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=NR) 2BiCl2 where R = tBu (1), 2', 6'-Me2C6H3 (2), or 4'-Me2NC6H4 (3) or N, C-chelated analogues C6H2-2- (CH=N-2', 6'-iPr2C6H3) -4, 6- (tBu) 2BiCl2 (4) and C6H2-2- (CH2NEt2) -4, 6- (tBu) 2BiCl2 (5) is reported. Reduction of compounds 1-3 gave monomeric N, C, N-chelated bismuthinidenes C6H3-2, 6- (CH=NR) 2Bi 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=N-2', 6'-iPr2C6H3) -4, 6- (tBu) 2Bi (9) as an unprecedented two-coordinated bismuthinidene that has been structurally characterized. In contrast, the dibismuthene C6H2-2- (CH2NEt2) -4, 6- (tBu) 2Bi2 (10) was obtained by the reduction of 5. Compounds 6-10 were characterized by using (1) H and (13) C 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.