Synthesis of selenenium ions: Isolation of highly conjugated, pH-sensitive 4,4′-Bis(methylimino)-1,1′-binaphthylene-5-diselenenium(II) triflate

Article abstract of DOI:10.1021/om400460z

The isolation of novel selenenium cations, stabilized by only one intramolecularly coordinating group (Se···N), is described. The electronic nature of the cations has been probed by calculating natural bonding orbital charges and Wiberg bond indices. [8-(Dimethylamino)-1-naphthyl] selenenyl(II) triflate oxidizes in methanol via C-C coupling to give a novel blue-colored 4,4′-bis(methylimino)-1,1′-binaphthylene-5- diselenenium(II) triflate. The pH dependence of the color has been investigated.

Full text of DOI:10.1021/om400460z

Article
pubs.acs.org/Organometallics
Synthesis of Selenenium Ions: Isolation of Highly Conjugated, pH-
Sensitive 4,4′-Bis(methylimino)-1,1′-binaphthylene-5-
diselenenium(II) Triflate
Prakul Rakesh,† Harkesh B. Singh,*,† and Ray J. Butcher‡
†Department of Chemistry, Indian Institute of Technology Bombay, Powai, Mumbai 400076, India
‡Department of Chemistry, Howard University, Washington D.C., 20059, United States
S
* Supporting Information
ABSTRACT: The isolation of novel selenenium cations,
stabilized by only one intramolecularly coordinating group
(Se···N), is described. The electronic nature of the cations has
been probed by calculating natural bonding orbital charges and
Wiberg bond indices. [8-(Dimethylamino)-1-naphthyl]-
selenenyl(II) triflate oxidizes in methanol via C−C coupling
to give a novel blue-colored 4,4′-bis(methylimino)-1,1′-
binaphthylene-5-diselenenium(II) triflate. The pH dependence
of the color has been investigated.
the case of 8.5 To our knowledge, there is not a single report on
the isolation of a selenenium ion that is stabilized by only one
coordinating group.
Several novel organoselenium compounds have been
INTRODUCTION
■
Organoselenium compounds, having an intramolecular inter-
action with a nearby heteroatom(s), have been widely studied as
electrophiles in addition reaction with olefins.1 It involves the
successfully isolated using only one intramolecularly coordinat-
formation of a seleniranium ion (3) as an intermediate, which on
ing donor atom substrate.6,7 The rigidity of the aromatic ring may
reaction with the nucleophile leads to the trans products (4)
increase the strength of the Se···N (sp3) intramolecular
interaction. The bond distance of Se···N (2.652(2) Å) of rigid
system 8-(dimethylamino)-1-naphthyl]diselenide (DiNaDi) is
shorter than the Se···N distance (2.856(3) Å) in nonrigid system
2-(dimethylaminomethyl)phenyl]diselenide (DiPhDi).6a,7c Fur-
ther, the strength of the Se···N (sp2) intramolecular interaction is
stronger in comparison with the Se···N (sp3) intramolecular
interaction.7g Moreover, the substrates having the sterically
hindered group exhibit stronger Se···N interactions.7h Recently,
Singh and co-workers successfully isolated [2-(1-(3,5-dimethyl-
phenyl)-2-naphthyl)-4,5-dihydro-4,4-dimethyl-1,3-oxazole]-
selenenyl(II) azide (DiNaSeAz) by using such a substrate that
has only one intramolecularly coordinating group.7i In the view
of these results, we have chosen substrates for the synthesis of
stable selenenium ions which are (i) bulky and show strong
intramolecular Se···N (sp2) interaction, i.e., 2-[1-(3,5-dimethyl-
phenyl)-2-naphthyl]-4,5-dihydro-4,4-dimethyl-1,3-oxazole, (ii)
less bulky ligands having quite strong intramolecular Se···N
(sp2) interaction, i.e., 2-(4,4-dimethyl-2-oxazoline)phenyl, and
also (iii) rigid and planar ligands having strong intramolecular
Se···N (sp3) interaction, i.e., 1-(dimethylamino)naphthalene.
(Scheme 1).2
Different noncoordinating bulky anions have been used to
generate selenenium ions 2 in situ (where X− = OTf−, BF4 , PF6 ,
−
−
3
OSO3H−, SbCl6 ) for better reactivity and selectivity. Although
electrophilic addition reactions of selenenium ions have attracted
much interest, reports on their isolation and structural
characterizations are limited. Furukawa and co-workers isolated
and characterized the first selenenium ion 5.4a The reaction of
2,6-bis[(dimethylamino)methyl]phenyl methyl selenide with
one equivalent of t-BuOCl/KPF6 afforded selenenium ion 5.
The same cation was also isolated by Poleschner and Seppelt
with a HF2− anion (6).4b Attempted synthesis of stable, selenenyl
halides by the reaction of N-[n-butyl-(3-nitrobenzylimino)]-
phenyl selenide and Br2 in the presence of triethylamine afforded
selenenium ions 7−9.5 Selenenium ions 5, 7, 8, and 9 are stable at
room temperature. All the isolated selenenium ions are stabilized
by intramolecular interactions by two coordinating groups. The
second coordinating group plays a crucial role in the ionization.5
The high positive charge on the selenium is influenced by both of
the coordinating groups near the selenium atom. The strong
intramolecular interactions between Se and N/O lengthen its
trans bond. The increase of the length of the trans bond is more in
the case of the two coordinating groups. For example, in 2-
(dimethylaminomethyl)phenyl]selenium bromide, the Se−Br
bond length is 2.634(1) Å;6a however, the Se−Br bond ionizes in
−
Received: May 24, 2013
© XXXX American Chemical Society
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Scheme 1. Electrophilic Addition of a Selenenium Ion (2) to an Olefin
Figure 1. Isolated selenenium ions (5−9) and some organoselenium compounds.
Scheme 2. Synthesis of Selenenium Salts
Scheme 3. Synthesis of Diselenenium Ion 19
14) is depicted in Scheme 2. In a typical reaction, [2-(1-(3,5-
dimethylphenyl)-2-naphthyl)-4,5-dihydro-4,4-dimethyl-1,3-
oxazole]selenenyl(II) triflate (11) was prepared by the dropwise
addition of silver triflate to a methanolic solution of [2-(1-(3,5-
RESULTS AND DISCUSSION
■
The synthesis of [2-(1-(3,5-dimethylphenyl)-2-naphthyl)-4,5-
dihydro-4,4-dimethyl-1,3-oxazole]selenenium(II) cations (11−
B
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Scheme 4. Plausible Mechanism for the Formation of 19
dimethylphenyl)-2-naphthyl)-4,5-dihydro-4,4-dimethyl-1,3-
oxazole]selenenyl(II) bromide (10) at 0 °C. Selenenium ions 12,
13, and 14 were similarly prepared. An analogous reaction of [2-
(4,4-dimethyl-2-oxazolinyl)phenyl]selenenyl(II) bromide (15)
with silver triflate afforded [2-(4,4-dimethyl-2-oxazolinyl)-
phenyl]selenenium(II) triflate (16). The yellow-colored selene-
nium ions 11−14 are stable under ambient conditions for a
period of six months. Selenenium ion 16 is stable under ambient
conditions only for a duration of 10 h. After this, the color
changed from white to black on standing overnight at room
temperature. However, it can be stored at −20 °C for a month.
Interestingly, the reaction of silver triflate with [8-
(dimethylamino)-1-naphthyl]selenenyl(II) bromide (17) at 0
°C initially afforded a yellowish solution, which then turned to
dark green and finally to a dark blue colored solution. Workup of
the blue solution afforded 4,4′-bis(methylimino)-1,1′-binaph-
thylene)-5-diselenenium(II) triflate (19) instead of the expected
monocation [8-(dimethylamino)-1-naphthyl]selenenium(II)
triflate (18). The identity of 19 was confirmed by elemental
analysis, HRMS data (MNa+, found 788.8571, calcd 788.8582),
and single-crystal X-ray diffraction studies (vide infra).
Diselenenium ion 19 is quite stable under ambient condition
for 2 months. The unstable green-colored selenenium ion 18
could be isolated by carrying out the reaction for a duration of 5
min in a solvent mixture of CHCl3/MeOH (10 mL:2 mL)
(Scheme 3). The identity of 18 was confirmed by further
derivatizing it into 20 and 21.
In order to establish the mechanism for the formation of
unexpected diselenenium ion 19, when the reaction of 17 was
carried out using NaOTf in place of AgOTf, diselenenium ion 19
was obtained in 18% yield. This observation indicates that silver
ions play no role in the carbon−carbon coupling reaction.
Therefore, the partial positive charge on the nitrogen atom due
to the strong intramolecular Se···N interaction probably leads to
dealkylation followed by dimerization (C−C coupling reaction)
to give 19. The dimerization reaction may be due to the aerial
oxidation (Scheme 4). A similar coupling of N,N-dimethylnaph-
thalene has been accomplished by electrochemical oxidation.8
Beckmann and Bolsinger have also isolated C−C coupled
compound 23, by the photo-oxidation of bis[8-(dimethylami-
no)-1-naphthyl]ditelluride (22) (Scheme 5).9 The preparation
of 19 was carried out in the presence of light. When the same
Scheme 5. Synthesis of (8-MeNC10H5TeO)4 by the Photo-
oxidation of Bis[8-(dimethylamino)-1-naphthyl]ditelluride
reaction and recrystallization were carried out in the absence of
light to probe the role of light in the reaction, compound 19 was
obtained in a similar yield. This shows that light does not play any
role in the reaction.
1
The H NMR spectrum of 17 exhibits a singlet for the six
protons of −N(CH3)2 at δ 3.11.7c However, the N-methyl peak
for 19 integrated for only three protons and exhibited a
downfield shift (δ 3.69) indicating the presence of an N-
methylimino moiety. The 13C NMR spectra of selenenium ions
11−14 were quite similar except for the presence of an additional
peak for the anions. In the 77Se NMR spectra, the signals of
selenenium ions 11 (δ 962), 12 (δ 962), 13 (δ 959), and 14 (δ
956) show a significant downfield shift as compared to the
precursor 10 (δ 836). It is worth noting that the 77Se NMR shift
of 14, which has trifluoroacetate as the counterion, is quite similar
to 12 and 13, which have noncoordinating anions tetrafluor-
oborate and perchlorate, respectively. Interestingly, the 77Se
NMR chemical shifts of 11−14 and 16 stabilized by one
coordinating group are upfield compared with the selenenium
ions 5 (δ 1208), 6 (δ 1213), 7 (δ 1185), and 9 (δ 1185), which
are stabilized by two coordinating groups. The significant
downfield shift for 19 (δ 1462) compared to 17 (δ 1015)
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indicates the change of −NMe2 (sp3 hybrid N donor in 17) to 
new peak at 1271 ppm. The peak at 1464 ppm assigned to 19
disappeared after the addition of a few more drops of the NaOH
solution (Figure S56 in the SI). The signal (1271 ppm) is in the
range of selenenic acid,7a,11 thus indicating the formation of 24.
In order to check the reversible nature of the changes observed in
the pH titration, 10 μL of a 10−4 N solution of 19 in acetate buffer
was added to 960 μL of acetate buffer in a 1 mL cuvette. Then 30
μL of a 0.2 N NaOH solution was added in the cuvette. The
strong peak in the region 500−775 nm disappeared. Further,
when the same amount of hydrochloric acid, i.e., 30 μL of 0.2 N
HCl, was added to the cuvette, the strong peak in the region
500−775 nm reappeared and confirmed the reversibility of this
reaction.
NMe (sp2 hybrid N donor in 19) moiety.
The intense blue color of 19 motivated us to study its
absorption spectrum in detail. The absorption spectrum of 19
showed a strong peak in the visible region at 637 nm and weaker
peaks at 406, 338, and 245 nm in methanol. The absorption
spectra of 19 at different pH values were also recorded following
a reported procedure.10 An acetate buffer solution of 19 (pH
5.75, 10−5 N) exhibited a strong peak in the visible at 623 nm and
weaker peaks at 408, 335, and 250 nm (Figure 2). As the pH of
The intensity of the absorbance of the regenerated peak was
not exactly the same as observed earlier due to the dilution of 19
by the addition of NaOH solution and HCl solution (Figure 3).
Figure 2. Absorbance scans of 19 in acetate buffer between pH 5.75 and
10.53.
the solution was raised to 7.64, the strong peak at 623 nm
disappeared and a hyperchromic shift was observed at 250 nm
(Figure 2). Simultaneously, the blue-colored 19 changed to a
colorless species (Scheme 6). The sharp color change may be due
Figure 3. Effect of the addition of base (NaOH) and acid (HCl) on the
absorbance spectrum of 19.
Scheme 6. Effect of pH on 19
The molecular structure of 13 is shown in Figure 4. The
coordination geometry around the Se atom can be considered as
to the disruption in the conjugation of the molecule. We
postulated that this may be due to formation of 24 (Scheme 6).
In order to ascertain the nature of 24, the reaction of 19 with base
was monitored by both 1H and 77Se NMR spectroscopy. In the
1H NMR spectrum, the addition of a few drops of the NaOH
solution to a solution of 19 in CD3OD resulted in a slight
broadening of the signals. Further addition of the NaOH solution
led to the appearance of a new peak at 4.6 ppm (Figure S57 in the
SI). This peak is assigned to the allylic proton peak of 24. In the
77Se NMR spectrum, the addition of a few drops of the NaOH
solution to a solution of 19 in CD3OD led to the appearance of a
Figure 4. Molecular structure of 13 and selected bond lengths (Å) and
angles (deg). Hydrogen atoms are omitted for clarity. Se−C1
1.8975(18), Se−N1 1.8563(15); C1−Se−N1 84.39(7).
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V-shaped with C1−Se−N1 = 84.39(7)°. The Se···N1 (sp2) bond
distance (1.8563(15) Å) is shorter than that of 10 (2.052(3)
Å).7h This is the shortest distance reported for any selenenium
ion (5 (2.180(7), 2.154(7) Å), 7 (1.899(2) Å), and 8 (1.895(0)
Å)4a,5 and is even shorter than the sum of the covalent radii of Se
and N atoms (1.91 Å).11 The bond length between Se and O1 of
perchlorate (2.934(5) Å) is longer than the sum of covalent radii
(1.90 Å)12 and shorter than the sum of van der Waals radii (3.42
Å).13 This indicates a weak interaction between RSe+ and the
perchlorate ion.
very close to that in selenenium ion 13 (1.8563(15) Å). Similar
to the cation−anion interaction of 13, a weak interaction
between Se of RSe+ and O of the triflate ion (2.585(5) Å) was
also observed in 19. This interaction is stronger than the Se···O
interaction (3.152(7) Å) in 1,5,9,13-tetraselenacyclohexadecane-
(II) trifluoromethanesulfonate.14
The torsion angles of C1−C10−C5−C6 (176.2(4)°) and
C9−C10−C5−C4 (−176.4(4)°) show the planarity of the
molecule. The torsion angles of C5−C6−C6#−C5# (144.8(4)°)
and C7−C6−C6#−C7# (139.6(4)°) show the twist between
two naphthyl moieties. The bond distance between N1 and C11
(1.461(8) Å) is slightly shorter than the bond length between N
(sp2) and C (sp3) (1.490(3) Å) in [o-((((1S,2R)-2-hydroxy-2-
phenyl-1-methylethyl)amino)methinyl)phenyl]tellurium(IV)
tribromide15 and much longer than the bond length between N
(sp2) and C (sp2) (1.288(5) Å) in compound 10.7h It shows that
the N1−C11 bond in 19 is between the N (sp2) and C (sp3)
atom. The bond length between C9 and N1 (1.331(8) Å) is in
between N(sp2)−C(sp3) and N(sp2)−C(sp2). It shows that
there is a conjugated double bond between N1 and C9. The
distance between C8 and C7 (1.368(9) Å) and C6 and C6#
(1.423(12) Å) shows that they are in the range of a conjugated
double bond.
The molecular structure of 17 is shown in Figure 5. The
coordination geometry around the Se is T-shaped, where C1 and
Figure 5. Molecular structure of 17 and selected bond lengths (Å) and
angles (deg). Hydrogen atoms are omitted for clarity. Se−C1 1.921(4),
Se−N 2.181(3), Se−Br 2.5744(6); C1−Se−N 83.51(15), N−Se−Br
177.30(9).
In selenenyl pseudohalide 20, the coordination geometry
around the Se atom is similar to that of corresponding selenenyl
bromide 17 (Figure 7). The intramolecular N1···Se distance
the two lone pairs are in the equatorial positions and N1 and Br
atoms are in the axial positions. The intramolecular Se···N
distance is 2.181(3) Å with the N1···Se−Br angle of 177.30(9)°
and indicates a good overlap between the donor (N1) and the
acceptor (Se−Br). The Se···N distance in 17 is shorter than the
c o r r e s p o n d i n g S e · · · N b o n d d i s t a n c e i n [ 2 -
(dimethylaminomethyl)phenyl]selenenyl(II) bromide
(2.143(6) Å).6a As expected, the intramolecular N···Se distance
in 17 was longer than the Se···N bond distance (2.174(5) Å) in
[8-(dimethylamino)-1-naphthyl]selenenyl(II) chloride; how-
ever, it is shorter than the Se···N bond distance (2.242(5) Å)
in [8-(dimethylamino)-1-naphthyl]selenenyl(II) iodide.7c
The molecular structure of the title compound 19 is shown in
Figure 6. The molecule is centrosymmetric, and the coordination
geometry around the Se atom is similar to that of selenenium ion
13. The most interesting feature of the structure is that the Se···
N1 (sp2) distance (1.862(5) Å) is even shorter than in related
selenenium ions having two groups coordinating to Se (5
(2.180(7), 2.154(7) Å), 7 (1.899(2) Å), and 8 (1.895(0) Å)) and
Figure 7. Molecular structure of 20 and selected bond lengths (Å) and
angles (deg). Hydrogen atoms are omitted for clarity. Se−C1
1.9328(16), Se−N1 2.4560(15), Se−C 1.912(2); C−Se−N1
172.64(7), C1−Se−C 94.77(9).
(2.4560(15) Å) is longer than the N···Se distance in 17
(2.181(3) Å) and [2-(1-(3,5-dimethylphenyl)-2-naphthyl)-4,5-
dihydro-4,4-dimethyl-1,3-oxazole]selenium(II) azide
(2.145(16) Å). The Se−C bond length (1.912(2) Å) is longer
as compared to the Se−C bond length (1.849(4) Å) in
PhSeCN.16 The elongation in Se−C bond length is due to a
strong secondary bonding interaction of N1···Se. The CN
bond distance (1.140(2) Å) of 20 is similar to the CN bond
distance (1.142(5) Å) in PhSeCN.16 The bond distances
between Se−C (1.912(2) Å) and Se−C1 (1.9328(16) (Å)) are
similar. The bond angle of N1−Se−C (172.64(7)°) shows the
linearity of the SeCN moiety.
The strong intramolecular coordination of the Se···N bond in
the selenenium cations makes the five-membered ring (of which
the Se···N bond is a part) aromatic. In order to gain insight about
the electronic structure of the selenenium cations as well as the
location of the positive charge, the geometries of [2-(1-(3,5-
dimethylphenyl)-2-naphthyl)-4,5-dihydro-4,4-dimethyl-1,3-
oxazole]selenenium(II) cation (13a), [2-(4,4-dimethyl-2-
oxazolinyl)phenyl]selenenium(II) cation (16a), [8-(dimethyla-
mino)-1-naphthyl]selenenium(II) cation (18a), and 4,4′-bis-
(methylimino)-1,1′-binaphthylene)-5-diselenenium(II) cation
(19a) were optimized.17 The computed intramolecular Se···N
Figure 6. Molecular structure of 19 and selected bond lengths (Å) and
angles (deg). Hydrogen atoms are omitted for clarity. Se−C1 1.921(4),
Se−N1 1.862(5), Se−O1 2.585(5), N1−C11 1.461(8); C1−Se−N1
115.1(5).
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Figure 8. Different forms of the structure of the [2-(4,4-dimethyl-2-oxazolinyl)phenyl]selenenium(II) cation (16a).
were recorded in the range 4000−400 cm−1 on a Nicolet Impact 400FT-
IR spectrometer. ES-MS spectra were recorded at room temperature on
a Q-Tof (YA-105) micromass spectrometer. Absorption spectra were
recorded at room temperature on a Jasco V-570 spectrophotometer.
Synthesis of [2-(1-(3,5-Dimethylphenyl)-2-naphthyl)-4,5-di-
hydro-4,4-dimethyl-1,3-oxazole]selenenium(II) Triflate (11). A
stirred solution of compound 10 (0.30 mmol, 0.15 g) in dry methanol
(15 mL) was treated dropwise with silver triflate (0.36 mmol, 0.094 g) in
dry methanol (5 mL) at 0 °C within a period of 5 min. After the addition
was complete, the reaction mixture was allowed to come to room
temperature and stirred for 2 h. The reaction mixture was filtered, and
the filtrate was concentrated to give a blackish oil. The oil was dissolved
in dry acetonitrile and passed through a small pad of Celite to remove
the excess silver triflate. The filtrate was concentrated to give a yellow oil,
which solidified on addition of hexane. The yellow solid was
recrystallized by the mixture of chloroform and hexane (1:3). Yield:
0.12 g, 72%. Mp: 205−207 °C. Anal. Calcd for C24H22F3NO4SSe: C,
distances for 13a, 16a, 18a, and 19a as well as other geometrical
parameters from geometry optimization are in good agreement
with the experimental values. Natural population analysis (NPA)
charges on atoms from nonbonding orbital (NBO) analysis
reveal that the selenium atom has a relatively high positive NPA
charge, i.e., +0.736 on Se in 13a, +0.787 on Se in 16a, +0.659 on
Se in 18a, and +0.890 on Se in 19a. The relative increase in
positive charge on Se is also in conformity with the experimental
chemical shifts of 77Se NMR, which also increase with the
increase of the positive charge on the selenium atom, i.e., 13 (959
ppm), 16 (982 ppm), and 19 (1462 ppm). Wiberg bond indices
for the Se−N bond of 13a, 16a, 18a, and 19a are 0.82, 0.83, 0.74,
and 0.89, respectively, thus making the Se···N interaction
practically a Se−N covalent single bond between Se and N.
Moreover, the imine bond (CN) is no longer a double bond
and has a Wiberg bond index of 1.31 for 19a, which should
otherwise be 2 for a perfect double bond. Similarly, for 16a and
13a, the CN Wiberg bond indices are 1.34 and 1.33,
respectively. This indicates that the positive charge is delocalized
over the molecule. A representation for delocalization of the
positive charge for 16a is shown in Figure 8.
1
51.80; N, 2.52; H, 3.98. Found: C, 51.57; N, 2.35; H, 4.29. H NMR
(CDCl3): δ 1.72 (s, 6H), 2.35 (s, 6H), 4.83 (s, 2H), 6.97 (s, 2H), 7.17 (s,
1H), 7.46 (t, 1H), 7.65 (m, 2H), 7.94 (d, 1 H), 8.93 (s, 1H). 1H NMR
(CD3OD): δ 1.71 (s, 6H), 2.36 (s, 6H), 4.89 (s, 2H), 7.02 (s, 2H), 7.21
(s, 1H), 7.53 (t, 1H), 7.67 (d, 1H), 7.75 (t, 1 H), 8.06 (s, 1H), 8.68 (s,
1H). 13C NMR (CD3OD): δ 21.4, 27.0, 68.1, 87.9, 116.0, 120.2, 123.4,
126.6, 126.8, 128.6, 128.8, 129.1, 131.4, 132.6, 136.0, 137.1, 139.0, 142.3,
146.8, 170.3. 77Se NMR (CD3OD): δ 962. 19F NMR (CD3OD): δ −78.
ES-MS: (m/z) 408 [(M − OTf)+]. IR (KBr, cm−1): 1591 (νCN), 1028
(νsym SO3), 1241 (νasym SO3).
CONCLUSIONS
■
Several selenenium cations stabilized by only one intra-
molecularly coordinating group have been isolated and
structurally characterized. The calculated natural bonding orbital
charges and Wiberg bond indices indicate that the positive charge
is delocalized over the molecule. The results further indicate that
isolation of stable selenenium salts is facilitated by not only steric
bulk and intramolecular coordination but also by extended
conjugation. The color of diselenenium ion 19 is pH dependent.
The blue color changes to colorless in basic medium. This may be
due to the disruption in the conjugation and the formation of 24
in basic medium.
Synthesis of [2-(1-(3,5-Dimethylphenyl)-2-naphthyl)-4,5-di-
hydro-4,4-dimethyl-1,3-oxazole]selenenium(II) Tetrafluorobo-
rate (12). The compound was prepared by a procedure similar to that
described for compound 11. The solid was recrystallized by the mixture
of chloroform and hexane (1:3). Yield: 67%. Mp: 214−216 °C. Anal.
Calcd for C23H22BF4NOSe: C, 55.90; N, 2.83; H, 4.49. Found: C, 55.86;
N, 2.86; H, 4.15. 1H NMR (CDCl3): δ 1.65 (s, 6H), 2.40 (s, 6H), 4.72 (s,
2H), 6.96 (s, 2H), 7.16 (s, 1H), 7.43 (t, 1H), 7.63 (d, 2H), 7.90 (d, 1 H),
8.88 (s, 1H). 1H NMR (CD3OD): δ 1.72 (s, 6H), 2.40 (s, 6H), 4.90 (s,
2H), 7.03 (s, 2H), 7.21 (s, 1H), 7.55−7.59 (m, 1H), 7.68 (d, 1H), 7.77−
7.79 (m, 1 H), 8.07 (s, 1H), 8.71 (s, 1H). 13C NMR (CD3OD): δ 21.0,
27.8, 68.5, 87.2, 117.1, 123.5, 126.9, 127.2, 128.3, 128.5, 128.2, 131.2,
132.9, 136.5, 137.6, 139.5, 141.8, 146.5, 170.9. 77Se NMR (CD3OD): δ
961. 19F NMR (CD3OD): δ −153. ES-MS: (m/z) 408 [(M − OTf)+].
IR (KBr, cm−1): 1607 (νCN), 644 (νsym BF4), 1033 (νasym BF4).
Synthesis of [2-(1-(3,5-Dimethylphenyl)-2-naphthyl)-4,5-di-
hydro-4,4-dimethyl-1,3-oxazole]selenenium(II) Perchlorate
(13). A similar procedure was followed to that used for the synthesis
of compound 11. The solid was recrystallized by the mixture of
chloroform and hexane (1:3). Yield: 59%. Mp: 195−197 °C. Anal. Calcd
for C23H22ClNO5Se: C, 54.50; N, 2.76; H, 4.38. Found: C, 55.04; N,
2.66; H, 4.39. 1H NMR (CD3OD): δ 1.71 (s, 6H), 2.40 (s, 6H), 4.89 (s,
2H), 7.03 (s, 2H), 7.21 (s, 1H), 7.55- 7.60 (t, 1H), 7.68 (d, 1H), 7.77−
7.81 (t, 1 H), 8.07 (s, 1H) 8.84 (s, 1H). 13C NMR (CD3OD): δ 21.8,
27.8, 67.8, 87.6, 116.2, 120.6, 123.3, 127.6, 126.6, 128.0, 128.8, 128.9,
131.0, 132.9, 136.1, 137.5, 139.8, 143.0, 148.8, 170.6. 77Se NMR
EXPERIMENTAL SECTION
■
General Procedures. All reactions were carried out under a N2
atmosphere. Methanol and chloroform were distilled over magnesium
hydroxide and P2O5, respectively, before use.18 Silver triflate (Aldrich,
99%), silver perchlorate (Aldrich, 97%), silver trifluoroacetate (Aldrich,
98%), and silver tetrafluoroborate (Aldrich, 98%) were purchased
commercially and used as received. [2-(1-(3,5-Dimethylphenyl)-2-
naphthyl)-4,5-dihydro-4,4-dimethyl-1,3-oxazole]selenenium(II) bro-
mide (10),7h [2-(4,4-dimethyl-2-oxazolinyl)phenyl]selenenium(II)
bromide (15),7e and [8-(dimethylamino)-1-naphthyl]selenenium(II)
bromide (17)7c were prepared by following the literature methods.
Chemical shifts are cited with respect to SiMe4 as internal (1H and 13C)
and Me2Se as external standard. Elemental analysis was performed on a
Carlo-Erba model EA 1106 CHNS elemental analyzer. Infrared spectra
F
dx.doi.org/10.1021/om400460z | Organometallics XXXX, XXX, XXX−XXX

Organometallics
Article
(CD3OD): δ 959. ES-MS: (m/z) 408 [(M − OTf)+]. IR (KBr, cm−1):
1586 (νCN), 1060 (νasym ClO4).
Anal. Calcd for C24H24N2OSe2: C, 56.04; N, 5.45; H, 4.75. Found: C,
54.14; N, 6.25; H, 4.65. 1H NMR (CDCl3): δ 2.76 (s, 6H), 7.35 (d, 1H),
7.45 (t, 1H), 7.62 (m, 2H), 7.76 (d, 1H), 8.17 (d, 1H). 13C NMR
(CD3OD): δ 48.4, 118.3, 121.7, 123.4, 125.8, 126.6, 127.9, 129.0, 135.3,
139.2, 150.1. 77Se NMR (CD3OD): δ 1180. ES-MS: (m/z) 250
(C12H12NSe)+, 100%.
X-ray Crystallographic Study. The diffraction measurements for
compounds 13, 17, 19, and 20 were performed on a Siemens R3m/V
diffractometer using graphite-monochromated Mo Kα radiation (λ =
0.7107 Å).. The structures were solved by routine heavy-atom technique
using SHELXS 9719 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.20 The hydrogens were partially located from difference
electron-density maps, and the rest were fixed at calculated positions.
Scattering factors were from common sources.21
Procedure Used in pH Titration (ref 10). A 50 mL stock solution
of 19 (10−5 N) was prepared in acetate buffer. The pH of the stock
solution was 5.75. A 710 μL NaOH solution (0.2 N) was added to
achieve a pH of 10.53. The absorption spectra were recorded in a 1 mL
cuvette at different pH values at room temperature.
Computational Details (ref 17). Geometries were fully optimized
at the B3PW91 level of density functional theory (DFT) with the use of
the 6-31G(d,p) basis sets. Atomic charges were analyzed by the natural
bond orbital method at the B3PW91/6-31G(d,p) level.
Synthesis of [2-(1-(3,5-Dimethylphenyl)-2-naphthyl)-4,5-di-
hydro-4,4-dimethyl-1,3-oxazole]selenenium(II) Trifluoroace-
tate (14). A similar procedure was followed to that used for the
synthesis of compound 11. The solid was recrystallized by the mixture of
chloroform and hexane (1:3). Yield: 57%. Mp: 220−222 °C. Anal. Calcd
for C25H22F3NO3Se: C, 57.70; N, 2.69; H, 4.33. Found: C, 57.28; N,
3.32; H, 4.26. 1H NMR (CDCl3): δ 1.67 (s, 6H), 2.40 (s, 6H), 4.54 (s,
2H), 6.92 (s, 2H), 7.14 (s, 1H), 7.44 (t, 1H), 7.56 (d, 1H), 7.65 (t, 1 H),
7.96 (s, 1H) 8.81 (s, 1H). 13C NMR (CD3OD): δ 21.1, 26.5, 68.8, 85.3,
116.6, 117.5, 121.3, 123.5, 127.9, 126.0, 128.8, 129.5, 129.6, 131.5, 133.5,
137.2, 137.8, 140.8, 143.5, 148.5, 160.2, 170.8. 77Se NMR (CD3OD): δ
956. 19F NMR (CD3OD): δ −75. ES-MS: (m/z) 408 [(M − OTf)+]. IR
(KBr, cm−1): 1606 (νCN), 1125 (νCF3), 1691, 1202 (νCOO).
Synthesis of [2-(4,4-Dimethyl-2-oxazolinyl)phenyl]-
selenenium(II) Triflate (16). A similar procedure was followed to
that used for the synthesis of compound 11. The solid was recrystallized
by the mixture of chloroform and hexane (1:3). Yield: 67%. Mp: 126−
128 °C. Anal. Calcd for C12H12F3NO4SSe: C, 35.83; N, 3.48; H, 3.01.
Found: C, 36.59; N, 4.14; H, 2.77. 1H NMR (CD3OD): δ 1.78 (s, 6H),
5.18 (s, 2H), 7.69 (t, 1H), 7.83 (t, 1H), 8.16 (d, 1H), 8.24 (d, 1H). 13C
NMR (CD3OD): δ 27.4, 69.2, 88.5, 119.2, 120.0, 128.3, 128.8, 129.0,
135.6, 152.2, 169.5. 77Se NMR (CD3OD): δ 982. 19F NMR (CD3OD): δ
−78. ES-MS: (m/z) 254 [(M − OTf)+]. IR (KBr, cm−1): 1606 (νCN),
1031 (νsym SO3), 1241 (νasym SO3).
Synthesis of [8-(Dimethylamino)-1-naphthyl]selenenium(II)
Triflate (18) and 4,4′-Bis(methylimino)-1,1′-binaphthylene-5-
diselenenium(II) Triflate (19). To a solution of 17 (0.1 g, 0.3 mmol)
in dry chloroform (15 mL) was added a solution of silver triflate (0.093
g, 0.36 mmol) in a mixture of dry chloroform and methanol (10:2) at 0
°C. The addition was complete in 5 min. The color of the reaction
mixture changed from yellow to dark green. The reaction mixture was
stirred for an additional 5 min at 0 °C. Then it was filtered, and the
filtrate was reduced to a dark green residue, which was washed with
CHCl3 and hexane to give green-colored 18. Yield: 45%. Mp: 168−170
°C. Anal. Calcd for C13H12F3NO3SSe: C, 39.21; N, 3.52; H, 3.04.
Found: C, 39.55; N, 4.36; H, 3.55. IR (KBr, cm−1): 1288 (νsym SO3),
1237 (νasym SO3).
ASSOCIATED CONTENT
■
S
* Supporting Information
Molecular structure of compound 21, H, 13C, 77Se 19F NMR,
1
mass, and FTIR spectra and elemental analysis of 11−14, 16, 18,
19, 20, and 21, 1H and 77Se NMR titrations of 19 with base, table
for the comparison of the experimentally obtained structural
parameters (13, 19) and optimized geometries obtained
structural parameters (13a, 19a), a CIF file giving crystallo-
graphic data for compounds 13, 17, 19, and 20, and some details
of data collection and refinement. This material is available free of
charge via the Internet at http://pubs.acs.org.
During recrystallization of 18 in dry methanol, compound 18
converted into dark blue colored crystals of 19. Yield: 19%. Mp: 228−
230 °C. Anal. Calcd for C24H16F6N2O6S2Se2: C, 37.21; N, 3.66; H, 2.11.
Found: C, 37.55; N, 4.33; H, 2.24. 1H NMR (CD3OD): δ 3.69 (s, 6H),
7.69 (m, 4H), 7.94 (m, 4H), 8.06 (d, 2H). 13C NMR (CD3OD): δ 58.1,
119.0, 120.2, 123.1, 126.3, 127.9, 128.7, 129.7, 130.9, 133.3, 136.0, 149.4.
77Se NMR (CD3OD): δ 982. 19F NMR (CD3OD): δ −78. ES-MS: (m/
AUTHOR INFORMATION
■
Corresponding Author
*E-mail: chhbsia@chem.iitb.ac.in.
Notes
The authors declare no competing financial interest.
z) 234 [(C11H8NSe)+, 100%], 468 [(C22H16N2Se2)+, 40%]. HRMS
(EI): m/z [C24H16F6N2O6S2Se2Na+ (MNa+) calcd 788.8582, found
788.8571].
ACKNOWLEDGMENTS
■
Synthesis of [8-(Dimethylamino)-1-naphthyl]selenenyl(II)
Cyanide (20). To a solution of NaCN (0.029 g, 0.6 mmol) in
methanol (10 mL) was added 18 (0.20 g, 0.5 mmol) at 0 °C. The green
color of the reaction mixture changed to a pale yellow color in 5 min.
The reaction mixture was stirred for an additional 30 min at 0 °C. It was
filtered, and the filtrate was reduced to get yellow-colored 20. The
yellow compound 20 recrystallized from a methanol and chloroform
solution (1:3). Yield: 59%. Mp: 198−200 °C. Anal. Calcd for
C13H12N2Se: C, 56.73; N, 10.18; H, 4.39. Found: C, 56.20; N, 9.61;
H, 4.44. 1H NMR (CD3OD): δ 2.72 (s, 6H), 7.43 (t, 1H), 7.58 (m, 2H),
7.81 (t, 2H), 7.92 (d, 1H). 13C NMR (CD3OD): δ 46.9, 111.9, 121.3,
123.7, 128.0, 128.1, 128.2, 128.5, 128.5, 129.7, 136.8, 149.7. 77Se NMR
(CD3OD): δ 402. ES-MS: (m/z) 250 (C12H12NSe (M − CN))+, 100%.
HRMS (EI): m/z [C13H12N2SeH+ (MH+) calcd 277.0242, found
277.0244].
Synthesis of Bis[(8-(dimethylamino)-1-naphthyl)selenium]
Oxide (21). To a stirred solution of NaOH (0.6 mmol, 0.024 g) in
methanol was added 18 (0.5 mmol, 0.20 g) in methanol (10 mL) at 0 °C.
Further, a similar procedure was followed that was used for the synthesis
of compound 20. The white powder (21) was recrystallized from a
methanol and chloroform solution (1:3). Yield: 65%. Mp: 155−157 °C.
H.B.S. is grateful to the Department of Science and Technology
(DST), New Delhi-110016 (India), for the Ramanna Fellowship.
P.R. wishes to thank CSIR for an SRF fellowship.
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