right|thumb|150x150px|Organoboron
Organoboron chemistry or organoborane chemistry studies organoboron compounds, also called organoboranes. These chemical compounds combine boron and carbon; typically, they are organic derivatives of borane (BH<sub>3</sub>), as in the trialkyl boranes. A chiral example is monoisopinocampheylborane, obtained by hydroboration of (−)‐α‐pinene with borane dimethyl sulfide. Although often written as IpcBH<sub>2</sub>, it is a dimer, [IpcBH<sub>2</sub>]<sub>2</sub>.
Dialkylboranes are also rare with small alkyls. One common preparation reduces dialkylhalogenoboranes with metal hydrides. An important application in organic synthesis is transmetallation to form organozinc compounds. Nevertheless, some diaryl and dialkylboranes are well known. Dimesitylborane is a dimer (C<sub>6</sub>H<sub>2</sub>Me<sub>3</sub>)<sub>4</sub>B<sub>2</sub>H<sub>2</sub>) that reacts only slowly with simple terminal alkenes. It adds to alkynes to give alkenylboranes. A hindered dialkylborane is disiamylborane, abbreviated Sia<sub>2</sub>BH, also a dimer. Owing to its steric bulk, it selectively hydroborates less hindered, usually terminal alkenes in the presence of more substituted alkenes. Disiamylborane must be freshly prepared as its solutions can only be stored at 0 °C for a few hours. Dicyclohexylborane Chx<sub>2</sub>BH exhibits improved thermal stability than Sia<sub>2</sub>BH.
A versatile dialkylborane is 9-BBN. Also called "banana borane", it exists as a dimer. It can be distilled without decomposition at 195 °C (12mm Hg). Reactions with 9-BBN typically occur at 60–80 °C, with most alkenes reacting within one hour. Tetrasubstituted alkenes add 9-BBN at elevated temperature. Hydroboration of alkenes with 9-BBN proceeds with excellent regioselectivity. It is more sensitive to steric differences than Sia<sub>2</sub>BH, perhaps because of it rigid C<sub>8</sub> backbone. 9-BBN is more reactive towards alkenes than alkynes.
Oxyacids and esters
Compounds of the type BR<sub>n</sub>(OR)<sub>3-n</sub> are called borinic esters (n = 2), boronic esters (n = 1), and borates (n = 0). Boronic acids are key to the Suzuki reaction. Trimethyl borate, debatably not an organoboron compound, is an intermediate in sodium borohydride production.
Adducts
Boranes and borinic, boronic, and borate esters all form adducts with appropriate Lewis bases.
Strong bases do not deprotonate boranes of the form R<sub>2</sub>BH. Instead these reactions afford the octet-complete adduct R<sub>2</sub>HB-base.
Boryl complexes and radicals
Organometallic compounds with metal-boron bonds (M–BR<sub>2</sub>) are boryl complexes, corresponding to the notional boryl anion R<sub>2</sub>B<sup>−</sup>, although the latter cannot be produced through deprotonation (see ). In one synthesis, the boryl anion moiety arose through lithium-halogen exchange: alt=Boryllithium|center|400x400px As shown, the product is isoelectronic to an N-heterocyclic carbene. Neutral analogues use NHC adducts, such as the following diborane(2) derivative: and boranylium ions are based on similar chemistry,
A compound with the B≡C triple bond was synthesized for the first time in 2025.
Synthesis
From Grignard reagents
Simple organoboranes such as triethylborane or tris(pentafluorophenyl)boron can be prepared from trifluoroborane (in ether) and the ethyl or pentafluorophenyl Grignard reagent. Further carbanion addition will effect a borate (R<sub>4</sub>B<sup>−</sup>).
Boronic acids RB(OH)<sub>2</sub> react with potassium bifluoride K[HF<sub>2</sub>] to form trifluoroborate salts K[RBF<sub>3</sub>], in borates, the nucleophicity suffices for intermolecular transfer to an electrophile.
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Tertiary alcohols with two identical groups attached to the alcohol carbon may be synthesized through an alkynylborane double migration:
References
Further reading
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