Aborane is a compound with the formulaBRxHy although examples include multi-boron derivatives. A large family ofboron hydride clusters is also known. In addition to some applications inorganic chemistry, the boranes have attracted much attention as they exhibit structures and bonding that differs strongly from the patterns seen in hydrocarbons. Hybrids of boranes and hydrocarbons, thecarboranes, are also a well developed class of compounds.[1]
The development of the chemistry of boranes led to innovations in synthetic methods as well as structure and bonding. First, new synthetic techniques were required to handle diborane and many of its derivatives, which are bothpyrophoric and volatile.Alfred Stock invented the glass vacuum line for this purpose.[2] The structure of diborane was correctly predicted in 1943 many years after its discovery.[3] Interest in boranes increased during World War II due to the potential ofuranium borohydride for enrichment of the uranium isotopes and as a source of hydrogen for inflating weather balloons. In the US, a team led bySchlesinger developed the basic chemistry of the anionic boron hydrides and the related aluminium hydrides. Schlesinger's work laid the foundation for a host of boron hydridereagents fororganic synthesis, most of which were developed by his studentHerbert C. Brown. Borane-based reagents are now widely used in organic synthesis. Brown was awarded theNobel Prize in Chemistry in 1979 for this work.[4]
Most boranes are prepared directly or indirectly fromdiborane. Diborane reacts with alkenes to give alkylboranes, a process known ashydroboration:
Alkyl and aryl boranes can also be produced byalkylation ofchloroboranes andboronic esters.
![9-Borabicyclo[3.3.1]nonane ("9-BBN")](/mt/?noimg=&dark=on&url=https%3a%2f%2fen.wikipedia.org%2fwiki%2fFile%3a9-BBN_dimer_structure.svg)
2BH_dimer.svg)
The parent boranes are binary boron hydrides, starting withborane (BH3) and its dimerdiborane (B2H6). Pyrolysis of these species leads to higher boranes, such astetraborane andpentaborane. These two are early members of theboron hydride clusters.
This family of boron hydrides includes mono- and dialkylboranes. The simplest members readily engage inredistribution reactions:
With bulky substituents, primary and secondary boranes are more readily isolable and even useful. Examples includethexylborane and9-BBN. Almost all primary and secondary boranes are dimeric with bridging hydrides.
Most work focuses on trialkyl and triaryl boranes. These are all monomers (in contrast to the corresponding trialkyl and triarylaluminium compounds). Their BC3 cores are planar. Well known examples aretrimethylboron,triethylboron, andtriphenylboron. Many tertiary boranes are produced byhydroboration.
The lowest borane,BH3 exists only transiently,dimerizing instantly to form diborane,B2H6. Its adductborane–tetrahydrofuran andborane–dimethylsulfide are useful inhydroboration reactions.