Phosphorus derivatives of mesoionic carbenes: synthesis and characterization of triazaphosphole-5-ylidene → BF 3 adducts.

Trimethylsilyl-substituted triazaphospholes were synthesized by a [3+2] cycloaddition reaction between organic azides and (CH 3 ) 3 Si-CP. In an attempt to isolate their N -alkylated products, the formation of BF 3 adducts of unprecedented triazaphosphol-5-ylidenes was found. The nature of the carbon carbene -boron bond was investigated within the DFT framework, revealing a strong donation of electrons from the carbene carbon atom to the boron atom combined with weak back-bonding.