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: LAr = [HC(NAr)2(CNMe2)2]-; LPh: Ar = Ph; LTol: Ar = p-tolyl; LXyl: Ar = m-xylyl). The title compounds were prepared in moderate yields (65 %) by in situ deprotonation of the corresponding ligands LArH 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. LArBX2, 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.