Adducts of organogallium chlorides with hydrazines and the formation of dimeric dialkylgallium hydrazides possessing different ring sizes

Article abstract of DOI:10.1016/j.jorganchem.2004.12.021

The dialkylgallium chlorides R₂GaCl (R = Me, Et, CMe ₃) reacted with hydrazines H₂N-N(H)R′ (R′ = CMe₃, C₆H₅) to form the adducts R ₂ClGa ← NH₂-N(H)R′ (1-4), in which the gallium atoms are coordinated by the NH₂ nitrogen atoms of the hydrazine ligands. Treatment of these adducts with tert-butyllithium as a base afforded dialkylgallium hydrazides (R₂Ga-N₂H₂R′) ₂ [5 (R = R′ = CMe₃) and 6 (R = CMe₃, R′ = C₆H₅)] by deprotonation of the hydrazine ligands and precipitation of LiCl in two cases only. The remaining adducts gave a substitution reaction at gallium or an unclear reaction course. The hydrazides 5 and 6 adopt different structures in the solid state. The tri(tert-butyl) compound 5 possesses a four-membered Ga₂N₂ heterocycle in its molecular core with two exocyclic N-N bonds, which represents the structural motif usually observed for dialkylgallium hydrazides. 6 has a five-membered Ga₂N₃ heterocycle with one endocyclic and one exocyclic N-N bond. That structure is preserved in solution as clearly shown by NMR spectroscopy. The behaviour of 5 in solution is more complicated, which may be caused by cis/trans isomerization.

Full text of DOI:10.1016/j.jorganchem.2004.12.021

Journal of Organometallic Chemistry 690 (2005) 1529–1539
www.elsevier.com/locate/jorganchem
Adducts of organogallium chlorides with hydrazines and
the formation of dimeric dialkylgallium hydrazides
possessing different ring sizes
*
Werner Uhl , Christian H. Emden
Fachbereich Chemie der Philipps-Universita¨t, Hans-Meerwein-Straße, D-35032 Marburg, Germany
Received 13 October 2004; accepted 7 December 2004
Available online 22 January 2005
Abstract
The dialkylgallium chlorides R2GaCl (R = Me, Et, CMe3) reacted with hydrazines H2N–N(H)R0 (R0 = CMe3, C6H5) to form the
adducts R2ClGa NH2–N(H)R0 (1–4), in which the gallium atoms are coordinated by the NH2 nitrogen atoms of the hydrazine
ligands. Treatment of these adducts with tert-butyllithium as a base afforded dialkylgallium hydrazides (R2Ga–N2H2R0)2 [5
(R = R0 = CMe3) and 6 (R = CMe3, R0 = C6H5)] by deprotonation of the hydrazine ligands and precipitation of LiCl in two cases
only. The remaining adducts gave a substitution reaction at gallium or an unclear reaction course. The hydrazides 5 and 6 adopt
different structures in the solid state. The tri(tert-butyl) compound 5 possesses a four-membered Ga2N2 heterocycle in its molecular
core with two exocyclic N–N bonds, which represents the structural motif usually observed for dialkylgallium hydrazides. 6 has a
five-membered Ga2N3 heterocycle with one endocyclic and one exocyclic N–N bond. That structure is preserved in solution as
clearly shown by NMR spectroscopy. The behaviour of 5 in solution is more complicated, which may be caused by cis/trans
isomerization.
ꢀ 2005 Elsevier B.V. All rights reserved.
1. Introduction
reactions could be initiated on heating of the gallium
hydrazides, which yielded interesting cage compounds
by alkane elimination [4,5,7]. Hydrazine N2H4 and
GaMe3 gave a singular bicyclic compound, (Me2Ga)4-
(N2H2)(NH–NH2)2, in which two five-membered het-
erocycles are connected by a common N–N bond and
in which the N-NH2 groups occupy exocyclic positions
[6]. All remaining dialkylgallium hydrazides published
so far contain the same structural motif in their molec-
ular centres consisting of a four-membered Ga2N2 het-
erocycle and two exocyclic N–N bonds. In contrast,
the homologous dialkylaluminum hydrazides show a
broader variability of structures with four- [2,3,11], five-
[12] and six-membered heterocycles [12–14] and none,
one, or two endocyclic N–N groups, respectively
(Scheme 1). The respective structural motif seems to
be determined by the steric demand of the substituents
Alkylgallium hydrazides found considerable interest
in recent literature because they may be suitable single
source precursors for the generation of gallium nitride
GaN [1]. Generally, they were obtained by the treatment
of trialkylgallium compounds [2–6] or stable gallium tri-
hydride adducts [7] with different alkylhydrazines, by the
reactions of dialkylgallium chlorides with lithium
hydrazides [6–8] or by the replacement reaction between
a hydrazine derivative and a gallium amide [9]. In some
cases, gallium hydrazine adducts could be isolated as
stable intermediates [5,6,10]. Furthermore, secondary
*
Corresponding author. Tel.: +49 6421 2825751; fax: +49 6421
2825653.
E-mail address: uhl@chemie.uni-marburg.de (W. Uhl).
0022-328X/$ - see front matter ꢀ 2005 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.12.021

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W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
R
H
H
uble in n-hexane, but readily soluble in toluene. A fast
exchange of the N–H protons led to the occurrence of
only one, generally broad resonance. Only the diethyl
compound 2 shows two distinct N–H signals, which
are broad and overlap partially. No coupling between
the protons of different nitrogen atoms could be
resolved.
H
N
N
R
H
N
N
N
CMe3
CMe3
Me3C
Me3C
CMe3
CMe3
Me3C
Me3C
Al
Al
Al
Al
N
H
N
N
H
R
H
H
R
(R = H, SiMe3)
H
R´
(R = SiMe3, C6H5)
H
N
N
R2GaCl
+
N2H3R´
R
R
Me3C
H
H
H
Ga
N
N
Cl
ð1Þ
R = CH3, C2H5, CMe3
R´ = CMe3, C6H5
1: R = CH3, R´ = CMe3
2: R = C2H5, R´ = CMe3
3: R = CMe3, R´ = CMe3
4: R = CMe3, R´ = C6H5
Me3C
CMe3
Al
Al
Me3C
CMe3
N
N
The four adducts were characterized by crystal struc-
ture determinations (Figs. 1–4). Two polymorphous
forms possessing different space groups were observed
for compound 1. Thus, two values of structural param-
eters are given in the discussion, in all cases the first one
refers to the monoclinic cell. Compound 2 has two inde-
pendent molecules in the asymmetric unit of the
unit cell, only one of which is depicted in Fig. 2.
All structures consist of adducts formed by the intact
H
CMe3
H
Scheme 1.
attached to aluminum or the hydrazido groups and by
the transannular electrostatic repulsion between the ring
atoms. Quantum-chemical calculations on the alumi-
num compounds revealed that the five-membered
Al2N3 heterocycles are the most favourable ones [12].
While NMR spectroscopic investigations of the alumi-
num hydrazides verified the preservation of the solid
state structures in solution, more complicated spectra
were detected with gallium hydrazides, which were inter-
preted by the occurrence of cis/trans isomers with re-
spect to the arrangement of the N–N or N–H bonds
[2,3,5]. This isomerization process should proceed by
the opening of one Ga–N bond in the ring. Here we re-
port on the isolation and characterization of two new
dialkylgallium hydrazides, for which different structures
were observed in the solid state and in solution.
2. Results and discussion
2.1. Formation of adducts R2GaCl NH2–N(H)R0
As was shown in preceding investigations of our
group [11,12], the treatment of hydrazine adducts of
the type R2AlCl NH2–N(H)R0 with n-butyllithium
afforded the corresponding dialkylaluminum hydrazides
by deprotonation and salt elimination in quite reason-
able yields. We hoped to employ this procedure for
the synthesis of gallium hydrazides, too. The corre-
sponding gallium hydrazine adducts R2GaCl NH2–
N(H)R0 were easily obtained by the direct treatment of
dialkylgallium chlorides (R = Me, Et, CMe3) with alkyl
or aryl hydrazines H2N–N(H)R0 (R0 = CMe3, C6H5) in
moderate to high yields, Eq. (1). All adducts (1–4) were
isolated as colorless solids. They are only sparingly sol-
Fig. 1. Molecular structure of 1. The thermal ellipsoids are drawn at
the 40% probability level. Methyl hydrogen atoms are omitted.
Important bond lengths (pm) and angles (ꢁ): Monoclinic cell: Ga–C1
195.1(4), Ga–C2 195.1(4), Ga–Cl 228.48(9), Ga–N1 206.5(3), N1–N2
145.1(4), C1–Ga–C2 128.8(2), C1–Ga–N1 104.6(1), C2–Ga–N1
107.2(2), C1–Ga–Cl 110.2(1), C2–Ga–Cl 106.8(1), N1–Ga–Cl
93.64(9). Triclinic cell: Ga–C1 196.4(8), Ga–C2 195.6(8), Ga–N1
206.4(6), Ga–Cl 229.1(2), N1–N2 144.9(8), C1–Ga–C2 128.6(4), C1–
Ga–N1 103.5(3), C2–Ga–N1 107.3(3), C1–Ga–Cl 110.7(3), C2–Ga–Cl
106.9(3), N1–Ga–Cl 94.3(2).

W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
1531
Fig. 2. Molecular structure of 2. The thermal ellipsoids are drawn at
the 40% probability level. Methyl groups of the tert-butyl group and
hydrogen atoms of the ethyl groups are omitted. Important bond
lengths (pm) and angles (ꢁ) (figures of the second molecule in square
brackets): Ga1–C11 196.5(3) [196.2(4)], Ga1–C13 195.9(4) [196.3(3)],
Ga1Cl1 228,8(1) [228,65(9)], Ga1–N1 206.7(3) [205.8(3)], N1–N2
145.7(4) [146.1(4)], C11–Ga1–C13 126.4(2) [125.9(2)], C11–Ga1–N1
106.7(1) [107.6(2)], C13–Ga1–N1 106.6(2) [106.2(2)], C11–Ga1–Cl1
110.9(1) [109.0(1)], C13–Ga1–Cl1 108.4(2) [110.4(1)], Cl1–Ga1–N1
92.2(1) [92.49(9)].
Fig. 3. Molecular structure of 3. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms of methyl groups are
omitted. Important bond lengths (pm) and angles (ꢁ): Ga1–Ct1 198(3),
Ga1–N1 210.8(7), Ga1–Cl1 228.7(2), N1–N2 143(2), N1–Ga1–Cl1
92.5(2).
relatively short Hꢀ ꢀ ꢀCl contacts between the chlorine
atoms attached to aluminum or indium and the hydro-
gen atom of the b-nitrogen atoms may indicate a weak
hydrogen bonding [10,15], such an interaction may be
constituents dialkylgallium chloride and hydrazine.
While the nitrogen atoms bonded to the tert-butyl or
phenyl groups are in terminal positions, the NH2 nitro-
gen atoms of the hydrazine ligands are attached to the
gallium atoms in all compounds, so that coordination
numbers of four in a distorted tetrahedral environment
result for the central metal atoms. The Ga–C distances
to the alkyl groups show a slight, but continuous in-
crease with increasing bulkiness of the substituents
[195.1 and 196.0 (1, R = Me) to 199.2 pm (4,
R = CMe3)]. Same holds for the Ga–N distances, which
vary between 206.5/206.4 (1) and 212.1 pm (4). In con-
trast, the Ga–Cl bond lengths are almost indistinguish-
able in all four compounds and deviate only slightly
from the average value of 228.7 ( 0.4) pm. The N–N
distances of the tert-butylhydrazine ligands (145.5 pm)
are longer than that of the phenylhydrazine ligand
(142.9 pm). Compound 3 may not be considered here
owing to a severe disorder and the uncertainty of the
determined bond lengths and angles. The tricoordinated
nitrogen atoms N2 of all compounds 1–4 possess a pyra-
midal environment [sum of the angles 330.8 and 339.0
(1), 325.5 and 332.1(2), 326.5 (3), 338.3 (4)]. While in
aluminum or indium hydrazine adducts similar to 1–4
Fig. 4. Molecular structure of 4. The thermal ellipsoids are drawn at
the 40% probability level. Hydrogen atoms of the phenyl and tert-butyl
groups are omitted. Important bond lengths (pm) and angles (ꢁ): Ga1–
Ct1 199.5(3), Ga1–Ct2 198.9(3), Ga1–Cl1 228.30(9), Ga1–N1 212.1(2),
N1–N2 142.9(4), Ct1–Ga1–Ct2 127.1(1), Ct1–Ga1–N1 106.4(1), Ct2–
Ga1–N1 106.6(1), Ct1–Ga1–Cl1 110.0(1), Ct2–Ga1–Cl1 108.89(9),
Cl1–Ga1N1 92.03(8).

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W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
Me3C
H
excluded for the gallium adducts 1–4. The shortest
Hꢀ ꢀ ꢀCl contact (259 pm) was observed for the disor-
dered compound 3. The longer ones of the remaining
compounds [284 (4) to 313/321 pm (1)] are clearly out-
side the range of significant interactions. The particular
behaviour of the gallium compounds may be caused by
the higher electronegativity of gallium compared to that
of aluminum or indium and the lower charge separation
resulting for the Ga–Cl bonds. Comparable adducts of
hydrazines with trialkylgallium compounds [5] or with
methylgallium dichloride [6,10] are reported in litera-
ture, however, only the last one was characterized by a
crystal structure determination.
N
N
H
Me3C
Me3C
CMe3
CMe3
Ga
Ga
N
N
H
CMe3
H
5
R´ = CMe3
+ 2 Me3CLi
- 2 Me3CH/- 2 LiCl
H
R´
H
ð2Þ
N
N
2
Me3C
2.2. Formation of hydrazides [R2Ga–N2H2R0]2
H
Ga
Me3C
Cl
3, 4
Starting with these adducts, we tried to synthesize
hydrazides by treatment with butyllithium. However,
we were successful in two cases only. The diethyl com-
pound 2 gave the quantitative replacement of the chlo-
rine atom by an n-butyl group instead. The adduct
Me2(nBu)Ga NH2–N(H)CMe3 was formed and
clearly identified by NMR spectroscopy [1H NMR:
d = 2.98 (2H, NH2), 2.53 (1H, NH), 1.73 and 1.59 (each
2H, CH2 of nBu), 1.44 (6H, Me of Et), 1.10 (Me of nBu),
0.60 (9H, CMe3), 0.59 (4H, CH2 of Et); one CH2 group
probably covered]. It was isolated as an oily product,
which could not be purified by recrystallization. Distilla-
tion succeeded at elevated temperature in vacuum, but
partial decomposition occurred as became obvious by
an alteration of the integration ratio between alkylgal-
lium and hydrazine residues. Thus, further experimental
details are not included here. Clearly, the substitution
reaction in that case is favoured by the low steric shield-
ing of the starting compound. The dimethyl compound
1 gave a mixture of unknown products, which could
not be separated.
The expected reactions were observed for both di-
(tert-butyl)gallium compounds (3 and 4). Treatment
with tert-butyllithium gave deprotonation and salt
elimination, and gallium hydrazides were isolated in
moderate yield, Eq. (2). The routine procedures given
in the experimental section do not involve the isola-
tion of the intermediate adducts, but the rough prod-
ucts of the adduct formation were directly treated
with the alkyllithium derivative. Both hydrazides were
isolated as colorless crystals and their constitution was
clarified by crystal structure determinations (see be-
low). They adopt different structures in the solid state.
A four-membered centrosymmetric Ga2N2 heterocycle
with two exocyclic N–N bonds was observed for the
tri(tert-butyl) compound 5, while for the phenylhyd-
razide product (6) a five-membered Ga2N3 ring with
one endo- and one exocyclic N–N bond was
determined.
R´ = C6H5
+ 2 Me3CLi
- 2 Me3CH/- 2 LiCl
H
C6H5
H
N
N
CMe3
Ga
Me3C
Me3C
Ga
CMe3
N
N
H
C6H5
H
6
The solution behavior is more complicated. The cen-
trosymmetric structure observed for 5 in the solid state
1
should result in a quite simple H NMR spectrum. In-
stead, four chemically different N–H protons were de-
tected at room temperature. Three resonances in an
integration ratio of about 1:2:1 were observed for the
tert-butyl groups attached to gallium, but only one res-
onance resulted for the tert-butyl group of the hydrazido
substituent. The last one splitted into two very narrow
resonances upon cooling to 285 K. Upon warming, the
signals of the tert-butyl groups attached to gallium coin-
cided at about 330 K, those of the N–H protons gave
two resonances at about 340 and 350 K, respectively.
The activation barrier for the exchange process was esti-
mated [16] to be about 70 kJ/mol, which is similar to val-
ues reported before [2,3]. The relative intensities of the
NMR signals of the two species at lower temperature
(200–320 K) remain constant and verify an almost equi-
molar distribution (average integration ratio 1–1.2).
Thus, the energy difference between both species seems
to be rather small. An equilibrium of monomeric and di-
meric formula units by partial dissociation can clearly be
ruled out, because the determination of the molar mass
in benzene by cryoscopy gave the exact value of the di-
mer. The behavior of 5 is similar to that reported in lit-
erature for other dialkylgallium hydrazides [2,3,5]. It

W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
1533
was interpreted in terms of cis/trans isomerization by the
opening of a Ga–N bond in the ring, rotation around
the remaining bond, inversion of configuration at nitro-
gen and ring closure. Monomerization in traces and
dimerization of differently oriented monomers may,
however, not be excluded. In our case, only one reso-
nance should result for the tert-butyl groups attached
to the gallium atoms of the trans-isomer, while two res-
onances are to be expected for the cis-isomer. This al-
lows the assignment of the different sets of resonances
to the respective isomeric forms.
The phenylhydrazido compound 6 only partially
shows the expected 1H NMR spectrum at room temper-
ature. The resonances of four chemically different tert-
butyl groups attached to gallium in equal intensity were
observed in accordance with the particular structure
containing a five-membered heterocycle. A strong
dependency of the relative chemical shifts (Dd) of the
outer two signals on temperature was detected. Dd de-
creased from 0.70 ppm at 190 K to 0.34 ppm at 370 K.
1
The alteration of the H NMR spectra depending on
temperature is partially summarized in Fig. 5. As
Fig. 5. Temperature dependent 1H NMR spectra of 6. Details of the NH (top) and phenyl regions (bottom) of the spectra are depicted. Resonances
of the solvent toluene are marked by an asterisk.

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W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
expected from the molecular structure, also four chemi-
cally different N–H protons were observed at room tem-
perature, which showed an equal intensity and a
coupling across the N–N bond. One doublet at
d = 5.24 was markedly separated from the remaining
three ones at d = 4.39, 4.28 and 4.17. Dd was largest at
high temperature (370 K), while with decreasing temper-
ature the three high field doublets approached to give a
broad, only slightly splitted resonance at 200 K. Most
complicated was the phenyl region of the 1H NMR spec-
trum. Two different phenyl groups are to be expected,
one attached to a nitrogen atom of the ring bearing a
negative charge and one bonded to the terminal nitrogen
atom of the exocyclic N–N bond. Thus, six different res-
onances of phenyl hydrogen atoms should occur. But
only one doublet and three triplets in a strange integra-
tion ratio of 2 (t):2 (t):2 (t):4 (d) were observed at 280 K.
The triplet at d = 6.68 deviated most strongly from the
ideal shape. At lower temperature that particular triplet
and the doublet at d = 6.52 split into two triplets or dou-
blets, respectively. The two other triplets remained al-
most unchanged apart from small alterations of their
chemical shifts. They approached at higher tempera-
tures. A splitting of the triplet at d = 6.68 and the dou-
blet at d = 6.52 was also observed for temperatures
above 280 K. The integration ratio of the resulting six
resonances is 2:2 (triplets, both meta-H, not affected
on cooling or warming):1:1 (triplets, both para-H, split-
ting was observed):2:2 (doublets, ortho-H, splitting was
observed). These values correspond to those expected
for the heterocyclic molecule. It seems that by accident
a much too simple spectrum was observed at room tem-
perature, while at higher or lower temperatures spectra
resulted which were expected by molecular symmetry.
A crossing of the resonances at about 280 K is responsi-
ble for that particular observation. The strong altera-
tions of the shape of the spectra may be caused by
conformational changes of the molecules in solution
with respect to the strongly faulted heterocycle observed
for the solid state. Or it may depend on the strength of
the mesomeric interaction between the phenyl group and
the anionic nitrogen atom of the endocyclic hydrazido
group.
Fig. 6. Molecular structure of 5. The thermal ellipsoids are drawn at
the 40% probability level. Methyl groups are omitted. Important bond
lengths (pm) and angles (ꢁ): Ga1–Ct1 202.9(2), Ga1N1 203.8(2), N1–
N2 144.6(4), Ct1–Ga1–Ct1a 116.7(2), Ct1–Ga1–N1 114.7(1), Ct1–
Ga1–N1a 111.7(1), N1–Ga1–N1a 82.9(1), Ga1–N1–Ga1a 97.1(1);
Ct1a generated by ꢁx,y,ꢁz; N1a and Ga1a generated by ꢁx,ꢁy,ꢁz.
326ꢁ, disordered hydrogen atom). The preference of
the four-membered heterocycle in that case may be fa-
voured by steric interactions between the bulky substit-
uents. The hydrazine tert-butyl groups are bonded to the
exocyclic nitrogen atoms and are, thus, in an optimum
distance with respect to the tert-butyl groups attached
to gallium.
In contrast, the phenylhydrazido compound 6 adopts
a structure containing a five-membered heterocycle (Fig.
7), which may be favoured by the less steric stress in the
molecule owing to the reduced bulkiness of the phenyl
ring compared to that of the tert-butyl group and by
the diminution of transannular electrostatic repulsions
[12]. 6 crystallizes with two independent molecules; bond
parameters of the second molecule are given in brackets.
The endocyclic hydrazide has an NH2 group (N21),
which is attached to Ga2 by a coordinative bond. The
amido nitrogen atom (N22) of that hydrazido ligand is
bonded to Ga1 and bears the phenyl ring. The second
hydrazido group bridges both Ga atoms via its amido
nitrogen atom N11, which is further bonded to a hydro-
gen atom and the second, terminal nitrogen atom N12.
The N–N bond is exocyclic, and N12 bears the phenyl
ring and the second hydrogen atom. Thus, the hydraz-
ido ligands differ with respect to their bridging positions
and the distribution of their hydrogen atoms. The GaN
distances depend on the particular bonding mode. The
shortest bond lengths on average [198.9 pm
(198.3 pm)] were observed for those bonds involving
Fig. 6 shows the molecular structure of the tert-butyl
hydrazido compound 5. It possesses a four-membered
Ga2N2 heterocycle with two exocyclic N–N bonds.
The molecules are located on special positions with sym-
metry 2/m. The Ga–C bonds of 5 (202.9 pm) are longer
than those of the starting compound 3, while a shorten-
ing of the Ga–N bonds (203.8 pm) was observed com-
pared to the donor-acceptor bond of the adduct 3.
The N–N bond lengths are in the expected range
(144.6 pm). The nitrogen atom N1 attached to two gal-
lium atoms has a distorted tetrahedral coordination
sphere, while the second, exocyclic nitrogen atom N2
has a pyramidal surrounding (sum of the bond angles

W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
1535
Fig. 7. Molecular structure of 6. The thermal ellipsoids are drawn at the 40% probability level. Methyl groups and hydrogen atoms of the phenyl
groups are omitted. Two independent molecules were found, structural parameters of the second one are given in square brackets. Important bond
lengths (pm) and angles (ꢁ): Ga1–N11 207.4(3) [208.5(4)], Ga1–N22 198.9(3) [198.3(3)], Ga2–N21 210.6(3) [209.6(4)], Ga2–N11 199.8(4) [198.9(4)],
N11–N12 144.9(5) [143.6(5)], N21–N22 143.5(5) [143.3(5)], Ga1–N11–Ga2 114.9(2) [113.2(2)], N11–Ga1–N22 91.6(1) [92.9(1)], Ga1–N22–N21
115.4(2) [116.1(3)], N22–N21–Ga2 114.3(3) [114.6(3)], N21–Ga2–N11 90.7(1) [92.5(1)].
the amido nitrogen atom N22 of the endocyclic hydra-
zine. The bridging atom N11 has a short and a long
Ga–N distance of 199.8 (198.9) and 207.4 pm
(208.5 pm). The longest separations were found for the
dative bonds Ga2–N21 [210.6 pm (209.6 pm)]. The N–N
bond lengths are quite similar despite the different co-
ordination behaviour of the hydrazido ligands and
deviate only slightly from the average value of
143.8 pm. The nitrogen atom N22 has an almost planar
coordination sphere [353.1ꢁ (355.1ꢁ)], which may be
caused by a mesomeric stabilization of the negative
charge through an interaction of nitrogen lone pairs
with the aromatic system of the phenyl rings. This inter-
pretation may also be verified by the coplanar arrange-
ment of the phenyl ring and the further atoms
attached to nitrogen [angle between the normals of the
planes phenyl versus Ga1,N22,N21,C21 20.3ꢁ (15.6ꢁ)].
Owing to the uncertainty of the refined hydrogen posi-
tions, we refrain from a discussion of structural para-
meters involving hydrogen atoms. The five-membered
heterocycles adopt an envelope conformation. The four
atoms N22, Ga1, N11 and Ga2 are almost in a plane
with the largest deviation of an atom from that plane
of 8.7 pm (7.7 pm). The nitrogen atom N21 of the
NH2 group is located 50.0 pm (45.5 pm) above that
plane. Thus, two different structural motifs were deter-
mined for the gallium hydrazides reported here similar
to the situation of the aluminum hydrazides described
in Section 1. Different ring sizes with four-, five- and
six-membered heterocycles were also observed for alu-
minum and gallium hydroxylamides [17].
3. Experimental
All procedures were carried out under purified argon.
Toluene was dried over Na/benzophenone, n-pentane, n-
hexane and cyclopentane over LiAlH4. Di(tert-
butyl)gallium chloride [18], diethylgallium chloride and
dimethylgallium chloride [19] were obtained according
to literature procedures. Commercially available phen-
ylhydrazine (Aldrich) was degassed and stored over
molecular sieves prior to use. MOCHEM GmbH (Mar-
burg) supported us with tert-butylhydrazine.
3.1. Synthesis of (tert-butylhydrazine)dimethylgallium
chloride (1)
Dimethylgallium chloride (0.246 g, 1.82 mmol) dis-
solved in 25 ml of n-pentane was treated with 194 ll

1536
W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
(0.160 g, 1.82 mmol) of tert-butyl hydrazine at room
temperature. The product immediately precipitated as
a colorless solid, which is filtered off and dried in vac-
uum. A second fraction of the product was isolated
upon concentration and cooling of the filtrate. Owing
to NMR spectroscopic characterization the precipitated
product is pure. It may be recrystallized from cyclopen-
tane for further purification. Yield: 0.248 g (61%). M.p.
(argon, sealed capillary): 126 ꢁC. 1H NMR (C6D6,
300 MHz): d = 3.26 (3H, s, br, N–H), 0.51 (9H, s,
CMe3), 0.09 (6H, s, GaMe2). 13C NMR (C6D6,
50.3 MHz): d = 54.0 (N–C), 25.8 (methyl of tert-butyl),
ꢁ4.0 (GaC). IR (CsBr plates, paraffin, cmꢁ1): 3308 m,
3270 w, 3195 w, 3151 vw mNH; 2955 vs, 2922 vs, 2853
vs, 2700 w, 2639 w (paraffin); 2500 m dNH; 1644 vw,
1592 m dNH2; 1461 s, 1377 m (paraffin); 1220 w, 1201
m dCH3; 1125 w, 1051 vw, 1037 vw, 954 w, 928 w, 851
vw dCH, mCN, mNN, mCC; 811 vw masNN; 730 m (paraf-
fin); 601 w, 548 vw, 511 w, 464 m, 393 w, 357 w dC3C,
mGaC, mGaN, mGaCl.
br, N–H), 1.29 (18 H, s, Ga–CMe3), 0.58 (9 H, s, N–
CMe3). 13C NMR (C6D6, 50.3 MHz): d = 53.9 (N– C),
30.4 (Me of Ga–CMe3), 25.5 (Me of N–CMe3), 24.1
(GaC). IR (CsBr plates, paraffin, cmꢁ1): 3284 m, 3266
m, 3224 w, 3157 w mNH; 2923 vs, 2853 vs (paraffin);
1592 m dNH; 1462 s, 1376 s (paraffin); 1277 w, 1231 w
dCH3; 1216 w, 1197 vw, 1050 w, 1010 w, 949 w dCH,
mCN, msNN, mCC; 815 w masNN; 733 w (paraffin); 667
w dC3C; 551 vw, 464 vw, 390 vw mGaC, mGaN, mGaCl.
3.4. Synthesis of (phenylhydrazine)di(tert-butyl)gallium
chloride (4)
Di(tert-butyl)gallium chloride (0.495 g, 2.26 mmol)
dissolved in 50 ml of n-hexane was treated with 222 ll
(0.244 g, 2.56 mmol) of phenylhydrazine at room tem-
perature. The product precipitated as a colorless, volu-
minous solid, which was filtered off and recrystallized
from toluene (20/8 ꢁC). Yield: 0.664 g (90%). Dec. (ar-
gon, sealed capillary): 136 ꢁC. 1H NMR (C6D6,
300 MHz): d = 6.94 (2H, pseudo-t, meta-H of phenyl),
6.76 (1H, pseudo-t, para-H of phenyl), 6.15 (2H,
pseudo-d, o-H of phenyl), 4.6 (3H, very broad, N–H),
1.21 (18 H, s, CMe3). 13C NMR (C6D6, 75.5 MHz):
d = 147.7, 129.7, 122.6 and 114.1 (all phenyl), 30.3
(methyl of tert-butyl), 24.4 (GaC). IR (CsBr plates, par-
affin, cmꢁ1): 3341 w, 3261 w, 3196 w, 3143 w mNH; 2924
vs, 2852 (paraffin); 1934 vw, 1843 vw, 1775 vw, 1711 vw
(phenyl); 1590 m dNH, 1588 m, 1500 m, 1496 m (phe-
nyl); 1463 vs, 1377 s (paraffin); 1311 vw, 1264 m
dCH3; 1208 w, 1177 vw, 1153 w, 1110 vw, 1083 w,
1048 vw, 1022 vw, 1010 w, 939 vw, 889 vw, 844 vw
dCH, mCN, mNN, mCC; 813 w masNN; 764 m, 723 w,
697 vw, 664 m dC3C, phenyl; 567 w, 493 w, 463 vw,
385 w mGaC, mGaN, mGaCl.
3.2. Synthesis of (tert-butylhydrazine)diethylgallium
chloride (2)
A
solution of diethylgallium chloride (0.209 g,
1.28 mmol) in 10 ml of n-pentane was added to a cooled
(ꢁ30 ꢁC) solution of tert-butylhydrazine (133 ll,
0.113 g, 1.28 mmol) in 10 ml of the same solvent. After
slow warming to room temperature the solvent was re-
moved in vacuum. The colorless residue was recrystal-
lized from cyclopentane (20/ꢁ30 ꢁC). Yield: 0.176 g
1
(55%). M.p. (argon, sealed capillary): 92 ꢁC. H NMR
(C6D6, 300 MHz): d = 3.21 (1H, s, br, NH); 3.17 (2H,
s, br, NH2), 1.36 (6H, t, JH–H = 8.1 Hz, CH3 of ethyl),
3
3
0.68 (4H, q, JH–H = 8.1 Hz, CH2 of ethyl), 0.54 (9H, s,
CMe3). 13C NMR (C6D6, 50.3 MHz):d = 53.9 (N–C),
25.6 (Me of tert-butyl), 10.2 (Me of ethyl), 5.9 (GaC).
IR (CsBr plates, paraffin, cmꢁ1): 3643 w, 3297 m, 3274
m, 3197 m, 3146 m mNH; 2925 vs, 2856 vs, 2727 w,
2639 w paraffin; 2500 m dNH; 1591 s dNH2; 1461 vs,
1375 s paraffin; 1280 w, 1219 m, 1201 m dCH2, dCH3;
1123 w, 1049 w, 1006 m, 944 m, 850 vw dCH, mCN,
mNN, mCC; 814 w masNN; 738 w paraffin; 659 m, 567
m, 516 m, 464 w, 390 w, dC3C, mGaC, mGaN, mGaCl.
3.5. Synthesis of bis[di(tert-butyl)gallium(tert-butylhy-
drazide)] (5)
Di(tert-butyl)gallium chloride (0.313 g, 1.43 mmol)
was dissolved in 10 ml of toluene by slight warming
and treated with 160 ll of tert-butylhydrazine (0.126 g,
1.43 mmol) at room temperature. After stirring for 1 h
at room temperature the solution was cooled (ꢁ60 ꢁC)
and treated with 0.90 ml of a solution of tert-butylli-
thium in n-hexane (1.6 M, 1.43 mmol). After slow warm-
ing to room temperature and stirring for 3–4 h LiCl was
separated by filtration. The filtrate was concentrated in
vacuum and cooled to ꢁ15 ꢁC to obtain colorless crystals
of the product. Yield: 0.123 g (32%); the crystals do not
melt until 220 ꢁC; sublimation without decomposition
3.3. Synthesis of (tert-butylhydrazine)di(tert-
butyl)gallium chloride (3)
A cooled (ꢁ20 ꢁC) suspension of di(tert-butyl)gal-
lium chloride (0.156 g, 0.71 mmol) in 10 ml of toluene
was treated with 80 ll of tert-butylhydrazine (0.063 g,
0.71 mmol). A clear solution was obtained, which was
concentrated at room temperature and cooled to
ꢁ15 ꢁC. The product crystallized as colorless needles.
Yield: 0.102 g (47%). Dec. (argon, sealed capillary):
100 ꢁC. 1H NMR (C6D6, 300 MHz): d = 3.70 (3H, s,
1
occurred at 140 ꢁC (10ꢁ2 Torr). H NMR (toluene-D8,
400 MHz, 300 K): d = (trans isomer) 3.61 (1H, s, br,
Ga–N–H), 2.85 (1H, s, br, N(H)–C), 1.31 (18H, s, Ga–
CMe3); (cis isomer) 3.31 (1H, s, br, Ga–N–H), 2.99
(1H, s, br, N(H)–C), 1.42 and 1.21 (each 9H, s,

Table 1
Crystal data, data collection parameters and structure refinement for 1 (monoclinic), 1 (triclinic), 2, 3, 4, 5 and 6a
1 (monoclinic)
1 (triclinic)
2
3
4
5
6
Formula
Temperature (K)
Crystal system
Space group [21]
a (pm)
C6H18ClGaN2
193(2)
C6H18ClGaN2
193(2)
Triclinic
C8H22ClGaN2
193(2)
Triclinic
C12H30ClGaN2
193(2)
C14H26ClGaN2
193(2)
Triclinic
C24H58Ga2N4
193(2)
C28H50Ga2N4
193(2)
Monoclinic
P21/n (no. 14)
1102.58(6)
609.91(5)
1672.9(1)
90
Orthorhombic
Pnma (no. 62)
1993.1(1)
1356.2(1)
635.09(5)
90
Monoclinic
C2/m (no. 12)
1662.4(1)
1127.08(9)
885.38(5)
90
Monoclinic
P21/c (no. 14)
1850.7(1)
1695.89(7)
2150.3(1)
90
ꢀ
ꢀ
ꢀ
P1 (no. 2)
P1 (no. 2)
P1 (no. 2)
608.95(8)
921.8(1)
1105.0(1)
113.93(1)
90.32(1)
101.11(1)
553.9(1)
2
599.34(6)
1265.1(1)
1735.3(2)
79.19(1)
86.41(1)
84.43(1)
1285.0(2)
4
616.86(8)
868.0(1)
1649.4(2)
81.67(2)
82.31(2)
74.13(1)
836.4(2)
2
b (pm)
c (pm)
a (ꢁ)
b (ꢁ)
101.899(5)
90
90
90
115.180(4)
90
114.600(4)
90
c (ꢁ)
V (10ꢁ30 m3)
Z
1100.8(1)
4
1.348
1716.7(2)
4
1.190
1501.2(2)
2
1.199
6136.4(5)
8
1.260
Dcalc (g cmꢁ3
)
1.339
2.671
1.300
2.311
1.300
1.792
l (mmꢁ1
)
2.688
0.50 · 0.28 · 0.14
Mo Ka; graphite-monochromator
1.741
0.32 · 0.12 · 0.05
1.811
0.33 · 0.21 · 0.15
1.777
0.20 · 0.13 · 0.14
Crystal size (mm)
Radiation
0.20 · 0.12 · 0.05
0.36 · 0.30 · 0.24
0.45 · 0.09 · 0.09
Theta range for data collection (ꢁ)
Index ranges
2.04 6 h 6 26.19
ꢁ13 6 h 6 13
7 6 k 6 7
2.03 6 h 6 26.04
2.64 6 h 6 25.88
ꢁ7 6 h 6 7
ꢁ15 6 k 6 15
ꢁ21 6 l 6 21
2518
2.04 6 h 6 26.04
ꢁ24 6 h 6 24
ꢁ16 6 k 6 16
ꢁ7 6 l 6 7
2.46 6 h 6 26.01
ꢁ7 6 h 6 7
ꢁ10 6 k 6 10
ꢁ20 6 l 6 20
2417
3.62 6 h 6 26.10
ꢁ20 6 h 6 20
ꢁ13 6 k 6 13
ꢁ10 6 l 6 10
1505
1.59 6 h 6 26.30
ꢁ22 6 h 6 23
ꢁ21 6 k 6 21
ꢁ26 6 l 6 26
7443
ꢁ7 6 h 6 6
ꢁ11 6 k 6 11
ꢁ13 6 l 6 13
1797
ꢁ20 6 l 6 20
Reflections observed
Independent reflections
Parameters
1974
1388
2215 (Rint = 0.1013) 2187 (Rint = 0.0885) 3438 (Rint = 0.0473) 1764 (Rint = 0.1050) 3077 (Rint = 0.0447) 1559 (Rint = 0.0519) 12,390 (Rint = 0.0786)
85
108
108
0.0695
0.1820
251
0.0314
0.0813
153
0.0602
0.1750
181
0.0333
0.0793
822
0.0431
0.1144
P
P
R = jjFoj ꢁ jFcjj/ jFoj [I > 2r(I)] 0.0389
0.0310
0.0907
P
2
2 2
w2 ¼ f wðj F oj ꢁ j F cj Þ =
0.1117
P
2
1=2
j F oj g (all data)
Max./min. residual electron
density (1030 e mꢁ3
0.564/ꢁ1.046
2.841/ꢁ0.704
0.388/ꢁ0.447
0.764/ꢁ1.056
0. 643/ꢁ0.894
0.765/ꢁ0.369
0.422/0.555
)
a
Programme SHELXL-97 [20]; solutions by direct methods, full matrix refinement with all independent structure factors.

1538
W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
Ga–CMe3); 0.94 (ꢂ18H, s, one resonance for N–CMe3 of
both isomers). 1H NMR (toluene-D8, 400 MHz, 363 K):
d = 3.45 (2H, s, br, Ga–N–H), 2.91 (2H, s, br, N(H)–C),
1.27 (36 H, s, br, Ga–CMe3), 0.97 (18H, s, N–CMe3). 1H
NMR (toluene-D8, 400 MHz, 200 K): d = (trans isomer)
3.69 (1H, s, Ga–N–H), 2.85 (1H, s, N(H)–C), 1.42 (18H,
s, Ga–CMe3), 0.87 (9 H, s, N–CMe3); (cis isomer) 3.37
(1H, s, Ga–N–H), 3.07 (1H, s, N(H)–C), 1.58 and 1.30
(each 9H, s, Ga–CMe3), 0.89 (9H, s, N–CMe3); the inte-
gration ratio between both isomers (about 1:1.2) is al-
most independent from temperature. 13C NMR (C6D6,
100 MHz): d = 54.4 and 54.2 (N–C), 33.0 (Me of Ga–
CMe3), 27.3 and 27.1 (Me of N–CMe3), 26.6 and 25.2
(GaC). IR (CsBr plates, paraffin, cmꢁ1): 3282 vw, 3269
vw, 3228 vw, 3156 vw mNH; 2924 vs, 2853 vs (paraffin);
1592 w dNH; 1460 vs, 1376 s (paraffin); 1269 vw, 1245
w dCH3; 1229 m, 1207 m, 1172 w, 1048 w, 1008 w, 942
w, 918 vw dCH, mCN, mNN, mCC; 812 s, 767 w masNN;
730 m (paraffin); 576 w, 534 w, 472 m, 451 m, 399 w,
357 w mGaC, mGaN. Molar mass (in benzene by cryos-
copy): Found 540, calc. 542.18.
1.19, 1.08, and 0.77 (each 9H, s, CMe3). 13C NMR (tol-
uol-D8, 100 MHz): d = 155.9, 149.9, 124.5, 117.4,
112.4, and 111.0 (phenyl), 32.9, 31.9, 31.8, and 31.4
(CMe3), 26.3, 24.2, 23.8, and 22.8 (Ga–C). IR (CsBr
plates, paraffin, cmꢁ1): 3388 w, 3222 vw, 3183 vw
mNH; 2923 vs, 2853 vs (paraffin); 1599 s dNH; 1577
m, 1568 m, 1492 m (phenyl); 1464 vs, 1377 m (paraf-
fin); 1364 m, 1338 vw, 1305 m, 1270 s, 1245 m dCH3;
1211 w, 1175 w, 1155 w, 1083 vw, 999 w, 984 m, 936
w, 898 w, 862 w, 848 m, 813 m dCH, mCN, mNN,
mCC, dCC; 749 m (paraffin); 692 m, 671 m, 631 w
dCC; 529 w, 497 m, 465 w, 399 w mGaC, mGaN.
3.7. Crystal structure determinations of compounds (1–6)
Single crystals of compounds 1–6 were obtained on
cooling of saturated solutions (1-monoclinic: n-pen-
tane/ꢁ15 ꢁC, 1-triclinic: cyclopentane/ꢁ15 ꢁC, 2: cyclo-
pentane/ꢁ30 ꢁC, 3, 4 and 6: cyclopentane/ꢁ15 ꢁC, 5:
toluene/ꢁ45 ꢁC). The crystallographic data were col-
lected with a STOE IPDS diffractometer. The struc-
tures were solved by direct methods and refined with
the program SHELXL-97 [20] by a full-matrix least-
squares method based on F2. Crystal data, data collec-
tion parameters and structure refinement details are gi-
ven in Table 1. Compound 1 crystallizes in two
different space groups (monoclinic and triclinic), the re-
sults of both structure determinations are included in
Table 1. 2 has two independent molecules in the asym-
metric unit. The molecules of 3 are disordered over a
crystallographic mirror plane. The gallium atom is lo-
cated on the mirror plane, all remaining atoms are dis-
ordered and were refined with occupation factors of
0.5. The molecules of 5 reside on special positions
and possess 2/m symmetry. Compound 6 crystallizes
with two independent molecules in the asymmetric
unit. The tert-butyl groups of Ct4 and Ct6, Ct7, Ct8
(of the second molecule not drawn in Fig. 7) are disor-
dered over two or three (Ct8) positions; the atoms of
the methyl groups were refined with restrictions of
bond lengths and bond angles and with site occupation
factors of (0.53/0.47), (0.63/0.37), (0.49/0.51), and
(0.40/0.30/0.30), respectively.
3.6. Synthesis of bis[di(tert-butyl)gallium(phenylhydra-
zide)] (6)
Di(tert-butyl)gallium chloride (0.295 g, 1.35 mmol)
was dissolved in 50 ml of cyclopentane and treated with
132 ll of phenylhydrazine (0.146 g, 1.35 mmol) at room
temperature. The intermediate adduct precipitated
spontaneously. The suspension was treated with
0.84 ml of a solution of tert-butyllithium in n-hexane
(1.6 M, 1.35 mmol). After filtration and concentration
of the filtrate the product crystallized at ꢁ15 ꢁC as col-
orless platelets. Yield: 0.142 g (36%). M.p. (argon,
closed capillary): 154 ꢁC. 1H NMR (toluene-D8,
400 MHz, 370 K): d = 7.09 and 7.03 (each 2H, pseudo-
t, meta-H of phenyl), 6.65 (1H, pseudo-t, para-H of phe-
nyl), 6.60 (2H, pseudo-d, ortho-H of phenyl), 6.58 (1H,
pseudo-t, para-H of phenyl), 6.55 (2H, pseudo-d,
ortho-H of phenyl), 5.28 and 4.17 (each 1H, d,
3JH–H = 4.8 Hz, NH), 4.53 and 4.38 (each 1H, d,
3JH–H = 8.7 Hz, NH of the second hydrazine group),
1.22, 1.13, 1.09, and 0.88 (each 9 H, s, CMe3). 1H
NMR (toluene-D8, 400 MHz, 280 K): d = 7.16 and
7.06 (each 2H, pseudo-t, meta-H of phenyl), 6.68 (2H,
pseudo-t, para-H of phenyl), 6.52 (4H, pseudo-d,
ortho-H of phenyl), 5.24 and 4.17 (each 1H, d,
3JH–H = 5.2 Hz, N–H), 4.39 and 4.28 (each 1H, d,
3JH–H = 9.5 Hz, N–H of the second hydrazine group),
4. Supplementary material
Crystallographic data for the structural analyses have
been deposited with the Cambridge Crystallographic
Data Centre, CCDC Nos. 235693–235698 for com-
pounds 1–6. Copies of this information may be obtained
free of charge from The Director, CCDC, 12 Union
Road, Cambridge CB1 1EZ, UK (fax: +44-1233-
336033; e-mail: deposit@ccdc.cam.ac.uk or www:
http://www.ccdc.cam.ac.uk).
1
1.29, 1.15, 1.10, and 0.85 (each 9H, s, CMe3). H NMR
(toluene-D8, 400 MHz, 200 K): d = 7.21 and 6.98 (each
2H, pseudo-t, meta-H of phenyl), 6.78 and 6.73 (each
1H, pseudo-t, para-H of phenyl), 6.51 and 6.28
(each 2H, pseudo-d, ortho-H of phenyl), 5.09 (1H, d,
3JH–H = 6.2 Hz, N–H), 4.21 (3H, broad, superposition
of the signals of the remaining N–H protons), 1.46,

W. Uhl, C.H. Emden / Journal of Organometallic Chemistry 690 (2005) 1529–1539
1539
[6] H. No¨th, T. Seifert, Eur. J. Inorg. Chem. (2002) 602.
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We are grateful to the Deutsche Forschungsgemein-
schaft and the Fonds der Chemischen Industrie for gen-
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[11] W. Uhl, J. Molter, B. Neumuller, W. Saak, Z. Anorg. Allg.
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