The basicity of phosphines

Article abstract of DOI:10.1139/v82-106

The basicities of the triarylphosphines P(4-XC6H4)3 (X = Cl, F, H, CH3, CH3O, (CH3)2N), P(3-CH3C6H4)3, and P(2-CH3C6H7)3 as well as the trialkylphosphines P(t-Bu)3 and PCy3 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 = (CH3)2N 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 wit ?_p, ?^Φ, and ν as well as with the lone pair ionisation potentials of the triarylphosphines.Generally the ¹H,³¹P, and ¹³C nmr spectral parameters of the free and protonated phosphines do not correlate well with pK_a.