Exceptionally Long C−C Single Bonds in Diamino‐o‐carborane as Induced by Negative Hyperconjugation

Abstract

The synthesis of as eries of 1,2-diamino-o-carboranes (1-4)i sr eported. The molecular structures of these diamino-o-carboranes are remarkable as the inner-cluster CÀC bonds are all ultra-long (162.7-193.1 pm) and vary substantially with small variations in the substituents.T he results of quantum mechanical investigations suggest that the origin of the bond elongation is significant in-plane negative hyperconjugation of lone pairs of the nitrogen substituents with the s*o rbitals of the CÀCb onds in o-carboranes.

Synthesis, Characterization, and Properties of Three-Dimensional Analogues of 9-Borafluorenes

“…1.89 Å) single bonds. The C–C bonds within the carborane clusters ( 1 , C1–C2 1.661(9) Å, C3–C4 1.653(10) Å; 2 , C1–C2 1.652(7) Å, C3–C4 1.654(8) Å) are somewhat longer than that of a free o -carborane (1.642 Å) . Besides, the C 4 B-endocyclic B–C bonds varied in their bond length ( 1 , C1–B1 1.556(12) Å, C4–B1 1.591(10) Å; 2 , C1–B1 1.580(9) Å, C4–B1 1.591(8) Å), and the dihedral angles C4–C3–C2–C1 of 1 and 2 are −15.2(7)° and −14.6(6)°, respectively, reflecting the twisted geometry of the C 4 B ring (Figure , rms deviation of five atoms from least-squares planes: 1 , 0.0669; 2 , 0.0644).…”

The borderless world of chemical bonding across the van der Waals crust and the valence region

“…The interest in long carbon-carbon bonds has materialized in the last few years in several experimental and computational reports. 17,113,[207][208][209][210] In the context of this work, it is interesting to calibrate what a "long bond" means in terms of penetration indices. Let us consider the C-C distances in dicarbadodecaboranes, R 2 C 2 B 10 H 10 , which have been noted to be quite long.…”

Reactivity Studies of a Bis(π-η5:σ-η1-benzofulvene)titanium Complex Including Simultaneous N–H and C(sp2)–H Activation of Dibenzylamine

“…In comparison to the starting material 1 (1.456(4) Å), the C1–C10 bond length of 1.5348(10) Å is elongated and now typical of a C­(sp 2 )–​C­(sp 3 ) single bond, which is in good agreement with the transition of a benzofulvene ligand in 1 to a substituted indenyl ligand in 2 . The significant elongation of the C10–C25 bond (1.6200(10) Å) in comparison to typical C­(sp 3 )–​C­(sp 3 ) single bonds is characteristic of complexes derived from pentafulvene complexes of group 4 metals and carbonyl compounds. , Negative hyperconjugation between the lone pair of the oxygen and the antibonding σ orbital of the C–C bond can be supposed as the explanation . Consequently, contribution of the resonance form B is likely (Scheme , top).…”