Bis(pinacolato)diboron

Bis(pinacolato)diboron

Bis(pinacolato)diboron

Chemical compound

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.[1]

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Preparation and structure

This compound may be prepared by treating tetrakis(dimethylamino)diboron with pinacol in acidic conditions.[1] The B-B bond length is 1.711(6) Å.

Dehydrogenation of pinacolborane provides an alternative route:[2]

2 (CH3)4C2O2BH → (CH3)4C2O2B-BO2C2(CH3)4 + H2

Reactions

Pinacolborane is a closely related reagent.

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:[3]

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. [4]

References

  1. [1]
    Tatsuo Ishiyama; Miki Murata; Taka-aki Ahiko & Norio Miyaura (2004). "Bis(pinacolato)diboron". Organic Syntheses; Collected Volumes, vol. 10, p. 115.
  2. [2]
    Neeve, Emily C.; Geier, Stephen J.; Mkhalid, Ibraheem A. I.; Westcott, Stephen A.; Marder, Todd B. (2016). "Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse". Chemical Reviews. 116 (16): 9091–9161. doi:10.1021/acs.chemrev.6b00193. hdl:1807/78811. PMID 27434758.
  3. [3]
    Xinyu Liu "Bis(pinacolato)diboron" Synlett 2003, pp 2442–2443. doi:10.1055/s-2003-43344
  4. [4]
    "Bis(pinacolato)diboron, B2pin2".
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