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, J_Lip 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 P^III 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.