Synthesis, structural characterization and fluorescence properties of organoselenium compounds bearing a ligand containing both bulky and nonbonding groups - The first observation of both intramolecular Se...N and Se...O interactions in a diselenide structure

Article abstract of DOI:10.1002/ejic.200300603

The synthesis of bis[3-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl)-4-(3,5- dimethylphenyl)-2-naphthyl] diselenide, R₂Se₂ (4), was achieved by a facile ortholithiation route. Further reaction of the diselenide with a stoichiometric amount of SO₂Cl₂ or Br₂ afforded the corresponding selenenyl halides RSeX [X = Cl (5), X = Br (6)]. The novel selenenyl iodide RSeI (7), in which the selenium and iodine are covalently bonded to each other, was obtained by treatment of the diselenide with an equimolar amount of iodine. The stable aryl benzyl selenide 8 was prepared by the reaction of benzyl chloride with lithium areneselenolate (3) at low temperature. Surprisingly, the reaction of the diselenide with 1,2-dibromo-o-xylene gave the selenenyl bromide (6) instead of the arylselenium derivative 9. Elemental analysis, multinuclear (¹H, ¹³C, ⁷⁷Se) NMR spectroscopic and mass spectrometric techniques were used for the identification of products. Compounds 4, 6, 7, and 8 were also characterized by single-crystal X-ray diffraction studies. Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2004.

Full text of DOI:10.1002/ejic.200300603

FULL PAPER
Synthesis, Structural Characterization and Fluorescence Properties of
Organoselenium Compounds Bearing a Ligand Containing Both Bulky and
Nonbonding Groups ؊ The First Observation of Both Intramolecular Se···N
and Se···O Interactions in a Diselenide Structure
Karuppasamy Kandasamy,[a] Sangit Kumar,[a] Harkesh B. Singh,*[a] Ray J. Butcher,[b] and
K. Travis Holman[c]
Keywords: Selenium / Intramolecular coordination / X-ray diffraction / Fluorescence
The synthesis of bis[3-(4,5-dihydro-4,4-dimethyl-1,3-oxazol-
2-yl)-4-(3,5-dimethylphenyl)-2-naphthyl] diselenide, R2Se2
(4), was achieved by a facile ortholithiation route. Further
reaction of the diselenide with a stoichiometric amount of
SO2Cl2 or Br2 afforded the corresponding selenenyl halides
with lithium areneselenolate (3) at low temperature. Surpris-
ingly, the reaction of the diselenide with 1,2-dibromo-o-xy-
lene gave the selenenyl bromide (6) instead of the arylselen-
ium derivative 9. Elemental analysis, multinuclear (1H, 13C,
77Se) NMR spectroscopic and mass spectrometric techniques
RSeX [X = Cl (5), X = Br (6)]. The novel selenenyl iodide RSeI were used for the identification of products. Compounds 4,
(7), in which the selenium and iodine are covalently bonded
to each other, was obtained by treatment of the diselenide
with an equimolar amount of iodine. The stable aryl benzyl
selenide 8 was prepared by the reaction of benzyl chloride
6, 7, and 8 were also characterized by single-crystal X-ray
diffraction studies.
( Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim,
Germany, 2004)
Introduction
groups to stabilize unstable organoselenium compounds.
Intramolecular Se···X (X ϭ H,[7] S,[8] O,[9] F,[10] N,[4i,11] Cl
and Br[10b,12]) interactions have also been successfully used
for the same purpose. Ramasubbu et al.,[13] Goldstein et
al.,[14] and Barton et al.[15] have analyzed the nature of the
intramolecular interactions, and the electronic structure
around the selenium atom has been interpreted in terms of
a three center, four electron X···SeϪR bond (hypervalent
bond). These interactions are also expected to be respon-
sible for the specific redox reactivity of organoselenium
compounds[16] as well as stabilization of selenenic acid, the
key intermediate in the glutathione peroxidase catalytic
cycle.[4]
Although intramolecular coordination and steric effects
have been employed individually for the synthesis of stable
organoselenium compounds, to the best of our knowledge
there are no reports of their combined use for the stabilis-
ation of organoselenium compounds. The use of (4,4-di-
methyl-2-phenyl)oxazoline for the preparation of some no-
vel organoselenium compounds has been reported recently
by our group.[11d] Metal thiolates[17] and selenolates[2k] in-
corporating the same substrate have also been synthesized
and characterized. In zinc thiolate and selenolate com-
plexes, chirality was observed as a result of the dia-
stereotopic methylene protons of the oxazoline ring, which
arises from the strong ‘‘hard-hard’’ interactions between the
zinc and the imine nitrogen atoms. However, attempts to
In recent years organoselenium chemistry has been re-
ceiving much attention from the whole chemical community
because of its potential applications in various fields. Sel-
enium reagents have been extensively used in a variety of
organic reactions.[1] Other major applications are: i) ligand
chemistry,[2] ii) precursors for the preparation of thin films
in metal-organic chemical vapor deposition (MOCVD),[3]
and iii) biochemistry.[4] Nevertheless, organoselenium com-
pounds are known to be very unstable, highly reactive and
very difficult to synthesize. Recent studies show that the
use of sterically more hindered groups and intramolecularly
coordinating groups has been successful in synthesizing
some stable organoselenium compounds. Arnold et al.[5]
and Bochmann et al.[6] have used sterically more hindered
[a]
Department of Chemistry, Indian Institute of Technology,
Bombay,
Powai, Mumbai 400 076, India
Fax: (internat.) ϩ 91-22/2572-3480
E-mail: chhbsia@chem.iitb.ac.in
[b]
Department of Chemistry, Howard University,
Washington, DC 20059, USA
Fax: (internat.) ϩ 1-202-806-5442
E-mail: rbutcher@fac.howard.edu
[c]
Department of Chemistry, Georgetown University,
Washington, DC 20057, USA
Fax: (internat.) ϩ 1-202-687-6209
E-mail: kth7@georgetown.edu
1014
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Organoselenium Compounds Containing Both Bulky and Nonbonding Groups
FULL PAPER
obtain crystals of group 12 tellurolates[18] were unsuccessful Results and Discussion
due to the facile decomposition of the complexes in com-
Synthesis
mon solvents. In this context, we thought it worthwhile to
use a ligand that can induce both steric and intramolecular
coordination effects together as it could provide greater sta-
bility than ligands having either an o-chelating group or a
sterically more demanding group. This would also provide
an opportunity to study Se···N interactions in the presence
of sterically more demanding group.
The synthesis of the synthetically important diselenide 4
was achieved by an ortholithiation route. The lithium arene-
selenolate 3 was prepared by the direct metalation of 2-[1-
(3,5-dimethylphenyl)-2-naphthyl]-4,5-dihydro-4,4-dimethyl-
1,3-oxazole (1) with a 1.6  solution of nBuLi in hexane
followed by the addition of finely ground selenium powder.
We report here the synthesis and characterization of Oxidative work up gave the desired diselenide. Treatment of
some novel organoselenium complexes of 2-[1-(3,5-dimeth- the diselenide with sulfuryl chloride gave the stable se-
ylphenyl)-2-naphthyl]-4,5-dihydro-4,4-dimethyl-1,3-oxazole. lenenyl chloride 5. The stable bromo derivative 6 was ob-
This substrate has been synthesized as one of the intermedi- tained as a yellow crystalline solid by the reaction of dis-
ates in the preparation of mevanolactones, which are used elenide with a stoichiometric amount of bromine. Isolation
as inhibitors in cholesterol biosynthesis.[19] A comparison of the stable binary compounds containing selenium and
of structural and spectroscopic properties with similar com- iodine was difficult because of their similar electronegativity
pounds derived from the sterically less hindered 4,4-di- and their tendency to form charge-transfer adducts.[20] Al-
methyl-2-phenyloxazoline and other ligands is also de- though isolation has been possible using more hindered
scribed.
groups, like the 2,4,6-tri-tert-butylphenyl group,[21] a slight
Scheme 1. Synthetic route for the synthesis of organoselenium derivatives
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K. Kandasamy, S. Kumar, H. B. Singh, R. J. Butcher, K. T. Holman
FULL PAPER
reduction of their steric bulkiness again led to the formation 8 confirmed this very weak Se···N interaction (vide infra).
of the charge-transfer adduct.[22] However, our group has The 77Se NMR chemical shifts of compounds 5, 6, and 7
succeeded in isolating stable binary compounds containing are very close to each other and downfield of the diselenide.
selenium and iodine using ligands such as 4,4-dimethyl-2- This shows that their Se···N interactions are almost equal
phenyl-1,3-oxazoline,[11d]
N,N-dimethylbenzylamine,[11e] and stronger than Se···N interaction of 4. This is also con-
and N,N-dimethylnaphthylamine.[11c] Here also, the reac- firmed by the crystal structures of 6 and 7 (vide infra).
tion of the diselenide with stoichiometric amounts of iodine In the IR spectra, the νCϭN vibrations for compounds
led to the formation of the novel mono-iodide 7. This con- 4Ϫ8 are found in the range 1670Ϫ1760 cmϪ1 and are
sistent isolation of stable SeϪI bonded compounds regard- shifted by 20Ϫ100 cmϪ1 to higher frequency relative to the
less of bulkiness proves that the intramolecular approach is free ligand, indicating that the nitrogen of the oxazoline
a more effective method for the isolation of unstable com- ring is coordinated to the selenium atom. These shifts to
pounds than the steric approach. In general, aryl benzyl higher frequencies may be due to the presence of negative
and allyl aryl selenides are unstable and decompose readily hyperconjugation between the selenium and the nitrogen
to give coupled hydrocarbon products and free selenium.[23] atom. The νCϭN frequencies of compounds 5 and 6 are ob-
Treatment of the lithium areneselenolate 3 with equimolar served at higher frequencies than compounds 4 and 8, indi-
amounts of benzyl chloride gave the stable benzylselenium cating the stronger coordination of nitrogen in the selenenyl
derivative 8. All these reactions are shown in Scheme 1.
The treatment of α,α-dibromo-o-xylene with the lithium
halides than in the diselenide or benzyl selenide.
Compounds 4, 6, 7, and 8 exhibit similar absorption
areneselenolate 3 gave, unexpectedly, the selenenyl bromide spectra, with a strong peak in the 280Ϫ310 nm region and
6 instead of the expected compound 9. The reaction of an absorption maximum at 295 nm due to the ligand core.
Se(dtc)2 with the lithiated product 2 was expected to give Fluorescence emission spectra for compounds 4, 5, 6, 8, and
a stable symmetrical selenide. The yellow-colored product free ligand 1 were recorded to probe their fluorescence em-
formed in this reaction decomposed immediately to give the ission properties in methanol at an excitation wavelength of
starting material. It is worth mentioning that the reaction of 285 nm. The quantum yield of fluorescence emission was
4,4-dimethyl-2-phenyl-1,3-oxazoline with Se(dtc)2 afforded determined with naphthalene (Φf ϭ 0.23) as a standard.[25]
the expected bis(4,4-dimethyl-2-phenyl-1,3-oxazolin-2-yl) se- From the quantum yield of the fluorescence emission of
lenide.[24] Hence, the decomposition may be due to the selenium derivatives 4 (Φf ϭ 0.038), 5 (Φf ϭ 0.018), 6 (Φf ϭ
steric crowding around the selenium atom. All attempts to 0.021), and 8 (Φf ϭ 0.043) compared to the fluorescence
synthesize a stable bis{2-[1-(3,5-dimethylphenyl)-2-naph- emission of free ligand 1 (Φf ϭ 0.067) it is clear that the
thyl]-4,5-dihydro-4,4-dimethyl-1,3-oxazol-2-yl}
lithium selenolate and selenol were unsuccessful.
selenide, fluorescence emissions are quenched in the selenium com-
pounds compared to the ligand 1 due to the substitution of
heavy metal atoms.[26]
Spectroscopic Studies
Mass spectra were recorded for compounds 4Ϫ6, and 8
1
The H NMR spectra of the diselenide 4 and aryl benzyl to identify the constitution of the product under mass spec-
selenide 8 are not particularly informative as the peaks are trometric conditions. The presence of seven isotopes of sel-
only shifted slightly downfield (ca. 0.09 ppm) from those in enium leads to a highly characteristic group of selenium
the free ligand 1, thus indicating the presence of a weak fragments. Molecular ion peaks were observed in low inten-
Se···N interaction. However, much larger downfield shifts sities for all compounds. In all cases except 5, the base
(ca. 0.7 ppm for the methylene proton and ca. 0.4 ppm for peaks observed at m/z ϭ 402Ϫ412 with high intensity can
the methyl protons) were observed for the selenenyl halides be assigned to RSeϩ fragments. This strongly suggests a
5, 6, and 8. This indicates a strong Se···N interaction. These weakening of the SeϪX (X ϭ SeR, Br, CH2Ph) bond trans
1H NMR chemical shifts are in good agreement with those to the Se···N fragment.
in other intramolecularly stabilized organoselenium
compounds.[11cϪ11e]
X-ray Crystallographic Studies
The 77Se NMR chemical shifts are quite informative
The significant bond lengths and bond angles of com-
pounds 4, 6, 7, and 8 are listed in Table 1.
about the Se···N nonbonding interactions. The 77Se NMR
spectrum of 4 exhibits a single peak at δ ϭ 450 ppm, which
is more downfield shifted than systems having sp3 nitrogen
Molecular Structure of 4
atoms.[11c,11e] However, it is close to the diselenide of 4,4-
dimethyl-2-phenyl-1,3-oxazoline.[11d] Interestingly, the crys-
The X-ray crystal structure of 4 is shown in Figure 1.
tal structure of the diselenide reveals that only one of the The coordination geometry around the selenium atom is
nitrogen atoms interacts with the Se atom, with the other distorted T-shaped with each selenium atom bonded to sel-
being much further away (vide infra). The 77Se NMR enium, carbon and a nitrogen/oxygen atom. The most inter-
chemical shift of compound 8 lies upfield (δ ϭ 351 ppm) esting feature of the structure is the existence of both Se···N
from that of the corresponding diselenide (4; δ ϭ 450 ppm). and Se···O interactions between selenium and nitrogen/oxy-
This may be due to the presence of the benzyl group, which gen in the same molecule. This is the first structure, to the
cannot accept electron density from the selenium; the Se···N best of our knowledge, to be reported where both intramol-
interaction may also be very weak. The crystal structure of ecular Se···N and Se···O interactions exist in the same mol-
1016
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Organoselenium Compounds Containing Both Bulky and Nonbonding Groups
FULL PAPER
˚
Table 1. Important bond lengths (A) and bond angles (°) for 4, 6, 7, and 8
Compound 4
Se(1A)···N(1A)
2.976(8)
2.3216(15)
152.28(2)
118.28(12)
101.5(3)
Se(1B) ···O(1B)
2.9815(5)
173.88(17)
164.3(2)
Se(1A)ϪSe(1B)
N(1A)···Se(1A)ϪSe(1B)
C(24C)ϪSe(1C)ϪN(1C)
C(1A)ϪSe(1A)ϪSe(1B)
O(1B) ···Se(1B)ϪSe(1A)
N(1B) ···Se(1B)ϪSe(1A)
C(1B)ϪSe(1B)ϪSe(1A)
101.9(3)
Compound 6
Compound 7
Se···N
2.052(3)
2.6485(7)
1.353(5)
Se···N
2.059(5)
2.8297(8)
1.337(7)
SeϪBr
SeϪI
OϪC(11)
NϪC(11)
N···SeϪBr
C(1)ϪSeϪBr
C(1)ϪSe···N
OϪC(11)
NϪC(11)
N···SeϪI
C(1)ϪSeϪI
C(1)ϪSe···N
1.288(5)
1.289(7)
175.15(10)
95.91(12)
81.03(15)
175.26(14)
97.51(15)
80.8(2)
Compound 8
Se(1A)ϪC(1A)
Se(1B)ϪC(1B)
Se(1C)ϪC(24C)
Se(1D)ϪC(1D)
C(1A)ϪSe(1A)ϪC(24A)
C(24C)ϪSe(1C)ϪC(1C)
C(1A)ϪC(10A)ϪC(11A)ϪN(1A)
C(1B)ϪC(10B)ϪC(11B)ϪN(1B)
C(1C)ϪC(10C)ϪC(11C)ϪN(1C)
C(1D)ϪC(10D)ϪC(11D)ϪN(1D)
1.916(5)
1.903(6)
1.911(7)
1.935(5)
98.0(2)
98.1(3)
Ϫ72.6(7)
73.1(8)
Se(1A)ϪC(24A)
Se(1B)ϪC(24B)
Se(1C)ϪC(1C)
Se(1D)ϪC(24D)
C(1B)ϪSe(1B)ϪC(24B)
C(1D)ϪSe(1D)ϪC(24D)
C(1A)ϪC(10A)ϪC(11A)ϪO(1A)
C(1B)ϪC(10B)ϪC(11B)ϪO(1B)
C(1C)ϪC(10C)ϪC(11C)ϪO(1C)
C(1D)ϪC(10D)ϪC(11D)ϪO(1D)
1.979(7)
1.952(7)
1.918(5)
1.944(7)
98.4(3)
98.0(2)
106.7(6)
104.9(6)
102.6(6)
104.9(6)
Ϫ77.8(7)
75.2(7)
Figure 1. Molecular structure of 4
ecule. Several structures of selenium compounds incorpor- tions were observed. Thus, the unusual observation of an
ating 4,4-dimethyl-2-phenyloxazoline,[2k,4i,17,18,24,27] have intramolecular Se···O interaction in the structure of 4 may
been reported by our group. In all cases only Se···N interac- be explained by the orientation of the oxazoline rings.
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K. Kandasamy, S. Kumar, H. B. Singh, R. J. Butcher, K. T. Holman
FULL PAPER
These rings are twisted about the C(18)ϪC(19) axis in op- molecular Se···N and Se···O interactions, the shorter SeϪSe
posite orientations such that in one oxazoline ring the nitro- distance, and the ‘‘cisoid’’ conformation it may be con-
gen
atom
is
directed
towards
the
selenium cluded that the SeϪSe and Se···N bond lengths are length-
[C(1A)ϪC(18A)ϪC(19A)ϪN(1A)
ϭ
Ϫ48.27(14)° vs. ened to minimize the steric crowding imposed by the steri-
C(1A)ϪC(18A)ϪC(19A)ϪO(1A) ϭ 131.72(8)°], whereas in cally more demanding group present in this system. There
the other ring the oxygen atom is directed towards the sel- are no significant intermolecular Se···Se contacts. The
˚
enium [C(1A)ϪC(18A)ϪC(19A)ϪO(1A) ϭ 53.69(12)° vs. shortest intermolecular Se···Se distance [8.618 A] is much
˚
˚
C(1A)ϪC(18A)ϪC(19A)ϪN(1A) ϭ Ϫ127.58(10)°]. The longer than the sum of the van der Waals radii (3.8 A).
orientation of the oxazoline rings may be due to the influ- However, intermolecular Se···H [Se1A···H13AA: 3.1096 A;
˚
˚
ence of steric crowding imposed by the sterically bulkier Se1A···H2BA: 3.2678 A; Se1B···H2AA: 2.7981 A;
˚
substituents present in the system. The Se(1A)···N(1A) Se1B···H13BB: 2.8697 A] contacts exist that are much
˚
˚
˚
[2.976(8) A] and Se(1B)···O(1B) [2.9815 A)] distances are shorter than the sum of the van der Waals radii (3.35 A).
similar to the respective distances in other related diseleni- These short Se···H contacts may be a result of optimized
des.[4i,28] The observed SeϪSe distance [2.3216(16) A] is also dense packing of the molecules.
˚
shorter than in bis(4,4-dimethyl-2-phenyl-1,3-oxazolin-2-yl)
[11d]
˚
diselenide [2.354(8) A],
bis{2-[(dimethylamino)methyl]-
Molecular Structure of 6
[11e]
˚
phenyl} diselenide [2.357(1) A]
and bis[2-(dimethylami-
no)naphthyl] diselenide[11c] [2.383(2) A]. Another interest-
An ORTEP view of 6 is shown in Figure 2. The geometry
˚
ing feature in this structure is the ‘‘cisoid’’ conformation of around Se is T-shaped and the methyl groups attached to
the diselenide. Sandman et al.[29] have reported the crystal the oxazoline are disordered. The strong nonbonded Se···N
˚
structures of two conformational polymorphs of bis(2- interaction [2.052(3) A] is very close to the corresponding
naphthyl) ditelluride. The ‘‘cisoid’’ conformations have a distance in [2-(4,4-dimethyl-1,3-oxazolin-2-yl)phenyl]selen-
[11d]
˚
CϪSeϪSeϪC torsion angle of less than 90° and the ium bromide [2.063(3) A]
and shorter than in {2-
‘‘transoid’’ conformations have a CϪSeϪSeϪC torsion an- [(dimethylamino)methyl]phenyl}selenium bromide [2.143(6)
[11e]
˚
˚
gle greater than 90°. In the case of
4
the A].
The SeϪBr bond length [2.6485(7) A] is longer than
C(1A)ϪSe(1A)ϪSe(1B)ϪC(1B) torsion angle is 81.42° and the sum of the single-bond covalent radii of Se and Br (2.31
thus has a ‘‘cisoid’’ conformation. From the unusual intra- A). The lengthening of the SeϪBr bond length can be attri-
˚
Figure 2. Molecular structure of 6
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Organoselenium Compounds Containing Both Bulky and Nonbonding Groups
FULL PAPER
˚
˚
buted to the strong trans influence of the Se···N interaction. Br···H19Aa: 3.1953 A; Br···H4Ab: 3.1463 A; Br···H5Ab:
˚
˚
A similar observation has been made for the molecular 3.0838 A) and Se···H12C (3.1405 A) contacts are observed
structure of 2-formylbenzeneselenenyl bromide.[30] The in the packing diagram. The Br···H and Se···H distances
˚
SeϪBr bond length in 6 [2.6485(7) A] is also similar to the are shorter than the sum of their van der Waals radii, at
reported values for [2-(4,4-dimethyl-1,3-oxazolin-2-yl)phen- 3.45 A and 3.35 A, respectively. The short Se···H contacts
yl]selenium bromide [2.631(9) A] and {2-[(dimethyl- may be a result of optimized dense packing of molecules as
amino)methyl]phenyl}selenium bromide [2.634(1) A]. The for the above structure.
˚
˚
˚
˚
Se···NϪBr angle [175.16 (10)°] is close to linear. From the
C(1)ϪSeϪBr [95.91(12)°] and C(1)ϪSe···N [81.03(15)°]
bond angles the coordination around selenium can be re-
garded as trigonal bipyramidal if the lone pairs are taken
Molecular Structure of 7
The molecular structure of 7 is given in Figure 3. This
into account. However, the packing pattern of this structure is isostructural with 6. In this structure the methyl groups
is significantly different from the other intramolecularly sta- attached to the oxazoline rings are disordered. The ob-
˚
bilized organoselenium bromides, including [2-(4,4-di- served intramolecular Se···N distance [2.059(5) A] is con-
methyl-2-phenyloxazolinyl)phenyl]selenium bromide. In all siderably shorter than the corresponding distances in [2-
the organoselenium bromides the formation of weak dimers (4,4-dimethyl-2-oxazoline)phenyl]selenium iodide [2.133(4)
[11d]
˚
by intermolecular interactions between selenium and bro- A],
and [8-(dimethylamino)-1-naphthyl]selenium iodide
mine were observed.[11cϪ11e,31] However, in the case of 6 [2.242(5) A],
whereas the SeϪI distance [2.8297(8) A] is
[11c]
˚
˚
such intermolecular Se···Br interactions are absent. The considerably longer than the corresponding distance in
˚
shortest intermolecular Se···Br contact [4.8914 A] is greater [2-(4,4-dimethyl-1,3-oxazolin-2-yl)phenyl]selenium iodide
˚
˚
than the sum of the van der Waals radii (3.9 A). The ab- [2.7773(7) A] and [8-(dimethylamino)-1-naphthyl]selenium
˚
sence of intermolecular Se···Br interactions clearly suggests iodide [2.742(9) A]. The SeϪI distance is also longer than in
that the sterically more demanding group present in this 2,4,6-tri-tert-butylphenyl iodo selenide [2.529(1) A].
[21]
˚
The
system prevents the formation of weak dimers and thus elongation of the SeϪI bond length may be attributed to
confirms the formation of a truly monomeric selenium bro- the presence of a shorter (strong) Se···N interaction trans
˚
mide. Intermolecular Br···H (Br···H2A: 2.7190 A; to the SeϪI fragment. The N···SeϪI bond angle
Figure 3. Molecular structure of 7
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K. Kandasamy, S. Kumar, H. B. Singh, R. J. Butcher, K. T. Holman
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[175.26(14)°] is close to linear. In the packing diagram of 7 2-(4,4-dimethyl-1,3-oxazolin-2-yl)phenyl selenide [1.966(3)
˚
the shortest intermolecular contact between the selenium A], even though the intramolecular Se···N interaction
˚
˚
˚
and iodine is 4.811 A, about 0.8 A greater than the sum of (3.3842 A) was found to be much weaker than in the latter
˚
˚
the van der Waals radii (4.02 A). Intermolecular Se···H and case [2.798(3) A]. The lengthening of the SeϪCH2Ph dis-
Se···H contacts are also observed here that are shorter than tance even in the presence of a weak Se···N interaction sug-
the sum of the van der Waals radii, which may be due to gests that the sterically more demanding group present in
the optimized dense packing of the molecules.
the system plays an important role. The very weak Se···N
interaction may be a result of the perpendicular orientation
of the oxazoline ring, which is twisted about the
C(10)ϪC(11) bond axis such that the nitrogen atom is
slightly away from the selenium. Figure 4 shows that Se and
N atoms lie in a different plane, in contrast to the benzyl
(4,4-dimethyl-1,3-oxazolin-2-yl)phenyl selenide where both
the selenium and nitrogen are in same plane.
Molecular Structure of 8
The molecular structure of 8 is shown in Figure 4 as an
ORTEP view. This compound crystallizes in the monoclinic
system with four symmetry-independent molecules in the
asymmetric unit cell. The geometry around the selenium
atom is V-shaped. The selenium atom is bonded to two car-
bon atoms derived from two different organic substituents.
It is worth noting that the C(1)ϪSe(1) [C(1A)ϪSe(1A):
Conclusion
˚
˚
˚
1.916(5) A; C(1B)ϪSe(1B): 1.903(6) A; C(1C)ϪSe(1C):
˚
1.918(5) A; C(1D)ϪSe(1D): 1.935(5) A] and C(24)ϪSe(1)
Novel organoselenium compounds, including a diselen-
˚
˚
˚
˚
[C(24A)ϪSe(1A): 1.979(7) A; C(24B)ϪSe(1B): 1.952(7) A; ide, with both intramolecular Se···N and Se···O interactions,
C(24C)ϪSe(1C): 1.911(7) A; C(1D)ϪSe(1D): 1.944(7) A] incorporating a ligand with steric and intramolecularly co-
bond
lengths,
and
the
98.0(2)°;
C(1)ϪSe(1)ϪC(24) ordinating groups, have been prepared and characterized.
C(1B)ϪSe(1B)Ϫ From the current results and their comparison with intra-
[C(1A)ϪSe(1A)ϪC(24A):
C(24B): 98.4(3)°; C(1C)ϪSe(1C)ϪC(24C): 98.1(3)°; molecularly stabilized organoselenium compounds derived
C(1D)ϪSe(1D)ϪC(24D): 98.0(2)°] bond angle are signifi- from sterically less-hindered ligands, it is apparent that the
cantly different for all four independent molecules. The strength of the Se···N interaction also depends on the nat-
SeϪC(Ph) and SeϪCH2Ph bond lengths are in good agree- ure of the substituents (steric groups) present in the system,
ment with the corresponding distances reported for the re- in addition to the nature of the nitrogen atom used as an
lated systems.[11d,32] One of the interesting features is the ortho chelating group and the electronegativity of the group
˚
longer SeϪCH2Ph [Se(1A)ϪC(24A): 1.979(7) A] distance attached to the selenium atom. The Se···N nonbonding in-
compared to that in the sterically less hindered benzyl teractions are considerably stronger than in organoselenium
Figure 4. Molecular structure of 8
1020
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1014Ϫ1023

Organoselenium Compounds Containing Both Bulky and Nonbonding Groups
FULL PAPER
1.29 (s), 2.37 (s), 3.78 (s), 1.29 (s), 2.37 (s), 3.78 (s), 7.05 (s), 7.35
(t), 7.65 (t), 7.75 (t), 8.3 (s) ppm. 13C NMR (300 MHz, CDCl3,
298 K): δ ϭ 21.2, 28.0, 68.1, 79.4, 126.1, 127.0, 127.6, 127.8, 128.0,
129.0, 129.4, 131.2, 134.6, 137.1, 137.6, 140.9, 160.1 ppm. 77Se
NMR (300 MHz, CDCl3, 298 K): δ ϭ 450 ppm. IR (KBr): ν˜ ϭ
1670 cmϪ1 ν(CϭN). FAB-MS: m/z ϭ 816 [Mϩ].
compounds derived from the sterically less-hindered li-
gands. The Se···N nonbonding interactions lengthen the
Se···X bond (X ϭ ϪSe, Br, I, or CH2) and enhance the
possibility of nucleophilic attack at the selenium atom. The
intermolecular Se···X (X ϭ Cl, Br, I) interactions generally
observed in the other reported organoselenium halides are
absent, possibly due to the presence of the sterically more- Synthesis of Selenenyl Chloride 5: Treatment of a solution of the
diselenide (0.16 g, 0.2 mmol) in carbon tetrachloride (25 mL) with
a carbon tetrachloride solution of SO2Cl2 (0.6 mL of 2.1 g, 50 mL,
0.2 mmol) at room temperature gave a yellow precipitate after 1
hour. The mixture was evaporated to dryness under vacuum in or-
der to give the desired compound. The yellow crystalline product
was obtained after recrystallization from methanol/chloroform
demanding group. Thus, selenium halides derived from this
substrate can be considered as true monomers in the solid
state. Although the intermolecular Se···X interactions of the
organoselenium halides described here are not within the
sum of the van der Waals radii, the intermolecular Se···X
contacts decrease (strong interaction) as the size of the hal-
ogen atom increases. This may be attributed to the decrease
of ligand-ligand repulsions (steric repulsions) as the size of
the atom increases.
(2:1). Yield: 0.083 g, 93%. M.p. (decomp.)
Ͼ
200 °C.
C23H22ClNOSe (443.05): calcd. C 62.39, H 5.01, N 3.16; found C
62.33, H 5.33, N 3.23. 1H NMR (300 MHz, CDCl3, 298 K): δ ϭ
1.63 (s), 2.39 (s), 4.45 (s), 6.92 (s), 7.13 (s), 7.45 (t), 7.59 (d), 7.7
(t), 8.05 (d), 9.36 (s) ppm. 13C NMR (300 MHz, CDCl3, 298 K):
δ ϭ 21.3, 27.9, 65.3, 84.9, 115.8, 126.4, 127.4, 127.6, 128.2, 129.0,
129.9, 131.0, 134.9, 135.8, 137.2, 141.9, 143.8, 167.1 ppm. 77Se
NMR (300 MHz, CDCl3, 298 K): δ ϭ 839 ppm. IR (KBr): ν˜ ϭ
1755 cmϪ1 ν(CϭN). FAB-MS: m/z ϭ 443 [Mϩ].
Experimental Section
General: All reactions were carried out in an inert atmosphere using
nitrogen or argon with standard vacuum-line techniques. All sol-
vents were purified by following the literature method and freshly
distilled prior to use.[33] 2-[1-(3,5-Dimethylphenyl)-2-naphthyl]-4,5-
dihydro-4,4-dimethyloxazole (Aldrich) and n-butyllithium (E.
Merck) were reagent grade and used as received. Se(dtc)2 was pre-
pared by a reported procedure.[34] Melting points were recorded in
Synthesis of Selenenyl Bromide 6: The procedure followed was the
same as that used for the preparation of compound 5, except the
addition of Br2/CCl4 was carried out for 4 hour at 0 °C. The com-
pound was recrystallized from a dichloromethane/hexane mixture
to give yellow crystals. Yield: 0.06 g, 68%. M.p. (decomp.) Ͼ 216
°C. C23H22BrNOSe (487.0): calcd. C 56.70, H 4.55, N 2.87; found
C 56.51, H 4.39, N 2.70. UV/Vis (dichloromethane): λmax (ε) ϭ
399.5 nm (9540 dm3 molϪ1 cmϪ1), 303.5 (11950). 1H NMR
(300 MHz, CDCl3, 298 K): δ ϭ 1.64 (s), 2.39 (s), 4.47 (s), 6.9 (s),
7.13 (s), 7.43 (t), 7.53 (d), 7.63 (t), 8.01 (d), 9.4 (s) ppm. 13C NMR
(300 MHz, CDCl3, 298 K): δ ϭ 21.3, 27.9, 65.2, 84.7, 115.9, 126.4,
127.6, 128.2, 129.1, 129.5, 129.8, 131.2, 134.9, 135.9, 137.2, 139.7,
143.8, 166.7 ppm. 77Se NMR (300 MHz, CDCl3, 298 K): δ ϭ
836 ppm. IR (KBr): ν˜ ϭ 1660 cmϪ1 ν(CϭN). FAB-MS: m/z ϭ 488
[M ϩ 1]ϩ, 487 [Mϩ].
1
capillary tubes and are uncorrected. H, 13C and 77Se NMR were
obtained at 300, 75.42 and 57.22 MHz, respectively, in CDCl3 on
a Varian VXR 300S spectrometer. Chemical shifts are cited with
respect to SiMe4 as internal (1H and 13C) and Me2Se (77Se) as ex-
ternal standard. Elemental analyses were determined with a
CarloϪErba model EA 1112 CHNS analyzer. Infrared spectra were
recorded in the range of 4000Ϫ400 cmϪ1 on a Nicolet Impact 400
FT-IR spectrometer. UV/Vis spectra were recorded on a Shimadzu
UV-160A spectrophotometer and fluorescence spectra on
a
PerkinϪElmer LS-55 Luminescence spectrometer. Fast atomic
bombardment (FAB) mass spectra were recorded at room tempera-
ture on a JEOL SX 102/DA-6000 mass spectrometer/data system
with xenon (6 kV, 10 mV) as the bombarding gas. The accelerating
voltage was 10 kV. m-Nitrobenzyl alcohol was used as the matrix
with cation detection. For isotopes the value given is for the most
intense peak.
Synthesis of Selenenyl Iodide 7: Here the procedure used for the
preparation of compound 6 was also followed, with the addition
of I2 instead of SO2Cl2. The solution obtained was concentrated to
give a yellow crystalline product. The compound was recystallized
from a dichloromethane/hexane mixture (1:2). Yield: 0.42 g, 79%.
M.p. (decomp.) Ͼ 240 °C. C23H22INOSe (535.0): calcd. C 51.71,
H 4.15, N 2.62; found C 51.68, H 4.12, N 2.46. UV/Vis (dichloro-
methane): λmax (ε) ϭ 400 nm (7890 dm3 molϪ1 cmϪ1), 303 (17760).
1H NMR (300 MHz, CDCl3, 298 K): δ ϭ 1.59 (s), 2.4 (s), 3.8 (s),
4.3 (s), 6.9 (s), 7.4 (m), 7.6 (m), 7.72 (d), 8.0 (d), 9.31 (s) ppm. 13C
NMR (300 MHz, CDCl3, 298 K): δ ϭ 21.6, 28.4, 65.4, 84.2, 117.0,
126.4, 127.5, 127.7, 127.9, 128.8, 129.7, 131.6, 132.3, 134.9, 136.2,
137.1, 143.5 ppm. 77Se NMR (300 MHz, CDCl3, 298 K): δ ϭ
782 ppm.
Synthesis of Diselenide 4: Addition of 1.6  solution of nBuLi in
hexane (3.45 mL, 5.5 mmol) to a diethyl ether (50 mL) solution of
2-[1-(3,5-dimethylphenyl)-2-naphthyl]-4,5-dihydro-4,4-dimethyl-
oxazole (1.647 g, 5 mmol) under N2 at 0 °C resulted in a dark
brown solution of the lithiated compound. After 2 hours, finely
ground selenium powder (0.4 g, 5 mmol) was added at 0 °C and
the temperature maintained for 2 hours to give the lithium arenese-
lenolate. The reaction mixture was then poured into a beaker con-
taining cold aqueous NaHCO3 and O2 was passed at a moderate
Synthesis of Aryl Benzyl Selenide 8: The benzyl chloride (0.635 mL,
rate for 30 min and the mixture extracted with diethyl ether 5 mmol) was added to the lithium selenolate at 0 °C and stirring
(50 mL). The organic phase was washed with water, and dried over
Na2SO4. The filtrate was concentrated to give a yellow oil, which
solidified upon addition of hexane. The compound was recrys-
tallized from a hexane/dichloromethane (4:1) mixture to give yellow
continued for 2 hours. The usual work up followed by evaporation
under reduced pressure gave the desired yellow compound, which
was recrystallized from an acetonitrile/dichloromethane mixture
(2:1). Yield: 0.7 g, 28%, M.p. 158Ϫ160 °C. C30H29NOSe (500.2):
crystals of 4. Yield: 0.97 g, 25%. M.p. 196Ϫ198 °C. C46H44N2O2Se2 calcd. C 72.29, H 5.86, N 2.81; found C 72.59, H 5.95, N 2.66.
(816.2): calcd. C 67.83, H 5.44, N 3.44; found C 67.52, H 5.41, N
UV/Vis (dichloromethane): λmax (ε) ϭ 350 nm (3000 dm3 molϪ1
3.22. UV/Vis (dichloromethane): λmax (ε) ϭ 303.5 nm (18000 dm3 cmϪ1), 303.5 (18420). 1H NMR (300 MHz, CDCl3, 298 K): δ ϭ
molϪ1 cmϪ1), 350 (8000). 1H NMR (300 MHz, CDCl3, 298 K): δ ϭ
1.12 (s), 2.35 (s), 3.83 (s), 4.22 (s), 7.02 (s), 7.39 (t), 7.6Ϫ7.49 (t),
Eur. J. Inorg. Chem. 2004, 1014Ϫ1023
www.eurjic.org
 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
1021

K. Kandasamy, S. Kumar, H. B. Singh, R. J. Butcher, K. T. Holman
FULL PAPER
Table 2. Crystal data and structure refinement for 4, 6, 7 and 8
Compound
4
6
7
8
Empirical formula
Molecular mass
Crystal system
Space group
C46H44N2O2Se2
814.75
Monoclinic
P21/c
24.394(5)
8.1678(16)
21.307(5)
106.944(17)
4061.0(15)
4
C23H22BrNOSe
487.29
Monoclinic
P21/c
11.3367(15)
9.8765(13)
18.873(2)
93.826(2)
2108.5(5)
4
C23H22INOSe
534.28
Monoclinic
P21/c
11.4446(14)
9.8991(12)
18.675(2)
91.865(7)
2114.6(4)
4
C30H29NOSe
498.50
Monoclinic
Cc
14.6082(12)
14.6368(11)
47.449(4)
92.7850(10)
10133.5(14)
16
˚
a (A)
˚
b (A)
˚
c (A)
β (deg)
3
˚
V (A )
Z
D(calcd.) (Mg/m3)
1.333
1.860
1.535
3.688
1.678
3.248
1.307
1.504
Abs coeff (mmϪ1
)
Obsd. refls. [I Ͼ 2σ(I)]
Final R(F) [I Ͼ 2σ(I)][a]
wR(F2) [I Ͼ 2σ(I)]
5310
0.0732
0.1073
5310/0/ 521
1.002
5066
0.0556
0.1222
5066/6/270
0.874
2885
0.0515
0.1510
2885/4/ 270
1.173
22326
0.0539
0.1193
22326/2/1206
1.024
Data/restraints/parameters
Goodness of fit on F2
[a]
2
2
2 2
2 2
R(Fo) ϭ ||Fo| Ϫ |Fc||/|Fo| and wR(Fo ) ϭ {[w(Fo Ϫ Fc ) ]/[w(Fc ) }1/2
.
7.72 (d), 7.87 (s) ppm. 13C NMR (300 MHz, CDCl3, 298 K): δ ϭ
21.2, 27.7, 67.9, 126.4, 126.7, 127.4, 128.2, 129.0, 130.4, 131.4,
133.3, 134.0, 137.0, 137.5, 138.3, 141.1, 161.7 ppm. 77Se NMR
(300 MHz, CDCl3, 298 K): δ ϭ 351 ppm. IR (KBr): ν˜ ϭ 1670 cmϪ1
ν(CϭN). FAB-MS: m/z ϭ 500 [Mϩ].
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 2004 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim
www.eurjic.org
Eur. J. Inorg. Chem. 2004, 1014Ϫ1023

Organoselenium Compounds Containing Both Bulky and Nonbonding Groups
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Stern, I. A. Cotgreave, C. M. Andersson, J. Am. Chem. Soc.
Eur. J. Inorg. Chem. 2004, 1014Ϫ1023
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