Silylenes with ruthenium

Silylene 1 reacts with Fe(CO)s or Fe2(CO)9 to give the complex (l)Fe(CO)4, also reported earlier [2], With ruthenium pentacarbonyl, however, 1 reacts with removal of two CO groups, yielding (1)2Ru(CO)3 [9], This complex has an unusual unit cell containing two different structures. As shown in Fig. 5, both kinds of molecules have essentially a trigonal bipyramidal geometry, but in half of the molecules two CO groups occupy the (near) axial positions, and in the other half the silylenes take the (near) axial sites. 

Carbene and silylene complexes - Carbene complexes of ruthenium [312] and osmium [313] porphyrins were formed from the neutral dimers [M(P)]2 with diazoalkanes (Eq. 26). 

The coordination of stable silylenes to metal complexes was also reported to produce transition metal silylenoids.40,41 Exposure of unsaturated silylene 16 to Ni(CO)4 resulted in the formation of the disilylene-substituted tetrahedral nickel complex 17 (Scheme 7.3).42,43 Similarly, mixing Ph PAuCI with decamethylsilico-cene 18 produced the silylgold complex 19.44 The 29 Si H NMR spectrum of 19 (8 78 ppm) revealed its silylenoid character. In addition to nickel and gold, other metals, including tungsten,41 platinum,45 iron,40 and ruthenium,46 have been utilized to form silylmetal complexes of stable silylenes. 

In addition to ruthenium, Tilley and coworkers also reported that cationic iridium silylenoid complexes were efficient olefin hydrosilation catalysts [reaction (7.6)].56 This silylene complex catalyzes the hydrosilation of unhindered mono- or disubsti-tuted olefins with primary silanes to produce secondary silanes with anti Markovni-kov selectivity. Iridium catalyst 32 exhibited reactivity patterns similar to those of ruthenium 30 only primary silanes were allowed as substrates. In contrast to 30, cationic iridium 32 catalyzed the redistribution of silanes. Exposing phenylsilane to 5 mol% of 32 in the absence of olefin produced diphenylsilane, phenylsilane, and silane. 

In the silylative coupling reactions of olefins and dienes with vinylsubsti-tuted silanes, ruthenium catalysts, containing initially or generating in situ Ru-H/Ru-Si bonds, catalyze polycondensation of divinylsubstituted silicon compounds to yield unsaturated silylene (siloxylene, silazanylene)-vinyl-ene-alkenylene (arylene) products (Eq. 112). For recent results see Refs. [177, 178] and for reviews see Refs. [6,7,117,118]. 

A second type of reactive metal-silicon bond involves multiple bonding, as might exist in a silylene complex, LnM=SiR2. The synthesis of isolable silylene complexes has led to the observation of new silicon-based reactivity patterns redistribution at silicon occurs via bi-molecular reactions of silylene complexes with osmium silylene complexes, reactions have been observed that mimic proposed transformations in the Direct Process. And, very recently, ruthenium silylene complexes have been reported to be catalytically active in hydrosilylation reactions. 

The reactivity of metal-silylene complexes is more limited than the reactivity of carbene complexes. The cationic base-stabilized ruthenium-silylene complex in Equation 13.37 does not react with olefins or alkynes to undergo [2-1-2] addition reactions. However, a related complex did undergo [2-1-2] addition reactions with isocyanates, as shown in Equation 13.46. Other reactions of silylene complexes are distinct from those of carbene complexes or those of other conventional organometallic compounds. For example, the reaction of the silylene hydride with an acetylene generates a p-silylvinylarene complex... 

The polymer showed significantly high thermal stability and was not decomposed even at 400°C (77). It was reported that poly(silylenephenylene)s can be S5m-thesized from the reaction of dichloromethylsilane or dicblorophenylsilane with p- and m-diUthiobenzene (78). An efficient method to prepare poly(silylene-m-phenylene) (12)(Afw = 4000-20,000), that is, a ruthenium-catalyzed desilylative condensation of m-bis(trihydrosilyl)benzene (eq. 12), was reported (79). 

The reaction of the bis(silylene)-ruthenium complex [Ru / (3 /,3 /)-(SiMe2)20Me Gp(PPh3)] 183 with methanol affords the hydrido-bis(silyl)-Ru(iv) derivative 186 which, in the presence of a large excess of methanol, is slowly... 

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