Trans- and cis- cobalt(III), iron(III), and chromium(III) complexes based on α- and γ-diimine Schiff base ligands: Synthesis and evaluation of the complexes as catalysts for oxidation of L-cysteine

Article abstract of DOI:10.1002/zaac.200700578

The synthesis of a new series of trans and racemic cis isomers of cobalt(III)-, iron(III)-, and chromium(III)-based complexes with the α- and γ-diimine Schiff base ligands, N,N′-bis(X)-2,3-butandiimine and N,N′-bis(X)-1,2-phenyldiimine (X = cyclohexyl, 2-isopropylphenyl, 1-naphthyl) is described. To confirm the identity of the complexes prepared in the present study, a variety of techniques including elemental analysis, magnetic susceptibility, infrared-, mass- (EI), and UV/Vis- spectroscopy have been utilized. Some of the isolated complexes have been evaluated as catalysts for the oxidation of L-cysteine. Preliminary results showed that the metal atoms, geometry of the complexes, auxiliary substituents, and the backbone of the ligand influenced the rate of oxidation reaction.

Full text of DOI:10.1002/zaac.200700578

DOI: 10.1002/zaac.200700578
Trans- and cis- Cobalt(III), Iron(III), and Chromium(III) Complexes Based on
α- and γ-Diimine Schiff Base Ligands: Synthesis and Evaluation of the
Complexes as Catalysts for Oxidation of L-Cysteine
Adnan S. Abu-Surrah*, Hamzeh M. Abdel-Halim, and Feda’a M. Al-Qaisi
Zarqa/Jordan, Hashemite University, Department of Chemistry
Received September 29th, 2007; accepted December 18th, 2007.
Abstract. The synthesis of a new series of trans and racemic cis
isomers of cobalt(III)-, iron(III)-, and chromium(III)-based com-
plexes with the α- and γ-diimine Schiff base ligands, N,NЈ-bis(X)-
2,3-butandiimine and N,NЈ-bis(X)-1,2-phenyldiimine (X ϭ cyclo-
hexyl, 2-isopropylphenyl, 1-naphthyl) is described. To confirm the
identity of the complexes prepared in the present study, a variety
of techniques including elemental analysis, magnetic susceptibility,
infrared-, mass- (EI), and UV/Vis- spectroscopy have been utilized.
Some of the isolated complexes have been evaluated as catalysts for
the oxidation of L-cysteine. Preliminary results showed that the
metal atoms, geometry of the complexes, auxiliary substituents, and
the backbone of the ligand influenced the rate of oxidation reac-
tion.
Keywords: Cobalt; Iron; Chromium; Diimine ligands; Catalysis;
L-cysteine
1 Introduction
spectroscopy, de Vekki et al. [8] studied the reaction of
the optically active geometrical isomers of the platinum(II)
complex (-)-[Pt(Me-p-TolSO)(Py)Cl2] with several nucleo-
philic reagents (Py, Ph3PS, Ph3P, Ph3As, and MeSO).
The effect of geometrical isomerism in platinum com-
plexes, used as antitumor agents, has been studied by Farrell
et al. [9]. They found that the binuclear platinum complexes
Numerous publications describing the coordination chemis-
try of phosphorus donor ligands and the application of
their complexes in homogeneous catalysis have been dis-
closed [1]. However, few papers have been reported about
the organic nitrogen ligands. This may be due to the fact
that their complexes have not been used extensively for syn-
thetic organic applications. Recently, some research groups
have highlighted the application of nitrogen donors, par-
ticularly because they are easily obtained from chiral pool
[2, 3] and due to their application in synthesis of optically
active organic molecules [4]. Furthermore, transition metal
complexes containing the bidentate diimine ligands have
been successfully employed in a number of catalytic reac-
tions; including polymerization of alkenes [5], polymeriz-
ation of polar monomers [3], enantioselective 1,3-dipolar
cycloaddition reaction [6], and borylation of vinylarenes [7].
Geometrical isomerisms are common among coordi-
nation compounds. They contain the same number of
ligands, but arranged differently around the metal atom.
Study of isomers provides much of the experimental knowl-
edge used to develop and defend coordination theory.
Several investigators have studied the effect of geometrical
isomerism on the reactivity of some isomers with various
reagents. Using optical rotatory dispersion, IR- and NMR-
[{trans-PtCl(NH3)2}2-μ-{NH2(CH2)nNH2}](NO3)2 (n
ϭ
4,6) and [{cis-PtCl(NH3)2}2-μ-{NH2(CH2)nNH2}](NO3)2
(n ϭ 4,6)] exhibit antitumor activity comparable with cis-
platin. Also, they found that at 37 °C, the initial binding
and reaction of the cis isomer is slower than that for the
trans isomer. Toma et al. [10] reviewed linkage isomerization
reactions from the aspect of kinetics and mechanisms in-
volved, with some focusing on selected cases of direct for-
mation. Also, they investigated the electrochemical, photo-
chemical, thermal and pH-induced generation of linkage
isomers. The biodegradation kinetics of geometric isomers
of model naphthenic acid in water has been studied by Peru
et al. [11]. The rates of biodegradation of six model naph-
thenic acids by heterotrophic bacteria were compared.
Specifically, they monitored by gas chromatography, the
biodegradation of cis- and trans-isomers of 4-methylcyclo-
hexenylacetic acids, 4-methylcyclohexanylcarboxylic acids,
and 3-methylcyclohexenylcarboxylic acids.
In a previous article, we have described the application
of some α-diimine-based palladium(II) and nickel(II) com-
plexes as polymerization catalysts [12] and the influence of
the terminal substituents (naphthyl, 2-isopropyl, and cyclo-
hexyl) on the catalytic activity of some iron(II) complexes
in polymerization reactions [13].
Recently, we have reported that the rates of oxidation of
L-cysteine by pairs of trans- and racemic cis-isomers of
CoIII- and FeIII- complexes bearing the ligands, ethylenedi-
* Dr. Adnan S. Abu-Surrah
Hashemite University, Department of Chemistry
P.O. Box: 150 459
Zarqa-13115/Jordan
Tel. ϩ 962 5 390 3333/ ext. 4315
Fax: ϩ 962 5 390 3349
E-mail address: asurrah@hu.edu.jo (A. S. Abu-Surrah)
956
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Trans- and cis- Cobalt(III), Iron(III), and Chromium(III) Complexes
amine, 2,2Ј-bipyridyl, and 1,10-phenanthroline [14]. Rates
were found to be one to three orders of magnitudes higher
for the trans-isomer. The differences in rates are attributed
to the steric factor. The less crowded trans-isomers facilitate
electron transfer making the oxidation process faster than
that for the cis-isomers.
As an extension of our studies on both the coordination
chemistry of heteroatom containing ligands [15Ϫ17] and on
the catalytical application of their metal complexes [18Ϫ20],
we report the synthesis and characterization of new pairs
of trans- and racemic cis-isomers of cobalt(III), iron(III),
and chromium(III) complexes containing α-diimine and
γ-diimine bidentate nitrogen ligands. The new complexes
were characterized by their physical properties, elemental
analysis, magnetic susceptibility, IR-, MS (EI), and UV-Vis
spectroscopy. The influence of the metal center, the ge-
ometry around the metal atom, the type of the auxiliary
groups of the ligands and the backbone structures on the
rate of oxidation of L-cysteine are described.
ratio of the corresponding bidentate ligand in EtOH, fol-
lowed by oxidation with H2O2. The cationic species were
formed by the addition of excess HCl (Scheme 2 and 3).
Heating the solution in ethanol and with slow evaporation
of the solvent led to the formation of the corresponding cis-
isomers, 9a, 9b, 10b, 10c, 15a-15c, and 16a-16c.
The trans dichloro CrIII-based complexes (8a, 8c, 14a,
14b, and 14c) were synthesized by the treatment of
CrCl3 ·6H2O with two equivalents of the corresponding bi-
dentate ligand in methanol. The cationic trans-species were
formed by the addition of a small amount of HCl. Crystalli-
zation of the trans isomer in hot ethanol afforded the corre-
sponding cis isomers (11c and 17c) [21]. The isolated com-
plexes are microcrystalline or powder-like and they are
stable at atmospheric conditions. Attempts to isolate the
rest of the complexes were unsuccessful (Scheme 2 and 3).
The complexes prepared in the present study were
characterized by their physical properties, magnetic suscep-
tibility (μeff, BM), infrared-, mass- (EI), and UV/Vis spec-
troscopy. All the trans-isomers and most of their corre-
sponding cis-isomers were also identified by elemental
analysis. Based on these results, the isomerization process
did not led to any degradation for the complexes.
2 Results and Discussion
2.1 Ligand synthesis
IR-analyses of the complexes indicate the presence of the
ligands. A slight shift of the imine band (νCϭN) was ob-
served due to complexation. Also elemental analyses
showed that the metal to ligand ratio in the dichloro com-
plexes is 2:1. Therefore, an octahedral arrangement around
the metal atom is formed. Moreover, precipitation with sil-
ver nitrate indicates the formation of the mono cationic
complexes.
The coordination reactions were also followed by UV/Vis
spectroscopy. A sharp peak in the visible region due to the
coordination of ligand was observed. The complexes 12a
and 13a showed peaks at 402 and 368 nm, respectively,
compared to the corresponding ligand (5a) which showed
an absorption peak at 329 nm.
The bidentate α-diimine ligands (4a-4c) and γ-diimine
ligands (5a-5c) were prepared in moderate to high yields by
the condensation reaction of 2,3-butanedione (1) or
1,2-phenylendicarboxyldehyde (3) with stoichiometric
amounts of the desired amine (2a-2c) in the presence of a
catalytical amount of formic acid (Scheme 1). The isolated
diimine ligands were characterized by their physical proper-
ties, elemental analysis, IR- and UV-Vis spectroscopy.
Scheme 1 Synthesis of α-(4aϪ4c) and γ-diimine (5aϪ5c) ligands
The condensation reactions were followed by IR spec-
troscopy. The total vanishing of the carbonyl band (due to
the ketone group at about 1700 cmϪ1) and the appearance
of a new band between 1618-1642 cmϪ1, which is assigned
to the imine band (ν CϭN), indicates the formation of the
diimine ligands.
2.2 Complex synthesis
The trans-dichloro FeIII- and CoIII-based complexes 6a, 6b,
and 7a-7c, 12a-12c, and 13a-13c were synthesized by the
treatment of MCl2 ·6H2O (M ϭ Co, Fe) with two molar
Scheme 2 Synthesis and suggested structures of Co(III)-, Fe(III)-,
and Cr(III)-based α-diimine complexes (6Ϫ11)
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957

A. S. Abu-Surrah, H. M. Abdel-Halim, F. M. Al-Qaisi
Scheme 3 Synthesis and suggested structures of Co(III)-, Fe(III)-, and Cr(III)-based γ-diimine complexes (12Ϫ17)
The cis-, and the trans-isomers were distinguished by
their distinct absorption spectra in the UV/Vis region and
also by their melting points (trans-[Co(BIPBD)Cl2]Cl (6b),
m.p (dec) ϭ 232 °C, the corresponding cis-isomer (9b) de-
composes at 200 °C). Some of the isolated cis-isomers were
converted to the more stable trans-isomers upon heating
(complexes 11c and 15b convert to 8c and 12b, respectively,
at about 150 °C).
k ϭ 9.10ϫ10Ϫ2; 15b, k ϭ 4.19ϫ10Ϫ2). We believe that this
is due to the facile ligand substitution reactions on the
trans-isomer (less hindrance) compared with the cis-isomer
(crowded) that inhibits the substitution reaction.
The Magnetic susceptibilities (μeff, BM) of the complexes
were measured at room temperature. All complexes were
found to have a formal oxidation state of ϩ3. The electronic
environment of the complexes was influenced by the back-
bone of the ligand and the bulkiness of the auxiliary sub-
stituents. Both iron(III) complexes 10c and 16c are high
spin species with magnetic moment values of 3.04 and
5.78 BM, respectively. This indicates that the coordination
strength of the α-diimine ligands (10c) is higher than that
for the γ-diimines (16c). The trans-cobalt(III) complexes
(12a, and 12c) are diamagnetic (low spin state species),
while the corresponding complex (12b), with isopropyl
terminals, is a high spin state species that has a magnetic
moment (μeff) of 4.87 BM. The magnetic moment of the
complexes, trans-cobalt(III)- (12c), trans-iron(III)- (13c),
and trans-chromium(III)- (14c), which bear the same li-
gand, depends also on the metal center. Compared to 12c
which is diamagnetic, the complexes 13c and 14c are high
spin state species with a magnetic moment (μeff) of 5.48 and
1.89 BM, respectively [22].
Scheme 4 Oxidation of Cysteine by the complexes prepared in the
present study.
Moreover, the rates of oxidation reactions by the cobalt
complexes bearing the α- or γ-diimine with 2-isopropylphe-
nyl terminals are faster than those bearing the cyclohexyl
substituents (15b, k ϭ 4.19ϫ10Ϫ2; 15a, k ϭ 2.10ϫ10Ϫ2).
However, the complexes based on the naphthyl terminals
were non-reactive. Such influence of the auxiliary groups
on the activity of transition metal complexes towards poly-
merization reactions has been observed before [13].
In summary, new families of cationic, octahedral, CoIII-,
FeIII-, and CrIII-based transition metal complexes bearing
α- and γ-diimine ligands have been synthesized and charac-
terized. The reactivity of some of the isolated complexes
towards the oxidation reaction of L-cysteine has been inves-
tigated. Results showed that the rate of oxidation depends
on the metal center, geometry of the complexes, and size
of the ligand. In addition, it also depends on the auxiliary
substituents on the ligand and its backbone. Further studies
on the kinetics of L-cysteine oxidation of by these com-
plexes will be reported in details.
Some of the isolated CoIII and FeIII complexes were util-
ized as catalysts for the oxidation of L-cysteine in aqueous
solution at 25 °C and constant pH (Scheme 4). Preliminary
investigation showed that the cobalt complexes are faster
oxidation catalysts compared with the corresponding
iron(III) complexes (12a, k ϭ 2.10ϫ10Ϫ2; 13a, k ϭ
7.16ϫ10Ϫ3). The trans-isomers were also found to react fas-
ter with L-cysteine than the corresponding cis-isomers (12b,
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Trans- and cis- Cobalt(III), Iron(III), and Chromium(III) Complexes
5a: Yield: 5.4 g (71 %). M.p. (dec) 236 °C. UV/Vis (EtOH): λmax ϭ
324 nm. IR: ν/cmϪ1
1618 m (CϭN). Anal. Calcd. for
3 Experimental Section
ϭ
3.1 General
C20H31N2O1.5: C, 74.26; H, 9.66; N 8.66 %. Found: C, 74.20; H,
9.31; N 8.49 %. 5b: Yield: 3.13 g (21 %). M.p. (dec) 148 °C. UV/Vis
(EtOH): λmax ϭ 291 nm. IR: ν/cmϪ1 ϭ 1642 m (CϭN). Anal.
Calcd. for C26H30N2O: C, 80.79; H, 7.82; N, 7.25. Found: C, 81.16;
H, 7.99; N, 7.06 %. 5c: Yield: 8.10 g (57 %). M.p. (dec) 112 °C. UV/
vis (EtOH): λmax ϭ 342 nm (500 nm). IR: ν/cmϪ1 ϭ 1636 m (Cϭ
N). MS (EI, 70 eV): m/z (%) ϭ 383.3 [Mϩ]. Anal. Calcd. for
C28H20N2 ·0.25H2O: C, 86.44; H, 5.31; N, 7.20. Found: C, 86.10;
H, 5.19; N, 6.76 %.
CrCl3 ·3THF, CrCl3 ·6H2O, CoCl2 ·6H2O, and FeCl2 ·6H2O were
purchased from (ACROS), isopropylaniline, naphthylamine, and
anhydrous FeCl3 from Aldrich, cyclohexylamine from Sigma, and
L-cysteine (minimum assay 99 %) was purchased from BDH Lab-
oratory Supplies (England). All chemicals were used without
further purifications.
Elemental analyses were performed using a (EURO EA 3000 in-
strument). Infrared spectra (KBr pellets) were measured on a Nico-
let- Magna-IR 560 Spectrophotometer. Mass spectra (EI) were
acquired using a Shimadzu-QP5050A. Magnetic susceptibility
measurements were carried out using Magnetic susceptibility
balance from Alfa Johnson Mathey Company. Kinetic measure-
ments were performed using Diod Array Spectrophotometer model
8453E from HP Agilent. Melting points were measured by a Stuart
Scientific melting Apparatus (uncorrected 0.1 °C).
3.3 Synthesis of complexes
3.3.1 Trans-[Co(BCBD)2Cl2]Cl (6a) and
trans-[Co(BIPBD)2Cl2]Cl (6b):
A solution of the corresponding ligand (4a or 4b) (2.03 mmol) in
ethanol (5.0 ml) was added dropwise to a solution of CoCl2 ·6H2O
(0.198 g; 0.834 mmol) in ethanol (5.0 ml). The mixture was stirred
at room temperature for 2 hrs, then H2O2 (30 %) (3.0 ml) was added
dropwise. Stirring was continued for an additional hour then hydro-
chloric acid (37 %, 5.00 ml) was added. After stirring for 1 hr at
room temperature, the solution was concentrated by heating to
150 °C until a crust was formed. After slow cooling of the system to
room temperature the obtained crystals were isolated, rinsed with
ethanol (5.0 ml) and diethyl ether (2ϫ5.0 ml) and dried in vacuum.
3.2 Synthesis of ligands
The ligands were prepared following similar procedures described
in literature [15].
3.2.1 N,NЈ-bis(cyclohexyl)-2,3-butanediimine
(BCBD, 4a), N,NЈ-bis(2-isopropyl-phenyl)-2,3-
butanediimine (BIPBD, 4b), and N,NЈ-bis(1-
napthyl)-2,3-butanediimine (BNBD, 4c) [12]:
6a: Yield: 0.24 g (44 %), green. M.p. (dec) 142 °C. UV/Vis (EtOH):
λmax (lg ε) ϭ 400 nm (2.23ϫ102). IR: ν/cmϪ1 ϭ 1629 m (CϭN).
Anal. Calcd. for C32H56N4CoCl3: C, 58.05; H, 8.53; N, 8.46.
Found: C, 57.92; H, 8.47; N 8.09 %. 6b: Yield: 0.34 g (51 %), light-
blue. M.p. (dec) 232 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 419 nm
(3.47ϫ101). IR: ν/cmϪ1 ϭ 1642 m (CϭN). Anal. Calcd. for
C44H56N4CoCl3: C, 65.55; H, 7.00; N 6.95. Found: C, 65.86; H,
7.43; N 7.40 %.
A solution of 2,3-butanedione (1) (1.00 g; 0.012 mol) in methanol
(10 ml) was added to a solution of the desired amine (2a-2c)
(0.028 mol) in methanol (20 ml) with continuous stirring. The mix-
ture was stirred at room temperature for 3 hr, during which, a pre-
cipitate was formed. After additional 2 hrs stirring, the product
formed was filtered, washed with methanol and dried in vacuum.
4a: Yield: 2.45 g (85 %), brown. M.p. 63 °C. UV/Vis (EtOH):
λmax ϭ 303 nm (439 nm). IR: ν/cmϪ1 ϭ 1636 m (CϭN). Anal.
Calcd. for C16H28N2: C, 77.36; H, 11.36; N, 11.28. Found: C, 77.80;
H, 11.16; N, 10.78 %. 4b: Yield: 2.5 g (67 %), yellow. M.p. 83 °C.
UV/vis (EtOH): λmax ϭ 382 nm (488 nm). IR: ν/cmϪ1 ϭ 1632 m
(CϭN). Anal. Calcd. for C22H28N2: C, 82.45; H, 8.81; N, 8.74.
Found: C, 82.50; H, 9.13; N, 8.51 %. 4c: Yield: 1.75 (45 %), dark-
yellow. M.p. 141 °C. UV/Vis (EtOH): λmax ϭ 355 nm (491 nm). IR:
ν/cmϪ1 ϭ1637 m (CϭN). Anal. Calcd. for C24H20N2: C, 85.68; H,
5.99; N, 8.33. Found: C, 86.02; H, 6.36; N, 8.36 %.
3.3.2 Trans-[Fe(BCBD)2Cl2]Cl (7a),
trans-[Fe(BIPBD)2Cl2]Cl (7b), and
trans-[Fe(BNBD)2Cl2]Cl (7c):
A solution of the ligand (4a, 4b, or 4c) (1.56 mmol) in 10.0 ml etha-
nol was added drop wise to a solution of FeCl2 ·6H2O (0.17 g;
0.71 mmol) in the same solvent (20.0 ml). The mixture was stirred
at room temperature for 2 hrs, then H2O2 (30 %) (3.0 ml) was added
drop wise. Stirring was continued for another 1 hr, and then hydro-
chloric acid (37 %, 5.00 ml) was added. After stirring for 1 hr at
room temperature, the solution was concentrated by heating to
150 °C for 1 hr. Slow cooling of the mixture to room temperature
resulted in a brown crystals formation which was rinsed with etha-
nol (5.0 ml) and diethyl ether (2ϫ5.0 ml) then dried under vacuum.
3.2.2 N,NЈ-bis(cyclohexyl)-1,2-phenyldiimine
(BCPD, 5a), N,NЈ-bis(2-isopropyl-phenyl)-1,2-
phenyldiimine (BIPPD, 5b), and N,NЈ-bis(1-
naphthyl)-1,2-phenyldiimine (BNPD, 5c).
7a: Yield: 0.30 g (58 %). M.p. (dec). 250 °C. UV/Vis (EtOH): λmax
(lg ε) ϭ 488 nm (1.97ϫ102). Ϫ IR: ν/cmϪ1 ϭ 1630 m (CϭN). Anal.
Calcd. for C32H64N4O4FeCl3: C, 52.57; H, 8.82; N, 7.66. Found:
C, 52.56; H, 9.17; N, 8.01 %. 7b: Yield: 0.15 g (26 %). Ϫ M.p. (dec.)
250 °C. UV/vis (EtOH): λmax (lg ε) ϭ 490 nm (1.88ϫ103). IR:
ν/cmϪ1 ϭ 1628 m (CϭN). 7c: Yield: 0.25 g (40 %). M.p. (dec.)
350 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 400 nm (8.55ϫ103). IR:
ν/cmϪ1 ϭ 1617 m (CϭN). Anal. Calcd. for C48H46N4O3FeCl3: C,
64.84; H, 5.21; N, 6.30. Found: C, 64.87; H, 5.10; N, 5.97 %.
A solution of 1,2-phenylendicarboxyldehyde (3) (5.00 g; 0.037 mol)
in ethanol (10 ml) was added to a solution of cyclohexylamine (2a),
isopropylamine (2b), or 1-naphtylamine (2c) (0.086 mol) in ethanol
(20 ml) withcontinuous stirring .The mixture was stirred at room
temperature for 3 hrs, during which, a white precipitate was
formed. The product was filtered, washed with ethanol (4ϫ15 ml)
and dried in vacuum.
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959

A. S. Abu-Surrah, H. M. Abdel-Halim, F. M. Al-Qaisi
3.3.3 Trans-[Cr(BCBD)2Cl2]Cl (8a) and
trans-[Cr(BNBD)2Cl2]Cl (8c):
3.3.6 Trans-[Co(BCPD)2Cl2]Cl (12a),
trans-[Co(BIPPD)2Cl2]Cl (12b),
trans-[Co(BNPD)2Cl2]Cl (12c),
trans-[Fe(BCPD)2Cl2]Cl (13a),
trans-[Fe(BIPPD)2Cl2]Cl (13b),
trans-[Fe(BNPD)2Cl2]Cl (13c),
trans-[Cr(BCPD)2Cl2]Cl (14a),
trans-[Cr(BIPPD)2Cl2]Cl (14b), and
trans-[Cr(BNPD)2Cl2]Cl (14c).
A solution of the ligand (4a or 4c) (0.81 mmol) in 10.0 ml methanol
was added dropwise to
a solution of CrCl3 ·6H2O (0.14 g,
0.37 mmol) in the same solvent (5.0 ml). Upon addition, the color
of the solution was changed from pink to green. The mixture was
stirred at room temperature for 24 h, then hydrochloric acid
(1.0 ml) (HCl, 37 %) was added. After stirring for 1 h, the solution
was concentrated at 150 °C until a green crust was formed. The
mixture was cooled and the complex was separated as a dark yellow
precipitate. The product was thoroughly rinsed with THF (5.0 ml)
followed by pet.ether (2ϫ5.0 ml), and dried in vacuum.
All of these trans-complexes were prepared according to the pro-
cedures described above. Starting from the corresponding metal
salt and the desired γ-diimine ligand (5a, 5b, and 5c, respectively)
the complexes were produced.
8a: Yield: 0.18 g (74 %). M.p. (dec.) 250 °C. UV/vis (EtOH): λmax
(lg ε) ϭ 432 nm (3.04ϫ101). IR: ν/cmϪ1) ϭ 1617 m (CϭN). Anal.
Calcd. for C32H56N4CrCl3: C, 58.90; H, 8.61; N, 8.55. Found: C,
59.54; H, 10.49; N, 7.20 %. 8c: Yield: 0.14 g (44 %), green. M.p.
(dec) 247 °C. UV/vis (EtOH): λmax (lg ε) ϭ 390 nm (1.60ϫ103). IR:
ν/cmϪ1 ϭ 1628 m (CϭN). Anal. Calcd. for C48H44N4O2CrCl3: C,
66.75; H, 5.11; N, 6.46. Found: C, 66.24; H, 5.00; N, 5.14 %.
12a: Yield: (49 %), light-green. M.p. (dec) 238 °C. UV/Vis (EtOH):
λmax (lg ε) ϭ 402 nm (2.68ϫ101). IR: ν/cmϪ1 ϭ 1619 m (CϭN).
Anal. Calcd. for C40H56N4CoCl3: C, 63.37; H, 7.44; N, 7.39.
Found: C, 64.13; H, 7.30; N, 7.39 %. μeff: (0.0) BM. 12b: Yield:
(84 %), green. M.p. (dec) 251 °C. UV/Vis (EtOH): λmax (lg ε) ϭ
400 nm (3.42ϫ101). IR: ν/cmϪ1 ϭ 1621 m (CϭN). Anal. Calcd. for
C52H57N4O0.5CoCl3: C, 68.53; H, 6.30; N, 6.15. Found: C, 68.35;
H, 6.21; N 5.89 %. μeff: 4.87 BM. 12c: Yield: (24 %), green. M.p.
(dec) 130 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 385 nm (4.77ϫ102).
IR: ν/cmϪ1 ϭ 1627 m (CϭN). MS (EI, 70 eV): m/z (%) ϭ 544.2
[Mϩ- C28H20N2Cl]. Anal. Calcd. for C56H42N4OCoCl3: C, 70.63;
3.3.4 Cis-[Co(BCBD)2Cl2]Cl (9a) and
cis-[Co(BIPBD)2Cl2]Cl (9b)
H, 4.45; N, 5.88. Found: C, 70.32; H, 4.01; N, 5.96 %. Ϫ μeff
(0.0) BM. 13a: Yield: (54 %), light-green. M.p. (dec) 145 °C. UV/
Vis (EtOH): λmax (lg ε) ϭ 368 nm (9.97ϫ102). IR: ν/cmϪ1
:
ϭ
Small portions of the corresponding trans-isomers (6a, and 6b)
were dissolved in minimum volume of ethanol and gently evapo-
rated until brown crystals were formed. The crystals were isolated
and dried under vacuum.
1636 m (CϭN). Anal. Calcd. for C40H62N4FeCl9: C, 49.33; H, 6.43;
N, 5.75. Found: C, 49.39; H, 6.40; N, 5.76 %.
13b: Yield: (53 %), green. M.p. (dec) 107 °C. UV/Vis (EtOH): λmax
(lg ε) ϭ 390 nm (9.69ϫ101). IR: ν/cmϪ1 ϭ 1638 m (CϭN). Anal.
Calcd. for C52H64N4OFeCl3: C, 64.30; H, 6.64; N, 5.77. Found: C,
64.77; H, 7.04; N, 5.88 %. 13c: Yield: (61 %), light-brown. M.p.
(dec) 138 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 400 nm (4.59ϫ103).
IR: ν/cmϪ1 ϭ 1629 m (CϭN). MS (EI, 70 eV): m/z (%) ϭ 544.2
[Mϩ- C28H20N2], 471.3 [Mϩ- C28H20N2Cl2], 383.3 [Mϩ-
C28H20N2FeCl3]. Anal. Calcd. for C56H40N4FeCl3: C, 72.23; H,
4.33; N, 6.02. Found: C, 72.46; H, 4.27; N 5.62 %. μeff: 5.48 BM.
14a: Yield: (70 %), green. M.p. (dec) 164 °C. UV/Vis (EtOH): λmax
(lg ε) ϭ 390 nm (9.79ϫ101). IR: ν/cmϪ1 ϭ 1637 m (CϭN). Anal.
Calcd. for C40H68N4O6CrCl3: C, 55.91; H, 7.98; N, 6.52. Found:
C, 55.65; H, 7.79; N 7.04 %. 14b: Yield: (65 %), green. M.p. (dec)
122 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 487 nm (3.72ϫ102). IR:
ν/cmϪ1 ϭ 1625 m (CϭN). Anal. Calcd. for C52H70N4O7CrCl3: C,
61.14; H, 6.91; N, 5.48. Found: C, 61.24; H, 6.47; N 5.90 %. 14c:
Yield: (59 %), green. M.p. (dec) 132 °C. UV/Vis (EtOH): λmax (lg
ε) ϭ 347 nm (1.71ϫ103). IR: ν/cmϪ1 ϭ 1628 m (CϭN). Anal.
Calcd. for C56H46N4O3CrCl3: C, 68.82; H, 4.72; N, 5.71. Found:
C, 68.61; H, 4.77; N 5.52 %. μeff : 1.89 BM.
9a: Yield: (31 %). M.p. (dec) 130 °C. UV/Vis (EtOH): λmax (lg ε) ϭ
488 nm (1.07ϫ102). IR: ν/cmϪ1 ϭ 1629 m (cmϪ1). Anal. Calcd. for
C32H56N4CoCl3: C, 57.67; H, 8.82; N, 7.91. Found: C, 57.75; H,
8.69; N 7.92 %. 9b: Yield: (8.4 %), brown. M.p. (dec) 200 °C. UV/
vis (EtOH): λmax (lg ε) ϭ 490 nm (1.92ϫ102). IR: ν/cmϪ1
ϭ
1629 m (cmϪ1).
3.3.5 Cis-[Fe(BIPBD)2Cl2]Cl (10b),
cis-[Fe(BNBD)2Cl2]Cl (10c), and
cis-[Cr(BNBD)2Cl2]Cl (11c)
Small portions of the corresponding trans-isomers (7b, 7c, and 8c)
were dissolved in minimum volume of ethanol and gently evapo-
rated until violet (10b and 10c) or light brown (11c) crystals were
formed. The isolated crystals were filtered, washed with THF
(5.0 ml), pet. ether (2ϫ5.0 ml), and dried under vacuum.
3.3.7 Cis-[Co(BCPD)2Cl2]Cl (15a), cis-
[Co(BIPPD)2Cl2]Cl (15b), cis-[Co(BNPD)2Cl2]Cl
(15c), cis-[Fe(BCPD)2Cl2]Cl (16a), cis-
[Fe(BIPPD)2Cl2]Cl (16b), cis-[Fe(BNPD)2Cl2]Cl
(16c), and cis-[Cr(BNPD)2Cl2]Cl (17c).
10b: Yield: (47 %), dark-violet. M.p. (dec) 140 °C. UV/Vis (EtOH):
λmax (lg ε) ϭ 545 nm. IR: ν/cmϪ1 ϭ 1624 m (cmϪ1). μeff: 3.34 BM.
10c: Yield: (83 %), violet. M.p. (dec) 350 °C. UV/Vis (EtOH): λmax
(lg ε) ϭ 510 nm (2.84ϫ103). IR: ν/cmϪ1 ϭ 1630 m (cmϪ1). Anal.
Calcd. for C48H44N4O2FeCl3: C, 66.18; H, 5.09; N, 6.43. Found:
C, 66.24; H, 5.00; N, 6.24 %. μeff: 3.04 BM. 11c: Yield: (89 %), light-
brown. M.p. (dec) convert to trans at 150 °C. UV/Vis (EtOH): λmax
(lg ε) ϭ 437 nm (1.29ϫ103). IR: ν/cmϪ1 ϭ 1624 m (cmϪ1).
All of these cis-isomers were prepared according to the above men-
tioned procedures but starting from the corresponding trans-isomers.
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© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
Z. Anorg. Allg. Chem. 2008, 956Ϫ961

Trans- and cis- Cobalt(III), Iron(III), and Chromium(III) Complexes
15a: Yield: (53 %), pink. M.p. (dec) converts to trans at 130 °C.
[5] M. Brookhart, L. K. Johnson, C. M. Killian, J. Am. Chem.
Soc. 1995, 117, 6414.
UV/vis (EtOH): λmax (lg ε) ϭ 490 nm (1.15ϫ103). IR: ν/cmϪ1
ϭ
1618 m (CϭN). 15b: Yield: (10 %), pink. M.p. (dec) converts to
trans at 150 °C. UV/vis (EtOH): λmax (lg ε) ϭ 459 nm (1.51ϫ101).
IR: ν/cmϪ1 ϭ 1621 m (CϭN). 15c: Yield: (16 %), brown. M.p. (dec)
120 °C. UV/vis (EtOH): λmax (lg ε) ϭ 500 nm (9.51ϫ102). IR:
ν/cmϪ1 ϭ 1629 m (CϭN). Anal. Calcd. for C56H48N4O4CoCl3: C,
66.84; H, 4.81; N, 5.57. Found: C, 67.01; H, 4.52; N, 5.26 %. 16a:
Yield: (22 %), yellow. M.p. (dec) 130 °C. UV/Vis (EtOH): λmax (lg
ε) ϭ 400 nm (2.28ϫ102). IR: ν/cmϪ1 ϭ 1637 m (CϭN). Anal.
Calcd. for C40H68N4O6FeCl3: C, 55.66; H, 7.94; N, 6.49. Found:
C, 55.90; H, 8.20; N, 7.35 %. 16b: Yield: (15 %), yellow. M.p. (dec)
78 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 432 nm (2.06ϫ102). IR:
ν/cmϪ1 ϭ 1617 m (CϭN). The elemental analysis of the corre-
sponding trans isomer (13b) was carried out. 16c: Yield: (94 %),
violet. M.p. (dec) 114 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 510 nm
(5.49ϫ103). IR: ν/cmϪ1 ϭ 1618 m (CϭN). Anal. Calcd. for
C56H40N4FeCl3: C, 72.23; H, 4.33; N, 6.02. Found: C, 72.05; H,
4.48; N, 5.79 %. μeff: 5.78 BM. 17c: Yield: (79 %), red. M.p. (dec)
215 °C. UV/Vis (EtOH): λmax (lg ε) ϭ 501 nm (1.76ϫ103). IR:
ν/cmϪ1 ϭ 1617 m (CϭN). Anal. Calcd. for C56H40N4CrCl3 ·5 H2O:
C, 66.38; H, 4.95; N, 5.51. Found: C, 66.29; H, 5.24; N, 5.36 %.
μeff: 3.75 BM.
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Z. Anorg. Allg. Chem. 2008, 956Ϫ961
© 2008 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim
www.zaac.wiley-vch.de
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