Quasi-isomeric gallium amides and imides GaNR2 and RGaNR (R = organic group): Reactions of the digallene, Ar′GaGaAr′ (Ar′ = C6H3-2,6-(C6H3-2,6-Pr i2)2) with unsaturated nitrogen compounds

Article abstract of DOI:10.1021/ja063072k

Reactions of the digallene Ar′GaGaAr′(1) (Ar′ = C₆H₃-2,6-(C₆H₃-2,6-Pr ⁱ₂)₂), which dissociates to green :GaAr′ monomers in solution, with unsaturated N-N-bonded molecules are described. Treatment of solutions of :GaAr′ with the bulky azide N₃Ar# (Ar# = C₆H₃-2,6-(C₆H₂-2,6-Me ₂-4-Bu^t)₂), afforded the red imide Ar′GaNAr# (2). Addition of the azobenzenes, ArylNNAryl (Aryl = C ₆H₄-4-Me (p-tolyl), mesityl, and C₆H ₃-2,6-Et₂) yielded the 1,2-Ga₂N₂ ring compound Ar′GaN(p-tolyl)N(p-tolyl)GaAr′ (3) or the products MesN=NC₆H₂-2,4-Me₂-6-Ga(Me)Ar′ (4) and 2,6-Et₂C₆H₃N=NC₆H ₃-2-Et-6-Ga(Et)Ar′ (5). Reaction of GaAr′ with N ₂CPh₂ yielded the 1,3-Ga₂N₂ ring compound Ar′Ga(μ:η¹-N₂CPh₂) ₂GaAr′ (6), which is quasi-isomeric to 3. Calculations on simple model isomers showed that the Ga(I) amide GaNR₂ (R = Me) is much more stable than the isomeric Ga(III) imide RGaNR. This led to the synthesis of the first stable monomeric Ga(I) amide, GaN(SiMe ₃)Ar″ (8) (Ar″ = C₆H₃-2,6-(C ₆H₂-2,4,6-Me₃)₂ from the reaction of LiN(SiMe₃)Ar″ (7) and Gal . Compound 8 is also the first one-coordinate gallium species to be characterized in the solid state. The reaction of 8 with N₃Ar″ afforded the amido-imide derivative Ar″NGaN(SiMe₃)Ar″ (9), a gallium nitrogen analogue of an allyl anion. All compounds were spectroscopically and structurally characterized. In addition, DFT calculations were performed on model compounds of the amide, imide, and cyclic 1,2- and 1,3-species to better understand their bonding. The pairs of compounds 2 and 8 as well as 3 and 6 are rare examples of quasi-isomeric heavier main group element compounds.

Full text of DOI:10.1021/ja063072k

Published on Web 09/02/2006
Quasi-Isomeric Gallium Amides and Imides GaNR2 and
RGaNR (R ) Organic Group): Reactions of the Digallene,
Ar′GaGaAr′ (Ar′ ) C6H3-2,6-(C6H3-2,6-Pri2)2) with Unsaturated
Nitrogen Compounds
Robert J. Wright, Marcin Brynda, James C. Fettinger, Audra R. Betzer, and
Philip P. Power*
Contribution from the Department of Chemistry, One Shields AVenue,
UniVersity of California, DaVis, California 95616
Received May 10, 2006; E-mail: pppower@ucdavis.edu
Abstract: Reactions of the “digallene” Ar′GaGaAr′(1) (Ar′ ) C6H3-2,6-(C6H3-2,6-Pri2)2), which dissociates
to green :GaAr′ monomers in solution, with unsaturated N-N-bonded molecules are described. Treatment
of solutions of :GaAr′ with the bulky azide N3Ar# (Ar# ) C6H3-2,6-(C6H2-2,6-Me2-4-But)2), afforded the red
imide Ar′GaNAr# (2). Addition of the azobenzenes, ArylNNAryl (Aryl ) C6H4-4-Me (p-tolyl), mesityl, and
C6H3-2,6-Et2) yielded the 1,2-Ga2N2 ring compound Ar′GaN(p-tolyl)N(p-tolyl)GaAr′ (3) or the products MesNd
NC6H2-2,4-Me2-6-Ga(Me)Ar′ (4) and 2,6-Et2C6H3NdNC6H3-2-Et-6-Ga(Et)Ar′ (5). Reaction of GaAr′ with
N2CPh2 yielded the 1,3-Ga2N2 ring compound Ar′Ga(µ:η1-N2CPh2)2GaAr′ (6), which is quasi-isomeric to 3.
Calculations on simple model isomers showed that the Ga(I) amide GaNR2 (R ) Me) is much more stable
than the isomeric Ga(III) imide RGaNR. This led to the synthesis of the first stable monomeric Ga(I) amide,
GaN(SiMe3)Ar′′ (8) (Ar′′ ) C6H3-2,6-(C6H2-2,4,6-Me3)2 from the reaction of LiN(SiMe3)Ar′′ (7) and “GaI”.
Compound 8 is also the first one-coordinate gallium species to be characterized in the solid state. The
reaction of 8 with N3Ar′′ afforded the amido-imide derivative Ar′′NGaN(SiMe3)Ar′′ (9), a gallium nitrogen
analogue of an allyl anion. All compounds were spectroscopically and structurally characterized. In addition,
DFT calculations were performed on model compounds of the amide, imide, and cyclic 1,2- and 1,3-species
to better understand their bonding. The pairs of compounds 2 and 8 as well as 3 and 6 are rare examples
of quasi-isomeric heavier main group element compounds.
Introduction
below in which ligands are removed progressively to yield a
simple metal nitride. The nitrides AlN, GaN, and InN have
important electronic applications, and this is a major justification
for the study of their imide, amide, or amine adduct precursors.2-4
There is an extensive chemistry of species with bonding
between heavier group 13 elements (Al-Tl) and nitrogen.1-8
The simple derivatives can be classified according to the scheme
R3MNR′3 -RR′8 R2MNR′2 -RR′8 RMNR′ -RR′8 MN
(1) Downs, A. J., Ed. Chemistry of Aluminium, Gallium, Indium and Thallium;
Blackie Academic & Professional: London, 1993.
(2) Jones, A. C., O’Brien, P., Eds. CVD of Compound Semiconductors:
Precursor Synthesis, DeVelopment and Applications: VCH: Weinheim,
Germany, 1996.
amine adduct
amide
imide
nitride
(3) Jegier, J. A.; Gladfelter, W. L. Coord. Chem. ReV. 2000, 206-207, 631-
The amine adducts5 and amides6-8 have been widely studied.
The imides have also received synthetic and theoretical attention,
but they are usually found as strongly associated species
(RMNR′)n (n g 4; R or R′ ) alkyl, aryl, or H) that have cage
structures.8,9 There are a few lower aggregate rings, (RM-
NR′)310,11 or (RMNR′)2,12-18 that have three-coordinate metals
where M-N multiple bonding is possible. The small number
of dimeric imides (RMNR′)2 currently known contain a sym-
metric 1,3-M2N2 core, which has been postulated to form by
the head-to-tail dimerization of two RMNR′ monomers.9 The
related 1,2-M2N2 isomer has only been reported for boron.19
650.
(4) Cowley, A. H.; Jones, R. A. Angew. Chem. 1989, 101, 1235-1243.
(5) Gardiner, M. G.; Raston, C. L. Coord. Chem. ReV. 1997, 166, 1-34.
(6) Brothers, P. J.; Power, P. P. AdV. Organomet. Chem 1996, 39, 1-69.
(7) Carmalt, C. J. Coord. Chem. ReV. 2001, 223, 217-264.
(8) Lappert, M. F.; Sanger, A. R.; Srivastava, R. C.; Power, P. P. Metal and
Metalloid Amides: Synthesis, Structure, and Physical and Chemical
Properties; Ellis Harwood/Wiley: New York, 1980.
(9) Timoshkin, A. Y. Coord. Chem. ReV. 2005, 249, 2094-2131.
(10) Waggoner, K. M.; Power, P. P. J. Am. Chem. Soc. 1991, 113, 3385-3393.
(11) Waggoner, K. M.; Hope, H.; Power, P. P. Angew. Chem., Int. Ed. Engl.
1988, 100, 1765-1766.
(12) Wehmschulte, R. J.; Power, P. P. Inorg. Chem. 1998, 37, 2106-2109.
(13) Wehmschulte, R. J.; Power, P. P. Inorg. Chem. 1998, 37, 6906-6911.
(14) Wehmschulte, R. J.; Power, P. P. J. Am. Chem. Soc. 1996, 118, 791-797.
(15) Schulz, S.; Voigt, A.; Roesky, H. W.; Haeming, L.; Herbst-Irmer, R.
Organometallics 1996, 15, 5252-5253.
(16) Schulz, S.; Haeming, L.; Herbst-Irmer, R.; Roesky, H. W.; Sheldrick, G.
M. Angew. Chem., Int. Ed. Engl. 1994, 33, 1969-1070.
(17) Jutzi, P.; Neumann, B.; Reumann, G.; Stammler, H.-G. Organometallics
1999, 18, 2037-2039.
(18) Fisher, J. D.; Shapiro, P. J.; Yap, G. P. A.; Rheingold, A. L. Inorg. Chem.
1996, 35, 271-272.
(19) Thiele, B.; Paetzold, P.; Englert, U. Chem. Ber. 1992, 125, 2681-2686.
9
12498
J. AM. CHEM. SOC. 2006, 128, 12498-12509
10.1021/ja063072k CCC: $33.50 © 2006 American Chemical Society

Quasi-Isomeric Heavier Main Group Element Compounds
A R T I C L E S
were synthesized from the aniline and KMnO4.35 N3Ar#25 was synthe-
1
sized from LiAr# and TsN3 according to the procedure for N3Ar′′. H
and 13C NMR spectra were recorded on Varian 300 and 400
spectrometers and referenced to known standards. UV/vis data were
recorded on a Hitachi-1200 spectrophotometer, and the melting points
were recorded using a Meltemp apparatus and were not corrected.
Ar′GaNAr# (2). Ar′GaGaAr′ (0.390 g, 0.418 mmol) was dissolved
in hexane (60 mL) to give a deep-green solution. A solution of N3Ar#
(0.366 g, 0.835 mmol) in hexane (30 mL) was added dropwise with
stirring to yield a deep-red solution and red precipitate. The reaction
mixture was stirred for 4 h and then concentrated to ca. 15 mL. The
mother liquor was removed from the precipitated product 2 and
discarded. Yield: 0.524 g, 68%; mp 215-216 °C. Overnight storage
at ca. -15 °C of a saturated hexane solution of 2 afforded X-ray-quality
Monomeric imides are of interest because they have formal
group 13 element-nitrogen triple bonds. Such compounds had
been known only for BN species,20-24 but in a preliminary report
we showed that, with use of the bulky terphenyl substituents,
the first heavier group 13 element monomeric imides Ar′MNAr#
(M ) In or Ga) could be synthesized by reaction of Ar′MMAr′
(Ar′ ) C6H3-2,6-(C6H3-2,6-Pri2)2) or C6H3-2,6(Xyl-4-But)2 with
N3Ar# (Ar# ) C6H3-2,6-(C6H2-2,6-Me2-4-But)2).25 These com-
pounds had short Ga-N and In-N bond lengths, but they had
trans-bent structures that were indicative of weakened M-N
bonding. The diminished M-N bond strength was supported
by calculations on model compounds.25,26 Unexpectedly, these
calculations also indicated that the monomeric and isomeric M(I)
amides, MNH2 were considerably (Al ) 42.5 kcal‚mol-1; Ga
) 45.1 kcal‚mol-1; In ) 61.6 kcal‚mol-1) more stable than the
imides.26 However, to date only a few thallium(I) amides27,28
have been isolated and characterized by X-ray crystallography,
while the parent hydrogen derivatives, MNH2 (M ) Al-In)
were found to be stable only in the frozen matrices in which
they were generated.29,30 We therefore wished to show that a
stable monomeric low-valent group 13 element amide that is
isomeric or quasi-isomeric (i.e. the core structures, but not the
entire molecule, are isomeric) to the corresponding imide could
be synthesized. We now describe the synthesis and characteriza-
tion of the stable (mp ) 181-183 °C) monomeric gallium(I)
amide, GaN(SiMe3)Ar′′ as well as its reaction with a bulky
terphenyl azide to afford the monomeric amido-imide Ar′′NGaN-
(SiMe3)Ar′′ which is a heavier group 13 element nitrogen
analogue of an allyl anion. In addition, we describe the reaction
of :GaAr′ with a variety of unsaturated nitrogen species such
as azides, azobenzenes, and a diazomethane compound to afford,
inter alia, monomeric gallium imides, 1,3- and 1,2-Ga2N2 ring
species and C-C bond activation products.
1
crystals of 2. H NMR (400 MHz, C6D6, 25 °C): δ ) 0.97 (d, 12H,
3
3
o-CH(CH3)2, JHH ) 6.4 Hz), 0.98 (d, 12H, o-CH(CH3)2, JHH ) 6.4
Hz), 1.42 (s, 18H, p-C(CH3)3, 2.03 (s, 12H, o-CH3) 2.54 (sept, 4H,
CH(CH3)2, 3JHH ) 6.4 Hz), 6.67 (t, 1H, p-central Ph of Ar′, 3JHH ) 7.2
Hz), 6.75 (d, 2H, m-central Ph of Ar#, JHH )7.6 Hz), 7.03 (m, 3H,
3
Ar-H), 7.12 (s, 4H, m-(4-But-Xyl)), 7.15 (d, 4H, m-Dipp, 3JHH ) 7.6
Hz), 7.25 (t, 2H, p-Dipp, JHH ) 7.6 Hz). 13C{1H}NMR (100.6 MHz,
3
C6D6, 25 ° C): δ 21.33 (o-CH3), 24.85 (o-CH(CH3)2), 25.44 (o-CH-
(CH3)2), 31.29 (o-CH(CH3)2), 32.05 (p-C(CH3)3), 34.57 (p-C(CH3)3),
117.42 (p-central Ph of Ar′), 123.91 (m-Dipp), 124.87 (m-(4-But-Xyl)),
128.82, 129.94 (m-Ph unassigned), 130.40 (p-Ph unassigned), 134.54,
136.57 (o-(4-But-Xyl)), 140.52, 140.75, 145.44, 147.06 (o-central Ph
of Ar′), 147.60, 148.17, 150.52 (p-(4-But-Xyl)), 152.76 (i-central Ph
of Ar′). UV/vis (hexanes) λmax nm (ꢀ, mol‚L-1‚cm-1): 303 (26500),
366 (3900).
Ar′GaN(p-tolyl)N(p-tolyl)GaAr′ (3). Ar′GaGaAr′ (0.233 g, 0.25
mmol) was dissolved with stirring in toluene (25 mL). To this solution
was added 1,2-di-p-tolyldiazene (0.052 g, 0.250 mmol) as a solution
in toluene (20 mL). Over the 10-min addition period the resulting
solution developed a deep blue-green color. The solution was allowed
to stir for 6 h and then was concentrated to ca. 10 mL under reduced
pressure. Storage at ca. -30 °C overnight afforded the product 3 as
large, blue-green X-ray-quality crystals. Yield: 0.148 g, 52%; mp )
275 °C (turned orange). 1H NMR (300 MHz, C6D6, 25 °C): δ 0.46 (d,
6H, CH(CH3)2) 3JHH ) 6.9 Hz, 0.56 (d, 6H, CH(CH3)2) 3JHH ) 6.9 Hz,
0.75 (d, 6H, CH(CH3)2, 3JHH ) 6.9 Hz), 1.12 (d, 12H, CH(CH3)2, 3JHH
) 6.9 Hz), 1.22 (d, 6H, CH(CH3)2, 3JHH ) 6.9 Hz), 1.29 (d, 12H, CH-
3
(CH3)2, JHH ) 6.9 Hz), 2.03 (3H, 4-MeC6H4), 2.10 (3H, 4-MeC6H4),
2.47 (sept, 2H, CH(CH3)2, 3JHH ) 6.9 Hz), 2.95 (sept, 2H, CH(CH3)2,
3JHH ) 6.9 Hz), 3.11 (sept, 2H, CH(CH3)2, 3JHH ) 6.9 Hz), 3.44 (sept,
2H, CH(CH3)2, 3JHH ) 6.9 Hz), 6.21 (d, 4H, m-Dipp, 3JHH ) 8.1 Hz),
6.40 (d, 2H, 3JHH ) 8.1 Hz) 6.63 (d, 4H, m-Dipp, 3JHH ) 8.1 Hz), 6.83
Experimental Section
General Procedure. All manipulations were carried out by using
modified Schlenk techniques under an atmosphere of N2 or in a Vacuum
Atmospheres HE-43 drybox. All solvents were distilled from molten
Na/K alloy and degassed three times prior to use. H2NAr′′,31 “GaI”,32
Ph2CN2,33 and Ar′GaGaAr′34 were synthesized by literature methods.
(p-tolyl)NN(p-tolyl), MesNNMes, and 2,6-Et2C6H3NNC6H3-2,6-Et2
3
(d, 2H, JHH ) 8.1 Hz), 6.96-7.21 (m, 10H) 7.42 (d, 2H, tolyl), 8.04
(d, 2H, tolyl). 13C{1H}NMR (75.45 MHz, C6D6, 25 °C): δ 20.74 (4-
MeC6H4), 21.27 (4-MeC6H4), 22.80 (CH(CH3)2), 23.34 (CH(CH3)2),
23.87 (CH(CH3)2), 24.15 (CH(CH3)2), 24.83 (CH(CH3)2), 25.36 (CH-
(CH3)2), 25.56 (CH(CH3)2), 26.02 (CH(CH3)2), 28.49 (CH(CH3)2), 30.69
(CH(CH3)2), 30.99 (CH(CH3)2), 31.64 (CH(CH3)2), 115.24 (m-Dipp),
117.56 (m-Dipp), 120.60-154.65 (multiple aromatic carbon signals).
UV/vis (hexanes) λmax nm (ꢀ mol-1‚L‚cm-1): 405 (1900), 601 (240).
(20) Elter, G.; Neuhaus, M.; Meller, A.; Schmidt-Baese, D. J. Organomet. Chem.
1990, 381, 299-313.
(21) Paetzold, P. AdV. Inorg. Chem. 1987, 31, 123-170.
(22) Paetzold, P.; Von Plotho, C.; Schmid, G.; Boese, R.; Schrader, B.; Bougeard,
D.; Pfeiffer, U.; Gleiter, R.; Schaefer, W. Chem. Ber. 1984, 117, 1089-
1102.
(23) Haase, M.; Klingebiel, U.; Boese, R.; Polk, M. Chem. Ber. 1986, 119, 1117.
(24) Luthin, W.; Elter, G.; Heine, A.; Stalke, D.; Sheldrick, G. M.; Meller, A.
Z. Anorg. Allg. Chem. 1992, 608, 147.
MesNdNC6H2-2,4-Me2-6-Ga(Me)Ar′ (4). Ar′GaGaAr′ (0.233 g,
0.25 mmol) was dissolved in toluene (25 mL) with stirring to give a
green solution. To this solution was added 1,2-dimesityldiazene (0.133
(25) Wright, R. J.; Phillips, A. D.; Allen, T. L.; Fink, W. H.; Power, P. P. J.
Am. Chem. Soc. 2003, 125, 1694-1695.
(26) Himmel, H.-J.; Downs, A. J.; Green, J. C.; Greene, T. M. J. Chem. Soc.,
Dalton. Trans. 2001, 535-545.
(31) Wright, R. J.; Steiner, J.; Beaini, S.; Power, P. P. Inorg. Chim. Acta 2006,
359, 1939-1946.
(27) Wright, R. J.; Brynda, M.; Power, P. P. Inorg. Chem. 2005, 44, 3368-
3370.
(32) Green, M. L. H.; Mountford, P.; Smout, G. J.; Speel, S. R. Polyhedron
1990, 9, 2763; Baker, R. J.; Jones, C. Dalton Trans. 2005, 1341-1348.
(33) Kumar, S.; Murray, R. W. J. Am. Chem. Soc. 1984, 106, 1040-1045.
(34) Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. J. Am. Chem.
Soc. 2003, 125, 2667-2679.
(28) Peters, J. C.; Harkins, S. B.; Brown, S. D.; Day, M. W. Inorg. Chem. 2001,
40, 5083-5091.
(29) Lanzisera, D. V.; Andrews, L. J. Phys. Chem. A 1997, 101, 5082-5089.
(30) Himmel, H.-J.; Downs, A. J.; Greene, T. M. J. Am. Chem. Soc. 2000, 122,
9793-9807.
(35) Barman, D. C.; Saikia, P.; Prajapati, D.; Sandhu, J. S. Synth. Commun.
2002, 32, 3407-3412.
9
J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006 12499

A R T I C L E S
Wright et al.
g, 0.50 mmol) in toluene (20 mL). The color of the solution became
orange. The solvents were removed under reduced pressure, and the
residue was extracted with hexane (20 mL). Overnight storage of the
solution at ca. -30 °C afforded orange, X-ray-quality crystals of the
pressure to ca. 25 mL. Overnight storage at ca. -15 °C afforded 0.358
g of X-ray quality crystals. Yield: 70.5%; mp ) 165-167 °C. 1H NMR
(300 MHz, C6D6, 25 °C): δ ) -0.32 (s, 9H, Si(CH3)), 1.91 (s, 12H,
o-CH3), 2.21 (s, 6H, p-CH3), 2.24 (s, 6H, p-CH3), 2.28 (s, 12H, o-CH3),
6.64-6.80 (m, 4H, p-Ph, p-Ph, m-Ph), 6.87 (s, 4H, m-Mes), 6.92 (s,
4H, m-Mes), 7.00 (d, 2H, m-Ph, 3JHH ) 7.5 Hz); 13C{1H}NMR (75.46
MHz, C6D6, 25 °C): δ 2.463 (Si(CH3)3), 21.30 (p-CH3), 21.33 (p-CH3),
21.50 (o-CH3), 21.52 (o-CH3), 115.02 (m-Mes), 121.41 (m-Mes),
128.66, 129.03, 129.09, 131.07, 131.11, 131.95, 133.25, 133.72, 134.89,
137.26, 140.16, 140.61, 140.80, 146.36, 152.47. UV-vis (hexanes) λmax
nm (ꢀ mol-1‚L‚cm-1): 250 (7700), 294 (8000), and 522 (450).
1
product 4. Yield: 0.256 g, 70%; mp ) 183-185 °C. H NMR (400
MHz, C6D6, 25 °C): δ -0.75 (3H, Ga-CH3), 1.11 (d, 24H, CH(CH3)2,
3JHH ) 6.9 Hz), 1.89 (6H, o-CH3), 2.02 (3H, p-CH3), 2.10 (3H, o-CH3),
3
2.53 (3H, o-CH3) 3.08 (sept, 4H, CH(CH3)2, JHH ) 6.9 Hz), 6.58 (s,
2H, m-Mes), 6.61 (s, 1H, m-Mes), 6.78 (s, 1H m-Mes) 7.01-7.21 (m,
9H, m-C6H3, p-C6H3, m-Dipp, p-Dipp). 13C{1H}NMR (C6D6, 75.46
MHz, 25 °C): δ -5.39 (Ga-Me), 17.79 (p-CH3), 18.66 (CH3), 20.53
(CH3), 21.81 (CH3), 26.01 (CH(CH3)2), 30.52 (CH(CH3)2), 122.42 (m-
Dipp), 126.69, 129.82, 130.31, 130.46, 131.83, 133.66, 137.45, 140.133,
143.35, 143.88, 146.43, 148.76, 149.57 (o-Dipp), 149.94, 153.51. UV/
vis (hexanes): decreasing absorbance at longer wavelengths which
diminishes to zero at 510 nm.
Computational Methods
The calculations were performed using DFT theory with B3LYP
functional, using the GAUSSIAN 03 package,36 and the representations
of the molecular structures and molecular orbitals were generated with
the MOLEKEL program.37 The model compounds used were based
on the frozen geometries extracted from the corresponding crystal
structures, where some of the bulky aryl groups were replaced with
phenyl rings. The geometries of the dimeric imide models were
optimized at the B3LYP/6-31g* level. Calculations were also performed
on the model complexes RGaNR and GaNR2 (R ) H and Me) at the
B3LYP/6-31g* level. The Wiberg bond orders were calculated for the
geometries optimized at the B3LYP/6-31g* level, using AOMIX
program.38
2,6-Et2C6H3NdNC6H3-2-Et-6-Ga(Et)Ar′ (5) was synthesized in a
manner similar to that for 4. Yield: 67%; mp ) 195-197 °C. 1H NMR
3
(300 MHz, C6D6, 25 °C): δ -0.052 (q, 2H, Ga-CH2CH3, JHH ) 7.5
Hz), 0.73 (t, 3H, Ga-CH2CH3, 3JHH ) 7.5 Hz), 0.97 (t, 6H, o-CH2CH3,
3
3JHH ) 7.5 Hz), 1.04 (d, 12H, o-CH(CH3)2, JHH ) 6.9 Hz), 1.11 (d,
12H, o-CH(CH3)2, 3JHH ) 6.9 Hz), 2.24 (q, 2H, o-CH2CH3, 3JHH ) 7.5
Hz), 2.77 (q, 4H, o-CH2CH3, 3JHH ) 7.5 Hz), 2.99 (sept, 4H, CH(CH3)2,
3JHH ) 6.9 Hz), 6.96-7.16 (m, 15H, arene-H). 13C{1H}NMR (C6D6,
75.46 MHz, 25 °C): δ 5.24 (Ga-CH2CH3), 11.31 (Ga-CH2CH3)), 13.84
(o-CH2CH3), 16.03 (o-CH2CH3), 23.06 (CH(CH3)2), 23.92 (o-CH2CH3),
24.45 (o-CH2CH3), 26.18 (CH(CH3)2), 30.77 (CH(CH3)2), 122.84 (m-
Dipp), 126.19, 126.65, 127.26, 128.57, 130.66, 133.54, 133.86, 137.38,
143.69, 146.06, 146.42, 146.63, 149.41, 149.65, 152.09, 154.38. UV/
vis (hexanes): decreasing absorbance at longer wavelengths which UV
diminishes to zero at 485 nm.
X-ray Crystallography
Crystals of 2, 3, 4, 5, 6, 8, and 9 were removed from a
Schlenk tube under a stream of argon and immediately covered
with a thin layer of hydrocarbon oil. A suitable crystal was
selected, attached to a glass fiber, and quickly placed in a low-
temperature stream.39 The data for 2, 3, 4, 5, 6, and 8 were
recorded near 90 K on a Bruker SMART 1000 (Mo KR radiation
and a CCD area detector), while 9 was collected on a Bruker
APEX (Mo KR radiation and a CCD area detector). For
compounds 2, 3, 4, 5, 6, 8 the SHELX version 6.1 program
package was used for the structure solutions and refinements.
Absorption corrections were applied using the SADABS
program.40 Crystals of 9 were determined to be twinned, and
an alternative procedure (see Supporting Information) was used
to “de-twin” the data and afford a solution. The crystal structures
were solved by direct methods and refined by full-matrix least-
squares procedures. All non-H atoms were refined anisotropi-
cally. H atoms were included in the refinement at calculated
positions using a riding model included in the SHELXTL
program. A summary of the data collection parameters for 2-6,
8, and 9 is provided in Table 1.
(Ar′GaNNCPh2)2 (6). Ar′GaGaAr′ (0.300 g, 0.32 mmol) was
dissolved in PhMe (30 mL). To this solution was added Ph2CN2 (0.124
g, 0.64 mmol) in PhMe (20 mL). Upon addition the deep-green color
faded to pale-orange. The reaction was stirred overnight. Removal of
the solvent under reduced pressure, extraction with hexanes (20 mL),
and overnight storage at ca. -30 °C afforded orange, X-ray-quality
1
crystals of 6. Yield: 0.154 g, 36.3%; mp ) 210-212 °C. H NMR
(300 MHz, C6D6, 60 °C): δ 0.90 (broad, 24H, o-CH(CH3)2), 0.97
(broad, 24H, o-CH(CH3)2), 2.89 (broad, 8H, CH(CH3)2), 6.740-7.26
(mult, 38H, arene-H). 13C{1H}NMR (75.46 MHz, C6D6, 50 °C): δ
23.00 (CH(CH3)2), 23.85 (CH(CH3)2), 26.07 (CH(CH3)2), 30.53
(CH(CH3)2), 31.94 (CH(CH3)2), 124.21 (m-Dipp), 127.36, 127.44,
128.53, 128.80, 129.76, 130.15, 131.96, 132.05, 140.72, 142, 85, 146.17,
147.17, 147.53, 152.78.
GaN(SiMe3)Ar′′ (8). A rapidly stirred slurry of LiN(SiMe3)Ar′′ (1.22
g, 3.00 mmol) in toluene (60 mL) was added dropwise over 1.5 h to a
toluene (20 mL) slurry of “GaI” (0.589 g, 3.00 mmol) with cooling to
ca. -78 °C. The mixture was allowed to warm to room temperature
over 12 h. The resulting pale-yellow solution was decanted from the
precipitates (LiI and some Ga) and filtered through a Celite-padded
frit. The solution was concentrated to ca. 30 mL and stored overnight
at ca. -20 °C, affording 0.303 g (0.644 mmol) of pale-yellow X-ray-
quality crystals of 8. Yield: 21.5%; mp ) 181-183 °C. 1H NMR (300
MHz, C6D6, 25 °C): δ ) -0.110 (s, 9H, Si(CH3)), 2.150 (s, 6H,
Results
The “digallene” Ar′GaGaAr′, which has been shown to have
a weak Ga-Ga bond, dissociates to :GaAr′ monomers in
hydrocarbon solution.34,41 Such solutions have an intense green
color due to an allowed n-p transition. As a result, reactions
of :GaAr′ that involve the gallium lone pair are often ac-
companied by dramatic color changes.25 Treatment of :GaAr′
with the azide N3Ar# (eq 1)
3
p-CH3), 2.243 (s, 12H, o-CH3), 6.828 (t, 1H, p-Ph), JHH ) 7.5 Hz,
3
6.871 (s, 4H, m-Mes), 6.974 (d, 2H, m-Ph), JHH ) 7.5 Hz. 13C NMR
(75.46 MHz, C6D6, 25 °C): δ ) 4.031 (Si(CH3)3), 21.10 (p-CH3) 21.59
(o-CH3), 119.19 (m-Mes), 129.84 (m-Ph) 130.79 (p-Ph), 133.86, 136.98,
137.32, 137.97, 139.38, 150.12.
(36) Frisch, M. J.; et al. Gaussian 03, Revision A.01; Gaussian, Inc.: Pittsburgh,
PA, 2003. A full reference is given in the Supporting Information file.
(37) Flukiger, P.; Luthi, H. P.; Portmann, S.; Weber, J. MOLEKEL 4.3; Swiss
Center for Scientific Computing: Manno, Switzerland, 2000-2002.
(38) Gorelsky, S. I. AOMix program, rev. 5.44; http://www.obbligato.com/
software/aomix/.
(39) Hope, H. Prog. Inorg. Chem. 1995, 34, 1.
(40) SADABS. An empirical absorption correction program, part of the SAINT-
Plus NT version 5.0 package; Bruker AXS: Madison, WI, 1998.
Ar′′NGaN(SiMe3)Ar′′ (9). GaN(SiMe3)Ar′′ (0.300 g, 0.638 mmol)
was dissolved in toluene (40 mL) to give a nearly colorless solution.
To this solution a toluene solution (20 mL) of N3Ar′′ (0.226 g, 0.638
mmol) was added dropwise over 10 min. The resulting reddish purple
solution was stirred for 2 h and then concentrated under reduced
9
12500 J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006

Quasi-Isomeric Heavier Main Group Element Compounds
A R T I C L E S
Table 1. Selected X-ray Crystallographic Parameters of 2-6, 8, and 9
cmpd
2
3
4
5
formula
fw
color, habit
cryst syst
space group
a, Å
b, Å
c, Å
R, deg
â, deg
γ, deg
V, Å3
C63H81NGa (C6H12)0.5
922.01
red block
monoclinic
P21/n
11.7036(6)
24.8171(12)
18.4566(9)
90
91.4380(10)
90
C88H104Ga2N2
1329.17
green block
monoclinic
C2/c
25.919(6)
14.966(3)
22.663(5)
90
123.089(3)
90
7365(3)
4
C48H60GaN2
734.70
orange block
triclinic
P1h
11.347(3)
12.766(4)
16.505(4)
72.430(4)
70.736(4)
66.315(4)
2026.9(10)
2
C50H63GaN2
761.74
orange block
monoclinic
P21/c
12.8419(14)
10.8132(12)
31.065(4)
90
90.861(4)
90
4313.3(8)
4
5359.0(5)
4
Z
cryst dim, mm
0.47 × 0.22 × 0.16
0.40 × 0.39 × 0.26
0.32 × 0.23 × 0.22
0.34 × 0.31 × 0.22
d
calc, g cm-3
1.143
1.199
1.204
1.173
µ mm-1
0.552
41703
7669
0.0517
0.778
32652
6470
0.0369
0.713
20483
8258
0.0545
0.673
40369
8055
0.0410
no. of reflns
no. of obsd reflns
R1 obsd reflns
wR2, all
0.0755
0.1063
0.1315
0.0946
cmpd
6
8
9
formula
fw
color, habit
cryst syst
space group
a, Å
C95H115Ga2N4
1452.35
orange block
monoclinic
P21/n
14.4015(10)
26.1551(19)
21.8374(16) Å
90
C27H34GaNSi
470.36
pale yellow block
triclinic
[C51H59N2SiGa]2[C7H8]3.5
1918.09
red plate
monoclinic
P21/n
20.503(4)
18.564(4)
28.657(6)
90
97.543(3)
90
10813(4)
4
P1h
11.0720(7)
11.6811(8)
11.9741(8)
118.6700(10)
114.1440(10)
90.1510(10)
1201.05(14)
2
b, Å
c, Å
R, deg
â, deg
98.2590(10)°.
90
γ, deg
V, Å3
8140.2(10) Å3
4
Z
cryst dim, mm
0.30 × 0.28 × 0.27
0.38 × 0.22 × 0.19
0.44 × 0.25 × 0.09
d
calc, g cm-3
1.185
1.301
1.178
µ mm-1
0.708
69361
18706
0.0472
1.209
8541
4938
0.0360
0.571
18052
18052
0.0846
no. of reflns
no. of obsd reflns
R1 obsd reflns
wR2, all
0.1282
0.1079
0.1127
25 °C, PhMe
# + N2
(1)
#
internal ring angles of 74.19(6) and 105.64(6)°. The galliums
are planar coordinated, but the nitrogens have a noticeably
pyramidal coordination (∑ °N ) 347.1(2)), and there is a
C(31)-N(1)-N(1A)-C(31A) torsion angle of 77.5°.
In sharp contrast to eq 2 the reaction of :GaAr′ with diazenes
that carry ortho-substituted aryl groups afforded the insertion
products shown in eqs 3 and 4.
:GaAr′
Ar′GaNAr
+ N3Ar
8
1
2
affords an immediate color change from green to deep red with
formation of the imide Ar#NGaAr′ (2) in essentially quantitative
yield. The Ar# substituent was chosen for the azide in order to
facilitate crystallization. The imide structure is shown in Figure
1 and features the shortest Ga-N bond distance (1.701(3) Å)
in a stable compound. The C(ipso)-Ga-N-C(ipso) array is
nearly planar but deviates from linearity with interligand angles
of 148.2(2)° at gallium and 141.7(3)° at nitrogen.
Reaction of a solution of the GaAr′ with the diazene
(p-tolyl)NdN(p-tolyl) afforded the ring compound 3 shown in
eq 2
The product 3 was isolated as blue-green crystals in good
yield. It has a four-membered Ga2N2 ring structure (Figure 2).
The Ga-Ga, Ga-N, and N-N bond lengths 2.4964(8),
1.909(2), and 1.460(4) Å, respectively, are consistent with those
of single bonds. The trapezoidal Ga2N2 core is planar with
9
J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006 12501

A R T I C L E S
Wright et al.
Figure 3. Thermal ellipsoid (30%) drawing of 4. Hydrogen atoms and
isopropyl groups on 2,6-diisopropylphenyl groups are not shown. Selected
bond lengths (Å) and bond angles (deg) are as follows: Ga(1)-C(38) )
1.968(4); Ga(1)-C(1) ) 1.990(4); Ga(1)-C(48) ) 2.013(4); Ga(1)-N(1)
) 2.2001(3); N(1)-N(2) ) 1.266(4). C(38)-Ga(1)-C(1) ) 121.17(14);
C(38)-Ga(1)-C(48) ) 112.32(15); C(1)-Ga(1)-C(48) ) 121.90(15);
C(38)-Ga(1)-N(1) ) 79.31(13); C(1)-Ga(1)-N(1) ) 112.14(13); C(48)-
Ga(1)-N(1) ) 97.82(13). Sum of the angles at N(1) ) 355.8(3).
Figure 1. Thermal ellipsoid (30%) drawing of 2. Hydrogen atoms are not
shown. Selected bond lengths (Å) and bond angles (deg) are as follows:
Ga(1)-N(1) ) 1.701(3); Ga(1)-C(1) ) 1.940(3); N(1)-C(31) ) 1.377(5).
N(1)-Ga(1)-C(1) ) 148.2(2); Ga(1)-N(1)-C(31) ) 141.7(3); C(1)-
Ga(1)-N(1)-C(31) ) 177.7(4).
Figure 4. Thermal ellipsoid (30%) drawing of 5. Hydrogen atoms and
isopropyl groups on 2,6-diisopropylphenyl groups are not shown. Selected
bond lengths (Å) and bond angles (deg) are as follows: Ga(1)-C(38) )
1.984(3); Ga(1)-C(1) ) 1.994(3); Ga(1)-C(49) ) 1.987(3); Ga(1)-N(1)
) 2.218(2); N(2)-N(1) ) 1.266(3). C(38)-Ga(1)-C(1) ) 121.53(12);
C(38)-Ga(1)-C(49) ) 112.60(12); C(1)-Ga(1)-C(49)) 121.28(12);
C(38)-Ga(1)-N(1)) 78.75(10); C(1)-Ga(1)-N(1)) 112.89(10); C(49)-
Ga(1)-N(1) ) 97.67(11). Sum of the angles at N(1) ) 357.6(2).
Figure 2. Thermal ellipsoid (30%) drawing of 3. Hydrogen atoms are not
shown. Selected bond lengths (Å) and bond angles (deg) are as follows:
Ga(1)-Ga(1A) ) 2.4964(8); N(1)-N(1A) ) 1.460(4); Ga(1)-N(1) )
1.909(2); N(1)-C(31) ) 1.405(3). N(1)-Ga(1)-Ga(1A) ) 74.19(6);
Ga(1)-N(1)-N(1A) ) 105.64(6); C(1)-Ga(1)-Ga(1A) ) 166.61(7);
C(31)-N(1)-N(1A) ) 115.24(18); C(6)-C(1)-C(2) ) 119.0(2); C(6)-
C(1)-Ga(1) ) 126.67(11).
However, no dinitrogen elimination was observed, and subse-
In these two cases the N-N double bond remains intact, and
there is insertion of the gallium(I) center into the sp2-sp3 C-C
bond between the aryl ring and the ortho substituent. Thus, the
gallium becomes bound to two aryls and an alkyl carbon and is
also complexed by a nitrogen (Ga-N ) ca. 2.21 Å) from the
diazene (Figures 3 and 4). The N-N bond lengths (1.266(4)
Å) are consistent with the retention of the N-N double bond.
The treatment of solutions of :GaAr′ with N2CPh2 (eq 5) was
studied with the object of preparing a galla-alkene species.
quent workup indicated that a cyclic Ga2N2 product (6) had
formed (Figure 5), in which two Ph2CN2 moieties bridge two
GaAr′ units through their terminal nitrogens. The Ga2N2 core
9
12502 J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006

Quasi-Isomeric Heavier Main Group Element Compounds
A R T I C L E S
Figure 6. Thermal ellipsoid (30%) drawing of 8. Hydrogen atoms are not
shown. Selected bond lengths (Å) and bond angles (deg) are as follows:
Ga(1)-N(1) ) 1.980(2); Si(1)-N(1) ) 1.743(2); N(1)-C(1) ) 1.408(3).
C(1)-N(1)-Si(1) ) 127.5(2); C(1)-N(1)-Ga(1) ) 119.8(3); N(1)-C(1)-
C(6) ) 123.8(2); N(1)-C(1)-C(2) ) 119.0(2); C(6)-C(1)-C(2) ) 117.1-
(2); C(1)-C(2)-C(7) ) 120.4(2). Dihedral between N(1) coordination plane
and central phenyl plane ) 41.5°
Figure 5. Thermal ellipsoid (30%) drawing of 6. Hydrogen atoms and
isopropyl groups on 2,6-diisopropylphenyl groups are not shown. Selected
bond lengths (Å) and bond angles (deg) are as follows: Ga(1)-N(2) )
1.874(3); Ga(1)-N(1) ) 1.895(3); Ga(1)-C(31) ) 1.968(3); Ga(2)-N(2)
) 1.862(3); Ga(2)-N(1) ) 1.899(3); Ga(2)-C(1) ) 1.973(3); N(1)-N(3)
) 1.371(4); N(2)-N(4) ) 1.400(4); N(3)-C(74) ) 1.304(4); N(4)-C(61)
) 1.292(4).
is nearly planar and contains average Ga-N bonds lengths of
1.883(3) Å, while the exocyclic N-N bond lengths are 1.371(4)
Å and 1.400(4) Å.
Calculations on the gallium amides HGaNH26 and MeGaNMe
(see below) showed that their GaNH2 and GaNMe2 isomers were
considerably more stable, than their imide counterparts. These
results provided the impetus for our work toward the synthesis
of monomeric Ga(I) amides. Previous work by Schno¨ckel and
Schnepf42 showed that the reaction of LiN(SiMe3)2 with GaBr
yielded the metal-rich [Ga84(N(SiMe3)2)20].4 We therefore
decided to synthesize the much bulkier LiN(SiMe3)Ar′′ (7) as
a transfer reagent for [N(SiMe3)Ar′′]-, an amide that was
deemed sufficiently bulky to prevent the formation of Ga clusters
or Ga(II) products.31 Reaction of 7 with “GaI” in toluene solvent
yielded the first stable Ga(I) amide GaN(SiMe3)Ar′′ (8) in ca.
20% yield as yellow crystals (eq 6).
Figure 7. Thermal ellipsoid (30%) drawing of one of the crystallographi-
cally independent molecule of 9. Hydrogen atoms are not shown. Selected
bond lengths (Å) and bond angles (deg) are as follows: Ga(2)-N(4) )
1.743(5); Ga(2)-N(3) ) 1.862(5); Ga(2)-C(58) ) 2.395(6). N(4)-Ga-
(2)-N(3) ) 144.0(2); C(79)-N(4)-Ga(2) )133.9(4).
of 1.408(2) and 1.743(2) Å. There is a dihedral angle of 41.5°
between the coordination plane of nitrogen and the plane of
the C(1) aryl ring. Treatment of GaN(SiMe3)Ar′′ with one
equivalent of N3Ar′′ in toluene (eq 7) resulted in N2 evolution
(in a manner similar to that in eq 1) with concomitant production
of the imido-gallium amide Ar′′NGaN(SiMe3)Ar′′ (9) as purple
crystals in good yield
PhMe
LiN(SiMe )Ar′′
+ “GaI”
8
3
-78 °C
7
+ N3Ar′′ 25 °C, PhMe8
GaN(SiMe )Ar′′
+ LiI + Ga (6)
3
:GaN(SiMe3)Ar′′
8
8
Ar′′N(SiMe )NGaAr′′
+ N2 (7)
3
Structural characterization of these showed that the compound
had a monomeric structure (Figure 6). The gallium is coordi-
nated to nitrogen Ga-N ) 1.980(2) Å, and there is long
interaction between gallium with C(13) (Ga(1)-C(13) ) 2.65
Å) of the flanking mesityl ring of the terphenyl nitrogen
substituent. The nitrogen is essentially planar coordinated (∑°
N(1) ) 358.82(8)) with N(1)-C(1) and N(1)-Si(1) distances
9
Its structure (Figure 7) afforded average Ga-N distances of
1.743(5) Å and 1.862(5) Å. The N(1)-Ga-N(2)-C(1) array
has an essentially planar trans-bent structure with angles of
144.0(2)° at gallium and 133.9(4)° at nitrogen. In addition, there
is a relatively close contact (2.395(6) Å) between gallium and
the ipso carbon of a flanking mesityl substituent.
(41) Hardman, N. J.; Wright, R. J.; Phillips, A. D.; Power, P. P. Angew. Chem.,
Int. Ed. 2002, 41, 2842-2844.
(42) Schnepf, A.; Schno¨ckel, H. Angew. Chem., Int. Ed. 2001, 40, 712-715.
Calculated Structures of Model Species. The relative
energies of the linear and trans-bent imides (MeGaNMe) and
9
J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006 12503

A R T I C L E S
Wright et al.
Figure 8. Relative energies (kcal‚mol-1) of the MeNGaMe and GaNMe2 isomers at the B3LYP/6-311+g* level.
the isomeric amide (GaNMe2) were calculated at the B3LYP/
6-311+g* level. The linear geometry was predicted to be only
slightly less stable (2.2 kcal‚mol-1) than the trans-bent geometry
(C-Ga-N ) 157.6°; Ga-N-C ) 145.0°). However, the
gallium(I) amide is considerably more stable than its imido
counterpart (Figure 8). The Kohn-Sham orbital surfaces for
the trans-bent imide are shown in Figure 9. The HOMO and
HOMO - 1 correspond to out-of-plane and in-plane π overlaps,
which are strongly polarized toward nitrogen. The LUMO
possesses substantial 4s character at gallium, while the LUMO
+ 1 features an antibonding Ga-N π combination. For
additional DFT calculations on models of 2 and 9, see the
Supporting Information.
The Monomeric Amides GaNMe2 and GaN(SiMe3)Ar (Ar
) C6H2-2,6-Ph2). Geometry optimization of the GaNMe2 and
GaN(SiMe3)Ar (Ar ) C6H2-2,6-Ph2) structures were performed
at the B3YLP/6-31g* level. For GaN(SiMe3)Ar these calcula-
tions reproduced the major structural parameters (Ga-N )
1.976 Å; Si-N ) 1.759 Å; Cipso-N ) 1.421 Å; C-N-Ga )
117.3°; C-N-Si ) 125.6°; Si-N-Ga ) 115.1°) of 8 with
good accuracy, while the calculated Ga-N distance in GaNMe2
was 1.905 Å. The HOMO - 1 for GaNMe2 has substantial 4s
character at gallium (Figure 10), while the HOMO corresponds
to a Ga-N π bond polarized toward nitrogen. The LUMO
resembles a 4p orbital on Ga, while the LUMO + 1 features an
antibonding π interaction between Ga and N. The Kohn-Sham
orbital surfaces for GaN(SiMe3)Ar showed that the HOMO is
contains a p type orbital located on nitrogen and Ga possesses
minor lone pair character. The HOMO - 1 is mainly a lone
pair (i.e. 4s) type orbital. The LUMO and LUMO + 1 contain
an interaction between the 4p orbitals on gallium and the π
system of the flanking phenyl substituent.
and C-N-Ga (141.7(3)°) arrays. The trans-bending in 2 is in
sharp contrast to the geometry of the lighter iminoboranes,
ButBNBut,22 (Me3Si)3SiBNBut,23 Mes*BNBut,20 and Mes*NBN-
(SiMe3)But,24 which feature linear RBNR′ arrangements and
B-N distances in the range 1.22-1.26 Å. Calculations for
HBNH support triple B-N bonding and afford a B-N bond
strength of 88 kcal‚mol-1, which is comparable to the strength
of the C-C triple bond (94 kcal‚mol-1) in acetylene.43
The trans-bent structure of 2 results from an accumulation
of nonbonding electron density at both gallium and nitrogen.
Four Lewis dot structures may be written. The bending at
gallium is consistent with some contribution from C. The bent
geometry at N may be due to a contribution from B, C, or D.
However, the charge distribution for C is inconsistent with the
electronegativity values of Ga and N. Structure A is consistent
with multiple Ga-N bonding, but its marginal stabilization
relative to the trans-bent structure suggests it makes only a minor
contribution.
An alternative way of rationalizing the structure of 2 is to
consider it as an interaction between an organogallium(I) species
and a nitrene (NR) in which the electron donation represented
by the arrows is incomplete. This is consistent with the bent
geometry at both N and Ga.
Dimeric Imides, 1,2-Ga2N2Ph4 and 1,3-Ga2N2Ph4. The
relative energies and Kohn-Sham orbitals of the 1,2-Ga2N2-
Ph4 and 1,3-Ga2N2Ph4 isomers, models of 3 and 6, were also
calculated. The 1,3-isomer is ca. 70 kcal‚mol-1 more stable than
the 1,2-isomer, see Supporting Information and Discussion for
more details.
Wiberg Bond Order Calculations. Wiberg bond order
calculations were performed at the B3LYP/6-31g* level on the
species shown in Table 2, using the AOMIX software.38 All
the alkyl subsituents were included on the imides 2, 8, 9, and
{H(CMeCDipp2N)2}GaNAr*.
DFT calculations on the model compounds MeGaNMe
(Figure 9) and ArGaNAr (Ar ) C6H3-2,6-Ph2; Supporting
Information) show the presence of nonbonding electron density
at both N and Ga. The Ga-N bond order was further probed
by Wiberg bond order calculations, which afforded a value of
2.19 in MeGaNMe and 1.62 in 2. The trans-bent structure of 2
and the theoretical data thus support the view that the Ga-N
bond order is much less than 3.
The unsaturated nature of the Ga-N bond suggested that it
might undergo cycloaddition reactions. It is known that imi-
noboranes undergo these reactions21,44 which have also been
Discussion
The Monomeric Imide, Ar′GaNAr#. Treatment of 1 with
N3Ar# afforded the gallium imide 2 in high yield. It contains
the shortest known Ga-N distance of 1.701(3) Å in a stable
molecular species as well as trans-bent N-Ga-C (148.2(2)°)
(43) Baird, N. C.; Datta, R. K. Inorg. Chem. 1972, 11, 17-19.
(44) Kroeckert, B.; van Bonn, K.-H.; Paetzold, P. Z. Anorg. Allg. Chem. 2005,
631, 866-868.
9
12504 J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006

Quasi-Isomeric Heavier Main Group Element Compounds
A R T I C L E S
with water to generate the amine H2NAr# and other, unidentified
components.
Reaction of Ar′GaGaAr′ with Unsaturated Dinitrogen
Containing Molecules. Reactions of 1 with (p-tolyl)NdN(p-
tolyl) generated the blue green Ar′GaN(p-tolyl)N(p-tolyl)GaAr′
(3), the first structurally characterized group 13 element 1,2-
diaza-3,4-dimetallocyclobutane. The only other group 13 ele-
ment example is the boron species (But)BN(Et)N(Et)B(But) but
structural details are unknown.19 The 1,2-Ga2N2 core of 3 is
isomeric with the 1,3-Ga2N2 core of the dimeric imide
(Cp*GaNXyl)2 (Xyl ) C6H3-2,6-Me2.17 However, their core
geometries differ significantly. Compound 3 is trapezoidal (N-
N-Ga ) 105.64(4)°; Ga-Ga-N ) 74.19(6)°), due to the
longer Ga-Ga bond, while (Cp*GaNXyl)2 contains an almost
square core (Ga-N-Ga ) 90.82(8)°; N-Ga-N ) 89.186(8)°).
The Ga-N distance in 3 (1.909(2) Å) is slightly longer than
those (Ga-N ) 1.851(2), 1.870(2) Å) in (Cp*GaNXyl)2. The
oxidation state of gallium in 3 is +2, whereas it is + 3 in
(Cp*GaNXyl)2, and this may account for the difference in bond
lengths.
Calculations at the B3LYPG-31g* level on the model species
1,2-Ga2N2Ph4 and 1, 3-Ga2N2Ph4 the latter was predicted to be
69.8 kcal‚mol-1 more stable. These calculations are consistent
with those on the hydrogen-substituted boron-nitrogen ana-
logues, 1,2-B2N2, and 1,3-B2N2 isomers, for which the 1,3
isomer was found to be more stable by ca. 53 kcal‚mol-1 48
.
The group 13 element-nitrogen species are isoelectronic to
cyclobutadiene, and their Lewis structures may be written as
However, analysis of the Kohn-Sham orbitals for the model
compounds, 1,2-Ga2N2Ph4 and 1,3-Ga2N2Ph4 (Supporting In-
formation), did not indicate the presence of significant Ga-N
π bonding in the HOMO to HOMO - 4 levels. In addition, the
LUMO and LUMO + 1 did not indicate the presence of Ga-N
π interactions. Instead the electron density surfaces suggest a
more ionic structure in which the electron density is strongly
polarized toward nitrogen. In addition, the Ga-N bond distances
in 3 are considerably longer than those in 2, another indication
of weak Ga-N π bonding.
Reaction of 1 with the 1,2-diaryldiazenes, ArylNNAryl (Aryl
) mesityl or C6H3-2,6-Et2), that contain ortho-alkyl substituted
aryl groups gave MesNdNC6H2-2,4-Me2-6-Ga(Me)Ar′ (4) and
Figure 9. LUMO + 2 to HOMO - 1 Kohn-Sham orbitals for the trans-
bent MeGaNMe.
2,6-Et2C6H3NdNC6H3-2-Et-6-Ga(Et)Ar′ (5) which involved
insertion of the gallium(I) center into the sp2-sp3 C-C bond
of a methyl or ethyl substituent. It is known that the ortho
position of azobenzene can be metalated by direct reaction with
a variety of transition metal species to afford the corresponding
2-(phenyl)azophenyl complexes.49-52 However, products 4 and
5, formed by the insertion of a Ga(I) center into a C-C bond,
are unprecedented.53
investigated computationaly.45-47 However, stirring of 2 with
Me3SiCtCSiMe3, HCtCPh, or PhNdNPh in toluene overnight
and subsequent heating to reflux led to the recovery of starting
materials. The reluctance of 2 to react with unsaturated species
may be a result of the extreme crowding at the Ga-N center
(less hindered gallium imides undergo head-to-tail dimerization,
forming associated species). Compound 2 does, however, react
(45) Gilbert, T. M.; Gailbreath, B. D. Organometallics 2001, 20, 4727-4733.
(46) Gilbert, T. M. Organometallics 2005, 24, 6445-6449.
(47) Gilbert, T. M. Organometallics 2003, 22, 2298-2304.
(48) Bridgeman, A., J.; Rothery, J. Inorg. Chim. Acta 1999, 288, 17-28.
(49) Curic, M.; Babic, D.; Visnjevac, A.; Molcanov, K. Inorg. Chem. 2005, 44,
5975-5977.
9
J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006 12505

A R T I C L E S
Wright et al.
Figure 10. Selected Kohn-Sham orbitals for the model compounds GaNMe2 (left), and GaN(SiMe3)Ar (right) obtained at the B3LYP/6-31g* level.
While a detailed mechanism for the formation of 3, 4, and 5
is not presently available, a series of plausible steps are shown
in Scheme 1. Previous freezing point depression experiments
have established that Ar′GaGaAr′ is essentially dissociated to
GaAr′ monomers in hydrocarbon solvent.41 The :GaAr′ mono-
mer may interact with the diazene by donation of a nitrogen
lone pair to the gallium(I) center, which contains two formally
empty 4p orbitals to give initially a three-membered GaN2 ring.
The possibility that association takes place through interaction
of the gallium lone pair and the N-N π* orbital also exists.
The basicity of :GaAr′ is well established, and it interacts
(50) Bruce, M. I.; Iqbal, M. Z.; Stone, F. G. A. J. Chem. Soc. A 1971, 2820-
2828.
(51) Fahey, D. R. J. Organomet. Chem. 1971, 27, 283-292.
(52) Stone, F. G. A.; Bruce, M. I.; Iqbal, M. Z. J. Chem. Soc. A 1970, 3204-
3209.
(53) For reaction of the related {H(CMeCDipp2N)2}Al with azobenzene, see:
Zhu, H.; Chai, J.; Fan, H.; Roesky, H. W.; Nehete, U. N.; Schmidt, H.-G.;
Noltemeyer, M. Eur. J. Inorg. Chem. 2005, 2147.
9
12506 J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006

Quasi-Isomeric Heavier Main Group Element Compounds
A R T I C L E S
Table 2. Wiberg Bond Orders for a Variety of Ga-N-Bonded
heavier In and Tl dimetallenes Ar′MMAr′ did not react with
diphenyldiazomethane to afford products analogous to 6. Instead,
dinitrogen evolution was observed, and Ph2CdN-NdCPh2, a
common decomposition product of diphenyldiazomethane, was
obtained.
Compounds
cmpd
bond (bond order)
GaNMe2
MeGaNMe (trans-bent)
1,3-Ga2N2Ph4
Ga-N (1.22)
Ga-N (2.19)
Ga-N (0.97)
Monomeric Gallium(I) Amide. Monomeric gallium(I) amides
are extremely rare and have only been studied in low-
temperature matrices as the parent hydride species.30 Calcula-
tions on these species and the methyl derivatives showed that
the monovalent amides were considerably more stable than their
imido isomers, RGaNR.26 Therefore, we postulated that employ-
ment of a sufficiently bulky amido ligand at gallium would allow
the isolation and structural characterization of a stable gallium-
(I) amide. We found that reaction of the recently reported lithium
amide LiN(SiMe3)Ar′′31 (7) with “GaI” in toluene solvent
afforded :GaN(SiMe3)Ar′′ (8), a pale-yellow crystalline solid.
It is the first structurally characterized monomeric gallium(I)
amide and is a quasi-isomer of the monomeric gallium imide
2. It contains a planar nitrogen environment with a Ga-N
distance of 1.980(2) Å. This distance is longer than those
displayed in monomeric three-coordinate gallium(III) amides
[R2NGaR2] (R ) aryl, alkyl, or related species) which range
from 1.829 to 1.923 Å.7 However, it is shorter than the average
Ga-N distances in {H(CMeCDipp2N)2}Ga58 (Ga-N ) 2.054(2)
Å), [DippNC(NCy2)NDipp]Ga59 (Ga-N ) 2.091(2) Å), and
TpBut2Ga60 (TpBut2 ) tris(3,5-di-tert-butylpyrazolyl)hydrobo-
rato) (Ga-N ) 2.230(5), which features two- and three-
coordinate gallium(I) centers.
1,2-Ga2N2Ph4
Ga-N (0.93)
Ga-Ga (0.85)
N-N (1.02)
Ar′GaNAr# (2)
GaN(SiMe3)Ar′′ (8)
Ar′′NGaN(SiMe3)Ar′′ (9)
Ga-N (1.63)
Ga-N (1.39)
Ga-N, imido (1.53)
Ga-N, amido (0.93)
Ga-N, imido (1.60)
Ga-N, â-diketiminate (0.77)
{H(CMeCDipp2N)2}GaNAr*
strongly with B(C6F5)3 to give Ar′Ga f B(C6F5)3.41,54 If the
1,2-diaryldiazene is bulkier, as in 1,2-di-(C6H3-2,6-Pri2)diazene
or 1,2-di-(2,4,6-triphenylphenyl)diazene, no reaction with :GaAr′
occurs. This is probably a result of the larger aryl substituents
preventing association of :GaAr′ and the diazene. The initial
:GaAr′ adduct can rearrange apparently in two ways. If the
nitrogen aryl substituents carry ortho substitutents, the gallium
lone pair can attack at the activated ortho carbon, and subsequent
insertion into the C(aryl)-C(alkyl) bond may occur. Where the
ortho substituents are hydrogens, the lower steric requirement
may allow the three-membered Ga2N ring (which requires the
C(ipso)NNC(ipso) torsion angle to have a relatively low torsion
angle) to form. Subsequent insertion of the :GaAr′ may occur
to afford 3. Attempts to isolate the three-membered GaN2 ring
species always afforded 3 and unreacted 1.
The formation of products 3, 4, and 5 are unique to the
gallium system. The heavier “dimetallenes”, Ar′MMAr′ (M )
In55 and Tl56), did not react with 1,2-diaryldiazenes to afford
heavier analogues of 3, 4, 5. It was also found that phenyl- and
silyl-substituted alkynes did not react with 1, indicating that
the lone pairs of the diazene may play an important role in
association with 1.
Reactions of 1 with diphenyldiazomethane did not afford the
intended Ar′GaCPh2, a species with a gallium-carbon multiple
bond, and dinitrogen. Instead, the diazo unit of diphenyldiazo-
methane reacted with the gallium(I) center to give Ar′Ga(µ:η1-
N2CPh2)2GaAr′ (6) with a 1,3-Ga2N2 core. Oxidation of Ga(I)
and subsequent reduction of the N-N moiety was accompanied
by a lengthening of the N-N bond (1.371(4)-1.400(4) Å) ca.
0.2 Å relative to diazomethanes, while the C-N distance was
not substantially perturbed. The Ga-N distances in 6 span the
range 1.862(3)-1.895(3) Å and are similar to the Ga-N
distances (1.850(2) Å and 1.870(2) Å) in (Cp*GaNXyl)2.17
However, while the Ga2N2 core of 6 is slightly puckered (Ga-
(1)-N(1)-N(2)-Ga(2))8.6°),theGa2N2 coreof(Cp*GaNXyl)2
is planar.
The Ga-N distance in 8 is nearly identical to that calculated
(1.976 Å) for the model compound, GaN(SiMe3)Ar but is longer
than those predicted for GaNH2 (1.85 Å) and GaNMe2 (1.905
Å). The only other Ga interaction is with the ipso carbon of the
flanking Mes substituent. This distance is ca. 0.6 Å longer than
typical Ga-C single bonds, indicating that the gallium center
is essentially one-coordinate. The bonding in 8 may be
represented as:
Reduction of a diazo unit at a low-valent group 13 element
center has been previously reported by Uhl and Hannemann.57
Reaction of R2AlAlR2 (R ) CH(SiMe3)2) with (Me3Si)2CNd
N afforded the insertion product R2Al[N-NC(SiMe3)2]AlR2
which contains a three-membered AlN2 heterocycle. The two
Structure E is consistent with a localized electron pair on
nitrogen, while F possesses a Ga-N π bond formed by donation
of the nitrogen lone pair to an empty 4p orbital on gallium.
DFT calculations on the gallium(I) amide GaNMe2 showed that
(54) Cowley, A. H. Chem. Commun. 2004, 2369-2375.
(55) Wright, R. J.; Phillips, A. D.; Hardman, N. J.; Power, P. P. J. Am. Chem.
Soc. 2002, 124, 8538-8539.
(58) Hardman, N. J.; Eichler, B. E.; Power, P. P. Chem. Commun. 2000, 1991-
1992.
(59) Jones, C.; Junk, P. C.; Platts, J. A.; Stasch, A. J. Am. Chem. Soc. 2006,
(56) Wright, R. J.; Phillips, A. D.; Hino, S.; Power, P. P. J. Am. Chem. Soc.
2005, 127, 4794-4799.
128, 2206-2207.
(60) Kuchta, M. C.; Bonanno, J. B.; Parkin, G. J. Am. Chem. Soc. 1996, 118,
10914-10915.
(57) Uhl, W.; Hannemann, F. Eur. J. Inorg. Chem. 1999, 201-207.
9
J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006 12507

A R T I C L E S
Wright et al.
Scheme 1. Possible Mechanism for the Formation of 3, 4, and 5
the HOMO is consistent with some π bonding between Ga and
N (Figure 10). However, the bond is quite polarized toward
nitrogen. The HOMO - 1 contains 4s character at gallium, while
the LUMO and LUMO + 1 are essentially 4p orbitals on
gallium. These calculations suggest that 8 should behave both
as a Lewis acid and Lewis base. Calculations for GaN(SiMe3)-
Ar, a more complete model of 8, were also undertaken. The
results indicated that the HOMO and HOMO -1 contained 4s
lone pair character at gallium, consistent with Lewis basicity.
The LUMO and LUMO + 1 consisted in part of a bonding
interaction between a Ga 4p orbital and the π system of a
flanking phenyl substituent. Wiberg bond order calculations for
the Ga-N bonds in GaNMe2 and GaN(SiMe3)Ar afforded
indices of 1.22 and 1.39, respectively. These calculations
indicate that structure F makes some contribution to the overall
bonding observed in 8.
Treatment of 8 with (p-tolyl)NdN(p-tolyl) in toluene to
generate a product analogous to 3 afforded no reaction.
However, reaction with the sterically hindered azide N3Ar′′31
produced the amido-imide, Ar′′NGaN(SiMe3)Ar′′ (9), and N2
in an analogous manner to the synthesis of 2. Compound 9 was
isolated as a red-purple solid, and the structure was determined
by X-ray crystallography (Figure 7). A comparison of the
structural parameters of 9, 2, and {H(CMeCDipp2N)2}GaNAr*61
are provided in Figure 11.
Å) in {H(CMeCDipp2N)2}GaNAr*. The Ga1-N1 amido dis-
tance (1.862(6) Å) is typical for compounds of formula
R2GaNR2, where the gallium is in the +3 oxidation state.7 Most
notably it is ca. 0.12 Å shorter than that in 8, presumably as a
result of the increase in the gallium oxidation state to +3. The
trans-bending at N(1) of 133.9(1)° is the largest of the series.
The bending angle at gallium is 144.0(2)°, and there is also a
close contact of 2.395(6) Å between Ga and the ipso carbon of
a mesityl substituent. This interaction is significant as shown
by a ca. 4° closing of the angle at C(53) relative to C(57).
Compound 9 is the first heavier group 13 element-nitrogen
analogue of an allyl anion. However, unlike allyl anions which
feature a delocalized π bonding system, there is little evidence
of such delocalization in 9. DFT calculations on 9 were
undertaken to better understand the bonding (Supporting
Information). It was found that, like 2 and {H(CMeCPh2N)2}-
GaNAr*, the HOMO and HOMO - 1 can be described as
polarized π bonds between the imido nitrogen and gallium.
There is no evidence of a delocalized three-centered π bond
involving the N-Ga-N array. In addition, Wiberg bond orders
of 1.53, and 0.93 were calculated for the Ga-N(imido) and
Ga-N(amido) bonds (Table 2). Wiberg bond orders of 1.62
and 1.60 were calculated for the imido Ga-N bonds of 2 and
{H(CMeCPh2N)2}GaNAr*. These calculations showed that all
the monomeric gallium imides possess Ga-N bonds with
multiple bond character of similar magnitude, but the bond
orders are significantly weaker than those in iminoboranes.
Compound 9 has an imido Ga-N distance of 1.743(5) Å,
which is nearly identical to the imido Ga-N distance (1.742(3)
(61) Hardman, N. J.; Cui, C.; Roesky, H. W.; Fink, W. H.; Power, P. P. Angew.
Chem., Int. Ed. 2001, 40, 2172-2174.
9
12508 J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006

Quasi-Isomeric Heavier Main Group Element Compounds
A R T I C L E S
Figure 11. Structural parameters of three crystallographically characterized gallium imides 9, 2, and {H(CMeCDipp2N)2}GaNAr*.
Relative Stability of Isomers. Calculations by a number of
groups on heavier group 13-group 15 hydride model com-
pounds have shown that the :MNH2 isomers are much lower in
energy than HMNH (M ) Al-Tl), whereas for boron deriva-
tives the opposite is the case.26 The lower energy seems
counterintuitive on the basis of a superficial examination. For
example, RMNR (R ) Me or H) has five bonds (3σ + 2π
between Ga, N, and ligands), whereas :MNR2 has only three
(3σ). However, calculations for RGaNR and GaNR2 (R ) Me)
showed that the Ga-N bond orders in the two isomers differed
by less than one unit. Furthermore, when bond order calculations
were performed directly on 2 and 8, the Ga-N bond order
differed by only ca. 0.2 units. Thus, the multiple bonding in 2
contributes little to its stabilization. In addition, :GaNR2 contains
two N-R bonds, whereas RGaNR has one N-R bond and a
weaker Ga-R bond. A further important factor is that the lone
pair orbital at the metal in :GaNR2 has more 4s character than
it has in RMNR and the lone pair orbital in :GaNR2 is not the
HOMO but the HOMO - 1. The electronegative NR2 substitu-
ent apparently stabilizes the lone pair on gallium, and this is
consistent with the fact that the color of 8 is pale yellow (cf.
green for :GaAr′). This indicates that the n-p absorption has
been moved into the UV region, consistent with a lowering of
the energy of the gallium lone pair and an increase in the
HOMO-LUMO gap.62
both of these bonds. In addition, the nitrogens have a pyramidal
coordination. The Ga-N bonds in 3 are longer than they are in
a variety of 1,3-Ga2N2 ring species, including 6, suggesting that
that they are weaker than those in the 1,3-isomer. The unique
synthetic route to 3, via reaction with a species in which the
N-N bond is preformed, and the steric protection provided by
the gallium substituent permit its isolation. It is the only reaction
undergone by 1 in which a Ga-Ga bond is observed.
Conclusions
It has been shown that the use of bulky terphenyl ligands
affords the gallium imide (RGaNR) 2 and its quasi-isomeric
amide, :GaNR2, 8. These compounds feature only weak Ga-N
multiple bonding however. Wiberg bond order calculations for
the imides afforded values of 1.62 and 1.53 for the formally
triple Ga-N bond in 2 and 9, respectively. The corresponding
value for the amide was only slightly less at 1.39. The
calculations showed that the gallium(I) amide :GaNMe2 was
considerably more stable than its imido isomer MeGaNMe,
which is a consequence of the similarity in energies in Ga-N
π bonding and the stabilization of the Ga lone pair by the
electronegative NMe2 substiutent. Compounds 3 and 6 which
contain isomeric 1,2-Ga2N2 and 1,3-Ga2N2 arrays were also
synthesized. The 1,3-isomer was predicted by DFT calculations
to be more stable than the M-M-bonded 1,2-isomer. The
compounds 2, 8, and 9 as well as 3 and 6 are very rare examples
of quasi-isomeric heavier main group element compounds. This
work suggests that it may be possible to isolate several other
isomers or quasi-isomers of the heavier main group elements.
The use of the very large substituents at both N and Ga,
together with a suitable synthetic approach, allowed the synthesis
of the less stable imide prior to the synthesis of the more stable
amide. However, the stabilization of the gallium amide required
the use of a very crowding amide ligand containing two large
substituents at the nitrogen atom. This is sterically more difficult
to achieve because of the smaller size of nitrogen.
Acknowledgment. We are grateful to the National Science
Foundation for financial support and Anne F. Richards for
crystallographic assistance with compound 6.
Bond strength considerations readily account for the greater
stability of the 1,3-M2N2 versus the 1,2-M2N2 ring species. The
1,3-isomer contains four M-N bonds that are strengthened
because of polar contributions as in Mδ+-Nδ-. In contrast the
1,2-isomer contains two M-N bonds, a weak N-N bond and
a weak M-M bond. There are unfavorable polarizations across
Supporting Information Available: X-ray data (CIFs) for 3,
4, 5, 6, 8, and 9 and a summary table of crystallographic data
for 3-6, 8, and 9; selected Kohn-Sham orbital surfaces of 1,2-
Ga2N2Ph4, 1,3-Ga2N2Ph4, ArGaNAr, ArNGaN(SiMe3)Ar, and
{H(CMeCPh2N)2}GaNAr (Ar ) C6H3-2,6-Ph2); the complete
ref 36 citation. This material is available free of charge via the
Internet at http://pubs.acs.org.
(62) Macdonald, C. L. B.; Cowley, A. H. J. Am. Chem. Soc. 1999, 121, 12113-
12126.
JA063072K
9
J. AM. CHEM. SOC. VOL. 128, NO. 38, 2006 12509