Light-Induced Rearrangement of Thioether-Substituted Phosphanide Ligands: Scope and Limitations of a Remarkable Isomerization

Authors

  • Dr. Keith Izod,

    Corresponding author
    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
    • Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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  • Dr. Ewan R. Clark,

    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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  • Pamela Foster,

    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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  • Rebecca J. Percival,

    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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  • Ian M. Riddlestone,

    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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  • Prof. William Clegg,

    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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  • Dr.  Ross W. Harrington

    1. Main Group Chemistry Laboratories, School of Chemistry, Bedson Building, University of Newcastle, Newcastle upon Tyne, NE1 7RU (UK)
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Abstract

Treatment of the thioether-substituted secondary phosphanes R2PH(C6H4-2-SR1) [R2=(Me3Si)2CH, R1=Me (1PH), iPr (2PH), Ph (3PH); R2=tBu, R1=Me (4PH); R2=Ph, R1=Me (5PH)] with nBuLi yields the corresponding lithium phosphanides, which were isolated as their THF (15Pa) and tmeda (15Pb) adducts. Solid-state structures were obtained for the adducts [R2P(C6H4-2-SR1)]Li(L)n [R2=(Me3Si)2CH, R1=nPr, (L)n=tmeda (2Pb); R2=(Me3Si)2CH, R1=Ph, (L)n=tmeda (3Pb); R2=Ph, R1=Me, (L)n=(THF)1.33 (5Pa); 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(C6H4-2-SMe)]M(THF)n [M=Na (1Pd), K (1Pe)]. With the exception of 2Pa and 2Pb, photolysis of these complexes with white light proceeds rapidly to give the thiolate species [R2P(R1)(C6H4-2-S)]M(L)n [M=Li, L=THF (1Sa, 3Sa5Sa); M=Li, L=tmeda (1Sb, 3Sb5Sb); M=Na, L=THF (1Sd); M=K, L=THF (1Se)] as the sole products. The compounds 3Sa and 4Sa may be desolvated to give the cyclic oligomers [[{(Me3Si)2CH}P(Ph)(C6H4-2-S)]Li]6 ((3S)6) and [[tBuP(Me)(C6H4-2-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−.

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