Electronically Induced Steric Clash: Synthesis of NMe2-Modified β-Diketiminate-Supported Boron Difluoride Compounds.

We report on the synthesis and structural features of NMe₂-modified β-diketiminate-supported boron difluoride compounds (LArBF₂ : L^Ar = [HC(NAr)₂(CNMe₂)₂]^–; L^Ph : Ar = Ph; L^Tol : Ar = p -tolyl; L^Xyl : Ar = m -xylyl). The title compounds were prepared in moderate yields (~65 %) by in situ deprotonation of the corresponding ligands L^ArH using KH, followed by the addition of BF₃OEt₂. According to solid-state and theoretical analyses of the BF₂ compounds, the lone pair at each NMe₂ group is involved in electron delocalization within the central BC₃N₂ ring. As a result, the N -aryl substituents sterically clash with the NMe₂ groups, causing this central ring to pucker. Several attempts were made to prepare heavy analogues (e.g. L^ArBX2 , X = Cl, Br, I) but only unidentifiable product mixtures were observed. It appears that the observed steric clash between the N -aryl substituents and the NMe₂ groups prevented the formation of these heavy analogues. Electronic delocalization involving NMe₂ groups and the central six-membered ring resulted in a steric clash between the NMe₂ groups and Ar substituents. This steric clash was identified as the main reason for these ligand systems being able to stabilize only a BF₂ fragment, while attempts to prepare heavy analogues resulted in product mixtures. [ABSTRACT FROM AUTHOR]