Preparation, crystal structure determination, and properties of adducts of halogenomethyl compounds of indium with Group 16 donors

Article abstract of DOI:10.1016/S0022-328X(01)00659-3

The bis-1,4-dioxane (diox) adduct of bromomethyl-dibromo-indium(III), Br₂In(diox)₂CH₂Br, reacts with triphenylphosphine oxide, triphenylphosphine sulfide and benzyl sulfide to produce the compounds Br₂In[OP(C₆H₅)₃]₂CH ₂Br and Br₃InCH₂L (L=benzyl sulfide, triphenylphosphine sulfide). The crystal structures of these new organoindium compounds have been solved by X-ray diffraction methods. The structural results are compared with those for related organoindium compounds. Quantum mechanical calculations, by the PM3 method, satisfactorily predict the measured bond distances and angles in all compounds, and hence furnish reliable net atomic charge maps, which demonstrate the presence of a sulfur ylid ligand, H₂C^δ--^δ+S(CH₂C ₆H₅)₂, and a triphenylphosphonium-sulfur methylide ligand, ^δ-CH₂S-^δ+P(C₆H ₅)₃, in the Br₃InCH₂L compounds. Mass spectra and thermal decomposition studies establish that Br₃InCH₂S(CH₂C₆H₅) ₂ decomposes via an intramolecular nucleophilic attack of a bromide ligand, either to the InCH₂ carbon atom to produce benzyl sulfide, or to the C₆H₅CH₂ carbon to yield benzyl bromide and benzyl-methyl-sulfide.

Full text of DOI:10.1016/S0022-328X(01)00659-3

Journal of Organometallic Chemistry 626 (2001) 68–75
www.elsevier.nl/locate/jorganchem
Preparation, crystal structure determination, and properties of
adducts of halogenomethyl compounds of indium with Group 16
donors
Clovis Peppe a,*, Jose´ Arimateia Nobrega b, Marcelo Zaldini Hernandes b,
Ricardo Luiz Longo b, Dennis G. Tuck c
a Laborato´rio de Materiais Inorgaˆnicos, Departamento de Qu´ımica, Uni6ersidade Federal de Santa Maria, Campus UFSM, 97105-900,
Santa Maria-RS, Brazil
b Departamento de Qu´ımica Fundamental, Uni6ersidade Federal de Pernambuco, 50670-901, Recife-PE, Brazil
c Department of Chemistry and Biochemistry, Uni6ersity of Windsor, Windsor, Ontario, Canada N9B 3P4
Received 11 September 2000; received in revised form 20 December 2000
Abstract
The bis-1,4-dioxane (diox) adduct of bromomethyl-dibromo-indium(III), Br2In(diox)2CH2Br, reacts with triphenylphosphine
oxide, triphenylphosphine sulfide and benzyl sulfide to produce the compounds Br2In[OP(C6H5)3]2CH2Br and Br3InCH2L
(L=benzyl sulfide, triphenylphosphine sulfide). The crystal structures of these new organoindium compounds have been solved
by X-ray diffraction methods. The structural results are compared with those for related organoindium compounds. Quantum
mechanical calculations, by the PM3 method, satisfactorily predict the measured bond distances and angles in all compounds, and
hence furnish reliable net atomic charge maps, which demonstrate the presence of a sulfur ylid ligand, H2Cd−ꢀd+S(CH2C6H5)2,
and a triphenylphosphonium-sulfur methylide ligand, d−CH2Sꢀd+P(C6H5)3, in the Br3InCH2L compounds. Mass spectra and
thermal decomposition studies establish that Br3InCH2S(CH2C6H5)2 decomposes via an intramolecular nucleophilic attack of a
bromide ligand, either to the InCH2 carbon atom to produce benzyl sulfide, or to the C6H5CH2 carbon to yield benzyl bromide
and benzyl-methyl-sulfide. © 2001 Elsevier Science B.V. All rights reserved.
Keywords: Indium; Sulfur ylid; Triphenylphosphonium-sulfur methylide; Bromomethyl; Triphenylphosphine oxide complex; Crystal structures
1. Introduction
are believed to be structurally related to the active
organoindium intermediates in these reactions, and the
preparation of these has allowed us to study the proper-
ties of these compounds in detail [3–5]. The
X2InCR1R2X molecules have been shown to have two
electron deficient sites, namely the indium atom and the
halogenomethylic carbon. Addition of halide anions to
X2InCR1R2X leads to the corresponding salts of
[X3InCR1R2X]− which were fully characterized by X-
ray methods (X=Br, R1=R2=H [3]; X=Cl, Br,
R1=H, R2=X [6]). A series of Group 15 adducts of
general structure X3InCH2L (X=Br, L=(C2H5)3N [7],
(CH3)2NCH2CH2N(CH3)2 [5], L=(C6H5)3P [5],
(C6H5)3As [7], (C6H5)3Sb [7]; X=I, L=(C6H5)3As [7])
has also been synthesized and fully characterized.
The potential application of main group metal ylids
in organic synthesis as storable precursors of Wittig
and other ylids has lead us to extend this work by
Recent work has shown that a-halogeno-
organoindium reagents promote carbonꢀcarbon bond
formation. This class of reagents, readily obtained [1]
from indium metal and Br2CR2 (R=ꢀCN, ꢀCO2Et),
has been successfully employed in the cyclopropanation
of electron-deficient alkenes, and in the epoxidation of
carbonyl compounds (R=ꢀCO2Et). More recently [2],
it was found that bromocyanomethylation of a variety
of carbonyl compounds to produce the corresponding
2-bromo-3-hydroxynitriles can be carried out by the
action of dibromoacetonitrile and indium(I) bromide.
Indium(III) compounds of the general structure
X2InCR1R2X (R1=H, R2=H, Cl, Br, I; X=Cl, Br, I)
* Corresponding author. Fax: +55-55-2208031.
E-mail address: peppe@quimica.ufsm.br (C. Peppe).
0022-328X/01/$ - see front matter © 2001 Elsevier Science B.V. All rights reserved.
PII: S0022-328X(01)00659-3

C. Peppe et al. / Journal of Organometallic Chemistry 626 (2001) 68–75
69
preparing adducts of Br2InCH2Br with Group 16 lig-
ands, namely triphenylphosphine oxide, triphenylphos-
phine sulfide and benzyl sulfide. The structures and
some properties of these species are discussed in the
JCꢀP=2.3 Hz, aromatic para; l 131.48, JCꢀP=9.9 Hz,
aromatic ortho; l 128.76, JCꢀP=12.1, aromatic meta;
InCH2Br not detected. 31P-NMR (DMSO-d6), l 26.28
(from H3PO4).
light
of
quantum
mechanical
semi-empirical
calculations.
2.2.2. Br3InCH2S(CH2C6H5)2 (2)
To a solution of Br2In(diox)2CH2Br, prepared as
above from 2.05 mmol of InBr, was added solid benzyl
sulfide (439 mg, 2.05 mmol). Colorless crystals suitable
for X-ray analysis precipitated from the undisturbed
solution on gradual concentration. If the rate of con-
centration is increased, a white powder precipitates (932
mg, 1.60 mmol, 78% yield). Both products are the
dibenzyl sulfide adduct of Br2InCH2Br. Anal. Calc. for
C15H16Br3InS: In, 19.7; Br, 41.1. Found. In, 19.5; Br,
2. Experimental
2.1. General
Indium monobromide was prepared [8] by heating
metal and indium tribromide in a vacuum sealed tube
at 450°C. Methylene bromide (Aldrich) was dried over
1
,
Linde 4 A molecular sieves. Br2In(diox)2CH2Br was
41.1%. H-NMR (THF-d8), l 7.25 s, 5H, C6H5CH2S; l
prepared from InBr and CH2Br2 as described earlier [3].
Triphenylphosphine oxide, triphenyl phosphine sulfide
and benzyl sulfide were used as supplied (Aldrich).
1,4-dioxane (diox) was dried over sodium and ben-
zophenone, and distilled just before use from the blue
ketyl form.
4.33, dd, 2 H C6H5CH2S; l 2.05 s, 1H, InCH2S. 13C-
NMR (DMSO-d6),
l
130.54, 129.25, 129.03,
C6H5CH2S; l 67.13, C6H5CH2S; InCH2S not detected.
2.2.3. Br3InCH2SP(C6H5)3 (3)
Procedures identical to those described for 1 above,
produced 1.02 g (1.54 mmol, 75% yield) of 3. Colorless
single crystals for X-ray analysis were grown from
Indium and bromine analysis were as described previ-
ously [9]. Proton and carbon NMR were recorded on a
Varian Unity Plus 300 instrument; phosphorus NMR
on a Bruker DPX-400 instrument. Thermogravimetric
analysis were carried out on a Shimadzu TGA-50 in-
strument (flow rate 50 ml min−1); the sample (ca. 5 mg)
contained in an alumina cell, was heated from 30–
800°C. Mass spectra were recorded on a Finnigan
GC-MS spectrometer operating at 70 eV.
acetone–ethanol
(2:1,v/v).
Anal.
Calc.
for
C19H17Br3InPS: In, 17.3; Br, 36.2. Found. In, 17.0; Br,
36.1%. 1H-NMR (acetone-d6), l 7.80–8.03 m, 15H,
SP(C6H5)3; l 2.00 d, JPꢀH=8.6 Hz, 2H, InCH2S. 13C-
NMR (acetone-d6), l 119.92, JCꢀP=83.1 Hz, aromatic
ipso; l 136.39, JCꢀP=3.0 Hz, aromatic para; l 134.69,
J
CꢀP=10.7 Hz, aromatic ortho; l 131.39, JCꢀP=13.0
All preparative work was carried out under dry
nitrogen, using standard vacuum line techniques, up to
Hz, aromatic meta; InCH2S not detected. 31P-NMR
(acetone, C6D6 as internal locker), l 50.78 (from
H3PO4).
the
isolation
of
the
final
products.
The
Br3InCH2S(CH2C6H5)2 (2) compound is sensitive to air
and must be handled under nitrogen.
2.3. Thermal decomposition of 2
2.2. Preparati6e details
2.3.1. In the solid state
A sample of 2 ( 500 mg) was sealed in a glass tube
under vacuum The tube was heated for 24 h at 110–
120°C, after which the residue was partitioned in a
silica-gel chromatographic column in hexane–ethyl ace-
tate (4:1, v/v), and the hexane–acetate solution ana-
lyzed by GC-MS. The compounds which were identified
included benzyl bromide: m/z (70 eV) 170–172 (M+,
3%), 91 (100%), 65 (27%), benzyl-methyl-sulfide: m/z
138 (M+, 38%), 91 (100%), 65 (14%), and benzyl
sulfide: m/z 214 (M+, 43%), 122 (100%), 91 (95%).
2.2.1. Br2In[OP(C6H5)3]2CH2Br (1)
A solution of Br2In(diox)2CH2Br was prepared from
400 mg (2.05 mmol) of InBr and 0.72 ml (10.3 mmol) of
CH2Br2 in 1,4-dioxane (20 ml); after which all volatiles
were removed under vacuum, until complete removal of
excess CH2Br2. The white Br2In(diox)2CH2Br solid was
redissolved in dioxane (20 ml) and solid triphenylphos-
phine oxide (1.14 g, 4.10 mmol) added to the solution.
This mixture was stirred for 4 h; on concentration, 1.35
g (1.46 mmol, 71%) of 1 was deposited. This solid was
collected by filtration, and dried under vacuum. Color-
less single crystals were obtained by recrystallization
from ethanol (95%) in an open vessel. Anal. Calc. for
C37H32Br3InO2P2: In, 12.4; Br, 25.9. Found. In, 12.4;
Br, 25.9%. 1H-NMR (CDCl3), l 7.50–7.75 m, 15H,
OP(C6H5)3; l 2.63 s, 1H, InCH2Br. 13C-NMR (DMSO-
d6), l 132.7, JCꢀP=102.1 Hz, aromatic ipso; l 132.04,
2.3.2. In solution
A solution of 2 (500 mg, 0.86 mmol) in dioxane (25
ml) was refluxed for 8 h, after which all volatiles were
removed under vacuum, and the residue re-dissolved in
ethanol (95%, 20 ml). Addition of tetraethylammonium
bromide (181 mg, 0.86 mmol) produced a white precip-
itate, which was collected by filtration, dried and iden-

70
C. Peppe et al. / Journal of Organometallic Chemistry 626 (2001) 68–75
tified as [(C2H5)4N][InBr4] (233 mg, 0.41 mmol). Anal.
Calc. for C8H20NBr4In: In, 20.3; Br, 56.6. Found. In,
20.0; Br, 55.9%. The ethanol solution was submitted to
GC-MS analysis and the products detected were benzyl
bromide, benzyl-methyl-sulfide and benzyl sulfide (MS
as above).
2.4. Reaction of Br3InCH2S(CH2C6H5)2 (2) with
carbonyl compounds
Compound 2 (1 mmol) and an equimolar amount of
benzaldehyde (or acetophenone) were refluxed in diox-
ane (5 ml) for 8 h. GC-MS analysis on the resultant
solution showed benzyl bromide, benzyl-methyl-sulfide
and benzyl sulfide (MS as above) as the prod-
Fig. 3. The molecular structure of Br3InCH2SP(C6H5)3 (3), (ORTEP
diagram), with atoms shown as 30% probability ellipsoids. Hydrogen
atoms have been omitted for clarity.
ucts, together with unreacted benzaldehyde (or
acetophenone).
2.5. Crystallographic studies
Suitable crystals of 1, 2 and 3 were mounted on glass
fiber on a Siemens SMART three-circle diffractometer
with graphite-monochromated Mo–Ka radiation and a
CCD area detector, controlled by a Pentium-based PC.
The structures were solved by direct methods. All non-
hydrogen atoms were refined anisotropically; hydrogen
atoms were initially introduced in ideal positions and
subsequently refined isotropically The software pack-
age, data collection strategy, methodology for struc-
tural solutions, and corrections, were as described in an
earlier paper [7]. Figs. 1–3 show the molecular struc-
tures of 1, 2, and 3, respectively, and Table 1 summa-
rizes crystal and structural refinement data. Those
structural results relevant to the present paper are given
at Table 2.
Fig. 1. The molecular structure of Br2In[OP(C6H5)3]2CH2Br (1),
(
ORTEP diagram), with atoms shown as 30% probability ellipsoids.
Hydrogen atoms have been omitted for clarity.
2.6. Calculations: methods and models
The PM3 semi-empirical Hamiltonian [10–12], im-
plemented in the GAUSSIAN 98 package [13], was used
in all calculations, employing the standard parameters.
Molecular geometry was optimized with default conver-
gence criteria, starting from the X-ray structure. For
compound 1, the angles BrꢀCꢀIn, OꢀInꢀO and PꢀOꢀIn
were constrained to their experimental values; only the
SꢀCꢀIn angle was constrained for compound 2, while
SꢀCꢀIn and PꢀSꢀC angles were fixed during geometry
optimization of 3.
Fig. 2. The molecular structure of Br3InCH2S(CH2C6H5)2 (2), (ORTEP
diagram), with atoms shown as 30% probability ellipsoids. Hydrogen
atoms have been omitted for clarity.

C. Peppe et al. / Journal of Organometallic Chemistry 626 (2001) 68–75
71
Table 1
Crystal data and structural refinement for 1–3
1
2
3
Empirical formula
Formula weight
Temperature (K)
C37H32Br3InO2P2
925.12
296(2)
C
582.89
298(2)
15H16Br3InS
C19H17Br3InPS
662.91
296(2)
,
Wavelength (A)
Crystal system
Space group
0.71073
Monoclinic
P21/c
0.71073
Monoclinic
P21/n
0.71073
Monoclinic
P21/c
,
a (A)
15.0637(5)
14.5682(5)
17.4788(5)
109.868(2)
3607.4(2)
4
9.4196(7)
11.4496(8)
17.798(1)
102.757(1)
1872.1(2)
4
14.5623(6)
10.8675(6)
16.1124(8)
114.805(2)
2314.6(2)
4
,
b (A)
,
c (A)
i (°)
V (A )
3
,
Z
Dcalc (g cm−3
)
1.703
4.098
2.068
7.765
1.902
6.360
Absorption coefficient (mm−1
Crystal size (mm)
)
0.30×0.20×0.20
1.44–22.50
12373
4597/406
0.0624
0.40×0.40×0.40
2.13–23.24
7012
2662/181
0.0269
0.40×0.20×0.20
1.54–22.50
8487
2994/227
0.0401
2q collection range (°)
Total number of reflections
Unique data/parameters
R[I\2|(I)]
Rw[I\2|(I)]
zmax difference peak and hole (e A
0.1174
0.667/−1.002
0.1129
0.586/−0.615
0.0757
0.630/−0.610
−3
,
)
3. Results and discussion
Triphenylphosphine oxide was found to coordinate
at the indium center leading to 1 (Fig. 1) giving a
trigonal bipyramidal structure with the two
3.1. Structural results
The general features of the structures 1, 2 and 3 are
in good agreement with those reported for the anion
Br3InCH2Br− [3], and for the neutral adducts of Group
15 ligands, Br3InCH2L. The average indiumꢀbromine
bond distances of 2.507(1) for 1, 2.5150(7) for 2 and
Table 2
,
Important bond distances (A) and angles (°) for 1–3
1
2
3
,
2.534 A for 3, are close to that for the anion of 2.518(2)
Bond distances
InꢀBr a
2.507(1), [0.026] 2.5150(7),
[0.0175]
2.534(1), [0.075]
2.177(6)
,
A and for the neutral species, Br3InCH2L {L=
(C2H5)3N, 2.529(1) [7]; (C6H5)3P, 2.512(2) [5];
(C6H5)3As, 2.508(6) [7]; (C6H5)3Sb, 2.509(5) A [7]}.
Similarly, the InꢀC bond distances in 1 [2.183(9)], 2
[2.189(5)] and 3 [2.177(6) A] agree well with the value of
2.13(1) A in the anion, and with the corresponding
values for the neutral compounds, [(C2H5)3N, 2.185(5)
A; (C6H5)3P, 2.18(1) A; (C6H5)3As, 2.17(5)A;
(C6H5)3Sb, 2.16(3) A].
The structural difference between 1, 2 and 3 can be
understood in terms of the tautomeric relationship, and
hence reactivity, of the parent Br2InCH2Br molecule [3]
Scheme 1.
It was shown earlier [3] that this behavior is the
consequence of the presence of an indium empty accep-
tor orbital in IA, which strongly favors intramolecular
bromide transfer. The net atomic charges calculated for
IA and IB confirmed the existence of two electron
deficient sites in the molecule, namely the indium and
carbon atoms. The nucleophilicity of an incoming lig-
and, and its ability to support positive charges at either
of these sites, will determine the coordination mode in
the resultant organoindium compound.
InꢀCH2
InꢀO a
CH2ꢀBr
OꢀP a
2.183(9)
2.189(5)
,
2.281(6), [0.007]
1.89(1)
,
1.493(7), [0.008]
1.79(1), [0.02]
1.37(2), [0.06]
a
PꢀCar
1.806(7), [0.018]
1.381(1), [0.04]
1.815(7)
,
a
CarꢀCar
1.38(1), [0.04]
1.759(5)
InCH2ꢀS
SꢀCH2Car
CH2ꢀCar
,
,
,
a
1.840(5), [0.020]
1.497(5), [0.011]
,
a
SꢀP
2.068(2)
Bond angles
BrꢀInꢀBr a
BrꢀInꢀCH2
113.84(5)
106.63(3), [3.72] 105.84(4), [4.84]
a
123.1(3), [5.0]
178.4(2)
112.1(1), [7.2]
112.5(2), [17.1]
OꢀInꢀO
BrꢀInꢀO a
OꢀInꢀC a
InꢀOꢀP a
InꢀCꢀBr
InꢀCꢀS
90.5(2), [0.3]
89.2(3), [0.6]
149.8(5), [7.8]
112.8(5)
113.6(3)
103.7(3), [3.2]
109.3(3)
CꢀSꢀC a
CꢀSꢀP
SꢀPꢀCar
101.5(2)
109.7(2)
a
a Mean value; parentheses indicate experimental uncertainty;
square brackets is the difference between highest and lowest values.

72
C. Peppe et al. / Journal of Organometallic Chemistry 626 (2001) 68–75
very similar to the situation in the analogous complexes
with Group 15 ligands discussed above.
The structure of InX3(Me3MS) (X=Cl, Br; M=P,
As) are pseudo-tetrahedral [15], which shows that such
S donors can coordinate to In under suitable condi-
tions, and hence emphasizes that the presence of a
positive charge on the carbon is important in determin-
ing the coordination in these organoindium com-
pounds. Another way of rationalizing the interactions
of these ligands with Br2InCH2Br is in terms of hard
and soft acid-bases. The harder phosphine oxide coor-
dinates at the hard indium acid site, whereas the softer
sulfur ligands prefer the carbon atom.
Scheme 1.
Table 3
Final heat of formation (in kJ mol−1) of 1–3 and related structures
3.2. Quantum mechanical calculations
Molecule
Energy
Table 3 gives the calculated final heat of formation of
1–3, and of various related molecules, and Table 4
shows the appropriate energy levels for the HOMO and
LUMO orbitals in 1–3. The data in Table 3 allow the
DE for the processes
Br2InCH2Br
(C6H5)3PO
1
(C6H5CH2)2S
2
(C6H5)3PS
3
−184.74
141.14
41.75
188.91
−204.12
417.28
−16.79
−250.72
362.48
−65.87
90.30
Br2InCH2Br+nL“Br2InCH2Br·nL
(1)
InBr3
to be derived. We find, for Lꢁ(C6H5)3PꢁO (n=2),
DE= −55.79 kJ mol−1; for Lꢁ(C6H5CH2)2S (n=1),
DE= −208.29 kJ mol−1; and for Lꢁ(C6H5)3PꢁS (n=
1), DE= −249.33 kJ mol−1, suggesting that adduct
formation is energetically favorable in keeping with the
ready reaction observed under the mild conditions de-
scribed in Section 2.
(C6H5CH2)2SꢁCH2
Br2InCH2SCH2C6H5
C6H5CH2Br
Table 4
Calculated HOMO and LUMO energy levels (in kJ mol−1) for 1–3
Table 5 shows the calculated bond distances, angles,
and bond orders for compounds 1–3. These values
agree well with the experimentally determined X-ray
results. The relative difference between calculated and
crystallographic parameters is always less than ca. 7%
except for the InꢀBr distances, which seems to be an
inherent difficulty in this method that produces InꢀBr
bond lengths considerably shorter than experimental
values [12,16]. The good fit establishes the reliability of
the calculations. Another useful set of data listed in
Table 6 gives the net atomic charges on the molecules,
and these confirm the ylid and the methylide ligands in
compounds 2 and 3, for which the calculated net
atomic charge on the methylene carbon atoms is −0.58
and −0.50 a.u., respectively.
Compound
HOMO
LUMO
1
2
3
−871.351
−1032.294
−997.270
−43.268
−235.008
−275.651
triphenylphosphine oxide ligands in apical positions,
with an average InꢀO bond distance of 2.281(6) A. This
is significantly greater than the values of 2.164(1) and
2.171(7) A reported for the six-coordinate adduct of
trimethylphosphine oxide and indium trichloride, and
in the more closely related bis-adduct of InCl3 and
Me2PhPO, for which the InꢀO distance is 2.196(7) A
[14].
,
,
,
The PꢁO distances in these adducts are 1.493(12),
1.507(7) for the six-coordinate molecule, and 1.507(10)
3.3. Spectroscopic results
,
A for the five coordinate case, in reasonably good
agreement with the present results.
The calculated charges on the methylene carbon
atoms of the compounds prepared in this work and
their parent molecule, Br2In(diox)2CH2Br [3], are corre-
Benzyl sulfide and triphenylphosphine sulfide, on the
other hand, are found to coordinate to the methylenic
carbon atom leading to the sulfur ylid 2 (Fig. 2) and the
triphenylphosphonium-sulfur-methylide
derivatives. The stereochemistry at the indium atom of
1
lated with their H-NMR spectra in Table 7. There is a
clear relationship between the observed 1H chemical
shift and the calculated charge; compounds 2 and 3
with high negative electron density at the methylene
carbon atom absorb at a higher fields than compound
3
(Fig. 3)
2 and 3 is essentially tetrahedral in both cases, and are

C. Peppe et al. / Journal of Organometallic Chemistry 626 (2001) 68–75
73
Table 5
1, whose charge is closer to the parent molecule. Unfor-
tunately, we were not able to detect the corresponding
13C resonances for compounds 1–3, even after long
accumulation times, due to the high quadrupolar mo-
ment of indium. This problem has been observed in our
previous studies [7,17] of organoindium compounds.
The decoupled 31P-NMR spectra of 1 and 3 (see Sec-
tion 2) show, in both cases, the expected single line
pattern. The observed chemical shift for 1 (l 26.28
ppm), is readily comparable with the corresponding
value measured [18] for the free ligand, (C6H5)3PO (l
27 ppm). For compound 3, the observed 31P resonance
signal (l 50.78 ppm) is shifted downfield from the
corresponding signal [19] of the free ligand, (C6H5)3PS
(l 39.9–43.5 ppm), and this is, again, in keeping with
,
Important calculated bond distances (A), angles (°) and orders for
1–3 a
1
2
3
Bond distances
InꢀBr b
2.51(0), [0.73] b 2.17(13.72),
[0.91] b
2.17(14.36),
[0.91] b
2.13(2.16),
[0.85]
InꢀCH2
InꢀO b
CH2ꢀBr
OꢀP b
2.13(2.43),
[0.93]
2.14(2.23),
[0.88]
2.12(7.04),
[0.49] b
1.94(2.43),
[0.94]
1.55(3.33),
[1.11] b
b
PꢀCar
1.81(1.12),
[0.75] b
1.80(0.33),
[0.85] b
the presence of
a
triphenylphosphonium-sulfur
b
CarꢀCar
1.39(1.46),
1.39(0.72),
[1.41] b
1.39(0.72),
methylide ligand, d−CH2Sꢀd+P(C6H5)3.
[1.42] b
[1.41] b
InCH2ꢀS
1.74(1.14),
[0.99]
1.86(1.09),
[0.90]
1.72(5.23),
[1.05]
3.4. Thermal decomposition studies
b
SꢀCH2Car
We have examined the thermal decomposition of
compounds 1–3 by TGA analysis. The temperature
dependence–weight loss curves for compounds 1 and 3
exhibit a single stage weight loss over the temperature
ranges 204–430°C (for 1) and 230–515°C (for 3), leav-
ing final residues of 5 and 10% of the initial mass,
respectively. The sulfur ylid, 2, lost weight in four
different range of temperatures: ca. 100–200°C (16.3%),
207–274°C (26.2%), 275–429°C (22.6%) and 430–
460°C (5.0%). It was not possible to derive any simple
decomposition pathway from these results, and we
therefore carried out two further experiments in at-
tempts to induce thermal decomposition on compound
2, under vacuum in a sealed tube at 120°C and in
refluxing dioxane. Product analysis, by GC-MS, in both
cases, revealed, inter alia, the production of benzyl
bromide, benzyl-methyl-sulfide and benzyl sulfide (Eq.
(2)).
b
CH2ꢀCar
1.48(0.67),
[1.01] b
SꢀP
2.12(2.51),
[0.85]
Bond angles
BrꢀInꢀBr b
114.3(0.40)
122.9(0.16)
178.4 c
109.6(2.84)
109.3(2.50)
108.8(2.84)
110.1(2.13)
b
BrꢀInꢀCH2
OꢀInꢀO
BrꢀInꢀO b
OꢀInꢀC b
InꢀOꢀP b
InꢀCꢀBr
InꢀCꢀS
89.6(0.97)
90.8(1.79)
149.8 c
112.8 c
113.9 c
104.7(0.96)
109.3 c
CꢀSꢀC b
CꢀSꢀP
101.5 c
b
SꢀCH2ꢀCar
114.3(1.42)
b
SꢀPꢀCar
111.6(1.73)
a Parentheses indicate relative error between calculated and crystal-
lographic measured parameters and values in square brackets corre-
spond to bond orders.
D
b Mean value.
Br3InCH2S(CH2C6H5)2“InBr3+C6H5CH2Br
c Constrained parameter during calculations.
+CH3SCH2C6H5
(2)
Table 6
These results demonstrate that fission of the indium
carbon bond in 2 to generate the sulfur ylid (Eq. (3)) is
more difficult than
Net atomic charges (a.u.) in 1–3
Atom
1
2
3
Br3InCH2S(CH2C6H5)2“InBr3+CH2ꢁS(CH2C6H5)2
In
0.44
0.44
−0.37
−
−0.58
0.21
0.43
−0.38
−
−0.50
0.19
a
Br(ꢀInBr)
Br(ꢀCH2Br)
−0.51
−0.15
−0.22
0.13
(3)
the intramolecular nucleophilic substitutions (Eqs. (4)
and (5))
C(ꢀInCH2)
H(ꢀInCH2) a
O a
S
−0.70
0.68
−0.10
1.84
−0.23
Br3InCH2S(CH2C6H5)2
P
Car
C(ArCH2Sꢀ)
2.36
−0.63
a
“C6H5CH2Br+Br2InCH2SCH2C6H5
(4)
−0.17
−0.36
Br3InCH2S(CH2C6H5)2“Br2InCH2Br+(C6H5CH2)2S
a Mean value.
(5)

74
C. Peppe et al. / Journal of Organometallic Chemistry 626 (2001) 68–75
dium, X2InCR1R2X reflects the presence of two elec-
tron deficient sites, namely the metal center and the
halogenomethylic carbon. This concept also explains
the results reported in the present paper. Given a ligand
capable of accommodating a positive charge, coordina-
tion will occur at the carbon atom generating
organometallic ylids of the general structure
X3InCR1R2L, as isolated for the sulfur ligands used in
this work. On the other hand, the harder base
triphenylphosphine oxide was found to coordinate to
the indium center leading to organoindium species of
general structure X2In(L)nCR1R2X. These have proved
to be useful starting materials for the synthesis of
Table 7
1H-NMR chemical shifts (ppm from TMS) and net atomic charges
(a.u.) of the methylene groups in 1–3 and their parent molecules
Compound
Net atomic charge
1H (l)
Br2In(diox)2CH2Br a
−0.07
−0.22
−0.58
−0.50
2.77
2.63
2.05
2.00
Br2In[(C6H5PO)2CH2Br (1) b
Br3InCH2S(CH2C6H5) (2) c
Br3InCH2SP(C6H5)3 (3) d
a In CD3CN.
b In CDCl3.
c In THF-d8.
d In acetone-d6.
di-indium, [Br3InCH2InX3]2−
, [20] and tri-indium,
[(Br3In)3CH]3−, [21] methane derivatives, by the oxida-
tive insertion of indium bromide into the CꢀBr bond of
[Br3InCH2Br]− and [Br3InCHBr2]−, respectively.
Semi-empirical calculations in this and earlier work,
again, provide a rationale for the spectroscopic proper-
ties, for the thermal decomposition pathway, and for
the lack of reactivity of the X3InCR1R2L compounds as
ylid carriers.
Scheme 2.
5. Supplementary material
and, therefore, a reasonable pathway for the decompo-
sition is depicted in Scheme 2.
Crystallographic data for the structural analysis have
been deposited with the Cambridge Crystallographic
Data Center, CCDC No. 148 838 for compound 1,
CCDC No. 148 839 for 2 and CCDC No. 148 840 for 3.
Copies of this information may be obtained free of
charge from The Director, CCDC, 12 Union Road,
Cambridge CB2 1EZ, UK (Fax: +44-1223-336033;
e-mail: deposit@ccdc.cam.ac.uk or www: http://
www.ccdc.cam.ac.uk).
These experimental results are in agreement with the
heats of reaction calculated from the data in Table 3,
which give DE=315.9 kJ mol−1 for Eq. (3), compared
with 228.6 for Eq. (4) and 208.3 kJ mol−1 for Eq. (5),
so that intramolecular substitution is the favored route
for these thermal decomposition processes.
In fact, generation of free ylids by the route of Eq.
(6) proved to be impractical, as predicted [7] by the
highly positive calculated DE for this process for a
series of adducts ( X=Br; R1=R2=H; L=P: 241,
As: 243, Sb: 276 and S: 316 kJ mol−1).
Acknowledgements
This work was supported in part by Operating
Grants (to C.P.) from CAPES. Two of us (J.A.N. and
M.Z.H.) thank CNPq-Brazil for the award of scholar-
ships. D.G.T acknowledges receipt of Research Grants
from the Natural Sciences and Engineering Research
Council of Canada. Dr Glenn Yap (University of
Windsor) is thanked for the X-ray crystallographic
results.
X3In-CR1R2L“InX3+R1R2CꢁL
(6)
Furthermore, these values are, in every case, consid-
erably more endothermic than for the reverse reaction
(Eq. (7)) leading to the Br2InCH2Br starting material
(L=P: 199, As: 50, Sb:−58, S: 208 kJ mol−1
X3In-CR1R2L“X2InCR1R2X+L
)
(7)
and this explains the lack of reactivity of 2 and other
related organoindium ylids toward carbonyl
compounds.
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