Synthesis, structure and reactivity of [o-(2,6- diisopropylphenyliminomethinyl)phenyl]selenenyl selenocyanate (RSeSeCN) and related derivatives

Article abstract of DOI:10.1039/c4dt00157e

The synthesis and the first X-ray structural characterization of a selenenyl selenocyanate, [o-(2,6-diisopropylphenyliminomethinyl)phenyl]selenenyl selenocyanate (DiPhSeSeCN), with a stable Se-Se bond are described. The isolation of stable DiPhSeSeCN, both in the solid state and in solution, is facilitated by strong intramolecular Se...N interaction. The compound DiPhSeSeCN, an example of unsymmetrical diselenide, did not exhibit any glutathione peroxidase-like activity. The reaction of DiPhSeSeCN with thiophenol afforded (3H-benzo[c][1,2]diselenol-3-yl)(phenyl)sulfane.

Full text of DOI:10.1039/c4dt00157e

Volume 43 Number 25 7 July 2014 Pages 9365–9796
Dalton
Transactions
An international journal of inorganic chemistry
www.rsc.org/dalton
ISSN 1477-9226
PAPER
Harkesh B. Singh et al.
Synthesis, structure and reactivity of
[o-(2,6-diisopropylphenyliminomethinyl)phenyl]selenenyl selenocyanate
(RSeSeCN) and related derivatives

Dalton
Transactions
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PAPER
Synthesis, structure and reactivity of [o-(2,6-
diisopropylphenyliminomethinyl)phenyl]selenenyl
selenocyanate (RSeSeCN) and related derivatives†
Cite this: Dalton Trans., 2014, 43,
9431
Prakul Rakesh,a Harkesh B. Singh,*a Jerry P. Jasinskib and James A. Golenb
The synthesis and the first X-ray structural characterization of a selenenyl selenocyanate, [o-(2,6-diisopro-
pylphenyliminomethinyl)phenyl]selenenyl selenocyanate (DiPhSeSeCN), with a stable Se–Se bond are
described. The isolation of stable DiPhSeSeCN, both in the solid state and in solution, is facilitated by
strong intramolecular Se⋯N interaction. The compound DiPhSeSeCN, an example of unsymmetrical dis-
elenide, did not exhibit any glutathione peroxidase-like activity. The reaction of DiPhSeSeCN with thio-
phenol afforded (3H-benzo[c][1,2]diselenol-3-yl)(phenyl)sulfane.
Received 16th January 2014,
Accepted 25th February 2014
DOI: 10.1039/c4dt00157e
www.rsc.org/dalton
Introduction
Glutathione peroxidase (GPx),
a selenoenzyme, reduces
harmful hydrogen peroxide and organic peroxides at the
expense of co-factor glutathione (GSH).1,2 The active site of the
enzyme contains a selenocysteine residue, which undergoes a
redox cycle. Selenol (ESeH), the active form of selenoenzyme,
reduces peroxides and gets oxidized to selenenic acid (ESeOH).
Then the selenenic acid (ESeOH) reacts with reduced gluta-
thione (GSH) to form the selenenyl sulfide adduct (ESeSG).
The active form of the enzyme is regenerated by the attack of
the second glutathione on ESeSG to form oxidized glutathione
(GSSG) (Fig. 1).
Diorganodiselenides act as synthetic mimics of GPx
enzyme.1–5 The GPx-like activity of diorganodiselenides
depends on the activation of the Se–Se bond towards the oxi-
dative cleavage and generation of selenols and selenosulfides
as the key intermediates. The Se–Se bond can be activated by
an intramolecular secondary bonding interaction of the type
Se⋯N/O. However, Sarma and Mugesh have reported that the
Se⋯N/O intramolecular interaction also increases the electro-
philicity of the Se centre and hence increases the possibility of
attack of the RS− ion on the selenium centre of the
Fig. 1 Proposed catalytic mechanism of glutathione peroxidase.
selenosulfide adduct rather than the sulfur centre (Fig. 2).6
This is detrimental to GPx-like activities of the enzyme
mimics.
Alternatively, the Se–Se bond in diselenides can also be acti-
vated by using unsymmetrical diselenides (RSeδ+–δ−SeR′) with
different organic substituents bonded to the selenium atoms.
aDepartment of Chemistry, Indian Institute of Technology Bombay, Powai,
Mumbai 400 076, India. E-mail: chhbsia@chem.iitb.ac.in; Fax: +9122 2576 7152;
Tel: +9122 2576 7190
bDepartment of Chemistry, Keene State College, 229 Main Street, Keene,
NH 03435-2001, USA
†Electronic supplementary information (ESI) available: The spectroscopic data
(1H, 13C, 77Se NMR spectra, CHN analysis, ESI-Mass spectra and FT-IR spectra)
for all the compounds (11, 13, 14, 15, 17, 18 and 22). CCDC 959142–959145. For
ESI and crystallographic data in CIF or other electronic format see DOI: 10.1039/
c4dt00157e
Fig. 2 Nucleophilic attack of thiol at the selenium or sulfur centre.
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This would lead to a polar Se–Se bond. However, reports on
the synthesis of unsymmetrical diorgano diselenides are rare.
Rheinboldt and Giesbrecht reported the synthesis of unsym-
metrical diselenides (RSeSeR′ where R = o-O2NC6H4, 4,2-Cl-
(O2N)C6H3, o-O2NC6H4 R′ = Ph).7 The synthesis of the unsym-
metrical diselenides was achieved by the reaction of the corres-
ponding RSe+ (R = o-O2NC6H4SeCl) with PhSe− (R = Ph).
However, these unsymmetrical diselenides were poorly charac-
terized. The problem with this synthetic route is the formation
of two more symmetrical side products along with the desired
product. The purification of the desired product proved very
difficult since the polarities of the product and the side pro-
ducts were almost the same. The first well characterized
unsymmetrical diselenide, i.e. CF3SeSeCF2Cl, was synthesized
by electrophilic addition of CF3SeCl to SevCF2.8 Unsymmetri-
cal diselenide, CF3SeSeCH3, has also been synthesised by
mixing an equimolar mixture of CH3SeSeCH3 and
CF3SeSeCF3.8
Rheinboldt and Giesbrecht have reported the synthesis of
arylselenenyl selenocyanates (1–4) containing a polar Se–Se
bond by the reaction of arylselenenyl bromides and potassium
selenocyanate.9 The first study on the well characterized aryl-
selenenyl selenocyanates (5–7) was described by Renson and
Piette.10 The chemical structures of 1–7 suggest that the intra-
molecular interaction may be responsible for the stability of
these compounds. However, the compounds have not been
characterized by single crystal X-ray diffraction studies.
Further, the GPx-like activity of any ArSeSeCN has not been
reported in the literature.
Intramolecular secondary bonding interaction has been
extensively used for the isolation of unstable organoselenium
compounds.1,11,12 Recently, Singh and coworkers have success-
fully isolated a series of organoselenenyl azides (8 and 9) by
using the intramolecular interaction approach.13 The selenenyl
azide, [o-(2,6-diisopropylphenyliminomethinyl)phenyl]selene-
nyl azide (9), was the most stable azide among the reported
organoselenium azides due to the shortest Se⋯N bond dis-
tance.13 Selenenyl azide 9 has the highest secondary bonding
interaction energy as well. This clearly indicated that the
increasing bulkiness around nitrogen could also result in sig-
nificant gain in the stabilization energy. In view of the iso-
lation of the most stable azide (9), it was envisaged that [o-(2,6-
diisopropylphenyliminomethinyl)phenyl]selenenyl substrates
could prove to be suitable synthons for the isolation of stable
ArSeSeCN. Moreover, in view of the shortest Se⋯N bond dis-
tance calculated in 9, we were also interested in structural
aspects of other related low-valent selenium derivatives con-
taining an o-(2,6-diisopropylphenyliminomethinyl)phenyl
moiety (Fig. 3).
Fig. 3 Aromatic selenenyl selenocyanates and azides.
chloride (12) with potassium selenocyanate in dry methanol at
0 °C (Scheme 1). Precursor 12 was prepared by chlorination of
bis[o-(2,6-diisopropylphenyliminomethinyl)phenyl]diselenide
(11)13,14 and the Schiff base diselenide (11) was obtained by
the reaction of bis(o-formylphenyl)diselenide (10) with 2,6-di-
isopropylbenzenamine in the presence of a catalytic amount of
acetic acid. Diselenide 11 was further derivatized into [o-(2,6-
diisopropylphenyliminomethinyl)phenyl]selenenyl(II) bromide
(13) and [o-(2,6-diisopropylphenyliminomethinyl)phenyl]sele-
nenyl(II) iodide (14) by reactions of Br2 and I2 respectively at
0 °C. In order to synthesize a Se(IV) derivative, the precursor
selenide (17) was prepared by the reaction of bis(o-formylphe-
nyl)selenide (16)14 with 2,6-diisopropylbenzenamine. Selenide
17 was oxidized by NaIO4 in the presence of a catalytic amount
of a phase transfer catalyst, tertiarybutylammonium bromide
(TBAB), to get bis[o-(2,6-diisopropylphenyliminomethinyl)-
phenyl]selenoxide (18).
The title compound 15 is stable for 15 days at room temp-
erature and −20 °C for a period of six months. All the other
compounds (12, 13 and 14) are stable at room temperature for
1
an indefinite period of time. In the H NMR spectrum of 15,
the azomethine proton is observed at 8.71 ppm, which is
upfield shifted as compared to that observed for 12 (8.94 ppm)
and 13 (8.84 ppm). However, it is downfield shifted compared
Results and discussion
[o-(2,6-Diisopropylphenyliminomethinyl)phenyl]selenenyl sele-
nocyanate (15) was obtained by the metathesis reaction of
Scheme 1 Synthesis
of
[o-(2,6-diisopropylphenyliminomethinyl)-
[o-(2,6-diisopropylphenylimino-methinyl)phenyl]selenium(II) phenyl]selenenyl derivatives.
9432 | Dalton Trans., 2014, 43, 9431–9437
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to that observed for 14 (8.50 ppm). The –CH3 peak of 15 indi-
cated chemical non-equivalency of both the –CH3 groups in
solution. The chemical non-equivalency of both the –CH3
groups in solution was further indicated by 13C NMR spectra
of 15, 13 and 14 as they showed two peaks for both the –CH3
groups. The chemical shift of 77Se NMR of 13 (1021 ppm) is
downfield as compared to bis[o-(R)-(methylbenzyliminomethi-
nyl)-phenyl]selenenyl bromide (1006 ppm) and {2-[1-(3,5-
dimethylphenyl)-2-naphthyl]-4,5-dihydro-4,4-dimethyl-1,3-
oxazol-2-yl}selenenyl bromide (837 ppm).14 However, it is
slightly upfield as compared to the chemical shift of 77Se NMR
of (2-phenylazophenyl-C,N′)selenenyl bromide (1093 ppm).13
The observation of two signals in the 77Se NMR spectrum of 15
at 892 and 110 ppm indicated the presence of two types of Se
atoms. The peak at 892 ppm is close to the chemical shift
observed in [o-(2,6-diisopropylphenyliminomethinyl)phenyl]-
selenenyl azide (1026 ppm)13 and the peak at 110 ppm is close
to the chemical shift observed for metal selenolates, in which
the selenium centre is anionic in nature.15 In order to get a
better insight into the charge on both selenium centres in 15,
the geometry of [o-(2,6-diisopropylphenyliminomethinyl)-
phenyl]selenenyl selenocyanate (15) was optimized at the
B3LYP level of theory with the use of the 6-31+G(d,p) basis
sets.16 The natural bond orbital (NBO) charges showed that
both selenium atoms were positively charged, i.e. Se1 (+0.443)
and Se2 (+0.043) (Fig. S41 of ESI†). However, the Se2 atom was
less positive than the Se1 atom. The calculated 77Se NMR
chemical shifts (905, 69 ppm) of 15 are close to the observed
values. The νCvN stretching frequency of 15 (1599 cm−1) was
similar to that observed for the other halo derivatives
[12 (1595 cm−1), 13 (1591 cm−1) and 14 (1589 cm−1)]. However,
the peak at 2110 cm−1 corresponding to –CuN is significantly
shifted as compared with KSeCN (2070 cm−1).17
Fig. 4 (a) Molecular structure of 15 and selected bond lengths (Å) and
angles (°). Hydrogen atoms are omitted for clarity. Se1–C1 1.917(2), Se1–
Se2 2.6069(4), Se1⋯N1 2.116(2); N1–Se1–Se2 172.93(6), C1–Se1–Se2
97.60(8), C20–Se2–Se1 101.93(9). (b) Molecular structure of 13 and
selected bond lengths (Å) and angles (°). Se1–C1 1.890(3), Se1–Br1
2.7012(4), Se1⋯N1 1.982(2); N1–Se1–Br1 176.23(7), C1–Se1–Br1
94.96(8).
bond angle of C20–Se2–Se1 is 101.93(9)°. The coordination
geometries around the Se1 atoms in compounds 13 (Fig. 4b)
and 14 (Fig. S1†) are quite similar to that observed for 15.
Interestingly, the intramolecular N1⋯Se1 distance of 13
(1.982(2) Å) is shorter than the corresponding N⋯Se distances
of
{2-[1-(3,5-dimethylphenyl)-2-naphthyl]-4,5-dihydro-4,4-
dimethyl-1,3-oxazol-2-yl}selenenyl bromide (2.052(2) Å) and
(2-phenylazophenyl-C,N′)selenenyl bromide (2.025(2) Å).13
However, it is slightly longer than the observed distance
(1.899(2) Å) in selenenium cations, (2-nitro-6-((phenylimino)-
methyl)phenyl)selenenyl(II) tribromide12 and bis[o-(R)-(methyl-
benzyliminomethinyl)-phenyl]selenenyl bromide (1.943(3) Å).14
The Se1–Se2 bond length (2.6069(4) Å) in 15 is longer than
the Se–Se bond length in related symmetrical diselenides, i.e.
bis[3-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-4-(3,5-dimethyl-
phenyl)-2-naphthyl] diselenide19 (2.3216(15) Å) and [2-(2-oxa-
zolinyl)phenyl]diselenide20 (2.343(13) Å). The Se1–Se2 bond
length (2.6069(4) Å) is even longer than the longest Se–Se bond
distance reported for diselenides, i.e. [N-(6′-n-propyl-4′-pyrimi-
done) (6-n-propyl-2-selenouracil)2(Se–Se)] (2.4427(6) Å).21
The molecular structure of 17 is shown in Fig. 5. The
coordination geometry around the Se atom can be considered
as T-shaped, in which the ClB atom and the two lone pairs are
in the equatorial positions and N1B and C1A atoms are in the
axial positions. The intramolecular N1B⋯Se distance is
2.803(13) Å and the N1B⋯Se–C1A angle is about 164.36(5)°.
The distance is shorter than that reported for bis[(N,N-di-
methylamino)benzyl]selenide22 (3.190 Å); however, it is longer
1
In the H NMR spectrum of 18, the peaks due to –CH3 and
–CH show downfield shift as compared to precursor 17. The
peak observed at 1329 ppm in the 77Se NMR spectrum of 18
compares well with other selenoxides;18 however, it is signifi-
cantly downfield shifted as compared to selenide 17
(396 ppm). Selenoxide 18 shows peaks at 1597 cm−1 and
749 cm−1 in the FT-IR spectrum. These correspond to νCvN
18
and νSevO
.
The lower νCvN stretching frequency (1597 cm−1
)
of selenoxide 18 compared to selenide 17 (1637) indicates
stronger coordination of N to Se.
The molecular structure of 15 is shown in Fig. 4a. The
coordination geometry around the Se1 atom can be considered
as T-shaped, in which the C1 atom and the two lone pairs are
in the equatorial position and N1, Se2 atoms are in the axial
positions. The bond angle of N1–Se1–Se2 (172.93(6)) is close to
180°. The intramolecular N1⋯Se1 distance (2.116(2) Å) of 15 is
longer than the intramolecular N(sp2)⋯Se selenenyl halides 13
(1.982(2) Å) and 14 (1.993(17) Å). This indicates a weaker intra-
molecular interaction in 15 as compared to 13 and 14. The N1
(sp2)⋯Se1 distance of 15 is close to the intramolecular N(sp2)
⋯Se interaction (2.145(16) Å) of [2-[1-(3,5-dimethylphenyl)-2-
naphthyl]-4,5-dihydro-4,4-dimethyloxazole]selenenyl(II) azide.13
Fig. 5 Molecular structure of 17 and selected bond lengths (Å) and
angles (°). Hydrogen atoms are omitted for clarity. Se–C1A 1.928(17),
Se–C1B 1.929(15) N1B–Se 2.803(13); N1B–Se1–C1A 164.36(5), C1A–Se–
The geometry around the other Se2 atom is V-shaped and the C1B 96.34(7).
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than the Se⋯N bond distance of bis-(2-phenylazophenyl-C,N′)-
selenide23 (2.621 Å). In 17 only one of the N atoms, i.e. N1B,
coordinates with Se, and the other N1A is twisted away from
Se. This behaviour is similar to that of bis-(2-phenylazophenyl-
C,N′)selenide. However, in bis[(N,N-dimethylamino)benzyl]-
selenide, both nitrogens weakly coordinate to Se.
The GPx-like activity of 15 was measured using ebselen as
the reference.3b The catalytic reaction was monitored by
measuring the rate of formation of Ph2S2 spectrophotometri-
cally at 305 nm (εmax = 1.24 × 103 M−1 cm−1). The initial rates
for all the compounds were measured at least three times and
were calculated from the first 5–10% of the reaction. Com-
pound 15 was found to be almost inactive (Table 1).
In order to rationalize the poor GPx-like activity, the reac-
tions of 15 with the substrate i.e. PhSH and H2O2 were fol-
lowed by 77Se NMR spectroscopy experiments (Scheme 2).
When 15 was treated with PhSH (2 equiv.) in CDCl3, three new
peaks (629, 529 and 365 δ) were observed (Fig. 6). The peaks at
529 and 365 δ were assigned to compound 22 (vide infra) and
the peak at 629 δ was due to the corresponding selenenyl
sulfide 19.3,4,24 The titration experiments suggest that 15,
when treated with thiophenol, converts into 22 and the corres-
ponding selenenyl sulfide 19. On treatment of 15 with H2O2
(2 equiv.), a new signal at 424 ppm was observed. This peak is
in the region of 77Se NMR chemical shifts of selenides or di-
selenides.3 Further addition of H2O2 (12 equiv.) did not lead to
any change in the 77Se NMR spectrum. There is no evidence
for the formation of seleninic acid 21 in this experiment. This
Fig. 6 The 77Se NMR spectrum of (a) catalyst 15, (b) catalyst 15 and
2 equiv. of PhSH, and (c) catalyst 15, 2 equiv. of PhSH and 2 equiv. of
H2O2.
Scheme 3 Synthesis of 3H-benzo[c][1,2]diselenol-3-yl)(phenyl)sulfane
(22).
Table 1 GPx-like activities of organoselenium compounds (initial
reduction rates (V0) of H2O2 (2 mM) with PhSH (1 mM) in methanol
(solvent) in the presence of selenium catalyst (0.01 mM))
Entry
Catalyst
Vo (µM min−1
)
could be the reason for the inactivity of catalyst 15 towards
GPx-like activities.
1
2
3
None
Ebselen
15
2.25 0.04
2.98 0.01
3.43 0.04
When compound 15 was compound reacted with thiophe-
nol in order to isolate 19, an unexpected (3H-benzo[c][1,2]di-
selenol-3-yl)(phenyl)sulfane (22) was obtained (Scheme 3). In
the 1H NMR spectrum of 22, the expected peaks of –CHvN,
–CH and –CH3 were absent. The peak at 6.11 ppm in 22 indi-
cates the presence of a highly downfield shifted aliphatic
proton. The azomethine peak was absent in the 13C NMR spec-
trum and one aliphatic carbon peak (61.7 ppm) was present in
22. Compound 22 also shows two signals (364, 528 ppm) in
the 77Se NMR spectrum; however, both signals are in the range
for the diorgano diselenides. Singh and coworkers have earlier
isolated a similar compound, i.e. 7-nitro-3H-benzo[c][1,2]dise-
lenol-3-yl)(phenyl)sulfane by the reaction of the selenenium
cation with thiophenol.12 The formation of 22 can be
explained in two steps: (i) addition elimination reaction, i.e.
nucleophilic addition reaction of thiophenol on the –CvN
bond followed by the intramolecular elimination reaction of
amine and (ii) nucleophilic addition reaction of Se on the
–CvS bond (Scheme 4). All attempts to isolate the compound
having a chemical shift of 424 ppm in 77Se NMR were
unsuccessful.
Scheme 2 Expected reactions of PhSH and H2O2 with 15.
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remove the unreacted amine. The solid thus obtained was crys-
tallized from chloroform–hexane (1 : 4) to give pale yellow crys-
tals of 11. Yield: 0.84 g, 45%; mp 159–161 °C. Anal. Calcd for
C38H44N2Se2: C, 66.46; N, 4.08; H, 6.46. Found C, 66.79; N,
1
4.42; H, 6.35. H NMR (CDCl3): δ 1.19 (d, 24H), 3.05–3.11 (m,
4H), 7.14–7.20 (m, 6H), 7.31–7.33 (m, 4H), 7.66 (m, 2H), 8.01
(d, 2H), 8.49 (s, 2H). 13C NMR (CDCl3): δ 23.9, 28.2, 123.2,
124.8, 126.0, 131.3, 131.8, 132.7, 134.6, 134.8, 138.1, 147.5,
162.5. 77Se NMR (CDCl3): δ 467. ES-MS: (m/z) 344 (C19H22NSe+
+
(100%)). HRMS (EI): m/z [C38H22N2Se2 (M+) calcd: 689.1913,
Found: 689.1929. IR (KBr, cm−1): 1634 (νCvN).
[o-(2,6-Diisopropylphenyliminomethinyl)phenyl]selenenyl(II)
bromide (13). To a solution of bis[o-(2,6-diisopropylphenylimi-
nomethinyl)phenyl]diselenide (11) (0.15 g, 0.21 mmol) in dry
CCl4 (10 mL) was added drop-wise a solution of Br2 (0.03 g,
0.21 mmol) in dry CCl4 (10 mL) at 0 °C. The reaction was
further stirred for 2 hour at room temperature. The solvent
was removed under vacuum and the sticky solid so obtained
was treated with hexane to obtain an off-white solid. The solid
thus obtained was crystallized from dichloromethane–hexane
to give pale yellow crystals (13). Yield: 0.13 g, 72%; mp
184–186 °C. Anal. Calcd for C19H22NSeBr: C, 53.92; N, 3.31; H,
Scheme 4 Plausible mechanism for the synthesis of 22.
Conclusions
Compound 15 is the first example of a structurally character-
ized RSeSeCN. The elongation in the bond length of Se–Se
(2.6069(4) Å) and a large difference in the 77Se NMR chemical
shifts (892, 110 ppm) of the two different Se atoms suggest
that the Se–Se bond is partially ionic in 15. Compound 15 was
an inactive catalyst in the thiophenol assay for GPx-like activi-
ties. The reaction of 15 with thiophenol gives an unusual
product 22 in the place of the expected selenenyl sulphide.
DFT calculations on 15 show that both Se atoms were posi-
tively charged; however, the charge on the Se1 atom was more
positive than the charge on the Se2 atom.
1
5.24. Found C, 53.51; N, 4.10; H, 5.19. H NMR (CDCl3): δ 1.12
(d, 6H), 1.24 (d, 6H), 2.58 (m, 2H), 7.26 (d, 2H), 7.43 (t, 1H),
7.64 (t, 1H), 7.80 (t, 1H), 8.11 (d, 1H), 8.84 (s, 1H), 9.11 (d, 1H).
13C NMR (CDCl3): δ 24.2, 25.2, 28.6, 124.2, 127.1, 130.2, 130.4,
131.7, 131.8, 133.0, 136.5, 143.5, 152.4, 159.0. 77Se NMR
(CDCl3): δ 1021. ES-MS: (m/z) 344 (C19H22NSe+ (100%)). IR
(KBr, cm−1): 1591 (νCvN).
[o-(2,6-Diisopropylphenyliminomethinyl)phenyl]selenenyl(II)
iodide (14). To a stirred solution of 11 (0.1 g, 0.14 mmol) in
dry CCl4 (40 mL) was added a solution of I2 (0.035 g,
0.014 mmol) and the reaction followed in a similar manner to
Experimental section
General procedures
All reactions were carried out under a N2 atmosphere. Solvents that described above for the synthesis of 13 to obtain a brown
were purified and dried by standard techniques.25 Melting precipitate. The compound was recrystallized from a CHCl3–
points were recorded in capillary tubes and are uncorrected. hexane (1 : 4) mixture to give brown crystals of 15. Yield:
1H and 13C spectra were obtained at 399.88 and 100.56 MHz, 0.095 g, 73%; mp 127–129 °C. Anal. Calcd for C19H22NSeI: C,
respectively, in CDCl3 on a Bruker AV 400 spectrometer. 77Se 48.53; N, 2.98; H, 4.72. Found C, 48.22; N, 3.45; H, 4.68. 1H
NMR spectra were recorded at 94.75 MHz in CDCl3 on a NMR (CDCl3): δ 1.12 (d, 6H), 1.24 (d, 6H), 2.65 (m, 2H), 7.27
Bruker AV 400 spectrometer. Chemical shifts are cited with (d, 2H), 7.43 (t, 1H), 7.66 (t, 1H), 7.73 (t, 1H), 7.99 (d, 1H), 8.50
respect to SiMe4 as internal (1H and 13C) and Me2Se (77Se) as (s, 1H), 8.94 (d, 1H). 13C NMR (CDCl3): δ 23.9, 25.0, 28.5, 124.1,
external standards. Elemental analysis was performed on a 127.1, 129.6, 130.8, 132.2, 132.8, 135.0, 137.1, 142.9, 147.4,
Carlo-Erba model 1106 CHNS elemental analyzer. Infrared 158.3. 77Se NMR (CDCl3): δ 970. ES-MS: (m/z) 344 (C19H22NSe+
spectra were recorded in the range 4000–400 cm−1 on a Nicolet (100%)). IR (KBr, cm−1): 158 (νCvN).
Impact 400 FT-IR spectrophotometer. ES-MS spectra were
[o-(2,6-Diisopropylphenyliminomethinyl)phenyl]selenenyl
recorded at room temperature on a Q-Tof (YA-105) micromass selenocyanate (15). To a solution of [o-(2,6-diisopropylphenyl-
spectrometer. The catalytic activities were recorded in a 1 mL imino-methinyl)phenyl]selenium(II) chloride13 (12) (0.1 g,
cuvette on a Cary 100 bio UV-Vis spectrophotometer at room 0.26 mmol) in a mixture of dry CHCl3 (2 mL) and dry metha-
temperature.
nol (5 mL) was added dropwise a solution of KSeCN (0.03 g,
Bis[o-(2,6-diisopropylphenyliminomethinyl)phenyl]diselenide 0.26 mmol) in dry methanol (5 mL) at 0 °C. After the addition
(11). Bis(o-formylphenyl)diselenide (10)14 (1 g, 2.7 mmol), 2,6- was complete, the reaction mixture was allowed to stir at room
diisopropylphenylamine (0.63 g, 5.4 mmol) and two drops of temperature for 2 hours. The reaction mixture was filtered and
acetic acid were refluxed azeotropically in benzene (200 mL) the solvent was removed under vacuum to get a pale yellow
using a Dean-Stark trap till the completion of the reaction (by solid. The solid thus obtained was crystallized from CHCl3–
IR). The reaction was complete in 72 hours. The resulting reac- hexane to give pale yellow crystals (15). Yield: 0.09 g, 76%; mp
tion mixture was evaporated and washed with cold ethanol to 129–131 °C. Anal. Calcd for C20H22N2Se2: C, 53.58; N, 6.25; H,
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4.95. Found C, 53.51; N, 6.10; H, 5.19. 1H NMR (CDCl3): δ 2H). 13C NMR (CDCl3): δ 61.7, 125.8, 127.1, 127.6, 128.4, 128.8,
1.19–1.25 (d, 12H), 2.73 (m, 2H), 7.25 (d, 2H), 7.33 (m, 1H), 129.2, 134.0, 134.4, 137.8, 142.8. 77Se NMR (CDCl3): δ 364, 528.
7.56 (t, 1H), 7.70 (t, 1H), 7.92 (d, 1H), 8.46 (d, 1H), 8.71 (s, 1H). ES-MS: (m/z) 248 (C7H5Se2+ (100%)).
13C NMR (CDCl3): δ 24.2, 24.7, 28.5, 104.6, 123.9, 126.9, 128.4,
131.5, 131.8, 132.85, 132.9, 139.5, 141.4, 143.5, 161.3. 77Se
X-ray crystallographic studies
NMR (CDCl3): δ 892, 110. ES-MS: (m/z) 344 (C19H22NSe+
The diffraction measurements for compounds 13, 14, 15 and
(100%)). HRMS (EI): m/z [C20H22N2Se2K+ (M+) calcd: 488.9750,
17 were performed at 200 K on a Oxford Diffraction Gemini
Found: 488.9773. IR (KBr, cm−1): 1599.4 (νCvN), 2110 (νCuN).
diffractometer using graphite-monochromated Mo Kα radi-
Bis[o-(2,6-diisopropylphenyliminomethinyl)phenyl]selenide
(17). Bis(o-formylphenyl)selenide (16)14 (0.5 g, 1.7 mmol) was
refluxed azeotropically in benzene (100 mL), with 2,6-diisopro-
pylphenylamine (0.39 g, 3.4 mmol) and two drops of acetic
acid. The reaction was continued in a similar manner to that
described above for the synthesis of 11. The resulting reaction
mixture was evaporated and washed with cold ethanol to
remove the unreacted amine. The yellow compound was recrys-
tallized from the CHCl3–hexane (1 : 4) mixture to give pale
yellow crystals of 17. Yield: 0.54 g, 50%; mp 159–161 °C. Anal.
ation (λ = 0.7107 Å). The structures were solved by routine
heavy-atom using SHELXS 9726 and Fourier methods and
refined by full-matrix least squares with the non-hydrogen
atoms anisotropic and hydrogens with fixed isotropic thermal
parameters of 0.07 Å2 using the SHELXL 97 program.27 The
hydrogens were partially located from difference electron-
density maps, and the rest were fixed at calculated positions.
Scattering factors were from common sources.28 Some details
of data collection and refinement are given in Table S2, ESI.†
Calcd for C38H44N2Se: C, 75.10; N, 4.61; H, 7.30. Found C, Computational studies
74.82; N, 4.42; H, 7.05. 1H NMR (CDCl3): δ 1.06 (d, 24H),
All the theoretical calculations were executed using the Gaus-
2.87–2.95 (m, 4H), 7.05–7.13 (m, 6H), 7.31–7.36 (m, 4H), 7.41
(m, 2H), 8.00 (d, 2H), 8.54 (s, 2H). 13C NMR (CDCl3): δ 23.7,
28.0, 123.1, 124.4, 127.7, 130.9, 131.7, 134.3, 135.3, 136.6,
137.8, 148.6, 162.9. 77Se NMR (CDCl3): δ 396. ES-MS: (m/z) 344
(C19H22NSe+ (100%)). IR (KBr, cm−1): 1637 (νCvN).
sian 03 suite of quantum chemical programs. The geometry
optimizations were carried out at the B3LYP level of DFT by
using the 6-31+G(d) basis sets. The 77Se NMR calculations were
performed at the B3LYP/6-311+G (d,p) level on B3LYP/
6-31+G(d)-level optimized geometries by using the gauge-
including atomic orbital (GIAO) method (referenced with
respect to the peak of Me2Se).29 The quantifications of orbital
interaction were done by natural bond orbital (NBO) analysis
at the B3LYP/6-311+G(d,p) level.30
Bis[o-(2,6-diisopropylphenyliminomethinyl)phenyl]selenoxide
(18). To a stirred solution of bis[o-(2,6-diisopropylphenyl-
imino-methinyl)phenyl]selenide (17) (0.15 g, 0.24 mmol) in a
mixture of CHCl3 (2 mL) and ethanol (10 mL), with tetrabutyl-
ammonium bromide in a catalytic amount, was added drop-
wise a solution of NaIO4 (0.05 g, 0.24 mmol) in distilled water
(5 mL) at room temperature. The reaction mixture was allowed
to stir at room temperature for 24 hours. The solvent was fil-
tered and removed under vacuum and the sticky solid so
obtained was treated with hexane to obtain a white solid. The
solid thus obtained was crystallized from dichloromethane–
hexane to give white crystals (18). Yield: 0.04 g, 28%; mp
115–117 °C. Anal. Calcd for C38H44N2SeO: C, 73.17; N, 4.49; H,
7.11; O, 2.57. Found C, 73.82; N, 4.62; H, 7.05; O, 2.29. 1H
NMR (CDCl3): δ 1.21 (d, 24H), 3.35 (m, 4H), 7.23 (m, 6H), 7.42
(t, 4H), 7.67 (m, 4H), 8.14 (d, 2H). 77Se NMR (CDCl3): δ 1329.
ES-MS: (m/z) 361 (C19H22NOSe+ (100%)). IR (KBr, cm−1): 1597
(νCvN), 749 (νSevO).
Acknowledgements
HBS is grateful to the Department of Science and Technology
(DST), New Delhi-110016 (India), for the Ramanna Fellowship.
PR wishes to thank CSIR for a SRF fellowship. JPJ acknowl-
edges the NSF-MRI program (grant no. CHE1039027) for funds
to purchase the X-ray diffractometer.
Notes and references
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9436 | Dalton Trans., 2014, 43, 9431–9437
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