B2 Reactions of organoboranes

The empty p orbital on the boron atom of organoboranes renders them electrophilic and highly susceptible to attack by nucleophiles. The tetrahedral species so formed is known as an organoborate (Equation B2.1). 

As will be seen below and in following chapters, attack by nucleophiles and subsequent 1,2-migration reactions dominate much of the reactivity of organoboranes. 

Boron-oxygen bond strengths (480-565 kJ mol 1) are greater than boron-carbon bond strengths (350-400 kJ mol 1). This reflects an interaction between the empty p orbital on boron and an electron pair in one of the oxygen s two filled non-bonding sp3 orbitals. 

Oxidation of alkylboranes by alkaline hydrogen peroxide produces alcohols. The reaction is essentially quantitative and has been successfully applied to a wide variety of alkylboranes (Equations B2.3-5). It is important to note that the stereochemistry of the carbon atom attached to the boron atom is retained in this conversion of a carbon-boron bond to a carbon-oxygen bond (Equation B2.5). 

On combination with alkene hydroboration, the resulting two-step process is a very important, widely-used transformation which may be regarded as anft-Markovnikov hydration of the alkene (Equation B2.6). 

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