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Catalytic activity of iridium siloxide complexes in cross-linking of silicones by hydrosilylation
Applied Catalysis A: General 317 (2007) 53–57 www.elsevier.com/locate/apcata
Catalytic activity of iridium siloxide complexes in cross-linking of silicones by hydrosilylation§ Ireneusz Kownacki a, Bogdan Marciniec a,*, Anna Macina a, Sławomir Rubinsztajn b, David Lamb c a
Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, 60780 Poznan, Poland b GE Global Research Center, One Research Circle, Niskayuna, NY 12309, USA c GE Silicones, Waterford, NY, USA
Received 4 August 2006; received in revised form 14 September 2006; accepted 30 September 2006 Available online 16 November 2006
Abstract A series of catalytic examinations have shown that monomeric iridium siloxides ([Ir(cod)(PCy3)(OSiMe3)] (II), [Ir(CO)(PPh3)2(OSiMe3)] (III) and [Ir(CO)(PCy3)2(OSiMe3)] (IV)) are effective catalysts for model homogeneous hydrosilylation of vinyltris(trimethylsiloxy)silane as well as cross-linking of commercial polysiloxane system. The results of stoichiometric reactions of iridium siloxide with heptamethyltrisiloxane and observed catalytic properties are consistent with the mechanism of catalysis involving a generation of the key-intermediate (16e tetracoordinate Ir– H complex) responsible for the catalytic cycle. Experiments allowed explaining the effect of oxygen on the catalytic activity of phosphinecontaining iridium siloxide complexes. The curing process of polysiloxanes catalyzed by iridium siloxide II and IV complexes occurs at a higher temperature (about 200 8C) than the same system catalyzed by Karstedt—diallylmaleate system (130 8C). The enthalpies of the reaction are comparable ( 30 to 38 kJ/mol) for both catalysts but the inhibitor is not required for the iridium-catalyzed process. # 2006 Elsevier B.V. All rights reserved. Keywords: Silicones; Cross-linking; Hydrosilylation; Iridium complexes
1. Introduction Molecular compounds incorporating TM–O–Si groups (where TM is transition metal) are of great interest, particularly as models of metal complexes immobilized on silica and silicate surfaces known to catalyze a variety of organic transformations [1–3]. Since 1982, more than 80 new welldefined TM-siloxide complexes including terminal and/or also bridging siloxy ligands have been synthesized and characterized by X-ray and spectroscopic methods to determine the molecular structure (for a recent review see ref. [1] and references therein). The properties of siloxide as ancillary ligand in the system TM–O–SiR3 have been effectively utilized in molecular catalysis but predominantly by early transition metal complexes. Our recent study of the synthesis, structure
§
Part XXXVIII in the series Catalysis of Hydrosilylation. * Corresponding author. E-mail address: [email protected] (B. Marciniec).
0926-860X/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2006.09.037
and catalytic properties of rhodium and iridium dimeric and monomeric siloxide complexes indicate that those complexes can be very useful as catalysts and as catalysts precursors in a variety of reactions involving olefins, in particular silylative coupling (trans-silylation) [4], silylcarbonylation [5] and hydroformylation [6]. In addition, rhodium siloxide complexes appear to be much more effective than the respective chlorocomplexes in hydrosilylation of a variety of olefins such as 1hexene [7], vinylsilanes and polyvinylsiloxanes as well as allyl alkyl ethers [8]. The hydrosilylation processes are commonly used in catalytic cross-linking of polysiloxanes. However, descriptions in literature and patents are generally limited to systems involving well-known or modified platinum complexes in particular Karstedt’s catalyst (for recent reviews see ref. [9]). Therefore, the aim of this paper is to examine iridium siloxide complexes as catalysts for hydrosilylation of model compounds as well as hydrosilylation of the vinylstopped polydimethylsiloxane in the presence of polyhydrosiloxane that leads to the network formation.
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I. Kownacki et al. / Applied Catalysis A: General 317 (2007) 53–57
2. Results and discussion The well-defined iridium siloxide complexes such as dimeric [{Ir(m-OSiMe3)(cod)}2] (I) and monomeric [Ir(cod)(PCy3) (OSiMe3)] (II) and [Ir(CO)(PPh3)2(OSiMe3)] (III), were synthesized according to a published procedure [4d,10]. Their X-ray structures were also reported previously [4d,10]. A new square-planar iridium siloxide complex consisting of two tricyclohexylphosphine ligands [Ir(CO)(PCy3)2(OSiMe3)] (IV) was synthesized following the previously published procedure [10]. Those complexes were examined as catalysts of the model system involving reaction of vinyltris(trimethylsiloxy)silane with heptamethyltrisiloxane in the temperature range 110– 120 8C which occurs according to the following equation:
free conditions but the hydrosilylation reaction is a strongly accompanied by the H/vinyl exchange of the substrates and yields also products (3) or (4). Interestingly, exposure of the complex I to air completely stops the hydrosilylation process. Contrary to the dimeric complex I, all phosphine monomeric complexes show much higher catalytic activity in the air than in oxygen-free conditions. This effect is a result of facile oxygenation and dissociation of phosphine ligand (more PCy3 than PPh3). 1H NMR spectrum of the stoichiometric mixture of exemplary monomeric complex II and the model hydrotrisiloxane (HSiMe(OSiMe3)2) in C6D6 recorded at room temperature immediately after mixing the substrates, revealed the presence of doublet at d = 13.19 ppm and JH-P = 22 Hz. It is a direct evidence of oxidative addition of
(1)
The reaction leads to the formation of hydrosilylation product (1), which is accompanied by product of the dehydrogenative silylation (2) and, in some cases, respective products (3) and (4) (Table 1). The products (3) and (4) are result of preliminary H/vinyl exchange between reactants, followed by their hydrosilylation (3) and dehydrogenative silylation (4). This process is characteristic for TM catalyzed reactions of hydro- and vinyl-polysiloxanes [11]. All catalytic data are compiled in Table 1. The dimeric iridium siloxide complex I shows high yield under oxygen-
Si–H bond to the complex II according to the Eq. (2) (complex V).
(2)
The 1H NMR spectrum of the reaction mixture recorded after 3 h shows a doublet at d = 6.85 ppm and JH-P = 27 Hz. A
Table 1 Irydium catalyzed hydrosilylation of vinyltris(trimethylsiloxy)slane with heptamethyltrisiloxane Catalyst
Atmosphere
Temprature (8C)
Time (h)
Molar ratio [BBSiH]:[Ir]
Yield (%) 1
I
1 24
1:10 1:10
2
24
1:10
1 2 24
80 110 110
Argon Air
3 2
9 + 10 0 + 17
2
4
1
16 + 0
1:10 1:10 1:10
2
78 95 10
3 3 1
3 + 11 0 0
24 1 1
1:10 1:10 1:10
4
90 95 97
4 2 1
0 Traces Traces
100 120
24 24
1:10 2 1:5 10
44 72
22 26
0 0
Argon
120
24
1:10
3
27
0
0
Air
80 120 120
24 2 1
1:10 1:10 1:10
4
57 81 81
1 9 9
0 0 0
Argon
Air
III IV
3+4
72 70
Argon
110
Air II
2
[BBSiH]:[CH2 CHSiBB] = 1:1.
110
2
3 4
4 5
3 4
3
I. Kownacki et al. / Applied Catalysis A: General 317 (2007) 53–57
55
formation of MeSi(OSiMe3)3 was confirmed by GC–MS analysis. These observations are consistent with the formation of tetracoordinated complex VI via reductive elimination of siloxane according to the Eq. (3):
(3) Decomposition of compound V was observed and tricyclohexylphosphine oxide was detected by 31P NMR technique (d = 34.4 ppm.) after introduction of oxygen to the reaction mixture (31P NMR chemical shift of OPCy3 was confirmed experimentally by oxidation of PCy3 in NMR tube). Reaction performed between heptamethyltrisiloxane and vinyltris(trimethylsiloxy)silane in the presence of catalyst II confirmed formation of the complex V (doublet at d = 13.19 ppm), but under argon atmosphere even at higher temperature no hydrosilylation product was formed. The hydrosilylation reaction was initiated by introduction of small amount of oxygen into the NMR tube at temperature above 80 8C. In that case, the presence of the hydrosilylation product ((Me3SiO)3SiCH2CH2SiMe(OSiMe3)2), as well as OPCy3 and MeSi(OSiMe3)3 was confirmed by 1H NMR, 31P NMR and GC–MS techniques (MS spectrum of OPCy3 confirmed by MS library NIST 98). The presented results suggested that a dissociation of M–P bond via oxygenation of tertiary phosphine ligand is the crucial step for generation of Ir(cod)H(vinylsiloxane) species. The latter complex VI seems to be a key intermediate of olefin hydrosilylation catalyzed by iridium siloxide complexes (similar to rhodium siloxide [8c]) and initiates the real catalytic cycle (Scheme 1). The observed catalytic activity of monomeric iridium siloxide complexes II and IV in the model hydrosilylation of vinylsiloxane with hydrosiloxane particularly in the presence of air suggests their potential usefulness as catalysts for commercially important process of cross-linking of polysiloxanes fluids, which leads to the formation of silicone elastomers.
scanning calorimetry (DSC). Enthalpy is almost the same for Karstedt’s catalyst ( 38.0 J/g) and iridium complexes ( 30.9 J/ g II and 34.5 J/g IV). DSC curves for the curing process performed in the presence of 100 ppm catalyst show that cross-
The studied polymeric system involves vinylstopped linear polydimethylsiloxane fluid and polyhydrosiloxane as a crosslinker. The catalytic activity of catalyst II and IV was compared to the Karstedt’s catalysts. Diallylmaleate (DAM) was used as inhibitor to prevent a premature cure of the catalyzed mixture. The progress of the reaction was followed by differential
linking reaction catalyzed by iridium siloxides occurs at higher temperature (about 200 8C) with broader exothermal peaks than the reaction catalyzed by Pt/DAM system. (see e-components) In contrast to the Pt-catalyzed reaction, the reaction catalyzed by iridium complexes does not require to presence of DAM to inhibit hydrosilylation process at room temperature. The
Scheme 1. .
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I. Kownacki et al. / Applied Catalysis A: General 317 (2007) 53–57
viscosity of the reaction mixture with 100 ppm of iridium catalyst did not change after several days at room temperature. On the other hand, the presence of DAM in the reaction mixture did not change the course of the reaction at higher temperatures. 3. Experimental All syntheses and manipulations were carried out under argon using standard Schlenk and vacuum techniques. 1H, 13C and 29Si NMR spectra were recorded on a Varian Gemini 300 VT and Varian Mercury 300 VT spectrometers in C6D6. The mass spectra of the products were determined by GC–MS (Varian Saturn 2100T equipped with a DB-1, 30 m capillary column). GC analyses were carried out on a Varian 3400 CX series gas chromatograph with a capillary column DB-1, 30 m and TC detector. The chemicals were obtained from the following sources: sodium trimethylsilanolate (Aldrich), HSiMe(OSiMe3)2 and CH2 CHSi(OSiMe3)3 from ABCR, polyhydrosiloxane, vinylstopped polydimethylsiloxane from GE Silicones, benzene from POCH Gliwice (Poland) CH2Cl2 and benzene-d6 from Aldrich. All solvents and vinylsubstituted silanes were dried and distilled under argon prior to use. [IrCl(CO)(PCy3)2] was prepared according to the previously reported procedure [12]. 3.1. Synthesis of [Ir(CO)(PCy3)2(OSiMe3)] (IV) 0.5 g (0.98 mmol) of [(IrCl(CO)(PCy3)2] and 0.08 g (1.08 mmol) of NaOSiMe3 were placed in a Schlenck’s flask under argon atmosphere. Then 6 mL of dried and deoxygenated benzene was added. The reaction was conducted for 12 h at 50 8C on intense stirring with a magnetic stirrer. After the reaction completion, the suspension was filtered off by a cannula system and the solvent from the filtrate was evaporated under reduced pressure. The Schlenck’s flask content was supplemented with 4 ml of dried and deoxygenated CH2Cl2 and mixture obtained again was filtered off and the filtrate was concentrated. The bright-yellow precipitate obtained after addition of pentane was decanted with three portions of pentane and dried under vacuum. The siloxy complex was obtained with a yield of 92%. Anal. Cal. for C40H75IrO2P2Si: C, 55.20; H, 8.69. Found: C, 54.48; H, 9.23 1
H NMR
13
C NMR
31
P NMR
d(ppm, C6D6) = 0.29 (s, 9H, –CH3) 1.13, 1.74, 2.18, 2.66(m, 66H, –CH2–) d(ppm, C6D6) = 4.81 (–Me); 27.79, 28.92, 28.56, 30.54, 32.65, 32.99 (–Cy); 179.87 (CO) d(ppm, C6D6) = 32.76
(OSiMe3)2 was added to the solution. The first 1H NMR spectrum was recorded immediately after addition of heptamethyltrisiloxane. The reaction mixture was kept at room temperature for the 3 h and the second 1H NMR spectrum was recorded. The progress of reaction was also controlled by GC– MS technique. According to the procedure described above, the reaction was also performed in the air. 3.3. Stoichiometric reaction of [Ir(cod)(PCy3)(OSiMe3)] (II) with HSiMe(OSiMe3)2 and CH2 CHSi(OSiMe3)3 [Ir(cod)(PCy3)(OSiMe3)] (0.030 g; 4.48 10 5 mole) was dissolved under argon in 0.6 mL of C6D6 in a NMR tube. 0.0400 g (1.79 10 4 mole) HSiMe(OSiMe3)2 and 0.0577 g (1.79 10 4 mole) CH2 CHSi(OSiMe3)3 were added to the solution. The first 1H NMR spectrum was recorded immediately after addition of organosiloxanes. The reaction mixture was kept at room temperature for 3 h and the second 1 H NMR spectrum was recorded. The progress of reaction was also controlled by GC–MS technique. According to the procedure described above, the reaction was also performed in the air. 3.4. Catalytic examinations in model system The catalytic tests of the iridium(I) siloxide complexes in the model reaction were performed in glass ampoules or Schlenk’s tubes filled with a mixture of vinyltris(trimethylsiloxy)silane, heptamethyltrisiloxane and decane as an internal standard. The ampoules (or Schlenk’s tubes) were heated to a desired temperature. The distribution of substrates and products, conversion of substrates and the yield of products were determined by GC and GC–MS analyses. 3.5. Catalytic examinations in polymeric system The catalytic activity of the iridium(I) siloxide complexes were studied in a system consisting of vinylterminated polydimethylsiloxane and polyhydrosiloxane. The reaction progress was monitored by DSC test method. All samples were mixed well for one hour before DSC analysis. DSC measurements were made using a DSC 204 NETCH. The instrument was calibrated with indium (DH = 28.4 J/g). Analysis conditions (DSC): hold for 5.0 min at 30 8C; heat from 20 to 220 8C at 10 8C/min; cool from 250 to 30 8C at 20 8C/min; DSC experiments were made in triplicate for each ramp rate, and for each concentration
3.2. Stoichiometric reaction of [Ir(cod)(PCy3)(OSiMe3)] (II) with HSiMe(OSiMe3)2
4. Conclusions
0.035 g (5.23 10 5 mole) of [Ir(cod)(PCy3)(OSiMe3)] was dissolved under argon in 0.6 mL of C6D6 in NMR tube. Subsequently, 0.0467 g (2.09 10 4 mole) of HSiMe
1. All catalytic data and results of the stoichometric reaction of the iridium siloxide complex II with hydroheptamethyltrisiloxane are consistent with the mechanism involving a
I. Kownacki et al. / Applied Catalysis A: General 317 (2007) 53–57
generation of 16e tetracoordinated Ir–H complex, containing coordinated vinylsiloxane molecule as a key intermediate responsible for catalysis of hydrosilylation. 2. Monomeric iridium siloxide complexes such as II–IV are effective catalysts for model homogeneous hydrosilylation of vinyltris(trimethylsiloxy)silane with heptamethyltrisiloxane as well as for cross-linking of the commercial polysiloxane system. 3. The curing process catalyzed by iridium siloxide proceeds at higher temperature (about 200 8C) than the process catalyzed by Karstedt’s—DAM system and does not require an inhibitor to maintain low viscosity of the reaction mixture at room temperature for several days. Acknowledgment The financial support from General Electric Company is gratefully acknowledged. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.apcata.2006.09.037. References [1] B. Marciniec, H. Maciejewski, Coord. Chem. Rev. 223 (2001) 301 (and references therein). [2] (a) F.R. Hartley, Supported Metal Complexes, Reidel, Boston, 1985; (b) Y. Iwasawa (Ed.), Tailoral Metal Catalysts, Reidel, Boston, 1986; (c) B. Marciniec, I. Kownacki, M. Kubicki, E. Walczuk, P. BlazejewskaChadyniak, in: C.G. Screttas, B.R. Steele (Eds.), Perspectives in Organometallic Chemistry, Royal Society of Chemistry, Cambridge, 2003, p. 253; (d) B. Marciniec, in: A. Trzeciak (Ed.), Education in Advanced Chemistry, vol. 9, 2005, p. 195. [3] (a) F.J. Feher, J. Am. Chem. Soc. 108 (1986) 3850; (b) T. Wolczanski, Polyhedron 14 (1995) 3335.
57
[4] (a) B. Marciniec, E. Walczuk-Gusciora, P. Blazejewska-Chadyniak, J. Mol. Catal. A: Chem. 160 (2000) 165; (b) B. Marciniec, E. Walczuk-Gusciora, C. Pietraszuk, Organometallics 20 (2001) 3423; (c) B. Marciniec, M. Lewandowski, E. Bijpost, E. Malecka, M. Kubicki, E. Walczuk-Gusciora, Organometallics 18 (1999) 2033; (d) B. Marciniec, I. Kownacki, M. Kubicki, Organometallics 21 (2002) 3263. [5] I. Kownacki, B. Marciniec, K. Szubert, M. Kubicki, Organometallics 24 (2005) 6179. [6] E. Mieczynska, A.M. Trzeciak, J.J. Ziolkowski, I. Kownacki, B. Marciniec, J. Mol. Catal. 237 (2005) 246. [7] B. Marciniec, P. Krzyzanowski, E. Walczuk-Gusciora, J. Mol. Catal. 144 (1999) 263. [8] (a) H. Maciejewski, B. Marciniec, P. Blazejewska-Chadyniak, in: N. Auner, J. Weis (Eds.), Organosilicon Chemistry VI, vol.1, WileyVCH Verlag GmbH & Co. KgaA, Weinheim, 2005, p. 408; (b) B. Marciniec, P. Blazejewska-Chadyniak, M. Kubicki, Can. J. Chem. 81 (2003) 1292; (d) B. Marciniec, P. Blazejewska-Chadyniak, E. Walczuk, M. Kujawa, WP 372/02 (2001).; (e) B. Marciniec, P. Blazejewska-Chadyniak, I. Kownacki, K. Szubert, Pol. App. Patent 368,485 (2005). [9] (a) B. Marciniec, J. Gulinski, W. Urbaniak, Z.W. Kornetka, in: B. Marciniec (Ed.), Comprehensive Handbook on Organosilicon Chemistry, Pergamon Press, Oxford, 1992, p. 758; (b) B. Marciniec, Silicon Chem. 1 (2002) 155; (c) B. Marciniec, in: B. Cornils, W.A. Herrmann (Eds.), Applied Homogeneous Catalysis with Organometallic Compounds, vol. 1, 2002, p. 487; (d) L.N. Lewis, J. Stein, Y. Gao, R.E. Colborn, G. Hutchins, Platinum Met. Rev. 41 (1997) 66; (e) I. Ojima, Z. Li, J. Zhu, in: Z. Rapapport, Y. Apeloig (Eds.), The Chemistry of Organic Silicon Compounds, J. Wiley and Sons, Chichester, 1998, , chapter 29. [10] (a) H. Schmidbaur, J. Adlkofer, Chem. Ber. Recl. 107 (1974) 3680; (b) I. Kownacki, M. Kubicki, B. Marciniec, Inorg. Chim. Acta 334 (2002) 301. [11] (a) J.L. Speier, J.A. Webster, G.H. Bames, J. Am. Chem. Soc. 79 (1957) 974; (b) M.D. Curtis, P.S. Epstein, Adv. Organomet. Chem. 19 (1981) 213. [12] K. Vrieze, J.P. Collman, C.T. Sears Jr., M. Kubota, Inorg. Synth. 11 (1968) 101.
Catalytic activity of iridium siloxide complexes in cross-linking of silicones by hydrosilylation§ Ireneusz Kownacki a, Bogdan Marciniec a,*, Anna Macina a, Sławomir Rubinsztajn b, David Lamb c a
Adam Mickiewicz University, Faculty of Chemistry, Grunwaldzka 6, 60780 Poznan, Poland b GE Global Research Center, One Research Circle, Niskayuna, NY 12309, USA c GE Silicones, Waterford, NY, USA
Received 4 August 2006; received in revised form 14 September 2006; accepted 30 September 2006 Available online 16 November 2006
Abstract A series of catalytic examinations have shown that monomeric iridium siloxides ([Ir(cod)(PCy3)(OSiMe3)] (II), [Ir(CO)(PPh3)2(OSiMe3)] (III) and [Ir(CO)(PCy3)2(OSiMe3)] (IV)) are effective catalysts for model homogeneous hydrosilylation of vinyltris(trimethylsiloxy)silane as well as cross-linking of commercial polysiloxane system. The results of stoichiometric reactions of iridium siloxide with heptamethyltrisiloxane and observed catalytic properties are consistent with the mechanism of catalysis involving a generation of the key-intermediate (16e tetracoordinate Ir– H complex) responsible for the catalytic cycle. Experiments allowed explaining the effect of oxygen on the catalytic activity of phosphinecontaining iridium siloxide complexes. The curing process of polysiloxanes catalyzed by iridium siloxide II and IV complexes occurs at a higher temperature (about 200 8C) than the same system catalyzed by Karstedt—diallylmaleate system (130 8C). The enthalpies of the reaction are comparable ( 30 to 38 kJ/mol) for both catalysts but the inhibitor is not required for the iridium-catalyzed process. # 2006 Elsevier B.V. All rights reserved. Keywords: Silicones; Cross-linking; Hydrosilylation; Iridium complexes
1. Introduction Molecular compounds incorporating TM–O–Si groups (where TM is transition metal) are of great interest, particularly as models of metal complexes immobilized on silica and silicate surfaces known to catalyze a variety of organic transformations [1–3]. Since 1982, more than 80 new welldefined TM-siloxide complexes including terminal and/or also bridging siloxy ligands have been synthesized and characterized by X-ray and spectroscopic methods to determine the molecular structure (for a recent review see ref. [1] and references therein). The properties of siloxide as ancillary ligand in the system TM–O–SiR3 have been effectively utilized in molecular catalysis but predominantly by early transition metal complexes. Our recent study of the synthesis, structure
§
Part XXXVIII in the series Catalysis of Hydrosilylation. * Corresponding author. E-mail address: [email protected] (B. Marciniec).
0926-860X/$ – see front matter # 2006 Elsevier B.V. All rights reserved. doi:10.1016/j.apcata.2006.09.037
and catalytic properties of rhodium and iridium dimeric and monomeric siloxide complexes indicate that those complexes can be very useful as catalysts and as catalysts precursors in a variety of reactions involving olefins, in particular silylative coupling (trans-silylation) [4], silylcarbonylation [5] and hydroformylation [6]. In addition, rhodium siloxide complexes appear to be much more effective than the respective chlorocomplexes in hydrosilylation of a variety of olefins such as 1hexene [7], vinylsilanes and polyvinylsiloxanes as well as allyl alkyl ethers [8]. The hydrosilylation processes are commonly used in catalytic cross-linking of polysiloxanes. However, descriptions in literature and patents are generally limited to systems involving well-known or modified platinum complexes in particular Karstedt’s catalyst (for recent reviews see ref. [9]). Therefore, the aim of this paper is to examine iridium siloxide complexes as catalysts for hydrosilylation of model compounds as well as hydrosilylation of the vinylstopped polydimethylsiloxane in the presence of polyhydrosiloxane that leads to the network formation.
54
I. Kownacki et al. / Applied Catalysis A: General 317 (2007) 53–57
2. Results and discussion The well-defined iridium siloxide complexes such as dimeric [{Ir(m-OSiMe3)(cod)}2] (I) and monomeric [Ir(cod)(PCy3) (OSiMe3)] (II) and [Ir(CO)(PPh3)2(OSiMe3)] (III), were synthesized according to a published procedure [4d,10]. Their X-ray structures were also reported previously [4d,10]. A new square-planar iridium siloxide complex consisting of two tricyclohexylphosphine ligands [Ir(CO)(PCy3)2(OSiMe3)] (IV) was synthesized following the previously published procedure [10]. Those complexes were examined as catalysts of the model system involving reaction of vinyltris(trimethylsiloxy)silane with heptamethyltrisiloxane in the temperature range 110– 120 8C which occurs according to the following equation:
free conditions but the hydrosilylation reaction is a strongly accompanied by the H/vinyl exchange of the substrates and yields also products (3) or (4). Interestingly, exposure of the complex I to air completely stops the hydrosilylation process. Contrary to the dimeric complex I, all phosphine monomeric complexes show much higher catalytic activity in the air than in oxygen-free conditions. This effect is a result of facile oxygenation and dissociation of phosphine ligand (more PCy3 than PPh3). 1H NMR spectrum of the stoichiometric mixture of exemplary monomeric complex II and the model hydrotrisiloxane (HSiMe(OSiMe3)2) in C6D6 recorded at room temperature immediately after mixing the substrates, revealed the presence of doublet at d = 13.19 ppm and JH-P = 22 Hz. It is a direct evidence of oxidative addition of
(1)
The reaction leads to the formation of hydrosilylation product (1), which is accompanied by product of the dehydrogenative silylation (2) and, in some cases, respective products (3) and (4) (Table 1). The products (3) and (4) are result of preliminary H/vinyl exchange between reactants, followed by their hydrosilylation (3) and dehydrogenative silylation (4). This process is characteristic for TM catalyzed reactions of hydro- and vinyl-polysiloxanes [11]. All catalytic data are compiled in Table 1. The dimeric iridium siloxide complex I shows high yield under oxygen-
Si–H bond to the complex II according to the Eq. (2) (complex V).
(2)
The 1H NMR spectrum of the reaction mixture recorded after 3 h shows a doublet at d = 6.85 ppm and JH-P = 27 Hz. A
Table 1 Irydium catalyzed hydrosilylation of vinyltris(trimethylsiloxy)slane with heptamethyltrisiloxane Catalyst
Atmosphere
Temprature (8C)
Time (h)
Molar ratio [BBSiH]:[Ir]
Yield (%) 1
I
1 24
1:10 1:10
2
24
1:10
1 2 24
80 110 110
Argon Air
3 2
9 + 10 0 + 17
2
4
1
16 + 0
1:10 1:10 1:10
2
78 95 10
3 3 1
3 + 11 0 0
24 1 1
1:10 1:10 1:10
4
90 95 97
4 2 1
0 Traces Traces
100 120
24 24
1:10 2 1:5 10
44 72
22 26
0 0
Argon
120
24
1:10
3
27
0
0
Air
80 120 120
24 2 1
1:10 1:10 1:10
4
57 81 81
1 9 9
0 0 0
Argon
Air
III IV
3+4
72 70
Argon
110
Air II
2
[BBSiH]:[CH2 CHSiBB] = 1:1.
110
2
3 4
4 5
3 4
3
I. Kownacki et al. / Applied Catalysis A: General 317 (2007) 53–57
55
formation of MeSi(OSiMe3)3 was confirmed by GC–MS analysis. These observations are consistent with the formation of tetracoordinated complex VI via reductive elimination of siloxane according to the Eq. (3):
(3) Decomposition of compound V was observed and tricyclohexylphosphine oxide was detected by 31P NMR technique (d = 34.4 ppm.) after introduction of oxygen to the reaction mixture (31P NMR chemical shift of OPCy3 was confirmed experimentally by oxidation of PCy3 in NMR tube). Reaction performed between heptamethyltrisiloxane and vinyltris(trimethylsiloxy)silane in the presence of catalyst II confirmed formation of the complex V (doublet at d = 13.19 ppm), but under argon atmosphere even at higher temperature no hydrosilylation product was formed. The hydrosilylation reaction was initiated by introduction of small amount of oxygen into the NMR tube at temperature above 80 8C. In that case, the presence of the hydrosilylation product ((Me3SiO)3SiCH2CH2SiMe(OSiMe3)2), as well as OPCy3 and MeSi(OSiMe3)3 was confirmed by 1H NMR, 31P NMR and GC–MS techniques (MS spectrum of OPCy3 confirmed by MS library NIST 98). The presented results suggested that a dissociation of M–P bond via oxygenation of tertiary phosphine ligand is the crucial step for generation of Ir(cod)H(vinylsiloxane) species. The latter complex VI seems to be a key intermediate of olefin hydrosilylation catalyzed by iridium siloxide complexes (similar to rhodium siloxide [8c]) and initiates the real catalytic cycle (Scheme 1). The observed catalytic activity of monomeric iridium siloxide complexes II and IV in the model hydrosilylation of vinylsiloxane with hydrosiloxane particularly in the presence of air suggests their potential usefulness as catalysts for commercially important process of cross-linking of polysiloxanes fluids, which leads to the formation of silicone elastomers.
scanning calorimetry (DSC). Enthalpy is almost the same for Karstedt’s catalyst ( 38.0 J/g) and iridium complexes ( 30.9 J/ g II and 34.5 J/g IV). DSC curves for the curing process performed in the presence of 100 ppm catalyst show that cross-
The studied polymeric system involves vinylstopped linear polydimethylsiloxane fluid and polyhydrosiloxane as a crosslinker. The catalytic activity of catalyst II and IV was compared to the Karstedt’s catalysts. Diallylmaleate (DAM) was used as inhibitor to prevent a premature cure of the catalyzed mixture. The progress of the reaction was followed by differential
linking reaction catalyzed by iridium siloxides occurs at higher temperature (about 200 8C) with broader exothermal peaks than the reaction catalyzed by Pt/DAM system. (see e-components) In contrast to the Pt-catalyzed reaction, the reaction catalyzed by iridium complexes does not require to presence of DAM to inhibit hydrosilylation process at room temperature. The
Scheme 1. .
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viscosity of the reaction mixture with 100 ppm of iridium catalyst did not change after several days at room temperature. On the other hand, the presence of DAM in the reaction mixture did not change the course of the reaction at higher temperatures. 3. Experimental All syntheses and manipulations were carried out under argon using standard Schlenk and vacuum techniques. 1H, 13C and 29Si NMR spectra were recorded on a Varian Gemini 300 VT and Varian Mercury 300 VT spectrometers in C6D6. The mass spectra of the products were determined by GC–MS (Varian Saturn 2100T equipped with a DB-1, 30 m capillary column). GC analyses were carried out on a Varian 3400 CX series gas chromatograph with a capillary column DB-1, 30 m and TC detector. The chemicals were obtained from the following sources: sodium trimethylsilanolate (Aldrich), HSiMe(OSiMe3)2 and CH2 CHSi(OSiMe3)3 from ABCR, polyhydrosiloxane, vinylstopped polydimethylsiloxane from GE Silicones, benzene from POCH Gliwice (Poland) CH2Cl2 and benzene-d6 from Aldrich. All solvents and vinylsubstituted silanes were dried and distilled under argon prior to use. [IrCl(CO)(PCy3)2] was prepared according to the previously reported procedure [12]. 3.1. Synthesis of [Ir(CO)(PCy3)2(OSiMe3)] (IV) 0.5 g (0.98 mmol) of [(IrCl(CO)(PCy3)2] and 0.08 g (1.08 mmol) of NaOSiMe3 were placed in a Schlenck’s flask under argon atmosphere. Then 6 mL of dried and deoxygenated benzene was added. The reaction was conducted for 12 h at 50 8C on intense stirring with a magnetic stirrer. After the reaction completion, the suspension was filtered off by a cannula system and the solvent from the filtrate was evaporated under reduced pressure. The Schlenck’s flask content was supplemented with 4 ml of dried and deoxygenated CH2Cl2 and mixture obtained again was filtered off and the filtrate was concentrated. The bright-yellow precipitate obtained after addition of pentane was decanted with three portions of pentane and dried under vacuum. The siloxy complex was obtained with a yield of 92%. Anal. Cal. for C40H75IrO2P2Si: C, 55.20; H, 8.69. Found: C, 54.48; H, 9.23 1
H NMR
13
C NMR
31
P NMR
d(ppm, C6D6) = 0.29 (s, 9H, –CH3) 1.13, 1.74, 2.18, 2.66(m, 66H, –CH2–) d(ppm, C6D6) = 4.81 (–Me); 27.79, 28.92, 28.56, 30.54, 32.65, 32.99 (–Cy); 179.87 (CO) d(ppm, C6D6) = 32.76
(OSiMe3)2 was added to the solution. The first 1H NMR spectrum was recorded immediately after addition of heptamethyltrisiloxane. The reaction mixture was kept at room temperature for the 3 h and the second 1H NMR spectrum was recorded. The progress of reaction was also controlled by GC– MS technique. According to the procedure described above, the reaction was also performed in the air. 3.3. Stoichiometric reaction of [Ir(cod)(PCy3)(OSiMe3)] (II) with HSiMe(OSiMe3)2 and CH2 CHSi(OSiMe3)3 [Ir(cod)(PCy3)(OSiMe3)] (0.030 g; 4.48 10 5 mole) was dissolved under argon in 0.6 mL of C6D6 in a NMR tube. 0.0400 g (1.79 10 4 mole) HSiMe(OSiMe3)2 and 0.0577 g (1.79 10 4 mole) CH2 CHSi(OSiMe3)3 were added to the solution. The first 1H NMR spectrum was recorded immediately after addition of organosiloxanes. The reaction mixture was kept at room temperature for 3 h and the second 1 H NMR spectrum was recorded. The progress of reaction was also controlled by GC–MS technique. According to the procedure described above, the reaction was also performed in the air. 3.4. Catalytic examinations in model system The catalytic tests of the iridium(I) siloxide complexes in the model reaction were performed in glass ampoules or Schlenk’s tubes filled with a mixture of vinyltris(trimethylsiloxy)silane, heptamethyltrisiloxane and decane as an internal standard. The ampoules (or Schlenk’s tubes) were heated to a desired temperature. The distribution of substrates and products, conversion of substrates and the yield of products were determined by GC and GC–MS analyses. 3.5. Catalytic examinations in polymeric system The catalytic activity of the iridium(I) siloxide complexes were studied in a system consisting of vinylterminated polydimethylsiloxane and polyhydrosiloxane. The reaction progress was monitored by DSC test method. All samples were mixed well for one hour before DSC analysis. DSC measurements were made using a DSC 204 NETCH. The instrument was calibrated with indium (DH = 28.4 J/g). Analysis conditions (DSC): hold for 5.0 min at 30 8C; heat from 20 to 220 8C at 10 8C/min; cool from 250 to 30 8C at 20 8C/min; DSC experiments were made in triplicate for each ramp rate, and for each concentration
3.2. Stoichiometric reaction of [Ir(cod)(PCy3)(OSiMe3)] (II) with HSiMe(OSiMe3)2
4. Conclusions
0.035 g (5.23 10 5 mole) of [Ir(cod)(PCy3)(OSiMe3)] was dissolved under argon in 0.6 mL of C6D6 in NMR tube. Subsequently, 0.0467 g (2.09 10 4 mole) of HSiMe
1. All catalytic data and results of the stoichometric reaction of the iridium siloxide complex II with hydroheptamethyltrisiloxane are consistent with the mechanism involving a
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generation of 16e tetracoordinated Ir–H complex, containing coordinated vinylsiloxane molecule as a key intermediate responsible for catalysis of hydrosilylation. 2. Monomeric iridium siloxide complexes such as II–IV are effective catalysts for model homogeneous hydrosilylation of vinyltris(trimethylsiloxy)silane with heptamethyltrisiloxane as well as for cross-linking of the commercial polysiloxane system. 3. The curing process catalyzed by iridium siloxide proceeds at higher temperature (about 200 8C) than the process catalyzed by Karstedt’s—DAM system and does not require an inhibitor to maintain low viscosity of the reaction mixture at room temperature for several days. Acknowledgment The financial support from General Electric Company is gratefully acknowledged. Appendix A. Supplementary data Supplementary data associated with this article can be found, in the online version, at doi:10.1016/j.apcata.2006.09.037. References [1] B. Marciniec, H. Maciejewski, Coord. Chem. Rev. 223 (2001) 301 (and references therein). [2] (a) F.R. Hartley, Supported Metal Complexes, Reidel, Boston, 1985; (b) Y. Iwasawa (Ed.), Tailoral Metal Catalysts, Reidel, Boston, 1986; (c) B. Marciniec, I. Kownacki, M. Kubicki, E. Walczuk, P. BlazejewskaChadyniak, in: C.G. Screttas, B.R. Steele (Eds.), Perspectives in Organometallic Chemistry, Royal Society of Chemistry, Cambridge, 2003, p. 253; (d) B. Marciniec, in: A. Trzeciak (Ed.), Education in Advanced Chemistry, vol. 9, 2005, p. 195. [3] (a) F.J. Feher, J. Am. Chem. Soc. 108 (1986) 3850; (b) T. Wolczanski, Polyhedron 14 (1995) 3335.
57
[4] (a) B. Marciniec, E. Walczuk-Gusciora, P. Blazejewska-Chadyniak, J. Mol. Catal. A: Chem. 160 (2000) 165; (b) B. Marciniec, E. Walczuk-Gusciora, C. Pietraszuk, Organometallics 20 (2001) 3423; (c) B. Marciniec, M. Lewandowski, E. Bijpost, E. Malecka, M. Kubicki, E. Walczuk-Gusciora, Organometallics 18 (1999) 2033; (d) B. Marciniec, I. Kownacki, M. Kubicki, Organometallics 21 (2002) 3263. [5] I. Kownacki, B. Marciniec, K. Szubert, M. Kubicki, Organometallics 24 (2005) 6179. [6] E. Mieczynska, A.M. Trzeciak, J.J. Ziolkowski, I. Kownacki, B. Marciniec, J. Mol. Catal. 237 (2005) 246. [7] B. Marciniec, P. Krzyzanowski, E. Walczuk-Gusciora, J. Mol. Catal. 144 (1999) 263. [8] (a) H. Maciejewski, B. Marciniec, P. Blazejewska-Chadyniak, in: N. Auner, J. Weis (Eds.), Organosilicon Chemistry VI, vol.1, WileyVCH Verlag GmbH & Co. KgaA, Weinheim, 2005, p. 408; (b) B. Marciniec, P. Blazejewska-Chadyniak, M. Kubicki, Can. J. Chem. 81 (2003) 1292; (d) B. Marciniec, P. Blazejewska-Chadyniak, E. Walczuk, M. Kujawa, WP 372/02 (2001).; (e) B. Marciniec, P. Blazejewska-Chadyniak, I. Kownacki, K. Szubert, Pol. App. Patent 368,485 (2005). [9] (a) B. Marciniec, J. Gulinski, W. Urbaniak, Z.W. Kornetka, in: B. Marciniec (Ed.), Comprehensive Handbook on Organosilicon Chemistry, Pergamon Press, Oxford, 1992, p. 758; (b) B. Marciniec, Silicon Chem. 1 (2002) 155; (c) B. Marciniec, in: B. Cornils, W.A. Herrmann (Eds.), Applied Homogeneous Catalysis with Organometallic Compounds, vol. 1, 2002, p. 487; (d) L.N. Lewis, J. Stein, Y. Gao, R.E. Colborn, G. Hutchins, Platinum Met. Rev. 41 (1997) 66; (e) I. Ojima, Z. Li, J. Zhu, in: Z. Rapapport, Y. Apeloig (Eds.), The Chemistry of Organic Silicon Compounds, J. Wiley and Sons, Chichester, 1998, , chapter 29. [10] (a) H. Schmidbaur, J. Adlkofer, Chem. Ber. Recl. 107 (1974) 3680; (b) I. Kownacki, M. Kubicki, B. Marciniec, Inorg. Chim. Acta 334 (2002) 301. [11] (a) J.L. Speier, J.A. Webster, G.H. Bames, J. Am. Chem. Soc. 79 (1957) 974; (b) M.D. Curtis, P.S. Epstein, Adv. Organomet. Chem. 19 (1981) 213. [12] K. Vrieze, J.P. Collman, C.T. Sears Jr., M. Kubota, Inorg. Synth. 11 (1968) 101.