Addition of Boron Hydrides to Alkenes. Organoboranes

An especially valuable group of intermediates can be prepared by addition 

The reaction is called hydroboration and is a versatile synthesis of organoboron compounds. One example is the addition of diborane, B2H6, to ethene. Di-borane behaves as though it is in equilibrium with BH3 (B2H6 = 2BH3), and addition proceeds in three stages  

CH2=CH2 + BH3 (from B2H6) — CH3CH2BH2 ethylborane CH2=CH2 + CH3CH2BH2 — (CH3CH2)2BH diethylborane CH2=CH2 + (CH3CH2)2BH — (CH3CH2)3B triethylborane 

The monoalkylborane, RBH2, and the dialkylborane, R2BH, seldom are isolated because they rapidly add to the alkene. These additions amount to reduction of both carbons of the double bond  

Organoboranes can be considered to be organometallic compounds. Elemental boron does not have the properties of a metal, and boron-carbon 

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