From Dibismuthenes to Three- and Two-Coordinated Bismuthinidenes by Fine Ligand Tuning: Evidence for Aromatic BiC3N Rings through a Combined Experimental and Theoretical Study.”

The reduction of N,C,N-chelated bismuth chlorides [C6H3-2,6-(CH[DOUBLE BOND]NR)2]BiCl2 [where R=tBu (1), 2′,6′-Me2C6H3 (2), or 4′-Me2NC6H4 (3)] or N,C-chelated analogues [C6H2-2-(CH[DOUBLE BOND]N-2′,6′-iPr2C6H3)-4,6-(tBu)2]BiCl2 (4) and [C6H2-2-(CH2NEt2)-4,6-(tBu)2]BiCl2 (5) is reported. Reduction of compounds 1–3 gave monomeric N,C,N-chelated bismuthinidenes [C6H3-2,6-(CH[DOUBLE BOND]NR)2]Bi [where R=tBu (6), 2′,6′-Me2C6H3 (7) or 4′-Me2NC6H4 (8)]. Similarly, the reduction of 4 led to the isolation of the compound [C6H2-2-(CH[DOUBLE BOND]N-2′,6′-iPr2C6H3)-4,6-(tBu)2]Bi (9) as an unprecedented two-coordinated bismuthinidene that has been structurally characterized. In contrast, the dibismuthene {[C6H2-2-(CH2NEt2)-4,6-(tBu)2]Bi}2 (10) was obtained by the reduction of 5. Compounds 6–10 were characterized by using 1H and 13C NMR spectroscopy and their structures, except for 7, were determined with the help of single-crystal X-ray diffraction analysis. It is clear that the structure of the reduced products (bismuthinidene versus dibismuthene) is ligand-dependent and particularly influenced by the strength of the N→Bi intramolecular interaction(s). Therefore, a theoretical survey describing the bonding situation in the studied compounds and related bismuth(I) systems is included. Importantly, we found that the C3NBi chelating ring in the two-coordinated bismuthinidene 9 exhibits significant aromatic character by delocalization of the bismuth lone pair.