Catecholborane (abbreviated HBcat) is an

organoboron compound Organoborane or organoboron compounds are chemical compounds of boron and carbon that are organic derivatives of BH3, for example trialkyl boranes. Organoboron chemistry or organoborane chemistry is the chemistry of these compounds. Organoboron ...

that is useful in

organic synthesis Organic synthesis is a special branch of chemical synthesis and is concerned with the intentional construction of organic compounds. Organic molecules are often more complex than inorganic compounds, and their synthesis has developed into one o ...

. This colourless liquid is a derivative of

catechol Catechol ( or ), also known as pyrocatechol or 1,2-dihydroxybenzene, is a toxic organic compound with the molecular formula . It is the ''ortho'' isomer of the three isomeric benzenediols. This colorless compound occurs naturally in trace amoun ...

and a

borane Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula . The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemistry of boranes, as it indicated ...

, having the formula C₆H₄O₂BH.

Synthesis and structure

Traditionally catecholborane is produced by treating catechol with

(BH₃) in a cooled solution of

THF Tetrahydrofuran (THF), or oxolane, is an organic compound with the formula (CH2)4O. The compound is classified as heterocyclic compound, specifically a cyclic ether. It is a colorless, water- miscible organic liquid with low viscosity. It is ...

. However, this method results in a loss of 2 mole equivalents of the hydride. Nöth and Männig described the reaction of alkali-metal boron hydride (LiBH₄, NaBH₄, of KBH₄) with tris(catecholato)bisborane in an ethereal solvent such as

diethyl ether Diethyl ether, or simply ether, is an organic compound in the ether class with the formula , sometimes abbreviated as (see Pseudoelement symbols). It is a colourless, highly volatile, sweet-smelling ("ethereal odour"), extremely flammable liq ...

. In 2001, Herbert Brown and coworkers prepared catecholborane by treatment of tri-''o''-phenylene bis-borate with

diborane Diborane(6), generally known as diborane, is the chemical compound with the formula B2H6. It is a toxic, colorless, and pyrophoric gas with a repulsively sweet odor. Diborane is a key boron compound with a variety of applications. It has attracte ...

. Unlike borane itself or alkylboranes, catechol borane exists as a monomer. This behavior is a consequence of the electronic influence of the aryloxy groups that diminish the Lewis acidity of the boron centre.

Pinacolborane Pinacolborane is the borane Trihydridoboron, also known as borane or borine, is an unstable and highly reactive molecule with the chemical formula . The preparation of borane carbonyl, BH3(CO), played an important role in exploring the chemist ...

adopts a similar structure.

Reactions

Catecholborane is less reactive in hydroborations than borane-THF or borane-dimethylsulfide. When catecholborane is treated with a terminal

alkyne \ce \ce Acetylene \ce \ce \ce Propyne \ce \ce \ce \ce 1-Butyne In organic chemistry, an alkyne is an unsaturated hydrocarbon containing at least one carbon—carbon triple bond. The simplest acyclic alkynes with only one triple bond and n ...

, a trans vinylborane is formed: :C₆H₄O₂BH + HC₂R → C₆H₄O₂B-CHCHR The product is a precursor to the

Suzuki reaction The Suzuki reaction is an organic reaction, classified as a cross-coupling reaction, where the coupling partners are a boronic acid and an organohalide and the catalyst is a palladium(0) complex. It was first published in 1979 by Akira Suzuki, ...

. Catecholborane may be used as a

stereoselective In chemistry, stereoselectivity is the property of a chemical reaction in which a single reactant forms an unequal mixture of stereoisomers during a non-stereospecific creation of a new stereocenter or during a non-stereospecific transformation of ...

reducing agent In chemistry, a reducing agent (also known as a reductant, reducer, or electron donor) is a chemical species that "donates" an electron to an (called the , , , or ). Examples of substances that are commonly reducing agents include the Earth meta ...

when converting β-hydroxy ketones to syn 1,3-diols. Catecholborane oxidatively adds to low valent metal complexes, affording

boryl complex In chemistry, a transition metal boryl complex is a molecular species with a formally anionic boron center coordinated to a transition metal. They have the formula LnM-BR2 or LnM-(BR2LB) (L = ligand, R = H, organic substituent, LB = Lewis base). ...

es.{{cite journal , doi=10.1021/acs.chemrev.6b00193, title=Diboron(4) Compounds: From Structural Curiosity to Synthetic Workhorse, year=2016, last1=Neeve, first1=Emily C., last2=Geier, first2=Stephen J., last3=Mkhalid, first3=Ibraheem A. I., last4=Westcott, first4=Stephen A., last5=Marder, first5=Todd B., journal=Chemical Reviews, volume=116, issue=16, pages=9091–9161, pmid=27434758, doi-access=free :C₆H₄O₂BH + Pt(PR₃)₂ → (C₆H₄O₂B)Pt(PR₃)₂H

References

Benzene derivatives Organoboron compounds Boranes