Synthesis and characterization of alkynes β-diketonate copper(I) complexes

Article abstract of DOI:10.1016/j.ica.2004.03.023

The reactions of 1,3,5-tris-(trimethylsilylethynyl)benzene (1) with Cu ₂O and 1,1,1,5,5,5,-hexafluoroacetylacetone in alkyne to Cu ratios 1:0.5, 1:1 and 1:3 in CH₂Cl₂ at room temperature give copper complexes (η²

Full text of DOI:10.1016/j.ica.2004.03.023

Inorganica Chimica Acta 357 (2004) 3205–3210
www.elsevier.com/locate/ica
Synthesis and characterization of alkynes b-diketonate
copper(I) complexes
*
ꢀ
Salome Delgado , Dolores Corripio, Consuelo Moreno
Departamento de Quꢀımica Inorgꢀanica, Universidad Autꢀonoma de Madrid, Cantoblanco, 28049 Madrid, Spain
Received 11 December 2003; accepted 13 March 2004
Available online 9 April 2004
Abstract
The reactions of 1,3,5-tris-(trimethylsilylethynyl)benzene (1) with Cu2O and 1,1,1,5,5,5,-hexafluoroacetylacetone in alkyne to Cu
ratios 1:0.5, 1:1 and 1:3 in CH2Cl2 at room temperature give copper complexes (g2-1,3,5-tris(trimethylsilylethynyl)ben-
zene)(Cu(hfac)) (2), (g2:g2-1,3,5-tris(trimethylsilylethynyl)benzene)(Cu(hfac))2 (3) and (g2:g2:g2-(1,3,5- tris(trimethylsilylethy-
nyl)benzene))2(Cu(hfac))3(4), respectively. In the same conditions, 2,5-bis-(trimethylsilylethynyl)thiophene (5) reacts with 0.5 or 1
equiv. of Cu2O to give (g2:g2-2,5-bis(trimethylsilylethynyl)thiophene)(Cu(hfac)) (6) and (g2:g2-2,5-bis(trimethylsilylethynyl)thio-
phene)(Cu(hfac))2 (7), respectively, and 1,4-bis(trimethylsilyl)-1,3-butadiyne (8) with 0.5 equiv. of Cu2O give (g2:g2-1,4-bis(trim-
ethylsilyl)-1,3-butadiyne)(Cu(hfac))2 (9). All the new compounds have been characterized by analytical and spectroscopic methods
and their thermal properties were examined by thermal gravimetric analysis (TGA) and differential scanning calorimetry (DSC).
Ó 2004 Elsevier B.V. All rights reserved.
Keywords: Copper(I); b-Diketonate complexes; Polyynes
1. Introduction
the copper(I) center, parallel to the copper b-diketonate
plane [8].
Chemical vapor deposition (CVD) is a useful tech-
nique for depositing conformal films over substrates
with varying topography [1]. Research geared toward
the identification and synthesis of volatile metal pre-
cursors specifically for chemical vapor deposition
(CVD) of high-purity films is actively being pursued.
The utility of a specific precursor depends upon the
precursor’s chemical structure and its resulting chemical
and physical properties. A wide variety of Cu(I) com-
plexes have been synthesized and characterized to date
with the intention to be used as copper precursor com-
plexes in metal-organo chemical vapor deposition [2].
The reactive copper(I) b-diketonate moiety may be
ligated with phosphines [3] or unsaturated organics,
such as alkenes [4], dienes [5] and alkynes [6,7] to obtain
an assortment of precursors with different physico-
chemical properties. In the mononuclear copper(I)-al-
kyne b-diketonate complexes, the alkyne is g2 bonded to
As a continuation on the preparation of polyynes
transition metal complexes [9,10], we report in this work
the synthesis and spectroscopic data of novel multicoor-
dinated b-diketonate copper(I) polyyne ligand
complexes. The alkynes employed are the 1,3-bis (trim-
ethylsilyl)
butadiyne,
2,5-bis(trimethylsilylethynyl)
thiophene and 1,3,5-tris(trimethylsilylethynyl)benzene,
which allow different coordination modes.
2. Experimental
2.1. Reagents and general techniques
All manipulations were carried out by using standard
Schlenk vacuum-line and syringe techniques under an
atmosphere of oxygen-free Ar. All solvents for synthetic
use were reagent grade, dried as appropriate and dis-
tilled under Ar. All solvents were bubbled with Ar for 30
minutes after distillation and then stored under Ar, or
degassed by means of at least three freeze-pump-thaw
* Corresponding author. Tel.: +349-149-74846; fax: +349-149-74833.
E-mail address: salome.delgado@uam.es (S. Delgado).
0020-1693/$ - see front matter Ó 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2004.03.023

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S. Delgado et al. / Inorganica Chimica Acta 357 (2004) 3205–3210
cycles after distillation and before use. 1,3,5-tribromo-
benzene, 1,4-bis (trimethylsilyl)-1,3-butadiyne, Me3Si–
CBCH (TMSA), 2,5-dibromothiophene (Aldrich), and
Cu2O, 1,1,1,5,5,5-hexafluoroacetylacetone (Fluka) were
used as received. The 1,3,5-tris(trimethylsilyl)ethynyl-
benzene [10] and 2,5-bis(trimethylsilylethynyl)thiophene
[11] were prepared according to literature procedures.
104.92 (s, C3); 95.92 (s, C4); 89.92 (s, C6); )0.41 (s, –
CSiMe3). MS (FABþ, m/z): 636.0 (Mþ). PF 128.3 °C.
(3) Yield: 90%. IR (KBr, cmꢀ1): m(uncoordinated
CBC) 2168 (s); m(coordinated CBC) 1969.9 (m); m(C@O)
1642.1 (s); d(C–F) 1471.4 (m). IR (CH2Cl2, cmꢀ1):
m(coordinated CBC) 1965 (m). 1H NMR (300 MHz,
CDCl3) d: 7.82 (s, 3H, benzene); 6.17 (s, 2H, hfac); 0.34
(s, 27H, SiMe3). 13C NMR (125 MHz, CDCl3) d: 178.26
(q, C7O, JCF ¼ 34:7 Hz); 135.47 (s, C1); 123.92 (s, C2);
117.66 (q, C8F3, JCF ¼ 285:3 Hz); 106.60 (s, C3); 96.24
(s, C4); 89.95 (s, C6); )0.53 (s, –CSiMe3). MS (FABþ, m/
z): 700.8 (Mþ-hfac). Anal. Calc. for C31H32O4F12Cu2Si3:
C, 40.97; H, 3.52. Found: C, 40.65, H, 3.45%. PF
143 °C.
1
The H, 13C and HMBC (Heteronuclear Multiple Bond
Correlation) NMR spectra were recorded on a Bruker
AMX-300 or 500 instrument. 1H NMR spectra were
referenced to tetramethylsilane. Infrared spectra were
measured on a Perkin–Elmer 1650 infrared spectrome-
ter. Elemental analysis were performed by the Micro-
ꢀ
analytical Laboratory of the University Autonoma of
Madrid on a Perkin–Elmer 240 B microanalyzer. Mass
spectra were measured on a VG-Autospec mass spec-
trometer for FAB by the Mass Laboratory of the Uni-
(4) Yield: 60%. IR (KBr, cmꢀ1): m(CBC) 1974.2 (m);
m(C@O) 1639.2 (s); d(C–F) 1462.7 (m). IR (CH2Cl2,
cmꢀ1): 1970 (m). 1H NMR (300 MHz, CDCl3) d: 7.76 (s,
6H, benzene); 6.17 (s, 3H, hfac); 0.31 (s, 54H, SiMe3).
13C NMR (125 MHz, CDCl3) d: 178.25 (q, C7O,
JCF ¼ 37:0 Hz); 135.39 (s, C1); 123.82 (s, C2); 117.65 (q,
C8F3, JCF ¼ 284:82 Hz); 105.84 (s, C3); 96.09 (s, C4);
89.95 (s, C6); )0.47 (s, –CSiMe3). Anal. Calc. for
C57H63O6F18Cu3Si6: C, 44.30; H, 4.08. Found: C, 44.12,
H, 3.98%. PF 115 °C.
ꢀ
versity Autonoma of Madrid.
The thermal properties of all complexes were exam-
ined by thermal gravimetric analysis (TGA) and differ-
ential scanning calorimetry (DSC). The gravimetric data
were obtained on a Seiko DTA/TG 320 U using an open
pan which was purged with N2 and a heating rate of 5
°C/min. The calorimetric data were obtained with a
Perkin–Elmer Pyris 1DSC instrument using a sealed
pan with a heating rate of 5 °C/min. The melting points
were also obtained via a conventional melting point
apparatus.
2.3. Preparation of (g2:g2-2,5-bis(trimethylsilylethy-
nyl)thiophene)(Cu(hfac)) (6) and (g2:g2-2,5-bis(trim-
ethylsilylethynyl)thiophene)(Cu(hfac))2 (7)
2.2. Preparation of (g2-1,3,5-tris(trimethylsilylethynyl)
benzene)(Cu(hfac)) (2), (g2:g2-1,3,5-tris(trimethylsily-
lethynyl)benzene) (Cu(hfac))2 (3) and (g2:g2:g2-(1,3,5-
tris(trimethylsilylethynyl)benzene))2(Cu(hfac))3 (4)
By a similar procedure, to a solution of 0.05 g (0.35
mmol) of 2,5-bis(trimethylsilylethynyl)thiophene (5) in
CH2Cl2(40 mL) was added 0.5 equiv. (6) or one equiv-
alent (7) of Cu2O, respectively. Hexafluoroacetylacetone
(0.22 mL, 1.4 mmol) was added dropwise. After similar
working, 6 and 7 were separated as yellow solids.
(6) Yield: 63%. IR (KBr, cmꢀ1): m(uncoordinated
CBC) 2146; m(coordinated CBC) 1957.4 (m); m(C@O)
1639.2 (s); (C–F) 1473.3 (m). IR (CH2Cl2, cmꢀ1): m(co-
ordinated CBC) 1954 (m). 1H NMR (300 MHz, CDCl3)
d: 7.31 (s, 2H, thiophene); 6.18 (s, 1H, hfac); 0.34 (s,
18H, SiMe3). 13C NMR (125 MHz, CDCl3) d: 178.3 (q,
C7O, JCF ¼ 34:8 Hz); 133.03 (s, C1); 125.76 (s, C2);
117.65 (q, C8F3, JCF ¼ 285:2 Hz); 100.92 (s, C3); 99.82
(s,C4); 90.02 (s, C6); )0.49 (s, –CSiMe3). MS (FABþ, m/
z): 546.0(Mþ). PF 180 °C (dec.).
A three-neck round-bottom flask was charged with
0.13 g (0.35 mmol) of 1,3,5-tris(trimethylsilylethy-
nyl)benzene (1) and 0.5 equiv. (2), 1 equiv. (3) or 3
equiv. (4) of Cu2O, respectively, and stirred in 30 mL of
spectroscopic grade methylene chloride. Hexafluoro-
acetylacetone (0.1 mL, 0.7 mmol) was added dropwise
to the stirred suspension. After the mixture was stirred
for 3 h at room temperature the solution becomes yel-
low. Isolation of the products was achieved by filtering
off the excess cuprous oxide and washing several times
with CH2Cl2. The filtrates and washes were combined
and removed under vacuum. The compounds were iso-
lated and purified as yellow (2, 3) or green (4) solids by
recrystallization from hot hexane.
(7) Yield: 85%. IR (KBr, cmꢀ1): m(CBC) 1945.8 (m);
m(C@O) 1637.3 (s); d (C–F) 1469.5 (m). IR (CH2Cl2,
1
cmꢀ1): 1942.5 (m). H NMR (300 MHz, CDCl3) d: 7.40
(2) Yield: 93%. IR (KBr pellet, cmꢀ1): m(uncoordi-
nated CBC) 2166 (s), m(coordinated CBC) 1976.8 (m);
m(C@O) 1637.3 (s); d(C–F) 1471.4 (m). IR (CH2Cl2,
cmꢀ1): m(coordinated CBC) 1972 (m). 1H NMR (300
MHz, CDCl3): d 7.67 (s, 3H, benzene); 6.17 (s, 1H,
hfac); 0.28 (s, 27H, SiMe3). 13C NMR (125 MHz,
CDCl3): d 178.29 (q, C7O, JCF ¼ 34:8 Hz); 135.25 (s,
C1); 123.77 (s, C2); 117.67 (q, C8F3, JCF ¼ 285:3 Hz);
(s, 2H, thiophene); 6.18 (s, 2H, hfac); 0.38 (s, 1,8H,
SiMe3). 13C NMR (125 MHz, CDCl3) d: 179.2 (q, C7O,
JCF ¼ 34:8 Hz); 134.13 (s, C1); 126.95 (s, C2); 118.8 (q,
C8F3, JCF ¼ 285:3 Hz); 102.84 (s, C3); 100.64 (s,C4);
90.92 (s, C6); 0.35 (s, –CSiMe3). MS (FABþ, m/z):
610.9(Mþ-hfac). Anal. Calc. for C24H22O4F12SSi2Cu2:
C, 35.22; H, 2.70. Found: C, 35.08; H, 2.52%. PF 180 °C
(dec.).

S. Delgado et al. / Inorganica Chimica Acta 357 (2004) 3205–3210
3207
2.4. Preparation of (g2:g2-1,4-bis(trimethylsilyl)-1,3-but-
adiyne)(Cu(hfac))2 (9)
for all complexes reported herein as shown in Table 1.
These values are indicative of g2-coordination mode of
the Me3SiCBC units to Cu(hfac) with predominant r
bonding contribution acting each triple bond as a two-
electron donor with poor back-donation from Cu(I) to
the alkynes [14]. When the C2 unit of the alkyne ligand is
g2-coordinated to two copper(I) centers acting as a four-
electron donor, larger vibrational changes are observed
(Dt ¼ 368 cm ꢀ1) for BTSA (Cu(hfac))2[6a]. The eno-
lized 1,3-dicarbonyl stretching frequencies are ca. 1640
cmꢀ1 and all complexes have sharp C–F deformation
The same procedure was followed in the preparation
of this compound using 1:0.5 ratio (1,4-bis(trimethylsi-
lyl)-1,3-butadiyne (8): Cu2O). A yellow solid is isolated.
(9) Yield: 67%. IR (KBr, cm-1): m(CBC) 1895.6 (s);
m(C@O) 1644.0 (f); d(CF) 1462.7 (m). IR (CH2Cl2,
cmꢀ1): 1893.5 (m). 1H NMR (300 MHz, CDCl3) d: 6.16
(s, 2H, hfac); 0.36 (s, 18H, SiMe3). 13C NMR (75 MHz,
CDCl3) d: 178.36 (q, C5O, JCF ¼ 34.8 Hz); 117.6 (q,
C6F3, JCF ¼ 285.3 Hz); 97.3 (s, C1 and C2); 90.02 (s, C4);
)0.95 (s, –CSiMe3). MS (FABþ, m/z): 528.9(Mþ-hfac).
Anal. Calc. for C20H20O4F12Cu2Si2: C, 32.63; H, 2.72.
Found: C, 32.45; H, 2.60%. PF 115 °C.
frequencies at ca. 1470 cmꢀ1
.
1
The H and 13C NMR spectra in CDCl3 of all new
synthesized compounds consist of sharp and well re-
solved signals for each of the organic ligands present.
The 1H chemical shifts (Dd) of the ‘‘free’’ alkyne with the
copper coordinated alkyne for the complexes are listed
in Table 2. In all cases, deshielding of the hydrogens
(protons) on the a carbon atom (a to the alkyne moiety)
is observed. The Dd varies from +0.19 (2) to +0.36 (7);
these NMR chemical shift changes are similar to other
Cu(hfac) (alkyne) complexes [6c,15].
3. Results and discussion
Synthesis of the alkyne-copper complexes in this re-
port was inspired by previously reported methods. Thus,
the complexes have been obtained by reaction of Cu2O
on the free acid b-diketone in the presence of alkyne
[6a,12]. By changing the stoichiometry of reagents, we
obtained complexes with different numbers of copper
hfac groups bound to the alkyne.
For
(g2-1,3,5-tris(trimethylsilylethynyl)benzene)
(Cu(hfac)) (2), (g2:g2-1,3,5-tris(trimethylsilylethynyl)
benzene) (Cu(hfac))2 (3) and (g2:g2:g2-(1,3,5-tris(tri-
methylsilylethynyl)benzene))2(Cu(hfac))3 (4), also the
integration of the methine protons (H6), SiMe3 groups
(H5) and aromatic protons (H1) of the ligand peaks
confirms the 1:1, 1:2 and 2:3 (alkyne:hfac) ratio, re-
spectively. The deshielding of the hydrogens on the
SiMe3 groups observed with respect to free ligand is
proportional to the Cu(hfac) units coordinated to al-
kyne (Dd ¼ þ0:06 ppm (2), +0.12 ppm (3) and +0.09
ppm (4)). All compounds show a single signal for the
benzene ring and SiMe3 groups and it is indicative of
symmetric coordination mode wherein, according to
alkyne:hfac ratio, one (2), two (3) or three (4) Cu(hfac)
units are coordinated to one (2), two (3) or three (4)
triple bonds of 1,3,5-tris(trimethylsilylethynyl)benzene
ligands, respectively. For 2 and 3, each Cu(hfac) unit
could be bonded to one or two triple bonds, respectively,
and, in solution at room temperature, they exchange
each other quickly. This is supported by the IR spectra
(KBr) where two t(CBC)(uncoordinated and coordi-
nated) are observed and by the variable-temperature 1H
NMR experiments in CD2Cl2 over the range )95° to
25°. It is clearly seen that the signal due to aromatic
protons is broader to lower temperature ()95 °C) al-
though the split is not observed, while the methine
protons signal is not affected. It could suggest a too
quickly exchange process with an estimated activation
energy lesser than 6 kcal/mol. These low values indicate
that the exchange motion is easy according to a weak
interaction Cu(hfac)-triple bond. Similar exchange is
proposed by [Cu(hfac)O2S(CBCtBu)2] [16a] and analo-
gous diynes compounds [16b]. For complex 4, a dimeric
So, 1,3,5-tris-(trimethylsilylethynyl)benzene (1) reacts
with Cu2O and 1,1,1,5,5,5,-hexafluoroacetylacetone in
alkyne to Cu ratios 1:0.5, 1:1 and 1:3 in CH2Cl2 at
room temperature to give after workup copper
complexes (g2-1,3,5-tris(trimethylsilylethynyl)benzene)
(Cu(hfac)) (2), (g2:g2-1,3,5-tris(trimethylsilylethynyl)
benzene) (Cu(hfac))2 (3) and (g2:g2:g2-(1,3,5-tris(trim-
ethylsilylethynyl)benzene))2(Cu(hfac))3(4), respectively.
In the same conditions, 2,5-bis-(trimethylsilylethy-
nyl)thiophene (5) reacts with 0.5 or 1 equiv. of Cu2O to
give
(g2:g2-2,5-bis(trimethylsilylethynyl)thiophene)
(Cu(hfac)) (6) and (g2:g2-2,5-bis(trimethylsilylethy-
nyl)thiophene)(Cu(hfac))2 (7), respectively, and 1,4-
bis(trimethylsilyl)-1,3-butadiyne (8) with 0.5 equiv. of
Cu2O gives (g2:g2-1,4-bis(trimethylsilyl)-1,3-butadiyne)
(Cu(hfac))2 (9).
All these compounds have been characterized by
1
analytical and spectroscopic data (IR, H-, 13C NMR,
MS). Details are given in Section 2 (Scheme 1).
The dominant bonding mode in the alkyne-metal
complexes may be evaluated by vibrational spectroscopy
(IR) and NMR spectral shift. In Table 1 we compare the
‘‘free’’ alkyne stretch frequencies t(CBC) to those in the
copper(I) b-diketonato complexes. Alkyne-transition
metal bonding usually decreases the bond order of the
alkyne (from sp to sp2) and thereby lowers the frequency
of the alkyne stretching vibration ðDtÞ [8,13]. The
magnitude of this change is directly related to the alkyne
bond order and nuclearity of the complex. Relatively
1
small frequency changes (Dt ꢁ 190 cm ) are observed

3208
S. Delgado et al. / Inorganica Chimica Acta 357 (2004) 3205–3210
8
CF3
6
F3C
F3C
7
6
8
CF3
7
1
O
O
O
Me3Si
Me3Si
Cu
Cu
O
1
Me3Si
5
2
SiMe3
SiMe3
3
4
5
2
3
SiMe3
1 Cu2O
2 hfacH
CH2Cl2
4
2
1
0.5 Cu2O
2 hfacH
CH2Cl2
3
O
Cu
Me3Si
CF3
3
O
2
4
1
5
SiMe3
SiMe3
F3C
2.5 Cu2O
4 hfacH
8
5
CF3
4
CH2Cl2
Me3Si
3
6
O
1
2
7
Cu
SiMe3
O
F3C
CF3
CF3
O
Cu
O
Me3Si
Me3Si
SiMe3
O
Cu
O
Me3Si
F3C
4
CF3
S
Me3Si
SiMe3
1 Cu2O
2 hfacH
5
0.5 Cu2O
2 hfacH
CH2Cl2
CH2Cl2
8
F3C
CF3
O
1
7
6
2
3
4
F3C
5
O
CF3
S
1
Me3Si
SiMe3
O
Cu
Cu
4
O
2
7
Cu
6
5
O
O
7
S
3
Me3Si
SiMe3
CF3
8
CF3
6
F3C
CF3
1
O
O
Cu
2
3
CH2Cl2
Me3Si
SiMe3
Me3Si
SiMe3
2 hfacH
0.5 Cu2O
Cu
9
8
O
O
5
F3C
CF3
6
4
Scheme 1.
structure is proposed where two 1,3,5-tris(trimethylsil-
ylethynyl)benzene ligands are bridged by three Cu(hfac)
building blocks (Scheme 1). This structural type is
described on {[LnM(CBCR)2}MIX (MI ¼ Cu, Ag)
complexes [17]. No change is observed in the variable-
protons (H6), SiMe3 groups (H5) and aromatic protons
(H1) of the thiophene ligands peaks confirms the 1:1 and
1:2 (alkyne:hfac) ratio, respectively. For 6 a single signal
for the thiophene ring, methine and SiMe3 groups is ob-
served in the 1H NMR spectrum at room temperature, but
at variable-temperature, carried out on same conditions
than for 2 and 3, an analogous behavior is observed. It is
also in agreement with the fact that Cu(hfac) unit is co-
ordinated to only triple bond and, in solution at room
1
temperature H NMR experiment.
For (g2:g2-2,5-bis(trimethylsilylethynyl)thiophene)
(Cu(hfac)) (6) and (g2:g2-2,5-bis(trimethylsilylethynyl)
thiophene)(Cu(hfac))2 (7), the integration of the methine

S. Delgado et al. / Inorganica Chimica Acta 357 (2004) 3205–3210
3209
Table 1
Vibrational frequencies for the alkyne stretch (mðCBCÞ) for the ‘free’
alkynes and the alkyne–Cu(hfac) complexes
going from 2 to 3. For complex 4, where three
Cu(hfac) units are coordinated to two ligands, the
downfield shift is intermediate between both. The
same variation is observed for complexes 5 and 6. We
have assigned the carbons of the triple bonds unam-
biguously by using HMBC experiments.
Compound
mðCBCÞ (cmꢀ1
)
DmðCBCÞ (cmꢀ1
)
1
2
3
4
5
6
7
8
9
2164.0
1976.8
1969.9
1974.2
2146.0
1957.4
1945.8
2065.4
1895.7
185.2
192.1
187.8
The thermal properties of all compounds were ex-
amined by thermal gravimetric analysis (TGA/DTA)
and differential scanning calorimetry (DSC). 2 begins
to sublime and loses mass, less than 1% residue, at
about 98 °C and the maximum rate of weight loss
occurs at 122.7 °C. The thermal behavior of com-
pounds 3 and 4 is similar, with maximum rate at
141.5 and 93.3 °C, respectively. The decomposition
temperature is higher for 2 and 4 than for 3, because
at 165 °C 2 and 4 have lost about 30% and 40%,
respectively, of the original mass and 3, at the same
temperature, only about 4%. DSC analysis of a her-
metically sealed sample of 2 displays a sharp endo-
thermic at 122.63 °C, which corresponds to the
melting point; in 3 an endothermic peak at 107 °C is
observed, attributed to a phase change, and at 142.10
°C a sharp endothermic appears corresponding to the
melting point. The same endothermic peak is observed
at 109.8 °C for 4. The sublimation of 6 and 7 has an
onset of 50 °C, with also less than 1% residue and
maximum rate of weight loss occurring at 144.7 and
66.4 °C, respectively. At 165 °C, 6 has lost the 41.3%
and 7 only the 15.9%. DSC of 6 has an endothermic
peak at 175.37 °C attributed to melting and another
endothermic peak at 199.13 °C, while 7 shows an
exothermic peak at 84.77 °C. Finally, the sublimation
of 9 has an onset at 85 °C and maximum rate of
weight loss occurs at 137.3 °C with an endothermic
peak at 136.8 °C in agreement with the melting point.
These behaviors are also observed in copper b-diket-
onate compounds [20]. It is apparent from the TG/
DTA data that these compounds exhibit low volatility,
although 4 and 6 have higher volatility and could
be tested as precursors in copper chemical vapor
deposition.
188.6
200.2
169.8
temperature, they exchange each other quickly. The solid-
state IR spectrum (KBr pellet) shows both t(CBC) signals
corresponding to uncoordinated (2146 cmꢀ1) and coor-
dinated alkyne (1957 cmꢀ1). Finally, for (g2:g2-1,4-
bis(trimethylsilyl)-1,3-butadiyne)(Cu(hfac)2) (9), the
integration of the 1H NMR peaks confirms the 1:2
(alkyne:hfac) ratio.
In general, 13C NMR spectral changes are more
useful for evaluating the dominant bonding mode in
alkyne-metal complexes. In Table 2, the alkyne–car-
bon DdðCBCÞ are given for our complexes, where Dd
represents the experimentally measured chemical shift
and coordination chemical shift. For both p and r
bonding to copper(I) hfac, the Dd for the alkyne
carbons will always result in shielding of the alkyne
carbons. Therefore, in case of dominant r bonding,
deshielding of these carbons will be observed [18]. In
Table 2 we can observe that the 13C NMR signal for
the carbon atoms of the CBC triple bond is only
slightly shifted on coordination to copper(I); a small
downfield shift is observed. The same trend is ob-
served for other alkyne–copper complexes [18,19] and
is indicative of dominant r bonding mode and weak
interaction between the CBC triple bond and copper
center in the title compounds. If we compare
complexes 2 and 3, where one or two Cu(hfac) are
coordinated to 1,3,5-tris(trimethylsilylethynyl)benzene
ligand, the small downfield shift observed increases on
Table 2
Experimentally measured chemical shift and coordination chemical shift (Dd) obtained from 1H NMR and 13C NMR of the ‘free’ alkyne and the
alkyne Cu(I)hfac
Compound
H1
H3
H5
C1
C2
C3
C4
95.50
1
2
3
4
5
6
7
8
9
7.48
7.67
7.82
7.76
7.04
7.31
7.40
0.22
0.28
0.34
0.31
0.24
0.34
0.38
103.1
104.92
106.60
105.84
97.02
95.92
96.24
96.09
99.72
99.82
100.64
100.92
102.84
0.18
0.36
87.95
97.30
85.81
97.30

3210
S. Delgado et al. / Inorganica Chimica Acta 357 (2004) 3205–3210
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4. Conclusions
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ethylsilylethynyl)benzene ligand, show the stability
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General de Investigacion Cientıfica y Tecnologica
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