Structural diversity in the first metal complexes of 2,5- dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles

Article abstract of DOI:10.1039/b802506a

Metal complexes of 2,5-dicarboxamidopyrroles and 2,5- dicarbothioamidopyrroles have been structurally characterised for the first time, complementing the significant amount of work that has been reported for the analogous pyridine ligands. N,N′-Bis(3,5-dinitrophenyl)-3,4-diphenyl- 1H-pyrrole-2,5-dicarboxamide forms octahedral bis(tridentate) complexes with cobalt(iii) and nickel(ii), where the ligands are bound to the metal centres through deprotonated pyrrole and amide N atoms. N,N′-Dibutyl-3,4-diphenyl- 1H-pyrrole-2,5-dicarboxthioamide and N,N′-diphenyl-3,4-diphenyl-1H- pyrrole-2,5-dicarboxthioamide also form bis(tridentate) cobalt complexes but are only deprotonated at the pyrrole N atom, the remainder of the coordination sphere comprising the thioamide S atoms. The dibutyl derivative was isolated as a Co(ii) complex, whereas the diphenyl system deposited a Co(iii) complex. In contrast, N,N′-dibutyl-3,4-dichloro-1H-pyrrole-2,5-dicarboxamide was found to act as a bidentate ligand, in an octahedral cobalt(ii) complex comprising of two bidentate pyrrole ligands, and two aqua ligands. Synthesis of N,N-bis(pyridin-2-ylmethyl)-3,4-diphenyl-1H-pyrrole-2,5-carboxamide gave a pyrrole ligand with increased denticity. Reaction with cobalt(ii) chloride resulted in the isolation of a dinuclear helicate complex. The ligand was found to have undergone addition of a methoxy group to one of the linking methylene carbons, presumably as a result of the oxidative addition of solvent methanol.

Full text of DOI:10.1039/b802506a

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Structural diversity in the first metal complexes of 2,5-dicarboxamidopyrroles
and 2,5-dicarbothioamidopyrroles†
Gareth W. Bates,a Philip A. Gale,*a Mark E. Light,a Mark I. Ogden*b and Colin N. Warrinera
Received 13th February 2008, Accepted 24th April 2008
First published as an Advance Article on the web 9th June 2008
DOI: 10.1039/b802506a
Metal complexes of 2,5-dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles have been
structurally characterised for the first time, complementing the significant amount of work that has
been reported for the analogous pyridine ligands. N,Nꢀ-Bis(3,5-dinitrophenyl)-3,4-diphenyl-
1H-pyrrole-2,5-dicarboxamide forms octahedral bis(tridentate) complexes with cobalt(III) and
nickel(II), where the ligands are bound to the metal centres through deprotonated pyrrole and amide N
atoms. N,Nꢀ-Dibutyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxthioamide and N,Nꢀ-diphenyl-3,4-
diphenyl-1H-pyrrole-2,5-dicarboxthioamide also form bis(tridentate) cobalt complexes but are only
deprotonated at the pyrrole N atom, the remainder of the coordination sphere comprising the
thioamide S atoms. The dibutyl derivative was isolated as a Co(II) complex, whereas the diphenyl
system deposited a Co(III) complex. In contrast, N,Nꢀ-dibutyl-3,4-dichloro-1H-pyrrole-2,5-
dicarboxamide was found to act as a bidentate ligand, in an octahedral cobalt(II) complex comprising
of two bidentate pyrrole ligands, and two aqua ligands. Synthesis of N,N-bis(pyridin-2-
ylmethyl)-3,4-diphenyl-1H-pyrrole-2,5-carboxamide gave a pyrrole ligand with increased denticity.
Reaction with cobalt(II) chloride resulted in the isolation of a dinuclear helicate complex. The ligand
was found to have undergone addition of a methoxy group to one of the linking methylene carbons,
presumably as a result of the oxidative addition of solvent methanol.
structural diversity possible in this new class of transition metal
complex.
Introduction
Metal complexes of ligands containing pyridine-2,6-dicarboxa-
mide groups have been investigated as models for enzyme active
sites, as therapeutic agents, and as fundamentally interesting
ligand systems with quite extensive structural diversity.1–4 The level
of activity is such that over 150 structures involving a pyridine-
2,6-dicarboxamide moiety directly bound to a metal atom can be
found on the Cambridge Crystallographic Database.5 In addition,
these ligands have been shown to bind anions6–9 and neutral
species.10,11 In terms of anion binding, the analogous pyrrole-
2,5-dicarboxamides have been intensively studied, and found
to be very effective receptors.12–14 Pyrrole-2,5-dicarboxamides
functionalised with electron-withdrawing groups can undergo
deprotonation at the pyrrole nitrogen upon addition of a basic
anion.15–17 It therefore seemed probable to us that such systems
would be viable ligands for transition metal cations. Remarkably,
no such complexes have been structurally characterised to date. In
this paper, we report the synthesis and structural characterisation
of cobalt and nickel complexes of pyrrole dicarboxamides and
dicarbothioamides 1–5. This series of ligands illustrates the great
aSchool of Chemistry, University of Southampton, Southampton, UK, SO17
1BJ. E-mail: philip.gale@soton.ac.uk; Fax: +44 23 80 596 805; Tel: +44 23
80 593 332
bNanochemistry Research Institute, Department of Applied Chemistry,
Curtin University of Technology, Perth, Australia. E-mail: m.ogden@curtin.
edu.au; Fax: +61 89 266 4699; Tel: +61 89 266 2483
† Electronic Supplementary Information (ESI) available: Characterisation
data for compounds 3–5. CCDC reference numbers 678031–678037.
For crystallographic data in CIF or other electronic format see DOI:
10.1039/b802506a
4106 | Dalton Trans., 2008, 4106–4112
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give the product as a pale yellow crystalline powder in 63% yield
(1.82 g, 3.7 mmol).
Experimental
N,Nꢀ -Bis(3,5-dinitrophenyl)-3,4-diphenyl-1H-pyrrole-2,5-dicar-
boxamide 1,17 N,Nꢀ-dibutyl-3,4-dichloro-1H-pyrrole-2,5-dicarbo-
xamide 2,15 were synthesised according to literature methods.
1H NMR (400 MHz, DMSO-d6) d (ppm): 4.45 (d, 4H, J= 5 Hz,
CH2), 7.10–7.20 (m, 4H, Ar–H), 7.21–7.25 (m, 10H, Ar–H), 7.71
(dt, 2H, J= 7.5 Hz, 1.5 Hz, Ar–H), 7.89 (t, 2H, J= 5.5 Hz, Ar–
H), 8.38–8.41 (m, 2H, amide NH), 12.05 (s, 1H, pyrrole NH);
1
13C{ H} NMR (100 MHz, DMSO-d6) d (ppm): 45.2 (CH2), 122.3
Compound 3 N2,N5,3,4-tetraphenyl-1H-pyrrole-2,5-
bis(carbothioamide)
(Ar–CH), 123.2 (Ar–CH), 125.1, 127.8 (Ar–CH), 128.2, 128.8
(Ar–CH), 131.8 (Ar–CH), 134.9, 137.8 (Ar–CH), 149.7 (Ar–CH),
158.4, 161.2; IR m (cm−1): 3388 s, 3237 s, 3053 s, 3029 s, 1644 s,
1556 s, 1535 s, 1303 s, 1261 s; LRMS ES+: 488.5 (M + H)+, 975.9
(2M + H)+. Microanalysis for C30H25N5O2. Calc. (%) C = 73.90,
H = 5.17, N = 14.36. Found (%) C = 74.11, H = 5.22, N = 14.34;
Mp: 181–183 ◦C.
N2,N5,3,4-Tetraphenyl-1H-pyrrole-2,5-dicarboxamide12 (1.0 g,
2.4 mmol) was suspended in THF (100 mL) and Lawesson’s
reagent18 (2.52 g, 6.24 mmol) was added. The reaction was heated
at reflux for 24 h and then allowed to cool and the solvent removed
in vacuo. The residue was purified by column chromatography on
silica gel eluting with dichloromethane–5% hexane affording the
product as a yellow powder. The powder was recrystallised from
dichloromethane–acetonitrile 1 : 1 v/v affording the product as
pale-yellow crystals (0.66 g, 58% yield).
Nickel complex of compound 1
N,Nꢀ -Bis(3,5-dinitrophenyl)-3,4-diphenyl-1H-pyrrole-2,5-dicar-
boxamide 1 (50 mg, 0.08 mmol), nickel(II) chloride hexahydrate
(10 mg, 0.04 mmol), and potassium hydroxide (15 mg, 0.27 mmol)
were suspended in methanol (30 mL) and stirred at room
temperature for 24 h. Diffusion of ether into the resulting dark
yellow–brown solution resulted in deposition of a fine yellow
powder mixed with a small number of dark brown needle-like
crystals. Yield, 5%.
1H NMR (400 MHz, CDCl3) d (ppm): 7.17 (t, 2H, Ar–H), 7.26
(m, 4H, Ar–H), 7.40 (m, 12H, Ar–H), 8.87 (s, 2H, NH), 11.14
(s, 1H, NH). 13C{ H} NMR (100 MHz CDCl3) d (ppm): 122.1,
1
123.8, 126.3, 128.76, 128.83, 129.4, 131.0, 131.1, 132.6, 138.4,
182.6. HRMS ES+ (M + Na+): calc.: 512.1225, found: 512.1209.
Microanalysis for C30H23N3S2·MeCN. Calc. (%) C = 72.42, H =
4.94, N = 10.56. Found (%) C = 72.37, H = 4.84, N = 10.22.
(MeCN observed in 1H NMR). Mp: 233–234 ◦C.
Cobalt complex of compound 1
Compound 4 N2,N5-dibutyl-3,4-diphenyl-1H-pyrrole-2,5-
N,Nꢀ -Bis(3,5-dinitrophenyl)-3,4-diphenyl-1H-pyrrole-2,5-dicar-
boxamide 1 (50 mg, 0.08 mmol), cobalt(II) chloride hexahydrate
(10 mg, 0.04 mmol), and potassium hydroxide (9 mg, 0.16 mmol)
were suspended in methanol (30 mL) and stirred at room
temperature for 24 h. Diffusion of ether into the resulting dark red–
brown solution resulted in the deposition of dark brown needles.
Yield, 60%.
bis(carbothioamide)
N2,N5-Dibutyl-3,4-diphenyl-1H-pyrrole-2,5-dicarboxamide12
(1.05 g, 2.3 mmol) was suspended in THF (100 mL) and Lawesson’s
reagent18 (2.52 g, 6.24 mmol) was added. The reaction was heated
at reflux for 24 h and then allowed to cool and the solvent removed
in vacuo. The residue was purified by column chromatography on
silica gel eluting with dichloromethane and then recrystallised
from dichloromethane solution affording the product as pale-
yellow crystals (0.68 g, 63% yield).
Cobalt complex of compound 2
1H NMR (400 MHz, CDCl3) d (ppm): 0.73 (t, 6H, CH3), 0.95
(m, 4H, CH2CH3), 1.18 (m, 4H, CH2), 3.49 (m, 4H, NCH2), 7.08 (s,
2H, amide NH), 7.18 (m, 4H, Ar), 7.28 (m, 6H, Ar), 10.94 (s, 1H,
N,Nꢀ-Dibutyl-3,4-dichloro-1H-pyrrole-2,5-dicarboxamide 2 (28 mg,
0.08 mmol), cobalt(II) chloride hexahydrate (10 mg, 0.04 mmol),
and excess sodium hydride were suspended in dimethylformamide
(30 mL) and stirred at room temperature for 24 h. A black
microcrystalline powder was deposited. Upon prolonged standing
and exposure to the atmosphere, a small number of pink tablets,
appropriate for single-crystal structure determination, crystallised
from the mixture. Yield, 5%.
1
NH). 13C{ H} NMR (100 MHz, DMSO-d6) d (ppm): 13.6, 19.9,
29.8, 45.4, 123.7, 128.3, 129.1, 129.2, 130.6, 132.9, 185.2. HRMS
ES+ (M + Na+): calc.: 472.1851, found: 472.1839. Microanalysis
for C26H31N3S2. Calc. (%) C = 69.45, H = 6.95, N = 9.34. Found
(%) C = 69.29, H = 6.94, N = 9.22; Mp: 214–215 ◦C.
Compound 5 N,N-Bis(pyridin-2-ylmethyl)-3,4-diphenyl-1H-
Cobalt complexes of compounds 3 and 4
pyrrole-2,5-carboxamide
N2,N5-dibutyl-3,4-diphenyl-1H-pyrrole-2,5-bis(carbothioamide)
4 (38 mg, 0.08 mmol), cobalt(II) chloride hexahydrate (10 mg,
0.04 mmol), and potassium hydroxide (9 mg, 0.16 mmol) were
suspended in methanol (30 mL) and stirred at room temperature
for 24 h. The resulting brown powder was allowed to settle, and
the methanol solvent was decanted. Acetonitrile (20 mL) was
added to dissolve the majority of the precipitate. After filtration,
the solvent was allowed to evaporate slowly, depositing deep red
prisms appropriate for single-crystal structure determination,
along with some amorphous material. Yield, 30%. To obtain the
complex of compound 3 the same procedure was followed using
3,4-Diphenyl-1H-pyrrole-2,5-dicarboxylic acid19,20 (1.80 g,
5.9 mmol) was refluxed in thionylchloride (40 mL) for 3 h. The
reaction mixture was cooled and reduced in vacuo and the resultant
solid was dissolved in dichloromethane (50 mL). This was then
added drop-wise to a stirred solution of 2-(aminomethyl)pyridine
(1.30 g, 12 mmol), triethylamine (2 mL) in dichloromethane
(50 mL) with a catalytic amount of DMAP. The reaction mixture
was stirred for 48 h. Water (100 mL) was added and the organic
layer was separated, dried with MgSO4, filtered and reduced
in vacuo. The product was then recrystallised from acetonitrile to
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N2,N5,3,4-tetraphenyl-1H-pyrrole-2,5-bis(carbothioamide) 3.
Yield, 40%.
cobalt(III)§ complex were successfully crystallised as dark brown
prisms, and their structures elucidated. The nickel complex can be
formulated as K4[Ni(1–3H)2](CH3OH)6(H2O), (Fig. 1 and 2) and
the cobalt complex as K3[Co(1–3H)2](CH3OH)3(H2O)2 (Fig. 3).
The pyrrole and amide N atoms are deprotonated so that each
ligand is a tri-anion. Both complex anions are bis-tridentate
complexes (Fig. 1 and 2), the two orthogonal ligands resulting in
a distorted octahedral coordination environment about the metal
centres in the cobalt complex. Similar coordination complexes
have been reported for pyridine-2,6-dicarboxamide ligands, for
both cobalt(III)22–24 and nickel(II).2,25
Cobalt complex of compound 5
N,N-Bis(pyridin-2-ylmethyl)-3.4-diphenyl-1H-pyrrole-2,5-car-
boxamide 5 (50 mg, 0.10 mmol), cobalt(II) chloride hexahydrate
(24 mg, 0.10 mmol), and potassium hydroxide (17 mg, 0.30 mmol)
were suspended in methanol (30 mL) and stirred at room tem-
perature for 24 h. Small dark green needles were deposited from
the solution. These dissolved upon addition of dichloromethane
(10 mL). Upon slow evaporation of the solvent, dark green
needles appropriate for single-crystal structure determination were
deposited, along with some amorphous material. Yield, 20%.
Results and discussion
Synthesis
Thioamides were prepared according to literature procedures by
treating the corresponding amide12 with Lawesson’s reagent18 at
reflux in THF. Analogous pyrrole thioamides that do not contain
phenyl substituents in the 3- and 4-positions of the pyrrole ring
have been prepared by Jurczak and Zielinski.21 Compound 5
was prepared by preparation of the pyrrole bis-acid chloride and
subsequent coupling with 2-(aminomethyl)pyridine.
The syntheses of the complexes were generally achieved follow-
ing a modification of the procedure reported by Grossel et al. for
analogous pyridine amides.22 The appropriate metal(II) chloride
and ligand were slurried in methanol, followed by the addition
of a slight excess of potassium hydroxide. Addition of the base
induced dissolution of the ligand and intensely coloured solutions
were formed. Crystals appropriate for single-crystal structure
determination were obtained by slow evaporation of the solvent,
or diffusion of ether into the solution. The crystals were deposited
along with amorphous material that complicated attempts to
obtain accurate microanalytical data.
An exception to this procedure was the cobalt complex of
ligand 2. In methanol solution the intensity of the colour that
formed upon addition of the base faded over time, possibly due
to hydrolysis of the complex. Using sodium hydride as the base
and DMF as the solvent produced a black precipitate immediately.
Upon prolonged standing in ambient conditions a small number
of pink crystals deposited from the mixture that were appropriate
for structural characterisation.
Fig. 1 The nickel complex Ni124−. Counter cations, solvent molecules
and hydrogen atoms have been omitted for clarity.
Both structures form complex 3D networks through coordina-
tion of the potassium ions to the nitro and carbonyl groups. The
K coordination number varies from 6–9 and is completed via a p
interaction to a phenyl ring, solvent water and methanol.23
Complex of dicarboxamidopyrrole 2
The chloro-substituted pyrrole 2 was introduced as an example of a
ligand where the acidity of the NH protons is increased through the
introduction of electron-withdrawing groups on the pyrrole ring
While additional work is required to optimise the synthesis
of the amido–pyrrole complexes, the work carried out here is
sufficient to allow investigation of the coordination modes of these
ligands for the first time.
collected: 16 842, independent reflections: 4460 (Rint = 0.0995), final R
indices [I > 2rI]: R1 = 0.0797, wR2 = 0.2010, R indices (all data): R1 =
0.1374, wR2 = 0.2307. One of the solvent molecules is disordered over 2
sites, and a partially occupied water is present. This data was collected
using a Bruker Nonius KappaCCD with a Mo rotating anode generator;
standard data collection and processing procedures were followed.
Complexes of dicarboxamidopyrrole 1
Ligand 1 was selected for initial investigations as the electron-
withdrawing dinitrophenyl groups would enhance the acidity of
the amide and pyrrole protons, and it was anticipated this would
facilitate isolation of the metal complexes. A nickel(II)‡ and a
§ Crystal data for 1–Co: C63H48CoK3N14O25, Mr = 1577.38, T = 120(2)
K, monoclinic, space group P21/n, a = 14.6300(16), b = 29.024(3), c =
◦
3
15.4370(17) A, b = 95.507(2) , V = 6524.6(12) A , qcalc. = 1.606 g cm −3
,
˚
˚
l = 0.552 mm−1, Z = 4, reflections collected: 48 591, independent
reflections: 11 503 (Rint = 0.0888), final R indices [I > 2rI]: R1 = 0.0866,
wR2 = 0.2436, R indices (all data): R1 = 0.1330, wR2 = 0.2854. One of the
solvent molecules is disordered over 2 sites. This data was collected using
a Bruker SMART APEX2 CCD diffractometer at the SRS station 9.8 at
Daresbury.35,36
‡ Crystal data for 1–Ni: C66H58K4N14NiO27, Mr = 1694.37, T = 120(2)
˚
K, tetragonal, space group P42/n, a = 15.602(1), c = 15.9970(6) A, V =
3
3894.0(4) A , qcalc. = 1.445 g cm −3, l = 0.550 mm−1, Z = 2, reflections
˚
4108 | Dalton Trans., 2008, 4106–4112
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The synthesis proved to be problematic, with the only crystalline
product resulting from what is presumed to be a slow hydrolysis
of the product initially formed in DMF solvent in the presence
of sodium hydride. The pink tablets that slowly deposited were
suitable for structure determination, the results of which are
consistent with the formulation [Co(2-H)2(OH2)2].¶ As expected,
the pyrrole ligand is deprotonated once only, at the pyrrole N
atom. Each ligand is bidentate only, bound through the pyrrole
N atom and one of the amide O atoms (Fig. 4). The remaining
two sites in the octahedral coordination sphere are occupied by
the two water molecules.
Fig. 2 Part of the 3D network in the nickel complex of compound 1
formed via coordination through the potassium counter cations, viewed
down the c axis. The potassium is coordinated to 6 oxygens; 2 from separate
NO2 groups, 2 from methanols, 1 from a carbonyl group and the other from
water. i = 0.5 − y, x, 1.5 − z.
Fig. 4 Cobalt complex of receptor 2.
The complex exhibits two intramolecular hydrogen bonds: N1–
i
˚
H1 · · · O2 (N · · · O = 2.963(2) A) from the amide NH to the
oxygen of the adjacent ligand, and N3–H3 · · · Cl2 (D · · · A =
˚
3.212(2) A) between the other amide and Cl2 of the same
ligand. The two coordinated water molecules link the complexes
together into a chain along the [101] direction such that inversion
centres lie between adjacent molecules. The interactions include
O3–H98 · · · O1ii (O · · · O = 2.802(2) A), and a bifurcated O3–
˚
H99 · · · Cl1iii (O · · · Cl = 3.33(2) A), O3–H99 · · · O1 (O · · · O =
iii
˚
˚
2.764(2) A) interaction leading to all donors and acceptors being
satisfied. i−x + 1, y, −z + 1/2, iix + 1/2, −y + 1/2, z + 1/2, iii −x +
1/2, −y + 1/2, −z.
Relating this structure once again to analogous pyridine-
based ligands, a comparable structure is found in two cobalt(II)
complexes of N,N,Nꢀ,Nꢀ-tetraethylpyridine-2,6-dicarboxamide
(deap).26 The compounds [Co(deap)2(H2O)2](X)2, where X = PF6
−
or ClO4−, exhibit a very similar coordination complex structure,
but here the bidentate ligands are neutral and the charge is offset
by the counter anions. A key difference between the pyridine and
pyrrole complexes is that while the pyrrole N atoms are trans, the
pyridine N atoms are cis. Once again, the charge on the pyrrole
ring is a probable explanation for this difference. While both
the pyridine and pyrrole complexes are connected by a network
Fig. 3 The X-ray crystal structure of the cobalt complex Co123−. Counter
cations, solvent molecules and hydrogen atoms have been omitted for
clarity.
¶ Crystal data for 2–Co: C28H44Cl4CoN6O6, Mr = 761.42, T = 120(2)
K, monoclinic, space group ◦C2/c, a = 15.3090(6), b = 21.0300(14), c =
3
13.4079(6) A, b = 124.112(3) , V = 3573.9(3) A , qcalc. = 1.415 g cm −3, l =
0.826 mm−1, Z = 4, reflections collected: 24 246, independent reflections:
4072 (Rint = 0.0633), final R indices [I > 2rI]: R1 = 0.0385, wR2 = 0.0805,
R indices (all data): R1 = 0.0689, wR2 = 0.0909. This data was collected
using a Bruker Nonius KappaCCD with a Mo rotating anode generator;
standard data collection and processing procedures were followed.
˚
˚
rather than on the amide groups. The amide butyl substituents will
not tend to stabilise the deprotonated amide N atoms, and it was
therefore anticipated that the ligand may only deprotonate readily
at the pyrrole N atom, under the crystallisation conditions used.
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of hydrogen bonds, the details differ because of this difference
in coordination geometries. The water molecules form hydrogen
bonds to adjacent complexes resulting in a chain formation in the
solid state (Fig. 5).
Fig. 5 Hydrogen-bonded chains extend in the [101] direction in the cobalt
complex of 2, butyl groups omitted for clarity, (i) −x + 1, y, −z + 1/2.
Complexes of dicarbothioamidopyrroles 3 and 4
The thioamide ligands 3 and 4 were treated with cobalt(II)
chloride under comparable reaction conditions to those used
for 1. The deep red prisms isolated were suitable for structural
characterisation, and the results are consistent with the formulae
[CoII(4–H)2]ꢁ and [CoIII(3–H)2](CoIIICl4).** Both structures are
free of solvent in the crystal lattice. As found in the complex of 2,
the thioamide ligands are only singly deprotonated, at the pyrrole
N atom. In this case, however, the pyrrole ligands once again
form octahedral bis(tridentate) complexes about the cobalt atoms
(Fig. 6 and 7), with both amide moieties coordinated through the
S atoms. The complex of 4 is assumed to be a cobalt(II) complex
based on charge balance considerations, whereas the complex of
3 is presumably a cobalt(III) complex, with the charge balanced
Fig. 6 The X-ray crystal structure of the cobalt (II) complex of receptor
4.
by the CoIIICl4 counter anion. In the complex of compound 4,
−
there is significant contact between the N–H to the p system of
the phenyl rings, with N · · · ring centroid distances ranging from
˚
3.570(4) to 4.065(6) A. In the case of the complex of compound
3, significant interactions are observed between the amide N–H
to p system of the phenyl rings with the N · · · centroid distances
˚
ranging from 3.473(4) to 3.901(6) A.
Cobalt complexes of the dicarbothioamidopyridine ligands are
known, but in all cases the cobalt is coordinated to only one
ligand, with the remainder of the coordination sphere comprising
of anions, such as halides or thiocyanate.27 This may be due to
ꢁ Crystal data for 4–Co: C52H60CoN6S4, Mr = 956.23, T = 120(2) K,
¯
triclinic, space group P1, a = 11.820(5), b = 12.819(5), c = 17.669(5)
◦
3
˚
˚
A, a = 111.096(5), b = 100.723(5), c = 92.892(5) , V = 2434.0(16) A ,
qcalc. = 1.305 g cm −3, l = 0.566 mm−1, Z = 2, reflections collected: 39 694,
independent reflections: 11 133 (Rint = 0.0905), final R indices [I > 2rI]:
R1 = 0.0774, wR2 = 0.1858, R indices (all data): R1 = 0.1479, wR2
=
0.2146. Both butyl groups are disordered, as is the rotation angle of one
of the phenyl groups. This data was collected using a Bruker Nonius
KappaCCD with a Mo rotating anode generator; standard data collection
and processing procedures were followed.
Fig. 7 The X-ray crystal structure of the cobalt (III) complex of receptor
3.
** Crystal data for 3–Co: C60H44Cl4Co2N6S4, Mr = 1236.91, T = 120(2) K,
¯
triclinic, space group P1, a = 10.9056(12), b = 15.0◦017(17), c = 20.544(2)
3
˚
˚
A, a = 70.153(6), b = 77.191(6), c = 89.844(6) , V = 3073.0(6) A ,
qcalc. = 1.337 g cm −3, l = 0.891 mm−1, Z = 2, reflections collected: 48 354,
independent reflections: 10 811 (Rint = 0.1411), final R indices [I > 2rI]:
subtle differences in the pyrrole and pyridine ligand geometries, or
may be associated with the negative charge on the pyrrole ligand.
The latter hypothesis is supported by the structure of the cobalt(III)
complex of pyridine-2,6-bis(monothiocarboxylate), which has a
comparable bis(tridentate) coordination sphere albeit as a complex
R1 = 0.1962, wR2 = 0.4795, R indices (all data): R1 = 0.2665, wR2
=
0.5137. Getting a good data set from these poorly diffracting crystals was
not possible. The structure reported here was solved and refined from a
data set containing ill-defined reflections and diffuse scattering. This data
was collected using a Bruker Nonius KappaCCD with a Mo rotating
anode generator; standard data collection and processing procedures were
followed.
anion.28 The average Co–N bond distance in 3 is 1.873(8) A
˚
˚
compared to that of 1.913(7) A for the cobalt(III) complex
4110 | Dalton Trans., 2008, 4106–4112
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of pyridine-2,6-bis(monothiocarboxylate), and the average Co–S
The diphenyl pyrrole can be compared to the unsubstituted
pyridine analogue in that they both form hydrogen-bonded
dimers. However, the conformation of the molecules and the
supramolecular assemblies are very different. In the case of the
pyrrole, the geometry adopted is more open with the angles
between the substituent pyridine rings and the central pyrrole
being 23.43(4) and 56.49(6)◦ compared to 63.62(6) and 78.86(5)◦
with the latter case also being more symmetrical. The amide groups
are anti-relative to the pyrrole NH and this has the effect of twisting
both phenyls into a position favouring p · · · H–N interactions and
allowing a simple bi N–H · · · O centrosymmetric hydrogen-bonded
dimer to form. In the case of the pyridine the molecule adopts a
conformation leading to a cleft being formed as the amides are
syn relative to the pyridine nitrogen. This encourages hydrogen-
bond formation between the substituent pyridines into the cleft to
form a dimer with a 2-fold rotation axis.30 The pyridine analogue
of 5 has been reported to form mononuclear,2,22,31 dinuclear2,32
and tetranuclear2 complexes. It is notable that the mononuclear
complexes are formed with iron(III) and cobalt(III), whereas the
polynuclear complexes are isolated as metal(II) complexes. Reac-
tion of 5 with cobalt(II) chloride in the presence of a base resulted
in the deposition of dark green needles, which were of sufficient
quality for structure determination. The results are consistent
with the formation of a dinuclear helicate structure, where the
ligands are fully deprotonated, indicating that a cobalt(III) helicate
has been isolated (Fig. 9).‡‡ The crystallographic refinement
provides unambiguous proof of formation of a helicate Co(III)
structure. However, there exist additional electron density peaks
on the periphery of the molecule that can be best modelled
as a partially substituted methoxy group. Similar reactivity has
been observed previously in related systems, where a C–H bond
a to coordinated amidate has been oxidised.33,34 The methoxy-
substituted ligand was proposed to be formed as a result of the
attack of solvent methanol upon an intermediate imine34 and a
comparable mechanism is consistent with the observations made
here.
˚
bond distances are 2.272(5) and 2.243(7) A.
The difference in cobalt oxidation states in the isolated com-
plexes of 3 and 4 is intriguing. It is possible that this is a result
of differences in solubilities or subtle changes in the reaction
conditions. It is also plausible that the phenyl amide substituents
on 3 allow greater delocalisation of the metal cation charge,
stabilising the higher oxidation state, in comparison to the alkyl
substituents of ligand 4. Further work is required to confirm
this hypothesis, but the isolation of a cobalt(II) and a cobalt(III)
complex with very similar coordination spheres and geometries
suggests that subtle control of oxidation state in these systems will
be possible.
Complex of pyridine-functionalised dicarboxamidopyrrole 5
Ligands 1–4 are potentially tridentate ligands. Adding donor
atoms to the amide substituents expands the denticity of these sys-
tems, as illustrated by the pyridine-functionalised ligand 5. Such
pentadentate ligands can form complexes of greater structural di-
versity, including polynuclear helicate complexes.29 Reaction of the
pyrrole–diacid chloride with 2-(aminomethyl)pyridine afforded
the bis-pyridine pentadentate ligand 5, which was structurally
characterised after crystallisation from acetonitrile (Fig. 8).†† This
compound forms a centrosymmetric dimer via N3–H93 · · · O2i
˚
(D · · · A = 2.987(2) A) hydrogen bonds from the pyrrolic nitrogen
to the carbonyl of the amide. i−x + 1, −y + 1, −z.
Conclusions
The first structural studies of metal complexes of 2,5-
dicarboxamidopyrroles and 2,5-dicarbothioamidopyrroles have
shown that many features of the analogous and widely studied
pyridine-based systems are accessible in these pyrrole ligands.
The acidic proton on the pyrrole moiety provides an additional
negative charge, which results in subtle variations in the structural
chemistry when compared to the pyridine analogues. Changes in
the amide substituent appear to result in changes in the relative
stabilities of the oxidation state of the metal centre, at least for
Fig. 8 The X-ray crystal structure of receptor 5, which forms a dimer in
the solid state. (i) −x + 1, −y + 1, −z.
‡‡ Crystal data for 52–Co2: C62H48Co2N10O6, Mr = 1146.96, T = 120(2)
K, monoclinic, space group ◦C2/c, a = 13.8197(5), b = 24.1188(10), c =
3
19.9231(7) A, b = 107.468(2) , V = 6334.4(4) A , qcalc. = 1.203 g cm −3, l =
0.578 mm−1, Z = 4, reflections collected: 34 159, independent reflections:
5610 (Rint = 0.0851), final R indices [I > 2rI]: R1 = 0.1147, wR2 = 0.2865,
R indices (all data): R1 = 0.1544, wR2 = 0.3124. The methoxy group
is disordered over two possible locations (70 : 30) in the molecule. The
modelling of this is somewhat hampered by one of the potential sites
being on the edge of a channel that is most likely filled with disordered
solvent. This data was collected using a Bruker Nonius KappaCCD with
a Mo rotating anode generator; standard data collection and processing
procedures were followed.
˚
˚
†† Crystal data for compound 5: C30H25N5O2, Mr = 487.55, T = 120(2)
¯
K, triclinic, space group P1, a = 9.6907(3), b = 10.9090(3), c = 12.3922(3)
◦
3
˚
˚
A, a = 87.119(2), b = 67.8340(10), c = 77.531(2) , V = 1183.91(6) A ,
qcalc. = 1.368 g cm −3, l = 0.088 mm−1, Z = 2, reflections collected: 22 295,
independent reflections: 5409 (Rint = 0.0467), final R indices [I > 2rI]:
R1 = 0.0483, wR2 = 0.1059, R indices (all data): R1 = 0.0627, wR2
=
0.1129. This data was collected using a Bruker Nonius KappaCCD with
a Mo rotating anode generator; standard data collection and processing
procedures were followed.
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7 P. A. Gale, J. Garric, M. E. Light, B. A. McNally and B. D. Smith,
Chem. Commun., 2007, 1736–1738.
8 S. O. Kang, D. Powell and K. Bowman-James, J. Am. Chem. Soc., 2005,
127, 13478–13479.
9 P. A. Gale, S. E. Garc´ıa-Garrido and J. Garric, Chem. Soc. Rev., 2008,
37, 151–190.
10 S.-K. Chang, D. van Engen, E. Fan and A. D. Hamilton, J. Am. Chem.
Soc., 1991, 113, 7640–7645.
11 M. G. Fisher, P. A. Gale and M. E. Light, New J. Chem., 2007, 31,
1583–1584.
12 P. A. Gale, S. Camiolo, G. J. Tizzard, C. P. Chapman, M. E. Light, S. J.
Coles and M. B. Hursthouse, J. Org. Chem., 2001, 66, 7849–7853.
13 P. A. Gale, Chem. Commun., 2005, 3761–3772; P. A. Gale, M. E. Light,
B. McNally, K. Navakhun, K. E. Sliwinski and B. D. Smith, Chem.
Commun., 2005, 3773–3775.
14 P. A. Gale, Acc. Chem. Res., 2006, 39, 465–475.
15 S. Camiolo, P. A. Gale, M. B. Hursthouse, M. E. Light and A. J. Shi,
Chem. Commun., 2002, 758–759.
16 P. A. Gale, K. Navakhun, S. Camiolo, M. E. Light and M. B.
Hursthouse, J. Am. Chem. Soc., 2002, 124, 11228–11229.
17 S. Camiolo, P. A. Gale, M. B. Hursthouse and M. E. Light, Org. Biomol.
Chem., 2003, 1, 741–744.
18 M. P. Cava and M. I. Levinson, Tetrahedron, 1985, 41, 5061–5087;
the IUPAC name of Lawesson’s reagent is 2,4-bis(4-methoxyphenyl)-
1,3,2,4-dithiadiphosphetane-2,4-disulfide (C14H14O2P2S4).
19 C. J. Medforth, M. O. Senge, K. M. Smith, L. D. Sparks and J. A.
Shelnutt, J. Am. Chem. Soc., 1992, 114, 9859–9869.
20 M. Friedman, J. Org. Chem., 1965, 30, 859–863.
21 J. Jurczak and T. Zielinski, Tetrahedron, 2005, 61, 4081–4089.
22 A. N. Dwyer, M. C. Grossel and P. N. Horton, Supramol. Chem., 2004,
16, 405–410.
23 J. L. Bricks, G. Reck, K. Rurack, B. Schulz and M. Spieles, Supramol.
Chem., 2003, 15, 189–197.
24 M. Ray, D. Ghosh, Z. Shirin and R. Mukherjee, Inorg. Chem., 1997,
36, 3568–3572.
Fig. 9 The helical cobalt(III) complex formed by the reaction of cobalt(II)
with receptor 5.
cobalt, and further work is under way to explore these effects in
more detail.
25 A. K. Patra and R. Mukherjee, Inorg. Chem., 1999, 38, 1388–1393.
26 R. Kapoor, A. Pathak, P. Kapoor and P. Venugopalan, Polyhedron,
2006, 25, 31–38.
Acknowledgements
27 R. Kapoor, A. Kataria, P. Venugopalan, P. Kapoor, G. Hundal and M.
Corbella, Eur. J. Inorg. Chem., 2005, 3884–3893; for a recent account
of palladium complexes of a pyridine-2,6-dithiocarboxamide (which in
some cases form imines due to deprotonation the thioamide groups)
see: R. A. Begum, D. Powell and K. Bowman-James, Inorg. Chem.,
2006, 45, 964–966.
PAG thanks the EPSRC for support (CNW and GWB) and the
EPSRC together with Professor Mike Hursthouse for access to
the crystallographic facilities at the University of Southampton.
The authors gratefully acknowledge the help of Professor William
Clegg of the synchrotron component of the EPSRC National
Crystallography Service for data collection.
28 H. J. Kruger and R. H. Holm, J. Am. Chem. Soc., 1990, 112, 2955–
2963.
29 E. C. Constable, Tetrahedron, 1992, 48, 10013–10059.
30 S. L. Jain, P. Bhattacharyya, H. L. Milton, A. M. Z. Slawin, J. A.
Crayston and J. D. Woollins, Dalton Trans., 2004, 862–871.
31 D. S. Marlin, M. M. Olmstead and P. K. Mascharak, Inorg. Chem.,
1999, 38, 3258–3260.
32 D. S. Marlin, M. M. Olmstead and P. K. Mascharak, Inorg. Chim. Acta,
2001, 323, 1–4.
33 J. M. Rowland, M. M. Olmstead and P. K. Mascharak, Inorg. Chem.,
2002, 41, 2754–2760.
34 S. R. Zhu, W. W. Brennessel, R. G. Harrison and L. Que, Inorg. Chim.
Acta, 2002, 337, 32–38.
Notes and references
1 R. K. Afshar, R. Bhalla, J. M. Rowland, M. M. Olmstead and P. K.
Mascharak, Inorg. Chim. Acta, 2006, 359, 4105–4113.
2 N. W. Alcock, G. Clarkson, P. B. Glover, G. A. Lawrance, P. Moore
and M. Napitupulu, Dalton Trans., 2005, 518–527.
3 S. Hazra, S. Naskar, D. Mishra, S. I. Gorelsky, H. M. Figgie, W. S.
Sheldrick and S. K. Chattopadhyay, Dalton Trans., 2007, 4143–4148.
4 A. K. Singh and R. Mukherjee, Inorg. Chim. Acta, 2007, 360, 3456–
3461.
35 R. J. Cernik, W. Clegg, C. R. A. Catlow, G. Bushnell-Wye, J. V. Flaherty,
G. N. Greaves, M. Hamichi, I. Burrows, D. J. Taylor and S. J. Teat,
J. Synchrotron Radiat., 1997, 4, 279–286.
5 F. H. Allen, Acta Crystallogr., Sect. B: Struct. Sci., 2002, 58, 380–388.
6 K. Kavallieratos, C. M. Bertao and R. H. Crabtree, J. Org. Chem., 1999,
64, 1675–1683.
36 W. J. Clegg, J. Chem. Soc., Dalton Trans., 2000, 3223–3232.
4112 | Dalton Trans., 2008, 4106–4112
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The Royal Society of Chemistry 2008
©