The basicity of phosphines

Abstract

The basicities of the triarylphosphines P(4-XC 6 H 4 ) 3 (X = Cl, F, H, CH 3 , CH 3 O, (CH 3 ) 2 N), P(3-CH 3 C 6 H 4 ) 3 , and P(2-CH 3 C 6 H 7 ) 3 as well as the trialkylphosphines P(t-Bu) 3 and PCy 3 have been measured by the nitromethane titration method. The range of basicity available by aryl substitution is very large, being pK a = 8.65 for X = (CH 3 ) 2 N to 1.03 for X = Cl. The most basic phosphine is P(t-Bu) 3 whose pK a = 11.40. The measured basicities correlate well with σ p , [Formula: see text], and ν as well as with the lone pair ionisation potentials of the triarylphosphines. Generally the 1 H, 31 P, and 13 C nmr spectral parameters of the free and protonated phosphines do not correlate well with pK a .