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Synthesis and characterization of Ru(III) chiral schiff base complexes derived from salicylaldehyde and L-aminoacids
09574166/91$3.00+.00 Pe1gam0n Press plc
Tehzhedron: AsymmetryVol. 2, No. 10, pp. 1015-1020. 1991 Priited in Great Britain
SYNTHESIS AND CHARACTERIZATION OF Ru(III) CHIRAL SCHIFF BASE COMPLEXES DERIVED FROM SALICYLALDEHYDE AND L-AMINOACIDS M.M.
Taqui
Khan,
R.I.
Kureshy
and
N.H.
Khan
Discipline of Coordination Chemistry & Homogeneous Catalysis Central Salt and Marine Chemicals Research Institute, Bhavnagar 361002, India.
(Received 1 July 1991)
Abstract: The synthesis and characterisation of several chiral ruthenium (III) Schiff base complexes of the type K[(Ru(L)(C1)2(H20)] where L = Schiff base derived from L-aminoacids The electronic absorption, optical rotation and circular with salicylaldehyde are reported. dichroism spectra of the complexes in methanol are discussed.
Introduction Transition
metal complexes
of aminoacids
constitute
model systems for the study of metalloproteinsl
including their molecular structure2 as well as their electronic and magnetic properties.334 The chemistry
of metal complexes
bases596 or porphyrins7 especially
those of respiratory
with L-aminoacids pyramidal
reported.6
pigments or the coenzymes
like L-glycine,
geometry
oxovanadium(V)
with multidentate
ligands with delocalized
rc-orbitals such as Schiff
has recently gained much interest because of their use as models in biological systems
L-serine,
and are of potential
and oxovanadium(IV)
The chiral
phosphine
of vitamin B12. The complexes
L-hydroxyproline
utility as homogeneous complexes
complexes
of [RuClZ(PPh3)3]
and L-allohydroxyproline catalysts.5
with quadridentate
of ruthenium(U)
show a square
The catalytic
properties
of
Schiff base ligands have also been
have gained
importance
in asymmetric
hydrogenation.8 In order to develop new chiral ruthenium(II1) complexes complexes L-serine
derived from L-aminoacids (L-ser), L-aspartic
we have synthesised
such as L-alanine (L-ala), L-phenylalanine
acid (L-asp), L-methionine
(L-meth),
tyrosine (L-tyr) and L-arginine (L-arg) with salicylaldehyde.
L-histidine
Ru(II1) chiral Schiff base
(L-pheala), L-valine (L-val), (L-his), L-cystein
The steric and conformational
(L-cys), L-
effects with various
R groups attached to the aminoacid moiety in chiral Schiff base metal complexes are reported in this paper.
Results
and
Discussion
All optically active Schiff base ligands were synthesised yellow in colour and are highly air sensitive. character&d
The complexes
by the reported procedure.9
were synthesised
by elemental analysis, IR and ‘H NMR spectroscopic
1015
methods.9Jo
The ligands are all
under an argon atmosphere
and
I
Analytical data, base complexes molar
conductance,
optical
rotation
and
absolute
configuration
in
Chiral
Ru(II1)
Schiff
Sal-L-Argdichloroaquoruthenate(
Salt-L-Hisdichloroaquoruthenate(II1)
Sal-L-Aladichloroaquoruthenate(II1)
Sal-L-Methdichloroaquoruthenate(II1)
Sal-L-Aspdichloroaquoruthenate(II1)
Sal-L-phealadichloroaauoruthenate(II1)
Sal-L-cysdichloroaquoruthenate(II1)
Sal-L-Tyrdichloroaquoruthenate(II1)
2.
3.
4.
5.
6.
7.
8.
9.
lO.Sal-L-Serdichloroaquoruthenate(II1)
Sal-L-Valdichloroaquoruthenate(II1)
1.
Complexes
III)
j33.19 (33.26) 33.00 (33.06) 33.22 (33.31) 28.53 (28.59) 32.08 (32.12) 32.22 (32.28) 38.29 (38.32) 27.51 (27.54) 37.42 (37.49) 27.50 (27.54)
%C
3.40 (3.46) 3.12 (3.17) 2.50 (2.56) 2.59 (2.61) 3.30 (3.34) 1.90 (1.95) 2.95 (2.99) 2.50 (2.52) 2.89 (2.92) 2.50 (2.52)
%H
Found (Calc) -~-~--~---__~~~~--~~~~~~~~
3.19 (3.23) 8.82 (8.89) 8.91 (8.96) 3.30 (3.33) 3.09 (3.12) 3.40 (3.42) 2.73 (2.79) 3.18 (3.21) 2.71 (2.73) 3.17 (3.22)
%N
95
105
85
05
90
105
100
85
90
85
Molar conductance A M 0hm-l
R
R
R
R
R
R
R
R
R
R
-1
62.2”
-
-
-
77.2O
49.8’=
64.8’
-192.62
-119.8”
-202.4O
-227.4O
-
-119.8O
-214.8’=
Abs. Ea3D deg. con-2 figuracm
________-_____-__----__________--_~~~~----~--------~~~~~~~~~~~~~~--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-----~~~~~~~~~~~
Table
II
Electronic
Absorption
and
C.D.
spectral
data
for
Ru(III)
Chiral
Schiff
A max
(E M-1
cme2 )
493(71), 273(553) 578(259), 326(1302), 640(525), 296(205?) 560(106), 3Gl( 1s;: 591(204), 261(2498) 393(604),
608(120),
559(589),
Salt-L-Hisdichloroaquoruthenate(Ii1)
Sal-L-Aladichloroaquoruthenate(II1)
Sal-L-Methdichloroaquoruthenate(II1)
Sal-L-Aspdichloroaauoruthenate(II!)
Sal-L-phealadichloroaquoruthenate(
Sal-L-cysdichloroaquoruthenate(II1)
Sal-L-Tyrdichloroaquoruthenate(II1)
3.
4.
5.
6.
7.
8.
9.
10 .Sal-L-Serdichloroaouoruthenate(II1)
____________________-_~__---_-----___-_-
570(162),
Sal-L-Argdichloroaquoruthenate(lI1)
2.
III)
581(360),
Sal-L-Valdichloroaquoruthenate(II1)
1.
375(1318),
360(864)
349(117),
347(130).
399(1302),
389(1480),
368(1082), 306(1305)
?Q6(96),
386(1131),
378(1345).
344(1510)
303(192)
305(183),
317(157!,
347(1645),
345(1297)
336(151),
305(1800)
302(1876)
---------__-_______-__5_________________~~~__--_--__-___---_--__---_______-~-___----~--~__-~~-~~~~~~~~~~~----
Complexes 3 kK
base
.
27.7(-1.4), 23.5(-0.18),
31.2(-1.2). 22.7(-0.08),
30.7(+0.20), 26.6(+0.30)
31.2(-1.59), 16.6(+0.16)
L_
‘2 -5(+0.50),
31.2(&0.25),
27.9(-1.4), 16.6(+0.13)
27.7(-1.70). 16.8(+0.30)
28.9(-0.32), 20(+0.13),
30.7(+0.29), 24.6(+0.49)
)
25.9(+0.68), 20(+0.36)
25.6(+0.08) 14.7(+0.12)
28.?(-0.08)
25.9(+0.23)
26.3(-0.89), 16.6(+0.2@)
25.9(+0.71),
22.4(-0.40).
26.3(+0.28), 17.6(-0.12)
28.9(-0.49)
25.9(+0.38) 20(+0.49)
complexes
(AE
27.6(-1.4), 22.7(-0.56).
---------_--__-____---~~~-~~~~~~~~~~~~~~~~~_--~--~--~---~------~-~~--____--~~~~-~---~-~~~~~_-~~-~~---~-~~-------
Table
1018
M. M. TAQUIKAHNet al.
R=CH3, CHz-CrjHg, CHzOH, CH-(CH3)2, CH2-S-CH3, CH#&@H, CH~-C~H~NZ, (CH2)3C(NHz)=NH, CHzCOOH, CH2SH
K’
The analytical data and molar conductance
of all complexes are listed in Table I. Molar conductivities
the complexes in methanol indicate that they are univalent electrolytes. complexes
fall in the range 1.98 - 2.07 B.M. indicating
of
The magnetic moment keff values of these
the presence
of Ru(II1) ion with a spin paired 4d5
electronic configuration. A band near 1640 - 1590 cm-l in the infrared spectra of the ligands and complexes may be. assigned to the azomethine bands.
absorption
with an overlap of the u-COO asymmetric
This band undergoes
a modest decrease in frequency
assigned to the symmetric U-COO vibration. the complexes.
after complexation.11
The band at 1450 cm-l is
The ring stretching vibrations lie at 1354, 1430 and 1475 cm-1 in all
These vibrations
have been assigned
to 6 (O-H) and 2) (O-H) modes, respectively.
Similar
were made by Ruano et al. I2 The 2) (Ru-Cl) and u (Ru-N) lie near 325-340 cm-l.
The UV-visible
spectral data of the complexes
396 nm may be assigned respectively.
and the C=C/C=N ring stretching
Two additional bands at 1100 and 1170 cm-t along with a broad band at 3400 cm-* appear for all
the complexes. observations
stretching
to n --f a*
After complexation
are summarised
and q -+ x* transitions
with ruthenium(II1)
in Table II. The bands near 296 nm and
of the double bond of the azomethine
the band at 396 nm shows a hypsochromic
group,
shift which
depends on the R group attached to the azomethine group of aminoacid moiety,6 the energy of the band decreases in the order Sal-Meth > Sal-val > Sal-cys >Sal-ser >Sal-pheala
> Sal-Asp > Sal-arg > Sal-ala > Sal-tyro > Sal-
his. A moderately intense band near 490 nm can be attributed to the charge transfer transition of the chloride ion. All bands are undoubtedly
charge transfer in origin except a band near 640 nm which can be assigned
to
forbidden ligand field transition of Ru(II1). Two representative
circular dichroism
spectra for the Ru(II1) Schiff base complexes
Figures IA and 1B. The CD. data for all the complexes spectra of the two complexes the same absolute configuration
in methanol are summarised
in
derived from R-(-)-ala (1A) and R-(-)-cys (1B) show that both amino acids have in the complexes but R (-) cys is stereospecifically
moiety so that the gauche chelate ring is located in the 6 conformation
coordinated
of h form. Similar relationships
to the ruthenium
with very little contribution
isomer while the former complex in solution is in an equilibrium mixture of the conformational with a preference
are presented
in Table II. The C.D.
from the h
isomers (6 and k)
among CD. spectra were reported elsewhere.1396 Thus in all
the complexes the steric interaction between substituents at the azomethine carbon and those on the central chelate ring provides the driving force for both the preferred conformation In the ligand field region,
and configuration.
14.7 - 20 kK, CD bands of opposite
sign are displayed.
This has been
assigned to both the d-d bands and spin forbidden ligand bands. As expected an increase in the donor strength of the Schiff base in going from CH3 to (X2-R causes a blue shift of the ligand field band.6 The charge transfer
1019
Ru(II1) Chiral Schiff base complexes
-1.0
-1.2 33.3
, 25
I 20
1 16.6
14.2
kK Fig. IA
CD Spectrum of [Sal-L-aladichloroaquoruthenate](III) complex in methanol. +
0.41 I-
+ 0.2O-0.2-
I
-0*4-0.6; - 0.8 u -1.0 Q -1.2 i -I.4 -1.6 -1.8
r
-2.033.3
i
I 25
I 20
, 16.6
14.2
kK Fig. 1B
CD Spectrum of [Sal-L-cysdichloroaquoruthenate](III) complex in methanol.
region of the spectra 22.4 - 26.3 kK indicates a band which can be assigned to d + n* azomethine transition. The ligand R + x* (azomethine) transition band is seen in the higher energy region 27.7 - 3 1.2 kK. The shift of
1020
M. M. TAQUIKAHNet al.
both the charge transfer and the ligand transition with azomethine
substituents
is consistent
with the inductive
salicylaldehyde,
L-alanine,
L-histidine,
L-serine, L-valine
effect of the change of substituent from CH3 to (X2-R on the ligand II levelsI
Experimental RuC13.3H20 phenylalanine,
was from Johnson
L-tyrosine,
were from Aldrich synthesised
L-cystein,
Chemicals.
and Matthey.
The compounds
L-aspartic acid, L-methionine,
The Schiff bases derived
L-arginine,
from all aminoacids
with salicylaldehyde
by the known procedure. 9 All the complexes were prepared under argon atmosphere.
L-
were
The progress
of the reaction were checked by TLC from time to time. To a hot methanolic K2[RuCls(H20)] atmosphere.
solution (1.0 mmol) of the above Schiff base ligands were added (1.0 mmol) of
in a 1:l metal:ligand
The completion
argon atmosphere.
The reaction mixture was refluxed up to lo-15 hrs. in an argon
The filtrate was concentrated
The complexes were recrystallised Microanalyses conductance
ratio.
of the reaction was checked on TLC. After that the solution was filtered under an
were performed
on a Carlo Erba Analyser
on a Digisun Electronic Conductivity
on Carl Ziess Specord M-80 spectrophotometer
recorded on a Shimadzu UV-Vis recording spectrophotometer
in Nujol mull/KBr.
The optical rotation
for dia-magnetism.
polarimeter DIP-360 Jasco Machine.
Model bridge.
1106.
Molar
The I.R. spectra
Electronic
spectra were
model 160. The magnetic moment measurements
were made at 298 K by the Gouy method using Hg[Co(SCN)4] were corrected
by diethyl ether.
in the same solvent. They were dried in vacua. Yield 60%.
of the complexes
was measured at room temperature
were recorded
to about 10 ml and the complexes precipitated
as calibrant
of the complexes
and experimental in methanol
susceptibilities
was measured
by
The CD. spectra were recorded in methanol by Jobin YVON - Paris.
References 1.
R. Calvo, P.R. Levstein,
E.E. Castellano,
S.M. Fabiane,
O.E. Piro and S.B. Oseroff, Inorg.
C&m.,
1991, 30, 216. 2.
3.
Adv. Protein Chem., 1967, 22, 257.
H.C. Freeman,
G.L. Eichhom,
Elsevier, Amsterdam,
H.C. Freeman,
Ed. In Inorganic
Biochemistry,
1973, Chapter 3.
R. Calvo, H. Isern, M.A. Mesa, Chem. Phys., 1985, 100, 89.
4.
C.A. Steren, A.M. Gennaro, P.R. Levstein,
5.
W.S. Sheldrick
R.J. Calvo, Phys. Condens, Matter, 1989, 1,637.
and R. Exner, Inorg. Chim. Acta 1990,175,261. K. Kojima, M. Kojima, J. Fujita, Bull. Chem. Sot. Jpn., 1990, 63, 2620.
6.
K. Nakajima,
7.
(a) M. Yuasa, H. Nishide and E. Tsuchida, J. Chem. Sot., Dalton Trans., 1987, 2493. (b) E.Tsuchida,
H. Maeda, M. Yuasa and H. Nichide, J. Chem. Sot., Dalton Trans., 1987, 2455. 8. Chem.,
V. Massonneau, 1987,26,
P.L. Maux, R. Dabard,
G. Simonneaux,
P. Aviron-violet
and P.T. Dang, Inorg.
773.
9.
D. Heinert and A.E. Martell, J. Am. Chem. Sot., 1962.84,
10.
I. Sasaki, D. Pujol and A. Gaudemer,
11.
D.A. Edwards and R. Richards., J. Chem. Sot., Dalton Trans., 1975,637.
3257.
Inorg. Chim. Acta., 1987, 134, 53.
12.
M.A. Bangres, M. Gonzalez,
13.
L.J. Boucher,
C.G. Coe, Inorg. Chem., 1976, 15, 1334.
M.E. Peres and R.J. Ruano, Polyhed., 1986,5,
14.
L.J. Boucher,
Inorg. Nucl. Chem., 1974, 36, 531.
1371.
Tehzhedron: AsymmetryVol. 2, No. 10, pp. 1015-1020. 1991 Priited in Great Britain
SYNTHESIS AND CHARACTERIZATION OF Ru(III) CHIRAL SCHIFF BASE COMPLEXES DERIVED FROM SALICYLALDEHYDE AND L-AMINOACIDS M.M.
Taqui
Khan,
R.I.
Kureshy
and
N.H.
Khan
Discipline of Coordination Chemistry & Homogeneous Catalysis Central Salt and Marine Chemicals Research Institute, Bhavnagar 361002, India.
(Received 1 July 1991)
Abstract: The synthesis and characterisation of several chiral ruthenium (III) Schiff base complexes of the type K[(Ru(L)(C1)2(H20)] where L = Schiff base derived from L-aminoacids The electronic absorption, optical rotation and circular with salicylaldehyde are reported. dichroism spectra of the complexes in methanol are discussed.
Introduction Transition
metal complexes
of aminoacids
constitute
model systems for the study of metalloproteinsl
including their molecular structure2 as well as their electronic and magnetic properties.334 The chemistry
of metal complexes
bases596 or porphyrins7 especially
those of respiratory
with L-aminoacids pyramidal
reported.6
pigments or the coenzymes
like L-glycine,
geometry
oxovanadium(V)
with multidentate
ligands with delocalized
rc-orbitals such as Schiff
has recently gained much interest because of their use as models in biological systems
L-serine,
and are of potential
and oxovanadium(IV)
The chiral
phosphine
of vitamin B12. The complexes
L-hydroxyproline
utility as homogeneous complexes
complexes
of [RuClZ(PPh3)3]
and L-allohydroxyproline catalysts.5
with quadridentate
of ruthenium(U)
show a square
The catalytic
properties
of
Schiff base ligands have also been
have gained
importance
in asymmetric
hydrogenation.8 In order to develop new chiral ruthenium(II1) complexes complexes L-serine
derived from L-aminoacids (L-ser), L-aspartic
we have synthesised
such as L-alanine (L-ala), L-phenylalanine
acid (L-asp), L-methionine
(L-meth),
tyrosine (L-tyr) and L-arginine (L-arg) with salicylaldehyde.
L-histidine
Ru(II1) chiral Schiff base
(L-pheala), L-valine (L-val), (L-his), L-cystein
The steric and conformational
(L-cys), L-
effects with various
R groups attached to the aminoacid moiety in chiral Schiff base metal complexes are reported in this paper.
Results
and
Discussion
All optically active Schiff base ligands were synthesised yellow in colour and are highly air sensitive. character&d
The complexes
by the reported procedure.9
were synthesised
by elemental analysis, IR and ‘H NMR spectroscopic
1015
methods.9Jo
The ligands are all
under an argon atmosphere
and
I
Analytical data, base complexes molar
conductance,
optical
rotation
and
absolute
configuration
in
Chiral
Ru(II1)
Schiff
Sal-L-Argdichloroaquoruthenate(
Salt-L-Hisdichloroaquoruthenate(II1)
Sal-L-Aladichloroaquoruthenate(II1)
Sal-L-Methdichloroaquoruthenate(II1)
Sal-L-Aspdichloroaquoruthenate(II1)
Sal-L-phealadichloroaauoruthenate(II1)
Sal-L-cysdichloroaquoruthenate(II1)
Sal-L-Tyrdichloroaquoruthenate(II1)
2.
3.
4.
5.
6.
7.
8.
9.
lO.Sal-L-Serdichloroaquoruthenate(II1)
Sal-L-Valdichloroaquoruthenate(II1)
1.
Complexes
III)
j33.19 (33.26) 33.00 (33.06) 33.22 (33.31) 28.53 (28.59) 32.08 (32.12) 32.22 (32.28) 38.29 (38.32) 27.51 (27.54) 37.42 (37.49) 27.50 (27.54)
%C
3.40 (3.46) 3.12 (3.17) 2.50 (2.56) 2.59 (2.61) 3.30 (3.34) 1.90 (1.95) 2.95 (2.99) 2.50 (2.52) 2.89 (2.92) 2.50 (2.52)
%H
Found (Calc) -~-~--~---__~~~~--~~~~~~~~
3.19 (3.23) 8.82 (8.89) 8.91 (8.96) 3.30 (3.33) 3.09 (3.12) 3.40 (3.42) 2.73 (2.79) 3.18 (3.21) 2.71 (2.73) 3.17 (3.22)
%N
95
105
85
05
90
105
100
85
90
85
Molar conductance A M 0hm-l
R
R
R
R
R
R
R
R
R
R
-1
62.2”
-
-
-
77.2O
49.8’=
64.8’
-192.62
-119.8”
-202.4O
-227.4O
-
-119.8O
-214.8’=
Abs. Ea3D deg. con-2 figuracm
________-_____-__----__________--_~~~~----~--------~~~~~~~~~~~~~~--~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~-----~~~~~~~~~~~
Table
II
Electronic
Absorption
and
C.D.
spectral
data
for
Ru(III)
Chiral
Schiff
A max
(E M-1
cme2 )
493(71), 273(553) 578(259), 326(1302), 640(525), 296(205?) 560(106), 3Gl( 1s;: 591(204), 261(2498) 393(604),
608(120),
559(589),
Salt-L-Hisdichloroaquoruthenate(Ii1)
Sal-L-Aladichloroaquoruthenate(II1)
Sal-L-Methdichloroaquoruthenate(II1)
Sal-L-Aspdichloroaauoruthenate(II!)
Sal-L-phealadichloroaquoruthenate(
Sal-L-cysdichloroaquoruthenate(II1)
Sal-L-Tyrdichloroaquoruthenate(II1)
3.
4.
5.
6.
7.
8.
9.
10 .Sal-L-Serdichloroaouoruthenate(II1)
____________________-_~__---_-----___-_-
570(162),
Sal-L-Argdichloroaquoruthenate(lI1)
2.
III)
581(360),
Sal-L-Valdichloroaquoruthenate(II1)
1.
375(1318),
360(864)
349(117),
347(130).
399(1302),
389(1480),
368(1082), 306(1305)
?Q6(96),
386(1131),
378(1345).
344(1510)
303(192)
305(183),
317(157!,
347(1645),
345(1297)
336(151),
305(1800)
302(1876)
---------__-_______-__5_________________~~~__--_--__-___---_--__---_______-~-___----~--~__-~~-~~~~~~~~~~~----
Complexes 3 kK
base
.
27.7(-1.4), 23.5(-0.18),
31.2(-1.2). 22.7(-0.08),
30.7(+0.20), 26.6(+0.30)
31.2(-1.59), 16.6(+0.16)
L_
‘2 -5(+0.50),
31.2(&0.25),
27.9(-1.4), 16.6(+0.13)
27.7(-1.70). 16.8(+0.30)
28.9(-0.32), 20(+0.13),
30.7(+0.29), 24.6(+0.49)
)
25.9(+0.68), 20(+0.36)
25.6(+0.08) 14.7(+0.12)
28.?(-0.08)
25.9(+0.23)
26.3(-0.89), 16.6(+0.2@)
25.9(+0.71),
22.4(-0.40).
26.3(+0.28), 17.6(-0.12)
28.9(-0.49)
25.9(+0.38) 20(+0.49)
complexes
(AE
27.6(-1.4), 22.7(-0.56).
---------_--__-____---~~~-~~~~~~~~~~~~~~~~~_--~--~--~---~------~-~~--____--~~~~-~---~-~~~~~_-~~-~~---~-~~-------
Table
1018
M. M. TAQUIKAHNet al.
R=CH3, CHz-CrjHg, CHzOH, CH-(CH3)2, CH2-S-CH3, CH#&@H, CH~-C~H~NZ, (CH2)3C(NHz)=NH, CHzCOOH, CH2SH
K’
The analytical data and molar conductance
of all complexes are listed in Table I. Molar conductivities
the complexes in methanol indicate that they are univalent electrolytes. complexes
fall in the range 1.98 - 2.07 B.M. indicating
of
The magnetic moment keff values of these
the presence
of Ru(II1) ion with a spin paired 4d5
electronic configuration. A band near 1640 - 1590 cm-l in the infrared spectra of the ligands and complexes may be. assigned to the azomethine bands.
absorption
with an overlap of the u-COO asymmetric
This band undergoes
a modest decrease in frequency
assigned to the symmetric U-COO vibration. the complexes.
after complexation.11
The band at 1450 cm-l is
The ring stretching vibrations lie at 1354, 1430 and 1475 cm-1 in all
These vibrations
have been assigned
to 6 (O-H) and 2) (O-H) modes, respectively.
Similar
were made by Ruano et al. I2 The 2) (Ru-Cl) and u (Ru-N) lie near 325-340 cm-l.
The UV-visible
spectral data of the complexes
396 nm may be assigned respectively.
and the C=C/C=N ring stretching
Two additional bands at 1100 and 1170 cm-t along with a broad band at 3400 cm-* appear for all
the complexes. observations
stretching
to n --f a*
After complexation
are summarised
and q -+ x* transitions
with ruthenium(II1)
in Table II. The bands near 296 nm and
of the double bond of the azomethine
the band at 396 nm shows a hypsochromic
group,
shift which
depends on the R group attached to the azomethine group of aminoacid moiety,6 the energy of the band decreases in the order Sal-Meth > Sal-val > Sal-cys >Sal-ser >Sal-pheala
> Sal-Asp > Sal-arg > Sal-ala > Sal-tyro > Sal-
his. A moderately intense band near 490 nm can be attributed to the charge transfer transition of the chloride ion. All bands are undoubtedly
charge transfer in origin except a band near 640 nm which can be assigned
to
forbidden ligand field transition of Ru(II1). Two representative
circular dichroism
spectra for the Ru(II1) Schiff base complexes
Figures IA and 1B. The CD. data for all the complexes spectra of the two complexes the same absolute configuration
in methanol are summarised
in
derived from R-(-)-ala (1A) and R-(-)-cys (1B) show that both amino acids have in the complexes but R (-) cys is stereospecifically
moiety so that the gauche chelate ring is located in the 6 conformation
coordinated
of h form. Similar relationships
to the ruthenium
with very little contribution
isomer while the former complex in solution is in an equilibrium mixture of the conformational with a preference
are presented
in Table II. The C.D.
from the h
isomers (6 and k)
among CD. spectra were reported elsewhere.1396 Thus in all
the complexes the steric interaction between substituents at the azomethine carbon and those on the central chelate ring provides the driving force for both the preferred conformation In the ligand field region,
and configuration.
14.7 - 20 kK, CD bands of opposite
sign are displayed.
This has been
assigned to both the d-d bands and spin forbidden ligand bands. As expected an increase in the donor strength of the Schiff base in going from CH3 to (X2-R causes a blue shift of the ligand field band.6 The charge transfer
1019
Ru(II1) Chiral Schiff base complexes
-1.0
-1.2 33.3
, 25
I 20
1 16.6
14.2
kK Fig. IA
CD Spectrum of [Sal-L-aladichloroaquoruthenate](III) complex in methanol. +
0.41 I-
+ 0.2O-0.2-
I
-0*4-0.6; - 0.8 u -1.0 Q -1.2 i -I.4 -1.6 -1.8
r
-2.033.3
i
I 25
I 20
, 16.6
14.2
kK Fig. 1B
CD Spectrum of [Sal-L-cysdichloroaquoruthenate](III) complex in methanol.
region of the spectra 22.4 - 26.3 kK indicates a band which can be assigned to d + n* azomethine transition. The ligand R + x* (azomethine) transition band is seen in the higher energy region 27.7 - 3 1.2 kK. The shift of
1020
M. M. TAQUIKAHNet al.
both the charge transfer and the ligand transition with azomethine
substituents
is consistent
with the inductive
salicylaldehyde,
L-alanine,
L-histidine,
L-serine, L-valine
effect of the change of substituent from CH3 to (X2-R on the ligand II levelsI
Experimental RuC13.3H20 phenylalanine,
was from Johnson
L-tyrosine,
were from Aldrich synthesised
L-cystein,
Chemicals.
and Matthey.
The compounds
L-aspartic acid, L-methionine,
The Schiff bases derived
L-arginine,
from all aminoacids
with salicylaldehyde
by the known procedure. 9 All the complexes were prepared under argon atmosphere.
L-
were
The progress
of the reaction were checked by TLC from time to time. To a hot methanolic K2[RuCls(H20)] atmosphere.
solution (1.0 mmol) of the above Schiff base ligands were added (1.0 mmol) of
in a 1:l metal:ligand
The completion
argon atmosphere.
The reaction mixture was refluxed up to lo-15 hrs. in an argon
The filtrate was concentrated
The complexes were recrystallised Microanalyses conductance
ratio.
of the reaction was checked on TLC. After that the solution was filtered under an
were performed
on a Carlo Erba Analyser
on a Digisun Electronic Conductivity
on Carl Ziess Specord M-80 spectrophotometer
recorded on a Shimadzu UV-Vis recording spectrophotometer
in Nujol mull/KBr.
The optical rotation
for dia-magnetism.
polarimeter DIP-360 Jasco Machine.
Model bridge.
1106.
Molar
The I.R. spectra
Electronic
spectra were
model 160. The magnetic moment measurements
were made at 298 K by the Gouy method using Hg[Co(SCN)4] were corrected
by diethyl ether.
in the same solvent. They were dried in vacua. Yield 60%.
of the complexes
was measured at room temperature
were recorded
to about 10 ml and the complexes precipitated
as calibrant
of the complexes
and experimental in methanol
susceptibilities
was measured
by
The CD. spectra were recorded in methanol by Jobin YVON - Paris.
References 1.
R. Calvo, P.R. Levstein,
E.E. Castellano,
S.M. Fabiane,
O.E. Piro and S.B. Oseroff, Inorg.
C&m.,
1991, 30, 216. 2.
3.
Adv. Protein Chem., 1967, 22, 257.
H.C. Freeman,
G.L. Eichhom,
Elsevier, Amsterdam,
H.C. Freeman,
Ed. In Inorganic
Biochemistry,
1973, Chapter 3.
R. Calvo, H. Isern, M.A. Mesa, Chem. Phys., 1985, 100, 89.
4.
C.A. Steren, A.M. Gennaro, P.R. Levstein,
5.
W.S. Sheldrick
R.J. Calvo, Phys. Condens, Matter, 1989, 1,637.
and R. Exner, Inorg. Chim. Acta 1990,175,261. K. Kojima, M. Kojima, J. Fujita, Bull. Chem. Sot. Jpn., 1990, 63, 2620.
6.
K. Nakajima,
7.
(a) M. Yuasa, H. Nishide and E. Tsuchida, J. Chem. Sot., Dalton Trans., 1987, 2493. (b) E.Tsuchida,
H. Maeda, M. Yuasa and H. Nichide, J. Chem. Sot., Dalton Trans., 1987, 2455. 8. Chem.,
V. Massonneau, 1987,26,
P.L. Maux, R. Dabard,
G. Simonneaux,
P. Aviron-violet
and P.T. Dang, Inorg.
773.
9.
D. Heinert and A.E. Martell, J. Am. Chem. Sot., 1962.84,
10.
I. Sasaki, D. Pujol and A. Gaudemer,
11.
D.A. Edwards and R. Richards., J. Chem. Sot., Dalton Trans., 1975,637.
3257.
Inorg. Chim. Acta., 1987, 134, 53.
12.
M.A. Bangres, M. Gonzalez,
13.
L.J. Boucher,
C.G. Coe, Inorg. Chem., 1976, 15, 1334.
M.E. Peres and R.J. Ruano, Polyhed., 1986,5,
14.
L.J. Boucher,
Inorg. Nucl. Chem., 1974, 36, 531.
1371.