Design of non-ionic carbon superbases: second generation carbodiphosphoranes

Abstract

The edge-cutting design, synthesis and characterization of the so far strongest non-ionic carbon superbases is presented.

Phosphorus‐Containing Superbases: Recent Progress in the Chemistry of Electron‐Abundant Phosphines and Phosphazenes

“…Starting from readily available bis(dimethylaminophosphino)methane or the respective pyrrolidyl derivative, oxidative amination with CCl 4 afforded the desired dicationic species in all cases (Scheme 18), which were transferred into their air and water stable HBF 4 salts according to described literature procedures. The neutral carbodiphosphoranes 50 ( THF p K =30.1–32.9) and 51 ( THF p K =35.8) were liberated via twofold deprotonation with KHMDS or NaNH 2 in yields of 60 % and 70 %, respectively [146] . Guanidyl derivative 51 is the strongest carbon Brønsted base presently known and surpasses ylide H 2 C=P(2,4,6‐(MeO) 3 ‐C 6 H 2 ) 2 Ph with a THF p K value of 33.5 [19] …”

“…A second deprotonation step at the carbon atom, however, does not occur. In contrast to the desired carbodiphosphorane 52 (calculated THF p K =39.1), Sundermeyer obtained the phosphazenylphosphine 53 as the selective product via elimination of a peripheric dimethylamino group, by which he clearly demonstrated a potential basicity limit for dimethylaminophosphazene‐incorporated superbases [146] …”

“…The neutral carbodiphosphoranes 50 ( THF pK BH þ = 30.1-32.9) and 51 ( THF pK BH þ = 35.8) were liberated via twofold deprotonation with KHMDS or NaNH 2 in yields of 60 % and 70 %, respectively. [146] Guanidyl derivative 51 is the strongest carbon Brønsted base presently known and surpasses ylide H 2 C=P(2,4,6-(MeO) 3 -C 6 H 2 ) 2 Ph with a THF pK BH þ value of 33.5. [19] The higher dicationic phosphazenyl homologue [52H 2 ] 2 + can be efficiently transferred into the monocation [52H] + by treatment with NaNH 2 (69 %,Scheme 18).…”

Is It Possible to Achieve Organic Superbases beyond the Basicity Limit Using Tetrahedrane Scaffolds?

“…Table shows investigated bases with one tetrahedrane cage 1–7 , which all feature the carbon atom as the proton accepting site, a design strategy which is strongly supported by a recent progress in preparing strong carbon‐based superbases . Still, to probe the suitability of this approach, we also considered their amino analogues 8–14 , since nitrogen is usually more basic than carbon.…”

Substituted ketenes offer exceptional carbon bases in gas phase: Computational study by density functional theory method

“…[ 2–5 ] The other organosuperbases that are not naphthalene based were also examined experimentally and computationally. [ 6–17 ] Some of the introduced superbases meet much higher basicity than DMAN, which is mainly due to the unique stability of their conjugate acids. In general, stability and positive charge delocalization in the conjugate acid of the base are provided by the solvation, resonance, IHBs, and use of electron‐donating groups.…”