Synthesis and structures of the group 1 metal/germanium cage complexes [M(μ-OC6H3Ph2-2,6)3Ge] (M = Li, Na, K, Rb, Cs); periodic trends and alkali metal dependent arene bonding

Article abstract of DOI:10.1039/b301623d

Reaction of three equivalents of the alkali salts of 2,6-diphenylphenoxide, [MOC₆H₃Ph₂-2,6] (M = Li, Na, K, Rb, Cs) with GeI₂ provides the corresponding cage complexes [M(μ-OC ₆H₃Ph₂-2,6)3Ge], all of which have been structurally characterized. These species contain a germanium(II) metal and an alkali metal connected by the oxygen atoms of the bridging aryloxide ligands. The two metal atoms are at the apices of a five-atom trigonal bipyramidal metal framework. The alkali cations are also bound to the carbon atoms of three of the 2,6-diphenyl substitutents of the aryloxide ligands. The number of bonds to these arene rings is strongly dependent on the identity of the alkali metal. This results in high formal coordination numbers for the group 1 metals K, Rb and Cs. The germanium and alkali metal form similar bonds to all three aryloxide oxygens except in the case of the caesium compound. In this case some localization of bonding occurs with structural parameters more consistent with a caesium aryloxide adduct of a germanium(II) bis(aryloxide). The Royal Society of Chemistry 2003.

Full text of DOI:10.1039/b301623d

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Synthesis and structures of the group 1 metal/germanium cage
complexes [M(ꢀ-OC6H3Ph2-2,6)3Ge] (M ؍ Li, Na, K, Rb, Cs);
periodic trends and alkali metal dependent arene bonding
Charles S. Weinert,* Phillip E. Fanwick and Ian P. Rothwell*
Department of Chemistry, Purdue University, 560 Oval Drive, West Lafayette, IN 47907-2084,
USA
Received 11th February 2003, Accepted 10th March 2003
First published as an Advance Article on the web 25th March 2003
Reaction of three equivalents of the alkali salts of 2,6-diphenylphenoxide, [MOC6H3Ph2-2,6] (M = Li, Na, K, Rb, Cs)
with GeI2 provides the corresponding cage complexes [M(µ-OC6H3Ph2-2,6)3Ge], all of which have been structurally
characterized. These species contain a germanium() metal and an alkali metal connected by the oxygen atoms of
the bridging aryloxide ligands. The two metal atoms are at the apices of a five-atom trigonal bipyramidal metal
framework. The alkali cations are also bound to the carbon atoms of three of the 2,6-diphenyl substitutents of the
aryloxide ligands. The number of bonds to these arene rings is strongly dependent on the identity of the alkali metal.
This results in high formal coordination numbers for the group 1 metals K, Rb and Cs. The germanium and alkali
metal form similar bonds to all three aryloxide oxygens except in the case of the caesium compound. In this case
some localization of bonding occurs with structural parameters more consistent with a caesium aryloxide adduct of a
germanium() bis(aryloxide).
[Tl(OtBu)3Sn],26 which has been shown to form complexes with
Introduction
transition metal pentacarbonyl fragments.27
Cage and cluster compounds of the main group elements have
We have reported the synthesis and structure of the complex
[Li(µ-OC6H3Ph2-2,6)3Sn] (OC6H3Ph2-2,6 = 2,6-diphenylphen-
recently attracted a great deal of interest.1,2 These materials
adopt a wide variety of structural motifs, and often contain
oxide), which is a rare group 14 complex containing bridging
bridging ligands, which serve to bring two or more metal or
aryloxide ligands and structurally resembles [Tl(µ-OtBu)3Sn].28
metalloidal atoms into close proximity with one another. These
As a continuation of our investigation into the chemistry of
species can be comprised of one or more main-group elements,
and the bridging ligands typically coordinate to the metal
centers through chalcogenide or pnictide elements. Addi-
tionally, these materials can exist as discrete molecular frame-
germanium() aryloxide29 and binaphthoxide30 complexes, we
have obtained the series of group1/germanium aryloxide cage
compounds [M(µ-OC6H3Ph2-2,6)3Ge] (M = Li, Na, K, Rb, Cs)
and wish to report on aspects of their solid state structures.
These compounds are of interest in that they allow an entire
comparison of the effect of the alkali metal upon the solid state
structure.
works, or exhibit extended polymeric structures.
The use of alkoxide and siloxide ligands in group 14 com-
plexes has been the focus of many studies,3 as the complexes
prepared can potentially serve as molecular precursors for the
synthesis of ceramics and/or superconducting materials.4–6
A
number of lead alkoxide and siloxide species have been
reported, including [Pb(OiPr)2]∞,7 [Pb(OtBu)2]3,7,8 and [Pb7-
(µ3-O)(µ4-O)(µ3-OSiMe3)10].9 The isopropoxide derivative forms
an infinite chain structure held together via bridging iso-
propoxide ligands, while the tert-butoxide derivative forms a
trimeric structure containing lead() atoms in both six- and
three-coordinate environments.7 This species has been used for
the preparation of [Pb3ZrO(OtBu)8], which could potentially
serve as a precursor for the formation of mixed group 4/14
metal oxide materials.8 Several tin-containing species contain-
ing bridging alkoxide or siloxide ligands have also been pre-
pared,10–23 and germanium analogs, although less common, are
also known.19,20,22
Results and discussion
Synthesis of compounds
The group 1 metal/germanium tris(aryloxide) cluster complexes
[M(µ-OC6H3Ph2-2,6)3Ge] (M = Li, 1; Na, 2; K, 3; Rb, 4; Cs, 5)
were prepared via treatment of [GeI2] with three equivalents
of the corresponding alkali metal salt of 2,6-diphenylphenol,
as shown in Scheme 1. Complex 1 was initially obtained
Compounds of the type [M(µ-OR)3MЈ], where µ-OR is a
bridging alkoxy or siloxy group, MЈ is a group 14 metal, and M
is a group 14 or other type of metal, share a common structural
motif. These species typically adopt a trigonal bipyramidal
framework comprised of five atoms-the two metal atoms
and the three oxygen atoms of the bridging ligands. When M
is a group 1 or group 2 metal, these species are considered
to be “-ate” complexes of the M(OR)3 fragment, and the group
1
or 2 metal is typically encapsuled by the oxygen
atoms of the bridging ligands. Examples include the group 14/
group 2 complex [Ge(µ-OtBu)3Mg(µ-OtBu)3Ge],24 the group14/
group
1
complexes [NaPb{µ-OSi(OtBu)3}3] and [KSn-
{µ-OSi(OtBu)3}3],25 and the group 13/group 14 complex
Scheme 1
T h i s j o u r n a l i s © T h e R o y a l S o c i e t y o f C h e m i s t r y 2 0 0 3
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 5 – 1 8 0 2
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Table 1 Key structural parameters for [M(µ-OC6H3Ph2-2,6)3Ge]a
Li
1
Na
2
K
3
Rb
4
Cs
5
M = Compound
rmetal/Å
rion/Å
M–Ge/Å
Ge–O/Å
1.57
0.76
2.624(7)
1.958(1)
1.91
1.02
2.941(2)
1.939(2)
2.35
1.38
2.50
1.49
2.72
1.70
3.407(1)
1.933(3)
1.935(3)
1.929(3)
2.753(3)
2.684(3)
2.709(3)
91.6(1)
93.6(1)
93.0(1)
118.8(2)
125.5(2)
121.5(2)
138.2(2)
134.1(2)
134.9(2)
262
3.407(1)
1.932(3)
1.938(3)
1.927(3)
2.769(3)
2.719(3)
2.653(3)
91.1(1)
92.5(1)
94.8(1)
121.0(2)
122.2(2)
119.3(2)
139.1(2)
135.2(2)
135.6(2)
266
3.6018(4)
1.930(2)
1.930(2)
1.940(2)
2.854(2)
2.932(2)
2.861(2)
95.73(6)
93.27(7)
95.28(6)
118.8(2)
125.4(2)
122.1(2)
135.5(2)
136.8(2)
134.6(2)
262
3.849(1)
1.923(3)
1.960(3)
1.929(3)
3.236(3)
2.922(3)
3.219(3)
92.97(9)
102.2(1)
93.39(1)
134.4(3)
122.9(2)
137.3(2)
109.6(2)
133.5(2)
107.5(2)
265
M–O/Å
2.000(5)
83.0(2)
2.306(2)
87.25(6)
119.7(1)
139.3(1)
M–O–Ge/Њ
Ge–O–C/Њ
M–O–C/Њ
120.0(1)
142.7(2)
Σ(O–Ge–O)/Њ
Σ(O–M–O)/Њ
246
239
256
208
176
176
166
153
a Atomic and ionic radii are taken from ref. 59.
serendipitously in our efforts to prepare the aryloxide complex
[Ge(OC6H3Ph2-2,6)2] from 2,6-diphenylphenol and [Ge(N-
{SiMe3}2)2].29 When the starting bisamide was prepared accord-
ing to the original literature procedure,31,32 complex 1 was the
only isolable product and no [Ge(OAr)2] was obtained.
However, synthesis of [Ge(N{SiMe3}2)2] by a more recently
published method33 produced the desired [Ge(OAr)2] com-
pound in excellent yield. The Li/Ge complex 1 was undoubtedly
produced due to an uncharacterized lithium complex generated
in the attempted preparation of [Ge(N{SiMe3}2)2].
General structural considerations and periodic trends
All five compounds were subjected to single crystal X-ray dif-
fraction analysis. Selected structural parameters are compared
in Table 1. In Tables 2–6 more explicit parameters are listed
including close contacts between the alkali metal and ortho-
phenyl ring carbon atoms. Complexes 1–5 each contain a five-
atom cage comprised of the germanium atom, the alkali metal,
and the three bridging oxygen atoms of the aryloxide ligands
(Figs. 1–5). In each case, the alkali metal atom coordinated to
Fig. 2 ORTEP diagram of [Na(µ-OC6H3Ph2-2,6)3Ge] 2. Thermal
ellipsoids are drawn at 50% probability.
Fig. 1 ORTEP diagram of [Li(µ-OC6H3Ph2-2,6)3Ge] 1. Thermal
ellipsoids are drawn at 50% probability.
Fig. 3 ORTEP diagram of [K(µ-OC6H3Ph2-2,6)3Ge] 3 (molecule 1).
Thermal ellipsoids are drawn at 50% probability.
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 5 – 1 8 0 2
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Table 2 Selected bond lengths (Å) and angles (Њ) for [Li(µ-OC6H3Ph2-
2,6)3Ge] (1)
Table 6 Selected bond lengths (Å) and angles (Њ) for [Cs(µ-OC6H3Ph2-
2,6)3Ge] (5)
Ge–O(1)
Li–O(1)
1.958(1)
2.000(5)
Li–C(62)
2.720(4)
Ge–O(1)
Ge–O(3)
Cs–O(2)
Cs–C(121)
Cs–C(125)
Cs–C(221)
Cs–C(223)
Cs–C(225)
Cs–C(321)
Cs–C(325)
1.923(3)
1.929(3)
2.922(3)
3.408(4)
3.775(4)
3.512(4)
3.625(4)
3.847(4)
3.440(4)
3.798(4)
Ge–O(2)
Cs–O(1)
Cs–O(3)
Cs–C(122)
Cs–C(126)
Cs–C(222)
Cs–C(224)
Cs–C(226)
Cs–C(322)
Cs–C(326)
1.960(3)
3.236(3)
3.219(3)
3.821(5)
3.381(4)
3.455(4)
3.804(4)
3.707(4)
3.754(4)
3.472(4)
O(1)–Ge–O(1)
O(1)–Li–C(62)
O(1)–Li–C(62)
81.89(6)
77.30(6)
153.1(1)
Ge–O(1)–Li
O(1)–Li–C(62)
C(62)–Li–C(62)
83.0(2)
109.44(7)
97.3(2)
Table 3 Selected bond lengths (Å) and angles (Њ) for [Na(µ-OC6H3Ph2-
2,6)3Ge] (2)
Ge–O
Na–O
1.939(2)
2.306(2)
Na–C(22)
Na–C(23)
2.742(3)
3.100(3)
O(1)–Ge–O(2)
O(2)–Ge–O(3)
Ge–O(2)–Cs
O(1)–Cs–O(2)
O(2)–Cs–O(3)
86.2(1)
91.9(1)
102.2(1)
50.76(7)
53.88(7)
O(1)–Ge–O(3)
Ge–O(1)–Cs
Ge–O(3)–Cs
O(1)–Cs–O(3)
87.2(1)
92.97(9)
93.39(1)
48.60(7)
O–Ge–O
Ge–O–Na
85.43(7)
87.25(6)
O–Na–O
69.55(8)
Table 4 Selected bond lengths (Å) and angles (Њ) for [K(µ-OC6H3Ph2-
2,6)3Ge] (3)
Molecule 1
Molecule 2
Ge(1)–O(1)
Ge(1)–O(2)
Ge(1)–O(3)
K(1)–O(1)
K(1)–O(2)
K(1)–O(3)
K(1)–C(161)
K(1)–C(162)
K(1)–C(163)
K(1)–C(261)
K(1)–C(262)
K(1)–C(263)
K(1)–C(264)
K(1)–C(265)
K(1)–C(266)
K(1)–C(321)
K(1)–C(326)
K(1)–C(325)
1.933(3)
1.935(3)
1.929(3)
2.753(3)
2.684(3)
2.709(3)
3.376(4)
3.085(4)
3.166(5)
3.171(4)
3.281(5)
3.388(5)
3.374(5)
3.259(5)
3.135(4)
3.250(4)
3.190(4)
3.347(4)
Ge(2)–O(4)
Ge(2)–O(5)
Ge(2)–O(6)
K(2)–O(4)
K(2)–O(5)
K(2)–O(6)
K(2)–C(461)
K(2)–C(462)
K(2)–C(463)
K(2)–C(521)
K(2)–C(522)
K(2)–C(523)
K(2)–C(524)
K(2)–C(525)
K(2)–C(526)
K(2)–C(621)
K(2)–C(622)
K(2)–C(623)
1.932(3)
1.938(3)
1.927(3)
2.769(3)
2.719(3)
2.653(3)
3.415(4)
3.097(4)
3.219(4)
3.206(4)
3.202(4)
3.222(4)
3.207(4)
3.187(4)
3.177(4)
3.232(4)
3.249(4)
3.380(4)
Fig. 4 ORTEP diagram of [Rb(µ-OC6H3Ph2-2,6)3Ge] 4. Thermal
ellipsoids are drawn at 50% probability.
O(1)–Ge(1)–O(2)
O(2)–Ge(1)–O(3)
O(1)–Ge(1)–O(3)
O(1)–K(1)–O(2)
O(2)–K(1)–O(3)
O(1)–K(1)–O(3)
K(1)–Ge(1)–O(1)
K(1)–Ge(1)–O(2)
K(1)–Ge(1)–O(3)
87.6(1)
87.2(1)
86.7(1)
58.97(8)
59.21(8)
58.10(8)
53.86(8)
51.83(8)
52.56(8)
O(5)–Ge(2)–O(6)
O(4)–Ge(2)–O(6)
O(4)–Ge(2)–O(5)
O(4)–K(2)–O(5)
O(5)–K(2)–O(6)
O(4)–K(2)–O(6)
K(2)–Ge(2)–O(4)
K(2)–Ge(2)–O(5)
K(2)–Ge(2)–O(6)
86.5(1)
87.2(1)
87.5(1)
58.37(8)
59.07(8)
58.75(8)
54.34(8)
52.88(7)
50.90(8)
Table 5 Selected bond lengths (Å) and angles (Њ) for [Rb(µ-OC6H3Ph2-
2,6)3Ge] (4)
Ge–O(1)
Ge–O(3)
Rb–O(2)
1.930(2)
1.940(2)
2.932(2)
3.364(3)
3.583(3)
3.469(3)
3.438(3)
3.274(3)
3.319(3)
3.364(3)
3.417(3)
Ge–O(2)
Rb–O(1)
Rb–O(3)
1.930(2)
2.854(2)
2.861(2)
3.469(3)
3.587(3)
3.349(3)
3.198(3)
3.558(3)
3.314(3)
3.424(3)
3.363(3)
Rb–C(121)
Rb–C(123)
Rb–C(125)
Rb–C(221)
Rb–C(223)
Rb–C(321)
Rb–C(323)
Rb–C(325)
Rb–C(122)
Rb–C(124)
Rb–C(126)
Rb–C(222)
Rb–C(224)
Rb–C(322)
Rb–C(324)
Rb–C(326)
Fig. 5 ORTEP diagram of [Cs(µ-OC6H3Ph2-2,6)3Ge] 5. Thermal
ellipsoids are drawn at 50% probability.
O(1)–Ge–O(2)
O(2)–Ge–O(3)
Ge–O(2)–Rb
O(1)–Rb–O(2)
O(2)–Rb–O(3)
87.99(8)
87.42(8)
93.27(7)
55.20(5)
54.97(5)
O(1)–Ge–O(3)
Ge–O(1)–Rb
Ge–O(3)–Rb
O(1)–Rb–O(3)
86.72(8)
95.73(6)
95.28(6)
55.42(5)
No direct, intramolecular alkali metal–germanium interaction
occurs. Furthermore, the steric bulk of the 2,6-diphenyl-
phenoxide ligands prohibits any extensive oligomerization
through intermolecular Ge–M bonding. This type of bond-
ing has precedence, however. The complex [Tl(µ-OtBu)3Sn]
was shown to form complexes of the type [(CO)5M–
Sn(µ-OtBu)3Tl] (M = Cr, Mo) upon thermal or photolytic
reaction with M(CO)6,27 and the trimeric complexes
three oxygen atoms of a pyramidalized germanium tris(aryl-
oxide). The remaining lone pair of electrons on germanium is
presumably located pointing away from the three Ge–O bonds.
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[M(µ-OtBu)3Pb(µ-OtBu)3M] (M = Ge, Sn) were also found to
form complexes with the [Fe(CO)4] fragment by thermal reac-
tion with [Fe2(CO)9].34 We recently reported the structure of the
silver()/germanium complex [Ag(µ-OC6HPh4-2,3,5,6)3Ge-
(AgOSO2CF3)],30 in which the germanium lone pair interacts
with the silver atom of the AgOSO2CF3 fragment.30,35 The lack
of oligomerization in 1–5 is presumably a consequence of steric
factors and/or the stabilization of the formally three coordinate
group 1 metals by interactions with the ortho-phenyl rings of
the bridging aryloxide ligands. The nature of this interaction
depends strongly on the identity of the group 1 metal (vide
infra).
The structures of 1–5 consist of a five-atom cage containing
the germanium atom, the three µ-oxygen atoms, and the group
1 metal. The structure of the framework approaches trigonal
bypryamidal in all cases. It can be seen (Table 1) that the M–Ge
distance increases gradually as one moves down the group 1
metals. The M–Ge distance correlates extremely well with both
the ionic and metallic radii for the alkali metals (Table 1, Fig. 6).
to 123Њ for the other aryloxide bridge. We believe these large
angles are present in order to accommodate the arene–Cs inter-
actions present within this cluster.
Arene–alkali metal interactions
Compounds 1–5 contain a pyramidalized alkali metal with the
three (O–M–O) angles summing to values of between 293 and
153Њ on moving down the group from Li to Cs. Hence in all five
compounds the alkali metal atom is formally extremely electron
deficient with a large, vacant site of electrophilicity. This open
cavity is occupied in all cases by three ortho-phenyl rings, one
each from each of the bridging 2,6-diphenylphenoxide ligands.
The extent of arene–M interaction depends strongly on the size
of the group 1 metal. The lithium atom in 1 exhibits a close
contact with one ortho-carbon atoms of one ortho-phenyl ring
of each aryloxide ligand. The arene–Li interactions are high-
lighted in Fig. 7. The Li–C(62) distance is 2.720(4) Å, which is
close to the upper limit for an electrostatic interaction between
a Li atoms and π-electron cloud of an aromatic ring.36–38
Dimeric base-free phenyllithium was reported to have inter-
molecular Li–Caromatic contacts ranging from 2.40(1) to 2.86(1)
Å.39 The lithium thiolate complex (LiSC6H2Ph3-2,4,6)4ؒC7H8
exhibits intramolecular Li–C contacts up to 2.73(2) Å in
length,40 and the gallium/lithium µ-iodo complex [Li(THF)4]-
[GaI(SiPh3)3] has two Li–C intermolecular contacts of 2.630(1)
and 2.854(9) Å.41 Based on the available structural data, only
the Li–C(62) interaction is significant. The other lithium–
carbon distances range from 3.185(4) Å for Li–C(61) to
4.443(4) Å for Li–C(65). The structure of the isomorphous and
isostructural tin congener, [Li(µ-OC6H3Ph2-2,6)3Sn] 6, has been
reported and closely resembles that of 1.28 This species exhibits
a π-interaction between the Li atom and the same (ortho)
carbon atom of the 2,6-phenyl rings of the ligands.
Fig. 6 Plots showing correlation of M–Ge distances (Å) in [M(µ-OC6-
H3Ph2-2,6)3Ge] 1–5 and ionic and metallic radii for the group 1 metals
M = Li, Na, K, Rb, Cs.
However, there is a significant difference in the structure of the
caesium cluster 5 compared to the other four (Fig. 5). In com-
pounds 1–4 the Ge–O distances span the very narrow range of
1.927(3)–1.958(1) Å. These distances are slightly longer than
the Ge–O distances of 1.822(1) and 1.817(1) Å reported for
[Ge(OC6H3Ph2-2,6)2].29 The M–O distances increase with metal
atomic number, but within each cluster are very similar. In the
lithium and sodium compounds 1 and 2 there is a crystallo-
graphic three-fold axis of symmetry so that all three sets of
parameters are identical (Figs. 1 and 2). For potassium com-
pound 3 there are two independent molecules within the unit
cell. However, the six non-equivalent K–O distances are very
similar and an ORTEP plot of molecule 1 is shown in Fig. 3.
One of the Rb–O distances in 4 (Fig. 4) is slightly longer than
the other two; although in this compound the three Ge–O dis-
tances are essentially the same. Within compounds 1–4 the M–
O–Ge angle increases upon moving down the group, paralleling
the M–Ge distance. The Ge–O–Ar angles in 1–4 are in the nar-
row range of 118–125Њ. In [Ge(OC6H3Ph2-2,6)2] the Ge–O–Ar
angles are found to be very similar, 117Њ.29 In contrast there is
definite localization of the bonding in caesium compound 5
(Table 1, Fig. 5). Specifically it can be seen that there is one
short Cs–O distance of 2.922(3) Å and two longer distances of
3.219(3) and 3.236(3) Å. The corresponding distances to ger-
manium are 1.960(3) Å, and short 1.923(3), 1.929(3) Å. This
localization is consistent with a formulation in this case of a
caesium aryloxide adduct of a germanium() aryloxide as
shown in Scheme 1. Another important difference between 5
and its lighter congeners lies in the Ge–O–Ar angles (Tables 1
and 6). The two aryloxides with the shortest Ge–O distances
have relatively large Ge–O–Ar angles of 134 and 137Њ compared
Fig. 7 Diagram illustrating the coordination environment about
lithium in [Li(µ-OC6H3Ph2-2,6)3Ge] 1.
The sodium complex [Na(µ-OC6H3Ph2-2,6)3Ge] 2 crystallizes
¯
in the cubic space group Pa3. As for 1, a crystallographic C3
axis passes through both the Na and Ge atoms rendering all
three aryloxide ligands equivalent. Compound 2 also exhibits
interactions between the sodium atom and the π-electron cloud
of the ortho-phenyl rings (Fig. 8). The typical range for Na–C
contacts for the carbon atoms of arene or cyclopenadienyl rings
is 2.6–3.0 Å,42 and the Na–C(21), Na–C(22) and Na–C(23)
distances of 3.204(3), 2.742(3) and 3.100(3) Å, respectively,
represent close contacts. As with 1 the strongest interaction is
again with the ortho-carbons. A series of thiolate complexes
[MSC6H3Trip2-2,6]2 (M = La, Na, K, Rb, Cs; Trip = 2,4,6-tri-
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 5 – 1 8 0 2
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Fig. 10 Diagram illustrating the coordination environment about
potassium in molecule 2 of [K(µ-OC6H3Ph2-2,6)3Ge] 3.
Fig. 8 Diagram illustrating the coordination environment about
sodium in [Na(µ-OC6H3Ph2-2,6)3Ge] 2.
intramolecular K–C contacts ranging from 3.279(5) to 3.564(5)
Å.40
isopropylphenyl) has been prepared and structurally character-
ized, and the Na–C distances in the sodium derivative [NaS-
C6H3Trip2-2,6]2ؒ0.5 C7H8 range from 2.839(5) to 3.266(5) Å.40
The complex NaC(SiMe2Ph)3 also exhibits such interactions,
ranging from 2.80(1) to 3.39(2) Å.43 The other sodium–carbon
distances in 2 vary from 3.807(3) to 4.146(3) Å, which are too
long to be considred bonding ineractions.
The potassium analog [K(µ-OC6H3Ph2-2,6)3Ge] 3, is of lower
symmetry in the solid state, crystallizing in the orthorhombic
space group Pca21. Compound 3 contains two unique mole-
cules in the unit cell and the ORTEP diagram for molecule 1 is
shown in Fig. 3 and the environment about the each of the
potassium atoms is illustrated in Figs. 9 and 10. The potassium
ions in complex 3 interact with the π-electron clouds of the
ortho-phenyl rings to a larger extent than for 1 and 2. In mole-
cule 1, the K atom is bound in two different fashions to the
three ortho-phenyl rings. The approximate range of distances
for K–C bonding is 3.1–3.3 Å.42 However, longer K–C distances
have been reported for bonds between a potassium cation and
an arene ring. For example, the coordinated toluene molecules
in [K([18]crown-6)]3[C60](C6H5CH3)2 were reported to bind as
η3 ligands, with K–C bond lengths ranging from 3.230(8) to
3.517(5) Å,44 and the complex KS(C6H3Trip2-2,6)2 exhibits
The ring encompassing C(161) to C(166) contains three K–C
contacts that roughly fall into the 3.1–3.3 Å range, and thus
coordinates to the K atom in an η3 fashion, as does the ring
containing C(361)–C(366). The other proximal phenyl ring con-
taining C(261)–C(266) is coordinated in what can be considered
an η6 fashion. The potassium atom of molecule 2 is in a similar
environment. The phenyl ring containing C(461)–C(466)
coordinates in an η2 fashion, as the K–C(461) contact of
3.415(4) Å is slightly too long for bonding to occur. The ring
containing C(521)–C(526) coordinates in an η6 bonding mode,
and the ring containing C(621)–C(666) is coordinated in an η4
bonding mode. Thus, both discrete molecules of 3 contain
formally very highly-coordinated potassium metal centers.
An ORTEP diagram for the rubidium-containing species
[Rb(µ-OC6H3Ph2-2,6)3Ge] (4) is shown in Fig. 4, selected bond
distances and angles are collected in Table 5, and the coordin-
ation environment about the rubidium atom is illustrated in
Fig. 11. Like the potassium compound 3, the rubidium center is
in a high coordination environment in 4, as it exhibits a total of
16 interactions to the carbon atoms of the ortho-phenyl rings.
The majority of complexes containing arene rings coordinated
to rubidium exhibit Rb–C contacts of 3.1–3.6 Å,42 and the two
Rb–C contacts between Rb–C(225) and Rb–C(226) have dis-
tances of 3.761(3) and 3.716(3) Å, which are longer than typical
Fig. 9 Diagram illustrating the coordination environment about
potassium in molecule 1 of [K(µ-OC6H3Ph2-2,6)3Ge] 3.
Fig. 11 Diagram illustrating the coordination environment about
rubidium in [Rb(µ-OC6H3Ph2-2,6)3Ge] 4.
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 5 – 1 8 0 2
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33
reported values.40,43,45–48 Thus, the two phenyl rings attached to
C(12) and C(32) are both coordinated to Rb in an η6 fashion,
while the remaining phenyl ring attached to C(22) is closer to an
η4 boding mode. Highly coordinated rubidium metal centers
phenylphenol,51 MOC6H3Ph2-2,6,52 and Ge[N(SiMe3)2]2 were
prepared according to literature procedures or slight variations
thereof. Germanium() iodide was purchased from Aldrich and
used as received.
43
are not uncommon, and examples include RbC(SiMe2Ph)3,
[Ph3CRbؒPMDTA]n,48 and the selenolate complex [RbSeC6H3-
Preparation of [Li(ꢀ-OC6H3Ph2-2,6)3Ge] (1)
i
Trip2-2,6] (Trip = C6H2 Pr3-2,4,6).47
Germanium() iodide (0.44 g, 1.7 mmol) was suspended in
benzene (10 mL). To this was added LiOC6H3Ph2-2,6 (0.18 g,
0.55 mmol) in benzene (5 mL). The suspension was stirred for
12 h, then filtered through Celite to yield a yellow solution. The
volatiles were removed in vacuo, resulting in a while solid which
was recrystallized from hot benzene (5 mL) to give 0.16 g (34%)
of 1 as colorless crystals. Anal. Calc. for C54H39GeLiO3: C,
79.54; H, 5.07. Found: C, 79.19; H, 5.07%.
The structure of the [CsO3Ge] core in the caesium complex
[Cs(µ-OC6H3Ph2-2,6)3Ge] 5 was shown to be significantly dif-
ferent than those in complexes 1–4. An ORTEP diagram of 5 is
shown in Fig. 5, and the coordination environment about the
caesium atom is shown in Fig. 12. Selected bond distances and
angles are listed in Table 6. Examination of the Cs–C inter-
actions present in 5 show the phenyl ring attached to C(22) is
coordinated to the caesium metal center though all six carbon
atoms. The C(22) atom is attached to O(2), which exhibits the
shortest Cs–O contact of 2.922(3) Å. The other two proximal
phenyl rings, which contain the atoms C(121)–C(126) and
C(321)–C(326), are both coordinated to the Cs metal center
in an η4 fashion. The non-bonded distances for the four
uncoordinated carbon atoms range from 4.077(4) to 4.173(4) Å,
which are outside the typical range, 3.3–3.8 Å, of bonding con-
tacts.42 In the complex [(C6H3)3CsC(SiMe3)2SiMe2CH2]2, the
benzene solvate molecules coordinate to the Cs metal center in
η4, η2 and η1 bonding modes and exhibit Cs–C contacts in the
range of 3.5–3.7 Å.49
Preparation of [Na(ꢀ-OC6H3Ph2-2,6)3Ge] (2)
Compound 2 was prepared using 0.25 g (0.76 mmol) of GeI2
and 0.66 g (2.5 mmol) of NaOC6H3Ph2-2,6 by the same pro-
cedure used for the synthesis of 1. Yield: 0.46 g (73%). Anal.
Calc. for C54H39GeNaO3: C, 78.00; H, 4.73. Found: C, 78.15; H,
4.98%.
Preparation of [K(ꢀ-OC6H3Ph2-2,6)3Ge] (3)
A suspension of KOC6H3Ph2-2,6 (0.20 g, 0.70 mmol) in
benzene (10 mL) was added to a suspension of GeI2 (0.071 g,
0.22 mmol) in benzene (10 mL). The reaction mixture was gen-
tly heated to reflux, allowed to cool, and then was stirred for
15 h at room temperature, resulting in a yellow suspension. The
volatiles were removed in vacuo and benzene (10 mL) was added
to the resulting yellow solid. The mixture was heated to reflux,
shaken and filtered while still warm. The filtrate was reserved
and the remaining yellow solid was again extracted by an iden-
tical procedure. The filtrates were combined and the benzene
was removed in vacuo. To the resulting white powder was added
a 1 : 1 mixture of benzene–hexane (10 mL). The suspension was
heated until all solids dissolved; slow cooling yielded color-
less crystals of 3. Yield: 0.060 g (33%). Anal. Calc. for
C54H39GeKO3: C, 76.52; H, 4.64. Found: C, 76.37; H, 4.83%.
Preparation of [Rb(ꢀ-OC6H3Ph2-2,6)3Ge] (4)
A suspension of RbOC6H3Ph2-2,6 (0.76 g, 2.3 mmol) in
benzene (20 mL) was added to a suspension of GeI2 (0.25 g,
0.77 mmol) in benzene (10 mL). The mixture was gently heated
to reflux, allowed to cool, and was stirred for 48 h, resulting in a
pink precipitate. The solid was isolated by filtration, washed
with benzene (3 × 5 mL) and hexane (3 × 5 mL) and dried in
vacuo. The desired product was obtained by a method analo-
gous to that used for 3 to yield 0.47 g (69%) of 4 as colorless
crystals. Anal. Calc. for C54H39GeO3RbؒC6H6: C, 74.13; H,
4.67. Found: C, 73.92; H, 4.74%.
Fig. 12 Diagram illustrating the coordination environment about
caesium in [Cs(µ-OC6H3Ph2-2,6)3Ge] 5.
Conclusions
The entire series of germanium/group 1 cage complexes
[M(µ-OC6H3Ph2-2,6)3Ge] (M = Li 1, Na 2, K 3, Rb 4, Cs 5) have
been prepared from the corresponding aryloxide salt and
germanium() iodide. The species adopt a common structural
motif in which the group 1 metal is encapsulated by the three
oxygen atoms of the 2,6-diphenylphenoxide ligands. In the
complexes 1–4, the alkali metal atom, the germanium atom,
and the three oxygen atoms form a trigonal bipyramidal cage,
and these four species are approximately isostructural. In the
case of the caesium complex 5, the structure of this fragment
more closely resembles a CsOAr adduct of a germanium()
aryloxide. Complexes 1–5 all exhibit interactions between the
alkali metal cation and the π-electron cloud of the ortho-phenyl
rings of the aryloxide ligands. The number of these interactions
increases with increasing size of the alkali cation.
Preparation of [Cs(ꢀ-OC6H3Ph2-2,6)3Ge] (5)
A suspension of CsOC6H3Ph2-2,6 (0.63 g, 1.7 mmol) in benzene
(25 mL) was added to a suspension of GeI2 (0.17 g, 0.52 mmol)
in benzene (25 mL). The reaction mixture was stirred for 48 h,
resulting in a deep purple precipitate. The solvent was removed
in vacuo and the solid was extracted with hot benzene (4 ×
20 mL). Removal of the solvent yielded a white powder which
was recrystallized from a hot solution of 2 : 1 benzene/hexane
(15 mL), yielding 0.22 g (45%) of 5 as colorless crystals. Anal.
Calc. for C54H39CsGeO3: C, 68.90; H, 4.18. Found: C, 68.05; H,
4.24%.
X-Ray data collection and reduction
Experimental
All manipulations were carried out using standard syringe,
Schlenk, and glovebox techniques.50 The compounds 2,6-di-
Crystal data and data collection parameters are contained
in Table 7. A suitable crystal was mounted on a glass fiber in
a random orientation under a cold stream of dry nitrogen.
D a l t o n T r a n s . , 2 0 0 3 , 1 7 9 5 – 1 8 0 2
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Table 7 Crystallographic data for compounds 1–5
1ؒC6H6
2ؒ0.5C6H6
3ؒC6H6
4ؒC6H6
5
Formula
Space group
a/Å
b/Å
c/Å
α/Њ
C60H45GeLiO3
R3 (no. 146)
15.7846(6)
15.7846(6)
15.839(2)
90
C57H42GeNaO3
Pa3 (no. 205)
20.7127(3)
20.7127(3)
20.7127(3)
90
C60H45GeKO3
Pca21 (no. 29)
17.7319(3)
16.987332)
31.0061(5)
90
C60H45GeO3Rb
P21/c (no. 14)
15.6217(3)
17.1706(4)
17.7554(4)
90
C54H39CsGeO3
C2/c (no. 15)
38.6426(9)
10.7401(2)
21.2400(4)
90
¯
β/Њ
90
120
3417.7(7)
3
1.302
90
90
8886.1(2)
8
1.301
150
90
90
9339.6(3)
8
1.317
100.662(1)
90
4680.4(2)
4
1.379
150
108.184(1)
90
8374.9(3)
8
1.493
150
γ/Њ
V/Å3
Z
Dc/g cmϪ3
T /K
150
150
λ(Mo-Kα)/Å
R
Rw
0.71073
0.031
0.061
0.71073
0.046
0.113
0.71073
0.038
0.078
0.71073
0.037
0.077
0.71073
0.047
0.103
16 M. J. Hampden-Smith, T. A. Wark, A. L. Rheingold and
J. C. Huffman, Can. J. Chem., 1991, 69, 121.
17 R. Nesper and H. G. von Schnering, Z. Naturforsch., Teil B, 1982,
37, 1144.
18 C. Zybill and G. Müller, Z. Naturforsch., Teil B, 1988, 43, 45.
19 M. Veith, P. Hobein and Rösler, Z. Naturforsch., Teil B, 1989, 44,
1067.
20 M. Veith, C. Mathur and V. Huch, J. Chem. Soc., Dalton Trans.,
1997, 995.
21 L. R. Sita, R. Xi, G. P. A. Yap, L. M. Liable-Sands and A. L.
Rheingold, J. Am. Chem. Soc., 1997, 119, 756.
22 L. R. Sita, J. R. Babcock and R. Xi, J. Am. Chem. Soc., 1996, 118,
10912.
23 R. Xi and L. R. Sita, Inorg. Chim. Acta, 1998, 270, 118.
24 M. Veith, J. Hans, L. Stahl, P. May, V. Huch and A. Sebald,
Z. Naturforsch., Teil B, 1991, 46, 403.
25 K. W. Terry, K. Su, T. D. Tilley and A. L. Rheingold, Polyhedron,
1998, 17, 891.
26 M. Veith and R. Rösler, Angew. Chem., Int. Ed. Engl., 1982, 21, 858.
27 M. Veith and K. Kunze, Angew. Chem., Int. Ed. Engl., 1991, 30, 95.
28 G. D. Smith, P. E. Fanwick and I. P. Rothwell, Inorg. Chem., 1989,
28, 618.
Preliminary examination and final data collection were per-
formed with Mo-Kα radiation (λ = 0.71073 Å) on a Nonius
KappaCCD. Lorentz and polarization corrections were
applied to the data.53 An empirical absorption correction using
SCALEPACK was applied.54 Intensities of equivalent reflec-
tions were averaged. The structure was solved using the struc-
ture solution program PATTY in DIRDIF92.55 The remaining
atoms were located in succeeding difference Fourier syntheses.
Hydrogen atoms were included in the refinement but restrained
to ride on the atom to which they are bonded. The structure was
refined in full-matrix least squares where the function mini-
mized was Σw(|Fo|2 Ϫ |Fc|2)2 and the weight w is defined as w =
1/[σ2(Fo ) ϩ (0.0585P)2ϩ1.4064P] where P = (Fo ϩ 2Fc2)/3.
Scattering factors were taken from the “International Tables
for Crystallography”.56 Refinement was performed on a Alpha-
Server 2100 using SHELX-97.57 Crystallographic drawings
were done using programs ORTEP.58
2
2
CCDC reference numbers 203281 (1), 203290 (2), 203292 (3),
203289 (4) and 203293 (5).
See http://www.rsc.org/suppdata/dt/b3/b301623d/ for crystal-
lographic data in CIF or other electronic format.
29 C. S. Weinert, A. E. Fenwick, P. E. Fanwick and I. P. Rothwell,
J. Chem. Soc., Dalton Trans., 2003, 532.
30 C. S. Weinert, P. E. Fanwick and I. P. Rothwell, J. Chem. Soc.,
Dalton Trans., 2002, 2948.
31 D. H. Harris and M. F. Lappert, J. Chem. Soc., Chem. Commun.,
1974, 895.
Acknowledgements
32 M. J. S. Gynane, D. H. Harris, M. F. Lappert, P. P. Power, P. Rivière
and M. Rivière-Baudet, J. Chem. Soc., Dalton Trans., 1977, 2004.
33 Q. Zhu, K. L. Ford and E. J. Roskamp, Heteroat. Chem., 1992, 3,
647.
This work was supported by a grant from the National Science
Foundation (Grant CHE-0078405).
34 M. Veith and J. Hans, Angew. Chem., Int. Ed. Engl., 1991, 20, 878.
35 C. S. Weinert, P. E. Fanwick and I. P. Rothwell, Acta Crystallogr.,
Sect. E, 2002, 58, m718.
36 W. N. Setzer and P. v. R. Schleyer, Adv. Organomet. Chem., 1985, 24,
353.
37 K. Jonas, Adv. Organomet. Chem., 1981, 19, 97.
38 P. Jutzi, Adv. Organomet. Chem., 1986, 26, 217.
39 R. E. Dinnebier, U. Behrens and F. Olbrich, J. Am. Chem. Soc.,
1998, 120, 1430.
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