Dehydrogenative Ga-Ga coupling and hydrogallation in gallium hydride complexes of 3,5-dimethylpyridine

Article abstract of DOI:10.1021/om049393r

The 2:1 complex of 3,5-dimethylpyridine (L′) and dichlorogallane, (L′)₂GaHCl₂, undergoes dehydrogenative Ga-Ga coupling in boiling toluene to give high yields of (L′)Cl ₂Ga-GaCl₂(L′). The structure of the dinuclear product (which has C₂h symmetry) has been determined [Ga-Ga′ 2.4000(8) A]. By contrast, the 1:1 complex of L′ and gallium trihydride, (L′)GaH₃, on prolonged standing at 20°C or when treated with excess ligand L′, is converted into the hydrogallation product, (L′)(L′H)GaH₂. In this product, the gallium atom is attached to a pyridine donor ligand L′ and a 4-hydropyridyl substituent, as proven by a crystal structure determination and by NMR and IR spectral studies. The Ga-N bond length is very significantly shorter for the hydropyridyl as compared to the pryridine group, and the carbon atom C ⁴ of the former has become the center of an aliphatic CH₂ group with its ¹H and ¹³C resonances shifted into the corresponding upfield regions. The C³-C⁴ and C ⁴-C⁵ linkages have been converted into single bonds, with double bonds localized at C²-C³ and C⁵-C ⁶ of the (L′H) heterocycle. While the N-Ga-N angle is very small at only 103(1)°, the H-Ga-H angle is exceedingly large at 127(2)°, indicating a strong steric pressure of the seemingly small hydride ligands and that hydride functions thus are to be considered as bulky substituents.

Full text of DOI:10.1021/om049393r

Organometallics 2004, 23, 5877-5880
5877
Dehydrogenative Ga-Ga Coupling and Hydrogallation in
Gallium Hydride Complexes of 3,5-Dimethylpyridine
Stefan D. Nogai and Hubert Schmidbaur*
Department Chemie, Technische Universita¨t Mu¨nchen, Lichtenbergstrasse 4,
85747 Garching, Germany
Received August 5, 2004
Summary: The 2:1 complex of 3,5-dimethylpyridine (L′)
and dichlorogallane, (L′)2GaHCl2, undergoes dehydro-
genative Ga-Ga coupling in boiling toluene to give high
yields of (L′)Cl2Ga-GaCl2(L′). The structure of the
dinuclear product (which has C2h symmetry) has been
determined [Ga-Ga′ 2.4000(8) Å]. By contrast, the 1:1
complex of L′ and gallium trihydride, (L′)GaH3, on
prolonged standing at 20 °C or when treated with excess
ligand L′, is converted into the hydrogallation product,
(L′)(L′H)GaH2. In this product, the gallium atom is
attached to a pyridine donor ligand L′ and a 4-hydro-
pyridyl substituent, as proven by a crystal structure
determination and by NMR and IR spectral studies. The
Ga-N bond length is very significantly shorter for the
hydropyridyl as compared to the pryridine group, and
the carbon atom C4 of the former has become the center
of an aliphatic CH2 group with its 1H and 13C resonances
shifted into the corresponding upfield regions. The C3-
C4 and C4-C5 linkages have been converted into single
bonds, with double bonds localized at C2-C3 and C5-
C6 of the (L′H) heterocycle. While the N-Ga-N angle is
very small at only 103(1)°, the H-Ga-H angle is
exceedingly large at 127(2)°, indicating a strong steric
pressure of the seemingly small hydride ligands and that
hydride functions thus are to be considered as bulky
substituents.
account we report two unusual side-reactions that were
observed during experiments with the complexes with
L ) 3,5-dimethylpyridine (L′).
Preparative and Structural Results
Dehydrogenative Coupling. The complexes (L′)-
HGaCl2 and (L′)2HGaCl2 are obtained from reactions of
the components in the appropriate molar ratio according
to eqs 1 and 2. The former has a tetrahedral structure,
while the latter is best described as based on a trigonal
bipyramid (tbp) with the ligands L′ in axial positions.4
The 1:1 complex is stable, but solutions of the 2:1
complex have now been found to evolve molecular
hydrogen in boiling toluene (ca. 110 °C). The reaction
gives a ca. 90% isolated yield of the dinuclear product
of dehydrogenative Ga-Ga coupling (eq 3), which can
be separated from the excess ligand released in the
process by crystallization. It thus appears that the
second ligand L′ and therefore a tbp structure is
responsible for the activation of the Ga-H function for
dehydrogenative coupling.
(HGaCl2)2 + 2L′ f 2(L′)HGaCl2
(HGaCl2)2 + 4L′ f 2(L′)2HGaCl2
(1)
(2)
(3)
Introduction
2(L′)GaCl2 f (L′)Cl2Ga-GaCl2(L′) + 2L′ + H2
(L′ ) 3,5-dimethylpyridine)
Dichlorogallane (HGaCl2)2 is one of the most readily
accessible gallium hydrides: Readily prepared in quan-
titative yield from anhydrous (GaCl3)2 and a trialkyl-
silane R3SiH, without any solvent, it is stable below 0
°C and soluble in many common solvents, which makes
it a convenient starting material for gallium chemis-
try.1,2 Its complexes and its conversion into other
molecular gallium halides, chalcogenides, and pnictides
have recently been investigated extensively.3-6 In this
context, pyridines were shown to be the most suitable
ligands L in the coordination chemistry of dichlorogal-
lane, and a series of complexes of the types (L)HGaCl2
and (L)2HGaCl2 have been studied.4 In the present
The product (L′)Cl2Ga-GaCl2(L′) is a colorless, crys-
talline solid of high thermal stability (mp 228 °C), which
was readily identified by its analytical and spectroscopic
data (Experimental Part). The NMR spectra of solutions
in CD2Cl2 have shown that the compound is diamagnetic
and that the L′ ligands are equivalent and have local
C2v symmetry. The 1H resonance of the Ga-H function
present in the NMR spectrum of (L′)HGaCl2 has dis-
appeared, as has the ν(Ga-H) stretching frequency in
the IR spectrum.
Crystals grown from toluene are monoclinic, space
group C2/m, with Z ) 2 formula units (of point group
symmetry C2h) in the unit cell. The asymmetric unit
contains one quarter of the dinuclear molecule, the
remainder being generated by symmetry (Figure 1). The
carbon and nitrogen atoms of both ligands L′ and the
two gallium atoms reside in a crystallographic mirror
plane. The substituents of the two tetrahedrally coor-
dinated gallium atoms are in a staggered anti-confor-
mation. Note also that the orientation of the two
pyridine molecules is staggered, i.e., bisecting both Cl-
* To whom correspondence should be addressed. E-mail:
H.Schmidbaur@lrz.tum.de.
(1) Schmidbaur, H.; Findeiss, W.; Gast, E. Angew. Chem., Int. Ed.
Engl. 1965, 4, 152.
(2) Nogai, S.; Schmidbaur, H. Inorg. Chem. 2002, 41, 4770.
(3) Nogai, S. D.; Schmidbaur, H. Dalton Trans. 2003, 2488.
(4) Nogai, S.; Schriewer, A.; Schmidbaur, H. Dalton Trans. 2003,
3165.
(5) McMurran, J.; Kouvetakis, J.; Nesting, D. C.; Smith, D. J.;
Hubbard, J. L. J. Am. Chem. Soc. 1998, 120, 5233.
(6) Schmidt, E. S.; Jockisch, A.; Schmidbaur, H. J. Chem. Soc.,
Dalton Trans. 2000, 1039.
10.1021/om049393r CCC: $27.50 © 2004 American Chemical Society
Publication on Web 10/20/2004

5878 Organometallics, Vol. 23, No. 24, 2004
Notes
Figure 2. Molecular structure of (L′)(L′H)GaH2 (ORTEP,
50% probability ellipsoids for the heavier atoms, arbitrary
radii for hydrogen atoms) Selected bond lengths [Å] and
angles [deg] (with standard deviations): Ga1-H1 1.40(3),
Ga1-H2 1.47(3), Ga1-N11 2.072(2), Ga1-N21 1.898(2),
N11-C12 1.341(3), C12-C13 1.385(4), C13-C14 1.388(4),
C14-C15 1.387(4), C15-C16 1.385(4), C16-N11 1.342(3);
N21-C22 1.392(3), C22-C23 1.344(4), C23-C24 1.497(4),
C24-C25 1.501(4), C25-C26 1.337(4), C26-N21 1.390(4);
H1-Ga1-H2 127(2), N11-Ga-N21 102.6(1), H1-Ga1-
N11 99(2), H1-Ga1-N21 109(1), H2-Ga1-N11 105(1),
H2-Ga1-N21 111(1).
Figure 1. Molecular structure of (L′)Cl2Ga-GaCl2(L′)
(ORTEP, 50% probability ellipsoids, H atoms omitted). The
molecule has C2h symmetry. Selected bond lengths [Å] and
angles [deg] (with standard deviations): Ga1-Ga1′ 2.4000-
(8), Ga1-N1 2.015(4), Ga1-Cl1 2.189(1), N1-C2 1.342-
(6), C2-C3 1.373(7), C3-C4 1.399(6), C4-C5 1.387(7), C5-
C6 1.379(6), C6-N1 1.348(6); Cl1-Ga1-Cl1′ 105.71(7),
Cl1-Ga1-N1 101.31(7), Cl1-Ga1-Ga1′ 117.03(3), N1-
Ga1-Ga1′ 112.2(1).
ligand L′ and to a ligand that is monohydrogenated in
the 4-position (Experimental Part). Both ligands appear
to have local C2v symmetry, which notably includes the
equivalence of the two protons in the 4-position of the
hydropyridyl ligand. The resonances of these protons
and of their common carbon atom C4(L′H) appear in the
aliphatic region at δ 3.21 and 36.0 ppm, respectively,
while those of the HC4 unit in the pyridine ligand L′
remain in the aromatic region at δ 6.55 (1HC4) and 138.8
ppm (13C4).
The hydrogen atoms residing at the gallium atom give
rise to a quadrupole-broadened singlet resonance at δ
5.5 ppm with the relative intensity of 2 H. The GaH2
group can also be traced in the IR spectrum (Nujol on
KBr), which shows two bands at 1882 and 1902 cm-1
for ν(GaH2) vibrations. The absorption bands of the
pyridine ligand L′ can be identified by comparing the
data with those of the (L′)GaH3 complex, but these are
clearly complemented by a set of new bands to be
assigned to the hydropyridyl group L′H.
Crystals of (L′H)(L′)GaH2 are monoclinic, space group
P21/n, with Z ) 4 molecules in the unit cell. The
asymmetric unit contains one molecule, the geometry
of which approaches mirror symmetry quite closely
(Figure 2). All hydrogen atoms, including in particular
those of the GaH2 group, have been located as demon-
strated in the electron density map presented in Figure
3. The pyridine ligand L′ and the 4-hydropyridyl group
L′H can be easily distinguished by the extra hydrogen
atom at C24 in the latter and by the individual bond
lengths and angles.
Ga-Cl angles. The Ga-Ga′ distance of 2.4000(8) Å
represents a true single bond and is in good agreement
with reference data.7 The four equivalent Ga-Cl bond
lengths are rather short, at 2.1886(10) Å, and together
with the equally short Ga-N distances of 2.015(4) Å also
indicate tight bonding of all substituents to the di-
nuclear Ga-Ga unit.
Hydrogallation. The reaction of lithium gallium
hydride Li[GaH4] with equimolar quantities of 3,5-
dimethylpyridinium chloride [L′H]Cl in diethyl ether at
-78 °C affords the 1:1 adduct (L′)GaH3 in ca. 70% yield
(mp 67 °C with decomposition) (eq 4).4 It has now been
observed that this product undergoes slow decomposi-
tion upon storage at room temperature to give gaseous
hydrogen H2, gray particles of metallic gallium, and
orange crystals of a new complex, which was identified
as the hydrogallation product (HL′)(L′)GaH2. The de-
composition can thus be formulated as proposed in eq
5. This mass balance suggested that a ligand L′ liber-
ated in the decomposition of a complex (L′)GaH3 is the
substrate for hydrogallation by a second molecule of the
complex. Therefore the same product should be acces-
sible by treating (L′)GaH3 with excess ligand L′, and
solutions of the complex in L′ without a solvent were
indeed found to give the hydrogallation product after
72 h at 20 °C (eq 6). Separation of the (L′H)(L′)GaH2
complex from excess ligand proved to be difficult, and
only a few crystals of pure material could be grown for
characterization in both cases. The yields are estimated
to be ca. 50% for eqs 5 and 6. Elemental analysis of the
bulk material was not satisfactory.
The distance Ga-N11 ) 2.072(2) Å (for Ga-L′) is
significantly longer than the distance Ga-N21 ) 1.898-
(2) Å (for L′H). The former thus qualifies as a donor-
acceptor bond, while the latter represents a strong
gallium-amide linkage, but both heterocycles (of L′ and
L′H) are yet essentially planar. The C-C and C-N ring
Li[GaH4] + [L′H]Cl f (L′)GaH3 + H2 + LiCl
2(L′)GaH3 f (L′)(L′H)GaH2 + Ga + (3/2)H2 (5)
(L′)GaH3 + L′ f (L′)(L′H)GaH2 (6)
(4)
The orange crystals are stable at room temperature
and can be readily dissolved in benzene. The NMR
(7) (a) Small, R. W. H.; Worrall, I. J. Acta Crystallogr. 1982, B38,
86. (b) Beamish, J. C.; Boardman, A.; Small, R. W. H.; Worrall, I. J.
Polyhedron 1985, 4, 983. (c) Gordon, E. M.; Hepp, A. F.; Duraj, S. A.;
Habash, T. S.; Fanwick, P. E.; Schupp, J. D.; Eckles, W. E.; Long, S.
Inorg. Chim. Acta 1997, 257, 247.
1
spectra of the solutions show two sets of H and 13C
resonances, which can be assigned to one unchanged

Notes
Organometallics, Vol. 23, No. 24, 2004 5879
Homovalent dinuclear complexes have been isolated
2
with L ) PR3 or other ligands,7,9 the structures of
which are analogous to that now demonstrated for a
pyridine complex. The reaction proceeds on heating of
the substrates in toluene. Even under the applied
forcing conditions (boiling toluene, excess ligand L′) the
complexes (L′)GaHCl2 and (L′)2GaHCl2 show no hydro-
gallation reactions which would afford hydropyridyls of
the type [(L′H)GaCl2]n or (L′)(L′H)GaCl2.
By contrast, the complex (L′)GaH3 undergoes pyri-
dine-hydrogallation even under mild conditions (at room
temperature), again provided that excess ligand L′ is
supplied. Note, however, that at room temperature (L′)-
GaH3 does not add a second equivalent of the ligand L′
to give a stable 2:1 complex (L′)2GaH3. Yet the excess
ligand applied in the reaction is also activating the
Ga-H function for hydrogallation by promoting the
transfer of a hydride anion to the 4-position of the
pyridine ligand.
The product of the formula (L′)(L′H)GaH2 has a
pyridine and a 4-hydropyridyl ligand attached to a
common gallium atom. Upon hydride transfer, the
aromatic system of the pyridine heterocycle L′ with its
C-C and C-N bonds of about equal lengths is inter-
rupted in the process as shown by the spectroscopic data
of the CH2 group and the structural data of the ligands
L′ and L′H listed in the caption to Figure 2. In
particular, a comparison of the NMR data of the L′ and
L′H groups in the compound leads to the same conclu-
sion.
Similar hydrometalation reactions have been ob-
served previously for the reactions of Li[BH4], Li[AlH4],
and (Me3N)AlH3 with pyridines.10-12 In every example
all three or four hydride functions are reported to be
involved in the hydrometalation. In one of these reports
it has been stated that no similar reaction is observed
using (Me3N)GaH3 as hydridic component.12 No other
gallium hydrides, which have the least hydridic char-
acter among the three group 13 element hydrides, had
been investigated in the context of the hydrogallation
of pyridines. Hydrogallation reactions with other un-
saturated substrates are well documented.13
Figure 3. Cross section through the electron density
difference map in the H1-Ga1-H2 plane illustrating the
hydride locations in (L′)(L′H)GaH2. The map was obtained
using phases based on all atoms except H1 and H2, and
the final refined positions are superimposed. Contours are
drawn at an interval of 0.1 e/Å-3. Positive and negative
contours are shown as solid and dashed lines, respectively.
distances of L′ are similar to those found, for example,
in [(L′)GaCl2]2 (above), while for the hydropyridyl group
L′H the short C-C distances C22-C23 ) 1.344(4) Å and
C25-C26 ) 1.337(4) Å indicate localized double bonds,
as opposed to the distances C23-C24 ) 1.497(4) Å and
C24-C25 ) 1.501(4) Å, which are proof for C-C single
bonds at the hydrogenated carbon atom C24.
It is particularly noteworthy that the angle N11-Ga-
N21 is exceedingly small, at 101.59(9)°, although the
bulk of the two large substituents would suggest other-
wise. This result means that the two hydride substit-
uents at the gallium atom, probably intuitively consid-
ered as “small”, require a seemingly unproportional
share of space, as indicated by the large angle H1-Ga-
H2 of 127(2)°. This structural result nicely reflects the
hydridic character of Ga-bound hydrogen atoms. The
data also corroborate observations4 for (L′)GaH3, as well
as for complexes with tertiary amines and phosphines,8a-f
where the GaH3 pyramide was consistently found to be
surprisingly flat. Quantum-chemical calculations on the
phenomenon are in progress.8g
Experimental Part
All experiments were carried out in an atmosphere of dry
nitrogen. Solvents were dried, distilled, and saturated with
nitrogen, and glassware was oven-dried and filled with nitro-
gen. Standard equipment was used throughout. (HGaCl2)2,
(L′)GaHCl2, and (L′)GaH3 were prepared as described previ-
ously.1,2,4 NMR chemical shifts are given in δ values [ppm]
Discussion
The work presented in this short account has shown
that dehydrogenative Ga-Ga coupling appears to be a
general reaction for dichlorogallane and its complexes.
This type of elimination had previously been observed
for the parent compound (HGaCl2)2, but in the absence
of ligands it leads to the mixed-valent product Ga-
[GaCl4], in which no Ga-Ga bonding is established.
(9) (a) Beamish, J. C.; Small, R. W. H.; Worrall, I. J. Inorg. Chem.
1979, 18, 220. (b) Rickard, C. E. F.; Taylor, M. J.; Kilner, M. Acta
Crystallogr. 1999, C55, 1215. (c) Pashkov, A. Yu.; Bel’sky, V. K.;
Bulychev, B. M.; Zvukova, T. M. Russ. Chem. Bull. 1996, 2078.
(10) No¨th, H.; Warchold, M. Z. Naturforsch. 2003, 58b, 123.
(11) (a) Lansbury, P. T.; Peterson, J. O. J. Am. Chem. Soc. 1963,
85, 2236. (b) Tanner, D. D.; Yang, C.-M. J. Org. Chem. 1993, 58, 1840.
(12) Hensen, K.; Lemke, A.; Stumpf, T.; Bolte, M.; Fleischer, H.;
Pulham, C. R.; Gould, R. O.; Harris, S. Inorg. Chem. 1999, 38, 4700.
(13) (a) Pulham, C. R.; Downs, A. J.; Goode, M. J.; Rankin, D. W.
H.; Robertson, H. E. J. J. Am. Chem. Soc. 1991, 113, 5149. (b) Johnsen,
E.; Downs, A. J.; Goode, M. J.; Greene, T. M.; Himmel, H.-J.; Mu¨ller,
M. Inorg. Chem. 2001, 40, 4755. (c) Schmidbaur, H.; Findeiss, W. Chem.
Ber. 1966, 99, 2187. (d) Schmidbaur, H.; Klein, H.-F. Chem. Ber. 1967,
100, 1129. (e) Schmidbaur, H.; Klein, H. F. Angew. Chem. 1966, 78,
306. (f) Ohshita, J.; Schmidbaur, H. J. Organomet. Chem. 1993, 453,
7. (g) Schumann, H.; Hartmann, U.; Wassermann, W. Polyhedron 1990,
9, 353.
(8) (a) Andrews, P. C.; Gardiner, M. G.; Raston, C. L.; Tolhurst, V.-
A. Inorg. Chim. Acta 1997, 259, 249. (b) Atwood, J. L.; Bott, S. G.;
Elms, F. M.; Jones, C.; Raston, C. L. Inorg. Chem. 1991, 30, 3793. (c)
Baxter, P. L.; Downs, A. J.; Rankin, D. W. H. J. Chem. Soc., Dalton
Trans. 1984, 1755. (d) Brain, P. T.; Brown, H. E.; Downs, A. J.; Greene,
T. M.; Johnsen, E.; Parsons, S.; Rankin, D. W. H.; Smart, B. A.; Tang,
C. Y. J. Chem. Soc., Dalton Trans. 1998, 3685. (e) Tang, C. Y.; Coxall,
R. A.; Downs, A. J.; Greene, T. M.; Kettle, L.; Parsons, S.; Rankin, D.
W. H.; Robertson, H. E.; Turner, A. R. Dalton Trans. 2003, 3526. (f)
Tang, C. Y.; Downs, A. J.; Greene, T. M.; Parsons, S. Dalton Trans.
2003, 540. (g) Ro¨sch, N.; et al. Technical University Munich, personal
communication, 2004.

5880 Organometallics, Vol. 23, No. 24, 2004
Notes
Table 1. Crystal Data, Data Collection, and
Structure Refinement for Compounds (L′)2Ga2Cl4
and (L′)(L′H)GaH2
referring to the residual signals of the deuterated solvent (CD2-
Cl2, C6D6) converted to TMS, and coupling constants J are in
Hz.
sym-Bis(3,5-dimethylpyridine)tetrachlorodigallium-
(Ga-Ga′), (L′)2Ga2Cl4. (L′)GaHCl2 (0.300 g, 0.843 mmol) was
dissolved in toluene (5 mL) and the solution heated to reflux
for 5 h. The solution was filtered from small amounts of a
precipitate while hot and allowed to cool slowly to room
temperature. After 3 days the crop of colorless crystals was
separated by filtration, washed with small portions of hexane
(2 × 5 mL), and dried in a vacuum: 0.186 g, 89% yield, mp
(L′)2Ga2Cl4
(L′)(L′H)GaH2
empirical formula
C
14H18Cl4Ga2N2
C14H21GaN2
M
495.56
287.05
cryst syst
space group
a/Å
monoclinic
C2/m
monoclinic
P21/n
17.1994(3)
7.3604(2)
8.6468(2)
117.0185(10)
975.17(4)
1.688
8.0226(3)
10.9023(4)
16.8366(7)
100.895(2)
1446.07(10)
1.318
b/Å
c/Å
b/deg
1
V/Å3
228 °C. NMR (CD2Cl2, 20 °C), H: 2.46 (s, 12H, Me); 7.79 (s,
2H, HC4); 8.56 (s, 4H, HC2/6); 13C{1H}: 18.6 (s, Me); 137.1 (s,
C3/5); 144.1 (s, C4); 144.4 (s, C2/6). Anal. Found: C 34.08, H 3.61,
N 5.63, Cl 27.99. Calcd for C14H18Cl4Ga2N2 (495.56): C 33.93,
H 3.66, N 5.65, Cl 28.62.
F
calc/g cm-3
Z
4
4
F(000)
T/K
492
600
143
143
no. of refls measd
no. of refls unique
no. of params/restraints
R1 [I g 2σ(I)]
wR2a
10 964
43 260
Dihydro(3,5-dimethylpyridine)(3,5-dimethyl-4-hydro-
pyridyl)gallium, (L′)(L′H)GaH2. A sample of colorless, crys-
talline (L′)GaH3 (ca. 150 mg, 0.83 mmol) was kept in a closed
flask under nitrogen at room temperature for 2 months. The
material slowly deteriorated, developing a gray precipitate of
metallic gallium accompanied by crystal growth in parts of the
vessel. On reopening, a slight gas pressure was noticed. The
orange crystals (ca. 60 mg) were collected and investigated on
the diffractometer, by NMR spectroscopy in benzene solution
and by IR spectroscopy in a Nujol mull on KBr disks.
Another sample of colorless, crystalline (L′)GaH3 (200 mg,
1.11 mmol) was dissolved in 3 mL (excess) of L′ and the
mixture stirred magnetically for 3 days. The color of the
solution turned via yellow to orange, and small amounts of
gray metallic gallium precipitated. The reaction mixture was
filtered, and the pyridine L′ was removed from the filtrate in
a vacuum to leave a resinous residue containing small crystals
of the same product as identified in the above experiment. Its
NMR spectra indicated the presence of small amounts of a few
unidentified byproducts, which were difficult to separate. No
sharp melting point was detected because of rapid decomposi-
tion on heating, and elemental analysis was not fully satisfac-
tory. The crude yield is estimated to ca. 50%.
974
2615
87/0
238/0
0.0351
0.0334
0.0937
0.0749
weighting scheme
a ) 0.0541
b ) 3.5706
3.046/-0.452
a ) 0.0254
b ) 0.8985
0.240/-0.248
σfin(max/min)/e Å-3
a wR2 ) {∑[w(Fo - Fc )2]/∑[w(Fo2)2]}1/2; w ) 1/[σ2(Fo2) + (ap)2
2
2
2
2
+ bp]; p ) (Fo + 2Fc )/3.
mounted on the ends of quartz fibers in inert perfluoropoly-
alkyl ether and used for intensity data collection on a Nonius
DIP2020 diffractometer, employing graphite-monochromated
Mo KR radiation. The structures were solved by a combination
of direct methods (SHELXS-97) and difference Fourier syn-
theses and refined by full matrix least-squares calculations
on F2 (SHELXL-97).14 The thermal motion was treated aniso-
tropically for all non-hydrogen atoms. All hydrogen atoms were
located and refined with isotropic displacement parameters.
Absorption corrections for both structures were carried out
using DELABS, as part of the PLATON suite of programs.15
Further information on crystal data, data collection, and
structure refinement is summarized in Table 1.
NMR (C6D6, 20 °C), 1H: 1.63 [s, 6H, Me(L′)]; 1.77 [s, 6H,
Me(L′H)]; 3.21 [s, 2H, H2C4(L′H)], 5.50 [br s, 2H, GaH2]; 6.52
[s, 2H, HC2/6(L′H)]; 6.55 [s, 1H, HC4(L′)]; 8.13 [s, 2H, HC2/6(L′)];
13C{1H}: 17.7 [s, Me(L′)]; 21.6 [s, Me(L′H)]; 36.0 [s, C4(L′H)],
130.7 [s, C2/6(L′H)]; 133.7 [s, C3/5(L′)]; 138.8 [s, C4(L′)]; 146.5
[s, C2/6(L′)]; C2/5(L′) was not detected because of overlap with
the solvent signal. IR (Nujol, KBr): 1882 and 1902 cm-1 (s)
ν(GaH2); 1676, 1629, 1601, 1314, 1246, 1174, 1148, 1092, 1045,
986, 963, 942, 862, 802, 722, 703, 680, 600, 538 cm-1 for L′
and L′.
Acknowledgment. This work was generously sup-
ported by Fonds der Chemischen Industrie.
Supporting Information Available: Details about the
X-ray crystal structures in CIF format. This information is
available free of charge via the Internet at http://pubs.acs.org.
OM049393R
(14) Sheldrick, G. M. SHELX-97, Programs for crystal structure
analysis; University of Go¨ttingen: Germany, 1997.
(15) Spek, A. L. Acta Crystallogr., Sect. A 1990, 46, 194.
Determination of the Crystal Structures. Specimens of
suitable quality and size of (L′)2Ga2Cl4 and (L′)(L′H)GaH2 were