Sterically Controlled Mono- or Dimetalation of a Thioether-Functionalized Phosphine and an Unusual Light-Induced Phosphide−Thiolate Rearrangement

The thioanisole-functionalized secondary phosphine {(Me3Si)2CH}PH(C6H4-2-SMe) (1) is
readily accessible via the reaction of 2-LiC6H4SMe and {(Me3Si)2CH}PCl2, followed by
reduction with LiAlH4. Compound 1 reacts with 1 equiv of n-BuLi in the presence of 1 equiv
of tmeda in diethyl ether to give the lithium phosphide [{(Me3Si)2CH}P(C6H4-2-SMe)]Li(tmeda) (2) [tmeda = N,N,N,N-tetramethylethylenediamine]. In the absence of tmeda,
compound 1 reacts with either 1 or 2 equiv of n-BuLi to give the phosphide−thiolate complex
[{(Me3Si)2CH}P(C6H4-2-S)]{Li(OEt2)}2 (4a), which may be recrystallized in the presence of
tmeda as the adduct [{(Me3Si)2CH}P(C6H4-2-S)]{Li(tmeda)}2 (4b). Compound 2 undergoes
an unusual rearrangement on photolysis with white light to give the lithium thiolate
[{(Me3Si)2CH}P(Me)(C6H4-2-S)]Li(tmeda) (6a), which may be recrystallized in the presence
of 12-crown-4 as the adduct [{(Me3Si)2CH}P(Me)(C6H4-2-S)]Li(12-crown-4) (6b). EPR experiments suggest that this rearrangement does not involve radical intermediates, but consists
of a concerted migration of a methyl group from sulfur to phosphorus. Compounds 1, 2, 4a,
4b, 6a, and 6b have been characterized by multielement NMR spectroscopy; in addition,
compounds 2, 4b, and 6b have been structurally characterized by X-ray crystallography.