A new class of dianionic sulfur-ylides: alkylenediazasulfites

The compounds [[(thf)Li2-[H2CS(NtBu)2]]2] (1) and [((thf)Li2[(Et)-(Me)CS(NtBu)2])2] (2) can be synthesized in a two-step reaction. Firstly addition of an alkyllithium to sulfur diimide gives the diazaalkylsulfinate [RS(NtBu)2] (R =Me, sBu). In a second step the alpha-carbon atom in R is metalated with one equivalent of methyllithium to give the S-ylides. This new class of compounds can be rationalized as sulfite analogues, in which two oxygen atoms are each isoelectronically replaced by a NtBu group and the remaining oxygen atom is replaced by a CR2 group. Similar to Corey's S-ylides (R2(O)S+-CR2) and Wittig's phosphonium ylides (R3P+ - -CR2), these molecules contain a positively charged sulfur atom next to a carbanionic center. Therefore nucleophilic addition reactions of the carbon atom are feasible. The reaction of a sulfur diimide with the anionic carbon center in [H2CS-(NtBu)2]2- gives the intermediate alkylbis(diazasulfinate) [(tBuN)2SCH2S(NtBu)2]2-. The acidity of the hydrogen atoms at the bridging CH2 group is high enough to give, upon deprotonation, the [(tBuN)2SCHS(NtBu)2]3- trianion in [[(thf)Li3[(tBuN)2SCHS(NtBu)2]]2] (3). In [(Et)(Me)CS(NtBu)2]2 the nucleophilic carbon atom is sterically hindered and transimidation instead of deprotonation is observed. In a complex redox process [(thf)6Li6S((NtBu)3S]2] is recovered. The two new classes of compounds broaden the rich coordination chemistry of the triazasulfites by the introduction of a hard carbon center.