Group 13 β-ketoiminate compounds: Gallium hydride derivatives as molecular precursors to thin films of Ga2O3

Article abstract of DOI:10.1021/ic3006794

Bis(β-ketoimine) ligands, [R{N(H)C(Me)-CHC(Me)=O}₂] (L ₁H₂, R = (CH₂)₂; L₂H ₂, R = (CH₂)₃), linked by ethylene (L ₁) and propylene (L₂) bridges have been used to form aluminum, gallium, and indium chloride complexes [Al(L₁)Cl] (3), [Ga(L_n)Cl] (4, n = 1; 6, n = 2) and [In(L_n)Cl] (5, n = 1; 7, n = 2). Ligand L₁ has also been used to form a gallium hydride derivative [Ga(L₁)H] (8), but indium analogues could not be made. β-ketoimine ligands, [Me₂N(CH₂)₃N(H) C(R′)-CHC(R′)=O] (L₃H, R′ = Me; L₄H, R′ = Ph), with a donor-functionalized Lewis base have also been synthesized and used to form gallium and indium alkyl complexes, [Ga(L ₃)Me₂] (9) and [In(L₃)Me₂] (10), which were isolated as oils. The related gallium hydride complexes, [Ga(L _n)H₂] (11, n = 3; 12, n = 4), were also prepared, but again no indium hydride species could be made. The complexes were characterized mainly by NMR spectroscopy, mass spectrometry, and single crystal X-ray diffraction. The β-ketoiminate gallium hydride compounds (8 and 11) have been used as single-source precursors for the deposition of Ga₂O ₃ by aerosol-assisted (AA)CVD with toluene as the solvent. The quality of the films varied according to the precursor used, with the complex [Ga(L₁)H] (8) giving by far the best quality films. Although the films were amorphous as deposited, they could be annealed at 1000 °C to form crystalline Ga₂O₃. The films were analyzed by powder XRD, SEM, and EDX.

Full text of DOI:10.1021/ic3006794

Article
pubs.acs.org/IC
Group 13 β-Ketoiminate Compounds: Gallium Hydride Derivatives As
Molecular Precursors to Thin Films of Ga2O3
David Pugh, Peter Marchand, Ivan P. Parkin, and Claire J. Carmalt*
Materials Chemistry Centre, Department of Chemistry, University College London, 20 Gordon Street, London WC1H 0AJ
S
* Supporting Information
ABSTRACT: Bis(β-ketoimine) ligands, [R{N(H)C(Me)-
CHC(Me)O}2] (L1H2, R = (CH2)2; L2H2, R = (CH2)3),
linked by ethylene (L1) and propylene (L2) bridges have been
used to form aluminum, gallium, and indium chloride
complexes [Al(L1)Cl] (3), [Ga(Ln)Cl] (4, n = 1; 6, n = 2)
and [In(Ln)Cl] (5, n = 1; 7, n = 2). Ligand L1 has also been
used to form a gallium hydride derivative [Ga(L1)H] (8), but
indium analogues could not be made. β-ketoimine ligands,
[Me2N(CH2)3N(H)C(R′)-CHC(R′)O] (L3H, R′ = Me; L4H, R′ = Ph), with a donor-functionalized Lewis base have also been
synthesized and used to form gallium and indium alkyl complexes, [Ga(L3)Me2] (9) and [In(L3)Me2] (10), which were isolated
as oils. The related gallium hydride complexes, [Ga(Ln)H2] (11, n = 3; 12, n = 4), were also prepared, but again no indium
hydride species could be made. The complexes were characterized mainly by NMR spectroscopy, mass spectrometry, and single
crystal X-ray diffraction. The β-ketoiminate gallium hydride compounds (8 and 11) have been used as single-source precursors
for the deposition of Ga2O3 by aerosol-assisted (AA)CVD with toluene as the solvent. The quality of the films varied according
to the precursor used, with the complex [Ga(L1)H] (8) giving by far the best quality films. Although the films were amorphous
as deposited, they could be annealed at 1000 °C to form crystalline Ga2O3. The films were analyzed by powder XRD, SEM, and
EDX.
complexes prevented the isolation of gallium and indium bis(β-
diketonate) complexes.18
INTRODUCTION
■
Thin films of gallium oxide, Ga2O3, can be used as gas sensors
for both reducing gases (e.g., CO, EtOH)1,2 and oxidizing gases
(O2)3,4 depending on the sensor temperature. They have been
deposited using a variety of methods, e.g., sputtering,3 spray
pyrolysis,5 and chemical vapor deposition (CVD). Recently, a
significant amount of attention has focused on single-source
CVD methods where a single molecular precursor, which
contains at least one direct Ga−O bond, is used.6 The most
common type of single-source precursor is gallium alkoxides:7
these compounds have been synthesized in a variety of ways,
but the most well-used methods are the reaction of GaCl3 with
an alkali metal alkoxide,8 the reaction of trialkylgallium
compounds with an alcohol,9 the reaction of stabilized gallium
hydrides with an alcohol,10 and the reaction of gallium amide
compounds with an alcohol.11,12 The final method is the most
versatile, affording mono-, bis-, or tris-alkoxide compounds of
gallium.13 A comprehensive review of single-source precursors
to gallium and indium oxide has recently been published.14
Homoleptic β-diketonate complexes of gallium have also
been used as precursors, with some, e.g., [Ga(acac)3] (acac =
acetylacetonate), being commercially available.15−17 However,
these precursors are relatively involatile; therefore, high
temperatures are needed to volatilize the precursor. To
overcome this drawback, we attempted the synthesis of bis(β-
diketonate) complexes of gallium and indium with a small third
ligand, e.g., hydride. Unfortunately, we found that the high
thermodynamic stability of the homoleptic tris(β-diketonate)
The hydrides of heavy group 13 metals (Ga, In, Tl) are an
under-researched area of chemistry, with the main issue being
the thermal instability of most of the compounds. However,
gallium hydride complexes are low mass and have a clean
decomposition pathway; hence a hydride would be an ideal
“coligand” for a molecular precursor. The binary hydrides MH3
(M = Ga, In, Tl) all decompose well below room temperature,
with strong Lewis bases needed to stabilize adducts of GaH3,19
although a couple of gallium alkoxide hydride complexes have
been reported starting from [GaH3(NMe3)]. The only room-
temperature stable adducts of InH3 have been reported by
Jones, comprising bulky trialkylphosphine and NHC (N-
heterocyclic carbene) adducts.20 No TlH3 complexes are
known. A convenient entry point for gallium hydride chemistry
is the adduct [GaH3(NMe3)], which has limited stability at
room temperature.21
As described above, precursors to thin films of gallium oxide
have evolved from commercially available compounds, such as
[Ga(acac)3], to carefully designed molecules that take into
account the requirements of the deposition technique.14 CVD
often requires the precursor to be volatile, although solution-
based techniques offer an alternative method of getting the
precursor into the gas phase, and here solubility is the key
Received: April 1, 2012
Published: May 17, 2012
© 2012 American Chemical Society
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a
Scheme 1. Synthesis of Bis(β-ketoimine) Ligands L1H2 and L2H2 and Bis(β-ketoiminate) Metal Complexes 1−8
a
Conditions: [a] solvent free, 150 °C; [b] 2.1 NaH, thf; [c] MCl3 (M = Al, Ga, In), hexane; [d] LiH/NaH/NaBH4/LiAlH4/NaBEt3H, thf, −78 °C
− RT; [e] [MH3(NMe3)] (M = Ga, In), Et2O, −78 °C − RT.
criterion. The β-ketoiminate ligand offers a potential means to
address the aforementioned issues since the ability to
functionalize the imino residue of the ligand means that the
thermal stability (and solubility) of the precursor can be
increased by tuning the groups attached to the nitrogen atom.
Furthermore, it should be possible to isolate monomeric
complexes and hence complexes with a high vapor pressure,
particularly if hydride is used as the “coligand”. Another
advantage of employing this ligand type is the potential to
enhance the surface reaction between the metal β-ketoiminates
and the surface of a substrate. However, there have been very
few previous reports on the reactivity of β-ketoiminate ligands
with heavy group 13 metals and none specifically investigating
the tuning of the ligand for CVD applications.
Dimethyl-gallium and -indium N-aryl-substituted β-ketoimi-
nates have been reported, although the presence of an aryl
group could lead to carbon contamination of the resulting
films.22 Reaction of a lithiated β-ketoiminate with GaCl3
surprisingly resulted only in a β-ketoimine adduct of GaCl3,
rather than the expected β-ketoiminate complex.23 A donor-
functionalized lithium β-ketoiminate complex was reacted with
InMe3, affording the dimethylindium β-ketoiminate species,24
and the crystal structure of complex 4 (Scheme 1) was
previously reported by Vohs et al.,25 albeit no other
characterization data were given. However, none of these
compounds have been used as precursors for the CVD of group
13 oxide thin films, nor to stabilize gallium hydrides. Given that
current precursors still suffer from chemical instability, poor
reproducibility in the growth process, and less than favorable
vapor pressures, an investigation into the use of group 13 β-
ketoiminate complexes as single-source precursors was
important given the advantages of the ligand outlined above.
In this paper, we report the synthesis of new β-ketoimine
ligands (and their sodium salts); their reactivity toward group
13 chloride, alkyl, and hydride compounds; and the viability of
the new hydride complexes as precursors to thin films of
gallium oxide.
RESULTS AND DISCUSSION
Compound Synthesis: Bis(β-ketoiminates). Ligand
■
L1H2 was synthesized according to the literature procedure
and was isolated as a beige crystalline solid.26 Ligand L2H2 was
synthesized in a similar manner, using 1,3-diaminopropane
instead of 1,2-diaminoethane.27 By reacting a thf solution of
L1H2 or L2H2 with a slight excess of NaH, the disodium salts 1
and 2 were formed (see the Supporting Information). These
were isolated as white solids in good yield by removing
solvents. However, it was also possible to form complexes 1 and
2 in situ before adding the required metal chloride.
A hexane suspension of salt 1 was reacted with AlCl3 in a 1:1
ratio, forming complex [Al(L1)Cl] (3) with concomitant
elimination of NaCl. Similarly, complex 4 was synthesized by
reacting an in situ-generated thf solution of 1 with GaCl3.
Compounds 3 and 4 were isolated in reasonable yields as
yellow solids with elemental analyses of the solids consistent
1
with the [M(L1)Cl] formulation. The H NMR spectra of the
complexes were similar, showing a backbone CH resonance at
ca. 5 ppm, ethylene bridge resonances at ca. 3.5 ppm, and
methyl group peaks around 1.5−2.0 ppm. Complex 3 was
crystallized by cooling a toluene solution to −18 °C, but the
crystals were of poor quality and were unsuitable for single
crystal X-ray diffraction. The solid state structure of complex 4
was previously reported by Vohs et al.25 The proton resonances
of the ethylene bridge in both 3 and 4, while appearing as a
1
broad singlet in the H NMR spectrum of L1H2, were seen as
separate resonances in the metal complexes, showing an
inequivalence of the two proton environments as a result of
coordination to the metal center compared to the equivalent
environments for the uncomplexed, freely rotating β-ketoimine.
The observation of broad singlets in the case of 3 and
multiplets in the case of 4 corresponding to the ethylene bridge
protons suggests that the molecules possess a degree of
fluxionality in solution.
Compound 5, an indium analogue, was synthesized using the
hexane suspension method used for compound 3. This was
crystallized by layering a concentrated CH2Cl2 solution with
hexane, affording yellow needles, which were suitable for single
crystal X-ray diffraction (Figure 1a, Table 1).
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Figure 1. (a) ORTEP diagram showing complex 5a bridged by one equivalent of ligand L1H2. Thermal ellipsoids are drawn at 50% probability,
hydrogen atoms (bar H1) omitted for clarity. Hydrogen bonds are denoted by dashed lines, and atoms marked “i” are at the equivalent position (−x,
1 − y, −z). (b) ORTEP diagram of compound 5. Thermal ellipsoids at 50% probability, hydrogen atoms omitted for clarity. Atoms marked “i” are at
the equivalent position (−x, −y − 1, −z − 1).
Table 1. Selected Bond Lengths for Compounds 5, 5a, 5·thf, 6, and 7
bond (Å)
5 (M = In) [In(L1)Cl]
5a (M = In) [In(L1)Cl]·L1H2
5·thf (M = In) [In(L1)Cl]·thf
6 (M = Ga) [Ga(L2)Cl]
7 (M = In) [In(L2)Cl]
d
M−O
2.105(2)
2.181(2)
2.125(1)
2.113(1)
2.097(2)
2.101(2)
1.875(1)
1.976(1)
2.122(2)
d
2.075(2)
a
b
c
e
2.257(2)
2.387(1)
2.413(2)
2.096(2)
e
2.113(2)
d
M−N
2.185(2)
2.215(2)
2.186(2)
2.182(1)
2.171(2)
2.183(2)
1.982(1)
2.023(1)
2.164(2)
d
2.181(2)
e
2.183(2)
e
2.196(2)
d
M−Cl
C−O
2.4420(9)
2.4488(5)
2.4539(8)
2.231(7)
2.3826(7)
e
2.4002(7)
d
1.303(3)
1.346(3)
1.305(2)
1.302(2)
1.299(3)
1.293(4)
1.2972(19)
1.308(2)
1.296(3)
d
1.313(3)
b
e
1.270(2)
1.289(3)
e
1.289(3)
d
C−N
1.321(3)
1.297(3)
1.303(2)
1.309(2)
1.300(4)
1.304(2)
1.309(2)
1.323(2)
1.313(4)
d
1.308(4)
b
e
1.328(2)
1.322(4)
e
1.310(4)
a
b
c
d
e
Bridging In−O bond length. Bond lengths for the neutral ligand. Bond length to thf. Molecule 1 (trigonal bipyramidal geometry). Molecule 2
(square-based pyramidal geometry).
The solid state structure showed that ligand L1 had bonded
to indium in the expected manner through both oxygens and
both nitrogens, with a chloride ligand also bound to indium.
However, instead of the anticipated five-coordinate In complex,
a six-coordinate octahedral species (5a) was isolated with one
equivalent of ligand L1H2 bridging between two In centers
through the ketone oxygens. The complex is slightly distorted
away from ideal octahedral geometry [trans bond angles
between 159.68(6)−168.40(3)°] as a result of the relatively
large and electronegative chloride group, as well as the short
ethylene backbone on L1. The anionic In−O bond lengths
while slightly differentare significantly shorter than the In−O
bond length to the bridging L1H2 molecule (Table 1). This is
also reflected in the C−O bond lengths, with the delocalized
bonding to the indium centers involving O(1) and O(2)
resulting in C−O bond lengths that are significantly longer than
typical CO distances. The third oxygen, O(3), being solely a
two-electron donor to the indium center, is involved in a much
shorter C−O bond length, which is consistent with a typical
carbonyl. The proton attached to the amine nitrogen of the
neutral ligand is involved in hydrogen bonding both with O(3)
on the same ligand and also with the adjacent O(1) of the
dianionic ligand. The 1H NMR spectrum is consistent with the
presence of two different ligand environments. One set of
resonances (including an NH peak at 10.98 ppm) is very close
to that of the free ligand; the other set corresponds to the
dianionic ligand attached to 5a. The ratio of the two sets of
peaks is 1:2, as expected.
The extra equivalent of L1H2 probably came from the
incomplete reaction of L1H2 with NaH prior to the in situ
addition of InCl3. In order to prevent the formation of the
bridged species, an isolated sample of salt 1 was reacted with
1
InCl3. This afforded a yellow solid in 45% yield, and the H
NMR spectrum showed only one set of ligand resonances.
Crystallization from layering a concentrated CH2Cl2 solution of
5 with hexane afforded yellow crystals of compound 5 (Figure
1b, Table 1).
Although the solid state structure confirmed that there was
no extra ligand bridging between two metal centers, compound
5 does exist as an oxygen-bridged dimer. The ketoiminate
ligand was bound to indium in the expected manner with one
chloride trans to the bridging oxygen comprising the
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Figure 2. (a) ORTEP diagram of compound 6 and (b) ORTEP diagram showing one of two symmetry-independent molecules (with the severely
distorted trigonal bipyramidal geometry) in the asymmetric unit of complex 7, see Figure S1 (Supporting Information) for the second molecule.
Thermal ellipsoids at 50% probability, hydrogen atoms omitted for clarity.
coordination sphere. This was an unexpected result and is
probably due to the inflexibility of the 2-carbon bridge in ligand
L1. By restricting the ligand from occupying a sufficient amount
of the coordination sphere at indium, it enables a sixth donor
group to coordinate to the vacant site, and in the absence of a
suitable external Lewis base, dimerization occurs. This is
evidenced from the trans angles around the indium center
which involve L1: at 155.94(6)° and 164.06(7)°, they are a long
way from the ideal 180°.
The In−O bond lengths (Table 1) confirm that the dative
bridging In−O bond length is significantly longer than both the
anionic In−O bond lengths. Unsurprisingly, there is a marked
difference in length of the anionic In−O bonds owing to O(2)
being involved in bridging. However, this difference may not be
solely a result of O(2) being involved in bridging because the
In−N bond lengths are also significantly different from each
other. The C−O bonds of L1 are also different from each other
(as are the C−N bonds): this is different from other β-
ketoiminate complexes reported in this paper, but not
surprising owing to the differences noted for the In−O and
In−N bond lengths. The 1H NMR spectrum of 5 was similar to
those found for monomeric aluminum and gallium species 3
and 4 such that the inability of the ligand molecule to rotate
freely results in an inequivalence of the two proton environ-
ments of the ethylene bridge.
can be seen from the largest bond angle at gallium: the O(1)−
Ga(1)−N(2) angle of 172.66(5)° is not far from the ideal 180°.
There is a significant difference in bond lengths between the
equatorial and axial groups. The equatorial Ga−O length
[1.875(1) Å] is much shorter than the axial Ga−O bond length
[1.976(1) Å], and a similar effect is observed with the Ga−N
bond lengths, albeit the difference of 0.04 Å is not as marked as
the case for the Ga−O bonds (0.1 Å). However, this difference
is not manifested in the C−O bond lengths, which are identical
within experimental error. They are also identical to the
delocalized C−O bond lengths in compound 5a, despite the
smaller ionic radius of Ga3+ compared to In3+. However, there
is a very small difference between the C−N bonds, and the
longer of the two bonds is also slightly longer than the
delocalized C−N bonds in complex 5a.
Compound 7 also crystallized as a five-coordinate species in
the triclinic space group P1 with L again occupying four of the
̅
2
coordination sites with a chloride ligand occupying the fifth.
Although the molecular structure is extremely similar to that of
compound 6, with the only difference being the slightly larger
In(III) cation in place of Ga(III), there is a significant difference
in the manner in which compound 7 crystallizes, with two
symmetry-independent molecules in the asymmetric unit. This
results in an overall Z value of 4 as opposed to 2 in compound
6. The two independent molecules occupy vastly different
geometries, with the molecule centered around In(1) existing
in a severely distorted trigonal bipyramidal geometry (τ = 0.70;
Figure 2), whereas the molecule centered around In(2) adopts
an almost ideal square-based pyramidal geometry (τ = 0.03;
Figure S1, Supporting Information). The origin for this is not
clear, but the fact that compound 6 does not exhibit a similar
distortion may indicate a more significant reason than simply
crystal packing effects.
The disodium salt 2 was similarly reacted with both GaCl3
and InCl3, forming complexes 6 [Ga(L2)Cl] and 7 [In(L2)Cl]
(Scheme 1). Both complexes were isolated as yellow solids and
were crystallized by layering concentrated CH2Cl2 solutions
1
with hexane. The H NMR spectra indicated that L2 was
binding to the metals in the expected manner with no NH
proton observed: this was confirmed by structural character-
ization of both 6 and 7 (Figure 2, Table 1).
Compound 6 crystallized as a five-coordinate slightly
distorted trigonal bipyramidal species in the triclinic space
The In−O bond lengths across both molecules are in a range
between 2.075(2) and 2.122(2) Å, but each molecule contains
one “longer” In−O bond and one “shorter” In−O bond, with
the difference between the two being statistically significant for
each molecule. The same is true of the In−N bond lengths with
the “longer” and “shorter” In−N bonds for each molecule being
significantly different. However, the C−O bonds for each
molecule are not different within experimental error, and the
same is true for the In−N bonds (Table 1).
group P1, with L occupying four coordination sites and a
̅
2
chloride completing the coordination sphere. As expected, the
largest ligand (chloride) occupies one of the equatorial sites.
The degree of distortion away from ideal trigonal bipyramidal
can be measured by calculating the τ value, which shows how
far a five-coordinate complex is from ideal square-based
pyramidal (τ = 0) or trigonal bipyramidal (τ = 1).28 For
compound 6, the τ value of 0.82 indicates that the degree of
distortion away from ideal trigonal bipyramidal is small. This
1
The H and 13C NMR spectra for 6 and 7 both supported
the formation of the desired monomeric complexes. Similarly to
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that seen for 3, 4, and 5, a separation of the two NCH2
resonances of the propylene bridge was observed in both cases
as a result of coordination to the gallium (6) and indium (7)
centers, showing an inequivalence of the proton environments.
The broad resonances seen again suggest fluxional behavior of
the molecules in solution.
bonds from the ligand and the In−O bond of the thf ligand.
They are also very similar to the In−O and In−N bonds found
in complexes 5a and 7. This is also borne out by the C−O and
C−N bonds, which are identical within experimental error.
Although it is surprising that compound 5 did not react with
C8K, it is probable that carrying out the reaction in thf caused
complex 5·thf, which is kinetically inert, to form prior to the
reaction with C8K. However, switching the solvent to Et2O and
repeating the reaction of 5 with C8K also did not lead to any
reaction taking place.
Compounds 4 and 5 were both reacted with a variety of
hydride sources (LiH, NaH, NaBH4, LiAlH4, NaBEt3H) in an
attempt to replace the chloride ligand with hydride. However,
1
in all cases, no reaction was observed, and the H NMR
spectrum merely indicated that starting material remained. In
order to try to remove the chloride ligand completely, a THF
solution of compound 5 was reacted with one equivalent of
freshly formed C8K. Although no color change was observed,
slow diffusion of hexane into the THF solution of the reaction
product yielded yellow crystals, which were suitable for single
crystal X-ray analysis (Figure 3, Table 1).
Owing to the unreactivity of compound 4, in order to
prepare a gallium hydride derivative of ligand L1H2, it was
reacted directly with a freshly prepared ethereal solution of
[GaH3(NMe3)] (Scheme 1). A pale yellow solution with a
white suspension formed, and the solid was removed by
filtration. Compound 8 was isolated as a yellow powder in 71%
1
yield by removal of the volatiles, and the H NMR spectrum
showed no resonance associated with the NH proton, in
addition to a small peak at 5.56 ppm characteristic of gallium
hydrides. All attempts at crystallizing compound 8 only resulted
in the formation of a microcrystalline solid unsuitable for single
crystal X-ray diffraction, but elemental analysis was consistent
with the formation of compound 8.
In an attempt to synthesize an indium analogue of
compound 8, ligand L1H2 was reacted with a freshly prepared
ethereal solution of [InH3(NMe3)] (Scheme 1). At −78 °C, no
reaction was observed, but upon slow warming to RT, a gray
precipitate of indium metal formed in a pale brown solution.
After filtration and removal of the solvents, 1H NMR
spectroscopic analysis found that the brown solution only
contained ligand L1H2. While complexes of the type [InH(L)2]
(L = formamidinate) have been previously isolated,29 in our
case, it is unknown whether any reaction between L1H2 and
[InH3(NMe3)] took place: given the kinetic and thermal
sensitivity of indium hydride complexes, it is possible that the
indium hydride starting material decomposed before any
reaction took place. The use of isolated [InH3(NHC)]30 as a
starting material did not lead to the formation of [InH(L1)],
with no reaction observed to take place.
Figure 3. ORTEP diagram of compound 5·thf. Thermal ellipsoids at
50% probability, hydrogen atoms omitted for clarity.
Compound 5·thf crystallized as an octahedral species with
one equivalent of L1, one chloride ligand, and one thf molecule
comprising the coordination sphere. The chloride and thf
ligands are mutually trans with the four ligand donor atoms to
the metal existing in a single plane [RMS deviation for O(1),
O(2), N(1), N(2) = 0.0455 Å]. The metal atom is out of this
plane by 0.277(1) Å. The In−O bond lengths involving the
ligand are identical within experimental error, as are the In−N
bonds, although there is a marked difference between the In−O
Compound Synthesis: Donor-Functionalized β-Ketoi-
minates. Compounds such as [Ga(OiPr)3] usually exist as
oligomers, but by using donor-functionalized alkoxides (which
have a Lewis base attached to the alkoxide moiety), it is
possible to isolate monomeric and dimeric alkoxides.31,32
Through a judicious choice of the primary amine, it should
Scheme 2. Synthesis of Donor-Functionalized β-Ketoimine Ligands L3H and L4H and Donor-Functionalized β-Ketoiminate
a
Complexes 9−12
a
Conditions: [a] solvent free, 150°; [b] MMe3 (M = Ga, In), toluene, 110 °C, 16 h; [c] [GaH3(NMe3)], Et2O, −78 °C − RT.
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be possible to form a β-ketoimine ligand with an extra Lewis
base, i.e., donor-functionalized β-ketoiminates. The presence of
the extra Lewis base should lead to coordinative saturation of
the metal center, enabling isolation of additional hydride
species. Hence, L3H (R = Me) was synthesized by combining
acetylacetone with N,N-dimethylpropylenediamine, then heat-
ing the mixture to 150 °C for four hours (Scheme 2). After
cooling and extraction into diethyl ether, drying over anhydrous
Na2SO4 removed sufficient residual water such that no H2O
coordinated to a metal, notably a lack of amine NH and a
triplet for the methylene group next to the amide N−. However,
it proved impossible to crystallize compound 11; thus it was
not possible to confirm the solid state structure, although a five-
coordinate species with three coordination sites occupied by L3
and two hydrides is likely observed on the basis of mass
spectrometric and NMR spectroscopic data.
In an attempt to improve on the low yield of compound 11,
an alternative synthesis was employed. By forming the
hydrochloride salt of ligand L3H, it was possible to react
L3H·HCl directly with LiGaH4 instead of going through the
intermediate [GaH3(NMe3)]. A white solid in a green solution
was again produced, and after removing the Et2O and extracting
the residue into hexane, a viscous green-yellow oil was isolated
in an improved 61% yield. Upon standing overnight at RT,
colorless crystals formed which were suitable for X-ray
diffraction analysis. Unfortunately, the crystals turned out to
be the unreacted hydrochloride salt L3H·HCl (Figure S2,
Supporting Information).
1
signal was observed in the H NMR spectrum of the crude
product. Indeed, the crude product (an orange oil) was of
sufficient purity for further reactivity studies. Ligand L4H (R =
Ph) was synthesized in a similar manner, starting from
dibenzoylmethane instead of acetylacetone. The product was
isolated as an extremely viscous orange-brown oil, again with no
purification step necessary as judged from the 1H NMR
spectrum. In both cases, the NH peak was observed at a very
downfield position of 10.75 ppm (L3H) and 11.87 ppm (L4H).
Coupling of the NH proton to the CH2 group was also
observed, with the signal corresponding to the latter group
appearing as a doublet of triplets at 3.20 (L3H) and 2.99 (L4H)
ppm.
In an attempt to form a crystalline gallium hydride complex
analogous to compound 11, it was thought that adding steric
bulk to the ligand backbone would result in a solid product.
Thus, an ethereal solution of ligand L4H was reacted with a
freshly prepared solution of [GaH3(NMe3)] in Et2O (Scheme
2). The reaction proceeded as expected, and compound 12 was
isolated in 54% yield as a yellow-green oil. Although compound
12 was significantly more viscous than compound 11
(consistent with the higher viscosity of L4H compared to
L3H), it was still oily and could not be crystallized.
Nonetheless, strong indications that compound 12 had been
In an attempt to gauge the reactivity of ligand L3H, it was
reacted with one equivalent of GaMe3 in Et2O at −78 °C. After
warming to RT and stirring for 16 h, removal of all volatiles
1
afforded a gelatinous pale brown oil. H NMR spectroscopy of
the oil revealed a reaction had taken place, but two products (in
a 1:1 ratio) were present. By analyzing the integrals of the peaks
in the Ga−Me region of the spectrum (ca. 0.0 ppm) relative to
that for the CH peak on the backbone (ca. 5.0 ppm), in
addition to the peak corresponding to the CH2 group next to
the amine NH (or N−), it was determined that the two
products were (i) a simple adduct of L3H with GaMe3
(probably through the lone pair of the NMe2 group) and (ii)
compound 9 (Scheme 2). Dissolving the oil in thf and refluxing
for 4 h resulted in increased conversion to compound 9 of 68%,
but a prolonged reflux in toluene (16 h) was required in order
for complete conversion to compound 9 to occur. This
indicated that ligand L3H was not very reactive, with long
reaction times at high temperatures needed for complete
conversion to occur. Reaction of L3H with InMe3 followed
similar lines, with prolonged reflux at high temperatures needed
for full conversion to complex 10: further evidence that L3H
does not react quickly with the reactive MMe3 (M = Ga, In).
Compound 9 was isolated as a gelatinous brown oil with the
1H NMR spectrum exhibiting the expected differences from
that of L3H, namely, no NH proton in the 11−12 ppm range
and a triplet (rather than a doublet of triplets) for the
methylene group next to the amide nitrogen. A singlet at 0.02
ppm corresponding to the Ga−Me groups was characteristic of
Ga−Me protons. Similarly, compound 10 was also isolated as a
1
made were found in the H NMR spectrum where signals
characteristic of the coordinated β-ketoiminate were observed,
namely, no NH signal at 11.9 ppm and a triplet at 3.22 ppm for
the methylene group next to the amide nitrogen.
The Ga/O ratio in complexes 11 and 12 is only 1:1, but for
Ga2O3 the ratio is 1:1.5. In order to synthesize a precursor,
which would not afford oxygen-deficient films, attempts were
made to react a second equivalent of L3H with complex 11.
However, when one equivalent of L3H was added to a toluene
solution of 11, no reaction occurred. Adding excess L3H had no
effect, and refluxing the reaction merely led to decomposition
of 11, with the formation of metallic gallium. Similar results
were obtained with ligand L4 and complex 12. Although the
formation of oxygen-deficient films is undesirable, postdeposi-
tion annealing of films in the air is known to afford
stoichiometric Ga2O3.33
Unfortunately, due to compounds 9−12 all being oils,
elemental analysis could not be carried out under anaerobic
conditions. Attempting elemental analysis rapidly under aerobic
conditions only resulted in decomposition. However, the purity
1
of these complexes has been confirmed via H and 13C{1H}
1
gelatinous brown oil with the chemical shifts in the H and
NMR spectroscopy and also mass spectrometry, where the
molecular ion was observed for all compounds.
13C{1H} NMR spectra occurring at very similar values.
With gallium β-ketoiminate hydride complexes 11 and 12 in
hand, attention turned to the synthesis of indium hydride
analogues. Ligand L3H was reacted with a freshly prepared
ethereal solution of [InH3(NMe3)] at −78 °C, but upon
After discovering that ligand L3H did react, albeit slowly, in
the expected manner with GaMe3, a freshly prepared solution
of [GaH3(NMe3)] in Et2O was added to an ethereal solution of
L3H (Scheme 2). A small amount of gas was given off, and a
color change to pale yellow-green was observed, along with the
formation of a white solid. After removing the Et2O, extracting
the solid into hexane afforded a yellow-green oil in 35% yield,
which had a broad peak at 5.50 ppm in the 1H NMR spectrum,
1
warming to RT a gray precipitate of indium metal formed: H
NMR spectroscopic analysis of the solution only revealed the
presence of L3H. A similar result was obtained when L4H was
used. Further investigations into the reaction between
[InH3(NMe3)] and β-ketoimine ligands revealed that the
onset of formation of In metal in each case was ca. −30 °C, a
1
characteristic of gallium hydrides. The H NMR spectrum of
compound 11 contained the expected peaks for the ligand
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Figure 4. XRD pattern of the film deposited on quartz by AACVD of compound 8 after annealing at 1000 °C for 12 h, consistent with crystalline
Ga2O3 (solid bars).
similar temperature to the known decomposition temperature
of [InH3(NMe3)].34 This could possibly indicate that the β-
ketoimine ligands are insufficiently reactive at low temperatures
(−78 °C), and the indium hydride starting material
decomposes before any reaction with the ligand can take place.
Chemical Vapor Deposition. Anticipating that the use of
hydride ligands would enhance the volatility of gallium-
containing precursors, compounds 8 and 11 were used as
precursors to thin films of Ga2O3. Initial studies were carried
out using a simple low pressure (LP)CVD tube furnace, but it
was found that the compounds decomposed before any
significant sublimation occurred and no films were obtained.
In order to get the precursors into the reactor, attention turned
to using aerosol-assisted (AA)CVD instead. This setup uses a
solution of the precursor (usually in toluene) which is
nebulized and carried into the reactor chamber using a stream
of N2, whereby the solvent evaporates leaving the precursor to
decompose onto the substrate.
temperature than the bottom plate. Films deposited on the
substrate were used in the analysis below.
Powder XRD analysis of the as-deposited transparent film
revealed that the material was amorphous, but depositing on
quartz and annealing in the air at 1000 °C for 12 h resulted in
the formation of a crystalline film of Ga2O3 (Figure 4). EDX
analysis of the as-deposited film again showed breakthrough to
the glass substrate making calculation of an accurate Ga/O ratio
difficult, although the presence of gallium in the films was
confirmed. SEM images showed that the as-deposited film was
composed of aggregated spherical globules (Figure 5), but after
annealing, the film composition became much smoother and
more uniform, with few globular surface features.
The best deposition conditions were found to be 1 L min−1
of N2 carrier gas and a substrate temperature of 450 °C. The
films grown using compound 11 as a precursor were patchy and
poorly adherent to the substrate, with a large amount of white
powdery deposit observed. Powder X-ray diffraction (XRD)
showed the films to be amorphous, as is expected from gallium
oxide grown at low temperatures. Energy dispersive X-ray
(EDX) analysis of the film showed that gallium was present, but
the film was too thin to calculate the Ga/O ratio because
breakthrough to the underlying glass substrate took place.
Altering the deposition conditions did not result in the
formation of better-quality films; hence, compound 11 was
abandoned as an unsuitable precursor.
Films grown from compound 8 proved to be of much better
quality. The coverage of the substrate was much improved with
a transparent, adherent film deposited on the bottom plate, and
a small amount of white powdery material also deposited onto
the top plate, which is the glass plate that rests 8 mm above the
surface of the substrate. Deposition on the substrate and top
plate is due to the thermophoretic force that gas-phase particles
are subjected to during AACVD. Since the flow of gas in the
reactor is laminar rather than turbulent, thermophoresis is
usually the dominant force in determining the deposition
location of particles; hence, deposition also occurs on the
elevated surfaces above the actual surface that requires coating.
The top plate was measured to be ∼50−70 °C lower in
Figure 5. SEM images of the film obtained by AACVD of a toluene
solution of 8 on (a) glass and (b) quartz. The quartz film was annealed
at 1000 °C for 4 h.
The optical properties of the films deposited from 8 were
studied by UV/visible spectroscopy between 90 and 1100 nm.
Conducting a Tauc plot of the UV/visible data indicated that
the band gap of the films deposited from 8 were ∼4.65 eV,
which provides further support for the formation of Ga2O3
since the band gap of gallium oxide is ∼4.2−4.7 eV.
Transmission and reflectance measurements between 200 and
2550 nm showed that the films displayed minimal reflectivity
(5−10%) and were highly transparent, as shown in Figure 6
with transparency ranges from 80% to 90% in the visible.
Previous deposition of Ga2O3 via AACVD of dialkylalkox-
ogallanes of the type [R2Ga(OR′)]2 (R = Me, Et; R′ =
CH2CH2NMe2, CH2CH2OMe, etc.) typically resulted in the
deposition of gray or brown films indicative of carbon
contamination, probably due to the retention of carbon from
the Ga−C bond.32,33,35 In contrast, compound 8 afforded
transparent films (as deposited), suggesting minimal carbon
contamination. Indeed, no carbon was detected via EDX
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Figure 6. Vis/IR transmission spectra of a film obtained by AACVD of a toluene solution of 8.
δH (400.1 MHz, CDCl3): 5.04 (2H, s, CH), 3.21 and 2.65 (each
2H, br s, CH2), 1.99 (6H, s, COCH3), 1.43 (6H, s, CNCH3) ppm.
δC (100.6 MHz, CDCl3): 180.6 (CO), 173.6 (CN), 100.7 (CH),
45.8 (CH2), 25.8 (CH3, COCH3), 22.4 (CH3, CNCH3) ppm.
Mass spec (m/z): 284 [M]+, 249 [M − Cl]+.
analysis, so carbon contamination levels as a direct result of the
precursors used are low (<5 at.%), which could be attributed to
the presence of the hydride ligand in 8 resulting in minimal
contamination.
Analysis Calcd. for C12H18N2O2AlCl: C, 50.62; H, 6.37; N, 9.84.
Found: C, 50.71; H, 6.49; N, 9.28.
CONCLUSIONS
■
[Ga(L1)Cl] (4). A suspension of compound 1 (2.68 g, 10.0 mmol) in
thf (40 mL) was added to a solution of GaCl3 (1.76 g, 10.0 mmol) in
thf (20 mL) at −78 °C and stirred for 30 min. The reaction was
warmed to RT then refluxed for 16 h. After this time, the reaction was
cooled and filtered and the resulting NaCl extracted with thf. The
filtrates were combined, and solvents were removed in vacuo. The
resulting yellow solid was dissolved in minimal CH2Cl2 (ca. 10 mL)
and precipitated out by the rapid addition of hexane, affording 2.29 g
of complex 4 in 70% yield.
In conclusion, we have demonstrated that it is possible to
synthesize a wide range of β-ketoimine ligands and attach them
to group 13 metals. The synthesis of gallium β-ketoiminate
hydrides can be accomplished by reacting the free ligand
directly with [GaH3(NMe3)], but analogous indium complexes
cannot be made, with indium β-ketoiminate chloride complexes
proving to be unreactive toward hydride sources (as well as
even more reactive species such as C8K). Gallium hydride
complexes 8 and 11 have been used as precursors to thin films
of gallium oxide. Compound 8 proved the superior precursor,
affording transparent, adherent films. Extension of the β-
ketoiminate chemistry to other main group metals is currently
in progress.
δH (400.1 MHz, CDCl3): 5.26 (2H, s, CH), 3.62 and 3.51 (each
2H, m, CH2), 2.08 (6H, s, COCH3), 2.02 (6H, s, CNCH3) ppm.
δC (100.6 MHz, CDCl3): 183.6 (CO), 173.3 (CN), 98.8 (CH), 45.1
(CH2), 26.7 (CH3, COCH3), 22.6 (CH3, CNCH3) ppm.
Mass spec (m/z): 326 [M]+, 291 [M − Cl]+.
Analysis Calcd. for C12H18N2O2GaCl: C, 44.01; H, 5.54; N, 8.55.
Found: C, 44.00; H, 5.49; N, 8.26.
EXPERIMENTAL SECTION
■
[In(L1)Cl] (5). A suspension of compound 1 (2.68 g, 10.0 mmol) in
hexane (40 mL) was added to a suspension of InCl3 (2.21 g, 10.0
mmol) in hexane (20 mL) at −78 °C and stirred for 30 min. The
reaction was warmed to RT, then refluxed for 16 h. After this time, the
reaction was cooled and filtered and the resulting NaCl extracted with
hexane. The filtrates were combined, and solvents were removed in
vacuo. The resulting yellow solid was dissolved in minimal CH2Cl2 (ca.
10 mL) and crystallized through vapor diffusion of hexane into the
CH2Cl2 solution, affording 1.67 g of complex 5 in 45% yield
δH (400.1 MHz, CDCl3): 5.26 (2H, s, CH), 3.62 and 3.51 (each
2H, m, CH2), 2.08 (6H, s, COCH3), 2.02 (6H, s, CNCH3) ppm.
δC (100.6 MHz, CDCl3): 183.6 (CO), 173.3 (CN), 98.8 (CH), 45.1
(CH2), 26.7 (CH3, COCH3), 22.6 (CH3, CNCH3) ppm.
Mass spec (m/z): 372 [M]+, 337 [M − Cl]+.
All reactions involving metal complexes were carried out under
nitrogen using standard Schlenk and glovebox techniques. AlCl3 was
obtained from Acros Organics. GaCl3 (10 mesh beads, 99.99%), LiH,
and amines were bought from Sigma Aldrich, β-diketones and InCl3
from Alfa Aesar: all were used without further purification. GaMe3 and
InMe3 were supplied by SAFC Hitech Ltd. [GaH3(NMe3)]21 and
[InH3(NMe3)],34 along with ligands L1H2 and L2H2,26,27 were
synthesized according to literature procedures. Details of the ligand
syntheses, sodium salt formation, and compounds 5a and 5·thf are
contained in the Supporting Information.
1H and 13C{1H} NMR spectra were obtained on a Bruker AMX-400
spectrometer, operating at 295 K and 400.12 MHz (1H). Signals are
reported relative to SiMe4 (δ = 0.00 ppm), and the following
abbreviations are used: s (singlet), d (doublet), t (triplet), m
(multiplet), br (broad). Deuterated solvents were obtained from
Goss Scientific and were dried and degassed over molecular sieves
prior to use. Mass spectra were obtained using a Micromass 70-SE
spectrometer using chemical ionization (CI) with methane reagent
gas. The expected pattern for each [M]+ reported was observed.
Elemental analyses were obtained at UCL.
[Al(L1)Cl] (3). Compound 1 (540 mg, 2.0 mmol) was suspended in
hexane (20 mL) and added slowly to a solution of AlCl3 (270 mg, 2.0
mmol) in hexane (20 mL) at −78 °C. The reaction was stirred for 30
min, then warmed to RT and stirred for 16 h. After this time, solvents
were removed, the solid extracted into toluene and filtered. The
resulting yellow solution was cooled to −18 °C, affording 200 mg of a
yellow crystalline material (35% yield).
Analysis Calc. for C12H18N2O2InCl: C, 38.69; H, 4.87; N, 7.52.
Found: C, 38.82; H, 5.01; N, 7.46.
[Ga(L2)Cl] (6). A suspension of compound 2 (570 mg, 2.0 mmol) in
hexane (30 mL) was cooled to −78 °C and added to a solution of
GaCl3 (352 mg, 2.0 mmol) in hexane (20 mL) at −78 °C. The
reaction was stirred for 15 min, warmed to RT, and then stirred for 16
h. After this time, the reaction was filtered, solvents removed, and the
resulting yellow/brown solid dissolved in minimal CH2Cl2 (ca. 5 mL)
and layered with hexane. Yellow crystals (270 mg) of the title
compound formed in 38% yield.
δH (400.1 MHz, CDCl3): 5.06 (2H, s, CH), 3.71 and 3.46 (each
2H, br s, NCH2), 2.01 (6H, s, COCH3), 2.00 (6H, s, CNCH3), 1.87
(2H, quintet, J = 6.5 Hz, CH2) ppm.
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Table 2. Crystallographic Data for Structurally Characterized Compounds Reported in This Paper
compound
5
5a
5·thf
6
7
L3H·HCl
chemical formula
C24H36Cl2In2N4O4
745.11
C36H56Cl2In2N6O6
969.41
C16H26ClInN2O3
444.66
C13H20ClGaN2O2
341.48
C13H20ClInN2O2
386.58
C10H21ClN2O
220.74
fw (g mol−1
)
crystal system
space group
a (Å)
monoclinic
P21/c
triclinic
monoclinic
P21/c
triclinic
triclinic
monoclinic
P21
P1
̅
P1
̅
P1
̅
11.276(4)
11.797(4)
12.513(3)
8.2191(1)
9.4727(2)
14.0874(2)
73.982(1)
75.889(1)
86.436(1)
1022.39(3)
1
8.0171(3)
14.7596(5)
17.1126(5)
7.4177(9)
8.6862(11)
12.4715(15)
72.534(2)
75.996(2)
77.103(2)
733.82(16)
2
8.8098(8)
12.6328(11)
14.7568(13)
94.327(1)
95.448(1)
110.058(1)
1525.5(2)
4
5.4450(1)
11.4384(3)
10.0709(3)
b (Å)
c (Å)
α (deg)
β (deg)
γ (deg)
V (Å3)
Z
120.50(2)
114.806(2)
104.629(2)
1434.2(8)
2
1838.09(11)
4
606.90(3)
2
ρcalcd (g cm−3
μ (mm−1
)
1.725
1.574
1.607
1.545
1.683
1.208
)
1.830
1.308
1.446
2.056
1.724
0.289
reflns collected
unique reflns
7466
23101
18466
5937
10370
7150
3268
4701
4201
3152
5135
1447
Rint
0.023
0.0395
0.0373
0.0188
0.0166
0.0468
R1 and wR2 [I > 2σ(I)]
R1 and wR2 [all data]
0.0239, 0.0472
0.0294, 0.0489
0.0225, 0.0516
0.0254, 0.0530
0.0320, 0.0601
0.0421, 0.0651
0.0219, 0.0566
0.0235, 0.0576
0.0235, 0.0624
0.0275, 0.0644
0.0874, 0.2442
0.0888, 0.2449
δC (100.6 MHz, CDCl3): 98.8 (CH), 47.2 (NCH2), 30.3 (CH2),
26.5 (CH3, COCH3), 18.8 (CH3, CNCH3), ppm. (CO) and (CN) not
detected.
Analysis Calcd. for C13H20N2O2GaCl: C, 45.75; H, 5.90; N, 8.20.
Found: C, 45.44; H, 6.04; N, 8.28.
Mass spec (m/z): 283 [M]+.
[In(L3)Me2] (10). The procedure for compound 9 was followed
with InMe3 (800 mg, 5.0 mmol) being used in place of GaMe3. A total
of 1.51 g of complex 10 was isolated as a gelatinous brown liquid in
92% yield.
[In(L2)Cl] (7). The procedure described for compound 6 was
followed, with InCl3 (442 mg, 2.0 mmol) used in place of GaCl3.
Yellow crystals (270 mg) of 7 were isolated in 35% yield.
δH (400.1 MHz, CDCl3): 4.94 (2H, s, CH), 3.76 and 3.47 (each
2H, br s, NCH2), 2.63 (2H, br s, CH2), 2.02 (6H, s, COCH3), 1.99
(6H, s, CNCH3) ppm.
δH (400.1 MHz, C6D6): 4.81 (1H, s, CH), 3.04 (2H, t, J = 6.0 Hz,
NCH2), 2.00 (3H, s, COCH3), 1.93 (2H, t, J = 6.0 Hz, Me2NCH2),
1.76 [6H, s, N(CH3)2], 1.56 (3H, s, CNCH3), 1.25 (2H, quintet, J =
6.0 Hz, CH2), 0.00 (6H, s, InCH3) ppm.
δC (100.6 MHz, C6D6): 183.90 (CO), 171.67 (CN), 97.59 (CH),
58.38 (NCH2), 49.15 (Me2NCH2), 45.38 [N(CH3)2], 28.06 (CH3,
COCH3), 27.89 (CH2), 21.03 (CH3, CNCH3), −6.78 (CH3, InCH3)
ppm.
δC (100.6 MHz, CDCl3): 185.8 (CO), 176.0 (CN), 98.0 (CH), 51.9
(NCH2), 29.1 (CH2), 27.6 (CH3, COCH3), 23.2 (CH3, CNCH3)
ppm.
Mass spec (m/z): 328 [M]+.
Mass spec (m/z): 386 [M]+, 351 [M − Cl]+, 238 [L2H2]+.
Analysis Calcd. for C13H20N2O2InCl: C, 40.39; H, 5.21; N, 7.25.
Found: C, 40.17; H, 5.30; N, 7.59.
[Ga(L3)H2] (11). (Method 1) A freshly prepared solution of
[GaH3(NMe3)] (5.0 mmol) in Et2O (30 mL) was cooled to −78 °C,
and ketoimine L3H (920 mg, 5.0 mmol) was added dropwise. A white
precipitate formed; the suspension was warmed to RT and stirred for
16 h. After this time, solvents were removed, the solid extracted with
hexane (2 × 20 mL), and the hexane extracts concentrated, affording
446 mg of a yellow-green oil in 35% yield.
(Method 2) A freshly prepared solution of LiGaH4 (5.0 mmol) in
Et2O (30 mL) at −78 °C was added to L3H·HCl (1.10 g, 5.0 mmol).
The reaction was stirred for 15 min, warmed to RT, and stirred for 16
h. After this time, solvents were removed and the solid extracted with
hexane (3 × 20 mL), and the hexane extracts were combined and
concentrated, affording 777 mg of a yellow oil in 61% yield.
δH (400.1 MHz, C6D6): 5.50 (2H, v br s, GaH), 4.69 (1H, s, CH),
3.08 (2H, t, J = 7.0 Hz, NCH2), 1.97 (2H, m, Me2NCH2), 1.94 [6H, s,
N(CH3)2], 1.82 (3H, s, COCH3), 1.46−1.49 (2H, m, CH2), 1.45 (3H,
s, CNCH3) ppm.
[Ga(L1)H] (8). A freshly prepared solution of [GaH3(NMe3)] (5.0
mmol) in Et2O (50 mL) was cooled to −78 °C and added to a
suspension of L1H2 (1.12 g, 5.0 mmol) in Et2O (20 mL) at −78 °C.
The suspension was stirred for 15 min, then warmed to RT and stirred
for 16 h. After this time, a yellow solution with a white suspension had
formed. The reaction was filtered, and volatiles were removed in vacuo,
affording 1.04 g of a yellow solid in 71% yield.
δH (400.1 MHz, C6D6): 5.56 (1H, v br s, GaH), 4.80 (2H, s, CH),
2.80−2.89 and 2.58−2.68 (each 2H, m, CH2), 1.90 (6H, s, COCH3),
1.39 (6H, s, CNCH3) ppm.
δC (100.6 MHz, C6D6): 182.45 (CO), 171.25 (CN), 97.62 (CH),
45.28 (CH2), 26.70 (CH3, COCH3), 21.52 (CH3, CNCH3) ppm.
Analysis Calcd. for C12H19N2O2Ga: C, 35.69; H, 6.99; N, 6.94.
Found: C, 35.75; H, 6.91; N, 7.06.
[Ga(L3)Me2] (9). A solution of GaMe3 (574 mg, 5.0 mmol) in
toluene (30 mL) was cooled to −78 °C, and ligand L3H (920 mg, 5.0
mmol) was added dropwise. The solution was gradually warmed to RT
with the evolution of methane gas, then refluxed for 16 h. After this
time, solvents were removed, affording 1.35 g of a gelatinous brown
liquid in 95% yield.
δH (400.1 MHz, C6D6): 4.67 (1H, s, CH), 3.13 (2H, t, J = 7.5 Hz,
NCH2), 1.94−1.99 (8H, m, Me2NCH2 + N(CH3)2), 1.85 (3H, s,
COCH3), 1.51 (3H, s, CNCH3), 1.49 (2H, quintet, J = 7.0 Hz, CH2),
0.02 (6H, s, GaCH3) ppm.
δC (100.6 MHz, C6D6): 180.43 (CO), 171.46 (CN), 97.96 (CH),
56.67 (NCH2), 46.80 (Me2NCH2), 45.30 (N(CH3)2), 28.32 (CH2),
26.35 (CH3, COCH3), 20.53 (CH3, CNCH3), −6.78 (CH3, GaCH3)
ppm.
δC (100.6 MHz, C6D6): 181.14 (CO), 172.30 (CN), 98.40 (CH),
56.48 (NCH2), 47.71 (Me2NCH2), 45.19 [N(CH3)2], 27.23 (CH2),
26.20 (CH3, COCH3), 20.61 (CH3, CNCH3) ppm.
Mass spec (m/z): 255 [M]+.
[Ga(L4)H2] (12). Procedure 1 for compound 11 was followed, using
ketoimine L4H (1.54 g, 5.0 mmol). A total of 1.03 g of complex 12 was
isolated as a yellow-green oil in 54% yield.
δH (400.1 MHz, C6D6): 7.87−7.91 (2H, m, Ar), 7.04−7.11 (6H, m,
Ar), 6.97−7.01 (2H, m, Ar), 5.81 (1H, s, CH), 5.55 (2H, v br s, GaH),
3.22 (2H, t, J = 7.0 Hz, NCH2), 2.00 (2H, t, J = 6.0 Hz, Me2NCH2),
1.92 [6H, s, N(CH3)2], 1.42 (2H, quintet, J = 6.5 Hz, CH2) ppm.
δC (100.6 MHz, C6D6): 177.31 (CO), 175.10 (CN), 139.53, 139.40
(C, Ar), 130.46, 128.98, 128.59, 128.34, 127.50, 127.27 (CH, Ar),
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Inorganic Chemistry
Article
96.95 (CH), 57.51 (NCH2), 51.32 (CH2, Me2NCH2), 45.14
[N(CH3)2], 28.49 (CH2) ppm.
Notes
The authors declare no competing financial interest.
Mass spec (m/z): 379 [M]+.
AACVD. For AACVD experiments, nitrogen (99.99%) was
obtained from BOC and used as supplied. Depositions were obtained
on SiCO barrier layer (50 nm) float-glass of dimensions ca. 90 mm ×
45 mm × 4 mm. Prior to use, the glass substrates were cleaned using
ACKNOWLEDGMENTS
■
We would like to thank the EPSRC (grant nos. EP/H00064X/
1 and EP/F035675/1), UCL (Impact Studentship Scheme),
and the Horshall fund for financial support. We would also like
to thank SAFC Hitech Ltd. for supplying GaMe3 and InMe3;
Pilkington for supplying the float glass; and Drs. Peter Horton,
Mateusz Pitak, and Graham Tizzard at the EPSRC National
Crystallography Service for data set collection of 5, 5a, 5·thf,
and L3·HCl.
i
petroleum ether (60−80 °C) and PrOH, then dried in the air. The
precursor (ca. 300 mg) was dissolved in toluene (ca. 30 mL) and
vaporized at room temperature by use of a PIFCO ultrasonic
humidifier. The aerosol was carried into the reactor using nitrogen
through a brass baffle to obtain a laminar flow. A graphite block
containing a Whatman cartridge heater was used to heat the glass
substrate. The temperature of the substrate was monitored by a Pt−Rh
thermocouple, and the horizontal bed reactor was heated to the
required temperature before diverting the nitrogen line through the
aerosol and hence to the reactor. The total time for the deposition
process was ca. 2 h. The coated glass substrate was cut into ca. 1 cm ×
1 cm squares for subsequent analysis by scanning electron microscopy
(SEM).
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* Supporting Information
Experimental and spectroscopic details for the synthesis of
ligands L1H2, L2H2, L3H, and L4H (and L3H·HCl) and
spectroscopic data for compounds 5a and 5·thf are included as
supporting data, along with X-ray crystallographic data in CIF
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Corresponding Author
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*E-mail: c.j.carmalt@ucl.ac.uk.
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