Borylene

A borylene is the boron analogue of an carbene. The general structure is R-B: with R an organic residue and B a boron atom with two unshared electrons. Borylenes are of some academic interest in the field of chemistry. A singlet ground state is predominant with boron having two vacant sp2 orbitals and one doubly occupied one. With just one additional substituent the boron is more electron deficient than the carbon atom in a carbene. For this reason stable borylenes are more uncommon than stable carbenes. Some borylenes such as boron monofluoride and boron monohydride have been detected in microwave spectroscopy. Other borylenes exist as reactive intermediates and can only be inferred by chemical trapping.

The first stable borylene ((CO)₅WBN(SiMe₃)₂) was reported in 1998. In this compound a borylene was coordinated to a transition metal as a ligand. Another way to stabilise borylenes is as mono Lewis base adduct with a NHC carbene, in one exploit the key intermediate was found to dimerise to the diborene with a double boron-boron bond . Other strategies are the use of cyclic alkyl amino carbenes (CAAC) and their use as bis-adducts.

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