Volatile square planar β-imino carbonyl enolato complexes of Pd(II) and Ni(II) as potential MOCVD precursors

Article abstract of DOI:10.1016/j.poly.2009.02.017

A series of palladium(II) and nickel(II) [ML₂] complexes (1-6: 1, Pd, L^Me; 2, Pd, L^iBu; 3, Pd, L^nBu; 4, Pd, L^nHe; 5, Ni, L^Me; 6, Ni, L^iBu) has been synthesised by reacting the pr

Full text of DOI:10.1016/j.poly.2009.02.017

Polyhedron 28 (2009) 1229–1234
Contents lists available at ScienceDirect
Polyhedron
journal homepage: www.elsevier.com/locate/poly
Volatile square planar b-imino carbonyl enolato complexes of Pd(II) and Ni(II)
as potential MOCVD precursors
a,*
a
a
b
Marino Basato , Elena Faggin , Cristina Tubaro , Augusto Cesare Veronese
a
Dipartimento di Scienze Chimiche, Università degli Studi di Padova, and ISTM-CNR, via Marzolo 1, I-35131 Padova, Italy
Dipartimento di Scienze Farmaceutiche, Università degli Studi di Ferrara, via Fossato di Mortara 17, I-44100 Ferrara, Italy
b
a r t i c l e i n f o
a b s t r a c t
A series of palladium(II) and nickel(II) [ML ] complexes (1-6: 1, Pd, LMe; 2, Pd, LiBu; 3, Pd, LnBu; 4, Pd, LnHe
;
Article history:
2
Received 17 December 2008
Accepted 12 February 2009
Available online 3 March 2009
Me
iBu
5, Ni, L ; 6, Ni, L ) has been synthesised by reacting the proper acetato salt with the b-enamino keto-
esters (MeCO)(MeOCO)C@C(NH )R (R = Me, i-Bu, n-Bu, n-hexyl). The chain length has practically no effect
2
on the output of the synthetic procedure so that complexes are obtained always in good yields. They are
all square planar and the potentially tridentate ligand is coordinated via the N,O donor atoms of the imino
Keywords:
Me
and keto groups. Their thermal behaviour has been fully studied and [Ni(L
2
) ] demonstrated to be a con-
Metal b-imino carbonyl enolato complexes
venient precursor for the Metal Organic Chemical Vapour Deposition of Ni and NiO thin films.
N,O coordination
Palladium(II)
Nickel(II)
Ó 2009 Elsevier Ltd. All rights reserved.
MOCVD
b-Enaminodiones
1
. Introduction
We have recently exploited the potentiality of a general proce-
to check first of all the effectiveness of the synthetic procedure
and secondly how the type of alkyl chain may affect the physico-
chemical properties of the resulting complexes.
dure for the synthesis of b-imino carbonyl enolato complexes by
reacting the proper metal acetate with b-enaminodiones of the
0
00
2. Experimental
type (R CO)(R CO)C@C(NH
is extremely variable and, for example, R can be an electron-with-
drawing (CN [1], CCl [2a], PhCO [2], EtOCO [3], CH CN [4]) or -
2
)R (HL). The nature of the substituents
2.1. Reagents and apparatus
3
2
donating group (Me [5], Et [3]). These protonated ligands can be
easily synthesised by a method developed in our laboratories
involving a metal-catalysed or -promoted reaction of the nitrile
The reagents were high purity products and generally used as
received. Solvents were dried before use and the reaction appara-
tus carefully deoxygenated. Reactions were performed under argon
and all operations were carried out under an inert atmosphere. The
0
00
RCN with the b-dicarbonyl (R CO)(R CO)CH
of the metal complexes is based on an M(OAc)
2
[6–8]. The synthesis
/2HL exchange pro-
2
1
13
1
solution H and C{ H} NMR spectra were recorded on a Bruker
cess in which the acetate is protonated by the b-enaminodione and
1
13
ꢀ
200 AC (200.12 MHz for H and 50.32 MHz for C) or on a Bruker
liberated in solution as acetic acid. The coordinated L ligand is
1
13
DRX 400 (400.13 MHz for H and 100.63 MHz for C) spectrome-
ter. The chemical shifts are determined by reference to the residual
solvent peaks, using tetramethylsilane as internal standard. The
potentially tridentate through two oxygen and one nitrogen donor
atoms, however in the very numerous investigated cases it acts
only as bidentate (N,O or O,O). N,O coordination is largely preferred
with Ni(II) and Cu(II) metal centres and it is the only one with
Pd(II). The obtained complexes are square planar, very stable and
volatile, and, as a consequence, interesting as precursors in MOCVD
processes [9].
In this paper we have utilized in the reaction with palladium
and nickel acetate the b-enaminodiones shown in Chart 1, which
are characterised by different lengths of the alkyl chains, in order
1
15
solution H– N NMR spectra were recorded on a Bruker Avance
1
15
6
00 (600.13 MHz for H and 60.82 MHz for N) spectrometer.
The H and C assignments were performed by means of conven-
tional homonuclear 2D COSY or 2D H– C HETCORR experiments.
3 2
The N resonances relative to CH NO were detected in the in-
verse acquisition mode through 2D H/ N correlation via double
inept transfer with decoupling during acquisition. The FT IR spectra
were recorded on a Biorad FT S7 PC or on Bruker IFS 66 IR spectro-
1
13
1
13
1
5
1
15
ꢀ
1
photometers at 2 cm
resolution in KBr disks. UV–Vis spectra
were recorded on a Perkin–Elmer Lambda 5 spectrophotometer.
Mass spectra were obtained with a single focus mass spectrometer
*
Corresponding author. Tel.: +39 049 8275217; fax: +39 049 8275223.
E-mail address: marino.basato@unipd.it (M. Basato).
0
277-5387/$ - see front matter Ó 2009 Elsevier Ltd. All rights reserved.
doi:10.1016/j.poly.2009.02.017

1
230
M. Basato et al. / Polyhedron 28 (2009) 1229–1234
HLMe R = methyl
d = 25.6 and 26.7 (CH
and CH
OCO, 1a and 1a ), 106.0 ((CH
CO, 1a), 26.1 and 27.0 (CH
and
Me
3
3
3
0
0
O
O
NH2
R
iBu
CH
CO, 1a ), 51.6 (CH
CO)C, 1a and
3
3
3
HL
HL
HL
R = i-butyl
R = n-butyl
R = n-hexyl
0
0
0
nBu
nHe
1a ), 164.7 (CNH, 1a), 165.4 (CNH, 1a ), 170.9 (CH
3
OCO, 1a ),
0
171.1 (CH
3
OCO, 1a), 179.5 (CH
cm , KBr]: 3322 [ (NH)], 1692 [
]: 3348, 3316(sh) [
3
CO, 1a), 181.4 (CH
(MeOC@O)], 1577 [
(NH)], 1702 [ (MeOC=O)],
(kmax/nm, CHCl ): 328
260 = 21100 ± 2100 dm
3
CO, 1a ). FTIR
OMe
-1
[
m
m
m
(C .•. .O)].
-1
FTIR [cm , CDCl
3
m
m
Chart 1.
1
587
[
m
(C .•. .O)].
UV–Vis
3
3
ꢀ1
ꢀ1
3
(e
= 6400 ± 500 dm mol cm ),
(e
ꢀ1
ꢀ1
Me
+
1
VG MM16 operating in electron ionisation mode at 70 eV electron
beam energy and an ion source temperature of 180 °C. TGS–DSC
analysis were performed with a Perkin–Elmer TGS-2, DSC-4
apparatus.
mol cm ). MS-EI: m/z 418 ([Pd(L
CDCl ): d = 2.15 (s, 3H, CH CO), 2.17 (s, 3H, CH
CO), 6.80 (s, 1H, NH). C NMR (in CDCl ): d = 25.9 and 26.7 (CH
and CH CO), 51.6 (CH OCO), 106.0 ((CH CO)C), 165.2 (CNH),
171.0 (CH OCO), 180.7 (CH
(NH)], 1684 and 1675 [ (MeOC@O)], 1584 and 1576 [
]: 3348 and 3313 [ (NH)], 1702 [ (MeOC@O)],
(kmax/nm, CHCl ): 326
= 22300 ± 1600 dm
] ). Complex (1a) decom-
)
2
] ). (1b). H NMR (in
3
3
3
), 3.75 (s, 3H, CH O-
3
1
3
3
3
3
3
3
-1
X-ray photoelectron spectroscopy (XPS) analyses were per-
3
3
CO). FTIR [cm , KBr]: 3325 and 3310
(C .•. .O)].
formed with a Perkin–Elmer
chromatised Al K radiation (1486.6 eV), calibrated vs. Au4f7/2 at
3.9 eV [10]. XRD data were collected with a Philips diffractometer
with thin film equipment (Cu K , k = 1.54 Å, incident angle 1°).
U
5600ci spectrometer, with mono-
[
m
m
m
-1
a
FTIR [cm , CDCl
3
m
m
8
1576
[
m
(C .•. .O)].
UV–Vis
3
3
ꢀ1
ꢀ1
3
a
(e
= 7400 ± 500 dm
mol cm ), 260
(e
ꢀ
1
ꢀ1
Me
+
mol cm ). MS-EI: m/z 418 ([Pd(L
)
2
poses at 178 °C at atmospheric pressure, while it sublimes at
2
.2. Synthesis of the ligands
ꢀ2
1
56 °C at 4 ꢁ 10 mbar; FTIR analysis reveals that both the subli-
mate (FTIR: 3321 [
and the residue are still (1a) (FTIR: 3322 [
C=O)], 1574 [
(C .•. .O)]). Complex (1b) decomposes at 210 °C at
m
(NH)], 1689 [
m
(MeOC@O)] and 1576 [
m
(C .•. .O)])
(MeO-
The b-enaminodiones (MeCO)(MeOCO)C@C(NH
2
)R (R = Me
m
(NH)], 1690 [
m
Me
iBu
nBu
nHe
(HL ); R = i-Bu (HL ); R = n-Bu (HL ); R = n-hexyl (HL )),
m
were prepared by reaction of methyl acetoacetate with the appro-
priate nitrile in the presence of a stoichiometric amount of SnCl
with the same procedure already reported for HL [11,12].
atmospheric pressure, while it sublimes at 156 °C at
4
,
ꢀ2
4
(
ꢁ 10 mbar; FTIR analysis reveals that the sublimate is (1a)
Me
FTIR: 3320 [
the residue is still (1b) (FTIR: 3323 and 3310 [
673 [ (MeOC@O)], 1574 [
(C .•. .O)]).
] (2a, 2b). [Pd(OAc) ] (0.17 g, 0.76 mmol) was dis-
m
(NH)], 1688 [
m
(MeOC@O)] and 1576 [
m
(C .•. .O)]) while
nBu
1
HL
H, 2CH
CO), 5.68 (s, 1H, NH), 11.21 (s, 1H, NH). FTIR [cm , KBr]: 3370
(NH)], 2959–2872 [d(CH)], 1709 [ (MeOC@O)], 1603 [ (C@O)].
): d = 0.91 (d, 6H, CH(CH ), 1.84 (m,
CO), 2.32 (d, 2H, CH ), 3.70 (s, 3H, CH O-
CO), 6.00 (s, 1H, NH), 11.18 (s, 1H, NH). FTIR [cm , KBr]: 3364
(NH)], 2961–2872 [d(CH)], 1703 [ (MeOC@O)], 1603 [ (C@O)].
): d = 0.87 (m, 3H, CH ), 1.20–1.70 (m,
CO), 2.44 (m, 2H, CH ), 3.75 (s, 3H, CH O-
CO), 5.64 (s, 1H, NH), 11.21 (s, 1H, NH).
:
H NMR (in CDCl
3
): d = 0.93 (t, 3H, CH
3
), 1.30–1.75 (m,
m
(NH)], 1685 and
4
2
), 2.26 (s, 3H, CH CO), 2.45 (m, 2H, CH
3
2
), 3.76 (s, 3H, CH
3
O-
1
m
Pd(L
m
ꢀ
1
iBu
[
)
2
2
[m
m
m
solved in anhydrous ethanol (15 ml) and the resulting solution
iBu
1
HL
:
H NMR (in CDCl
3
3
)
2
iBu
was additioned with HL (0.30 g, 1.50 mmol, in 15 ml anhydrous
1
H, CH), 2.20 (s, 3H, CH
3
2
3
ethanol). The reaction mixture was left under stirring for 2 h at
room temperature, then evaporated under reduced pressure. The
residue was dissolved with dichloromethane (15 ml) and filtered
through Celite. The filtrate was again evaporated to small volume
and finally, treated with diethylether (20 ml), affording a yellow
precipitate (2), which was filtered and dried under vacuum
-
1
[m
m
m
nHe
1
HL : H NMR (in CDCl
3
3
8
H, 4CH ), 2.24 (s, 3H, CH
2
3
2
3
(
0.24 g, 63% yield). Anal. Calc. for C20
32 2 6
H N O Pd (MW = 502.88):
2
.3. Synthesis of the complexes
C, 47.77; H, 6.41; N, 5.57. Found: C, 46.96; H, 6.40; N, 5.38%. (2):
-1
FTIR [cm , KBr]: 3297, 3270 and 3248 [
1584
(C. . .O)]. UV–Vis (kmax/nm, CHCl ): 330
500 dm mol cm ), 260 (e = 19000 ± 1400 dm mol cm ).
m
(NH)], 1715 [
m
(MeOC@O)],
Complexes 1–6 were obtained by reaction of the metal acetate
[
m
(e
= 6600 ±
•
3
3
ꢀ1
ꢀ1
3
ꢀ1
ꢀ1
with the appropriate ligand in 1/2 molar ratio, in anhydrous etha-
nol, at room temperature under argon; the resulting solutions were
left under stirring for variable times and the complexes can either
precipitate spontaneously from the reaction mixture or be recov-
ered from the solution evaporated to dryness. In many cases the
compounds are isolable in different forms, distinguished as a or
b, which exhibit identical composition but different spectroscopic
properties; the symbols a and b indicate only the order in which
iBu
+
MS-EI: m/z 502 ([Pd(L ) ] ). The NMR spectra revealed that the
2
isolated solid was a mixture of two isomers (2a, 2b) in 2.5/1 ratio.
1
(2a).
3 3 2 2
H NMR (in CDCl ): d = 0.89 (d, 6H, (CH ) CHCH ,
3
JHH = 6.6 Hz), 1.83 (m, 1H, (CH ) CHCH ), 2.18 (s, 3H, CH CO),
2.37 (d, 2H, (CH ) CHCH , JHH = 7.4 Hz), 3.74 (s, 3H, CH OCO),
6.34 (s, 1H, NH). C NMR (in CDCl ): d = 22.8 ((CH ) CHCH ),
3 2
2
3
3
3
2
1
2
3
3
3
3 2
2
26.6 (CH CO), 28.1 ((CH ) CHCH ), 49.5 ((CH ) CHCH ), 52.2
3
3 2
2
3 2
2
the complexes have been isolated.
3 3 3
(CH OCO), 106.2 ((CH CO)C), 169.0 (CNH), 171.6 (CH OCO), 181.7
Me
] (0.17 g, 0.76 mmol) and HLMe
15
1
[
Pd(L
)
2
] (1a, 1b). [Pd(OAc)
2
3 3 3
(CH CO). N NMR (in CDCl ): d = 145.4. (2b). H NMR (in CDCl ):
3
(
0.25 g, 1.60 mmol) were dissolved in anhydrous ethanol (20 ml)
3 2 2
d = 0.92 (d, 6H, (CH ) CHCH , JHH = 6.6 Hz), 1.83 (m, 1H,
and the resulting solution was stirred for 4 h at room temperature,
then filtered. The solid was recrystallised from dichloromethane/
hexane, affording pure (1a) as a bright yellow solid (0.090 g, 27%
yield). The yellow alcoholic filtrate was evaporated to small vol-
ume under reduced pressure and treated with diethylether
(CH ) CHCH ), 2.09 (s, 3H, CH CO), 2.33 (d, 2H, (CH ) CHCH ,
3
2
2
3
3 2
13
2
3
JHH = 7.4 Hz), 3.74 (s, 3H, CH OCO), 6.74 (s, 1H, CNH). C NMR
3
(in CDCl ): d = 22.9 ((CH ) CHCH ), 26.2 (CH CO), 27.9
3
3 2
2
3
((CH ) CHCH ), 49.0 ((CH ) CHCH ), 52.2 (CH OCO), 106.4
3
2
2
3 2
2
3
15
((CH CO)C), 168.0 (CNH), 171.8 (CH OCO), 179.9 (CH CO).
3
3
3
N
(
10 ml), giving (1b) as a light yellow solid, which was filtered
and dried under vacuum (0.157 g, 47% yield). Anal. Calc. for
Pd (MW = 418.72): C, 40.16; H, 4.81; N, 6.69. Found
for (1a): C, 40.28; H, 4.71; N, 6.37. Found for (1b): C, 39.57; H,
NMR (in CDCl ): d = 166.9. Complex (2) decomposes at 195 °C at
3
atmospheric pressure, while it sublimes at 155 °C at
ꢀ2
C
14
20
H N
2
O
6
6 ꢁ 10 mbar; FTIR analysis reveals that the sublimate is (2b)
ꢀ1
(FTIR [cm , KBr]: 3270 and 3248 [
1585 [
(C. . .O)]) while the residue is still a mixture of (2a) and
(2b) (FTIR: 3298, 3270 and 3248 [
1584 [
(C. . .O)]).
m(NH)], 1713 [m(MeOC@O)],
1
4
.76; N, 6.68%. (1a). H NMR (in CDCl
3
), two species, labelled a
m
•
0
and a , in approximately 2/1 ratio are present in solution:
d = 2.09 (s, 3H, CH
(
6
m(NH)], 1715 [m(MeOC@O)],
3
CO, 1a), 2.16 (s, 3H, CH
3
, 1a), 2.18 and 2.19
m
•
0
0
nBu
2s, 3H, CH
3
CO and CH
3
, 1a ), 3.76 (s, 4.5H, CH
3
OCO, 1a and 1a ),
[Pd(L )2] (3). A yellow solid was obtained with the same
0
13
.34 (s, 0.5H, NH, 1a ), 6.79 (s, 1H, NH, 1a). C NMR (in CDCl
3
):
experimental procedure of complex (2) (0.29 g, 77% yield). Anal.

M. Basato et al. / Polyhedron 28 (2009) 1229–1234
1231
Calc. for C20
H
32
N
2
O
6
Pd (MW = 502.88): C, 47.77; H, 6.41; N, 5.57.
the residue is complex (5) (FTIR: 3320 [
m
(NH)], 1688 [
m
(MeOC@O)],
1
Found: C, 46.89; H, 6.30; N, 5.41%. H NMR (in CDCl
3
): d = 0.87 (t,
(CH ), 1.52
CO), 2.42 (t, 2H,
OCO), 6.38 (s, 1H,
), 22.7 (CH ), 25.6
OCO), 105.7 ((CH CO)C),
1570 [
m
(C .•. .O)]).
3
iBu
] (6). A solution of HLiBu (0.25 g, 1.60 mmol) in anhy-
3
(
H, CH
m, 2H, CH
CH (CH CH
3
(CH
2
)
3
,
J
HH = 7.2 Hz), 1.28 (m, 2H, CH
CH CH ), 2.14 (s, 3H, CH
HH = 8.0 Hz), 3.72 (s, 3H, CH
): d = 13.8 (CH (CH
), 39.3 (CH ), 51.7 (CH
68.7 (CNH), 171.1 (CH OCO), 179.3 (CH
295 [ (NH)], 1719 [ (MeOC=O)], 1582 [
CHCl ): 328 = 7100 ± 500 dm mol cm ),
= 20200 ± 1500 dm mol cm ). MS-EI: m/z 503 ([Pd(LnBu)
3
CH
2
2
)
2
[Ni(L
)
2
.
3
CH
J
2
2
2
3
drous ethanol (20 ml) was added to a solution of [Ni(OAc)
2
] 4H
2
O
3
3
2
)
2
2
,
3
(0.19 g, 0.78 mmol, in 15 ml anhydrous ethanol). The resulting
mixture was stirred for 12 h at room temperature and then evapo-
rated to small volume under reduced pressure. The resulting resi-
due was treated with ethanol (20 ml) under stirring for 1 h and the
solvent was again removed. Treatment with diethylether (20 ml)
afforded a reddish precipitate, which was filtered and dried under
vacuum. The solid was recrystallised from dichloromethane/dieth-
ylether, affording pure (6) as a pink solid (0.26 g, 75% yield). Anal.
13
NH). C NMR (in CDCl
CH CO), 30.4 (CH
3
3
2
)
3
2
(
1
3
3
2
2
3
3
1
-
3
3
CO). FTIR [cm , KBr]:
m
m
m
(C .•. .O)]. UV–Vis (kmax
/
3
ꢀ1
ꢀ1
nm,
3
(
e
260
3
ꢀ1
ꢀ1
+
(e
2
] ).
Complex (3) decomposes at 195 °C at atmospheric pressure, while
ꢀ
2
it sublimes at 172 °C at 4 ꢁ 10 mbar; FTIR analysis reveals that
both the sublimate (FTIR: 3293 [ (NH)], 1717 [ (MeOC@O)],
582 [
(C .•. .O)]) and the residue are complex (3) (FTIR: 3293
(NH)], 1719 [ (MeOC@O)], 1582 [
(C .•. .O)]).
] (4). [Pd(OAc) ] (0.16 g, 0.73 mmol) was dissolved in
anhydrous ethanol (15 ml) and the resulting solution was addi-
Calc. for C20
32 2 6
H N NiO (MW = 455.19): C, 52.77; H, 7.09; N, 6.15.
1
m
m
Found: C, 51.44; H, 7.01; N, 5.98%. H NMR (in CDCl
3
): d = 0.90
CHCH ),
HH = 7.2 Hz), 3.70
), 5.37 (s, 1H, CNH). C NMR (in CDCl ): d = 22.8
), 26.7 (CH CO), 27.9 ((CH CHCH ), 49.0
), 51.8 (CH OCO), 106.1 ((CH CO)C), 170.7 (CNH),
N NMR (in CDCl ): d = 162.7.
FTIR [cm , KBr]: 3279 and 3268 [ (NH)], 1709 [ (MeOC@O)],
1582 ): 346 = 3000 ±
(C .•. .O)]. UV–Vis (kmax/nm, CHCl
200 dm mol cm ), 272
3
1
m
(d, 6H, (CH
1.94 (s, 3H, CH
(s, 3H, CH CO
((CH CHCH
((CH CHCH
171.1 (CH
3
)
2
CHCH
2
,
JHH = 6.8 Hz), 1.72 (m, 1H, (CH
3
)
2
2
3
[
m
m
m
3
CO), 2.28 (d, 2H, (CH ) CHCH , J
3 2 2
nHe
13
[
Pd(L
)
2
2
3
2
3
3
)
2
2
2
3
3
)
2
2
nHe
tioned with HL
(0.33 g, 1.45 mmol) dissolved in anhydrous eth-
3
)
2
3
3
1
5
anol (15 ml) and ethyl acetate (1 ml). The reaction mixture was left
under stirring for 1 h at room temperature, then evaporated to
small volume under reduced pressure. The residue was treated
with ethanol (20 ml) under stirring for 1 h and the solvent was re-
moved. The residue was dissolved with dichloromethane (15 ml)
and filtered through Celite. The filtrate was again evaporated to
small volume and finally treated with diethylether (20 ml), afford-
ing a yellow precipitate, which was filtered and dried under vac-
3
1
OCO), 181.5 (CH
3
CO).
3
-
m
m
[
m
3
(e
3
ꢀ1
ꢀ1
3
ꢀ1
ꢀ1
(e = 26300 ± 1700 dm mol cm ),
3
ꢀ1
ꢀ1
244 (e = 34600 ± 2300 dm mol cm ). MS-EI: m/z 454 ([Ni-
iBu
+
(L
sure, while it sublimes at 125 °C at 7.5 ꢁ 10 mbar; FTIR analysis
reveals that both the sublimate (FTIR: 3279 and 3268 [ (NH)],
(C .•. .O)] and the residue (FTIR: 3279
2
) ] ). Complex (6) decomposes at 180 °C at atmospheric pres-
ꢀ2
m
uum (0.25 g, 61% yield). Anal. Calc. for
C
24
H
40
N
2
O
6
Pd
1707 [
m
(MeOC@O)], 1582 [
m
(MW = 558.99): C, 51.57; H, 7.21; N, 5.01. Found: C, 51.61; H,
and 3268 [
m
(NH)], 1709 [
m
(MeOC@O)], 1582 [
m
(C .•. .O)]) are com-
1
7
J
CH
CH
.31; N, 4.90%. H NMR (in CDCl
3
): d = 0.85 (t, 3H, CH
HH = 6.1 Hz), 1.25–1.50 (m, 8H, CH (CH CH ), 2.15 (s, 3H,
3JHH = 7.3 Hz), 3.72 (s, 3H,
NMR (in CDCl ): d = 14.0
CO), 28.2 (CH ), 29.2 (CH ), 31.4
CO)C), 169.0 (CNH),
3
2
(CH )
5
,
plex (6).
3
3
2
)
4
2
)
2 4
CH
C
2
,
2.4. Vapour deposition of complex [Ni(LMe
) ] (5)
2
3
CO), 2.40 (t, 2H, CH
3
(CH
1
3
3
OCO), 6.19 (s, 1H, NH).
3
(
(
CH
CH
3
(CH
2
5
) ), 22.5 (CH
2
), 25.9 (CH
3
2
2
All deposition experiments were performed in a cold wall reac-
tor using O , N , N /O or N /O /H O mixtures as gas carrier (purity
2
), 39.6 (CH
2
), 51.6 (CH
3
OCO), 105.6 ((CH
3
2
2
2
2
2
2
2
-1
1
1
71.1 (CH
711 (MeOC@O)], 1580
): 328 ( = 7600 ± 500 dm mol cm ), 260 (
3
OCO), 180.6 (CH
3
CO). FTIR [cm , KBr]: 3297 [
m
(NH)],
99.999%). The precursor was sublimed from a small crucible lo-
cated close to the reactor (for a similar reactor see Ref. [13]).
[
m
[m
(C .•. .O)]. UV–Vis (kmax/nm,
3
ꢀ1
ꢀ1
CHCl
500 dm mol cm ). MS-EI: m/z 558 ([Pd(L
4) decomposes at 189 °C at atmospheric pressure, while it sub-
3
e
e
= 20100 ±
Deposition on silicon under N
2
: temperature of precursor
3
ꢀ1
ꢀ1
nHe
+
1
(
2
) ] ). Complex
132 °C, of substrate 450 °C, total pressure 0.08 mbar, gas flow
ꢀ1
8.1 cc min ; deposition on glass under O
2
: temperature of precur-
ꢀ2
limes at 180 °C at 5 ꢁ 10 mbar; FTIR analysis reveals that both
the sublimate (FTIR: 3295 [ (NH)], 1713 [ (MeOC=O)], 1582
(NH)], 1711
sor 130 °C, of substrate 450 °C, total pressure 0.08 mbar, gas flow
ꢀ1
m
m
8.1 cc min ; deposition on silicon under O
2 2
+ H O: temperature
[
[
m
m
(C .•. .O)]) and the residue (FTIR: 3297
[m
of precursor 133 °C, of substrate 450 °C, total pressure 0.03 mbar,
ꢀ1
(MeOC@O)], 1580 [
m
(C .•. .O)]) are complex (4).
2 2
gas flow 10 cc min ; deposition on glass under O + H O: temper-
Me
Me
[
Ni(L
)
2
] (5). A solution of HL
(0.63 g, 4.02 mmol) and
ature of precursor 133 °C, of substrate 450 °C, total pressure
.
ꢀ1
[
Ni(OAc)
2
] 4H
2
O (0.50 g, 2.00 mmol) in anhydrous ethanol (20 ml)
0.03 mbar, gas flow 10 cc min
.
was stirred for 1 h at room temperature, then evaporated to small
volume under reduced pressure. The residue was treated with eth-
anol (20 ml) and again the solvent was removed. This treatment
was continued until the smell of acetic acid disappeared; 3–4 cy-
cles were generally sufficient. Finally, treatment with diethylether
The Si(100) substrate before the deposition was degreased
using boiling trichloroethylene and rinsed with isopropyl alcohol.
3
. Results and discussion
(
10 ml) gave a light red solid, which was filtered and dried under
vacuo (0.47 g, 63%). Anal. Calc. for C14 NiO (MW = 371.03):
C, 45.32; H, 5.43; N, 7.55. Found: C, 45.34; H, 5.34; N, 7.58%.
NMR (in CDCl ): d = 1.95 (s, 3H, CH CO), 2.08 (s, 3H, CH CNH),
.68 (s, 3H, CH OCO), 5.37 (s, 1H, NH). C NMR (in CDCl ):
d = 25.9 and 27.2 (CH CNH and CH CO), 51.2 (CH OCO), 105.8
CO)C), 167.7 (CNH), 170.3 (CH OCO), 181.7 (CH CO). FTIR
(MeOC@O)], 1570 [
(C .•. .O)].
The results obtained in this study confirm the validity of the
20
H N
2
6
procedure for the synthesis of b-imino carbonyl enolato complexes
starting from metal(II) acetates and b-enaminodiones (Eq. (1)). The
factors governing the success of this exchange reaction have been
recently fully
1
H
3
3
3
1
3
3
3
3
3
3
3
0
00
(
[
(CH
3
3
3
MðOAcÞ þ 2ðR COÞðR COÞC@CðNH
2
ÞR
2
-
1
cm , KBr]: 3320 [
m
(NH)], 1688 [
m
m
0
00
!
½MððR COÞðR COÞCCðNHÞRÞ ꢂ þ 2HOAc
ð1Þ
3
ꢀ1
ꢀ1
2
UV–Vis (kmax/nm, CHCl
2
3
3
): 342 ( = 3500 ± 300 dm mol cm ),
e
3
ꢀ1
ꢀ1
72
(
e
= 30200 ± 2800 dm mol cm ),
244
(e
= 36500 ±
exploited and depend on: (i) the relative stabilities of metal acetates
and metal complexes and on (ii) the acidity of the b-enaminodiones
compared with that of acetic acid [2a]. The chain length in the series
3
ꢀ1
ꢀ1
Me
+
000 dm mol cm ). MS-EI: m/z 370 ([Ni(L
)
2
] ). Complex (5)
decomposes at 193 °C at atmospheric pressure, while it sublimes
ꢀ2
at 130 °C at 4 ꢁ 10 mbar; FTIR analysis reveals that the subli-
of investigated b-enamino ketoesters (MeCO)(MeOCO)C@C(NH
2
)R
mate is a mixture of (5) and another isomer (FTIR: 3342 and
(R = Me, i-Bu, n-Bu, n-hexyl) has practically no effect on the output
Me
3
320 [
m
(NH)], 1690 [
m
(MeOC=O)], 1591 and 1572 [
m
(C .•. .O)]), while
2
of the synthetic procedure so that complexes [ML ] (1–6: 1, Pd, L
;

1
232
M. Basato et al. / Polyhedron 28 (2009) 1229–1234
2
, Pd, LiBu; 3, Pd, LnBu; 4, Pd, LnHe; 5, Ni, LMe; 6, Ni, LiBu) are obtained
dent. The absence of these expected correlations may be due
perhaps to a turning away of the methyl oxo. It should be under-
lined that the position of the N–H signal attributable to the minor
always in good yields. In most cases the complexes precipitate
spontaneously otherwise the reaction is forced toward the desired
products by co-distillation from the reaction mixture of solvent
and the acetic acid produced in the ligand exchange process.
The results are coherent with those obtained with the ethyl
substituent at the imino group [3]. The potentially tridentate
N,O,O ligand acts in all cases as bidentate through the nitrogen
and the keto oxygen atoms to give monomeric square planar neu-
tral complexes. These are air and moisture stable solids, which can
be stored safely under inert atmosphere; they are soluble in com-
0
species labelled a strongly depends on the type of solvents and, for
example, passing from CDCl to anhydrous C D moves from 6.34
3
6 6
to 5.10 ppm, thus suggesting the possibility of intermolecular
hydrogen bonding. With more sterically demanding groups, like
n-butyl or n-hexyl, only one species has been isolated, thus indicat-
ing that the rotation of the ester group is hindered and that acetyl
and methyl ester groups are preferentially faced to each other
(conformation A in Fig. 1)
mon organic solvents, such as ethanol, CH
mostly insoluble in n-hexane or diethylether.
2
Cl
2
, and CHCl
3
, but
In the UV–Vis spectra, palladium(II) complexes (1)–(4) show
two maxima at ca. 330 and 260 nm of medium and strong intensi-
The IR spectra in KBr of all complexes are very similar as the
whole, being characterised by: (i) the N–H band approximately
ties respectively. The shortest wavelength absorption at 260 nm
*
p ? p transition of the ligand, while the
absorption at 330 nm ca. may be due to metal-to-ligand charge
may be assignable to
ꢀ1
ꢀ1
around 3300 cm , (ii) a band at 1570–1585 cm , which can be
easily attributed to the coordinated acetyl carbonyl, (iii) an absorp-
transfer transitions. The nickel compounds (5) and (6) present a
ꢀ1
*
tion in the range 1675–1719 cm due to the C@O stretching vibra-
third absorption at 240 nm ca., which is still assigned to a
transition of the ligand.
p ? p
tion of the uncoordinated ester. In fact, the wavenumber values for
0
O,O -chelation in b-diester complexes are always close to
The complexes are volatile and remarkably stable as it appears
evident from the presence of very intense molecular ions in the
mass spectra of all compounds (1)–(6) (see Supplementary Infor-
mation). The primary fragmentations are the same for both forms
(a and b) and can be divided in two main categories: fragmenta-
tions of the ligand moiety anchored to the metal and those of the
‘‘free” ligand. The mass spectra of all the complexes are also char-
ꢀ1
1
600 cm , as an effect of electronic delocalisation which occurs
in the metallocycle ring [14]. These features confirm N,O ligand
to metal coordination.
In addition the H and 13C NMR spectra are consistent with the
1
proposed picture; in particular the ketonic carbonyl C signal
(
179.3–181.7 ppm) is shifted upfield in comparison with the signal
+
of the corresponding carbon in the free ligand [2b,3]. No informa-
tion can be gained instead from the chemical shift values of the
C@N and C(O)OMe carbons which remain practically unchanged.
Preferential coordination of the keto group with respect to the es-
ter one has been widely observed in analogous complexes [1–3].
The palladium complexes (1) and (2) have been isolated in two
forms, labelled a and b, whereas palladium(II) complexes (3) and
acterised by the presence of HML ions containing only one coordi-
nated ligand and related fragmentations.
The high stability of this type of complexes is also confirmed by
melting point measurements and TGA analysis (Table 1 and Fig. 2).
The effect of the length of R chain on the melting point is rather
limited, even if a decrease of the value with the lengthening of
the chain is observed, probably due to reduced H-bonding interac-
tions. Comparing palladium(II) and nickel(II) complexes it is evi-
dent a greater stability of the former ones, as indicated by the
somewhat higher melting point values (215–178 °C versus 193–
180 °C). TGA studies of the palladium complexes (1)–(4) show that
they decompose in two steps; the first around 300 °C gives a resi-
due (ca. 30%), which transforms in palladium black upon heating at
950 °C. Also in the case of nickel complexes (5)–(6) there are two
losses of weight: the major one takes place between 110–350 °C
and gives a residue that vaporizes almost completely at tempera-
tures below 750 °C.
(
4) and the nickel ones (5) and (6) have been isolated only in one
form.
This explains some small differences between the NMR spectra
of samples (1a) and (1b) or (2a) and (2b). NOE experiments carried
out on sample 2a revealed a strong dipolar interaction between the
protons of the i-butyl substituent and the imino hydrogen. More-
over a strong dipolar interaction between the hydrogen atoms of
the acetyl and methyl ester groups indicates that they are spatially
very close to each other (conformation A in Fig. 1). The same exper-
iments carried out on sample (2b), indicate that the oxo and meth-
oxy substituents on (2b) are turned and the methyl ester is
preferentially faced toward the i-butyl group (conformation B).
Thus the small differences observed in the solution NMR spectra
of (2a) and (2b) can be easily attributed to these conformational
changes of the ester substituent of the chelate ring. Similar consid-
erations may apply to the solution chemistry of the palladium
complex (1) for which three different sets of signals relative to a,
DSC measurements show a markedly different behaviour for the
two metal centres. Nickel complexes are characterised by a strong
ꢀ
1
endothermic peak (31.3 and 54.3 kJ mol ) at approximately the
fusion temperatures 193 (5) and 180 (6) °C. For the palladium com-
plexes the
DH versus temperature diagram is much more compli-
ꢀ1
cated: low energy endothermic peaks (ca. 3 kJ mol ), probably
associated to conformational processes, are observed, in addition
to very intense peaks in the correspondence of state changes like
fusion and evaporation.
0
a and b are observed. NOE experiments are not conclusive for this
complex; in fact a sample of (1b) shows strong dipolar interactions
consistent with conformation B. However sample (1a) shows two
N–H proton signals of different intensity relative to the two species
The nickel complex (5) has been tested under MOCVD condi-
tions to verify its suitability as precursor in the formation of thin
films over glass or silicon substrates. Its high volatility allows
rather accessible temperatures (130–133 °C) and pressures
0
labelled a and a , both correlating only with the corresponding imi-
no methyl substituent, and no other spatial correlations are evi-
ꢀ
2
ꢀ2
(
4
3 ꢁ 10 –8 ꢁ 10 mbar), whereas the substrate was kept at
50 °C to ensure fast decomposition of the complex.
Me Me
Me
The film surface morphology was investigated by SEM (Fig. 3),
O
N
O
O
N
O
O
confirming a uniform substrate coverage, typical of a three-dimen-
sional growing, characterised by well-interconnected agglomer-
ates with mean sizes around 100 nm.
2\Pd
2\Pd
O
H
i-Bu
A)
H
i-Bu Me
The nature of the thin films depends on the employed carrier
gases: use of N
respectively, whereas a mixture of water with either N
fords a co-deposition of both. The presence of nickel oxide in the
2
and of O
2
gives nickel metal and nickel oxide
(
(B)
2
or O af-
2
Fig. 1. Proposed conformations of complex (2).

M. Basato et al. / Polyhedron 28 (2009) 1229–1234
1233
Table 1
Thermal data for complexes (1)–(6) and for [M(LEt)
2
] (M = Pd, Ni).
Complex
m. p.
°C)
178 (dec.)
DSC
T (°C)
93
TGA
(
D
H (kJmol-1
)
T (°C) range
Wt.% loss
(
1a)
1b)
2.9
12.9
1.9
18.2
0.6
17.4
142.2
70–150
2.2
1
1
29
94
150–290
290–950
110–320
320–950
58.66
12.15
68.63
10.73
(
210-220 (dec.)
196
2
2
16
42
[
[
(
Pd(LEt
Pd(LEt
2)
)
2
] form aa
] form ba
>250
178–301
150–440
75.44
6.16
68.3
6.95
78.28
13.68
440–915
)
2
>250
117
19.9
101.2
0.4
3
4.8
17.2
55.3
6.9
3.2
1.4
130–290
290–935
115–300
300–950
208–310
194–199 (dec.)
178
190
220
250
(
3)
4)
195–200 (dec.)
189 (dec)
223
46
148
130–285
285–950
185–290
290–950
71.83
9.25
74.95
8.79
2
(
2
2
12
20
31.7
31.3
(5)
193
183
197
210–350
92.42
5.61
92.6
6.6
350–950
[
Ni(LEt
)
2
]a
126
17.3
31.2
95.7
54.3
150–280
280–900
1
3
83
22
(6)
178–181 (dec.)
182
110–310
93.9
6.22
310–950
a
The synthesis and characterisation of these complexes have been reported in Ref. [3].
Fig. 2. Comparison of the thermal behaviour (TGA and DSC) of complexes (1a) and (5).
films obtained under nitrogen can not be detected by X-ray tech-
nique, even if ESCA analysis indicates the presence of NiO (see fur-
ther); these results suggest an amorphous phase for NiO [15]. X-
rays analysis on the deposited films reveals preferential
a

1
234
M. Basato et al. / Polyhedron 28 (2009) 1229–1234
2 2
Fig. 3. Selected SEM images of the thin films deposited on glass using O + H O carrier.
Table 2
gives rise to octahedral high melting, non volatile, oligomeric via
O-bridges structures [20].
Superficial composition of films obtained by MOCVD of complex [Ni(LMe)
] (5).
2
Substrate/carrier
Si/N
2
Glass/O
2
Si/O
2
+ H
2
O
2 2
Glass/O + H O
Acknowledgement
C/%
64.0
18.3
15.4
2
21.0
40.7
32.9
0
47.7
26.6
24.7
1
51.4
25.4
22.0
1
O/%
Ni/%
N/%
Si/%
We thank Mr.A. Ravazzolo for skilled technical assistance.
0
5.0
0
0
Appendix A. Supplementary data
Supplementary data associated with this article can be found, in
the online version, at doi:10.1016/j.poly.2009.02.017.
orientation (111) for nickel metal and (200) plus (111) for nickel
oxide.
The superficial composition determined by ESCA (Table 2)
shows in all cases a high carbon content, mostly due to a superficial
contamination, and very low quantity of nitrogen derived from li-
gand decomposition.
Silicon is practically absent in the surface so ensuring a good
homogeneity of the deposit. The Ni/O ratio is within the experi-
mental errors close to 1. Analysis of the films deposited in the pres-
ence of water reveals two contributions to the O1s peak: the first
one at 529.9 eV is attributed to Ni–O bonds in the NiO, whereas
the contribution at higher binding energy (531.6 eV) suggest the
presence of OH groups present on the NiO surface [16–18]. The
Ni2p peaks are found at a value consistent with literature data
for NiO with hydroxyl groups on the surface [17]; the NiO (111)
faces can be in fact stabilised by hydroxylation [19].
References
[
[
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(
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6
(
[
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[
[
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[
[
10] E. Brescacin, M. Basato, E. Tondello, Chem. Mater. 11 (1999) 314.
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. Conclusions
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[
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14] D.A. Thornton, Coord. Chem. Rev. 104 (1990) 173.
In conclusion, the synthesis of b-imino carbonyl enolato com-
[
plexes of palladium(II) and nickel(II), by reaction of the acetato salt
and the required b-enaminodione, appears rather general. The ob-
tained complexes are square planar, stable and volatile, with a lim-
ited effect of the imino alkyl chain on their thermal behaviour. The
N,O square planar coordination observed also for nickel(II) com-
[15] M. Becht, F. Atamny, A. Baiker, K.-H. Dahemen, Surf. Sci. 371 (1997) 399.
[
16] J.F. Moulder, W.F. Stickle, P.E. Sobol, K.D. Bomben, Handbook of X-ray
Photoelectron, J. Chastain, Perkin Elmer Corporation, USA, 1992.
17] (a) R.P. Furstenau, G. McDougall, M.A. Langell, Surf. Sci. 150 (1985) 55;
(b) N.S. McIntyre, M.G. Cook, Anal. Chem. 47 (1975) 2208.
[
[
[
18] M.M. Natile, A. Glisenti, Chem. Mater. 14 (2002) 4895.
19] (a) M.A. Langell, M.H. Nassir, J. Phys. Chem. 99 (1995) 4162;
plexes is particularly interesting, because it makes possible to uti-
(
b) D. Cappus, C. Xu, D. Ehrlich, B. Dillmann, C.A. Ventrice Jr., K. Al Shamery, H.
Me
lize, for example, [Ni(L
2
) ], as convenient MOCVD precursor for
Kuhlenbeck, H.-J. Freund, Chem. Phys. 177 (1993) 533.
the production of Ni or NiO thin films. It should be underlined that
O,O coordination to nickel(II), as in b-carbonyl enolato complexes,
[20] R.C. Mehrotra, R.C. Bohra, D.P. Gaur, Metal b-Diketonates and Allied
Derivatives, Academic Press, New York, 1978.