Coligand modulated oxidative: O -demethylation of a methyl ether appended tetradentate N-ligand in Co(ii) complexes

Article abstract of DOI:10.1039/c9dt04609g

Two Co(ii) complexes of the formula CoL^OMeX₂ (X = Cl^- (1a); X = I^- (1b)), where L^OMe is 2-methoxy-N,N-bis(pyridin-2-ylmethyl) aniline, were synthesized and their structure, spectra and reactivity were studied. Upon oxidation of 1a and 1b, the ligand L^OMe undergoes demethylation at the metal centre resulting in the formation of Co(iii) complexes with modified phenoxide ligands. This is the very first example of oxidative O-demethylation reported at a Co(ii) centre. The oxidative behaviour exhibits a striking dependence on the nature of coligands coordinated to the metal centre. The Co(ii) complex 1a with stronger chloro coligands requires a strong oxidising agent like t-BuOOH for oxidative demethylation and the subsequent formation of a mononuclear Co(iii) complex with a demethylated ligand, CoL^O-Cl₂ (2). On the other hand, complex 1b with weaker iodo coligands undergoes oxidation in the presence of the weak oxidant O₂ to form a dihydroxo bridged binuclear Co(iii) complex [Co₂(L^O-)₂(OH)₂]²⁺ (3) with modified phenoxide ligands. The oxidation of 1b to 3 is monitored and the intermediate Co(ii) iodo aqua complex [CoL^OMeI(H₂O)]⁺ and Co(ii) diaqua complex [CoL^OMe(H₂O)₂]²⁺ are isolated and characterised.

Full text of DOI:10.1039/c9dt04609g

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DOI: 10.1039/C9DT04609G
ARTICLE
Coligand Modulated Oxidative O-demethylation of Methylether
Appended Tetradentate N-Ligand on Co(II) Complexes
S. S. Anjana,*a#, B. Vargheseb and N. N. Murthy*a
Received 00th January 20xx,
Accepted 00th January 20xx
DOI: 10.1039/x0xx00000x
Two Co(II) complexes of the formula CoLOMeX2 (X= Cl- (1a); X= I- (1b)), where LOMe is 2-methoxy-N,N-bis(pyridin-2-ylmethyl)
aniline were synthesized and their structure, spectroscopy and reactivity were studied. Upon oxidation of 1a and 1b, the
ligand LOMe undergo demethylation at the metal centre resulting in the formation of Co(III) complexes with modified
phenoxide ligand. This is the very first examples of oxidative O-demethylation reported at a Co(II) centre. The oxidative
behaviour shows striking dependance on the nature of coligands coordinated to the metal centre. The Co(II) complex 1a
with stronger chloro coligands requires a strong oxidising agent like t-BuOOH for oxidative demethylation and the
subsequent formation of a mononuclear Co(III) complex with demethylated ligand, CoLO-Cl2 (2). On the other hand, the
complex 1b with weaker iodo coligands undergoes oxidation in presence of weak oxidant O2 to form a dihydroxo bridged
binuclear Co(III) complex [Co2(LO-)2(OH)2]2+ (3) with modified phenoxide ligand. The oxidation of 1b to 3 is monitored and
the intermediate Co(II) iodo aqua complex, [CoLOMeI(H2O)]+ and Co(II) diaqua complex, [CoLOMe(H2O)2]2+ are isolated and
characterised.
show that Cu-O2 adducts of this ligand are capable of C-H bond
oxidation of toluene and alkyl benzene.15 This report indicates
that the oxidation reactions of other metal complexes with
Introduction
Modifications of coordinated ligands, such as hydroxylation of
aliphatic1-3 and aromatic C-H bonds4,5, N-dealkylation6-8 and O-
dealkylation are often observed in the oxidation reactions of
biomimicking model complexes of non-heme enzymes, which
employ either O2 or its activated forms as oxidants. O-
dealkylation is a well studied reaction in heme chemistry; since
it is involved in the catalytic cycle of cytochrome p-450
enzymes and is responsible for the detoxification of
xenobiotics.9-12 However, reports about similar reactions in
non-heme sites are quite rare. Over the past few decades,
studies have been carried out by employing copper and iron
complexes of tetra and pentadentate N-ligands with
strategically placed alkoxo groups to accomplish metal assisted
O-dealkylation.13 In most of these reactions, O-dealkylation
was observed as a side reaction and a clean conversion was
not achieved. Recently, Mandon et al. successfully showed the
oxidative O-demethylation at a Fe(II) complex using modified
TPA ligand; but isolation of the Fe(III) phenoxide product was
found to be difficult, owing to its sensitivity.14
similar methyl ether appended ligands may be more
interesting. Since oxidation reactions at ferrous centres are
more significant in bioinorganic point of view, we started our
studies with the ferrous complex FeLOMeCl2, where LOMe is 2-
methoxy-N,N-bis(pyridin-2-ylmethyl) aniline. To our delight, it
was noted that the complex undergo oxidative O-
demethylation in presence of oxidant t-BuOOH. Demethylation
was partial and observed only for the chloro analogue.
However, the Fe(III) phenoxide product was very stable and
could be isolated and characterised both in solid and solution
state. The mechanism for O-demethylation is proposed to
proceed via a high valent Fe(IV) intermediate.16
Since methylether appended ligands show different oxidation
behavior with copper and iron, it will be of interest to see the
reaction of other metal complexes of LOMe with oxidants. A
recent report by Kroutil et al. has showed that the cobalamin-
dependent methyl transferase enzymes are capable of
reversible C-O-ether bond formation and breakage via a CoIII
and the highly reactive CoI cycle.17 The advantage of cobalt
complexes over copper and iron analogues is their higher
stability owing to high CFSE. However, no O-demethylation
was reported at Co(II) centers of non heme complexes till date.
In this article we describe the O-demethylation of LOMe in Co(II)
Karlin et al. had studied the copper-dioxygen chemistry of a
tetradentate ligand 2-methoxy-5-tert-butyl-N,N-bis(pyridin-2-
ylmethyl) aniline (OL) with methylether append and the results
aDepartment of Chemistry, IIT Madras, Chennai 600 036, India, E-mail: complexes upon oxidation. Observations suggest that the
anjanacy11d044@gmail.com, nnmurthy@iitm.ac.in
coligands play an important role in reactivity, which is
bSophisticated Analytical Instruments Facility (SAIF), IIT Madras, India
#Present Address: Department of Chemistry, IIT Bombay, Powai 400 076
Electronic Supplementary Information (ESI) available: [details of any
supplementary information available should be included here]. See
DOI: 10.1039/x0xx00000x
expected as it is known that coligands can influence
coordination number, crystal packing pattern and also
magnetic properties.18-20 The reactivity of few other redox
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inactive metal (Mn, Ni and Zn) complexes of LOMe are also oxygen. An identical trend was observed for the Co(II)
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DOI: 10.1039/C9DT04609G
explored and the details are discussed.
complexes of TPAs with similar geometry. Though TPAs are
reported to form both five and six coordinated Co(II)
complexes with halide coligands, LOMe exclusively formed six
coordinated complexes.21, 22
Results and Discussion
Two Co(II) complexes of the formula CoLOMeX2 (X= Cl-, 1a; I-,
1b) have been synthesized and characterised. On reaction with
oxidants, both these complexes underwent oxidative O-
demethylation resulting in the formation of Co(III) complexes
with phenoxide ligands (Scheme 1). The chloro complex, 1a
required a stronger oxidant like t-BuOOH for oxidation and
resulted in the formation of a mononuclear Co(III) complex,
2
whereas the iodo complex, 1b underwent demethylation in
presence of mild oxidant O2 and formed a dihydroxo bridged
binuclear Co(III) complex, 3. Cobalt was proved to be a better
choice on comparison with ferrous complexes, as the oxidation
reactions were straight forward and the Co(III)-phenoxide
complexes were stable enough to isolate and characterise.
Figure 1. Displacement ellipsoid (50% probability) plots of
Co(II) complexes CoLOMeCl2, 1a and CoLOMeI2, 1b. H atoms are
not shown for sake of clarity.
Me
UV-Vis-NIR spectra of these complexes, recorded in CH2Cl2,
showed well defined bands at 580 and 592 nm respectively for
1a and 1b with ε values in the range 110-160 Mol-1cm-1 (Figure
S1). High ε values (>100 Mol-1cm-1) are typical of five
coordinated trigonal bipyramidal complexes. Moreover, the
splitting pattern of the peaks also matches with the spectra of
penta-coordinated complexes.23 These observations conclude
that both 1a and 1b exist as penta-coordinated trigonal
bipyramidal species in solution when a non-polar solvent like
CH2Cl2 is used. This may be due to the dissociation of one labile
chlorine atom or due to the detachment of anisole moiety
from the coordination sphere, which subsequently lead to the
formation of a five-coordinated species.
Me
N
O
N
O
N
N
I
I
Cl
Cl
CoII
CoII
CoCl2
N
CoI2
N
N
O
N
N
OMeI
2, 1b
CoLOMeCl
LOMe
CoL
2, 1a
CH2Cl2
H
2O O2
t-BuOOH
2+
H
O
N
O
N
N
N
N
Cl
Cl
O
CoIII
III N
Co
CoIII
N
O
N
N
O
H
CoLO-Cl
2+, 3
[Co2(LO-)2(OH)2]
2, 2
Scheme 1. Representation of oxidative demethylation of Co(II)
complexes in presence of oxidants
Spectra of the complexes were recorded in variety solvents to
understand their solution behavior and both complexes exhibit
distinct solution properties (Fig. S2). For 1a, the λmax was blue
shifted to 550 nm in alcohol, on comparison with the spectrum
in CH2Cl2 (580 nm). The ε values are in the range 50 Mol-1cm-1,
typical for six coordinate Co(II) complexes24 and it was
concluded that the solid state structure is retaining as such in
these solvents. The λmax was further blue shifted to 510 nm
with much lower molar absorption coefficients (20-30 Mol-
1cm-1) when H2O was used as a solvent. This very low value and
the blue shift in absorption can be due to the formation of an
aqua complex, in which the labile halides were replaced with
water molecules. Thus it is noted that, as polarity of solvent
increases, the λmax gets blue shifted with lower ε values.
Similar, but more striking trend was observed for iodo complex
1b (Fig 2, S3) also. Hence it is concluded that both these
complexes exhibit solvatochromism and exist as five
coordinated species in non-polar solvents like CH2Cl2. Whereas
in more polar coordinating solvents like H2O and MeOH, they
show properties of regular octahedral complexes and retain
octahedral geometry.
Sythesis and characterisation of Co(II) complexes
The precursor Co(II) complexes 1a and 1b were synthesized as
fine solids in good yield (>75%) by mixing corresponding metal
salts and ligand in 1:1 molar ratio in EtOH/MeOH under inert
atmosphere. Single crystal X-ray analysis shows that both
these complexes are mononuclear (Fig. 1, Table S1). The
molecules consist of a Co(II) centre bound by a molecule of
LOMe coordinated in a standard tripodal tetradentate fashion.
The two other coordination sites are occupied by terminally
bound halide coligands, which are cis to each other. The metal
centre in each complex adopt an approximate octahedral
geometry with one halide trans to anisole oxygen and the
other trans to the tertiary amine nitrogen. The square plane of
octahedron was made by one of the coligands and the
nitrogen atoms from ligand. The anisole O atom from the
ligand backbone and the halide coligand trans to it occupy
axial positions. The anisole -CH3 group lies parallel to the
square plane as in the Fe(II) analogue.16 The metal halide bond
lengths are non-uniform and the halide trans to the anisole
oxygen coordinate weakly due to the trans effect of ether
2 | J. Name., 2012, 00, 1-3
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group, which is getting detached from the metal in presence of
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DOI: 10.1039/C9DT04609G
non-polar solvents and not the coordinated halide.
This observation matches with the conclusion drawn from UV-
Vis studies, where spectra of 1a showed the characteristic
1
features of five coordinated species in CH2Cl2. Further, the H
NMR spectrum of 1a recorded in D2O is identical with the
spectrum of aqua complex [CoLOMe(OH2)2]+ recorded in D2O
(vide infra, Fig S15). Based on these observations, the solution
speciation of 1a can be depicted as in scheme 2.
2+
Me
Me
Figure 2. UV-Vis spectra of CoLOMeI2, 1b in different solvents.
OH2
OH2
N
N
O
N
O
Cl
Cl
Cl
Cl
CoII
H2O
CH2Cl2
N
CoII
CoII
N
N
O
CH3
In literature, UV-Vis studies of five and six coordinated Co(II)
complexes of N and O donor ligands are known to show similar
solvatochromic behaviour.25 Previously reported cobalt(II)
complexes of TPA also showed similar structural changes in
solvents.26 1H NMR spectra of the six coordinated complex
Co(TPA)Cl2 and five coordinated [Co(TPA)Cl]+ were identical,
which suggest that the six coordinated complex can undergo
chloride dissociation to form five coordinated species in
solution.
N
N
N
Scheme 2. Solution speciation of 1a in different solvents.
1H NMR spectra of iodo complex 1b was recorded in CD3OD
and was compared with that of 1a to understand the influence
of coligands on spectral features (Fig S4). Spectra were similar
with eleven sharp signals (two up-field and nine down-field) in
a wide spectral window; but some minor differences were
noticed as coligand changes. As ligand field strength of the
halide decreases, the up-field shift also decrease (-52 ppm for
1a to -37 ppm for 1b). The down-field shift and the pattern of
the signals did not show any such trend and remained more or
less same for both complexes.
Assignment of signals in the paramagnetic 1H NMR spectrum is
challenging owing to the hyperfine shift and broadening of
signals.28 All signals in the 1H NMR spectra of 1a were
1
unambiguously assigned (Fig. 4) with the help of H-1H COSY
(Fig. S5) and T1 and T2 relaxation time measurements (Table
S3).29-32 Further, to understand the temperature dependence
of paramagnetic 1H NMR signals, variable temperature spectra
of 1a was recorded in the temperature range -85 to +55˚C (228
- 328 K). As temperature increased, the most down-field peaks
gradually shifted up-field, whereas the up-field peaks showed
gradual down-field shift (Fig S6). Curie plots show that the
isotropically shifted resonances change linearly as a function of
T-1 (Fig S7). Magnetic susceptibility of 1a and 1b (CD3OD, 298
K) indicate μeff values of 5.2 and 5.4 μB respectively, consistent
with an S = 3/2 ground state.33
Figure 3. 1H NMR spectra of CoLOMeCl2, 1a in different solvents.
More evidences for the influence of solvent on the structural
1
and spectral properties of 1a and 1b are obtained from H
NMR studies (Fig 3). The spectrum recorded in CD3OD showed
eleven very sharp signals (two up-field and nine down-field) in
the spectral range -60 to 200 ppm. Presence of up-field shifted
signals is an indication of significant pseudo contact
contribution to isotropic shifts.27 Though spectral width was
much lesser in D2O (-20 to 150 ppm), the pattern was similar
confirming that the octahedral geometry is remained more or
less same in both these solvents. However, the spectrum in
CDCl3 has only one up-field shifted signal and the other signal
was present in the diamagnetic region, indicating the
detachment of the anisole -OMe group (vide infra for signal
assignment) from the metal centre and the consequent
formation of a five coordinated Co(II) complex. Hence it is
1
Figure 4. Paramagnetic H NMR spectra of 1a in CD3OD at RT
(500 MHz) and the assignment of signals
1
concluded from H NMR spectra that it is the methyl ether
Electrochemistry of Co(II) complexes are also investigated to
understand the feasibility of oxidation. CV of 1a, recorded in
This journal is © The Royal Society of Chemistry 20xx
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CH3CN has a one-electron redox wave (E1/2, 274 mV vs. Fc/Fc+) comprised of two pyridine nitrogens, phenoxide oxygen and
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corresponding to metal oxidation. CV of 1b in CH3CN shows one terminal chloride. The other chloriDdOeI:a1n0d.10t3e9r/tCia9DryT0a4m60in9Ge
two redox waves; one at E1/2 = 160 mV vs. Fc/Fc+ corresponds nitrogen take the axial positions. The amine N made longer
to the redox couple I-/I2, and the second one at E1/2 = -209 mV bond with the metal (1.953(3) Å) on comparison with the
vs. Fc/Fc+ indicating the one electron metal redox couple pyridines (1.9445(3) Åav). The three trans angles around the
Co2+/3+ (Fig 5).34, 35 The Cu(II) complex of LOMe exhibited similar metal center showed values of 167.03(13), 178.69(9) and
reversible redox processes with a E1/2 value of -510 mV vs. 176.68(9) indicating that the complex is less distorted on
Fc/Fc+. The lower E1/2 value indicates its high reactivity to O2 comparison with the Co(II) analogue, 1a and has more perfect
and the facile formation of Cu-O2 complexes. Fe(II) complex of octahedral geometry. Similar mononuclear Co(III) complexes
LOMe has much higher E1/2 value (-55 mV vs. Fc/Fc+) and was with labile coligands such as Cl- or H2O are known as good
stable to air. Hence, the comparatively lower oxidation catalysts for phosphate ester hydrolysis.36, 37
potential of Co(II) iodo complex 1b, on comparison with 1a
,
indicates that it may be more reactive to O2.
Figure 5. CVs of 1a (left) and 1b (right) in CH3CN with 0.1 M
nBu4PF6 as an electrolyte. Scan rate: 0.05 V/s; glassy carbon
working electrode, Ag/AgCl/KCl(aq) reference electrode.
Figure 6. Displacement ellipsoid (50% probability) plots of
Co(III) complex [CoLO-Cl2, 2. H atoms, counter anions and
solvents of crystallisation are not shown for sake of clarity
As expected based on electrochemical studies, Co(II) chloro
complex 1a was stable and did not show any reactivity to air in
solid or in solution state even after exposing for longer period
of time. Reaction of 1a with stronger oxidant like H2O2 resulted
in the decomposition of the starting material and did not bring
any oxidation. After few trials, it was found that 1a undergo
oxidation with t-BuOOH in CH2Cl2 medium. On refluxing the
blue solution of 1a in CH2Cl2 with two equivalents of t-BuOOH,
a parrot green solution of Co(III) complex was obtained after
Unlike choro complex 1a, 1b was not stable to air and the dull
green complex turns red on exposure to moisture, indicating
reactivity (Fig S8). Though O-demethylation was expected,
reaction of 1b with t-BuOOH in CH2Cl2 resulted in the
decomposition of the precursor complex. Similar result was
obtained with other strong oxidants like H2O2 also. On varying
reaction conditions, it was found that 1b undergoes oxidative
O-demethylation in presence of O2 in CH3CN-H2O mixture,
20 h. Based on our studies with the ferrous complexes of LOMe
,
the possibility of oxidative O-demethylation and the formation
of a Co(III) phenoxide complex is expected, which is confirmed
by structural and spectral analysis of the product. Solvent
removal followed by washing the residue with diethyl ether,
yielding Co(III) complex
3 with phenoxide ligand. The oxidized
product was isolated as brown-red solid in 40% yield after
overnight reaction. However, no reaction was noticed in the
absence of O2 or H2O.
the Co(III)-phenoxide complex
2 was isolated as a gray solid in
excellent yield (> 95%). The reaction was clean and took place
only under specific conditions. On using more than two
equivalents of oxidant, the complex got decomposed, whereas
less than two equivalents of oxidant leads to longer reaction
time. Solvents play an important role in the oxidative O-
demethylation and the reaction took place only in chlorinated
solvents.
Single crystal X-ray analysis shows that complex
3 has a
binuclear structure in which the Co(III) centers are held
together by two hydroxo bridges (Fig. 7, Table S4). The
complex is symmetric and has an inversion center that relates
one half to the other. The phenoxide ligand LO- is coordinated
in a tripodal fashion around Co(III) and the octahedral
coordination is satisfied by coordination with two bridging
hydroxo groups. The pyridines make weaker bonds (1.9715(6)
Åav) and occupy axial positions of the octahedron. The metal
atom lies on the square plane made by two hydroxo groups,
phenoxide oxygen and tertiary amine nitrogen. The amine N
forms shorter bond with the metal (1.915(5) Å) than the
pyridines. This is in stark contrast with that observed for the
Single crystal X-Ray analysis shows that
2 is mononuclear with
distorted octahedral geometry around Co(III) (Fig. 6, Table S4).
The most interesting feature is the coordination of the
phenoxide O-atom, which is formed as a result of O-
demethylation of the anisole append of LOMe during oxidation,
with the Co(III) centre. Except the Co-Cl bonds (2.2559(9) Åav)
all bonds made to metal are less than 2 Å, which is typical for
Co(III) complexes. The square plane of the octahedron is
other Co(III) complex 2. The Co-Co distance is 2.929(3) Å and
O-O’ distance is 2.423(4) Å which are expected, on comparison
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with binuclear Co(III) complexes having similar CoIII2(μ-OH)2
diamond core.38
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DOI: 10.1039/C9DT04609G
N
Cl
Cl
N
N
Cl
Cl
CoII
Cl
N
Cl
t-BuOOH
CH2Cl2
CoIII
N
N
CoIII
O
N
O
N
O
N
O
O
CH3
O
O
But
But
H
CH3
C
1a
H2
Cl
Cl
N
N
Cl
CoIII
O
N
CoIII
N
Cl
O
-ButOH
-CH2O
CH2
N
N
O
2
Scheme 3. Proposed mechanism for the oxidative O-
demethylation of 1a and the formation of
2
.
Figure 7. Displacement ellipsoid (50% probability) plots of
Co(III) complex [Co2LO-(OH)]2.Cl0.75 1.25
.4H2O.CH3CN, 3. H atoms,
I
The mechanism of conversion of 1b to
3 is likely to follow a
counter anions and solvents of crystallisation are not shown
for sake of clarity
different route. It was noticed that 1b undergoes oxidation
only in presence of H2O, suggesting the involvement of an
aqua complex as a precursor for oxidation. To understand the
mechanistic details and to identify the actual Co(II) precursor
which undergoes oxidative O-demethylation, the iodo complex
was reacted with H2O. The red colour of complex 1b in CH3CN
faded to orange on addition of H2O and to very pale pink in
presence of excess H2O. This can be an indication of the
subsequent iodide replacement by H2O molecules and the
formation of Co(II) aqua complexes with formula
[CoLOMe(OH2)I](I), 1c and [CoLOMe(OH2)2](I)2, 1d. However, no
such conclusion could be obtained from UV-Vis spectra, as the
spectra remained more or less same in H2O (a broad peak
around 500 nm, Fig 2), irrespective of the amount of solvent
used. Initial attempts to isolate and crystallize the H2O
coordinated complexes were unsuccessful. However, by
UV-Vis spectra of Co(III) complexes
2 and 3 show well defined
d-d bands at 582 (ε, 117 Mol-1cm-1) and 519 nm (ε, 503 Mol-
1cm-1) respectively. In addition, a high energy shoulder was
also present around 400 nm in the spectra of both complexes
(Fig. S9).39 1H NMR spectra of Co(III) complexes
2 and 3 show
signals corresponding to 16 protons, whereas the ligand has 19
protons; absence of signals corresponding to three protons
provides further evidence for demethylation (Fig. S10). The IR
spectrum of dihydroxo bridged binuclear Co(III) complex
3 has
strong band at 3343 cm-1, characteristic of the bridging
hydroxo group (Fig S11).
Proposed mechanism for O-demethylation
-
Few examples of N-dealkylation reactions were reported in
literature and these reactions are proposed to proceed via the
formation of a metal-dioxygen adduct. This metastable
intermediate attacks the N-alkyl C-H bond in a rate
determining step, resulting in the formation of dealkylated
ligand and corresponding aldehyde as byproduct.40-43 Similar
mechanism is expected to operate for O-demethylation also.
Though O-demethylation occurs for both 1a and 1b, the
difference in the nature of oxidized products confirms that the
reaction pathways are different. For 1a, demethylation occurs
only in CH2Cl2, in which the complex exists as a penta-
coordinated species and favors the attack of oxidant. On
reaction with t-BuOOH, the pentacoordinated 1a is postulated
to form an octahedral Co(III) tertiary butyl peroxo
intermediate. Such species are known to afford alkoxy radicals,
which can oxidise hydrocarbons.44-47 In the present case, it is
proposed that the peroxo intermediate forms a tertiary butoxy
radical, which abstract a hydrogen radical from the methoxo
group oriented in a favorable position. As a result, a cyclic
intermediate forms with the loss of a molecule of butanol. The
intermediate on further rearrangement resulted the Co(III)
exchanging the iodo counter anion with –ClO4 , both these
complexes could be crystallised as [CoLOMe(OH2)I](ClO4), 1c’
and [CoLOMe(OH2)2](ClO4)2, 1d’. The iodo-aqua complex 1c’
could be synthesised easily, whereas the formation of diaqua
complex 1d’ required high temperature and longer reaction
period. This indicates that the replacement of first iodide is
relatively facile on comparison with the removal of second
halide.48
Crystal structures confirm that these complexes have regular
octahedral geometry around Co(II) as in 1a and 1b (Fig. 8).
However, an interesting geometric change was noticed for the
diaqua complex 1d’. In all other Co(II) complexes, LOMe was
coordinated around the metal in a standard tripodal manner
and the N-atoms are meridionally placed. In 1d’, however, the
orientation of N- atoms of the ligand is changed and they form
the face of an octahedron maintaining the arrangement of
coligands cis to each other. Another interesting difference is
the change in bond lengths. Similar to 1a and 1b, 1c’ also have
shorter Co-N(pyridine) bonds (2.115(3) and 2.126(3) Å) and
longer Co-N(amine) bond (2.170(3) Å). But for aqua complex
1d’, the trend was reversed with longer Co-N(pyridine) bonds
(2.153(4) and 2.111(4) Å) and shorter Co-N(amine) bond
(2.097(4) Å).
complex
2 with phenoxide ligand and a molecule of
formaldehyde (Scheme 3). However, our attempts to detect
the presence of formaldehyde were hindered by longer
reaction time and comparatively higher reaction temperature.
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of H2O confirmed that the aqua complex, 1d is the precursor
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for oxidation. When the iodo complex 1DbOIi:s10t.r1e0a39te/Cd9DwTi0th46H092OG
in presence of air, the diaqua complex 1d forms in situ and
reacts with O2 resulting in the Co(III) complex 3. The structural
analyses of the diiodo and aqua complexes further confirm
that the Co(II) diaqua complex is the precursor for oxidation. In
the iodo complex 1b, the –OCH3 group is positioned far away
from the coligands. However in the diaqua complex 1d’, the
anisole moiety is rearranged in such a way that it comes in
close proximity to the aqua coligands, thereby facilitating the
demethylation process.
Figure 8. Displacement ellipsoid (50% probability) plots of
Oxidation of 1b is proposed to proceed via the formation of a
metastable Co(III)-dioxygen intermediate, which abstract
hydrogen atoms from the favourably placed anisole methyl
groups.1 The mechanism then proceed via a pathway similar to
Co(II)
complexes
[CoLOMe(OH2)I](ClO4),
1c’
and
[CoLOMe(OH2)2](ClO4)2, 1d’. H atoms, counter anions and
solvents of crystallisation are not shown for sake of clarity.
that proposed for the conversion of 1a to
formation of Co(III) complex with modified phenoxide ligand
and bridging hydroxo groups (Scheme 4).
2, resulting in the
Both aqua complexes 1c’ and 1d’ are characterised in solution
by various spectral techniques. The iodo- aqua complex 1c’
showed similar solvatochromic behaviour as 1a and 1b. In
CH2Cl2, 1c’ exhibited parrot green color with a strong band in
the UV Vis spectrum at 614 nm (ε= 235 Mol-1 cm-1). In addition,
two weak bands were also present in the NIR region,
confirming the formation of a five-coordinated species. On the
other hand, the complex was pale pink in EtOH and showed a
band at 540 nm with much lower molar extinction coefficient
(ε =55 Mol-1 cm-1), which is typical for octahedral complexes
(Fig S12). Interestingly, both these solutions give similar pale
pink blocks of 1c’ on crystallization, indicating that the species
is same in solid state. No solvatochromic studies could be
carried out for the diaqua complex 1d’, as it was soluble only
in polar solvents like alcohol and H2O, in which it show
features typical for octahedral complexes (490 nm; ε = 32 Mol-
1 cm-1). λmax for 1c’ and 1d’, recorded in polar solvents, showed
gradual blue shift as the coligand change from weak field
iodide (540 nm) to moderate field H2O (490 nm) (Fig S13).
3
+
2+
Me
Me
OH2
N
N
O
O
OH2
I
N
I
H2O
H2O
CoII
OH2
CH3
CoII
CoII
N
N
N
O
I
N
N
N
1d
1c
1b
4+
2+
H
N
H3C
O2
N
N
O
N
O
N
O2
O
CoIII
N
III N
CoIII
O
CoIII
Co
N
N
-2CH2O
O
H
N
N
O
N
CH3
3
Scheme 4. Proposed mechanism for the oxidative O-
demethylation of 1b and the formation of Co(III) complex
3
The experiments on Co(II) and Fe(II) complexes shed light on
the O-demethylation reactions of LOMe and it is identified that
the redox properties and hard soft nature of metals play
crucial role in supporting oxidative O-demethylation. To
confirm this point, the oxidation behaviour of few other metal
complexes of LOMe is studied. The metals (Mn, Ni and Zn) were
selected in such a way that they are less redox active and
cannot achieve higher oxidation state under normal
conditions, which indicate that they are not expected to
support O-demethylation.
1
Paramagnetic H NMR spectra of 1c‘ and 1d‘ are recorded in
CD3OD and D2O respectively. The spectrum of 1c’ has eleven
signals (two up-field and nine down-field) in the spectral range
-40 to 200 ppm, like the other Co(II) complexes (Fig S14).
However, the signals were broad and not well defined which
could be due to the fast electronic relaxation time. The
spectrum of diaqua complex 1d’ also showed eleven signals,
which were sharp, in a comparatively shorter spectral window
of 180 ppm (-20 to 160 ppm) (Fig S15). Magnetic susceptibility
values of 1c‘ (CD3OD, 298 K) and 1d‘ (D2O, 298 K) indicate μeff
values of 4.18 and 5.04 μB respectively, consistent with an S =
3/2 ground state.
Syntheses of precursor M(II) complexes were straightforward
and all of them were precipitated as stable fine powders in
excellent yield by mixing corresponding metal(II) chloride salt
and ligand in equimolar ratio in EtOH. The manganese complex
MnLOMeCl2, 1e was isolated as a flesh colored powder and
crystal structure shows that the complex has a geometry
identical to the Co(II) complexes 1a and 1b (Fig S16, Table S4).
To study the oxidation behaviour, the complex was refluxed in
CH2Cl2 with two equivalent of t-BuOOH for 48 h. No visible
changes were observed and the precursor Mn(II) complex 1e
was completely crystallised out from the reaction mixture on
cooling, confirming that there is no reaction.
-
Complexes 1c’ and 1d’ with –ClO4 counter anions are stable
and could be stored for months under closed condition; but
their iodide counterparts 1c and 1d are comparatively more
reactive and subsequently get converted to the oxidised
complex, 3. However, it is noted that there is no reactivity
when the diiodo complex 1b is stored in a moisture free
environment. The inability to undergo oxidation in the absence
6 | J. Name., 2012, 00, 1-3
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complex, 1b with iodo coligands is not stable to air and
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NiLOMeCl2 was isolated as sea green solid in good yield. The oxidised to Co(III) complex with demetDhOylIa: 1t0e.d103li9g/aCn9dDTv0i4a60t9hGe
crystal structure of the complex is reported and it has a formation of Co(II) diaqua complexes. The incapability of
mononuclear structure with distorted octahedral geometry metals such as Cu, Mn and Ni to carry out oxidative O-
around metal centre as in 1e 49
. The complex was characterised demethylation emphasize the importance of metal redox
by UV-Vis spectroscopy and the spectrum showed two well properties in such reactions.
defined bands at 674 (ε = 21 Mol-1 cm-1) and 406 nm (ε = 48 Experimental Section
Mol-1 cm-1) and a shoulder at 315 nm. Ni(II) complexes are not
expected to undergo easy oxidation because of the unstable
General Procedures
Unless otherwise stated, all solvents and chemicals used were
nature of Ni(III) oxidation products. The complex was dissolved
in CH2Cl2 and refluxed with an equivalent of t-BuOOH for 48 h.
UV-Vis spectrum of the resultant solution showed identical
features of the initial Ni(II) complex (Fig S17). The precursor
complex 1f could be fully recovered by washing the residue
with diethyl ether.
of commercially available analytical grade, and were used as
such without further purification. Co(ClO4)2.6H2O was
synthesized by reacting CoCO3 with HClO4 in aqueous medium,
followed by crystallisation from H2O. CH3CN was dried by
double distillation over P2O5 and CaH2 after passing through a
long column of activated alumina. CH2Cl2 was dried by
employing standard procedure.52 EtOH (99.9%) was purchased
from Hayman Ltd and used as such. The deuterated solvents
were obtained from Aldrich. Preparation and handling of air-
sensitive compounds were performed under an argon
atmosphere using standard Schlenk techniques. The UV-Vis
Reactions were repeated using upto 5 equivalents of oxidant;
but no demethylation took place in any case, indicating the
inability of Mn(II) and Ni(II) complexes to undergo oxidation.
As mentioned earlier, no demethylation is noticed for the Cu(I)
complexes of LOMe also. For Cu2+, which is a borderline acid, the
coordination geometry is effectively satisfied by bonding with
soft ether O atom than hard phenoxide O-atom, which
explains the observed inertness of Cu(I) complexes to O-
demethylation whereas for Ni2+ and Mn2+ complexes, their
inability to achieve and stabilise higher oxidation states resist
the reaction. Co2+ is a very suitable contestant in this aspect, as
it can easily achieve +3 oxidation state and the hard acid Co3+
prefers coordination with hard phenoxide oxygen atom over
ether O atom. Hence it is proven that the redox properties of
metals play significant role in the demethylation of LOMe. The
electrochemical studies of these complexes further helps to
analyze the observed oxidation behavior. Copper complex of
LOMe has a very low one electron redox potential (E1/2 = -510
mV Vs. Fc/Fc+) and undergoes metal oxidation; no O-
demethylation was noticed. On the other hand, Iron complex
has much higher one electron potential at -55 mV Vs. Fc/Fc+
and undergoes oxidative O-demethylation.16 Cobalt complexes
with comparable CV profiles also undergo oxidative O-
demethylation as described before. The electrochemical
studies of Mn complex (1e) did not give any useful data.
However the CV of NiLOMeCl2, 1f shows a redox couple with a
high E1/2 value of 545 mV Vs. Fc/Fc+ (Fig S18). From the
electrochemical analysis it is concluded that metals with low
redox potential (For Eg: Cu) support metal oxidation whereas
those with medium redox potential (Egs: Fe and Co) can assist
oxidative O-demethylation. However, metals with very high
redox potential (Eg: Ni and Mn) do not aid any type of
oxidation. It is interesting to note that the potential of the
spectra were recorded on
a
Jasco
V
650 UV-Vis
spectrophotometer or Shimadzu 3100 UV- Vis- NIR
spectrophotometer. IR spectra were recorded on a Jasco
FT/IR-4100 spectrophotometer after making pellets with KBr.
1H and 13C NMR spectral data were obtained from a Bruker
400 MHz/ 500 MHz FT-NMR spectrometers at ambient
temperatures by using TMS as an external reference. All
electrochemical experiments were performed using a CH
Instrument (model CH6003D Electrochemical Analyzer). A
three electrode system was used, consisting of a platinum
(diameter of the active zone: 2.0 mm) working electrode, a
platinum wire counter electrode, and a Ag/AgCl/KCl(aq)
reference electrode. The CV measurements were performed in
dry
acetonitrile
solutions
containing
0.1
M
tetrabutylammonium hexafluorophosphate (TBAPF6, Fluka,
recrystallized from methanol), and 2 mM substrate under N2
atmosphere at room temperature. Scan rate of 50 mV/s were
applied for all the complexes. Ferrocene was used as an
internal standard and the E1/2 value for Fc/Fc+ couple is found
at 450 mV vs Ag/AgCl in CH3CN.
Preparation of ligand and complexes
LOMe (2-methoxy-N, N-bis(pyridin-2-ylmethyl)aniline). Toluene
solution (3.0 mL) of picolinic aldehyde (4.0 g, 37.3 mmol) was
taken in an air free addition funnel and o-anisidine (4.6 g, 37.3
mmol) in toluene (3.0 mL) was added drop-wise with
continuous stirring under N2. Formed red oil and orange
supernatant was stirred under inert atmosphere for an hour.
The supernatant was decanted and solvent removed under
reduced pressure to obtain the imine as orange oil (7.8 g,
99%). The imine was dissolved in MeOH (15 mL) and reduced
by adding NaBH4 (1.4 g, 37.0 mmol) in small portions over a
period of 24 hours under ice cold condition. After complete
addition, the solution was kept stirring overnight under N2. The
reaction was stopped, solvent removed and excess NaBH4 was
quenched by adding 6N HCl and the reaction mixture was then
•
-
redox couple O2/O2 in CH3CN is -1.25 V vs. Fc/Fc+.50, 51
In summary, we have reported the first oxidative O-
demehylation reactions at Co(II) centers by employing a
tetradentate N-ligand with anisole append (LOMe) and halide
coligands (Cl- or I-). The Co(II) complex, 1a with chloro
coligands, is stable and underwent oxidative demethylation in
presence of strong oxidant like t-BuOOH. However, the Co(II)
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made basic with 4N NaOH. Extraction to CH2Cl2 followed by solid obtained by removing solvent from the supernatant was
View Article Online
DOI: 10.1039/C9DT04609G
solvent removal yielded the secondary amine as yellow orange dried well and yield noted (70 mg, 70%). Pale pink blocks were
oil (7.1 g, 90 %). The amine was dissolved in CH3CN (40 mL) obtained after two days from CH2Cl2 or EtOH by slow
and treated with picolyl chloride (4.3 g, 33.7 mmol) under inert evaporation. Anal.Calcd for C19H21ClCoIN3O6: C, 37.76; H, 3.17;
atmosphere. To this reaction mixture, solid Na2CO3 (1.85 g, N, 6.95. Found: C, 37.99; H, 1.45; N, 6.21. UV-Vis (λmax, nm; ε,
17.5 mmol) was added in small portions with continuous M-1cm-1): 530 (53), 1174 (7) (EtOH); 556 (146), 496 (87),
stirring. The reaction mixture was kept heating at 50oC for 610(233) (CH2Cl2). FTIR (KBr, cm-1): 3399, ν(-OH2); 1120, 627,
-
three days. Solvent was removed and the crude product ν(ClO4 ); 770, ν(pyridyl-CH). ESI-MS (m/z, H2O): 399 (100%,
obtained was purified by column chromatography using silica [LOMeCo(OH2)(OH]+); 491 (93%, [LOMeCo(I)]+); 426 (85%,
gel. Elution with petroleum ether removed the un-reacted 2° [LOMeCo(EtOH)(OH]+). µ (CD3OD, 298 K): 4.18 µB/Co(II). 1H NMR
-
amine and picolyl chloride, whereas elution with ethyl (CD3OD):
δ
-31.69, 14.96, 8.79, 12.06, 17.83, 32.45, 42.91,
acetate/hexane (1:1) yielded LOMe (1.3 g, 48%) as off-white 59.97, 73.14, 80.54, 147.39, 194.09 (CDCl3): -27.22, -15.35, -
rectangular crystals (Rf = 0.25, silica gel, ethyl acetate/hexane 2.50, 18.02, 69.82, 80.24, 116.56, 210.31.
1:1). Yield: 48%. 1H NMR (CDCl3): 3.84 (s, 3H), 4.51 (s, 4H), 6.77 [CoIILOMe(H2O)2](ClO4)2, 1d’. The dull green precipitate of 1b
(m, 1H), 6.89 (m, 3H), 7.08 (m, 2H), 7.50 (d, 2H), 7.57 (m, 2H), (150 mg, 0.24 mmol) was suspended in EtOH and treated with
8.49 (d, 2H). 13C NMR (CDCl3): 55.56 (-CH2), 58.76 (-OCH3), aqueous NaClO4 solution (60 mg, 0.49 mmol). The dark orange
111.72 (Ph), 120.76 (Ph), 120.80 (Py), 121.84 (Ph), 122.36 (Py), reaction mixture was heated at 60o C for 2 hours. Cooled to
136.45 (Py), 139.30 (Ph), 149.00 (Py), 152.82 (Ph), 159.82 (Py). room temp, solvent removed and the product was extracted to
LOMe was synthesized by Lucas et al.15, by using a slightly CH3CN. The residue obtained from CH3CN was dissolved in
different procedure.
deionised water and heated overnight again at 60o C. The red
CoIILOMeCl2, 1a. To a dark blue solution of CoCl2.6H2O (179.0 oil obtained after solvent removal on keeping closed for three
mg, 0.75 mmol) in EtOH, LOMe solution (228.5 mg, 0.75 mmol) days yielded the diaqua complex as brown red crystalline solid
in EtOH was added drop wise with stirring at room (Yield: 87 mg, 60%). Pale pink blocks were obtained from
temperature. After stirring for 4 h at RT, the precipitated dark butanol after a week by vapour diffusion of diethyl ether.
purple powder was separated and dried (Yield: 276.0 mg, Anal.Calcd for C19H23Cl2CoN3O11: C, 38.08; H, 3.87; N, 7.01.
85%). Purple needles were obtained from CH2Cl2 overnight, by Found: C, 38.23; H, 2.28; N, 6.80. UV-Vis (λmax, nm; ε, M-1cm-1;
evaporation. Anal.Calcd for C19H19Cl2CoN3O: C, 52.43; H, 4.40; H2O/ MeOH]: 492 (32), 1074 (5). FTIR (KBr, cm-1): 3400, ν(-
-
N, 9.66. Found: C, 52.40; H, 3.85; N, 9.58. UV-Vis (λmax, nm; ε, OH2); 1089, 626, ν(ClO4 ); 770, ν(pyridyl-CH). ESI-MS (m/z,
M-1 cm-1): 582 (113), 1234 (6) (CH2Cl2); 584 (79), 1256 (5) H2O): 399 (100%, [LOMeCo(OH2)(OH]+); 463 (87%,
(CH3CN); 548 (43), 1302 (6) (EtOH or MeOH); 502 (25), 1056 (6) [LOMeCo(ClO4)]+); 426 (85%, [LOMeCo(EtOH)(OH]+. µ (D2O, 298
1
(H2O). FTIR (KBr, cm-1): 2923, m, ν(C-C); 1605, s, ν(C=Npy); 1498, K): 5.04 µB/Co(II). H NMR (D2O): -14.25, -7.43, 10.73, 15.51,
1444, s, ν(C=Car); 1249, s, ν(C–O). µ (CD3OD, 298 K): 5.19 25.26, 26.17, 46.65, 54.72, 63.68, 146.68, 156.02.
1
µB/Co(II). H NMR (500 MHz, CD3OD): -51.37, -25.95, 6.60, MnIILOMeCl2, 1e. To a pale pink solution of MnCl2.4H2O (156.0
12.76, 28.66, 48.98, 50.40, 70.03, 76.50, 151.48, 187.89.
mg, 0.79 mmol) in EtOH, LOMe solution (244.3 mg, 0.8 mmol) in
CoIILOMeI2, 1b. To a freshly prepared dark green solution of EtOH was added drop wise with stirring at room temperature.
CoI2.6H2O (80.3 mg, 0.19 mmol) in EtOH, ligand solution (59.0 After stirring for 2 h at RT, the precipitated flesh colour
mg, 0.19 mmol) in EtOH was added drop wise with stirring powder was separated and dried (Yield: 310 mg, 90%). Faint
under N2, yielding purplish red clear solution. On stirring under pink coloured blocks were obtained from CH2Cl2 after
N2 for overnight, orange red supernatant and grey green overnight, by evaporation. Anal. Calcd for C19H19Cl2MnN3O: C,
precipitate formed. The precipitate was separated, dried and 52.92; H, 4.44; N, 9.74. Found: C, 52.56; H, 3.95; N, 9.85.
yield of the dull green powder noted (88.5 mg, 75%). Bright NIIILOMeCl2, 1f. To a solution of NiCl2.6H2O (85.1 mg, 0.36
green block shaped crystals were obtained from CH2Cl2 after a mmol) in EtOH, ligand solution (111.2 mg, 0.36 mmol) in EtOH
day, by vapour diffusing diethyl under N2. Anal.Calcd for was added drop wise with stirring under N2. The reaction
C19H19I2CoN3O: C, 36.92; H, 3.10; N, 6.80. Found: C, 37.08; H, mixture was stirred for two hours and the precipitated apple
2.56; N, 6.66. UV-Vis (λmax, nm; ε, M-1 cm-1): 360 (2495), 514 green product was separated (128.3 mg, 82%). Dark green
(96), 560 (136), 594 (143), 1446 (11) (CH2Cl2); 376(1289), 520 block shaped crystals were obtained from CH3NO2 after a day,
(75), 1176 (8) (CH3CN); 362 (673), 536 (51), 1130 (5) (MeOH); by slow evaporation. Anal.Calcd for C19H19Cl2NiN3O: C, 52.46;
370 (1583), 540 (72), 1278 (6) (EtOH). FTIR (KBr, cm-1): 2912, H, 4.40; N, 9.66. Found: C, 52.18; H, 3.74; N, 9.39. UV-Vis
m, ν(C-C); 1604, s, ν(C=Npy); 1496, 1441, s, ν(C=Car); 1245, s, (λmax, nm; ε, M-1 cm-1, CH2Cl2): 406 (48), 674 (21), 982 (9),
1
ν(C–O). µ (CD3OD, 298 K): 5.40 µB/Co(II). H NMR (500 MHz, 1312 (6). FTIR (KBr, cm-1): 2930, w, ν(C-C); 1604, s, ν(C=Npy);
CD3OD): -37.55, -20.39, 7.44, 13.78, 28.58, 40.05, 56.56, 69.99, 1446, s, ν(C=Car); 1012, s, ν(C–O). 1H NMR (500 MHz, CD3NO2):
76.29, 141.40, 189.99.
2.09, 4.33, 7.15, 13.45, 22.17, 43.11, 51.25, 113.13, 138.82.
[CoIILOMeI(H2O)](ClO4), 1c’. The dull green precipitate of 1b ZnIILOMeCl2, 1g. To the colourless solution of ZnCl2 (101.6 mg,
(100 mg, 0.16 mmol) was suspended in EtOH and treated with 0.75 mmol) in EtOH, LOMe solution (226.2 mg, 0.74 mmol) in
an equivalent of NaClO4 (20 mg, 0.16 mmol). The reaction same solvent was added drop wise with stirring at room
mixture was stirred overnight to obtain bright pink solution temperature. Precipitated white solid was separated and dried
and thin white precipitate which was filtered off. The pink-red (Yield: 311 mg, 95%). Anal.Calcd for C19H19Cl2ZnN3O: C, 51.67;
8 | J. Name., 2012, 00, 1-3
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H, 4.34; N, 9.51. Found: C, 51.88; H, 3.82; N, 9.62. 1H NMR (400 contains a molecule of complex and half molecule of H2O as
View Article Online
DOI: 10.1039/C9DT04609G
MHz, CDCl3): 3.88 (3H, s), 4.93 (2H, s), 6.74 (2H, d), 7.04 (1H, solvent of crystallisation as in 1a. The Co(III) chloro complex
2
d), 7.09 (2H, t), 7.38 (2H, t), 7.44 (1H, d), 7.69 (2H, t), 9.31 (2H, was crystallised in orthorhombic system with space group
d). Pna21. The asymmetric unit consisted of a molecule of
LO-CoIIICl2. H2O, 2. To the dark blue solution of 1a (211.3 mg, complex and a H2O molecule as solvent of crystallisation. The
0.48 mmol) in CH2Cl2, 6M t-BuOOH, (122 uL, 0.73 mmol) was Co(III) dihydroxo complex crystallises in orthorhombic
3
added under N2 with stirring. The reaction mixture was system with Pnma space group. The complex is highly
refluxed at 40˚C for 20 h, yielding dark green solution with symmetrical and the asymmetric unit contain just half
little grey precipitate. Solvent removed and the sticky grey molecule of complex. The charge is neutralised by 1.36 I-
residue was washed thrice with diethyl ether to remove excess atoms and 0.64 Cl- atoms. In addition, four molecules of H2O
t-BuOOH and any butanol formed. Dried well and the yield of and a molecule of highly disordered CH3CN also present in the
the fine grey powder was noted (195.0 mg, 95%). Parrot green lattice as solvents of crystallisation.
needles were obtained after three days from CH3CN solution X-ray data were collected with a Bruker AXS Kappa Apex II CCD
by slow evaporation. Anal.Calcd for C18H16Cl2CoN3O: C, 51.45; diffractometer equipped with graphite monochromated Mo-
H, 3.84; N, 10.00. Found: C, 50.98; H, 3.41; N, 9.84. UV-Vis Kα (λ = 0.7107 Å) radiation. The structures were solved by
(λmax, nm; ε, M-1 cm-1; CH3CN): 415 (217), 584 (117). FTIR (KBr, direct methods using SHELXT-2015, and refined by full-matrix
cm-1): 3529, 3404, br, ν(-OH2), 1609, m, ν(C=Npy); 1585, m, least-squares techniques using the SHELXL-2016 computer
1
1480, s, ν(C=Car); 1283, m, ν(C–O). H NMR (400 MHz, CD3CN): program. All hydrogen atoms were fixed at chemically
4.63 (2H, d), 5.68 (2H, d), 6.48 (2H, t), 6.74 (1H, t), 7.35 (2H, d), meaningful positions. Molecular graphics were generated
7.52 (2H, t), 7.61 (1H, d), 7.88 (2H, t), 9.45 (2H, d). 13C NMR using diamond programs.
(400 MHz, CD3CN): 58.59 (-OCH3), 60.05 (-CH2), 121.96 (Py),
122.77 (Py), 123.02 (ar) 127.59 (ar), 128.30 (ar), 129.22 (ar),
Conflicts of interest
There are no conflicts of interest to declare.
136.45 (Py), 139.08 (ar), 148.94 (Py), 159.82 (py).
[CoLO-(OH)]2.Cl0.75 1.25
.4H2O.CH3CN, 3. The in situ prepared
I
Co(II) iodo complex 1b (166 mg, 0.27 mmol) was suspended in
CH3CN and millipore H2O was added till a bright red clear
solution forms. The reaction mixture was purged with O2 and
heated overnight at 60˚C. Cooled to room temperature and
Acknowledgements
S. A thanks CSIR, India for a fellowship. We gratefully
acknowledge the single-crystal X-ray diffractometer facility
funded by SAIF, IIT Madras and Dept. of Chemistry, IIT Madras.
kept open to get dark brown rectangles of
3 (125 mg, 62%)
after 3 days. Isolated product was washed well with CH3CN
and H2O separately, to remove impurities. Dark red needles
were obtained after overnight from CH3CN-H2O mixture by
evaporation. Anal.Calcd for C36H34Co2I2N6O4: C, 43.84; H, 3.47;
N, 8.52. Found: C, 44.28; H, 2.89; N, 8.98. UV-Vis (λmax, nm; ε,
M-1 cm-1; CH3CN+H2O): 519 (503), 375 (1313). FTIR (KBr, cm-1):
3536, s, ν(-OH), 3343, br, ν(-OH2), 1609, s, ν(C=Npy), 1491, s,
Notes
‡Crystal data 1a
Orthorhombic, P212121, a = 9.5758(2)
15.2197(2) , V = 2011.63(7), Rint = 0.0137, Z = 4, ρcald = 1.463
g cm-3, = 1.134 mm-1, F(000) = 908, T = 298(2) K, R(F2 > 2
) =
0.0207, wR2 = 0.0514, 3421 independent reflections, 2 = 50
and 246 parameters, GOF of F2 = 1.039. For 1b: C19H19CoI2N3O,
M = 618.10, monoclinic, P21/c, a = 12.9288(3) , b = 9.5177(2)
, c = 18.2171(5) = 108.7800(10) , V = 2122.32(9), Rint
0.0218, Z = 4,
cald = 1.934 g cm-3, = 3.73 mm-1, F(000) = 1180,
T = 296(2) K, R(F2 > 2
) = 0.0275, wR2 = 0.0619, 3736
independent reflections, 2 = 49.98 and 247 parameters, GOF
:
C19H19Cl2CoN3O1.50
,
M
=
443.20,
, c =
Å
, b = 13.8028(3)
Å
Å
1
1435 s, ν(C=Car); 1246, m, ν(C-O). H NMR (CD3CN+D2O, 400
µ
σ
MHz): 4.90 (2H, d), 5.90 (2H, d), 6.25 (1H, d), 6.53 (1H, t), 6.70
(1H, m), 6.95 (2H, t), 7.52 (2H, d), 7.65 (1H, d), 7.86 (2H, m),
7.99 (2H, d).
θ
˚
Å
Å
Å
,
β
˚
=
X-ray crystallography
ρ
µ
Complex 1a was crystallised in orthorhombic system with
space group P212121. Asymmetric unit was formed by a
molecule of complex and half water molecule. Complex 1b was
crystallised in monoclinic system with space group P21/c and
the iodo aqua complex 1c was crystallised in triclinic system
with P-1 space group. The asymmetric unit of 1c consist of a
σ
θ
˚
of F2 = 1.058. For 1c’: C19H21ClCoIN3O6, M = 608.67, triclinic, P-
1, a = 9.0682(3) Å, b = 11.6181(4) Å, c = 12.1412(4) Å, α =
103.0870(10)˚, β = 104.1930(10)˚, γ = 90.1940(10)˚, V =
1205.53(7), Rint = 0.0176, Z = 2, ρcald = 1.677 g cm-3, μ = 2.141
mm-1, F(000) = 602, T = 296(2) K, R(F2 > 2σ) = 0.0312, wR2 =
-
molecule of complex and a –ClO4 counter anion which is
disordered. The diaqua complex 1d is crystallised in monoclinic
system with space group P21/c. The asymmetric unit consists
0.0774, 4420 independent reflections, 2
θ = 50˚ and 327
parameters, GOF of F2 = 1.049. For 1d’: C19H25Cl2CoN3O12, M =
617.25, monoclinic, P21/c, a = 10.8936(5) Å, b = 19.2866(10) Å,
c = 13.2468(6) Å, β = 112.981(2), V = 2562.3(2), Rint = 0.0356, Z
= 4, ρcald = 1.600 g cm-3, μ = 0.944 mm-1, F(000) = 1268, T =
293(2) K, R(F2 > 2σ) = 0.0401, wR2 = 0.1019, 4555 independent
-
of a molecule of complex, two molecules of –ClO4 counter
anions which are disordered and a molecule of H2O as solvent
of crystallisation. Just as the Co(II) chloro complex 1a, The
Mn(II) chloro complex 1e also crystallised in orthorhombic
system with space group P212121. The asymmetric unit
reflections, 2
θ
= 49.2˚ and 430 parameters, GOF of F2 = 1.083.
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Journal Name
21 C. J. Davies, G. A. Solan and J. Fawcett, Polyhedron, 2004, 23
,
For 1e: C19H19.50Cl2MnN3O1.25, M = 435.71, orthorhombic,
P212121, a = 9.6360(3) Å, b = 13.9208(4) Å, c = 15.4915(5) Å, V
= 2078.04(11), Z = 4, ρcald = 1.393 g cm-3, μ = 0.906 mm-1,
F(000) = 894, T = 296(2) K, R(F2 > 2σ) = 0.0237, wR2 = 0.0526,
View Article Online
3105.
DOI: 10.1039/C9DT04609G
22 S. M. Massoud, K. T. Broussard, F. A. Mautner, R. Vicente, M.
K. Saha and I. Bernal, Inorg. Chim. Acta., 2008, 361, 123
23 C. R. Easley, J. Li, A. Banerjee, M. Panda, W. W. Brennessel,
R. Loloee, E. Colacio and F. A. Chavez, Eur. J. Inorg. Chem.,
2015, 2092.
24 A. B. P. Lever, 1968, Inorganic electronic spectroscopy.
Elsevier, Amsterdam
25 P. C. Kunz, M. Börgardts and F. Mohr, Inorg. Chim. Acta.,
2012, 380, 392
26 T. M. Kooistra, K. F. W. Hekking, Q. Knijnenburg, B. Bruin, P.
H. M. Budzelaar, R. Gelder, J. M. M. Smits and A. W. Gal, Eur.
J. Inorg. Chem., 2003, 648
3655 independent reflections, 2
θ = 50˚ and 251 parameters,
GOF of F2 = 1.047. For
2
: C18H18Cl2CoN3O, M = 438.18,
orthorhombic, Pna21, a = 13.7658(5) Å, b = 15.0676(6) Å, c =
8.9198(3) Å, V = 1850.12(12), Z = 4, ρcald = 1.573 g cm-3, μ =
1.234 mm-1, F(000) = 896, T = 296(2) K, R(F2 > 2σ) = 0.0245,
wR2 = 0.0599, 3098 independent reflections, 2
243 parameters, GOF of F2
1.053. For
C38H45Cl0.64Co2I1.36N7O8, M = 1040.71, orthorhombic, Pnma, a =
16.0730(4) , b = 16.5200(4) , c = 16.8530(4) , V =
4474.91(19), Rint = 0.0322, Z = 4, = 1.771
cald = 1.545 g cm-3,
mm-1, F(000) = 2091, T = 293(2) K, R(F2 > 2
) = 0.0555, wR2 =
= 49.60 and 317
θ = 50.96˚ and
=
3:
27 J. Hyun, S. M. Park and H. So, Bull. Korean Chem. Soc., 1997,
18, 1090
Å
Å
Å
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µ
28 I. Bertini, C. Luchinat and G. Parigi, 2001, Solution NMR of
Paramagnetic Molecules, Elsevier Science
σ
29 I. Bertini, C. Luchinat, G. Parigi and R. Pierattelli,
0.1659, 4083 independent reflections, 2
θ
˚
ChemBioChem, 2005, 6, 1536
parameters, GOF of F2 = 1.071.
30 N. N. Murthy, K. D. Karlin, I. Bertini and C. Luchinat, J. Am.
Chem. Soc., 1997, 119, 2156.
31 D. Mandon, A. Machkour, S. Goetz and R. Welter, Inorg.
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10 | J. Name., 2012, 00, 1-3
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52 K. M. Kadish and J. E. Anderson, Pure & Appl. Chem., 1987,
59, 703
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DOI: 10.1039/C9DT04609G
Coligand controlled oxidative O-demethylation of a tetradentate ligand on Co(II) complexes