Bis(pinacolato)diboron

Bis(pinacolato)diboron is a covalent compound containing two boron atoms and two pinacolato ligands. It has the formula [(CH3)4C2O2B]2; the pinacol groups are sometimes abbreviated as "pin", so the structure is sometimes represented as B2pin2. It is a colourless solid that is soluble in organic solvents. It is a commercially available reagent for making pinacol boronic esters for organic synthesis. Unlike some other diboron compounds, B2pin2 is not moisture-sensitive and can be handled in air.

Preparation and structure
This compound may be prepared by treating tetrakis(dimethylamino)diboron with pinacol in acidic conditions. The B-B bond length is 1.711(6) Å.

Dehydrogenation of pinacolborane provides an alternative route:
 * 2(CH3)4C2O2BH → (CH3)4C2O2B-BO2C2(CH3)4 + H2

Reactions
The B-B bond adds across alkenes and alkynes to give the 1,2-diborylated alkanes and alkenes. Using various organorhodium or organoiridium catalysts, it can also be installed onto saturated hydrocarbons:
 * CH3(CH2)6CH3 + [pinB]2 → pinBH + CH3(CH2)7Bpin

These reactions proceed via boryl complexes. Bis(pinacolato)diboron can also be used as reducing agent for example in transition metal catalyzed hydrogenations of alkenes and alkynes.