Sophie Mann, Günther Horrer, Maik Finze, Udo Radius
The synthesis and characterization of a new family of N-boron-functionalized anionic NHCs (NBA-NHCs), IiPrB(CN)3 - (5), IiPr(C2F5)BF2 - (6), IMesB(CN)3 - (7), and IMes(C2F5)BF2 - (8), accessible on gram-scale from air- and moisture-stable precursors, is reported. Multinuclear NMR, IR spectroscopy, and single-crystal X-ray diffraction confirm highly electron-rich carbenic carbon centers and strengthened B-N interactions in these molecules. Selenium adducts 9-12 of these NBA-NHCs indicate an enhanced π-acceptor character relative to neutral NHCs, while Tolman electronic parameters of nickel tricarbonyl complexes [(NBA-NHC)Ni(CO)3]-K+ 13-16 demonstrate their strong donor ability, similar to dianionic carbenes. Steric maps and buried volume (%Vbur) analyses of linear gold(I) complexes [(NBA-NHC)Au(PPh3)] 17-20 reveal tunable steric profiles, ranging from anisotropic to strongly shielding environments by varying the N-substituents. These results establish NBA-NHCs as a modular ligand platform enabling control of electronic properties and steric demand at the metal center for future applications in coordination chemistry and catalysis.