The species
RB: containing an electrically neutral univalent boron atom with two formally non-bonding electrons.
See: carbene analogues
Source:
PAC, 1995, 67, 1307. 'Glossary of class names of organic compounds and reactivity intermediates based on structure (IUPAC Recommendations 1995)' on page 1323 (https://doi.org/10.1351/pac199567081307)