Hydrosilylation of functionalized olefins

In the patent specification [147] there data on the chemical attachment to hydridesilica surface in the presence of the Reney nickel, chloroplatinic acid or metallic platinum deposited on activated carbon as a catalyst of the following unsaturated functional compounds divinylbenzene, ethylene glycol diacrylate, acetylene, allyl alcohol, allyl glycidyl ether, allyl isocyanate, acrylic acid. The chemical reactions result in the transformation of Si-H bonds of hydridesilica surface into Si-C bonds. Such transformations may be also classified as processes of solid-phase catalytic hydrosilylation of functional olefins. 

Table 1. Hydrosilylation of Functionalized Olefins Catalyzed by Chloroplatinic Acid... 

Table 1. Hydrosilylation of functionalized olefins catalyzed by chloroplatinic acid... 

In recent years the solid-phase hydrosilylation reaction was successfully employed for synthesis of hydrolytically stable surface chemical compounds with Si-C bonds. Of special interest is application of this method for attachment of functional olefins, in particular of acrolein and some chiral ligands. Such matrices can be used for subsequent immobilization of a wide range of amine-containing organic reagents and in chiral chromatography. 

Asymmetric hydrosilylation of 2-phenyl-1-butene yields enantiomeric excess ee) values as high as 68% [149]. Products obtained by sequential cyclization/ silylation reactions of 1,5-dienes and 1,6-dienes feature in the suggested mechanistic scenario (Scheme 8) [149, 155]. Furthermore, hydrosilylation of terminal olefins achieved both excellent chemoselectivity in the presence of any internal olefin, and functional-group compatibility with halides, ethers, and acetals [155]. 

The complex [PtCl2(styrene)2] is a catalyst precursor for the hydrosilylation of terminal olefins and acetylenes, the reduction of carbonyl functions (with pyridine or amines as co-catalysts), and for the formation of RaSiOR from RaSiH and alcohols. During the hydrosilylation the complex is reduced to [Pt(styrene)3], which could not be isolated but was characterized by While... 

Ir(I)-oxazolinyl-phosphane complexes are also effective catalysts for hydrosilylation of imines (246). Chiral poisoning of iridium complexes containing racemic DIOP with PRONOP provides an enantioselective catalyst (247). Iridium complexes containing phosphinooxazoline or dithioether ligands (like DIOSPr or DIOSPh) catalyze the enantioselective hydrogenation of functionalized olefins (248). 

As usual, there are some limitations in attachment of various organic groups to siloxane backbone. In some instances, direct hydrosilylation of an olefin derivative of the intended functional group can lead to serious side reactions it may give poor yield or may simply call for unusual and difficult to prepare intermediates. In any case, hydrosilylation of polymers with Si—H is a good source of preceramic polymeric materials (4,18). A variety of linear polysilanes and polycarbosilanes have been reported, but because they tend to depolymerize on heating and afford little ceramic jdeld, they are not useful as SiC precursors. To increase the... 

The cationic palladium methyl complex [(phen)Pd(CH3)-(OEt2)](BAr4) (where Ar = 3,5-(CF3)2CgH3) has shown high efficiency in carbon-silicon bond forming processes such as hydrosilylation of unfunctionalized olefins and tandem cycliza-tion/hydrosilylation of functionalized 1,6-dienes (eq 2). ... 

One or both carbonyls in /3-diketones can be reduced, as well as the carbonyl function in acyl cyanides (210). Similar treatment of a,/3-unsat-urated ketones and aldehydes can lead to the saturated carbonyl products via selective reduction of the olefinic bond (207, 208, 210) see Eq. (51) in Section III,A,4. Some terpenes (a- and /3-ionone, pulegone) were reduced in this way (208). Platinum(II) phosphine complexes have been used for the hydrosilylation of saturated ketones and could be used for the reduction (211). 

Alkyl complexes of the type (C5Me5)2LnCH(SiMe3)2 (Ln = Y,Nd) have been reported to catalyze the hydrosilylation of various substituted and functionalized olefines to a mixture of linear and branched products, Eq. (16) [70]. 

Scheme 10. Hydroelementation reactions in the functionalization of hexa-olefin stars hydrosilylation, hydrozirconation, and hydroboration.

In recent years, we have been investigating easy and economical functionalization of widely nsed carbon based polymers snch as polybntadienes. The preliminary results of these studies have led our group to discover a highly selective and mild synthetic route to silyl-functionalization of 1,2-polybutadienes (PBD) via Pt-nanocluster catalyzed hydrosilylation of olefin bonds. Unlike other catalytic systems, our system was found to be equally effective with all varieties of functional silanes such as halo-, alkyl-, aryl- and alkoxy- silanes affording high yields and selectivities. In addition, all the hydrosilylation reactions were found to be very clean with the ease of product separation and purifications (Scheme 2). 

The inorganic nanobuilding blocks were found to be attached to the hard segments and greatly enhanced the tensile modulus and strength of the elastomer. Haddad et al. [Ill] and Fu et al. [128] have similarly provided works on condensation polymerization. The well-defined functionalized POSS have been prepared by the hydrosilylation reaction of terminal olefins with octahy-dridosilsesquioxane or direct hydrolytic condensation reactions of silanebearing compounds [75,100,129]. However, clear explanation on the mechanism of direct hydrolytic condensation reaction has not been explored yet. 

Numerous complexes of nickel(II) and nickel(O) catalyze the addition of the Si-H bond to olefins. Among such catalysts are nickel-phosphine complexes, e.g., Ni(PR3)2X2 (where X=C1, I, NO3 R=alkyl and aryl), Ni(PPh3)4, and Ni-(CO)2(PPh3)2, as well as bidentate complexes of NiCl2-(chelate) and Ni(acac)2L (I phosphine), and Ni(cod)2(Pr3)2 [1-5]. A characteristic feature of nickel-phosphine-catalyzed olefin hydrosilylation is side reactions such as H/Cl, redistribution at silicon and the formation of substantial amounts of internal adducts in addition to terminal ones [69]. Phosphine complexes of nickel(O) and nickel(II) are used as catalysts in the hydrosilylation of olefins with functional groups, e.g., vinyl acetate, acrylonitrile [1-4], alkynes [70], and butadiynes [71]. 

The Ziegler system ML -A1(C2H5)3 (M=Ni, Co or Fe n=2, 3 L=acac or Cl) has been used mostly in the addition of trialkyl and triphenylsilanes to conjugated dienes and trienes (especially Ni(acac)2-A1(C2H5)3) as well as in hydrosilylation of olefins with functional groups (the three-component system with additional PPh3) [2, 5]. 

Below we shall consider some experience acquired in carrying out reactions of catalytic and thermal solid-phase hydrosilylation with the participation of hydride-modified silicas, simple terminal olefins, and a number of functional compounds with double bonds. 

REACTIONS OF SOLID-PHASE CATALYTIC HYDROSILYLATION WITH THE PARTICIPATION OF HYDRIDE-MODIFIED SILICAS AND SOME FUNCTIONAL OLEFINS... 

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