
are four doublets for the each of the magnetically nonequiva-
1
GeFe
are also significantly distorted from their ideal values of 60°.
The internal angles in the GeFe triangles measure 52.14-
2)°, 53.10(2)°, and 74.77(2)° for the Ge(1)-Fe(1)-Fe(2),
2
triangles, and the bond angles within these groups
lent methylene protons of 7 as also found in the H NMR
spectra of compounds 1 and 6. A resonance at δ 4.70 ppm
2
(
J ) 10.2 Hz) arises from the protons attached to C(7) which
are directed toward the GeFe triangles while that at δ
.42 ppm (J ) 10.2 Hz) corresponds to the protons on C(7)
(
2
Ge(1)-Fe(2)-Fe(1), and Fe(1)-Ge(1)-Fe(2) angles, re-
spectively, indicating the presence of significant angle strain
3
which are directed away from this fragment. The other two
doublets at δ 4.12 (J ) 12.9 Hz) and 3.72 ppm (J )
12.9 Hz) are assigned to the protons attached to C(11), which
in these moieties.
4-46
The spirocyclic complex Ge[Fe
2
(CO)
8
]
2
(8)4
contains
2-
two Fe
2
(CO)
8
groups bridged by a bare germanium atom,
are directed toward and away from the GeFe triangles,
2
and the structure of 8 has been reported on two separate
occasions.4 The two reported structures that were deter-
mined are nearly identical, with one having an average Ge-
Fe distance of 2.40(1) Å and an average Fe-Fe bond length
of 2.823(2) Å44 and the other having average Ge-Fe and
respectively.
4,45
Several other carbonyl compounds containing the GeFe
structural motif have been reported and characterized
as have complexes containing GeCo
2
4
7-52
triangles.5
3-59
In
2
addition, a number of higher nuclearity clusters containing
4
5
60-63
53-55,64-68
69-71
Fe-Fe distances of 2.407(2) and 2.823(3) Å, respectively.
3
µ -
or µ
4
-germanium atoms,
2 2
Ge Fe arrays,
The longer Ge-Fe and shorter Fe-Fe distances in 8 versus
those in 7 are likely a result of the attachment of the two
germanium atoms in 7 to electron-withdrawing phenolic
(47) Anema, S. G.; Mackay, K. M.; Nicholson, B. K. Inorg. Chem. 1989,
2
8, 3158-3164.
(
48) Anema, S. G.; Mackay, K. M.; McLeod, L. C.; Nicholson, B. K.;
Whittaker, J. M. Angew. Chem., Int. Ed. Engl. 1986, 25, 759-760.
(49) Mohamed, B. A. S.; Kikuchi, M.; Hashimoto, H.; Ueno, K.; Tobita,
(43) Chin, H. B.; Smith, M. B.; Wilson, R. D.; Bau, R. J. Am. Chem. Soc.
1
974, 96, 5285-5287.
H.; Ogino, H. Chem. Lett. 2004, 33, 112-113.
(50) Kawano, Y.; Sugawara, K.; Tobita, H.; Ogino, H. Chem. Lett. 1994,
(
44) Batsanov, A. S.; Rybin, L. V.; Rybinskaya, M. I.; Struchkov, Y. T.;
Salimgareeve, I. M.; Bogatova, N. G. J. Organomet. Chem. 1983, 249,
293-296.
319-326.
(51) Bonny, A.; Mackay, K. M.; Wong, F. S. J. Chem. Res., Synop.1985,
(
(
45) Melzer, D.; Weiss, E. J. Organomet. Chem. 1983, 255, 335-344.
46) Anema, S. G.; Barris, G. C.; Mackay, K. M.; Nicholson, B. K. J.
Organomet. Chem. 1988, 350, 207-215.
40-41.
(52) Bonny, A.; Mackay, K. M. J. Chem. Soc., Dalton Trans. 1978, 722-
726.
7584 Inorganic Chemistry, Vol. 46, No. 18, 2007

Unusual Germanium(II) Calixarene Complexes
or rings containing germanium, iron, and cobalt62,72-75 are
also known. The synthesis of these species typically involves
using germanium(IV) precursors, while preparative routes
involving the oxidation of germanium(II) precursors such
as that employed for the synthesis of 7 are more uncommon.
with Fe
containing four GeFe
calix[8]arene framework. This process indicates that these
germanium(II) calixarenes can serve as platforms for the
support of multiple transition-metal centers.
(CO)
to give a highly symmetric octairon complex
triangles attached to the macrocyclic
2
9
2
One notable exception is the synthesis of [Et
-CO)(µ -Ge{Fe(CO) })] from [Et N] [Fe (CO)
Reaction of 1 with 2 equiv of Fe (CO) neither furnished a
complex similar to 7 nor resulted in the formation of Ge-
Fe(CO) fragments. Although a reaction did occur, the
products were identified as 1 and fine particles of iron metal.
Presumably, the decarbonylation of Fe (CO) by complex 1
4
N]
8
] and GeI
2 3 9
[Fe (CO) -
.6
0
Experimental Section
(
µ
3
3
4
4
2
2
2
2
9
General Considerations. All manipulations were carried out
2
under an inert N atmosphere using standard glovebox, Schlenk,
and syringe techniques.76 Solvents were dried and purified using a
Glass Contour solvent purification system. Calix[4]arene, calix[8]-
4
2 9
arene, and Fe (CO) were purchased from Aldrich and used without
2
9
3 2 2
further purification, and Ge[N(SiMe ) ] was prepared according
results in an unstable species, which releases all of the
remaining carbonyl ligands to furnish the iron metal.
to the literature method.7
7-79
Infrared spectra were obtained using
a Hewlett-Packard FT-IR spectrometer, and NMR spectra were
recorded on either a Varian Gemini 2000 or a Varian Unity INOVA
Conclusions
400 operating at 300 or 400 MHz, respectively, and were referenced
We have prepared and structurally characterized two
unusual germanium(II) calixarene complexes via the proto-
nolysis reaction between the bulky germanium(II) amide Ge-
to residual protio solvent. The numbering system used below refers
to that in the crystal structures of 1, 6, and 7.
Synthesis of {Calix[4]}Ge
(0.404 g, 0.952 mmol) in benzene (25 mL) in a Schlenk tube was
added a solution of Ge[N(SiMe (0.750 g, 1.91 mmol) in benzene
2
(1). To a solution of calix[4]arene
[
N(SiMe
complex is highly symmetric and contains two germanium
atoms arranged in a central Ge rhombus, while the latter
species represents the first germanium(II)-calix[8]arene
complex that contains two of these Ge rhombi located
inside a bowl-shaped macrocycle. The latter complex reacts
3 2 2
) ] and calix[4]arene or calix[8]arene. The former
3 2 2
) ]
O
2 2
(5 mL). The tube was sealed with a Teflon plug, and the reaction
was heated at 85 °C in an oil bath for 24 h. The volatiles were
removed in vacuo to yield an off-white solid, which was washed
with hexane (3 × 5 mL) and subsequently recrystallized from hot
2 2
O
benzene (10 mL) to yield 1 (0.301 g, 56%) as colorless crystals.
1
6 6
H NMR (C D , 25 °C): δ 7.07 (d, J ) 7.5 Hz, 4H, meta-H C(1)-
(
(
(
(
(
53) Lee, S. K.; Mackay, K. M.; Nicholson, B. K.; Service, M. J. Chem.
Soc., Dalton Trans. 1992, 1709-1716.
C(6)), 6.86 (t, J ) 7.5 Hz, 2H, para-H C(1)-C(6)), 6.68 (d, J )
.5 Hz, 4H, meta-H C(8)-C(13)), 6.16 (d, J ) 7.5 Hz, 2H, para-H
C(8)-C(13)), 4.41 (d, J ) 12.9 Hz, 4H, -C(7)H -), 3.23 (d, J )
2.9 Hz, 4H, -C(14)H -) ppm.
Stepwise Reaction of Ge[N(SiMe
a solution of calix[4]arene (0.095 g, 0.22 mmol) in benzene-d
0.50 mL) in a screw top NMR tube was added a solution of Ge-
[N(SiMe (0.088 g, 0.22 mmol) in benzene-d (0.25 mL). The
54) Anema, S. G.; Lee, S. K.; Mackay, K. M.; McLeod, L. C.; Nicholson,
B. K.; Service, M. J. Chem. Soc., Dalton Trans. 1991, 1209-1217.
55) Anema, S. G.; Lee, S. K.; Mackay, K. M.; Nicholson, B. K.; Service,
M. J. Chem. Soc., Dalton Trans. 1991, 1201-1208.
7
2
1
2
56) Foster, S. P.; Mackay, K. M. J. Organomet. Chem. 1982, 238, C46-
C48.
57) Gerlach, R. F.; Mackay, K. M.; Nicholson, B. K.; Robinson, W. T. J.
Chem. Soc., Dalton Trans. 1981, 80-84.
3 2 2
) ] with Calix[4]arene. To
6
(
(58) Wong, F. S.; Mackay, K. M. J. Chem. Res., Synop. 1980, 180.
59) Gerlach, R. F.; Graham, B. W. L.; Mackay, K. M. J. Organomet. Chem.
)
2
]
2
3
6
(
1
H NMR spectrum was recorded 30 min after mixing the sample.
The NMR tube was subsequently opened in the glovebox and an
1
979, 182, 285-298.
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
(
60) Whitmire, K. H.; Lagrone, C. B.; Churchill, M. R.; Fettinger, J. C.;
Robinson, B. H. Inorg. Chem. 1987, 26, 3491-3499.
61) Anema, S. G.; Mackay, K. M.; Nicholson, B. K.; Van Tiel, M.
Organometallics 1990, 9, 2436-2442.
additional solution of Ge[N(SiMe
3 2 2
) ] (0.043 g, 0.11 mmol) in
benzene-d (0.15 mL) was added. After the reaction mixture was
6
1
mixed, the H NMR spectrum of the sample was recorded. This
62) Anema, S. G.; Mackay, K. M.; Nicholson, B. K. J. Chem. Soc., Dalton
Trans. 1996, 3853-3858.
process was repeated with further addition of Ge[N(SiMe
(0.051 g, 0.13 mmol) to the tube.
3 2 2
) ]
63) Duffy, D. N.; Mackay, K. M.; Nicholson, B. K.; Thomson, R. A. J.
Chem. Soc., Dalton Trans. 1982, 1029-1034.
Synthesis of {Calix[8]}Ge
0.252 g, 0.297 mmol) in benzene (20 mL) in a Schlenk tube was
added a solution of Ge[N(SiMe (0.514 g, 1.31 mmol) in benzene
10 mL). The tube was sealed with a Teflon plug, and the reaction
4
(6). To a solution of calix[8]arene
64) Evans, C.; Mackay, K. M.; Nicholson, B. K. J. Chem. Soc., Dalton
Trans. 2001, 1645-1649.
(
65) Lee, S. K.; Mackay, K. M.; Nicholson, B. K. J. Chem. Soc., Dalton
Trans. 1993, 715-722.
3 2 2
) ]
(
66) Foster, S. P.; Mackay, K. M.; Nicholson, B. K. Inorg. Chem. 1985,
was heated at 85 °C in an oil bath for 48 h. The volatiles were
removed in vacuo to yield an off-white solid, which was washed
with hexane (3 × 5 mL) and subsequently recrystallized from hot
24, 909-913.
67) Foster, S. P.; Mackay, K. M.; Nicholson, B. K. J. Chem. Soc., Chem.
Commun. 1982, 1156-1157.
68) Gerlach, R. F.; Mackay, K. M. J. Organomet. Chem. 1979, 178, C30-
C32.
benzene (10 mL) to yield 6 (0.298 g, 89%) as colorless crystals.
1
69) Lei, D.; Hampden-Smith, M. J.; Duesler, E. N.; Huffman, J. C. Inorg.
Chem. 1990, 29, 795-798.
70) Audett, J. A.; Mackay, K. M. J. Chem. Soc., Dalton Trans. 1988,
6 6
H NMR (C D , 25 °C): δ 7.26 (d, J ) 7.5 Hz, 1H, meta-H C(55)),
7.25 (d, J ) 7.5 Hz, 1H, meta-H C(15)), 7.09 (d, J ) 7.5 Hz, 1H,
meta-H C(43)), 7.08 (d, J ) 7.5 Hz, 1H, meta-H C(85)), 6.95-
2
635-2643.
71) Bonny, A.; Mackay, K. M. J. Chem. Soc., Dalton Trans. 1978, 1569-
573.
72) Elder, M.; Hutcheon, W. L. J. Chem. Soc., Dalton Trans. 1972, 175-
80.
1
(76) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air SensitiVe
Comounds, 2nd ed.; John Wiley and Sons: New York, 1986.
(77) Harris, D. H.; Lappert, M. F. J. Chem. Soc., Chem. Commun. 1974,
895-896.
(78) Gynane, M. J. S.; Harris, D. H.; Lappert, M. F.; Power, P. P.; Rivi e` re,
P.; Rivi e` re-Baudet, M. J. Chem. Soc., Dalton Trans. 1977, 2004-
2009.
1
73) Anema, S. G.; Barris, G. C.; Mackay, K. M.; Nicholson, B. K. J.
Organomet. Chem. 1992, 441, 35-43.
74) Anema, S. G.; Mackay, K. M.; Nicholson, B. K. J. Organomet. Chem.
1989, 371, 233-246.
75) Anema, S. G.; Audett, J. A.; Mackay, K. M.; Nicholson, B. K. J.
Chem. Soc., Dalton Trans. 1988, 2629-2634.
(79) Zhu, Q.; Ford, K. L.; Roskamp, E. J. Heteroat. Chem. 1992, 3, 647-
649.
Inorganic Chemistry, Vol. 46, No. 18, 2007 7585

Wetherby et al.
6
7
5
.85 (m, aromatics, 9 H), 6.79-6.91 (m, Ar 8 H), 6.66 (d, J )
.5 Hz, 1H, meta-H C(35)), 6.11 (t, J ) 7.8 Hz, 1H, para-H C(24)),
.97 (d, J ) 7.8 Hz, 1H, meta-H C(25)), 5.83 (d, J ) 16.8 Hz, 2H,
Table 4. Crystallographic Data for Compounds 1, 6‚C6H6, and 7‚C6H6
1
6‚C6H6
7‚C6H6
formula
space group
a (Å)
b (Å)
c (Å)
C28H20Ge2O4
Pbcn
16.988(1)
8.8914(7)
14.630(1)
90
90
90
2209.9(3)
4
1.700
100(2)
Mo KR
0.71073
0.0290
0.0626
C62H46Ge4O8
C94H46Fe8Ge4O40
P4(2)/n
18.4671(6)
18.4671(6)
15.956(1)
90
90
90
5441.5(4)
4
1.603
203(2)
Mo KR
0.71073
0.0476
0.1528
H(4a), H(8a)), 4.77 (d, J ) 12.6 Hz, 2H, H(1b), H(5b)), 4.60 (d,
J ) 15.8 Hz, 2H, H(2b), H(3b)), 4.57 (d, J ) 15.0 Hz, 2H, H(6b),
H(7b)), 3.46 (d, J ) 15.8 Hz, 2H, H(2a), H(3a)), 3.43 (d, J )
P1j
12.923(4)
13.690(4)
14.589(4)
92.868(6)
96.527(6)
93.774(6)
2554(1)
2
1.571
198(2)
Mo KR
0.71073
0.0654
1
6.8 Hz, 2H, H(4b), H(8b)), 3.41 (d, J ) 15.0 Hz, 2H, H(6a),
H(7a)), 3.24 (d, J ) 12.6 Hz, 2H, H(1a), H(5a)) ppm.
Synthesis of {Calix[8]}Ge [Fe (CO) (7). To a solution of 6
0.150 g, 0.132 mmol) in benzene (15 mL) in a Schlenk tube was
added a suspension of Fe (CO) (0.212 g, 0.583 mmol) in benzene
20 mL). The tube was sealed with a Teflon plug, and the mixture
R (deg)
â (deg)
γ (deg)
4
2
8
]
4
3
(
V (Å )
Z
2
9
Fcalcd (g cm-1)
temp (K)
radiation
wavelength (Å)
R
(
was heated at 85 °C for 24 h. The reaction mixture was filtered,
and the solid was washed with benzene (4 × 10 mL) to yield a
dark red filtrate. The volatiles were removed in vacuo to yield 7 as
1
Rw
0.1751
a dark-red solid (0.240 g, 73%). H NMR (CD
3
CN, 25 °C): δ
ment coefficients, and hydrogen atoms were treated as idealized
contributions. All software and sources of scattering factors are
contained in the SHELXTL (5.10) program package (G. Sheldrick,
Bruker XRD, Madison, WI). ORTEP diagrams were drawn using
the ORTEP3 program (L. J. Farrugia, Glasgow).
7
1
.13-6.97 (m, Ar 8H), 6.84-6.57 (m, Ar 18H), 4.70 (d, J )
0.2 Hz, 8H, H(7b)), 4.12 (d, J ) 12.9 Hz, 8H, H(11a)), 3.72 (d,
J ) 12.9 Hz, 8H, H(11b)), 3.43 (d, J ) 10.2 Hz, 8H, H(7a)). IR
-1
(CH
2 2 3
Cl ): 2109(w), 2059(s), 2044(m), and 2020(s) cm . UV (CH -
4
CN) λmax ) 327 nm (ꢀ ) 3.32 × 10 ).
X-ray Structure Determinations. Diffraction intensity data were
collected with a Siemens P4/CCD diffractometer. Crystallographic
data and details of the X-ray studies are shown in Table 4.
Absorption corrections were applied for all data by SADABS. The
structures were solved using direct methods, completed by Fourier
syntheses, and refined by full-matrix least-squares procedures on
Acknowledgment. We are grateful for the funding for
this work which was provided by Oklahoma State University.
Supporting Information Available: Crystallographic data for
compounds 1, 6, and 7 in CIF format. This information is available
free of charge via the Internet at http://pubs.acs.org.
2
F . All non-hydrogen atoms were refined with anisotropic displace-
IC700969M
7586 Inorganic Chemistry, Vol. 46, No. 18, 2007