Synthetic Modification of Acyclic Bent Allenes (Carbodicarbenes) and Further Studies on Their Structural Implications and Reactivities

Abstract

The paper describes the synthetic development of Bertrand-type acyclic carbodicarbene scaffolds derived from an unsymmetrical bis(benzimidazol-2-yl)methane bearing two sterically demanding pendant arms, isopropyl (6a) or cyclohexyl (6b). X-ray crystallographic analysis shows that the impact of these pendant arms on the overall structural parameters of carbodicarbenes is minimal. The chemical reactivity of the carbodicarbenes was evaluated with iodomethane to afford compound 7, illustrating its nucleophilic properties. Finally, experiments were also undertaken to investigate the coordination ability of carbodicarbene toward the formation of rhodium carbonyl (10) and palladium allyl complexes (11). The crystal structures of the metal complexes have been determined, revealing that their metal−carbene distances are elongated only slightly, this fact was rationalized on the basis of geometrical steric considerations with regard to the ligand.

Carbodicarbenes or Bent Allenes

“…For this reason, our group undertook the first synthetic effort to increase the solubility of CDC in organic solvents by modifying the side arm in the framework of CDCs . The work included the synthetic development of acyclic CDC scaffolds derived from a bis(benzimidazole‐2‐yl)methane bearing two sterically demanding pendant arms, namely isopropyl ( 6a ) or cyclohexyl ( 6b ), as shown in Figure .…”

Recent Advances in the Field of Main‐Group Mono‐ and Diatomic “Allotropes” Stabilised by Neutral Ligands

“…We would however note, that a similar growth in the use of the carbodicarbene as a ligand has not yet occurred, with only some very recent activity. [35] It is somewhat surprising, given the attractive feature of the carbodicarbene as a powerful neutral donor ligand demonstrated in the initial synthetic report. These two compounds have also been central in an increasing discussion of molecular carbon chemistry outside of what is traditionally considered organic chemistry; for example, thinking of carbon as a Lewis acid in donor-acceptor complexes.…”

CO2 Adducts of Carbodicarbenes: Robust and Versatile Organocatalysts for Chemical Transformation of Carbon Dioxide into Heterocyclic Compounds

“…CO 2 adduct 1 b was synthesized in a similar manner to 1 a , but starting from 2,2′‐methylenebis(1‐isopropyl‐3‐methyl‐1 H ‐benzo[d]imidazol‐3‐ium) trifluoromethanesulfonate to give 1 b as light yellow solid in 55 % yield. 1 b : 1 H NMR (400 MHz, CDCl 3 ): δ =7.48 (d, J= 7.6 Hz, 2 H), 7.37 (d, J= 7.6 Hz, 2 H), 7.23–7.17 (m, 4 H), 4.88–4.81 (m, 2 H), 3.33 (s, 6 H), 1.62 (d, J= 6.8, 6 H), 1.57 ppm (d, J= 6.8, 6 H).…”