Preparation, structural characterization, and photochemical reactions of silyl- and germylborates

Article abstract of DOI:10.1021/om050733y

Silylborates (Li[Ph_nMe_3-nSiBPh₃], n = 1-3) and germylborates (Li[Ph_nMe_3-nGeBPh₃], n = 1-3; M[Et_3- GeBPh₃], M = Li, Na, K) were prepared by the reaction of the corresponding silyl- and germylalkali metals with triphenylborane in a hexane/benzene mixed solvent. The silyl- and germylborates were fully identified by ¹H, ¹³C, ¹¹B, and ⁷Li NMR spectroscopic methods. The solid-state structure of germylborates Li[Ph₃GeBPh₃] and M[Et₃GeBPh ₃] (M = Li and Na) were determined by X-ray diffraction analyses. The polymeric structure of M[Et₃GeBPh₃] was observed in the solid state and in hydrocarbon solution. The alkali metal atoms were located near the center of the benzene ring of triphenylborane and interacted with the neighboring borate molecules by Li⁺-π interaction. The polymeric structure was broken by the addition of MeOH. However, M[Et ₃GeBPh₃] was coordinated by three MeOH molecules to form a dimeric structure without methanolysis reaction. The primary processes in photochemical reactions of silyl- and germylborates were investigated by chemical trapping experiments and the CIDEP (chemical-induced dynamic electron polarization) method. The cleavage of the Ge-B (or Si-B) bonds of germylborates (or silylborates) was considered most probably to occur from their triplet states.

Full text of DOI:10.1021/om050733y

832
Organometallics 2006, 25, 832-838
Preparation, Structural Characterization, and Photochemical
Reactions of Silyl- and Germylborates
Masato Nanjo,† Kazuhiko Matsudo,† Mari Kurihara,† Sayaka Nakamura,†
Yoshio Sakaguchi,‡ Hisaharu Hayashi,†,‡ and Kunio Mochida*,†
Department of Chemistry, Faculty of Science, Gakushuin UniVersity, 1-5-1 Mejiro, Toshima-ku, Tokyo
171-8588, Japan, and The Institute of Physical and Chemical Research, Wako, Saitama 351-0198, Japan
ReceiVed August 25, 2005
Silylborates (Li[PhnMe3-nSiBPh3], n ) 1-3) and germylborates (Li[PhnMe3-nGeBPh3], n ) 1-3; M[Et3-
GeBPh3], M ) Li, Na, K) were prepared by the reaction of the corresponding silyl- and germylalkali
metals with triphenylborane in a hexane/benzene mixed solvent. The silyl- and germylborates were fully
identified by 1H, 13C, 11B, and 7Li NMR spectroscopic methods. The solid-state structure of germylborates
Li[Ph3GeBPh3] and M[Et3GeBPh3] (M ) Li and Na) were determined by X-ray diffraction analyses.
The polymeric structure of M[Et3GeBPh3] was observed in the solid state and in hydrocarbon solution.
The alkali metal atoms were located near the center of the benzene ring of triphenylborane and interacted
with the neighboring borate molecules by Li+-π interaction. The polymeric structure was broken by the
addition of MeOH. However, M[Et3GeBPh3] was coordinated by three MeOH molecules to form a dimeric
structure without methanolysis reaction. The primary processes in photochemical reactions of silyl- and
germylborates were investigated by chemical trapping experiments and the CIDEP (chemical-induced
dynamic electron polarization) method. The cleavage of the Ge-B (or Si-B) bonds of germylborates
(or silylborates) was considered most probably to occur from their triplet states.
Introduction
Results and Discussion
Tetraorganoborate salts have attracted considerable interest
in organic chemistry and organic synthesis.1 While the tetraor-
ganoborate salts have been well studied, far less attention has
been devoted to tetracoordinated borates containing group 14
elements (silicon or germanium)-boron bonds. Seyferth et al.
pioneered the preparation of aryl-substituted silylborate (Li[Ph3-
SiBPh3]) and germylborate (Li[Ph3GeBPh3]) in 1961,2 and later,
alkyl-substituted silylborates (Li[Me3SiBMe3]) were introduced
by No¨th in 1980.3,4 Recently, crystal structures of tetraalkylsi-
lylborate (Li[Me3Si]4B) and trialkyl-substituted silylborate (Li-
[(Me3Si)3BMe]) have been determined.5 However, few reports
on the solid-state structure of germylborates or any reactivitity
studies of silyl- or germylborates have appeared.6,7 Very
recently, trihydro(triphenylgermyl)borate (Li[Ph3GeBH3]) and
trihydro(triphenylstannyl)borate (Li[Ph3SnBH3]) have been syn-
thesized and characterized by Habereder and No¨th.8,9 In this
paper, we describe the preparation and characterization of silyl-
and germylborates. The primary photochemical process of silyl-
and germylborates probed by chemical experiments and CIDEP
techniques is discussed.
Preparation and Characterization of Silyl- and Germyl-
borates. Phenyl-substituted silyllithiums (PhnMe3-nSiLi, n )
1-3) were prepared by reactions of the corresponding disilanes
with lithium metal in tetrahydrofuran (THF) under an argon
atmosphere.1010 Treatment of the resulting PhnMe3-nSiLi (n )
1-3) with 1 equiv of triphenylborane (Ph3B) in benzene/hexane
mixed solvent under argon produced the corresponding phenyl-
substituted silylborates ([Li(PhnMe3-nSiBPh3)], 1-3, n ) 1-3,
respectively) as pale yellow crystals in 60-90% yields (E )
Si, eq 1).
PhnMe3-nELi + Ph3B f
Li[PhnMe3-nEBPh3]
(1)
E ) Si, 1-3 (n ) 1-3); Ge, 4-6 (n ) 1-3)
The phenyl-substituted silylborates 1-3 were recrystallized
from THF at room temperature to give colorless crystals in 48%
(1), 72% (2), and 85% (3) isolated yield. The silylborates 1-3
were fully characterized by 1H, 13C, 11B, and 7Li NMR spectra.
The 1H NMR spectroscopic examination of a CD3CN solution
of the white solid 1 displayed the methyl signal of the
dimethylphenylsilyl group (Me2PhSi) at 0.09 ppm, signals of
three coordinated THF molecules at 1.83-1.94 ppm and 3.66-
3.80 ppm, and the phenyl groups of Me2PhSi and Ph3B at 6.91-
7.35 ppm. The 11B NMR signal of 1 in CD3CN was significantly
shifted upfield at δ ) -11.4 ppm, due to the anionic nature of
the boron atom compared with that of a neutral species. The
11B NMR spectra of C6D6 solutions of borates such as lithium
tetrahydroborate (LiBH4), lithium isopropyltrihydroborate (Lii-
PrBH3), and lithium tetraisopropylborate (LiiPr4B), [Li(Me3-
GeBH3)], and [Li(Ph3GeBH3)] have been observed to be in the
* To whom correspondence should be addressed. E-mail:
kunio.mochida@gakushuin.ac.jp. Fax: +81-3-5992-1029.
† Gakushuin University.
‡ The Institute of Physical and Chemical Research, Wako.
(1) Wakefield, B. J. In ComprehensiVe Organic Chemistry; Barton, D.,
Ollis, W. D., Jones, W. D. Eds.; Pergamon Press: Oxford, U.K., 1979;
Vol. 3, p 883.
(2) Seyferth, D.; Raab, G.; Grim, S. O. J. Org. Chem. 1961, 26, 3034.
(3) Biffar, H.; No¨th, H. Angew. Chem. 1980, 92, 65.
(4) Biffar, H.; No¨th, H. Chem. Ber. 1982, 115, 934.
(5) Lippert, W.; No¨th, H.; Ponikwar, W.; Seifert, T. Eur. J. Inorg. Chem.
1999, 817.
(6) Bulten, E. J.; Noltes, J. G. J. Organomet. Chem. 1971, 29, 409.
(7) Nanjo, M.; Matsudo, K.; Mochida, K. Chem. Lett. 2001, 1086.
(8) Habereder, T.; No¨th, H. Z. Anorg. Allg. Chem. 2001, 627, 1003.
(9) Habereder, T.; No¨th, H. Z. Anorg. Allg. Chem. 2001, 627, 789.
(10) Gilman, H.; Lichtenwalter, G. D. J. Am. Chem. Soc. 1958, 80, 608.
10.1021/om050733y CCC: $33.50 © 2006 American Chemical Society
Publication on Web 01/13/2006

Silyl- and Germylborates
Organometallics, Vol. 25, No. 4, 2006 833
range -43.1 to -15.4 ppm.8,11,12 On the other hand, the 11B
NMR signals of neutral compounds such as Ph3B in CD3CN
i
and Pr3B in C6D6 are seen at 45 and 85 ppm, respectively.12
7
The Li NMR signal of a CD3CN solution of 1 was shifted a
little upfield at -1.30 ppm. The 7Li NMR resonance of
triphenylsilyllithium (Ph3SiLi) coordinated by THF is observed
at -0.1 ppm.13 The 11B and 7Li NMR spectra of CD3CN
solutions of 2 and 3 displayed trends (δ ) -11.0 and -1.30
ppm for 2, and δ ) -11.4 and -1.30 ppm for 3) similar to the
silylborate 1. The NMR spectra of silylborates 2 and 3 showed
the presence of three coordinated THF molecules. The solid
silylborates 1-3 are stable at 100 °C for 2 days in the absence
of air. In contact with air, the silylborates 1-3 decomposed
gradually to pale yellow pasty crystals. The silylborates 1-3
are soluble in methanol or CH3CN and are insoluble at room
temperature in hydrocarbon or aromatic solvents. At higher
temperatures (>80 °C), the solubility of silylborates 1-3
increased. Solutions of the silylborates 1-3 in MeOH or CH3-
CN are very stable when heated at reflux for 1 day. However,
the silylborates 1-3 reacted with acetic acid at room temperature
for 6 h to give the corresponding organosilicone hydrides in
quantitative yield.
The reactions of phenyl-substituted germyllithiums (PhnMe3-n
-
GeLi, n ) 1-3), which were prepared by treatment of the
corresponding chlorogermanes with lithium metal in THF,14,15
with 1 equiv of Ph3B in a benzene/hexane mixed solvent under
argon gave the corresponding phenyl-substituted germylborates
([Li(PhnMe3-nGeBPh3)], 4-6, n ) 1-3, respectively) as pale
yellow crystals in 30-85% yield (E ) Ge, eq 1).
Figure 1. Molecular structure of 5 at the 50% probability level.
Hydrogen atoms are omitted for clarity.
Table 1. Selected Atomic Distances (Å) and Bond Angles
(deg) of 5
Ge(1)-C(1)
Ge(1)-C(2)
Ge(1)-C(8)
Ge(1)-B(1)
B(1)-C(14)
B(1)-C(20)
B(1)-C(26)
1.984(6)
1.992(5)
1.968(6)
2.138(6)
1.627(8)
1.646(8)
1.628(7)
Li(1)-O(1)
Li(1)-O(2)
Li(1)-O(3)
Li(1)-O(4)
Li(1)-O(5)
Li(1)-O(6)
2.098(12)
2.069(12)
2.210(14)
2.083(11)
2.100(12)
2.412(15)
The phenyl-substituted germylborates 4-6 were isolated as
colorless crystals by recrystallization from THF at room
temperature in 15% (4), 42% (5), and 78% (6) isolated yield.
1
The germylborates 4-6 were identified by H, 13C, 11B, and
7Li NMR spectra. The solid-state structure of 5 was determined
by X-ray diffraction analysis. The 1H NMR spectrum of a CD3-
CN solution of white solid 5 displayed the methyl signal of
MePh2Ge at 0.29 ppm, signals of three THF molecules at 1.75-
1.90 ppm and 3.60-3.73 ppm, and the phenyl groups of MePh2-
C(1)-Ge(1)-C(2)
C(1)-Ge(1)-C(8)
C(2)-Ge(1)-C(8)
C(1)-Ge(1)-B(1)
C(2)-Ge(1)-B(1)
C(8)-Ge(1)-B(1)
Ge(1)-B(1)-C(14)
Ge(1)-B(1)-C(20)
103.6(2)
Ge(1)-B(1)-C(26)
C(14)-B(1)-C(20)
C(14)-B(1)-C(26)
C(20)-B(1)-C(26)
O(1)-Li(1)-O(2)
O(3)-Li(1)-O(4)
O(5)-Li(1)-O(6)
102.9(3)
109.7(4)
111.4(4)
115.9(4)
77.7(4)
77.3(4)
74.0(4)
101.6(2)
103.2(2)
117.0(3)
114.1(2)
115.5(2)
109.3(3)
107.2(3)
Ge and Ph3B at 6.88-7.23 ppm. As in the case of Li[PhnMe3-n
-
SiBPh3],8,11,12 the 11B NMR signal of 5 in CD3CN was shifted
significantly upfield δ ) -7.2 ppm due to the anionic nature
7
of the boron atom. The Li NMR signal of a CD3CN solution
compared with that of the neutral germylene-borane adduct, Ge-
[C6H3(NMe2)2-2,6]2BH3 (2.041 Å).16 This suggests that the
Ge-B bond is essentially covalent with a small ionic contribu-
tion. The closest distance between the lithium cation and the
phenyl carbon atom of Ph3B in 5 is over 6 Å, well beyond any
significant interaction. The solvent-separated lithium cation is
complexed with three DME molecules with Li-O bond lengths
of 2.069(12)-2.412(15) Å and Li-O-Li bond angles of 74.0-
(5)-78.4(4)°. The lithium atom shows an octahedral conforma-
tion. The solid germylborates 4-6 are very stable (100 °C, 2
days) in the absence of air, but gradually decomposed to pale
yellow pasty crystals in air. They are soluble in polar solvents
(MeOH and CH3CN) and insoluble in nonpolar solvents. The
solubility of the germylborates in nonpolar solvents increased
with increasing temperatures (80 °C). They reacted with MeOH
at 50 °C over 6 h to give the corresponding organogermanium
hydrides. The formation of Li[Ph3SiBPh3] and Li[Ph3GeBPh3]
was first reported by Seyferth et al.,2 but their crystal structures
were not determined.
of 5 was shifted somewhat upfield to -1.4 ppm. For compari-
7
son, the Li NMR resonances of PhMe2GeLi coordinated by
THF and Ph3GeLi coordinated by diethyl ether in C6D6 were
observed at 0.83 and 1.46 ppm, respectively.8 The 11B and 7Li
NMR spectra of CD3CN solutions of 4 and 6 displayed trends
(-8.3 and -1.5 ppm for 4, and -7.2 and -1.01 ppm for 6)
similar to the germylborate 5. The 1H NMR spectra of
germylborates 4 and 6 also showed them to be coordinated by
THF molecules.
The molecular structure of 5, recrystallized from dimethoxy-
ethane (DME), was analyzed by X-ray diffraction as shown in
Figure 1. Selected bond lengths and bond angles for 5 are
summarized in Table 1. The crystallographic data are sum-
marized in the Experimental Section.
The Ge-C bond lengths of 1.968(6)-1.992(5) Å are normal.
The Ge-B bond length of 2.138(6) Å is slightly longer
(11) Biffar, W.; No¨th, H.; Pommerening, H.; Schwerthoffer, R.; Storch,
W.; Wrackmeyer, B. Chem. Ber. 1981, 114, 49.
(12) Biffar, W.; No¨th, H.; Sedlak, D. Organometallics 1983, 2, 579.
(13) Dias, H. V. R.; Olmstaed, M. M.; Ruhlandt-Senge, K.; Power, P.
P. J. Organomet. Chem. 1993, 462, 1.
Unsolvated triethylgermyl-alkali metal compounds (Et3GeM,
M ) Li, Na) were prepared by the metal exchange reaction of
(14) Gilman, H.; Gerow, C. W. J. Am. Chem. Soc. 1956, 78, 5435.
(15) Tamborski, C.; Ford, F. E.; Lehn, W. L.; Moore, G. J.; Soloski, E.
J. J. Org. Chem. 1962, 27, 619.
(16) Drost, C.; Hitchcock, P. B.; Lappert, M. F. Organometallics 1998,
17, 3838.

834 Organometallics, Vol. 25, No. 4, 2006
Nanjo et al.
Table 2. Selected Atomic Distances (Å) and Bond Angles
(deg) of 7
Ge(1)-C(1)
Ge(1)-C(3)
Ge(1)-C(5)
Ge(1)-B(1)
B(1)-C(7)
B(1)-C(13)
B(1)-C(19)
Li(1)-C(7)
Li(1)-C(8)
1.987(4)
1.994(3)
1.984(3)
2.145(4)
1.642(4)
1.642(4)
1.630(4)
2.679(6)
2.519(6)
Li(1)-C(9)
2.405(7)
2.390(7)
2.468(7)
2.590(6)
2.565(6)
2.737(7)
2.482(6)
2.689(6)
Li(1)-C(10)
Li(1)-C(11)
Li(1)-C(12)*
Li(1)-C(13)*
Li(1)-C(14)*
Li(1)-C(19)*
Li(1)-C(24)*
C(1)-Ge(1)-C(3)
C(1)-Ge(1)-C(5)
C(3)-Ge(1)-C(5)
C(1)-Ge(1)-B(1)
C(3)-Ge(1)-B(1)
C(5)-Ge(1)-B(1)
103.8(1)
100.5(1)
103.8(1)
113.6(1)
121.1(1)
111.6(1)
Ge(1)-B(1)-C(7)
Ge(1)-B(1)-C(13)
Ge(1)-B(1)-C(19)
C(7)-B(1)-C(13)
C(7)-B(1)-C(19)
C(13)-B(1)-C(19)
98.4(2)
111.6(2)
113.9(2)
112.5(2)
111.4(2)
108.8(2)
the Ge-B bond is covalent with a small ionic contribution. The
boron atom in germylborate 7 shows a tetrahedral configuration.
The Ge(1)-B(1)-C bond angles of 98.4(2)°, 113.9(2)°, and
111.6(2)° are contracted. The structure of germylborate 7 in
the solid state is a zigzag polymeric structure. Lithium cations
are linked to germylborates by the Li+-π interaction, which
leads to a linear one-dimensional coordination polymer. Each
lithium cation is surrounded by three phenyl groups of BPh3
and is placed above one side of the three horizontal phenyl
planes of BPh3. The coordination distances between the lithium
cation and the three phenyl ring planes in 7 are 2.072(5) Å
(intramolecular) and 2.452(6) and 2.532(6) Å (intermolecular).
The lithium atom is not located directly over the center of the
benzene rings, but is in rather close contact with the para and
meta carbon atoms of the benzene rings. These Li-C distances
(Li-C(10) 2.390(7), Li(1)-C(9) 2.405(7), Li-C(11) 2.468(7),
Li-C(8) 2.519(6), Li(1)-C(12) 2.590(6), and Li(1)-C(7)
2.679(6) Å) are typical for π-complexed organolithiums.18 Such
interactions apparently are caused by electrostatic attraction
Figure 2. Molecular structure of 7 at the 50% probability level.
Hydrogen atoms are omitted for clarity.
(Et3Ge)2Hg with alkali metals in benzene using a modified
method reported by Vyazankin et al.17 Treatment of unsolvated
Et3GeM with 1 equiv of Ph3B in benzene/hexane mixed solvent
produced alkali metal (triethylgermyl)triphenylborates (M[Et3-
GeBPh3], M ) Li (7), Na (8), K (9)) as colorless crystals in
quantitative yield (eq 3). The triethyllgermylborates 7 and 8
were recrystallized from toluene at -20 °C to give colorless
needles in 74 and 72% isolated yields, respectively. The
germylborates 7 and 8 were fully characterized by spectroscopic
and X-ray analyses. However, attempts to obtain X-ray quality
crystals of 9 were not unsuccessful.
7
between the lithium ion and the benzene rings. The Li NMR
spectrum of germylborate 7 in toluene-d8 rather than in CD3-
OD suggests that the polymeric structure was broken by the
addition of MeOH to the lithium atoms. The dimeric structure
of [7‚(3MeOH)]2 was also established by X-ray diffraction
analysis (Figure 3). Selected atomic distances and bond lengths
are listed in Table 3. Each lithium cation is complexed by three
MeOH molecules, and one of three MeOH molecules bridges
two lithium cations by µ-oxygen atoms. The two lithium cations
and two µ-oxygen atoms constitute a planar four-membered ring
with Li-O bond lengths of 2.003(6) and 2.034(6) Å, an Li-
O-Li bond angle of 92.4(2)°, and Li-Li distance of 2.79(1)
Å. The closest distance between the lithium cation and the
phenyl carbon atom is 3.91(0) Å (for C(14)), beyond any
significant interaction to form a solvent-separated ion pair. The
Ge-B bond length of 2.152(4) Å is slightly longer than that
found in the polymeric germylborate. The bond angles of the
boron range from 104.8(1)° to 114.0(2)°. The sum of the angles
is equal to 656(0)°. The molecular structure of Na[Et3GeBPh3]
8 was confirmed by X-ray diffraction, and its selected bond
lengths and bond angles are shown in Figure 4 and in Table 4.
Crystallographic data of [7‚(3MeOH)]2 and 8 are summarized
in the Experimental Section.
(Et3Ge)2Hg + 2M f 2Et3GeM + Hg
Et3GeM + Ph3B f M(Et3GeBPh3)
(2)
M ) Li (7), Na (8), K (9) (3)
1
The H NMR spectrum of 7 showed a quartet at 0.51 ppm
and a triplet at 0.82 ppm due to the Et3Ge group, and phenyl
resonances at 6.84-7.19 ppm. The triethylgermylborate 7 was
not coordinated by solvents. The 11B and 7Li NMR of 7 in CD3-
CN showed signals at -8.6 and -1.93 ppm, respectively. The
7Li NMR signal of germylborate 7 depends on the solvent used.
In toluene-d8 at 80 °C it was significantly upfield-shifted at δ
) -7.0 ppm due to the shielding effect of the phenyl groups.
However, in methanol-d4 it was observed at δ ) -0.15 ppm,
indicating that the lithium cation no longer is shielded by the
phenyl groups due to complexation with CD3OD. Indeed, this
phenomenon was observed by X-ray diffraction analysis. The
molecular structure of 7 was unequivocally confirmed by X-ray
diffraction as shown in Figure 2. Selected bond lengths and
bond angles of 7 are summarized in Table 2. Crystallographic
data are summarized in the Experimental Section.
Compound 8, recrystallized from toluene, has also a zigzag
polymeric structure. The Ge-C and Ge-B bond lengths are
1.984(1)-1.990(2) and 2.137(2) Å, respectively. The Ge-B
bond length is similar to that in 5 and 7. The boron atom in 8
The Ge-C bond lengths (1.984(3)-1.994(3) Å) are normal
compared with that found in tetraphenylgermane. The Ge-B
bond length of 2.145(4) Å is slightly longer compared with that
of the neutral germylene-borane adduct.16 This suggests that
(17) Vyazankin, N. S.; Bychkov, V. T.; Vostokov, I. A. Zh. Obshch.
Kim. 1968, 38 1345.
(18) Setzer, W. N.; Schleyer, P. v. R. AdV. Organomet. Chem. 1985, 24,
353.

Silyl- and Germylborates
Organometallics, Vol. 25, No. 4, 2006 835
Figure 3. Molecular structure of [7‚3MeOH]2 at the 50% prob-
ability level. Hydrogen atoms are omitted for clarity.
Figure 4. Molecular structure of 8 at the 50% probability level.
Hydrogen atoms are omitted for clarity.
Table 3. Selected Atomic Distances (Å) and Bond Angles
(deg) of [7‚3MeOH]2
Table 4. Selected Atomic Distances (Å) and Bond Angles
(deg) of 8
Ge(1)-C(1)
Ge(1)-C(3)
Ge(1)-C(5)
Ge(1)-B(1)
B(1)-C(7)
B(1)-C(13)
1.984(3)
1.975(3)
1.986(3)
2.152(3)
1.624(4)
1.642(4)
B(1)-C(19)
Li(1)-O(1)
Li(1)-O(2)
Li(1)-O(3)
Li(1)-O(1)*
Li(1)-Li(1)*
1.632(4)
2.003(6)
1.887(6)
1.877(6)
2.034(6)
2.79(1)
Ge(1)-C(1)
Ge(1)-C(3)
Ge(1)-C(5)
Ge(1)-B(1)
B(1)-C(7)
B(1)-C(13)
B(1)-C(19)
Na(1)-C(7)
Na(1)-C(8)
1.984(1)
1.987(1)
1.990(2)
2.137(1)
1.639(2)
1.637(2)
1.623(2)
2.742(1)
2.991(2)
Na(1)-C(12)
Na(1)-C(13)
Na(1)-C(14)
Na(1)-C(19)*
Na(1)-C(20)*
Na(1)-C(21)*
Na(1)-C(22)*
Na(1)-C(23)*
Na(1)-C(24)*
2.827(1)
2.774(1)
3.045(1)
3.004(1)
2.876(1)
2.779(2)
2.748(2)
2.779(1)
2.890(1)
C(1)-Ge(1)-C(3)
C(1)-Ge(1)-C(5)
C(3)-Ge(1)-C(5)
C(1)-Ge(1)-B(1)
C(3)-Ge(1)-B(1)
C(5)-Ge(1)-B(1)
Ge(1)-B(1)-C(7)
Ge(1)-B(1)-C(13)
Ge(1)-B(1)-C(19)
103.7(1)
C(7)-B(1)-C(13)
C(7)-B(1)-C(19)
C(13)-B(1)-C(19)
Li(1)-O(1)-Li(1)*
O(1)-Li(1)-O(2)
O(1)-Li(1)-O(3)
O(2)-Li(1)-O(3)
O(1)-Li(1)-O(1)*
113.1(2)
114.0(2)
112.9(2)
87.6(2)
112.9(3)
116.9(3)
111.9(3)
92.4(2)
103.5(1)
101.7(1)
112.3(1)
117.1(1)
116.7(1)
104.9(1)
105.3(1)
105.7(1)
C(1)-Ge(1)-C(3)
C(1)-Ge(1)-C(5)
C(3)-Ge(1)-C(5)
C(1)-Ge(1)-B(1)
C(3)-Ge(1)-B(1)
C(5)-Ge(1)-B(1)
100.81(8)
104.07(8)
104.02(8)
112.66(7)
111.58(7)
121.40(7)
Ge(1)-B(1)-C(7)
Ge(1)-B(1)-C(13)
Ge(1)-B(1)-C(19)
C(7)-B(1)-C(13)
C(7)-B(1)-C(19)
C(13)-B(1)-C(19)
114.4(1)
111.62(9)
99.80(9)
105.1(1)
112.0(1)
105.1(1)
also shows a tetrahedral configuration with Ge-B-C bond
angles of 99.80(9)°, 111.62(9)°, and 114.4(1)°. The sodium
cations are surrounded by three phenyl groups of BPh3 and are
placed above one side of the three horiozontal phenyl planes
of BPh3. The sodium atom is located almost over the center of
the benzene rings. The distances between Na(1) and the phenyl
planes [C(7)-C(12), C(13)-C(18), C(19)-C(24)] are 2.648-
(0), 2.669(0), and 2.469(0) Å, respectively. They are apparently
longer than that found in 7 due to the larger size of the ionic
radius of sodium.
solutions containing 2, 5, or 6 in a quartz photolysis cell were
degassed and then irradiated with a xenon lamp at room
temperature. The reaction products were analyzed by gas
chromatography and GC-MS spectrometry. The main products
of this photochemical reaction are the corresponding hydrides.
The triethylgermylborates 7 and 8 were stable under an inert
gas atmosphere, but were unstable in air. They are soluble in
protic solvents such as water and MeOH, but nearly insoluble
in benzene and toluene. Surprisingly, they are very stable at
room temperature for 4 days even in degassed water. No
alcoholysis by MeOH or EtOH was observed at 50 °C for 10
h.
Photochemical Reactions of Silyl- and Germylborates. The
absorption spectra of phenyl-substituted silyl- (2, 3) and
germylborates (5, 6) in THF are shown in Figure 5. Each of
the borates has an absorption peak at ca. 270 nm, which can be
explained in terms of a σ-σ* transition from the bonding orbital
of the Si (or Ge)-B bond to its antibonding orbital. The THF
Figure 5. Absorption spectra of phenyl-substituted silyl- and
germyl-borates in THF at 23 °C. Optical path length is 1 cm.

836 Organometallics, Vol. 25, No. 4, 2006
Table 5. Photochemical Reactions of Silylborate 2 and Germylborates 5 and 6 at 23 °C for 30 min
Nanjo et al.
borate
quencher
conv/%
products, yields/%
Li(Ph2MeSiBPh3) 2
none
9
Ph2MeSiH (4), (Ph2MeSi)2 (trace)
2
CHCl3 (5 equiv)
84
Ph2MeSiCl (63), Ph2MeSiH (6), (Ph2MeSi)2 (trace)
(CHCl2)2 (23), CH2Cl2 (3)
Ph2MeGeH (3), (Ph2MeGe)2 (trace)
Ph2MeGeCl (23), Ph2MeGeH (trace), (Ph2MeGe)2 (trace),
(CHCl2)2 (7), CH2Cl2 (2)
Ph3GeH (4)
Ph3GeCl (20), (CHCl2)2 (12), CH2Cl2 (4)
Li(Ph2MeGeBPh3) 5
5
none
CHCl3 (5 equiv)
12
35
Li(Ph3GeBPh3) 6
6
none
CHCl3 (5 equiv)
10
35
Dimers, disilane for 2 and digermane for 5 and 6, were also
detected as minor products. These hydrides and dimers are
considered to be derived from the silyl and germyl radicals
generated by photocleavage of Si-B and Ge-B bonds of silyl-
and germylborates, respectively.19-21 In the presence of chlo-
roform, a trapping agent for group 14 element-centered radicals,
photolysis of silyl- and germylborates 2, 5, and 6 afforded the
corresponding chlorosilane and chlorogermanes, respectively.19-21
The results of photochemical reactions of 2, 5, and 6 at room
temperature for 30 min are listed in Table 5.
[PhnMe3-nE-BPh3]- 9hν8 PhnMe3-nE• + BPh3
(4)
•-
PhnMe3-nE• SH8 PhnMe3-nEH
2PhnMe3-nE• f (PhnMe3-nE)2
(5)
(6)
Figure 6. Transient absorption spectrum observed 500 ns after
excitation of the THF solution containing 6.
Thus, the phenyl-substituted silyl and germyl radicals are
suggested to be generated as shown by reaction 4.
Transient optical absorption measurements were performed
-4
on degassed THF solutions containing 6 (5.0 × 10
mol/L)
at room temperature using the fourth harmonic (266 nm) of an
Nd:YAG laser as an exciting light source. We measured the
time profiles of the transient absorbance, A(t) curves, in the
wavelength region 310-700 nm in the time region 0-35 µs.
The curves below 310 nm could not be observed by the
absorption of 6. From the observed A(t) curves in the wavelength
region, we could obtain time-resolved optical absorption spectra
with the time resolution of about 10 ns. Figure 6 shows the
spectrum observed at 500 ns after laser excitation. The spectral
shape was almost unchanged in the time region 0-35 µs. As
far as the signal intensity is concerned, the signal grew from 0
µs to 1 µs and kept almost constant from 1 µs to 35 µs. The
6
growth rate was found to be 7.7 × 10 s-1
.
As shown in Figure 6, appreciable signals were obtained in
the wavelength region 310-400 nm with a peak at 325 nm.
Previously, we found the transient absorption peak of the
triphenylgermyl radical in THF at 330 nm.22 In the present study,
we synthesized the triphenylboron anion radical by the method
of Leffler et al.,23 finding its peak in THF at 318 nm. Thus, the
peak observed at 325 nm in Figure 6 may be ascribed to an
overlap of the peak of the triphenylgermyl radical and that of
the triphenylboron anion radical. From the above-mentioned
time profiles of the signals, the growth rate may be ascribed to
the decay rate of their precursor, which will be shown to be the
triplet state of 6 from transient ESR measurements. Because
Figure 7. CIDEP spectrum observed with 6.
the signals did not decay until 35 µs, the lifetimes of both
radicals may be longer than 35 µs.
Transient ESR measurements were also performed on de-
gassed THF solutions containing 6 (5.0 × 10-4 mol/L) at room
temperature using the fourth harmonic (266 nm) of an Nd:YAG
laser as an exciting light source. Although the time resolution
of our ESR apparatus was about 100 ns, we carried out time
integration of the ESR spectra because the spectra had poor
S/N ratios. Figure 7 shows the transient ESR spectrum observed
during 400-600 ns after laser excitation. As shown in Figure
7, a sharp absorptive signal was observed at a low-field site
and a broad absorptive one at a high-field site. The peak position
of the sharp signal was B ) 336.12 mT and that of the broad
signal was B ) 337.22 mT. The g-value of the former and the
latter positions correspond to 2.0052 and 1.9987, respectively.
Sakurai et al.24 already observed the g-value of the triphenylger-
myl radical in DTBP to be 2.0054 and also found that its spectral
width was as small as about 0.5 mT.
(19) Sakurai, H. Free Radicals; Kochi, J. K., Ed.; Wiley: New York,
1973; Vol. II, Chapter 25.
(20) Sakurai, H.; Mochida, K. J. Chem. Soc., Chem. Commun. 1971,
1581.
(21) Sakurai, H.; Mochida, K.; Hosomi, A.; Mita, F. J. Organomet. Chem.
1972, 38, 275.
(22) Mochida, K.; Wakasa, M.; Sakaguchi, Y.; Hayashi, H. J. Am. Chem.
Soc. 1987, 109, 7942.
(23) Leffler, J. E.; Watts, G. B.; Tanigaki, T.; Dolan, E.; Miller, D. S. J.
Am. Chem. Soc. 1970, 92, 6825.

Silyl- and Germylborates
Organometallics, Vol. 25, No. 4, 2006 837
Preparation of Phenyl-Substituted Silylborates, Li[Phn-
Me3-nSiBPh3] (n ) 1-3). As a representative example, preparation
of Li[PhMe2SiBPh3] (n ) 1) (1) is described. Triphenylborane (2.42
g, 10.0 mmol) was added to a THF solution (15 mL) of dimeth-
ylphenylsilyllithium (0.7 N), prepared by the reaction of dimeth-
ylphenylchlorosilane with lithium metal.14 The reaction was
exothermic, and the mixture was stirred overnight to give the pale
yellow solid as a precipitate. Recrystallization from THF afforded
1‚3THF (1.84 g, 4.8 mmol) in 48% yield as colorless crystals.
Silylborate 1 in a sealed tube had no sharp melting point; 1 turned
yellow and partially melted at 200 °C on heating. 1H NMR (CD3-
CN, δ) 0.09 (s, 6 H), 1.83-1.94 (m, 12 H, THF), 3.66-3.80 (m,
12 H, THF), 6.91 (t, 3 H, J ) 7 Hz), 7.02-7.11 (m, 9 H), 7.25-
7.35 (m, 8 H); 13C NMR (CD3CN, δ) -1.2, 23.0 (THF), 65.3
Thus, the sharp signal may be ascribed to the triphenylgermyl
radical. The broad signal seems to be due to the triphenylboron
anion radical because Leffler et al.23 found that its spectral width
was as large as about 4 mT. On the other hand, they did not
obtain its g-value. In the present study, we synthesized the
triphenylboron anion radical with their method, finding its
g-value to be 2.0041. Thus, the observed ESR spectrum shown
in Figure 7 may be ascribed to be an overlap of the signal of
the triphenylgermyl radical and that of the triphenylboron anion
radical.
The observed transient ESR signals of 6 in THF decayed
within 3 µs after laser excitation, but the transient optical signals
of the same system did not decay until 35 µs. Thus, the observed
transient ESR signals are not due to those at thermal equilibrium
but due to CIDEP. Both the triphenylgermyl radical and the
triphenylboron anion radical showed absorptive phase patterns
as shown in Figure 7. Such totally absorptive patterns may be
explained in terms of the p-type triplet mechanism.25 Thus, we
can safely conclude that the reaction precursor of the cleavage
of the Ge-B bond is the triplet state of 6. We also performed
transient ESR measurements on degassed THF solutions con-
taining 2 and 5 at room temperature using the fourth harmonic
(266 nm) of an Nd:YAG laser as an exciting light source.
Although we obtained similar transient ESR signals for 2 and
5, they were very noisy and had no clear structure. Although
we could not analyze their signals, we can speculate that the
radical species are probably produced at the initial stages of
their photochemical reactions.
7
(THF), 119.0, 123.3, 123.4, 132.7, 133.2, 148.3, 160.1 (br); Li
NMR (CD3CN, δ) -1.3; 11B NMR (CD3CN, δ) -11.4. Anal. Calcd
for C38H50O3SiBLi: C, 75.99; H, 8.39. Found: C, 76.50; H, 8.42.
Li[Ph2MeSiBPh3]‚3THF (2): colorless crystals, 72% yield. Silylbo-
rate 2 in a sealed tube had no sharp melting point; 2 turned yellow
1
and partially melted at 200 °C on heating. H NMR (CD3CN, δ)
0.35 (s, 3 H), 1.80-1.95 (m, 12 H, THF), 3.65-3.78 (m, 12 H,
THF), 6.88-6.95 (m, 3 H), 6.97-7.07 (m, 10 H), 7.08-7.19 (m,
6 H), 7.19-7.27 (m, 6 H); 13C NMR (CD3CN, δ) -3.2, 23.0 (THF),
65.3 (THF), 119.4, 123.3, 123.7, 123.9, 133.5, 133.7, 145.7, 159.3
7
(br); Li NMR (CD3CN, δ) -1.3; 11B NMR (CD3CN, δ) -11.0.
Anal. Calcd for C43H52O3SiBLi: C, 77.93; H, 7.91. Found: C,
78.30; H, 8.32. Li[Ph3SiBPh3]‚3THF (3):2 colorless crystals, 85%
1
yield. H NMR (CD3CN, δ) 1.80-1.95 (m, 12 H, THF), 3.65-
3.78 (m, 12 H, THF), 6.88-6.95 (m, 3 H), 6.97-7.07 (m, 10 H),
7.08-7.19 (m, 6 H), 7.19-7.27 (m, 6 H); 13C NMR (CD3CN, δ)
26.0 (THF), 68.1 (THF), 119.4, 123.3, 123.7, 123.9, 133.5, 133.7,
Experimental Section
7
145.7, 159.3 (br); Li NMR (CD3CN, δ) -1.3; 11B NMR (CD3-
General Procedures. All experiments were performed under an
inert atmosphere of argon by standard vacuum line techniques. All
solvents were dried by standard methods and freshly distilled prior
to use. Column chromatography was performed with Kanto
Chemical silica gel 60N. Samplings of air-sensitive compounds
were performed in an MBrown Lab Master 130 glovebox under
argon atmosphere. Mass spectra were recorded on a JEOL AX505H
spectrometer. The product yields were determined by gas-liquid
chromatography (Shimadzu GC-14A) on a Frontier Laboratories
capillary column UA5 (30 m × 0.25 mm) using n-C20H42 as an
internal standard. 1H (400 MHz), 13C (100 MHz), 7Li (155 MHz),
and 11B (128 MHz) NMR spectra were recorded on a Varian Inova
CN, δ) -11.0.
Preparation of Phenyl-Substituted Germylborates, Li[Phn-
Me3-nGeBPh3] (n ) 1-3). As a representative example, prepara-
tion of Li[PhMe2GeBPh3] (n ) 1) (4) is described. Triphenylborane
(2.42 g, 10.0 mmol) was added to a THF solution (15 mL) of
dimethylphenylgermyllithium (0.7 N), prepared by the reaction of
dimethylphenylchlorogermane with lithium metal.14 The mixture
was stirred for 4 h to give the crude product as a milky white solid.
Recrystallization from THF afforded 4‚3THF (0.64 g, 1.5 mmol)
in 15% yield as colorless crystals. Germylborate 4 in a sealed tube
had no sharp melting point; 4 turned yellow and partially melted
1
at 200 °C on heating. H NMR (CD3CN, δ) 0.06 (s, 6 H), 1.83-
1
400 spectrometer. H and 13C chemical shifts were referenced to
1.88 (m, 6 H, THF), 3.67-3.74 (m, 6 H, THF), 6.88-6.93 (m, 3
H), 7.01-7.07 (m, 9 H), 7.20-7.25 (m, 6 H), 7.26-7.30 (m, 2 H);
13C NMR (CD3CN, δ) -2.9, 23.0 (THF), 65.2 (THF), 119.5, 122.9,
7
Me4Si as an external standard. The chemical shifts of Li NMR
spectra were referenced to external LiCl (1.0 M in methanol). 11
B
chemical shift was referenced to BF3‚Et2O as an external standard.
CW ESR spectra were recorded on a JEOL JES-FE3XGA spec-
trometer. X-ray crystallographic data and diffraction intensities were
collected on a MacScience DIP2030 diffractometer utilizing
graphite-monochromated Mo KR (λ ) 0.71073Å) radiation. The
structures were solved by direct methods using the program system
SIR-9226 and refined with all data on F2 by means of SHELXL-
97.27 Refinement was performed by a Silicon Graphics O2 with
MaXus.
Materials. BPh3 was commercially available. PhnMe3-nSiLi (n
) 1-3),10 PhnMe3-nGeLi (n ) 1-3),14,15 Et3GeM (M ) Li, Na,
K),17 Li[Ph3SiBPh3],2 and Li[Ph3GeBPh3]2 were prepared as
described in the cited references.
7
123.5, 124.1, 132.5, 133.0, 151.5 158.8 (br); Li NMR (CD3CN,
δ) -1.5; 11B NMR (CD3CN, δ) -8.3. Anal. Calcd for C38H50O3-
GeBLi: C, 75.99; H, 8.39. Found: C, 76.50; H, 8.42. Li[Ph2-
MeGeBPh3]‚3THF (5): colorless crystals, 42% yield. Germylborate
5 in a sealed tube had no sharp melting point; 5 turned yellow and
1
partially melted at 200 °C on heating. H NMR (CD3CN, δ) 0.29
(s, 3 H), 1.75-1.90 (m, 8 H, THF), 3.60-3.73 (m, 8 H, THF),
6.88-6.93 (m, 3 H), 6.96-7.07 (m, 12 H), 7.10-7.15 (m, 4 H),
7.17-7.23 (m, 6 H); 13C NMR (CD3CN, δ) -3.5, 23.0 (THF), 65.3
(THF), 119.8, 123.2, 123.5, 124.2, 133.5, 133.7, 149.2, 158.1 (br);
7Li NMR (CD3CN, δ) -1.5; 11B NMR (CD3CN, δ) -7.2. Anal.
Calcd for C43H52O3GeBLi: C, 77.93; H, 7.91. Found: C, 78.30;
H, 8.32. Li[Ph3GeBPh3]‚3THF (6)2: Colorless crystals, 85% yield.
1H NMR (CD3CN, δ) 1.83 (m, 12 H, THF), 3.07 (m, 12 H, THF),
6.92-7.02 (m, 21 H), 7.08-7.12 (m, 21 H), 7.19-7.21 (m, 6 H);
13C NMR (CD3CN, δ) 26.0 (THF), 68.1 (THF), 122.9, 126.3, 126.4,
127.0, 136.5, 137.0, 149.6, 159.7 (br); 7Li NMR (CD3CN, δ) -1.0;
11B NMR (CD3CN, δ) -7.2.
(24) Sakurai, H.; Mochida, K.; Kira, M. J. Am. Chem. Soc. 1976, 94,
929; J. Organomet. Chem. 1977, 124, 235.
(25) Hayashi, H. Introduction to Dynamic Spin Chemistry; World
Scientific: Singpore, 2004.
(26) Altomare, A.; Burla, M. C.; Camalli, M.; Cascarano, M.; Giaco-
vazzo, C.; Guagliardi, A.; Polidoro, G. J. Appl. Crystallogr. 1994, 27, 435.
(27) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; University of Go¨ttingen, 1997.
Preparation of Triethylgermylborates E[Et3GeBPh3] (E ) Li,
Na, K). As a representative example, preparation of Li[Et3GeBPh3]

838 Organometallics, Vol. 25, No. 4, 2006
Nanjo et al.
Table 6. Summary of Crystallographic Data for 5, 7, [7‚3MeOH]2, and 8
5
7
[7‚3MeOH]2
8
formula
fw
cryst syst
space group
a (Å)
b (Å)
c (Å)
C43H58BGeLiO8
761.23
triclinic
P1h
C24H30BGeLi
408.82
monoclinic
P21/n
12.1640(12)
11.3280(5)
16.1220(14)
90
C27H42BGeLiO3
504.99
triclinic
P1h
C24H30BGeNa
424.87
monoclinic
P21/n
12.4970(4)
11.6750(4)
15.5740(4)
90
11.661(4)
12.151(2)
16.271(5)
82.807(19)
69.852(13)
84.226(19)
2143.3(11)
2
11.1920(9)
11.0830(6)
11.5370(10)
84.692(5)
84.914(4)
86.971(5)
1417.88(18)
2
R (deg)
â (deg)
γ (deg)
V (Å3)
Z
100.114(4)
90
102.449(2)
90
2187.0(3)
4
2218.86(12)
4
T (K)
200
200
200
200
F
calcd (g cm-3
)
1.180
1.242
1.103
1.272
F(000)
808
856
518
888
no. of unique reflns
no. of reflns used for refinement
no. of refined params
R1 (I > 2σ(I))
6940
3066
3899
5007
4832
2647
3684
4719
440
275
311
245
0.0806
0.0362
0.1153
0.945
0.0367
0.0344
0.1221
1.117
wR2 (all data)
0.2325
0.1238
GOF
1.454
1.125
max./min. ∆F (e Å-3
)
0.604/-0.578
+0.310/-0.573
+0.510/-0.438
+0.504/-0.511
(7) is described. A benzene/hexane mixed solution (10 mL) of
unsolvated triethylgermyllithium18 (9.3 mmol) was added to triph-
enylborane (2.01 g, 8.3 mmol). The mixture was stirred for 2 days
to give the crude product as a white solid. Recrystallization from
toluene afforded 7 (1.98 g, 5.8 mmol) in 71% yield as colorless
crystals. Mp > 200 °C. 1H NMR (C7D8, 80 °C, δ) 0.67 (q, 6 H, J
) 7.9 Hz), 0.89 (t, 9 H, J ) 7.9 Hz), 6.80-6.90 (m, 3 H), 6.94-
7.06 (m, 6 H), 7.17-7.32 (m, 6 H); 13C NMR (C7D8, 80 °C, δ)
7.1, 10.5, 124.8, 128.4, 135.2, 154.4-156.4 (br); 7Li NMR (C7D8,
80 °C, δ) -7.0 (ν1/2 ) 26.8 Hz); 11B NMR (C7D8, 80 °C, δ) -11.3.
Anal. Calcd for C24H30GeBLi: C, 71.02; H, 7.45. Found: C, 71.55;
H, 7.12. Spectral data for 7 in methanol: 1H NMR (CD3OD, δ)
0.52 (q, 6 H, J ) 8 Hz), 0.79 (t, 9 H, J ) 8 Hz), 6.81 (t, 3 H, J )
7 Hz), 6.98 (t, 6 H, J ) 7 Hz), 7.26 (d, 6 H, J ) 7 Hz); 13C NMR
(CD3OD, δ) 6.0, 9.3, 120.1, 124.5, 135.0, 161.8 (q, J(11B-13C) )
53 Hz); 7Li NMR (CD3OD, δ) -0.15; 11B NMR (CD3OD, δ) -8.6.
Na[Et3GeBPh3] (8): colorless crystals, 77% yield. Mp > 200 °C.
1H NMR (CD3CN, δ) 0.51 (q, 6 H, J ) 8 Hz), 0.82 (t, 9 H, J ) 8
Hz), 6.84 (t, J ) 7 Hz, 3 H), 7.00 (t, J ) 7 Hz, 6 H), 7.19 (d, J )
7 Hz, 6 H); 13C NMR (CD3CN, δ) 4.4, 8.0, 119.1, 123.3, 133.2,
160.0 (q, J(11B-13C) ) 50 Hz); 11B NMR (CD3CN, δ) -8.5. Anal.
Calcd for C24H30GeBNa: C, 67.84; H, 7.12. Found: C, 68.20; H,
6.95. K[Et3GeBPh3] (9): colorless crystals, 58% yield. Mp > 200
in a quartz tube connected to a Pyrex tube at the upper part. The
tube was degassed under vacuum and filled with argon. The sample
was irradiated with a xenon lamp at room temperature for 30 min.
After irradiation, the photoproducts were identified by comparing
the retention times on GLC and GC-MS with those of authentic
samples.
Photochemical Reactions of the Borates in the Presence of
Trapping Agents. The borate (30 mmol) and chloroform (150
mmol) were dissolved in dry THF (1 cm3) in a quartz tube. The
tube was degassed in a vacuum and filled with argon. The sample
was irradiated with a xenon lamp at room temperature for 30 min.
After irradiation, the photoproducts were identified by GLC and
GC-MS.
Transient Optical Absorption Measurements. Laser flash
photolysis measurements were performed at 293 K. They were
basically the same as described previously.28 The sample solutions
were excited with the fourth harmonic (266 nm) of an Nd:YAG
laser (Quanta Ray GCR-3, Spectra-Physics). In the measurements
of the profiles of the transient absorbance, A(t) curves, we averaged
the data of 5 shots. The time resolution of the apparatus was about
10 ns.
ESR Measurements. Transient ESR measurements were per-
formed at 293 K using an X-band spectrometer (JEOL RSV 2000)
without field modulation. They were basically the same as described
previously.29 The sample solutions were excited with the fourth
harmonic (266 nm) of an Nd:YAG laser (Quanta Ray GCR-3,
Spectra-Physics). We averaged the data of 50 transient ESR spectra.
To obtain good S/N ratios, we averaged 5 scans for one spectrum.
Conventional ESR measurements were performed at 293 K using
an X-band spectrometer with field modulation of 100 kHz.
1
°C. H NMR (CD3CN, δ) 0.51 (q, 6 H, J ) 8 Hz), 0.82 (t, 9 H, J
) 8 Hz), 6.84 (t, J ) 7 Hz, 3 H), 7.00 (t, J ) 7 Hz, 6 H), 7.19 (d,
J ) 7 Hz, 6 H); 13C NMR (CD3CN, δ) 4.5, 8.0, 119.1, 123.3, 133.3,
160.0 (q, J(11B-13C) ) 50 Hz); 11B NMR (CD3CN, δ) -8.6.
X-ray Crystal Structure Analyses for 4, 5, 7, and 8. Crystal
data for all structures are presented in Table 6. Crystallographic
data for 5, 7, [7‚3MeOH]2, and 8 have been deposited with the
Cambridge Crystallographic Data Centre as supplementary publica-
tion nos. CCDC-244796, -178044, -178043, and -244797, respec-
tively. Copies are available free of charge on application to CCDC,
12 Union Road, Cambridge CB2 1EZ, UK [fax: int. code + 44-
1223/336-033; e-mail: deposit@ccdc.cam.ac.uk].
Absorption Spectra of the Borates. The silyl- and germylbo-
rates are extremely sensitive to oxygen and moisture. A closed
absorption cell was used to observe the absorption spectra of the
borates. The absorption cell apparatus used in these studies consists
of a 1-cm quartz absorption cell sealed to a sidearm of a round-
bottomed flask. The apparatus was connected to a high-vacuum
system for alternate degassing and flushing with argon. Access to
the flask was through a second sidearm closed by a rubber string
cap. The borate was quickly placed in throughly degassed THF in
a round-bottomed flask.
Acknowledgment. The authors thank Prof. Toshihiro Ta-
kahashi of Gakushuin University for the ESR spectrum of the
triphenylboron anion radical. The authors also thank Mr. Yuki
Watanabe for preliminary experiments of phenyl-substituted
germyl borates. This work was supported by a Grant-in-Aid
from the Ministry of Education, Culture, Science, Sports, and
Technology, Japan (No. 15550041).
Supporting Information Available: This material is available
free of charge via the Internet at http://pubs.acs.org.
OM050733Y
(28) Sakaguchi, Y.; Hayashi, H. J. Phys. Chem. A 2004, 108, 3421.
(29) Woodward, J. R.; Lin, T.-S.; Sakaguchi, Y.; Hayashi, H. J. Phys.
Chem. A 2000, 104, 557.
Photochemical Reactions of the Borates. The THF solution
(1 cm3) containing the borate (30 mmol) was sealed under vacuum