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.2 The B-B bond length is 1.711(6) Å.
Dehydrogenation of pinacolborane provides an alternative route:3
2 (CH3)4C2O2BH → (CH3)4C2O2B-BO2C2(CH3)4 + H2Reactions
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:4
CH3(CH2)6CH3 + [pinB]2 → pinBH + CH3(CH2)7BpinThese 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. 5
References
Tatsuo Ishiyama; Miki Murata; Taka-aki Ahiko & Norio Miyaura (2004). "Bis(pinacolato)diboron". Organic Syntheses; Collected Volumes, vol. 10, p. 115. /wiki/Norio_Miyaura ↩
Tatsuo Ishiyama; Miki Murata; Taka-aki Ahiko & Norio Miyaura (2004). "Bis(pinacolato)diboron". Organic Syntheses; Collected Volumes, vol. 10, p. 115. /wiki/Norio_Miyaura ↩
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. https://doi.org/10.1021%2Facs.chemrev.6b00193 ↩
Xinyu Liu "Bis(pinacolato)diboron" Synlett 2003, pp 2442–2443. doi:10.1055/s-2003-43344 /wiki/Doi_(identifier) ↩
"Bis(pinacolato)diboron, B2pin2". https://www.organic-chemistry.org/chemicals/reductions/bis(pinacolato)diboron-B2pin2.shtm ↩