MNDO calculations on borazine derivatives. 2. Substitution of two [HNBH] fragments for two [HCCH] fragments in benzene to form the diazadiborines and the novel open structure of the 1,2,4,5-isomer

Facile Access to Unprecedented Electron‐Precise Monohydrodiboranes(4), cis‐1,2‐Dihydrodiboranes(4), and a 1,1‐Dihydrodiborane(5)

“…The C 2 N 2 B 2 ring of 4 a is quasi‐planar, with N1‐C1‐C2‐N2 and N1‐B1‐B2‐N2 torsion angles of 2.7 and 6.2°, respectively. The B1−B2 bond length of 1.719(2) Å is substantially longer than that calculated for the parent, formally 6π‐aromatic 1,4,2,3‐diazadiborinine, C 2 N 2 B 2 H 6 [1.6514 Å], and typical of B−B single bonds in tetra(amino)diborane(4) compounds. Conversely, the C1−C2 vinylene bridge (1.330(2) Å) is significantly shorter than that calculated for C 2 N 2 B 2 H 6 (1.3677 Å) …”

Synthesis and structures of monocyclic 1,4-diaza-2,3-diborine species

“…2,3-diaza-1,4-diborine ring system was the first isolated example of an isoelectronic analogue of benzene with two BN units, despite computations suggesting that heterocycle is less stable than the 1,3-diaza-2,4-diborine ring by over 50 kcal/mol [3,5]. Subsequent treatment of 2,3-diaza-1,4-diborine with (MeCN)3Cr(CO)3 resulted in the corresponding ƞ-Cr(CO)3 complexes, which were also studied crystallographically [6].…”

“…Although few examples of 1,4-diaza-2,3-diborinine ring systems have been reported, there are no examples of monocyclic species [7,8], wheres calculations suggest that the ring is more stable than the 2,3-diaza-1,4-diborine ring by -10 kcal/mol [3,5]. In this work, we report the synthesis and characterisation of new monocyclic 1,4-diaza-2,3-diborine derivatives 3ad, 3bc and 3ae and new bicyclic structure 8a.…”

“…Some diazadiborine isomers have been studied using MNDO (modified neglect of diatomic overlap) calculations (Scheme 1). Thermodynamically stable diazadiborines include 1,3-diaza-2,4-diborine (2u, heat of formation -60.16 kcal/mol), 2,3-diaza-1,4-diborine (4u, -12.60 kcal/mol) and 1,4-diaza-2,3-diborine (3u, -22.04 kcal/mol) [3].…”

Tuning electronic eigenvalues of benzene via doping

“…18 Indeed, while 1,3-azaborine, BC 4 NH 6 , exhibits significant bond delocalization, the 1,2-and 1,4-isomers appear to be best described as heterocyclic dienes. 19 Similar calculations have been done for diazadiborines, B 2 C 2 N 2 H 6 , containing one ͓HCCH͔ and two ͓HNBH͔ moieties. 18 In this study, we apply the recently introduced molecular grand-canonical ensemble density functional theory 7,10,13 ͑DFT͒ to the problem of predicting the changes in HOMO eigenvalues of benzene derivatives due to doping at various sites in the molecule without the actual evaluation of the electronic structure of the corresponding mutants.…”