Synthesis and Characterization of Tungsten Nitrido Amido Guanidinato Complexes as Precursors for Chemical Vapor Deposition of WNxCy Thin Films

Article abstract of DOI:10.1002/ejic.201701225

Tungsten nitrido amido guanidinato complexes of the type WN(NR₂)[(NR′)₂C(NR₂)]₂ (R = Me, Et_; R′ = iPr, Cy) were synthesized as precursors for aerosol-assisted chemical vapor deposition (AACVD) of WN_xC_y thin films. The reaction of tungsten nitrido amido complexes of the type WN(NR₂)₃ (R = Me, Et) with two equivalents of a carbodiimide R′N=C=NR′ (R′ = iPr, Cy) resulted in two insertions of a carbodiimide into W–N(amido) bonds, affording bis(guanidinato) amido nitrido tungsten complexes. These compounds were characterized by ¹⁴N NMR, indicating distinctive chemical shifts for each type of N-bound ligand. Crystallographic structure determination of WN(NMe₂)[(NiPr)₂C(NMe₂)]₂ showed the guanidinato ligands to be non-equivalent. The complex WN(NMe₂)[(NiPr)₂C(NMe₂)]₂ was demonstrated to serve as a precursor for AACVD of WN_xC_y thin films, resulting in featureless, X-ray amorphous thin films for growth temperatures 200–400 °C.

Full text of DOI:10.1002/ejic.201701225

DOI: 10.1002/ejic.201701225
Full Paper
Tungsten Carbonitride Films | Very Important Paper |
Synthesis and Characterization of Tungsten Nitrido Amido
Guanidinato Complexes as Precursors for Chemical Vapor
Deposition of WNxCy Thin Films
Michelle M. Nolan,[a][‡] Alexander J. Touchton,[a][‡] Nathaniel E. Richey,[a] Ion Ghiviriga,[a]
James R. Rocca,[b] Khalil A. Abboud,[a] and Lisa McElwee-White*[a]
Abstract: Tungsten nitrido amido guanidinato complexes of tungsten complexes. These compounds were characterized by
the type WN(NR2)[(NR′)2C(NR2)]2 (R = Me, Et; R′ = iPr, Cy) were 14N NMR, indicating distinctive chemical shifts for each type
synthesized as precursors for aerosol-assisted chemical vapor of N-bound ligand. Crystallographic structure determination of
deposition (AACVD) of WNxCy thin films. The reaction of tung- WN(NMe2)[(NiPr)2C(NMe2)]2 showed the guanidinato ligands to
sten nitrido amido complexes of the type WN(NR2)3 (R = Me, be non-equivalent. The complex WN(NMe2)[(NiPr)2C(NMe2)]2
Et) with two equivalents of a carbodiimide R′N=C=NR′ (R′ = iPr, was demonstrated to serve as a precursor for AACVD of WNxCy
Cy) resulted in two insertions of
a carbodiimide into thin films, resulting in featureless, X-ray amorphous thin films
W–N(amido) bonds, affording bis(guanidinato) amido nitrido for growth temperatures 200–400 °C.
Introduction
thermal stability, and minimal chemical reactivity with existing
circuit materials.[4] Previously reported single source precursors
for deposition of WNxCy have utilized N-bound ligands such
as nitrido, imido, hydrazido, amido, guanidinato, and amidinato
moieties to provide the nitrogen in the resulting material.[5] Op-
timization of the precursors has primarily targeted low temper-
ature deposition (<350 °C) to minimize the thermal damage to
the substrate. Our studies of tungsten nitrido complexes of the
type WN(NR2)3 demonstrated that the W≡ N and W–NR2 moie-
ties are acceptable sources of N in depositions carried out at
temperatures as low as 125 °C. In addition, variation of the sub-
stituents in the amido moieties of WN(NR2)3 provided a means
to tune the precursor volatility.[5g,6]
Chemical vapor deposition (CVD) is a critical tool in the elec-
tronics industry for the fabrication of thin film and nanostruc-
ture materials. During CVD, vapor-phase precursors undergo a
chemical reaction to deposit a material of interest on a heated
substrate. Some of the key advantages of CVD over other physi-
cal deposition methods include its high deposition rates, con-
trol over film thicknesses and morphologies, efficacy in con-
formal film growth, and flexibility towards process modifica-
tions for specific applications.[1] Additional control over deposit
stoichiometry and the prevention of premature precursor reac-
tion are accessible through the use of single source precursors,
in which all components of the deposited material derive from
a single complex.[2] The design of single source precursors for
CVD represents a significant challenge because it relies on opti-
mizing many compound properties, including volatility, toxicity,
stability, and decomposition reproducibility.[2b]
A general strategy to improve the thermal stability of a CVD
precursor while maintaining volatility is the addition of chelat-
ing ligands, such as guanidinato ligands.[7] Guanidinato ligands
are N-bound, bidentate ligands which have been extensively
employed in CVD precursors due to their electronic versatility,
thermal stability, and nitrogen contribution to deposits.[8] Late
transition-metal guanidinates have been used in deposition of
metal films, including Cu and Ni.[7,9] However, early transition-
metal guanidinate precursors have yielded metal nitride and
metal carbonitride thin films under CVD conditions. Mixed
guanidinato amido complexes of Ta and Nb have been em-
ployed in the CVD of TaN and NbN thin films.[10] Growth of
ZrNxCy and TiNxCy films was achieved from bis(guanidinato)
complexes.[8,11]
We have used aerosol-assisted (AA)CVD of tungsten carbo-
nitride (WNxCy) as a platform for exploring the mechanism-
based design of single source CVD precursors.[3] This material
had been considered as a candidate for copper diffusion barri-
ers in integrated circuits due to its low electrical resistivity, high
[a] Department of Chemistry, University of Florida
Gainesville, FL 32611-27200, USA
E-mail: lmwhite@chem.ufl.edu
http://lmwhite.chem.ufl.edu/
[b] McKnight Brain Institute, University of Florida
Gainesville, FL 32610-0015, USA
[‡] M. M. N. and A. J. T. made equal contributions to the work.
Supporting information and ORCID(s) from the author(s) for this article are
available on the WWW under https://doi.org/10.1002/ejic.201701225.
Our previous study of the tungsten imido guanidinato pre-
cursor W(NiPr)Cl3[(iPrN)2CNMe2] demonstrated that guanidinato
ligands are suitable for use in precursors for the AACVD of
WNxCy.[5d] We now report the synthesis of tungsten nitrido am-
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ido guanidinato precursors along with a demonstration of the goes transamination with secondary amines to access different
use of WN(NMe2)[(NiPr)2C(NMe2)]2 (1) as a single source precur- amido ligands,[5g] a similar procedure was attempted to gener-
sor for the AACVD of WNxCy thin films.
ate additional dialkylamido derivatives of 1. However, this strat-
egy was ultimately unsuccessful. An alternate route starting
from WN(NEt2)3 (4) was utilized to synthesize complexes 5 and
6 through the insertion of DIC and DCC (Scheme 1).
Results and Discussion
Precursor Design
Tungsten nitrido amido complexes of the type WN(NR2)3 were
previously synthesized as precursors for AACVD of WNxCy films.
Considerations employed in the design of WN(NMe2)3 (2), in-
cluded a multiply bonded W≡ N moiety, only N-bound ligands,
and facile access to a small library of derivatives.[5f,5g] The incor-
poration of a terminal nitrido moiety was associated with a low
film deposition temperature (125 °C) from this precursor. The
relationship between the volatility of WN(NR2)3 complexes and
amido ligand structure was also explored in order to improve
the vapor-phase transport of the precursors, which is a critical
property in deposition methods that use bubblers for volatiliza-
tion, such as CVD and ALD. Derivatives were synthesized
though transamination of 2 with secondary amines, a simple
method for substitution of the dimethylamido ligands for di-
alkylamido ligands. Improved volatility was associated with the
introduction of sterically hindered dialkylamido groups and li-
gand sets that resulted in low symmetry.[6] As an extension of
these approaches, guanidinato ligands were substituted for two
of the –NR2 moieties in WN(NR2)3 complexes to generate a
small series of nitrido amido guanidinato compounds for
assessment as CVD precursors. These bis(guanidinato) com-
plexes have an octahedral coordination sphere and should
therefore have improved chemical stability and reduced metal–
metal intermolecular interactions with respect to the tetra-
hedral WN(NR2)3 starting materials. The guanidinato N-alkyl
substituents also provide a site for increasing the steric bulk
and reducing the symmetry of the complex.
Scheme 1. Synthesis of 1, 3, 5, and 6.
Crystallographic Structure Determination of 1
Crystals suitable for X-ray crystallography were grown from a
concentrated pentane solution of 1 at –15 °C. Crystal data and
structure refinement are described in Table 1. The compound
exhibits pseudoctahedral geometry with the nitrido and amido
Table 1. Crystal data and structure refinement for 1.[a]
Empirical formula
C20H46N8W
Formula weight
Temperature [K]
Wavelength [Å]
Crystal system
Space group
Unit cell dimensions
a [Å]
b [Å]
c [Å]
α [°]
ꢀ [°]
582.50
100(2)
0.71073
monoclinic
P21/n
9.3428(9)
17.8934(17)
15.6519(15)
90
92.8040(14)
90
2613.5(4)
4
1.480
4.441
γ [°]
Volume [Å3]
Z
Precursor Synthesis
Density [Mg/m3]
Absorption coefficient [mm–1
F(000)
Guanidinato complexes of a variety of metals have been pre-
pared by insertion of N,N′-dialkylcarbodiimides (RN=C=NR) into
metal amide bonds.[10,12] A relevant example is the preparation
of group V metal imido amido guanidinato complexes by se-
lective insertion of carbodiimides into Ta–amido and Nb–amido
bonds in the presence of an imido ligand.[10] This synthetic
strategy is attractive for preparation of derivatives of 2 because
it utilizes commercially available carbodiimides.
Reaction of 2 with two equivalents of N,N′-diisopropyl-
carbodiimide (DIC) (Scheme 1) afforded the nitrido amido
guanidinato complex WN(NMe2)[(NiPr)2C(NMe2)]2 (1). Reducing
the amount of DIC to one equivalent did not result in formation
of a mono-guanidinato complex. Complex 3 was prepared anal-
ogously with N,N′-dicyclohexylcarbodiimide (DCC) (Scheme 1).
The attempted synthesis of N-tert-butyl guanidinato derivatives
of 1 by addition of N,N′-di-tert-butylcarbodiimide to solutions
of 2 resulted in recovery of starting material, even after ex-
tended reflux at temperatures up to 115 °C, suggesting steric
limitations to the insertion reaction. Because 2 readily under-
]
1184
Crystal size [mm]
θ range for data collection [°]
Index ranges
0.309 × 0.287 × 0.238
1.730–27.498
–12 ≤ h ≤ 12
–23 ≤ k ≤ 23
20 ≤ l ≤ 20
51292
5986 (0.0114)
99.9
empirical
Reflections collected
Independent reflections
Completeness to θ = 25.242° [%]
Absorption correction
Refinement method
full-matrix least squares on F2
5986/240/276
1.122
R1 = 0.0105
wR2 = 0.0247 (5832)
R1 = 0.0109
wR2 = 0.0249
n/a
Data/restraints/parameters
Goodness-of-fit on F2
Final R indices [I > 2σ(I)]
R indices (all data)
Extinction coefficient [Å3]
Largest diff. peak and hole [Å3]
0.382 and –0.375
[a] R1 = Σ(||Fo| – |Fc||)/Σ|Fo|; wR2 = Σ{w(Fo – Fc2)2/Σ[w(Fo2)2]}1/2; S = Σ[w(Fo
Fc2)2/(n-p)]1/2; w = 1/[σ2(Fo2) + (m x p)2 + n x p], p = [max(Fo2,0) + 2Fc2]/3.
–
2
2
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ligands cis to one another, as shown in Figure 1. Selected bond
lengths and angles are reported in Table 2. The nitrido W≡ N
bond length [W1–N1, 1.6906(12) Å] is similar to the 1.680(2) Å
previously observed for 2.[5f] The amido W–N bond length of 1
[W1–N5, 1.9552(1) Å] is also similar to the parent compound 2,
which had an average W–N bond length of 1.952(2) Å for its
three amido ligands. The sum of the bond angles around the
amido nitrogen is 359.99°, indicating sp2 hybridization of the
amido N.
Figure 2. Major resonance structure for 1.
NMR Characterization of 1 and 3
Because of the large numbers of similar chemical shifts in com-
1
plex 1, H–13C indirect detection experiments were performed
in [D8]toluene at –50 °C to assign the signals. The spectra were
consistent with two guanidinato and one dimethylamido moie-
ties, with 14 non-equivalent methyl groups (Figure S-9, Sup-
porting Information) in agreement with the structure deter-
mined by X-ray diffractometry. Attempts to obtain the 15N
1
chemical shifts of 1 by H–15N indirect detection experiments
at –25 °C were thwarted by the low solubility of 1. At 25 °C, the
solubility was better, but line broadening of the 1H NMR signals
for the guanidinato –NMe2 groups resulted in the exocyclic
nitrogen in the guanidinato groups not being detected. De-
1
tected H, 13C, and 15N chemical shifts for 1 are given in Fig-
ure 3.
Figure 1. Displacement ellipsoid model of 1; ellipsoids are shown at 50 %
probability. Protons are omitted for clarity.
Table 2. Selected bond lengths [Å] and angles [°] for 1.
W1–N1
W1–N5
W1–N6
W1–N3
W1–N2
W1–N7
N2–C1
N3–C1
N4–C1
N6–C12
N7–C12
N8–C12
1.6906(12)
1.9552(12)
2.0637(11)
2.1749(11)
2.1892(11)
2.5698(11)
1.3307(16)
1.3354(17)
1.3854(17)
1.3808(17)
1.3063(17)
1.3876(16)
N1–W1–N5
N1–W1–N6
N1–W1–N3
N6–W1–N3
N1–W1–N2
N5–W1–N2
N3–W1–N2
N1–W1–N7
N6–W1–N7
N2–C1–N3
N7–C12–N6
96.57(6)
98.18(5)
103.60(5)
149.28(4)
100.66(5)
153.79(5)
60.29(4)
154.94(5)
56.77(4)
110.58(11)
113.49(11)
Figure 3. 1H (blue), 13C (green), and 15N (red) chemical shifts (ppm) of 1 as
measured by 1H–13C and 1H–15N indirect detection in [D8]toluene at 25 °C.
Unlabeled N atoms were not detected.
1
The H-13C gHMBC spectrum of compound 3 in [D8]toluene
at –50 °C facilitated assignment of the methine and methyl res-
onances in two guanidinato and one dimethylamido moieties
(Figure 4), in agreement with a structure similar of that of com-
The two guanidinato ligands are non-equivalent, with their
W–N bond lengths and ligand bite angles varying based on
their positions relative to the strongly π-donating nitrido moi-
ety. The guanidinato ligand bound by N2 and N3 exhibits two
similar W–N bond lengths [W1–N2, 2.1892(11) Å and W1–N3,
2.1749(11) Å]. However, the guanidinato ligand bound by N6
and N7 shows two significantly different bond lengths [W1–
N6, 2.0637(11) Å and W1–N7, 2.5698(11) Å]. The trans influence
imparted by the nitrido ligand is observed in the lengthening
of the W1–N7 bond, similar to reported WVI, TaV and NbV imido
complexes.[5c,10b] The greater degree of bond alternation of the
C–N bonds [N6–C12 1.3808(17) and N7–C12 1.3063(17) Å] and
the long W1–N7 distance in the unsymmetrical guanidinato li-
gand are consistent with a substantial contribution from the
resonance structure shown in Figure 2.
Figure 4. Selected 1H (blue) and 13C (green) chemical shifts (ppm) of 3 as
measured by 1H–13C indirect detection in [D8]toluene at –50 °C.
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pound 1. All 20 methylene groups were evident in the gHSQC of 2 under similar conditions.[6] Analogous deinsertion has been
spectrum but extensive overlap made the assignment of indi- reported for other guanidinato complexes.[7,9c,15] The TGA of 1
vidual chemical shifts impossible. The solubility of 3 was insuffi- (Figure S-10) indicates an initial decomposition step at 200 °C.
cient for indirect detection of 15N.
The residual mass of 63 % corresponds to the loss of one guan-
idinato ligand and one amido ligand, consistent with the prod-
ucts observed by GC-EI-MS.
1
When H-15N indirect detection experiments failed to afford
a signal for the nitrido moiety due to insufficient long range
coupling, the 14N NMR spectrum of 1 was obtained (Figure 5).
In the 14N NMR spectrum of 1, resonances for the metal bound
N-atoms can be clearly resolved despite the large linewidths
associated with the quadrupolar 14N nucleus.[13] The chemical
shifts observed for the guanidinato and amido moieties of 1
Film Growth and Characterization
Compound 1 was tested as a single source precursor for the
AACVD of WNxCy. The AACVD was performed from heptane so-
lutions of 1 at substrate temperatures between 200–400 °C, re-
sulting in dark, iridescent deposited films. Films exhibited good
adhesion to the Si substrates and passed a qualitative peel test
using adhesive tape. Deposited material at all growth tempera-
tures was found to be amorphous by XRD. The morphologies
of the deposits were determined by SEM, as shown in Figure 6.
At temperatures of 200 and 300 °C, films resembled Stranski–
Krastanov type growth: a layer of material covered the substrate
surfaces with islands of growth appearing on top. At 400 °C,
these islands appeared to grow into more pronounced vertical
features. Cross-sectional SEM indicated average film thicknesses
of 29, 25, and 14 μm at deposition temperatures of 200, 300,
and 400 °C, respectively.
correlate with the resonances observed by H–15N indirect de-
1
tection. The terminal nitrido resonance in 1 can be assigned as
the broad peak at δ = 753 ppm, with the analogous signal of
2 appearing at δ = 760 ppm. Both of these values are consistent
with other previously reported chemical shifts for the nitrido
moiety in group VI metal complexes.[14]
Figure 5. 14N NMR spectrum of 1 in [D6]benzene at 25 °C.
Thermolysis of 1
Because CVD is a thermal process, examining the pyrolysis
of a precursor under non-deposition conditions can provide
valuable insight into possible breakdown pathways that occur
during deposition. The thermal decomposition of 1 was investi-
gated by pyrolysis of neat samples and by thermogravimetric
analysis (TGA). Decomposition products from solid state pyroly-
sis were isolated by heating a neat sample of 1 to 200 °C under
1 atm of N2 and condensing the volatile components at 77 K.
1
Analysis of the condensate by H NMR, 13C NMR, FTIR, and GC-
MS revealed the presence of dimethylamine and diisopropyl-
carbodiimide 7 (Scheme 2). Isolation of DIC indicates that the
deinsertion of carbodiimide is an accessible decomposition
pathway. This deinsertion would regenerate the original di-
methylamido ligand, which could then decompose further
through pathways previously established for 2. For example, the
presence of dimethylamine is consistent with the thermolysis
Figure 6. SEM images of WNxCy films deposited at (a,b) 200 °C, (c,d) 300 °C,
and (e, f) 400 °C.
The compositions of the deposits were determined by XPS.
Nitrogen content ranged from 11.6 to 17.0 atom percent of the
Scheme 2. Thermolysis of 1.
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deposits, whereas tungsten comprised approximately 20 at. %. from WN(NR2)3 complexes. However, no deposit from 1 showed
Carbon accounted for approximately 20 to 30 at. % of the de- a peak at 31.5 eV which has previously been reported for W
posited material. These deposits showed higher N and C con- metal observed in depositions from WN(NR2)3.[5h] It is possible
tent, but lower W content, than the deposits previously grown that any W metal formed in these samples was oxidized during
from WN(NR2)3 complexes.[5g,5h,6] Oxygen was present in signifi- handling.
cant amounts in all films and was attributed to post-deposition
oxidation of the samples when handling in air prior to obtain-
ing XPS. Due to the amorphous nature of the films, significant
in-diffusion of oxygen is possible post-growth. Although depth
profiling was not carried out for these samples, we have previ-
ously determined by AES depth profiling that oxygen content
in our WNxCy films is highest in the upper layers, consistent
with oxidation during handling.[5b]
Deconvolution of the N 1s signal revealed two peaks at all
temperatures (Figure 7b). A peak with a BE of 400.0 eV was
observed at all temperatures and has been assigned as CNx,
which typically exhibits BEs of 398.5 to 400.6 eV. A second peak
was observed at BE 397.4 eV, corresponding to WN. This peak
comprised most of the N at deposits grown at 400 °C and was
attributed to more extensive decomposition of the precursor
than was seen in deposits from lower temperature growths.
Likewise, the C 1s signal was deconvoluted into two distinct
High-resolution XPS was taken to determine the chemical
environment of the different elements by comparison to known signals (Figure 7c). Amorphous C is typically observed at a BE
data.[16] Deconvolution of the W 4f signal revealed two signals of 284.6 eV and can be observed at all growth temperatures.
for deposits grown at 400 °C, and three peaks at 200 and 300 °C This peak was more intense in deposits grown at 400 °C, which
(Figure 7a). For all deposits, a W 4f7/2 peak was observed with is consistent with increased solvent decomposition during
a binding energy (BE) of 33.2 eV with the corresponding higher temperature growth. A peak at BE 286.2 eV was also
W 4f5/2 peak at a BE of 35.3 eV. Peaks were also observed in all observed at all growth temperatures and was attributed to CNx
deposits with BEs of 35.4 eV, representing W 4f7/2, and 37.6 eV in the deposits. Interestingly, no peaks were observed for
for 4f5/2. For deposits grown at 300 °C and below, W 4f7/2 and carbidic C, which has a characteristic BE of 283.5 eV. Oxide was
4f5/2 peaks were observed with BEs of 34.2 and 36.4 eV, respec- observed in samples from all growth temperatures due to the
tively. The W 4f7/2 peaks at BEs of 33.2, 34.2, and 35.4 eV are rapid oxidation of WNxCy deposits when handling the samples
consistent with values reported for W in the +4, +5, and +6 in air prior to analysis. This oxygen peak was assigned as WO3
oxidation states, respectively.[16] The W 4f7/2 peaks at 35.4 and with a BE of 530.7 eV and used as the internal reference for
33.2 eV have previously been observed from deposits grown samples after sputtering (Figure 7d).
Figure 7. XPS spectra for primary peaks of (a)W 4f7/2 and 4f5/2, (b) N 1s, (c) C 1s, and (d) O 1s. Dashed lines are included for visual reference.
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ture quickly darkened to an amber color. This mixture was allowed
to stir for 10 min and then was filtered through a fine frit to yield
a yellow filtrate, which was concentrated under vacuum. The
mother liquor was removed and the pure product was dried under
Conclusions
In conclusion, several tungsten nitrido amido guanidinato
complexes of the type WN(NR2)[(NR′)2C(NR2)]2 have been pre-
pared and characterized. The thermal decomposition of
WN(NMe2)[(NiPr)2C(NMe2)]2 (1) was studied and was found to
be consistent with its performance as a viable precursor for the
deposition of WNxCy thin films.
1
vacuum, yielding 2.9 g (5.0 mmol, 69 %) of 1 as yellow crystals. H
NMR (500 MHz, C6D6): δ = 1.03 [d, 3 H, CH(CH3)2], 1.16 [d, 3 H,
CH(CH3)2], 1.18 [d, 3 H, CH(CH3)2], 1.18 [d, 3 H, CH(CH3)2], 1.37 [d, 3
H, CH(CH3)2], 1.39 [d, 3 H, CH(CH3)2], 1.63 [d, 3 H, CH(CH3)2], 2.07 [d,
3 H, CH(CH3)2], 2.48 [s, 6 H, CN(CH3)2], 2.53 [s, 6 H, CN(CH3)2], 3.60
[sept, 1 H, CH(CH3)2], 3.71 [s, 3 H, WN(CH3)CH3], 3.89 [sept, 1 H,
CH(CH3)2], 4.10 [sept, 1 H, CH(CH3)2], 4.12 [sept, 1 H, CH(CH3)2], 4.82
[s, 3 H, WN(CH3)CH3] ppm. 13C NMR (C6D6, 151 MHz): 22.9, 24.1,
24.6, 25.1, 25.6, 25.7, 25.9, 27.8 [CH(CH3)2], 40.1 [CN(CH3)2], 46.6
[CH(CH3)2], 47.1 [CH(CH3)2], 47.5 [CH(CH3)2], 48.9 [WN(CH3)CH3],
50.8 [CH(CH3)2], 68.0 [WN(CH3)CH3], 166.2, 166.7 (N3C). 15N NMR
Experimental Section
General Procedures: All manipulations were performed under an
inert atmosphere of dry N2 using standard Schlenk and glovebox
techniques. [D6]Benzene and [D8]toluene were purchased from
Cambridge Isotope Laboratories, Inc., degassed, and stored over ac-
tivated 3 Å molecular sieves (15 %, w/v) for at least 24 h prior to
use. Heptane was dried and deoxygenated using an MBraun MB-
SPS solvent purification system and stored over activated 3 Å mo-
lecular sieves. Anhydrous pentane and N,N′-dicyclohexylcarbodi-
imide (DCC) were purchased from Sigma Aldrich and used as re-
ceived. The N,N′-diisopropylcarbodiimide (DIC) was purchased from
Sigma–Aldrich, degassed, and stored over activated 3 Å molecular
sieves (15 %, w/v) prior to use. Compound 4 was synthesized as
described previously.[6] 1H and 13C NMR spectra were recorded us-
ing Mercury 300 MHz spectrometers utilizing residual protons of
the deuterated solvents as reference peaks. Indirect detection spec-
tra for compounds 1 and 3 were run on a 3-RF channel 500 MHz
Varian Inova spectrometer equipped with a 5 mm indirect detection
probe with z-axis gradients. The chemical shifts were referenced to
(C6D5CD3, 51 MHz):
δ
=
139.2, 146.6, 183.2, 187.2
{W[(iPrN)2C(NMe2)]2}, 236.5 (WNMe2). 14N NMR (C6D6, 43 MHz): δ =
133, 181 {W[(iPrN)2C(NMe2)]2}, 237 (WNMe2), 753 (W≡ N) ppm. MS
(DART-TOF): calcd. for [M
20H46N8W (582.49): calcd. C 41.24, H 7.96, N 19.24; found C 40.83,
H 7.80, N 18.87.
+
H]+ 583.3428, found 583.3440.
C
WN(NMe2)[(CyN)2C(NMe2)]2 (3): Inside the glovebox, 2 (0.26 g,
0.77 mmol) was combined with 15 mL of pentane in a glass vial to
form a tan suspension. After agitating the mixture, DCC (0.43 g,
2.1 mmol) was added, and a color change to from tan to yellow
was observed. The reaction mixture was allowed to sit for 5 min
and then was filtered through a fine frit to yield a yellow filtrate,
which was transferred to a clean vial. The solution was concentrated
under vacuum and left in the glovebox freezer (–15 °C) overnight.
The mother liquor was removed and the pure product was dried
under vacuum to yield 0.23 g (0.32 mmol, 41 %) of 3 as yellow
crystals. 1H NMR (C6D6, 500 MHz): δ = 1.02–2.17 [m, 37 H, CH(CH2)5],
2.30 [m, 1 H, CH(CH2)5], 2.43 [m, 1 H, CH(CH2)5], 2.54 [s, 6 H,
CN(CH3)2], 2.61 [s, 6 H, CN(CH3)2] 3.26 [m, 1 H, CH(CH2)5], 3.42 [m, 1
H, CH(CH2)5], 3.21 [m, 1 H, CH(CH2)5], 3.53 [m, 1 H, CH(CH2)5], 3.70
[m, 1 H, CH(CH2)5], 3.77 [s, 3 H, WN(CH3)CH3], 4.87 [s, 3 H,
WN(CH3)CH3] ppm. 13C NMR (C6D6, 151 MHz): δ = 26.20, 26.31,
26.46, 26.54, 26.63, 26.66, 26.68, 26.92, 27.03, 27.43, 27.53, 33.34,
34.03, 35.30, 35.40, 35.44, 35.84, 36.48, 36.65, 38.79 [NCH(CH2)5],
40.24 [N2CN(CH3)2], 48.92 [WN(CH3)CH3], 55.50, 55.90, 56.85, 60.16
[NCH(CH2)5], 68.17 [WN(CH3)CH3], 166.28, 166.54 (N3C) ppm. MS
(DART-TOF): calcd. for [M + H]+ 743.4680, found 743.4695.
1
tetramethylsilane for H (all coupling values are 7 Hz, unless other-
wise specified) and 13C, and to liquid ammonia for 15N, using the Ξ
values from the IUPAC recommendations.[17] Some 13C and all 14N
NMR spectra were acquired using a Bruker Avance III 600 MHz spec-
trometer, using dissolved N2 as the reference; a more detailed ex-
perimental procedure is included in the Supporting Information.
Mass spectra of synthesized compounds were obtained with an
Agilent 6200 ESI-TOF mass spectrometer using the direct analysis in
real time time-of-flight (DART-TOF) mode of operation. Samples for
thermogravimetric analysis were prepared and sealed in crimped
40 μL aluminum sample pans inside an Ar atmosphere glovebox.
Thermogravimetric analyses were performed using a Mettler TGA/
sDTA 851e: the pans were pierced using a Mettler piercing kit and
heated at 10 °C/min from room temperature to 600 °C under an N2
atmosphere. Mass spectra of the condensed pyrolysis products
were obtained by GC/EI-MS using a ThermoScientific DSQ II mass
spectrometer and a ThermoScientific Trace GC Ultra gas chromato-
graph equipped with a Restek Corp. tabilwax-DA column. Elemental
analysis results were obtained from Robertson Microlit. Powder XRD
patterns of the deposited films were collected using a PANalytical
X′Pert3 Powder diffractometer. The surface morphologies of depos-
ited films were imaged using an FEI Nova NanoSEM 430 micro-
scope. The elemental compositions of deposited films were deter-
mined by XPS using an ULVAC-PHI XPS, and spectra were deconvo-
luted using the MultiPak software. Pretreatment of the films for XPS
involved sputtering for 2 min to remove surface contamination.
WN(NEt2)[(NiPr)2C(NEt2)]2 (5): Inside the glovebox, 4 (0.28 g,
0.70 mmol) was combined with 15 mL of pentane in a glass vial
to form an amber solution. After briefly agitating the mixture, DIC
(0.22 mL, 1.40 mmol) was added. No color change was observed.
The reaction mixture was allowed to sit for 5 min and then was
filtered through a fine frit to yield an amber filtrate, which was
transferred to a clean vial. The solution was concentrated under
vacuum and left in the glovebox freezer (–15 °C) overnight. The
mother liquor was removed and the pure product was dried under
vacuum, providing 0.1609 g (0.24 mmol, 35 %) of 5 as amber crys-
1
tals. H NMR (C6D6, 500 MHz): δ = 0.91 (t, 6 H, CH2CH3) 0.98 (t, 3 H,
CH2CH3), 1.03 [d, 3 H, CH(CH3)2], 1.16 [d, 3 H, CH(CH3)2], 1.17 [d, 3
H, CH(CH3)2], 1.24 [d, 3 H, CH(CH3)2], 1.42 [d, 3 H, CH(CH3)2], 1.50 (t,
3 H, CH2CH3), 1.51 [d, 3 H CH(CH3)2], 1.68 [d, 3 H CH(CH3)2], 2.06 [d,
3 H CH(CH3)2], 2.84, 2.86, 2.91, 3.05 [q, 8 H, CN(CH2CH3)2], 3.54 [q, 1
H, WNC(H)HCH3], 3.60 [sept, 1 H, CH(CH3)2], 3.85 [sept, 1 H,
CH(CH3)2], 4.14 [sept, 1 H, CH(CH3)2], 4.16 [sept, 1 H, CH(CH3)2], 4.88
[q, 1 H, WNC(H)HCH3], 4.96 [q, 1 H, WNC(H)HCH3], 5.61 [q, 1 H,
WNC(H)HCH3] ppm. 13C NMR (C6D6, 75 MHz): δ = 13.8, 14.1, 14.2,
15.8, 16.9 (CH2CH3) 23.2, 23.8, 24.8, 24.9, 25.2, 25.6, 25.7, 29.0
WN(NMe2)3 (2): Compound 2 was synthesized as previously re-
ported and characterized by comparison to literature data.[5f] 14
N
NMR (C6D6, 43 MHz): δ = 159 (W–NMe2), 760 (W≡ N).
WN(NMe2)[(iPrN)2C(NMe2)]2 (1): Inside the glovebox, 2 (2.4 g,
7.3 mmol) was combined with 200 mL of pentane in a 250 mL
Schlenk flask to form a light tan suspension. To this suspension, DIC
(2.4 mL, 15 mmol) was added in a single aliquot. The reaction mix- [CH(CH3)2], 41.6, 43.27, 43.5 [CN(CH2CH3)2], 46.9 [CH(CH3)2], 47.0
Eur. J. Inorg. Chem. 2018, 46–53
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[CH(CH3)2], 48.1 [CH(CH3)2], 49.7 (WNCH2CH3), 50.2 [CH(CH3)2], 67.3
(WNCH2CH3), 166.9, 167.6 (N3C) ppm. MS (DART-TOF): calcd. for [M
+ H]+ 667.4367, found 667.4342.
F2 rather than F values. R1 is calculated to provide a reference to
the conventional R value but its function is not minimized.
CCDC 1563665 (for 1) contains the supplementary crystallographic
data for this paper. These data can be obtained free of charge from
The Cambridge Crystallographic Data Centre.
WN(NEt2)[(CyN)2C(NEt2)]2 (6): Inside the glovebox, 4 (0.22 g,
0.53 mmol) was combined with 15 mL of pentane in a glass vial to
form an amber solution. After briefly agitating the mixture, DCC
(0.33 g, 1.6 mmol) was added. The color of the solution lightened
slightly after addition. The reaction mixture was allowed to sit for
5 min and then was filtered through a fine frit. The resulting amber
filtrate was transferred to a clean glass vial. The solution was con-
centrated under vacuum and left in the glovebox freezer (–15 °C)
overnight. The mother liquor was removed and the pure product
was dried under vacuum, providing 0.25 g (0.30 mmol, 56 %) of 6
as yellow crystals. 1H NMR (C6D6, 500 MHz): δ = 0.87 (t, 3 H, CH2CH3),
0.97 (t, 9 H, CH2CH3), 1.04 (t, 3 H, CH2CH3), 1.52–1.20 [m, 17 H,
NCH(CH2)5], 1.55 (t, 3 H, CH2CH3), 2.15–1.58 [m, 19 H, NCH(CH2)5],
Acknowledgments
Financial support of this work was provided by the University
of Florida as matching funds for the UF Beckman Scholars Pro-
gram. A portion of the work was performed in the University
of Florida's McKnight Brain Institute at the National High Mag-
netic Field Laboratory's AMRIS Facility, which is supported by
National Science Foundation Cooperative Agreement No. DMR-
1157490 and the State of Florida. The magnetic resonance in-
2.33 [m, 1 H, NCH(CH2)5], 2.47 [m, 1 H, NCH(CH2)5], 2.73 [m, 1 H, strumentation was supported in part by an NIH award,
NCH(CH2)5], 2.92, 3.00, 3.02, 3.17 [q, 8 H, CN(CH2CH3)2], 3.23 [m, 1
H, NCH(CH2)5], 3.45 [m, 1 H, NCH(CH2)5], 3.45 [m, 1 H, NCH(CH2)5],
3.60 [q, 1 H, WNC(H)HCH3], 3.74 [m, 2 H, NCH(CH2)5], 4.91 [q, 1 H,
S10RR031637. We thank Prof. Aaron Odom for helpful discus-
sion on 14N NMR spectroscopy. K. A. A. wishes to acknowledge
the National Science Foundation and the University of Florida
for funding of the purchase of the X-ray equipment. The Major
Analytical Instrumentation Center of the Engineering Depart-
ment at the University of Florida for provided the materials
characterization equipment. Thermogravimetric analysis of 1
was performed by Roman Korotkov (Arkema, Inc.).
WNC(H)HCH3], 5.04 [q,
1 H, WNC(H)HCH3], 5.66 [q, 1 H,
WNC(H)HCH3] ppm. 13C NMR (C6D6, 75 MHz): δ = 13.8, 14.1, 14.2,
15.8, 16.9 (CH2CH3), 23.2, 23.8, 24.8, 24.9, 25.2, 25.6, 25.7, 29.0
[CH(CH3)2], 41.6, 43.27, 43.5 [CN(CH2CH3)2], 46.9 [CH(CH3)2], 47.0
[CH(CH3)2], 48.1 [CH(CH3)2], 49.7 (WNCH2CH3), 50.2 [CH(CH3)2], 67.3
(WNCH2CH3), 166.9, 167.6 (N3C) ppm. MS (DART-TOF): calcd. for [M
+ H]+ 827.5619, found 827.5591.
Keywords: Chemical vapor deposition · Inorganic
synthesis · Precursor design · Thin films · Tungsten
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temperature. Precursor 1 was dissolved in 20 mL of heptane at a
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Received: October 9, 2017
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