Cobalt Ion Promoted Redox Cascade: A Route to Spiro Oxazine-Oxazepine Derivatives and a Dinuclear Cobalt(III) Complex of an N-(1,4-Naphthoquinone)-o-aminophenol Derivative

Article abstract of DOI:10.1021/acs.inorgchem.7b01961

The study discloses that the redox activity of N-(1,4-naphthoquinone)-o-aminophenol derivatives (L^RH₂) containing a (phenol)-NH-(1,4-naphthoquinone) fragment is notably different from that of a (phenol)-NH-(phenol) precursor. The for

Full text of DOI:10.1021/acs.inorgchem.7b01961

Article
pubs.acs.org/IC
Cite This: Inorg. Chem. XXXX, XXX, XXX-XXX
Cobalt Ion Promoted Redox Cascade: A Route to Spiro Oxazine-
Oxazepine Derivatives and a Dinuclear Cobalt(III) Complex of an
N‑(1,4-Naphthoquinone)‑o‑aminophenol Derivative
Sandip Mondal, Sachinath Bera, Suvendu Maity, and Prasanta Ghosh*
Department of Chemistry, R. K. Mission Residential College, Narendrapur, Kolkata 103, West Bengal, India
S
* Supporting Information
ABSTRACT: The study discloses that the redox activity of N-
(1,4-naphthoquinone)-o-aminophenol derivatives (LRH2) con-
taining a (phenol)-NH-(1,4-naphthoquinone) fragment is
notably different from that of a (phenol)-NH-(phenol)
precursor. The former is a platform for a redox cascade.
LRH2 is redox noninnocent and exists in Cat-N-(1,4-
naphthoquinone)(2−) (LR 2−) and SQ-N-(1,4-naphthoqui-
none) (LR •−) states in the complexes. Reactions of LRH2
with cobalt(II) salts in MeOH in air promote a cascade
affording spiro oxazine-oxazepine derivatives (OXLR) in good
t
yields, when R = H, Me, Bu. Spiro oxazine-oxazepine
derivatives are bioactive, and such a molecule has so far not
been isolated by a schematic route. In this context this cascade
is significant. Dimerization of LRH2 → OXLR in MeOH is a (6H+ + 6e) oxidation reaction and is composed of formations of four
covalent bonds and 6-exo-trig and 7-endo-trig cyclization based on C−O coupling reactions, where MeOH is the source of a
proton and the ester function. It was established that the active cascade precursor is [(LMe •−)CoIIICl2] (A). Notably, formation of
a spiro derivative was not detected in CH3CN and the reaction ends up furnishing A. The route of the reaction is tunable by R,
when R = NO2, it is a (2e + 4H+) oxidation reaction affording a dinuclear LR 2− complex of cobalt(III) of the type
[(LNO2 2−)2CoIII2(OMe)2(H2O)2] (1) in good yields. No cascade occurs with zinc(II) ion even in MeOH and produces a LMe •−
complex of type [(LMe •−)ZnIICl2] (2). The intermediate A and 2 exhibit strong EPR signals at g = 2.008 and 1.999, confrming
the existence of LMe •− coordinated to low-spin cobalt(III) and zinc(II) ions. The intermediates of LRH2 → OXLR conversion were
analyzed by ESI mass spectrometry. The molecular geometries of OXLR and 1 were confirmed by X-ray crystallography, and the
spectral features were elucidated by TD DFT calculations.
Scheme 1. Redox States of LRH2 Ligands
INTRODUCTION
■
The redox activity of bis(3,5-di-tert-butyl-2-phenol)amine
(LONOH3), a ONO donor ligand that contains a (phenol)-
NH-(phenol) fragment, is versatile and significant in chemical
science. Transition-metal complexes of LONOH3 are worthy in
the context of electronic structure, catalytic activity, valence
tautomerism, and spin-crossover phenomena.1−3 Numerous
CoII/CoIII complexes of LONOH3 having Cat-N-BQ(1−) and
Cat-N-SQ(2−) electronic states that exhibit valence tautomer-
ism were reproted.4,5 In this regard, the coordination chemistry
of a molecule that contains a (phenol)-NH-(quinone) fragment
It was established that the reaction of LRH2 with cobalt(II)
and its functionality have been the subjects of investigation.
The same was explored in this project, and it was authenticated
that the reactivities of the two types of fragments are
remarkably different. In this investigation the chemistry of N-
(1,4-naphthoquinone)-o-aminophenol derivatives (LRH2) hav-
ing a phenol-NH-(1,4-naphthoquinone) fragment which exists
as Cat-N-(1,4-naphthoquinone)(2−) (LR 2−), SQ-N-(1,4-naph-
thoquinone) (LR •−), and Q-N-(1,4-naphthoquinone) (LR 0)
states as depicted in Scheme 1 is disclosed.
salts in MeOH promotes a redox cascade generating spiro
oxazine-oxazepine derivatives, methyl 2-(2′,6-bis(R)-7′,12′-
dioxo-12′,13′-dihydro-7′H-spiro[benzo[b][1,4]oxazine-2,6′-
benzo[b]naphtho[2,3-e][1,4]oxazepin]-3-ylcarbonyl)benzoate
t
(
OXLR), as shown in Chart 1, when R = H, Me, Bu and the
Received: August 1, 2017
© XXXX American Chemical Society
A
DOI: 10.1021/acs.inorgchem.7b01961
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Chart 1. Isolated OXLR Derivatives and Metal Complexes
cascade precursor is [(LMe •−)CoIIICl2] (A), which was
successfully isolated from the same reaction in CH3CN.
Finding a cascade route to isolate a bioactive organic
molecule is a challenge in chemical science and pharmacy.6
Cascades are significant in reducing chemical waste and
increasing atom economy.7 Various types of cascades have
been established to devolop the syntheses of functional organic
molecules.8,9 However, a cascade that is composed of multistep
redox reactions is rare.10 Recently a metal ion promoted redox
cascade converting N′-(1,4-dioxo-1,4-dihydronaphthalen-2-yl)-
benzohydrazide (LH2) to a stable zwitterionic triphenylphos-
phonio-hydrazyl radical (PPh3L• ) and a hitherto unknown
diarylindazolo[3a,3c]indazole (IndL2) derivative were re-
ported.11 In this particular project a redox cascade that yields
bioactive spiro oxazine-oxazepine derivatives containing a p-
quinone fragment was authenticated. The multicomponent
cascade, which involves metal coordination, C−C coupling,
tautomerization, oxidation, nucleophilic addition of alcohol,
ring cleavage, and 6-exo-trig and 7-endo-trig C−O coupling
reactions converting LRH2 to OXLR reported in this article, is
overall a (6e + 6H+) oxidation reaction.
mechanistic aspects of LRH2 → OXLR conversions have been
critically analyzed by ESI mass spectrometry. The molecular
geometries of OXLR and 1 were succsessfully authenticated by
single-crystal X-ray crystallography.
EXPERIMENTAL SECTION
■
Materials and Physical Measurements. Reagents or analytical
grade materials were obtained from commercial suppliers and used
without further purification. Spectroscopic grade solvents were used
for spectroscopic and electrochemical measurements. The C, H, and N
contents of the compounds were obtained from a PerkinElmer 2400
Series II elemental analyzer. Infrared spectra of the samples were
measured from 4000 to 400 cm−1 with KBr pellets at room
temperature on a PerkinElmer Spectrum RX 1 FT-IR spectropho-
tometer. 1H and 13C NMR spectra in CDCl3 solvent were recorded at
296 K on a Bruker Avance 500/300 MHz spectrometer. ESI mass
spectra were recorded on a Shimadzu LCMS 2020 mass spectrometer
equipped with an electrospray ionization (ESI) ion source. Electronic
absorption spectra in solution were obtained on a PerkinElmer
Lambda 750 spectrophotometer in the range 3300−175 nm. The
electroanalytical instrument BASi Epsilon-EC for cyclic voltammetry
experiments in CH2Cl2 solutions containing 0.2 M tetrabutylammo-
nium hexafluorophosphate as supporting electrolyte was used. A BASi
platinum working electrode, platinum auxiliary electrode, and Ag/
AgCl reference electrode were used for the measurements. The redox
potential data are referenced vs the ferrocenium/ferrocene (Fc+/Fc)
couple.
The wide range of biological activities of oxazine12 and
oxazepine13 heterocycles imply that a molecule having both
oxazine and oxazepine fragments will be more promising in
exploring pharmaceutical activities. The numerous other
functionalities of the oxazine and oxazepine derivatives make
these heterocycles precious in chemical science.14 However, no
substantive report on a spiro oxazine-oxazepine derivative is
available so far. In this context the report is relevant and
worthy.
One of the significant observations is that the route of the
reaction can be tuned by changing R. It was established that,
when R = NO2, LR 2− acts as a tridentate dianionic ONO donor
ligand and no 1,4-addition and C−O coupling reactions
generating OXLNO2 were substantiated. Rather, the reaction
affords a dinuclear cobalt(III) Cat-N-(1,4-naphthoquinone)
(2−) complex of the type [(LNO2 2−)2CoIII2(OMe)2(H2O)2]
(1). Because of the nitro group, the Cat-N-(1,4-naphthoqui-
none) chelate is stabilized in 1. The reaction path depends also
on the solvent and metal ion used. In CH3CN, no cascade
progresses. No cascade was established using zinc(II) ion even
in MeOH solvent; rather the reaction affords a LMe •− complex
of zinc(II) of the type [(LMe •−)ZnIICl2] (2) in good yields. The
Syntheses. 2-((2-Hydroxyphenyl)amino)naphthalene-1,4-dione
(LHH2). To a solution of 1,4-naphthoquinone (1.58 g, 10 mmol) in
MeOH was added 2-aminophenol (1.1 g, 10 mmol), and the resulting
mixture was stirred for 24 h at room temperature in air. A red solid
separated out, which was filtered and dried in air. Yield: 2.10 g (75%).
Anal. Calcd for C16H11NO3: C, 72.45; H, 4.18; N, 5.28. Found: C,
72.02; H, 4.09; N, 5.20. Mass spectrum (ESI): m/z 264 for [LHH2]−.
1H NMR (300 MHz, CDCl3): δ (ppm) 9.02 (s, 1H), 8.57 (s, 1H),
7.83−7.78 (m, 2H), 7.71 (d, J = 7.8 Hz, 1H), 7.44 (t, J = 7.5 Hz, 1H),
7.3 (t, J = 7.8 Hz, 1H), 7.20 (d, J = 7.2 Hz, 1H), 7.00 (t, J = 6.9, 1H),
6.94 (d, J = 6.8 1H), 6.86 (t, J = 7.8 1H). IR/cm−1 (KBr): ν 3439 (s,
−OH), 3281 (s, NH), 1682 (s, CO), 1598 (s), 1553 (s), 1459 (s),
1274 (s), 1104 (m), 990 (m), 740 (m).
2-((2-Hydroxy-5-methylphenyl)amino)naphthalene-1,4-dione
(LMeH2). To a solution of 1,4-naphthoquinone (1.58 g, 10 mmol) in
MeOH was added 2-amino-4-methylphenol (1.1 g, 10 mmol), and the
resulting mixture was stirred for 24 h at room temperature in air. A red
solid separated out, which was filtered and dried in air. Yield: 1.5 g
(54%). Anal. Calcd for C17H13NO3: C, 73.37; H, 4.35; N, 5.03. Found:
C, 73.03; H, 4.28; N, 4.92. Mass spectrum (ESI): m/z 277 for
B
DOI: 10.1021/acs.inorgchem.7b01961
Inorg. Chem. XXXX, XXX, XXX−XXX

Inorganic Chemistry
Article
Table 1. X-ray Crystallographic Data of OXLMe, OXLtBu, and 1
OXLMe
OXLtBu
1
formula
C35H24N2O7
1561962
584.56
C41H33N2O7
1561963
665.62
C34H28Co2N4O14
1561964
834.43
CCDC no.
fw
cryst color
red
red
black
cryst syst
monoclinic
P21/c
triclinic
monoclinic
P21/n
space group
P1
̅
a (Å)
8.3860(5)
17.4124(11)
18.5375(12)
90
10.6902(4)
11.6467(4)
15.6382(6)
109.546(2)
1698.55(11)
2
7.5672(2)
22.3208(6)
10.0679(3)
101.129(1)
1668.55(8)
2
b (Å)
c (Å)
β (deg)
V (Å)
2706.9(3)
4
Z
T (K)
293(2)
293(2)
293(2)
no. of rflns collected (2θmax
)
27529/50.14
1.434
23925/51.46
1.308
19099/52.78
1.653
ρcalcd (g cm−3
)
no. of unique rflns/rflns with I > 2σ
μ (mm−1)/λ (Å)
4766/4317
0.101/0.71073
1216.0
6429/3924
0.090/0.71073
704.0
3419/2812
1.074/0.71073
844
F(000)
b
c
R1 /goodness of fit
0.0950/1.189
0.3047
0.0581/0.978
0.1455
0.0407/1.140
0.1051
d
wR2 (I > 2σ(I))
no. of params/restraints
residual density (e Å−3
400/0
466/0
254
)
0.454/−0.458
c
0.312/−0.282
0.702/−0.365
a
b
d
Observation criterion: I > 2σ(I). R1 = ∑||Fo| − |Fc||/∑|Fo|. GOF = {∑[w(Fo2 − Fc2)2]/(n − p)}1/2. wR2 = {∑[w(Fo2 − Fc2)2]/∑[w(Fo )2]}1/2
,
2
2
2
where w = 1/[σ2(Fo ) + (aP)2 + bP] and P = (Fo + 2Fc2)/3.
1
[LMeH2]−. H NMR (300 MHz, CDCl3): δ (ppm) 8.01 (broad, 2H),
6H2O, and the yield was 18 mg (25% with respect to LHH2). Anal.
Calcd for C33H20N2O7: C, 71.22; H, 3.62; N, 5.03. Found: C, 70.98;
7.76−7.55 (m, 4H), 7.15 (s, 1H), 6.78 (t, J = 7.5 Hz, 2H), 6.34 (s,
1H), 2.29(s, 3H). IR/cm−1 (KBr): ν 3437 (s, OH), 3319 (s, NH),
2924 (m), 1682 (s, CO), 1624 (m), 1599 (s), 1566 (s), 1360 (m),
1300 (m), 1166 (m), 610 (m).
1
H, 3.51; N, 4.89. Mass spectrum (ESI): m/z 556 for [OXLH]+. H
NMR (500 MHz, CDCl3): δ (ppm) 8.41 (s, NH), 8.18 (d, J = 10,
1H), 8.06 (d, J = 10 Hz, 1H), 7.99 (d, J = 9.5 Hz, 1H), 7.74 (t, J = 10
and 10 Hz, 2H), 7.72 (t, J = 10 and 10 Hz, 1H), 7.61−7.51(m, 3H),
7.26−7.11 (m, 3H), 6.93−6.91(m, 2H), 6.61(d, J = 10, 1H), 6.38 (d, J
= 11.5, 1H), 3.73(s, 3H). 13C NMR (500 MHz, CDCl3): δ (ppm)
193.1, 181.2, 180.9, 167.6, 154, 144, 143, 140, 139.9, 135.5, 134.1,
133.0, 131.9, 131.7, 131.1, 129.9, 129.3, 128.4, 127, 126.9, 126.7, 126,
125.6, 125.2, 124, 124.5, 123.5, 120.7, 120, 116.6, 116, 52.3, 29.8, IR/
cm−1 (KBr): ν 3313 (s, NH), 1736 (s, −COOMe), 1677 (s, CO),
1590 (s), 1507 (s), 1443 (m), 1300 (s), 1127 (s), 1084 (s), 760 (m).
Methyl 2-(2′,6-Dimethyl-7′,12′-dioxo-12′,13′-dihydro-7′H-spiro-
[benzo[b][1,4]oxazine-2,6′-benzo[b]naphtho[2,3-e][1,4]oxazepin]-
3-ylcarbonyl)benzoate (OXLMe). To a suspension of LMeH2 (70 mg,
0.25 mmol) in MeOH (25 mL) in a round-bottom flask were added
carefully CoCl2·6H2O (60 mg, 0.25 mmol) followed by triethylamine
(1 drop, 0.50 mmol) in MeOH (5 mL). The solution turned green and
slowly changed to red; it was then allowed to evaporate slowly in air.
After 4−5 days, red crystals of OXLMe separated out, which were
collected upon filtration and dried in air. Yield: 28 mg (41% with
respect to LMeH2). The same reaction was performed with Co(NO3)2·
6H2O, and the yield was 31.5 mg (46% with respect to LMeH2). Anal.
Calcd for C35H24N2O7: C, 71.91; H, 4.14; N, 4.79. Found: C, 71.63;
2-((5-(tert-Butyl)-2-hydroxyphenyl)amino)naphthalene-1,4-
dione (LtBuH2). To a solution of 1,4-naphthoquinone (1.58 g, 10
mmol) in MeOH was added 2-amino-4-(tert-butyl)phenol (1.65 g, 10
mmol), and the resulting mixture was stirred for 24 h at room
temperature in air. A red solid separated out, which was filtered and
dried in air. Yield: 2.4 g (75%). Anal. Calcd for C20H19NO: C, 74.75;
H, 5.96; N, 4.36. Found: C, 74.52; H, 5.87; N, 4.26. Mass spectrum
(ESI): m/z 320 for [LtBuH2]−. 1H NMR (300 MHz, CDCl3): δ (ppm)
8.09 (broad, 2H), 7.74−7.57 (m, 4H), 7.10 (s, 1H), 6.88 (t, J = 7.5 Hz,
2H), 6.20 (s, 1H), 1.64 (s, 9H). IR/cm−1 (KBr): ν 3432 (s, OH), 3350
(s, NH), 1679 (s, CO), 1597(s), 1500 (m), 1360 (m), 1300 (m), 994
(m), 723 (m).
2-((2-Hydroxy-5-nitrophenyl)amino)naphthalene-1,4-dione
(LNO2H2). To a solution of 1,4-naphthoquinone (1.58 g, 10 mmol) in
MeOH was added 2-amino-4-nitrophenol (1.54 g, 10 mmol), and the
resulting mixture was stirred for 24 h at room temperature in air. A red
solid separated out, which was filtered and dried in air. Yield: 2.22 g
(71%). Anal. Calcd for C16H10N2O5: C, 61.94; H, 3.25; N, 9.03.
Found: C, 61.63; H, 3.19; N, 8.94). Mass spectrum (ESI): m/z 309 for
[LNO2H2]−. 1H NMR (300 MHz, CDCl3): δ (ppm) 11.6 (s, OH), 8.83
(s, NH), 7.99 (d, J = 7.5 Hz, 1H), 7.95 (t, J = 7.2 Hz, 2H), 7.90 (d, J =
7.8 Hz, 1H), 7.86−7.80 (m, 3H), 7.13 (d, J = 8.5 Hz, 1H). IR/cm−1
(KBr): ν 3385 (s, OH), 3300 (s, NH), 1670 (s, CO), 1620 (S), 1565
(S), 1503 (m), 1350 (s), 1128 (m), 1086 (m), 923 (m).
Methyl 2-(7′,12′-Dioxo-12′,13′-dihydro-7′H-spiro[benzo[b][1,4]-
oxazine-2,6′-benzo[b]naphtha[2,3-e][1,4]oxazepin]-3-ylcarbonyl)-
benzoate (OXLH). To a suspension of LMeH2 (66 mg, 0.25 mmol) in
MeOH (25 mL) in a round-bottom flask were carefully added CoCl2·
6H2O (60 mg, 0.25 mmol) followed by triethylamine (1 drop, 0.50
mmol) in MeOH (5 mL). The solution turned green and slowly
changed to red; it was then allowed to evaporate slowly in air. After 4−
5 days, a red crystalline compound of OXLH separated out, which was
collected upon filtration and dried in air. Yield: 15 mg (20% with
respect to LHH2). The same reaction was performed with Co(NO3)2·
1
H, 4.02; N, 4.68. Mass spectrum (ESI): m/z 584 for [OXLMe]+. H
NMR (300 MHz, CDCl3): δ (ppm) 8.35 (s, 1H, −NH), 8.17 (d, J =
7.5, 1H), 8.06 (d, J = 7.2, 1H), 7.99 (d, J = 7.2, 1H), 7.78−7.67 (m,
2H), 7.63−7.49 (m, 3H), 7.32 (s, 1H), 7.03 (d, J = 7.8, Hz, 1H), 6.94
(s, 1H), 6.73 (d, J = 8.1, 1H), 6.52 (d, J = 8.4, 1H), 6.28(d, J = 8.1,
1H), 3.73 (s, 3H, −OMe), 2.33 (s, 6H). IR/cm−1 (KBr): ν 3260 (s,
NH), 2985 (m), 1736 (s, −COOMe), 1677 (s, CO), 1590 (s), 1507
(s), 1443 (m), 1300 (s), 1127 (s), 1084 (s), 760 (m).
Methyl 2-(2′,6-Di-tert-butyl-7′,12′-dioxo-12′,13′-dihydro-7′H-
spiro[benzo[b][1,4] oxazine-2,6′-benzo[b]naphtho[2,3-e][1,4]-
oxazepin]-3-ylcarbonyl)benzoate (OXLtBu). It was prepared by the
above procedure from LtBuH2 using CoCl2·6H2O and MeOH as a
solvent. Yield: 40 mg (54% with respect to LtBuH2). Yield: 50 mg (68%
with respect to LtBuH2) when Co(NO3)2·6H2O was used. Anal. Calcd
C
DOI: 10.1021/acs.inorgchem.7b01961
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Inorganic Chemistry
Article
for C41H36N2O7: C, 73.64; H, 5.43; N, 4.19. Found: C, 73.49; H, 5.35;
double-ζ with diffuse and polarization functions 6-31+G* basis set23
was employed for all calculations. The 60 lowest singlet excitation
energies on the optimized geometry of [(LNO2 2−)CoIII(OMe)(H2O)]
(with a singlet spin state) in CH3CN using the CPCM model24 were
calculated by the TD-DFT method.25
1
N, 4.09. Mass spectrum (ESI): m/z 668 for [OXLtBu]+. H NMR (300
MHz, CDCl3): δ (ppm) 8.38 (s, 1H, −NH), 8.16 (d, J = 8.4 Hz, 1H),
8.04 (d, J = 7.2 Hz, 1H), 7.99 (d, J = 7.2 Hz, 1H), 7.71 (t, J = 9.6 Hz,
2H), 7.60−7.50 (m, 4H), 7.10 (s, 1H), 6.98 (d, J = 9.5 Hz, 1H), 6.95
(d, J = 9.5 Hz, 1H), 6.58 (d, J = 8.7 Hz, 1H), 6.37 (d, J = 8.4 Hz, 1H),
3.73 (s, 3H), 1.32 (s, 9H), 1.25 (s, 9H). IR/cm−1 (KBr): ν 3255 (s,
NH), 2970 (m), 1736 (s, COOMe), 1680 (s, CO), 1612 (s), 1540
(m), 1289 (s), 1134 (m), 983 (m), 720 (m).
RESULTS AND DISCUSSION
■
Details of the syntheses are presented in the Experimental
Section. The multicomponent redox reaction of LRH2 with
cobalt(II) salts in MeOH in the presence of triethylamine at
room temperature affords OXLR in higher yields. The metal salts
and solvents used, including the yields of the reactions, are
summarized in Table 2. The 1H and 13C NMR spectra of OXLR
[(LMe •−)CoIIICl2] (A). To a solution of LMeH2 (70 mg, 0.25 mmol) in
CH3CN (25 mL) in a 100 mL round-bottom flask were added
carefully CoCl2·6H2O (60 mg, 0.25 mmol) followed by triethylamine
(1 drop, 0.50 mmol). The solution turned green. It was stirred for 2 h
and a green precipitate separated out, which was collected upon
filtration and dried in air. Yield: 51 mg (50% with respect to cobalt).
Anal. Calcd for C17H11Cl2CoNO3: C, 50.15; H, 2.72; N, 3.44. Found:
C, 49.98; H, 2.67; N, 3.36. Mass spectrum (ESI): m/z 406 for [A]+.
IR/cm−1 (KBr): ν 2935 (m), 1684 (s, CO), 1596 (m), 1514 (S), 1297
(m), 1245(s), 1110 (m), 819 (m), 720 (s).
Table 2. Optimized Syntheses of OXLR
[(LNO2 2−)2CoIII2(OMe)2(H2O)2] (1). To a solution of LNO2H2 (78 mg,
0.25 mmol) in MeOH (25 mL) in a 100 mL round-bottom flask, were
added carefully CoCl2·6H2O (60 mg, 0.25 mmol) followed by
triethylamine (1 drop, 0.50 mmol), and the mixture was stirred. The
solution turned green and was allowed to evaporate slowly in air. After
2−3 days, black crystals of 1 separated out, which were collected upon
filtration and dried in air. Yield: 41 mg (40% with respect to cobalt).
Anal. Calcd for C34H26Co2N4O14: C, 49.06; H, 3.15; N, 6.73. Found:
C, 48.92; H, 3.11; N, 6.66. Mass spectrum (ESI): m/z 832 for [1]+. H
NMR (500 MHz, CDCl3): δ (ppm) 8.21 (s, 1H), 7.9 (d, 2H), 7.6 (d,
2H), 6.25 (s, 1H), 5.96 (t, 2H), 3.38(s, 3H), 2.5 (s, 2H). IR/cm−1
(KBr): ν 3420 (s, H2O), 2924 (m), 1597 (s), 1516 (s), 1299 (S), 1254
(S), 1119 (m), 812 (m), 712 (m).
entry
MX2·6H2O
solvent
R
OXLR
OXLH
OXLH
OXLMe
OXLMe
OXLtBu
OXLtBu
yield (%)
1
2
3
4
5
6
CoCl2·6H2O
MeOH
MeOH
MeOH
MeOH
MeOH
MeOH
H
20
25
41
46
54
68
Co(NO3)2·6H2O
CoCl2·6H2O
H
Me
Me
tBu
tBu
Co(NO3)2·6H2O
CoCl2·6H2O
Co(NO3)2·6H2O
[(LMe •−)ZnIICl] (2). To a suspension of LMeH2 (70 mg, 0.25 mmol)
in MeOH (25 mL) in a 100 mL round-bottom flask were added
carefully ZnCl2·6H2O (61 mg, 0.50 mmol) followed by triethylamine
(1 drop, 0.50 mmol). The solution turned bluish-green and was
allowed to evaporate slowly in air. After 2−3 days, a blue mass of 2
separated out, which was collected upon filtration and dried in air.
Yield: 71 mg (75% with respect to zinc). Anal. Calcd for
C17H11ClNO3Zn : C, 54.00; H, 2.93; N, 3.70. Found: C, 53.75; H,
2.87; N, 3.62. Mass spectrum (ESI): m/z 376 for [1]+. IR/cm−1
(KBr): ν 2915 (m), 1650 (m), 1586 (m), 1502 (s), 1450 (m), 1312
(m), 1250 (s), 853 (m), 1254 (S), 766 (m).
are illustrated in Figures S1−S4 in the Supporting Information.
The NMR shielding tensors and the spin−spin coupling
1
constants are summarized in Syntheses. The H NMR signals
were assigned by comparing the H NMR spectra of OXLH,
1
OXLMe, and OXLtBu. The spectra of OXLMe and OXLtBu display
three singlets. Two of them appear at 7.0−7.4 ppm and are
absent in the case of OXLH. These signals are assigned to
aromatic CH protons. The other singlet is observed at 8.3−8.4
ppm, which is present in all cases and is assigned to the NH
proton. A similar singlet of such an NH proton in the 1H NMR
spectra of a series of 1,4-naphthoquinone-based sulfonamides
has been documented in the literature.26
Single-Crystal X-ray Structure Determinations of the
Complexes (CCDC 1561962−1561964). Single crystals of OXLMe
,
OXLtBu, and 1 were picked up with nylon loops and were mounted on a
Bruker AXS D8 QUEST ECO diffractometer equipped with a Mo
target rotating-anode X-ray source and a graphite monochromator
(Mo Kα, λ = 0.71073 Å). Final cell constants were obtained from
least-squares fits of all measured reflections. Intensity data were
corrected for absorption using intensities of redundant reflections. The
structures were readily solved by direct methods and subsequent
difference Fourier techniques. The crystallographic data are given in
Table 1. The Siemens SHELXS-97 software package was used for
solution, and SHELXL-97 was used for the refinement.15 All non-
hydrogen atoms were refined anisotropically. Hydrogen atoms were
placed at calculated positions and refined as riding atoms with
isotropic displacement parameters.
The plausible intermediates of LMeH2 → OXLMe conversions
that were detected by ESI mass spectrometry are shown in
Scheme 2. The reaction mixture of LMeH2 with CoCl2 and Et3N
in MeOH initially turned dark green and then slowly turned
red, affording red crystals of OXLR. The overall reaction is given
in eq 1. In this reaction [(LMe •−)CoIIICl2] (A), obtained after
oxidation of the [(LMe 2−)CoII] unit in air, is the active cascade
precursor that conducts stepwise (6e + 6H+) oxidatitive
dimerization of the ligand, where MeOH is a source of one
proton and the ester function.
Density Functional Theory (DFT) Calculations. All calculations
reported in this article were done with the Gaussian 03W16 program
package supported by Gauss View 4.1. The DFT17 calculations were
performed at the level of the Becke three-parameter hybrid functional
with the nonlocal correlation functional of Lee−Yang−Parr
(B3LYP).18 The gas-phase geometry of [(LNO2 2−)CoIII(OMe)(H2O)],
a mononuclear unit of 1 with singlet spin state, was optimized using
Pulay’s direct inversion19 in the iterative subspace (DIIS) “tight”
convergent SCF procedure,20 ignoring symmetry. In all calculations, a
LANL2DZ basis set along with the corresponding effective core
potential was used for cobalt metal.21 The valence double-ζ basis set 6-
3122 was used for the H atoms. For C, N, and O atoms, the valence
CoII/Et3N
2LRH2 + MeOH + 3/2O2 ⎯⎯⎯⎯⎯⎯⎯⎯⎯→ OXLR + 3H2O
(1)
air
The formation of A was detected by peaks at m/z 405, 406, and
407 (calculated exact mass 406.9) in the mass spectrum and an
EPR signal at g = 2.008. The intermediate A was successfully
isolated using CH3CN as a solvent (vide infra). The ESI mass
spectra of the reaction mixture were recorded at several
intervals, and the spectra are shown in Figures S5 and S6 in the
Supporting Information. The peaks at m/z 406 and 507
D
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Scheme 2. Cascade Route of the Conversion LMeH2 → OXLMe Promoted by Cobalt Ion in MeOH
(dominant peak) corresponding to intermediates A and [A +
Et3N] were detected from the green solution after 15 min of
the reaction. A undergoes an electrophilic 1,4-addition reaction
with LMeH2, resulting in the formation of the intermediate B,
which undergoes tautomerization and two-electron−one-
proton oxidation to intermediate C. The 1,4-addition reaction
of the 1,4-naphthoqinone fragment in the presence of a
transition-metal ion has also been documented in the
literature.27 The nucleophilic addition of MeOH to a
noncongugated CO function of intermediate C leads to a
ring cleavage reaction, affording D. This is an example of an
aromatic ring cleavage reaction assisted by an alcohol. The
aromatic ring cleavage is a subject of investigation in different
aspects of bioinorganic chemistry,28 and thus this observation is
significant in chemical science. The peaks at m/z 686 and 718
corresponding to the intermediates B and D were detected by
ESI mass spectrometry (see Figure S6) of the reaction mixture
after 5 h. D undergoes deprotonation, one-electron oxidation,
and decoordination to E. The pendant amidophenolato
function of E promotes a 6-exo-trig C−O cyclization,29a
generating the oxazine fragment F. F further undergoes
tautomerization and a 7-endo-trig C−O coupling reaction29b
(by a 1,4-proton shift) by another pendant phenolato function,
furnishing an oxazepine moiety as in G. G is a hydroquinone
derivative that undergoes two-electron−one-proton oxidation
reaction in air and affords OXLMe. 6-exo-trig C−O followed by
7-endo-trig C−O cyclizations that lead to an p-hydroquinone
intermediate which undergoes easy oxidation to the product
was considered preferable to 7-endo-trig C−O followed by 6-
exo-trig C−O cyclization reactions that result in an o-
amidophenalato intermediate. The calculated masses of E−G
are similar to that of OXLMe (calculated mass 584.2) and a
stronger peak at m/z 585 was detected in the ESI mass
spectrum. The change in spectral features of the reaction
E
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mixture in MeOH that exhibit several isosbestic points was
recorded for a period of 3 h and is illustrated in Figure 1. The
in CH3CN. Notably, the reaction in a mixture of CH3CN and
MeOH solvents generates the spiro derivative. The same
reaction under argon in MeOH does not furnish either any
green solution or the spiro product, authenticating that air is an
oxidant of this reaction where LRH2 is oxidized to LR •− and
cobalt(II) is oxidized to cobalt(III). This implies that the
intermediate A containing an electron-deficient LR •− state
coordinated to cobalt(III) ion promotes the cascade reaction.
The role of triethylamine in this reaction is significant. In
presence of triethylamine LRH2 undergoes deprotonation,
generating LR 2−, which coordinates cobalt(II) ion and further
undergoes oxidation in the presence of air. In the absence of
triethylamine no reaction of LRH2 with a transition-metal ion
occurs. In this particular reaction coordination of triethylamine
to cobalt(III) ion stabilizing an intermediate was also detected
(see Figure S5 in the Supporting Information). The driving
force of the oxidative dimerization of the LRH2 in MeOH is the
formation of four covalent bonds in lieu of a cleavage of a C−C
bond. It is noteworthy that formation of an ester, cleaving a C−
C bond, is followed by two cyclization reactions involving two
C−O bond formations. Overall the reaction progresses with the
formation of a C−C bond and three C−O bonds with the
production of three water molecules.
Figure 1. Changes in electronic spectra during LMeH2
→
OXLMe
conversion in MeOH in the presence of cobalt ion in air.
spectrum initially displays a lower energy absorption at 730 nm
due to the radical intermediate A, which gradually disappears
due to the formation of OXLR, giving an absorption band at 505
nm (vide infra).
Et3N
LRH2 + CoCl2 + 1/2O2 ⎯⎯⎯→⎯ A + H2O
Notably, the yield of the reaction using cobalt nitrate is
higher than that when cobalt chloride is used. This may be due
to the easier decoordination of cobalt ion when nitrate is
present as a coligand. The trend follows the spectrochemical
series where nitrate is a weaker ligand than chloride.
Semiquinonate anion radical complexes of cobalt(III) having
chloride as coligands are numerous,30 while stable semi-
quinonate anion radical complexes of cobalt(III) containing
nitrate as a coligand have not been documented in the
literature. Moreover, in this reaction cobalt ion is not a catalyst.
After the first cycle of the reaction the decoordinated cobalt is a
solvated cobalt(III) ion, which is relatively inert. Thus, the
coordination of cobalt(II) ion is preferred and the yield of the
reaction containing a stoichiometric ratio of cobalt(II) salt and
ligand was relatively higher than that when a catalytic amount
of cobalt was used.
In this reaction MeOH acts as a reagent and is essential to
yield a spiro derivative. No spiro derivative containg an ethyl
easter as a funtional group was successfully isolated from a
reaction of LMeH2 with cobalt salt in EtOH. One of the reasons
is that MeOH is more acidic than EtOH and even more
strongly acidic than water. For a successful reaction triethyl-
amine and a solvent that can provide a proton is required. A
similar reaction was performed in CH3CN. The reaction does
not yield the spiro product, but upon stirring for 2 h a green
precipitate of A (see Figure S7 in the Supporting Information)
separated out. The overall reaction in CH3CN is given in eq 2.
The search affirms that in both MeOH and CH3CN the
reaction proceeds via the intermediate A, which is less soluble
(2)
In the presence of an NO2 group the path of the reaction is
different and no cascade was followed. The reaction of LNO2H2
with cobalt(II) salt affords 1, following eq 3. No spiro derivative
was isolated from this reaction. Isolation of 1 further confirmed
the existence of cobalt(III) ion in the active precursor and
supports the proposed path of the conversion of LRH2 → OXLR.
Equation 3 also clarifies the significance of triethylamine in such
a reaction involing o-aminophenol derivative as a ligand. In the
presence of a −NO2 function the LR 2− chelate that exhibits
several resonance structures as shown in Chart 2 was stabilized.
The 1,4-addition reaction as proposed in Scheme 2 did not
proceed, and the reaction furnishes the phenolato-bridged
complex 1. LNO2 2− behaves more like a LONOH3 precursor,
stabilizing the Cat-N-(1,4-naphthoquinone)(2−) state, while
t
LR •− (R = H, Me, Bu) becomes a cascade agent.
2LNO2H2 + 2CoIICl2·H2O + 4Et3N + 1/2O2 + 2MeOH
→ 1 + 11H2O + 4Et3NH+Cl−
(3)
The succsess of the cascade reaction depends on the metal
ion also coordinated to LR •−. The existence of the radical
intermediate LR •− in the intermediate A was further established
by isolating a dark bluish green LR •− complex of zinc(II) of the
type [(LMe •−)ZnIICl] (2) (see, Figure S8 in the Supporting
Information) from a reaction of ZnCl2 and LMeH2 in MeOH at
room temperature. However, the reaction does not yield the
spiro derivative.
Chart 2. Canonical Structures of [Co(LNO2 2−)] Unit
F
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Figure 2. Molecular geometries of (a) OXLMe, (b) OXLtBu, and (c) 1 in the crystal state (40% thermal ellipsoids, hydrogen atoms omitted for clarity).
Table 3. Selected Experimental Bond Lengths (Å) and Angles (deg) of OXLMe, OXLtBu, and 1
1
OXLMe
OXLtBu
C(1)−OQ
C(4)−OQ
C(3)−Noxazepine
C(11)−Noxazepine
C(2)−Cspiro
C(18)−Cspiro
Cspiro−Ooxazepine
Cspiro−Ooxazine
C(18)−Noxazine
C(27)−Noxazine
C(2)−C(17)−O(3)
C(18)−C(17)−O(3)
O(3)−C(17)−O(4)
C(2)−C(17)−C(18)
O(4)−C(17)−C(18)
O(4)−C(17)−C(2)
1.237(7)
1.211(7)
1.340(7)
1.403(8)
1.522(7)
1.514(7)
1.422(6)
1.426(6)
1.287(7)
1.399(7)
112.4(4)
101.6(4)
109.9(4)
116.5(5)
111.0(4)
105.4(4)
1.230(3)
1.217(3)
1.354(3)
1.406(3)
1.509(3)
1.529(3)
1.424(3)
1.428(3)
1.283(3)
1.402(3)
114.11(19)
100.83(19)
109.69(19)
115.3(2)
111.19(19)
105.8(2)
C(1)−O(1)
C(4)−O(4)
C(2)−N(1)
C(11)−N(1)
C(12)−O(3)
C(15)−N(2)
C(1)−C(2)
C(2)−C(3)
C(3)−C(4)
C(12)−C(11)
O(1)−Co(1)
N(1)−Co(1)
O(3)−Co(1)
O(6)−Co(1)
O(7)−Co(1)
1.232(3)
1.284(3)
1.323(3)
1.401(4)
1.307(3)
1.453(4)
1.513(4)
1.399(4)
1.386(4)
1.438(4)
2.135(3)
2.079(2)
2.044(2)
2.116(2)
2.051(3)
X-ray Crystallography. The molecular geometries of OXLR
were confirmed by the single-crystal X-ray structure determi-
nations of OXLMe and OXLtBu. Similarly the molecular geometry
of 1 in the crystal state was established by X-ray crystallography.
The crystallographic data are summarized in Table 1. OXLMe
and OXLtBu crystallize respectively in P2 /c and P1 space groups
̅
1
(CCDC 1561962−1561963). The molecular structures in the
crystals and the atom labeling schemes of OXLMe and OXLtBu are
G
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Figure 3. Cyclic voltammograms of (a) OXLH, (b) OXLMe, and (c) OXLtBu in CH2Cl2 (d) A in DMF. (e) 1 in CH3CN. and (f) 2 in DMF at 298 K.
Conditions: 0.2 M [N(n-Bu)4]PF6 supporting electrolyte; scan rate, 100 mV s−1; platinum working electrode.
illustrated in Figure 2a,b. The selected bond parameters are
summarized in Table 3. The gross geometries and the selected
bond parameters of OXLMe and OXLtBu are approximately similar.
The bond parameters around the spiro carbon significantly
deviate from the ideal values: e.g., the C(18)−Cspiro−O(3)
angle is 101.6(4)° for OXLMe. The average Cspiro−Ooxazepine and
Cspiro−Ooxazine lengths are 1.423(6) and 1.427(6) Å, respec-
tively. The average C(3)−Noxazepine length, 1.347(7) Å, is
consistent with a C−NH single bond. Two C−Noxazepine lengths
are significantly different. Because of the conjugation of the
−NH with a −CO group, the C(3)−Noxazepine lengths are
relatively shorter. The shorter C(18)−Noxazine length, 1.285(5)
Å, correlates to a CN bond. The average C(27)−Noxazine
length is 1.400(5) Å. The average CO length of OXLMe and
OXLtBu is 1.224(4) Å.
none) redox couples. The redox activity of the cascade
precursor A is notably different from those of OXLR and 1.
The cyclic voltammogram of A displays one reversible anodic
wave at +0.14 V, as shown in Figure 3d, due to the LR •−/ LR 0
redox couple. In the case of 2, no such anodic wave was
recorded and the cathodic wave due to the LR •−/LR 2− redox
couple is irreversible (see Figure 3f).
The X-band EPR spectrum of the powder sample of A that
exhibits a strong signal at g = 2.008 at room temperature is
shown in Figure 4a. The spectrum displays hyperfine splitting
1 cystaliizes in space group P21/n (CCDC 1561964). The
molecular structure in the crystal state and the atom labeling
scheme of 1 are depicted in Figure 2c. The selected bond
parameters are summarized in Table 3. The octahedral
coordination of the cobalt ion was achieved by bridging
phenolato functions. The C−O and C−N lengths are
consistent with the Cat-N-(1,4- naphthoquinone) state of the
LNO2 2− ligand. The C(1)−O(1) and C(4)−O(2) lengths are
1.232(3) and 1.284(3) Å. The relatively longer C(11)−N(1)
length, 1.401(4) Å, is consistent with an amido-phenolato state
of the LNO2 2− ligand. The C(12)−O(3) length is relatively
shorter due to resonance with the nitro group, as shown in
Chart 2. The C(2)−N(1) length, 1.323(3) Å, is also shorter
because of the resonance with one of the CO functions. A
similar trend is also noted in the cases of OXLMe and OXLtBu. The
CoIII−N length is 2.079(2) Å. The CoIII−OQ length is
expectedly longer than the CoIII−Ophenolato length. The CoIII−
OMe length is 2.092(2) Å and is similar to those reported in
other cobalt(III) complexes.31
Redox Activity and Electron Paramagnetic Resonance
(EPR) and UV−Vis−NIR Absorption Spectra. The OXLR
derivatives are redox active and exhibit a reversible cathodic
wave at −1.1 V referenced to the Fc/Fc+ couple as shown in
Figure 3a−c, due to the 1,4-naphthoquinone/1,4-naphthose-
miquinone redox couple. The corresponding redox wave of 1 as
depicted in Figure 3e is irreversible. 1 also exhibits two
successive anodic peaks, respectively, at −0.14 and 0.07 V due
to the SQ-N-(1,4-naphthoquinone)/Cat-N-(1,4-naphthoqui-
Figure 4. X-band EPR spectra of (a) A (powder) and (b) 2 (powder)
at 298 K (experimental, black; simulated, red).
(AN = 13.1 G) due to 14N nuclei (I = 1). The EPR spectrum of
the DMF solution is similar to that of the powder sample. No
shift of the charge from the ligand to metal was observed even
in a frozen glass at 110 K, confirming the existence of LR •−
coordinated to low-spin cobalt(III) ion in A. The similar EPR
spectrum of the mass obtained after evaporation of the resulting
green solution of the reaction of cobalt(II) chloride with LMeH2
in MeOH in air was recorded, confirming the formation of
radical intermediate A in the reaction. The EPR spectra of the
powder sample and a DMF solution of 2 are similar to that of
A, as depicted in Figure 4b. The simulated g value is 1.999,
which authenticates the coordination of LR •− with zinc(II) ion
in 2.
The UV−vis−NIR absorption spectra of LRH2 and OXLR as
depicted in Figure 5 were recorded in CH2Cl2, while the
spectrum of 1 was recorded in CH3CN. The spectral data are
summarized in Table 4. The spectra of OXLR (R = H, Me, tBu)
derivatives display a characteristic absorption band at 505 nm.
H
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Figure 5. UV−vis/NIR absorption spectra of (a) LHH2 (black), LMeH2 (red), LtBuH2 (blue), and LNO2H2 (green), (b) OXLH (blue), OXLMe (red), and
OXLtBu (black) in CH2Cl2 and 1 (green) in CH3CN, and (c) A (green) and 2 (blue) in DMF at 298 K.
Table 4. UV−Vis−NIR Absorption Spectral Data of RLH2 (R
isolated from an unprecedented cascade route is disclosed. The
= −Me, −tBu, −NO2), OXLH, OXLMe, OXLtBu, 1, A, and 2 at
reaction of cobalt(II) chloride with N-(1,4-naphthoquinone)-o-
aminophenol derivatives (LRH2) in MeOH promotes a redox
cascade, producing oxazine-oxazepine derivatives (R = H, Me,
298 K
compound
LHH2
solvent
CH2Cl2
λmax, nm (ε, 105 M−1 cm−1
)
tBu) in good yields. The cascade precursor is [(LMe •−)CoIIICl2]
(A) obtained after (2e + 2H+) oxidation of [(LMe 2−)CoII] unit
in air. The (6e + 6H+) oxidative dimerization of LRH2 is
composed of C−C bond formation, C−C bond cleavage, and
6-exo-trig and 7-endo-trig cyclizations based on C−O coupling
reactions, where MeOH is the source of a proton and the ester
function. Both the route (with minimum chemical waste and
higher atomic economy) and the product are useful in
pharmacy in designing broad-spectrum drugs. Notably, the
route of the reaction is tunable by R. No cascade progresses
when R = NO2, and the (2e + 4H+) oxidation reaction ends,
furnishing a dinuclear cobalt(III) complex that stabilizes a Cat-
N-(1,4-naphthoquinone)(2−) state. The reaction also depends
on the solvent and the metal ion used. In CH3CN it gives only
A, while the reaction in MeOH with zinc(II) ion affords a stable
LR •− complex, [(LMe •−)ZnIICl] (2). The study implies that the
redox activity of LRH2 containing a (phenol)-NH-(1,4-
naphthoquinone) fragment is notably different from that of a
(phenol)-NH-(phenol) precursor. The former can be used as a
cascade precursor, while the latter generates complexes that
exhibit VT.
440 (0.25), 392 (0.37), 371 (0.36), 338 (0.34),
279 (1.25)
LMeH2
CH2Cl2
496 (0.19), 452 (0.23), 397 (0.26), 334 (0.29),
285 (0.97)
LtBuH2
LNO2H2
OXLH
OXLMe
OXLtBu
A
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
CH2Cl2
DMF
450 (0.21), 335 (0.24), 284 (1.00), 271 (1.11)
443 (0.15), 420 (0.19), 342 (0.40), 285 (0.86)
499 (0.15), 335 (0.35), 279 (1.09)
508 (0.15)343 (0.34), 284 (1.13)
506 (0.19), 344 (0.39), 284 (1.47)
820 (0.20), 480 (0.39), 370 (1.30), 342 (1.19)
1
CH3CN 790 (0.13), 654 (0.20), 424 (0.42), 336 (0.73)
DMF 700 (0.50), 480 (0.47), 380 (0.78)
2
Notably, OXLR species are weakly fluorescent. The excitation
and emission wavelengths are given in Table S1 in the
Supporting Information. Excitations of OXLR at 337−340 nm
emit at 380 nm with quantum yields of lower than 0.01%. The
selected excitation and emission spectra of OXLR are shown in
Figure S9 in the Supporting Information. The electronic
spectrum of 1 displays a broader NIR absorption band at 500−
900 nm.
The origin of this NIR band was investigated by the TD DFT
calculations on the mononuclear [(LNO2 2−)CoIII(OMe)(H2O)]
unit in CH3CN using the CPCM model. The calculated
wavelengths (λcal) and the oscillation strengths (f) of the
significant transitions are summarized in Table S2 in the
Supporting Information. The NIR λcal value with f = 0.089 is
768.95 nm, which is due to an o-amidophenolato (HOMO) →
πQ* (LUMO) transition (91%). Thus, the NIR absorption of 1
at 650−700 nm (λex) is assigned to a spin-allowed closed-shell
singlet to open-shell singlet ILCT transition. The NIR band is
absent in OXLR derivatives. The UV−vis−NIR absorption
spectra of A and 2 containing LR •− display a lower energy
absorption band, as shown in Figure 5c. In DMF A exhibits a
NIR band at 820 nm, while the NIR band of 2 appears at 700
nm due to an ILCT transition. Notably the initial green
solution of MeOH containing intermediate A of the reaction of
cobalt chloride and LRH2 exhibits a strong NIR band at 730 nm
(see Figure 1).
ASSOCIATED CONTENT
* Supporting Information
The Supporting Information is available free of charge on the
ACS Publications website at DOI: 10.1021/acs.inorg-
chem.7b01961.
■
S
1H and 13C NMR spectra, ESI mass spectra, excitation
and emission wavelengths, excitation energies, oscillator
strengths, transition types, and dominant contributions
of UV−vis−NIR absorption bands obtained from TD
DFT calculations, and gas-phase optimized coordinates
(PDF)
Accession Codes
CCDC 1561962−1561964 contain the supplementary crystal-
lographic data for this paper. These data can be obtained free of
charge via www.ccdc.cam.ac.uk/data_request/cif, or by email-
ing data_request@ccdc.cam.ac.uk, or by contacting The
Cambridge Crystallographic Data Centre, 12 Union Road,
Cambridge CB2 1EZ, UK; fax: +44 1223 336033.
CONCLUSION
■
AUTHOR INFORMATION
Corresponding Author
*P.G.: e-mail, ghosh@pghosh.in; tel, +91-33-2428-7347; fax,
+91-33-2477-3597.
The biofunctionality of a molecule that contains both oxazine
and oxazepine fragments has been the subject of investigation.
However, no such molecule has been reported so far. In this
study, a family of spiro oxazine-oxazepine derivatives which are
■
I
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2993−3009.
ORCID
Prasanta Ghosh: 0000-0002-2925-1802
Notes
The authors declare no competing financial interest.
ACKNOWLEDGMENTS
■
Financial support received from the University Grants
Commission (F. No. 43-214/2014(SR)), SERB-DST, New
Delhi (EMR/2016/005222), and WB-DST, India, is gratefully
acknowledged. S.M. is grateful to the UGC, New Delhi, India,
for a fellowship (F. No. 11-24/2013 (SA-1) dated 08.07.1014).
(10) Zhang, Y.; Ye, S.; Ji, M.; Li, L.; Guo, D.; Zhu, G. Copper-
Catalyzed Radical Cascade Difluoromethylation/Cyclization of 2-(3-
Arylpropioloyl)benzaldehydes: A Route to Difluoromethylated Naph-
thoquinones. J. Org. Chem. 2017, 82, 6811−6818.
(11) Mondal, S.; Maity, S.; Ghosh, P. A Redox-Active Cascade
Precursor: Isolation of a Zwitterionic Triphenylphosphonio−Hydrazyl
Radical and an Indazolo−Indazole Derivative. Inorg. Chem. 2017, 56,
8878−8888.
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