Ortho versus α-Metalation of Ethyl Phenyl Sulfide by n-Butyllithium/N,N,N‘,N‘-Tetramethylethylenediamine:  Synthesis, Reactivity, and Crystal Structures of (2-(Ethylthio)phenyl)- and (1-(Phenylthio)ethyl)lithium

Metalation of ethyl phenyl sulfide by n-BuLi/tmeda (tmeda = N,N,N‘,N‘-tetramethylethylenediamine) is strongly solvent dependent. In n-hexane and diethyl ether ortho lithiation took place, yielding (2-(ethylthio)phenyl)lithium, while in tetrahydrofuran (THF) α-lithiation occurred, yielding (1-(phenylthio)ethyl)lithium. From n-hexane solutions [{Li(C₆H₄SEt-2)(tmeda)}₂] (4) was isolated as a white powder. Dissolution of 4 in THF resulted in isomerization, forming quantitatively the α-lithiated compound [Li(CHMeSPh)(tmeda)] (5). Compounds 4 and 5 reacted with n-Bu₃SnCl, yielding n-Bu₃Sn(C₆H₄SEt-2) (1a) and n-Bu₃SnCHMeSPh (2a), respectively. The identities of 4, 5, 1a, and 2a were confirmed by ¹H, ¹³C, and ¹¹⁹Sn (1a/2a) NMR measurements. Single-crystal X-ray diffraction analysis of 4 showed it to be dimeric, with a nonplanar four-membered ring composed of two lithium atoms and two ortho phenyl carbon atoms. The distorted-tetrahedral donor set of Li is completed by two nitrogen atoms (tmeda). Furthermore, from solutions of 4 in n-hexane crystals of [{Li(CHMeSPh)(tmeda)}₂(μ-tmeda)] (5‘) were obtained. X-ray structure analysis revealed the presence of centrosymmetric dimers. The primary donor set of Li is made up of one carbon atom and three nitrogen atoms, two of them from a chelating tmeda and the other from a bridging tmeda ligand.