Synthesis of α-, γ-phosphorus functionalized alkyl lithium species; X-ray structures of [{Li(L)(Ch₂PMeR)}₂][L =NNN′N′-tetramethylethylenediamine (tmen), R = Me or Ph; L =(–)sparteine, R = Ph] and [Li(tmen){CH(SiMe₃)C₆H₄PPh₂-o}]

Abstract

[{Li(L)(CH2PMeR)}2][L = tetramethylethylenediamine (tmen), R = Me (1) or Ph (2); L =(–)-sparteine (sp), R = Ph (3)], prepared by treating the appropriate phosphine with LiBun(L) in hexane or diethyl ether, are dimeric in the solid. The phosphinomethyl ligands bridge the two lithium atoms as part of six-atom heterocycles; Li–C, P 2.145, 2.604; 2.14, 2.64; 2.20, 2.72Å, respectively; (2) and (3) are homochiral and thus have a meso configuration. In benzene (1), (2), and [Li(tmen)(CH2PPh2)](5), are monomeric (cryoscopy), and 7Li–31P coupling only below ca. –70 °C for (1)–(3) and (5) in toluene (1 : 1 doublet, 7Li; 1 : 1 : 1 : 1 quartet, 31P, JLip 44.0–53.4 Hz) is consistent with the presence of symmetrical dimers of the type found in the solid for (1)–(3). [[graphic omitted]Ph2-o}], (4), similarly prepared, has the lithium as part of a chelate ring in the solid, binding through the ipso carbon and PIII centre; Li–C,P 2.25(1), 2.65(1)Å. Trilithio species based on P(C6H4CHR–)3(R = H or SiMe3) are generated via metallation using LiBun(tmen). Treating the monolithio species derived from P(O)Me2Ph and LiBun(sp) with Etl yields P(O)MePhPrn of 14% estimated optical purity.