Halogenido and pseudohalogenido complexes of (2,3,7,8,12,13,17,18- octaethyl-5,15-di-p-tolylcorrolato)manganese(IV)

Article abstract of DOI:10.1002/zaac.200700058

A set of porphyrinoid manganese(IV) complexes with the 2,3,7,8,12,13,17,18- octaethyl-5,15-di-p-tolylcorrolato ligand [(oedtc)Mn^IVX] (X = Cl, Br, I) was prepared by oxidation of a manganese(III) precursor. The most unexpected complex in this series, [(oedtc)Mn^IVI], was found to display significant thermal stability despite the unusual Mn^IV-I bond and could be investigated by X-ray diffraction. Attempted ligand exchange reactions of the chlorido derivative with the pseudohalide anions cyanide, azide, cyanate and thiocyanate yielded the desired [(oedtc)Mn^IVX] complex only as the isothiocyanate derivative while for the other species the reduction to manganese(III) was observed.

Full text of DOI:10.1002/zaac.200700058

DOI: 10.1002/zaac.200700058
Halogenido and Pseudohalogenido Complexes of (2,3,7,8,12,13,17,18-Octaethyl-
5,15-di-p-tolylcorrolato)manganese(IV)
Martin Bröring*, Christian Hell, Melanie Steiner, and Carsten D. Brandt
Marburg, Fachbereich Chemie der Philipps-Universität
Received January 26th, 2007.
Abstract. A set of porphyrinoid manganese(IV) complexes with
the 2,3,7,8,12,13,17,18-octaethyl-5,15-di-p-tolylcorrolato ligand
[(oedtc)MnIVX] (X ϭ Cl, Br, I) was prepared by oxidation of a
manganese(III) precursor. The most unexpected complex in this
series, [(oedtc)MnIVI], was found to display significant thermal sta-
bility despite the unusual MnIV-I bond and could be investigated
by X-ray diffraction. Attempted ligand exchange reactions of the
chlorido derivative with the pseudohalide anions cyanide, azide,
cyanate and thiocyanate yielded the desired [(oedtc)MnIVX] com-
plex only as the isothiocyanate derivative while for the other species
the reduction to manganese(III) was observed.
Keywords: Manganese; High valence; Corrole ligands; Crystal
structures; Porphyrinoids
Scheme 1 Synthesis of manganese(III) corrole (2) by the action of MnII and molecular dioxygen on 2,2Ј-bidipyrrin (1).
Introduction
One such ligand capable of stabilizing high oxidation
states is the tetrapyrrolic macrocycle corrole, which deviates
from the parent porphyrin by the formal loss of one meth-
ine carbon atom [4]. Corroles have often been employed in
recent years in order to stabilize unusually high oxidation
states of manganese like ϩ5 [2(b), 5] and even ϩ6 [6]. As
we could show earlier manganese(III) corroles like 2 are
formed in an oxidative macrocyclization reaction upon
treatment of the open-chain tetrapyrrole 2,2Ј-bidipyrrin (1)
with Mn(OAc)2 and molecular dioxygen in reasonable
yields (scheme 1) [7]. We have now used 2 as a precursor
in order to investigate the accessibility of halogenido and
pseudohalogenido complexes of tetravalent manganese in a
corrole environment and present here the results from our
study.
A well-established reaction of the halogenide anions ClϪ,
BrϪ and IϪ is their ready oxidation to the corresponding
diatomic halogenes and beyond upon contact with MnIV
and other high-valent manganese species. The oxidative
power of a Mn ion, however, can easily be tuned by binding
it to a suitable ligand, and several isolable chlorido- and
even bromido complexes of manganese in higher oxidation
states have been obtained in the past by this approach [1,
2]. In order to prepare iodido- and pseudohalogenidoman-
ganese(IV) species an even larger degree of stabilization of
the high oxidation state at the metal atom would be re-
quired. However, suitable ligands for this purpose are rare,
and to the best of our knowledge examples of stable com-
pounds of this class have not appeared in the scientific
literature so far [3].
Results and Discussion
The manganese(III) ion in corrolato complexes is very
prone to oxidation [2, 7] and can easily be transformed to
the ϩ4 oxidation state by e.g. chromatography on silica
with dichloromethane in air. In a more controlled fashion
the treatment of [(oedtc)MnIII] (2) with dilute hydrochloric
acid and air in the biphasic system water/dichloromethane
* Prof. Dr. Martin Bröring
Fachbereich Chemie, Philipps-Universität Marburg
Hans-Meerwein-Straße
D-35043 Marburg/Germany
Fax: int. (0)6421 2825356
E-mail: Martin.Broering@chemie.uni-marburg.de
1082
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Halogenido and Pseudohalogenido Complexes of Octaethyl-5,15-di-p-tolylcorrolato)manganese(IV)
Scheme 2 Preparation of halogenidomanganese(IV) corroles (3-5) by oxidation of manganese(III)corrole (2) with HCl/air, HBr/air or
molecular iodine, respectively.
Table 1 Selected metrical parameters of halogenidomanganese
corroles and porphyrins.
a
b
˚
˚
compound
Mn-X /A
Mn-Ct(N4) /A
N-Mn-X /°
[(oec)MnIVCl] [2(a)]
[(tpfc)MnIVCl] [2(b)]
[(tpfc)MnIVBr] [2(b)]
[(oedtc)MnIVI] (5)
[(tpp)MnIIII] [8]
2.310
2.312
2.428
2.6332/2.6461
2.767/2.730
0.437
0.43
0.42
0.3615/0.3667
0.240/0.251
103.42
102.93
102.45
100.60/100.98
96.31/96.88
a Distance of the Mn ion from the mean plane of the four N atoms.
b Mean value.
the methyl groups C32/C32Ј of molecule A is disordered
over two positions with occupancy factors of 0.683 and
0.317. Figure 1 shows the molecular structure of 5 (mol-
ecule A) and summarizes selected data.
Fig. 1 Molecular structure of molecule A of 5.
˚
Selected bond lengths /A and -angles /° for molecule A [data in square
brackets: equivalent positions of molecule B]: Mn-I 2.6332(8) [2.6461(8)],
Mn-N1 1.930(4) [1.939(4)], Mn-N2 1.922(4) [1.926(3)], Mn-N3 1.914(4)
[1.921(4)], Mn-N4 1.947(4) [1.942(4)]; N1-Mn-I 103.69(12) [101.04(11)], N2-
Mn-I 97.37(13) [102.65(11)], N3-Mn-I 97.50(12) [100.61(11)], N4-Mn-I
103.80(12) [99.62(11)], N1-Mn-N2 87.9(2) [88.5(2)], N1-Mn-N3 157.3(2)
[157.0(2)], N1-Mn-N4 94.4(2) [95.7(2)], N2-Mn-N3 81.3(2) [79.4(2)], N2-Mn-
N4 157.5(2) [156.1(2)], N3-Mn-N4 88.4(2) [88.2(2)].
The iodido ligand is bound to the manganese(IV) atom
˚
in a distance of 2.6332(8) and 2.6461(8) A for molecules A
and B, respectively. As expected these values are smaller
than those found in a related case for a manganese(III)
˚
tetraphenylporphyrin [(tpp)MnI] with 2.767 A [8]. The Mn-
˚
cleanly yields the chloridomanganese(IV) derivative 3 in an
isolated yield of 98 %. The bromido species 4 is obtained in
an analogous fashion and again in close to quantitative
yield upon the use of dilute hydrobromic acid (scheme 2).
The reaction of the MnIII chelate 2 with a slight excess
of molecular iodine in dichloromethane results in a clean,
though unexpected transformation to the iodidomangane-
se(IV)corrole (5) which is isolated in 95 % yield. The same
complex was obtained from an attempt to arylate the chlor-
ido derivative 3 with phenylmagnesium iodide. Thermally,
3-5 are surprisingly stable and decompose only above
240 °C, even in the iodido case. The presence of the halog-
enido ligands was confirmed by combustion analyses, while
the mass spectra of the three compounds only produced
one major signal at m/z ϭ 754 that can be assigned to the
[M-X]ϩ ion in all cases.
N bond lengths are found from 1.914 to 1.947 A with the
bonds to the N atoms of the bipyrrole fragment being
shorter than the other ones. The average Mn-N bond length
˚
of 1.928 and 1.932 A, however, are very similar to those
˚
found for two chlorido- (1.932 and 1.934 A) and the one
˚
bromidomanganese(IV) corrole (1.925 A) [3] which had
been structurally characterized before. The manganese
˚
atom of 5 is displaced 0.3615(8) and 0.3667(7) A from the
least-squares plane formed by the pyrrole nitrogen atoms
and displays a domed square-pyramidal coordination.
These displacement values are much larger than in the
MnIII case of [(tpp)MnI], but resemble roughly those found
in other halogenidomanganese(IV) corroles (table 1), for
which only insignificantly smaller value have been reported.
The high degree of substitution Ϫ ten out of eleven posi-
tions of the corrole ligand of 5 carry alkyl- or aryl substitu-
ents Ϫ does not influence the macrocycle conformation to
a measurable amount. Almost planar tetrapyrroles are
found with deviations of single atoms of the C19N4
perimeters from the mean plane of a maximum of
A suitable crystal for a X-ray diffraction study was ob-
tained from [(oedtc)MnI] (5) by slow evaporation of a satu-
rated solution of the compound in a dichloromethane/n-
hexane mixture. 5 crystallizes in the triclinic system, space
˚
¯
group P1, with four formula units in the unit cell. Two dis-
0.282(6) A. The steric congestion is however visible in the
tinct molecules A and B are present in the crystal. One of
conformation of the tolyl substituents which are rotated by
Z. Anorg. Allg. Chem. 2007, 1082Ϫ1086
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1083

M. Bröring, Ch. Hell, M. Steiner, C. D. Brandt
might be responsible for the tilted I1 binding. The obser-
vation can in fact be fully explained by a sterical argument,
i.e. a generic packing effect. As can be seen in figure 2 (top)
two methylene groups C70 and C98 of an adjacent molecule
˚
come as close as 3.847 and 3.929 A to the iodo atom I1 of
molecule A and displace it from the expected equilibrium
site. The methyl group C32 is situated in juxtaposition with
˚
a very small C···I distance of only 3.785 A but reduces the
sterical strain in part by a positional disorder of about
30 %. A different scenario is observed for the iodido ligand
I2 of molecule B (figure 2, bottom). In this case only weaker
contacts are found to one CH moiety and the CH3 group
of the tolyl substituent of a neighbor molecule which are
oriented in such a way that a displacement of the iodo atom
is not supported.
The successful stabilization of an iodido ligand on a high-
valent manganese ion by use of a corrole visitor ligand casts
promise on the availability of further stable complexes with
hitherto unexplored bonding situations. Attempted ligand
exchange reactions of [(oedtc)MnCl] (3) with the pseudo-
halogenide salts KCN, NaN3, KOCN or KSCN, however,
show the limitations of the stabilization concept. Only for
the latter case an isolable compound [(oedtc)MnNCS] (6)
was obtained, while for the other cases the reduction to
MnIII is observed (scheme 3). Although the formation of a
nitridomanganese(V) species was described before for the
action of azide ions onto a manganese(IV) corrole with ir-
radiation [2(a)], an analogous product has not been found
in our experiment. 6 was analyzed by combustion analysis.
As for 3Ϫ5 mass spectra of 6 showed the (oedtc)Mn frag-
ment at m/z ϭ 754 only. The end-on binding mode of the
NCS ligand via the N atom was derived from the IR spec-
Fig. 2 Short CHx···I contacts and differences in the tilt of the
iodido ligand in molecules A (I1, top) and B (I2, bottom) of 5,
promoted by packing forces. Selected C···I distances /A: C32···I1
˚
3.785, C70···I1 3.847, C98···I1 3.929, C78···I2 4.037, C80···I2 3.960.
trum of 6, which shows a strong absorption at 2066 cmϪ1
.
For a S-bonded species a value below 2050 cmϪ1 could be
expected, while for bridging µ-SCN ligands typically wave-
numbers above 2080 cmϪ1 are observed [9]. Unfortunately,
6 crystallizes in needles which were not suited for a X-ray
crystallographic determination of the molecular structure.
In summary we have described the preparation and sta-
bility for a series of halogenido and pseudohalogenidoman-
ganese(IV) complexes including structural details for an un-
usual iodidomanganese(IV) complex and shown, that the
concept of “stabilizing high oxidation states” can apply not
only for the metal ion in question, but to some extent also
for the stability of redox sensitive co-ligands.
68.9(4)°, 88.3(3)° (molecule A), 75.8(2)° and 85.5(2)°
(molecule B) with respect to the C5,C14,C19 plane, so that
the three aromatic moieties of 5 are in almost orthogonal
arrangements throughout.
A prominent feature of the angles within the MnN4I co-
ordination unit of 5-A is the tilt of the iodido ligand of
about 3° towards the bipyrrolic subunit of the corrole li-
gand. Since the shorter Mn-N distances are also found in
this direction it seems reasonable to discuss attractive I···N
contacts by secondary interactions at this site. The compari-
son with the metrics of molecule B, however, shows that a
similar tilt is not present for I2, and that a different effect
Scheme 3 Ligand exchange experiments of [(oedtc)MnCl] (3) with pseudohalide anions.
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Z. Anorg. Allg. Chem. 2007, 1082Ϫ1086

Halogenido and Pseudohalogenido Complexes of Octaethyl-5,15-di-p-tolylcorrolato)manganese(IV)
Ϫ M.p. 188 °C (decomp.). Ϫ Anal. calc. for C50H55N5MnS: C
Experimental Section
73.87, H 6.82, N 8.61 %; found C 73.82, H 7.06, N 8.49 %. Ϫ IR
Materials and Methods: [(oedtc)MnIII] (2) was prepared according
to a published procedure [7]. All other chemicals were purchased
from Aldrich or Merck and were used without further purification.
Solvents were dried by standard procedures and distilled from ap-
propriate drying agents. Melting points were determined in open
capillaries and are uncorrected. EI mass spectra were measured on
a Finnigan 90 MAT instrument. m/z values are given for the most
abundant isotopes only. The IR spectrum of 6 was recorded in
Nujol paste on a Bruker Vector 22.
(Nujol): ν ϭ 2066 cmϪ1. Ϫ MS (EI): m/z 754 ([M-NCS]ϩ).
Collection and Reduction of X-ray Data
A single crystal of 5 was mounted on the tip of a glass capillary
using perfluoropolyether oil. Intensity data was collected at
173(2) K, using a Bruker Smart Apex X-ray diffractometer with
D8 goniometer. Graphite monochromated Mo KͰ radiation
˚
(0.71073 A) was used. The structure was solved by the Patterson
method with SHELXS-97 [10]. Refinements were carried out by
full-matrix least-squares techniques against F2 using SHELXL-97
[11]. All non-hydrogen atoms were refined anisotropically. Hydro-
gen atoms were assigned to idealized positions. Crystallographic
data (excluding structure factors) for the structures reported in this
paper has been deposited with the Cambridge Crystallographic
Data Centre as supplementary publication no. CCDC-634833.
Copies of the data can be obtained free of charge on application
to CCDC, 12 Union Road, Cambridge CB2 1EZ, UK [Fax:
ϩ44(1223) 336-033; E-mail: deposit@cam.ac.uk].
Chlorido(2,3,7,8,12,13,17,18-octaethyl-5,15-di-p-
tolylcorrolato)manganese(IV)
[(oedtc)MnCl] (3). Manganese(III)corrole (2) (75.4 mg, 0.1 mmol),
dichloromethane (100 mL) and hydrochloric acid (10 mL of a
0.1 mol/L solution in water) are stirred open to air for 4 hours. The
organic layer is separated, dried with sodium sulfate, filtered and
reduced in vacuo to 10 mL. The title compound is obtained after
addition of n-hexane (50 mL) as a violet-black powder. Yield:
77 mg (98 %). Ϫ M.p. 297 °C (decomp.). Ϫ Anal. calc. for
C49H55N4MnCl: C 74.46, H 7.01, N 7.09 %; found C 74.68, H 7.16,
N 6.88 %. Ϫ MS (EI): m/z 754 ([M-Cl]ϩ).
Crystal data for 5: C49H55IMnN4, 881.29, triclinic, space group
˚
¯
P1, a ϭ 11.3053(9), b ϭ 17.8890(14), c ϭ 22.8437(18) A, Ͱ ϭ
3
˚
94.955(1)°, β ϭ 101.952(1)°, γ ϭ 106.038(1)°, V ϭ 4292.9(6) A ,
Z ϭ 4, ρcalc ϭ 1.364 g cmϪ3, µ(Mo-Kα) ϭ 11.44 cmϪ1, θmin ϭ 0.92°,
θmax ϭ 25.35°, 64172 reflections measured, 15701 independent,
13907 observed with I > 2σ(I), 1022 parameters, 3 restraints, R1
(all data) ϭ 0.0729, wR2 (all data) ϭ 0.1351, max./min. peak ϭ
Bromido(2,3,7,8,12,13,17,18-octaethyl-5,15-di-p-
tolylcorrolato)manganese(IV)
Ϫ3
˚
1.578/Ϫ0.806 eA
.
[(oedtc)MnBr] (4). Manganese(III)corrole (2) (75.4 mg, 0.1 mmol),
bromoform (100 mL) and hydrobromic acid (10 mL of a 0.1 mol/
L solution in water) are stirred open to air for 24 hours. The or-
ganic layer is separated, dried with sodium sulfate, filtered and re-
duced in vacuo to 10 mL. The title compound is obtained after
addition of n-hexane (50 mL) as a violet-black powder. Yield:
82 mg (99 %). Ϫ M.p. 242 °C (decomp.). Ϫ Anal. calc. for
C49H55N4MnBr: C 70.50, H 6.64, N 6.71 %; found C 70.69, H 6.45,
N 6.90 %. Ϫ MS (EI): m/z 754 ([M-Br]ϩ).
Acknowledgements. We gratefully acknowledge financial support
for this work by the Deutsche Forschungsgemeinschaft (DFG).
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Iodido(2,3,7,8,12,13,17,18-octaethyl-5,15-di-p-
tolylcorrolato)manganese(IV)
[(oedtc)MnI] (5). Manganese(III)corrole (2) (75.4 mg, 0.1 mmol),
iodine (13 mg, 0.055 mmol) and dichloromethane (100 mL) are
stirred open to air for 2 hours. The solution is reduced in vacuo to
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(50 mL) as violet blocks. Yield: 84 mg (95 %). Ϫ M.p. 249 °C (de-
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6.35 %; found C 67.00, H 6.43, N 6.27 %. Ϫ MS (EI): m/z 754
([M-I]ϩ).
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[(oedtc)MnNCS] (6). Chloridomanganese(IV)corrole (3) (79.0 mg,
0.1 mmol), dichloromethane (25 mL) and a solution of potassium
thiocyanate (250 mg) in water (25 mL) are stirred for 24 hours. The
organic layer is separated, dried with sodium sulfate, filtered and
reduced in vacuo to 10 ml. The title compound is obtained after
filtration on silica with dichloromethane and recrystallization from
dichloromethane/n-hexane as a green needles. Yield: 81 mg (94 %).
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Z. Anorg. Allg. Chem. 2007, 1082Ϫ1086