Light-induced rearrangement of thioether-substituted phosphanide ligands : Scope and limitations of a remarkable isomerization

Treatment of the thioether-substituted secondary phosphanes R 2PH(C6H4-2-SR1) [R 2=(Me3Si)2CH, R1=Me (1 PH), iPr (2PH), Ph (3PH); R2=tBu, R1=Me (4PH); R2=Ph, R1=Me (5 PH)] with nBuLi yields the corresponding lithium phosphanides, which were isolated as their THF (1-5Pa) and tmeda (1-5Pb) adducts. Solid-state structures were obtained for the adducts [R 2P(C6H4-2-SR1)]Li(L)n [R2=(Me3Si)2CH, R1=nPr, (L) n=tmeda (2Pb); R2=(Me3Si) 2CH, R1=Ph, (L)n=tmeda (3Pb); R 2=Ph, R1=Me, (L)n=(THF)1.33 (5 Pa); R2=Ph, R1=Me, (L)n=([12]crown- 4)2 (5Pc)]. Treatment of 1PH with either PhCH2Na or PhCH2K yields the heavier alkali metal complexes [{(Me3Si)2CH}P(C6H 4-2-SMe)]M(THF)n [M=Na (1Pd), K (1 Pe)]. With the exception of 2Pa and 2Pb, photolysis of these complexes with white light proceeds rapidly to give the thiolate species [R2P(R1)(C6H 4-2-S)]M(L)n [M=Li, L=THF (1Sa, 3 Sa-5Sa); M=Li, L=tmeda (1Sb, 3 Sb-5Sb); M=Na, L=THF (1Sd); M=K, L=THF (1 Se)] as the sole products. The compounds 3Sa and 4 Sa may be desolvated to give the cyclic oligomers [[{(Me 3Si)2CH}P(Ph)(C6H4-2-S)]Li] 6 ((3S)6) and [[tBuP(Me)(C6H 4-2-S)]Li]8 ((4S)8), respectively. A mechanistic study reveals that the phosphanide-thiolate rearrangement proceeds by intramolecular nucleophilic attack of the phosphanide center at the carbon atom of the substituent at sulfur. For 2Pa/2Pb, competing intramolecular β-deprotonation of the n-propyl substituent results in the elimination of propene and the formation of the phosphanide-thiolate dianion [{(Me3Si)2CH}P(C6H4-2-S)] 2-. Copyright © 2013 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.