An orthomanganation route to 2-substituted derivatives of N-methyl-1,8-naphthalimide

Article abstract of DOI:10.1016/j.jorganchem.2012.06.035

N-methyl naphthalimide can be readily cyclomanganated at the 2-position, directed by the adjacent amide O atom. Di-cyclomanganation also occurs readily to attach Mn(CO)₄ groups at both 2, 7 positions. An X-ray structure determination of the mono-substituted example confirmed the five-membered metallocyclic ring. Cleavage of the Mn-C bond by HgCl₂ or ICl generates 2-substituted HgCl or I derivatives respectively. Reaction of the mono-cyclomanganated N-methyl naphthalimide with phenylacetylene gives an (η⁵-cyclohexadienyl)Mn(CO)₃ complex where the cyclohexadienyl ring has formed by two PhCCH adding in a formal [2 + 2 + 2] process across the C(1)-C(2) bond of the naphthalimide, breaking the aromaticity of the naphthalene ring as shown by a single crystal structure determination.

Full text of DOI:10.1016/j.jorganchem.2012.06.035

Journal of Organometallic Chemistry 716 (2012) 49e54
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Journal of Organometallic Chemistry
journal homepage: www.elsevier.com/locate/jorganchem
An orthomanganation route to 2-substituted derivatives of N-methyl-1,
8-naphthalimide
*
Brian K. Nicholson , Paul M. Crosby, Kieran R. Maunsell, Megan J. Wyllie
Chemistry Department, Faculty of Science and Engineering, University of Waikato, Hamilton 3240, New Zealand
a r t i c l e i n f o
a b s t r a c t
Article history:
N-methyl naphthalimide can be readily cyclomanganated at the 2-position, directed by the adjacent
amide O atom. Di-cyclomanganation also occurs readily to attach Mn(CO)4 groups at both 2, 7 positions.
An X-ray structure determination of the mono-substituted example confirmed the five-membered
metallocyclic ring. Cleavage of the MneC bond by HgCl2 or ICl generates 2-substituted HgCl or I deriv-
atives respectively. Reaction of the mono-cyclomanganated N-methyl naphthalimide with phenyl-
Received 30 May 2012
Received in revised form
19 June 2012
Accepted 24 June 2012
acetylene gives an (h
5-cyclohexadienyl)Mn(CO)3 complex where the cyclohexadienyl ring has formed by
Keywords:
two PhCCH adding in a formal [2 þ 2 þ 2] process across the C(1)eC(2) bond of the naphthalimide,
breaking the aromaticity of the naphthalene ring as shown by a single crystal structure determination.
Ó 2012 Elsevier B.V. All rights reserved.
Naphthalimide
Cyclometalation
Manganese carbonyl
X-ray crystal structure
Alkyne
1. Introduction
synthetic routes. There are presently 41 structures reported for 4-
substituted N-alkyl-1,8-naphthalimides, but none for 2-substitu-
The chemistry of N-alkyl-1,8-naphthalimides (for example the
N-methyl compound 1, also known as N-methyl-1,8-naphtha-
lenedicarboximide) is well-developed. Derivatives find applica-
tion as colorimetric and fluorescent sensors [1e3], and have
promising chemotherapeutic properties [4,5]. Their photophysical
properties are also of interest for electrochemical applications [6].
ted analogues in the CCDC files [7].
Cyclometalation is a useful method of directing reactions at
specific sites (for a recent review see Ref. [8]). We have previously
reported extensively on the use of cyclomanganation of aryl
ketones, amides, aldehydes, and other substrates as a means of
specifically directing reactions at the ortho position of the aromatic
ring [9e15], and as an extension of these studies have now exam-
ined 1 as a substrate.
Me
We herein report the directed mono- and di-cyclomanganation
of 1 at the 2-positions to give 2 and 3, and demonstrate the use of
the new complex 2 as an intermediate for preparing 2-halo- and 2-
(chloromercurio)-N-alkyl-1,8-naphthalimides. The reaction of 2
with alkynes is also discussed, with PhCCH leading to de-
aromatisation of the naphthalene core.
O
N
O
Me
N
Me
N
(1)
O
O
O
O
Mn(CO)4
(OC)4Mn
Mn(CO)4
A very large number of papers (>10,000) discuss derivatives
substituted at the 4-position, but in contrast there are very few 2-
substituted examples (w100 papers) because of a paucity of
(2)
(3)
* Corresponding author.
E-mail address: b.nicholson@waikato.ac.nz (B.K. Nicholson).
0022-328X/$ e see front matter Ó 2012 Elsevier B.V. All rights reserved.
http://dx.doi.org/10.1016/j.jorganchem.2012.06.035

50
B.K. Nicholson et al. / Journal of Organometallic Chemistry 716 (2012) 49e54
2. Experimental details
MeOH (10 mL) and heated to reflux for 75 min. The mixture was
cooled and the precipitate was collected by filtration and washed
with MeOH to give an off-white powder of 2-(chloromercurio)-N-
methyl-1,8-naphthalimide (4) (0.030 g, 61%). Anal.: Calc for
C13H8ClHgNO12 C 34.99; H 1.81; N 3.14%. Found C 34.68; H 1.85; N
3.04%. IR: (KBr disk, cmꢂ1) 1698 m, 1643 vs, 1612 w, 1577 m. The
compound was too insoluble for NMR spectra.
2.1. General procedures
Spectroscopic data were obtained on a PerkineElmer Spectrum
100 FTIR and a Bruker BRX400 NMR, the latter withsamples dissolved
in CDCl3. ESI-MS were from a Bruker MicrOTOF instrument, with
solutions made up in methanol, operated under standard conditions.
NaOMe was added to aid ionisation for the metal carbonyl samples
[16]. PhCH2Mn(CO)5 was prepared by the literature method [17] and
naphthalic anhydride and the alkynes were purchased from Aldrich.
Chromatography was carried out on 20 ꢀ 20 cm silica gel plates.
Petroleum spirit refers to a 60e80 ꢁC fraction. Reactions were carried
out under a nitrogen atmosphere in Schlenk equipment, but no
precautions to exclude air were taken during work-up.
2.5. Preparation of 2-iodo-N-methyl-1,8-naphthalimide (5)
A solution of ICl (0.023 g, 0.14 mmol) in CCl4 (1 mL) was added to
2 (0.05 g, 0.13 mmol) in CCl4 (2 mL). The mixture was left for 2 h.
Solvent was removed and the residue chromatographed on silica
plates, eluting with CH2Cl2:petroleum spirits (1:1). A yellow band at
Rf 0.3 was unreacted 2, while a pale yellow band at Rf 0.1 was
removed and shown to be the mono-iodinated product 5, (4 mg,
2.2. Preparation of N-methyl-1,8-naphthalimide (1)
9%). NMR (CDCl3) 1H:
d 3.61 s (eCH3), 7.80 apparent t (dd),
(J ¼ 8 Hz), 7.80 d (J ¼ 9 Hz), 8.21 dd (J ¼ 8, 1 Hz), 8.38 d (J ¼ 9 Hz),
8.69 dd (J ¼ 7, 1 Hz) (all CeH); 13C: 29.7 (eCH3), 101.5, 126.9, 127.2,
131.2, 131.3, 131.5, 133.3, 133.9, 134.1, 141.7 (aryl CeH), 162.3, 163.2
(C]O). IR: (KBr disk, cmꢂ1) 1697 m, 1657 vs, 1646 sh, 1583 m. ESI-
MS: m/z 359.952 [M þ Na]þ, calc. 359.949; m/z 696.915 [2M þ Na]þ,
calc. 696.909. The structure of 5 was also determined by X-ray
crystallography (see below).
1,8-Naphthalic anhydride (2.0 g, 0.01 mol) was dissolved in
absolute ethanol (150 mL) and 5 mL of 25% MeNH2(aq) was added.
The solution was stirred at room temperature for 3 d, and the solid
product which had crystallised from the reaction mixture was
filtered and dried to give N-methyl-1,8-naphthalimide (2.2 g,100%),
pure by IR (KBr disc, nC]O 1701 m, 1668 vs cmꢂ1), 1H NMR [
d
3.55 s
(eCH3), 7.74 apparent t (dd), 8.19 dd, 8.58 dd (eCeH)], 13C NMR [
d
27.0 (eCH3), 126.9, 131.2, 133.9 (all eCeH), 122.6, 128.1, 131.6 (quart
C), 164.5 (C]O)] and ESI-MS [m/z 212.068 [M þ H]þ (calc 212.071),
m/z 234.047 [M þ Na]þ (calc 234.052)].
2.6. Reaction of cyclomanganated N-methy-1,8-naphthalimide
with phenylacetylene to give 6
Cyclomanganated naphthalimide 2, (0.040 g, 0.11 mmol) was
dissolved in benzene (15 mL). PhCCH (0.1 mL, excess) was added
and the stirred mixture was brought to reflux in an oil bath at
100 ꢁC. After 90 min, a small sample removed for solution IR
analysis showed all starting material was consumed. The solvent
and excess alkyne were removed under vacuum and the residue
chromatographed on silica plates, eluting with 1:1 CH2Cl2/pet
spirits. This gave one major yellow band. This was removed and
recrystallised from a mixture of CH2Cl2 and pet spirits to give
2.3. Cyclomanganation of N-methyl-1,8-naphthalimide
A mixture of PhCH2Mn(CO)5 (0.51 g, 1.78 mmol) and N-methyl-
1,8-naphthalimide(0.43 g, 2.04 mmol) in heptane(50 mL)washeated
under gentle reflux for 2 h, by which time an IR spectrum of an
aliquot of the reaction mixture showed nCO bands from
PhCH2Mn(CO)5 were absent. The mixture was evaporated to dryness
and the residue was chromatographed on silica, with CH2Cl2/petro-
leum spirits (2:9) as eluent. Two yellow bands were resolved.
The slower moving band (Rf 0.15) was removed and recrystal-
lized from CH2Cl2/petroleum spirits at ꢂ20 ꢁC to give orange
crystals of orthomanganated N-methyl-1,8-naphthalimide (2)
(0.27 g, 40%). Anal.: Calc for C17H8MnNO6: C 54.13; H 2.14; N 3.71%.
Found C 54.44; H 2.21; N 3.66%. IR: v(CO) cmꢂ1 (CH2Cl2) 2086 m,
1999 vs, 1942 s; (KBr disc) 2083 s, 1995 vs, 1940 s, 1690 m, 1621 m,
orange crystals of 6 (0.044 g, 73%). Anal.: Calc for C32H20MnNO5
69.45; H 3.64; N 2.52%. Found C 69.42; H 3.73; N 2.53%. IR: (CH2Cl2,
cmꢂ1) 2019 s, 1954 s,br. NMR (CDCl3) 1H:
3.03 s (eCH3), 5.60 s,
C
d
5.89 s (CeH of cyclohexadienyl ring), 5.94 d, 6.38 d (CeH of de-
aromatised ring), 7.0e7.8 m, (aromatic CeH). ESI-MS: m/z 576.064
[M þ Na]þ, calc. 576.061; m/z 1129.136 [2M þ Na]þ, calc 1129.134.
1575 s, 1533 m. NMR (CDCl3) 1H:
d
3.55 s (eCH3), 7.66 apparent t
28.3 (eCH3), 126.6,
2.7. X-ray crystal structures
(dd),8.00 d, 8.23 d, 8.39 d, 8.48 d (all CeH). 13C:
d
132.1, 132.9, 136.3, 140.6 (all CeH), 120.3, 128.8, 130.4 (quart. C). ESI-
MS (ꢂve ion, NaOMe added [16]): m/z 408.027, ([M þ OMe]ꢂ calc.
407.991); (þve ion): m/z 399.966 [M þ Na]þ calc. 399.962; m/z
776.936 [2M þ Na]þ calc. 776.936.
Crystals of 2 and 5 were from CH2Cl2/Et2O, while those of 6 were
from CH2Cl2/petroleum spirits. Intensity data were obtained on
a Bruker SMART diffractometer with Mo-Ka X-rays, and were cor-
rected for absorption using a multi-scan procedure. The structures
were solved by direct methods and developed and refined on Fo2. For
compound 2, after the main part of the structure had been revealed
it became clear there was disorder involving a 180ꢁ rotation of the
planar naphthalimide rings relative to the Mn(CO)4 group, giving an
alternative orientation. This disordered component was resolved
for all of the naphthalimide atoms and also for the Mn atom, and
these were refined with isotropic temperature factors. The relative
site occupancies were refined to give a major/minor orientation of
78%/22%. There was also concomitant disorder for the CO ligands
but this was not resolved. H atoms were included in calculated
positions for the major component but were omitted for the minor
one. The structure of the main component is shown in Fig. 1a, with
the disorder illustrated in Fig. 1b.
The faster moving band (Rf 0.60) was removed to give an orange
powder of di-manganated N-methyl-1,8-naphthalimide (3) (0.05 g,
10%). Anal.: Calc for C21H7Mn2NO10 C 46.44; H 1.30; N 2.58%. Found C
47.98; H 1.84; N 2.54%. IR: v(CO) cmꢂ1 (CH2Cl2) 2084 m, 2002 vs,1942
s; (KBr disc) 2086 s, 2012 w,sh,1993 s,1965 s,1943 vs,1613 s,1606 sh.
NMR (CDCl3) 1H: 3.56 s (eCH3), 8.05 d, 8.32 d (both CeH).13C:
d d 27.2
(eCH3), 133.1, 137.9 (both CeH), 125.9, 126.8, 127.5 (quart. C) 176.4
(C]O), 204.0 (MneC), 210.5, 212.6, 220.9 (MneCO). ESI-MS (ꢂve ion,
NaOMe added [16]): m/z 573.967, ([M þ OMe]ꢂ calc 573.901).
2.4. Preparation of 2-(chloromercurio)-N-methyl-1,8-
naphthalimide (4)
Cyclomanganated N-methyl-1,8-naphthalimide (0.030 g,
0.08 mmol) and HgCl2 (0.033 g, 0.12 mmol) were dissolved in
The crystal structure of 2 also appeared to have a minor (ca 3%)
orientational disorder for one of the two independent molecules,

B.K. Nicholson et al. / Journal of Organometallic Chemistry 716 (2012) 49e54
51
Fig. 1. a. The structure of the mono-manganated N-methyl-naphthalimide (2) with the disordered component omitted. b. A composite diagram showing the disorder found for the
structure of 2. The main component is shown with large spheres, the minor one with small ones.
showing a peak assignable to a fractional I atom on the opposite 20-
Table 1
Crystal data and refinement details for the structure of 2, 5 and 6.
position, though other atoms associated with this small disorder
were not apparent.
Formula
C17H8MnNO6 (2)
C13H8 INO2 (5)
C32H20MnNO5 (6)
For 6 refinement was routine for the two independent mole-
cules in the asymmetric unit and included all non-H atoms as
anisotropic, with H atoms included in calculated positions.
All calculations were with the SHELX97 programs [18] run under
WinGX [19]. Figures were generated with ORTEP-III [20] and with
Crystalmaker [21]. Crystal and refinement details are given in
Table 1 and the structures of 2, 5 and 6 are illustrated in Figs. 1e3
respectively. Bond parameters are listed in the Supplementary
information.
Mr
T(K)
377.18
89(2)
337.10
95(2)
553.43
93(2)
Crystal system Triclinic
Space group
a(Å)
b(Å)
c(Å)
Monoclinic
P21/n
7.9017(3)
16.3976(5)
16.9415(5)
Monoclinic
P21/c
17.3874(5)
12.8339(4)
22.6002(7)
P-1
7.1544(2)
9.4209(3)
12.4315(4)
85.311(1)
77.482(1)
69.239(1)
764.85(4)
2
a
(ꢁ)
(ꢁ)
b
91.450(2)
90.295(2)
g
(ꢁ)
V(Å3)
2194.39(12)
8
2.041
5043.1(3)
8
1.458
Z
r
(g cmꢂ3
(mmꢂ1
)
)
1.638
0.898
3. Results and discussion
m
2.91
0.568
Tmax, min
0.840, 0.758
1.000, 0.779
1.000, 0.860
3.1. Preparation of cyclomanganated complexes
Size (mm3)
F(000)
0.25 ꢀ 0.20 ꢀ 0.19 0.38 ꢀ 0.10 ꢀ 0.05 0.35 ꢀ 0.32 ꢀ 0.20
380
28
1296
28
2272
28
122,942
12,111 (Rint 0.0547)
0.0336
When the N-methyl-1,8-naphthalimide 1 was heated under
reflux with PhCH2Mn(CO)5 in heptane for 1.5e2 h (c.f. Ref. [9])
complete reaction occurred as monitored by the loss of the
2105 cmꢂ1 nCO band of the starting complex, and appearance of
the 2086 cmꢂ1 band of the product, from infrared spectra on
aliquots removed from the reaction mixture. Evaporation of the
qmax(ꢁ)
Reflns collected 13,202
Unique reflns 3776 (Rint 0.034)
R1 [I > 2 (I)]
77,856
5225 (Rint 0.079)
0.0310
0.0724
1.046
s
0.0479
0.1480
1.118
wR2 (all data)
0.0894
1.016
GOF on F2

52
B.K. Nicholson et al. / Journal of Organometallic Chemistry 716 (2012) 49e54
than 0.2 Å. Because of the disorder of the naphthalimide ligand
a detailed comparison of bond parameters is not warranted, but
the MneC and MneO bond distances [2.036(3) and 2.088(2) Å
respectively] appear to be in the usual range for orthomanganated
aryl ketones, as is the C(2)eMn(1)eO(11) ’bite’ angle of 80.5ꢁ [9].
The coordinated C]O is longer than the free one [1.256(3) vs
1.213(7) Å], consistent with the IR vibrational changes.
The faster moving band from the chromatography was shown to
be the di-manganated species 3. The NMR spectra reflected the
symmetrical arrangement, as did the IR spectrum which together
with nCO bands at the same positions as those of 2 for the metal
carbonyl groups, also showed a simple pattern at ca 1600 cmꢂ1 for
the now-equivalent C]O groups, with frequencies lowered from
those in the free naphthalimide arising from coordination to the
Mn atoms.
The mono-substituted complex 2 was the major one formed
when a 1:1 ratio of reactants was used, but the di-substituted was
always a significant component from the reaction suggesting
reactivity at one C]O group of 1 has little effect on the reactivity at
the other C]O position. This behaviour is reminiscent of that
observed with di-acetylbenzene as a substrate where both mono-
and di-manganated compounds were formed with PhCH2Mn(CO)5
even at 1:1 ratios [10].
Fig. 2. The structure of one of the independent molecules of the iodinated product 5.
solvent and chromatography of the residue on silica gave two
major bands. The slower moving band was the mono-manganated
compound 2, as shown by microanalysis, high resolution ESI-MS,
and by NMR and IR spectra. The IR spectrum contained the
characteristic pattern for the Mn(CO)4 group found near
2000 cmꢂ1 in other cyclomanganated compounds, and also had
a complicated set of bands at ca 1600 cmꢂ1 arising from the free
and coordinated C]O groups. The compound was also charac-
terised by an X-ray structure analysis, the first for an ortho-
manganated aryl amide. This is illustrated in Fig. 1 and shows the
Mn(CO)4 group is attached via a MneC bond at the 2-position on
one of the aromatic rings, with the adjacent O of the amide
making up the coordination sphere. Other than the two trans CO
groups, the rest of the molecule is essentially planar, with none of
the non-H atoms deviating from the least squares plane by more
3.2. Reaction with HgCl2
It has been shown that transmetalation of cyclomanganated
arenes by Hg2þ occurs readily [22]. Accordingly when 2 was heated
with HgCl2 in MeOH, the corresponding 2-(chloromercurio)
compound 4 was readily isolated in good yield and characterised.
The frequency of the C]O vibrations in the IR spectrum
resemble those of a simple naphthalimide, suggesting only a weak,
if any, interaction between the Hg and the adjacent O atom. This is
as expected from related compounds that have been structurally
characterised [23,24]. This ready synthesis of the mercury deriva-
tive of naphthalimide provides a substrate for the many different
syntheses that are established based on aryl-mercury compounds
[25], giving many potential 2-substituted naphthalimide
compounds.
Fig. 3. A view of one of the independent molecules in the structure of 6 formed in the reaction of 2 with 2 mol of PhCCH.

B.K. Nicholson et al. / Journal of Organometallic Chemistry 716 (2012) 49e54
53
Despite the limitation of low yield, this MneC cleavage reaction
provides a direct route to 2-iodo-naphthalimides for further reac-
tions in, for example, Heck coupling reactions and nucleophilic
aromatic substitution chemistry.
Me
N
O
O
X
3.4. Reaction with PhCCH
Orthomanganated arenes are known to react readily with
alkynes. For examples with acyl groups there is insertion into the
MneC bond followed by a cyclisation reaction involving the acyl
groups to form indenols and related species [14,15,28,29]. In the
case of orthomanganated P(OPh)3 or Ph3P]S, insertion reactions
with alkynes led to products with enlarged metallocyclic rings
[30,31]. In other cases multiple insertions and cyclisations led to
(4) X = HgCl
(5) X = I
3.3. Reaction with ICl
Cleavage of the MneC bond of orthomanganated arenes by
halogens (Br2 or ICl) is a useful way of generating aryl halides
specifically ortho to an acyl group [26]. When 2 was reacted with ICl
the reaction was less efficient than in earlier reported examples,
leading to only low isolated yields (ca 10%) of the 2-
iodonaphthalimide (5). This was characterised by spectroscopic
means, and also by a single crystal structure, the first for a 2-
substituted N-alkyl-1,8-naphthalimide. The structure is illustrated
in Fig. 2 for one of the two independent molecules in the asym-
metric unit. This shows the expected skeleton with an iodine atom
at the 2-position. The molecule is essentially planar, though the I
and O(1) atoms are twisted towards opposite sides (þ0.49/ꢂ0.10 Å
and þ0.29/ꢂ0.25 Å respectively for molecules 1 and 2) presumably
to reduce the steric interactions between these adjacent groups,
giving I/O distances of 3.04 and 3.06 Å. This non-bonded steric
interaction is also manifested in the C(1)eC(2)eI angle of 125ꢁ and
C(1)eC(11)eO(1) of 124ꢁ. Compared with the structure of N-Et-1,8-
naphthalimide [27] the ring CeC bonds adjacent to the iodo
substituent are elongated. Molecules of 5 are stacked above each
other with a ring-to-ring distance of 3.47 Å, very similar to the
stacking in the unsubstituted N-Et-1,8-naphthalimide (3.45 Å).
(h
5-cyclohexadienyl)Mn(CO)3 compounds with the arene attached
to the new ring [14].
When the cyclomanganated naphthalimide 2 was reacted with
an excess of PhCCH a bright yellow compound was isolated in good
yields. This contained the characteristic nCO bands of a Mn(CO)3
group, and ESI-MS indicated that two equivalents of PhCCH had
been added. Confirmation of the assignment as 6 came from
a crystal structure determination. One of the two independent
molecules in the asymmetric unit is illustrated in Fig. 3.
Me
O
N
O
Ph
Ph
Mn(CO)3
(6)
Me
Me
Me
(CO)4
O
N
O
Mn
Mn(CO)4
C
O
N
O
Ph
O
N
O
C
CH
Ph
Mn(CO)4
C
CH
Ph
C
H
(2)
(7)
Me
O
Me
N
N
O
O
Ph
O
C
Ph
CH
C
Ph
Ph
C
H
Mn
(CO)4
Mn(CO)3
(6)
(8)
Scheme 1. A proposed mechanism for the formation of compound 6.

54
B.K. Nicholson et al. / Journal of Organometallic Chemistry 716 (2012) 49e54
Two molecules of PhCCH have coupled and added across the
Appendix A. Supplementary material
C1eC2 bond of the naphthalimide to generate a new six-membered
ring, a cyclohexadienyl one to which a Mn(CO)3 moiety is attached.
This arrangement has surprisingly led to the de-aromatisation of the
robust naphthalene ring of the imide. A possible mechanism is out-
lined in Scheme 1. Initial insertion of PhCCH would give the seven-
membered ring in 7. Based on the corresponding reaction of
alkynes with cyclomanganated dialkylbenzamides [14] it would be
expected that this would interact with the C]O bond to generate
a new five-membered ring, but presumably the rigidity of the imide
group in 2 prevents a suitable conformation for a similar process.
Instead a second PhCCH inserts to give a larger ring. Transfer of the
MnfromtheO totheC1eC2 bond, as in8 would encourage additionof
the MneC bond across the C1eC2 “double” bond, with the Mn(CO)3
group attaching tothe face of the newly formed cyclohexadienyl ring.
CCDC 8844089e884091 contain the supplementary crystallo-
graphic data for this paper. These data can be obtained free of
charge from The Cambridge Crystallographic Data Centre via www.
ccdc.cam.ac.uk/data_request/cif.
Appendix B. Supplementary material
Supplementary data related to this article can be found online at
http://dx.doi.org/10.1016/j.jorganchem.2012.06.035.
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have been found before in the reactions of orthomanganated arenes
with alkynes [14]. However in all previous examples the cyclo-
hexadienyl ring has been formed by trimerisation of three alkynes, the
original aryl group ending up as a substituent on the new six-
membered ring. It is not clear why a similar product was not
produced in the present case, since an excess of PhCCH was used. The
reaction is remarkably specificfor6, with only very minor by-products.
The structure determination of 6 shows that the naphthalene
unit of the molecule remains quite planar, despite the disruption of
the aromaticity, with no atom displaced more than 0.23 Å, (molecule
1) or 0.13 Å (molecule 2) from the least squares planes through the
ten C atoms. The imide group has twisted and is folded out of the
naphthalene plane byca 33ꢁ. The five C atoms of the cyclohexadienyl
group which are bonded to Mn are coplanar to within ꢃ0.05 Å, with
MneC distances in the range 2.109e2.282 Å. The main difference
between the two independent molecules of 6 is in the orientation of
the two phenyl groups which form dihedral angles with the cyclo-
hexadienyl plane of 31ꢁ and 37ꢁ for ring C(21)eC(26) and 25ꢁ and
39ꢁ for ring C(31)eC(36) respectively for molecules 1 and 2.
De-aromatisation of naphthalimides by addition reactions
across the C1eC2 bond has been reported for photochemical reac-
tions with alkenes or alkynes, leading to formation of cyclobutane
or cyclobutene rings [32e34], but as far as we are aware there is no
precedent for formation of a six-membered ring as in 6, under
relatively mild thermal conditions.
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4. Conclusions
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The efficient cyclomanganation of N-methyl-1,8-naphthalimide
provides a means of specifically directing subsequent reactions to
the 2-position. This has been demonstrated by simple cleavage of the
MneC bond by HgCl2 or ICl to give potentially useful substrates for
further development. The reaction of the cyclomanganated complex
with PhCCH follows an annulation route not observed previously for
other manganated arenes, in forming a new six-membered ring
fused to the naphthalene unit, thereby breaking the aromaticity.
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Acknowledgements
[33] Q.-J. Liu, Y.-M. Shen, H.-Y. An, G. Grampp, S. Landgraf, J.-H. Xu, Tetrahedron 62
(2006) 1131.
[34] Q.-J. Liu, D.-Q. Shi, J.-H. Xu, J. Chem. Crystallogr. 33 (2003) 263.
We thank Dr Tania Groutso, University of Auckland for collection
of X-ray intensity data, and Tiffany Smith for NMR spectra.