Addition of Si-H bond

Complex (92) has been obtained from the reaction of 1,2-disilylbenzene and [Ni(dmpe)2] at 80°C.315 The reaction is assumed to proceed via oxidative addition of Si—H bonds and subsequent elimination of H2, and some intermediates have been detected spectroscopically. (92) is described as a Nilv species, but care has to be taken, since a related hexasilylpalladium complex, initially formulated as PdVI,316 should better be viewed as Pd11 with two side-on bound Si—Si... 

The addition of Si—H bonds and the reactions of silyls with platinum complexes is of significance because of the early discovery of chloroplatinic acid as a hydrosilylation catalyst.53 This section focuses on the formation of hydrides from silanes. 

Olefins usually give the terminal product. The reaction is catalyzed by transition metal complexes, e.g., H2Ptd6 or RhCl(PPh3)3 it may involve the oxidative addition of Si—H bonds across a transition metal as shown in Fig. 8-2. 

Addition of Si-H bonds to aUcene can take place either in an anti-Markovnikov (P-addition) fashion resulting in silicon being attached at the terminal position or in Markovnikov (a-addition) fashion resulting in silicon bonded to the iso-position of the 1,2 alkene. Moreover, as stated in the introduction, regioselectivity of organic incorporations into the silicones was reported to play a crucial role in... 

Hydrogenation may be considered a specific case of the addition of H X molecules to unsaturates where X = H. There has been of late considerable interest in developing systems for which X can be a number of other elements. One of the goals of research into C-H activation (discussed in the next section) is to develop catalysts for the addition of C H bonds to unsaturates. While this goal has not been met, the addition of Si-H bonds to unsaturates may be accomplished withanumberofiridium complexes as catalysts. Although iridium complexes are not among the most active for hydrosilation, there are a number of active ones and studies into the interactions of iridium with silanes has provided useful information about important steps in catalytic hydrosilation. 

The synthesis of molybdocene compounds containing a Mo-Si bond commonly proceeds via the oxidative addition of Si-H bonds to the 16 VE molybdocene fragment (vide infra). We present a new and very convenient synthetic approach to complexes of this type [6],... 

Additions of Si-H bonds to alkynes occur under similar conditions and with the same catalysts as hydrosilation of alkenes. Free radical addition to terminal alkynes gives cis products by a stereospecific terminal trans addition . Supported platinum catalysts give trans products by a terminal cis addition . Chloroplatinic acid catalyzed additions to terminal alkynes give mixtures of trans-1-alkenylsilanes and trans-2-alkenylsilanes in a ratio ranging from 1 1 to 1 5 depending on the substituents on silicon . Addition of SiH2Cl2 to CH2=CHC(CH3)3 gives trans-1-alkenyl- and bis(trans-l-alkenyl)silane products, but no (2-alkenyl)silane °. Internal alkynes react more slowly than terminal alkynes, and even reactions catalyzed by chloroplatinic acid require heat. 

The addition of Si-H bonds to organic unsaturations such as olefins, acetylenes, and ketones is known as the hydrosilation reaction. A majority of the hydrosilation reactions are catalyzed by soluble transition-metal complexes and are known as homogeneous hydrosilation reactions [43]. Catalytic hydrosilation reactions are known to be very complex reactions. However, a few generalizations have been drawn about the mechanism of such reactions (Figure 15.4). Homogeneous olefin hydrosilation are presumed to start with an obligatory oxidative addition of the Si-H bond in a cis fashion to the catalytic metal [44]. This process is followed... 

The addition of Si—H bonds to olefins and acetylenes is of some importance industrially in the production of intermediates for silicone manufacture. 

Two isomers of the cationic rhodium cluster [( /-Cp)2Rh3(CO)(CF3Cs CCF3)(CNR)3]PFe exist in solution. The major isomer is fluxional and its limiting low-temperature NMR spectrum is consistent with an unsymmetrical structure in which the alkyne is a-bonded to one (f/-Cp)Rh —Rh(CNR)3 bond and 7t-bonded to the remaining (/j-CpjRh. The mixed rhodium/ silicon trinuclear cluster [Rh2(//-SiRH)(H)2(CO)2(dppm)2] exhibits exchange between Si —H and Rh—H protons, presumably by facile reductive elimina-tion/oxidative addition of Si—H bonds to the Rh centers (Scheme 28). ... 

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