Volatility and high thermal stability in mid-to-late first-row transition-metal complexes containing 1,2,5-triazapentadienyl ligands

Article abstract of DOI:10.1021/ic302787z

Treatment of first-row transition-metal MCl₂ (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the potassium 1,2,5-triazapentadienyl salts K(tBuNNCHCHNR) (R = tBu, NMe₂) afforded M(tBuNNCHCHNR)₂ in 18-73% isolated yields after subl

Full text of DOI:10.1021/ic302787z

Communication
pubs.acs.org/IC
Volatility and High Thermal Stability in Mid-to-Late First-Row
Transition-Metal Complexes Containing 1,2,5-Triazapentadienyl
Ligands
Lakmal C. Kalutarage,† Mary Jane Heeg,† Philip D. Martin,† Mark J. Saly,‡ David S. Kuiper,§
and Charles H. Winter*,†
†Department of Chemistry, Wayne State University, Detroit, Michigan 48202, United States
‡SAFC Hitech, 1429 Hilldale Avenue, Haverhill, Massachusetts 01832, United States
§SAFC Hitech, 5485 County Road V, Sheboygan Falls, Wisconsin 53085, United States
S
* Supporting Information
dienyl ligands are rare (Chart 1, C) and are limited to a few
ABSTRACT: Treatment of first-row transition-metal
MCl2 (M = Ni, Co, Fe, Mn, Cr) with 2 equiv of the
potassium 1,2,5-triazapentadienyl salts K-
(tBuNNCHCHNR) (R = tBu, NMe2) afforded M-
(tBuNNCHCHNR)2 in 18−73% isolated yields after
sublimation. The X-ray crystal structures of these
compounds show monomeric, tetrahedral molecular
geometries, and magnetic moment measurements are
consistent with high-spin electronic configurations. Com-
plexes with R = tBu sublime between 155 and 175 °C at
0.05 Torr and have decomposition temperatures that range
from 280 to 310 °C, whereas complexes with R = NMe2
sublime at 105 °C at 0.05 Torr but decompose between
181 and 225 °C. This work offers new nitrogen-rich
ligands that are related to widely used β-diketiminate and
1,3,5-triazapentadienyl ligands and demonstrates new
complexes with properties suitable for use in atomic-
layer deposition.
nickel(II) and copper(II) complexes containing 1-phenyl, 3-
acyl or 3-benzoyl, and 5-alkyl substituents,4 although the 1,2,5-
triazapentadienyl ligand core is also found within more complex
chelating ligands.5 Our laboratory is interested in the
development of volatile and thermally stable first-row mid-to-
late-transition-metal complexes that can be used for the atomic-
layer deposition (ALD) growth of metallic transition-metal thin
films. Such materials have many applications, including copper
metallization, copper/manganese alloys for self-forming copper
diffusion barriers, seed layers for copper metallization, and
magnetic alloys.6 We have reported the synthesis and properties
of some main-group metal complexes that contain β-
diketiminate ligands,7 and others have examined the use of β-
diketiminate complexes for the chemical vapor deposition
(CVD) and ALD growth of copper metal films.8 However,
group 2 and copper complexes containing β-diketiminate
ligands have generally low thermal stabilities and may not be
appropriate for widespread use as ALD precursors.8
Herein, we describe the synthesis, structure, volatility, and
thermal stability of a series of nickel(II), cobalt(II), iron(II),
manganese(II), and chromium(II) complexes that contain
1,2,5-triazapentadienyl ligands. These complexes adopt tetrahe-
dral, monomeric structures, exhibit good volatilities and very
high thermal stabilities, and thus have excellent properties for
use as ALD precursors. Additionally, 1,2,5-triazapentadienyl
ligands are easily prepared with a variety of nitrogen and carbon
atom substituents and should uniquely complement the rapidly
expanding chemistry of metal complexes with β-diketiminate
and 1,3,5-triazapentadienyl ligands.1−3
etal complexes containing β-diketiminate ligands have
M
been widely explored.1 The κ2-coordination mode
through the nitrogen atoms is most common (Chart 1, A),
Chart 1. β-Diketiminate (A), 1,3,5-Triazapentadienyl (B),
and 1,2,5-Triazapentadienyl (C) Ligands
The protonated ligand precursors containing two tBu or one
tBu and one NMe2 substituents on the 1- and 5-nitrogen atoms
were prepared as described in the Supporting Information
through stepwise treatment of glyoxal with tBuNHNH2/
tBuNH2 or Me2NNH2/tBuNHNH2.9 Treatment of the
protonated ligands with KH in tetrahydrofuran (THF),
followed by the addition of anhydrous MCl2, afforded
complexes 1−9 upon sublimation (Scheme 1).9 These
complexes were characterized by spectral and analytical
and the steric and electronic nature of the ligand can be tuned
through variation of the nitrogen and carbon atom substituents.
Recently, there have been many reports of late-transition-metal
complexes containing related 1,3,5-triazapentadienyl ligands.2,3
In addition to the terminal κ2-coordination mode to the 1- and
5-nitrogen atoms (Chart 1, B), coordination of 1,3,5-
triazapentadienyl ligands can also occur at the 3-nitrogen
atom, leading to new terminal and bridging coordination
modes.2,3 Complexes containing the isomeric 1,2,5-triazapenta-
Received: December 19, 2012
Published: January 23, 2013
© 2013 American Chemical Society
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Inorganic Chemistry
Communication
between 112.3(1) and 122.0(1)°. Within the NiN3C2 ligand
cores, the N−N bond lengths are 1.314(4) and 1.307(4) Å, the
N−C distances are between 1.304(5) and 1.322(5), and the
C−C bond lengths are 1.414(2) and 1.415(2) Å. These values
are between N−N, C−N, and C−C single and double bonds
and suggest delocalized, monoanionic 1,2,5-triazapentadienyl
ligands.
Scheme 1. Synthesis of 1−9
To assess the suitability of 1−9 for use as CVD and ALD
precursors, their volatilities and thermal stabilities were
determined by preparation sublimation experiments, solid-
state decomposition point measurements, and thermogravi-
metric analysis (TGA).9 Complexes 1−5 sublime on ∼0.5 g
scales over 2−3 h with <2% nonvolatile residues between 155
and 175 °C at 0.05 Torr, whereas the N-dimethylamino
complexes 6−9 sublime at 105 °C under similar conditions
(Table 1). We have previously demonstrated that magnesium
methods and by X-ray crystallography, as described below. All
of the new complexes are paramagnetic in solution and
exhibited very broad resonances in the 1H NMR spectra.
Magnetic moments for 1−9 in the solid state and in solution
were consistent with high-spin tetrahedral geometries.
Table 1. Sublimation and Thermal Stability Data for 1−9
sublimation temp
melting point
decomposition point
compound
(°C)
(°C)
(°C)
X-ray crystal structures of 1−7 were determined. Complexes
1−5 exhibit merohedral twinning, which leads to an inherent
50/50 occupancy of the core 2-nitrogen/4-carbon atoms. Such
disorder is not present in 6 and 7 because of asymmetric ligand
substitution, and the structure of 6 described herein presents
typical structural features for 1−7 (Figure 1).9 Complex 6 is
1
2
3
4
5
6
7
8
9
155
160
175
165
165
105
105
105
105
262
260
275
284
257
99
290
296
310
310
280
188
225
181
200
105
106
108
and calcium β-diketiminate complexes containing N-dimethy-
lamino groups sublime at considerably lower temperatures than
analogous complexes containing tert-butyl or isopropyl
substituents.7a,b The lower sublimation temperatures in the
former complexes were attributed to intermolecular lone pair−
lone pair repulsions between the nonbonded dimethylamino
groups, which lowers the lattice energies and thereby increases
the volatilities. Complexes 6−9 have melting points that are
close to the sublimation temperatures; hence, these complexes
evaporate from the liquid state. Liquid precursors are highly
desirable in CVD and ALD to promote steady vapor-phase
delivery and to avoid particle incorporation into the growing
films.11 The solid-state decomposition temperatures of 1−5
range between 280 and 310 °C, which are extraordinarily high
for complexes containing these elements. High thermal stability
is desirable for ALD precursors because thermal decomposition
of the precursor usually signals loss of the self-limited growth
mechanism and the onset of CVD-like growth.11,12 Complexes
6−9 have decomposition temperatures that range between 181
and 225 °C, which are much lower than those of 1−5.
However, 6−9 have much lower sublimation temperatures than
1−5, and their decomposition points are still high enough to be
useful in the ALD growth of transition-metal thin films.8b,12
The TGA data for 1−4 showed single-step weight losses and
residues of <10% upon reaching 300 °C, 5 gave poor behavior
likely because of its extreme air sensitivity, and 6−9 showed
single-step weight losses up to about the decomposition
temperatures that are shown in Table 1.9
Figure 1. Perspective views of 6 with thermal ellipsoids at the 50%
level. Selected bond lengths (Å) and angles (deg): Ni−N1 1.932(3),
Ni−N3 1.969(3), Ni−N5 1.949(3), Ni−N7 1.952(3), N1−N2
1.314(4), N2−C5 1.319(5), C5−C6 1.415(5), C6−N3 1.304(4),
N5−N6 1.307(4), N6−C13 1.322(5), C13−C14 1.414(5), C14−N7
1.309(5); N1−Ni−N3 92.8(1), N1−Ni−N5 117.7(1), N1−Ni−N7
122.03(1), N3−Ni−N5 121.8(1), N3−Ni−N7 112.3(1), N5−Ni−N7
92.7(1).
monomeric and four-coordinate, contains κ2-1,2,5-triazapenta-
dienyl ligands bound through the 1- and 5-nitrogen atoms, and
has distorted tetrahedral geometry about the nickel ion, as
exemplified by the 84.0° angle between the best planes of the
NiN3C2 groups. The Ni−N bond lengths range between
1.932(3) and 1.969(3) Å, which are similar to other high-spin
tetrahedral nickel(II) complexes containing κ2-β-diketiminate
ligands.10 The intraligand N−Ni−N angles are 92.7(1) and
92.8(1)°, while the corresponding interligand angles range
To assess its initial viability for use in ALD film growth, 6 was
treated with anhydrous hydrazine in THF at 23 °C. A metallic
black precipitate was observed within 0.25 h. The precipitate
stuck to the magnetic stir bar, and a powder X-ray diffraction
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Inorganic Chemistry
Communication
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reduced rapidly by hydrazine, and this chemistry may lead to a
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and have very high thermal decomposition temperatures. As a
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(iPrNCMeNiPr)2 undergoes solid-state decomposition at
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hydrazine. Film growth studies with 6 and related complexes
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ASSOCIATED CONTENT
* Supporting Information
■
S
Synthetic procedures and analytical and spectroscopic data for
1−9 and X-ray crystallographic data for 6 and 7 in CIF format.
This material is available free of charge via the Internet at
http://pubs.acs.org.
AUTHOR INFORMATION
Corresponding Author
*E-mail: chw@chem.wayne.edu.
■
Notes
The authors declare no competing financial interests.
ACKNOWLEDGMENTS
■
This work was supported by the U.S. National Science
Foundation (Grants CHE-0910475 and CHE-1212574) and
SAFC Hitech.
(9) Details of the synthetic work and characterization of the new
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