Ruthenium complex-catalyzed hydrosilylation of allyl chloride with trimethoxysilane

Journal of Molecular

Catalysis, 81 (1993)

Elsevier Science Publishers

207-214 B.V.. Amsterdam

207

MO92

Ruthenium complex-catalyzed trimethoxysilane

hydrosilylation

of ally1 chloride

with

Masato Tanaka*, Teruyuki Hayashi and Zhi-Yuan Mi National

Chemical Laboratory/or

298)514587,

Industry,

Tsukuba, Ibaraki 305 (Japan); tel. (+81

fax. (i-81 -298)551397

(Received November

2,1992; accepted December 24, 1992)

Abstract The hydrosilylation of ally1 chloride with trimethoxysilane has been examined in the presence of several homogeneous complex catalysts. Iridium and ruthenium complexes exhibit higher selectivities in the reaction to give 3chloropropyltrimethoxysilane. Other complexes usually give propylene and/or tetramethoxysilane as side products in large quantities. The Ru, (CO) ,+zatalyzed reactions effected at lower temperatures or by using a large excess of trimethoxysilane relative to ally1 chloride give the chloropropylsilane in good yields. Key words: ally1 chloride; trimethoxysilane

carbonyl

complexes;

hydrosilylation;

silane

coupling

agent;

Introduction 3-Chloropropyltrimethoxysilane ( 1) is not only an important silane coupling agent in its own right, but is a key intermediate for various other coupling agents [ 11. The current process for its production comprises hydrosilylation of ally1 chloride with trichlorosilane, followed by alcoholysis of the resulting 3chloropropyltrichlorosilane. A difficulty that is encountered in the process occurs during the alcoholysis, which evolves hydrogen chloride -the alcohol reacts with hydrogen chloride to form an alkyl chloride and water, and the latter, in turn, hydrolyzes 3-chloropropyltrichlorosilane leading to its oligomerization. One of several alternative ways that can circumvent the difficulty is to use trimethoxysilane directly in place of trichlorosilane. Because of the great deal of effort put into the desired realization of a chlorine free organosilicon industry, the process of trimethoxysilane production has become industrially feasible [2]. There are only four publications to date on the hydrosilylation of ally1 chloride with trialkoxysilane: the reaction with chloroplatinic acid [3] or a rhodium-phosphine complex [ 41 as catalyst is usually hampered by extensive formation of undesired propylene. Ruthenium-phosphine complexes do not *Corresponding

0304-5102/93/$06.00

author.

0 1993 - Elsevier Science Publishers

B.V. All rights reserved.

208

M. Tanaka et al./J. Mol. Catal. 81 (1993) 207-214

form 1 either, but “substitution products” usually result [ 51. Iridium complexes are claimed in a patent application to exhibit high performance [ 61. However the high price of the metal warrants further searching for an alternative catalyst. Here we describe that carbonyl complex catalysts of ruthenium, which are far cheaper than iridium, are able to promote the reaction in relatively high selectivity under certain conditions.

Experimental Materials and instrumentation Ally1 chloride and trimethoxysilane were distilled and stored under nitrogen. Toluene was dried over molten sodium and distilled under nitrogen. Ir,Cl,(coe), (coe=cyclooctene) [7],IrCl(CO) (PPh3)2 [8],R~&l,(C0)~ [9] and Ru(C,H,) (chd) (chd= 1,3-cyclohexadiene) [lo] were prepared by published procedures. Other metal complexes were commercial products and were used as received. Analysis of gaseous products was carried out using a GL Sciences model 373FG fuel gas analyzer. Reaction solutions were analyzed on a Shimadzu model GC-9A gas chromatograph equipped with a DEGA-ST 10% supported on a Uniport B column. The products were identified by comparison of their GC retention times with those of authentic samples and/or by GCMS analysis using a Shimadzu model QP-1000 instrument (EI, 70 eV). Typical reaction procedure Ru, (CO) 12 (0.01 mg-atom Ru) was placed in a stainless steel autoclave, which was flushed with nitrogen. Ally1 chloride (10 mmol), trimethoxysilane (10 mmol) and toluene (1 ml) were injected, and the reactor was heated at 80” C for 16 h with magnetic stirring. After being cooled, the gas phase and the solutions were analyzed as described above.

Results Screening of catalysts Hydrosilylation of ally1 chloride with trimethoxysilane was surveyed using several group VIII metal complexes under the standard conditions (80’ C, 16 h). Besides 1, allyltrimethoxysilane, propyltrimethoxysilane, tetramethoxysilane, propylene, propane, 1-chloropropane, 1-hexene and hydrogen were also formed (eqn. (1) ). However, formation of the possible internal adduct (2 ), the regio-isomer of 1, was not confirmed for any reaction. The results are summarized in Table 1.

10.00 8.99 2.58 0.50 8.63 8.66 2.93 2.07 3.43

AllClb 9.98 9.96 4.56 2.17 9.98 10.00 4.14 3.22 4.19

HSi”

Conversion (mmol)

1.84 0.95 0.06 0.23 2.64 2.84 -0 0.02 0.70

la

0.18 0.19 0.10 0.28 0.12

0.35 0.33 =O -0 0.07

-0

0.68 2.02 1.35 0.86 2.70 2.19 X0 0.77 0.82

0.26 0.40 0.01

0.06 0.02 0.09 -0

MeOSi’

PrSic,d

AllSib,”

Yield (mmol)

0.13 -0 0.15 0.18 0.29 0.34 0.08 0.15 0.12

H2 0.09 5.30 0.69 0.22 0.61 0.71 0.52 0.44 0.21

C,H, 0.01 0.09 ZO ZO 0.04 0.05 0.02 -0 0.01

C,Hs

0.01 0.03 0.10 0.05 0.17 0.10 0.03 0.04 0.05

1-Hex’

0.19 0.11 0.11 0.12 0.28 0.31 0.11 0.18 0.19

PrCld

*Catalyst 0.01 mg-atom, toluene 1.0 ml, ally1chloride 10 mmol, trimethoxysilane 10 mmol, reaction temperature 8O”C, reaction time 16 h. ‘All = ally1group. Si=Si(OMe), group. dPr = n-propyl group. ‘l-Hex= 1-hexene. %oe = cyclooctene. rAt 60°C. ‘Chd= 1,3cyclohexadiene.

Ru(C,H,) (chd)h

RuCl,(CO)zW%)z

Ru(CO)zW’h,)2

Ir,Cl,(coe),’ HzPtC&*6Hz0 Co,(CO), IrCl(C0) (PPh3)2p Ru,(CO),z Ru,Cl, (CO h

Catalyst

Effect of catalysta

TABLE 1

M. Tanaka et al./J. Mol. Catal. 81 (1993) 207-214

210 &Cl

+

HSi(OMe)S

-

C?-‘?i(OMe),

+

+

@Si(OMe)z

+

A

+

FSI(OMe)3

+cr-+A+

-

Sl(OMeLt

+

H2

(1)

As disclosed already the iridium-cyclooctene complex selectively gave 1 in high yield [6]. Hexachloroplatinic acid, the most typical hydrosilylation catalyst, mainly yielded propylene and tetramethoxysilane. In addition, the material balance with respect to the silicon was very unsatisfactory. Cobaltand iridium-phosphine complexes were less active, and the major product was tetramethoxysilane. Ruthenium carbonyl was more active in converting ally1 chloride, and a considerable amount of 1 was obtained. However, the formation of propylene and tetramethoxysilane was also rather extensive. Although ruthenium carbony1 is known to promote dehydrogenative silylation of olefins [ 111, we did not observe any 3-chloroprop-1-enyltrimethoxysilane which forms from such a process between ally1 chloride and trimethoxysilane (de infra) . Since ruthenium carbonyl exhibits the highest performance beside that of the iridium-cyclooctene complex, the catalytic activity Iof several ruthenium complexes was investigated (also listed in Table 1) . Ruthenium carbonyl chloride complex was found to promote the reaction as well. The other ruthenium complexes were less active and less selective in respect of the formation of 1. The formation of propylene may be explained in terms of the p-elimination [ 121 of the chlorine atom of the intermediate (3) leading to the possible internal adduct (2 ), as suggested in a review article [ 131. +Cl

+

H-Run-Si

-

Cf-y

-ky Run-Si 3 ‘lil C+f Si 2

However, other mechanisms which involve the oxidative addition of ally1 chloride are also conceivable (de infru) . In any event, the chlorine atom originally bound to the allylic carbon must have eventually been picked up by the silicon. Indeed, we did detect chlorotrimethoxysilane by means of GC-MS (column: silicone OV-17) in the mixture. However, it has nearly the same GC retention time as the toluene solvent so that its yield could not be correctly determined. The formation of tetramethoxysilane is presumably due to the redistribution of trimethoxysilane [ 141. Hydrogen formation is also considered to have come from the redistribution. However, no dimethoxysilane, methoxysilane and unsubstituted silane were detected in the mixture.

M. Tanaka et al./J. Mol. Catal. 81 (1993) 207-214

00000000

oooooooc

dddddddd v+~,+,+hl-cF-~

oooooooc oooooqq~ dddddooc

c-4~%+7413r(Dld

%ooooooc ~~oo~comrna

211

212

M. Tanaka et al./J. Mol. Catal. 81 (1993) 207-214

Effect of reaction conditions The effects of the reaction temperature and the molar ratio of ally1 chloride to trimethoxysilane was briefly examined, and the results are listed in Table 2. The selectivity for 1 was dramatically improved by lowering the reaction temperature at the expense of the rate; the selectivities based on the consumption of ally1 chloride in the first four experiments, Table 2, were 531, 63, and 68% at 120,80, 50,25”C, respectively. The improvement observed at lower temperatures is due to the decrease of the redistribution (relative to the consumption of the hydrosilane). However, the extent of the redistribution was apparently also small at 120°C. What other byproducts were formed at 120’ C is ambiguous at the moment. As to the ratio of the reactants, the use of an excess of trimethoxysilane proved very beneficial for a higher selectivity for 1. When more than 2 equiv. of trimethoxysilane to ally1 chloride were used, the yield of 1 was over 70%. Propylene formation was negligible. Note that the redistribution was also suppressed, even though the reaction was effected in the presence of an excess of the hydrosilane compound.

Discussion

Although discussion of the reaction mechanism is premature, a possible catalytic cycle that the ruthenium complex carries is illustrated in Scheme 1. In the absence of olefinic compounds, triruthenium dodecacarbonyl is known to react with hydrosilanes to form mono-, di- and tri-nuclear bis(silyl)ruthenium species [ 15,161. These processes are thought to take place via HRu,-Si species generated as intermediates. Indeed, mono-nuclear H-Ru-Si species were also isolated under photolytic conditions [ 151. In the catalytic system where olefinic compounds are present, the olefinic bond intercepts the H-Ru species and undergoes insertion. Subsequent reductive elimination af-

I\ 1 H-3

Cl-Si

6

/-x/C’

H\ RU” S,’ : -Cl

Scheme 1.

H\

flu, Si’

\

,RU”

H

M. Tanaka et al./J. Mol. Catal. 81 (1993)

207-214

213

fords the desired product(s). On the other hand, it is known that the ruthenium carbonyl-catalyzed reaction of olefins with triorganohydrosilanes gives vinylsilanes [ 111. Allylic silane formation, when Ru(cod) (cot) (cod= 1,5-cyclooctadiene; cot = 1,3,5-cyclooctatriene) is used as the catalyst, has also been reported [ 171. In the mechanisms proposed for these reactions, the key step is the insertion of an olefin into a Ru-Si bond. In our reaction of ally1 chloride with trimethoxysilane, however, formation of vinylic (i.e., 3-chloro-l-propenyl-) or allylic (i.e., 3-chloro-2-propenyl) silane was not observed. Hence, we believe that the major insertion pathway is the conventional hydrometalation of the H-Ru bond, and the insertion of the C=C bond of the ally1chloride into the Ru-Si bond (silylmetalation) [ 11,17,18] is not involved to any great extent. This is presumably associated with the Ru-Si bond being strong when electronegative groups are bound to the silicon, as supported by published report [ 191. Even though the methoxy group is less electronegative than the chloride, it may be sufficiently electronegative so that the silylmetalation is inhibited. Several recent publications on catalytic reactions with hydrosilanes report similar mechanistic differentiation between hydrometalation and silylmetalation that is dictated by the nature of the substituents on the silicon [l&20].

As suggested in a previous section, a mechanistic possibility for the formation of propylene is a sequence consisting of the oxidative addition of ally1 chloride, reduction of the resulting Ru-Cl bond with a hydrosilane molecule, and reductive elimination of ally1 and hydride ligands from the ruthenium center. In fact, many examples of transition metal-catalyzed reduction of organic halides with hydrosilanes that may involve such a sequence have been described [ 211. We speculate that the equilibrium concentration of H-Ru,-Si under the hydrosilylation conditions is not so high. In general, transition metal complexes which can catalyze hydrosilylation readily undergo oxidative addition with hydrosilanes. As discussed above, however, the strength of the Si-M bond is highly dependent on the structure of the silyl moiety. Accordingly, it appears reasonable to consider that unless the substituent on the silicon is extremely electronegative like the chloride, the reverse reaction (reductive elimination of the H-Si species) [ 221 may regenerate a low valent ruthenium species. Thence, ally1 chloride may find further opportunity to undergo oxidative addition with the ruthenium species to end up with the formation of propylene. The oxidative addition of ally1 chloride with ruthenium carbonyl is reported to take place at rather low temperatures to give ($-allyl) RuCl (CO ) 3 [ 231. The need for the excess of hydrosilane to suppress the propylene formation may be associated with the higher equilibrium concentration of the HRu,-Si species hindering the oxidative addition of ally1 chloride. In the platinum-catalyzed hydrosilylation of ally1 chloride with alkyl, alkoxy and chlorosilanes, the extent of propylene formation was most extensive for the alkylsilanes, least for the chlorosilanes, and alkoxysilanes were in between [ 31. This observation is in good agreement with the foregoing reasoning. Improvement of the selectivity for 1 upon lowering the reaction temper-

214

M. Tanaka et al./J. Mol. Catal. 81 (1993) 207-214

ature is also likely to be partly due to the equilibrium Ru,-Si species being higher.

concentration

of the H-

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