Preparations of Metal Trichalcogenophosphonates from Organophosphonate Esters

Abstract

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 ^<i>n</i>BuLi as the organometallic reagent, the lithium trithiophosphonate complexes [Li₂(S₃PCH₂Ph)­(THF)­(TMEDA)]₂ (<b>1</b>) and [Li₄(S₃P^<i>n</i>Pr)₂(TMEDA)₃]_∞ (<b>3</b>), where THF = tetrahydrofuran and TMEDA = <i>N</i>,<i>N</i>,<i>N</i>′,<i>N</i>′-tetramethylethylenediamine, have been prepared. In both cases, the formation of byproducts is also evident, including, for <b>1</b>, the tetrathiohypodiphosphonate complex [(PhCH₂P­(S₂))₂Li₂(THF)₄] (<b>2</b>), which has been structurally characterized. Replacement of ^<i>n</i>BuLi with ^<i>n</i>Bu₂Mg as the metallating agent led to much cleaner products and improved yields, with the new trithio- and triselenoorganophosphonate complexes [Mg­(S₃PCH₂Ph)­(TMEDA)]₂ (<b>4</b>) and [Mg­(Se₃P^<i>n</i>Pr)­(TMEDA)]₂ (<b>5</b>) reported. All trichalcogenophosphonate complexes have been structurally characterized in the solid state: <b>1</b> adopts a dimer structure in which the [PhCH₂PS₃]^2– ligand exhibits a unique μ₃-η²,η²,η²-coordination mode; <b>3</b> is polymeric comprising of [Li₄(S₃P^<i>n</i>Pr)₂(TMEDA)₂] dimers linked via additional bridging bis­(monodentate) TMEDA molecules; <b>4</b> and <b>5</b> both adopt dimeric motifs with μ₂-η²,η² coordination of the magnesium centers