Mass spectrometric study of the thermal decomposition mechanism of vapors of 2,2,6,6-tetramethyl-3-iminoheptane-5-one and its copper(II) complex

Article abstract of DOI:10.1016/j.jorganchem.2007.07.032

Thermal conversions of vapors of ketoimine C(CH₃)₃C(NH)CH₂C(O)C(CH₃)₃ (Htmha = 2,2,6,6-tetramethyl-3-iminoheptane-5-one) and its chelate coordination compound with copper Cu(tmha)₂ is studied by in situ mass spectrometry in a vacuum and in the presence of hydrogen. Experiments are carried out under conditions close to low pressure chemical vapor deposition at the evaporator temperature of 130 °C and the reactor temperature range 130-500 °C. It is found that compounds are monomeric in the gas phase. Based on temperature dependences of the composition of primary gaseous products, the mechanism of thermal decomposition is proposed. The decomposition of ketoimine on the heated surface begins at 350 ± 10 °C and proceeds by the elimination of terminal groups. Its copper complex decomposes in two directions and yields both molecular and radical products. The latter provide the assumption that metallic copper forms as the only one solid product. The results obtained are compared with those for copper dipivaloylmethanate(2,2,6,6-tetramethylheptane-3,5-dionate).

Full text of DOI:10.1016/j.jorganchem.2007.07.032

Journal of Organometallic Chemistry 692 (2007) 5001–5006
www.elsevier.com/locate/jorganchem
Mass spectrometric study of the thermal decomposition mechanism
of vapors of 2,2,6,6-tetramethyl-3-iminoheptane-5-one and
its copper(II) complex
*
Assia E. Turgambaeva , Vladislav V. Krisyuk, Pavel A. Stabnikov, Igor K. Igumenov
Nikolaev Institute of Inorganic Chemistry SD RAS, Novosibirsk 630090, Russia
Received 11 June 2007; received in revised form 17 July 2007; accepted 18 July 2007
Available online 31 July 2007
Abstract
Thermal conversions of vapors of ketoimine C(CH3)3C(NH)CH2C(O)C(CH3)3 (Htmha = 2,2,6,6-tetramethyl-3-iminoheptane-5-one)
and its chelate coordination compound with copper Cu(tmha)2 is studied by in situ mass spectrometry in a vacuum and in the presence of
hydrogen. Experiments are carried out under conditions close to low pressure chemical vapor deposition at the evaporator temperature
of 130 °C and the reactor temperature range 130–500 °C. It is found that compounds are monomeric in the gas phase. Based on tem-
perature dependences of the composition of primary gaseous products, the mechanism of thermal decomposition is proposed. The
decomposition of ketoimine on the heated surface begins at 350 10 °C and proceeds by the elimination of terminal groups. Its copper
complex decomposes in two directions and yields both molecular and radical products. The latter provide the assumption that metallic
copper forms as the only one solid product. The results obtained are compared with those for copper dipivaloylmethanate(2,2,6,6-
tetramethylheptane-3,5-dionate).
Ó 2007 Elsevier B.V. All rights reserved.
Keywords: Ketoimine; Copper ketoiminate; b-Diketonate derivative; Thermal decomposition mechanism; Mass spectrometry; CVD precursor
1. Introduction
found a rather wide application for investigating the mech-
anism of chemical conversions.
A successful development of various technologies using
metal complexes with organic ligands in order to obtain
diverse materials requires understanding the mechanism
of the underlying chemical transformations. In particular,
for chemical vapour deposition (CVD) [1] that applies vol-
atile organometallic complexes, the chemical aspects, such
as adsorption, activation, conversion of the complex mole-
cules on the surface, become decisive in the selection of
starting compounds and deposition conditions. Owing to
rapidity and relative simplicity in interpreting the experi-
mental data, different mass spectrometric techniques have
The mechanism of thermal conversions of the organo-
metallic compound has been studied by mass spectrometry
on both relatively simple compounds, for example, examin-
ations of aluminum alkoxides [2,3] or silver(I) tri-n-butyl-
phosphine complexes [4], and more complex such as
metal b-diketonates [5–7]. The authors of the present paper
have much experience in applying mass spectrometry to the
investigation of these complexes [8–11]. The peculiarity of
these investigations is the use of the input system for mass
spectrometer that imitates the CVD reactor. Only the
vapors of the initial compound are supplied to such a reac-
tor; thermal conversions take place on the surface, whereas
the reaction mixture flows into the mass analyzer through
the effusion hole in the reactor. Thus, the possibility of ana-
lyzing the gas phase composition almost in situ avoiding
probable secondary reactions is achieved.
*
Corresponding author. Present address: ENSIACET/CIRIMAT, 118
Route de Narbonne, 31077 Toulouse cedex 4, France. Tel.: +33
562885766; fax: +33 562885600.
E-mail address: tassia@mail.ru (A.E. Turgambaeva).
0022-328X/$ - see front matter Ó 2007 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2007.07.032

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A.E. Turgambaeva et al. / Journal of Organometallic Chemistry 692 (2007) 5001–5006
Our present study was inspired by the perspectives of
It should be noted that because ketoiminate is difficult for
the investigation being a system of many different atoms,
here we speak not about the study of the mechanism at
the level of elementary acts, but about the identification of
the reaction products, possible ways of their formation,
and temperature ranges of the process. Such a qualitative
approach provides the possibility of estimating the compo-
sition of the vapor of the initial complex and its vaporization
stability and of predicting the composition of the solid phase
in the decomposition of vapors on the surface [22,23].
We have described the synthesis and characterization of
the compounds studied here in [24]. The compounds were
preliminary purified by sublimation. The data obtained
are specially compared with those previously reported on
the thermal behavior of 2,2,6,6-tetramethylheptane-3,5-
dione Htmhd and their copper(II) complex Cu(tmhd)2 [25].
using volatile metal b-ketoiminates as precursors for
depositing pure metal films due to a lower content of oxy-
gen, giving some advantage to these compounds over metal
b-diketonates. Furthermore, metal b-ketoiminates and
b-diketonates possessing the same substituents have similar
volatility [12].
Coordination chemistry of bidentate ketoiminate ligands
containing N, O donor atoms are well known [13]. Along
with b-diketones, these ligands have been used to prepare
volatile complexes of main group elements, lanthanides
and transition metals for CVD applications to obtain metal
and oxide films [14–20].
Perhaps, the only one article devoted to the investiga-
tion of thermal behavior and decomposition of ketoiminate
vapors is the work on dimethylgold ketoiminates [21]. The
authors present the results of the systematic study of a ser-
ies of dimethylgold ketoiminates in the gas and condensed
phases.
2. Results and discussion
The focus of the study reported here is the revelation
of the mechanism of decomposition of copper(II) 2,2,6,6-
tetramethyl-3-iminoheptane-5-onate Cu(tmha)2 vapors.
Thermal conversions of the compound vapor on the
heated surface were studied in a vacuum and in the pres-
ence of hydrogen using a mass spectrometric technique.
Decomposition of free Htmha ligand vapor is also stud-
ied to clearly understand the decomposition of the cop-
per compound.
2.1. Mass spectrum of the compounds
The fragmentation of the ligand under electron impact is
similar to that for Htmhd and mainly proceeds by eliminat-
ing one terminal C4H9 group with the formation of the ion
peak at m/z 126 (Table 1).
For the copper complex, there are no peaks in mass
spectra with m/z exceeding the molecular ion mass
(427 a.m.u. for 63Cu(tmha)2) indicating that the compound
Table 1
Mass spectra of Htmha and dipivaloylmethane Htmhd and theirs copper(II) complexes (EI, ionization energy – 70 eV)
Ion,a R = C4H9
m/z
Relative intensity (%)
m/z
Relative intensity (%) [22]
CuL2
HL, L = tmha
CuL2
HL, L = tmhd
[CuL2]+
427
78
12
59
16
30
13
90
7
–
–
–
–
429
373
315
247
189
184
127
12
25
53
8.5
19
–
–
–
–
–
9
100
[CuL2–R]+
[CuL2–2R]+
[CuHL]+
[CuL–R]+
[HL]+
313
246
188
183
126
110
–
18
100
8
11
100
[HL–2R]+
109
85
8
11
13
96
8
83
81
69
68
57
55
43
42
41
39
29
28
27
15
10
8
8
7
5
7
81
69
18
10
10
6
[N„CCH2CHO]+
[C4H9]+
10
12
100
25
17
22
84
37
55
24
31
15
26
14
8
17
40
21
24
14
17
12
57
43
52
80
19
17
50
58
[CH3CO]+
[C3H5]+
[C3H3]+
[C2H5]+
41
39
29
25
13
[C2H3]+
[CH3]+
a
27
15
Here copper-containing ions are presented as the most occurring isotope 63Cu.

A.E. Turgambaeva et al. / Journal of Organometallic Chemistry 692 (2007) 5001–5006
5003
is monomeric in the gas phase. The fragmentation path
under electron impact with the elimination of terminal
groups of the ligand is typical of copper b-diketonates
[11,26]. The 100% intensity of the molecular ion among
copper-containing peaks should be noted, while for cop-
per(II) dipivaloylmethanate Cu(tmhd)2 the intensity of
the molecular ion is low and the most intensive is
[63Cu(tmhd)2–2C4H9]+ with m/z 315 (Table 1). Evidently,
the presence of the imino-group makes the molecular ion
more stable for the copper complex. As well as for the
majority of metal complexes with non-fluorinated b-dike-
tones, there are peaks corresponding to free ligand Htmha
and products of its fragmentation.
.
.
.
.
.
2.2. Thermal decomposition study
Fig. 2. Temperature dependence of intensity of the main peaks in the mass
spectrum characterizing gas phase composition upon Cu(tmha)2 thermol-
ysis in vacuum.
New peaks are not observed in the mass spectra
recorded under heating the vapors of the titled com-
pounds; only a change in the intensity is observed. It
means that products upon thermal decomposition and
electron impact ionization are the same. In other words,
ions with the same m/z form both upon the fragmentation
of the molecular ion of the initial compound and ioniza-
tion of thermal decomposition products under electron
impact. However, it is possible to separate these two paths
by analyzing the thermal dependence of the mass spectra
because the intensity of the ion peaks changes when the
vapor of compounds is heated. In mass spectrum intensity
of fragmentary ion peak is constant value with respect to
intensity of the parent ion, thus curve of temperature
dependence of fragmentary ion peak has the same shape
as that one for parent ion. Difference in this shape indi-
cates that such a fragmentary ion originates from two
(or more) parent particles and separation of the integral
curve is carried out if necessary.
.
.
.
.
.
Fig. 3. Temperature dependence of intensity of the main peaks in the mass
spectrum characterizing gas phase composition upon Cu(tmha)2 thermol-
ysis in the hydrogen presence.
Figs. 1–3 display the temperature dependences of the
intensity of ions peaks in the mass spectrum characterizing
the gas phase composition.
2.2.1. Thermal decomposition of Htmha vapours
The temperature dependence of the gas phase composi-
tion (Fig. 1) was used to evaluate thermal stability. A
decomposition onset temperature was determined as the
temperature when a decrease in the molecular peak inten-
sity is observed in the mass spectrum simultaneously with
an increase in the intensity of the products peaks. In a vac-
uum it occurs at 350 10 °C. According to Ref. [25], the
decomposition of dipivaloylmethane Htmhd starts at
590 10 °C. Therefore, it could be concluded that substi-
tution of keto-group for imino-group results in a consider-
able decrease in thermal stability.
The products of decomposition are recorded in the mass
spectrum as peaks at m/z 57 (with the fragmentary ions at
m/z 41, 29) for C4H9 and 69 (with the fragmentary 68) for
N„CCH2CHO. Following the composition of gaseous
products, the heterogeneous decomposition of Htmha pro-
ceeds through elimination of two tert-butyl groups and
finally can be presented by Eq. (1)
Fig. 1. Temperature dependence of intensity of the main peaks in the mass
spectrum characterizing gas phase composition upon Htmha thermolysis.

5004
A.E. Turgambaeva et al. / Journal of Organometallic Chemistry 692 (2007) 5001–5006
onset temperature. The described trend is kept in the pres-
ence of hydrogen, though the curves have a sharper slope.
Also we were astonished at unusual behavior of the curves
corresponding to the peaks of the molecular ion
[Cu(tmha)2]+ and [Cu(tmha)2–2R]+ (R = C4H9) ion. With
the temperature rising, the intensity of [Cu(tmha)2–2R]+
does not decrease in parallel with the molecular ion
[Cu(tmha)2]+, and at a temperature above 250 °C its inten-
sity becomes higher than the intensity of the molecular ion.
It occurs on the background of the gradual growth of the
intensity of peaks for decomposition products. This feature
was well reproduced from one experiment to another. Ear-
lier, the authors have investigated quite a number of metal
b-diketonates including the complexes of copper(II)
[11,26]. Unlike other complexes, the compound under
investigation shows distinct behavior of metal-containing
peaks when heated. Such a behavior of [Cu(tmha)2–2R]+
may be explained by that its parent particle forms in the
decomposition of the initial compound on the surface
and then it desorbs in a gas phase that enables its record
in the mass spectra.
NHCðC4H9ÞCH2CðC4H9ÞO
! 2C4H9 þ NBCCH2CHO
Note that this simple way differs from that one for dipi-
valoylmethane which decomposes with the abstraction of
H2O to produce C4H9C(O)C„CC4H9 [25].
ð1Þ
2.2.2. Thermal decomposition of Cu(tmha)2 vapours
The copper complex has sufficient vaporisation stability
at least up to 150 °C that is confirmed by the fact that there
are no changes in the mass spectrum under repeated heat-
ing and cooling cycles of the evaporator.
To study thermal conversions, the compound vapor
incoming from the evaporator was heated in the reactor
from 150 to 500 °C in a vacuum and in the presence of
hydrogen. Several repeated experiments have been made
with the same heating and cooling rate. The mass spectra
are recovered completely after cooling the reactor and the
composition of products does not change in subsequent
experiments.
Fig. 2 displays the temperature dependences of ion
peaks of the mass spectrum recorded in a vacuum and
hydrogen presence. The form of these curves merits our
special consideration. In a vacuum, the intensity of cop-
per-containing peaks starts to decrease at a temperature
above 200 °C and reaches the background level at 300 °C.
Note that these curves are mildly sloping – there is no char-
acteristic pronounced reduction of the intensity after the
Apart from the above particle, the following peaks cor-
responding to reaction products are observed in the mass
spectrum: free ligand Htmha at m/z 183 (with the most
intensive fragmentary ion at m/z 126), tert-butyl-radical
C4H9 at m/z 57 and C4H7 at m/z 55, N„CCH2CHO at
m/z 69 with a more intensive fragmentary ion at m/z
68. It should be also noted that free ligand is a typical
Scheme 1. Mechanism of decomposition of the investigated complex on heated surface.

A.E. Turgambaeva et al. / Journal of Organometallic Chemistry 692 (2007) 5001–5006
5005
decomposition product for non-fluorinated metal b-diket-
onates, and in particular for copper(II) complexes [22,23].
Gaseous products of decomposition in a vacuum are sim-
ilar to those formed in the presence of hydrogen.
metallic copper forms as the only one solid product. Both
compounds described possess sufficient storage and vapor-
ization stability. A relatively low temperature of decompo-
sition and a smaller oxygen content in comparison with b-
diketonate makes the copper(II) complex a promising pre-
cursor for the deposition of pure (oxygen-free) copper
films.
Based on the revealed composition of gaseous products,
we assume the following mechanism of decomposition of
the investigated complex on the heated surface (Scheme
1). The process of free ligand formation (A) is the result
of an intramolecular proton transfer from one ligand to
another with the breakage of one Cu–O bond. It occurs
in parallel with the elimination of tert-butyl groups (B)
and a number of rearrangements leading to the particle
recorded in the mass spectrum as [Cu(tmha)2–2R]+ ion.
Further both ways result in that C4H9, C4H7 radical parti-
cles and the N„CCH2CHO molecular product (m/z 69)
escape to the gas phase. Despite the presence of identical
products, we exclude the possibility of formation of the
particle with m/z 69 owing to thermolysis of the formed
ketoimine upon the decomposition of copper(II) ketoimi-
nate. The study of ketoimine thermolysis performed shows
that this process occurs in another temperature interval
and decomposition begins at a temperature higher by 50°.
From the composition of gaseous products of thermal
decomposition that is suggested based on the analysis of
the temperature dependence it follows that the main solid
product is metallic copper (as a film on the walls of the
reactor). Moreover, the formation of exactly metallic cop-
per in the solid phase is indirectly confirmed by the follow-
ing. Peaks of the particles similar to RC„CC(O)R,
RCH@CHC(O)R are absent in the mass spectrum, while
they indicate the breakage of the C–O bond in the ligand,
as it was shown in the case of copper and lead dipivaloyl-
methanates. It is this bond breakage that results in the for-
mation of a metal oxide in the solid phase [22,25]. It should
be added that copper films have been prepared by CVD
from the investigated copper complex in the predicted tem-
perature range and the results will be reported later in sep-
arate paper.
Apart from the data on the mechanism of thermal
decomposition which develop our ideas of the chemistry
of organometallic compounds, we obtain valuable informa-
tion for the practical application. In particular, we again
demonstrate the possibility of making an assumption on
the composition of the solid product of decomposition
based on the analysis of primary gaseous product. The
technological aspect of the study performed is to test vari-
ous volatile organometallic compounds for their applicabil-
ity in CVD processes. A doubtless advantage of this is the
use of small amounts of the initial substance and avoidance
of the tedious routine search for the temperature range.
To develop the study performed and confirm its conclu-
sions about the solid phase composition, it is expected to
continue the experiments and obtain copper films from
the compound in question. The data on the temperature
ranges obtained at that we will use to find the deposition
conditions.
4. Experimental
The thermal decomposition of the compound vapours
was studied by the mass spectrometric technique which is
the combination of Knudsen effusion method with mass
spectrometric measurements of the gas phase composition
[27]. The experimental details are described in Ref. [11].
The compound (about 5 mg) in a glass ampoule was heated
in the evaporator to 85 °C for Htmha and 130 °C for
Cu(tmha)2, respectively. Evaporator temperature kept con-
stant and vapors of the initial compound supplied to the
reactor through a heated pipeline. During the experiment,
the reactor temperature was changed from the above tem-
perature to 500 °C with a heating rate of 5 degrees per min-
ute. The reaction mixture flows through the effusion hole
(0.2 mm) from the reactor into the mass analyzer of the
mass spectrometer. It should be noted that vapors only
were heated in the reactor and the experiment conditions
were as such that decomposition occurred on the walls of
the reactor. Working pressure changed within the order
of 10ꢀ6 Torr magnitude, while vapor pressure of the com-
pound was not higher than 10ꢀ3 Torr). The fast recording
of the gas phase composition was carried out: the time
from the moment when a particle leaved the reactor to
the moment when it is recorded did not exceed a millisec-
ond. This enables us to record primary gaseous decompo-
sition products in situ, as well as to measure the
temperature ranges in which they form. The reagent gas
(hydrogen) is introduced directly into the reactor.
The comparison with b-diketonates shows that the stud-
ied complex with ketoiminate and copper is less thermally
stable than dipivaloylmethanate whose decomposition
starts at 330 °C. As for the compound studied, the degree
of its decomposition reaches its maximum at 300 °C, which
is indicated by a high intensity of the peaks of reaction
products and almost the background intensity of the peaks
of the initial compound. Note that Cu(tmha)2 when heated
in the condensed phase is less stable than Cu(tmhd)2 [24].
3. Conclusions
Having investigated the mechanism of the thermal
decomposition of vapors of compounds on the surface,
we state that the decomposition of ketoimine proceeds in
one stage with the elimination of terminal groups. The
decomposition of its complex with copper occurs in two
directions and leads to the formation of both molecular
and radical products. They provide the assumption that
Mass spectra were recorded at the energy of ionizing elec-
trons of ꢁ70 eV with a time-of-flight mass spectrometer. In

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A.E. Turgambaeva et al. / Journal of Organometallic Chemistry 692 (2007) 5001–5006
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tion were produced from the mass spectra at different
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This research was supported by the Russian Foundation
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