Modification of (poly)siloxanes via hydrosilylation catalyzed by rhodium complex in ionic liquids

Article abstract of DOI:10.1007/s00706-006-0461-9

The hydrosilylation of 1-heptene, allyl glycidyl ether and, allyl polyether by heptamethylhydrotrisiloxane and poly(hydro, methyl)(dimethyl)siloxane catalyzed by rhodium(I) complexes (particularly [{Rh(μ-OSiMe ₃)(cod)}₂]) in imidazolium ionic liquids (especially [TriMIM]MeSO₄) gives heptyl and glycidyloxy functional (poly)siloxanes and silicone polyethers with high yield and selectivity. The catalytic system based on rhodium siloxide can be easily separated from the product and successfully reused up to five times. Springer-Verlag 2006.

Full text of DOI:10.1007/s00706-006-0461-9

Monatshefte f€ur Chemie 137, 605–611 (2006)
DOI 10.1007/s00706-006-0461-9
Modification of (Poly)Siloxanes
via Hydrosilylation Catalyzed
by Rhodium Complex in Ionic Liquids#
ꢀ
and Magdalena Kurdykowska
Bogdan Marciniec , Hieronim Maciejewski, Karol Szubert,
ꢀ
Faculty of Chemistry, Adam Mickiewicz University, Grunwaldzka 6, 60-780 Poznan, Poland
Received December 12, 2005; accepted (revised) February 6, 2006
Published online April 20, 2006 # Springer-Verlag 2006
Summary. The hydrosilylation of 1-heptene, allyl glycidyl ether and, allyl polyether by heptamethyl-
hydrotrisiloxane and poly(hydro, methyl)(dimethyl)siloxane catalyzed by rhodium(I) complexes (par-
ticularly [{Rh(ꢀ–OSiMe3)(cod)}2]) in imidazolium ionic liquids (especially [TriMIM]MeSO4) gives
heptyl and glycidyloxy functional (poly)siloxanes and silicone polyethers with high yield and selec-
tivity. The catalytic system based on rhodium siloxide can be easily separated from the product and
successfully reused up to five times.
Keywords. TM complexes; Catalysis; (Poly)Siloxanes; Hydrosilylation; Ionic liquids.
Introduction
The chemistry and technology of silicon-based polymers, particularly silicones, is
a very broad and still growing research area. The interest in these compounds has
aroused owing to their many unique properties such as thermal and oxidative
stability, low surface tension, gas permeability, excellent dielectric properties, phys-
iological inertness, and moisture resistance [1–3]. Because of these properties
silicones have found a tremendous number of applications [4, 5]. Modifications
of polysiloxanes side groups have been extensively explored in order to obtain
polymers with special properties or to make them chemically active, thus giving
access to new industrial applications [6–9]. The desired properties are achieved
thanks to the possibility of introducing a great variety of functional groups in the
side chain of polysiloxanes, e.g., epoxy-, polyether-, or alkyl-groups containing
silicones [6, 10–13].
ꢀ
Corresponding author. E-mail: marcinb@amu.edu.pl
Dedicated to Professor Ulrich Schubert on the occasion of his 70th birthday in recognition of his
#
significant contributions to silicon and materials chemistry

606
B. Marciniec et al.
The major method used for attachment of an organofunctional group to a
siloxane backbone is hydrosilylation catalyzed predominately by platinum com-
plexes [14–17]. Platinum catalysts tolerate a variety of functional groups, however,
some impurities may interact with them leading to catalyst poisoning [18]. This
problem has stimulated much research aimed at employing other transition metal
compounds as potential catalysts.
Our contribution to this field was the synthesis, isolation, and full characteriza-
tion of a few new rhodium and iridium siloxide complexes, both dimeric [19] and
monomeric [20]. Catalytic activity of these Rh(I) siloxide complexes has been
demonstrated in some reactions, i.e. in the hydrosilylation of alkenes [21] and allyl
alkyl ethers [20, 22, 23] as well as in the silylative coupling of vinylsilanes with
alkenes [24].
Biphasic catalysis in a liquid–liquid system seems to be an ideal solution allow-
ing a combination of the advantages of both homogeneous and heterogeneous
catalysis [25]. The ionic liquids (ILs) generally form the phase in which the cat-
alyst is dissolved and immobilized. The first example of the homogeneous transi-
tion metal catalysis in ionic liquids was the platinum catalysed hydroformylation of
ethene, described by Parshal in 1972 [26], but the use of ionic liquids for biphasic
catalysis was reported by Wilkes describing the first air and moisture stable imid-
azolium salts, based on tetrafluoroborate and hexafluorophosphate [27]. This
approach has seen explosive growth during the past decade.
Nowadays, many examples of biphasic reactions employing ionic liquids, i.e.
hydroformylation, hydrogenation, oxidation, dimerization, coupling reactions are
known [25, 28, 29], however, there are only a few examples of hydrosilylation with
the use of ILs [30–32]. These reactions were catalysed by platinum complexes.
The aim of this work was to examine the synthesis of organomodified silicones
via hydrosilylation employing ionic liquids for the immobilization of rhodium
(and, for comparison, platinum) complexes as catalysts.
Results and Discussions
Rhodium(I) siloxide complexes have shown high catalytic activity in the hydro-
silylation with (poly)hydrosiloxanes [23b, c], even at room temperature (in contrast
to platinum catalysts), however, due to the difficulty in separating the homoge-
nously dissolved catalyst from the reaction products (especially from the polymeric
product of high viscosity), the recovery and reuse of the catalyst was not possible.
Therefore, one of our objectives was to search for suitable ionic liquids, which via
immobilization of the metal complex would permit easy isolation of the catalyst
from the product. Ionic liquids with weakly coordinating, inert anions and inert
cations can activate homogenously dissolved TM complexes. They can at the same
time play the role of ordinary solvents [29]. Ionic liquids employed in our studies
were based on imidazolium derivatives. In order to establish basic conditions
for hydrosilylation of olefins by polysiloxanes, some experiments were carried
out using the model reaction of Scheme 1 between heptamethylhydrotrisiloxane
and olefins.
Contrary to the polymeric system, this model reagents made the GC analysis of
the reaction mixture possible. The rhodium complexes [{Rh(ꢀ–OSiMe3)(cod)}2]

Modification of (Poly)Siloxanes via Hydrosilylation
607
Scheme 1
(1), [{Rh(ꢀ-Cl)(cod)}2] (2), and platinum complex H2PtCl6 in cyclohexanone (3)
were selected as catalysts of the reactions. The results for the different catalytic
systems are presented in Table 1. In most reactions only one main product and
small amounts of products of olefin isomerization were observed.
We tested also other imidazolium salts, containing various anions i.e. Clꢁ, Brꢁ,
ꢁ
NO3 , etc., however, either because of the catalysts insolubility or the problems
with separation of ILs from the product phase they had to be rejected.
The products obtained in most of the reactions examined were easily isolated
from the ILs and coꢁuld be reused. However, the catalytic activity of imidazolium
ꢁ
salts containing BF4 or SO3CF3 anions in the next cycles decreased. One of the
Table 1. The conversion of substrates and the yield of product obtained in the reaction between heptamethyltrisiloxane and
CH2¼CHCH2Z catalyzed by different catalytic systems
Z (cf. Scheme 1)
ILs
Catalysta
Conversion
of SiH=%b
Yield of product=%b
H2PtCl6 in cyclohexanone
[{Rh(ꢀ-Cl)(cod)}2]
[{Rh(ꢀ–OSiMe3)(cod)}2]
0
0
[MIM]BF4
89 (87, 29)
91 (44, 20)
86 (81, 29)
88 (39, 18)
H2PtCl6 in cyclohexanone
20 (4)
20 (4)
[EMIM]BF4
[{Rh(ꢀ-Cl)(cod)}2]
86 (10)
86 (10)
–C4H9
H2PtCl6 in cyclohexanone
93 (50, 3)
92 (61, 0)
91 (48, 3)
90 (56, 0)
[MIM]SO3CF3
[{Rh(ꢀ-Cl)(cod)}2]
H2PtCl6 in cyclohexanone
[{Rh(ꢀ-Cl)(cod)}2]
[{Rh(ꢀ–OSiMe3)(cod)}2]
98 (95, 89, 75)
97 (93, 85, 69)
[TriMIM]MeSO4
96 (93, 88, 80, 77)
100 (98, 97, 93, 90)
94 (90, 85, 75, 70)
98 (95, 94, 90, 88)
H2PtCl6 in cyclohexanone
10 (0)
0
7 (0)
0
[EMIM]BF4
[{Rh(ꢀ-Cl)(cod)}2]
H2PtCl6 in cyclohexanone
[{Rh(ꢀ-Cl)(cod)}2]
[{Rh(ꢀ–OSiMe3)(cod)}2]
74 (74, 74, 74, 29)
78 (77, 76, 74, 71, 22)
92 (86, 83, 80,
71 (70, 70, 70, 25)
71 (68, 61, 58, 58, 20)
86 (81, 78, 77,
[TriMIM]MeSO4
80, 78, 64)
75, 69, 56)
H2PtCl6 in cyclohexanone
[{Rh(ꢀ-Cl)(cod)}2]
[{Rh(ꢀ–OSiMe3)(cod)}2]
97 (75, 38, 5)
90 (68, 25, 2)
ꢁðOCH2CH2Þ7OH
[TriMIM]MeSO4
90 (82, 71, 35)
99 (95, 90, 87, 72)
85 (77, 65, 26)
90 (82, 78, 72, 65)
a
[HSi]:[CH¼CH]:[cat] ¼ 1:1.2:10ꢁ5, [Ils] ¼ 1% based on total weight of combined substrates, T ¼ 90ꢂC, t ¼ 2 h; b value of the
conversion and the yield in next catalytic cycles with the same recovered catalytic system given in parentheses

608
B. Marciniec et al.
reasons for this decrease could be the decomposition of ionic liquid’s anion (as a
result of the contact with moisture) involving liberation of fluoride ions acting as
catalyst poison. [TriMIM]MeSO4 (4) which was used earlier by Weyershausen et al.
for immobilisation of platinum catalyst in similar processes [31, 32] seems to be
the most suitable also for the reactions catalysed by rhodium complexes.
The results confirmed the high catalytic activity of the siloxy rhodium complex
1 in the reactions. The facility of product separation and the possibility of multiple
use of the catalyst depend on the hydrophobicity of the silicones modified as
mentioned earlier [31, 32]. Alkyl modified siloxanes are more hydrophobic than
epoxy or polyether ones. Therefore, the catalytic activity observed for the former
was almost the same after a few times repeated use of the catalytic system (1 þ 4).
On the basis of the results for the model reactions, the reactions between
poly(hydro, methyl)(dimethyl)siloxanes and olefins were carried out in a similar
way, according to Scheme 2.
These reactions were carried out in the presence of 3 or 1 immobilized in 4.
After the reaction, the resulting viscous mixture was characterized by IR and NMR
methods. In most cases, the pure product without any side products was obtained
after 2 hours at 90ꢂC. The results are summarized in Table 2. These data confirmed
the high catalytic activity of the rhodium siloxide complex and showed that the
catalyst was very well immobilized in 4.
Scheme 2
Table 2. The conversion of poly(hydro, methyl)(dimethyl)siloxane obtained in the hydrosilylation of
CH2¼CHCH2Z catalyzed by Pt and Rh complexes immobilized in [TriMIM]MeSO4
Z
Catalysta
Conversion of HSi=%b
H2PtCl6 in cyclohexanone
99 (95, 90, 80, 69)
ꢁC4H9
[{Rh(ꢀ–OSiMe3)(cod)}2]
100 (96, 94, 87, 80, 78)
H2PtCl6 in cyclohexanone
95 (89, 80, 70, 45)
[{Rh(ꢀ–OSiMe3)(cod)}2]
99 (95, 92, 89, 88, 75)
H2PtCl6 in cyclohexanone
91 (85, 75, 38)
ꢁ(OCH2CH2)7OH
[{Rh(ꢀ–OSiMe3)(cod)}2]
99 (93, 90, 85, 80, 78)
a
[HSi]:[CH¼CH]:[cat] ¼ 1:1.2:10ꢁ5, [[TriMIM]MeSO4] ¼ 1% based on total weight of combined
b
substrates, T ¼ 90ꢂC, t ¼ 2 h; value of the conversion in next catalytic cycles with the same
recovered catalytic system given in parentheses

Modification of (Poly)Siloxanes via Hydrosilylation
609
Conclusion
The rhodium siloxide complex 1 dissolved in 4 appeared to be a very efficient cat-
alytic system in the hydrosilylation of alkenes, allyl glycidyl ether, and allyl poly-
ether with hydrotrisiloxane and hydro(poly)siloxanes to obtain alkylsiloxanes and
silicone waxes, as well as silicone polyethers and epoxyfunctional (poly)siloxanes.
Compared to Pt-complex catalyzed reactions, high yields and selectivities were
observed even after fivefold usage of rhodium-siloxide-ionic liquid catalytic system.
Experimental
All reagents were dried and purified before use by the usual procedures. Rhodium complexes
[{Rh(ꢀ–OSiMe3)(cod)}2] (1), [{Rh(ꢀ-Cl)(cod)}2] (2), and platinum complex H2PtCl6 in cyclohexa-
none (3) were prepared as described in Refs. [19a, 33]. Ionic liquids 1,2,3-trimethylimidazolium
methylsulfate [TriMIM]MeSO4 (4), 1-methylimidazolium tetrafluoroborate [MIM]BF4 (5), 1-ethyl-3-
methylimidazolium tetrafluoroborate [EMIM]BF4 (6), and 1-methylimidazolium trifluoromethylsulfo-
nate [MIM]SO3CF3 (7) were purchased from Aldrich. All ILs were dried prior to use under vacuum at
60ꢂC over 8 h. Heptamethyltrisiloxane (8) and poly(hydro, methyl)(dimethyl)siloxane (9) were pur-
chased from Gelest, olefins and other reagents from Aldrich.
The NMR spectra (1H, 13C, 31P, 29Si) were recorded on a Varian XL 300 spectrometer. C6D6 or
CDCl3 were used as the solvents; GC–MS analyses were carried out with a Varian 3300 chromato-
graph (equipped with a DB-1, 30 m capillary column), connected to a Finnigan Mat 700 mass
detector. GC analysis was also carried out with a Varian 3800 chromatograph with Megabore
column (30 m, DB-1).
General Procedure for Catalytic Test
All manipulations were carried out under Ar using standard Schlenk techniques. The Si–H functional
siloxane (or polysiloxane) and 1.2 equiv of the olefin (calculated to each Si–H group) were placed into
the reaction vessel and heated up to 90ꢂC. Then the appropriate amount of catalyst (in the ratio
10ꢁ5 mol per mol Si–H) and the ionic liquid (1% based on total weight of combined substrates) were
added. After 2 h, the reaction mixture was separated from the phase of catalytic system by decantation.
The mixture was analysed by GC method and the formation of desired products was verified by GC–
MS and NMR analysis. The recovered catalytic system (catalyst in ionic liquid) was reused in the next
reaction cycle.
3-(3-Glycidyloxypropyl)heptamethyltrisiloxane (C13H33Si3O4)
1H NMR (CDCl3, 298 K, 300 MHz): ꢁ ¼ ꢁ0.02 (s, –OSiMeO–), 0.06 (s, –OSiMe3), 0.43 (m, –CH2Si),
1.59 (m, –CH2CH2Si), 2.59 (m), 2.76 (t, –CH–CH2–O), 3.13 (m, –CH–O), 3.38 (m, –OCH2CH2CH2Si,
–OCH2CH–O), 3.67 (dd, –OCH2CH–O) ppm; 13C NMR (CDCl3, 298 K, 75.46 MHz): ꢁ ¼ ꢁ0.46
(–OSiMeO–), 1.77 (–OSiMe3), 13.44 (–CH2Si), 23.21 (–CH2CH2Si), 44.25 (CH2–O), 50.80
(–O–CH–), 71.34 (–OCH2CH2CH2Si), 74.16 (–OCH2CH–O–) ppm; 29Si NMR (CDCl3, 298 K,
59.61 MHz): ꢁ ¼ ꢁ21.01 (SiMe), 7.88 (–OSiMe3) ppm.
Poly(3-glycidyloxypropyl, methyl)(dimethyl)siloxane (C281H668Si77O126
)
1H NMR (CDCl3, 298 K, 300 MHz): ꢁ ¼ 0.03, 0.06 (s, –OSiMe2–, –OSiMe3), 0.49 (m, –CH2Si), 1.61
(m, –CH2CH2Si), 2.58 (m), 2.77 (t, –CH–CH2–O), 3.12 (m, –CH–O), 3.39 (m, –OCH2CH2CH2Si,
–OCH2CH–O), 3.67 (dd, –OCH2CH–O) ppm; 13C NMR (CDCl3, 298K, 75.46 MHz): ꢁ ¼ ꢁ0.60,
1.06, 1.75 (–OSiMe2O–, –OSiMe3), 13.34 (–CH2Si), 23.13 (–CH2CH2Si), 44.26 (–CHCH2–O), 50.80
(–O–CH–), 71.36 (–OCH2CH2CH2Si), 74.11 (–OCH2CH–O–) ppm; 29Si NMR (CDCl3, 298 K,
59.61 MHz): ꢁ ¼ ꢁ21.15, ꢁ22.84 (–OSiMe2O–) ppm.

610
B. Marciniec et al.
3-Heptylheptamethyltrisiloxane (C14H36Si3O2)
1H NMR (C6D6, 298 K, 300 MHz): ꢁ ¼ 0.18, 0.20 (s, –OSiMeO–, –OSiMe3), 0.65 (m, –CH2Si), 0.93
(t, –CH3), 1.41 (bm, –CH2–) ppm.
Poly(heptyl, methyl)(dimethyl)siloxane (C306H768Si77O76)
1H NMR (C6D6, 298 K, 300 MHz): ꢁ ¼ 0.21, 0.23, 0.38 (bs, –OSiMeO–, –OSiMe2O–, –OSiMe3),
0.79 (m, –CH2Si), 0.96 (m, –CH3), 1.41 (bm, –CH2–) ppm.
3-Polyetherheptamethyltrisiloxane (C24H56Si3O10)
1H NMR (C6D6, 298 K, 300 MHz): ꢁ ¼ 0.08, 0.18, 0.20 (s, –OSiMeO–, –OSiMe2O–, –OSiMe3), 0.60
(m, –CH2–), 1.72 (m, –CH2CH2Si), 3.03, 3.26–3.52, 3.65 (m, –OCH2–) ppm.
Silicone polyether (C556H1268Si77O276
)
1H NMR (C6D6, 298 K, 300 MHz): ꢁ ¼ 0.08, 0.18, 0.20 (s, –OSiMeO–, –OSiMe2O–, –OSiMe3), 0.61
(m, –CH2–), 1.76 (m, –CH2CH2Si), 3.03 (m), 3.28–3.56 (m), 3.64 (m, –OCH2–) ppm.
Acknowledgements
This work was supported by the State Committee for Scientific Research (Poland), project No. 3 T09B
121 26.
References
[1] Clarson SJ, Semlyen JH (eds) (1993) Siloxane Polymers, Prentice Hall, New York
[2] Kircheldorf HR (ed) (1996) Silicon in Polymer Synthesis, Springer, Berlin
[3] Yilgor I, McGrath JE (1998) Adv Polym Sci 86: 1
[4] Kirk-Othmer Encyclopedia of Chemical Technology (1997) 4th ed, vol 22, Wiley, New York
[5] Rappoport Z, Apeloig Y (eds) (1998) The Chemistry of Organic Silicon Compounds, Wiley,
Chichester
[6] Jones RG, Ando W, Chojnowski J (eds) (2000) Silicon-Containing Polymers, Kluwer Academic
Publisher, Dordrecht
[7] Interrante JU, Hampden-Smith MJ (1998) Chemistry of Advanced Materials, An Overview,
Wiley, New York
[8] Tomanek A (1991) Silicones and Industry, Munich, Wacker Chemie
[9] Ullman’s Encyclopedia of Industrial Chemistry (1993) 5th ed, vol A24, Organic Silicon
Compounds, VCH, Weinheim
[10] Holmberg K (ed) (1998) Novel Surfactants, Marcel Dekker Inc, New York
[11] Hill RM (ed) (1999) Silicone Surfactants, Marcel Dekker Inc, New York
[12] Reed D (1995) Urethanes Technol 22
[13] Oertel G (ed) (1994) Polyurethane Handbook, 2nd ed, Carl Hanser, Munich
[14] a) Marciniec B (ed) (1992) Comprehensive Handbook on Hydrosilylation, Pergamon Press,
Oxford; b) Marciniec B (2002) Applied Homogeneous Catalysis with Organometallic Com-
pounds. In: Cornils B, Hermann WA (eds) Wiley-VCH, Weinheim
[15] Marciniec B (2002) Silicon Chem 1: 155
[16] Marciniec B, Gulinski J, Maciejewski H (2003) Hydrosilylation in Encyclopedia of Catalysis.
In: Horvath I (ed) John Wiley & Sons, Inc, Hoboken
[17] Ojima I, Li Z, Zhu I (1998) The Chemistry of Organosilicon Compounds. In: Patai S,
Rappoport Z (eds) Wiley, New York
[18] Brook MA (2000) Silicon in Organic, Organometallic and Polymer Chemistry, Wiley, New York

Modification of (Poly)Siloxanes via Hydrosilylation
611
[19] a) Marciniec B, Krzyzanowski P (1995) J Organometal Chem 493: 261; b) Krzyzanowski P,
Kubicki M, Marciniec B (1996) Polyhedron 15: 1; c) Marciniec B, Krzyzanowski P, Kubicki M
(1996) Polyhedron 15: 4233
[20] Marciniec B, Blazejewska-Chadyniak P, Kubicki M (2003) Can J Chem 81: 1292
[21] Marciniec B, Krzyzanowski P, Walczuk-Gusciora E, Duczmal W (1999) J Mol Catal 144: 263
[22] Marciniec B, Walczuk E, Blazejewska-Chadyniak P, Chadyniak D, Kujawa-Welten M,
Krompiec S (2003) Organosilicon Chemistry V – From Molecules to Materials. In: Auner N,
Weiss J (eds) Wiley VCH, Weinheim
[23] a) Pat PL-351 449 (2001), Marciniec B, Blazejewska-Chadyniak P, Walczuk-Gusciora E,
ꢀ
Kujawa-Welten M; b) Pat PL-351 450 (2001), Marciniec B, Chadyniak D, Pawluc P,
Maciejewski H, Blazejewska-Chadyniak P; c) Pat PL-351 451 (2001), Marciniec B, Chadyniak
ꢀ
D, Pawluc P, Maciejewski H, Blazejewska-Chadyniak P
[24] a) Marciniec B, Walczuk-Gusciora E, Blazejewska-Chadyniak P (2000) J Mol Catal 160: 165;
b) Marciniec B, Walczuk-Gusciora E, Pietraszuk C (2001) Organometallics 20: 3423
[25] Adams DJ, Dyson PJ, Tavener SJ (2004) Chemistry in Alternative Reaction Media, Wiley,
Chichester
[26] Parschall GW (1972) J Am Chem Soc 94: 8716
[27] Wilkes JS, Zawrotko MJ (1992) J Chem Soc Chem Commun 965
[28] Rogers RD, Seddon KS (2002) Ionic Liquids. Industrial Applications to Green Chemistry, ACS,
Washington
[29] Wasserscheid P, Welton T (2003) Ionic Liquids in Synthesis, Wiley-VCH, New York
[30] Aubin S, Le Floch F, Carrie D, Guegan JP, Vaultier M (2002) Ionic Liquids: Industrial
Applications for Green Chemistry. In: Rogers D, Seddon KR (eds) ACS, Washington
[31] Goldschmidt AG Eur Pat Appl, EP 1382630 (2004) Hell K, Weyershausen B, Hesse U
[32] Weyershausen B, Hell K, Hesse U (2005) Green Chemistry 7: 283
[33] Giordano G, Crabtree RH (1973) Inorg Synth 19: 218