Group 11 amidinates and guanidinates: Potential precursors for vapour deposition

Article abstract of DOI:10.1002/ejic.201100262

Several guanidinates of copper and silver, as well as amidinates and guanidinates of gold were synthesized as potential precursors for vapour deposition methods. These compounds were found to be dimers in the case of copper and gold, and trimers in the case of silver. The copper compounds showed good thermal and photostability, and were isolable by sublimation. The silver compounds proved to be very reactive to both heat and light, and were found to deposit silver metal when heated, suggesting that these sensitive compounds might be used as single source precursors. The gold compounds were found to exhibit some heat and light sensitivity, but were much more stable than their silver counterparts. Specifically, [Au(NiPr)₂NMe₂] ₂ (8) was found to be sublimable at 85 °C and 20 mTorr, and deposited gold metal under higher temperatures. These metal-depositing thermal reactions were thought to abstract a hydrogen from the guanidinate ligand, which acts as the reducing agent. Interestingly, the gold amidinate compounds were found to produce diisopropylcarbodiimide when heated, suggesting that these compounds deinsert carbodiimide rather than abstract a hydrogen atom from the ligand.

Full text of DOI:10.1002/ejic.201100262

FULL PAPER
DOI: 10.1002/ejic.201100262
Group 11 Amidinates and Guanidinates: Potential Precursors for Vapour
Deposition
Todd J. J. Whitehorne,[a] Jason P. Coyle,[b] Ahsan Mahmood,[b] Wesley H. Monillas,[c]
Glenn P. A. Yap,[c] and Seán T. Barry*[b]
Keywords: Thermal reaction mechanism / Gold / Silver / Copper / N ligands / Chemical vapor deposition
Several guanidinates of copper and silver, as well as amidin-
ates and guanidinates of gold were synthesized as potential
precursors for vapour deposition methods. These compounds
were found to be dimers in the case of copper and gold, and
trimers in the case of silver. The copper compounds showed
good thermal and photostability, and were isolable by subli-
mation. The silver compounds proved to be very reactive to
both heat and light, and were found to deposit silver metal
when heated, suggesting that these sensitive compounds
but were much more stable than their silver counterparts.
Specifically, [Au(NiPr)2NMe2]2 (8) was found to be sublim-
able at 85 °C and 20 mTorr, and deposited gold metal under
higher temperatures. These metal-depositing thermal reac-
tions were thought to abstract a hydrogen from the guanidin-
ate ligand, which acts as the reducing agent. Interestingly,
the gold amidinate compounds were found to produce di-
isopropylcarbodiimide when heated, suggesting that these
compounds deinsert carbodiimide rather than abstract a hy-
might be used as single source precursors. The gold com- drogen atom from the ligand.
pounds were found to exhibit some heat and light sensitivity,
mal studies of the group 11 guanidinato species, as well as
some novel amidinatogold(I) compounds.
Introduction
Group 11 compounds are interesting as potential precur-
sors for chemical vapour deposition (CVD) or atomic layer
deposition (ALD) of metal films. Thin films of copper are
under intense scrutiny as an interconnect material for
microelectronics because of copper’s low bulk resistivity
and excellent resistance to electromigration.[1] Silver and
gold have strong surface plasmons, and thus can be em-
ployed in biosensors.[2] Amidinates and guanidinates are
very promising ligands for these metal centres.[3] Our recent
research interests have included a CVD process for copper
metal from a guanidinatocopper(I) dimer,[4] and have exten-
sively explored the thermal decomposition mechanism by
infrared spectroscopy (employing matrix isolation), time-of-
flight mass spectrometry, and calculational modelling.[5]
Amidinatocopper(I) dimers were first reported in 1988,[6]
and used in ALD of copper films in 2006.[7] This same
group reported a silver amidinate compound with a dimer-
trimer equilibrium structure in 2003, but did not detail any
thermal chemistry.[8] Gold amidinate complexes have pre-
viously been reported, although thermal data were not in-
cluded.[9] We have thus undertaken the synthesis and ther-
It should also be generally noted that, although the cop-
per compounds are stable with respect to heat and light, the
analogous silver and gold compounds can show significant
decompositions under these conditions.
Results and Discussion
Generally the syntheses of these group 11 compounds
were facile by salt metathesis of amidinate or guanidinate
ligands with a metal(I) chloride reactant, resulting in a vari-
ety of group 11 amidinates and guanidinates (Table 1). The
Table 1. The compounds reported in this article.
Metal
X
R
n
1
2
3
4
5
6
7
8
9
10
Cu
Cu
Ag
Ag
Ag
Au
Au
Au
Au
Au
NR2
NR2
NR2
NR2
NR2
NR2
NR2
NR2
R
Et
2
2
3
3
3
2
2
2
2
2
iPr
Me
iPr
Et
iPr
Et
Me
Me
nBu
[a] Départment of Chemistry, University of Montreal,
C.P. 6128, Succursale Centre-ville, Montreal (QC) H3C 3J7,
Canada
[b] Department of Chemistry, Carleton University,
1125 Colonel By Drive, Ottawa (ON) K1S 5B6, Canada
[c] Department of Chemistry and Biochemistry, University of
Delaware,
R
Newark, DE 19716, USA
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Group 11 Amidinates and Guanidinates
yields were varied, ranging from 25% for [Ag(NiPr)2- Table 3. Selected bond lengths and angles for compounds 1 and 2.
CNiPr2]2 (4) to 95% for the analogous gold compound 6.
Selected bond lengths [Å]
For copper (1 and 2) and silver (3–5), the syntheses gen-
erally occurred in a straightforward manner, and were car-
ried out by generating the ligand in situ by insertion of an
1
2
Cu–N1
Cu–N3
1.872(3)
1.878(3)
2.4294(8)
1.405(6)
1.394(6)
1.335(3)
1.341(3)
Cu–N1
Cu–N2
Cu–CuA
N3–C1
1.8818(17)
1.8854(16)
2.4209(8)
1.445(3)
amido into diisopropylcarbodiimide (CDI). This could be Cu–CuA
N2–C1
done in a one pot synthesis by stoichiometric addition of
N4–C7
copper(I) chloride to the generated ligand. The copper spe-
N1–C1
N1–C1
N2–C1
1.326(3)
1.331(3)
cies are particularly robust with respect to reaction condi-
N3–C7
tions.
Selected bond angles [°]
In the case of the gold compounds 6–10, it was necessary
to isolate and purify the amidinato or guanidinato ligand
as the alkali salt. We suspect that a slight excess of alkyllith-
ium (from the ligand formation) caused reduction of the
gold(I) starting material. Suspending the purified ligand
salt in the reaction solvent and adding gold chloride at re-
duced temperatures vastly improved the yields of these
compounds.
1
2
N1–C1–N2
N1–C1–N1A
N3–C7–N3A
120.46(17)
120.1(4)
120.9(4)
N1–Cu–N2
N1–Cu–N3
176.22(7)
175.78(12)
Sum of angles [°]
1
2
N1
N3
N2
N4
358.9
358.2
360
N1
N2
N3
359.8
358.8
355.9
A previous report showed the copper guanidinates to be
dimers sharing bridging ligands in the solid state.[4] The sin-
gle crystal data presented herein confirmed the dimeric
360.1
Torsion angles [°]
1
structures of 1 and 2, which was consistent with 1H and 13
C
2
NMR spectra. Compounds 1 and 2 (Table 2 and Table 3,
Figure 1) have copper···copper separations comparable to N3A
N1–N1A–N3–
N1–N2A–N2–
N1A
C11–N3–C1–N2 71.3
22.4
0
reported compounds.[4] In each case, the metallocylic N–C–
N angle of the ligand is close to 120°, and the sum of angles
for the chelate nitrogen atoms are close to planarity, dem-
onstrating full participation in π bond resonance. The sim-
ilar Cu–N bond lengths for both compounds in the chelat-
ing amido moieties are also consistent with bond resonance
and electron delocalization.
C11–N4–C7–N3
C5–N2–C1–N1
52.8
56.7
Table 2. Selected crystal data and structure refinement parameters
for compounds 1, 2, and 3.
C22H48Cu2N6 (1) C26H56Cu2N6 (2) C27H60Ag3N9 (3)
FW
T (K)
523.74
120
579.85
120
834.45
200
λ [Å] (Mo-Kα)
Crystal system
Space group
a [Å]
b [Å]
c [Å]
0.71073
orthorhombic
Pbcn
10.459
21.77
11.93
90
0.71073
orthorhombic
Pbca
10.02
11.77
0.71073
triclinic
P1
10.36
11.86
¯
25.3
90
15.30
98.86
Figure 1. Single crystal X-ray structures for compounds 1 and 2
respectively. Hydrogen atoms were omitted for clarity, and the ther-
mal ellipses are shown at 30%.
α [°]
β [°]
90
90
2717
4
1.280
90
90
2987
4
91.26
105.5
1786
2
1.552
1.658
R1 = 0.0505
wR2 = 0.0741
γ [°]
V [Å3]
Z
atom) and thus have a lower melting point. We have pre-
viously analysed copper guanidinates using this concept.[4]
ρ/g/cm3
1.289
Abs. coeff. [mm–1] 1.584
0.6608
R1 = 0.0361
wR2 = 0.0885
R indices
R1 = 0.0669
wR2 = 0.1055
[IϾ2σ(I)][a]
[a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = [Σw(|Fo| – |Fc|)2/Σw|Fo|2]1/2
.
The “core twist” is defined as the degree the dimer is
twisted as measured across the chelating nitrogen atoms in
a “Z” pattern (see Scheme 1). A dimer of higher core twist
would have participation of the exocyclic amide moiety in
Scheme 1. Torsion angle of the core as measured in a “Z” pattern
π resonance (demonstrated by greater planarization of this across the chelating groups.
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S. T. Barry et al.
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Compound 1 displays a higher core twist than 2 (22° and Table 4. Selected bond lengths and angles for compound 3.
0°). The bond length between the bridgehead carbon of the
guanidinate moiety and the exocyclic nitrogen is signifi-
cantly shorter in 1 than in 2. The chelating nitrogen atoms
are more pyramidalized in 1, while the exocylic nitrogen
Selected bond lengths [Å]
Ag1–N1
Ag1–N8
Ag2–N2
2.098(3)
2.094(3)
2.084(3)
Ag2–N4
Ag3–N5
Ag3–N7
2.091(3)
2.102(2)
2.117(2)
3.2173(5)
atom is more pyramidalized in 2. These observations sug- Ag1–Ag2
2.9545(5) Ag3–Ag1
2.9896(5)
Ag2–Ag3
gest that the exocyclic amide in 1 is participating in π bond-
N1–C4
ing to a greater degree than in 2. Perhaps these structural
N2–C4
1.338(4)
1.336(4)
1.402(4)
1.329(4)
1.338(4)
N6–C13
N7–C22
N8–C22
N9–C22
1.393(4)
1.316(4)
1.353(4)
1.385(4)
differences arise from the steric crowding contributed by the
N3–C4
larger alkyl groups at the exocyclic amido group, causing
further out-of-plane bending of the ligand for 2 (71.3°) than
for 1 (53–58 °C) and thereby frustrating π interaction. The
observed melting points of 1 and 2 adhere to the previously
reported melting point trend.[4]
N4–C13
N5–C13
Selected bond angles [°]
N1–Ag1–N8
N2–Ag2–N4
164.41(10) N1–C4–N2
168.87(10) N4–C13–N5
163.08(10) N7–C22–N8
120.4(3)
120.3(3)
118.8(3)
Amidinatosilver species have previously shown a dimer- N5–Ag3–N7
1
trimer equilibrium in solution (by H NMR), with these
species cocrystallizing in the solid phase.[8] In contrast,
compounds 3–5 have spectra analogous to the copper spe-
cies, suggesting that there was only one oligomer in solution
in every case on the NMR time-frame. Single crystal struc-
tural determination determined compound 3 to be a trimer
(Figure 2, Tables 2 and 4), and it is reasonable to suppose
that all of the reported silver compounds are trimers, since
Sum of angles [°]
N1
N2
N3
N4
N5
359.2
359.8
359.8
359.9
359.3
N6
N7
N8
N9
359.6
359.9
359.8
360.0
Torsion angles [°]
Ag2–N4–N5–Ag3 44.9
Ag3–N7–N8–Ag1
62.7
the larger metallocylic N–C–N angle of guanidinate ligands Ag1–N1–N2–Ag2 41.8
(compared to the range for amidinates) would accommo-
date these higher order oligomers.
has a smaller bite angle but much larger torsion angle (con-
sidered through the silver and nitrogen centres) than the
other two ligands.
The three ligands are each planar, and the Ag–N and
cyclic C–N bond lengths are comparable to the amidinato-
silver trimer,[8] while the exocyclic N–C bond lengths were
all longer than the chelate N–C bond lengths. This suggests
that the exocyclic nitrogens do not participate fully in the π
systems of the ligands in this structure.
Since the gold(I) ion is smaller than the silver(I) ion, it
is reasonable to expect that gold might more easily form
dimers instead of trimers in the solid phase. The gold com-
Table 5. Selected crystal data and structure refinement parameters
for the gold compounds.
C18H40Au2N6 (8) C16H34Au2N4 (9) C22H46Au2N4 (10)
Figure 2. Single crystal X-ray structures for compound 3. Hydro-
gen atoms were omitted for clarity, and the thermal ellipses are
shown at 30%.
FW
T [K]
734.49
200
676.40
120
760.56
120
λ [Å] (Mo-Kα)
Crystal system
Space group
a [Å]
b [Å]
c [Å]
α [°]
β [°]
γ [°]
V [Å3]
Z
0.71073
monoclinic
C2/c
19.48
11.35
12.08
90
113.21
90
2454
4
0.71073
monoclinic
C2/c
25.98
11.23
18.72
90
131.98
90
4059
0.71073
triclinic
P1
7.851
8.88
The structure of compound 3 (Figure 2) shows an ap-
proximately isosceles triangular arrangement of the silver
atoms. The metal-metal distances for Ag1–Ag2 or Ag2–Ag3
were comparable with the amidinate trimer,[8] while Ag1
and Ag3 were significantly further apart. This distortion
was due to the arrangement of the ligands. Consider a plane
described by the silver centres and C22 (which is coplanar
with the silver triangle within ca. 6°): the plane of the ligand
containing C22 intersects the silver plane at an angle of
67.5°, differentiating this ligand from the other two ligands
in the complex. The ligands containing the C4 and C13
quaternary carbons are wholly above and below the plane
¯
10.21
104.22
102.47
105.08
635
8
1
ρ (calcd.) [g/cm3] 1.988
Abs. coeff. [mm–1
R indices
[I Ͼ2s(I)][a]
2.214
1.987
11.54
R1 = 0.0325
wR2 = 0.0681
]
11.96
R1 = 0.0184
wR2 = 0.0500
14.443
R1 = 0.0276
wR2 = 0.0507
of the silver atoms, respectively. The C22-containing ligand [a] R1 = Σ||Fo| – |Fc||/Σ|Fo|; wR2 = [Σw(|Fo| – |Fc|)2/Σw|Fo|2]1/2
.
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Group 11 Amidinates and Guanidinates
Table 6. Selected bond lengths and angles for compounds 8, 9 and 10.
8
9
10
Selected bond lengths [Å]
Au1–N1
Au1–N2
Au1–Au1A
N1-C4
N2–C4
N3–C4
2.041(2)
2.038(2)
2.6559(6)
1.337(3)
1.337(4)
1.404(3)
Au1–N1
Au1–N2
Au1–Au1A
N1–C1
2.044(3)
2.037(3)
2.6529(5)
1.328(5)
1.346(5)
Au1–N1
Au1–N2
Au1–Au1A
N1–C4
2.044(5)
2.044(5)
2.6436(6)
1.339(7)
1.346(8)
N2–C1
N2–C4
Selected bond angles [°]
N1–Au1–N2
N1–C4–N2
170.64(9)
123.8(2)
N1–Au1–N2
N1–C1–N2
171.15(13)
122.6(4)
N1–Au1–N2
N1–C4–N2
171.63(19)
121.8(5)
Sum of angles [°]
N1
N2
N3
358.2
358.2
359.9
N1
N2
359.3
359.8
N1
N2
359.8
359.6
Torsion angles [°]
N1–N2–N1A–N2A
0
N1–N2–N2A–N1A
0
N1–N2–N2A–N1A
0
Figure 3. Single crystal X-ray structures for compounds 8, 9 and 10, respectively. Hydrogen atoms were omitted for clarity, and the
thermal ellipses are shown at 30%.
pounds show NMR spectra that indicate that they each shows itself to be very planar, but the chelating nitrogens
form a single, symmetric product, in general agreement with are only slightly deviated from planarity, suggesting the π
the dimer formation seen in the case of the copper ana- system is shared with the exocyclic position. However, the
logues. This is also typical of previously-reported similar longer C4–N3 bond length suggests that the exocyclic nitro-
gold compounds.[9] Again, single-crystal X-ray structures of gen does not participate in the π system as fully as the che-
8–10 also confirm these compounds to be dimers (Tables 5 late nitrogen atoms. The fact that the C–N bond lengths in
and 6, Figure 3).
the metallocycle of 8 are similar to those of 9 and 10, and
Considering these three structures, the bite angles on the that the core was planar in all cases corroborates this con-
bridging ligand are in the range 122–124°, with the guanidi- clusion.
nato adopting the largest bite angle, as expected. The Au–
The thermolysis studies were quite encouraging to con-
N bonds are all very similar, around 2.04 Å, which agrees sider these compounds as precursors for vapour deposition
with known gold guanidinate compounds.[9] The Au–Au of thin metal films. Thermolysis produced the reduced
separations are similar for all three cases with a slight devia- metal either as a deposited mirror or as finely divided metal
tion from a linear geometry at the metal centres. The nitro- particles for every compound reported herein. In the ther-
gen atoms in 9 and 10 show very planar geometries, demon- molysis studies, two general decomposition pathways are
strating the resonance of the π bond between the chelating known for compounds of this nature: CDI deinsertion and
nitrogen atoms. The exocyclic nitrogen in compound 8 also β-hydrogen elimination (Scheme 2).[5]
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S. T. Barry et al.
FULL PAPER
residual mass very close to the percent mass of the metal in
the compound, visual inspection determined there to be no
metal left at the end of this experiment, and that the resid-
ual was coincidentally close to 21.9% (Table 7).
This contrasted with the silver (3–5) and the gold guanid-
inate species (6–8), which showed reduced metal in the TG
pans at the conclusion of the experiment. This suggests that
these compounds underwent a redox process whereby the
ligand was oxidised, and the metal was reduced. For com-
pounds 3–7, there was likely very little or no volatilization
during this reaction, as their residual masses matched very
closely to the percent mass of the metal in the compound.
This suggests that these compounds were quantitatively re-
Scheme 2. Different decomposition pathways of diisopropyl amid-
inates and guanidinates. a) carbodiimide deinsertion, and b) β-hy-
drogen elimination.
With respect to the thermal decomposition pathways, duced. In contrast, compound 8 showed a very low residual
there are some general considerations that require illumina- mass (although gold metal was obviously left behind). This
tion. Firstly, the products of β-hydrogen elimination can suggests that the material mostly sublimed, and the deriva-
quite easily generate free guanidine when the transient tive TG curve did indeed show a characteristic shape for
“metal hydride” reacts with an intact metal guanidinate spe- sublimation, where there is an exponential ascent and rapid,
cies, which would result in reduced metal. Secondly, guan- almost asymptotic descent (Figure 4). This combination of
idines themselves can undergo deinsertion to produce an volatility and reactivity suggests that compound 8 will be a
amine and carbodiimide, and so this decomposition had to suitable precursor for the vapour deposition of gold, and
be investigated for the ligands used in this study. For exam- this research is presently being undertaken.
ple, a thermolysis experiment of tetraisopropylguanidine in
1
C6D6 in an NMR tube at 120 °C showed a H spectrum
that contained peaks characteristic of diisopropyl CDI (i.e.,
a doublet at δ = 1.04 ppm and a septet at δ = 3.33 ppm) as
well as peaks characteristic of diisopropylamine. The same
reactivity was found in the dimethyl analogue at 155 °C.
This can confuse the decomposition pathway for a given
compound, and careful consideration was necessary to de-
termine which pathway was followed.
The copper dimers 1 and 2 and the gold compound 8
were sufficiently thermally stable to allow sublimation,
while the remaining compounds could not be isolated by
sublimation, even when the sublimation was performed in
the absence of light (Table 7). In the case of 3–7, 9 and 10,
Figure 4. The thermogravimetric curve (black) and its derivative
curve (grey) for compound 8.
attempted sublimation resulted in a metallic mirror in the
sublimation pot.
The fact that compounds 3–5, 7 and 8 undergo reduction
upon heating suggests that the ligand system might be be-
coming oxidised. This in turn suggests that the primary
thermal reaction pathway for these compounds is either via
CDI elimination and subsequent reduction of the copper by
the transient amido moiety (Scheme 2, a) or by β-hydrogen
elimination followed by elimination of the metal hydride
(Scheme 2, b). Further thermolysis was studied by heating
these compounds in a deuterated benzene solution in sealed
NMR tubes, and monitoring thermal by-products by 1H
NMR spectroscopy. In every case, the free parent guanidine
was found to evolve when the thermolysis was allowed to
run at 120 °C overnight. Production of free guanidine im-
plies the production of an “oxidised” guanidine species as
a hydrogen source (Scheme 2). No evidence of this com-
Table 7. The thermal parameters for 1–10.
Sublimation temp.
[°C] @ p [mTorr]
Onset of thermolysis[a] Residual mass[b]
[°C]
[%]
1
2
3
4
5
6
7
8
9
10
130 @ 85
130 @ 80
78.1
19.1 (24.3)
21.4 (21.9)
41.0 (37.2)
33.8 (32.3)
36.0 (35.2)
46.0 (47.5)
50.0 (49.8)
4.0 (53.6)
87.5
114.9
58.4
99.4
25.5
100.5
52.0
85 @ 20
79.5
132.3
14.2 (58.2)
54.1 (51.8)
[a] The onset of thermolysis reported at 99.5% mass from thermo-
gravimetric analysis. [b] The number in brackets is the percent mass
of metal in the compound.
1
pound was found in the H NMR spectra, although ther-
molysis also resulted in a flocculent solid that might contain
The copper compounds show straight-forward thermal the oxidised guanidine species.
chemistry, with their thermogravimetric (TG) analysis
When compound 6 was heated at 120 °C for 2 h, di-
curves demonstrating a combination of volatilization and isopropylcarbodiimide and diisopropylamine were both evi-
thermal decomposition. Although compound 2 showed a dent in the thermolysis NMR, similar to what is observed
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Group 11 Amidinates and Guanidinates
for the thermolysis of the parent guanidine under similar appeared to undergo thermolysis by deinsertion of CDI,
conditions. Thus, it is possible that the free guanidine was which was unexpected given that the amidinate ligand must
produced (as above), and it subsequently underwent ther- cleave a C–C bond to do so.
molysis to produce the carbodiimide. However, this does
not rule out carbodiimide deinsertion.
The mechanism of these thermolyses require further in-
vestigation, and a careful study similar to our previous
Compounds 9 and 10 both showed CDI as a thermolysis work with the (dimethylguanidinato)copper is underway.[4]
1
by-product by H NMR when heated overnight at 120 °C
in the conditions described above. However, the parent
amidines showed no inclination to produce the carbodi-
Experimental Section
imide under these conditions. This suggests that the gold
amidinate compounds themselves thermally decomposed by inert atmosphere drybox. Solvents were degassed and dried on an
General: All manipulations were performed in an MBraun Unilab
MBraun solvent purification system. These were stored over acti-
vated 4A sieves. The chemicals: 1,3-diisopropyl carbodiimide, di-
ethylamine, diisopropylamine, butyllithium (2.5 m in hexanes),
methyllithium (1.6 m in diethyl ether), copper(I) chloride, silver(I)
chloride, and lithium dimethyl amide were purchased from Aldrich
Chemical Co. and used as received. The gold(I) starting material
AuCl·THT was synthesised by literature methods.[10] The com-
pounds Li[(iPrN)2CN(iPr)2], Li[(iPrN)2CN(Et)2], Li[(iPrN)2CN-
(Me)2], Li[(iPrN)2CMe], and Li[(iPrN)CnBu] were prepared by lit-
erature methods.[11] Nuclear Magnetic Resonance was done on
CDI deinsertion (Scheme 2, a). This was somewhat surpris-
ing, because these ligands have to undergo the cleavage of
a much stronger C–C bond in order for CDI to deinsert, as
compared to guanidinate ligands wherein a weaker N–C
bond would break. However, the TG curve for compound
9 showed an inflection at 64.6%, which matches closely to
the percent mass loss of CDI from this compound (Fig-
ure 5). The symmetry of the derivative curve features
showed these events to be decomposition or thermal reac-
tions, rather than straightforward sublimation. Thus, it is 300 MHz Avance 3 and 400 MHz Bruker AMX. Mass spectra were
obtained using the electron impact method on a VG ZAB-2HF
triple-focusing spectrometer. Guelph Chemical Laboratories per-
formed combustion analysis. Thermogravimetric analysis was per-
formed on a TA Instruments Q50 apparatus located in an MBraun
Labmaster 130 Dry box under a nitrogen atmosphere.
likely that 9 is undergoing sublimation and decomposition
in the same temperature range.
[Cu(NiPr)2CNEt2]2 (1): In a 50 mL flask, HNEt2 (0.0.283 g,
3.87 mmol) was diluted in 20 mL of ethyl ether. Butyllithium
(1.53 mL, 3.82 mmol) was added dropwise to the amine solution
and stirred for 1.5 h. Diisopropylcarbodiimide (0.482 g, 3.82 mmol)
was diluted in 5 mL of ethyl ether and added dropwise to the solu-
tion of lithiated amine. The solution was stirred for 3 h during
which time a colourless precipitate formed. Copper(I) chloride
(0.391 g, 3.95 mmol) was added and the mixture was stirred for
18 h, after which the cloudy solution was filtered to afford a light
green solid and a slightly pale yellow solution. The filtrate was
evacuated to dryness to afford an off-white solid of 1 (0.923 g,
Figure 5. The thermogravimetric curve (black) and its derivative
curve (grey) for compound 9.
92.3% crude yield). The solid was purified by sublimation (Tsub
=
130 °C, 85 mTorr) and collected as clear, colourless crystals
(0.811 g, 81.1%); m.p. 154 °C. C22H48Cu2N6 (523.75): calcd. C
50.45, H 9.24, N 16.05; found C 50.77, H 9.26, N 16.22. Mass
spectra m/z: 524 M+. 1H NMR [300 MHz, C6D6, 3J(1H,1H) =
7.1 Hz for ethyl; 6.2 Hz for isopropyl]: δ = 3.50 [sept, 4 H,
CH(CH3)2], δ = 2.94 [q, 8 H, CH2CH3], δ = 1.30 [d, 24 H, CH-
(CH3)2], δ = 0.89 [t, 12 H, CH2CH3] ppm. 13C{1H} NMR
(75 MHz, C6D6): δ = 170.9 [NCN], δ = 48.5 [CH(CH3)2], δ = 43.7,
[CH2CH3], δ = 27.57 [CH(CH3)2], δ = 13.4 [CH2CH3] ppm.
Conclusions
Guanidinato complexes of copper and silver gold were
shown to be potential precursors for chemical vapour depo-
sition of these metals. Both the silver and gold compounds
were found to produce the reduced metal upon thermolysis
(and photolysis in the case of silver), with the ligand acting
as a reducing agent through β-hydrogen elimination. This
[Cu(NiPr)2CNiPr2]2 (2): Compound 2 was prepared in a analogous
manner as compound 1, substituting HNiPr2 for HNEt2 (0.359 g,
promising chemistry opens the door to single-source silver 3.55 mmol) and using 1.38 mL of 2.5 m BuLi. Crude yield was
89.8%. Compound 2 was purified by sublimation (Tsub = 130 °C,
80 mTorr) and collected as clear, colourless crystals of 2 (0.630 g,
63.0%); m.p. 157 °C. C26H56Cu2N6 (579.86): calcd. C 53.85, H
9.73, N 14.49; found C 53.85, H 9.45, N 14.82. Mass spectra m/e:
580 M+. 1H NMR [300 MHz, C6D6, 3J(1H,1H) = 6.5 Hz for exocy-
clic isopropyl; 6.2 Hz for metallocyclic isopropyl]: δ = 3.73 {sept, 4
H, N[CH(CH3)2]2}, δ = 3.33 [sept, 4 H, NCH(CH3)2], δ = 1.31 {d,
24 H, N[CH(CH3)2]2}, δ = 1.12 [d, 24 H, NCH(CH3)2] ppm.
13C{1H} NMR (75 MHz, C6D6): δ = 168.3 [NCN], δ = 48.4
[NCH(CH3)2], δ = 47.4 {N[CH(CH3)2]2}, δ = 27.6 {N[CH-
and gold deposition processes.
The preferred oligomeric species appears to be dimers in
the case of copper and gold, and trimers in the case of sil-
ver, which nicely follows the periodic trend in atomic radii.
The silver trimer showed an interesting isosceles arrange-
ment of the silver centres, which can be attributed to the
peculiar ligand bonding arrangement.
Compound 8 showed the best promise as a gold precur-
sor, subliming well at 85 °C while also producing gold metal
at higher temperatures. The amidinates 9 and 10 of gold (CH3)2]2}, δ = 23.13 [NCH(CH3)2] ppm.
Eur. J. Inorg. Chem. 2011, 3240–3247
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3245

S. T. Barry et al.
FULL PAPER
[Ag(NiPr)2CNMe2]3 (3): In a 50 mL flask, lithium dimethylamide
(0.189 g, 3.70 mmol) was suspended in 30 mL of hexanes. Diisopro-
pylcarbodiimide (0.467 g, 3.70 mmol) was diluted with 8 mL of
hexanes and added dropwise to the suspension at –30 °C. The
cloudy, pale yellow suspension cleared to a homogeneous pale yel-
low solution over 2 h of stirring at room temperature. Owing to the
photosensitivity of silver(I) chloride, further reaction was carried
out with protection against light. Silver(I) chloride (0.530 g,
3.70 mmol) was added to the ligand suspension, and the mixture
was stirred overnight, after which a light brown solid was filtered
to afford a colorless solution. The volatiles were removed under
reduced pressure to afford white solid 3 (0.85 g, 3.15 mmol, 85.0%
crude yield). This was dissolved in a minimal volume of hexanes
and was kept at –35 °C overnight. Compound 3 was collected as
white crystals (0.45 g, 1.62 mmol, 45%). C18H40Ag2N6 (556.29):
calcd. C 38.86, H 7.25, N 15.11; found C 38.53, H 7.40, N 15.49.
washed with an additional 50 mL of hexanes. The solution was
concentrated under reduced atmosphere and returned to the freezer
for 24 h. A white precipitate of 6 formed. (1.02 g, 2.41 mmol,
91.1%); m.p. 87 °C (dec.). C26H56Au2N6 (846.70): calcd. C 36.88,
H 6.67, N 9.93; found C 36.79, H 7.06, N 10.03. 1H NMR
[300 MHz, C6D6, 3J(1H,1H) = 6.2 Hz for all peaks]: δ = 3.96 [sept,
4 H, NCH(CH3)2], δ = 3.26 [sept, 4 H, N(CH(CH3)2)2], δ = 1.39
[d, 24 H, NCH(CH3)2], δ = 1.06 [d, 24 H, N(CH(CH3)2)2] ppm.
13C{1H} NMR (75 MHz, C6D6): δ = 166.6 [NCN], δ = 50.1
[NCH(CH3)2], δ = 48.5 [N(CH(CH3)2)2], δ = 27.2 [NCH(CH3)2], δ
= 22.6 [N(CH(CH3)2)2] ppm.
[Au(NiPr)2CNEt2]2 (7): Compound 7 was prepared in a analogous
manner as compound
6
substituting: AuCl·THT (0.71 g,
2.23 mmol), Li[(iPrN)2CN(Et)2] (0.46 g, 2.23 mmol). Compound 6
was isolated by recrystallisation (0.71 g, 1.80 mmol, 80.6% yield);
m.p. 72 °C (dec.). C22H48Au2N6 (790.59): calcd. C 33.42, H 6.12,
N 10.63; found C 33.74, H 6.23, N 10.33. 1H NMR [300 MHz,
C6D6, 3J(1H,1H) = 7.0 Hz for ethyl; 6.2 Hz for isopropyl]: δ = 3.80
[sept, 4 H, CH(CH3)2], δ = 2.85 [q, 8 H, CH2CH3], δ = 1.39 [d, 24
H, CH(CH3)2], δ = 0.83 [t, 12 H, CH2CH3] ppm. 13C{1H} NMR
(75 MHz, C6D6): δ = 166.4 [NCN], δ = 50.5 [CH(CH3)2], δ = 44.2
[CH2CH3], δ = 27.1 [CH(CH3)2], δ = 13.3 [CH2CH3] ppm.
3
1H NMR [300 MHz, C6D6, J(1H,1H) = 6.2 Hz for all peaks]: δ =
3.57 [sept, 4 H, CH(CH3)2], δ = 2.62 [s, 12 H, N(CH3)2], δ = 1.34
[d, 24 H, CH(CH3)2] ppm. 13C{1H} NMR (75 MHz, C6D6): δ =
169.4 [NCN], δ = 48.2 [CH(CH3)2], δ = 40.8 [N(CH3)2], δ = 27.8
[CH(CH3)2] ppm.
[Ag(NiPr)2CNiPr2]3 (4): In
a 50 mL flask, diisopropylamine
(0.354 g, 3.50 mmol) was dissolved in 40 mL of hexanes at –30 °C
and MeLi (2.19 mL, 3.50 mmol) was added dropwise and stirred
for two hours, giving a white suspension. Diisopropylcarbodiimide
(0.442 g, 3.50 mmol) was diluted with 10 mL of hexanes and added
dropwise to this suspension at –30 °C. Owing to the photosensitiv-
ity of silver(I) chloride, further reaction was carried out with pro-
tection against light. Silver(I) chloride (0.50 g, 3.50 mmol) was
added, and the mixture was stirred overnight, after which a dark
brown/grey solid was filtered to afford pale yellow solution. The
volatiles were removed under reduced pressure to afford white solid
4 (0.819 g, 2.45 mmol, 70.0% crude yield). The solid was dissolved
in a minimal volume of hexanes and was kept at –35 °C overnight.
Compound 4 was collected as white crystals (0.29 g, 0.28 mmol,
24.9%). C26H56Ag2N6 (668.50): calcd. C 46.71, H 8.44, N 12.57;
found C 46.98, H 8.43, N 12.53. 1H NMR [300 MHz, C6D6,
3J(1H,1H) = 6.2 Hz for all peaks]: δ = 3.85 [sept, 4 H, NCH-
(CH3)2], δ = 3.46 {sept, 4 H, N[CH(CH3)2]2}, δ = 1.33 [d, 24 H,
NCH(CH3)2] δ = 1.20 {d, 24 H, N[CH(CH3)2]2} ppm. 13C{1H}
NMR (75 MHz, C6D6): δ = 167.3 [NCN], δ = 49.1 [NCH(CH3)2],
δ = 48.0 {N[CH(CH3)2]2}, δ = 27.6 [NCH(CH3)2], δ = 23.4
{N[CH(CH3)2]2} ppm.
[Au(NiPr)2CNMe2]2 (8): Compound 8 was prepared in a analogous
manner as compound
6
substituting: AuCl·THT (0.99 g,
3.09 mmol), Li[(iPrN)2CN(Me)2] (0.548 g, 3.09 mmol). Compound
8 was isolated by recrystallisation (0.99 g, 2.70 mmol, 87.4%); m.p.
83 °C (dec.). C18H40Au2N6 (734.49): calcd. C 29.43, H 5.49, N
11.44; found C 29.45, H 5.34, N 11.10. 1H NMR [300 MHz, C6D6,
3J(1H,1H) = 6.2 Hz for all peaks]: δ = 3.80 [sept, 4 H, CH(CH3)2],
δ = 2.43 [s, 12 H, N(CH3)2], δ = 1.37 [d, 24 H, CH(CH3)2] ppm.
13C{1H} NMR (75 MHz, C6D6): δ = 170.7 [NCN], δ = 50.3
[CH(CH3)2], δ = 40.9 [N(CH3)2], δ = 27.21 [CH(CH3)2] ppm.
[Au(NiPr)2CNMe]2 (9): Compound 9 was prepared in a analogous
manner as compound
6
substituting: AuCl·THT (0.57 g,
1.78 mmol) Li[(iPrN)2CCH3] (0.27 g, 1.78 mmol); Compound 9
was isolated by recrystallisation (0.43 g, 1.28 mmol, 71.8%); m.p.
79 °C (dec.). C16H34Au2N4 (676.40): calcd. C 28.41, H 5.07, N 8.28;
found C 28.27, H 5.28, N 8.44. 1H NMR [300 MHz, C6D6,
3J(1H,1H) = 6.2 Hz for isopropyl]: δ = 3.57 [sept, 4 H, CH(CH3)2],
δ = 1.62 [s, 6 H, (NCCH3)], δ = 1.25 [d, 24 H, (CH(CH3)2] ppm.
13C{1H} NMR (75 MHz, C6D6): δ = 168.5 [NCN], δ = 51.0
[CH(CH3)], δ = 26.8 [CH(CH3)2], δ = 16.1 [NCCH3] ppm.
[Au(NiPr)2CNnBu]2 (10): Compound 10 was prepared in a analo-
gous manner as compound 6 substituting: AuCl·THT (1.01 g,
3.15 mmol) Li[(iPrN)2CnBu] (0.60 g, 3.15 mmol); Compound 10
was isolated by recrystallisation (0.30 g, 0.79 mmol, 25.0%); m.p.
96 °C (dec.). C22H26Au2N4 (740.41): calcd. C 34.74, H 6.10, N 7.37;
found C 34.60, H 6.15, N 7.69. 1H NMR (300 MHz, C6D6,
3J(1H,1H) = 7.1 Hz for butyl; 6.2 Hz for isopropyl): δ = 3.74 [sept,
4 H, CH(CH3)2], δ = 2.26 [t, 4 H, CH2CH2CH2CH3], δ = 1.44 [q,
4H CH2CH2CH2CH3], δ = 1.33 [d, 24 H, CH(CH3)], δ = 1.17 (sex,
4 H, CH2CH2CH2CH3], δ = 0.80 [t, 6 H, CH2CH2CH2CH3] ppm.
13C{1H} NMR (75 MHz, C6D6): δ = 171.55 [NCN], δ = 50.61
[Ag(NiPr)2CNEt2]3 (5): Compound 5 was prepared in a analogous
manner as compound
4 substituting: Diethylamine (0.523 g,
7.20 mmol), MeLi (11.4 mL, 7.20 mmol), diisopropylcarbodiimide
(0.442 g, 7.20 mmol), and silver(I) chloride (1.03 g, 7.20 mmol).
Compound 6 was collected as white crystals (0.82 g, 2.62 mmol,
36.4% yield). C22H48Ag2N6 (612.40): calcd. C 43.15, H 7.90, N
13.72; found C 43.28, H 8.10, N 13.91. 1H NMR [300 MHz, C6D6,
3J(1H,1H) = 7.1 Hz for ethyl; 6.2 Hz for isopropyl]: δ = 3.65 [sept,
6 H, CH(CH3)2], δ = 3.01 [q, 12 H, CH2CH3], δ = 1.36 [d, 36
H, CH(CH3)2], δ = 0.95 [t, 18 H, CH2CH3] ppm. 13C{1H} NMR
(75 MHz, C6D6): δ = 168.4 [NCN], δ = 48.6 [N(CH(CH3)], δ = 43.9
[N(CH2CH3)2], δ = 27.8 [N(CH(CH3)], δ = 13.4 [N(CH2C-
H3)2] ppm.
[CH(CH3)2],
[CH2CH2CH2CH3]
[CH2CH2CH2CH3], 13.92 [CH2CH2CH2CH3] ppm.
δ
=
30.73 [CCH2CH2CH2CH3],
δ
=
29.85
23.06
δ
=
27.20 [CH(CH3)2],
[Au(NiPr)2CNiPr2]2 (6): In a 100 mL round bottomed flask,
AuCl·THT (0.85 g, 2.64 mmol) was suspended in 50 mL of hex-
anes. The slurry was cooled to –36 °C. Solid Li[(iPrN)2CN(iPr)2]
(0.62 g, 2.64 mmol) was added to the solution and allowed to react
in a freezer at –35 °C overnight. The reaction was then warmed to
X-ray Structural Analysis for 1, 2, 3, 8, 9 and 10: Crystals were
mounted using viscous oil onto plastic mesh and cooled to the
data collection temperature. Data were collected on a Bruker-AXS
APEX CCD diffractometer with graphite-monochromated Mo-Kα
radiation (λ = 0.71073 Å). Unit cell parameters were obtained from
room temperature and immediately filtered, and the LiCl was 60 data frames, 0.3° ω, from three different sections of the Ewald
3246 Eur. J. Inorg. Chem. 2011, 3240–3247
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© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim

Group 11 Amidinates and Guanidinates
sphere. The systematic absences in the diffraction data are consis-
tent with Cc and C2/c for 8 and 9, and, uniquely, for Pbcn for 1
and Pbca for 2. No symmetry higher than triclinic was observed
for 3 and 10. Solution in the centrosymmetric space group options
yielded chemically reasonable and computationally stable results of
refinement. The data-sets were treated with SADABS11 absorption
corrections based on redundant multiscan data. The structures
were solved by direct methods and refined with full-matrix, least-
squares procedures on F2. For 1, the compound molecule is located
at a twofold axis. For 2, 8, 9 and 10, each compound molecule
(two symmetry unique molecules for 9) was located on an inversion
center. All non-hydrogen atoms were refined with anisotropic dis-
placement parameters. All hydrogen atoms were treated as idealized
contributions. Structure factors are contained in the SHELXTL
6.12 program library.[12]
[1] International Technology Roadmap for Semiconductors, edi-
tion 2009; see: http://www.itrs.net.
[2] J. Homola, Anal. Bioanal. Chem. 2003, 377, 528.
[3] F. T. Edelmann, Adv. Organomet. Chem. 2008, 57, 183.
[4] J. P. Coyle, W. H. Monillas, G. P. A. Yap, S. T. Barry, Inorg.
Chem. 2008, 47, 683.
[5] J. P. Coyle, P. A. Johnson, G. A. DiLabio, S. T. Barry, J. Müller,
Inorg. Chem. 2010, 49, 2844.
[6] S. Maier, W. Hiller, J. Strahle, Z. Naturforsch., Teil B 1988, 43,
1628.
[7] Z. W. Li, A. Rahtu, R. G. Gordon, J. Electrochem. Soc. 2006,
153, C787.
[8] B. S. Lim, A. Rahtu, J.-S. Park, R. G. Gordon, Inorg. Chem.
2003, 42, 7951.
[9] A. A. Mohamed, H. E. Abdou, J. P. Fackler, Coord. Chem. Rev.
2010, 11–12, 1253.
[10] R. Usón, A. Laguna, A. M. Laguna, D. A. Briggs, H. H. Mur-
ray, J. P. Fackler Jr., Inorg. Synth. 1989, 26, 85.
[11] A. P. Kenney, G. P. A. Yap, D. S. Richeson, S. T. Barry, Inorg.
Chem. 2005, 44, 2926.
CCDC-782066 (for 1), -782067 (for 2), -782068 (for 3),
-782069 (for 8), -782070 (for 9), -782071 (for 10) contain the supple-
mentary crystallographic data for this paper. These data can be
obtained free of charge from The Cambridge Crystallographic
Data Centre via www.ccdc.cam.ac.uk/data_request/cif.
[12] G. M. Sheldrick, Acta Crystallogr., Sect. A 2008, 64, 112.
Received: March 16, 2011
Published Online: June 10, 2011
Eur. J. Inorg. Chem. 2011, 3240–3247
© 2011 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
3247