Preparation of monomeric LGa(NH2)2 and of LGa(OH)2 in the presence of a n-heterocyclic carbene as HCl acceptor

Article abstract of DOI:10.1021/om049304a

The reactions of LGaCl₂ (L = HC[C(Me)N(Ar)l₂, Ar = 2,6-iPr₂C₆H₃) with NH₃ and H ₂O, respectively, in the presence of a 1,3-bis-tert-butylimidazol-2- ylidene (N-heterocyclic carbene) as acceptor for the HCl lead to unique species of composition LGa(NH₂)₂ and LGa(OH)₂ in high yields under mild conditions. LGa(NH₂)₂ is the first known monomeric diamide of gallium.

Full text of DOI:10.1021/om049304a

Organometallics 2005, 24, 1511-1515
1511
Preparation of Monomeric LGa(NH2)2 and of LGa(OH)2
in the Presence of a N-Heterocyclic Carbene as HCl
Acceptor
Vojtech Jancik, Leslie W. Pineda, A. Claudia Stu¨ckl, Herbert W. Roesky,* and
Regine Herbst-Irmer
Institut fu¨r Anorganische Chemie der Georg-August-Universita¨t Go¨ttingen,
Tammannstrasse 4, D-37077 Go¨ttingen, Germany
Received September 7, 2004
The reactions of LGaCl2 (L ) HC[C(Me)N(Ar)]2, Ar ) 2,6-iPr2C6H3) with NH3 and H2O,
respectively, in the presence of a 1,3-bis-tert-butylimidazol-2-ylidene (N-heterocyclic carbene)
as acceptor for the HCl lead to unique species of composition LGa(NH2)2 and LGa(OH)2 in
high yields under mild conditions. LGa(NH2)2 is the first known monomeric diamide of
gallium.
Introduction
et al. reported the preparation of the first gallium
dihydroxide containing two terminal OH groups stabi-
lized by a bulky pincer type ligand from the correspond-
ing dihydride and water.14 Its surprising stability is
demonstrated by the presence of 10 equiv of water in
the crystal lattice.
Recently we have shown the possibility of preparing
unique species such as LAl(OH)2, LAl(NH2)2,1 and LGe-
(OH)2 (L ) HC[C(Me)N(Ar)]2, Ar ) 2,6-iPr2C6H3) from
the corresponding metal chlorides3,4 and H2O and NH3,
respectively, by means of different N-heterocyclic car-
benes as HCl acceptors. We became interested in using
this method for other metal halides to generate similar
species. Compounds containing two NH2 groups on one
gallium are not known. Up to date there are known only
five gallium amides containing one NH2 group on each
Results and Disscussion
A cold toluene solution (-25 °C) of 1,3-bis-tert-
butylimidazol-2-ylidene19 saturated by gaseous NH3 was
3
slowly added to a toluene solution of LGaCl2 at -35
5
gallium atom, dimeric [(Me3CCH2)2GaNH2]2 and tri-
°C. Warming the solution to ambient temperature
resulted in the formation of a slurry of 1,3-bis-tert-
butylimidazoyl chloride. After filtration, removal of all
the volatiles in vacuo, and recrystallization from pen-
tane, colorless microcrystalline LGa(NH2)2 (1) was
isolated in 70% yield. Furthermore, LGa(OH)2 (2) is the
only product isolated in 80% yield from the reaction
between a toluene solution of LGaCl2 and 1,3-bis-tert-
butylimidazol-2-ylidene in a 1:2 molar ratio with 2 equiv
of H2O at -5 °C. These results confirmed our expecta-
tions that the carbene NH3/H2O system offers interest-
ing synthetic possibilities also for gallium. As we
mentioned earlier,1 preparation of such species is prob-
lematic and very often leads to condensed products, if
protic byproducts are not properly trapped (e.g., HCl,
NR3H+X-).20 Thus, most of these products were pre-
pared by elimination of small nonprotic molecules such
as H2, alkanes, or weak acids (dialkylamines, etc.).20 The
almost irreversible bonding of the free protons to the
mers (R2GaNH2)3 (R ) H,6,7 Me,8,9 Et,10 and tBu11), but
only the (Me2GaNH2)3 and (tBu2GaNH2)3 have been
structurally characterized. Compared to the amides, the
chemistry of gallium hydroxides is much more explored;
numerous examples of species containing bridging OH
groups are known, and also several examples with
terminal ones have been described.11-18 In 1994 Atwood
* To whom correspondence should be addressed. Fax: (+49) 551-
39-3373. E-mail: hroesky@gwdg.de.
(1) Jancik, V.; Pineda, L. W.; Pinkas, J.; Roesky, H. W.; Neculai,
D.; Neculai, A. M.; Herbst-Irmer, R. Angew. Chem. 2004, 116, 2194-
2107; Angew. Chem., Int. Ed. 2004, 43, 2142-2145.
(2) Pineda, L. W.; Jancik, V.; Roesky, H. W.; Neculai, D.; Neculai,
A. M. Angew. Chem. 2004, 116, 1443-1445; Angew. Chem., Int. Ed.
2004, 43, 1419-1421.
(3) Prust, J.; Roesky, H. W.; Stender, M.; Eichler, B. E.; Hardman,
N. J.; Power, P. P. Inorg. Chem. 2001, 40, 2794-2799.
(4) Ding, Y.; Roesky, H. W.; Noltemeyer, M.; Schmidt, H.-G. Orga-
nometallics 2001, 20, 510-515.
(5) Beachley, O. T., Jr.; Pazik, J. C.; Noble, M. J. Organometallics
1998, 17, 2121-2123.
(6) Hwang, J.-W.; Hanson, S. A.; Britton, D.; Evans, J. F.; Jensen,
K. F.; Gladfelter, W. L. Chem. Mater. 1990, 2, 342-343.
(7) Hwang, J.-W.; Campbell, J. P.; Kozubowski, J.; Hanson, S. A.;
Evans, J. F.; Gladfelter, W. L. Chem. Mater. 1995, 7, 517-525.
(8) Almond, M. J.; Drew, M. G. B.; Jenkins, C. E.; Rice, D. A. J.
Chem. Soc., Dalton Trans. 1992, 5-9.
(14) Cowley, A. H.; Gabba¨ı, F.; Atwood, D. A. J. Am. Chem. Soc.
1994, 116, 1559-1560.
(15) Schnitter, C.; Roesky, H. W.; Albers, T.; Schmidt, H.-G.; Ro¨pken,
C.; Parsini, E.; Sheldrick, G. M. Chem. Eur. J. 1997, 3, 1783-1792.
(16) Linti, G.; Frey, R.; Ko¨stler, W.; Urban, H. Chem. Ber. 1996,
129, 561-569.
(9) Sengupta, D. J. Phys. Chem. B 2003, 107, 291-297.
(10) Park, H. S.; Waezsada, S. D.; Cowley, A. H.; Roesky, H. W.
Chem. Mater. 1998, 10, 2251-2257.
(17) Rettig, S. J.; Sandercock, M.; Storr, A.; Trotter, J. Can. J. Chem.
1990, 68, 59-63.
(11) Atwood, D. A.; Cowley, A. H.; Harris, P. R.; Jones, R. A.;
Koschmieder, S. U.; Nunn, C. M.; Atwood, J. L.; Bott, S. G. Organo-
metallics 1993, 12, 24-29.
(18) Linti, G.; Ko¨stler, W. Chem. Eur. J. 1998, 4, 942-949.
(19) Arduengo, A. J., III; Bock, H.; Chen, H.; Denk, M.; Dixon, D.
A.; Green, J. C.; Herrmann, W. A.; Jones, N. L.; Wagner, M.; West, R.
J. Am. Chem. Soc. 1994, 116, 6641-6649.
(12) Some examples of gallium hydroxides are listed in refs 22-29.
(13) Smith, G. S.; Hoard, J. L. J. Am. Chem. Soc. 1959, 81, 3907-
3910.
(20) Reference 1 and references therein.
10.1021/om049304a CCC: $30.25 © 2005 American Chemical Society
Publication on Web 02/24/2005

1512 Organometallics, Vol. 24, No. 7, 2005
Jancik et al.
Table 1. Crystallographic Data for Compounds 1
Scheme 1. Synthesis of Compounds 1 and 2
and 2‚0.5Toluene
1
2‚0.5toluene
formula
fw
cryst syst
temp, K
λ, Å
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C
29H45GaN4
C32.50H47GaN2O2
567.44
triclinic
100
1.54178
P1h
519.41
monoclinic
100
1.54178
P21/c
17.016(1)
13.101(1)
13.494(1)
13.332(1)
14.432(1)
18.190(1)
99.08(1)
95.01(1)
114.00(1)
3112(1)
4
109.14(1)
2842(1)
4
1.214
1.481
1112
Z
F
calcld, g/cm3
1.211
carbene results in high yields of the unique species 1
and 2. Scheme 1 summarizes the reaction for preparing
1 and 2.
µ, mm-1
F(000)
1.426
1212
cryst size, mm3
θ range for data
collection, deg
index ranges
0.10 × 0.05 × 0.05 0.30 × 0.20 × 0.20
In analogy with the aluminum derivative, 2 forms a
dimer, whereas 1 is strictly monomeric in both solid
state and solution as proved by X-ray structural analysis
and IR spectroscopy. Both compounds are thermally
stable and do not decompose even upon heating to 70
°C in a sealed tube as determined by temperature-
dependent 1H NMR spectroscopy and MS spectrometry.
Compound 1 is very sensitive toward moisture and
hydrolyzes rapidly under formation of NH3 and LGa-
(NH2)(OH). The hydrolysis occurs slowly even in a
glovebox with water levels below 0.2 ppm and during
any manipulation of the sample. Further hydrolysis of
LGa(NH2)(OH) leads to 2 in a quantitative yield as
2.75 to 58.93
2.50 to 58.98
-17 e h e 18
-14 e k e 13
-14 e l e 13
12 292
4002 (0.0392)
4002/6/336
-14 e h e 14
-15 e k e 15
-19 e l e 19
23 915
8679 (0.0299)
8679/10/726
no. of reflns collected
no. of indep reflns (Rint
no. of data/restraints/
params
)
GoF on F2
1.035
0.0282, 0.0722
0.0320, 0.0745
1.030
R1,a wR2b (I > 2σ(I))
R1,a wR2b (all data)
extinction coeff
largest diff peak/hole,
e‚Å-3
0.0261, 0.0678
0.0274, 0.0687
0.00018(6)
0.226/-0.285
0.274/-0.368
2
2
a R ) ∑||Fo| - |Fc||/∑|Fo|. b wR2 ) [∑w(Fo - Fc )2/∑w(Fo2)]1/2
.
1
proved by H NMR spectroscopy. The LGa(NH2)(OH)
has a solubility similar to that of the diamide; therefore
it is necessary to work carefully under strictly moisture-
free conditions to obtain pure 1 (more than 95% content
of 1). Compound 1 often contains 3-5% of LGa(NH2)-
1
(OH) as shown by H NMR spectroscopy (Figure S1 in
the Supporting Information). Nevertheless, pure 1 can
be obtained using a closed vacuum line equipped with
Teflon Swagelock fittings for the condensation of the
solvent and NH3(l) to the reagents. The reaction flask
should be equipped with Teflon Young valves and
treated prior to use with Me3SiCl to eliminate free OH
groups on the glass surface. So far, we have not been
successful in isolating the LGa(NH2)(OH).
Single crystals of 1 were obtained by storing its
saturated pentane solution at -32 °C. Compound 1
crystallizes in the monoclinic space group P21/c with one
molecule in the asymmetric unit (Table 1) and is
isostructural to the Al homologue1 (Figure 1).
Figure 1. Thermal ellipsoid plot of 1 showing the 50%
probability level. H atoms, except N-H, are omitted for
clarity.
Compound 1 is a discrete monomer in the solid state
with no observable hydrogen bonding. The GaN4 core
possesses a distorted tetrahedral geometry with the
smallest and largest N-Ga-N angle of 95.4° and 118.5°,
respectively. The N(1)-Ga(1)-N(2) angle (95.4°) within
the six-membered ring is in the normal range, whereas
the N(3)-Ga(1)-N(4) angle (111.8°) is significantly
larger than those in the trimeric cyclic species ([(Me2-
GaNH2)3] and [(tBu2GaNH2)3] 93.8-105.6°).8,9,11 This
difference is obviously due to the monomeric nature of
1, thus, avoiding the characteristic ring strain of the
cyclic congeners. As expected, the endocyclic Ga(1)-N(l)
and Ga(1)-N(2) bond lengths (1.955, 1.976 Å) are
significantly longer than the exocyclic ones (Ga(1)-N(3)
and Ga(1)-N(4) 1.852, 1.847 Å). The latter values
represent the shortest bond lengths for Ga-NH2 moi-
eties so far known (compared with 1.928-2.053 Å in
[(Me2GaNH2)3] and [(tBu2GaNH2)3]).8,9,11 A similar phe-
nomenon has also been observed for the Al analogue.
The hydrogen atoms of the NH2 groups were localized
in the difference electron density map, and the N-H
bond lengths (0.81, 0.81, 0.82, and 0.82 Å) are shorter
than those in [(Me2GaNH2)3] (0.95 Å) and [(tBu2-
GaNH2)3] (1.05 Å), but comparable to those in LAl(NH2)2
(0.85-0.88 Å).1,8,9,11 Selected bond lengths and angles
for 1 are listed in Table 2.
Although 1 is isostructural with the Al analogue, it
reveals one significant difference: the geometry of the

Preparation of Monomeric LGa(NH2)2
Organometallics, Vol. 24, No. 7, 2005 1513
Table 2. Selected Bond Lengths (Å) and Angles
(deg) for Compound 1
Ga(1)-N(1)
Ga(1)-N(2)
N(3)-H(1)
N(3)-H(2)
1.955(2)
1.976(2)
0.81(2)
0.81(2)
Ga(1)-N(3)
Ga(1)-N(4)
N(4)-H(3)
N(4)-H(4)
1.852(2)
1.847(2)
0.82(1)
0.82(2)
N(1)-Ga(1)-N(2)
N(1)-Ga(1)-N(3)
N(1)-Ga(1)-N(4)
H(3′)-N(3)-H(3′′)
H(3′)-N(3)-Ga(1)
95.4(1) N(2)-Ga(1)-N(3)
116.5(1) N(2)-Ga(1)-N(4)
107.8(1) N(3)-Ga(1)-N(4)
106.4(1)
118.5(1)
111.8(1)
112(3)
108(3)
114(2)
H(4′)-N(4)-H(4′′)
H(4′)-N(4)-Ga(1)
115(2)
H(3′′)-N(3)-Ga(1) 115(2)
H(4′′)-N(4)-Ga(1) 117(2)
NH2 groups in LAl(NH2)2 is almost planar with a sum
of angles of 357(2)° and 356(2)°1 compared to those in 1
(sum of angles 337(2)° and 344(2)°). We carried out DFT
calculations on both LAl(NH2)2 and LGa(NH2)2 with the
program DMOL.21 The isosurfaces at 0.05 e‚Å-3 of the
HOMO orbitals show that the electron density is mainly
localized at the N atom of the NH2 groups of both LAl-
(NH2)2 and LGa(NH2)2 (Figures S2, S3 in the Supporting
Information). The LUMOs are constructed from π-orbit-
als of the â-diketiminato ligand. To save calculation
time, several models can be used. We obtained the best
model by replacing the aryl groups at the nitrogen
atoms by phenyl groups, because in such a model all
the interactions between the π-orbitals of the phenyl
rings with the ligand backbone contribute to the proper
symmetry of the HOMO orbital of the ligand. However,
due to omitting the iPr moieties, the optimized calcula-
tion led to planar C3N2M rings. Hence, the coordinates
of the metal and the adjacent nitrogen atoms were fixed
at the positions given by the experiment, and the
optimization was performed for the bonding distances
and angles between metal and nitrogen atoms as well
as within the NH2 groups (Figures S4, S5 in the
Supporting Information). The results show that the
most stable conformation for LAl(NH2)2 has the NH2
groups slightly twisted toward each other to allow the
overlap of the free orbitals on the nitrogen atoms in the
HOMO orbital. Similar stabilization can be found in the
Ga derivative, with the difference that the NH2 groups
need to “bend” to allow similar overlap, mainly due to
the longer endocyclic Ga-N bonds and thus larger
distance between the corresponding nitrogen atoms.
This results in planar NH2 groups in LAl(NH2)2 (both
sums of angles 360(1)°), whereas they are almost
tetrahedral in LGa(NH2)2 with the sum of angles of 339-
(1)° and 335(1)°, respectively. The results are in a good
agreement with the experiment (see above). Further-
more, we could observe partial contribution of the
d-orbitals of gallium to the HOMO orbital, whereas
there is no metal orbital contribution in the aluminum
case (Figure S6 in the Supporting Information).
Figure 2. Thermal ellipsoid plot of dimer A of 2 showing
the 50% probability level. H atoms, except O-H, are omitted
for clarity.
Figure 3. Thermal ellipsoid plot of dimer B of 2 showing
the 50% probability level. H atoms, except O-H, are omitted
for clarity. The hydrogen atoms bonded to O(2A) and
O(2AA) are disordered within two positions with equal
occupancy factors.
obtain data of satisfactory quality for the monoclinic
form. The triclinic form contains two independent
molecules of 2 and one molecule of toluene in the
asymmetric unit (Table 1). Different positions of these
molecules toward the inversion centers result in the
formation of two dimers contrasting in the number and
kind of hydrogen bonds between the OH units. Dimer
A is formed by only two equivalent hydrogen bonds
O(1)‚‚‚H(2)-O(2) (O‚‚‚H 2.01 Å, O-H-O angle 174°)
having still two free terminal hydrogen atoms H(1) (of
the OH moieties) (Figure 2), whereas in dimer B there
are two incompatible O‚‚‚H interactions (Figure 3).
The first is similar to that in A, O(2A)‚‚‚H(1′)-O(1A)
(O‚‚‚H 2.51 Å, O-H-O angle 159°), and the second is
formed by two oxygen atoms equivalent by symmetry.
Triclinic single crystals of 2 suitable for X-ray struc-
tural analysis were obtained by keeping its saturated
toluene solution at -30 °C. The colorless blocks of 2
crystallize in the space group P1h and spontaneously
fracture when exposed to temperatures above -5 °C.
This is due to an irreversible phase change into a
monoclinic form under elimination of toluene and
crystallizing in the space group P21/n with one molecule
of 2 in the asymmetric unit. Unfortunately, due to the
high disorder of the molecules, we were not able to
(21) Delley, B. J. Chem. Phys. 1990, 92, 508-517.

1514 Organometallics, Vol. 24, No. 7, 2005
Jancik et al.
Table 3. Selected Bond Lengths (Å) and Angles
oil bubbler attached to the flask. The precipitate was filtered
off and washed twice with toluene (10 mL), and all the volatiles
were removed in vacuo. The oily residue was treated twice with
cold pentane (5 mL), and after filtration and drying in vacuo,
1 was obtained as a white microcrystalline powder: yield 0.78
(deg) for Compound 2‚0.5Toluene
Molecule 1
Ga(1)-N(1)
1.931(1)
1.938(1)
1.820(1)
98.0(1)
110.6(1)
112.0(1)
107.0(1)
Ga(1)-O(2)
1.777(1)
0.72(2)
0.74(2)
112.6(1)
115.3(1)
114(2)
Ga(1)-N(2)
O(1)-H(1)
g (70%); mp 175 °C (dec); 1H NMR (500 MHz, C6D6, 25 °C,
Ga(1)-O(1)
O(2)-H(2)
3
N(1)-Ga(1)-N(2)
N(1)-Ga(1)-O(1)
N(1)-Ga(1)-O(2)
N(2)-Ga(1)-O(1)
N(2)-Ga(1)-O(2)
O(1)-Ga(1)-O(2)
H(1)-O(1)-Ga(1)
H(2)-O(2)-Ga(1)
TMS) δ -0.58 (brs, JN-H ) 65 Hz, 4H, NH2), 1.16 (d, JH-H
)
3
6.9 Hz, 12H, CH(CH3)2), 1.37 (d, JH-H ) 6.9 Hz, 12H, CH-
3
(CH3)2), 1.60 (s, 6H, CH3), 3.49 (sept, JH-H ) 6.9 Hz, 4H,
113(2)
CH(CH3)2), 4.76 (s, 1H, γ-CH), 7.05-7.10 ppm (m, 6H, m, p-Ar-
H); 13C NMR (125.8 MHz, C6D6, 25 °C, TMS) δ 23.5, 24.8 (CH-
(CH3)2), 25.3 (CH(CH3)2), 28.4 (CH3), 95.1 (γ-CH), 124.3, 126.9,
141.3, 144.3 (i, o, m, p-C of Ar), 168.6 ppm (CdN); IR (KBr
pellet) ν˜ 3438 vw, 3359 vw (NH) cm-1; EI-MS (70 eV) m/z (%)
518 (8) [M+], 501 (60) [M+ - NH3], 486 (100) [M+ - 2NH2]. An
elemental analysis did not give satisfactory results for nitrogen
content due to the very high reactivity of 1 toward moisture
and thus partial replacement of the NH2 groups by OH
moieties. This replacement has nearly no influence on the
carbon and hydrogen content due to the similar molecular
mass of the NH2 and OH groups.
Molecule 2
Ga(1A)-N(1A)
Ga(1A)-N(2A)
Ga(1A)-O(1A)
Ga(1A)-O(2A)
1.933(1) O(1A)-H(1′)
1.933(1) O(2A)-H(2′)
1.801(1) O(2A)-H(2′′)
1.819(1)
0.72(2)
0.74(2)
0.73(2)
N(1A)-Ga(1A)-N(2A) 98.3(1) O(1A)-Ga(1A)-O(2A) 111.5(1)
N(1A)-Ga(1A)-O(1A) 112.3(1) H(1′)-O(1A)-Ga(1A) 105(2)
N(1A)-Ga(1A)-O(2A) 110.9(1) H(2′)-O(2A)-Ga(1A) 98(4)
N(2A)-Ga(1A)-O(1A) 114.2(1) H(2′′)-O(2A)-Ga(1A) 113(6)
N(2A)-Ga(1A)-O(2A) 109.0(1)
Therefore, the hydrogen atoms of these OH groups are
disordered into two positions with equal occupancy
factors. The O(2A)‚‚‚H(2′)-O(2A) hydrogen bond is
shorter than the previous one with an O‚‚‚H distance
of 2.09 Å and O-H-O angle of 174°, whereas H(2′′)
remains terminal. The Ga-O bond lengths vary (1.777-
1.820 Å) and are affected by the O‚‚‚H interactions.
However, they are very similar to those in [{2,6-(Me2-
NCH2)2C6H3}Ga(OH)2]3‚10H2O (1.81-1.83 Å)14 and are
shorter than those in the bridged hydroxides [tBu2Ga-
(µ-OH)]3 (1.96 Å)10 and [Me2Ga(µ-OH)]4 (1.94-1.99 Å).13
Selected bond lengths and angles for 2 are listed in
Table 3.
Synthesis of LGa(OH)2 (2). H2O (97 µL, 5.374 mmol) was
added quickly to a solution of LGaCl2 (1.500 g, 2.687 mmol)
and 1,3-bis-tert-butylimidazol-2-ylidene (1.017 g, 5.642 mmol)
in toluene (45 mL) cooled to -5 °C. Immediately after the
addition of water, a slurry of the 1,3-bis-tert-butylimidazolium
chloride was formed. The suspension was vigorously stirred
for an additional 10 min and filtered. The precipitate was
washed twice with toluene (5 mL), and all the volatiles were
removed in vacuo. The solid residue was treated twice with
cold pentane (5 mL), and after filtration and drying in vacuo,
2 was obtained as a white powder: yield 1.12 g (80%); mp 200
1
°C (dec); H NMR (200 MHz, C6D6, 25 °C, TMS) δ -0.27 (s,
3
2H, OH), 1.14 (d, JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.43 (d,
3JH-H ) 6.8 Hz, 12H, CH(CH3)2), 1.57 (s, 6H, CH3), 3.45 (sept,
3JH-H ) 6.8 Hz, 4H, CH(CH3)2), 4.79 (s, 1H, γ-CH), 7.04-7.10
ppm (m, 6H, m, p-Ar-H); 13C NMR (125.77 MHz, C6D6, 25 °C,
TMS) δ 23.3, 24.8 (CH(CH3)2), 25.0 (CH(CH3)2), 28.4 (CH3),
95.1 (γ-CH), 124.5, 127.5, 139.9, 144.6 (i, o, m, p-C of Ar), 170.1
ppm (CdN); IR (KBr pellet) ν˜ 3465 wbr (OH) cm-1; EI-MS (70
eV) m/z (%) 520 (5) [M+], 502 (22) [M+ - H2O], 487 (100)
[M+ - H2O - CH3]. Anal. Calcd (%) for C29H43GaN2O2
(521.39): C, 66.7; H, 8.2; N, 5.4. Found: C, 66.8; H, 8.3; N,
5.4.
Experimental Section
General Procedures. All reactions and handling of re-
agents were performed under an atmosphere of dry nitrogen
or argon using Schlenk techniques or a glovebox where the
O2 and H2O levels were usually kept below 1 ppm. All
glassware was oven-dried at 140 °C for at least 24 h, assembled
hot, and cooled under high vacuum prior to use. Gaseous NH3
(Messer) was purified by passing through drying tubes filled
Crystal Structure Determination. Data for the struc-
tures 1 and 2 were collected on a Bruker three-circle diffrac-
tometer equipped with a SMART 6000 CCD detector. The
structure was solved by direct methods (SHELXS-97)22 and
refined with all data by full-matrix least-squares on F2.23 The
hydrogen atoms of C-H bonds were placed in idealized
positions, whereas the hydrogen atoms of the NH2 and OH
groups were localized from the difference electron density map
and refined isotropically with distance restraints. Further
details are listed in Table 2.
Computational Details. Density functional methods were
applied by the use of the program DMOL,21 as implemented
in the Cerius program suite.24 To take into account the density
distribution within the extended ligand systems of the inves-
tigated compounds in a suitable way, the nonlocal density
functionals for exchange and correlation interactions according
to Becke25 and Lee, Yang, and Parr26 (BLYP) were chosen.
Double numerical basis sets were used for all elements and
extended by polarization functions for Al, Ga, and N.
3
with KOH and Na wire. LGaCl2 and 1,3-bis-tert-butylimida-
zol-2-ylidene19 were prepared according to literature proce-
dures. Elemental analyses were performed by the Analytisches
Labor des Instituts fu¨r Anorganische Chemie der Universita¨t
Go¨ttingen. 1H (200.13 and 500.13 MHz) and 13C (125.77 MHz)
NMR spectra were recorded on Bruker Avance 200 and Bruker
Avance 500 NMR spectrometers. Chemical shifts are reported
in ppm with reference to SiMe4 (external). IR spectra were
recorded on a Bio-Rad Digilab FTS7 spectrometer in the range
4000-350 cm-1 as KBr pellets. Only the absorptions of
significant groups (NH2, OH) are listed. Mass spectra were
obtained with a Finnigan MAT 8230 or a Varian MAT CH5
instrument (70 eV) by EI-MS methods. Melting points were
measured in sealed glass tubes on a Bu¨chi B-540 melting point
apparatus.
Synthesis of LGa(NH2)2 (1). 1,3-Bis-tert-butylimidazol-2-
ylidene (0.814 g, 4.514 mmol) and LGaCl2 (1.500 g, 2.150
mmol) were mixed as solids in a Schlenk flask equipped with
a Young valve. Toluene (70 mL) and NH3 (ca. 10 mL) were
subsequently transferred into the flask using a short vacuum
line provided with Swagelock fittings at -196 °C and allowed
to warm to ambient temperature. As the temperature in-
creased, a heavy precipitate of 1,3-bis-tert-butylimidazolium
chloride formed. The flask was disconnected from the vacuum
line, and the excess of ammonia was released via a mineral
(22) Sheldrick, G. M. SHELXS-97, Program for Structure Solution.
Acta Crystallogr. Sect. A 1990, 46, 467-473.
(23) Sheldrick, G. M. SHELXL-97, Program for Crystal Structure
Refinement; Universita¨t Go¨ttingen: Go¨ttingen, FRG, 1997.
(24) Cerius2 program suite; Accelrys Inc., 2001.
(25) Becke, A. D. Phys. Rev. A 1988, 38, 3098-3100.
(26) Lee, C.; Yang, W.; Parr, R. G. Phys. Rev. B 1988, 37, 785-789.

Preparation of Monomeric LGa(NH2)2
Organometallics, Vol. 24, No. 7, 2005 1515
Supporting Information Available: CIF files for com-
pounds 1 and 2‚0.5toluene and Figures S1-S6 (pdf) are
available free of charge via the Internet at http://pubs.acs.org.
Acknowledgment. We are grateful to the Deutsche
Forschungsgemeinschaft and the Go¨ttinger Akademie
der Wissenschaften for their financial support. V.J.
thanks the Fonds der Chemischen Industrie for a
predoctoral fellowship.
OM049304A