Facile reactions for the preparation of [(Me3CCH2)2GaNH2]2 and of GaN

Article abstract of DOI:10.1021/om9711234

Four reactions of neopentylgallium compounds with ammonia have been investigated. The dihydronaphthalene derivative C₁₀H₈[Ga(CH₂CMe₃)₂] ₂· 2NaCl has been observed to react with anhydrous ammonia at low temperature (-78 °C) to form (Me₃-CCH₂)₂GaNH₂, dihydronaphthalene (C₁₀H₁₀), and NaCl, whereas the related elimination reaction between Ga(CH₂-CMe₃)₃ and NH₃ occurred at 140-150 °C. The new compound (Me₃CCH₂)₂GaNH₂ was also prepared by reacting Ga(CH₂CMe₃)₂Cl with sodium in liquid ammonia at -70 °C. Bis(neopentyl)gallium amide was fully characterized and exists as a dimer at room temperature in benzene solution. Neopentylgallium(I) [Ga(CH₂CMe₃)]_n has been observed also to react with NH₃ at 460-480 °C to form GaN(s), CMe₄, and H₂.

Full text of DOI:10.1021/om9711234

Organometallics 1998, 17, 2121-2123
2121
Notes
F a cile Rea ction s for th e P r ep a r a tion of
[(Me3CCH2)2Ga NH2]2 a n d of Ga N
O. T. Beachley, J r.,* J ohn C. Pazik, and Matthew J . Noble
Department of Chemistry, State University of New York at Buffalo,
Buffalo, New York 14260-3000
Received December 22, 1997
Summary: Four reactions of neopentylgallium com-
pounds with ammonia have been investigated. The
dihydronaphthalene derivative C10H8[Ga(CH2CMe3)2]2‚
2NaCl has been observed to react with anhydrous
ammonia at low temperature (-78 °C) to form (Me3-
CCH2)2GaNH2, dihydronaphthalene (C10H10), and NaCl,
whereas the related elimination reaction between Ga(CH2-
CMe3)3 and NH3 occurred at 140-150 °C. The new
compound (Me3CCH2)2GaNH2 was also prepared by
reacting Ga(CH2CMe3)2Cl with sodium in liquid am-
monia at -70 °C. Bis(neopentyl)gallium amide was
fully characterized and exists as a dimer at room
temperature in benzene solution. Neopentylgallium(I)
[Ga(CH2CMe3)]n has been observed also to react with
NH3 at 460-480 °C to form GaN(s), CMe4, and H2.
hydrous ammonia at -78 °C to form (Me3CCH2)2-
GaNH2, C10H10, and NaCl in high yields (eq 1).
C10H8[Ga(CH2CMe3)2]2‚2NaCl + 2NH3 f
2(Me3CCH2)2GaNH2 + C10H10 + 2NaCl (1)
Hydrogen was not formed. Initially, the reaction mix-
ture had an intense golden-yellow color, which would
be indicative of the dihydronaphthalene intermediate
as an ammonia adduct. As the reaction mixture was
stirred for 18 h at -78 °C, the yellow color disappeared
and a colorless solution and a colorless precipitate
(NaCl) formed. The solution never became brown, a
color which would be indicative of the presence of the
gallium(I) compound1 [Ga(CH2CMe3)]n, a product from
the decomposition of C10H8[Ga(CH2CMe3)2]2. Filtration
of the final product mixture and removal of the solvent
led to the isolation and subsequent identification of
(Me3CCH2)2GaNH2, C10H10, and NaCl. All observations
confirm the occurrence of a very facile elimination
reaction between the dihydronaphthalene gallium(III)
intermediate and ammonia and indicate the absence of
an oxidation-reduction reaction. In comparison, the
elimination reaction between Ga(CH2CMe3)3 and am-
monia required heating at 140-150 °C for 4 days in a
sealed tube to effect the formation of (Me3CCH2)2GaNH2
and CMe4 (eq 2) in nearly quantitative yields. Thus,
Low oxidation state gallium clusters1 [Ga(CH2CMe3)]n
(n ) 6-12) have been prepared by the reduction of bis-
(neopentyl)gallium chloride by using either sodium or
lithium with naphthalene in THF solution. When the
reagents were combined at -78 °C, a yellow dihy-
dronaphthalene gallium(III) derivative C10H8[Ga(CH2-
CMe3)2]2‚2MCl (M ) Li, Na) was formed. Upon warm-
ing to room temperature, this intermediate was converted
to gallium(I) clusters (GaR)n (n ) 6-12), GaR3, and MCl.
We have investigated the reaction of this yellow dihy-
dronaphthalene gallium(III) intermediate C10H8[Ga(CH2-
CMe3)2]2‚2NaCl with anhydrous ammonia because of
our interest in the reactions of gallium compounds with
two different organic substituents.2-4 The reactivity of
this dihydronaphthalene derivative with ammonia was
compared, in turn, with that for Ga(CH2CMe3)3. Two
additional reactions of organogallium compounds are
also reported: (1) the reaction of the low oxidation state
gallium cluster [Ga(CH2CMe3)]n with ammonia and (2)
the reaction of Ga(CH2CMe3)2Cl with sodium in liquid
ammonia.
Ga(CH2CMe3)3 + NH3 f
(Me3CCH2)2GaNH2 + CMe4 (2)
this elimination reaction occurs at ∼200 °C above the
temperature needed for the reaction between the yellow
dihydronaphthalene intermediate1 and ammonia. The
latter is known to decompose to Ga(CH2CMe3)3, [Ga(CH2-
CMe3)]n, and C10H8, but (Me3CCH2)2GaNH2 cannot have
been formed by way of the initial decomposition of
C10H8[Ga(CH2CMe3)2]2 and the subsequent elimination
reaction of Ga(CH2CMe3)3 with ammonia.
The yellow gallium(III) derivative of dihydronaph-
thalene C10H8[Ga(CH2CMe3)2]2‚2NaCl reacts with an-
(1) Beachley, O. T., J r.; Pazik, J . C.; Noble, M. J . Organometallics
1994, 13, 2885.
(2) Beachley, O. T., J r.; Royster, T. L., J r.; Arhar, J . R.; Rheingold,
A. L. Organometallics 1993, 12, 1976.
(3) Beachley, O. T., J r.; Rosenblum, D. B.; Churchill, M. R.; Lake,
C. H.; Toomey, L. M. Organometallics 1996, 15, 3653.
(4) Beachley, O. T., J r.; Maloney, J . P.; Rogers, R. D. Organometallics
1997, 16, 3267.
Neopentylgallium(I) [Ga(CH2CMe3)]n reacted with
anhydrous ammonia in a sealed tube, but only at
temperatures in the range of 460-480 °C. After 24 h,
the products were separated and identified as CMe4, H2,
and GaN(s) in yields of 86%, 70% and 88%, respectively,
based on eq 3. Neopentane was identified by its
S0276-7333(97)01123-0 CCC: $15.00 © 1998 American Chemical Society
Publication on Web 04/21/1998

2122 Organometallics, Vol. 17, No. 10, 1998
Notes
characteristic 1H NMR spectrum, whereas H2 was
were recorded by using a Perkin-Elmer Physical Electronics
(PHI) model 5100 ESCA spectrometer with a Mg KR1,2 X-ray
source (1253.6 eV) with a 180° hemispherical detector. The
spectrometer was calibrated to the Ag3d5/2 peak at 367.9 eV.
Spectra were collected at an angle of 45°. The identity of the
elements at the surface were evaluated qualitatively with low-
resolution spectra (89.45 eV), whereas high-resolution spectra
(35.75 eV) were used to establish the binding energies and
peak areas for quantitative analysis. X-ray powder diffraction
data were recorded by using a Siemens D-500 X-ray diffrac-
tometer with Cu KR radiation. Melting points were observed
in a Mel-Temp by using flame-sealed capillaries. Molecular
weights were measured cryoscopically in benzene by using an
instrument similar to that described by Shriver and Drezdzon.7
Rea ction of C10H8[Ga (CH2CMe3)2]2‚Na Cl w ith An h y-
d r ou s NH3. The yellow gallium(III) dihydronaphthalene
derivative C10H8[Ga(CH2CMe3)2]2‚2NaCl was prepared in THF
at -78 °C as previously described1 by using sodium metal
(0.067 g, 2.9 mmol), naphthalene (0.380 g, 2.97 mmol), and
Ga(CH2CMe3)2Cl (0.721 g, 2.91 mmol). Then, excess dry NH3
was added to the flask by vacuum distillation. Initially, the
solution had an intense yellow color. As the solution was
stirred at -78 °C for 18 h, the color disappeared and a colorless
solution and a colorless precipitate formed. Pressure mea-
surements at -196 °C on the vacuum line confirmed the
absence of any noncondensable gas. The THF and excess NH3
were removed by vacuum distillation. The remaining reaction
products were subjected to dynamic vacuum for 40 h. The
products, which were volatile at room temperature, were
collected in a -196 °C trap and identified by 1H NMR
spectroscopy as dihydronaphthalene with very small amounts
of naphthalene and other unidentified impurities. Extraction
of the nonvolatile products with pentane through a glass frit
separated NaCl (0.168 g, 2.88 mmol, 99.0% yield based on Na)
from a pentane-soluble colorless solid. Sublimation of this
solid at 55 °C led to the isolation and identification of (Me3-
CCH2)2GaNH2 (0.344 g, 1.51 mmol, 52% yield based on Na).
(Me3CCH2)2Ga NH2. Mp: 51.8-54.0 °C. 1H NMR (C6D6):
δ 1.10 (s, 9.3H, -CH3), 0.63 (s, 2.2H, -CH2-), 0.34 (s, br, 1.0H,
-NH2). IR (Nujol mull, cm-1): 3870 (vw), 3400 (m), 3325 (m),
3295 (vw), 3205 (w, br), 2735 (w), 2705 (m), 2400 (vw), 2370
(vw), 2280 (vw), 2270 (vw), 2100 (vw), 2010 (vw), 1982 (vw),
1650 (w), 1565 (w), 1355 (s), 1230 (s), 1133 (m), 1099 (s), 1013
(m), 997 (s), 930 (m), 908 (w), 846 (m), 800 (s), 743 (s), 700 (s),
628 (s), 590 (m), 574 (m), 520 (w), 455 (sh), 435 (vs), 382 (m),
328 (w), 288 (m), 245 (w).
Rea ction of Ga (CH2CMe3)3 w ith NH3 a t 140-150 °C. A
break-seal tube was charged with Ga(CH2CMe3)3 (1.42 g, 5.02
mmol) and purified NH3 (5.03 mmol) and then sealed by fusion.
The tube was heated at 140-150 °C for 4 days in a tube
furnace and then opened. Noncondensable gas (-196 °C) was
absent. The volatile products were separated, weighed (0.384
g), and the neopentane was identified by 1H NMR spectroscopy.
The colorless solid remaining in the tube was sublimed at 60-
80 °C and identified as (Me3CCH2)2GaNH2 (0.996 g, 4.37 mmol,
87.3% yield based on Ga(CH2CMe3)3.
(Me3CCH2)2Ga NH2. Mp: 58.8-60.8 °C. Cryoscopic mo-
lecular weight, benzene solution, formula weight 228.03
(observed molality, observed mol wt, association): 0.0796, 490,
2.15; 0.0562, 477, 2.09; 0.0284, 499, 2.19. The 1H NMR and
IR spectra were identical to those described above.
Rea ction of [Ga (CH2CMe3)]n w ith Am m on ia . A break-
seal tube was charged with 0.440 g of [Ga(CH2CMe3)]n (3.13
mmol), and then 3.44 mmol of NH3 was added by vacuum
distillation. The tube was sealed by fusion and heated for 1
day at 460-480 °C. As the reaction occurred, the contents of
the tube changed from dark reddish-brown to light gray to
yellow gray and finally to shiny black. The tube was cooled
1/n [Ga(CH2CMe3)]n + NH3 f
GaN(s) + CMe4 + H2 (3)
identified by its typical properties in the vacuum line.
The shiny black solid remaining in the tube was
identified as GaN (hexagonal) by its X-ray powder
pattern and ESCA spectrum. The ESCA spectrum
confirmed the presence of gallium, nitrogen, carbon, and
oxygen. However, an elemental analysis of the shiny
black solid revealed very low carbon contamination,
1.24% C and 0.69% H. It is of interest to note that when
GaN(s) is prepared from GaMe3 and NH3, temperatures
in the range of ∼1000 °C are needed.5 Thus, the lower
temperatures used for the reaction of the gallium(I)
compound with ammonia might reflect a significant
relationship between the low oxidation state and inter-
mediates in the pathway for the formation of group 13-
15 materials.
The reaction between Ga(CH2CMe3)2Cl and sodium
in liquid ammonia also was studied. Addition of a
stoichiometric quantity of Ga(CH2CMe3)2Cl dissolved in
ammonia at -70 °C to the deep blue solution formed
between sodium and liquid ammonia resulted in the
formation of a colorless solution and a heavy colorless
precipitate. Subsequent use of the vacuum line revealed
the formation of slightly less than 0.5 mol of hydrogen
gas per mole of Ga(CH2CMe3)2Cl. Thus, the balanced
equation shown in eq 4 describes the reaction.
Ga(CH2CMe3)2Cl + Na + NH3 Liquid ammonia8
(Me3CCH2)2GaNH2 + 1/2H2 + NaCl (4)
The compound (Me3CCH2)2GaNH2 was fully charac-
terized by its melting point, 1H NMR and IR spectra, C
and H analyses, and a cryoscopic molecular weight
study in benzene solution. All data are consistent with
the presence of a dimer in solution and in the solid state
with a melting point of 58.0-60.5 °C. The correspond-
ing methyl derivative6 Me2GaNH2 exists as a trimer
with a higher melting point (100-101.5 °C).
Exp er im en ta l Section
All compounds described in this investigation were very
sensitive to oxygen and moisture and were manipulated by
using standard vacuum line techniques or under a purified
argon atmosphere in a Vacuum Atmospheres drybox equipped
with a Dry Train. All solvents were purified before use.
Elemental analyses were performed by E+R Microanalytical
Laboratories, Corona, NY. Infrared spectra of samples as
Nujol mulls between CsI plates were recorded by means of a
Perkin-Elmer 683 spectrometer. The 1H NMR spectra were
recorded at 300 MHz by using a Varian Gemini 300 spectrom-
eter. All samples for NMR spectra were contained in flame-
sealed NMR tubes. Chemical shifts are reported in δ (ppm)
and are referenced to tetramethylsilane (TMS) as δ ) 0.00 ppm
and benzene as δ ) 7.15 ppm. X-ray photoelectron spectra
(5) (a) Addamiano, A. J . J . Electrochem. Soc. 1961, 108, 1072. (b)
Munir, Z. A.; Searcy, A. W. J . Chem. Phys. 1965, 42, 4223. (c) Pichugin,
I. G.; Searcy, D. A. Inorg. Mater. 1970, 6, 1732. (d) Isherwood, B. J .;
Wickenden, D. K. J . Mater. Sci. 1970, 5, 869. (e) Ejder, E. J . Cryst.
Growth 1974, 22, 44. (f) Ogino, T.; Aoki, M. J . Appl. Phys. 1979, 18,
1049.
(7) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-Sensitive
Compounds; McGraw-Hill: New York, 1968; p 38.
(6) Coates, G. E. J . Chem. Soc. 1951, 2003.

Notes
Organometallics, Vol. 17, No. 10, 1998 2123
to -196 °C and opened, and the noncondenseable gas was
transferred and measured by using a Toepler-pump-gas-buret
assembly (2.20 mmol, 70.3% based on eq 3). The volatile,
condensable material (0.195 g) was transferred by vacuum
distillation to a small weighed trap. The 1H NMR spectrum
of these volatile compounds in C6D6 identified neopentane
(CMe4, δ 0.99, 86% yield based on eq 3). The nonvolatile, shiny
black solid was scraped out of the reaction tube in the drybox,
ground into a fine powder, and washed with 50 mL of pentane.
This crystalline phase was identified as GaN (0.232 g, 2.77
mmol, 88.5% based on eq 3).
Ga N. X-ray powder diffraction (d spacings in Å): 2.76, 2.58,
2.44, 1.89, 1.60, 1.46, 1.37 (lit.8 for hexagonal GaN 2.76, 2.59,
2.43, 1.88, 1.59, 1.46, 1.38). ESCA (binding energy, eV;
corrected to C1s): Ga3d3/2 20.3, Ga2p3/2 1119.5, N1s 398.3, C1s
285.0, O1s 531.7 (lit.9 for hexagonal GaN Ga3d3/2 19.8, Ga2p3/2
1124.1, N1s 397.0, C1s 285.0, O1s 531.9). Surface ratio from
ESCA (Ga:N): 1.32:1.00. Anal. Found for GaN: C, 1.24; H,
0.69.
Then liquid ammonia (25 mL), which had been previously
dried by stirring over sodium at -70 °C, was vacuum distilled
onto the fresh sodium metal and stirred for 0.5 h to form a
deep blue solution. After a small amount of ammonia was
distilled onto the Ga(CH2CMe3)2Cl to form a solution, the
reagents were combined. The dark blue solution immediately
turned light blue. More ammonia was distilled back into the
flask which originally contained the Ga(CH2CMe3)2Cl in order
to ensure the quantitative transfer of the reagent. The final
solution was colorless and contained a colorless precipitate.
After the mixture was stirred for 1 h at -70 °C, the noncon-
densable gas was measured at -196 °C with a Toepler-pump-
gas-buret assembly (0.458 mmol H2). The ammonia was
removed, and the products were extracted with pentane to
separate NaCl (0.068 g, 1.2 mmol, 100% yield) from (Me3-
1
CCH2)2GaNH2, which was identified by its melting point, H
NMR and IR spectra, and partial elemental analysis.
(Me3CCH2)2Ga NH2. Mp: 58.0-60.5 °C. Anal. Calcd. for
C
10H24GaN: C, 52.56; H, 10.61. Found: C, 52.83; H, 10.85.
Rea ction of Ga (CH2CMe3)2Cl w ith Sod iu m in Liqu id
Am m on ia . A Solv-seal flask was charged with 0.027 g of Na
(1.2 mmol) and then connected with an 80° elbow to another
flask which contained 0.290 g of Ga(CH2CMe3)2Cl (1.17 mmol).
1
The H NMR and IR spectra were identical to that described
above.
This work was supported in part by the Office of Naval
Research. We are especially grateful for the help of Prof.
Rossman F. Giese, University at Buffalo, for the X-ray powder
diffraction studies which were used to identify GaN and of
Prof. J oseph A. Gardella, J r. and Ms. Norma L. Hernandez
de Gatica, University at Buffalo, for recording and evaluating
the ESCA spectral data.
(8) J CPDS Powder Diffraction File Search Manual; International
Center for Diffraction Data: Swarthmore, PA.; Card 2-1078.
(9) (a) Gann, R. G.; Geib, K. M.; Wilmsen, C. W.; Costello, J .;
Hrychowain, G.; Zeto, R. J . J . Appl. Phys. 1988, 63, 506. (b) Wagner,
C. D.; Riggs, W. M.; Davis, L. E.; Moulder, S. F. Handbook of X-ray
Photoelectron Spectroscopy; Muilenberg, G. E., Ed.; Physical Electron-
ics: Eden Prairie, MN, 1979. (c) Murty, P. S.; Bhaskara Rao, S. V. N.;
Sharma, S. K.; Grampurohit, S. V. Curr. Sci. 1982, 51, 468.
OM9711234