Hydrosilylation phenylacetylene

Complexes 59 and 60 catalyse the hydrosilylation of phenylacetylene (but not other terminal alkyl alkynes) with HSi(Me)jPh. Generally, the Rh analogue is more active than the relative Ir. Both catalysts gave mixtures of all regioisomers, with a preference for the p-Z-isomer, in contrast to what has been reported with other non-NHC cationic complexes of Rh, where the p-f isomers are predominating. Here also the exact nature of the catalytic species is unclear [48],... 

Recently, a proposal has been put forth that a /raor-addition process may be possible through dinuclear ruthenium intermediates.34 As shown in Scheme 5, reaction of tetraruthenium aggregate A with phenylacetylene results in the fully characterized bridging dinuclear alkenyl complex B. The authors propose a direct /ra .r-dclivcry of hydride through a dinuclear intermediate may be active in the hydrosilylation catalyzed by A, though compound B itself is unreactive to Et3SiH. 

The robustness and excellent turnover numbers of platinum complexes with terminal alkynes have made it the catalyst of choice for the synthesis of polymers and other macromolecular architechtures. Alkyne hydrosilylation with platinum has also served as a key element in the synthesis of dendrimers. Sequential reaction of an alkyne with HSiMeCl2 and lithiated phenylacetylene afforded the branching unit of a dendrimer synthesis which has been used to afford a large variety of structures at high generation.44,4411 441 ... 

Over the past decade, literally dozens of new AB2-type monomers have been reported leading to an enormously diverse array of hyperbranched structures. Some general types include poly(phenylenes) obtained by Suzuki-coupling [54, 55], poly(phenylacetylenes prepared by Heck-reaction [58], polycarbosilanes, polycarbosiloxanes [59], and polysiloxysilanes by hydrosilylation [60], poly(ether ketones) by nucleophilic aromatic substitution [61] and polyesters [62] or polyethers by polycondensations [63] or by ring opening [64]. 

It is Hkely that the diene also remains coordinated during the hydrosilylation reactions of phenylacetylene with HSiEts, catalyzed by [Ir(diene)(NCMe)(PR3)]BF4 complexes [PR3 = P Pr3, PMe3 diene = 1,5-cyclo-octadiene, tetraflorobenzobarre-lene (TFB)]. However, detailed studies on the [Ir(COD)(NCMe)(PMe3)]BF4 complex show that cyclo-octadiene carmot be considered, in this case, as an ideal innocent Hgand because it transform into complexes containing cyclo-octadiene, cyclo-octadienyl or cyclo-octenyl Hgands in a variety of coordination modes, due to an... 

Computational and catalytic studies of the hydrosilylation of terminal alkynes have been very recently reported, with the use of [ Ir( r-Cl)(Cl)(Cp ) 2] catalyst to afford highly stereoselectively P-Z-vinylsilanes with high yields (>90%) [35]. B-isomers can be also found among the products, due to subsequent Z —> E isomerization under the conditions employed. The catalytic cycle is based on an lr(lll)-lr(V) oxidahve addition and direct reductive elimination of the P-Z-vinylsilane. Other iridium complexes have been found to be active in the hydrosilylation of phenylacetylene and 1-alkynes for example, when phenylacetylene is used as a substrate, dehydrogenative silylation products are also formed (see Scheme 14.5 and Table 14.3). 

K over the range 298-398 K. Partition eoeffieients for HFeCU between water and 1-octanol or dibutyl ether depend markedly on HCl and LiCl concentrations. For dibutyl ether as organic phase there is also a dependence of partition coefficient on Fe " " concentration as there is significant polynuclear complex formation in the ether layer. [FeCU] , in the form of its Et3BzN" salt, acts as a bifunctional or phase transfer catalyst for hydrosilylation of phenylacetylene. ... 

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... 

Dehydrogenative silylation has also been observed for terminal alkyne substrates. Doyle and co-workers reported in 1991 that a small amount (6%) of alkynylsilane was observed in the product mixture that results from reaction of phenylacetylene and Et3SiH catalyzed by Rh2(pfb)4.41 The remaining components of the product mixture resulted from hydrosilylation. Crabtree and co-workers have found that in reaction of terminal alkynes with various tertiary silanes, dehydrogenative silylation can become the predominant route, depending on reaction conditions [Eq. (7)].42... 

Exclusive polymerization of phenylacetylene takes place, unexpectedly, under hydrosilylation conditions in the presence of a zwitterionic Rh(I) complex, [Rh(COD)]+BPh4, and HSiEt3 to give all-ds-poly(phenylacetylene)285. 

Instead of adding two hydrogen atoms to an alkynyl silane we could add H and SiMe3 to a simple alkyne by hydrosilylation (addition of hydrogen and silicon). This is a cis addition process catalysed by transition metals and leads to a tram (E-) vinyl silane. One of the best catalysts is chloroplatinic acid (H2PtCl6) as in this formation of the E-vinyl silane from phenylacetylene. In this case photochemical isomerization to the Z-isomer makes both available. Other than the need for catalysis, this reaction should remind you of the hydroboration reactions earlier in the chapter. The silicon atom is the electrophilic end of the Si-H bond and is transferred to the less substituted end of the alkyne. 

Direct observation of seven intermediates involved in the hydrosilylation and dehydrogenative silylation of phenylacetylene by an lr"-NHCtype catalyst allowed the elucidation of both the hydro- and dehydrogenative silylation mechanisms (Scheme 5) [ 12], Analysis of fragmentation patterns produced by MS/MS experiments provided insight into the connectivity of species [1] and [111] where the mass assignment itself was ambiguous. Use of the modified substrate 4-aminophenylacetylene, which is visible by ESl-MS, confirmed formation of the products and indicated the dominant mechanism under each set of reaction conditions. 

Phenylacetylene did not form an adduct under similar conditions. The complex between 1,2-bis(dimethylphosphino)-1,2-dicarbaclosododeca-borane with nickel(II) chloride effectively catalyzed the hydrosilylation of olefins (209). Catalysis by this nickel complex differed, however, in that considerable amounts of internal adducts were formed ... 

A successful study of non-phosphine iridium complexes Ir", Ir , and Ir e. g., IrX(cod)2 [60], IrH2(triso)(SiMePh2)2 [61, 62], Ir(triso)(coe)2 (coe = cyclooctene triso = tris(diphenyloxophosphoranyl)methanide), Ir(triso)(C2H4)2 [61], has demonstrated effective hydrosilylation of alkenes and alkynes. Iridium phosphine complexes, e. g., Ir(C=CPh)(CO)2PCy2 [63] and IrCl(CO)(PPh3)2 [64], are also found to be active for hydrosilylation of phenylacetylene and 1-hexyne. 

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. 

Reaction of [l,2,3]selenadiazole 281 with tetrakis(triphenylphosphine)platinum leads to the formation of a novel selenoplatinum catalyst 283 <05TL1001>. This complex has been used as a catalyst for the hydrosilylation of terminal alkynes. Both 3,3-dimethylbut-l-yne and trimethylsilylacetylene undergo regioselective and sterereoselective hydrosilylation with dimethylphenylsilane in the presence of 0.0002 mol% of 283 to afford (E)-285 in good yields. In the case of phenylacetylene, the hydrosilylation is regioselective however, the stereoselectivity is reduced to 5 1 (E Z). 

The hydrosilylation of phenylacetylene with phenyldimethylsilane catalyzed by RhCl(PPh3)3 or RhCl(CO)(PPh3)2 gives j3-silylstyrene with only a small amount of a-silylstyrene in excellent yield65. The stereochemistry of the reaction is found to depend markedly upon the reaction temperature and the amounts of the catalyst (equation 16). 

The intermediacy of the complex [Os(SiEt3)Cl(H2)(CO)(P Pr3)2] in the catalytic hydrosilylation of phenylacetylene was first observed by Oro and co-workers when the neutral hydride [OsHCl(CO)(P Pr3)2] was reacted with triethylsilane and the alkyne [81]. A theoretical study of silane addition across the C-C triple bond has also been reported [82] and the general scope of this reaction has been amply reviewed [17],... 

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