Experimental Basicities of Phosphazene, Guanidinophosphazene, and Proton Sponge Superbases in the Gas Phase and Solution

Abstract

Experimental gas-phase superbasicity scale spanning 20 orders of magnitude and ranging from bicyclic guanidine 7-methyl-1,5,7-triazabicyclo[4.4.0]dec-5-ene to triguanidinophosphazenes and P3 phosphazenes is presented together with solution basicity data in acetonitrile and tetrahydrofuran. The most basic compound in the scale-triguanidinophosphazene Et-N═P[N═C(NMe2)2]3-has the highest experimental gas-phase basicity of an organic base ever reported: 273.9 kcal mol(-1). The scale includes besides the higher homologues of classical superbasic phosphazenes and several guanidino-substituted phosphazenes also a number of recently introduced bisphosphazene and bis-guanidino proton sponges. This advancement was made possible by a newly designed Fourier transform ion cyclotron resonance (ICR) mass spectrometry setup with the unique ability to generate and control in the ICR cell sufficient vapor pressures of two delicate compounds having low volatility, which enables determining their basicity difference. The obtained experimental gas-phase and solution basicity data are analyzed in terms of structural and solvent effects and compared with data from theoretical calculations.

Electronic nature of zwitterionic alkali metal methanides, silanides and germanides – a combined experimental and computational approach

“…On a final note, the calculated GPBs of M- 1 –M- 3 are fairly similar to those of classical organosuperbases such as t BuNP[NP(NMe 2 ) 3 ] 3 (–288 kcal mol –1 ) 27 , [(Me 2 N) 2 CN] 3 PNBu t (–279 kcal mol –1 ) 28 , HMPN (–270 kcal mol –1 ) 29 and Verkade's base (–261 kcal mol –1 ) 30 , which have found use in organic synthesis and organocatalysis. 31,32 Given the similar basicities, the ease of tuning basicity and the steric protection of the “naked” anion, E – , by proper choice of the metal cation and substituents, these types of zwitterions may offer new opportunities to be used in base and frustrated Lewis pair (FLP) catalysis as well as in the activation of small molecules.…”

On the Basicity of Organic Bases in Different Media

“…The revised basicity scale (Table ) is composed of previously published data, , and unpublished results for 9‐chloroacridine and 2‐aminoacridine (experimental conditions as in ref …”

Phosphazenyl Phosphines: The Most Electron‐Rich Uncharged Phosphorus Brønsted and Lewis Bases

“…[8] As imilar molecular superbase design has been investigated by theory [9] and experiment for uncharged carbon bases such as related phosphorus ylides [10] and their bisylide pincers. [6,10] Themain field of interest and application of these compounds lies in creating very strong donors in transition metal chemistry and catalysis.V erkadesp roazaphosphatranes are early representatives of rare superbasic phosphines. [6,10] Themain field of interest and application of these compounds lies in creating very strong donors in transition metal chemistry and catalysis.V erkadesp roazaphosphatranes are early representatives of rare superbasic phosphines.…”