Complexation of chiral di (N-Protected α-Amino)-β-diketones with some transition metals

Article abstract of DOI:10.14233/ajchem.2013.14080

Chiral Di (N-protected a-amino)-b-diketones and its transition metal complexes have been synthesized. Di(N-protected a-amino)-b- diketones were prepared by reaction of activation of N-protected- a-amino acids (imidazolide) with a-diazoketones derived from natural amino acids in presence of lithium diisopropyl amid in tetrahydrofuran as a solvent at -78 °C and treatment the product with rhodium acetate to remove diazo group. The synthesized compounds were characterized by analytical techniques viz: IR, NMR and elemental analysis. The thermal stability of the newly synthesized metal complexes have been studied.

Full text of DOI:10.14233/ajchem.2013.14080

Asian Journal of Chemistry; Vol. 25, No. 9 (2013), 4747-4752
http://dx.doi.org/10.14233/ajchem.2013.14080
Complexation of Chiral Di (N-Protected α-Amino)-β-Diketones with Some Transition Metals
IBRAHIM A.M. SARAIREH
Department of Chemistry, Al-Hussein Bin Talal University, Ma'an, Jordan
Corresponding author: E-mail: ibrahim9997@yahoo.com
(Received: 21 May 2012;
Accepted: 4 March 2013)
AJC-13062
Chiral Di (N-protected α-amino)-β-diketones and its transition metal complexes have been synthesized. Di(N-protected α-amino)-β-
diketones were prepared by reaction of activation of N-protected- α-amino acids (imidazolide) with α-diazoketones derived from natural
amino acids in presence of lithium diisopropyl amid in tetrahydrofuran as a solvent at -78 ºC and treatment the product with rhodium
acetate to remove diazo group. The synthesized compounds were characterized by analytical techniques viz: IR, NMR and elemental
analysis. The thermal stability of the newly synthesized metal complexes have been studied.
Key Words: Protecting mino acid, Diazomethane, β-Diketones, Carbonyldiimidazol metal ions.
groups separating the carbonyl groups typically coexist with
their enol tautomers. The reactions of such dicarbonyls are
very similar to those of simple ketones.
INTRODUCTION
β-Diketones are used as ligands for almost 120 years.
These derivatives were synthesized for the first time in 1887.
The nature of bonding and chelation was elucidated by Werner
and Morgan1,2. In the last decades, β-diketones and their metal
complexes have been used as model compounds in physical
chemistry studies. They have also been used as chelating
ligands for lanthanides and transition metals3. They are
bidentate ligands with the possibility of complexation with
almost all the metal ions4. β-Diketones have a wide range of
uses in metal extraction by chelation. 1,3-Diketones are very
important compounds in organic chemistry, because they
exhibits some biological activities, such as antioxidants, anti-
tumor and antibacterial activities and are also key intermediates
to various heterocyclic compounds5,6.
In the last years many scientific papers have been published
on synthesis of N-protected α-amino acid, α-diazoketones and
α-diazoketoles derived from natural amino acids by several
methods9. A series of N-protected α-aminodiazoketones has
been prepared from L-amino acids and dipeptides and used as
precursors in the synthesis of N-protected α-amino -β-diketones10.
The synthesis of α-amino protected acyldiazomethanes
involves the activation of the carboxyl group of N-protected-
α-amino acids followed by acylation of diazomethane. The
acid chloride11 active ester12 and the mixed anhydride methods13
have been employed for the activation. The acid chloride
method is not applicable for some protecting groups because
of the acid lability or oxazolone formation.
β-Diketone in its keto-enol form is also a important used
as chelating agents in some process based on supercritical CO27.
It is used as extractants for lanthanide ions8. β-Diketones (1,3-
ketones), such as acetylacetone, are particularly prone to form
stable enols or enolates because of conjugation of the enol or
enolate with the other carbonyl group and the stability gained in
forming a six-membered ring, (hydrogen bonded in the case of
the enol or containing the counter ion in the case of the enolate).
α-Diazocarbonyls (RCOCHN2) have an acidic hydrogen
on the methine group and readily removed by strong base to
furnish a nucleophilic anion capable to condensation14 with
activation N-protected amino acids15 to get high yields of diazo-
β-diketons. Lithium diisopropylamine (LDA) is the base of
choice when highly yields of condensation of α-diazocarbonyls
with activation N-protected amino acids. Carponyldiimidazol
(CDI) is a suitable activation group of N-protected amino
acids to produce imidazolide16-19. This imidazolide was treated
directly with diazolithio-ketones to get high percentage yield
of diazo-β-diketons. Rhodium-catalyst20 was subsequent to
preparation of novel di(N-protected α-amino)-β-dicarbonyl
compounds then complexation with some metal ions [Cu(II),
Ni(II) and Fe(III)].
H
O
O
O
O
The conjugate base derived from 1,3-ketones form comp-
lexes with metal ions. Diketones with one or two methylene

4748 Saraireh
Asian J. Chem.
(COCHN2). 1H NMR (300 MHz, CDCl3): δ = 1.21 (3H, d, J =
7.1 Hz, CH3CH), 4.30 (1H, m, CH(N)CO), 5.20 (2H, s,
OCH2Ph), 5.54 (1H, br s, CHN2), 5.76 (1H, br, s, NH), 7.26-
7.35 (5H, m, ArH). 13C NMR (75 MHz, CDCl3): δ = 18.5,
53.7, 54.5, 67.1, 128.2, 128.3, 128.6, 136.4, 155.9, 194.1.
Benzyl [(3R)-1-diazo-4-methyl-2-oxopentan-3-yl]-
carbamate (5): N-Benzyloxycarbonyl-l-valine (2) (27 mmol,
6.8 g) was converted into title compound (5). Purification using
EtOAc-hexane as eluent funished the pure diazoketone 5 (5.17
g, 75 %) as a yellow solid m.p 30-31 ºC, [α]20D = -31.5 (c 1,
MeOH). Found: C 61.05; H 6.19; N 15.2 %. C14H17N3O3
requires C 61.1; H 6.2; N 15.3 %.(KBr, νmax) 3330 (NH); 2110
(CN2); 1725 (CO2CH2Ph); 1635 cm-1 (COCHN2. 1H NMR (300
MHz, CDCl3): δ = 0.87-0.99 (6H, d, J = 6.75 Hz, -CH(CH3)2);
2.15 (1H, m, -CH(CH3)2); 4.45 (1H, m, -N-CH-CO-); 5.17
(2H, s, CH2Ph); 5.41 (1H, br, NH); 5.42 (1H, s, CHN2); 7.40
(5H, s, phenyl group). 13C NMR (75 MHz, CDCl3): δ = 17.4,
19.5, 31.2, 54.8, 63.0, 67.1, 128.1, 128.2, 128.6, 136.3, 156.5.
Benzyl [(2R)-4-diazo-3-oxo-1-phenylbutan-2-yl]-
carbamate (6): N-Benzyloxycarbonyl-l-phenylalanine (3) (27
mmol, 8.1 g) was converted into title compound (6). Purifi-
cation using EtOAc-hexane as eluent funished the pure
diazoketone 6 (6.40 g, 88 %) as a yellow solid m.p. 80-81 ºC,
[α]20D = -42.1 (c 1, MeOH). Found: C 66.69; H 5.25; N 12.93
%. C18H17N3O3 requires C 66.9; H 5.3; N 13.0 %. ºC. (KBr,
EXPERIMENTAL
Reactions requiring anhydrous conditions were performed
in flame-dried glassware under a positive pressure of nitrogen.
Reaction mixtures were stirred magnetically.Air -and moisture-
sensitive liquids and solutions were transferred via syringe or
cannula into the reaction vessels through rubber septa. Column
chromatography was performed using Rhon-poulenc silica gel
C60-H (40-60µm).
Commercial grade solvents were used without purification
except as indicated below. Tetrahydrofuran was distilled from
sodium benzophenone dianion, dichloromethane. Diis
opropylamine was purified by molecular seives then distillation,
n-butyllithium (1.6 M solution in hexane) was purchased from
across, 1,1’-carbonyldiimidazole, N-benzyloxycarbonyl-L-
alanine, N-benzyloxycarbonyl-L-valine and N-benzyloxy-
carbonyl-L-phenylalanine, were purchased from acros, N2 gas
was dried over copper pieces, silica gel and molecular sieve.
The hexane and ethyl acetate used for chromatography were
purified by distillation. Infrared spectra were recorded as KBr-
discs on Matsson 5000-FTIR spectrophotometer within the
13
range of 4000-500 cm-1, 1H and C-NMR were recorded on
Bruker AC 300 MHz and AC 75 MHz respectively.
Preparation of diazomethane (CH2N2): Ethereal di-azo-
methane was prepared from toluene-p-sulphonyl chloride and
methylamine in alkaline solution according to the literature
procedure21. [CH2N2 may explode in contact with sharp edges,
such as ground-glass joints, even scratches in glassware].
Glassware should be inspected before use and preparation
should take place behind a blast shield. Specialized kits to
prepare diazomethane with flame-polished joints are commer-
cially available. The compound explodes when heated beyond
100 ºC. it is a extremely sensitive explosive yellow gas, thus it
is almost universally used as a solution in diethyl ether.
General procedure for α-diazoketones preparation via
mixed anhydrides: The N-protected amino acid (27.0 mmol)
in dry Et2O (60 mL) and THF (60 mL) was stirred at -20 ºC
under a nitrogen atmosphere. To this solution, Et3N (3.8 mL,
1 equiv.) followed by isobutyl chloroformate (3.7 mL, 1 equiv.)
were added. The solution was stirred for 0.5 h and then allowed
to warm to -10 ºC.At this temperature etheral CH2N2 (2 equiv),
was added via a pressure equalizing dropping funnel over 0.5
h. The solution was stirred for a further 3 h whilst warming to
room temperature. The mixture was evaporated to a third of
its original volume using a rotary evaporator with an AcOH
trap to destroy residual CH2N2.The solution was diluted with
Et2O (50 mL) and washed with H2O (50 mL), saturated aqueous
NaHCO3 (50 mL) and brine (50 mL). The organic fraction
was dried and evaporated to give the crude α-diazoketone
which was purified by silica gel chromatography (EtOAc-hexane
2:8-3:7).
ν
max) 3322 (NH); 2106 (CHN2); 1696 (CO2-bnz); 1635 cm-1
(COCHN2). 1H NMR (300 MHz, CDCl3): δ = 3.03 (2H, d, J =
6.85 Hz, PhCH2); 4.45 (1H, m, CHNCO); 5.21 (2H, s,
O-CH2Ph); 5.31 (1H, s, CHN2); 5.35 (1H, br, NH); 7.18-
7.42(10 H, m, ArH). 13C NMR (75 MHz, CDCl3): δ = 38.31,
54.4, 58.7, 66.9, 127.0, 127.9, 128.1, 128.4, 128.5, 129.2,
135.9, 136.0,155.6, 192.6.
Synthesis of N-Protected-α-amino acids imodazolide
Benzyl [(2R)-1-(1H-imidazol-1-yl)-1-oxopropan-2-yl]-
carbamate (7): To a stirred solution of 1 (3.80 g, 17.2 mmol)
in dry THF (50 mL), carbonyldiimidazole (CDI) (3.07 g, 18.9
mmol) was added under nitrogen at 25 ºC. After stirring for
2 h at 25 ºC the alaninylimidazolide was obtained and used
directly in the next step without isolate and further purification.
Benzyl [(3R)-1-(1H-imidazol-1-yl)-3-methyl-1-
oxobutan-2-yl]carbamate (8): 4.75 g, of N-benzyloxycar-
bonyl-l-valine (17.2 mmol) and (3,07 g, 18.9 mmol) CDI in
THF were reacted according to the same procedure employed
in compound (7) and used directly in the next step without
further purification.
Benzyl [(2R)-1-(1H-imidazol-1-yl)-1-oxo-3-phenyl-
propan-2-yl]carbamate (9): 5.32 g, of N-benzyloxycarbonyl
-l-phenylalanine (17.2 mmol) and (3,07 g, 18.9 mmol) CDI in
THF were reacted according to the same procedure employed
in compound (7) and used directly in the next step without
further purification.
Benzyl [(2R)-4-diazo-3-oxobutan-2-yl]carbamate (4):
Following the general procedure N-benzyloxycarbonyl-l-
alanine 1 (27 mmol, 6 g) was converted into title compound 4.
Purification using EtOAc-hexane as eluent funished the
diazoketone 4 (5.7 g, 84 %) as a pale-yellow solid. m.p. 90-91
ºC, [α]20 = -59.08 (c 1, MeOH). Found: C 58.2; H 5.22; N
16.98 %. C12H13N3O3 requires C 58.3; H 5.3; N 17.0 %. (KBr,
max) 3315 (NH), 2105 (CHN2), 1722 (NHCO2Bnz), 1645 cm-1
Synthesis of 2-diazo-1,3-diketones derived from amino acids
Dibenzyl [(2R, 6R)-4-diazo-3,5-dioxoheptane-2,6-
diyl]carbamate (10): A cold (-78 ºC) solution of lithium
diisopropylamine (10.8 mL of a 1.6 M solution in cyclohexane,
17.2 mmol) was added over 15 min under nitrogen via syringe
to a stirred solution of carbamate 4, (2.13 g, 8.60 mmol) in
dry THF (30 mL) at -78 ºC. A solution of imidazolide 7 was
D
ν

Vol. 25, No. 9 (2013)
Complexation of Chiral Di (N-Protected α-Amino)-β-Diketones with Some Transition Metals 4749
added dropwise over 15 min under nitrogen via cannula at
such a rate so as to keep the temperature below -78 ºC and
stirring was continued for an additional 2 h. Acetic acid (12 µL,
17.2 mmol) in dry THF (5 mL) was added. The mixture was
allowed to warm to room temperature and H2O (20 mL) was
added. The product was extracted with Et2O (3 × 50 mL) and
the combined organic extracts washed with saturated aqueous
NaHCO3 (50 mL) and brine (50 mL), dried over anhydrous
Na2SO4 and concentrated under reduced pressure to give a
brown oil. Purification by column chromatography using
EtOAc:n-hexane (3:7) as eluent furnished the title compound
10 (2.996 g, 77 %) as a yellow oil.Anal. calcd. for C23H24N4O6
C 61.06, H 5.35, N 12.38 %. Found: C, 60.99 ; H, 5.21; N,12.24
%. (KBr, νmax) 3315 (NH); 2099 (CN2); 1705 (CO2CH2); 1631
Found: C, 64.83; H, 6.21; N, 6.531 %. (KBr, νmax) 3431 (OH
enol toutomer); 3315 (NH); 1705 (CO2CH2); 1640 (C=O);
1618 (=COH); 1138 (C-O); 1520 cm-1 (Ph). δH (CDCl3): 1.21
(6H, d, CH3CH), 3.54 (2H,s, -COCH2OC-) 4.48 (2H, m, 2N-
CH-CO), 5.11 (4H, s, 2 OCH2Ph), 5.41 (2H, br, 2NH), 7.2-
7.40 (10 H, m, 2 ph), 8.41 (s,1H, -CH=), 15.4 (1 H, OH enol
toutomer). 13C NMR (δ/ppm, CDCl3) 18.4, 65.3, 65.61, 67.1,
96.6 (CH=), 128.2, 128.3, 128.6, 136.4, 155.4, 191,191.6.
Benzyl (3R,7R)-2,8-dimethyl-4,6-dioxononane-3,7-
diyldicarbamate 14: 2-Diazo-1,3-diketone 11 (305.13 mg,
0.6 mmol) afforded pure 14 (233.35 mg, 83 %) Anal. calcd.
C27H34N2O6; C 67.20, H 7.10, N 5.80 %. Found: C, 67.187; H,
7.14; N, 5.77 %. (KBr, νmax), 3431 (OH enolic toutomer); 3325
(NH); 1643 (C=O); 1618 (=COH); 1140 (C-O); 1710 cm-1
(CO2CH2Ph). δH (CDCl3): 0.93-1.05 (12 H, d, 2(CH3)2-CH),
2.15 (2H, m, 2CH(CH3)2), 3.54 (2H, s, -COCH2OC-), 4.49
(2H, d, 2N-CH-CO), 5.15 (4H, s, 2CH2Ph) 5.42 (2H, br, 2NH),
7.2-7.39 (10 H, m, 2Ph), 15.7 (1 H, OH enol toutomer), 8.38
1
(COCN2);1520 cm-1 (Ph). H NMR (300 MHz, CDCl3): δ =
1.21 (6H, d, J = 7 Hz, CH3CH), 4.48 (2H, m, 2 N-CH-CO),
5.11 (4H, s, 2 OCH2Ph), 5.41 (2H, br s, 2NH), 7.2-7.40 (10 H,
m, 2 Ph), 13C NMR (75 MHz, CDCl3): δ = 18.4, 51.7, 55.1,
67.1, 128.2, 128.3, 128.6, 136.4, 155.9, 194.
13
(s, 1H, -CH=). C NMR (δ/ppm, CDCl3) 17.6, 19.45, 31.1,
65.63, 66.50, 67.0, 96.3 (CH=), 128.1, 128.2, 128.6, 136.3,
156.5, 192.9, 193.1.
Dibenzyl[(3R,7R)-5-diazo-2,8-dimethyl-4,6-dioxono-
nane-3,7-diyl]carbamate (11): N-Benzyloxycar-bonyl-l-
valinyl diazomethane (5) (2.37 g, 8.6 mmol) was lithiated a
according to the procedure employed for (10) and then treated
with imidilazide (7) to afford the compound (11), purification
using EtOAc: hexane as eluent furnished the pure compound
(11) (3.15 g, 72 %) as a pale-yellow oil.Anal. calcd. C27H32N4O6
C 63.77, H 6.34, N 11.01 %. Found: C, 63.42; H, 6.10 ; N,
10.97 %. (KBr, νmax), 3325 (NH); 2115 (CN2); 1710
Benzyl (2R,6R)-3,5-dioxo-1,7-diphenylheptane-2,6-
diyldicarbamate 15: 2-Diazo-1,3-diketone 12 (362.78 mg,
0.6 mmol) afforded pure 15 (281.23 mg, 81 %) Anal. calcd.
For C35H34N2O6; C 72.65; H 5.923; N 4.84 %. Found: C, 72.61;
H, 5.89; N, 4.87 %. (KBr, νmax), 3431 (OH enol toutomer);
1710 (CO2CH2Ph) 3318 (NH); 1625 (COCH); 1638 (C=O);
1620 (=COH) 1142 cm-1 (C-O). δH (CDCl3): 2.95 (4H, d,
2CHCH2); 4.52 (2H, m, 2CHCH2), 5.05 (4H, s, CH2Ph), 5.38
(2H, m, 2NH), 7.21-7.42 (24H, s, 4Ph), 15.9 (1 H, OH enol
toutomer) 8.40 (s,1H, -CH=). 13C NMR (δ/ppm, CDCl3) 38.25,
65.63, 67.6, 66.8, 96.5(CH=), 127.1, 127.7, 128.0, 128.36,
128.36, 129.1, 135.87, 136.0,155.56, 192.84, 193.
1
(CO2CH2Ph); 1632 cm-1 (COCN2). H NMR (300 MHz,
CDCl3): δ = 0.93-1.05 (12 H, d, J = 6.75Hz, 2(CH3)2-CH),
2.15 (2H, m, 2CH(CH3)2), 4.49 (2H, d, 2 N-CH-CO), 5.15
(4H, s, 2CH2Ph) 5.42 (2H, br, 2NH), 7.2-7.39 (10 H, m, 2Ph).
13C NMR (75 MHz, CDCl3): δ = 17.6, 19.45, 31.1, 54.6, 62.85,
67.0, 128.1, 128.2, 128.6, 136.3, 156.5.
General procedure for preparation of transition metal
complexes (16a-18c): A mixture of 5 mmol of ligands 13, 14
and 15 and 2.5 mmol of appropriate transition metal acetate
[Ni(II), Cu(II), zinc(II)] and 50 mL of anhydrous ethanol was
stirred at 50-60 ºC for 3 h. The coloured solid complex obtained
was washed with ethanol and then with ethyl acetate. The yield
was obtained in 74-79 %. The corresponding metal complexes
were crystallized by dichloromethane.
Dibenzyl[(2R,6R)-4-diazo-3,5-dioxo-1,7-diphenyl-
heptane-2,6-diyl]carbamate (12): N-Benzyloxycarbonyl-l-
phenyl alaninyl diazomethane (2.79 g, 8.6 mmol) was converted
into title compound (12) purification using EtOAc: hexane as
eluent furnished the pure compound (12) (4.16 g, 80 %) as a
yellow oil; anal. calcd. For C35H32N4O6; C, 69.52 ; H,5.34; N,
9.26 %. Found, C, 69.12; H, 5.11; N, 8.99 %. (KBr, νmax),
2100 (CN2); 1710 (CO2CH2Ph); 1625 cm-1 (COCH). 1H NMR
(300 MHz, CDCl3): δ = 2.95 (4H, d, J = 6.85 Hz, 2CHCH2Ph);
4.52 (2H, m, 2CHCH2), 5.05 (4H, s, 2OCH2Ph), 5.38 (2H, m,
2NH), 7.21-7.42 (24H, s, 4 Ph). 13C NMR (75 MHz, CDCl3):
δ = 38.25, 54.2, 58.65, 66.8, 127.1, 127.7, 128.0, 128.36,
128.36, 129.1, 135.87, 136.0,155.56, 192.54.
Bis-(β-diketonato) Cu(II) complexes 16a, 17a and 18a:
Pale green crystals of Cu(II) β-diketonate 16a Yield: 76 %.
Anal. calcd. For C46H50N4O12Cu: C 60.42; H 5.52; N 6.124;
Cu 6.95 %. Found: C, 60.35; H, 5.45; N, 6.021; Cu, 6.87 %.
(KBr, νmax) 1623 (C=O); 1118 cm-1 (C-O). δH (CDCl3): 8.78
(s,2H, -CH=). 13C NMR (δ/ppm, CDCl3) 96.87, 191,191.6.
Similarly, the complexes 17a and 18a were prepared by
the same method. Cu(II) β-diketonate 17aYield: 77 %. Anal.
calcd. For C54H66N4O12Cu: C 63.173; H 6.48; N 5.455; Cu
6.12 %. Found: C 63.02; H 6.32; N 5.29; Cu 5.95 %. (KBr,
Synthesis of 1,3-diketones derived from amino acids:
The 2-diazo-1,3-diketones in dry dichloromethane (0.01 M)
was treated with rhodium(II) acetate (0.5 mol %) under nitrogen
at room temperature for 1 h. The solvent was removed under
vacuo and the remaining product was purified by preparative
thin layer chromatography eluting with ethyl acetate-hexane
(4:6) to yield the pure product.
ν
max), 1619 (C=O); 1120 cm-1 (C-O. δH (CDCl3): 8.38 (s,2H,
-CH=). 13C NMR (δ/ppm, CDCl3): 96.91 (CH=), 193.2, 193.7.
Cu(II) β-diketonate 18a yield: 79 %. Anal. calcd. for
C70H66N4O12Cu: C 68.98; H 5.459; N 4.595; Cu 5.214 %.
Benzyl (2R, 6R)-3,5-dioxoheptane-2,6-diyldicarbamate
13: 2-diazo-1,3-diketone 10 (271.5 mg, 0.6 mmol) afforded
pure 13 (217.5 mg, 85 %), (predominantly in enolic form) as
an oil; Anal. calcd. C23H26N2O6 C 64.78, H 6.145, N 6.570 %.
Found: C 68.87; H 5.395; N 4.487; Cu 5.00 %. (KBr, νmax
)
1618 (C=O); 1122 cm-1 (C-O). δH (CDCl3): 8.75 (s, 2H, -CH=).
13C NMR (δ/ppm, CDCl3): 96.71 (CH=), 193.34, 193.76.

4750 Saraireh
Asian J. Chem.
H
O
O
Bis-(β-diketonato) Ni(II) complexes 16b, 17b and 18b:
Green crystals of Ni(II) β-diketonate 16b yield: 78 %. Anal.
calcd. For C46H54N4O14Ni: C 58.425; H 5.76; N 5.92; Ni 6.21
O
H
THF25oC/2h
N
O
+
N
N N
O
N
N
N
N
OH
O
R
%. Found: C, 58.150; H, 5.68; N, 5.86; Ni 5.98 %. (KBr, νmax
)
R
O
N
-benzyloxycarbonyl-
imidalzolide
7. R= -CH
l-aminoacid
1621 (C=O); 1121 cm-1 (C-O). δH (CDCl3): 8.80 (s, 2H, -CH=).
13C NMR (δ/ppm, CDCl3) 96.89, 191.2,191.7.
Carbonyldiimadazole
N
-benzyloxycarbonyl-
l-aminoacid
3
1.
2
R= -CH3
. R= -CH(CH3)2
3.
8
. R= -CH(CH)
3 2
9. R= -CHPh
2
Similarly, the complexes 17b and 18b were prepared by
the same method. Ni(II) β-diketonate 17b yield: 79 %. Anal.
calcd. For C54H70N4O14Ni: C 61.31; H 6.67; N 5.294; Ni 5.55
%. Found: C 61.01; H 6.53; N 5.220; Ni 5.43 %. (KBr, νmax),
1623 (C=O); 1121 cm-1 (C-O. δH (CDCl3): 8.40 (s, 2H, -CH=).
13C NMR (δ/ppm, CDCl3): 96.93 (CH=), 193.42, 193.79.
Ni(II) β-diketonate 18b Yield: 78 %. Anal. calcd. for
C70H70N4O14Ni: C 67.26; H 5.645; N 4.48; Ni 4.70 %. Found:
C 67.02; H 5.56 N 4.37; Ni 4.41%. (KBr, νmax) 1617 (C=O);
1119 cm-1 (C-O). δH (CDCl3): 8.79 (s,2H, -CH=). 13C NMR (δ
/ppm, CDCl3): 96.82 (CH=), 193.42, 194.16.
R= -CH2Ph
Scheme-II
The N-protected amino acid- derived diazoketone could be
easily metallated by addition to a solution of lithium diisopro-
pylamine in THF at -78 ºC. The resulting solution was treated
with imidazolide to form the diazo-β-diketone (Scheme-III) and
after the treatment of the products with aqueous work-up it is
purified by chromatography to get a good yield Table-2.
Di(N-protected-α-amino)-2-diazo-1,3-diketones was
treated with rhodium acetate to form di(N-protected-α-amino)-
1,3-diketones (Scheme-IV) and after purified by chromatog-
raphy to get yield (Table-3).
Bis-(β-diketonato) Zn(II) complexes 16c, 17c and 18c:
White crystals of Zn(II) β-diketonate 16c yield: 76 %. Anal.
calcd. for C46H50N4O12Zn: C 60.30; H 5.50; N 6.11; Zn 7.13
H
N
O
H
N
O
%. Found: C, 60.12; H, 5.42; N, 5.97; Zn 6.98 %. (KBr, νmax
)
+
O
1624 C=O); 1123 cm-1 (C-O). δH (CDCl3): 8.82 (s, 2H, -CH=).
13C NMR (δ/ppm, CDCl3) 96.9, 191.41, 191.74.
O
N
N
CHN2
O
R
R
O
Similarly, the complexes 17c and 18c were prepared by
the same method. Zn(II) β-diketonate 17c yield: 75 %. Anal.
calcd. For C54H66N4O12Zn: C 63.06; H 6.47; N 5.45; Zn 6.36
%. Found: C 62.92; H 6.35; N 5.32; Zn 6.301 %. (KBr, νmax),
1622 (C=O); 1118 cm-1 (C-O. δH (CDCl3): 8.46 (s,2H, -CH=).
13C NMR (δ/ppm, CDCl3): 96.95 (CH=), 193.51, 193.82.
Zn(II) β-diketonate 18c yield: 74 %. Anal. calcd. for
C70H66N4O12Zn: C 68.88; H 5.45; N 4.59; Zn 5.36 %. Found:
C 68.65; H 5.34 N 4.46; Zn 5.22 %. (KBr, νmax) 1622 (C=O);
LDA, THF
-78 oC
7. R=-CH
3
4
5
.R= -CH
3
.R= -CH-(CH )
8. R=-CH-(CH3)2
. R=-CH -Ph
3 2
9
2
6
.R= -CH -Ph
2
H
N
O
H
O
O
N
O
N2
O
R
R
O
10. R =-CH3
11. R =-CH(CH )
13
1120 cm-1 (C-O). δH (CDCl3): 8.82 (s, 2H, -CH=). C NMR
3 2
12. R =-CH2Ph
(δ/ppm, CDCl3): 96.86 (CH=), 193.52, 194.23.
Scheme-III
RESULTS AND DISCUSSION
H
O
O
H
N
N-protected amino acids were converted into α-diazoketones
via acid chloride or mixed anhydride by treatment with ethereal
diazomethane (Scheme-I) and after purification by chromato-
graphy gives good yield (Table-1). These N-protected amino
acids were converted into imidazolide by treatment with 1,1'-
carbonyldiimidazole (CDI) in THF solvent (Scheme-II).
O
O
N
R
R
N2
O
O
Rh (AcO)
2
4
O
O
H
H
N
O
H
1. (COCl) /DMF, 0oC
1. (COCl)2/DMF, 0 ºC
or ClCOOCH2CH(CH3)2/THF, -20 ºC
2
O
H
N
o
N
orClCOOCHCH(CH ) /THF,-20 C
O
2
3 2
O
N
2. CH2N2Et2O, 0 ºC
2. CH N ,Et2O, 0oC
CHN
O
O
O
2
2
2
OH
R
O
R
R
R
O
O
α−diazoketone
O
O
N
-benzyloxycarbonyl aminoacids
4. R=-CH3
5. R=-CH(CH )2
1
. R=-CH
3
2
3
. R=-CH(CH)
3
3 2
6
. R=-CH2Ph
. R=-CH Ph
2
H
N
OH
H
O
Scheme-I
O
N
TABLE-1
α-DIAZOKETONE DERIVED FROM
N-PROTECTED AMINO ACID
R
R
O
Yield (%)
13. R=-CH
α−Ddiazo ketone
3
4
5
6
84
75
88
14. R=-CH(CH )
3 2
15. R=-CH Ph
2
Scheme-IV

Vol. 25, No. 9 (2013)
Complexation of Chiral Di (N-Protected α-Amino)-β-Diketones with Some Transition Metals 4751
All the synthesized transition metal complexes (16a- 18c)
TABLE-2
DIAZO-β-DIKETONES
were soluble in dichloromethane, ethylacetate, acetone and
methanol. The metal complexes were obtained by stoichio-
metric reaction of the corresponding ligand with the transition
metal salt in a molar ratio M: L of 1:2.All the complexes were
found to be thermally stable. Physical measurements and
analytical data of the transition complexes (16a-18c) are given
in experimental section.
Yield (%)
Di(N-protected-α-amino)-2-diazo-1,3-diketones
10
11
12
77
72
80
TABLE-3
β-DIKETONES
Spectroscopic characterization of ligands (13-15) and
their transition metal complexes (16a-18c): The complexes
of synthesized compounds 13, 14 and 15 gives green coloured
Cu(II) β-diketonate 16a, 17a and 18a in high yield. The struc-
tures were then confirmed by the spectral analysis: IR (KBr),
1H and 13C NMR. The C=O band in complexes 16a, 17a and
18a shifted to lower frequency as compared to that of free
ligand which indicates the coordination of metal atom with
the carbonyl group of diketone. Similarly, other transition metal
complexes were prepared by the same method.
Yield (%)
Di(N-protected-α-amino)-1,3-diketones
13
14
15
85
83
81
Di(N-protected-α-amino)-1,3-diketones were used as
aligands to synthesis complexes with Cu(II), Ni(II) and Zn(II)
metal ions (Scheme-V) and after purified give good yields
(Table-4).
TABLE-4
β-DIKETONES COMPLEXES
IR spectra: The characteristic infrared spectral assign-
ment of ligands (13-15) and their Ni(II), Cu(II) and Zinc(II)
complexes are reported. The appearance of a strong band at
1640 cm-1 in the spectra of ligand is assigned to carbonyl group
(C=O) and 1140 cm-1 due to (C-O) stretch, exhibited a lower
shift of 10-20 cm-1 (1628-1620 and 1130-1118 cm-1) in metal
complexes (16a-18c). This shift indicates that the β-diketo
functionality in ligands (13-15) coordinated with the transition
metal ion. All the above evidences were further supported by
the emergence of new bands at 535-523 and 460-443 cm-1 due
to metal-oxygen vibrations. These new bands were only
observed in the spectra of the transition metal complexes and
not in their free ligands. As a conclusion, comparison of the
spectra of the ligands (13-15) and their metal complexes (16a-
18c) confirmed the coordination of ligand with the corresponding
metal ion, bidentately through β-diketo functionality.
Complex
16a
Yield (%)
76
78
76
77
79
75
79
78
74
16b
16c
17a
17b
17c
18a
18b
18c
H
N
OH
O
H
O
O
N
1
1H NMR spectra: The H NMR spectral data of the
R
R
O
O
ligands (13-15) and their transition metal complexes (16a-18c)
are provided in the experimental part. The displayed signals
of all the protons of free ligands due to aromatic groups were
found as to be in their expected region. The 1H NMR spectrum
of ligands (13-15) exhibited a singlet at δ 14.42 ppm due to
enolic proton, a singlet at δ 8.41 ppm (s,1H, -CH=). The coordi-
nation of the β-diketo functionality is assigned by the down
field shifting of the (-CH=‚) from δ 8.40 ppm in free ligand to
δ 8.77-8.86 ppm in its transition metal complexes. The enolic
proton at δ 14.42 ppm in the ligand (13-15) disappeared in the
spectra of all its metal complexes (16a-18c) indicating
deprotonation and coordination of the oxygen with the metal
ion. All other protons underwent down field shift by 0.15-
0.30 ppm due to the increased conjugation on complexation
with the transition metal atom.
13C NMR spectra:The 13C NMR spectra of the free ligands
and their transition metal chelates were done in CHCl3. The
13C NMR spectral data are reported along with their possible
assignments in the experimental section and all the carbons
were found in the expected regions. The carbonyl carbon
(C=O) and enolic carbon (C-O) of the ligand (13-15) appeared
in the region δ 191-192.8 ppm and δ 191.6-193.1 ppm, respec-
tively. The methine linkage appeared in the region δ 65.3-
66.5 ppm. Downfield shifting of the carbonyl carbon (C=O)
M(OAc)2
EtOH
O
R
O
R
N
O
N
O
H
O
O
H
OH
H2O
2
M
H
N
O
O
H
N
O
O
R
R
O
O
16a. R=-CH , M=Cu(II)
3
16b. R= -CH , M=Ni(II)
3
17a. R=-CH(CH3)2 , M= Cu(II) 17b. R=-CH(CH3)2, M=Ni(II)
18a. R=-CH Ph, M=Cu(II) 18b. R=-CH Ph, M=Ni(II)
2
2
16c. R= -CH , M= Zn(II)
3
17c. R=-CH(CH3)29, M=Zn(II)
18c. R=-CH Ph, M =Zn(II)
2
Scheme-V

4752 Saraireh
Asian J. Chem.
TABLE-6
THERMAL DATA OF THE COMPLEXES
and enolic carbon (C-O) from δ 191-192.8 ppm and δ 191.6-
193.1 ppm in the free ligand (13-15) to δ 192.2-194.1 ppm
and δ 192.4-194.4 ppm in its metal (II) complexes (16a-18c)
confirmed coordination of the carbonyl (C=O) and enolic
group (C-OH) to the transition metal atom. Furthermore, the
presence of the number of carbons agrees well with their
expected values.
Complex
number
Complex
formula
Coordination Decom- Weight Residue
position loss (%) comp.
water (%)
obs (calc.)
temp.
(oC )
obs(calc)
C46H50N4O12Cu
C54H66N4O12Cu
C70H66N4O12Cu
C46H54N4O14Ni
C54H70N4O14Ni
C70H70N4O14Ni
C46H50N4O12Zn
C54H66N4O12Zn
C70H66N4O12Zn
-
355
405
412
334
342
358
418
464
459
91.3
92.25
93.47
92.1
CuO
CuO
CuO
NiO
NiO
NiO
ZnO
ZnO
ZnO
16a
17a
18a
16b
17b
18b
16c
17c
18c
-
-
Conductance and magnetic susceptibility of Ni(II),
Cu(II) and Zn(II) complexes: The molar conductance values
were obtained in Ω-1 cm2 mol-1 at room temperature using DMF
as a solvent (Table-5). The complexes (16a-18c), showed their
molar conductance values in the ranges 14.6-16.8 Ω-1 cm2 mol-1
indicating their non-electrolytic nature.
4.16 (3.81)
3.23 (3.41)
92.94
94.024
91.12
92.09
93.33
3.10 (2.88)
-
-
-
The Ni(II) complexes are paramagnetic, which indicates
a high-spin-state Ni center characteristic of octahedral comp-
lexes of Ni(II). The Cu(II) complexes are paramagnetic. For
the Cu(II) complexes, the µeff values are in the range 1.82-1.91
B.M., which are slightly higher than those expected for a d9
system (1.73 B.M.) and may be due to the incomplete quenching
of orbital contribution to the magnetic moment or due to spin-
orbit coupling. The room temperature magnetic moment values
of Zn(II) complexes are found to be diamagnetic as expected
due to non-availability of unpaired electrons.
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TABLE-5
CONDUCTIVITY AND MAGNETIC DATA OF
METAL(II) COMPLEXES (16a-18c)
ΩM (Ω-1 cm2 mol-1)
BM (µeff) (obs) (calc.)
1.82 (1.93)
3.10 (2.83)
Dia
Metal complexes
15.7
16.8
14.9
15.4
16.6
14.6
15.5
16.7
14.7
16a
16b
16c
17a
17b
17c
18a
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Dia
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