New manganese-scaffolded organic triple-deckers based on quinoxaline, pyrazine and pyrimidine cores

Article abstract of DOI:10.1039/b513322j

The thermolytic coupling of Ph₂CN₂ and (t-Bu)(Ph)CN₂ with doubly cyclomanganated 2,5-diphenylpyrazine and 4,6-diphenylpyrimidine afforded substantial amounts of new triple decker compounds of either C_i and C₂ symmetry respectively containing, in both series, two η³-bonded Mn(CO)₃ fragments which intervene as scaffolds sustaining the helical non-conjugated triaryl backbone. The molecular structures of two pyrazine derivatives show a typical non-parallel stacking of the aromatic rings and the encapsulation of the central pyrazyl fragment with interplanar centroid-to-centroid distances of ca. 3.5 . The stacking of the aromatics in the triple-decker pyrimidine derivatives has been assessed by ¹H NMR experiments at low temperature. All the triple-decker-type compounds are electroactive. Pyrimidine triple-deckers can reversibly be electrochemically reduced to the corresponding anions. The Royal Society of Chemistry 2006.

Full text of DOI:10.1039/b513322j

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PAPER
www.rsc.org/dalton | Dalton Transactions
New manganese-scaffolded organic triple-deckers based on quinoxaline,
pyrazine and pyrimidine cores†
Jean-Pierre Djukic,* Christophe Michon, Zoran Ratkovic, Nathalie Kyritsakas-Gruber, Andre´ de Cian and
Michel Pfeffer
Received 20th September 2005, Accepted 23rd November 2005
First published as an Advance Article on the web 14th December 2005
DOI: 10.1039/b513322j
The thermolytic coupling of Ph2CN2 and (t-Bu)(Ph)CN2 with doubly cyclomanganated 2,5-diphenyl-
pyrazine and 4,6-diphenylpyrimidine afforded substantial amounts of new triple decker compounds of
3
either Ci and C2 symmetry respectively containing, in both series, two g -bonded Mn(CO)3 fragments
which intervene as scaffolds sustaining the helical non-conjugated triaryl backbone. The molecular
structures of two pyrazine derivatives show a typical non-parallel stacking of the aromatic rings and
the encapsulation of the central pyrazyl fragment with interplanar centroid-to-centroid distances of
˚
ca. 3.5 A. The stacking of the aromatics in the triple-decker pyrimidine derivatives has been assessed
by 1H NMR experiments at low temperature. All the triple-decker-type compounds are electroactive.
Pyrimidine triple-deckers can reversibly be electrochemically reduced to the corresponding anions.
In a previous report10 it was shown that such an architecture
Introduction
could readily be built by the thermolytic coupling of a pro-helical
bis-cyclomanganated quinoxaline derivative 1a with Ph2CN2 (eqn
(1)) leading to a stable C2 symmetric triple decker architecture
1b encapsulating a quinoxalyl core. The propensity of the latter
to sustain reduction by two successive reversible mono-electron
processes leading to the formation of the corresponding radical-
anion and the dianion has been established.11 Herein, we disclose
some results on the reactivity of various bis-cyclomanganated
quinoxaline, pyrazine and pyrimidine derivatives towards 1-
phenyldiazomethanes, the syntheses of new examples of metallo-
organic triple-decker molecular systems containing pyrazyl or
pyrimidyl heterocyclic cores and a preliminary study of their
electrochemical properties in reductive conditions.
It is well established that diaza-heterocycles, also known as
“diazines”, display a reasonable electron affinity, which stems
from their low lying vacant p-orbitals.1 This intrinsic property is
the base for the elaboration of electron transporting polymers2
intended to be used in organic semi-conducting devices. Even
though diazines can readily be converted to their parent radical-
anion, upon thorough chemical or electrochemical reductions in
aprotic solvents with more than one electron per molecule the
corresponding anions often collapse by intra- or inter-molecular
carbon–carbon coupling reactions.3 Diazines are convenient elec-
tron transfer mediators or radical traps,4 photo-initiators in
radical polymerization,5 and can be readily reduced by various
means and converted to their hydro analogs.6 p-Radical anions
of diazines tend to form charged diaromatic clusters with their
neutral parent.7
Even though coordination of the heterocyclic nitrogen atoms
to transition metals may result in an increase of the cathodic
reduction potentials and stable ligand-centered radical anions,8
highly reduced species are generally unstable and subject to ECE
processes that lead to de-coordination or ligand alteration.9 This
drawback should a priori disqualify electro-generated diazine p-
radicals as efficient spin-carriers. A reasonable solution could
reside in the elaboration of an “electron nest-type” architecture in
which the spin density generated at an aromatic diazine core would
be protected from external chemical interactions by encapsulation
within a rigid and relatively electrochemically inert structure.
(1)
Results and discussion
Bis-cyclomanganated quinoxaline, pyrazine and pyrimidine
derivatives, viz. 1a–4a and 6a (vide infra) were investigated for their
ability to undergo coupling reactions with aryldiazomethanes with
the aim of synthesizing new triple-decker systems with different
heterocyclic cores. In all cases the coupling reactions were carried
out in boiling solvents with a sufficient excess of diazoalkane
in order to compensate its decomposition, which takes place
unavoidably at high temperatures. Two aryldiazomethanes were
used in this study; 1,1-diphenyldiazomethane and 1-tert-butyl-1-
phenyldiazomethane.
Institut de Chimie de Strasbourg, UMR 7177, Laboratoire de Synthe`ses
Me´tallo-Induites, Universite´ Louis Pasteur, 4, rue Blaise Pascal, F-67000,
Strasbourg, France. E-mail: djukic@chimie.u-strasbg.fr; Fax: 33 (0) 390 24
50 01; Tel: 33 (0) 390 24 15 23
† Electronic supplementary information (ESI) available: Detailed experi-
mental procedures, analytical data, voltammograms and electrospray MS
spectra, tables of acquisition and refinement data. See DOI: 10.1039/
b513322j
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(2)
Triple deckers
We first set out to check the degree of stereoselectivity attainable
by coupling a non symmetric diazoalkane such as (t-Bu)(Ph)CN2
using 1a as a model substrate. Indeed, the insertion of the pro-
chiral diazoalkane (t-Bu)(Ph)CN2 into the two C-Mn bonds of
the substrate should give rise to two stereogenic centres, allowing
in principle the formation of three stereo-isomers containing either
the two t-Bu groups in an endo:endo, exo:endo or/and in an exo:exo
position. The treatment of 1a with an excess of (t-Bu)(Ph)CN2 in
refluxing toluene afforded a single product 1c in 45% yield after
chromatographic purification (eqn (2)), of which the structure
corresponds to the exo-exo t-Bu stereochemistry proposal. This
blue-colored compound was crystallized and analyzed by X-ray
diffraction analysis. Fig. 1 displays an ORTEP diagram of 1c,
which shows clearly that the double anti insertion of the carbene
moiety (t-Bu)(Ph)C: is controlled by steric factors that favor the
orientation of the less sterically encumbering substituent, e.g. the
phenyl group, in the endo position, leading to a triple-decker
arrangement akin to that noticed with 1b.11
Fig. 1 ORTEP diagram of compound 1c drawn at 30% probability level.
Hydrogen atoms and solvation molecule have been omitted for the sake
◦
˚
of clarity. Selected interatomic distances (A) and angles ( ): Mn(1)–N(1)
2.042(2), Mn(1)–C(21) 2.208(3), Mn(1)–C(20) 2.219(3), Mn(1)–C(15)
˚
2.283(3); C(21)–Mn–C(3) 94.4(1). Distance (A) between centroids
(C(22)–C(27))–(quinoxalyl): 3.396(6). Torsion angle (◦): C(13)–C(14)–
C(15)–C(16) 47.2, C(14)–C(13)–C(32)–C(33) 46.1. Interplanar angle (◦):
(phenyl)–(quinoxalyl): 28.
(3)
Pyrazine derivative 2a reacted cleanly with excesses of both
Ph2CN2 and (t-Bu)(Ph)CN2 in boiling mixtures of n-heptane
and toluene affording the corresponding products 2b and 2c,
respectively, in 67 and 61% yield (eqn (3)). The stereochemistry
of complex 2c and particularly the positions of the phenyl and
tert-butyl groups were assessed by X-ray diffraction analysis. An
ORTEP diagram of the structure of compound 2c is displayed
in Fig. 2. Again in this case the (t-Bu)(Ph)C moiety inserts in a
stereoselective way to yield a triple-decker arrangement.
Fig. 2 ORTEP diagram of compound 2c drawn at 30% probability level.
Hydrogen atoms and solvation molecule have been omitted for the sake
◦
˚
of clarity. Selected inter-atomic distances (A) and angles ( ): Mn(1)–
N(1) 2.045(8), Mn(1)–C(10) 2.197(9), Mn(1)–C(4) 2.23(1), Mn(1)–C(9)
˚
2.363(9); C(10)–Mn–C(3) 95.2(4). Distance (A) between centroids (C(15)–
C(20))–(pyrazyl): 3.445(9). Torsion angles (◦): N(1)–C(21)–C(9)–C(4)
54.1, C(21)–C(9)–C(4)–C(10) 9.8, C(9)–C(4)–C(10)–C(15) 49.2, C(4)–
C(10)–C(15)–C(16) 40.9. Interplanar angle (◦): (phenyl)–(pyrazyl): 32.
Due to the presence of a disordered molecule of toluene
surrounded with unassigned residual electron density in the unit
cell of 2b, the refinement of the structure could not be optimized.
However, partial X-ray data confirmed the structural similarity
of 2b with 2c (cf. the CIF provided).
complex 3c, of which the structure was confirmed by 1H NMR and
X-ray diffraction (Fig. 3), triple-decker complex 3d in 18% yield
and complex 3e in 62% yield. The latter seemingly results from a
homolytic hydrogenative mono-demetallation of 3d. An ORTEP
diagram representing the molecular structure of 3e is displayed in
Fig. 4. The triple-decker arrangement of the phenyl and pyrimidyl
rings in 3b and 3d could not be confirmed by X-ray diffraction
analysis due to repeated failure in obtaining suitable crystals.
The reaction of 3a12 with Ph2CN2 in a boiling mixture of n-
heptane and toluene afforded compound 3b in 84% yield after
chromatographic purification (Scheme 1). In contrast, the reaction
of 3a with (t-Bu)(Ph)CN2 proved to be sluggish and afforded a mix-
ture of three complexes (Scheme 1), which were separated by flash
chromatography at low temperature: traces of the double-decker
1
However, H NMR spectroscopy at sub-ambient temperature
provided some clear evidence that the phenyl groups were proximal
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Fig. 4 ORTEP diagram of compound 3e drawn at 30% probability
level. Hydrogen atoms have been omitted for clarity. Selected inter-
˚
atomic distances (A): Mn–N(1) 2.021(2), Mn–C(8) 2.344(5), Mn–C(13)
Scheme 1
˚
2.196(2), Mn–C(14) 2.217(2). Distance (A) between centroids: (pyrim-
idyl)–(C(15)–C(20)): 3.482(5). Torsion angles (◦): C(26)–C(25)–C(5)–C(6)
62.5, N(1)–C(7)–C(8)–C(13) 52.6, C(8)–C(13)–C(14)–C(15) 47.0.
the protons occupying the 5 and the 2 positions at the heterocycle,
respectively.
We set out to probe the reactivity of complex 4a towards
both Ph2CN2 and (t-Bu)(Ph)CN2 having in sight the possible
formation of a triple-decker such as 5 in which we expected the
anti-facial double coordination of the central phenyl group by
two manganese centers sharing the same p-electrons (Scheme 2).
Whereas several attempts to react 4a with Ph2CN2 resulted
essentially in the decomposition of the reagents into intractable
material, an experiment carried out with (t-Bu)(Ph)CN2 resulted in
the formation of four different products in low yields, 4b–e, among
which the latter, 4e, clearly results from the incorporation of two
(t-Bu)(Ph)C: moieties into 4a upon decarbonylation. Compound
Fig. 3 ORTEP diagram of compound 3c drawn at 30% probability level.
Hydrogen atoms have been omitted for clarity. Selected interatomic
˚
distances (A): Mn(1)–C(3) 1.799(3), Mn(1)–C(4) 1.851(3), Mn(1)–N(1)
2.070(2), Mn(1)–C(5) 2.047(3), Mn(1)–C(1) 1.826(3), Mn(1)–C(2)
1.858(3),
Mn(2)–N(2) 2.035(4), Mn(2)–C(15) 2.415(4), Mn(2)–C(20) 2.234(4),
˚
Mn(2)–C(21) 2.206(4). Distance (A) between centroids: (pyrimidyl)–
(C(22)–C(27)): 3.341(4). Torsion angles (◦): C(16)–C(15)–C(13)–C(14)
40.5, N(2)–C(13)–C(15)–C(20) 52.0, C(15)–C(20)–C(21)–C(22) 46.1,
C(20)–C(21)–C(22)–C(23) 39.2.
(endo) to the central pyrimidyl moiety. Indeed, like reported
previously for 1b,11 endo phenyl groups in both 3b and 3d sustain
a strong hindrance to rotation because of their vicinity to the
diazinyl moiety. In the 1H NMR spectrum (500 MHz, 223 K) of 1c,
for example, the five protons of the endo-phenyl groups appeared
as separate signals at d 5.92 (t*), 6.56 (t*), 6.61 (d) 6.73 (d) and
6.92 (t*) ppm. With 3d, at 223 K in deuterated chloroform, all five
protons of the endo-phenyl group were located as five separate and
well resolved signals at d 6.18 (d), 6.82 (t*), 7.00 (d), 7.05 (t*), 7.15
(t*) ppm. A two-dimensional 1H–1H ROESY experiment carried
out at 223 K (500 MHz) indicated that the triplet of the endo-
phenyl group at d 6.82 ppm and the doublet of the same group
at 7.00 ppm correlate “through space” with the two protons of
the pyrimidine group, which show up as singlets at d 4.60 and
7.37 ppm, respectively (cf . ESI†). These two signals are assigned to
Scheme 2
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4e, isolated after chromatographic separation in 14% yield, is
an interesting case of homodinuclear species containing two
Mn(CO)3 moieties bonded to the organic backbone following
two different hapto modes: a g –g benzyl and g -benzylidene
mode. Fig. 5 displays an ORTEP diagram of the latter’s structure.
In the initial stage of the reaction, (t-Bu)(Ph)CN2 reacts with
1
2
4a to give a first g :g -benzylic double-decker intermediate 4b,
which undergoes a second insertion of a (t-Bu)(Ph)C: alkylidene
to yield successively transients A and B. It is likely that the latter
evolves to give 4e rather than 5 because the p-system of the central
phenyl group, which is already involved in a bonding interaction
with one Mn(CO)3 fragment, cannot accommodate a second
electron-demanding Mn(CO)3 group. Compound 4c, which was
recovered in 29% yield, seemingly results from a hydrogenative
mono-demetallation of 4b. Compounds 4d and 4b were recovered
in yields lower than 5% and could only be subjected to limited
analytical characterization.
2
1
5
˚
The C(29)–C(28) bond distance of 1.353(3) A is similar to those
reported for exocyclic double bonds in analogous complexes.13
The structure of 4d was nonetheless established by X-ray
diffraction analysis (Fig. 6). The presence of the hydrazyl moiety
suggests that 4d results from a coupling reaction of 4b with the
=
residual amounts of hydrazone (t-Bu)(Ph)C N–NH2 present in
the sample of (t-Bu)(Ph)CN2 used in the experiment.
Fig. 5 ORTEP diagram of compound 4e drawn at 30% probability
level. Hydrogen atoms have been omitted for clarity. Selected interatomic
˚
distances (A): Mn(1)–N(1) 2.012(2), Mn(1)–C(14) 2.649(4), Mn(1)–C(13)
2.409(4), Mn(1)–C(8) 2.210(2), Mn(1)–C(7) 2.219(2), Mn(2)–C(30)
2.253(3), Mn(2)–C(31) 2.143(3), Mn(2)–C(32) 2.118(3), Mn(2)–C(33)
2.143(2), Mn(2)–C(34) 2.258(3), Mn(2)–C(29) 2.706(4), C(8)–C(9)
1.440(3), C(9)–C(10) 1.356(4), C(10)–C(11), 1.402(4), C(11)–C(12)
1.372(3), C(12)–C(13) 1.444(3), C(13)–C(8) 1.459(3), C(28)–C(29)
1.353(3), C(28)–C(12) 1.503(3). Selected interatomic angles (◦): C(29)–
C(28)–C(12) 118.4(2), C(29)–C(28)–C(35) 124.0(2), C(12)–C(28)–C(35)
116.5(2).
Fig. 6 ORTEP diagram of compound 4d drawn at 30% probability
level. Hydrogen atoms and solvents have been omitted for clarity.
˚
Selected interatomic distances (A): Mn–N(1) 2.019(4), Mn–C(16) 2.279(5),
Worthy to note here, the distance from atom O(5) to the centroid of
the pyrimidyl ring (C(14),N(2),C(17),C(16),C(15),N(1)) amounts
Mn–C(15) 2.227(5), Mn–C(4) 2.228(5), C(15)–C(16) 1.472(7), C(16)–C(17)
1.432(7), C(17)–C(18) 1.377(7), C(18)–C(19) 1.399(8), C(19)–C(20)
1.358(8), C(20)–C(15) 1.429(7), N(3)–N(4) 1.381(6), N(3)–C(17) 1.383(7),
N(4)–C(25) 1.283(7). Selected interatomic angles (◦): C(25)–N(4)–N(3)
116.3(4), N(4)–N(3)–C(17) 119.5(4).
˚
only ca. 2.55 A, suggesting a stabilizing carbonyl–p interaction.
The process leading to the formation of 4e necessarily involves
the haptotropic migration of one Mn(CO)3 moiety accompanied
with a cleavage of the N–Mn bond as proposed in Scheme 3.
Finally, repeated attempts to react either Ph2CN2 or (t-
Bu)(Ph)CN2 with 6a14 in boiling n-hexane were not granted with
success, the experiments producing a large amount of untractable
decomposition material. Upon thorough chromatographic treat-
ment however, a limited amount of compound 6b could be
recovered (eqn (4)). From the spectroscopic point of view, this
benzo-analog of compound 1b presents 1H and 13C NMR features
that support a triple decker molecular arrangement. If one
compares the IR spectra of 1c and 1b11 to that of 6b, it appears
that the C–O stretching bands generated by the Mn(CO)3 scaffold
of the latter appear at frequencies about 7–10 cm−1 higher. This is
a direct consequence of the extension of the p-heterocyclic system
from quinoxalyl to benzo[g]quinoxalyl, which induces a higher
p-accepting ability of the coordinated diazine and reduces the
back-donation of electron density from the Mn centre to the p*
orbitals of the carbonyls.
Scheme 3
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Scheme 4
Preliminary spectroscopic characterizations of radical anion 3b
(4)
Negative mode electrospray mass spectroscopy measurements
carried out with a fresh solution containing [3b]•− afforded a
composite spectrum containing a large signal corresponding to
[3b − H]− and other peaks of higher m/z ratio seemingly resulting
from various products of reaction with the solvent, namely 1,2-
dimethoxyethane (Fig. 7). In the conditions used for the generation
of the radical anion [3b]•−, e.g. by reaction of a solution of 3b with
a potassium mirror, it can be speculated that reactive dianionic
species may coexist in solution and therefore be responsible for the
formation of products of higher molecular weight either before or
during the formation of the sprayed droplets of solution in the
spectrometer’s injection chamber. Interestingly, [1b]−, which was
prepared by the same procedure was analyzed by electrospray mass
spectrometry upon direct injection, producing a clean spectrum
containing exclusively the molecular parent peak with an isotopic
pattern matching ideally the theory (cf. ESI†).
Electrochemical properties of the new triple-deckers
The electrochemical behaviour of 1c, 2b, 2c, 3b, 3d and 6b
was investigated by cyclic voltammetry at room temperature.
Under cathodic reduction conditions, 1c, 3b and 3d displayed two
reversible waves corresponding to the successive formation of the
radical-anions and dianions (Scheme 4), at moderately negative
potentials, well above those measured in similar conditions for the
baremetal-freeheterocycles (Table1), e.g. 2,3-diphenylquinoxaline
(−1.63 V vs. SCE in CH3CN)15 and 4,6-diphenylpyrimidine
(−1.88 V vs. SCE in CH3CN). Further reduction of 3b and
3d at lower potentials revealed a third reversible process, which
was not assigned. At a scan rate of 200 mV s−1 compounds
2b–c displayed a series of three-to-four close reduction waves at
potentials slightly higher than for 2,5-diphenylpyrazine (−1.85 V
vs. SCE in CH3CN) with reverse oxidation waves symptomatic of a
possible fast chemical degradation of the reduced species through
a ECE scheme. Interestingly another pyrazine-based triple-decker
terpenic derivative 816 displayed two relatively distant reversible
reduction waves, the first one occurring at a potential more positive
by 0.8 V than that measured for the metal-free parent pyrazine
ligand 7 (−2.24 V, DEc/a = 186 mV, scan rate 800 mV s−1, MeCN).
A comparison of the reduction potentials of 1b11 and 6b, although
measured in different conditions, gives a good illustration of how
the extension of the p-aromatic system at the central heterocycle
lowers the energy of the LUMOs, which are populated upon
reduction. The two reversible reduction processes measured for
6b occur at potentials about 0.4 V higher than for 1b.
Conclusion
In summary, we have demonstrated that the thermolytic coupling
of two phenyldiazomethanes with two examples of doubly metal-
lated pyrazine and pyrimidine derivatives could afford substantial
amounts of new triple-decker compounds of either C2 (3b and 3d)
or Ci (2b and 2c) symmetry. In all these cases the stereochemical
course of the double insertion of the alkylidene moiety obeyed the
“anti pathway” already observed in the formation of 1b11 and 1c
(this work). With other bis-cyclomanganated diazines, i.e. 4a and
6a, the coupling reaction with diazoalkanes was quite sluggish
and led to complex mixtures or decomposition. As observed
with 1b in a previous report,11 the reduction potentials of the
isolated triple-decker systems are more positive than for the parent
metal free ligands putatively as a consequence of the coordination
of the central heterocycle to the relatively electron-withdrawing
Mn(CO)3 moieties. Unfortunately, the complex electrochemical
behaviour of 2b–c suggests that reductive conditions possibly
induce structural changes and a loss of the triple-decker archi-
tecture. The electro-spray MS investigation of reduced 3b has
casted some doubt on the chemical inertness of the corresponding
anions. Thorough EPR spectroscopic investigations coupled with
Table 1 Reduction potentials measured at room temperature with 10−4 M solutions in the presence of ferrocene as the internal reference. Potentials were
extrapolated against the standard calomel electrode
1c
2b
2c
3b
3d
6b
8
Solvente
MeCN
400
THF
50
−1.42 (113)
−1.60 (104)b
−2.04 (119)b
THF
50
−1.22 (95)
−1.48 (95)b
−1.72 (115)b
−2.09 (180)b
MeCN
200
−1.24 (42)
−1.52 (86)
−1.91 (248)b
MeCN
200
−1.36 (87)
−1.57 (115)
−1.97 (247)b
DMF
80
MeCN
100
Scan ratea
c
d
E1/2 (DEc/a
)
−1.02 (71)
−0.59 (104)
−1.41 (76)
−1.80 (183)b
−1.44 (80)
−1.77 (70)
a In mV s−1
tetrahydrofurane, MeCN acetonitrile.
.
b Delayed reverse oxidation due uncompensated resistance. c In V. d |Ec − Ea| in mV. e Abbreviations: DMF dimethylformamide, THF
1568 | Dalton Trans., 2006, 1564–1573
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to published procedures. Chromatographic separations were per-
formed at sub-ambient temperatures with a Merck Geduran silica
(Si 60, 40–60 lm) in columns packed in n-hexane or n-pentane
with a maximum positive argon pressure of 0.5 bar. In special
cases, separations required the use of deactivated silica prepared
by suspending 200 g of SiO2 in a mixture of distilled acetone and
water (4 wt%); the resulting silica gel was washed with 200 mL of
n-hexane and briefly dried under reduced pressure prior to use.
Procedure for X-ray diffraction analyses and structure resolution
Acquisition and processing parameters are displayed in Table 2.
Reflections were collected with a Nonius KappaCCD diffrac-
tometer using Mo-Ka graphite-monochromated radiation (k =
˚
0.71073 A). The structures were solved using direct methods and
were refined against |F| and for all pertaining computations, the
Nonius OpenMoleN package was used.20 Hydrogen atoms were
introduced as fixed contributors.
CCDC reference numbers 284341–284346.
For crystallographic data in CIF or other electronic format see
DOI: 10.1039/b513322j
Electrochemical measurements
All measurements were made at room temperature, under an
atmosphere of dry argon with a Princeton Applied Research
273 (Model 270/250) potentiostat computer-controlled with
the EGCS Research Electrochemistry software v. 4.23. Tetra-n-
butylammonium hexafluorophosphate was used as the electrolyte
in solution in dry solvents saturated with argon (0.1 M, CH3CN,
DMF, DME, THF) and was generally dried under vacuum
two days at 70 ◦C before use. Cyclic voltammetry experiments
were carried out using an undivided cell comprising a three
electrode system: a Pt-bead or carbon-paste work electrode (2 mm
diameter), a Pt wire of 1 mm diameter as the counter electrode
and, due to the sensitivity of the reduced species to water, a
silver wire of 1 mm diameter as the pseudo-reference electrode.
All potentials were referenced against the ferrocenium–ferrocene
(Fc+/Fc) couple and subsequently extrapolated against standard
saturated calomel electrode (SCE).
Fig. 7 Negative mode electro-spray mass spectra obtained upon direct
injection of samples of 3b (a) and 1b (b) upon preliminary reduction over
a potassium mirror in 1,2-dimethoxyethane at room temperature.
the theoretical determination of the electronic structure of the
radical anions are underway in order to evaluate the extent and
the consequences of the possible geometrical distortions of the
triple-decker architectures. Our current efforts are also focussing
on evaluating the most reliable and suitable manganese-scaffolded
triple-decker systems for a use as electron hosts in spin carriers.
Experimental
Syntheses
All experiments were carried out under a dry atmosphere of argon
with dry and degassed solvents. NMR spectra were acquired
General procedure for the synthesis of bis-cyclomanganated
arenes. The ligand and PhCH2Mn(CO)5 were dissolved in a
mixture of n-heptane and toluene and the resulting solution was
heated to reflux under a gentle stream of argon during 8 h.
The solvents were evaporated, the resulting residue was dissolved
in dichloromethane and SiO2 was added. The suspension was
stripped of solvent under reduced pressure and the coated silica
gel was loaded on the top of a refrigerated SiO2 column packed in
n-hexane or n-pentane.
1
on Bruker DRX 500, AV 400 (13C and H nuclei) and AV 300
(1H nucleus) spectrometers at room temperature unless otherwise
stated. Chemical shifts are reported in parts per million downfield
of Me4Si and coupling constant are expressed in Hz. IR spectra
were measured with a Perkin-Elmer FT spectrometer. Mass
spectra were recorded at the Service of Mass Spectrometry of
University Louis Pasteur (FAB+ and ES) and at the Analytical
Center of the Chemical Institute of the University of Bonn (EI).
Electrospray MS measurements were carried out in the negative
polarity mode with a MicroTOF Bruker spectrometer. Elemental
analyses (reported in mass%) were performed at the Service
d’Analyses of the “Institut de Chimie de Strasbourg” and at the an-
alytical center of the “Institut Charles Sadron” in Strasbourg. 2,5-
Diphenylpyrazine,17 3a, 4a, 6a, 1,1-diphenyldiazomethane18 and
1-phenyl-1-tert-butyldiazomethane19 were synthesized according
[2,5-(Diphenyl-jC2ꢀ ,jC2ꢀꢀ )]pyrazine-(jN1,jN2)bis(tetracarbonyl-
manganese(I)), 2a. 2,5-Diphenylpyrazine (0.5 g, 2.2 mmol) was
mixed with PhCH2Mn(CO)5 (1.85 g, 6.5 mmol), n-heptane (10 mL)
and toluene (10 mL) were added and the resulting mixture was
refluxed for 9 h. Silica gel was added to the resulting solution and
the suspension was stripped of solvent. Flash chromatography
(6 ◦C) on silica gel using a mixture of dichloromethane and
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1570 | Dalton Trans., 2006, 1564–1573
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{2,5-Di[1ꢀ2ꢀ7ꢀ:g-2ꢀ-(phenyl(tert-butyl)methylene)phenyl]pyrazine-
jN1,jN2}bis(tricarbonylmanganese(I)), 2c. Compound 2a (0.2 g,
0.4 mmol) was dissolved in n-heptane (10 ml) and the resulting
solution brought to reflux. A solution of 1-phenyl-1ꢀ-tert-
butyldiazomethane (0.32 g, 1.9 mmol) in 3 ml toluene was
added over 20 min and the resulting mixture allowed to boil for
additional 20 min. Silica gel was added to the resulting solution
and the suspension was stripped of solvent. Chromatography
(5 ◦C) over silica gel using a mixture of dichloromethane and
n-hexane (7 : 3) allowed the elution of a deep red fraction. The
latter was stripped of solvents to afford a red-coloured solid
(0.21 g, 61% yield). Anal. Calc. for C44H38N2O6Mn2·1/3CH2Cl2:
C 64.16, H 4.67, N 3.37. Found: C 64.03, H 4.90, N 3.34%. IR
(CH2Cl2) m(CO)/cm−1: 1997 (vs), 1923 (m), 1908 (m). dH (CDCl3,
n-hexane (8 : 2) released a large fraction containing the product.
The latter was obtained in analytical pure form as an orange solid
(0.84 g, 1.8 mmol, 83% yield). 2a: Anal. Calc. for C24H10N2O8Mn2:
C 51.09, H 1.79, N 4.96. Found: C 50.97, H 1.70, N 4.94%. IR
(CH2Cl2) m(CO)/cm−1: 2076 (s), 2001 (vs), 1985 (vs), 1944 (s). dH
3
3
(CDCl3) 9.19 (s, 2H), 8.01 (d, 2H, J = 7.2), 7.85 (d, 2H, J =
3
3
7.8), 7.36 (t, 2H, J = 7.3), 7.27 (t, 2H, J = 7.3). dC (CDCl3)
219.5 (CO), 213.5 (CO), 212.4 (2 CO), 176.6, 158.3, 143.6, 142.5,
142.2, 131.5, 124.8, 124.4.
{2,3-Di[1ꢀ2ꢀ7ꢀ:g-2ꢀ -(phenyl(tert-butyl)methylene)phenyl]quin-
oxaline-jN1,jN2}bis(tricarbonylmanganese(I)) 1c. Compound
1a (0.16 g, 0.29 mmol) was dissolved in toluene (15 ml) and
the solution brought to reflux. A solution of 1-phenyl-1ꢀ-tert-
butyldiazomethane (0.8 g, 4.6 mmol) in toluene (3 ml) was
added dropwise over 45 min. and the resulting mixture was left
to boil for an additional 45 min. Silica gel was added to the
resulting solution and the suspension was stripped of solvent.
Chromatography (5 ◦C) over silica gel using a mixture of n-hexane
and dichloromethane (6:4) allowed the elution of a fraction, which
afforded a deep purple solid upon removal of the solvents under
reduced pressure. The latter was recrystallized from a mixture of
dichloromethane and n-hexane (0.11 g, 45% yield). Anal. Calc.
for C48H40N2O6Mn2: C 67.77, H 4.74, N 3.29. Found: C 67.87, H
4.90, N 3.16%. IR (CH2Cl2) m(CO)/cm−1: 1995 (vs), 1925 (s), 1903
3
3
223 K) 7.98 (d, 2H, J = 8.9, HPh coordinated), 7.60 (t, 2H, J = 7.8,
HPh coordinated), 7.35 (t, 2H, J = 7.4, HPh coordinated), 7.23 (d, 2H, J =
3
3
3
3
8.0, HPh coordinated), 7.20 (d, 2H, J = 7.9, HPh), 7.14 (t, 2H, J =
3
3
7.6, HPh), 7.05 (t, 2H, J = 7.4, HPh), 6.79 (t, 2H, J = 7.5, HPh),
6.47 (s, 2H, Hpyrazine), 6.20 (d, 2H, 3J = 7.7, HPh), 1.26 (s, 18H). dC
(CDCl3, 263 K) 229.7, 221.9, 219.4, 153.2, 143.0, 140.4, 138.6,
133.9, 133.6, 132.8, 131.8, 126.9, 126.8, 125.8, 125.1, 116.4, 88.9,
80.9, 39.4 (3 C), 29.9.
{4,6-Di[1ꢀ2ꢀ7ꢀ:g-2ꢀ -(diphenylmethylene)phenyl]pyrimidine-jN1,
jN2}bis(tricarbonylmanganese(I)), 3b. Compound 3a (0.23 g,
0.4 mmol) was dissolved in a mixture of heptane (10 mL) and
toluene (5 mL) and the resulting solution brought to reflux. A
solution of 1,1ꢀ-diphenyldiazomethane (0.32 g, 1.64 mmol) in
3 ml toluene was added over 20 min. and the resulting mixture
was left to boil for additional 40 min. Silica gel was added
to the resulting solution and the suspension was stripped of
solvent. Chromatography (5 ◦C) over silica gel using a mixture
of dichloromethane and n-hexane (7 : 3) allowed the elution
of a deep red-coloured fraction containing the product, which
was recovered a solid upon removal of the solvents under
reduced pressure. The latter was recrystallized from a mixture of
dichloromethane and n-hexane (0.292 g, 84% yield). Anal. Calc.
for C48H30N2O6Mn2: C 66.82, H 3.56, N 3.22. Found: C 66.93,
H 3.49, N 3.24%. IR (CH2Cl2) m(CO): 2004 (vs), 1929 (m), 1912
(m) cm−1. dH (d6.acetone) 7.75 (s, 1H), 7.72 (m, 4H), 7.63 (m,
3
(s). dH (CDCl3, 223 K) 7.93 (d, 2H, J = 9.2, HPh coordinated), 7.78
(m, 2H, HQuinoxaline), 7.67 (m, 2H, HQuinoxaline), 7.50 (t, 2H, 3J = 7.4,
3
3
HPh coordinated), 7.00 (t, 2H, J = 7.6, HPh coordinated), 6.95 (t, 2H, J =
7.0, HPh), 6.77 (d, 2H, 3J = 7.7, HPh coordinated), 6.73 (d, 2H, 3J = 8.0,
3
3
3J = 7.4, HPh), 6.62 (d, 2H, J = 7.6, HPh), 6.57 (t, 2H, J = 7.3,
HPh), 1.31 (s, 18H). dC (CDCl3) 230.4, 222.5, 219.5, 146.5, 143.0,
140.3, 137.7, 133.8, 132.8, 132.6, 131.8, 131.6, 126.6, 126.4, 124.8,
124.5, 123.6, 117.4, 83.1, 81.2, 39.2 (3 C), 30.8.
{2,5-Di[1ꢀ2ꢀ7ꢀ:g-2ꢀ-(diphenylmethylene)phenyl]pyrazine-jN1,jN2}-
bis(tricarbonylmanganese(I)) 2b. Compound 2a (0.18 g,
0.38 mmol) was dissolved in a mixture of heptane (10 mL) and
toluene (5 mL) and the resulting mixture brought to reflux. A
solution of 1,1ꢀ-diphenyldiazomethane (0.35 g, 1.8 mmol) in
3 ml toluene was added over 20 min. The resulting mixture
was allowed to boil for additional 1 h. Silica gel was added
to the resulting solution and the suspension was stripped of
3
3
2H), 7.60 (m, 4H), 7.45 (d, 2H, J = 8.1), 7.39 (t, 4H, J = 7.7),
3
7.25 (m, 3H), 7.10 (t, 2H, J = 7.5), 6.91 (m, 6H), 6.40 (d, 2H,
3J = 7.3). dC (d6-acetone) 231.0, 221.3, 219.4, 167.8, 160.8, 147.9,
147.5, 136.5, 134.5, 133.5, 132.1, 131.2, 129.7, 129.0, 128.6, 128.3,
126.7, 126.4, 116.4, 113.4, 101.6, 77.0.
◦
solvent. Chromatography (5 C) on silica gel using a mixture of
dichloromethane and n-hexane (8 : 2) allowed the elution of a red-
coloured fraction. The latter afforded a red solid upon removal
of the solvents under reduced pressure, which was recrystallized
from a mixture of dichloromethane and n-hexane (0.215 g, 67%
yield). HRMS (FAB+) Calc. for C45H30N2O3Mn2 (M − 3CO):
756.101736. Found 756.101736. IR (CH2Cl2) m(CO)/cm−1: 2002
(vs), 1931 (m), 1912 (m). dH (CDCl3) 7.77 (m, 2H), 7.59 (d, 1H,
3J = 7.9), 7.39 (m, 4H), 7.27 (m, 1H), 7.21 (m, 2H), 7.08 (m, 1H),
6.98 (t, 1H, 3J = 7.2), 6.87 (t, 1H, 3J = 7.6), 6.81 (s, 1H), 6.13 (d,
1H, 3J = 7.3). dC (CDCl3) 230.2, 220.4, 220.1, 153.0, 146.9, 146.5,
141.0, 136.3, 134.3 (2 C), 133.1, 131.8, 130.4, 130.2, 129.3, 128.8
(2 C), 128.4, 128.0, 127.9, 126.6, 126.1, 125.2, 113.6, 95.7, 75.9.
MS (FAB+): m/z 841 [M]+, 756 [M − 3CO]+, 672 [M − 6CO]+,
618 [M − 6CO − Mn]+, 563 [M − 6CO − 2Mn]+, 485 [M −
6CO − 2Mn − C6H5]+.
{4,6-Di[1ꢀ2ꢀ7ꢀ:g-2ꢀ -(phenyl(tert-butyl)methylene)phenyl]pyrimi-
dine-jN1,jN2}bis(tricarbonylmanganese(I)) 3d and {4-[1ꢀ2ꢀ7ꢀ:g-2ꢀ-
(phenyl(tert-butyl)methylene)phenyl]-6-[2ꢀ -1ꢀꢀ -(phenyl(tert-butyl)-
methylene)phenyl]pyrimidine-jN1}(tricarbonylmanganese(I)) 3e.
Compound 3a (0.2 g, 0.35 mmol) was dissolved in a mixture
of heptane (10 mL) and toluene (5 mL) and the resulting
solution brought to reflux. A solution of 1-phenyl-1ꢀ-tert-
butyldiazomethane (0.25 g, 1.45 mmol) in 3 ml toluene was added
over 30 min and the resulting mixture was left to boil for an
additional 30 min. Silica gel was added to the resulting solution
and the suspension was stripped of solvent. Chromatography
(5 ◦C) over deactivated silica using a mixture of n-hexane and
dichloromethane (8 : 2) allowed the elution of a red–orange
fraction containing trace amounts of 3c (less than 5 mg) and a
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red fraction (F1); elution with n-hexane and dichloromethane
(7 : 3) delivered an orange fraction (F2). Following the same
procedure, (F1) was purified by a second flash chromatography
with a 9 : 1 mixture of n-hexane and dichloromethane (0.5 l) to
afford a red band (F1ꢀ) and with a 1 : 1 mixture of n-hexane
and dichloromethane to afford an orange band (F2ꢀ). Fractions
(F1) and (F1ꢀ) were combined to afford upon removal of solvents
3d as a red solid (0.05 g, 18% yield). Fractions (F2) and (F2ꢀ)
were combined to afford upon removal of solvents 3e as an
orange solid (0.14 g, 62% yield). 3d: HRMS (FAB+) Calc. for
C41H38N2O3Mn2 (M+): 716.164333. Found: 716.164336. Anal.
Calc. for C44H38N2O6Mn2: C 66.01, H 4.78, N 3.50. Found: C
65.47, H 4.92, N 3.48%. IR (CH2Cl2) mCO/cm−1 2002 (vs), 1915
(4 ◦C) with a 9 : 1 mixture of n-hexane and dichloromethane,
allowed the elution of a red fraction containing 4b (0.045 g,
0.06 mmol, 14% yield); elution with a 1 : 1 mixture of n-hexane
and dichloromethane delivered an orange-coloured mixture (the
NMR 1H analysis indicated a mixture of two complexes); elution
with pure dichloromethane afforded an orange-coloured fraction
containing 4c (0.053 g, 0.12 mmol, 29% yield). The second fraction
was adsorbed on hydrated silica gel and submitted to a second
chromatographic separation over hydrated silica gel/n-hexane
(0 ◦C) with a 9 : 1 mixture of n-hexane and dichloromethane
(0.5 l) affording thus a red containing 4b (traces); elution with
a 1 : 1 mixture of dichloromethane and n-hexane afforded a
yellow fraction containing 4d (0.032 g, 0.05 mmol, 12% yield).
4e: HRMS (FAB+) Calc. for C38H35N4O3Mn (M+): 725.125601.
Found: 725.125605. Anal. Calc. for C38H34N2O6Mn2: C 62.99,
H 4.73, N 3.87. Found: C 63.31, H 4.94, N 3.65%. IR (CH2Cl2)
m(CO)/cm−1: 2019 (s), 1992 (vs), 1944 (m), 1903 (s). dH (CDCl3,
3
(s), 1909 (s). dH (500 MHz, CDCl3, 223 K) 7.97 (d, 2H, J =
3
9.0, HPh coordinated), 7.54 (t, 2H, J = 7.8, HPh coordinated), 7.37 (s, 1H,
3
3
Hpyrimidine), 7.21 (t, 2H, J = 7.5, HPh coordinated), 7.15 (t, 2H, J =
3
3
7.3, HPh) 7.05 (t, 2H, J = 7.3, HPh), 7.01 (d, 2H, J = 7.7, HPh),
3
3
6.82 (t*, 2H, HPh), 6.79 (d, 2H, J = 8.7, HPh coordinated), 6.18 (d,
263 K) 8.07 (m, 3H), 7.43 (m, 1H), 7.04 (d, 1H, J = 8.0), 6.79
3
3
3
3
2H, J = 7.5, HPh), 4.60 (s, 1H, Hpyrimidine), 1.44 (s, 18H, t-Bu). dH
(t, 1H, J = 7.5), 6.75 (t, 1H, J = 7.2), 6.70 (t, 1H, J = 7.1),
3
3
3
3
(300 MHz, C6D6, 298 K) 7.85 (d, 2H, J = 9.1), 7.13 (m, 5H),
6.64 (d, 1H, J = 7.0), 6.59 (t, 1H, J = 5.1), 6.28 (d, 1H, J =
3 3
6.98 (m, 4H), 6.81 (t*, 2H, 3J = 7.5), 6.64 (d, 2H, 3J = 8.3), 6.46
(t, 2H, 3J = 7.4), 5.95 (d, 2H, 3J = 7.6), 3.90 (s, 1H), 1.5 (s, 18H).
dC (125 MHz, CDCl3, 263 K) 229.8, 221.7, 220.2, 168.4, 158.6,
144.4, 139.1, 135.6, 133.8, 133.0, 131.3, 128.4, 125.8, 125.4 (2 C),
116.4, 114.8, 91.3, 82.4, 39.3 (3 C), 28.1. MS (FAB+) m/z 716
(M − 3CO), 661 (M − 3CO − Mn). 3e: HRMS (FAB+) Calc.
for C41H40N2O3Mn (M+): 663.241927. Found: 663.241940. Anal.
Calc. for C41H39N2O3Mn: C 74.31, H 5.93, N 4.23. Found: C
74.10, H 6.10, N 4.21%. IR (n-hexane) m(CO): 2002 (vs), 1922 (s),
1915 (s) cm−1. dH (CDCl3, 298 K) 8.38 (s, 1H, Ha), 8.06 (d, 1H,
7.8), 5.65 (t, 1H, J = 5.1), 5.05 (t, 1H, J = 6.5), 4.94 (t, 1H,
3 3
3J = 6.0), 4.33 (d, 1H, J = 7.7), 4.27 (d, 1H, J = 7.4), 1.42 (s,
broad, 9H), 1.00 (s, 9H). dC (CDCl3, 263 K) 232.0, 223.2, 222.1,
221.9 (3CO), 163.7, 158.4, 157.1, 146.5, 144.4, 139.3, 135.0, 134.7,
130.3, 128.2, 127.5, 126.5, 126.0, 125.8, 125.6, 124.6, 119.6, 116.1,
106.8, 97.9, 97.7, 82.6, 75.7, 72.5, 67.3, 39.6, 35.5, 30.9, 30.1 (3
C), 28.1. MS (FAB+) m/z 725 (M+), 640 (M − 3CO), 613 (M+ −
2CO − Mn), 585 (M − 3CO − Mn), 557 (M − 4CO − Mn),
502 (M − 4CO − 2Mn). 4c: Anal. Calc. for C24H21N2O3Mn: C
65.46, H 4.81, N 6.36. Found: C 65.10, H 4.79, N 6.40%. IR
(n-hexane) m(CO)/cm−1: 2004 (vs), 1930 (s), 1915 (s). dH (CDCl3,
3J = 9.1, HPh coordinated), 7.91 (d, 1H, J = 8.0, HPhenyl), 7.56 (t, 1H,
3
3J = 7.9, HPh coordinated), 7.41 (t, 1H, 3J = 7.7, HPhenyl), 7.28 (d*, 1H,
263 K) 8.16 (d, 1H, J = 5.1, Hpyrimidine), 8.09 (d, 1H, J = 9.1,
3
3
3
3
HPh1), 7.20 (m, 5H, 3HPh2 (t*) + 1HPh coordinated (t*) + 1HPhenyl (t*)),
HPh coordinated), 7.97 (d, 1H, J = 5.2, Hpyrimidine), 7.85 (d, 1H, J =
3
3
3
7.03 (d, 1H, J = 8.1, HPh coordinated), 6.91 (t, 1H, J = 7.6, HPh1),
8.5, HPh coordinated), 7.63 (t, 1H, J = 7.9, HPh coordinated), 7.33 (t, 1H,
6.82 (m, 3H, 1HPh1 (t*, 3J = 7.1) + 2HPh2 (d*, 3J = 6.1)), 6.63 (d,
3J = 7.5, HPh coordinated), 7.24 (d*, 1H, HPh), 6.83 (t, 1H, J = 7.6,
3
3
3
1H, J = 7.6, HPhenyl), 6.61 (t, 1H, J = 6.1, HPh1), 6.16 (d, 1H,
3J = 7.4, HPh1), 5.42 (s, 1H, Hb), 3.87 (s, 1H, Hc), 1.46 (s large,
9H, t-Bu(a)), 1.00 (s, 9H, t-Bu(b)). dC (CDCl3, 298 K) 230.4, 222.0,
221.9, 168.8, 167.4, 158.9, 144.9, 141.0, 140.0, 139.4, 134.6, 134.4,
134.0, 131.0, 130.5 (2 C), 129.1, 128.9, 128.5, 127.8 (2 C), 126.5,
126.1, 126.0 (2 C), 125.0, 124.9, 117.3, 116.4, 90.7, 82.4, 56.8,
39.2, 34.9, 32.7, 29.5 (3 C), 29.1, 27.0 (3 C). MS (FAB+): m/z 663
[M]+, 578 [M − 3CO]+, 523 [M − 3CO − Mn]+.
HPh), 6.69 (t, 1H, 3J = 7.3, HPh), 6.63 (t, 1H, 3J = 6.8, HPh), 6.58
(t, 1H, 3J = 5.2, Hpyrimidine), 6.16 (d, 1H, 3J = 7.6, HPh), 1.46 (s, 9H,
t-Bu). dC (CDCl3, 263 K) 230.4, 222.0, 221.3, 165.8, 158.4, 157.1,
143.9, 139.2, 134.5, 133.3 (2 C), 131.5, 126.7, 125.9, 125.2, 124.8,
118.9, 115.3, 94.0, 81.6, 39.3 (3 C), 28.2. 4d: HRMS (FAB+) Calc.
for C35H36N4O3Mn (M+): 615.216775. Found: 615.216788. Anal.
Calc. for C35H35N4O3Mn·1/2CH2Cl2: C 64.89, H 5.52, N 8.53.
Found: C 64.91, H 5.52, N 8.34%. IR (KBr) m(CO)/cm−1: 1997
(vs), 1919 (s), 1902 (s). dH (CDCl3, 263 K) 7.96 (m, 1H), 7.86 (d,
(2-{[1ꢀ,2ꢀ,7ꢀ:g-2ꢀ -(Phenyl(tert-butyl)methylene](phenyl-jC3ꢀ )}-
pyrimidine-jN1)tricarbonylmanganese(I)-jN2)tetracarbonylmanga-
nese(I) 4e, {2-[1ꢀ,2ꢀ,7ꢀ:g-2ꢀ -(phenyl(tert-butyl)methylenephenyl]-
pyrimidine-jN1 }tricarbonylmanganese(I) 4c, {2-[1ꢀ,2ꢀ,7ꢀ:g-2ꢀ -
(phenyl(tert-butyl)methylene-3ꢀ-(tert-butyl){tricarbonyl(g5-phenyl)-
manganese(I)}methylene)]pyrimidine-jN1}tricarbonylmanganese(I)
4b and {2-[1ꢀ,2ꢀ,7ꢀ:g-2ꢀ -(phenyl(tert-butyl)methylene-3ꢀ -(2,2-
dimethyl-1-phenylpropylidene)hydrazone]phenylpyrimidine-jN1 }-
tricarbonylmanganese(I) 4d. Compound 4a (0.204 g, 0.42 mmol)
was dissolved in 10 mL toluene and the resulting mixture brought
to reflux. A solution of 1-phenyl-1ꢀ-tert-butyldiazomethane
(0.285 g, 1.6 mmol) in 3 mL toluene was added over 25 min, and
the resulting solution was left to boil for 25 min. Silica gel was
added to the resulting solution and the suspension was stripped
of solvent. Chromatography over deactivated silica gel/n-hexane
1H, J = 4.0), 7.52 (t, 1H, J = 7.9), 7.34 (m, 3H), 7.20 (t, 1H,
3J = 8.1), 7.12 (m, 2H), 7.01 (d, 1H, 3J = 7.0), 6.88 (d, 1H, 3J =
7.2), 6.71 (t, 1H, 3J = 7.3), 6.61 (t, 1H, 3J = 6.9), 6.56 (t, 1H, 3J =
7.2), 6.25 (t, 1H, 3J = 5.5), 6.16 (d, 1H, 3J = 6.8), 3.50 (s, broad,
1H), 1.67 (s, 9H), 1.19 (s, 9H). dC (CDCl3, 263 K) 236.4, 222.1,
221.6, 162.9, 159.1, 157.9, 155.2, 148.5, 143.6, 138.9, 134.2, 133.8,
132.9, 128.9, 128.8, 128.7, 128.6, 127.9, 126.6, 125.5, 124.5, 120.2,
118.3, 116.4, 104.1, 82.6, 78.6, 39.4, 38.2, 28.4 (6 C). MS (FAB+):
m/z 615 [M]+, 530 [M − 3CO]+, 475 [M − 3CO − Mn]+. 4b: IR
(CH2Cl2) m(CO)/ cm−1: 2079 (w), 2004 (vs), 1985 (m), 1941 (m),
1916 (m). dH (CDCl3, 263 K) 8.06 (d, 1H, 3J = 4.7), 7.82 (m, 3H),
3
3
3
3
3
7.61 (d, 1H, J = 8.2), 7.45 (t, 1H, J = 7.8), 7.01 (t, 1H, J =
7.7), 6.73 (t, 1H, 3J = 7.5), 6.53 (t, 1H, 3J = 7.2), 6.38 (t, 1H, 3J =
5.5), 5.81 (d, 1H, 3J = 6.8), 1.50 (s, 9H). dC (CDCl3, 263 K) 230.7,
222.5, 219.1, 218.7, 214.1, 212.8, 212.5, 176.0, 165.8, 158.4, 158.2,
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145.8, 139.9, 137.7, 131.0, 130.9, 129.0, 126.5, 126.0, 125.6, 116.4,
114.7, 104.1, 81.3, 39.2, 32.6 (3 C).
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Bis(tricarbonylmanganese(I))(2,3-di-(g2-2ꢀ-(g1-diphenylmethylene-
jC)phenyl)benzo[g]quinoxaline-jN,jNꢀ),
complex
6b.
A
solution of Ph2CN2 (500 mg, 2.57 mmol) in toluene (1 mL) was
added dropwise to a boiling solution of 6a (300 mg, 0.45 mmol)
dissolved in a 10 : 1 mixture of n-hexane (10 mL) and toluene
(1 mL) for 1 h. The colour of the medium changed from deep
red to dark green within 40 min. The solvents were subsequently
removed under reduced pressure and the residue dissolved in
CH2Cl2. Silica gel was added to the resulting solution and the
suspension was stripped of solvent. The coated silica gel was
loaded on the top of a cooled SiO2 column packed in dry
n-hexane. Elution with a mixture of 30% CH2Cl2 in n-hexane
allowed the recovery of a brownish mixture of unstable and
unidentified compounds. Further elution with a 50% mixture
of CH2Cl2 and n-hexane allowed the recovery of a dark green
fraction containing 6b as the major component. This fraction was
stripped of solvents and the raw material was recrystallized thrice
from CH2Cl2 and n-hexane to afford a pure sample (15 mg, 3.5%
yield). Complex 6b: HRMS (FAB+) Calc. for C56H34N2O6Mn2:
940.117766. Found: 940.117780. IR (n-hexane) m(CO)/cm−1:
2002, 1935, 1912. dH (CDCl3) 8.20 (s, 2H), 8.01 (dd, 2H, 3J = 6.4,
4J = 3.2), 7.71 (d, 4H, 3J = 7.4), 7.61 (dd, 2H, 3J = 6.5, 4J = 3.2),
3
4
7.38 (m, 6H), 7.30–7.13 (m, 10H), 6.80 (t*d, 2H, J = 7.5, J =
1.0), 6.68 (d, 2H, 3J = 7.6), 6.21 (t*, 2H, 3J = 7.4), 5.93 (t*, 2H,
3J = 7.6, 4J = 1.2). dC (CDCl3, 263 K) 230.6, 220.8, 219.7, 146.4,
145.9, 134.9, 134.5, 133.8, 133.2 (broad), 133.1, 131.7, 131.2,
128.5 (broad, 2C), 128.3, 127.1, 126.5, 126.1, 125.3, 125.0, 123.9,
123.1, 115.6, 87.6, 75.8. MS (FAB+): m/z 940.8 [M]+, 855.8 [M −
3CO]+, 828.8 [M − 4CO + H]+, 801.0 [M − 5CO + H]+, 771.9
[M − 6CO − H]+, 717.0 [M − 6CO − Mn]+, 663.1 [M − 6CO −
2Mn + H]+.
12 J.-P. Djukic, C. Michon, D. Heiser, N. Kyritsakas-Gruber, A. de Cian,
K. H. Do¨tz and M. Pfeffer, Eur. J. Inorg. Chem., 2004, 2107–2122.
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15 The second reduction process is reportedly irreversible:H. Bock, A.
John, K. Na¨ther and K. Ruppert, Helv. Chim. Acta, 1994, 77, 1505–
1519.
Acknowledgements
The authors thank the CNRS (Z. R.) and the Alexander von
Humboldt foundation for their continuing support and gratefully
acknowledge the help provided by Patrick Wehrung in measuring
electro-spray mass spectra and Dr Lionel Allouche in carrying out
the two-dimensional NMR experiments.
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