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
LiAlH4 and subsequently treated with an organometallic
reagent and elemental sulfur or selenium to give the desired trichalcogenophosphonate
complex. Using this synthetic protocol with nBuLi as the organometallic reagent, the lithium trithiophosphonate
complexes [Li2(S3PCH2Ph)­(THF)­(TMEDA)]2 (1) and [Li4(S3PnPr)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 [(PhCH2P­(S2))2Li2(THF)4] (2), which has been structurally characterized. Replacement
of nBuLi with nBu2Mg as the metallating agent led to much cleaner products
and improved yields, with the new trithio- and triselenoorganophosphonate
complexes [Mg­(S3PCH2Ph)­(TMEDA)]2 (4) and [Mg­(Se3PnPr)­(TMEDA)]2 (5) reported. All trichalcogenophosphonate complexes
have been structurally characterized in the solid state: 1 adopts a dimer structure in which the [PhCH2PS3]2– ligand exhibits a unique μ3-η2,η2,η2-coordination
mode; 3 is polymeric comprising of [Li4(S3PnPr)2(TMEDA)2] dimers linked via additional bridging bis­(monodentate) TMEDA molecules; 4 and 5 both adopt dimeric motifs with μ2-η2,η2 coordination of the
magnesium centers.