Synthesis and characterization of monomeric organogallium-nitrogen compounds, Et2GaNMe[C6H2(2,4,6-t-Bu)3], Me2GaNMe[C6H2(2,4,6-t-Bu)3], MeGa{NH[C6H2(2,4,6-t-Bu)3]}2, and Ga{NH[C6H2(2,4,6-t-Bu)3]}3

Article abstract of DOI:10.1021/om001050f

Four gallium-nitrogen compounds, Et₂GaNMe[C₆H₂(2,4,6-t-Bu)₃], Me₂GaNMe[C₆H₂(2,4,6-t-Bu)₃], MeGa{NH[C₆H₂(2,4,6-t-Bu)₃]}₂, and Ga[N(H)C₆H₂(t-2,4,6-Bu)₃]₃ have been prepared by metathetical reactions. The monomeric derivatives Et₂GaNMe[C₆H₂(2,4,6-t-Bu)₃] and Me_2-GaNMe[C₆H₂(2,4,6-t-Bu)₃] are of interest because their ¹H NMR spectra at room temperature had resonances indicative of two magnetically nonequivalent organic groups bonded to gallium, a spectral feature consistent with restricted rotation about the gallium-nitrogen bond. Variable-temperature ¹H NMR spectral studies of a toluene solution of Me₂GaNMe[C₆H₂(2,4,6-t-Bu)₃] identified the barrier to rotation about the gallium-nitrogen bond as approximately 71 kJ/mol. This result suggests that steric effects might be responsible. The monomeric compound MeGa{NH[C₆H₂(2,4,6-t-Bu)₃]}₂ was prepared from MeGaCl₂ and LiNH[C₆H₂(t-Bu)₃] but was also the gallium-nitrogen product when Me₂GaCl was reacted with the same lithium amide in diethyl ether. Experimental data demonstrated that Me₂GaNH[C₆H₂(2,4,6-t-Bu)₃] underwent a ligand redistribution reaction at room temperature to form an equilibrium mixture with MeGa{NH[C₆H₂(2,4,6-t-Bu)₃]}₂ and GaMe₃. In contrast, the tertiary amide Ga{NH[C₆H₂(t-Bu)₃]}₃ does not readily undergo ligand redistribution reactions with GaMe₃.

Full text of DOI:10.1021/om001050f

Organometallics 2001, 20, 945-949
945
Syn th esis a n d Ch a r a cter iza tion of Mon om er ic
Or ga n oga lliu m -Nitr ogen Com p ou n d s,
Et2Ga NMe[C6H2(2,4,6-t-Bu )3],
Me2Ga NMe[C6H2(2,4,6-t-Bu )3],
MeGa {NH[C6H2(2,4,6-t-Bu )3]}2, a n d
Ga {NH[C6H2(2,4,6-t-Bu )3]}3
O. T. Beachley, J r.,* Daniel B. Rosenblum, and David J . MacRae
Department of Chemistry, State University of New York at Buffalo,
Buffalo, New York 14260-3000
Received December 8, 2000
Four gallium-nitrogen compounds, Et2GaNMe[C6H2(2,4,6-t-Bu)3], Me2GaNMe[C6H2(2,4,6-
t-Bu)3], MeGa{NH[C6H2(2,4,6-t-Bu)3]}2, and Ga[N(H)C6H2(t-2,4,6-Bu)3]3, have been prepared
by metathetical reactions. The monomeric derivatives Et2GaNMe[C6H2(2,4,6-t-Bu)3] and Me2-
1
GaNMe[C6H2(2,4,6-t-Bu)3] are of interest because their H NMR spectra at room temperature
had resonances indicative of two magnetically nonequivalent organic groups bonded to
gallium, a spectral feature consistent with restricted rotation about the gallium-nitrogen
1
bond. Variable-temperature H NMR spectral studies of a toluene solution of Me2GaNMe-
[C6H2(2,4,6-t-Bu)3] identified the barrier to rotation about the gallium-nitrogen bond as
approximately 71 kJ /mol. This result suggests that steric effects might be responsible. The
monomeric compound MeGa{NH[C6H2(2,4,6-t-Bu)3]}2 was prepared from MeGaCl2 and LiNH-
[C6H2(t-Bu)3] but was also the gallium-nitrogen product when Me2GaCl was reacted with
the same lithium amide in diethyl ether. Experimental data demonstrated that Me2GaNH-
[C6H2(2,4,6-t-Bu)3] underwent a ligand redistribution reaction at room temperature to form
an equilibrium mixture with MeGa{NH[C6H2(2,4,6-t-Bu)3]}2 and GaMe3. In contrast, the
tertiary amide Ga{NH[C6H2(t-Bu)3]}3 does not readily undergo ligand redistribution reactions
with GaMe3.
In tr od u ction
preparation and characterization of four new monomeric
gallium-nitrogen compounds that incorporate a super-
mesityl group on nitrogen, Et2GaNMe[C6H2(t-Bu)3],
Me2GaNMe[C6H2(t-Bu)3], MeGa{NH[C6H2(t-Bu)3]}2, and
Ga[N(H)C6H2(t-Bu)3]3, are described. The first two are
of special interest because of their potential to exhibit
magnetically nonequivalent organic groups on gallium
if there is restricted rotation about the gallium-
nitrogen bond.
Monomeric compounds with the simplest formula R2-
GaNR1R2 such as (t-Bu)2GaN(t-Bu)(SiPh3),1 (t-Bu)2GaN-
(1-adamantyl)(SiPh3),1 [(2,4,6-i-Pr)3C6H2]2GaNH[(2,6-i-
Pr)2C6H3]2,1 [(2,4,6-t-Bu)3C6H2]2GaN(H)Ph,2 R2GaN-
(t-Bu)(BMe2)3 (R ) Me, Et and CH2CPhMe2), and Et2-
GaN(t-Bu)(BMes2)4 have the potential to exhibit p-p
π-bonding3 between gallium and nitrogen, but the
experimental data suggest that these interactions are
not significant for determining either their structural
features or their unique NMR spectral properties at
room temperature. Thus, the GaR2 and the NR1R2
moieties are not coplanar even though each moiety is
planar within a given molecule according to the X-ray
structural data. Similarly, the asymmetries of the
NR1R2 moieties have the potential to magnetically
distinguish the two organic substituents bonded to
gallium, but the substituents were equivalent according
to NMR spectra at room temperature. Thus, rotation
about the gallium-nitrogen bond in these molecules is
not restricted under these conditions. In this paper the
Resu lts a n d Discu ssion
The new compound Et2GaNMe[C6H2(t-Bu)3], which is
closely related to the previously reported derivative Et2-
GaNH[C6H2(t-Bu)3],5 was synthesized in 90% yield by
a metathetical reaction between Et2GaCl6,7 and LiNMe-
[C6H2(t-Bu)3] in pentane and then fully characterized.
Even though both gallium-nitrogen compounds are
liquids at room temperature and are monomeric accord-
ing to cryoscopic molecular weight studies in benzene
solution in the concentration range of 0.04-0.08 m, they
have very different chemical properties and 1H NMR
spectra. The new derivative Et2GaNMe[C6H2(t-Bu)3]
(1) Waggoner, K. M.; Ruhlandt-Senge, K.; Wehmschulte, R. J .; He,
X.; Olmstead, M. M.; Power, P. P. Inorg. Chem. 1993, 32, 2557.
(2) Brothers, P. J .; Wehmschulte, R. J .; Olmstead, M. M.; Ruhlandt-
Senge, K.; Parkin, S. R.; Power, P. P. Organometallics 1994, 13, 2792.
(3) Linti, G. J . J . Organomet. Chem. 1994, 465, 79.
(5) Beachley, O. T., J r.; Rosenblum, D. B.; Churchill, M. R.;
Churchill, D. G.; Krajkowski, L. M. Organometallics 1999, 18, 2543.
(6) Eisch, J . J . J . Am. Chem. Soc. 1962, 84, 3830.
(4) Power, P. P. Chem. Rev. 1999, 99, 3463.
(7) Armer, B.; Schmidbaur, H. Chem. Ber. 1967, 100, 1521.
10.1021/om001050f CCC: $20.00 © 2001 American Chemical Society
Publication on Web 01/26/2001

946 Organometallics, Vol. 20, No. 5, 2001
Beachley et al.
was stable to decomposition at temperatures up to 120-
130 °C. In contrast, Et2GaNH[C6H2(t-Bu)3] decomposed
at room temperature and formed the metallacyclic
coalesence temperature of 51 °C, and the approximate
formula9 afforded a calculated barrier to rotation about
the gallium-nitrogen bond of 71 kJ /mol. This small
barrier is most likely the result of steric interactions
between the methyl groups bonded to gallium and the
nitrogen substituents, the bulky supermesityl group,
and the methyl group. In contrast, when the methyl
group on nitrogen was replaced by a proton, as in Et2-
GaNH[C6H2(t-Bu)3]5 and Me2GaNH[C6H2(t-Bu)3] (see
below), the steric effects were sufficiently small that free
rotation about the gallium-nitrogen bond was observed
at 20.7 °C. Thus, all observations suggest that π-bonding
between gallium and nitrogen appears to be minimal,
if it occurs at all.1-4 An X-ray structural study of Me2-
GaNMe[C6H2(t-Bu)3] was attempted, but X-ray quality
crystals could not be isolated. Single crystals were
grown by vacuum sublimation in a sealed tube. How-
ever, when the crystals were separated from the wall
of the tube in the drybox, they became opaque and did
not diffract a beam of X-rays. Recrystallization from
pentane was also investigated as a method of crystal
growth, but X-ray quality crystals could not be obtained
by this method either.
The preparation of Me2GaNH[C6H2(t-Bu)3] by a meta-
thetical reaction between Me2GaCl7,8 and LiNH[C6H2-
(t-Bu)3]5 (eq 1) was attempted so that its chemical,
physical, and spectral properties could be compared with
those of Et2GaNH[C6H2(t-Bu)3]5 and Me2GaNMe[C6H2-
(t-Bu)3]. However, Me2GaNH[C6H2(t-Bu)3] could not be
isolated as a pure compound because it underwent a
ligand redistribution reaction to form an equilibrium
mixture with MeGa{NH[C6H2(t-Bu)3]}2 and GaMe3 (eq
2) in diethyl ether and pentane, the reaction solvents.
compound {EtGaNH[C6H2(t-Bu)2(CMe2CH2)]}2, GaEt3,
1
and H2N[C6H2(t-Bu)3].5 The H NMR spectra of these
two gallium-nitrogen monomers are also very different.
The spectrum of Et2GaNMe[C6H2(t-Bu)3] is consistent
with restricted rotation of the GaEt2 group about the
gallium-nitrogen bond at 20.7 °C, whereas the two
ethyl groups of Et2GaNH[C6H2(t-Bu)3] are magnetically
equivalent under the same conditions. Thus, a benzene
solution of Et2GaNMe[C6H2(t-Bu)3] exhibited two sets
of sharp resonances of equal intensities for the methyl
and methylene protons for the ethyl groups bonded to
gallium, whereas Et2GaNH[C6H2(t-Bu)3] had only one
set of ethyl gallium resonances. Single resonances for
the N-methyl, the ortho and para tert-butyl groups, and
the phenyl protons completed the spectrum of Et2-
GaNMe[C6H2(t-Bu)3]. Thus, a methyl group and a
supermesityl group on nitrogen are able to restrict
rotation about the gallium-nitrogen bond at 20.7 °C and
make the ethyl groups on gallium magnetically non-
equivalent. Variable-temperature NMR studies of Et2-
GaNMe[C6H2(t-Bu)3] in toluene-d8 revealed that 75 °C,
the highest temperature investigated, did not supply
sufficient energy to enable the GaEt2 group to rotate
freely and make the ethyl(gallium) protons equivalent.
The synthesis of Me2GaNMe[C6H2(t-Bu)3] was under-
taken in order to determine if there was restricted
rotation of the GaMe2 moiety as there was for the GaEt2
moiety in Et2GaNMe[C6H2(t-Bu)3] and, if so, attempt
to determine whether steric hindrance between substit-
uents, p-p π-bonding between gallium and nitrogen, or
some other factor(s) was responsible. A metathetical
reaction between Me2GaCl7,8 and LiNMe[C6H2(t-Bu)3]
in pentane provided the desired gallium-nitrogen prod-
uct Me2GaNMe[C6H2(t-Bu)3] as a crystalline solid at
room temperature. The compound was readily purified
by vacuum sublimation at 60-70 °C and existed as a
monomeric species in benzene solution according to
cryoscopic molecular weight studies in the concentration
Me2GaCl + LiNH[C6H2(t-Bu)3] f
Me2GaNH[C6H2(t-Bu)3] + LiCl (1)
2Me2GaNH[C6H2(t-Bu)3] h
MeGa{NH[C6H2(t-Bu)3]}2 + GaMe3 (2)
When the synthetic reaction (eq 1) was carried out in
diethyl ether, the isolated gallium-nitrogen product
was MeGa{NH[C6H2(t-Bu)3]}2, not Me2GaNH[C6H2(t-
Bu)3]. The 1H NMR spectrum of this product was
identical to the compound independently prepared from
MeGaCl2 and LiNH[C6H2(t-Bu)3]5 (see below). The other
product, trimethylgallium diethyl ether adduct, must
have been removed with the ether during vacuum
distillation, a conclusion consistent with its physical
properties. When pentane was the reaction solvent, the
isolated product was a mixture of Me2GaNH[C6H2(t-
Bu)3] and MeGa{NH[C6H2(t-Bu)3]}2, two species in the
above ligand redistribution equilibrium (eq 2). The
remaining species in the above equilibrium, GaMe3, had
been removed from the nonvolatile product during
vacuum distillation of the solvent, as the flask contain-
ing the solvent that was separated by vacuum distilla-
tion smoked and smelled of GaMe3 when it was removed
1
range of 0.04-0.08 m. The H NMR spectrum of Me2-
GaNMe[C6H2(t-Bu)3] in benzene and toluene indicated
restricted rotation of the GaMe2 moiety, as two Ga-
CH3 singlets of equal intensity, each with a width at
half-height of 8.28 Hz, were observed at 20.7 °C. All
other lines in the spectrum were sharp, an observation
consistent with free rotation of the C6H2(t-Bu)3 group.
A variable-temperature 1H NMR spectral study of
Me2GaNMe[C6H2(t-Bu)3] in d8-toluene was undertaken
in order to learn more about the origin of the restricted
rotation about the gallium-nitrogen bond. When the
temperature was increased from 20.7 to 30.0 °C, the two
lines for the Ga-CH3 groups broadened from 8.28 to
16.08 Hz, whereas all other lines in the spectrum
remained sharp. Heating to 40 °C caused more broad-
ening as the width at half-height of each of the Ga-Me
lines increased to 37.70 Hz. Coalescence occurred at 51
°C. A further increase in temperature to 60 °C led to
sharpening of the single line as the width at half-height
decreased to 49.59 Hz. The maximum separation of the
two gallium-methyl lines of 0.231 ppm at 20.7 °C, a
1
from the vacuum line and exposed to air. The H NMR
spectrum of the nonvolatile mixture in C6D6 confirmed
the existence of the equilibrium, as the spectrum
exhibited lines for all three methyl gallium compounds
(8) Magee, C. P.; Sneddon, L. G.; Beer, D. C.; Grimes, R. N. J .
Organomet. Chem. 1975, 86, 159.
(9) Kost, D.; Carlson, E. H.; Raban, M. J . Chem. Soc., Chem.
Commun. 1971, 656.

Monomeric Organogallium-Nitrogen Compounds
Organometallics, Vol. 20, No. 5, 2001 947
variability but without success.5 The amine was not a product
of accidental hydrolysis. The provenance of the amine remains
in eq 2, Me2GaNH[C6H2(t-Bu)3], MeGa{NH[C6H2-
(t-Bu)3]}2, and GaMe3. The presence of both Me2GaNH-
[C6H2(t-Bu)3] and MeGa{NH[C6H2(t-Bu)3]}2 permitted
the formation of GaMe3 as required by the above
equation. The experimental observations for the reac-
tions in diethyl ether and pentane are reconciled if Me3-
Ga‚OEt2 undergoes a ligand redistribution with MeGa-
{NH[C6H2(t-Bu)3]}2 slower than does GaMe3. Four-
coordinate gallium compounds typically undergo ligand
redistribution reactions slower than do three-coordinate
species. Thus, Me3Ga‚OEt2 was removed by vacuum
distillation before it could react with MeGa{NH[C6H2-
(t-Bu)3]}2 and re-form Me2GaNH[C6H2(t-Bu)3]. It is
noteworthy that the 1H NMR resonances assigned to
Me2GaNH[C6H2(t-Bu)3] as part of the equilibrium mix-
ture included only one line for the Ga-Me protons. Thus,
neither Me2GaNH[C6H2(t-Bu)3] nor Et2GaNH[C6H2-
(t-Bu)3] exhibits restricted rotation about the gallium-
nitrogen bond at 20.7 °C.
unknown. Since the preparations of Me2GaCl7,8 and MeGaCl2
10
by ligand redistribution reactions in pentane solutions have
not been reported, they are described below. All solvents were
dried by conventional procedures. Elemental analyses were
performed by E+R Microanalytical Laboratory, Inc., Parsip-
1
pany, NJ . The H NMR spectra were recorded at 400 MHz by
using a Varian Unity-Inova 400 spectrometer. Proton chemical
shifts are reported in δ (ppm) units and are referenced to SiMe4
at δ 0.00 ppm and benzene at δ 7.15 ppm. All samples for NMR
spectra were contained in sealed NMR tubes. Infrared spectra
were observed for either neat liquids or Nujol mulls of solids,
as appropriate, between KBr plates and were recorded with a
Perkin-Elmer 683 spectrometer. Melting points were deter-
mined with a Mel-Temp by using flame-sealed capillaries filled
with purified argon and are uncorrected. Molecular weights
were measured cryoscopically for benzene solutions by using
an instrument similar to that described by Shriver and
Drezdzon.11
P r ep a r a tion of Me2Ga Cl. A 1.15 g (10.0 mmol) sample of
GaMe3 was added by vacuum distillation to 0.881 g (5.00
mmol) of freshly sublimed GaCl3 dissolved in approximately
25 mL of pentane. The reaction mixture was warmed from
-196 °C to room temperature over a 10 min period and then
stirred overnight. Removal of solvent by vacuum distillation
at 0 °C produced a colorless solid, which was purified by
sublimation at room temperature from the original reaction
flask through a glass elbow into a Schlenk flask maintained
at -196 °C. The product Me2GaCl (1.67 g 12.4 mmol) was
isolated in 82% yield as a colorless, crystalline solid. Me2-
GaCl: mp 45.3-45.5 °C (lit.7 45 °C); 1H NMR (C6D6,δ) 0.18 (s,
Ga-CH3).
The identity of MeGa{NH[C6H2(t-Bu)3]}2 and its
formation by the decomposition of Me2GaNH[C6H2-
(t-Bu)3] by a ligand redistribution reaction were con-
firmed by its independent synthesis and characteriza-
tion. This compound was prepared in 70% yield by a
10
metathetical reaction between MeGaCl2 and LiNH-
[C6H2(t-Bu)3]5 in a 1:2 mol ratio in diethyl ether and
then purified by recrystallization from ether. This
gallium-nitrogen product was a crystalline solid, mp
214.7-216.1 °C, and was monomeric in benzene solution
in the concentration range of 0.07-0.03 m according to
a cryoscopic molecular weight study. The resonances in
the 1H NMR spectrum of pure MeGa{NH[C6H2(t-Bu)3]}2
in benzene were identical to those assigned to this
compound, as found in the products of the reaction
between Me2GaCl and LiNH[C6H2(t-Bu)3] in diethyl
ether or pentane (eqs 1 and 2).
P r ep a r a tion of MeGa Cl2. A flask charged with 1.15 g of
freshly sublimed GaCl3 (6.52 mmol) was attached to a 90° glass
elbow which had been connected to a Schlenk flask. Then
approximately 20 mL of pentane and 0.375 g of GaMe3 (3.26
mmol) were vacuum distilled into the flask. As the reaction
mixture warmed to room temperature over 10 min, a colorless
precipitate formed. After the reaction mixture had been stirred
for 12 h, the solvent was removed by vacuum distillation at
room temperature. The resulting colorless solid was purified
at room temperature by dynamic sublimation through the
glass elbow into the Schlenk flask maintained at -196 °C. The
product MeGaCl2 (1.36 g, 8.74 mmol) was isolated in 89.3%
The derivative with three bulky substituents, Ga{NH-
[C6H2(t-Bu)3]}3, was prepared by reacting GaCl3 with
excess LiNH[C6H2(t-Bu)3].5 This gallium-nitrogen prod-
uct was soluble in pentane and benzene even though it
decomposed at the unusually high temperature of 258-
260 °C. When Ga{NH[C6H2(t-Bu)3]}3 was combined with
GaMe3 in 1:2 and 2:1 mol ratios in benzene solution in
attempts to prepare Me2GaNH[C6H2(t-Bu)3] and MeGa-
{NH[C6H2(t-Bu)3]}2 by stoichiometric ligand redistribu-
tion reactions, minimal, if any, reaction occurred even
after 12 months according to the 1H NMR spectra of the
reaction mixtures. Thus, three NH[C6H2(t-Bu)3] groups
are sufficiently bulky to protect the gallium from
reaction with GaMe3.
1
yield. MeGaCl2: mp 78.4-78.9 °C (lit.10 75-76 °C); H NMR
(THF-d8, δ) 0.14 (s, Ga-CH3).
P r ep a r a tion of LiNMe[C6H2(t-Bu )3]. A pressure-equal-
izing addition funnel was charged in the drybox with 6.21 g
(22.6 mmol) of HNMe[C6H2(t-Bu)3] and connected to a 500 mL
three-necked flask that was equipped with a 24/40 adapter
with a Teflon stopcock and a rubber septum. Then a solution
of Li(n-Bu) (1.6 M in hexanes, 15 mL, 24 mmol) was added by
syringe to the three-necked flask under cover of argon. Finally,
approximately 50 mL of pentane was transferred by cannula
both to the addition funnel to dissolve the amine and to the
flask to dilute the Li(n-Bu). The solution of Li(n-Bu) was cooled
to 0 °C, and then the solution of HNMe[C6H2(t-Bu)3] was added
with stirring at a rate of about 20 drops/min. Since no
precipitate was observed during the addition of the amine, the
reaction mixture was allowed to warm to room temperature
overnight, after which time a colorless precipitate had formed.
The precipitate was isolated by filtration and washed three
times with cold solvent to yield 3.05 g of LiNMe[C6H2(t-Bu)3]
(10.8 mmol, 48.1% based on HNMe[C6H2(t-Bu)3]). LiNMe[C6H2-
(t-Bu)3]: 1H NMR (THF-d8, δ) 7.09 (s, Ar-H, 2H), 3.10 (s,
N-CH3, 3H), 1.48 (s, o-Ph-(t-Bu), 18H), 1.23 (s, p-Ph-(t-Bu),
9H).
Exp er im en ta l Section
All compounds were manipulated in a standard vacuum line
or in a purified argon atmosphere. The starting materials
GaMe3, GaEt3, and Li(n-Bu) were purchased from Strem
Chemicals, Inc. and Aldrich Chemical Co., as appropriate,
whereas Et2GaCl5 and LiNH[C6H2(t-Bu)3]5 were prepared by
using literature methods. Crude products that incorporated
the NH[C6H2(t-Bu)3] ligand as described in the following
paragraphs were observed to have an impurity of the free
amine NH2[C6H2(t-Bu)3] that varied for the preparation of a
given compound from 1 to 15%. Extensive studies attempted
to identify the source of the amine and the reason for its
(11) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds; Wiley: New York, 1986; p 38.
(10) Schmidbaur, H.; Findeiss, W. Chem. Ber. 1966, 99, 2187.

948 Organometallics, Vol. 20, No. 5, 2001
Beachley et al.
P r ep a r a tion of Et2Ga NMe[C6H2(t-Bu )3]. A solution of
1.08 g (6.60 mmol) of Et2GaCl in approximately 25 mL of
pentane was added to a suspension of 2.01 g (7.12 mmol) of
LiNMe[C6H2(t-Bu)3] in about 25 mL of pentane that had been
cooled to 0 °C. The reaction mixture was stirred for 2 h and
then filtered. Two additional extractions of the precipitate
separated the pentane-soluble product from LiCl and unre-
acted lithium amide. Removal of the solvent by vacuum
distillation provided a mobile liquid that was purified by
vacuum distillation by using an oil bath at 120-130 °C. The
final product, Et2GaNMe[C6H2(t-Bu)3] (2.38 g, 5.91 mmol,
89.5% yield based on Et2GaCl), was isolated as a colorless
mobile liquid that was stable to overnight heating at 65 °C.
Et2GaNMe[C6H2(t-Bu)3]: 1H NMR (C6D6, δ) 7.53 (s, Ph-H,
2H), 3.00 (s, N-CH3, 3H), 1.55 (s, o-Ph-(t-Bu), 18H), 1.32 (s,
p-Ph-(t-Bu), 9H), 1.24 (t, J C-H ) 8 Hz, Ga-CH2CH3, 3H), 0.97
(t, J C-H ) 8 Hz, Ga-CH2CH3, 3H), 0.75 (q, J C-H ) 8 Hz, Ga-
CH2CH3, 2H), 0.47 (q, J C-H ) 8 Hz, Ga-CH2CH3, 2H). Anal.
Calcd for C23H42GaN: C, 68.67; H, 10.52. Found: C, 69.40; H,
10.43. Cryoscopic molecular weight, benzene solution, formula
weight 402 (observed molality, observed molecular weight,
association): 0.079, 393, 0.98; 0.052, 400, 1.00; 0.029, 390, 0.97.
[C6H2(t-Bu)3]), 1.39 (s, p-Ph-(t-Bu), H2N[C6H2(t-Bu)3]), 1.35
(s, p-Ph-(t-Bu) MeGa{NH[C6H2(t-Bu)3]}2), -0.31 (s, Me, MeGa-
{NH[C6H2(t-Bu)3]}2).
Rea ction of Me2Ga Cl a n d LiNH[C6H2(t-Bu )3] in P en -
ta n e. A flask was charged with 0.507 g (3.75 mmol) of Me2-
GaCl, while 1.02 g (3.81 mmol) of LiNH[C6H2(t-Bu)3] was
placed in a Schlenk flask connected by means of a medium-
porosity glass frit. After approximately 25 mL of pentane had
been added to each flask, the suspension of LiNH[C6H2(t-Bu)3]
was cooled to 0 °C. Then the solution of Me2GaCl was added,
and the mixture was stirred for 2 h. After the reaction mixture
was filtered, the residue was washed two additional times.
Removal of the pentane by vacuum distillation produced 1.195
1
g of a colorless solid. This crude product was identified by H
NMR spectroscopy as a mixture of Me2GaNH[C6H2(t-Bu)3] and
MeGa{NH[C6H2(t-Bu)3]}2 with a small impurity of H2N[C6H2-
1
(t-Bu)3]:5 mp 110-160 °C; H NMR (C6D6, δ) 7.55 (s, Ph-H,
MeGa{NH[C6H2(t-Bu)3]}2), 7.51 (s, Ph-H, Me2GaNH[C6H2(t-
Bu)3]), 7.40 (s, Ph-H, H2N[C6H2(t-Bu)3]), 3.63 (s, N-H, H2N-
[C6H2(t-Bu)3]), 3.49 (s, N-H, Me2GaNH[C6H2 (t-Bu)3]), 3.22 (s,
N-H, MeGa{NH[C6H2(t-Bu)3]}2), 1.63 (s, o-Ph-(t-Bu), MeGa-
{NH[C6H2(t-Bu)3]}2), 1.51 (s, o-Ph-(t-Bu), Me2GaNH[C6H2(t-
Bu)3]), 1.40 (s, o-Ph-(t-Bu), H2NC6H2(t-Bu)3), 1.39 (s, np-Ph-
(t-Bu), H2N[C6H2(t-Bu)3]), 1.36 (s, p-Ph-(t-Bu), Me2GaNH[C6H2-
(t-Bu)3]), 1.35 (s, p-Ph-(t-Bu), MeGa{NH[C6H2(t-Bu)3]}2), -0.15
(s, Me, Me2GaNH[C6H2(t-Bu)3]), -0.26 (s, Me, GaMe3), -0.31
(s, Me, MeGa{NH[C6H2(t-Bu)3]}2).
P r ep a r a tion of MeGa {NH[C6H2(t-Bu )3]}2. A Solv-seal
Schlenk flask with 1.02 g (3.82 mmol) of LiNH[C6H2(t-Bu)3]
was connected by means of a medium-porosity frit to a flask
that contained 0.289 g (1.86 mmol) of MeGaCl2. Approximately
25 mL of diethyl ether was vacuum distilled into the apparatus
at -196 °C. After the ether was divided between the two flasks,
the flask containing the suspension of LiNH[C6H2(t-Bu)3] in
ether was cooled to 0 °C and the solution of MeGaCl2 was
added. The resulting mixture was stirred for 12 h and then
filtered to remove LiCl and excess LiNH[C6H2(t-Bu)3]. The
residue was washed three additional times. The resulting
solution was cooled to -30 °C to induce crystallization.
Removal of the solvent by vacuum distillation at room tem-
perature produced 0.792 g of MeGa{NH[C6H2(t-Bu)3]}2 (1.31
mmol, 70.4% yield based on MeGaCl2) as a colorless solid.
MeGa{NH[C6H2(t-Bu)3]}2: mp 214.7-216.1 °C; 1H NMR (C6D6,
δ) 7.55 (s, Ph-H, 4H), 3.23 (s, N-H, 2H), 1.63 (s, o-Ph-(t-
Bu), 36H), 1.35 (s, p-Ph-(t-Bu), 18H), -0.30 (s, GaCH3, 3H);
IR (Nujol, cm-1) 3420 (m), 1599 (w), 1423 (s), 1360 (vs), 1262
(m), 1242 (m), 1220 (m), 1193 (m), 1111 (m), 1018 (w), 930
(w), 918 (w), 865 (m), 829 (m), 813 (w), 785 (w), 745 (w), 720
P r ep a r a tion of Me2Ga NMe[C6H2(t-Bu )3]. A solution of
0.793 g (5.86 mmol) of Me2GaCl in approximately 25 mL of
pentane was added to 1.65 g (5.86 mmol) of LiNMe[C6H2-
(t-Bu)3] suspended in 25 mL of pentane at 0 °C and stirred for
2 h. The reaction mixture was filtered to separate LiCl. After
the residue was washed two additional times with pentane,
the solvent was removed by vacuum distillation and a viscous
material remained. Subsequent dynamic evacuation of the
crude product for 12 h produced a solid that was purified by
vacuum sublimation at 60-70 °C. The compound Me2GaNMe-
[C6H2(t-Bu)3] (1.81 g, 4.83 mmol) was isolated as a colorless
solid in 82.4% yield. Me2GaN[MeC6H2(t-Bu)3]: mp 73.6-74.2
°C; 1H NMR (C6D6, δ) 7.57 (s, Ph-H, 2H), 2.99 (s, N-CH3,
3H), 1.54 (s, o-Ph-(t-Bu), 18H), 1.32 (s, p-Ph-(t-Bu), 9H),
-0.02 (s, Ga-CH3, 3H), -0.21 (s, Ga-CH3, 3H); (C6D5CD3, δ)
7.50 (s, Ph-H, 2H), 2.98 (s, N-CH3, 3H), 1.52 (s, o-Ph-(t-
Bu), 18H), 1.32 (s, p-Ph-(t-Bu), 9H), -0.002 (s, Ga-CH3, 3H),
-0.228 (s, Ga-CH3, 3H); IR (Nujol, cm-1) 2790 (s), 1598 (m),
1552 (w), 1472 (s), 1430 (s), 1410 (s), 1388 (vs), 1359 (s), 1282
(m), 1260 (s), 1237 (s), 1210 (s), 1199 (s), 1170 (m, br), 1142
(m), 1118 (s), 1050 (s), 930 (w), 838 (s), 816 (w), 788 (m), 765
(s), 745 (s), 719 (s), 643 (m), 589 (s), 540 (m), 518 (w), 460 (w),
419 (w). Anal. Calcd for C21H38GaN: C, 67.40; H, 10.23.
Found: C, 67.84; H, 10.71. Cryoscopic molecular weight,
benzene solution, formula weight 374 (observed molality,
observed molecular weight, association): 0.077, 374, 1.00;
0.059, 373, 1.00; 0.040, 375, 1.00. Crystals were grown by
placing a sample of the compound in a sealed evacuated tube
above the vent of an oven maintained at 150 °C. However,
when the crystals were removed from the wall of the tube in
the drybox, they became opaque and did not diffract a beam
of X-rays. Attempts to grow X-ray quality crystals by recrys-
tallization from a pentane solution were unsuccessful.
(w), 620 (w, br), 470 (w), 430 (w, br). Anal. Calcd for C37H63
-
GaN2: C, 73.38; H, 10.49; N, 4.63. Found: C, 73.78; H, 10.80;
N, 4.31. Cryoscopic molecular weight, benzene solution, for-
mula weight 606 (observed molality, observed molecular
weight, association): 0.068, 627, 1.03; 0.054, 616, 1.02; 0.033,
612, 1.01.
P r ep a r a tion of Ga {NH[C6H2(t-Bu )3]}3. A Schlenk flask
charged with 0.148 g (0.840 mmol) of freshly sublimed GaCl3
was connected by means of a medium frit to a second flask
charged with 0.718 g (2.69 mmol) of LiNH[C6H2(t-Bu)3]. Then,
approximately 35 mL of benzene was added by vacuum
distillation to each flask. After the flask containing the LiNH-
[C6H2(t-Bu)3] was cooled with ice, the GaCl3 solution was added
over a 2 h period to the slurry of LiNH[C6H2(t-Bu)3]. The
reaction mixture was permitted to warm to room temperature
and was stirred overnight. The benzene was removed by
vacuum distillation and approximately 70 mL of pentane was
added. The product mixture was filtered and then washed four
additional times to separate the LiCl and excess LiNH[C6H2-
(t-Bu)3] from the soluble product. Recrystallization of the
product from pentane at -78 °C yielded 0.475 g of Ga{NH-
[C6H2(t-Bu)3]}3 (0.558 mmol, 66.5% yield based on GaCl3) as a
Rea ction of Me2Ga Cl a n d LiNH[C6H2(t-Bu )3] in Dieth yl
Eth er . The reagents 0.431 g (3.19 mmol) of Me2GaCl and 0.908
g (3.39 mmol) of LiNH[C6H2(t-Bu)3] were combined in diethyl
ether at 0 °C. The reaction mixture was allowed to warm to
room temperature and was stirred for 2 h. The reaction
mixture was filtered, and then the insoluble components were
washed two times with the reaction solvent. The components
that were volatile at room temperature were removed from
the soluble fraction by vacuum distillation, and 0.973 g of a
colorless solid was obtained. This crude product was identified
by 1H NMR spectroscopy as primarily MeGa{NH[C6H2(t-
Bu)3]}2 with an impurity of H2N[C6H2(t-Bu)3]:5 mp 175.6-182.6
°C; 1H NMR (C6D6, δ) 7.55 (s, Ph-H, MeGa{NH[C6H2(t-Bu)3]}2),
7.40 (s, Ph-H, H2N[C6H2(t-Bu)3]), 3.63 (s, N-H, H2N[C6H2(t-
Bu)3]), 3.22 (s, N-H, MeGa{NH[C6H2(t-Bu)3]}2), 1.63 (s, o-Ph-
(t-Bu), MeGa{NH[C6H2(t-Bu)3]}2), 1.40 (s, o-Ph-(t-Bu), H2N-
1
colorless solid: mp 258-260 °C (dec); H NMR (C6D6, δ) 7.35

Monomeric Organogallium-Nitrogen Compounds
Organometallics, Vol. 20, No. 5, 2001 949
1
(s, Ph-H, 6H), 3.84 (s, N-H, 3H), 1.41 (s, o-Ph-(t-Bu), 54H),
1.36 (s, p-Ph-(t-Bu), 27H); IR (Nujol, cm-1): 3400 (vw, br),
1580 (vw), 1359 (vs), 1330 (m), 1280 (m), 1237 (m), 1220 (s),
1195 (m), 1162 (w), 1108 (m), 870 (m), 828 (m), 809 (vw), 780
(w). Anal. Calcd for C54H90GaN3: C, 76.21; H, 10.66. Found:
C, 75.85; H, 11.29.
Liga n d Red istr ibu tion Rea ction s betw een Ga {NH-
[C6H2(t-Bu )3]}3 a n d Ga Me3 in 2:1 a n d 1:2 Mol Ra tios. (a )
2:1 Mol Ra tio. An NMR tube was charged with 0.172 g (0.202
mmol) of Ga{NH[C6H2(t-Bu)3]}3 and 0.0116 g (0.101 mmol) of
GaMe3. Then ∼0.6 mL of C6D6 was added by vacuum distil-
lation, and the tube was flame sealed. 1H NMR (C6D6, δ, 12
months): 7.35 (s, Ph-H), 3.83 (s, N-H), 1.40 (s, o-Ph-(t-Bu)),
1.36 (s, p-Ph-(t-Bu), 27H), -0.15 (s, GaCH3).
Var iable-Tem per atu r e H NMR Spectr a of Me2GaNMe-
[C6H2(t-Bu )3]. The temperature dependence of the spectrum
was investigated in toluene-d8. Increasing the temperature
from 20.7 to 60 °C resulted in broadening of the two Ga-Me
lines of equal intensity until coalesence was observed at 51
°C. Then, the line sharpened at 60 °C, the highest temperature
studied. All other lines in the spectrum were unchanged over
this temperature range. The measurements of the widths of
the Ga-Me lines at half-height were determined by using the
Varian VXR-400 program. The approximate formula9 with the
coalesence temperature of 51 °C and the maximum peak
separation of 0.231 ppm afforded a rotation barrier around the
gallium-nitrogen bond of 71.5 kJ /mol.
(b) 1:2 Mol Ra tio. The reagents, 0.0567 g (0.0666 mmol)
of Ga{NH[C6H2(t-Bu)3]}3, 0.0153 g (0.133 mmol) of GaMe3, and
∼0.6 mL of C6D6, were combined in an NMR tube, and then
the 1H NMR spectra were recorded. 1H NMR (C6D6, δ, 12
months): 7.35 (s, Ph-H), 3.83 (s, N-H), 1.40 (s, o-Ph-(t-Bu)),
1.36 (s, p-Ph-(t-Bu), 27H), -0.15 (s, GaCH3).
Ack n ow led gm en t. This work was supported in part
by the Office of Naval Research.
OM001050F