N,O versus O,O coordination in β-imino diketonato complexes: Role of the metal center and of the imino substituent

Article abstract of DOI:10.1016/j.ica.2008.05.003

β-Imino carbonyl enolato metal(II) complexes of general formula [M((RCO)(R′CO)CC(R″)NH)₂] (M = Mn, Fe, Co, Ni, Cu, Zn, Pd, R = R′ = Me, R″ = CCl₃; M = Cu, Pd, R = R′ = Me, R″ = PhCO; R = Me, R′ = Ph, R″ = PhCO; R = R′ = Ph, R″ = PhCO

Full text of DOI:10.1016/j.ica.2008.05.003

Inorganica Chimica Acta 362 (2009) 531–536
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N,O versus O,O coordination in b-imino diketonato complexes: Role of the
metal center and of the imino substituent
a
a
a
b
Marino Basato a, , Marzio Bortolussi , Elena Faggin , Cristina Tubaro , Augusto Cesare Veronese
*
a Dipartimento di Scienze Chimiche, Università di Padova, and ISTM-CNR, Via Marzolo 1, I-35131 Padova, Italy
b Dipartimento di Scienze Farmaceutiche, Via Fossato di Mortara 17, I-44100 Ferrara, Italy
a r t i c l e i n f o
a b s t r a c t
b-Imino carbonyl enolato metal(II) complexes of general formula [M((RCO)(R0CO)CC(R00)NH)2] (M = Mn,
Fe, Co, Ni, Cu, Zn, Pd, R = R0 = Me, R00 = CCl3; M = Cu, Pd, R = R0 = Me, R00 = PhCO; R = Me, R0 = Ph, R00 = PhCO;
R = R0 = Ph, R00 = PhCO) are easily synthesized by the reaction of metal(II) acetates with the proper
b-enaminodiones in 1/2 molar ratio in ethanol at room temperature. In all the cases the trifunctional
NOO b-imino carbonyl enolate ligand acts as bidentate to give ML2 complexes, whose structure depends
on the metal center and on the nature of the substituent R00 at the imino carbon. With R00 = CCl3 an O,O
coordination is observed for all the metal centers but one, in fact palladium(II) exhibits an N,O coordina-
tion through the imino nitrogen and one keto oxygen. By contrast with R00 = PhCO the ligand is always
coordinated through the imino nitrogen and one keto oxygen atom.
Article history:
Received 5 March 2008
Received in revised form 24 April 2008
Accepted 1 May 2008
Available online 7 May 2008
Keywords:
Transition metal complexes
b-Enaminodiones
b-Imino diketonato complexes
Metal acetates
Ó 2008 Elsevier B.V. All rights reserved.
N,O coordination
1. Introduction
acetates with b-enaminodiones in ethanol at ambient temperature,
and it has been mainly applied until now to the synthesis of b-imi-
The use of acetylacetonato complexes of various transition met-
als as mild selective catalysts of C–C bond formation between C–H
acid substrates and nitriles is a well-recognized procedure for the
synthesis of substituted b-enaminones [1–4]. The scope of these
products (RCO)(Z)C@C(R0)NH2 is quite large and involves the reac-
tion of b-dicarbonyls (Z = RCO) [5], b-ketoamides (Z = C(O)NR2),
nitroacetoesters (Z = NO2) [6], b-ketophosphonates (Z = PO(OR)2)
[7] with nitriles bearing electron-withdrawing groups (R0 = CN,
CCl3, PhCO, CH2CN, ROCO). An extension of this synthetic proce-
dure to non-activated nitriles (R0 = alkyl, aryl, NH2) utilizes tin tet-
rachloride or cationic platinum nitrile complexes as promoters in
stoichiometric quantity [8].
The mechanism implies in the key steps coordination of the ni-
trile to the metal center and consequent electrophilic activation of
the cyano carbon, which undergoes nucleophilic attack by the C–H
carbon of the enolato ligand. The resulting metal intermediate can
adopt with b-carbonylenolato catalysts an N,O (linkage isomer I) or
O,O coordination (linkage isomer II) (Chart 1).
no carbonyl enolato complexes of Ni(II), Cu(II), Pd(II) of formula
[M((MeOCO)(RCO)CC(R0)NH)2] [11]. It should be underlined that
an N,O coordination was always observed.
These compounds are alternative to b-diketonates as precursors
in homogeneous and heterogeneous catalysis or in thin film chem-
ical vapor deposition [12], so it seemed interesting to check this
procedure with a more extended series of metal centers (Mn, Fe,
Co, Ni, Cu, Zn, and Pd) and b-enaminodiones, in order to verify
the generality of this synthesis and the type of coordination. The
employed b-enaminodiones derive from the C–C coupling reaction
of acetylacetone with trichloroacetonitrile, benzoyl cyanide, cyan-
ogen and of benzoylacetone and dibenzoylmethane with benzoyl
cyanide.
2. Experimental
2.1. Reagents and apparatus
These complexes were isolated in few cases by stoichiometric
reaction of nickel(II) or copper(II) acetylacetonates with the proper
nitrile (cyanogen or benzoyl cyanide) [9,10]. An alternative more
general procedure, which avoids the occurrence of side reactions
and/or decomposition pathways, involves the reaction of the metal
The reagents were high purity products and generally used as
received. Solvents were dried before use and the reaction appara-
tus was carefully deoxygenated. Reactions were performed under
argon and all the operations were carried out under an inert atmo-
sphere. The solution 1H and 13C{1H} NMR spectra were recorded on
a Bruker 200AC (200.12MHz for 1H and 50.32 MHz for 13C) or on a
Bruker DRX 400 (400.13 MHz for 1H and 100.63 MHz for 13C);
chemical shifts (d) are reported in units of ppm relative to the
* Corresponding author. Fax: +39 49 8275223.
E-mail address: marino.basato@unipd.it (M. Basato).
0020-1693/$ - see front matter Ó 2008 Elsevier B.V. All rights reserved.
doi:10.1016/j.ica.2008.05.003

532
M. Basato et al. / Inorganica Chimica Acta 362 (2009) 531–536
was concentrated to a small volume before filtering, because of
R
R
the greater solubility of the products. All these reactions may also
be performed in acetone, but they require longer times due to the
scarce solubility of the metal acetates in this solvent.
O
N
R
O
O
O
R'
2\M
H
2\M
NH
[Mn(atpd)2] (1): Light yellow solid (25% yield). M.p. 150 °C
(dec.). Anal. Calc. for C14H14Cl6MnN2O4 (MW = 541.93): C, 31.03;
R'
R
(II)
(I)
H, 2.60; N, 5.17. Found: C, 30.01; H, 2.57; N, 4.87%. FTIR [cmꢀ1
,
Chart 1.
. . .
KBr]: 3237 [
m
(NH)], 1628 [
B.
m(C@N)], 1597 [m(MeC O)]. Magnetic
•
moment: eff = 6.0
l
l
[Fe(atpd)2] (2): Light red solid (38% yield). M.p. 122 °C (dec.).
Anal. Calc. for C14H14Cl6FeN2O4 (MW = 542.84): C, 30.98; H, 2.60;
residual solvent signals, using tetramethylsilane as the internal
standard. The FT IR spectra were recorded on a Biorad FT S7 PC
or on Bruker IFS 66 spectrophotometers at 2 cmꢀ1 resolution in
KBr disks. Mass spectra were obtained with a single focus mass
spectrometer VG MM16, operating in electron ionization mode at
70 eV electron beam energy and at an ion source temperature of
180 °C. TGS–DSC analysis was performed with Perkin–Elmer TGS-
2, DSC-4 apparatus. Magnetic moments were determined by the
Faraday method at 300 K using an Oxford Instruments magnet cou-
pled with a Cahn 2000 microbalance. Elemental analysis was car-
ried out at the microanalytical laboratory of our department with
a Fisons EA 1108 CHNS-O apparatus.
N, 5.16. Found: C, 30.75; H, 2.45; N, 5.13%. FTIR [cmꢀ1, KBr]:
. . .
3233 [
m
(NH)], 1634 [
eff = 5.1 B.
m(C@N)], 1568 [m(MeC O)]. Magnetic mo-
•
ment:
l
l
[Co(atpd)2] (3): Light orange solid (54% yield). M.p. 146 °C
(dec.). Anal. Calc. for C14H14Cl6CoN2O4 (MW = 545.93): C, 30.80; H,
2.58; N, 5.13. Found: C, 29.32; H, 2.39; N, 4.82%. FTIR [cmꢀ1
,
. . .
KBr]: 3233 [
m
(NH)], 1628 [
B.
m(C@N)], 1593 [m(MeC O)]. Magnetic
•
moment: eff = 4.9
l
l
[Ni(atpd)2] (4): Light green solid (73% yield). M.p. > 190 °C
(dec.). Anal. Calc. for C14H14Cl6N2NiO4 (MW = 545.68): C, 30.81; H,
2.59; N, 5.13. Found: C, 30.83; H, 2.66; N, 4.97%. FTIR [cmꢀ1
,
. . .
KBr]: 3234 [
m
(NH)], 1628 [
B.
m(C@N)], 1593 [m(MeC O)]. Magnetic
•
moment: eff = 4.1
l
l
2.2. Synthesis of the ligands
[Cu(atpd)2] (5): Light blue solid (66% yield). M.p. 115 °C. Anal.
Calc. for C14H14Cl6CuN2O4 (MW = 550.53): C, 30.54; H, 2.56; N,
The b-enaminodione (MeCO)2C@C(NH2)CCl3 (Hatpd) (Chart 2)
was prepared by the reaction of CCl3CN and 2,4-pentanedione in
the presence of a catalytic amount of Ni(acac)2 [13]. Hatpo was
prepared by treatment of Hatpd with an alkaline solution [13].
The b-enaminodiones (MeCO)2C@C(COPh)NH2 (Haapd), (Me-
CO)(PhCO)C@C(COPh)NH2 (Habpd) and (PhCO)2C@C(COPh)NH2
(Haopd) were prepared according to the literature methods [14].
5.09. Found: C, 30.44; H, 2.60; N, 4.89%. FTIR [cmꢀ1, KBr]: 3236
. . .
[m
(NH)], 1628 [
m(C@N)], 1581 [m(MeC O)]. Magnetic moment:
•
leff = 1.9 lB. The alcoholic mother liquor solution was evaporated
to dryness and the residue was identified as the deacylated product
[Cu(atpo)2] (9).
[Zn(atpd)2] (6): Zn(OAc)2 ꢁ 2H2O (0.20 g, 0.92 mmol) and Hatpd
(0.45 g, 1.86 mmol) were dissolved in anhydrous ethanol (20 ml)
and the resulting solution was stirred for 2 h at room temperature.
The reaction mixture was concentrated to half of the volume and
again stirred at room temperature for 2 h. Finally, the white insol-
uble reaction product was isolated by filtration and dried under va-
cuo (0.20 g, 39% yield). M.p. 161 °C. Anal. Calc. for C14H14Cl6N2O4Zn
(MW = 552.36): C, 30.44; H, 2.55; N, 5.07. Found: C, 30.10; H, 2.30;
2.3. Synthesis of the complexes
2.3.1. Reactions of M(OAc)2 ꢁ nH2O (M = Mn, Fe, Co, Ni, Cu, Zn, Pd) salts
with 3-(1-amino-2,2,2-trichloroethylidene)pentane-2,4-dione
(Hatpd) and with 4-amino-5,5,5-trichloropent-3-en-2-one (Hatpo):
synthesis of complexes (1-10)
The reactions were performed by mixing the metal acetate and
the protonated ligand in 1/2 molar ratio, in anhydrous ethanol, at
room temperature under argon. Typically the metal salt (1 mmol)
and Hatpd (or Hatpo) (2 mmol) were dissolved (or suspended) in
30 ml of deoxygenated ethanol. After 5 min, a precipitate began
to separate and the reaction was completed in a few hours. The
precipitate was collected by filtration, washed with ethanol and
dried under vacuo. In the reaction with Hatpo the suspension
N, 4.55%. FTIR [cmꢀ1, KBr]: 3237 [
m(NH)], 1630 [m(C@N)], 1595
. . .
[m
(MeC O)]. 1H NMR (in dmso-d6): d = 2.12 (s, 6H, CH3CO), 8.30
•
(s, 1H, CNH).
[Pd(atpd)2] (7): Yellow solid (45% yield). M.p. 150 °C (dec.).
Anal. Calc. for C14H14Cl6N2O4Pd (MW = 593.39): C, 28.34; H, 2.38;
N, 4.72. Found: C, 27.16; H, 2.20; N, 4.46%. FTIR [cmꢀ1, KBr]:
. . .
3331 [m(NH)], 1695 [m(MeC@O)], 1566 [m
(MeC O)]. 1H NMR (in
•
CDCl3): d = 2.10 and 2.59 (2s, 6H, CH3CO), 8.14 (s, 1H, CNH).
Me
Me
Me
Me
Ph
Me
O
O
NH2
O
NH2
O
O
NH2
O
O
NH2
O
O
NH2
O
O
NH2
CN
CCl3
H
CCl3
COPh
COPh
COPh
Me
Me
Ph
Ph
Me
Hatpd
Hatpo
Haapd
Habpd
Haopd
Haaon
Hatpd:3-(1-amino-2,2,2-trichloroethylidene)pentane-2,4-dione
Hatpo: 4-amino-5,5,5-trichloropent-3-en-2-one
Haapd:3-acetyl-2-amino-1-phenylpent-2-ene-1,4-dione
Habpd: 2-amino-3-benzoyl-1-phenylpent-2-ene-1,4-dione
Haopd: 3-(1-amino-2-oxo-2-phenylethylidene)-1,5-diphenylpentane-1,2,4,5-tetraone
Haaon: 3-acetyl-2-amino-4-oxopent-2-enenitrile
Chart 2.

M. Basato et al. / Inorganica Chimica Acta 362 (2009) 531–536
533
+
. . .
and m(C C)]. MS-EI: m/z 566 ([Pd(aapd)2] ). The ethanol/ether
[Ni(atpo)2] (8): Greenish solid (85% yield). M.p. 220 °C. Anal.
Calc. for C10H10Cl6N2NiO2 (MW = 461.61): C, 26.02; H, 2.18; N,
6.07. Found: C, 26.08; H, 2.01; N, 6.33%. FTIR [cmꢀ1, KBr]: 3340
•
solution, containing some 12a and the more soluble form 12b,
was concentrated under vacuo; addition of hexane led to the pre-
cipitation of a mixture of complex 12b, contaminated by some 12a.
Characterization of (12b). 1H NMR (in CDCl3): d = 2.30 and 2.47 (2s,
6H, CH3CO), 7.2–7.9 (m, 6H, Ph and CNH). 13C NMR (in CDCl3):
d = 28.1 (CH3CO), 31.5 (CH3CO), 116.9 ((CH3CO)C), 128.5–134.5
(Ph), 169.9 ((PhCO)CN), 185.9 (CH3CO), 190.0 (PhCO), 198.0
(CH3CO).
(C N)]. 1H
. . . . . .
(C C) and m
•
. . .
(MeC O),
[
m(NH)], 1593 and 1516 [
m
m
•
•
NMR (in CDCl3): d = 1.87 (s, 3H, CH3CO), 5.55 (d, 1H, CH), 6.16
(br, 1H, CNH). 13C NMR (in CDCl3): d = 25.3 (CH3CO), 92.2 (CH),
93.6 (CCl3), 162.5 (C(CCl3)), 182.3 (CH3CO).
[Cu(atpo)2] (9): Green solid (86% yield). M.p. 155 °C. Anal. Calc.
for C10H10Cl6CuN2O2 (MW = 466.46): C, 25.75; H, 2.16; N, 6.01.
Found: C, 25.71; H, 2.14; N, 5.85%. FTIR [cmꢀ1, KBr]: 3347
[Cu(abpd)2] (13): Green solid (84% yield). M.p. 215–216 °C.
Anal. Calc. for C36H28CuN2O6 (MW = 648.16): C, 66.71; H, 4.35; N,
. . .
. . . . . .
(C C) and m(C N)]. Mag-
•
[
m
(NH)], 1581 and 1523 [
m
(MeC O),
m
•
•
netic moment: eff = 1.7
l
l
B.
4.32. Found: C, 66.53; H, 4.34; N, 4.23%. FTIR [cmꢀ1, KBr]: 3263
. . .
[Pd(atpo)2] (10a,b): Yellow solid (56% yield). M.p. ca. 170 °C.
Anal. Calc. for C10H10Cl6N2O2Pd (MW = 509.32): C, 23.58; H, 1.98;
[
[
m
m
(NH)], 1675 and 1625 [
m
(PhC@O)], 1597 [
eff = 1.9
[Pd(abpd)2] (14a,b): [Pd(OAc)2] (0.22 g, 1.0 mmol) and Habpd
m(MeC O)], 1558
•
. . . . . .
(C NH) and (C C)]. Magnetic moment:
m
l
lB.
•
•
N, 5.50. Found: C, 22.59; H, 1.81; N, 5.34%. FTIR [cmꢀ1, KBr]:
. . .
3343 and 3277
[m
(NH)], 1588, 1580 and 1516
[
m
(MeC O),
(0.58 g, 2.0 mmol) were dissolved in anhydrous ethanol (50 ml)
and the resulting solution was stirred for 20 h at room tempera-
ture, then evaporated to a small volume under reduced pressure.
Treatment of the residue with diethylether (20 ml) afforded a
light green solid, which was filtered, but resulted in a mixture
of compounds 14a and 14b. Treatment with acetone (200 ml)
led to an insoluble solid and a yellow solution. Recrystallization
of the solid from dichloromethane/acetone afforded pure 14a, as
a yellow-green solid (0.23 g, 33%). M.p. 258–259 °C. Anal. Calc.
for C36H28N2O6Pd (MW = 691.04): C, 62.57; H, 4.08; N, 4.05.
Found: C, 62.16; H, 4.09; N, 3.99%. 1H NMR (in CDCl3): d = 1.85
(s, 3H, CH3), 7.2–7.9 (m, 6H, Ph and CNH). 13C NMR (in CDCl3):
d = 27.2 (CH3CO), 113.2 ((CH3CO)C), 128.2–140.5 (Ph), 167.4
((PhCO)CN), 183.8 (CH3CO), 191.9 (PhCO), 197.1 (PhCO). FTIR
•
. . . . . .
m
(C C) and (C N)]. UV–Vis (CHCl3, kmax/nm, e in parenthesis):
m
•
•
382 (9400), 240 (19100). MS-EI: m/z 508 ([Pd(atpo)2]+). The NMR
spectra revealed that the isolated solid is a mixture of two com-
pounds in approximately 1/1 ratio. Compound 10a: 1H NMR (in
CDCl3): d = 2.09 (s, 3H, CH3CO), 5.58 (d, 1H, CH), 7.60 (s, 1H,
CNH). 13C NMR (in CDCl3): d = 25.9 (CH3CO), 91.6 (CH), 94.9
(CCl3), 160.8 (C(CCl3)), 182.8 (CH3CO). Compound 10b: 1H NMR
(in CDCl3): d = 2.20 (s, 3H, CH3CO), 5.68 (d, 1H, CH), 6.68 (s, 1H,
CNH). 13C NMR (in CDCl3): d = 25.6 (CH3CO), 92.7 (CH), 95.1
(CCl3), 161.3 (C(CCl3)), 185.0 (CH3CO). Solutions of this mixture in
CDCl3 show a slow conversion of 10b into 10a.
2.3.2. Reactions of M(OAc)2 ꢁ nH2O (M = Cu, Pd) salts with 3-acetyl-2-
amino-1-phenylpent-2-ene-1,4-dione (Haapd), 2-amino-3-benzoyl-
1-phenylpent-2-ene-1,4-dione (Habpd), 3-(1-amino-2-oxo-2-
phenylethylidene)-1,5-diphenylpentane-1,2,4,5-tetraone (Haopd)
Complexes 11–16 were obtained by the reaction of the metal
acetate with the appropriate protonated ligand in 1/2 molar ratio,
in anhydrous ethanol, at room temperature under argon; the
resulting solutions were left under stirring for variable times and
the complexes can either precipitate spontaneously from the reac-
tion mixture (for Cu, after 2–6 h) or be recovered from the solution
evaporated to dryness (for Pd, after 3–18 h). In many cases the pal-
ladium compounds are isolable in two different forms, labeled as a
and b, which exhibit identical composition but different spectro-
scopic properties; the symbols a, b indicate only the order in which
the complexes have been isolated.
[cmꢀ1, KBr]: 3261 [
m
(NH)], 1676 and 1630 [
. . . . . .
m(PhC@O)], 1597
. . .
[m
(MeC O)], 1565 [
m
(C C) and (C NH)]. The acetone solution
m
•
•
•
was concentrated and the addition of diethylether led to the pre-
cipitation of a complex 14b, still containing small amounts of 14a.
M.p. 270–272 °C. Anal. Calc. for C36H28N2O6Pd (MW = 661.04): C,
62.57; H, 4.08; N, 4.05. Found: C, 62.61; H, 4.07; N, 4.07%. 1H
NMR (in CDCl3): d = 1.52 (s, 3H, CH3CO), 7.25–7.95 (m, 11H, Ph
and CNH). 13C NMR (in CDCl3): d = 31.1 (CH3CO), 116.7
((CH3CO)C), 128.2–140.5 (Ph), 170.0 ((PhCO)CN), 184.0 (PhCO),
191.0 (PhCO), 199.6 (CH3CO). FTIR [cmꢀ1, KBr]: 3230 [
m
(NH)],
. . .
1676 [
1559 [
m
m
(PhC@O)], 1644 and 1632 [
m(MeC@O)], 1597 [m(PhC O)],
•
. . . . . .
(C C) and (C NH)].
m
•
•
[Cu(aopd)2] (15): Green solid (92% yield). M.p. 224–225 °C
(dec). Anal. Calc. for C46H32CuN2O6 (MW = 772.30): C, 71.54; H,
[Cu(aapd)2] (11): Light purple solid (71% yield). M.p. 194–
195 °C. Anal. Calc. for C26H24CuN2O6 (MW = 524.02): C, 59.59; H,
4.18; N, 3.63. Found: C, 71.39; H, 4.33; N, 3.48%. FTIR [cmꢀ1
,
. . .
KBr]: 3267 [
m
(NH)], 1663 and 1631 [
m
(PhC@O)], 1597 [m(PhC O)],
•
4.62; N, 5.35. Found: C, 59.69; H, 4.67; N, 5.27%. FTIR [cmꢀ1
,
1581 and 1547 [
eff = 1.7 B.
[Pd(aopd)2] (16): Green solid (62%). M.p. 270 °C. Anal. Calc. for
m(C NH) and m(C C)]. Magnetic moment:
. . .
. . .
• •
KBr]: 3254 [
m
•
(NH)], 1664 and 1650 [
m
(PhC@O)], 1617 [
m
(MeC@O)],
l
l
. . . . . .
. . .
1597 [
ment:
m
l
(MeC O)], 1556 [ (C NH) and m(C C)]. Magnetic mo-
eff = 1.9
m
•
•
lB.
C46H32N2O6Pd (MW = 815.18): C, 67.78; H, 3.96; N, 3.44. Found: C,
[Pd(aapd)2] (12a,b): [Pd(OAc)2] (0.22 g, 1.0 mmol) and Haapd
(0.46 g, 2.0 mmol) were dissolved in anhydrous ethanol (50 ml)
and the resulting solution was stirred for 18 h at room tempera-
ture, then evaporated to a small volume under reduced pressure.
The residue was treated with ethanol (10 ml) under stirring for
1 h and again the solvent was removed. This treatment was re-
peated three times. Finally, addition of ether (10 ml) gave a light
green solid, which was filtered. Recrystallization from dichloro-
methane/acetone afforded pure 12a, as a yellow-green solid
(0.29 g, 52%). M.p. 243–244 °C. Anal. Calc. for C26H24N2O6Pd
(MW = 566.90): C, 55.09; H, 4.27; N, 4.94. Found: C, 55.02; H,
4.27; N, 4.99%. 1H NMR (in CDCl3): d = 2.30 and 2.34 (2s, 6H,
CH3CO), 7.2–7.9 (m, 6H, Ph and CNH). 13C NMR (in CDCl3):
d = 27.7 (CH3CO), 31.5 (CH3CO), 116.9 ((CH3CO)C), 128.5–134.5
(Ph), 169.3 ((PhCO)CN), 185.1 (CH3CO), 190.4 (PhCO), 198.3
67.37; H, 4.05; N, 3.29%. 1H NMR (in dmso-d6): d = 5.74 (br, 1H,
CNH), 7.0–7.9 (m, 15H, Ph). FTIR [cmꢀ1, KBr]: 3252 [
m(NH)], 1662
. . .
and 1631
[
m
(PhC@O)], 1598 [m(PhC O)], 1581 and 1557
•
. . .
. . .
[m(C NH) and m(C C)].
• •
2.3.3. Reactions of M(OAc)2ꢁnH2O (M = Mn, Fe, Co, Zn) salts with 3-
acetyl-2-amino-1-phenylpent-2-ene-1,4-dione (Haapd) and 3-acetyl-
2-amino-4-oxopent-2-enenitrile (Haaon)
Reactions of M(OAc)2ꢁnH2O (M = Mn, Fe, Co, Cu, Zn, Pd) salts
with 3-acetyl-2-amino-1-phenylpent-2-ene-1,4-dione (Haapd)
or 3-acetyl-2-amino-4-oxopent-2-enenitrile (Haaon) were run
using the metal acetate and the protonated ligand in 1/2 molar
ratio, in anhydrous ethanol under various experimental condi-
tions (room temperature, reflux), without any evidence of forma-
tion of the expected products. In some cases the starting
aminodione underwent a cyclization reaction in the presence
of the acetato salts.
(CH3CO). FTIR [cmꢀ1
(PhC@O)], 1630 [ (MeC@O)], 1597 [
,
KBr]: 3293
[
m
(NH)], 1676 and 1664
. . . . . .
[
m
m
m
(MeC O)], 1567 [ (C NH)
m
•
•

534
M. Basato et al. / Inorganica Chimica Acta 362 (2009) 531–536
3. Results and discussion
Me
Me
O
N
O
— HOAc
The reaction of metal acetates with b-enaminodiones appears to
be a convenient procedure for the synthesis of a large variety of b-
imino carbonyl enolato complexes; however, its applicability
strongly depends on the nature of the substituent at the amino
group and of the metal center, best results being obtained with
the trichloromethyl derivative Hatpd.
H
2\M
H
M(OAc)2
+
1/2
H
H2N
CCl3
CCl3
M = Ni (8), Cu (9), Pd (10)
Scheme 2. Synthesis of complexes 8-10.
3.1. Synthesis of complexes [M(atpd)2] (M = Mn, Fe, Co, Ni, Cu, Zn, Pd)
(1-7) and [M(atpo)2] (M = Ni, Cu, Pd) (8–10)
All the complexes with the ligand atpd are thermally unstable,
as indicated by the low melting points, always accompanied by the
decomposition of the complex, by the very complex TGA–DSC
curves and by the mass spectra, in which only low-mass fragments
are present.
A possible decomposition pathway involves the deacylation of
atpd, which is observed either with this synthetic procedure or
in the direct attack of trichloroacetonitrile, for example, on copper
acetylacetonate, so that we checked the coordinating ability of the
deacylated ligand 4-amino-5,5,5-trichloropent-3-en-2-one Hatpo
toward the same series of metal centers (Scheme 2).
Only a chelating N,O coordination is possible in this case, and
both IR and NMR data are consistent with this configuration; in
particular the 13C resonances of the imino and keto carbon atom
have ppm values in the expected range (162.5, 182.3 (8) and
160.8–161.3, 182.8–185.0 (10a,b)) for N,O coordinated imino car-
bonyl enolato complexes. The palladium complex is isolated in
two isomeric forms a and b, the second one converting into the
first one in solution, most likely as a consequence of a cis–trans
equilibration. It is remarkable that Mn, Fe, Co, and Zn acetates do
not react with this b-enaminone, and this point will be discussed
later.
Metal(II) acetates (M = Mn, Fe, Co, Ni, Cu, Zn, Pd) react in etha-
nol with 3-(1-amino-2,2,2-trichloroethylidene)pentane-2,4-dione
Hatpd in 1:2 molar ratio to give the corresponding complexes
1–7 in a moderate yield (Scheme 1). They are generally air and
moisture stable solids, which can be safely stored under an inert
atmosphere, but they slowly decompose in solution and this
accounts for the medium yields in the synthesis reaction.
In all the cases the trifunctional b-imino carbonyl enolate ligand
acts as bidentate to give ML2 complexes, whose structure depends
on the metal center. For most metal centers the characterization
data indicate an O,O coordination through the two carbonyl oxy-
gens (linkage isomer II), whereas palladium(II) exhibits an N,O
coordination through the imino nitrogen and one keto oxygen. In
fact, the IR spectrum of complex 7 shows in particular a med-
ium-high intensity N–H band at 3331 cmꢀ1 and
a band at
1695 cmꢀ1 relative to the stretching of the uncoordinated C@O
group. Consistently its 1H and 13C NMR spectra show the presence
of two different sets of signals for the acetyl groups, as a conse-
quence of the coordination of only one oxygen donor atom.
By contrast, the IR spectra of complexes 1–6 show rather differ-
ent features; there is a band at 3237–3233 cmꢀ1 relative to the N–
H stretching, but whose intensity is much weaker if compared with
that found in complexes with N,O coordination. Moreover, only
one absorption attributable to the stretching of the carbonyl
groups is present at 1597–1568 cmꢀ1, thus indicating a symmetric
structure for the complexes with both the keto groups coordinated
to the metal center. The band at 1634–1628 cmꢀ1 is easily attrib-
uted to an N–H stretching of uncoordinated imino group by D/H
exchange experiments. Also the 1H and 13C NMR spectra for the
diamagnetic complex (6) show a single set of signals for the acetyl
groups, thus indicating a symmetric structure and the equivalency
of the acetyl groups. The magnetic measurements for complexes
[Mn(atpd)2] (1), [Fe(atpd)2] (2) and [Co(atpd)2] (3), [Ni(atpd)2]
(4) and [Cu(atpd)2] (5) show the presence of 5, 4, 3, 2 and 1 un-
paired electrons, respectively, in agreement with the literature val-
ues [15]. Moreover, they suggest for complexes 1–4 an octahedral
geometry for the metal centers resulting from an oligomeric struc-
ture with oxygen bridges, as already observed with acetylaceto-
nates complexes [16].
3.2. Synthesis of complexes [M(aapd)2], [M(abpd)2], [M(aopd)2]
(M = Cu, Pd) (11–16)
Metal(II) acetates of copper and palladium react in ethanol with
the b-enaminodiketones Haapd, Habpd, and Haopd to give the
corresponding bis(imino carbonyl enolato) complexes (11–16)
(Scheme 3) in good yields. In most cases the complexes precipitate
spontaneously, otherwise the reaction is forced toward the desired
products by reducing the volume of the reaction mixture under
vacuum; this procedure removes the solvent together with the
acetic acid produced in the ligand exchange process.
Also with the benzoyl substituent at the imino carbon the N,O,O
anionic ligand acts as bidentate to give monomeric square planar
neutral ML2 complexes, in which the donor atoms are the imino
nitrogen and a keto oxygen. The characterization of the complexes
is made rather easy by a previous accurate IR and NMR study,
including selective 13C labeling, on the nickel(II) analogues [17].
The copper(II) complexes 11, 13 and 15 are isolated only in one
Me
Me
Me
Me
O
O
CCl3
NH
O
N
Me
O
O
O
NH2
— HOAc
2\M
2\M
H
1/2
M(OAc)2
+
or
CCl3
CCl3
Me
(II)
(I)
M = Pd (7)
M = Mn (1), Fe (2), Co (3),
Ni (4), Cu (5), Zn (6)
Scheme 1. Synhesis of complexes 1-7.

M. Basato et al. / Inorganica Chimica Acta 362 (2009) 531–536
535
R
R'
R
O
N
R'
O
O
N
R
O
O
O
C(O)Ph
NH2
– HOAc
2\M
H
2\M
H
1/2 M(OAc)2
+
or
C(O)Ph
C(O)Ph
(I')
R'
(I)
R, R' = Me; M = Cu (11)
R = Me, R' = Ph; M = Pd (14b)
R, R' = Me; M = Pd (12a,b)
R = Me, R' = Ph; M = Cu (13)
R = Me, R' = Ph; M = Pd (14a)
R, R' = Ph; M = Cu (15)
R, R' = Ph; M = Pd (16)
Scheme 3. Synthesis of complexes 11-16.
R
O
2\M
O
+
H
N
C
R''
i)
R
R
O
O
R''
R'
O
N
R'
O
2\M
or
2\M
H
NH
R
R'
R''
O
O
CR''
NH2
1/2 M(OAc)2
+
ii)
R'
Scheme 4. Procedures for the synthesis of b-imino carbonyl enolato complexes.
form and their IR spectra show characteristic absorptions in the ex-
pected wavelength ranges: in particular, 3367–3254 [one band,
reaction of Haapd with NaOAc.1 So it is reasonable to envisage that
in the drastic conditions adopted, the Fe(II), Co(II) and Zn(II) acetates
can partly dissociate thus realizing in solution an appreciable con-
centration of the base responsible for the cyclization.
In this context, it should be underlined that also the protonated
cyano ligand Haaon does not react with the same set of metal ace-
tates to give the desired imino carbonyl enolate complexes, but
rather undergoes a cyclization reaction to give the cyclic pyrroline
isomer [18].
The whole of the data obtained in this and in our previous papers
gives a clear picture of the strategy to be adopted in the synthesis of
b-imino carbonyl enolato complexes. The synthetic procedure de-
pends markedly on the nature of the metal center and on the sub-
stituent at the imino carbon. The first applied procedure (i)
involves electrophilic attack by the nitrile on the methine carbon
atom of the coordinated b-carbonylenolato ligand (Scheme 4).
This C–C bond forming reaction requires nitriles bearing elec-
tron-withdrawing groups such as CN, CCl3, and PhCO and, in addi-
tion, metal centers with an ionic character of the M–O bond in the
chelate ring [19]: this last point explains, for example, why Pd(II),
Cr(III) and Fe(III) acetylacetonates are completely unreactive also
toward very electrophilically activated nitriles [20]. In general,
the control of the reaction conditions is very delicate, so that espe-
m
(N–H)], 1675–1625 [one or two bands,
m
(PhC@O)], 1617 [one
. . .
band,
13) or
m
(MeC@O) (11)], 1598–1597 [one band, m(MeC O) (11,
•
ꢀ1
. . .
(PhC O) (15)] cm
m
.
•
Palladium(II) complexes tend to give different forms, which are
fairly stable both in the solid state and in solution. For example, the
reaction of Haapd with palladium acetate allows the isolation of
two different solids, labeled 12a,b, with identical chemical compo-
sition but different spectroscopic features. The two forms have
very similar IR and NMR spectra, fully consistent with the N,O link-
age isomer I shown in Scheme 3; in particular both exhibit the typ-
ical signals of the coordinated and uncoordinated acetyl group. The
small differences detected between the NMR spectra of 12a and
12b [for example, 27.7 and 31.5 (CH3CO), 185.1 and 198.3 (CH3CO)
versus 28.1 and 31.5 (CH3CO), 185.9 and 198.0 (CH3CO)] could be
attributable to the difference in the torsion angles of the substitu-
ents of the metal–carbonylenolate ring, as already observed in the
analogous complex with nickel(II) [17] and in related b-imino car-
bonyl enolate palladium(II) complexes [11].
Also complex 14 [Pd(abpd)2] is isolable in two forms a and b,
which maintain an N,O coordination but differ in the oxygen donor
atom, of the acetyl and benzoyl group, respectively. In fact, the 13C
NMR spectrum of 14a shows the resonances typical of the coordi-
nated MeC@O at 27.2 and 183.8 ppm to be compared with the val-
ues of 31.1 and 199.6 ppm of the uncoordinated one found in 14b.
Attempts to apply this synthetic procedure to other metal ace-
tates (M = Mn(II), Fe(II), Co(II) and Zn(II)) were unsuccessful. In
particular in the reaction between Mn(II) acetate and Haapd the
starting materials have been recovered unchanged, whereas using
Fe(II), Co(II) or Zn(II) acetates under reflux, a cyclic compound,
identified as 2-acetyl-3-amino-4-hydroxy-4-phenylcyclopent-2-
enone, has been isolated. The cyclization process occurs in the
presence of free acetate anions in solution, as demonstrated by
1
A solution of Haapd (0.12 g, 0.5 mmol) and NaOAc (0.04 g, 0.5 mmol) in ethanol
(25 ml) was refluxed for 10 h and then further stirred at room temperature for 18 h.
The solvent was removed under vacuo and the residue recrystallized from dichlo-
romethane/diethylether. The resulting off-white product was isolated by filtration
and dried (0.10 g, 82% yield). M.p. 187–189 °C. Anal. Calc. for C13H13NO3
(MW = 231.15): C, 67.52; H, 5.67; N, 6.06. Found: C, 67.53; H, 5.66; N, 6.05%. FTIR
[cmꢀ1, KBr]: 3355 and 3216 [
and
m(NH) and m(OH)], 1684, 1635, 1608 and 1529 [m(C@O)
m
(C@C)]. 1H NMR (in dmso-d6): d = 2.37 (s, 3H, CH3CO), 2.65 (AB system, 2H, CH2),
6.37 (s, 1H, OH), 7.34 (br, 5H, Ph), 8.47 and 9.09 (s, 2H, CNH). 13C NMR (in dmso-d6):
d = 28.8 (CH3), 53.0 (CH2), 75.3 (C(OH)Ph), 109.0 ((CH3CO)C), 124.4–144.1 (Ph), 182.8
(CN), 195.0 and 195.7 (CO).

536
M. Basato et al. / Inorganica Chimica Acta 362 (2009) 531–536
cially in the reaction of cyanogen with the more ionic acetylaceto-
nates (M(II) = Mn, Fe, Co, Zn) the initially formed complexes are
very reactive and evolve to complex mixtures [21]. By contrast
benzoyl cyanide requires high temperatures in which the com-
plexes may be unstable, and this markedly reduces the yields.
Good results have been obtained with Ni(II), Cu(II) and, in part,
with Zn(II).
References
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[2] N.S. Simpkins (Ed.), 100 Modern Reagents, The Royal Society of Chemistry,
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The second more recent procedure (ii) implies reaction of the
metal acetates with the ‘‘preformed” b-enaminodione in an ex-
change process. Clearly, the position of this equilibrium is deter-
mined by the relative acidities of the b-enaminodione and HOAc,
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lato complexes. b-Enaminodiones with a trichloromethyl substitu-
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investigated metal acetates; the coordination is N,O only for the
soft palladium(II). The situation markedly changes in the b-enam-
inodiones derived from benzoyl cyanide; in fact, good results are
obtained only with Ni(II), Cu(II) and Pd(II), and under forced condi-
tions only cyclization of the ligand is observed. Quite remarkably,
N,O coordination is observed in this case also for Ni(II) and Cu(II)
metal centers, so underlining their borderline hard–soft character.
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type of imino substituent. However, sometimes it is limited with
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with respect to the acetic acid is not compensated by a slightly
greater stability of the b-imino carbonyl enolato complex with re-
spect to the starting acetato salt. This phenomenon is particularly
evident in the reaction of the N,O bidentate Hatpo with metal ace-
tates; in fact only the softer Ni(II), Cu(II) and Pd(II) undergo ex-
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Acknowledgement
[20] B. Corain, C. Crotti, A. Del Pra, F. Filira, G. Zanotti, Inorg. Chem. 20 (1981) 2044.
[21] B. Corain, M. Basato, A. Marcomini, Inorg. Chim. Acta 74 (1983) 1.
We thank Mr. A. Ravazzolo for his skilled technical assistance.