Hydrosilylation of 1-octene

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... 

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. 

Recently Ru3(CO)12 has been reported to be an effective catalyst for hydrosilylation of 1-octene [10] and of allyl chloride (Eq. 3) [11] by triethoxysilane.The latter process is of great importance for production of the main intermediate in manufacturing silane coupling agents. 

In principle, two regioisomers are produced by the reaction of terminal alkenes and hydrosilanes one where the terminal carbon forms a bond to the silyl group (normal product) and the other which has the silyl group at the inner carbon (branched product). Platinum and rhodium catalysts yield in general the normal products, whereas palladium catalysts sometimes prefer the reaction pathway leading to the branched products. Ruthenium and rhodium afford additional by-products such as alkenylsilanes and alkanes. A typical example is the hydrosilylation of 1-octene (equation 30). ... 

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). - ... 

Ru3(CO)i2l has been reported as a catalyst for hydrosilylation of 1-octene and, especially important for the production of silane coupling agents, in... 

However, reports on biphasic hydrosilylation are scarce. One of them is the Wilkinson complex-catalyzed hydrosilylation of 1-octene in fluorous ionic liquid at room temperature (121). 

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). 

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... 

Figure 5.4 (a) Silane conversion curves for the hydrosilylation of 1-octene (2) by MCyM... 

Figure 5.5 Silane conversion curves for the hydrosilylation of 1-octene (2) by MD M (3) catalyzed by platinum complexes. Reaction conditions MD M (0.5 mol T ), 1-octene...

Figure 5.7 Effect of the addition of fresh reactants on the kinetic profile of the reaction for the hydrosilylation of 1-octene (2) by MD M (3) catalyzed by (ICy)Pt(dvtms) 15c. Reaction conditions MD M (0.05 mol h ), 1-octene (0.05 mol T ), [Pt] (0.05 mol%), o-xylene, 72 °C. On the second and third...

Hydrosilylation of 1-Octene Using Different Silyl Hydrides... 

Hydrosilylation of 1-octene with triethoxysilane on polymer-supported catalysts (Table 15.2) proceeded, to a considerable extent, in the way similar to that of hexadecene. Platinum(II) acetylacetonate as a platinum catalyst precursor appeared to be again a more advantageous choice. 

Marko and co-workers reported the activity of monomeric, moisture and air-stable NHC-Pt such as 133 (Figure 13.15). When complex 133 was applied to the hydrosilylation of a variety of terminal alkenes, only the anti-Markovnikov adducts were obtained, with isomerization by-products representing less than 2% of the reaction products. This catalyst tolerated functional groups such as ethers, carbonyls and esters, but internal alkenes were inert under similar conditions. A related series of six- and seven-mem-bered ring-expanded NHC-Pt complexes 134 was tested in the hydrosilylation of 1-octene with bis(trimethylsiloxy)methylsilane excellent activity and regioselectivity were observed. ... 

Finally, silyl-donor-functionalized NHC-Co complexes 138 catalyzed the hydrosilylation of 1-octene with PhSiHj with very high activity and good selectivity (Figure 13.15). ... 

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