Cyclosiloxanes containing a gallium atom as ring member from the reaction of tert-butoxygallane with di- and trisiloxanediols

Article abstract of DOI:10.1021/om010544p

A study was performed on cyclosiloxanes containing a gallium atom as ring member from the reaction of tert-butoxygallane with di- and trisiloxanediols. The skeleton of cyclosiloxane obtained, consisted of a four-membered Ga₂O₂ ring t

Full text of DOI:10.1021/om010544p

380
Organometallics 2002, 21, 380-388
Cyclosiloxa n es Con ta in in g a Ga lliu m Atom a s Rin g
Mem ber fr om th e Rea ction of ter t-Bu toxyga lla n e w ith
Di- a n d Tr isiloxa n ed iols
Michael Veith,* Heidi Vogelgesang, and Volker Huch
Institut fu¨r Anorganische Chemie, Universita¨t des Saarlandes, Postfach 15 11 50,
66041 Saarbru¨cken, Germany
Received J une 21, 2001
tert-Butoxygallane, [tBuOGaH2]2, reacts with tetraphenyl-1,3-disiloxanediol, HO(Ph2)Si-
O-Si(Ph2)OH, with hydrogen elimination to form the bicyclic compound [(OSiPh2OSiPh2O)-
[Ga(H)]2(OtBu)2] (1). The skeleton of molecule 1 consists of a four-membered Ga2O2 ring to
which a five-membered O-Si-O-Si-O bridge is connected through Ga-O bonds. While
the gallium atoms each have a hydrogen atom as further substituent, the oxygen atoms of
the four-membered ring have tert-butyl substituents and the silicon atoms each bear two
phenyl groups. When the reactant ratio is changed to [tBuOGaH2]2:1,3-disiloxanediol ) 1:2,
two new products are formed in almost equal amounts: [(OSiPh2OSiPh2OSiPh2O)GaH]2 (2)
and [(OSiPh2OSiPh2OSiPh2O)GaOtBu]2 (3). Both compounds are centrosymmetric, forming
either a central Ga2O2 ring to which two eight-membered GaO4Si3 rings are fused with two
common GaO edges (2) or a central Ga2O2 ring, the gallium corners serving as spiro centers
for again eight-membered GaO4Si3 rings (3). In comparison to 1, molecules 2 and 3 contain
Si-O chains with one further SiO unit and have lost either tert-butyl alcohol (2) or hydrogen
(3) with respect to 1. Compound 2 can also be obtained when, instead of tetraphenyl-1,3-
disiloxanediol, hexaphenyl-1,5-trisiloxanediol (HO(Ph2)SiOSiPh2OSi(Ph2)OH) is reacted with
tert-butoxygalane. The central Ga2O2 rings in molecules 2 and 3 originate from Lewis acid
and base interactions but are of different stability. In 2, the ring is formed by oxygen atoms
bearing a silicon substituent and therefore should have reduced basicity: consequently, 2
can be split (into halves) by simple reaction with triethylamine, the nitrogen atom serving
as a donor to gallium. The product of this reaction is an eight-membered Si3O4Ga ring with
hydrogen and triethylamine as ligands at gallium and two phenyl groups on each of the
silicon atoms and has the formula [(OPh2SiOSiPh2OSiPh2O)GaH(NEt3)] (4). Further change
of the stoichiometry between tert-butoxygallane and the 1,5-trisiloxanediol in favor of the
silicon compound again has a consequence for the reaction products. Using NEt3 as
crystallization promotor gave [(OSiPh2OSiPh2OSiPh2O)2Ga‚HNEt3] (5). In this compound a
spiro-connected gallium atom is a member of two GaO4Si3 rings. The triethylamine group is
coordinating a proton which forms a bridge between an oxygen atom of the rings and nitrogen.
Compound 5 can also be obtained from 2 using a dilute solution of water in THF. Compounds
1
1-5 have been fully characterized by H, 13C, 29Si NMR and IRspectroscopy and have been
the subject of single-crystal X-ray diffraction studies.
In tr od u ction
alumosilicates.2 As a matter of fact, the hydroxy groups
on the aluminum atoms in [OSiPh2OSiPh2O]4[AlOH]4
can be deprotonated to form to lithium salts such as
[OSiPh2OSiPh2O]4[AlO]4Li4‚4OEt2.3
Meanwhile, alumosiloxanes and their metal deriva-
tives have been largely explored and have been included
in a compilation by Sullivan and King;4 in addition,
other metal derivatives of siloxanes have been reviewed
by Edelmann et al. and J urkschat and Beckmann.5 A
very recent paper of Gun’ko et al. reported the isolation
and structural characterization of a molecular alumo-
The tert-butoxyalane (tBuOAlH2)2 can be used very
elegantly for the direct synthesis of polycyclic alumo-
siloxanes such as [OSiPh2OSiPh2O]4[AlOH]4 by treat-
ment with diphenylsilanediol.1 In this complex reaction,
besides the formation of tert-butyl alcohol and hydrogen,
a condensation of diphenylsilanediol forming tetra-
phenyl-1,3-disiloxanediol is observed. We have also
shown in an alternative experiment that the hydride
ligands on aluminum are more reactive toward silanols
than the tert-butoxy groups.1 Alumosiloxanes of the type
described above may be considered as silaaluminates
wrapped up in an organic matrix (phenyl groups) and
may serve as metalloorganic counterparts of metal
(2) Montero, M. L.; Voigt, A.; Teichert, M.; Uson, I.; Roesky, H. W.
Angew. Chem. 1995, 107, 2761; Angew. Chem., Int. Ed. Engl. 1995,
34, 2504.
(3) Veith, M.; J arczyk, M.; Huch, V. Angew. Chem. 1998, 110, 109;
Angew. Chem., Int. Ed. Engl. 1998, 37, 105.
(4) King, L.; Sullivan, A. C. Coord. Chem. Rev. 1999, 189, 19.
(1) Veith, M.; J arczyk, M.; Huch, V. Angew. Chem. 1997, 109, 140;
Angew. Chem., Int. Ed. Engl. 1997, 36, 177.
10.1021/om010544p CCC: $22.00 © 2002 American Chemical Society
Publication on Web 12/21/2001

Cyclosiloxanes Containing a Gallium Atom
Organometallics, Vol. 21, No. 2, 2002 381
silicate, [PyH][{(Ph2Si)3O4}Al],6 which is remarkably
similar to one of our products (see below for compound
5).
spectrum, which showed ν(Ga-H) at 2021 cm-1. The
13C NMR spectrum is consistent with the data obtained
from the 1H NMR spectrum. The chemical shift of silicon
in the 29Si NMR spectrum is found at -45.7 ppm in the
region typical for cyclic siloxanes.16
The incorporation of gallium instead of aluminum into
siloxanes has attracted less attention, although reports
on this subject appeared almost 40 years ago. Trimeth-
ylgallium is known to react with trimethylsilanol to
form the dimeric dimethylgallium trimethylsiloxane
[Me2GaOSiMe3]2.7 Gallium trichloride reacts with so-
dium trimethylsilanolate to give dimeric tris(trimeth-
ylsiloxy)gallium,8 from which siloxygallates of the type
M[Ga(OSiR3)4] have been obtained9 (see also a review
of this early work10). Only recently have cage and
polycyclic compounds with silicon, oxygen, and gallium
and their X-ray structures been reported by Feher and
co-workers (compounds derived from silesquioxanes),11
by Roesky and co-workers (drum-shaped structures),12
and by Murugavel and his group (polycyclic lithium
gallosiloxanes).13
We have been interested in exploring whether the
reactivity pattern observed for the reaction of [tBuO-
AlH2]2 with Ph2Si(OH)2 (see above) could be transposed
to [tBuOGaH2]2.14 In preliminary experiments we found
that tert-butoxygallane and Ph2Si(OH)2 reacted differ-
ently, giving only a mixture of polymeric products, which
could not be isolated. We therefore replaced Ph2Si(OH)2
by its higher condensation products (HO)Ph2SiOSi-
Ph2(OH) and (HO)Ph2SiOSiPh2OSiPh2(OH) in order to
simplify the reaction with respect to the condensation
of Ph2Si(OH)2. This change resulted in the formation
of discrete and isolable products.
A change in the molar ratio of tert-butoxygallane and
tetraphenyl-1,3-disiloxanediol to 1:2 had a dramatic
effect on the products (Scheme 1, 1:2 reaction).
The two compounds 2 (36%) and 3 (25%) were
obtained in almost equal amounts and could be sepa-
rated easily, on the basis of their different solubilities
in diethyl ether, the hydride compound 2 precipitating
from the reaction mixture while 3 remains in solution.
Both compounds form colorless crystals, soluble either
in toluene or in diethyl ether (3). The 29Si NMR spectra
of 2 and 3 each have two resonances (in a 2:1 ratio),
indicating a lengthening of the -O-Si-O-Si-O-
chain by a further Si-O unit. While the 1H NMR
spectrum of 3 displays a signal for the tert-butyl group
along with resonances due to the hydrogen atoms of the
phenyl groups, the 1H NMR spectrum of 2 shows a
resonance of low intensity at 4.9 ppm consistent with a
hydrogen atom bonded to gallium. The 13C NMR spectra
parallel the findings of the 1H NMR spectra. The
attribution of the signal at 4.9 ppm in the 1H NMR
spectrum of 2 to Ga-H could be confirmed by an
absorption at 2015 cm-1 (νs(Ga-H)) in the infrared
spectrum.
The lengthening of the siloxane chain by one Si-O
unit in the products prompted us to replace (HO)SiPh2-
OSiPh2(OH) by (HO)SiPh2OSiPh2OSiPh2(OH) in the 1:2
equation of Scheme 1 and to repeat the reaction with
tert-butoxygallane using the 1,5-trisiloxanediol. This
had an effect neither on the products nor on their yields
relative to (tBuOGaH2)2. The spectral data obtained of
the reaction mixtures after 30 min of stirring were
almost identical with those obtained from the reaction
with the 1,3-disiloxanediol.
In retrospect, these results are not astonishing, as
“ring expansion reactions” of metallasiloxanes have been
described in various reports by Sullivan and co-
workers17-19 and by others.20,21 The expansion reactions
are believed to occur because siloxane rings with few
members are more strained than the larger rings. Thus,
cyclotrisiloxanes have strain energies of 16-21 kJ /mol,
while cyclotetrasiloxanes and larger cyclosiloxanes have
almost no strain energy.17,22
The mechanisms of these reactions are not fully
understood. There can be expansion reactions of free
silanols23 or of coordinated siloxanes, and the Lewis
acidity of metal atoms may play a role. Cyclic diphen-
ylsiloxanes containing Ti(IV) as a ring member of
Syn th eses of P h en yl-Su bstitu ted
Ga lla cyclosiloxa n es
When tert-butoxygallane, (tBuOGaH2)2,14 was allowed
to react with 1 equiv of tetraphenyl-1,3-disiloxanediol15
in diethyl ether at room temperature, almost spontane-
ous evolution of hydrogen gas was observed. After
separation from some precipitated oligomers, compound
1 could be isolated by simple crystallization from the
solution (Scheme 1, 1:1 reaction).
The yield of 1 was 63%, but may be higher when using
more dilute solutions. The 1H NMR spectrum of 1
contains one signal for the tert-butyl groups, a broad
resonance for a hydride connected to gallium, and the
hydrogen atoms of the phenyl group. The presence of
Ga-H bonds also could be deduced from the infrared
(5) (a) Lorenz, V.; Fischer, A.; Giessmann, S.; Gilje, J . W.; Gun’ko,
Y.; J acob, K.; Edelmann, F. T. Coord. Chem. Rev. 2000, 206-207, 321.
(b) Beckmann, J .; J urkschat, K. Coord. Chem. Rev. 2001, 267-300,
267.
(6) Gun’ko, Y. K.; Reilly, R.; Kessler, V. G. New J . Chem. 2001, 25,
528.
(7) Schmidbaur, H.; Schindler, F. Chem. Ber. 1966, 99, 2178.
(8) Schmidbaur, H. Chem. Ber. 1963, 96, 2696.
(9) Schmidbaur, H.; Schmidt, M. Angew. Chem. 1962, 74, 589.
(10) Schmidbaur, H. Angew. Chem. 1965, 77, 206; Angew. Chem.,
Int. Ed. Engl. 1965, 4, 201.
(16) O’Dowd, A. T.; Spalding, T. R.; Ferguson, G.; Gallagher, J . F.;
Reed, D. J . Chem. Soc., Chem. Commun. 1993, 1816.
(17) Hossain, M. A.; Hursthouse, M. B.; Mazid, M. A.; Sullivan, A.
C. J . Chem. Soc., Chem. Commun. 1988, 1305.
(18) Motevalli, M.; Shah, D.; Shah, S. A. A.; Sullivan, A. C. J . Chem.
Soc., Chem. Commun. 1994, 2427.
(11) Feher, F. J .; Budzichowski, T. A.; Ziller, J . W. Inorg. Chem.
1997, 36, 4082.
(12) Voigt, A.; Murugavel, R.; Parisini, E.; Roesky, H. W. Angew.
Chem. 1996, 108, 823; Angew. Chem., Int. Ed. Engl. 1996, 35, 5,
(13) Murugavel, R.; Walawalkar, M. G.; Prabusankar, G.; Davis,
P. Organometallics 2001, 20, 2639.
(19) Lazell, M.; Motevalli, M.; Shah, S. A. A.; Simon, C. K. S.;
Sullivan, A. C. J . Chem. Soc., Dalton Trans. 1996, 1449.
(20) Murugavel, R.; Voigt, A.; Walawalkar, M. G.; Roesky, H. W.
Chem. Rev. 1996, 96, 2205.
(21) Murugavel, R.; Shete, V. S.; Baheti, K.; Davis, P. J . Organomet.
Chem. 2001, 625, 195.
(14) Veith, M.; Faber, S.; Wolfanger, H.; Huch, V. Chem. Ber. 1996,
129, 381.
(15) Behbehani, H.; Brisdon, B. J .; Mahon, M. F.; Molloy, K. C. J .
Organomet. Chem. 1993, 463, 41.
(22) Hossain, M. A.; Hursthouse, M. B.; Ibrahim, A.; Mazid, M.;
Sullivan, A. C. J . Chem. Soc., Dalton Trans. 1989, 2347.
(23) Rubinsztajn, S.; Cypryk, M.; Chojnowsky, J . J . Organomet.
Chem. 1989, 367, 27.

382 Organometallics, Vol. 21, No. 2, 2002
Veith et al.
Sch em e 1
different ring sizes (TiO(OSiPh2)n with n ) 2-4) can
be obtained from precursors with almost identical Si-O
chain lengths, displaying slightly different basicities at
the terminal oxygen atoms (HOPh2SiOSiPh2OH, LiOPh2-
SiOSiPh2OLi, NaOPh2SiOSiPh2ONa), or from Ph2Si-
(OH)2.17,19,20,22
to the complete substitution of the ligands at gallium,
and the tetrasiloxygallate 5 is formed. It can be isolated
as the triethylamine adduct and has the composition
[(OSiPh2OSiPh2OSiPh2O)2Ga]-‚HNEt3+ (Scheme 1, 1:4
reaction). Compound 5 may also be obtained in an
alternative way starting with compound 2 and using
water as reactant (eq 1). We were able to separate
Compound 2 instantaneously reacted with triethyl-
amine to form the adduct 4. As can be seen from the
structural analysis (see below), this Lewis acid/base
reaction can be used to split the dimeric 2 into halves
(Scheme 1). The molecule 4 can be isolated by crystal-
lization from diethyl ether in almost quantitative yield.
[(OSiPh2OSiPh2OSiPh2O)GaH]2
+ 2 H2O + NEt3 f
2
-
+
2 H +
+
[(OSiPh2OSiPh2OSiPh2O)2Ga] ‚HNEt3
2
5
other products (1)
1
In the H NMR spectrum of 4 the ethyl resonances of
the amine, the Ga-H signal at 4.86 ppm and the signals
of the phenyl groups are easily discernible. Similar to
that of 2, the 29Si NMR spectrum of 4 contains two
resonances in a 1:2 ratio. The νs(Ga-H) band in the
infrared spectrum is found at 1914 cm-1, which is a
considerable shift to lower wavenumbers (2, 2015 cm-1).
Hence, the Ga-H bond energy is decreased in the NEt3
adduct compared to the original dimer. This is in accord
with a weak O-Ga acid/base interaction in 2, which
must be correlated to strong Si-O bonding inducing a
reduced Lewis basicity at the oxygen atoms linked to
gallium (see also structure determinations).
crystals of 5 from the reaction mixture in moderate yield
(40%) but did not identify the other reaction products,
which should contain Ga(OH)x or GaO entities.
Compound 5 was characterized in THF solution by
1
its H, 13C, and 29Si NMR spectra. The two resonances
in the 29Si NMR spectrum as well as the few lines in
the 13C NMR spectrum indicate an overall point sym-
metry of S4 or D2 for the molecule in solution rather
than Cs point symmetry, as would have been the case
for an alternative description of 5 with the proton
situated on one of the oxygen atoms coordinated to
gallium, as may be seen from formulas 5a and 5b.
Of course, the observed higher symmetry of 5 in
solution could also arise from equilibria between dif-
A further increase of the 1,5-trisiloxanediol/tert-
butoxygallane molar ratio, as shown in Scheme 1, led

Cyclosiloxanes Containing a Gallium Atom
Organometallics, Vol. 21, No. 2, 2002 383
Ta ble 1. Cr ysta l Da ta , Da ta Collection a n d Refin em en t P a r a m eter s for 1-5
1
2
3
4
5
empirical formula
C
32H40Ga2O5Si2
C72H62Ga2O8Si6‚
C7H8
C80H78Ga2O10Si6‚
C7H8
C42H46GaNO4Si3
C78H76GaNO8Si6‚
0.5C4H8O
fw
700.26
1455.33
1599.59
782.79
1429.76
cryst size, mm; color
0.5 × 0.4 × 0.4;
0.3 × 0.2 × 0.2;
0.6 × 0.3 × 0.4;
0.6 × 0.5 × 0.3;
colorless
triclinic, P1h
293
0.6 × 0.5 × 0.3;
colorless
colorless
colorless
colorless
cryst syst, space group
temp, K
monoclinic, P21/ n
293
triclinic, P1h
293
triclinic, P1h
293
monoclinic, P2/c
293
unit cell dimens
a, Å
b, Å
9.891(2)
17.099(3)
21.162(4)
90
98.94(3)
90
3535.6(12); 4
1.316
1.626
10.040(2)
12.070(2)
16.070(3)
76.28(3)
76.04(3)
89.01(3)
1834.3(6); 1
1.317
10.184(2)
13.513(3)
17.014(3)
67.46(3)
74.13(3)
80.54(3)
2075.4(7); 1
1.280
9.332(2)
11.009(2)
21.428(4)
85.14(3)
78.91(3)
68.84(3)
2014.4(7); 2
1.291
27.764(6)
13.641(3)
21.844(4)
90
92.38(3)
90
8266(3); 4
1.148
0.470
c, Å
R, deg
â, deg
γ, deg
V, Å3; Z
calcd density, g/cm3
abs coeff, mm-1 (Mo KR)
2θ range for data
collection, deg
no. of rflns collected
no. of indep rflns
no. of obsd rflns
abs cor
0.887
1.93-23.95
0.791
2.45-24.05
0.813
1.94-22.50
2.28-24.02
1.89-24.06
17 347
5220
3862
11 625
5377
4178
13 059
6060
5249
5250
5250
4126
49 309
12 759
8343
empirical
refinement method
no. of params refined
goodness of fit
final R indices (obsd data):
R1, wR2
full-matrix least squares on F2
384
1.148
0.0443, 0.1360
434
0.932
0.0313, 0.0690
454
0.898
0.0449, 0.1347
468
1.399
0.0647, 0.1664
938
1.023
0.0554, 0.1794
R indices (all data):
R1, wR2
0.0619, 0.1447
0.0452, 0.0730
0.0511, 0.1420
0.0878, 0.1858
0.0872, 0.1954
largest diff peak and hole, e/Å3
0.405, -0.390
0.330, -0.205
0.965, -0.607
1.772, -0.496
1.045, -0.407
ferent OH positions in 5b, which would be rapid with
respect to the NMR time scale. In the IR spectrum of 5
a broad band of low intensity at 2710 cm-1 can be
distinguished, which could arise from a proton coordi-
nated to two basic centers (free Et3NH+ has an absorp-
tion at 3150 cm-1, while [Et3N‚‚‚H‚‚‚py]+ absorbs around
2570 cm-1).24 As can be deduced from single-crystal
X-ray diffraction (see below), in the crystal 5 seems to
adopt a bonding which is better described as 5b. This
is in contrast to the recently characterized aluminum
derivate [PyH]+[{(Ph2Si)3O4}2Al]-, which even in the
crystal forms an ion pair with Al in an almost perfect
tetrahedral O4 environment.6
F igu r e 1. Structure of gallasiloxane 1, (OSiPhOSiPh2O)-
[Ga(H)]2(OtBu)2, from X-ray analysis, with 30% probability
(also in Figures 2-5) thermal ellipsoids. The unlabeled
atoms are either carbon or hydrogen. The hydrogen atoms
at the tert-butyl groups are not shown.
necting corners (see also Figure 1), a structural principle
already established in other metallasiloxanes.25 The
point symmetry of the molecule is almost C2, the pseudo
2-fold axis running through O(2) and the center of the
basal Ga2O2 ring. This four-membered ring is nearly
planar (sum of the angles 359.5°), with small angles at
the gallium atoms (80.5°) and larger ones at the oxygen
atoms (99.3°) (for bond distances and angles see Table
2). The mean Ga-O bond length (1.919(5) Å) within the
four-membered ring is longer compared to the Ga-
O(1,3) bond lengths (1.788(3) Å) as expected, because
the coordination numbers at O(1) and O(3) are smaller
Cr ysta l Str u ctu r es of th e Molecu les 1-5
X-ray structure determinations of compounds 1-5
have been performed, and the most relevant data are
assembled in Table 1. All compounds crystallize as
distinct molecules in crystal structures with intermo-
lecular van der Waals forces between the molecular
units.
Compound 1 may be described as a heterobicyclo-
[5.1.1]nonane, the two gallium atoms serving as con-
(25) Mazzah, A.; Haoudi-Mazzah, A.; Noltemeyer, M.; Roesky, H.
W. Z. Anorg. Allg. Chem. 1991, 604, 93.
(24) Borah, B.; Wood, J . L. J . Mol. Struct. 1974, 22, 237.

384 Organometallics, Vol. 21, No. 2, 2002
Veith et al.
Ta ble 2. Selected Bon d Len gth s a n d Dista n ces (Å)
a n d Bon d An gles (d eg) for 1-3
Compound 1
Ga(1)‚‚‚Ga(2)
Ga(1)-O(1)
Ga(1)-O(4)
Ga(1)-O(5)
Ga(2)-O(3)
Ga(2)-O(4)
Ga(2)-O(5)
Ga(1)-H
2.9250(8)
1.790(3)
1.912(3)
1.929(3)
1.787(3)
1.921(3)
1.915(3)
1.43(5)
Ga(2)-H
1.44(5)
Si(1)-O(1)
Si(1)-O(2)
Si(2)-O(2)
Si(2)-O(3)
O(4)-C(25)
O(5)-C(29)
Si-Cav
1.609(3)
1.620(3)
1.626(3)
1.611(3)
1.461(6)
1.462(6)
1.873(5)
O(1)-Ga(1)-O(4)
O(1)-Ga(1)-O(5)
O(4)-Ga(1)-O(5)
O(3)-Ga(2)-O(4)
O(3)-Ga(2)-O(5)
O(5)-Ga(2)-O(4)
O(1)-Ga(1)-Ga(2) 109.1(1)
O(3)-Ga(2)-Ga(1) 109.09 (9) C(25)-O(4)-Ga(2) 128.5(3)
99.1(2)
108.8(1)
105.2(2)
80.4(1)
105.3(1)
108.8(2)
80.5(1)
O(1)-Si(1)-O(2)
O(3)-Si(2)-O(2)
Si(1)-O(1)-Ga(1)
Si(2)-O(3)-Ga(2)
Si(1)-O(2)-Si(2)
Ga(1)-O(4)-Ga(2)
112.9(2)
113.2(2)
141.2(2)
141.1(2)
162.0(2)
99.5(2)
C(25)-O(4)-Ga(1) 129.2(3)
Ga(2)-O(5)-Ga(1)
C(29)-O(5)-Ga(1) 128.3(3)
C(29)-O(5)-Ga(2) 129.9(3)
O-Si-Cav
C-Si-Cav
108.2(2)
110.9(2)
F igu r e 2. Structure of gallasiloxane 2, [(OSiPh2OSiPh2-
OSiPh2O)GaH]2, from X-ray analysis (compare also caption
of Figure 1).
Compound 2
2.9108(9) Si(1)-O(1)
Ga(1)‚‚‚Ga(1)#1
Ga(1)-O(1)
Ga(1)-O(4)
Ga(1)-O(4)#1
Ga(1)-H
1.612(2)
1.640(2)
1.623(2)
1.627(2)
1.621(2)
1.657(2)
1.799(2)
1.919(2)
1.934(2)
1.38(6)
Si(1)-O(2)
Si(2)-O(2)
Si(2)-O(3)
Si(3)-O(3)
Si(3)-O(4)
Si-Cav
1.858(3)
O(1)-Ga(1)-O(4)
104.37(8) O(3)-Si(3)-O(4)
107.81(9)
132.0(1)
149.8(1)
165.6(1)
O(1)-Ga(1)-O(4)#1 104.20(8) Si(1)-O(1)-Ga(1)
O(4)-Ga(1)-O(4)#1
81.86(7) Si(2)-O(2)-Si(1)
O(1)-Ga(1)-Ga(1)#1 109.06(7) Si(3)-O(3)-Si(2)
O(1)-Si(1)-O(2)
O(2)-Si(2)-O(3)
110.01(9) Ga(1)-O(4)-Ga(1)#1 98.14(7)
110.46(9) Si(3)-O(4)-Ga(1) 131.7(1)
Si(3)-O(4)-Ga(1)#1 129.2(1)
O-Si-Cav
C-Si-Cav
108.9(1)
111.9(1)
Compound 3
2.892(1) Si(2)-O(2)
Ga(1)‚‚‚Ga(1)#1
Ga(1)-O(1)
Ga(1)-O(4)
Ga(1)-O(5)
Ga(1)-O(5)#1
Si(1)-O(1)
1.640(3)
1.617(3)
1.633(3)
1.625(3)
1.476(4)
1.869(4)
1.782(2)
1.795(2)
1.904(3)
1.894(2)
1.615(2)
1.640(3)
Si(2)-O(3)
Si(3)-O(3)
Si(3)-O(4)
O(5)-C(37)
Si-Cav
F igu r e 3. Structure of gallasiloxane 3, [(OSiPh2OSiPh2-
OSiPh2O)GaOtBu]2, from X-ray analysis (see also caption
of Figure 1).
Si(1)-O(2)
frequencies of the Ga-H bonds: 1, 2021 cm-1; (tBuO-
GaH2)2, 1906 cm-1; [(tBuO)2GaH]2, 1949 cm-1 (see also
below).
O(1)-Ga(1)-O(4)
O(1)-Ga(1)-O(5)
116.7(1) O(3)-Si(2)-O(2)
115.9(1) O(4)-Si(3)-O(3)
111.1(1)
109.5(1)
146.5(2)
144.5(2)
168.6(2)
129.1(2)
O(1)-Ga(1)-O(5)#1 110.1(1) Si(1)-O(1)-Ga(1)
The two tricyclic compounds 2 and 3, which result
from the same reaction, crystallize in a triclinic crystal
system, and both have centrosymmetric crystal sym-
metry. Although both are derived from trisiloxanes and
have central Ga2O2 rings, which originate from Lewis
acid/base interactions between gallium and oxygen, they
are nevertheless distinctly different (Figures 2 and 3).
In 2, two eight-membered Si3O4Ga rings are fused to
the central Ga2O2 ring, whereas in 3 the two eight-
membered rings are spirocyclically connected through
both gallium atoms and gallium-alkoxy bridges. The
electron deficiency at the gallium atoms is compensated
in different ways: in 2 the hydride function at gallium
is in a terminal position, forcing the weakly basic oxygen
O(4) of the siloxane ring to bond. On the other hand,
the tert-butoxy ligand at gallium in 3 is basic enough
to form the observed double bridge, the entire Si3O4Ga
rings being engaged in no further donor/acceptor bond-
ing. The central Ga2O2 ring in 2 displays bond lengths
(1.919(2) and 1.934(2) Å) which are distinctly longer
O(4)-Ga(1)-O(5)
O(4)-Ga(1)-O(5)#1 115.4(1) Si(2)-O(3)-Si(3)
O(5)#1-Ga(1)-O(5) 80.8(1) Si(3)-O(4)-Ga(1)
O(1)-Ga(1)-Ga(1)#1 120.86(8) Ga(1)#1-O(5)-Ga(1) 99.2(1)
O(4)-Ga(1)-Ga(1)#1 122.37(8) C(37)-O(5)-Ga(1)#1 128.7(2)
O(1)-Si(1)-O(2)
112.7(1) Si(2)-O(2)-Si(1)
111.2(1) C(37)-O(5)-Ga(1)
O-Si-Cav
128.4(2)
108.8(2)
110.8(2)
C-Si-Cav
(λ2-O) than at O(4) and O(5) (λ3-O). The five-membered
disiloxane bridge composed of O(1-3) and Si(1,2) is not
planar, with dihedral angles of O(3)-Si(2)-O(2)-Si(1)
) 2.78° and O(1)-Si(1)-O(2)-Si(3) ) -28.6°. The strain
within the Si2O3 bridge may be derived from O-Si-O
angles of 113.1(2)° (mean values) and Si-O-Si angles
of 141.2(2)° (O(1) and O(3)) and 162.0(2)° (for O(2)). The
hydrogen-gallium bond lengths in 1 (mean 1.43(5) Å)
are shorter than in (tBuOGaH2)2 (1.60(5) Å) or in
[(tBuO)2GaH]2 (1.53(7) Å).14 Although these bond lengths
should be discussed with caution because of the X-ray
method, they nevertheless correlate well with the IR

Cyclosiloxanes Containing a Gallium Atom
Organometallics, Vol. 21, No. 2, 2002 385
Ta ble 3. Selected Bon d Len gth s (Å) a n d Bon d
An gles (d eg) for 4 a n d 5
Compound 4
Ga(1)-O(1)
Ga(1)-O(4)
Ga(1)-N(1)
Si(1)-O(1)
Si(1)-O(2)
1.798(4)
1.820(4)
2.054(6)
1.603(4)
1.633(4)
Si(2)-O(2)
Si(2)-O(3)
Si(3)-O(3)
Si(3)-O(4)
Si-Cav
1.613(4)
1.617(4)
1.621(4)
1.585(4)
1.860(6)
O(1)-Ga(1)-O(4)
O(1)-Ga(1)-N(1)
O(4)-Ga(1)-N(1)
O(1)-Si(1)-O(2)
O(2)-Si(2)-O(3)
O(4)-Si(3)-O(3)
108.2(2)
101.3(2)
100.4(2)
110.3(2)
110.0(2)
114.3(2)
Si(1)-O(1)-Ga(1)
Si(2)-O(2)-Si(1)
Si(2)-O(3)-Si(3)
Si(3)-O(4)-Ga(1)
O-Si-Cav
133.6(2)
137.4(2)
148.6(3)
143.1(3)
108.9(2)
109.4(3)
C-Si-Cav
Compound 5
Ga(1)-O(1)
Ga(1)-O(4)
Ga(1)-O(5)
Ga(1)-O(8)
Si(1)-O(1)
Si(1)-O(2)
Si(2)-O(2)
Si(2)-O(3)
1.821(3)
1.801(3)
1.818(3)
1.860(3)
1.601(3)
1.639(4)
1.623(3)
1.615(3)
Si(3)-O(3)
Si(3)-O(4)
Si(4)-O(5)
Si(4)-O(6)
Si(5)-O(6)
Si(5)-O(7)
Si(6)-O(7)
Si(6)-O(8)
Si-Cav
1.647(3)
1.601(3)
1.589(3)
1.652(3)
1.630(3)
1.617(3)
1.622(3)
1.609(3)
1.866(5)
F igu r e 4. Structure of gallasiloxane 4, (OSiPh2OSiPh2-
OSiPh2O)Ga(H)NEt3, from X-ray analysis (see also caption
of Figure 1).
O(4)-Ga(1)-O(1)
O(5)-Ga(1)-O(1)
O(1)-Ga(1)-O(8)
O(4)-Ga(1)-O(5)
O(4)-Ga(1)-O(8)
O(5)-Ga(1)-O(8)
O(1)-Si(1)-O(2)
O(3)-Si(2)-O(2)
O(4)-Si(3)-O(3)
O(5)-Si(4)-O(6)
112.2(2)
109.6(2)
105.6(1)
109.6(2)
109.2(2)
110.8(1)
112.4(2)
111.2(2)
112.3(2)
112.5(2)
O(8)-Si(6)-O(7)
Si(1)-O(1)-Ga(1)
Si(2)-O(2)-Si(1)
Si(2)-O(3)-Si(3)
Si(3)-O(4)-Ga(1)
Si(4)-O(5)-Ga(1)
Si(5)-O(6)-Si(4)
Si(5)-O(7)-Si(6)
Si(6)-O(8)-Ga(1)
O-Si-Cav
112.3(2)
138.4(2)
143.3(2)
145.8(2)
147.2(2)
146.6(2)
132.7(2)
160.3(2)
129.9(2)
108.5(2)
110.5(2)
than those found in the four-membered Ga2O2 ring of 3
(1.904(3) and 1.894(2) Å), in accord with a less efficient
Lewis acid/base interaction in molecule 2 (Table 2). As
the electron donation to gallium in 2 is not very
effective, the Ga-H bonding should be strong: Interest-
ingly, a Ga-H bond length of 1.38(6) Å was found in
the crystal together with a high ν(Ga-H) wavenumber
of 2015 cm-1 in the IR spectrum. The Ga-H bond length
in 2 is comparable to that found in 1 and seems to be at
the lower end of Ga-H distances, which typically range
from 1.36 to 1.86 Å.26,27
The gallium-oxygen bonds not involved in Lewis
acid/base interactions in 2 (1.799(2) Å) and 3 (1.782(2),
1.795(2) Å) are comparable with respect to their bond
lengths. This is also true for the GaSi3O4 eight-
membered rings in 2 and 3, which despite the fact of
different bonding interactions have similar Si-O bond
lengths and angles at the silicon and oxygen atoms (2,
Si 107.8-110.5°, O 129.2-165.6°; 3, Si 109.5-111.2°,
O 129.1-168.6°) (see also Table 2). In comparison to 1,
which has eight-membered Si2Ga2O4 rings, the devia-
tion of bond angles at the silicon atoms from 109.5° is
less important. In both compounds the rings are se-
verely twisted, the central ring connections playing an
important part in the configurations of the rings (see
also further on).
C-Si-Cav
bonding and an important compensation of the electron
deficiency at the gallium atom. The Ga-O bond lengths
of 1.809(5) Å (mean value) are longer than the corre-
sponding Ga-λ2O bond lengths in 1-3 (see above), as
the electrophilicity of the gallium atom is reduced by
nitrogen bonding. Unfortunately, the location of the
hydrogen atom at gallium could not be determined from
difference Fourier synthesis, but the wavenumber of the
Ga-H vibration (νs 1914 cm-1) indicates a considerable
reduction of bonding strength compared to 1 and 2.
The mean Si-O bond length in the ring is found to be
1.612(4) Å, with O-Si-O angles ranging from 110 to
114.3° (see Table 3). Again, these values are similar to
those observed in the dimer 2. The less strained situ-
ation in 4, compared to 2, may be deduced from the
angles at the oxygen atoms, which range from 133.6(2)
to 148.6(3) Å and have fewer deviations from one
another (difference between extremes 15°) than in 2,
where a maximum difference of 36° is found.
In Figure 4, the structure of 4, the triethylamine
adduct of 2, is depicted. The molecular structure (see
also Table 3) consists of an eight-membered Si3GaO4
ring with phenyl substituents on the silicon atoms and
a hydride and triethylamine ligand on the gallium atom.
The molecule has no crystal symmetry, the GaSi3O4 ring
displaying an almost coplanar conformation in the Ga-
O(4)-Si(3)-O(3)-Si(2) section, while it is twisted in the
other part of the ring. The Ga(1)-N(1) bond length of
2.054(6) Å is comparatively short,28 indicating strong
Compound 5 is the only molecule in the series in
which all former ligands of [tBuOGaH2]2 have been
substituted: the gallium atom is spirocyclically con-
necting two Si3O4Ga rings and has a distorted-tetra-
hedral coordination from oxygen atoms (compare Figure
5 and Table 3). The crystal contains, besides the
spirocyclic compound, a NEt3 molecule in close proxim-
ity to the two rings of the spiro system and two THF
molecules which serve as space-fillers in the crystal
structure. The structure of the spiro system can also be
(26) Atwood, J . L.; Bott, S. G.; Elms, F. M.; J ones, C.; Raston, C. L.
Inorg. Chem. 1991, 30, 3793.
(27) Lorberth, J .; Dorn, R.; Massa, W.; Wocadlo, S. Z. Naturforsch.
1993, B48, 224.
(28) (a) Onyiriuka, E. C.; Rettig, St. J .; Storr, A.; Trotter, J . Can.
J . Chem. 1987, 65, 782. (b) Kopp, M. R.; Neumu¨ller, B. Z. Anorg. Allg.
Chem. 1999, 625, 1413.
described as a Ga3+ ion chelated by (Ph2Si)3O4 and
2-
(Ph2Si)3O3(OH)- anions. As may be deduced from in-
spection of Figure 5, the NEt3 base forms a hydrogen
bridge (N‚‚‚O found: 2.95(9) Å) to the oxygen atom

386 Organometallics, Vol. 21, No. 2, 2002
Veith et al.
replacing the organic groups by symbols. From these
representations several conclusions are obvious: the
comparatively high strain in compound 1, the different
fusions of the ring systems in 2 and 3, the structural
transformation from 3 to 4, and the asymmetry in 5
caused by the NEt3 interaction. In all molecules the
gallium atoms are placed in tetrahedral sites which are
slightly larger than those of the silicon but are compat-
ible with the structures.
Another general conclusion is depicted in Figure 7,
which is a plot of the Ga-H distances found in the X-ray
experiments (and which have of course large standard
deviations) against ν(Ga-H) values obtained from in-
frared spectra. We recognize a good correlation of the
data, which is not unexpected, as force constants and
bond lengths are mutually dependent. The plot may also
be used to approximately estimate bond distances as in
4, where the location of the hydrogen on gallium was
not possible due to the unsatisfactory crystal quality.
For 1914 cm-1 in 4 we should expect Ga-H bond
lengths of about 1.58 Å.
F igu r e 5. Structure of gallasiloxane 5, (OSiPh2OSiPh2-
OSiPh2O)2Ga‚HNEt3, from X-ray analysis. The hydrogen
atoms at the carbon atoms have been omitted for clarity
(see also caption of Figure 1).
O(8) which may be classified as long compared to other
O-H‚‚‚N bridges.1,29 In the infrared spectrum of crys-
talline 5, no absorption bands can be detected between
3050 and 3400 cm-1, which suggests a shift of the
hydrogen atom from oxygen to nitrogen. In contrast to
the recently reported6 [(Ph2Si)3O4]2Al anion, the four
corresponding gallium-oxygen bonds are found not to
be equal; the three bonds Ga-O(1,4,5) have bond
lengths of 1.801(3)-1.821(3) Å, and the fourth (Ga(1)-
O(8)) is distinctly longer (1.862(3) Å). At least in the
crystal this seems to be an indication of the hydrogen
being closer to oxygen O(8) than to nitrogen N(1);
otherwise, the Ga-O(8) bond lengthening is difficult to
understand. For Ga-O(H)-Ga bonding the reported
values are between 1.92 and 1.99 Å.30-33 For Ga-O(H)-
Si arrangements as in 5 we therefore expect values of
1.89 Å for Ga-O(H), taking into account the bond
lengths found in Al-O(H)-Si systems.1
The two eight-membered GaSi3O4 rings in 5 both
adopt twist conformations, with O-Si-O angles of
110.1-112.5° and Si-O-Si(Ga) angles of 129.5-160.3°
in the second ring (compare also Table 3). The deviation
from mean values is more pronounced in the second
ring, which is again consistent with our model, the O(8)
atom being part of a hydroxo group and therefore
inducing an asymmetry in this ring.
Exp er im en ta l Section
All compounds have been synthesized using Schlenk tech-
niques under a nitrogen atmosphere excluding oxygen and
water. Gallium(III) chloride was purchased from Aldrich;
[tBuOGaH2]2,14 (HO)Ph2SiOSiPh2(OH),15 and (HO)Ph2Si-O-
SiPh2-OSiPh2(OH)15 were prepared as described before. El-
emental analyses were obtained on a LECO CHN-900 ana-
lyzer, whereas IR spectra were recorded on a Bio-Rad FTS 165
apparatus. NMR spectra were recorded on a Bruker AC 200
F (1H, 200.1 MHz, 13C, 50.3 MHz) and a Bruker AC 200P
(29Si, 39.7 MHz) with TMS as internal and external reference,
respectively. The X-ray diffraction data for 4 were collected
on a Siemens AED 2 diffractometer using Mo KR radiation,
while those of 1-3 and 5 were obtained using a STOE IPDS
Image Plate System, again with Mo KR radiation (λ ) 0.710 69
Å). The structures have been solved with the aid of SHELXS-
97 and SHELXL-9734,35 and have been plotted using Dia-
mond.36 The hydrogen atoms bonded to carbon (phenyl,
methyl) were calculated in geometrically idealized positions
with C-H distances of 0.93 Å (phenyl) and 0.97 Å (methyl).
The hydrogen atoms bonded to gallium were found from
difference Fourier analyses, with the exception of structure
4. In 1 some tert-butyl groups are disordered around the C-O
axes, and split atom positions (50%) were used. Compound 2
crystallizes with a toluene molecule which occupies an inver-
sion center: therefore, the methyl group of this molecule is
split; the same holds for compound 3, in which the methyl
group could not be located. The crystal structure of 5 contains
two THF molecules on 2-fold axes which are randomly
distributed between these two places (50%) as well as one
phenyl group and the ethyl groups of NEt3, which show
statistical disorder.
Besides the molecular descriptions of structures 1-5,
there also is an alternative way of representation and
discussion of the structures that may be used which is
familiar to solid state chemistry and which is shown in
Figure 6. Here we represent the coordination polyhedra
around gallium and silicon, neglecting in a first ap-
proximation the nature of the ligand (O, C, or H) and
[HGa OtBu ]2(P h 2SiO)2O (1). To 0.602 g (2.08 mmol) of
[GaH2OtBu]2 in 20 mL of diethyl ether at room temperature
was added a solution of 0.861 g (2.08 mmol) of (Ph2SiOH)2O
in 20 mL of diethyl ether with stirring. Immediate evolution
of hydrogen took place, and after a while a colorless precipitate
formed. After 1 h the solid precipitate was separated by
filtration and the solution was concentrated until crystals
(29) Huheey, J .; Keiter, E.; Keiter, R. Anorganische Chemie, 2nd
ed.; Walter de Gruyter: Berlin, New York, 1995. This book is a German
translation and expansion of: Huheey, J . E. Inorganic Chemistry,
Principles of Structure and Reactivity; Harper and Row: New York,
1983.
formed. Yield: 0.92 g (63%) of [HGaOtBu]2(Ph2SiO)2O (1). H
1
(30) Linti, G.; Ko¨stler, W. Chem. Eur. J . 1998, 4, 942.
(31) Rendle, D. F.; Storr, A.; Trotter, J . Can. J . Chem. 1975, 53,
2944.
(32) Storre, J .; Klemp, A.; Roesky, H. W.; Schmidt, H. G.; Nolte-
meyer, M.; Fleischer, R.; Stalke, D. J . Am. Chem. Soc. 1996, 118, 1380.
(33) Schnitter, C.; Roesky, H. W.; Albers, T.; Schmidt, H. G.;
Ro¨pken, C.; Parisini, E.; Sheldrick, G. M. Chem. Eur. J . 1997, 3, 1783.
(34) Sheldrick, G. M. SHELXS-86 Program for Crystal Structure
Solution; University of Go¨ttingen, Go¨ttingen, Germany, 1986.
(35) Sheldrick G. M. SHELXL-97 Program for Crystal Structure
Refinement; University of Go¨ttingen, Go¨ttingen, Germany, 1997.
(36) Brandenburg, K. Diamond 2.1, Copyright Crystal Impact GbR,
Germany.

Cyclosiloxanes Containing a Gallium Atom
Organometallics, Vol. 21, No. 2, 2002 387
F igu r e 6. Structures of molecules 1-5 using tetrahedra around silicon (simple hatching) or gallium (double hatching).
The corners of these tetrahedra are occupied by O (oxygen), Ph (phenyl), H (hydrogen), or NEt3 (triethylamine).
NMR: δ 1.13 (s, 18 H, C-(CH3)3); 5.35 (broad s, 2H, Ga-H);
7.20 (m, 12 H, m-, p-H phenyl); 7.63 (m, 8H, o-H phenyl). 13C
NMR: δ 31.60 (s, 6 C, C(CH3)3); 77.18 (s, 2 C, C(CH3)3); 127.8
(s, 8 C, m-C phenyl); 129.5 (s, 4 C, p-C phenyl); 135.0 (s, 8 C,
o-C phenyl); 139.6 (s, 4 C, Si-C phenyl); 29Si NMR: δ -45.7.
IR: ν 2021 cm-1 (Ga-H). Anal. Calcd for C32H40Ga2O5Si2
(700.29): C, 54.88; H, 5.76. Found: C, 54.46; H, 5.71.
Syn th esis of [Ga H(P h 2SiO)3O]2 (2) a n d [Ga (OtBu )-
(P h 2SiO)3O]2 (3). To 0.582 g (2.01 mmol) of [GaH2OtBu]2 in
50 mL of diethyl ether at room temperature was added a
solution of 1.660 g (4.04 mmol) of (Ph2SiOH)2O in 50 mL of
diethyl ether with stirring. After 15 min of steady hydrogen
evolution a precipitate was formed. The suspension was stirred
for another 12 h and the solid residue separated from the
solution by filtration. The colorless solid was analyzed as 2
and was recrystallized from a 50 °C warm toluene solution
for X-ray purposes. The remaining solution was concentrated
under reduced pressure until a voluminous residue formed.
The residue was redissolved in a 1:1 mixture of toluene and
diethyl ether, from which crystals of 3 were obtained.
Data for 2 are as follows. Yield: 0.98 g (36%). 1H NMR
(THF): δ 2.13 (s, 3H, C6H5-CH3), 4.9 (broad, 2 H, Ga-H), 7.15
(m, 41 H, m-, p-H phenyl, toluene), 7.6 (m, 24 H, o-H phenyl);
13C NMR (THF): δ 21.3 (s, 1 C, C6H5-CH3), 125.6 (s, 1 C,
toluene), 127.7 (s, 16 C, m-C phenyl), 127.8 (s, 8C, m-C phenyl),
128.5 (s, 2 C, toluene), 129.3 (s, 2 C, toluene), 129.4 (s, 8C p-C
phenyl), 129.8 (s, 4C, p-C phenyl), 134.7 (s, 24 C, o-C phenyl),
136.9 (s, 4 C, Si-C phenyl), 137.7 (s, 1 C, toluene), 138.8 (s, 8
C, Si-C phenyl); 29Si NMR: δ -45.7 (s, 4 Si), -43.9 (s, 2 Si).
IR: ν 2015 cm-1 (Ga-H). Anal. Calcd for C79H70Ga2O8Si6

388 Organometallics, Vol. 21, No. 2, 2002
Veith et al.
47.41 (s, 3 C, N-(CH2CH3)3), 127.8 (s, 8 C, m-C phenyl), 127.9
(s, 4 C, m-C phenyl), 129.4 (s, 4 C, p-C phenyl), 129.9 (s, 2 C,
p-C phenyl), 134.7 (s, 8 C, o-C phenyl), 134.8 (s, 4 C, o-C
phenyl), 137.0 (s, 2 C, Si-C), 139.2 (s, 4 C, Si-C). 29Si NMR:
-1
δ -45.8 (s, 1 Si), -43.9 (s, 2 Si). IR: ν 1914 cm
(Ga-H).
Anal. Calcd for C42H46GaNO4Si3 (782.82): C, 64.44; H, 5.92;
N, 1.79. Found: C, 64.94; H, 5.87; N, 1.79.
Ga [(P h 2SiO)3O][(P h 2SiO)3OH]‚NEt3 (5). (a) To a solution
of 0.168 g (0.58 mmol) of [GaH2OtBu]2 in 10 mL of diethyl ether
was added a solution of 1.42 g (2.32 mmol) of HO(Ph2SiO)3OH
in 10 mL of diethyl ether dropwise with stirring. Hydrogen
evolution as well as precipitation of a colorless solid was
observed. After 12 h of stirring 5 mL of triethylamine in 10
mL of THF was added, which dissolved the entire precipitate.
When the solution was concentrated, colorless crystals of 5
were obtained. Yield: 0.95 g (59%).
(b) To a solution of 0.552 g (0.40 mmol) of 2 in 10 mL of
THF was added 2.0 mL (0.81 mmol) of a THF/water mixture
(from 0.146 g of H2O in 20 mL of THF) dropwise and stirred
overnight. Five milliliters of triethylamine was finally used,
and the solution was concentrated to obtain colorless crystals
of 5. Yield: 0.46 g (75%).
F igu r e 7. Correlation of Ga-H (100 × Å) distances and
ν(Ga-H) (cm-1) in compounds 1 and 2 compared to
t-BuOGaH2 and (tBuO)2GaH.14
(1455.38; 2‚(toluene)): C, 65.20; H, 4.85. Found: C, 64.89; H,
4.79.
1H NMR (THF): δ 0.41 (t, 9 H, N-(CH2CH3)3), 2.09 (q, 6H,
N-(CH2CH3)3), 7.1 (m, 36 H, m-, p-H phenyl), 7.59 (m, 24 H,
o-H phenyl). 13C NMR (THF): δ 8.50 (s, 3 C N-(CH2CH3), 45.9
(s, 3 C, N-(CH2CH3)3), 127.4 (s, 16 C, m-C phenyl), 127.6 (s,
8 C, m-C phenyl), 128.9 (s, 8 C, p-C phenyl), 129.5 (s, 4 C, p-C
phenyl), 134.9 (s, 8 C, o-C phenyl), 135.3 (s, 16 C, o-C phenyl),
137.2 (s, 4 C, Si-C), 139.3 (s, 8 C, Si-C). 29Si NMR: δ -45.6
(s, 2 Si), -43.8 (s, 4 Si). IR: ν 2710 cm-1 (Et3N‚‚‚H‚‚‚O-). Anal.
Calcd for C86H92GaNO10Si6 (1537.89; 5‚2THF): C, 67.16; H,
6.03; N, 0.81. Found: C, 66.82; H, 6.18; N, 0.91.
Data for 3 are as follows. Yield: 0.75 g (25%) 1H NMR
(dioxane): δ 1.14 (s, 18 H, C-(CH3)3), 2.13 (s, 3H, C6H5-CH3),
7.1 (m, 41 H, m-, p-H phenyl, toluene), 7.55 (m, 24 H, o-H
phenyl). 13C NMR (dioxane): δ 21.3 (s, 1 C, C6H5-CH3), 31.6
ppm (s, 6 C, C(CH3)3), 78.3 (s, 2 C, C(CH3)3), 125.6 (s, 1 C,
toluene), 128.1 (s, 16 C, m-C phenyl), 128.5 (s, 2 C, toluene),
128.8 (s, 8 C, m-C phenyl), 129.3 (s, 2 C, toluene), 129.9 (s, 8
C, p-C phenyl), 130.2 (s, 4 C, p-C phenyl), 134.8 (s, 8 C, o-C
phenyl), 135.0 (s, 16 C, o-C phenyl), 136.2 (s, 4 C, Si-C), 137.5
(s, 8 C, Si-C), 137.7 (s, 1 C, toluene). 29Si NMR: δ -46.1 (s, 2
Si), -42.2 (s, 4 Si). Anal. Calcd for C87H86Ga2O10Si6 (1599.59;
3‚(toluene)): C, 65.33; H, 5.41. Found: C, 65.02; H, 5.51.
The same products in comparable yields formed when (Ph2-
SiOH)2O was replaced by (Ph2SiOH)2(OSiPh2O) (4.04 mmol),
which was verified explicitly for 2.
Ga H(P h 2SiO)3O‚NEt3 (4). A 0.480 g (0.35 mmol) amount
of 2 was dissolved in 10 mL of THF, and 10 mL of triethy-
lamine was added. The solvent and the large excess of NEt3
were removed after 2 h at reduced pressure (10-2 atm). The
oily, voluminous residue was redissolved in diethyl ether, from
which, after concentration, colorless crystals of 4 formed.
Yield: 0.39 g (71%). 1H NMR (dioxane): δ 0.9 (broad, 9 H,
N-(CH2CH3)3), 2.6 (broad, 6 H, N-(CH2CH3)3), 4.85 (broad, 1
H, Ga-H), 7.17 (m, 18 H, m-, p-H phenyl), 7.6 (m, 12 H, o-H
phenyl). 13C NMR (dioxane): δ 9.26 (s, 3 C, N-(CH2CH3)3),
Ack n ow led gm en t. We thank the DFG for support-
ing this work in the framework of the Schwerpunkt
“Spezifische Pha¨nomene in der Silicium-Chemie” and
the Fonds der Chemischen Industrie for financial sup-
port.
Su p p or tin g In for m a tion Ava ila ble: Further details of
the crystal structure determination, including tables of bond
lengths, bond angles, and anisotropic and isotropic displace-
ment parameters. This material is available free of charge via
the Internet at http://pubs.acs.org.
OM010544P