1-Octene, hydrosilylation with

FIGURE 15.4 Catalytic activity for 1-octene hydrosilylation with triethoxysUane at 100°C in the presence of Pt supported on fluorinated carbon of different fluorine content. 

FIGURE 15.5 Yields of desirable products (hexadecyltiiethoxysilane and octyltriethoxysUane, respectively) obtained after 1 h in tests for multiple use of Pt/SDB catalyst in hexadecene and octene hydrosilylation with triethoxysUane (TES) at 100°C. 

Our interest in the hydrosilylation reaction began with a partnership with Rho-dia Silicones in the late 1990s. Their benchmark reaction for testing new catalysts was the hydrosilylation of 1-octene (2) with bis(trimethylsilyloxy) methykilane (MD M) (3) in hot xylene (Scheme 5.2). While 1-octene is a representative olefin, MD M is a cheap silane mimicking the linkage of siloxane polymers (Si-O-Si). Under these conditions, the Karstedt catalyst produces various side-products, among which the isomerized olefin 5 and M-octane (6) are... 

Hydrosilylation by Ziegler-type catalyst systems [e.g., Ni(acac)2/AlEt3] has been examined for the reaction of 1-octene with EtjSiH in benzene 178). Complications include competing isomerization and reduction to metal however, 1,3-dienes or terminal acetylenes are readily hydrosilylated withRC i CH, the major product is CH2 CR. CRiCHSiXj. 

Complexes of the type 48-53 (Scheme 2.7) have been targeted as pre-catalysts for the hydrosilylation of alkenes [44]. For example, in the hydrosilylation of 1-octene with (Me3SiO)2Si(Me)H, which was studied in detail as a model reaction, the activity of complexes 48-49 with alkyl substituted NHC ligands, is inferior to that of the Karstedt s system. However, selectivity and conversions are dramatically improved due to the suppression of side-product formation. In this reaction... 

Wilkinson s catalyst brings about the hydrosilylation of a range of terminal alkenes (1-octene, trimethylvinylsilane) by 2-dimethylsilylpyridine with good regioselectivity for the anti-Markovnikoff product. Both 3-dimethylsilylpyridine and dimethylphenylsilane are less reactive sources of Si-H. In contrast, these two substrates are far more reactive than 2-dimethylsilylpyridine for the hydrosilylation of alkynes by [Pt(CH2 = CHSiMe2)20]/PR3 (R = Ph, Bu ). This difference was explained to be due to the operation of the two different pathways for Si-H addition—the standard Chalk-Harrod pathway with platinum and the modified Chalk-Harrod pathway with rhodium.108... 

Studies on the immobilization of Pt-based hydrosilylation catalysts have resulted in the development of polymer-supported Pt catalysts that exhibit high hydrosilylation and low isomerization activity, high selectivity, and stability in solventless alkene hydrosilylation at room temperature.627 Results with Rh(I) and Pt(II) complexes supported on polyamides628 and Mn-based carbonyl complexes immobilized on aminated poly(siloxane) have also been published.629 A supported Pt-Pd bimetallic colloid containing Pd as the core metal with Pt on the surface showed a remarkable shift in activity in the hydrosilylation of 1-octene.630... 

Rhodium(I) complexes immobilized on silica using 3-(3-silylpropyl)-2,4-pentanedio-nato ligands (38) show good activity in the hydrosilylation of 1-octene with HSi(OEt)3 at 100°C60. The immobilized Rh catalysts are prepared by (i) reaction of (EtO)3Si(CH2)3C(COMe)2Rh(CO)2 with untreated silica (Catalyst A), (ii) reaction of Rh(acac)(CO)2 (acac = acetylacetonato = 2,4-pentanedionato) with silica modified by [(EtO)3Si(CH2)3C(COMe)2] prior to the complexation (Catalyst B), (iii) reaction of [Rh(CO)2Cl]2 with a polycondensate of [(EtO)3Si(CH2)3C(COMe)2] , Si(OEt)4 and water (Catalyst C) and (iv) sol-gel processing of (EtO)3Si(CH2)3C(COMe)2Rh(CO)2 and Si(OEt)4 (Catalyst D). The Catalysts A and B show ca three times better activity than their homogeneous counterparts, while the Catalyst D exhibits only low activity and the Catalyst C is inactive60. 

The reaction between olefins or acetylenes with silicon hydrides in the presence of phosphinenickel complexes has been studied for a variety of substituents on the phosphine and on the silane. In many cases two products are obtained, one of them is the expected simple adduct and the other is an adduct, the formation of which has involved an interchange of hydrogen and chlorine on silicon in the course of hydrosilylation (206) Eq. (90). When methyldichlorosilane was added to octene-1 at temperatures in excess of 120°, the two silanes obtained were CgHi7SiMeClH and CgHi7SiMeCl2. The results outlined in Table II... 

In literature there are data on the homogeneous thermal addition of trichlorosilane to aliphatic and cyclic alkenes as well as to alkodienes with isolated and conjugated double bonds which proceeds under high pressures at 280-300°C [161-163]. Voronkov et al. [164] succeeded in carrying out the thermal addition of trichlorosilane to phenylacetylene in a polar solvent at 200°C while without the solvent the reaction proceeds at 500°C. The authors of Refs.[27,165] have performed the addition of ethylene, propylene, butene, butadiene, octene to silica surface at elevated temperatures. These chemical processes may be referred to as reactions of solid-phase thermal hydrosilylation. Unfortunately, these works have not received a large development effort. 

Secondary alkyl silanes are also formed in the hydrosilylation of phenylethylene. In facfi the latter reaction has been studied in some detail, and primary alkyl silanes, hydrogenation product (i.e. ethylbenzene), andf -2-silylphenylethylenes are also formed (eq 13). Equimolar amounts of ethylbenzene (2) and -2-silyl-phenylethylene (4) are produced, implying these products arise from the same reaction pathway. It has been suggested that this involves dimeric rhodium species because the relative amounts of these products increase with the rhodium silane ratio however, competing radical pathways cannot be ruled out. Certainly, product distributions are governed by the proportions of aU the components in the reaction (i.e. catalyst, silane, and alkene), and the reaction temperature. Side products in the hydrosilylation of 1-octene include vinylsilanes and allylsilanes (eq 14). - ... 

However, not only microporous active carbon of high surface area but also mesoporous carbon black of lower surface area (216 m /g) can serve as an excellent support for Pt—Cu catalyst in the addition of trichlorosilane to alkenes as well as of polyhydrosiloxanes of allyl chloride and 1-octene to produce silicone waxes, with a long alkyl chain (>C8) (123). Platinum catalyst (0.5%) supported on porous (acidic) AI2O3 is very attractive in the industrially important hydrosilylation of cyclopentene and cyclohexene (130). 

A study in this field has revealed an essential difference between the morphologies of the Pt colloid formed under particular conditions in the hydrosilylation of various olefins with EtsSiH in the presence of Karstedt s catalyst (132). The clear conclusion is that the catalytic hydrosilylation under such conditions (silane, rich olefin, poor) is a molecular process proceeding via metal clusters and that the formation of colloids is associated with deactivation of the system. However, the latter process is avoided by a direct use of prefabricated colloids. The size of such colloids can be controlled and the process can be efficiently performed heterogeneously. A combination of bimetallic colloids consisting of a ligand-stabilized Pt shell on Pd cores supported on alumina improves markedly catalytic activity in the test reaction—hydrosilylation of 1-octene (133). 

Precious insights into a reaction mechanism can be collected through the isolation of reactive intermediates. While no reaction occurs between 1-octene (2) and bis(trimethylsilyloxy)methylsilane (3) m the absence of a suitable catalyst, mixtures of (NHC)Pt(dvtms) 15 and 1-octene (2) are unreactive even under harsh conditions (G. Berthon-Gelloz, S. Dierick, and I.E. Mark6, unpublished results). However, treatment of (ICy)Pt(dvtms) 15c with five equivalents of MD M (3), in hot and degassed toluene yields the dimeric complex 25 and the hydrosilylated diene 26 (Scheme 5.7) [16]. The structure of 25 was... 

To further probe the reactivity of complex 25, its reaction with 10 equivalents of 1-octene (2) in hot [dsj-toluene was monitored by NMR spectroscopy (Scheme 5.9) [16]. After 4h, complete conversion of 25 into (ICy)Pt(l-octene)228 was observed, along with the hydrosilylated product 29. Unfortunately, compound 28 is too unstable to be isolated from the reaction... 

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