Monomeric organogallium-nitrogen compounds. Chemistry of Et2GaNH[C6H2(2,4,6-t-Bu)3] with decomposition to the metallacycle {EtGaNH[C6H2(4,6-t-Bu)2CMe2CH 2-2]}2 and of EtGa{NH[C6H2(2,4,6-t-Bu)3]}2

Article abstract of DOI:10.1021/om990136+

Two monomeric gallium-nitrogen compounds, Et₂GaNH[C₆H₂(2,4,6-t-Bu)₃] and EtGa{NH-[C₆H₂(2,4,6-t-Bu)₃]}₂, have been prepared by metathetical reactions between either Et₂GaCl or EtGaCl₂, as appropriate, and LiNH[C₆H₂(2,4,6-t-Bu)₃] and have been characterized fully. Cryoscopic molecular weight studies demonstrated both compounds to be monomeric in benzene solution, whereas an X-ray structural study of the latter identified a monomer. The compound Et₂GaNH[C₆H₂(2,4,6-t-Bu)₃] decomposes at room temperature to form a new metallacyclic derivative {EtGaNH[C₆H₂(4,6-t-Bu)₂(CMe₂CH ₂-2)]}₂ GaEt₃, and H₂N[C₆H₂-(2,4,6-t-Bu)₃]. A ¹H NMR spectral study and an X-ray structural study were used to elucidate its structure. The compound EtGa{NH[C₆H₂(2,4,6-t-Bu)₃]}₂ does not decompose to the metallacycle, but it reacts readily with GaEt₃ to form Et₂GaNH[C₆H₂(2,4,6-t-Bu)₃].

Full text of DOI:10.1021/om990136+

Organometallics 1999, 18, 2543-2549
2543
Mon om er ic Or ga n oga lliu m -Nitr ogen Com p ou n d s.
Ch em istr y of Et2Ga NH[C6H2(2,4,6-t-Bu )3] w ith
Decom p osition to th e Meta lla cycle
{EtGa NH[C6H2(4,6-t-Bu )2CMe2CH2-2]}2 a n d of
EtGa {NH[C6H2(2,4,6-t-Bu )3]}2
O. T. Beachley, J r.,* Daniel B. Rosenblum, Melvyn Rowen Churchill,*
David George Churchill, and Lynn M. Krajkowski
Department of Chemistry, State University of New York at Buffalo,
Buffalo, New York 14260-3000
Received February 26, 1999
Two monomeric gallium-nitrogen compounds, Et2GaNH[C6H2(2,4,6-t-Bu)3] and EtGa{NH-
[C6H2(2,4,6-t-Bu)3]}2, have been prepared by metathetical reactions between either Et2GaCl
or EtGaCl2, as appropriate, and LiNH[C6H2(2,4,6-t-Bu)3] and have been characterized fully.
Cryoscopic molecular weight studies demonstrated both compounds to be monomeric in
benzene solution, whereas an X-ray structural study of the latter identified a monomer.
The compound Et2GaNH[C6H2(2,4,6-t-Bu)3] decomposes at room temperature to form a new
metallacyclic derivative {EtGaNH[C6H2(4,6-t-Bu)2(CMe2CH2-2)]}2, GaEt3, and H2N[C6H2-
(2,4,6-t-Bu)3]. A 1H NMR spectral study and an X-ray structural study were used to elucidate
its structure. The compound EtGa{NH[C6H2(2,4,6-t-Bu)3]}2 does not decompose to the
metallacycle, but it reacts readily with GaEt3 to form Et2GaNH[C6H2(2,4,6-t-Bu)3].
In tr od u ction
Resu lts a n d Discu ssion
The monomeric amide Et2GaNH[C6H2(t-Bu)3] was
synthesized in high yield by a metathetical reaction
between Et2GaCl and LiNH[C6H2(t-Bu)3] in pentane at
0 °C. Extraction with pentane gave a soluble, mobile
Compounds with the simplest formula R2GaER′2 (E
) N, P, As) are usually associated, mostly as dimers
but sometimes as trimers.1 However, monomers have
been observed when sterically demanding ligands are
incorporated into the molecule. The first fully character-
ized monomer was (C5Me5)2GaAs(SiMe3)2,2 whereas
the second was (t-Bu)2GaAs(t-Bu)2.3 It is of interest
that of the monomeric gallium-nitrogen compounds of
which we are aware [C6H2(2,4,6-i-Pr)3]2GaNH[C6H3-
(2,6-i-Pr)2],4 [C6H2(2,4,6-i-Pr)3]2GaNPh2,4 [C6H2(2,4,6-t-
Bu)3]2GaN(H)Ph,5 (t-Bu)2GaN(t-Bu)(SiPh3),4 and (t-
Bu)2GaN(1-adamantyl)(SiPh3),4 there is no compound
that has two simple alkyl groups on gallium and one
sterically demanding group on nitrogen. The derivative
Me2GaNH[C6H3(2,6-i-Pr)2] is a dimer.6 We now report
the synthesis, characterization, and reaction chemistry
of two new monomeric compounds, Et2GaNH[C6H2-
(2,4,6-t-Bu)3] and EtGa{NH[C6H2(2,4,6-t-Bu)3]}2.
1
liquid whose H NMR spectrum indicated the presence
of Et2GaNH[C6H2(t-Bu)3] with the free amine H2N-
[C6H2(t-Bu)3] as an impurity. The quantity of amine in
the product from 10 independent preparations of Et2-
GaNH[C6H2(t-Bu)3] varied from 1.6 to 16%, but there
was no correlation between the level of amine and any
known experimental variable. Extensive studies con-
firmed that the amine was not an impurity in LiNH-
[C6H2(t-Bu)3]. Rigorously purified reagents and solvents,
specially cleaned, handled, and dried glassware, and use
of a drybox dedicated to this study and monitored for
oxygen and water contamination suggested that the
amine was not a product of accidental hydrolysis, and
the provenance of the amine remains unknown. It
should be noted that the properties of Et2GaNH[C6H2-
(t-Bu)3], which will be described later, prevented re-
moval of the amine.
A cryoscopic molecular weight study of a sample of
Et2GaNH[C6H2(t-Bu)3] with less than 5% amine impu-
rity demonstrated the compound to be monomeric in
benzene solution. There was no dependence of the
observed molecular weight on concentration over the
range 0.073-0.047 M. The 1H NMR spectrum of Et2-
GaNH[C6H2(t-Bu)3] in C6D6 revealed only one set of
resonances for the two ethyl groups on gallium at the
(1) Taylor, M. J .; Brothers, P. J . In The Chemistry of Aluminum,
Gallium, Indium, and Thallium; Downs, A. J ., Ed.; Blackie-Chapman
Hall: New York, 1993; Chapter 3.
(2) Byrne, E. K.; Parkanyi, L.; Theopold, K. H. Science 1988, 241,
332.
(3) Higa, K. T.; George, C. Organometallics 1990, 9, 275.
(4) Waggoner, K. M.; Ruhlandt-Senge, K.; Wehmschulte, R. J .; He,
X.; Olmstead, M. M.; Power, P. P. Inorg. Chem. 1993, 32, 2557.
(5) Brothers, P. J .; Wehmschulte, R. J .; Olmstead, M. M.; Ruhlandt-
Senge, K.; Parkin, S. R.; Power, P. P. Organometallics 1994, 13, 2792.
(6) Waggoner, K. M.; Power, P. P. J . Am. Chem. Soc. 1991, 113,
3385.
10.1021/om990136+ CCC: $18.00 © 1999 American Chemical Society
Publication on Web 06/03/1999

2544 Organometallics, Vol. 18, No. 13, 1999
Beachley et al.
Sch em e 1. Cyclop en ta d ien e Elim in a tion Rea ction
Sequ en ce
The compound Et2GaNH[C6H2(t-Bu)3] decomposes at
room temperature to form a metallacyclic compound
{EtGaNH[C6H2(t-Bu)2(CMe2CH2)]}2, GaEt3, and H2N-
[C6H2(t-Bu)3] as summarized by eq 1. Since this reaction
normal operating temperature of the instrument. Thus,
the C6H2(t-Bu)3 substituent is not sufficiently bulky to
restrict rotation about the gallium-nitrogen bond and
make the two ethyl groups magnetically distinguishable.
The reagents Et2Ga(C5H5)7 and H2N[C6H2(t-Bu)3]
have the potential to undergo the cyclopentadiene
elimination reaction8-10 to form Et2GaNH[C6H2(t-Bu)3],
but no gallium-nitrogen products could be isolated
when this reaction was attempted. In contrast, Et2Ga-
(C5H5) reacts with many other amines and phosphines
at room temperature to form compounds of the type (Et2-
GaER′2)n in high purity and in high yield.8 The reagent
Me2Ga(C5H5)11 reacts similarily.9 To reconcile these
(1)
involved the conversion of a mobile liquid to a solid, the
rate of decomposition was readily observed. For un-
known reasons some samples of the monomeric gallium
amide remained mobile liquids for many hours or even
days, whereas others decomposed in less than 1 h at
room temperature. Even though these experimental
observations would suggest that the reaction might
involve a catalytic path, we were not able to identify a
reagent including H2N[C6H2(t-Bu)3], GaEt3, or Li(n-Bu)
that influenced the rate of formation of the metallacycle.
The decomposition reaction itself was also considered
as a potential source of the amine impurity in Et2GaNH-
[C6H2(t-Bu)3]. However, the 1H NMR spectra of solutions
of freshly prepared Et2GaNH[C6H2(t-Bu)3], which had
resonances for the amine, did not exhibit resonances
assignable to the metallacycle. The balanced equation
for decomposition (eq 1) requires the formation of
equimolar amounts of amine and metallacycle (mono-
mer).
1
apparently conflicting observations, a H NMR spectro-
scopic investigation of a reaction mixture of Et2Ga(C5H5)
and D2N[C6H2(t-Bu)3] in a 1:1 mol ratio in C6D6 was
carried out. Three closely spaced lines rather than the
typical intense singlet were observed for the cyclopen-
tadienide protons. These multiple lines are consistent
with the presence of a mixture of Et2Ga(C5H5), Et2Ga-
(C5H4D), Et2Ga(C5H3D2), etc., and confirm the occur-
rence of the cyclopentadiene elimination reaction. The
intensity of the N-H resonance for the amine increased
also, but its broadness prevented meaningful integra-
tion. This system was monitored for 17 days by record-
ing repeated 1H NMR spectra, but no change was
observed after the initial spectrum. These data suggest
that the cyclopentadiene elimination reaction occurs,
and the two equilibria shown in Scheme 1 must be used
to describe this system. The NMR data suggest that the
initial equilibrium shown in Scheme 1 is achieved
rapidly, but the equilibrium constant is small. Thus,
when Et2Ga(C5H5) reacts with H2N[C6H2(t-Bu)3], the
gallium-nitrogen product is a monomer which reacts
with cyclopentadiene, a weak protonic acid, to reform
the reactants. However, when the initially formed
gallium-nitrogen product dimerizes, the electron pair
on nitrogen is used in bonding and the initial equilib-
rium in Scheme 1 is shifted to the right to favor
formation of the associated organometallic product.
Removal of cyclopentadiene by distillation or dimeriza-
tion also minimizes the possibility of the back reaction
and favors the formation of the organogallium-nitrogen
product. These observations suggest that the absence
of an isolable product from the cyclopentadiene elimina-
tion reaction enables one to predict which gallium
compounds will be monomeric. Additional research to
test this hypothesis is in progress.
The metallacyclic product {EtGaNH[C6H2(t-Bu)2-
(CMe2CH2)]}2 has been fully characterized and found
to be dimeric in benzene solution by a cryoscopic
molecular weight study and in the solid state by an
X-ray structural study. This species crystallizes in the
space group C2/c, with Z ) 4. The dimeric molecule lies
about a crystallographic inversion center at (3/4, 3/4,
1/2) and has precise Ci (1h) symmetry. The basic crystal-
lographic asymmetric unit is numbered normally; atoms
in the “other half” of the molecule are related to the
basic unit by the transformation [3/2-x, 3/2-y, 1-z] and
are identified with the suffix “a”, as illustrated in Figure
1. The molecule consists of a symmetrical set of five
fused rings: a six-membered arene ring, a six-mem-
bered metallacycle, a four-membered Ga2N2 ring, a
second six-membered metallacycle, and a final arene
ring. The ethyl groups bonded to gallium and the GaNC4
metallacyclic rings are on opposite sides of the molecule
and thus have trans orientation. Important interatomic
bond distances and angles are collected in Table 1. The
central Ga2N2 portion of the molecule is required to be
strictly planar but has only Ci (rather than the possible
D2h) symmetry because the Ga-N distances show some
alternation (Ga(1)-N(1) ) Ga(1A)-N(1A) ) 2.068(6) Å
versus Ga(1)-N(1A) ) Ga(1A)-N(1) ) 2.021(6) Å, ∆ )
0.047(8) Å). The Ga(1)‚‚‚Ga(1A) distance of 2.971(2) Å
is nonbonding. The angle at Ga(1) is acute (N(1)-Ga-
(1)-N(1A) ) 86.8(2)°), while the supplementary angle
at N(1) is obtuse (Ga(1)-N(1)-Ga(1A) ) 93.2(2)°).
(7) Beachley, O. T., J r.; Rosenblum, D. B.; Churchill, M. R.; Lake,
C. H.; Krajkowski, L. M. Organometallics 1995, 14, 4402.
(8) Beachley, O. T., J r.; Rosenblum, D. B.; Churchill, M. R.; Lake,
C. H.; Toomey, L. M. Organometallics 1996, 15, 3653.
(9) Beachley, O. T., J r.; Royster, T. L., J r.; Arhar, J . R.; Rheingold,
A. L. Organometallics 1993, 12, 1976.
(10) Beachley, O. T., J r.; Maloney, J . P.; Rogers, R. D. Organome-
tallics 1997, 16, 3267.
(11) Beachley, O. T., J r.; Royster, T. L., J r.; Arhar, J . R. J .
Organomet. Chem. 1992, 434, 11.

Monomeric Organogallium-Nitrogen Compounds
Organometallics, Vol. 18, No. 13, 1999 2545
F igu r e 1. Labeling of atoms in the {EtGaNH[C6H2(t-Bu)2CMe2CH2]}2 molecules (an ORTEP2 diagram).24 The 30%
probability envelopes are shown for the vibration ellipsoids of all non-hydrogen atoms, while hydrogen atoms are artificially
reduced.
Ta ble 1. Selected Bon d Dista n ces (Å) a n d An gles
(d eg) for {EtGa NH[C6H2(t-Bu )2CMe2CH2]}2
(a) Gallium-Ligand Bond Lengths
Ga(1)-N(1)
Ga(1)-N(1A)
Ga(1)‚‚‚Ga(1A)
2.068(6) Ga(1)-C(1)
2.021(6) Ga(1)-C(22A)
2.971(2)
1.949(8)
1.952(7)
(b) Distances within Metallacyclic Ring
1.459(10) C(21)-C(22)
N(1)-C(11)
C(11)-C(12)
C(12)-C(21)
1.536(11)
1.952(7)
2.021(6)
1.414(7) C(22)-Ga(1A)
1.556(9) Ga(1A)-N(1)
(c) Distances within Carbocyclic Ring
1.412(10) C(13)-C(14)
C(16)-C(11)
C(11)-C(12)
C(12)-C(13)
1.371(11)
1.371(8)
1.389(13)
1.414(7) C(14)-C(15)
F igu r e 2. Twist-boat conformation of the six-membered
metallacyclic ring N(1)-Ga(1A)-C(22)-C(21)-C(12)-
C(11). Note the four-membered ring about N(1)-Ga(1A).
1.400(13) C(15)-C(16)
(d) Angles around Gallium
N(1)-Ga(1)-N(1A) 86.8(2)
C(1)-Ga(1)-C(22A) 117.2(3)
The 1H NMR spectrum of {EtGaNH[C6H2(t-Bu)2-
N(1)-Ga(1)-C(1)
113.6(4) C(1)-Ga(1)-N(1A)
122.7(3)
N(1)-Ga(1)-C(22A) 114.7(2) C(22A)-Ga(1)-N(1A) 97.8(3)
(CMe2CH2)]}2 in benzene solution is consistent with the
results of the structural study, as both the ethyl groups
bonded to gallium and the GaNC4 metallacyclic rings
have trans orientation. However, the phenyl protons are
nonequivalent due to the ring orientation. Thus, two
sets of closely spaced lines at 7.65 and 7.42 ppm are
observed. The resonance for the unique N-H protons
in the metallacycle occurs at 4.76 ppm and is readily
distinguished from the N-H resonance for Et2GaNH-
[C6H2(t-Bu)3] at 3.63 ppm. The -CH2C(CH3)2N bridge
contains diastereotopic methyl groups, which results in
two singlets of equal intensity at 1.76 and 1.59 ppm.
Resonances for the ortho and para tert-butyl group
singlets are of equal intensity and appear at 1.49 and
1.37 ppm. The bridging methylene group contains two
diastereotopic protons, and thus, two singlets are ob-
served. Since the ratio of the difference in frequency
between the two lines and their coupling constant is
large, a pseudoquartet appears in the range 1.00-1.20
ppm. A triplet at 0.95 ppm and a quartet at 0.46 ppm
due to the ethyl group on gallium complete the spectrum
of the metallacyclic compound.
(e) Angles around Nitrogen
Ga(1)-N(1)-Ga(1A) 93.2(2)
Ga(1)-N(1)-C(11) 123.6(4)
Ga(1A)-N(1)-C(11) 119.6(4)
(f) Angles within the Metallacyclic Ring
Ga(1A)-N(1)-C(11) 119.6(4) C(12)-C(21)-C(22)
N(1)-C(11)-C(12) 120.8(6) C(21)-C(22)-Ga(1A) 116.9(4)
C(11)-C(12)-C(21) 126.1(7) C(22)-Ga(1A)-N(1) 97.8(3)
111.9(4)
(g) Angles within the Carbocyclic Ring
C(16)-C(11)-C(12) 120.4(7) C(13)-C(14)-C(15)
C(11)-C(12)-C(13) 117.1(6) C(14)-C(15)-C(16)
C(12)-C(13)-C(14) 123.9(6) C(15)-C(16)-C(11)
116.6(9)
124.3(7)
117.3(5)
The original NH[C6H2(t-Bu)3] ligand has suffered
mono-dehydrogenation of a tert-butyl group in the
2-position, which results in the formation of a Ga-C(sp3)
σ-bond as part of a six-membered Ga-NH-C(sp2)-
C(sp2)-CMe2-CH2 ring. This metallacyclic ring has a
nonplanar twist-boat conformation (see Figure 2). Fi-
nally, it should be noted that the two very different
gallium-carbon linkages are both Ga-C(sp3) linkages
and have similar bond lengths, Ga(1)-C(1) ) 1.949(8)
Å (to the ethyl ligand) and Ga(1)-C(22A) ) 1.952(7) Å
(to the metallacycle). This Ga-C(Et) distance is com-
parable to that observed in such other ethyl-gallium
molecules as Et2Ga(C5H5),7 which range from 1.945(9)
Orthometalation reactions of aminoalanes12,13 and
gallanes14,15 have been reported. When the results of
the current study are compared to those in the litera-
ture, many differences including the nature of the
reactants, the products, and reaction conditions are
7
to 1.979(9) Å, EtGa(C5H5)2 at 1.960(13) Å, [Et2GaP(t-
10
Bu)2]2 at 1.999(6) and 1.998(6) Å, and [Et2GaS-
(SiPh3)]2 at 1.934(14) and 1.971(11) Å.
10

2546 Organometallics, Vol. 18, No. 13, 1999
Beachley et al.
Sch em e 2. Decom p osition of Et2Ga NH[C6H2(t-Bu )3] by In itia l Liga n d Tr a n sfer Rea ction s
noted, but the metallacyclic products are analogous. All
previous examples12-15 involved dimeric reactants with
decomposition temperatures around 200 °C, whereas
the current study reveals a monomer that decomposed
at room temperature. The decomposition of a dimer
produced a simple hydrocarbon from the organic sub-
stituent bonded to the group 13 atom and a proton from
the ortho alkyl substituent, whereas the decomposition
of monomeric Et2GaNH[C6H2(t-Bu)3] formed GaEt3 and
H2NC6H2(t-Bu)3. Ethane was not observed.
Two different reaction paths can be envisioned for the
conversion of Et2GaNH[C6H2(t-Bu)3] to the metallacycle,
GaEt3, and H2N[C6H2(t-Bu)3]. The pathway that is
consistent with our experimental data and the literature
involves formal transfer of an ethyl group and an NH
proton from one monomer to another to form an acety-
lenic type of intermediate EtGaN[C6H2(t-Bu)3] as well
as GaEt3 and H2N[C6H2(t-Bu)3], as illustrated in Scheme
2. The vacant orbital on gallium and the electron pair
on nitrogen in the monomeric unit might facilitate this
process. The final steps for the formation of the metal-
lacycle from the unsaturated intermediate EtGaN[C6H2-
(t-Bu)3] include the transfer of hydrogen from the tert-
butyl group to the imine nitrogen and then formation
of a new gallium-carbon bond. Dimerization via forma-
tion of gallium-nitrogen donor-acceptor bonds gives
the final observed product. An alternative pathway
(Scheme 3) involves an initial ligand redistribution
reaction to form EtGa{NH[C6H2(t-Bu)3]}2 and GaEt3.
Transfer of a proton from one amide group to another
in EtGa{NH[C6H2(t-Bu)3]}2 would lead to the formation
of the amine and the identical unsaturated intermediate
as proposed in Scheme 1. Abstraction of hydrogen from
a tert-butyl group by nitrogen, ring closure, and dimer-
ization would give the observed product.
The hypotheses presented by Scheme 3 was tested by
the independent synthesis and characterization of EtGa-
{NH[C6H2(t-Bu)3]}2. This compound was prepared by a
metathetical reaction between EtGaCl2 and LiNH[C6H2-
(t-Bu)3] in a 1:2 mol ratio in pentane. Even though the
elemental analyses of this product for carbon and
hydrogen were in good agreement with the empirical
formula and the melting point range of the compound
was less than two degrees, 141.7-143.1 °C, the 1H NMR
spectrum of the product in C6D6 indicated the presence
of the amine as an impurity. The level of the amine
impurity in products from different synthetic experi-
ments ranged from 6 to 21% according to 1H NMR
spectral data, but the metallacycle was present in only
trace amounts. Furthermore, EtGa{NH[C6H2(t-Bu)3]}2
does not decompose to form the metallacycle either at
room temperature or at the melting temperature of the
1
compound. Numerous H NMR spectra of these EtGa-
{NH[C6H2(t-Bu)3]}2-amine product mixtures have been
recorded over the course of two years without any
change in the concentration of EtGa{NH[C6H2(t-Bu)3]}2,
the metallacycle, or the amine. The compound EtGa-
{NH[C6H2(t-Bu)3]}2 is monomeric in benzene solution
over the concentration range 0.040-0.085 M according
to a cryoscopic molecular weight study and exhibits
chemistry typical of this type of compound. It reacts
readily with GaEt3 at room temperature to undergo a
ligand redistribution reaction to form Et2GaNH[C6H2-
(t-Bu)3].
(12) Hitchcock, P. B.; J asim, H. A.; Lappert, M. F.; Williams, H. D.
Polyhedron 1990, 9, 245.
(13) Dillingham, M. D. B.; Hill, J . B.; Lee, B.; Schauer, S. J .;
Pennington, W. T.; Robinson, G. H. J . Coord. Chem. 1993, 28, 337.
(14) Schauer, S. J .; Lake, C. H.; Watkins, C. L.; Krannich, L. K.
Organometallics 1996, 15, 5641.
(15) Beachley, O. T., J r.; Noble, M. J .; Churchill, M. R.; Lake, C. H.
Organometallics 1998, 17, 5153.

Monomeric Organogallium-Nitrogen Compounds
Organometallics, Vol. 18, No. 13, 1999 2547
Sch em e 3. Decom p osition of Et2Ga NH[C6H2(t-Bu )3] by In itia l Liga n d Red istr ibu tion Rea ction
for complete reaction.) The pentane was removed by vacuum
distillation while maintaining the reaction flask at 0 °C. The
remaining colorless liquid was purified by vacuum distilla-
tion by using a short-path still with an oil bath temperature
of 60 °C, a pressure of less than 10-3 Torr, and a receiving
flask at -196 °C. Et2GaCl: Colorless liquid at room temper-
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
GaEt3 and Li(n-Bu) were purchased from Strem Chemicals,
Inc., and Aldrich Chemical Co., respectively. All solvents were
dried by conventional procedures. Deuterated amine D2NC6H2-
(t-Bu)3 was prepared by an exchange reaction between H2-
NC6H2(t-Bu)3 and D2O in diethyl ether and then purified by
vacuum sublimation at 65 °C. Elemental analyses were
performed by E+R Microanalytical Laboratories, Inc., Corona,
1
ature; bp 40-45 °C (<10-3 Torr) (lit:17 60-62 °C, 2 Torr). H
NMR (C6D6,, δ): 1.19 (t, GaCH2CH3, 3H), 0.79 (q, GaCH2CH3,
2H). IR (Neat, cm-1): 2724 (w), 2363 (vw), 2140 (vw), 1412
(m), 1230 (m), 1191 (w), 1000 (s), 957 (m), 938 (m), 655 (vs),
566 (s), 512 (s).
1
NY. The H NMR spectra were recorded at 400 MHz by using
P r ep a r a tion of EtGa Cl2. A room-temperature ligand
redistribution reaction between 2.489 g (14.14 mmol) of freshly
sublimed GaCl3 and 1.109 g (7.07 mmol) of GaEt3 dissolved in
approximately 50 mL of pentane was used to prepare 3.498 g
of EtGaCl2 (20.61 mmol, 97.3% yield) as a colorless crystalline
solid. The compound was purified by sublimation at room
temperature between two flasks connected by an elbow.
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, 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.16
P r ep a r a tion of Et2Ga Cl. This compound was prepared in
essentially quantitative yield from GaEt3 and freshly sublimed
GaCl3 in a 2:1 mol ratio in pentane solution at room temper-
ature. (The literature17 describes a similar reaction between
the neat reagents, but elevated temperatures were required
1
EtGaCl2: Mp 50.5-51.4 °C (lit:18 44-45 °C). H NMR (C6D6,
δ): 0.89 (t, GaCH2CH3, 3H), 0.73 (q, GaCH2CH3, 2H). Anal.
Calcd for C2H5GaCl2: C, 14.16; H, 2.97; Cl, 41.79. Found: C,
14.20; H, 2.98; Cl, 41.91.
Rea ction of Et2Ga (C5H5) w ith D2NC6H2(t-Bu )3. After an
NMR tube was charged with 0.0027 g (0.014 mmol) of Et2Ga-
(C5H5),7 0.0037 g (0.014 mmol) of D2NC6H2(t-Bu)3, and 0.6 mL
of C6D6 to form a colorless solution, the tube was sealed and
spectra were recorded. 1H NMR (C6D6, δ): 7.40 [s, Ph-H,
amine], 6.28 [s, Ga(C5H5-xDx)], 6.25 [s, Ga(C5H5-xDx)], 6.22 [s,
Ga(C5H5-xDx)], 3.63 [s, N-H, amine], 1.40 [s, o-(t-Bu)], 1.39
[s, p-(t-Bu)], 0.97 [t, Ga CH2CH3], 0.18 [q, Ga CH2CH3].
(16) Shriver, D. F.; Drezdzon, M. A. The Manipulation of Air-
Sensitive Compounds; Wiley: New York, 1986; p 38.
(17) Eisch, J . J . J . Am. Chem. Soc. 1962, 84, 3830.
(18) Schmidbaur, H.; Klein, H.-F. Chem. Ber. 1967, 100, 1129.

2548 Organometallics, Vol. 18, No. 13, 1999
Beachley et al.
Resonances due to the ethyl groups for GaEt3 and EtGa-
(C5H5-xDx)2 formed by the ligand redistribution reactions
of the cyclopentadienyl gallium compounds7 were also ob-
served.
(m, sh), 1202 (m), 1198 (m), 1160 (m), 1140 (m), 1122 (vs), 1098
(w), 1060 (m), 996 (m), 940 (w, br), 890 (w), 877 (m), 830 (m),
820 (m), 802 (m), 777 (m), 729 (m), 707 (s), 665 (m), 612 (w),
535 (m), 470 (vw), 450 (vw), 395 (w, br). Anal. Calcd for C20H34
-
GaN: C, 67.06; H, 9.57. Found: C, 67.25; H, 9.31. Cryoscopic
molecular weight, benzene solution, formula weight 358
(observed molality, observed molecular weight, association):
0.067, 646, 1.80; 0.056, 649, 1.81; 0.037, 648, 1.81. Volatile
Liquid (GaEt3): 1H NMR (C6D6, δ) 1.17 (t, GaCH2CH3, 3H),
0.44 (q, GaCH2CH3, 2H). These resonances are identical to
those observed for an authentic sample of GaEt3. Volatile Solid
(H2N[C6H2(t-Bu)3]): Mp 144.7-145.8 °C. 1H NMR (C6D6, δ):
7.40 (s, Ph-H, 2H), 3.63 (s, N-H, 2H), 1.40 (s, o-(t-Bu), 18H),
1.39 (s, p-(t-Bu), 9H). These resonances are identical to those
observed for an authentic sample of H2N[C6H2(t-Bu)3] (mp
145-146 °C).
P r ep a r a tion of EtGa [N(H)C6H2(t-Bu )3]2. The reagent
EtGaCl2 (0.306 g, 1.80 mmol) dissolved in 25 mL of pentane
and cooled to 0 °C was added to 1.02 g (3.82 mmol) of LiNH-
[C6H2(t-Bu)3] slurried in 25 mL of pentane at 0 °C. After 2 h
of stirring, the mixture was filtered and the insoluble fraction
was washed two additional times with pentane. Recrystalli-
zation and subsequent removal of pentane by vacuum distil-
lation provided 0.989 g of EtGa[N(H)C6H2(t-Bu)3]2 (1.60 mmol,
88.6% yield based on EtGaCl2) as a colorless solid. EtGa[N(H)-
C6H2(t-Bu)3]2: Mp 146.6-149.2 °C. 1H NMR (C6D6, δ): 7.52
(s, Ph-H, 4H), 3.30 (s, N-H, 2H), 1.64 (s, o-(t-Bu), 36H), 1.36
(s, p-(t-Bu), 18H), 0.49-0.56 (m, GaCH2CH3, 5H). (The reso-
nances that were observed for the impurity H2N[C6H2(t-Bu)3]
have been omitted.) IR (Nujol, cm-1): 3405 (m), 1592 (w, br),
1422 (vs), 1358 (vs), 1288 (m), 1265 (m, br), 1225 (s), 1195 (m),
1112 (m), 1010 (w), 963 (w), 876 (m), 840 (w), 827 (m), 812
(w), 780 (w), 750 (w), 738 (w), 720 (w), 540 (w), 470 (w). Anal.
Calcd for C38H65GaN2: C, 73.66; H, 10.57. Found: C, 73.45;
H, 10.49. Cryoscopic molecular weight, benzene solution,
formula weight 620 (observed molality, observed molecular
weight, association): 0.085, 573, 0.92; 0.063, 583, 0.94; 0.040,
569, 0.92.
P r ep a r a tion of LiNH[C6H2(t-Bu )3]. The reagent LiNH-
[C6H2(t-Bu)3] was prepared by slowly adding by using an
addition funnel (20 drops/min) a solution of H2N[C6H2(t-Bu)3]
(5.86 g, 18.6 mmol dissolved in 30 mL of pentane) to a stirred
solution of Li(n-Bu) (1.6 M in hexanes, 12 mL, 19.2 mmol,
diluted with 20 mL of pentane) which had been cooled to 0
°C. A colorless precipitate was apparent after adding ap-
proximately 2 mL of amine solution ∼1 min). The reaction
mixture was stirred and allowed to warm to room temperature
overnight. After the mixture was filtered under vacuum with
a coarse frit, the remaining solid was washed three times to
provide 4.58 g of LiNH[C6H2(t-Bu)3] (17.2 mmol, 92.1% based
on H2N[C6H2(t-Bu)3]) as a colorless solid. When Li(n-Bu) was
added to the amine, a lower yield of an impure product (which
had to be washed with benzene to remove unreacted H2N[C6H2-
(t-Bu)3]) was obtained. LiNH[C6H2(t-Bu)3]: 1H NMR (THF-d8,
δ) 6.78 (s, Ph-H, 2H), 3.03 (s, N-H, 1H), 1.44 (s, o-(t-Bu),
18H), 1.18 (s, p-(t-Bu), 9H).
P r ep a r a t ion of E t2Ga NH [C6H 2(t -Bu )3].
A pentane
solution of Et2GaCl (0.954 g, 5.83 mmol) was added with
stirring to a slurry of LiNH[C6H2(t-Bu)3] (1.57 g, 5.87 mmol)
which had been cooled to 0 °C. After it had been stirred for
2 h, the product mixture was filtered and washed twice
with pentane. The solvent was removed by vacuum distillation
at room temperature to leave Et2GaNH[C6H2(t-Bu)3] as a
colorless, mobile liquid (0.989 g, 5.21 mmol, 89.3% yield based
on Et2GaCl). Et2Ga NH[C6H2(t-Bu )3]: Decomposes at room
temperature into GaEt3, H2N[C6H2(t-Bu)3], and {EtGaNH-
[C6H2(t-Bu)2CMe2CH2]}2 (see Results and Discussion section).
1H NMR (C6D6, δ): 7.46 (s, Ph-H, 2H), 3.63 (s, N-H, 1H),
1.53 (s, o-(t-Bu), 18H), 1.36 (s, p-Ph-(t-Bu), 9H), 1.05 (t, Ga-
CH2CH3, 6H), 0.55 (q, Ga-CH2CH3, 4H). (The resonances of
the impurity H2N[C6H2(t-Bu)3] have been omitted.) IR (neat,
cm-1): 3510 (vw), 3400 (w), 3090 (w), 2090 (vs), 2735 (vw),
1760 (vw), 1598 (w), 1460 (m), 1450 (m), 1424 (vs), 1372 (m),
1358 (s), 1349 (m), 1282 (m), 1260 (m), 1230 (vs), 1210 (m),
1192 (m), 1115 (m), 998 (m), 957 (w), 937 (w), 918 (w), 872
(m), 830 (m), 812 (w), 780 (m), 742 (m), 738 (w), 710 (w), 638
(m), 612 (m,br), 558 (m), 515 (m), 466 (w), 442 (w). Anal. Calcd
for C22H40GaN: C, 68.05; H, 10.38. Found: C, 68.57; H, 10.54;
C, 68.56; H, 10.50. Cryoscopic molecular weight, benzene
solution, formula weight 388 (observed molality, observed
molecular weight, association): 0.073, 360, 0.93; 0.047, 361,
0.93.
Liga n d Red istr ibu tion Rea ction betw een EtGa [N(H)-
C6H2(t-Bu )3]2 a n d Ga Et3. A sample of GaEt3 (0.134 g, 0.854
mmol) was reacted with EtGa[N(H)C6H2(t-Bu)3]2 (0.528 g,
0.852 mmol) in approximately 20 mL of pentane in a Solv-
seal tube. The volatile material was then removed after 2 h
by vacuum distillation to leave 0.490 g of Et2Ga[N(H)C6H2(t-
Bu)3] (1.26 mmol, 73.7% yield) as a colorless, mobile liquid.
1
The H NMR spectrum of the product was identical with that
observed for an authentic sample.
Collection of X-r a y Diffr a ction Da ta for {EtGa NH-
Decom p osition of Et2Ga NH[C6H2(t-Bu )3]. A 0.739 g (1.90
mmol) sample of Et2GaNH[C6H2(t-Bu)3] was heated with a 65
°C oil bath for about 12 h to form a colorless solid and a liquid
that was volatile at room temperature. The volatile material
was isolated by vacuum distillation at room temperature and
identified by 1H NMR spectroscopy as GaEt3 (0.083 g, 0.53
mmol). The remaining nonvolatile solid was heated to 80 °C,
and a colorless solid sublimed onto a -78 °C coldfinger. This
product was identified as H2N[C6H2(t-Bu)3] (0.194 g, 0.74
[C6H2(t-Bu )2-CMe2CH2]}2. A well-defined transparent color-
less crystal of dimensions 0.3 × 0.2 × 0.15 mm was sealed
into a thin-walled glass capillary under an argon atmosphere
under meticulous anaerobic and moisture-free conditions. Unit
cell parameters were determined and intensity data were
collected at 24 °C (297 K) on a Siemens R3m/V automated four-
circle diffractometer as described previously.19 Details are
provided in Table 2. The Laue symmetry (C2h) indicated the
monoclinic system. The systematic absences (hkl for h + k )
2n + 1 and h0l for l ) 2n + 1) indicated the possible space
groups C2/c or Cc. Intensity statistics favored the common
centrosymmetric space group C2/c (No. 15).20 This choice was
verified by the successful solution and refinement of the
structure. A total of 5335 reflections (representing two equiva-
lent forms) were collected, corrected for absorption, and merged
(R(int) ) 1.76%) to yield 2598 independent nonzero reflections
of which 1521 were considered observed under the condition
|Fo| g 6.0σ|Fo|).
1
mmol) by comparing its H NMR spectrum and melting point
with those of an authentic sample. The nonvolatile residue was
recrystallized from pentane and identified as {EtGaNH[C6H2(t-
Bu)2CMe2CH2]}2 (0.386 g, 0.99 mmol). X-ray quality crystals
were grown by recrystallization of a pentane solution.
{EtGaNH[C6H2(t-Bu)2CMe2CH2]}2: Mp 243.6-244.6 °C. 1H
NMR (C6D6, δ): 7.65 (s, Ph-H, 1H), 7.42 (s, Ph-H, 1H), 4.76
(s, N-H, 1H), 1.76 (s, Ph-C(CH3)-Ga, 3H), 1.59 (s, Ph-
C(CH3)-Ga, 3H), 1.49 (s, o-(t-Bu), 9H), 1.37 (s, p-(t-Bu), 9H),
1.10 (d, J ) 13.6 Hz, Ph-C(CH3)2CH2-Ga, 2H), 0.95 (t, GaCH2-
CH3, 3H), 0.46 (q, GaCH2CH3, 2H). IR (Nujol, cm-1): 3380 (m),
1414 (s), 1358 (s), 1282 (m), 1260 (m), 1236 (m), 1220 (m), 1210
(19) Churchill, M. R.; Lashewycz, R. A.; Rotella, F. J . Inorg. Chem.
1977, 16, 265.
(20) International Tables for X-ray Crystallography, Volume 1 (2nd
ed.); Kynoch Press: Birmingham, England, 1965; p 101.

Monomeric Organogallium-Nitrogen Compounds
Organometallics, Vol. 18, No. 13, 1999 2549
a VAX station 3100 computer by use of the
Ta ble 2. Da ta for X-r a y Cr ysta llogr a p h ic Stu d ies
formed on
SHELXTL PLUS (Release 4.11 (VMS)) program system.21
The analytical scattering factors for neutral atoms22a were
corrected for the ∆f′ and i∆f′′ components of anomalous
dispersion.22b The structure was solved by a combination of
direct methods, difference Fourier syntheses, and least-squares
refinement. All non-hydrogen atoms were refined anisotropi-
cally. All hydrogen atoms were included in calculated positions
based upon d(C-H) ) 0.96 Å.23 Refinement converged with R
) 3.98% for those data with |Fo| > 6.0σ(Fo). A final difference
Fourier map showed no unexpected features (F ) -0.35 f
0.42 e/Å3). Diagrams were drawn by using the ORTEP2
routine.24
of {EtGa NH[C6H2(t-Bu )2CMe2CH2]}2
molecular formula
C40H68Ga2N2
monoclinic
C2/c (No. 15)
24.953(4)
10.626(1)
18.463(2)
126.16(1)
3952.4(10)
4
cryst syst
space group
a, Å
b, Å
c, Å
â, deg
V, Å3
Z
fw
716.4
D, g/cm3
1.204
1.384
0.8191/0.9711
1536
5.0-45.0
0 to 26
µ(Mo KR), mm-1
T, max/min
F(000)
2θ range, deg
Ack n ow led gm en t. This work was supported in part
by the Office of Naval Research (O.T.B.). The purchase
of the X-ray diffractometer was made possible by Grant
89-13733 from the Chemical Instrumentation Program
of the National Science Foundation.
h
k
-11 to 11
-19 to 16
5335
l
reflns collected
ind reflns
R(int)
2598
1.76%
obsd (>6σ) reflns
weighting scheme
no. of params refined
final R indices (all data)a
1521 (58.5%)
σ2(F) + 0.0003F2
200
R ) 8.38%
wR ) 5.18%
R ) 3.98%
wR ) 4.26%
1.31
Su p p or tin g In for m a tion Ava ila ble: Complete tables of
positional parameters, interatomic distance and angles, aniso-
tropic thermal parameters, and calculated positions for hy-
drogen atoms for the compound studied. This material is
available free of charge via the Internet at http://pubs.acs.org.
R indices (6σ data)a
goodness-of-fit
largest, mean ∆/σ
data-to-param ratio
largest diff peak, e Å-3
largest diff hole, e Å-3
0.001, 0.000
7.6:1
OM990136+
0.42
-0.35
(21) Sheldrick, G. M. SHELXTL PLUS, Release 4.11 (VMS); Si-
emens Analytical Instrument Corp.: Madison, WI, 1989.
(22) International Tables for X-ray Crystallography, Volume 4;
Kynoch Press: Birmingham, England, 1974; (a) pp 99-101, (b) pp
149-150.
(23) Churchill, M. R. Inorg. Chem. 1973, 12, 1213.
(24) J ohnson, C. K. ORTEP-II, Report ORNL-5138; Oak Ridge
National Laboratory: Oak Ridge, TN, 1962.
a
R indices are defined as follows: R(%) ) 100∑||Fo| - |Fo||/
∑|Fo|; wR(%) ) 100∑w(|Fo| - |Fo|)2/∑w|Fo| .
2
Deter m in a tion of Cr ysta l Str u ctu r e of {EtGa NH[C6H2-
(t-Bu )2CMe2CH2]}2. Crystallographic calculations were per-