Reaction of alkali metals (Li, Na, K) with mesityldichlorophosphane (MesPCl(2), Mes = 2,4,6-Me3C6H2) in ethereal solvents leads to formation of the corresponding mesitylphosphanides MPHMes in good purity and yield. P-31 NMR spectroscopic studies in deuterated solvents strongly support a mechanism of the reaction that involves protonation/disproportionation steps in which the solvent is the only possible proton source. Li(thf)(tmeda)PHMes (1), [Na(tmeda)(mu-PHMes)(infinity) (2), and [K(pmdeta)(mu-PHMes)](2) (3) (tmeda = N,N,N',N'-tetramethylethylenediamine, pmdeta = N,N,N',N '',N ''-pentamethyldiethylenetriamine) were obtained; in the solid state, 2 forms zigzag chains while 3 is a dimeric compound.