Addition of silanes

Composite or Filled Tooth Restorative Resins. Improvements in the properties of resin-based restoratives, brought about by the addition of silane-treated inorganic fillers to unfilled resins, has made these the primary anterior restorative material used today. 

The oxidative addition of silanes (with silicon-hydrogen bonds) to coordinatively unsaturated metal complexes is one of the most elegant methods for the formation of metal-silicon bonds. Under this heading normally reactions are considered which yield stable silyl metal hydrides. However, in some cases the oxidative addition is accompanied by a subsequent reductive elimination of, e.g., hydrogen, and only the products of the elimination step can be isolated. Such reactions are considered in this section as well. 

Reaction of aryl silanes with fluoride Addition of silanes to alkenes... 

Lewis acid-catalyzed hydrostannylation has been observed using ZrCl4. With terminal alkynes the Z-alkenylstannane is formed.142 These reactions are probably similar in mechanism to Lewis acid-catalyzed additions of silanes (see p. 811). 

In the mid 1980s, Voronkov, Lukevics, and coworkers published results demonstrating the strong preference of terminal alkynes to react in platinum catalyzed hydrosilylation in the presence of 1-olefinic groups [10, 11], Enynes were found to give hydrosilylation products predominantly by addition of silanes across the triple bond. To check the versatility of these promising results, 2-allyloxy-3-butyne was chosen as an enyne to be reacted with an a, ui-dihydropoly(dimethylsiloxane) under normal hydrosilylation conditions (10"3 mole percent Pt, 120°C) (Eq. 3). 

In addition to transition metals, recent work has demonstrated that strong Lewis acids will catalyze the addition of silanes to alkynes in both an intra- and an intermolecular fashion.14,14a-14c The formation of vinylsilanes from alkynes is possible by other means as well, such as the synthetically important and useful silylcupration15,15a of alkynes followed by cuprate protonation to afford vinylsilanes. These reactions provide products which can be complementary in nature to direct hydrometallation. Alternatively, modern metathesis catalysts have made possible direct vinylsilane synthesis from terminal olefins.16,16a... 

Free-radical-catalysed additions have also been reported, and provide a genuine alternative to the more familiar base-catalysed addition routes. Thus the secondary diphosphine (28) readily adds to diphenylvinylphosphine in the presence of AIBN to give (29).25 Similarly, addition of di(pentafluorophenyl)phosphine to diphenylvinylphosphine affords26 the diphosphine (30). Sequential addition of silanes and secondary phosphines to terminal aco-dienes under the influence of u.v. light affords the silylalkylphosphines (31), which may be anchored via silicon to the surface of inorganic oxides and used as polymeric catalysts.27... 

The main difference between Pt and Mn is that the platinum complex has 16 electrons and undergoes addition of silane before eliminating ethylene, following path 1... 

Rhodium(I) and ruthenium(II) complexes containing NHCs have been applied in hydrosilylation reactions with alkenes, alkynes, and ketones. Rhodium(I) complexes with imidazolidin-2-ylidene ligands such as [RhCl( j -cod)(NHC)], [RhCl(PPh3)2(NHC)], and [RhCl(CO)(PPh3)(NHC)] have been reported to lead to highly selective anti-Markovnikov addition of silanes to terminal olefins [Eq. 

Because of the chemical and structural differences of this coupling agent interphase layer, the mechanical properties of this region would be expected to be quite different from the bulk epoxy. Indeed, Lipatov 62) has shown that the addition of silanes changes the mechanical strength and chemical resistance of interphase regions. 

The diplatinum complexes [Pt(jU-H)SiR3(PCy3)]2 catalyze the addition of silanes R3SiH (R = Me, Et, PhCH2) Ph, OEt, Cl) to pentene-1, hexene-1, styrene, allyl chloride and 2-methylpropene. The relative reactivity order in silane is given, and the catalyst substrate ratio is 10-4-10-6 1. The majority of the reactions are carried out at ambient temperature and are exothermic. Dienes are also hydrosilylated.223 The complexes also catalyze the hydrosilylation of butyne-1, phenylacetylene, butyne-2 and diphenylacetylene in 70-90% yield. The... 

Abstract— The use of organosilanes as adhesion promoters for surface coatings, adhesives and syntactic foams is described and reviewed in the light of published work. Data are presented on the beneficial effect of silanes, when used as pretreatment primers and additives, on the bond strength of two pack epoxide and polyurethane paints applied to aluminium and mild steel. It is shown that silanes when used as additives to structural epoxide and polyurethane adhesives are less effective than when used as pretreatment primers on metals but are highly effective on glass substrates. The compressive properties of glass microballoon/epoxide syntactic foams are shown to be markedly improved by the addition of silanes. 

Geribaldi and coworkers have examined the oligomerization of SiH4 with the rare earth ions Sc+, Y+ and Lu+60,61a. In these FT-ICR studies, clustering of up to seven silane molecules around a metal ion was observed. In the additions of silane molecules to the metal center, the excess energy of the initial complex was found to be dissipated via sequential H2 loss, thus giving rise to MSi H2n + ions among various other products (equation 3). 

The addition of silanes across alkenes has been investigated both experimentally145 and theoretically.146 The effect of optically active thiol catalysts to catalyse radical hydrosilylation (polarity reversal catalysis) has been studied. The use of 2,3,4,6-tetra-O-acetyl-thio-jS-D-glucopyranose as the chiral thiol (used to reduce the intermediate carbon-based radicals) furnished the hydrosilylated alkenes in low to moderate enantiomeric excesses.145 In addition to this work a theoretical study on the reactions of SiH3 with ethene and propene has been undertaken using PMP2(6-31G ) and QCISD(T)(6-31G ) methods. Results indicated that the alkene-addition pathway is favoured over the alternative possible mode of reaction (H-abstraction). This is contrary to that previously suggested for the reaction of SiF with propene.146... 

During the last twenty years a very interesting addition of silanes across multiple bonds became familiar in organosilicon chemistry - hydrosilylation. 

When hydrosilane is used instead of hydrogen in the Rh-catalysed carbonylation of alkynes, the silylformylation of alkynes occurs to give the / -silyl-a,/ -unsaturated aldehydes 71 [38,39]. Oxidative addition of silane to Rh generates the silylrhodium hydride 69. It should be noticed that insertion of alkyne to the Rh-SiR.3 bond, but not... 

The addition of silane cross-linkable PE copolymer to PE/metallic hydroxide systems can significantly improve the flame-retardant properties of these materials allowing lower filler levels to be used.69... 

Hu S, Farrell GJ, Cook C, Johnston R, Butkey TJ. Rearrangement of rf-CpMn(CO)2(HSiEt3) a missing step in the energy surface for the oxidative addition of silane to CpMn(CO)2 (heptane). Organometallics 1994 13(11) 4127—4128. 

Scheme 2 depicts the two routes to introduction of organic functionality under discussion. The template in each case is a long-chain amine such as M-dodecylamine (we have also used n-decylamine and M-octylamine and other workers have used block copolymer materials as templates) in a solvent system of c. 50 50 ethanol water by volume. Addition of silanes and ageing for c. 18 h at room temperature affords the crude product from which the template can be removed by refluxing in a suitable solvent. 

The Grignard or lithium route is of limited value for the preparation of perfluoroalkyl derivatives. Much of the early work was concerned with the addition of silanes to fluorinated alkenes [88, 89], leading to the preparation of important fluorinated poly-siloxanes, manufactured by Dow Coming Co. (Figure 10.39). 

---