Silicon—ruthenium bonds

The dicyclopentadienyl metal compounds undergo Friedel-Crafts alkylation and acylation, sulfonation, metalation, arylation, and formyla-tion in the case of ferrocene, dicyclopentadienyl ruthenium, and dicyclopentadienyl osmium, whereas the others are unstable to such reactions ( ). Competition experiments (128) gave the order of electrophilic reactivity as ferrocene > ruthenocene > osmocene and the reverse for nucleophilic substitution of the first two by n-butyl lithium. A similar rate sequence applies to the acid-catalysed cleavage of the cyclopentadienyl silicon bonds in trimethylsilylferrocene and related compounds (129), a process known to occur by electrophilic substitution for aryl-silicon bonds (130). 

Exhaustive cleavage of the carbon-silicon bond followed by treatment with an acid converted the complex benzo[f]furan 261 to phenol 262, as illustrated in Equation (154) <2003JA12994>. Villeneuve and Tam were able to interrupt this phenol formation by choosing Cp"Ru(COD)Cl as the catalyst. Thus, the reaction of 1,4-epoxy-1,4-dihydronaphthalene 263 with a ruthenium catalyst in 1,2-dichloroethane at 60 °C afforded the 1,2-naphthalene oxide 264 (Equation 155) <2006JA3514>. 

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. 

Our interest in silicon chemistry quite naturally led to a study of the hydrosilation reaction, the addition of the Si-H group across an olefin or an acetylene. This reaction is one of the most useful methods of making silicon-carbon bonds and is an important industrial process. Typically, homogeneous catalysts based on platinum, rhodium or ruthenium are used, and while very efficient, they are not recoverable(46). 

Among the latter group, iridium complexes (though less common than rhodium) and perhaps also ruthenium play crucial roles in many of the above-mentioned transformations of silicon compounds, leading to the creahon of sihcon-carbon bonds. Examples include the hydrosilylation or dehydrogenahve silylation of alkenes and alkynes, the hydroformylahon of vinylsilanes, and the silyhbrmylation of alkynes as well as activation of the sp C—H of arenes (by disilanes) and alkenes (by vinylsilanes). 

The silanol complex 57 exhibits a Si H M agostic interaction characterized by a /(Si-H) of 41 Hz and a Si-H distance of 1.70(7) It would be incautious to interpret such a low value of the Si-H coupling in terms of a significant Si-H bond activation, because the Si-H bond forms rather acute angles with the Si-C and Si-Si bonds (about 82 and 101°, respectively) and thus must have a considerable p character on silicon, which should contribute to the decrease of /(Si-H). The silanol ligand is -coordinate to ruthenium and the Ru-Si bond of 2.441(3) A is not exceptional, but the Si(SiMe3)3 deviates from the silanol plane by 19.0°, probably as a result of the Si-H interaction. Deprotonation of 57 by strong bases affords a neutral ruthenocene-like product. 

The search in recent years for silicon compounds with multiple bonds or cyclic n-systems has renewed interest in siloles (66)77 and their mono- and di-anions (48 and 49), and led to the successful isolation of stable silole anions coordinated to various metal counter ions (Li+, Na+, K+)10a-c 78 - 86 and as complexes with ruthenium (e.g. 6a and 6b)10d. 

When the silicon-transition-metal bond is reasonably strong, hydrogen attached to the metal may be replaced (mode 4b in Fig. 2) by halogens (entries 26,27, and 30) or deuterium (entry 29). In the case of the ruthenium example, halogenation can be followed by reductive elimination of RsSiH (226). 

An interesting diruthenium compound (entry 33) has the structure shown in (XLVII) the ring is planar, bisected by a metal-metal bond, and the Si-Ru distances vary noticeably according to their bridging or terminal position and, in the former case, whether they are trans to carbonyl or silicon. The remaining ruthenium derivatives in entries... 

In the presence of ruthenium, rhodium and cobalt complexes that initially contain or generate M-H and M-Si bonds, the divinylderivatives of silicon com-... 

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]. 

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