Table of Contents:
With the design and synthesis of new uncharged phosphorus, carbon, and nitrogen superbases additional staves at the upper end of the basicity ladder were established. The presented phosphazenyl phosphanes (PAPs) are not only the record holder of phosphorus bases, but even surpass the long-time dominant phosphazene superbases, being the new top-end markers of the self-consistent THF-based basicity scale. High electron density at the phosphorus(III) atom results in high Brönsted basicity as well as in high Lewis basicity and reduction potential. These attributes were validated in paradigmatic reactions with transition metal precursors, the main group element selenium and the simplest electrophile of all, the proton.
For the first time an experimental pK(BH+) value for carbodiphosphoranes (CDPs) was presented. It confirmed the bisylidic carbon atom as an exceptional basicity centre, reaching a similar basicity region as Schwesinger’s P4-phosphazenes, however with significantly lower molecular weight. The synthesis route to second-order CDPs opens-up a vast field of fine-tuned top-tier carbon superbases through simple modulation of the P-substituents.
A new nitrogen superbase was presented with augmented basicity through multiple intermolecular hydrogen bonding. Experimental and theoretical investigations shed light on the influence of the four-fold corona effect in solid state, in solution and in the gas-phase and revealed the strongest first-order phosphazene superbase.
Thus, several new representatives of non-ionic superbases were presented, which take into account the differences of phosphorus, carbon and nitrogen atom as basicity centres in their divergent reactivity towards the proton and other Lewis acids.