Silicon hydride reducing agent

Sodium borohydride seems less ready to cleave silicon-metal bonds (entries 81 and 82), and could be effective in selective reductions of the type shown above no other hydridic reducing agents seem to have been investigated in this context. 

The reaction of carbon-centered radicals with silicon hydrides is of great importance in chemical transformations under reducing conditions where an appropriate silane is either the reducing agent or the mediator for the formation of new bonds.23... 

This instability of silicon hydrides is not surprising in the laboratory these compounds are excellent reducing agents. However, the instability of the Si—H bond is disappointing because of the limitations it places on preparing silicon analogs of active carbon compounds. Most C—H bonds are stable in vivo, but a compound having a Si—H bond would be readily detoxified and eliminated. 

Silicon hydride reacts with bromine or iodine in solution with discoloration and is a strong reducing agent. All these properties and detailed studies of the oxidation of (SiH) led Schott and coworkers to conclude562, S64) that the silicon hydride isolated by them has an irregular structure. 

Silicon hydrides are an interesting class of carbonyl reducing agents as they are reasonably stable under normal conditions requiring activation with a transition metal complex,fluoride ion or Lewis acid. The correct choice of reaction conditions allows highly chemo- and stereo-selective reduction of particular classes of carbonyl compounds with these convenient reagents. 

Group 14 metal hydrides, especially those of silicon and tin, are satisfactory nonreactive hydride donors, as in the absence of a catalyst they are, generally, poor reducing agents. Transition metal complexes are attractive transfer agents because they insert readily into Si—H or Sn—bonds and they also bind specifically to various functional groups. 

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