0 Hits

  • Previous / Next

You are using Science Of Synthesis as a Guest.
Please login to access the full content or check if you have access via
2.1 Electronic Structure of Boron Reagents

DOI: 10.1055/sos-SD-230-00002

Carbó, J. J.; Maseras, F.Science of Synthesis: Advances in Organoboron Chemistry towards Organic Synthesis, (201915.

The element boron has three valence electrons that typically form three linkages to other atoms, such as main-group elements of the p-block, alkali and alkaline-earth metals, or transition metals. These trivalent boron compounds have a trigonal planar geometry with an empty p-orbital perpendicular to the molecular plane, the overall structure being isoelectronic to a carbocation. The electron deficiency at boron can be compensated for by π-donation from the substituents into the empty p-orbital of boron (Scheme 1). The pπ–pπ lone-pair donation from atoms such as oxygen has a significant stabilizing effect, while in transition-metal–boryl species, the dπ–pπ back donation is assumed to be weak. Therefore, both organoboron compounds and boryl–transition metal species have been traditionally regarded as electrophilic reagents via the Lewis acidity of the boron center. However, trivalent boron compounds can change from having electrophilic character to exhibiting nucleophilic behavior, depending on the substituents attached to the boron atom.

Meeeee 8 Meeeeeeee Meeeeee Meeeeeeeeee ee Meeee Meeeeee eeee Meeeee (M) eee Meeeeeeeee Meeeee (MM) ee Meeeeeeee Meeee Meeeeeeee

Mee eeeeeeeeeeee eeeeeee ee eee eeeeeee eeeeee ee eeeee eeeeeeeeee ee eee eeeeeeeee eeeeeeee ee eeeeeeeeeeeeee eee eeeeeeeeeee eeeeeee eeeeee α,β-eeeeeeeeeee eeeeeee. Mee eeeeeeeee eeeeeee eeeee-eeeeee(8,8-eeeeeeee-8,8,8-eeeeeeeeeeee-8-ee)eee(eeeeeeeeeeeeeeeeee)eeeeeeeee(MM) eeeeee ee ee eeeeeeeeeeee, eeeeeeeee eee 8,8-eeeeeeee eeeeeee eeee eee eeeee eeeeee eeeeee ee eee eeeeee eee eeeeeeeeeee eeeeeeeeeee ee eee β-eeeeee,[‌8‌] eeeee ee ee eeeeeeeee (eeeeeeeeeeeeeee)eeeeee eeeeeee, eee eeeee eeeeee eeee ee e eeeeeeeeeee, eeeeeeeeeeee eee eeeee eeee ee eee β-eeeeee ee eee eeeeeeeee.[‌88‌] Meeeee, Mee, eee ee-eeeeeee eeee eeeeeeeeeeeeeee eeeeeeeeeeee eeee eee eeeee eeeeeeee ee ee M-eeeeeeeeeeee eeeeeee–(eeeeeeeeeeeeee)eeeeee eeeeeee [Me(Meee)(MMM)] eee eeeeeeeeeeee eeeeeeeee, ee eeeeeeeee eee eeeeeeee ee e eeeee eeeeeeeeeeee eeeeeeeee, eeeee eeeeeeee eeeeeeeeeeeee eee eeeeeeeeeeee eeeeeeeeee.[‌88‌] Meee eeeee eeeeee eeee eee eeee-eeeee MeM σ-eeeeeee eeeeeeeee eeeeeee eeeeee eee eeeeeeeee ee eee eeeee eeeeee ee eee eeeeeeeeeeeee eeeeee ee eee eeeeeeee.

Meeeeeeeeeee eeeee eeeeeeee eee ee eeeeeeee eee eeeeeee eeee eeeee eeeeeeeee eeeeeeeeee: 8) eeeeeee eeeeeeeee eeeeeeeee ee Meeee eeeee; 8) eeeee eeeeeeeee eeeeee ee eeeeee ee eeeeeeee-eeeee eeeeee; eee 8) eeeee eeeeeeeee eeeeee ee eeeeeeeeee eeeeee eeee ee eeeeee ee eeeeeeee. Meeee eeeeeeeeeeeee eeeee, ee eee eeee eeeeeeee ee eeeeee eee eeeeeeee eeeeeeeee eeeeeeeeeee ee eeeee ee eeeee e eeeeeeee eee eeee eeeeeeeeee eeeeeeeee eeeee eeeeeeeee ee e eeeeeeee ee eeeee eeeeeeeeeeeee eee eeeeeeeeeeee eeeeeeeeee.[‌88‌] Mee eeeeeeeeee eeeeeeeeeee, eee eeeeee ee eee eeeee eeeeeeee, eee eee eeeee e/e eeeee ee eee MM σ-eeee, eee eeeeeeeeee eeee eee eeeeeeeeeeee eeeeeeeee eeeeeee ee eee eeeee eeeeeeeeeee eee eeee eee eeeeeeeee eeeeeeeeeeeeeee ee eee eeeee eeeeeeee, eeeeeeeeeeee. Meeee, eeee eee eeeeeeee ee e eeeeeeeeee ee eeeeeeee eee eeeeee eeeeeee ee eee eeeeeeee, e eeeeeeeeeeee eeeeeeeee–eeeeeeee eeeeeeeeeeee eee eeeeeeeee eee eee eeeeeeeeeeeeeee ee e eeeeeeeeeee eee ee eeeeeeeee eeeee eeeeeeeee, eeeeeeeeeeee eee eeeeeeeee eeeeeeeeee eeeee eee eeeee ee MM: M = Me > Me > M(ee8) > Me.[‌88‌]

Mee eeeeeeeee eeeeeeee eeeeeee e eeee eeeeeeee eeeeeeeeeee ee eee eeeeeeee eeeeeeeeee eee eee eeeeeeeeee eeeeee eee eeeeeeeee eeeee eeeeeeee eee eeeeeeee eeeeeeeee eeeeeeeee eeeeeeeee eeeeeeeeee eeeeee ee eeeeeeee eeeee eeeee eeeeeee.