Experimental Basicities of Phosphazene, Guanidinophosphazene, and Proton Sponge Superbases in the Gas Phase and Solution.
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.
Institute of Chemistry, University of Tartu , Ravila 14a Str, 50411 Tartu, Estonia.
Ivari
I
Kaljurand
Institute of Chemistry, University of Tartu , Ravila 14a Str, 50411 Tartu, Estonia.
Jaan
J
Saame
Institute of Chemistry, University of Tartu , Ravila 14a Str, 50411 Tartu, Estonia.
Toomas
T
Rodima
Institute of Computer Sciences, University of Tartu , J. Liivi 2 Str, 50409 Tartu, Estonia.
Ivar
I
Koppel
Institute of Chemistry, University of Tartu , Ravila 14a Str, 50411 Tartu, Estonia.
Ilmar A
IA
Koppel
Fachbereich Chemie, Philipps-Universität Marburg , Hans-Meerwein-Straße, 35032 Marburg, Germany.
Julius F
JF
Kögel
Fachbereich Chemie, Philipps-Universität Marburg , Hans-Meerwein-Straße, 35032 Marburg, Germany.
Jörg
J
Sundermeyer
Institut für Organische Chemie und Makromolekulare Chemie, Friedrich-Schiller-Universität Jena , Humboldtstraße 10, 07743 Jena, Germany.
Uwe
U
Köhn
School of Chemical and Physical Sciences, Victoria University of Wellington , P.O. Box 600, Wellington, New Zealand.
Martyn P
MP
Coles
Institute of Chemistry, University of Tartu , Ravila 14a Str, 50411 Tartu, Estonia.
Ivo
I
Leito