Synthesis and structural characterization of complexes derived from treatment of gallium trichloride with 3,5-diphenylpyrazole

Article abstract of DOI:10.1016/S0277-5387(02)00931-2

The adduct GaCl₃(Ph₂pzH) (Ph₂pzH, 3,5-diphenylpyrazole) was synthesized in 96% yield upon treatment of equimolar amounts of gallium trichloride with Ph₂pzH in toluene at room temperature. The tetrachlorogallate

Full text of DOI:10.1016/S0277-5387(02)00931-2

Polyhedron 21 (2002) 1117ꢂ1123
/
www.elsevier.com/locate/poly
Synthesis and structural characterization of complexes derived from
treatment of gallium trichloride with 3,5-diphenylpyrazole
Zhengkun Yu, Andrey V. Korolev, Mary Jane Heeg, Charles H. Winter *
Department of Chemistry, Wayne State University, Detroit, MI 48202, USA
Received 1 November 2001; accepted 25 February 2002
Abstract
The adduct GaCl3(Ph2pzH) (Ph2pzH, 3,5-diphenylpyrazole) was synthesized in 96% yield upon treatment of equimolar amounts
of gallium trichloride with Ph2pzH in toluene at room temperature. The tetrachlorogallate salt [Ph2pzH2]ꢀGaCl4ꢁ was obtained in
93% yield by treatment of a 2:1 stoichiometry of gallium trichloride and Ph2pzH at room temperature, followed by recrystallization
from toluene/dichloromethane. The X-ray crystal structures of GaCl3(Ph2pzH) and [Ph2pzH2]ꢀGaCl4 were determined, and
ꢁ
reveal weak hydrogen bond interactions between the nitrogen-bound hydrogen atoms and gallium-bound chlorine atoms.
Examination of the formation of [Ph2pzH2]ꢀGaCl4ꢁ from GaCl3(Ph2pzH) and gallium trichloride (1.0 equiv.) revealed that the
hydrogen chloride used to form [Ph2ꢁpzH2]ꢀGaCl4ꢁ arises from gallium trichloride-catalyzed chloromethylation of toluene. Under
conditions where [Ph2pzH2]ꢀGaCl4 was isolated in 82% yield upon treatment of GaCl3(Ph2pzH) and gallium trichloride (1.0
equiv.) in toluene/dichloromethane, a mixture of ditolylmethane isomers was isolated in 330% yield based upon gallium trichloride.
# 2002 Elsevier Science Ltd. All rights reserved.
Keywords: Gallium pyrazole complexes; Tetrachlorogallate salt; Gallium trichloride; 3,5-diphenylpyrazole
1. Introduction
gallium with nitrogen heterocyclic ligands may serve as
precursors to GaN films [46]. Of relevance to the present
work, GaCl-containing precursors have been recently
demonstrated to be extremely selective growth species in
epitaxial film growth of gallium-based semiconductor
materials [47]. In view of our recent reports of aluminum
The coordination chemistry of complexes containing
pyrazolato ligands has been extensively studied [1ꢂ3].
/
However, most of this work has focused on transition
metal and organolanthanide complexes. Recently, there
has been considerable interest in pyrazolato complexes
pyrazolato complexes [17ꢂ19], we sought to explore the
/
synthesis of new gallium pyrazolato complexes. Herein,
we describe the synthesis and structural characterization
of products that are obtained upon treatment of gallium
trichloride with diphenylpyrazole. Depending on the
reaction conditions, the complexes GaCl3(Ph2pzH) and
of the Group 13 elements [4ꢂ
efforts have related to aluminum complexes [4ꢂ
Pyrazolato complexes of gallium are well known [20ꢂ
39], although complexes containing bulky alkyl or aryl
substituents in the 3- and 5-positions of the pyrazolato
ligand have not been reported. Gallium trichloride is a
relatively weak Lewis acid [40], but is known to form
/
39]. Most of the recent
/19].
/
ꢁ
[Ph2pzH2]ꢀGaCl4 are obtained. The nitrogen-bound
hydrogen atoms in these complexes participate in
hydrogen
bonding
to
chlorine
atoms.
adducts with many nitrogen donor ligands [41ꢂ44]. The
/
[Ph2pzH2]ꢀGaCl4 is obtained upon capture of hydro-
gen chloride by GaCl3(Ph2pzH), and it is demonstrated
that the hydrogen chloride originates from gallium
trichloride-catalyzed chloromethylation of toluene by
dichloromethane. To our knowledge, this is the first
ꢁ
development of new source compounds for use in the
chemical vapor deposition of metal nitride films is a
long-term interest in our group [45], and complexes of
example of a Friedelꢂ
methane that is promoted by any gallium complex.
Dichloromethane is a poor electrophile in Friedelꢂ
/
Crafts reaction with dichloro-
* Corresponding author. Tel.: ꢀ
1377.
E-mail address: chw@chem.wayne.edu (C.H. Winter).
/
1-313-577-5224; fax: ꢀ1-313-577-
/
/
0277-5387/02/$ - see front matter # 2002 Elsevier Science Ltd. All rights reserved.
PII: S 0 2 7 7 - 5 3 8 7 ( 0 2 ) 0 0 9 3 1 - 2

1118
Z. Yu et al. / Polyhedron 21 (2002) 1117ꢂ1123
/
Crafts reactions, and gallium compounds are at best
moderate strength Lewis acids that should not be
capable of activating dichloromethane [40]. Accord-
ingly, observation of the chloromethylation reaction
described herein is surprising.
promotes the exchange through a low energy associative
transition state containing a 5-coordinate gallium cen-
ter.
As noted above, 1 could be prepared as a single pure
product through careful control of the gallium trichlor-
ide:diphenylpyrazole stoichiometry, followed by crystal-
lization from toluene. However, treatment of gallium
trichloride with Ph2pzH in a 2:1 ratio in toluene for 0.5
h, followed by recrystallization from toluene/dichloro-
2. Results and discussion
methane for 16 h at ꢁ20 8C, afforded 3,5-diphenylpyr-
/
2.1. Synthesis and characterization
azolium tetrachlorogallate (2, 93%) as a colorless
crystalline solid (Eq. (2)). The structure of 2 was
established by a combination of spectral and analytical
data, and by an X-ray crystal structure determination as
described below. The 1H NMR spectrum of 2 in
chloroform-d revealed the nitrogen-bound hydrogen
resonance at d 12.76. The infrared spectrum showed
Treatment of gallium trichloride with 3,5-diphenyl-
pyrazole (Ph2pzH) in a 1:1 molar ratio in toluene at
23 8C led to the formation of the adduct
GaCl3(Ph2pzH) (1), which was isolated as colorless
crystals in 96% yield after crystallization from toluene
at ꢁ20 8C (Eq. (1)). A similar reaction was conducted
/
in an NMR tube in chloroform-d. The 1H NMR
spectrum after 24 h indicated that 1 was the only
product that formed. The structure of 1 was established
by a combination of spectral and analytical data, and by
an X-ray crystal structure determination as described
medium intensity nitrogenÃ/hydrogen absorptions be-
tween 3255 and 3174 cmꢁ1, and the electron impact
mass spectrum revealed the cation [Ph2pzH2]ꢀ with
100% intensity. The microanalysis was consistent with
the formulation of 2. The formation of 2 from 1 and 1.0
equiv. of gallium trichloride was monitored by 1H NMR
in toluene-d8 and a toluene-d8/dichloromethane mixture
(1.0 ml/0.2 ml) at ambient temperature. After 20 h in
toluene-d8, the only product present was 1. However, 1
converted to 2 completely over 16 h at ambient
temperature when dissolved in 5:1 toluene-d8/dichloro-
methane. During this time, the reaction mixture turned
deep red and colorless crystals were observed to deposit
on the walls of the NMR tube. These observations are
consistent with the preparation of 2 outlined above. In
addition, new resonances were observed in the 1H NMR
spectrum, suggesting the formation of new organic
products.
1
below. The H NMR spectrum of 1 in chloroform-d
showed the nitrogen-bound hydrogen resonance at d
11.19, consistent with the coordinated Ph2pzH ligand.
The infrared spectrum of 1 revealed a sharp, strong
nitrogenÃ
nitrogenÃ
cmꢁ1
/
hydrogen absorption at 3350 cmꢁ1 and weak
hydrogen absorptions between 3274 and 3151
/
.
ð1Þ
When 1 was prepared using a 1.00:1.00 molar ratio of
gallium trichloride and diphenylpyrazole and was re-
1
crystallized from toluene, the H and 13C{1H} NMR
spectra revealed chemically distinct resonances for the
two types of phenyl groups present in 1. Such an
observation indicates that cleavage of the galliumÃ
/
ð2Þ
nitrogen bond in 1, followed by hydrogen atom transfer
between the pyrazole nitrogen atoms and recoordination
to gallium, is slow on the NMR timescale. In some
preparations of 1, only one type of phenyl group was
observed in 1H and 13C{1H} NMR spectra of the
product. An NMR tube experiment with recrystallized
1 demonstrated that excess gallium trichloride (up to
one full equivalent) had no effect on the 1H and 13C{1H}
NMR spectra of 1 in benzene-d6 at ambient tempera-
ture, and two chemically distinct phenyl groups were
observed. However, addition of as little as 5% excess
diphenylpyrazole to recrystallized 1 led to the observa-
An experiment was performed in which gallium
trichloride (1.0 equiv.) was treated with 1 (1.0 equiv.)
in 90:10 toluene/dichloromethane at 20 8C for 16 h.
Workup as described in the experimental section
afforded 2 in 82% yield. In addition, a brownꢂ
was isolated that was identified as three ditolylmethane
isomers 3ꢂ5 (88% of mixture) and eight or more isomers
/
red oil
/
of (methylbenzyl)ditolylmethane 6 (12% of mixture) by
1
GLC/MS and by analysis of the H and 13C{1H} NMR
spectra of the mixture (Scheme 1). The 1H NMR
spectrum indicated an 84:12:4 mixture of p,p?-ditolyl-
methane (3), o,p?-ditolylmethane (4), and o,o?-ditolyl-
methane (5). This identification was based upon
comparison with methyl and methylene 1H NMR
chemical shifts that have been previously reported for
1
tion of a single type of phenyl resonance in the H and
13C{1H} NMR spectra at ambient temperature, indicat-
ing rapid exchange of the phenyl sites on the NMR
timescale. We suggest that the excess diphenylpyrazole

Z. Yu et al. / Polyhedron 21 (2002) 1117ꢂ
/1123
1119
luene isomers react rapidly with toluene to afford the
mixtures of 3ꢂ5. The yield of 3ꢂ5 based upon gallium
trichloride is about 330%, thus indicating that the
formation of 3ꢂ5 is catalyzed by a gallium species
/
/
/
present in the reaction mixture. The first equivalent of
hydrogen chloride generated during the chloromethyla-
tion reaction is trapped by 1 to form 2. Thereafter, the
fate of the hydrogen chloride is less clear. ‘HGaCl4’ has
been previously described as a diethyl ether adduct [59].
However, the strongest bases remaining after complete
formation of 2 are toluene and 3ꢂ6. It is possible that
/
the deep red coloration of the reaction solution corre-
sponds to the formation of arenium cations, which are
Scheme 1. Chloromethylation of toluene.
known to be deeply colored in solution [60ꢂ
/
63].
The central discovery described herein is the Friedelꢂ
/
these compounds [48,49]. The GLC/MS of 3ꢂ5 all
/
Crafts chloromethylation of toluene promoted by 1, 2,
or some other gallium species present in solution. The
fact that gallium compounds can promote rapid
showed a parent ion of mass/charge 196, with a base
peak of 181 corresponding to loss of a methyl group
from the parent ion. In addition to the ditolylmethane
isomers, eight or more methylene resonances were
observed between d 3.82 and 3.87 in the 1H NMR
FriedelꢂCrafts alkylation reactions using a poor elec-
/
trophile such as dichloromethane is surprising in view of
the extensive literature in this area [40]. The high
solubility of 1 in toluene may be the reason why the
chloromethylation reaction proceeds at such a rapid
spectrum of the redꢂbrown oil. GLC/MS revealed at
/
least eight minor components exhibiting parent ions of
mass/charge 300, with base peaks of 195 corresponding
to loss of a methylbenzyl group from isomeric (methyl-
benzyl)ditolylmethanes. The (methylbenzyl)ditolyl-
methane mixture was not characterized further, due to
the small amount and large number of isomers.
rate. In the present work, the FriedelꢂCrafts alkylation
/
reaction manifested itself initially through the unex-
pected formation of 2 when 1 was recrystallized from
toluene/dichloromethane mixtures. We expect that simi-
lar FriedelꢂCrafts reactions will occur in systems that
/
Observation of the mixture containing 3ꢂ6 suggests
/
contain what are presumed to be weak Lewis acids and
poorly electrophilic alkyl halides.
that the pathway outlined in Scheme 1 is operant in the
formation of 2 under the conditions of excess gallium
trichloride. Gallium trichloride-promoted chloromethy-
lation of toluene can proceed to afford ortho- and para-
isomers of chloromethyltoluene as well as ‘HGaCl4’. As
noted in the introduction, this is the first example of a
2.2. Molecular structures of 1 and 2
The solid-state structures of 1 and 2 were determined
by X-ray crystallography. Perspective views are shown
in Figs. 1 and 2, crystallographic data are provided in
Table 1, and selected bond lengths and angles are listed
in Tables 2 and 3.
FriedelꢂCrafts alkylation reaction of dichloromethane
/
that is promoted by any gallium compound. Gallium
trichloride is considered to be a moderate strength Lewis
acid at best [40], and gallium compounds have been
Complex 1 crystallizes as a monomer with distorted
frequently used as FriedelꢂCrafts reaction catalysts with
reactive alkyl halides to avoid side products that are
observed with more reactive aluminum-based Lewis
/
tetrahedral geometry about the gallium center. The GaÃ
/
˚
N(1) bond distance is 1.971(2) A. The nitrogenÃ
/
hydro-
˚
gen bond length is 0.759(4) A. The nitrogen-bound
hydrogen participates in intramolecular hydrogen bond-
acids [50ꢂ
compounds with dichloromethane using aluminum
halide catalysts has been well documented [40,54ꢂ56].
/53]. The direct chloromethylation of aromatic
/
In addition, an aluminum trichloride-promoted chlor-
omethylation of an aluminum-bound phenoxy group by
dichloromethane to give non-aromatic product was
described [57]. Several reports have described the
chloromethylation of toluene using Lewis acid catalysis
and various reactive chloromethyl cation equivalents
such as methoxyacetyl chloride, bis(chloromethyl) ether,
or chloromethyl methyl ether [58]. Once formed, the
intermediate chloromethyl-substituted aromatic com-
pounds rapidly react to form diarylmethane derivatives.
In the present work, the intermediate chloromethylto-
Fig. 1. Perspective view of GaCl3(Ph2pzH) (1) with thermal ellipsoids
at the 50% probability level.

1120
Z. Yu et al. / Polyhedron 21 (2002) 1117ꢂ1123
/
Table 3
˚
Selected bond lengths (A) and angles (8) for 2
Bond lengths
GaÃCl(1)
GaÃCl(3)
N(1)ÃN(2)
N(2)ÃC(3)
H(N2)ÃN(2)
H(N2)ÃCl(2?)
2.1718(6) GaÃCl(2)
2.1607(7) GaÃCl(4)
2.2032(6)
2.1521(7)
1.339(3)
0.937(3)
2.533(3)
2.573(3)
1.345(3)
1.338(3)
0.827(3)
2.663(3)
N(1)ÃC(1)
H(N1)ÃN(1)
H(N1)ÃCl(1)
H(N2)ÃCl(2??)
Bond angles
Cl(1)ÃGaÃCl(2)
Cl(1)ÃGaÃCl(4)
Cl(2)ÃGaÃCl(4)
N(1)ÃN(2)ÃC(3)
N(1)ÃH(N1)ÃCl(1)
N(1)ÃH(N1)ÃCl(2?)
103.90(3) Cl(1)ÃGaÃCl(3)
111.53(3) Cl(2)ÃGaÃCl(3)
110.41(3) Cl(3)ÃGaÃCl(4)
N(2)ÃN(1)ÃC(1)
132.88(3) N(2)ÃH(N2)ÃCl(2?)
127.68(3)
112.68(3)
110.15(3)
108.15(3)
109.7(2)
Fig. 2. Perspective view of [Ph2pzH2]ꢀGaCl4 (2) with thermal
ellipsoids at the 50% probability level.
ꢁ
109.5(2)
165.65(3)
Table 1
Crystallographic data for 1 and 2
for N(1)Ã
/
GaÃ
/
Cl(1) (109.19(8)8) and N(1)Ã
/
GaÃ
/
Cl(2)
Formula
Formula weight
Space group
C
15H12Cl3GaN2 (1)
C15H13Cl4GaN2 (2)
432.79
P21/n
(111.79(9)8). This distortion may arise from the weak
hydrogen bond associated with Cl(3).
396.34
P21/n
˚
a(A)
10.461(7)
12.882(9)
11.913(8)
92.646(18)
1603.8(19)
2
11.8508(7)
7.3609(4)
21.0097(12)
96.2560(10)
1821.8(2)
4
Complex 2 crystallizes with a diphenylpyrazolium ion
that contains several different hydrogen bonds to the
tetrachlorogallate ion. The geometry about the gallium
˚
b(A)
˚
C (A)
b(8)
3
˚
atom is distorted tetrahedral. The galliumÃ
/chlorine
V (A )
˚
bond distances range from 2.1521(7) to 2.2032(6) A,
and are slightly longer than the range found in 1 due to
the reduced Lewis acidity of the gallium center in the
Z
T (K)
295 (2)
0.71073
1.641
295(2)
˚
l (A)
0.71073
1.578
2.093
rcalc.(g cmꢁ3
)
tetrachlorogallate ion. The chlorineÃ
angles range between 103.90(3)8 and 112.68(3)8. The
nitrogenÃhydrogen bond lengths are 0.937(5) and
/
galliumÃ
/chlorine
m (mmꢁ1
R(F) (%)
)
2.208
3.23
2.96
7.42
/
Rw(F) (%)
7.16
˚
0.827(5) A. The nitrogen-bound hydrogen atoms are
hydrogen-bonded to chlorine atoms of the tetrachlor-
ogallate ion with bond lengths of 2.533(3)
R(F)ꢃajjFojꢁjFcjj/ajFoj. Rw(F)2ꢃ[aw(Fo2ꢁFc2)2/Sw(Fo2)2]1/2
.
Table 2
((N1)HÁ Á ÁCl(1)),
2.663(5)
((N1)HÁ Á ÁCl(2?)),
and
˚
˚
Selected bond lengths (A) and angles (8) for 1
2.573(4) A ((N2)HÁ Á ÁCl(2??)). The nitrogenÃ
/
hydrogenÃ
/
chlorine angles associated with the hydrogen bonds are
132.88(3)8, 127.68(3)8, and 165.65(3)8, respectively. The
Bond lengths
GaÃN(1)
GaÃCl(2)
N(1)ÃN(2)
N(2)ÃC(3)
(N2)HÁ Á ÁCl(3)
1.971(2)
2.1589(15)
1.365(5)
1.347(3)
2.625(4)
GaÃCl(1)
GaÃCl(3)
N(1)ÃC(1)
N(2)ÃH
2.1448(13)
2.1568(17)
1.348(3)
nitrogenÃ
/
hydrogen bond lengths are similar to the value
found in 1. Interestingly, the two chlorine atoms
involved in weak hydrogen bonding (Cl(1), Cl(2))
0.759(3)
exhibit slightly longer galliumÃ
/chlorine bond lengths
Bond angles
than the two chlorine atoms that are not involved in
hydrogen bonding (Cl(3), Cl(4)). These bond length
differences, while small, suggest slightly stronger hydro-
gen bonding in 2, compared with 1. Stronger hydrogen
bonding in 2 can be rationalized on the basis of more
electrophilic hydrogen atoms and more electron rich
chlorine atoms due to the presence of ions in the solid.
Cl(1)ÃGaÃCl(2)
Cl(2)ÃGaÃCl(3)
N(1)ÃGaÃCl(2)
GaÃN(1)ÃN(2)
N(2)ÃHÃCl(3)
110.85(5)
110.85(5)
111.79(9)
116.74(17)
127.96(3)
Cl(1)ÃGaÃCl(3)
N(1)ÃGaÃCl(1)
N(1)ÃGaÃCl(3)
GaÃN(1)ÃC(1)
112.28(6)
109.19(8)
101.56(7)
135.98(18)
ing to Cl(3), with a hydrogen-chlorine distance of
The galliumÃ
to values ranging from 1.97 to 2.00 A that have been
documented in galliumꢂpyrazolate complexes [20ꢂ39].
The X-ray crystal structures of several pyrazolium salts
of the formula [t-Bu2pzH]ꢀXꢁ (Xꢃ
Cl, Br) have been
reported [64,65]. These compounds form distinct di-
meric aggregates featuring ten-membered X2H4N4 rings
in the solid state that are held together by strong, linear
/
nitrogen bond length in 1 is very similar
˚
˚
2.625(4) A. The N(2)Ã
There are no significant intermolecular hydrogen bonds.
The galliumÃchlorine bond distances range from
2.1448(13)ꢂ2.1589(15) A. All three galliumÃ
/
H(N2)ÃCl(3) angle is 127.96(3)8.
/
/
/
/
˚
/
/
chlorine
/
bond lengths are identical within the precision of the
structure determination, suggesting that the intramole-
cular hydrogen bond to Cl(3) is weak. The N(1)Ã
/
GaÃ
/
Cl(3) angle (101.56(7)8) is smaller than the related values
NÃ
/
HÁ Á ÁX hydrogen bonding. Ten-membered rings are

Z. Yu et al. / Polyhedron 21 (2002) 1117ꢂ
/1123
1121
present in 2, but these rings are present as part of an
extended hydrogen bonded network, as opposed to the
dimeric units in the pyrazolium halide salts. In 3,5-di-
131.64 (s, p-CH of Ph), 130.92 (s, p-CH of Ph), 129.82
(s, m-CH of Ph), 129.00 (s, m-CH of Ph), 128.85 (s, o-
CH of Ph), 127.86 (s, ipso-C of Ph), 126.34 (s, o-CH of
Ph), 125.39 (s, ipso-C of Ph), 105.79 (s, CH of
pyrazolato); MS (EI, 70 eV) 220 ([Ph2pzH]ꢀ, 100%).
Anal. Calc. for C15H12Cl3GaN2: C, 45.46; H, 3.05; N,
7.07. Found: C, 45.68; H, 3.13; N, 6.99%.
tert-butylpyrazolium chloride [64,65], the nitrogenÃ
/
chlorine distance containing the hydrogen bond was
˚
˚
3.057(2) A, the HÁ Á ÁCl distance was 2.12(3) A, and the
nitrogenÃhydrogenÃchlorine angle was 175(3)8. By
contrast, in 2 the related values were 3.244(2)ꢂ3.380(2)
165.65(5)8.
/
/
/
A, 2.533(4)ꢂ
/
2.663(4) A, and 127.68(5)8ꢂ
/
3.3. Synthesis of [Ph2pzH2]ꢀGaCl4 (2)
ꢁ
˚
˚
These values for 2 suggest much weaker hydrogen
bonding than is present in 3,5-di-tert-butylpyrazolium
chloride. The order of hydrogen bonding strength is
consistent with the lone pairs of electrons on GaCl4
being much less basic than those of chloride ion. Similar
A 100 ml Schlenk flask, equipped with a stir bar and a
rubber septum, was charged with 1 (0.26 g, 0.66 mmol),
gallium trichloride (0.12 g, 0.66 mmol), and toluene (10
ml). To this stirred solution was added dichloromethane
(0.5 ml). The solution color changed immediately to
yellow and deepened to dark red after 0.5 h. The
ꢁ
weak EÃ
/
HÁ Á ÁX hydrogen bonding (Eꢃ
/
O, N; Xꢃ
/
halogen) is well established in the solid state structures
of other metal halide complexes containing EH frag-
ments within the crystal [66].
reaction solution was placed in a ꢁ20 8C freezer for
/
16 h. Yellow crystals formed during this time, and a
dark red oil separated. The crystals were collected on a
medium glass frit and were washed with 1:1 toluene/
pentane (18 ml) followed by pentane (18 ml). Vacuum
drying afforded white crystals. The washings were
combined, producing more white crystals. These crystals
were collected on a medium glass frit, washed with
pentane (18 ml), and dried under vacuum. The crystals
were combined to afford 2 as a colorless solid (0.26 g,
3. Experimental
3.1. General considerations
All manipulations were performed under argon using
either drybox or Schlenk-line techniques. Gallium
trichloride was purchased from Strem Chemical Com-
pany. Ph2pzH was prepared using a reported procedure
93%): m.p. 135ꢂ
136 8C; IR (KBr, cmꢁ1) 3255 (m),
/
3219 (m), 3191 (m), 3174 (m), 1613 (m), 1590 (m), 1262
(w), 1227 (w), 1208 (w), 1188 (w), 1162 (w), 1095 (w),
1070 (w), 1053 (w), 1019 (w), 950 (w), 918 (w), 835
(w),765 (s), 704 (w), 691 (w), 681 (m); 1H NMR (CDCl3,
23 8C, d) 12.76 (s, 2H, NH), 7.75 (m, 4H, Ph CH), 7.62
1
[67]. H and 13C{1H} NMR spectra were obtained at
500 or 300 and 125 or 75 MHz, respectively, in the
indicated solvents. Infrared spectra were recorded using
KBr discs. Mass spectra were obtained on a Kratos MS-
50 spectrometer in the electron impact mode or on a
(m, 6H, Ph CH), 7.15 (t, 4JHH
ꢃ3.0 Hz, 1H, pyrazolato
/
Hewlettꢂ
/
Packard Model 5980 GLC/MS instrument.
CH); 13C{1H} NMR (CDCl3, 23 8C, ppm) 149.60 (s,
pyrazolato CPh), 132.94 (s, p-CH of Ph), 130.21 (s, m-
CH of Ph), 126.85 (s, o-CH of Ph), 123.95 (s, ipso-C of
Ph), 102.02 (s, CH of pyrazolato); MS (EI, 70 eV) 221
([Ph2pzH2]ꢀ, 100%).
Elemental analyses were performed by Midwest Micro-
lab, Indianapolis, IN. Melting points are uncorrected.
3.2. Synthesis of GaCl3(Ph2pzH) (1)
Anal. Calc. for C15H13Cl4GaN2: C, 41.62; H, 3.03; N,
6.47. Found: C, 41.49; H, 3.07; N, 6.55%.
A 100 ml Schlenk flask was charged with a stir bar,
gallium trichloride (0.42 g, 2.4 mmol), and diphenylpyr-
azole (0.52 g, 2.4 mmol). Toluene (30 ml) was added by
syringe to form a colorless solution. This mixture was
stirred at ambient temperature for 24 h. The volatile
components were removed under reduced pressure to
afford spectroscopically pure 1 as a white powder (0.91
g, 96%). X-ray and analytical quality crystals were
3.4. Isolation of ditolylmethane isomers upon treatment
of 1 with excess gallium trichloride
A Schlenk flask was charged with a stir bar, 1 (0.26 g,
0.66 mmol) and gallium trichloride (0.12 g, 0.66 mmol).
Toluene (10 ml) was added to the flask to produce a
colorless solution. Immediately thereafter, dichloro-
methane (1 ml) was added. The solution color changed
to yellow and deepened to medium red within 0.5 h. The
solution was stirred at ambient temperature for 6 h, and
the volatiles were removed under reduced pressure to
leave a dark red oil. Hexane (20 ml) was added to this oil
to afford a pale yellow solution and colorless crystals in
the dark red oil. This mixture was kept at ambient
temperature for 16 h without stirring. The solution was
obtained by recrystallization from toluene at ꢁ
/
20 8C:
m.p. 157ꢂ
/
158 8C; IR (KBr, cmꢁ1) 3350 (s), 3274 (w),
3151 (w), 1610 (m), 1569 (s), 1273 (m), 1182 (m), 1108
(m), 1085 (m), 990 (m), 821 (w), 761 (s), 705 (w), 703
1
(m), 684 (s), 563 (s); H NMR (CDCl3, 23 8C, d) 11.19
(br. s, 1 H, NH), 7.77 (m, 2H, Ph CH), 7.65, (m, 2 H, Ph
CH), 7.57 (m, 3 H, Ph CH), 7.51 (m, 3 H, Ph CH), 6.91
3.0 Hz, 1 H, pyrazole CH); 13C{1H} NMR
(d, Jꢃ
/
(CDCl3, 23 8C, ppm) 156.33 (s, CPh), 147.39 (s, CPh),

1122
Z. Yu et al. / Polyhedron 21 (2002) 1117ꢂ1123
/
decanted from the oily residue, and the oily residue was
washed again with hexane (6 ml). The hexane extracts
were combined and the volatile components were
removed under reduced pressure, leaving a red oil
mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
(0.41 g) that was identified as a mixture of 3ꢂ6 by
/
Acknowledgements
1
GLC MS and by correlation of the H NMR spectrum
with previously reported values for ditolylmethane
isomers. For further data, see below and in the text.
The hexane-insoluble crystals were collected on a
medium glass frit and then washed with 1:1 toluene/
hexane (18 ml) and hexane (18 ml). Drying under
vacuum for 1 h afforded spectroscopically pure 2 as a
pale brown crystalline solid (0.23 g, 82%). The identity
of 2 was confirmed by comparison of its 1H and
13C{1H} NMR spectra with those of authentic material
described above.
We are grateful to the National Science Foundation
(Grant No. CHE-9807269) and the Defense Advanced
Research Projects Agency for support of this research.
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