Synthesis of Li/OR phosphinidenoid complexes: on the evidence for intramolecular O–Li donation and the effect of cation encapsulation

Abstract

Synthesis of phosphinite complexes 12–14a–c, 15a and 16a was achieved via reaction of transient Li/Cl phosphinidenoid complexes 6–10, prepared from dichloro(organo)phosphane complexes [(OC)₅M{RPCl₂}] 1–5 (1,6: R = CPh₃, 2,7: R = C₅Me₅, 3–5, 8–10: R = CH(SiMe₃)₂, 1–3, 6–8: M = W, 9: M = Mo, 10: M = Cr), with different alcohols 11a–c (a: R = allyl, b: R = methyl, c: R = isopropyl). Deprotonation of complexes 12b, 13b with MeLi or ^tBuLi in the presence of two equivalents of 12-crown-4 led to the selective formation of phosphinidenoid complexes [Li(12-crown-4)₂] [(OC)₅W{RP(OCH₃)}] (18a R = CPh₃ and 18b R = C₅Me₅) which were stable in solution at ambient temperature, in contrast to Li/OMe phosphinidenoid complexes without 12-crown-4. To our surprise attempts to crystallise complex 18b yielded complex 21 having a Li–O–P subunit. The reaction of complex 17c with [Ph₃C]BF₄ yielded the P–C coupling product 26 and, hence, the first evidence for an oxidative SET reaction. All isolated products were characterised by multinuclear NMR spectroscopy, IR, MS and single-crystal X-ray crystallography in the case of complexes 12a,b, 13b, 14a–c, 15a, 16a and 21.