Synthesis and crystal structure of a germanium(II) calix[6]arene containing unusual diamidosilyl ether groups

Article abstract of DOI:10.1016/j.poly.2008.02.027

The reaction of Ge[N(SiMe₃)₂]₂ with calix[6]arene furnishes a novel macrocyclic product having two divalent germanium atoms incorporated into a Ge₂NO rhombus which contains a μ₂-oxygen atom and a μ₂-NH₂ group. The crystal structure of the product indicates the presence of a conformationally rigid molecule where three of the six oxygen atoms of the calix[6]arene are bound to the germanium atoms while the remaining three have been converted into -OSiMe₃ or unusual -OSi(H)(NH₂)₂ groups. Spectral (¹H, ¹³C, and ²⁹Si NMR) data in solution are consistent with the solid-state structure and indicate the germanium calix[6]arene retains its structure in solution.

Full text of DOI:10.1016/j.poly.2008.02.027

Polyhedron 27 (2008) 1841–1847
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Polyhedron
journal homepage: www.elsevier.com/locate/poly
Synthesis and crystal structure of a germanium(II) calix[6]arene containing unusual
diamidosilyl ether groups
Anthony E. Wetherby Jr. a, Arnold L. Rheingold b, Christa L. Feasley c, Charles S. Weinert a,
*
a Department of Chemistry, Oklahoma State University, Stillwater, OK 74078, USA
b Department of Chemistry and Biochemistry, University of California San Diego, La Jolla, CA 92093-0303, USA
c Department of Biochemistry and Molecular Biology, The Oklahoma Center for Medical Glycobiology, University of Oklahoma Health Science Center,
Oklahoma City, OK 73104, USA
a r t i c l e i n f o
a b s t r a c t
Article history:
The reaction of Ge[N(SiMe3)2]2 with calix[6]arene furnishes a novel macrocyclic product having two diva-
lent germanium atoms incorporated into a Ge2NO rhombus which contains a l2-oxygen atom and a l2-
NH2 group. The crystal structure of the product indicates the presence of a conformationally rigid mole-
cule where three of the six oxygen atoms of the calix[6]arene are bound to the germanium atoms while
the remaining three have been converted into –OSiMe3 or unusual –OSi(H)(NH2)2 groups. Spectral (1H,
13C, and 29Si NMR) data in solution are consistent with the solid-state structure and indicate the germa-
nium calix[6]arene retains its structure in solution.
Received 5 December 2007
Accepted 15 February 2008
Available online 1 April 2008
Keywords:
Germanium
Macrocycles
X-ray crystal structure
Calixarenes
Ó 2008 Elsevier Ltd. All rights reserved.
Silyl ether
Silyl amide
1. Introduction
plexes are uncommon, presumably due to the high conformational
mobility of the hexamers versus the related tetramers and octa-
Calix[n]arenes are an important class of macrocycles which
contain four or more phenol moieties connected together by
methylene bridges. These species have applications in the areas
of catalysis, self-assembly, and molecular or ionic recognition,
and can also serve as platforms for the support of multiple transi-
tion- or main group-metal centers [1–24], including silicon-
[13,16,17,21], phosphorus- [10–15,18,20,22–24], and arsenic [19].
Variation of the number of phenolic subunits present in the mole-
cule allows control over the cavity size in these systems, which in
turn has a profound effect on their properties and reactivity. The
presence or absence of conformational rigidity, which is typically
influenced by the attachment of peripheral substituents to the
para-positions (or upper rim) of the aromatic rings, is also impor-
tant in this regard [2,6,7,25–27].
Calix[6]arenes have been confirmed to be more flexible than ca-
lix[4]- and calix[8]arenes bearing identical para-substituents by
variable temperature NMR spectral studies [28,29]. Several oxy-
gen-functionalized calix[6]arenes have been employed for the
complexation of metal ions [30–43] and some bimetallic com-
plexes containing group 2 or 4 metals [44–46] bound directly to
the oxygen atoms have been prepared. The latter types of com-
mers. We recently described the syntheses and structures of ca-
lix[4]- and calix[8]arene complexes containing two or four
germanium(II) sites (respectively) bound to the oxygen atoms of
the macrocycles which were prepared via the protonolysis reaction
of Ge[N(SiMe3)2]2 with the para-unsubstituted parent calixarenes
[47]. The structures of these two compounds were similar in that
the germanium atoms were incorporated into Ge2O2 rhombi each
having one terminal and two bridging Ge–O attachments. The ca-
lix[8]arene species was also shown to undergo an oxidative addi-
tion reaction with Fe2(CO)9 resulting in an octa-iron compound
containing four GeFe2 triangles.
In light of these results, we attempted to prepare a similar
complex by treatment of the para-unsubstituted calix[6]arene
with three equivalents of Ge[N(SiMe3)2]2, and we now wish to re-
port the outcome of this investigation. Instead of forming a
complexe containing a Ge2O2 rhombus as observed in reactions
with calix[4]- and calix[8]arene, reaction of the germanium amide
with the calix[6]arene substrate furnished a Ge2NO rhombus
which contains a bridging amide group and has the two germa-
nium atoms bound to three of the six oxygen atoms present in
the macrocycle. One of the remaining three oxygen atoms has
been incorporated into a –OSiMe3 moiety while the other two
have been incorporated into structurally unprecedented
OSi(H)(NH2)2 groups.
–
* Corresponding author. Tel.: +1 405 744 6543; fax: +1 405 744 6007.
E-mail address: weinert@chem.okstate.edu (C.S. Weinert).
0277-5387/$ - see front matter Ó 2008 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2008.02.027

1842
A.E. Wetherby et al. / Polyhedron 27 (2008) 1841–1847
Table 1
2. Results and discussion
2.1. Synthesis and structure of compound 1
Selected bond distances (Å) and angles (°) for compound 1 ꢀ 0.5 (C6H6)
Ge(1)–O(1)
Ge(1)–O(3)
Ge(1)–N(5)
Ge(2)–O(2)
Ge(2)–O(3)
Ge(2)–N(5)
Si(1)–O(6)
Si(2)–O(5)a
Si(2)–N(3)a
Si(2)–N(4)a
Si(3)–O(4)a
Si(3)–N(1)a
Si(3)–N(2)a
1.860(3)
1.992(3)
2.011(4)
1.835(3)
1.993(3)
1.995(4)
1.664(3)
1.696(5)
1.816(8)
1.715(8)
1.712(4)
1.700(8)
1.806(9)
O(1)–Ge(1)–O(3)
O(1)–Ge(1)–N(5)
O(2)–Ge(2)–O(3)
O(2)–Ge(2)–N(5)
O(3)–Ge(1)–N(5)
O(3)–Ge(2)–N(5)
Ge(1)–O(3)–Ge(2)
Ge(1)–N(5)–Ge(2)
O(5)–Si(2)–N(3)a
O(5)–Si(2)–N(4)a
N(3)–Si(2)–N(4)a
O(4)–Si(3)–N(1)a
O(4)–Si(3)–N(2)a
N(1)–Si(3)–N(2)a
91.4(1)
89.7(1)
91.6(1)
91.4(1)
77.1(1)
Treatment of calix[6]arene with three equivalents of Ge[N-
(SiMe3)2]2 yielded complex 1 in 41% yield as shown in Eq. (1).
The identity of 1 was ascertained by obtaining its X-ray crystal
structure, and an ORTEP diagram of 1 is shown in Fig. 1 while se-
lected bond distances and angles are collected in Table 1. Of the
six phenolic oxygen atoms present in 1, three are bound to the
two Ge atoms in either a terminal or bridging fashion while the
remaining three oxygen atoms have been incorporated into to
either –OSiMe3 or –OSi(H)(NH2)2 groups. We have previously ob-
served the transformation of hydroxyl groups to trimethylsiloxy
groups in the reactions of 3,30-disubstituted binaphthols with me-
tal(II) amides M[N(SiMe3)2]2 (M = Be, Zn, Ge, Sn) [48]; however, the
conversion of –OH groups to silylamides has not been previously
described.
77.4(1)
103.0(1)
102.3(2)
111.6(3)
108.2(3)
122.8(5)
112.4(4)
108.8(4)
119.6(4)
a
The atoms Si(2) and Si(3) are disordered over two positions. The tabulated
values are for the average of the two positions.
O
OH
O
O
Ge
Ge
OH
OH
HO
HO
N
H2
3 equiv. Ge[N(SiMe3)2]2
C6H6, 85 oC, 72 h
- HN(SiMe3)2
ð1Þ
H
H
OSi(NH2)2 (H2N)2SiO
OSiMe3
OH
Ge(2) angle of 103.0(1)° is significantly more acute than the Ge–
Obr–Ge angles in 2 and 3 which range from 106.1(1) to 107.89(6)°
[47]. Furthermore, the Ge(1)–N(5)–Ge(2) angle measures
102.3(2)° which is more obtuse than the average Ge–Nbr–Ge angles
in 4 (100.0(1)°) [49]. The O(3)–Ge(1)–N(5) and O(3)–Ge(2)–N(5)
angles average 77.3(1)° which are wider than the Obr–Ge–Obr an-
gles in 2 and 3 but more acute than the Nbr–Ge–Nbr ligands angles
in 4. These structural differences can be attributed to the presence
of two different types of bridging atoms in 1 and the internal angles
in the Ge2NO rhombus can be regarded as being intermediate be-
tween the Ge2O2 rhombi of 2 and 3 and the Ge2N2 rhombus of 4.
The terminal Ge(1)–O(1) and Ge(2)–O(2) bond lengths in 1 are
typical for germanium(II)–oxygen distances and are comparable to
those in compounds 2 and 3 [47] as well as in other Ge(II) aryloxides
[50–54]. The bridging Ge(1)–O(3) and Ge(2)–O(3) bond lengths in 1
are 1.992(3) and 1.993(3) Å (respectively) which fall between the
average Ge–Obr bond distances in 2 (1.988 Å) and 3 (2.000 Å) [47].
The bridging N atom is not symmetrically disposed between the
two germanium atoms in 1 as indicated by the two Ge–N bond
lengths measuring 2.011(4) and 1.995(4) Å. These distances are
shorter than those found in the structure of 4 which has an average
Ge–N distance of 2.013(3) Å [49]. The Ge–N distances in 1 are longer
than those in germanium(II) compounds bearing ligands with
terminal Ge–N bonds, including the well-known bulky bisamide
Ge[N(SiMe3)2]2 which has Ge–N bond lengths of 1.873(5) and
1.878(5) Å [55] and the bis(piperidinato) complex Ge[NC5H6Me4-
2,2,6,6]2 which has distances of 1.87(1) and 1.90(1) Å [56]. However,
the Ge–N distances in 1 are considerably shorter than those in diva-
lent germanium compounds having dative N ? Ge bonds including
those in [Ge(2-{(Me3Si)2C}-C5H4N)R] which measure 2.082(4) or
2.089(7) Å (R = Cl or CH(PPh2)2, respectively) [57]. These distances
are also shorter than those in the divalent binhapthoxide complex
Compound 1 contains an unusual bridging –NH2– group be-
tween the two germanium centers, and the structure of 1 can be
compared to the two related calixarene complexes {calix[4]}Ge2
(2) and {calix[8]}Ge4 (3) [47] as well as the dimeric species
[(C6H3{C6H3Pri2-2,6}2-2,6)GeNH2]2 (4) which also contains bridging
–NH2– moieties [49]. Similar to the Ge2O2 rhombus in compound 2
the Ge2NO rhombus adopts a planar geometry. The Ge(1)–O(3)–
Fig. 1. ORTEP diagram of compound 1. Thermal ellipsoids are drawn at 50%
probability.

A.E. Wetherby et al. / Polyhedron 27 (2008) 1841–1847
1843
(R)-[Ge{O2C20H10(SiMe2Ph)2-3, 30}{NH3}] (d Ge–N = 2.093(4) Å)
which contains a coordinated NH3 molecule [51] and also in
[Ge{OCH(CF3)2}2{NH2Ph}] (d Ge–N = 2.092(3) Å) which contains a
coordinated aniline molecule [58].
the silylated oxygen atoms O(4) and O(5). The remaining doublet
at d 4.34 (J = 13.5 Hz) ppm arises from the proton attached to
C(1) which only has long (>2.6 Å) contacts with the neighboring
oxygen atoms.
The three remaining oxygen atoms in 1 are each attached to a
silicon atom. One of these is incorporated into a –OSiMe3 silyl ether
group which arises from the transfer of the –SiMe3 moiety from a –
N(SiMe3)2 ligand in Ge[N(SiMe3)2]2 to the phenolic oxygen atom
[48]. The geometry of the silyl ether moiety is normal with an
approximate tetrahedral environment at silicon and a typical Si–
O bond distance of 1.664(3) Å. The Si–O–Cipso angle is 123.7(2)°
and the –SiMe3 group is directed outward from the central cavity
of the molecule. The other two oxygen atoms have been incorpo-
rated into unusual –OSi(H)(NH2)2 groups. The silicon atoms in both
groups are disordered over two positions (50% occupancy) which
also results in each of the nitrogen atoms of the four attached –
NH2 groups also being disordered over two positions. The four
nitrogen atoms were also disordered with very small positional
differences over the two individual positions, and these were re-
fined with a broad thermal parameter which resulted in the large
ellipsoids present in the ORTEP plot of 1 (Fig. 1).
The Si–N bond distances (when taking into consideration the dis-
tortion of the silicon atoms) are 1.816(8), 1.715(8), 1.700(8), and
1.806(9) Å while, the N–Si–N angles are 122.8(5) and 119.6(4)° at
Si(2) and Si(3), respectively. Diaminosilyl ether groups similar to
those attached to O(4) and O(5) in 1 have not been described previ-
ously and thus a direct comparison to other structurally character-
ized species is not possible. However, a few small molecules
containing –NH2 groups bound to silicon and having –NH2 and –
OH groups attached to the same silicon atom have been reported
[59,60]. The structure of Mes2Si(NH2)2 has Si–N distances of
1.713(2) and 1.717(2) Å and a N–Si–N angle of 106.89(5)° [59] while
that of But2Si(OH)NH2 exhibits a Si–N distance of 1.746(4) Å [60].
The average of the four Si–N distances is 1.759(8) Å in 1 which
is longer than the corresponding bond distance in But2Si(OH)NH2
[60] and can be attributed to the attachment of the –Si(H)(NH2)2
moieties in 1 to a phenolic oxygen atom. The two N–Si–N angles
in 1 average 121.2(5)° which is significantly more obtuse than
the N–Si–N angle in Mes2Si(NH2)2 [59]. This structural difference
is expected since the latter compound contains two sterically
encumbering mesityl groups, while compound 1 instead has a pro-
ton and an oxygen atom bound to silicon.
Assignments for the upfield group of six resonances are based
on a COSY NMR experiment. The doublet at d 3.53 (J = 16.2 Hz)
ppm corresponds to the second proton bound to C(6), while the
four closely spaced features at
d 3.32 (J = 13.2 Hz), 3.30
(J = 14.7 Hz), 3.24 (J = 13.5 Hz), 3.23 (J = 12.6 Hz) ppm arise from
the remaining protons attached to C(5), C(4), C(1) and C(3) (respec-
tively). The resonance at d 3.19 (J = 11.7 Hz) ppm results from the
second proton bound to C(2). Due to the rigidity in the Ge2NO
rhombus, the protons in the bridging –NH2 group also are magnet-
ically non-equivalent, appearing as two broad but clearly resolved
doublets at d 1.66 (J = 9.6 Hz) and 1.04 (J = 9.6 Hz) ppm. The two Si-
H protons are also non-equivalent and appear as two singlets in the
1H NMR spectrum at d 6.34 and 6.32 ppm. The –Si(NH2)2 protons
appear as two upfield singlets at d 0.27 and 0.24 ppm while the
protons of the –OSiMe3 moiety appear as a singlet at d 0.42 ppm.
The 13C NMR spectrum of 1 also is consistent with its solid-state
structure and exhibits six distinct lines for the each of non-equiv-
alent ipso- and para-carbon atoms as well as twelve lines for both
the ortho- and meta-carbons. The six methylene groups result in six
features between d 31–35 ppm and there is only one resonance in
the –SiR3 region of the spectrum at d 1.6 ppm corresponding to the
carbon atoms of the –OSi(CH3)3 group.
The 29Si{1H} NMR spectrum of 1 contains three singlets at d
21.63, 21.17, and 21.07 ppm, where the downfield resonance arises
from the silicon atom in the –OSiMe3 group and the two upfield
resonances correspond to the silicon atoms in the two
–
Si(H)(NH2)2 groups. The chemical shift for the silyl ether feature
is similar to that of C6H5OSiMe3 which appears at d 19.43 ppm
[61]. The proton-coupled 29Si NMR spectrum of 1 was also re-
corded, and the singlet at d 21.63 in the 1H-decoupled spectrum
splits into a multiplet with eight of the ten expected lines being
clearly discernable. This arises from the two-bond coupling be-
tween the silicon atom and the protons of the methyl groups, with
a coupling constant of 6.43 Hz. The two features for the –
Si(H)(NH2)2 groups are more complex due to the presence of both
one-bond Si–H and three bond Si–NH2 coupling. Each of these fea-
tures are expected to appear as a doublet of quintets but their
proximity resulted in overlap with one another such that the ex-
pected one-bond Si–H coupling could not be clearly observed.
2.2. NMR spectra of compound 1
2.3. Analysis of compound 1 using mass spectrometry
Spectroscopic (1H, 13C and 29Si NMR) data in benzene-d6 are
consistent with the solid-state structure of 1. Similar to com-
pounds 2 and 3, the conformational flexibility of 1 is restricted ver-
sus the calix[6]arene starting material due to the presence of the
The mass spectrum of compound 1 acquired using electrospray
mass spectrometry (positive ion mode) exhibited a clear fragmen-
tation pattern having nine well-defined peaks which are listed in
Table 2. The proposed fragmentation pattern is illustrated in
Ge2NO rhombus and the relatively large –OSiMe3 and
–
OSi(H)(NH2)2 groups. This renders the individual protons of the
six methylene units in 1 magnetically non-equivalent, resulting
in twelve distinct doublets in the 1H NMR spectrum in the chemi-
cal shift range d 3.1–4.8 ppm which are divided into two sets of six
features. The downfield grouping of resonances correspond to the
methylene protons directed inward toward the Ge2NO rhombus
while the upfield features are attributed to those directed away.
In the downfield grouping of resonances, the doublet at d 4.74
(J = 13.2 Hz) ppm is assigned to the proton attached to C(5) which
has two close contacts with O(2) and O(3) measuring 2.498 and
2.549 Å (respectively). The two sets of closely grouped doublets
at d 4.66 (J = 14.7 Hz) and 4.64 (J = 12.6 Hz) ppm correspond to
the protons bound to C(4) and C(3) (respectively) due to their rel-
ative proximity to O(3) and O(1), and the features at d 4.53
(J = 16.2 Hz) and 4.51 (J = 11.7 Hz) ppm are assigned to the protons
attached to C(6) and C(2) (respectively) due to their proximity to
Table 2
Electrospray mass spectrometry data for compound 1
Ion m/z
Formula
Relative intensity
(%)
1a
1b
988.5 [(C6H3)6(CH2)6O3Ge2(NH2)
n/a
2
{OSi(H)(NH2)2}2OSiMe3]H+
927.5 [(C6H3)6(CH2)6O3Ge2(NH2)
OSi(H)(NH2)2OSiMe3O]H+
1c
1d
1e
1f
1g
1h
1i
898.5 [(C6H3)6(CH2)6O3Ge2(NH2)OSiH3OSiMe3OH]H+
826.4 [(C6H3)6(CH2)6O3Ge2(NH2)OSiH3(OH)2]H+
798.4 [(C6H3)6(CH2)6O2Ge2(NH3)(OH)4]H+
754.4 [(C6H3)6(CH2)6O2Ge(NH2)OSiH3(OH)3]H+
726.4 [(C6H3)6(CH2)6OGe(NH3)(OH)5]H+
682.4 [(C6H3)6(CH2)6O(NH2)OSiH3(OH)4]H+
654.4 [(C6H3)6(CH2)6(NH3)(OH)6]H+
637.3 [(C6H3)6(CH2)6(OH)6]H+
29
72
100
8
12
16
28
4
1j

1844
A.E. Wetherby et al. / Polyhedron 27 (2008) 1841–1847
Scheme 1. Although the parent molecular ion at m/z = 988.5 was
not observed a feature at m/z = 927.5 corresponding to the loss of
one –SiH(NH2)2 fragment and monoprotonation of the remaining
molecule was present in the spectrum. Subsequent fragmentations
involve the loss of the –SiMe3 group, the two germanium
atoms, the oxygen atoms, and the bridging –NH2– group. The –O
and –NH2 groups to which these fragments were bound appear
to be protonated during the course of this process to yield –OH
or NH3 groups (respectively). Ultimately, all of the substituents
in compound 1 undergo fragmentation to produce the parent ca-
lix[6]arene in protonated form.
treatment of calix[6]arene with 3 equiv. of Ge[N(SiMe3)2]2, a reso-
nance for the formation of free HN(SiMe3)2 at d 0.09 ppm was ob-
served after 10 min at room temperature and Ge[N(SiMe3)2]2 and a
trace amount of calix[6]arene were still present in solution. After
heating the sample at 85 °C for 1 h, the aromatic and methylene re-
gions of the spectrum were complex but the appearance of peaks at
d 0.42, 0.29 and 0.25 ppm indicated that compound 1 was already
present in solution. The absence of a resonance at d 10.50 ppm
attributable to the six phenolic protons also indicated all of the ca-
lix[6]arene had been consumed at this time.
After heating the sample at 85 °C for a total of 6 h, the overall
appearance of the spectrum had simplified and suggested that
compound 1 was present in solution along with a second interme-
diate species. The methylene region of the spectrum contained 24
doublets divided into an upfield and downfield grouping of 12 fea-
tures. Some overlap of these resonances was observed but four dis-
2.4. Pathway for the formation of compound 1
The pathway for the formation of 1 is likely complex, but two
key aspects for the generation of this species are evident. First,
compound 1 contains twelve protons distributed among the single
bridging –NH2– and the two –Si(H)(NH2)2 groups. Since calix[6]ar-
ene is the only proton source present in the reaction, all of these
must originate from this starting material. Furthermore, 2 equiv.
of calix[6]arene must be consumed for every one equiv. of 1 gener-
ated in the reaction since calix[6]arene contains only six phenolic
protons. This dictates a maximum theoretical yield of 50% for 1
with the concomitant formation of one or more other products,
and this postulate is further supported by the complete consump-
tion of calix[6]arene in the reaction. Compound 1 has been isolated
in a maximum of 41% during the course of these studies.
Second, the –N(SiMe3)2 ligands of Ge[N(SiMe3)2]2 are the source
of both the bridging –NH2– group and the –Si(H)(NH2)2 groups in
1. We have recently demonstrated that Ge[N(SiMe3)2]2 reacts with
binaphthols via formation of an intermediate bearing a –OGe[N-
(SiMe3)2] moiety which subsequently transfers a –SiMe3 fragment
to the oxygen atom of one –OH substituent of the binaphthol [48].
This results in generation of a –OGe[NH(SiMe3)] group and this
process can occur a second time to yield a –OGe[NH2] moiety
which could then serve as the source of the bridging amide in 1.
The –Si(H)(NH2)2 groups, however, must ultimately result from
the demethylation of a –SiMe3 group during the course of the reac-
tion. The transfer of a methyl group to gallium in the reaction of
GaCl3 with Li[N(SiMe3)2] has been reported [62], and similar
methyl group migrations have been found upon treatment of GaCl3
with N(SiMe3)3 [63] or SiMe4 [64]. The germanium atoms present
in 1 clearly are not methylated, but the generation of Me4Ge or
CH4 might be expected to occur during the course of this reaction.
In order to probe the pathway for the formation of 1, the
progress of the reaction of one, two and three equivalents of Ge[N-
(SiMe3)2]2 with calix[6]arene was monitored over time using 1H
NMR spectroscopy in benzene-d6 in three separate experiments.
The methylene (d 5.2–3.0 ppm) and alkylsilyl (d 0.4–0.0 ppm)
regions of these spectra contained diagnostic features which
were compared over a reaction period of 120 h in each case. Upon
tinct peaks at
d 5.08 (J = 15.0 Hz), 4.43 (J = 13.5 Hz), 3.15
(J = 12.3 Hz), and 3.13 (J = 12.9 Hz) ppm were visible, which clearly
are not attributable to 1 but arise from a second compound present
in solution. Similarly, two additional peaks at d 0.36 and 0.30 ppm
in the alkylsilyl region were observed at this time as were two
additional downfield singlets at d 6.32 and 6.30 ppm arising from
Si–H protons.
The presence of the four features at d 6.32, 6.30, 0.36 and
0.30 ppm along with the structural rigidity apparent in the inter-
mediate species suggest that all or part of the Ge2NO rhombus
and the two –Si(H)(NH2)2 groups are generated prior to silylation
of the remaining hydroxyl group to generate the silyl ether moiety.
Further evidence for this results from the presence of a broad sin-
glet at d 5.92 ppm which suggests the presence of a single hydroxyl
group in the intermediate species. Similar 1H NMR –OH features
were observed for the main group calixarenes {(OH)(calix[4]are-
ne)P} (d 5.4 ppm) [20], {(OH)(p-tert-butylcalix[4]arene)Si} (d
4.59 ppm) [21], {(OH)(calix[4]arene)As} (d 4.90 ppm) [19], and
{(OH)(p-tert-butylcalix[4]arene)As} (d 4.74 ppm) [19], all of which
have a single unbound –OH group and three oxygen atoms bound
to the main group element. The resonance at d 5.92 ppm had sig-
nificantly reduced in intensity after heating the sample for a total
of 48 h, as had the two features at d 6.32 and 6.30 ppm and the up-
field peaks at d 0.36 and 0.30 ppm. We therefore postulate that the
structure of the intermediate detected by 1H NMR spectroscopy is
that of 2 illustrated in Scheme 2, which undergoes an exchange of
the –SiMe3 group attached to the nitrogen with the remaining hy-
droxyl proton followed by closure of the Ge2NO rhombus.
After heating the sample for an additional 12 h resonances
corresponding only to 1, free HN(SiMe3)2, and unreacted Ge[N-
(SiMe3)2]2 remained. The appearance of the spectrum remained
unchanged with up to 120 h of heating at 85 °C. Nearly identical
results were obtained when calix[6]arene was treated with
2 equiv. of Ge[N(SiMe3)2]2 under the same reaction conditions
except that Ge[N(SiMe3)2]2 was absent after the reaction had gone
1a
- Si(H)(NH2)2
- 2 -NH2
+ 3 H+
- SiMe3
+ H+
1d
1b
1c
m/z = 988.5
not observed
m/z = 826.4
m/z = 927.5
m/z = 898.5
- SiH3
+ 3 H+
- Ge
+ H+
- Ge
+ H+
1e
1g
1i
m/z = 798.4
m/z = 726.4
m/z = 654.4
1d
- NH3
m/z = 826.4
- SiH3, - NH2
+ 2 H+
- Ge
+ H+
1j
- Ge
+ H+
1f
1h
m/z = 637.3
m/z = 754.4
m/z = 682.4
Scheme 1.

A.E. Wetherby et al. / Polyhedron 27 (2008) 1841–1847
1845
O
OH
OH
O
O
Ge
Ge
OH
OH
HO
HO
N
H2
3 Ge[N(SiMe3)2]2
H
H
OSi(NH2)2 (H2N)2SiO
OSiMe3
1
Ge[N(SiMe3)2]2
O
O
O
O
Ge
Ge
O
O
Ge
Ge
H
NH
Me3Si NH
HSi(NH2)2
O
(H2N)2SiH
O
HSi(NH2)2
O
(H2N)2SiH
O
OSiMe3
OH
2
Scheme 2.
to completion. The outcome of this process is consistent with the
overall reaction stoichiometry since two germanium atoms are
present in the framework of 1. The 1H NMR spectra of the reaction
of calix[6]arene with 1 equiv. of Ge[N(SiMe3)2]2 in benzene-d6
indicated the formation of a complex mixture of species which
included 1 and the intermediate 2 which remained present in
solution even after heating the reaction mixture for 120 h.
In the course of these studies, no conclusive evidence for the
formation of Me4Ge or CH4 was found which exhibit similar 1H
NMR resonances at d 0.14 and 0.15 ppm in benzene-d6. However,
identification of calix[6]arene as the source of all of the protons in
the two –Si(H)(NH2)2 groups and in the bridging –NH2– group
was confirmed by the reaction of three equiv. of Ge[N(SiMe3)2]2
with calix[6]arene-d6 which contained six deuterated hydroxyl
groups. The 1H NMR spectrum of the resulting product contained
only a single line at d 0.42 ppm arising from the –OSiMe3 moiety
as well as a feature corresponding to unreacted germanium
amide.
4. Experimental
All manipulations were carried out using standard Schlenk, syr-
inge, and glovebox techniques [65]. Calix[6]arene was purchased
from Alfa Aesar and Ge[N(SiMe3)2]2 was synthesized according to
the published procedure [66–68]. Solvents were dried using a Glass
Contour Solvent Purification System. One and two-dimensional 1
H
NMR spectra were recorded at 400 MHz on a Varian Unity INOVA
400 spectrometer and referenced to residual protio solvent. For
the 1H NMR assignments in 1, the numbering scheme of the carbon
atoms corresponds to the crystal structure of 1, i.e. –C(5)H2– refers
to a proton bound to C(5). 13C NMR spectra were recorded at a fre-
quency of 100.6 MHz on a Varian Unity INOVA 400 and referenced
to the solvent while 29Si NMR were acquired using a Varian Unity
INOVA 600 operating at 119.2 MHz and were referenced to exter-
nal SiMe4. Mass spectra were acquired using a Bruker Agilent
1100 LC/MSD System in acetonitrile solvent. Elemental analysis
was performed by Midwest Microlab, LLC (Indianapolis, IN).
4.1. Synthesis of compound 1
3. Conclusions
To a solution of calix[6]arene (0.458 g, 0.719 mmol) in benzene
In conclusion, the reactivity of calix[6]arene with Ge[N-
(SiMe3)2]2 differs considerably from that found in reactions
involving calix[4]arene and calix[8]arene. Instead of forming
complexes containing Ge2O2 rhombi, the germanium calix[6]ar-
ene complex 1 contains a central Ge2NO rhombus incorporating
three of the six oxygen atoms of the macrocycle. The remaining
three oxygen atoms have been converted to two –OSi(H)(NH2)2
moieties and one –OSiMe3 group. The pathway for the forma-
tion of 1 is likely complex, but involves the consumption of
two equivalents of calix[6]arene for each equivalent of 1 pro-
duced in the reaction.
(10 mL) was added
a solution of Ge[N(SiMe3)2]2 (0.852 g,
2.17 mmol) in benzene (4 mL). The mixture was sealed in a Schlenk
tube and heated at 85 °C for 72 h. The solvent was removed in va-
cuo to yield a white solid which was recrystallized from hot ben-
zene (5 mL) to yield 1 as colorless crystals which were washed
with hexane (3 ꢁ 5 mL) and dried in vacuo. Yield: 0.292 g (41%).
1H NMR (C6D6, 25 °C): d 7.29–6.75 (m, 18H, aromatics), 6.34 (s,
1H, –Si(H)(NH2)2), 6.32 (s, 1H, –Si(H)(NH2)2), 4.74 (d, J = 13.2 Hz,
1H –C(5)H2–), 4.66 (d, J = 14.7 Hz, 1H, –C(4)H2–), 4.64 (d,
J = 12.6 Hz, 1H, –C(3)H2-), 4.53 (d, J = 16.2 Hz, 1H, –C(6)H2–), 4.51

1846
A.E. Wetherby et al. / Polyhedron 27 (2008) 1841–1847
(d, J = 11.7 Hz, 1H, –C(2)H2–), 4.34 (d, J = 13.5 Hz, 1H, –C(1)H2–),
3.53 (d, J = 16.2 Hz, 1H, –C(6)H2-), 3.32 (d, J = 13.2 Hz, 1H, –
C(5)H2–), 3.30 (d, J = 14.7 Hz, 1H, –C(4)H2–), 3.24 (d, J = 13.5 Hz,
1H, –C(1)H2-), 3.23 (d, J = 12.6 Hz, 1H, –C(3)H2–), 3.19 (d,
J = 11.7 Hz, 1H, -C(2)H2–), 1.66 (br d, J = 9.6 Hz, 1H, –NH2–), 1.04
(br d, J = 9.6 Hz, 1H, –NH2–), 0.42 (s, 9H, –OSi(CH3)3), 0.27 (s, 4H,
–Si(H)(NH2)2), 0.24 (s, 4H, –Si(H)(NH2)2) ppm. 13C NMR (C6D6,
25 °C) d 156.1, 154.4, 152.0, 151.6, 151.1, 150.8 (ipso-C), 136.8,
136.6, 136.4, 136.1, 135.9, 135.2, 134.5, 133.3, 132.8, 132.6,
132.1, 132.0 (meta-C), 131.0, 130.8, 130.7, 130.5, 130.4, 130.3,
129.8, 129.7, 129.4, 129.3, 129.1, 128.8 (ortho-C), 123.6, 122.7,
122.3, 122.2, 120.9, 120.8 (para-C), 34.2, 34.0, 33.9, 33.4, 33.1,
31.1 (–CH2–), 1.6 (-OSi(CH3)3) ppm. 29Si{1H} NMR (C6D6, 25 °C): d
21.63, 21.17, and 21.07 ppm. IR (Nujol): 3348, 3266, 3255, 2720,
2664, 2288, 1916, 1859, 1807, 1713, 1661, 1589 cmꢂ1. Anal. Calc.
for C45H51Ge2N5O6Si3: C, 54.74; H, 5.21. Found: 54.15; H, 5.41%.
sources of scattering factors are contained in the SHEXTL (5.10) pro-
gram package (G. Sheldrick, Bruker XRD, Madison, WI). ORTEP dia-
grams were drawn using the ORTEP
Glasgow).
3 program (L.J. Farrugia,
Crystallographic data for 1 ꢀ 0.5(C6H6): Crystal size: 0 ꢁ 0.22 ꢁ
0.17 mm. Crystal color and habit: colorless block. Empirical for-
mula: C48H54Ge2N5O6Si3. Formula weight: 1026.42. Wavlength:
0.71073 Å. Temperature: 100(2) K. Crystal system: triclinic. Space
ꢀ
group: P1. Unit cell dimensions: a = 13.199(2) Å, b = 14.774(2) Å;
c = 16.569(4) Å; a = 105.373(4)°; b = 102.641(4)°; c = 115.225(3)°.
Volume = 2606.5(9) Å3. Z = 2. Dcalc = 1.309 g/cm3. Absorption coef-
ficient = 1.274 mmꢂ1
. F(000) = 1064. h-Range for data collec-
tion = 1.67–25.00°. Index ranges: ꢂ14 6 h 6 ꢂ15; ꢂ15 6 k 6 17;
ꢂ19 6 l 6 19. Reflections collected = 15228. Independent reflec-
tions = 9124
(Rint = 0.0295).
Completeness
to
h = 99.2%
(h = 25.00°). Absorption correction = multi-scan. Refinement meth-
od = full-matrix least-squares on F2. Data/restraints/parame-
ters = 9124/0/584. Goodness-of-fit on F2 = 1.014. Final R indices
[I > 2r(I)]: R1 = 0.0581; wR2 = 0.1414. R indices (all data): R1 =
0.0884; wR2 = 0.1580. Largest difference in peak and hole = 0.512
4.2. NMR scale reaction of calix[6]arene with 3 equiv. Ge[N(SiMe3)2]2
A solution of calix[6]arene (0.050 g, 0.078 mmol) in benzene-d6
(0.25 mL) was treated with a solution of Ge[N(SiMe3)2]2 (0.093 g,
0.24 mmol) in benzene-d6 (0.25 mL) in a screw-cap NMR tube.
and ꢂ0.547 e Åꢂ3
.
Acknowledgement
4.3. NMR scale reaction of calix[6]arene with 2 equiv. Ge[N(SiMe3)2]2
Funding for this project was provided by the Department of
Chemistry at Oklahoma State University.
A solution of calix[6]arene (0.050 g, 0.078 mmol) in benzene-d6
(0.25 mL) was treated with a solution of Ge[N(SiMe3)2]2 (0.062 g,
0.16 mmol) in benzene-d6 (0.25 mL) in a screw-cap NMR tube.
Appendix A. Supplementary data
4.4. NMR scale reaction of calix[6]arene with 1 equiv. Ge[N(SiMe3)2]2
CCDC 669869 contains the supplementary crystallographic data
for 1. These data can be obtained free of charge via http://
www.ccdc.cam.ac.uk/conts/retrieving.html or from the Cambridge
Crystallographic Data Centre, 12 Union Road, Cambridge CB2 1EZ,
UK; fax: (+44) 1223-336-033; or deposit@ccdc.cam.ac.uk. Supple-
mentary data associated with this article can be found, in the on-
line version, at doi:10.1016/j.poly.2008.02.027.
A solution of calix[6]arene (0.050 g, 0.078 mmol) in benzene-d6
(0.25 mL) was treated with a solution of Ge[N(SiMe3)2]2 (0.031 g,
0.079 mmol) in benzene-d6 (0.25 mL) in a screw-cap NMR tube.
4.5. Synthesis of calix[6]arene-d6
To a solution of calix[6]arene (0.300 g, 0.471 mmol) in diethyl
ether (30 mL) was added a solution of 2.5 M BunLi in hexanes
(1.51 mL, 3.78 mmol) at ꢂ78 °C. The reaction mixture was allowed
to come to room temperature and was stirred for 4 h. The reaction
mixture was quenched with D2O (5 mL) at ꢂ78 °C via cannula from
a sure-seal bottle. The organic layer was separated and dried over
anhydrous MgSO4 and the solvent was removed in vacuo to yield
calix[6]arene-d6 (0.221 g, 72%). The 1H NMR spectrum of the prod-
uct recorded in benzene-d6 did not exhibit an –OH resonance.
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