Cyclic dimethylsiloxanes as pseudo crown ethers: Syntheses and characterization of Li(Me2SiO)5[Al{OC(CF3) 3}4], Li(Me2SiO)6[Al{OC(CF 3)3}4], and

Article abstract of DOI:10.1002/anie.200504262

(Chemical Equation Presented) An unexpected guest: The salts LiD ₅[Al_F], LiD₆[Al_F], and LiD ₆[Al_PhF] (D_n = (Me₂SiO)_n; [Al_F] = Al{OC(CF₃

Full text of DOI:10.1002/anie.200504262

Angewandte
Chemie
[KD7]+ ions were unexpectedly isolated from reactions in
the presence of silicone grease,[13] although the mechanisms of
the reactions are unclear. In a reaction designed to give
Se6Ph2
[AlF], and Se2Ph2 in the presence of silicone grease, we
unexpectedly obtained crystals of LiD6[AlF]. Subsequently,
we prepared LiD5[AlF], LiD6[AlF], and LiD6[AlPhF] ([AlPhF] =
Al{OC(CF3)2Ph}4) in high yield by the reaction of Li[AlF] or
Li[AlPhF] with D5 or D6 in CH2Cl2 solution [Eq. (1)].
A
(CF3)3}4) from Se4
A
AHCTREUNG
AHCTREUNG
A
N
ACHTREUNG
A
ACHTREUNG
AHCTREUNG
Host–Guest Complexes
These results, and the calculated energies of related reactions
of alkali-metal cations with cyclic dimethysiloxanes imply the
existence of a new class of host–guest complexes for the cyclic
siloxanes that is similar to, but less extensive than, that for the
DOI: 10.1002/anie.200504262
Cyclic Dimethylsiloxanes as Pseudo Crown
Ethers: Syntheses and Characterization of
crown ethers; for example, the reaction of Li
ACHTREUNG
CH2Cl2 did not give the expected product LiD5
AHCTREUNG
Li
Li
Li
C
G
addition, these findings imply that new classes of metal
complexes of cyclosiloxane analogues (for example, cyclo-
phosphazenes) may be prepared by using metal salts of large
weakly coordinating anions, which minimize lattice-energy
changes and cation–anion interactions.[15]
ACHTREUNG
Andreas Decken, Jack Passmore,* and Xinping Wang
In memory of Chunying Liao
The IR and Raman spectra of the moisture-sensitive,
thermally stable, colorless salts LiD
N
N
LiD6[AlPhF] showed the characteristic peaks of the anions, as
AHCTREUNG
well as peaks very similar to those of the siloxane reactants.
Electron ionization mass spectrometry (EI-MS) and chemical
analysis of the products were consistent with the given
Although the chemistry of silicon is notably different from
that of carbon,[1] parallels between the chemistry of the two
elements continue to emerge, for example, the recent
formulations. The 29Si{1H} NMR signals of LiD6
[AlPhF] (d =
A
[2]
ꢀ
syntheses of a proposed Si Si triple bond, persilaaromatic
ꢁ10.14 ppm) and LiD6[AlF] (d = ꢁ9.22 ppm) in liquid SO2
R
rings,[3] silylium ions,[4] and silaadamantane.[5] However, few
stable adducts of silicon ethers (for example, (Me3Si)2O) have
been prepared,[6] and there have been no reports of direct
reactions of metal ions with cyclic dimethysiloxanes Dn (Dn =
(Me2SiO)n, n = 1–40)[7] or related compounds, in contrast to
the extensive and selective reaction of metal ions with the
structurally similar crown ethers.[8] Silacrown ethers contain-
ing one or two Me2SiO units have a drastically reduced ability
to bind metal cations compared to crown ethers.[9] This
observation has been attributed to the low basicity of oxygen
in siloxane compounds,[10] the reasons for which are of
continuing interest.[11] Nevertheless, two examples[12] of
were different from that of D6 (d = ꢁ22.69 ppm), implying the
presence of the [LiD6]+ ion, or an equilibrium mixture of
[LiD6]+, Li+, and D6.[16] The 29Si{1H} NMR chemical shift of
LiD
A
ꢁ21.67 ppm), indicating complete dissociation of the complex
into Li+, [AlF]ꢁ, and D5 in liquid SO2. This observation is
consistent with the less negative estimated energy (DE =
ꢁ210 kJmolꢁ1, HF/6-31G*) for the reaction of Li
D5 [Eq. (2)] compared to that for the corresponding reaction
with D6 (DE = ꢁ242 kJmolꢁ1; Scheme 1).[17]
Li½AlFŠðsÞ þ D5ðlÞ ! LiD5½AlFŠ
ð2Þ
ðsÞ
A preliminary single-crystal X-ray diffraction (XRD)
study of LiD
5[AlF][18] clearly showed that the structure of the
N
[*] Dr. A. Decken, Prof. J. Passmore, X. Wang
Department of Chemistry
University of New Brunswick
Fredericton, NB E3B6E2 (Canada)
Fax: (+1)506-453-4981
both LiD
in LiD
A
A
E-mail: passmore@unb.ca
AHCTREUNG
[**] Acknowledgement is made to NSERC (Canada) for financial
support of this research, Mikko Rautiainen for help with calcu-
lations, and Dr. Carsten Knapp for his helpful suggestions.
structure, in which the Li+ ion is in the plane of the Si6O6 ring.
The distortion from the ideal structure results from Li+···Fdꢁ
interactions between the cations and the anions. The strength
of these interactions, which can be judged by calculating their
Supporting information for this article is available on the WWW
under http://www.angewandte.org or from the author.
Angew. Chem. Int. Ed. 2006, 45, 2773 –2777
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
2773

out of the Si6O6 plane in LiD6
LiD6[AlF] (0.13(1) Š), and to a slightly stronger coordination
of four oxygen atoms to the Li+ ion in LiD6
2.03(2)–2.07(1) Š; s = 0.81 vu) than in LiD
E
R
H
C
A
T
[AlPhF] (0.423(3) Š) than in
Communications
AHCTREUNG
ꢁ
AHCTREUNG
ꢁ
6[AlPhF] (Li O
2.059(3)–2.099(4) Š; s = 0.77 vu). Related compounds with
five-coordinate Li+ ions include Li([12]crown-4)Cl (Li O
ꢁ
ꢁ
2.128(2) Š) and Li([12]crown-4)
N
(CH2)3OCH3] (Li
O 2.080(3)–2.187(3) Š).[22] The cyclohexaphosphonitrile ring,
which is isoelectronic to cyclohexasiloxane, acts as a macro-
cyclic ligand to Cu2+ and Co2+ in the ions [{N6P6-
(NMe2)12}MCl]+ (M = Cu, Co).[23] In these cations, the metal
Scheme 1. Born–Haber cycle for the reaction of LiX (X=[AlF] or I) with
atoms are coordinated by four nitrogen atoms of the cyclo-
hexaphosphazene ring and one chlorine atom, in a coordina-
tion geometry that is similar to that of the lithium atoms in
D6. Lattice energies DUL, energy of vaporization DEvap, binding
energies DEB (calculated at the HF/6-31G* level of theory), and
energies of formation DE are given in kJmolꢁ1
.
LiD6[AlPhF].
N
ꢁ
The average Si ONC bond lengths and Si-
NC-Si angles involving the noncoordinating
O
oxygen atoms (ONC) in the [LiD6]+ ions of LiD6-
A
N
similar to those found for the oxygen atoms in D6
by electron diffraction (ED).[24] For the coordi-
ꢁ
nating oxygen atoms, however, the average Si O
bond lengths are slightly longer, and the average
ꢁ
Si-O-Si angles are smaller. The average Si C
bond lengths for the silicon atoms adjacent to
two coordinating oxygen atoms are similar to
those for the silicon atoms adjacent to only one
coordinating oxygen atom. The average lengths
+
ꢁ
of all the Si C bonds in the [LiD6] ions are
slightly shorter than that in D6 (Table 1). These
differences are consistent with a strong electro-
static interaction between the lithium and
oxygen atoms,[25] and an induced polarization
Figure 1. a) Top view and b) side view of the optimized Cs geometry of the [LiD5]+ ion;
interatomic distances [Š] (bold) and angles [8] (italic) calculated at the HF/6-31G* (B) and
B3LYP/6-31G* (C) levels of theory are indicated. c) Side view of the [LiD5]+ ion in the
of the p2(O)!s*
(Si CH3) interactions, which
ꢁ
preliminary crystal structure of LiD
N
N
ꢁ
leads to a slight weakening of the Si O bonds
filled crossed O, open crossed C, small open H.
ꢁ
and a slight strengthening of the Si C bonds
(Figure 3). The calculated natural bond orbital
(NBO) charges support this picture: upon coordination of D6
to the Li+ ion, the charge on the coordinating oxygen atoms
becomes more negative, the charge on the SiMe2 fragments
bond valence s (in valence units vu),[21] is greater in the salt of
ꢁ
the more basic [AlPhF
]
ion (s = 0.125vu) than in LiD 6[AlF]
A
(s = 0.041 vu), leading to a greater displacement of the Li+ ion
Table 1: Experimental and calculated average distances [Š] and angles [8] for the [LiD5]+ and [LiD6]+ ions, and for the free D5 and D6 molecules.
[a]
[b]
ꢁ
Li O
ꢁ
Si O
ꢁ
Si ONC
ꢁ
Si C
Symmetry
Method
Si-ONC-Si
Si-O-Si
D5
Cs
Cs
HF/6-31G*
B3LYP/6-31G*
ED[d]
1.632
1.654
1.620(2)
1.629(1)
1.638
1.656
1.632
1.656
1.622(1)
1.631
1.874
1.876
1.845(4)
1.845(2)
1.862
1.863
1.874
1.876
1.846(1)
1.865
159.0
152.7
146.5(1)
148.0(1)
159.3
157.5
158.2
153.7
149.6(1)
151.5
[c]
D5d
Cs[c]
Cs
XRD[e]
A
HF/6-31G*
B3LYP/6-31G*
HF/6-31G*
B3LYP/6-31G*
ED[d]
HF/6-31G*
B3LYP/6-31G*
XRD ([AlF]ꢁ)
XRD ([AlPhF]ꢁ)
2.034
2.023
1.664
1.684
159.0
159.2
Cs
C2
C2
D3d
C2
C2
[c]
A
2.042
2.023
2.06(1)
2.078(3)
1.671
1.692
1.661(6)
1.655(1)
143.5
142.9
141.1(4)
141.7(1)
1.651
1.617(7)
1.620(2)
1.867
1.837(1)
1.836(2)
149.3
151.1(5)
146.5(1)
[c]
C2
C2
[c]
ꢁ
[a] The subscript NC denotes noncoordinating O atoms; O atoms without subscripts are coordinated to Li atoms. [b] Average length for all Si C
bonds. [c] Approximate symmetries. [d] The gas-phase structures of D5 and D6 were determined by electron diffraction (ED); the final structures are
not well defined.[24] [e] The single-crystal structure of D5 was determined by X-ray diffraction (XRD): S. Parson, D. Rankin, P. Wood, private
communication to the Cambridge Structural Database, CCDC-247844, The Cambridge Crystallographic Data Centre, 2004.
2774
www.angewandte.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 2773 –2777

Angewandte
Chemie
Table 2: Average atomic and fragment NBO charges (q) for D6 and its
alkali-metal complexes [MD6]+ (M=Li, Na, Rb), calculated at the B3LYP/
6-31G* level of theory.
D6
C2
C
G
G
symmetry
q(M+)
[a]
q
A
)
ꢁ1.275
q
C
1.275
0
C
[a] The subscript NC denotes noncoordinating O atoms; O atoms
without subscripts are coordinated to M atoms. In [NaD6]+ and [KD6]+,
the M atoms are coordinated by all O atoms equally. See Supporting
Information for details. [b] Difference between the average charges
q
(SiMe2) of [MD6]+ and of free D6.
A
coordination of the Li+ ion, the Si6O6 framework of
D6 becomes nearly planar. However, in LiD6-
[AlPhF], stronger Li···F and H···F contacts cause
some deformation (bending) of the Si6O6 plane
(Figure 2b).[26]
The syntheses of the LiD5
N
N
LiD6[AlPhF] salts are the first examples of the
AHCTREUNG
preparation of host–guest complexes directly from
cyclic dimethylsiloxanes, alkali-metal ions, and
weakly coordinating anions. Their structures
imply that the cyclic dimethylsiloxanes (D5 and
D6) act as pseudo crown ethers and provide rare
examples of silicon ethers behaving as Lewis bases.
The counterpoise-corrected binding energies for
Figure 2. a) Side view of the [LiD6]+ ion in LiD6
[AlF]. b) Side view and c) top view of
C
ꢁ
ꢁ
ꢁ
A
ꢁ
ꢁ
ONC, O2Si C, and O
(ONC)Si C; the subscript NC denotes noncoordinating O
atoms; O atoms without subscripts are coordinated to the Li atom) and angles [8]
(Si-O-Si and Si-ONC-Si) are indicated. d) Optimized C2 geometry of D6 at the HF/6-
31G* level of theory. D6 =(Me2SiO)6; [AlF]=Al{OC
A
the alkali-metal complexes [MD6]+ exhibit
remarkable similarity to that for [18]crown-6
a
ACHTREUNG
becomes more positive, and the
charge on lithium becomes slightly
less than 1, which implies a very
(Figure 4):[27] for both sets of complexes (in the gas phase),
the binding energies become less negative with increasing size
of the alkali-metal cation. However, the binding affinity of D6
calculated at the HF/3-21G level is approximately
100 kJmolꢁ1 less than that of [18]crown-6, reflecting the
lower basicity of the siloxanes. Thus, the reaction of D6(l) with
ꢁ
small amount of Li O covalent
bonding (Table 2). Further calcula-
tions on [MD6]+ (M = Na, K) imply
that replacement of the Li+ ion by
the less polarizing Na+ and K+ ions
increases the positive charge on the
metal atom, decreases the positive
charge on the SiMe2 fragments, and
decreases the negative charge on the
coordinating oxygen atoms. In con-
LiI(s) is thermodynamically unfavorable (DE = + 66 kJmolꢁ1
;
Scheme 1).[28] However, replacement of Iꢁ by the larger ion
[AlF]ꢁ reduces the unfavorable change in lattice energy on
Figure 3. Schematic rep-
resentation of the polar-
ꢁ
ization of the O Si
ꢁ
trast, there is little change in the C
bond and the p2(O)!
O bond lengths and C-O-C angles in
[18]crown-6 upon coordination to
alkali-metal cations,[25] consistent
with the absence of p2!s* hyper-
conjugation in the crown ether.
s*(Si-CH3) interaction
A
upon coordination of D6
to Li+ in the [LiD6]+ ion.
The structure of D6 was determined in the gas phase by
ED.[24] This study suggested that the D6 ring is puckered, with
some methyl groups pointing inward (see Figure 2d for the
geometry of D6 calculated at the HF/6-31G* level of theory).
Rotation of the inner methyl groups outward produces a
larger cavity at the center of the ring, which is occupied by Li+
in the [LiD6]+ ion (the calculated geometry of [LiD6]+ is
Figure 4. Binding energies DEB (counterpoise corrected) of D6 and
similar to that of the cation in LiD
A
[18]crown-6 with alkali-metal cations.
Angew. Chem. Int. Ed. 2006, 45, 2773 –2777
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
2775

Communications
ortho-C6H5), 128.688(s, meta-C6H5), 129.206 (s, para-C6H5),
136.069 ppm (s, ipso-C6H5); 1H NMR (400.0 MHz, SO2, RT): d =
0.288 (s, 36H, SiMe2), 7.898 (m, 8H, meta-C6H5), 7.330 (m, 4H,
para-C6H5), 7.233 ppm (m, 8H, ortho-C6H5); 19F NMR (376.3 MHz,
SO2, RT): d = ꢁ74.119 ppm (s, [AlPhF]); 27Al NMR (104.2 MHz, SO2,
RT): d = 29.552 ppm (s, [AlPhF]); 7Li NMR (155.4 MHz, SO2, RT): d =
0.180 ppm (s). FT-IR (KBr, neat, RT, n˜ assigned to [LiD6]+ marked
with *): n˜ = 3666 (w), 3576 (w), 3062 (vw), 2963 (w),* 2899 (vw),* 1622
(m), 1502 (w), 1485(w), 1446 (m),* 1412 (w),* 1331 (m), 1305(s), 1266
going from LiX to LiD6X (DUL
C
(LiD6X) =
and the energy of formation of LiD
A
ACHTREUNG
D6(l) is DE = ꢁ242 kJmolꢁ1 (Scheme 1). Thus, a new class of
salts with cyclosiloxane–metal cations and weakly coordinat-
ing anions can be anticipated.
(vs),* 1223 (s), 1193 (vs), 1198 (vs), 1133 (s), 1078 (s; #as
1026 (s), 1001 (s; #as(SiOSi)),* 996 (vs), 966 (vs), 932 (s), 915(m), 855
(s),* 821 (s),* 795(s; #a(SiC2)),* 761 (m), 743 (m), 713 (vs), 688 (m),*
658 (m; #s(SiOSi)),* 619 (w), 559 (w), 538 (w), 495 (w), 435 (m),
G
Experimental Section
AHCTREUNG
LiD5[AlF]: CH2Cl2 (50 mL) was added to D5 (0.45mL, 1.16 mmol)
E
AHCTREUNG
over solid Li[AlF] (0.985g, 1.01 mmol) in a 100-mL Schlenk flask. The
A
AHCTREUNG
resulting colorless, clear solution was concentrated to saturation by
stirring overnight at room temperature. Large crystals were obtained
after 1 day at ꢁ208C. The solvent was removed under vacuum, and
the crystallized product was washed three times with n-hexane. Yield:
1.25g (90%, based on Li
[AlF]). 29Si{1H} NMR (79.4 MHz, SO2, RT):
R
901 (100) [M+ꢁD6ꢁCF3ꢁ2F], 429 (40) [M+ꢁLi
C
d = ꢁ21.28 ppm (m, D5); 13C{1H} NMR (100.6 MHz, SO2, RT): d =
+
0.893 ppm (s, D5); 1H NMR (400.0 MHz, SO2, RT): d = 0.125ppm (s,
39.70, H 3.84. M.p.: 1328C (decomp).
D5); 19F NMR (376.3 MHz, SO2, RT): d = ꢁ74.113 ppm (s, Li
ACHTREUNG
The following are given in the Supporting Information: general
experimental techniques; a description of the reaction designed to
27Al NMR (104.2 MHz, SO2, RT): d = 35.107 ppm (s, Li
ACHTREUNG
7Li NMR (155.4 MHz, SO2, RT): d = ꢁ0.288 ppm (s, Li
ACHTREUNG
produce Se6Ph2
a comparison of the FT-IR, FT-Raman, and NMR spectra of
LiD5[AlF], LiD6[AlF], and LiD6[AlPhF] with those of the reactants;
different views of the crystal structures of LiD5[AlF], LiD6[AlF], and
LiD6[AlPhF]; and details of the calculations.
A
G
(KBr, solid, RT, n˜ assigned to [LiD5]+ marked with *, e.g. 2972 (w),*):
n˜ = 2972 (w),* 2907 (w),* 1626 (w), 1356 (s),* 1301 (s), 1275 (s),* 1236
A
N
ACHTREUNG
(s), 1215(vs), 1163 (m), 1026 (s; #as
ACHTREUNG
A
ACHTREUNG
(s),* 808 (s),* 752 (m; #a(SiC2)),* 726 (s; #s
G
ACHTREUNG
AHCTREUNG
#
s(SiOSi)),* 572 (w), 568 (m), 555 (m), 534 (m), 439 (m), 401 cmꢁ1
U
(m). FT-Raman (RT, n˜ assigned to [LiD5]+ marked with *): n˜ = 2975
Received: November 30, 2005
Published online: March 20, 2006
(m; #a(CH)),* 2914 (s; #s(CH)),* 1494 (w), 1402 (w), 1276 (w), 797
ꢁ1
(w),* 745(w),* 536 (m), 321 (w), 164 cm
(w). EI-MS (30 eV): m/z
522 (33)
[AlF]ꢁMe =
(%):
539
(20)
[M+ꢁD5ꢁOC
(CF3)3ꢁC2F8O],
G
Keywords: crown compounds · host–guest systems · lithium ·
[M+ꢁD5ꢁC
A
ACHTREUNG
.
+
siloxanes · weakly coordinating anions
D5 ꢁMe]. Elemental analysis (%) calcd: C 23.24, H 2.25; found: C
23.37, H 2.47. M.p.: 2168C (decomp).
LiD
A
N
LiD5[AlF] (Li
A
ACHTREUNG
CH2Cl2 50 mL). Yield: 1.12 g (95%, based on Li
A
[1] N. N. Greenwood, A. Earnshaw, Chemistry of the Elements,
2nd ed. Butterworth-Heinemann, Oxford, 1997, p. 328.
[2] A. Sekiguchi, R. Kinjo, M. Ichinohe, Science 2004, 305, 1755.
[3] M. Ichinohe, M. Igarashi, K. Sanuki, A. Sekiguchi, J. Am. Chem.
Soc. 2005, 127, 9978.
[4] C. Kim, C. A. Reed, D. W. Elliott, L. J. Mueller, F. Tham, L. Lin,
J. B. Lambert, Science 2002, 297, 5582, and references therein.
[5] J. Fischer, J. Baumgartner, C. Marschner, Science 2005, 310, 825.
[6] There is no definite evidence for the existence of neutral BF3
adducts of silicon ethers: H. J. EmelØus, M. Onyszchuk, J. Chem.
Soc. 1958, 604. A protonated silanol that is stable at room
(79.4 MHz, SO2, RT): d = ꢁ9.22 ppm (s, SiMe2); 13C{1H} NMR
(100.6 MHz, SO2, RT): d = 120.011 (q, J
(C,F) = 291 Hz, 3C, CF3),
79.219 (s, 1C, OCCF3), 0.202 ppm (s, 3C, SiMe2); 1H NMR
(400.0 MHz, SO2, RT): d = 0.296 ppm (s, SiMe2); 19F NMR
(376.3 MHz, SO2, RT): d = ꢁ75.193 ppm (s, [AlF]); 27Al NMR
(104.2 MHz, SO2, RT): d = 34.998 ppm (s, [AlF]); 7Li NMR
(155.4 MHz, SO2, RT): d = 0.190 ppm (s). IR (KBr, neat, RT, n˜
assigned to [LiD6]+ marked with *): n˜ = 2965(m),* 2916 (w),* 1537
(w), 1494 (w),* 1408 (m),* 1377 (w),* 1352 (s), 1300 (s), 1276 (s),*
1241 (s), 1216 (s), 1167 (s), 1132 (m), 1087 (s; #as
968 (s), 853 (s),* 822 (s),* 794 (s; #a(SiC2)),* 752 (m; #a
(s; #s(SiC2)),* 665(w; #s(SiOSi)),* 619 (m; #s(SiOSi)),* 560 (m), 532
ACHTREUNG
A
N
temperature occurs in the salt tBu3Si(OH2)[Br6CB11H6], which
E
A
N
R
has been isolated and crystallographically characterized: Z. Xie,
R. Bau, C. A. Reed, J. Chem. Soc. Chem. Commun. 1994, 2519.
For siloxonium ions unstable above ꢁ308C, see: a) G. A. Olah,
H. Doggweiler, J. D. Felberg, S. Frohlich, J. Org. Chem. 1985, 50,
4847; b) M. Kira, T. Hino, H. Sakurai, J. Am. Chem. Soc. 1992,
114, 6697; c) G. A. Olah, X. Li, Q. Wang, G. Rasul, G. K. S.
Prakash, J. Am. Chem. Soc. 1995, 117, 8962.
(m), 441 (m), 396 cmꢁ1 (s). Raman (RT, n˜ assigned to [LiD6]+ marked
with *): n˜ = 2975(s; #a(CH)),* 2915(vs; #s(ꢁC1H)),* 1495(w), 797 (w),*
745(w),* 452 (m), 320 (w), 168 cm
(w). EI-MS (30 eV):
m/z (%): 539 (15) [M+ꢁD6ꢁOC
ACHTREUNG
[M+ꢁD6ꢁC
R
U
+
D6 ꢁMe]. Elemental analysis (%) calcd: C 23.72, H 2.56; found C
23.77, H 2.60. M.p. 2868C (decomp).
[7] a) M. J. Hunter, J. F. Hyde, E. L. Warrick, H. J. Fletchers, J. Am.
Chem. Soc. 1946, 68, 667; b) W. Patnode, D. F. Wilcock, J. Am.
Chem. Soc. 1946, 68, 358; c) J. F. Hyde, R. C. Delong, J. Am.
Chem. Soc. 1941, 63, 1194; d) T. Alvik, J. Dale, Acta. Chem.
Scand. 1971, 25, 2131, and references therein.
[8] C. J. Pedersen, J. Am. Chem. Soc. 1967, 89, 7017.
[9] O. Mikio, I. Yoshihisa, K. Takashi, H. Tadao, Bull. Chem. Soc.
Jpn. 1984, 57, 887.
[10] a) R. West, L. Whatley, K. Lake, J. Am. Chem. Soc. 1961, 83, 761;
b) B. D. Shepherd, J. Am. Chem. Soc. 1991, 113, 5581, and
references therein. The lower basicity of siloxanes is also
reflected in their higher ionization energy Ei compared to
LiD6
ACHTREUNG
0.97 mmol) over solid Li
AHCTREUNG
Schlenk flask. The resulting yellowish, clear solution was stirred
overnight at room temperature. n-Hexane (40 mL) was added to the
solution, and a large amount of crystals was obtained after 1 day at
ꢁ208C. The crystals were separated by filtration, and the filtrate was
further concentrated to one third, producing more crystals, which
were washed with n-hexane. Total yield: 1.17 g (85%, based on
Li
SiMe2); 13C{1H} NMR (100.6 MHz, SO2, RT): d = 0.454 (s, SiMe2),
80.085(s, O C(CF3)2Ph), 125.763 (q, J(C,F) = 291 Hz, CF3), 128.186 (s,
[AlPhF]). 29Si{1H} NMR (79.4 MHz, SO2, RT): d = ꢁ10.14 ppm (s,
E
ACHTREUNG
2776
www.angewandte.org
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
Angew. Chem. Int. Ed. 2006, 45, 2773 –2777

Angewandte
Chemie
carbon analogues; for example, the Ei for (Me3Si)2O (9.64 eV) is
R1
N
G
0.83 eV higher than that for (Me3C)2O (8.81 eV).
291339 (LiD
ACHTREUNG
ꢁ
data for this paper. These data can be obtained free of charge
from The Cambridge Crystallographic Data Centre via
www.ccdc.cam.ac.uk/data_request/cif.
[11] The nature of the Si O bonding in siloxanes has been attributed
to strong Sid+···Odꢁ electrostatic interactions, dp–pp bonding, or
p2!s* negative hyperconjugation, and is still under debate:
a) R. J. Gillespie, E. A. Robinson, Chem. Soc. Rev. 2005, 34, 396;
b) H. Oberhammer, J. E. Boggs, J. Am. Chem. Soc. 1980, 102,
7241; c) S. Shambayati, J. F. Blake, S. G. Wierschke, W. L.
Jorgensen, S. L. Schreiber, J. Am. Chem. Soc. 1990, 112, 697;
d) Y. Mo, Y. Zhang, J. Gao, J. Am. Chem. Soc. 1999, 121, 5737,
and references therein.
[21] The bond valences s (in valence units vu) are defined as s =
exp
A
ꢁ
covalent bond length of the bond (bond order= 1; for Li F, Ro =
1.36 Š; for Li O, Ro = 1.466 Š), and B is an empirical parameter
set to 0.37. a) I. D. Brown in Structure and Bonding in Crystals,
Vol. 2 (Eds.: M. OꢀKeefe, A. Navrotsky), Academic Press,
London, 1981; b) I. D. Brown, The Chemical Bond in Inorganic
Chemistry (The Bond Valence Model), Oxford University Press,
Oxford, 2002.
=
[12]
A
[InH
(CH2tBu)3]4 and (KD7)[K{C
(SiMe3)2
N
N
K
A
ACHTREUNG
[22] a) F. Gingl, W. Hiller, J. Strahle, H. Borgholte, K. Dehnicke, Z.
Anorg. Allg. Chem. 1991, 606, 91; b) R. E. A. Dillon, C. L. Stern,
D. F. Shriver, Chem. Mater. 2000, 12, 1122.
[23] a) W. C. Marsh, N. L. Paddock, C. J. Stewart, J. Trotter, J. Chem.
Soc. D 1970, 1190; b) W. C. Marsh, J. Trotter, J. Chem. Soc. A
1971, 1482; c) W. Harrison, J. Trotter, J. Chem. Soc. Dalton. 1973,
61.
=
[SiMe2(CH CH2)] with methylpotassium, respec-
A
G
A
tively, both in the presence of silicone grease: a) M. R. Churchill,
C. H. Lake, S. H. Chao, J. O. T. Beachley, J. Chem. Soc. Chem.
Commun. 1993, 1577; b) C. Eaborn, P. B. Hitchcock, K. Izod,
J. D. Smith, Angew. Chem. 1995, 107, 2936; Angew. Chem. Int.
Ed. Engl. 1995, 34, 2679.
[13] Silicone grease consists principally of polydimethylsiloxane
[24] H. Oberhammer, W. Zeil, J. Mol. Struct. 1973, 18, 309.
[25] NBO and natural energy decomposition analysis of alkali-metal
complexes of [18]crown-6 indicated that electrostatic interac-
tions and polarization are the dominant bonding forces between
the host and guest; the contribution of charge transfer is much
less important: E. D. Glending, D. Feller, M. A. Thompson, J.
Am. Chem. Soc. 1994, 116, 10657.
(>80%), dimethylcyclosiloxane (< 1%, ring size unknown),
[14] Single-crystal XRD and FT-IR spectroscopic analysis of the
product showed it to be a new polymorph of the starting material
Li[AlPhF]. See Supporting Information for details.
C
[26] The angle between the O1-O2-O6 and O3-O4-O5planes in
[15] a) S. H. Strauss, Chem. Rev. 1993, 93, 927; b) C. Reed, Acc.
Chem. Res. 1998, 31, 133; c) I. Krossing, I. Raabe, Angew. Chem.
2004, 116, 2116; Angew. Chem. Int. Ed. 2004, 43, 2066; d) T. S.
Cameron, A. Decken, I. Dionne, M. Fang, I. Krossing, J.
Passmore, Chem. Eur. J. 2002, 8, 3386; e) T. S. Cameron, J.
Passmore, X. Wang, Angew. Chem. 2004, 116, 2029; Angew.
Chem. Int. Ed. 2004, 43, 1995.
[16] The associative–dissociative process of metal cation/crown ether
complexes in solution has been well determined: M. K. Amini,
M. Shamsipur, J. Phys. Chem. 1991, 95, 9601, and references
therein.
LiD
ACHTREUNG
and H···F contacts in LiD6
AHCTREUNG
we calculated the optimized geometry for the hypothetical
complex LiD6F. The initial geometry of LiD6F contained a
planar [LiD6]+ ion, with a Fꢁ ion bonded to the lithium atom.
Optimization led to a bent geometry, confirming that the
geometry of the [LiD6]+ ion in LiD6
[AlPhF] is remarkably
G
affected by strong Li···F and H···F contacts. See Supporting
Information for details.
[27] The binding affinity for [18]crown-6 with the alkali-metal cations
Li+, Na+, K+, and Rb+ was taken from ref. [25].
[17] For details of reaction-energy calculations, see Supporting
Information. Gaussian 03, Revision C.02, J. A. Pople, et al.
Gaussian, Inc., Wallingford CT, PA, 2004.
[28] For the vaporization energy DEvap, see: D. F. Wilcock, J. Am.
Chem. Soc. 1946, 68, 691. The lattice energies UL for LiX and
LiD6X (X = [AlF], I) were estimated using Jenkins and Pass-
[18] LiD5[AlF] crystallizes in the monoclinic space group P21/c, with
U
moreꢀs
volume-based
relationship
UL = 2I
[(a/V1/3) + b]
C
a = 10.9596(9), b = 28.564(2), c = 17.028(1) Š, b = 97.324(2)o,
V= 5302(2) Š3, and Z = 4. The structure was not completely
determined, because of disorder in the anion.
,
V [nm3] is the volume of the corresponding salt, and I is the
sum of the ionic strength: H. D. B. Jenkins, H. K. Roobottom, J.
Passmore, L. Glasser, Inorg. Chem. 1999, 38, 3609.
[19] Structure determination of LiD6[AlF]: Bruker AXS P4/SMART
R
1000 diffractometer, graphite-monochromatized MoKa radiation
¯
(l = 0.71073 Š), T= 173(1) K, P1, Z = 4, a = 11.0053(19), b =
22.828(4), c = 24.398(5) Š, a = 101.660(4), b = 102.974(3), g =
103.558(3)8, V= 5592.7(18) Š3, 1calcd = 1.664 mgmꢁ3
,
2qmax
50.08, 26311 reflections collected, 17449 independent reflec-
tions, 1485parameters, R1(I>2s) = 0.1049, R1(all data) =
0.1422. There are two symmetry-independent [LiD6]+ ions in
LiD6[AlF], one of which is shown in Figure 2a. The main
=
A
ACHTREUNG
ACHTREUNG
difference between the two cations is the differing strength of
their Li···F contacts (3.02(2) and 3.19(2) Š for the [LiD6]+ ion
not shown in Figure 2a). The structure of LiD
determined, owing to severe rotational disorder in the anion,
which prevents precise comparison with that of LiD6[AlPhF].
[20] Structure determination of LiD6[AlPhF]: Bruker AXS P4/
6[AlF] was not well
AHCTREUNG
AHCTREUNG
SMART 1000 diffractometer, graphite-monochromatized MoKa
¯
radiation (l = 0.71073 Š), T= 173(1) K, P1, Z = 2, a =
11.9673(9), b = 15.9362(12), c = 17.7554(12) Š, a = 88.198(2),
b = 87.127(2),
1.498 mgmꢁ3, 2qmax = 55.08, 22472 reflections collected, 14017
independent reflections, 823 parameters, R1(I>2s) = 0.0416,
g = 72.045(1)o,
V= 3216.8(4) Š3,
1calcd =
AHCTREUNG
Angew. Chem. Int. Ed. 2006, 45, 2773 –2777
ꢀ 2006 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.angewandte.org
2777