Simultaneous Dehalogenation of Polychloroarenes and Chlorination of HSiEt3 Catalyzed by Complexes of the Groups 8 and 9

Article abstract of DOI:10.1006/jcat.2000.2973

The catalytic activity of the complexes FeCl₂(PPh₃)₂, RuHCl (PPh₃)₃, RuH₂(CO)(PPh₃)₃, RuHCl(CO)(AsPh₃)₃, RuHCl(CO) (PⁱPr₃)<

Full text of DOI:10.1006/jcat.2000.2973

Journal of Catalysis 195, 187–192 (2000)
doi:10.1006/jcat.2000.2973, available online at http://www.idealibrary.com on
Simultaneous Dehalogenation of Polychloroarenes and Chlorination
of HSiEt Catalyzed by Complexes of the Groups 8 and 9
3
�
,1
�
Julia D ´ı az,† Miguel A. Esteruelas, Juana Herrero,† Luisa Moralejo,† and Montserrat Oliv a´ n
�
Departamento de Qu ´ı mica Inorg a´ nica, Instituto de Ciencia de Materiales de Arag o´ n, Universidad de Zaragoza-C.S.I.C., 50009 Zaragoza,
Spain; and †Departamento de Qu ´ı mica, Universidad de Cantabria, 39005 Santander, Spain
Received April 7, 2000; revised June 14, 2000; accepted June 14, 2000
dehalogenation of chlorobenzene but also the sequential
The catalytic activity of the complexes FeCl2(PPh3)2, RuHCl hydrogenolysis of 1,2,4-trichlorobenzene, 1,2-, 1,3-, and
PPh3)3, RuH2(CO)(PPh3)3, RuHCl(CO)(AsPh3)3, RuHCl(CO) 1,4-dichlorobenzene (15). With regard to the previously
(
(
i
i
i
P Pr3)2, OsHCl(CO)(P Pr3)2, OsH2Cl2(P Pr3)2, CoCl(PPh3)3,
mentioned methods, the use of HSiEt3 as hydrogen source
has the advantage of the formation of ClSiEt3 (Scheme 1),
which is a valuable intermediate in the silicon industry and
a useful reagent in organic synthesis.
i
i
RhH2Cl(P Pr3)2, IrH2Cl(P Pr3)2, IrCl(PPh3)3, and IrH2(SiEt3)
(
COD)(PCy3) (COD = 1,5-cyclooctadiene) in the simultaneous
dehalogenation of 1,2,4-trichlorobenzene and the chlorination of
HSiEt3 has been studied. The 3d metal complexes and the derivative
IrH2(SiEt3)(COD)(PCy3) are unactive, while the 4d and 5d metal
compounds simultaneously catalyze the dehalogenation of 1,2,4-
trichlorobenzene and the chlorination of HSiEt3. The osmium and
iridium derivatives are less effective catalysts than the derivatives
of ruthenium and rhodium and undergo deactivation. Complexes
i
RuHCl(PPh3)3 and RhH2Cl(P Pr3)2 also catalyze the dehalo-
genation of 1,2-, 1,3-, and 1,4-dichlorobenzene and chlorobenzene.
The dehalogenation of 1,3- and 1,4-dichlorobenzene is favored
over the dehalogenation of the 1,2-isomer. �c 2000 Academic Press
Key Words: homogeneous catalysis; polychloroarenes dehalo-
genation; HSiEt3 chlorination; Rh catalyst; Ru catalyst.
SCHEME 1
1
. INTRODUCTION
The accumulation of chloroarenes in the environment
The chlorination of silicon hydrides has attracted consid-
implies a serious health hazard, and their dehalogenation erable attention. Organosilicon halides have been prepared
must be, therefore, a target with high priority. However, as by metal-catalyzed chlorination of silicon hydrides with
result of the effort in this field (1–4), only a limited num- acid chlorides, CCl4, HCl, and alkyl halides (16–21). Kunai,
ber of methods for hydrogenolysis of chloroarenes employ- Ishikawa, and co-workers (22, 23) have recently observed
ing homogeneous metal catalysts have been reported up to that the treatment of organohydrosilanes with 2 equiv of
now. These methods involve the use of molecular hydro- CuCl2 in the presence of CuI also gives organochlorosilanes
gen (5–7), alcohols (8), cyclic amines (9), magnesium dihy- in high yield.
dride (10), sodium hydride (11), sodium formate (12), and
alkyl Grignard reagents (13) as hydrogen source.
From the mechanistic point of view, both the hydrogenol-
ysis of polychloroarenes with HSiEt3 and the chlorination
In 1996, Chatgilialoglu and co-workers (14) found of HSiEt3 with chloroarenes could be rationalized accord-
that the heterogeneous system formed from PdCl2 and ing to Scheme 2, which shows oxidative addition processes
HSiEt3 catalyzed the dehalogenation of chlorobenzene. of H–Si and Cl–aryl bonds, and reductive elimination reac-
Recently, we have observed that the homogeneous sys- tions of ClSiEt3 and arenes on a transition metal compound.
tem formed from RhCl(PPh3)3 or [Rh(�-Cl)(COE)2]2/PPh3 Since the above-mentioned elemental steps are common to
(
COE = cyclooctene) and HSiEt3 catalyzes not only the several homogeneous catalytic processes, which are cata-
lyzed by a variety of coordination complexes of metals
1
of the groups 8 and 9, one should expect that the reac-
tions shown in Scheme 1 were also catalyzed by compounds
To whom correspondence should be addressed. Fax: 34 976 761187.
E-mail: maester@posta.unizar.es.
187
0021-9517/00 $35.00
Copyright �c 2000 by Academic Press
All rights of reproduction in any form reserved.

´
DIAZ ET AL.
1
88
�
�
�
oven conditions were 35 C (hold 6 min) to 110 C at 7 C/min
hold 4 min). The reaction products were identified by com-
(
parison of their retention times with those observed for
pure samples.
2
.2. Procedure
The dehalogenation reactions were carried out at con-
stant temperature in a two-necked flask fitted with a con-
denser and containing a magnetic stirring bar. The second
neck was capped with a Suba seal to allow samples to be re-
moved by syringe without opening the system. Two sets of
reaction conditions were used: (i) with the polychloroarene
as solvent and (ii) with p-xylene as solvent.
SCHEME 2
(i) A 0.063 mmol amount of the corresponding catalyst
was dissolved in 3 ml of a polychloroarene solution contain-
ing 2.4 mmol of triethylsilane and 150 mg of n-octane. The
flask was then immersed in a bath at 98 C, and the reaction
solution was magnetically stirred.
related to the ones used in other catalytic reactions involv-
ing elementary steps similar to those shown in Scheme 2.
This promted us to carry out the present study.
In this paper, we report the catalytic activity, in the si-
multaneous dehalogenation of polychloroarenes and chlo-
rination HSiEt3, of coordination complexes of metals of the
groups 8 and 9, which are also active catalysts for the reduc-
tion and/or the hydrosilylation of unsaturated molecules
�
(
ii) A 0.063 mmol amount of the corresponding cata-
lyst was dissolved in 3 ml of a p-xylene solution containing
3
1
.9 g of 1,4-dichlorobenzene, 2.4 mmol of triethylsilane, and
50 mg of n-octane. The flask was then immersed in a bath
�
at 98 C, and the reaction solution was magnetically stirred.
(
24–28).
Homogeneity test. The experimental procedure was
similar to the one already described (i), but mercury (1 ml)
was added to the solution at the beginning of the run.
2
. EXPERIMENTAL
2
.1. General Considerations
All manipulations were conducted with rigorous exclu-
sion of air. 1,2,4-Trichlorobenzene, 1,2-dichlorobenzene,
,3-dichlorobenzene, and chlorobenzene were dried by
3
. RESULTS AND DISCUSSION
3
.1. Screened Compounds
1
Table 1 shows the complexes studied in the dehalogena-
known procedures and distilled prior to use. Triethylsi- tion of 1,2,4-trichlorobenzene with HSiEt3, and their cata-
�
lane, n-octane, and 1,4-dichlorobenzene were used with- lytic activities. The reactions were carried out at 98 C using
out further purification. The complexes FeCl2(PPh3)2 (29), the polychloroarene as solvent and a HSiEt3/catalyst molar
RuHCl(PPh3)3 (30), RuH2(CO)(PPh3)3 (31), RuHCl(CO) ratio of 38. The reaction products are dichlorobenzenes and
i
i
i
(
(
(
(
P Pr3)2 (32), OsHCl(CO)(P Pr3)2 (32), OsH2Cl2(P Pr3)2 ClSiEt3 in all cases. The formation of other products is not
i
33), CoCl(PPh3)3 (34), RhH2Cl(P Pr3)2 (35), IrH2Cl observed.
i
P Pr3)2 (35), IrCl(PPh3)3 (36), and IrH2(SiEt3)(COD)
The iron compound FeCl2(PPh3)2 is prepared by reaction
PCy3) (37) were prepared by published procedures. Com- of anhydrous ferrous chloride with triphenylphosphine in
pound RuHCl(CO)(AsPh3)3 was prepared using a proce- boiling toluene (29). As far as we know, for this complex,
dure similar to the one described for RuHCl(CO)(PPh3)3 significant catalytic properties have not been previously re-
(
(
31), starting from RuCl3 � 3H2O (0.26 g, 1 mmol) and AsPh3 ported, in agreement with itsnullactivityin the dehalogena-
1.827 g, 6 mmol), and giving 700 mg (65% ) of a yellow tion of 1,2,4-trichlorobenzene. In contrast to FeCl2(PPh3)2,
solid. Anal. Calcd for C55H46As3ClORu: C, 60.93; H, 4.28. the hydride–ruthenium(II) complex RuHCl(PPh3)3, which
�
1
Found: C, 60.70; H, 4.20. IR (Nujol, cm ): �(CO) 1951 (s), is an active catalyst for the reduction of olefins, alkynes,
�
1
�
(Ru–H) 1915 (m). H NMR (300 MHz, CDCl3, 20 C): � polynuclear heteroaromatic compounds, and nitro com-
.60–6.90 (m, 45 H, AsPh3), � 8.68 (s, 1H, Ru–H). pounds (24, 38–40), shows the highest activity of all the
The analysis of the products of the reactions was carried studied complexes.
out on a Hewlett-Packard 6890 series gas chromatograph The dihydride–carbonyl derivative RuH2(CO)(PPh3)3
7
with a flame ionization detector, using a 100% cross-linked also shows a significant activity for the hydrogenolysis of
methyl silicone gum column (30 m � 0.25 mm, with 0.25 �m 1,2,4-trichlorobenzene. Thus, 65% of ClSiEt3 is formed
film thickness) and n-octane as the internal standard. The after 19 h. Previously, this complex has been found to be

POLYCHLOROARENES DEHALOGENATION/HSiEt3 CHLORINATION
189
TABLE 1
Relationship of Compounds Screened for the Simultaneous Dehalogenation
of 1,2,4-Trichlorobenzene and Chlorination of HSiEt3
Entry
Compound
Products
Time (h)
% ClSiEt3
1
2
3
4
5
6
7
8
9
FeCl2(PPh3)2
RuHCl(PPh3)3
RuH2(CO)(PPh3)3
RuHCl(CO)(P Pr3)2
—
96
7
0
96
65
13
30
8
1,2-, 1,3-, 1,4-DCB (52, 26, 22)
1,2-, 1,3-, 1,4-DCB (56, 28, 16)
1,2-, 1,3-, 1,4-DCB (47, 23, 30)
1,2-, 1,3-, 1,4-DCB (43, 22, 35)
1,2-, 1,3-, 1,4-DCB (50, 25, 25)
1,2-, 1,3-, 1,4-DCB (50, 25, 25)
1,2-, 1,3-, 1,4-DCB (80, 10, 10)
1,2-DCB
19
15
22
6.5
6.25
6
8
8
25
20
i
RuHCl(CO)(AsPh3)3
i
OsHCl(CO)(P Pr3)2
i
OsH2Cl2(P Pr3)2
10
a
CoCl(PPh3)3
<2
i
RhH2Cl(P Pr3)2
80
4
5b
0
i
1
1
1
0
1
2
IrH2Cl(P Pr3)2
1,2-, 1,3-, 1,4-DCB (25, 40, 35)
1,2-, 1,3-, 1,4-DCB (40, 20, 40)
—
IrCl(PPh3)3
IrH2(SiEt3)(cod)(PCy3)
�
Conditions: 98 C, 3 ml of 1,2,4-trichlorobenzene, 2.4 mmol of HSiEt3, 0.063 mmol of catalyst. Percentages of
each product are given in parentheses.
a
After 70 h of reaction the yield of ClSiEt3 is 5% (1,2-DCB, 60% ; 1,3-DCB, 20% ; 1,4-DCB, 20% ).
After 43 h of reaction the yield of ClSiEt3 is 12% (1,2-DCB, 42% ; 1,3-DCB, 16% ; 1,4-DCB, 42% ).
b
an active catalyst for C–C coupling reactions. It catalyzes of phenylacetylene, the hydrogenation reactions of phenyl-
the dimerization of tert-butylacetylene to (Z)-1,4-di-tert- acetylene (54) and benzylideneacetone (55) in the presence
butylbutatriene (41) or the C–C coupling of aromatic and of the osmium catalyst proceed with high selectivities to-
heteroaromatic ketones with olefins to give the correspond- ward the formation of styrene and 4-phenylbutan-2-one,
i
ing ortho-alkylated aromatic ketones with high regioselec- respectively. The related complex OsH2Cl2(P Pr3)2 is also
tivity (42). The method has been applied to the regioselec- an active catalyst for the hydrogenation of olefins, diolefins,
tive introduction of a side chain to tricyclic terpenoid (43, and �,�-unsaturated ketones (33). However, attempts to
4
4) and to the copolymerization of various terminal dienes hydrogenate phenylacetylene showed a rapid deactivation
with acetophenone (45–50). The same type of reaction with of the catalyst due to the formation of a hydride–carbyne
esters also gives alkylated products (51).
derivative (56).
The monohydride–carbonyl compound RuHCl(CO)
For the dehalogenation of 1,2,4-trichlorobenzene, the
(
AsPh3)3 containing arsine instead of phosphine ligands previously mentioned results indicate that, in the iron triad,
is also an active catalyst. However, its activity is lower ruthenium gives rise to better catalysts than osmium, and
than that of RuH2(CO)(PPh3)3. The five-coordinate mono- the latter better than iron. The data collected in Table 1
i
hydride–carbonyl complex RuHCl(CO)(P Pr3)2 is also ac- show that the group 9 metals behave in a similar fashion.
tive for the dehalogenation of 1,2,4-trichlorobenzene.
The cobalt complex CoCl(PPh3)3 is a very poor cata-
i
Although the catalytic activity of RuHCl(CO)(P Pr3)2 lyst. Furthermore, it undergoes deactivation as it is con-
is the lowest of the ruthenium compounds studied, this verted into CoCl2(PPh3)2. The related iridium derivative
complex is a more efficient catalyst than the analogous IrCl(PPh3)3 also undergoes deactivation, but is slightly
i
osmium(II) derivative OsHCl(CO)(P Pr3)2. Initially, the more active than CoCl(PPh3)3. Both complexes are much
activity of both compounds is similar. However, the osmium less efficient than the Wilkinson’s catalyst RhCl(PPh3)3
complex undergoes a deactivation process as the catalytic (90% of Et3SiCl after 1 h) (15).
reaction is in progress. The six-coordinate dihydride–
The iridium complex IrCl(PPh3)3 is also practically un-
i
dichloro–osmium(IV) compound OsH2Cl2(P Pr3)2 shows a active in the hydrogenation of olefins. Although it reacts
i
behavior similar to that of OsHCl(CO)(P Pr3)2.
readily with molecular hydrogen to form the stable dihy-
There are precedents showing differences between the dride IrH2Cl(PPh3)3 (57), under normal conditions phos-
i
catalytic properties of RuHCl(CO)(P Pr3)2 and OsHCl phine is not dissociated from the dihydride and coordina-
i
i
(
CO)(P Pr3)2. For example, the RuHCl(CO)(P Pr3)2- tion of the substrate is thus impeded. The related complex
i
catalyzed hydrosilylation of phenylacetylene affords cis- IrH2Cl(P Pr3)2, which unlike IrH2Cl(PPh3)3 is coordina-
PhCH == CHSiEt3 with high regio-and stereoselectivity(52), tively unsaturated, catalyzes the hydrogenation of benzyli-
i
while under the same conditions the OsHCl(CO)(P Pr3)2- deneacetone to 4-phenylbutan-2-one (58). In contrast to the
i
catalyzed reaction yields a mixture of cis- and trans- hydrogenation of olefins, IrCl(PPh3)3 and IrH2Cl(P Pr3)2
PhCH == CHSiEt3 (53). In contrast with the hydrosilylation show a similarly poor behavior in the dehalogenation of

´
DIAZ ET AL.
1
1
90
,2,4-trichlorobenzene. However, the rhodium counterpart
TABLE 2
i
i
of IrH2Cl(P Pr3)2, the complex RhH2Cl(P Pr3)2 is active,
showing an activity similar to that of RuHCl(PPh3)3. Fur-
thermore, interestingly, it is the only one complex of the
those studied that selectively affords 1,2-dichlorobenzene.
Although complex IrH2(SiEt3)(COD)(PCy3) (COD =
Dehalogenation of Polychloroarenes and Chlorination
of HSiEt3 Catalyzed by RuHCl(PPh3)3
Substrate
Product (s)
Time (h)
% ClSiEt3
1
,5-cyclooctadiene) has been found to be an active cata-
lyst for the hydrosilylation and dehydrogenative silylation
of olefins (59, 60), it is completely unactive in the dehalo-
genation of 1,2,4-trichlorobenzene with HSiEt3.
7
96
The investigation of the catalytic activity in the dehalo-
genation of 1,2,4-trichlorobenzene with HSiEt3 of the com-
plexes collected in Table 1 suggests that for the iron and
cobalt triads, the 3d and 5d metals form less active catalysts
than the 4d metals. The inactivity of the 3d metal complexes
can be related to the poor nucleophilicity of the metallic
center of these species, which prevents the oxidative addi-
tion of the H–Si and Cl–aryl bonds, while the lower activity
of the 5d metal complexes with respect to the 4d metal com-
pounds can be related to the higher stability of the M–aryl
and M–silyl bonds in 5d metal complexes, when they are
compared with their 4d counterparts.
9
9
58
91
9
9
84
35
In addition, it should be mentioned that, according to
the results collected in Table 1, there do not appear to be
significant differences in activity between the metals of both
groups, contained in the same series.
�
Conditions: 98 C; 3 ml of polychloroarene, 2.4 mmol of HSiEt3,
.063 mmol of catalyst. (a) 1,2-dichlorobenzene (52% ), 1,3-dichloro-
0
benzene (26% ), 1,4-dichlorobenzene (22% ).
3
.2. Dehalogenation of Polychloroarenes and Chlorination
of HSiEt3 Catalyzed by RuHCl(PPh3)3
also than that of the 1,3-isomer. This, together with the
preferred formation of 1,2-dichlorobenzene during the de-
This complex catalyzes not only the dehalogenation halogenation of 1,2,4-trichlorobenzene, indicates that the
of 1,2,4-trichlorobenzene but it is also a homogeneous dechlorination of chloroarenes containing chlorines in ad-
catalyst for the dehalogenation of 1,2-, 1,3-, and 1,4- jacent positions is more difficult than the dehalogenation
dichlorobenzene and chlorobenzene (Table 2). Its homo- of those containing chlorines in nonadjacent positions. This
geneity was proved by addition of mercury (61) to the cata- difficulty could be related to the capacity for coordinating to
lytic solution, which does not produce significant changes the catalyst of the chlorine situated in the position adjacent
in the catalytic activity.
to the activated chlorine. The coordination could occur be-
The dehalogenation of 1,2,4-trichlorobenzene affords fore the Cl–C bond activation or/and after the cleavage of
,2-dichlorobenzene (52% ), 1,3-dichlorobenzene (26% ) the Cl–C bond. In the first case the dihaloarene should act
1
and 1,4-dichlorobenzene (22% ), while the dehalogena- as a chelating ortho-dihalobenzene ligand, while in the sec-
tion of 1,2-, 1,3- and 1,4-dichlorobenzene selectively ond case the dichloroarene should give rise to a �-bonded
affords chlorobenzene. The preferred formation of 1,2- aryl group with an ortho-chlorine secondary bond.
dichlorobenzene during the dehalogenation of 1,2,4-
There are precedents for both types of coordina-
trichlorobenzene suggests that, in the presence of this cata- tion. Complex cis,cis,trans-[IrH2(Me2CO)(PPh3)2]BF4 re-
lyst, the extraction of the chlorine in position 4 is favored. actswith variousortho-C6H4X2 halocarbons, which displace
2
This agrees well with the fact that the dehalogenation of 1,2- Me2CO to give cis,trans-[IrH2(� -X2C6H4)(PPh3)2]BF4,
2
dichlorobenzene is slower than the dehalogenation of the where the � -coordination of the halocarbons has been
related 1,4-isomer (Table 2). However, the preferred for- proven by the X-ray diffraction characterization of the di-
mation of 1,2-dichlorobenzene is in contrast with previous iodobenzene derivative (63). The X-ray diffraction analysis
�
studies on the oxidative addition of 1,2,4-trichlorobenzene of a single crystal of [Rh(C6Cl5)4] also proves that one of
to phosphine–nickel(0) complexes, which show that the ad- the four C6Cl5 groups coordinates to the rhodium atom
dition of the 4-Cl–C bond is less favored than the oxidative through both �-bonded aryl and ortho-chlorine secondary
addition of the 2-Cl–C bond (62).
bond (64).
The dehalogenation of 1,2-dichlorobenzene is slower not
The dehalogenations of 1,2,4-trichlorobenzene and
only than the dehalogenation of 1,4-dichlorobenzene but 1,2-, 1,3-, and 1,4-dichlorobenzene involve the selective

POLYCHLOROARENES DEHALOGENATION/HSiEt3 CHLORINATION
191
TABLE 3
4. CONCLUSION
Dehalogenation of Polychloroarenes and Chlorination
This study has revealed that in the iron and cobalt triads,
ruthenium and rhodium give rise to active catalysts for the
simultaneous dehalogenation of polychloroarenes and the
chlorination of HSiEt3. The hydrogenolysis is sequential
and selective according to the sequence 1,2,4-trichloro-
benzene–dichlorobenzene–chlorobenzene–benzene. Al-
though osmium and iridium also afford active systems,
they are less active and undergo deactivation.
i
of HSiEt3 Catalyzed by RhH2Cl(P Pr3)2
Substrate
Product (s)
Time (h)
% ClSiEt3
9
82
The dehalogenation of dichlorobenzenes is highly depen-
dent on the position of the chlorine at the aromatic ring.
Thus, in the presence of the unsaturated phosphine com-
9
75
i
plexesRuHCl(PPh3)3 and RhH2Cl(P Pr3)2, the hydrogenol-
ysis of chlorines in nonadjacent positions is favored over
those situated in adjacent position.
9
9
70
63
In summary, in this paper, we report new catalysts for
both the dehalogenation of polychloroarenes and the chlo-
rination of silicon hydrides. In addition, we show that the
chlorination of silicon hydrides can be carried out not only
with alkyl halides but also with aryl halides when com-
plexes of ruthenium and rhodium are used as homogeneous
catalysts.
9
67
�
Conditions: 98 C; 3 ml of polychloroarene, 2.4 mmol of HSiEt3,
.07 mmol of catalyst. (a) Chlorobenzene (84% ), benzene (16% ).
ACKNOWLEDGMENTS
0
We acknowledge financial support from the DGES of Spain (Project
PB98-1591) and from the Comisi o´ n Mixta Caja Cantabria, Universidad
de Cantabria. We thank Gabriel Llata for technical assistance.
extraction ofa chloride from the aromaticring. Since the de-
halogenation of 1,2,4-trichlorobenzene is faster than those
of the dichlorobenzenes, and the extraction of a chloride
from the last substrates is in the three cases faster than the
dehalogenation of chlorobenzene, the selective formation
of the C6H7� xClx� 1 products appears to be kinetic in origin,
and for that reason the rate of dehalogenation decreases
with the decrease in the number of the chlorine atoms on
the aromatic ring.
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i
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1
0. Carfagna, C., Musco, A., Pontellini, R., and Terzoni, G., J. Mol. Catal.
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1
1
1. Qian, C., Zhu, D., and Gu, Y., J. Mol. Catal. 63, L1 (1990).
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i
RhH2Cl(P Pr3)2 and RuHCl(PPh3)3, is similar, some fine-
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73, 173 (1992).
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(
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