Ruthenium silyl complexes

Very recently, Berry and coworkers reported the formation of a ruthenium-silene complex from (PMe3)4RuHSiMe3 and BPh4, and they observed the interconversion between silene and a 16-electron ruthenium silyl complex (Eq. 12) [13a]. 

Reactions of the silene hydride complex Cp Ru(P(Pr-/)3)(I I)(r 2-C.I I2=SiPh2) with hydrosilanes proceed via an initial migration of the hydride to the silene ligand, affording as the final products either the disilyl hydride or the mono silyl dihydrido ruthenium(IV) complexes as described in Scheme 21. Similar reductive elimination and... 

In contrast to the silyl-ruthenium complexes including triisopropylphosphine, the ruthenium hydride complex with triphenylphosphine directs the stereoselectivity toward the E product according to Eq. (14) (Table 2) [27]. 

Many ruthenium complexes have been tested in the silylative coupling reaction. In the synthetic procedure the absence of by-products of the homocoupling of vinylsilanes is required so an excess of the olefin has usually been used. However, the screening tests performed at the 1 1 ratio of styrene and phenyldimethylvinylsilane with a variety of ruthenium catalysts have shown that pentacoordinated monocarbonyl bisphosphine complexes appear to be the most active and selective catalysts of which RuHCl(CO)(PCy3)2 has shown high catalytic activity under conditions of catalyst loadings as low as 0.05 mol % [55]. Cuprous salts (chloride, bromide) have recently been reported to be very successful co-catalysts of ruthenium phosphine complexes, markedly increasing the rate and selectivities of all ruthenium phosphine complexes [54]. 

Organosubstituted octasilsesquioxanes (Fig. lb) have also been prepared by cross-metathesis (CM) and silylative coupling of vinylsilsesquioxane with olefins in the presence of the ruthenium carbene complex Cl2(PCy3)2Ru(=CHPh) (Grubbs catalyst) and Ru-H (Ru-Si) complexes, for example, RuHCl(CO)(PCy3)2, respectively [57]. 

Terminal alkynes and terminal alkenes can be selectively transformed into disubstituted dienes in the presence of ruthenium carbene complexes [94-96]. Reactions of a series of alkynes with H2C=CHCH2SiMe3 lead to silyl-substi-tuted conjugated dienes. 

The relative ease of ring formation from dienes decreases in the order six->seven->five-membered rings. Hoshi et al. [138] have recently reported the synthesis of a number of disilacycloalkenes via RCM of bis(allyldimethyl-silyl)substituted compounds, with the ruthenium vinylcarbene complex Cl2(PCy3)2Ru(=CHCH=CPh2) used as a catalyst. Successful formation of seven-and eight-membered rings has been achieved under mild reaction conditions. 

The ruthenium carbene complex (Grubbs catalyst) which has shown high efficiency in alkene methathesis and related processes, since it displays tolerance toward a wide variety of common functional groups, has also appeared of synthetic utility in the hydrosilylation of ketones to yield silyl ethers-one of the most widely used classes of protecting groups in synthetic chemistry (Eq. 97) [ 151 ]. The reaction requires temperatures above 50 °C, which generate a slightly increased amount of silylated by-products. 

Acetylenic silyl ethers are converted to the conjugated dienol silyl ethers by the catalysis of ruthenium hydride complexes (Eq. 12.8). 

Allyl silyl ethers 29 derived from the corresponding allylic alcohols 28 are selectively isomerized to silyl enol ethers 30 via carbon-carbon double bond migration catalyzed by a ruthenium hydride complex, RuH2(PPh3)4 (Eq. 12.11) [17], The generality of the reaction was demonstrated for the silyl ethers of methallyl alcohol, ciima-myl alcohol, 2,4-pentadienyl alcohol, and so on. 

It is well known that silylation of allyl derivatives with vinylsilane catalyzed by a ruthenium hydride complex is accompanied by isomerization ofpropen-l-yl to propen-2-yl derivatives as well as homo-coupling of vinylsilane when equimolar amounts of the initial substances are used. If catalyst I was used in the SC of allyl amide and allyl amine with vinylsilanes, a S-fold excess of olefin to vinylsilane was used to stop homocoupling of vinylsilane, but simultaneously no more than 5% of isomerization of allyl compound was observed [19, 26]. When allyl boronate is used instead of allylamine under mild conditions (20 - 40 °C), the two reactions catalyzed by I and IV yield stereoselectively -product (see Scheme 4) [26]. 

Therefore, the aim of this work was to synthesize new silacyclic and oligomeric organosilicon compounds containing easily modifiable Sl-O-R bonds, via competitive silylative coupling cyclization and polycondensation of divlnyl-substltuted silyl ethers in the presence of ruthenium hydride complex. 

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