Preparations of metal trichalcogenophosphonates from organophosphonate esters

A new method for the preparation of metal trichalcogenophosphonates is presented wherein organophosphonate esters are first reduced with LiAlH(4) and subsequently treated with an organometallic reagent and elemental sulfur or selenium to give the desired trichalcogenophosphonate complex. Using this synthetic protocol with (n)BuLi as the organometallic reagent, the lithium trithiophosphonate complexes [Li(2)(S(3)PCH(2)Ph)(THF)(TMEDA)](2) (1) and [Li(4)(S(3)P(n)Pr)(2)(TMEDA)(3)](∞) (3), where THF = tetrahydrofuran and TMEDA = N,N,N',N'-tetramethylethylenediamine, have been prepared. In both cases, the formation of byproducts is also evident, including, for 1, the tetrathiohypodiphosphonate complex [(PhCH(2)P(S(2)))(2)Li(2)(THF)(4)] (2), which has been structurally characterized. Replacement of (n)BuLi with (n)Bu(2)Mg as the metallating agent led to much cleaner products and improved yields, with the new trithio- and triselenoorganophosphonate complexes [Mg(S(3)PCH(2)Ph)(TMEDA)](2) (4) and [Mg(Se(3)P(n)Pr)(TMEDA)](2) (5) reported. All trichalcogenophosphonate complexes have been structurally characterized in the solid state: 1 adopts a dimer structure in which the [PhCH(2)PS(3)](2-) ligand exhibits a unique μ(3)-η(2),η(2),η(2)-coordination mode; 3 is polymeric comprising of [Li(4)(S(3)P(n)Pr)(2)(TMEDA)(2)] dimers linked via additional bridging bis(monodentate) TMEDA molecules; 4 and 5 both adopt dimeric motifs with μ(2)-η(2),η(2) coordination of the magnesium centers.