Synthesis and molecular structures of dialkylselenonium methylide complexes of indium tribromide

Article abstract of DOI:10.1016/j.jorganchem.2004.11.050

The reaction of bromomethyl-dibromo-indium(III), Br₂InCH ₂Br with dialkylselenides, R¹SeR² (R ¹ = CH₃, R² = CH₂C₆H ₅; R¹ = C₂H₅, R² = CH₂C₆H₅; R¹ = R² = CH₂C₆H₅) afforded the corresponding dialkylselenonium methylide complexes of indium tribromide, Br ₃InCH₂SeR¹R², which were fully characterized by NMR spectroscopy and single crystal X-ray diffraction studies.

Full text of DOI:10.1016/j.jorganchem.2004.11.050

Journal of Organometallic Chemistry 690 (2005) 1294–1299
www.elsevier.com/locate/jorganchem
Synthesis and molecular structures of dialkylselenonium
methylide complexes of indium tribromide
a
b
a,
b
Fabiano Molinos de Andrade , Werner Massa , Clovis Peppe *, Werner Uhl
a
´ ´ ˆ
Departamento de Quımica, Laboratorio de Materiais Inorganicos, Campus UFSM, Universidade Federal de Santa Maria,
Santa Maria-RS 97105-900, Brazil
b
Fachbereich Chemie der Philipps Universita¨t Marburg, Hans-Meerwein-Strasse, D-35032 Marburg, Germany
Received 5 November 2004; accepted 24 November 2004
Available online 12 January 2005
Abstract
The reaction of bromomethyl-dibromo-indium(III), Br2InCH2Br with dialkylselenides, R1SeR2 (R1 = CH3, R2 = CH2C6H5;
R1 = C2H5, R2 = CH2C6H5; R1 = R2 = CH2C6H5) afforded the corresponding dialkylselenonium methylide complexes of indium
tribromide, Br3InCH2SeR1R2, which were fully characterized by NMR spectroscopy and single crystal X-ray diffraction studies.
ꢀ 2004 Elsevier B.V. All rights reserved.
Keywords: Indium; Organoindium; Carbenoid; Ylid; Zwitterion; Crystal structure
1. Introduction
Organoindium compounds containing nucleophilic a-
halogenoalkyl substituents were obtained from gem-
dihalides containing electron withdrawing groups R1
and R2 (X = Br, R1 = CN, R2 = H [2]; X = Cl,
R1 = CN, R2 = Cl [3]; X = Cl, R1 = C6H5CO, R2 = H
[4]; X = Cl, Br, I, R1 = Cl, Br, I, R2 = H [5]), while the
carbenoids (I) derived from methylene dihalides,
X2InCH2X (X = Br, I), contain halomethylic substitu-
ents of considerable electrophilic character, resulting in
a strong interaction of the a-halogen atom with an empty
metal orbital. This analysis allows an interpretation of
the reactivity of the X2InCH2X molecules in terms of
the tautomeric relationship shown in Scheme 1 [6].
The addition of a soft neutral ligand L to the
X2InCH2X molecules yields the corresponding
X3InCH2L adduct, in which the ligand L is directly at-
tached to the methylene carbon. This paper reports on
an extension of these studies. We have now prepared
new selenonium methylide complexes of indium tribro-
mide, which were fully characterized by NMR and
X-ray diffraction studies.
The oxidative insertion of indium monohalides, InX,
into a carbon–halogen bond of gem-dialkyldihalides,
R1R2CX2 produces the a-halogenoalkyl-indium(III)
compounds of general formula X2InCR1R2X (Eq. (1))
[1]. It is possible to modulate the electronic character
of the a-halogenoalkyl substituent by the correct choice
of the R1 and R2 substituents on the parent
dialkyldihalide.
1
R
1
X
X
R
X
X
2
ð1Þ
C
In
C
X
R
InX +
2
R
*
Corresponding author. Tel.: +55552208868; fax: +55552208031.
E-mail address: peppe@quimica.ufsm.br (C. Peppe).
0022-328X/$ - see front matter ꢀ 2004 Elsevier B.V. All rights reserved.
doi:10.1016/j.jorganchem.2004.11.050

F.M. de Andrade et al. / Journal of Organometallic Chemistry 690 (2005) 1294–1299
1295
1
R1
Benzyl-methyl-selenide, 2a (colorless oil): H NMR
(CDCl3): d = 7.22 (s, 5H), 3.69 (s, 2H), 1.85 (s, 3H);
77Se NMR (CDCl3): d = 170 [8].
X
X
X
δ
δ
In
C
R2
In
Benzyl-ethyl-selenide, 2b (colorless oil): 1H NMR
(CDCl3): 7.22 (s, 5H), 3.73 (s, 2H), 2.44 (q, J = 7.5 Hz,
2 H), 1.31 (t, J = 7.5 Hz, 3H); 77Se NMR (CDCl3):
d = 284.
X
CR1R2
X
X
Dibenzylselenide, 2c [yellow solid, mp = 45–46 ꢁC
(Lit. [7] 45.5 ꢁC)]: 1H NMR (CDCl3): 7.18 (m, 5H),
3.75 (s, 2H); 77Se NMR (CDCl3): d = 331 [8].
IB
IA
Scheme 1.
2.3. Preparation of dialkylselenonium methylide
complexes of InBr3, Br3InCH2SeR1R2, 3 (a = R1 = CH3,
R2 = CH2C6H5; b = R1 = C2H5, R2 = CH2C6H5;
c = R1 = R2 = CH2C6H5)
2. Experimental
2.1. General
InBr (195 mg, 1 mmol) was suspended in 1,4-dioxan
(8 mL) in a Schlenk flask under dry N2 atmosphere.
To this solution was added CH2Br2 (869 mg, 0.35 mL,
5 mmol) and the suspension was stirred until complete
dissolution of the red InBr solid. A clear colorless solu-
tion was obtained. The volatiles were removed from this
solution under high vacuum to produce a white solid
(the bis-dioxan adduct of Br2InCH2Br). The solid was
re-dissolved in dioxan (8 mL) and to this solution was
added the corresponding dialkylselenide 2a–c (1 mmol).
The reaction was kept under stirring for 6 h, after which
the volatiles were again removed under high vacuo to
produce oily materials, which were dissolved in hot chlo-
roform (15 mL). From the solutions, crystalline
Br3InCH2SeR1R2 compounds precipitate upon cooling
to room temperature. The crystals were filtered and
dried under vacuo (Yield: 3a = 40%, 3b = 70%,
3c = 75%). The Br3InCH2SeR1R2 compounds were
characterized by NMR spectroscopy and single crystal
X-ray diffraction studies.
Indium monobromide was prepared by heating in-
dium metal and indium tribromide in a vacuum sealed
tube at 450 ꢁC. Methylene bromide (Aldrich) was dried
˚
over Linde 4 A molecular sieves. Br2In(diox)2CH2Br
was prepared from InBr and CH2Br2 as described ear-
lier [6]. 1,4-Dioxane (diox) was dried over sodium and
benzophenone, and distilled just before use from the
blue ketyl form. Chloroform (ACS grade) was used
as supplied. All preparative work was carried out un-
der dry nitrogen atmosphere, up to the isolation of fi-
nal products. Proton, carbon and selenium (diphenyl
diselenide as internal standard) NMR spectra were re-
corded on the Bruker DPX-200 and DPX-400
instruments.
2.2. Preparation of dialkylselenides, R1SeR2, 2
(a = R1 = CH3, R2 = CH2C6H5; b = R1 = C2H5,
R2 = CH2C6H5; c = R1 = R2 = CH2C6H5)
The dialkylselenide ligands were all prepared from
dibenzyldiselenide, which was made from NaBH4, ele-
mental selenium and benzyl chloride, according to the
literature [7]. Thus, 510 mg (1.50 mmol) of dibenzyldisel-
enide was suspended in ethanol (20 mL) in a round bot-
tom flask. NaBH4 (3 mmol) was added as a solid to the
suspension and the reaction kept under magnetic stirring
until a clear solution was obtained. At this point, 3
mmol of the corresponding alkyl halide R1X
(a = R1 = CH3, X = I; b = R1 = C2H5, X = Br; c =
R1 = C6H5CH2, X = Cl) was added via syringe and the
mixture stirred for additional 4 h. After this period,
the reaction was quenched with water, the organics ex-
tracted with CH2Cl2 (2 · 20 mL). The organic phase
was dried (Na2SO4), evaporated to dryness to give an
oil, which was purified by column chromatography over
silical gel with hexane. This procedure gives 2a–c in the
following yields (a = 82%, b = 67%, c = 69%). Com-
pounds 2a–c were characterized by 1H NMR
spectroscopy:
Benzyl-methyl-selenonium-methylide-tribromo-ind-
1
ate(III) (3a), (mp = 113–115 ꢁC): H NMR [(CD3)2CO]:
2
d = 7.47–7.59 (m, 5H), 4.86 (d, J = 11.7 Hz, 1H), 4.78
2
2
(d, J = 11.7 Hz, 1H), 2.78 (s, 3H), 2.47 (d, J = 10.6
Hz, 1H), 2.38 (d, 2J = 10.6 Hz, 1H); 13C NMR
[(CD3)2CO]: d = 132.66, 131.48, 131.31, 131.21, 47.29,
22.36; (DEPT = 135): 132.66 (Car–H), 131.48 (Car–H),
131.21 (Car–H), 47.29 (CH2), 22.36 (CH3); 77Se NMR
((CD3)2CO): d = 370.
Benzyl-ethyl-selenonium-methylide-tribromo-indate
1
(III) (3b), (mp = 131–132.5 ꢁC): H NMR [(CD3)2CO]:
2
d = 7.46–7.64 (m, 5H), 4.86 (d, J = 11.8 Hz, 1H), 4.79
2
(d, J = 11.8 Hz, 1H), 3.37 (m, 2H), 2.47 (s, 2H), 1.54
(t, J = 7.50 Hz, 3H); 13C NMR [(CD3)2CO]:
d = 132.44, 131.72, 131.42, 131.30, 45.60, 36.26, 21.93,
11.32; (DEPT = 135): 132.44 (Car–H), 131.42 (Car–H),
131.30 (Car–H), 45.60 (CH2), 36.26 (CH2), 11.32
(CH3); 77Se NMR ((CD3)2CO): d = 415.
Dibenzyl-selenonium-methylide-tribromo-indate(III)
(3c), (mp = 152–154 ꢁC): 1H NMR [(CD3)2CO]:

1296
F.M. de Andrade et al. / Journal of Organometallic Chemistry 690 (2005) 1294–1299
2
d = 7.42–7.55 (m, 10H), 4.80 (d, J = 11.7 Hz, 2H), 4.73
(d, 2J = 11.7 Hz, 2H), 2.39 (s, 2H); 13C NMR
[(CD3)2CO]: d = 132.44, 131.49, 131.34, 131.23, 46.33,
22.74; (DEPT = 135): 132.44 (Car–H), 131.34 (Car–H),
131.23 (Car–H), 46.33 (CH2); 77Se NMR ((CD3)2CO):
d = 432.
C = 120ꢁ) in the refinement and for all C atoms isotropic
displacement parameters were used. The hydrogen
atoms were treated as riding on idealized positions with
fixed isotropic displacement parameters taken as 1.2 U
of the corresponding bonding partner. The structure
contains two independent molecules (molecules I and
II) of similar shape in the asymmetric unit. Other pro-
grams used in the crystal structure determination are
listed in [12–14].
2.4. Crystallographic studies
Crystals of 3b–c were mounted in glass capillaries on
a STOE IPDSII diffractometer for data collection (see
Table 1 for crystal data and structure refinements de-
tails). The structure of compound 3b is disordered; the
Se, C(2), C(3) and C(31) atoms adopt two independent
positions in the cell with occupancies of 14% and 86%,
respectively. The structure was, therefore, refined con-
sidering these occupancy factors, with C(31) fixed in
3. Results and discussion
Bromomethyl-dibromo-indium(III), 1 prepared from
indium monobromide and dibromomethane in 1,4-diox-
ane (diox.) [6], and the dialkyldisselenides, 2a–c react to
afford the dialkylselenonium methylide-tribromo-inda-
te(III) zwitterions, 3a–c (Scheme 2). The products were
obtained as colorless solids from hot chloroform.
The 1H NMR spectra of 3a–c (see Section 2) show the
resonance signal of the methylide group at
d = 2.42 0.05 ppm (1H) and d = 22.33 0.04 ppm
(13C). The methylide 13C resonance is difficult to detect,
as the result of the large quadrupole moment of the in-
dium atom (I = 9/2); nevertheless we were able to detect
it, except for 3a, after a large number of scans and using
a large line broadening parameter (LB = 20). Com-
pounds 3a–c contain an asymmetric selenium center.
Accordingly, we have detected, in 3a, magnetically
U
eq. (for the structure with 14% of occupancy) and with
all hydrogen atoms in idealized positions. The crystal of
3c proved to be a monoclinic (001) reflection twin.
Using the non-overlapping reflections of the stronger
exemplar, the structure could be solved by direct meth-
ods (SIR2002 [9]). For refinement of the twin model (op-
tion HKLF5 in SHELXL-97 [10]), additionally all
reflections with good overlap of both exemplars were se-
lected with program TWINXL [11]. Nevertheless, due to
many partial overlaps, only 2059 reflections remained
available (completeness of 31.6%). The phenyl rings
˚
were included as rigid groups (C–C = 1.39 A, C–C–
Table 1
Crystal data and structural refinement for 3b–c
Compound
3b
3c
Empirical formula
Formula weight (g molꢀ1
Temperature (K)
C
567.72
10H14Br3InSe
C15H16Br3InSe
629.79
153(1)
)
193(1)
0.71073
Monoclinic, C2/c
˚
Wavelength (A)
0.71073
Monoclinic, P21/c
Crystal system, space group
Unit cell dimensions
˚
a (A), a (ꢁ)
21.779(2), 90
8.6424(9), 107.192(9)
17.489(2), 90
3144.7(6)
11.3687(8), 90
9.3843(4), 92.355(6)
˚
b (A), b (ꢁ)
˚
c (A), c (ꢁ)
34.905(2), 90
3720.8(4)
3
˚
Volume (A )
Z, Dcalc (mg/m3)
8, 2.398
11.413
8, 2.249
9.659
Absorption coeff. (mmꢀ1
Absorption correction
F(000)
)
Numerical
2096
Semiempirical T(min/max) = 0.424/0.699
2352
Crystal size (mm3)
0.18 · 0.06 · 0.06
1.96–25.99
0.18 · 0.09 · 0.03
2.10–24.72
h Range for data collection (ꢁ)
Limiting indices
ꢀ26 6 h 6 26, ꢀ10 6 k 6 10, ꢀ19 6 l 6 21
ꢀ12 6 h 6 12, 0 6 k 6 9, ꢀ41 6 l 6 41
Reflections total/unique
Used for twin refinement
Completeness to h (%)
Refinement method
7838/3036
10555/4618
2059
31.6
–
98.3
Full-matrix least-squares on F2
3036/13/159
0.793
Full-matrix least-squares on F2 as (0 0 1) reflection twin
2059/0/165
0.982
Data/restraints/parameters
Goodness of fit on F2
R indices [I > 2r(I)]
R indices (all data)
Larg. diff. peak/hole (e A
R1 = 0.0398, wR2 = 0.0630
R1 = 0.0988, wR2 = 0.0730
1.288/ꢀ0.647
R1 = 0.0860, wR2 = 0.2083
R1 = 0.1301, wR2 = 0.2421
0.793/ꢀ0.845
ꢀ3
˚
)

F.M. de Andrade et al. / Journal of Organometallic Chemistry 690 (2005) 1294–1299
1297
1
2
diox
In
Br
Br
R
R
1
R
R
Br
Br
H
C
H
H
C
H
Diox., r.t.
Br
In
Se
+
Se
Br
2
diox
3
2
1
1
2
R
R
Yield (%)
a
CH
CH Ph
40
70
75
3
2
C H
CH Ph
b
c
2
5
2
CH Ph
CH Ph
2
2
Scheme 2.
non-equivalent methylide and benzylic protons that give
rise to typical AB patterns spectra with 2JA–B close to 11
Hz. In 3b–c, only the benzylic protons are magnetically
non-equivalent. The 77Se NMR resonance signals of
compounds 3a–c (see Section 2.3) were detected between
370–432 ppm, in the range (249–538 ppm) reported [8]
for other selenium ylids. These signals are considerably
deshielded (150 50 ppm) when compared to the corre-
sponding signals of the parent selenides, 2a–c (see Sec-
tion 2.2). The magnitude of this shift is similar to the
values (180–250 ppm) normally observed upon alkyl-
ation of selenides [8].
The structures of the new selenonium ylids of InBr3
3b–c were determined by single crystal X-ray diffraction
studies. The molecular structure of compound 3b is de-
picted in Fig. 1 (molecule with 86% of occupancy). Fig.
2 represents molecule II of compound 3c. Important
bond lengths and angles are summarized in Table 2.
The general features of the structures of 3b–c are in
good agreement with those reported for the neutral ad-
ducts of ylids of group 15 and 16, Br3InCH2L. The aver-
Fig. 2. The molecular structure of 3c with atoms shown as 50%
probability ellipsoids.
˚
age indium–bromine bond distances of 2.510(1) A for
˚
˚
3b, 2.521(6) A for 3c (molecule I) and 2.531(6) A for
Table 2
˚
Important bond lengths (A) and angles (ꢁ) for 3b–c
3ba
3c (Molecule I)
3c (Molecule II)
In–Brb
2.510(1)
2.521(6)
2.13(4)
1.90(3)
2.08(4)
1.97(5)
1.49(4)
1.52(5)
1.39c
2.531(6)
2.21(3)
1.86(3)
1.95(4)
1.98(4)
1.50(4)
1.55(4)
1.39c
In–C(1)
Se–C(1)
Se–C(2)
Se–C(3)
C(2)–C(21)
C(3)–C(31)
Car–Car
2.175(8)
1.889(9)
1.958(8)
1.956(9)
1.48(1)
1.45(2)
1.38(2)
Br–In–Brb
Br–In–C(1)b
C(1)–Se–C(2)
C(1)–Se–C(3)
In–C(1)–Se
a
111.07(4)
110.0
106.4(2)
112(1)
108(2)
105.6(2)
113(1)
102(2)
100.8(5)
99.4(4)
112.8(4)
97(2)
113(2)
100(2)
112(1)
Molecule with 86% of occupancy.
Mean value.
Constraint value.
b
c
Fig. 1. The molecular structure of 3b with atoms shown as 50%
probability ellipsoids.

1298
F.M. de Andrade et al. / Journal of Organometallic Chemistry 690 (2005) 1294–1299
Fig. 3. Selected torsion angles (ꢁ) for 3c (molecules I and II).
3c (molecule II) compare well to those observed in the
˚
Br3InCH2L compounds {L = (C2H5)3N, 2.529(1) A
ylides are stable compounds and lack reactivity as ylide
carriers by thermal rupture of the indium–carbon bond.
Other chemical properties, however, still remain com-
pletely unexplored, and the study of these properties will
be the subject of further research to be reported in due
time.
˚
[15]; L = (C6H5)3P, 2.512(2) A [16]; L = (C6H5)3As,
˚ ˚
A [15]; L = (C6H5)3Sb, 2.509(5) A [15];
˚
2.508(6)
L = (C6H5CH2)2S, 2.5150(7) A [17]}. Similarly, the In–
˚
C bond distances in 3b [2.18(1) A], 3c (molecule I)
˚
[2.13(4) A] and 3c (molecule II) [2.21(3) A] are readily
˚
comparable to the values encountered in the cited
˚
Br3InCH2L compounds {L = (C2H5)3N, 2.185(5) A;
5. Supporting material
˚
˚
L = (C6H5)3P, 2.18(1) A; L = (C6H5)3As, 2.17(5) A;
˚
L = (C6H5)3Sb, 2.16(3) A; L = (C6H5CH2)2S, 2.189(5)
˚
A}.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Centre; CCDC Nos. 254745 (for compound 3b)
and 254746 (for compound 3c). Copies of this informa-
tion may be obtained free of the charge from The Direc-
tor, CCDC, 12 Union Road, Cambridge, CB2 1 EZ, UK
(fax: +44 1223 336033; email: deposit@ccdc.cam.ac.uk
or http://www.ccd.cam.ac.uk).
The measured bond lengths and angles in molecules
I and II of the twinned crystal 3c are the same within
the experimental error. The main difference relating the
two structures is in the Br–In–C1–Se torsion angles.
Fig. 3 shows the Newman projections along the C1–
In axis for both molecules with the important torsion
angles. In molecule 1, a regular staggered conforma-
tion is observed, while in molecule II the dibenzylsele-
nide substituent is rotated by 20ꢁ with respect to the
Acknowledgements
position in molecule
I
towards an eclipsed
conformation.
C.P. thanks FAPERGS – Brazil and DAAD – Ger-
many for financial support. F.M.D. thanks CNPq for
the award of a scholarship.
4. Conclusion
Bromomethyl-dibromo-indium(III) is an organome-
tallic compound containing two electrophilic sites,
namely the metal center and the bromomethylic carbon
atom. Ligand coordination to the metal is achieved by
bromide anion and hard ligands, such as ethers and tri-
phenylphosphine oxide [6]. The soft dialkylselenide li-
gands, R1SeR2 coordinate to the soft halomethylic
carbon of the carbenoid, forming the dialkylselenonium
methylide adducts of indium tribromide, Br3InCH2-
SeR1R2. The new selenonium ylides are members of a
series of related Br3InCH2L adducts, in which L is a
group 15 (N, P, As, Sb) and 16 (S) neutral ligand. As
for the related Br3InCH2L compounds, the selenonium
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