Chemistry of Di-borylated Carbene/Carbenoid

Carbene is a two-coordinate neutral carbon species, characterized by two non-bonding electrons on the carbon atom. By the configuration of non-bonding electrons, singlet carbene can be classified into two types, σ2π0 and σ0π2. While σ2π0 carbenes, represented by N-heterocyclic carbene or cyclic alkyl(amino)carbene, have been well-studied, properties of σ0π2 carbenes have yet to be fully revealed. Diborylcarbene (DBC), wherein two boryl groups are attached to the carbene carbon, has long been theoretically predicted to adopt the σ0π2 configuration and exhibit highly electrophilic nature. However, to date, no experimental investigation beyond trapping reactions with some Lewis bases has been accomplished. In this situation, we focused on carbenoid, which is often employed as a synthon for carbene in synthetic organic chemistry, for an equivalent to DBC. This article summarizes our recent progress in the investigation of the properties of diborylcarbenoid and DBC.