Five-membered Rings with Two Adjacent Heteroatoms with at least One Boron

Abstract

The five-membered ring heterocycles containing boron and another adjacent heteroatom include rings with boron–nitrogen, boron–oxygen, boron–sulfur, boron–phosphorus, boron–boron, and boron–silicon bonds. The boron-nitrogen rings are by far the largest class of compounds, followed by the boron–oxygen and boron–sulfur rings. Compounds with boron–boron and boron–silicon bonds are rare. 1,2-Azaborolyl, 1,2-thiaborolyl, and 1,2-oxaborolyl rings are isoelectronic with the cyclopentadienyl ring and have been used as surrogates for cyclopentadienyl in many transition metal complexes. 1,2-Azoniaboratolidines and the related B–O, B–S, and B–P rings are internal σ-coordinated boron–Lewis base complexes. These compounds are generally very stable. A large number of these B–N rings have been structurally characterized. The boron–oxygen rings include cyclic esters of boronic acids.