"Chemistry of the Main Group Elements, Part 2: Rings, Chains and Macromolecules, Based on Main Group Elements"
If you like this sort of thing, you'll like
this article.
Boron–nitrogen chemistry
Greenwood & Earnshaw, p. 207: instructive to compare B-N compounds with their C-C counterparts, since they are isoelectronic and have similar sizes and electronegativities (ish)
The bonding in B-N compounds can be confusing. Amine-borane adducts can be represented as R3N+-B−R3. In this
formalism, the charges are meant to be relative to the charges in the separate neutral fragments R3N and BR3, but this is still misleading.
N in R3N has a large δ−, which is reduced to a small δ− upon formation of R3N→BR3. The negative charge on N decreases, but is still negative.
Similarly, B in BR3 has a large δ+, which decreases to a small δ+ upon formation of R3N→BR3. The positive charge on B decreases, but is still positive.
Without bulky substituents (i.e. without
kinetic stabilisation), aminoboranes tend to cyclise and readily hydrolyse
Aminoboranes usually cyclise to 4-membered B2N2 rings due to steric hindrance, but some 6-membered B3N3 ring compounds are known. For example, aminoborane itself, H2NBH2, is in reversible equilibrium between monomer and dimer in the gas phase, and can cyclotrimerise to cyclotriborazane in the solid state.
but significant ΔEN means electron density more localised on nitrogen
only weak delocalisation/aromaticity
tends to undergo addition (e.g. of HCl or H2O across BN bonds) rather than the
electrophilic aromatic substitution characteristic of benzene (although benzene is only kinetically and not thermodynamically stable with respect to HCl or water addition - Housecroft 3rd edn. p. 355)
Borates and
borate minerals (e.g.
borax) - many structures, either discrete anions or anionic chains and rings - contain planar BO3 triangles and/or BO4 tetrahedra
"Chemistry of the Main Group Elements, Part 2: Rings, Chains and Macromolecules, Based on Main Group Elements"
If you like this sort of thing, you'll like
this article.
Boron–nitrogen chemistry
Greenwood & Earnshaw, p. 207: instructive to compare B-N compounds with their C-C counterparts, since they are isoelectronic and have similar sizes and electronegativities (ish)
The bonding in B-N compounds can be confusing. Amine-borane adducts can be represented as R3N+-B−R3. In this
formalism, the charges are meant to be relative to the charges in the separate neutral fragments R3N and BR3, but this is still misleading.
N in R3N has a large δ−, which is reduced to a small δ− upon formation of R3N→BR3. The negative charge on N decreases, but is still negative.
Similarly, B in BR3 has a large δ+, which decreases to a small δ+ upon formation of R3N→BR3. The positive charge on B decreases, but is still positive.
Without bulky substituents (i.e. without
kinetic stabilisation), aminoboranes tend to cyclise and readily hydrolyse
Aminoboranes usually cyclise to 4-membered B2N2 rings due to steric hindrance, but some 6-membered B3N3 ring compounds are known. For example, aminoborane itself, H2NBH2, is in reversible equilibrium between monomer and dimer in the gas phase, and can cyclotrimerise to cyclotriborazane in the solid state.
but significant ΔEN means electron density more localised on nitrogen
only weak delocalisation/aromaticity
tends to undergo addition (e.g. of HCl or H2O across BN bonds) rather than the
electrophilic aromatic substitution characteristic of benzene (although benzene is only kinetically and not thermodynamically stable with respect to HCl or water addition - Housecroft 3rd edn. p. 355)
Borates and
borate minerals (e.g.
borax) - many structures, either discrete anions or anionic chains and rings - contain planar BO3 triangles and/or BO4 tetrahedra