Silicon-transition metal bonds cleavage

Scheme 60. Possible pathways for the electrophilic cleavage of silicon-transition metal bonds.

Cleavage of Silicon (or Germanium)-Transition Metal Bonds by... 

A related effect is that silicon-transition-metal compounds, once formed, undergo Si-M bond cleavage when dissolved in polar solvents (252,262,300,305,306,310). The products are often complex, but have been shown to include a cluster compound in one case involving cobalt (252). 

Transition metal-catalyzed cleavage of silicon-silicon and silicon-heteroatom bonds follo ved by addition of each component to triple bonds is an efficient method for the preparation of polyfunctional alkenylsilanes [44]. For example, (Z)-l-silyl-2-stannylethene 127, prepared by Pd-catalyzed silastannylation of ethyne with stannylsilane 126, is allowed to couple with two different aryl iodides step by step in one pot in the presence of BnPdCl(PPh3)2 and Cut as catalysts, giving rise to unsymmetrical (Z)-stilbene 129 (Scheme 5.33) [45],... 

Two closely related reactions, (a) and (b), illustrated by Eq. (12) (Rj = HPhj, Etj, Phj, CI3, CljPh) and (13), of silicon hydrides with transition metal complexes generate compounds with Si—M bonds with elimination of hydrogen (a) cleavage of metal-metal bonds and (b) reaction with transition metal hydrides. Reactions discussed in this section are relevant to... 

Direct Cleavage of Transition Metal-Silicon of Germanium Bonds. . . 93... 

The introduction of a group IV metal into transition metal complexes modifies the behavior of these complexes and a wide variety of reaction sites may result. Thus, reactions at silicon without cleavage of the transition metal-silicon bond are possible in some cases. 

One of the first observed C/Cl exchanges on Si mediated by a transition metal complex was the stoichiometric cleavage of the alkyne-silicon bond shown in Eq. (44) (28). In the presence of ethanol, the Si—Cl bond is solvolyzed and an active Pt species is formed with the liberation of diethyl ketal. Under these conditions, the process is catalytic and Zeise s salt (K[(C2H, )RC13 ]) is also an effective catalyst precursor [Eq. (45)]. 

Organosilanes bearing an electronegative heteroatom(s) at the a-carbon are susceptible to nucleophihc activation leading to silicon-carbon bond-cleavage, because of the electronic effect of the heteroatom. a-Heteroatom-substituted organosilanes are therefore quite valuable as protected carbon nucleophiles. The silicon-carbon bond is also readily activated by a transition metal complex. The reactivity is successfully utilized for catalytic carbon-carbon bond formation. 

A typical method of formation of a transition metal-silicon bond is the oxidative addition of silane derivatives, involving either Si-H or Si-Si bond cleavage, to a low valent, coordinatively unsaturated transition metal complex. Various kinds of transition metal silyl or silylene complexes have so far been synthesised via this method. However, in contrast to the rich chemistry of the late transition metal complexes with an M-Si bond, a limited number of syntheses of Group 6 metal complexes with an M-Si bond have been reported. ... 

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