Novel Asymmetrical Dianionic Polyimido-Sulfur(IV)-Ylides

Abstract

Sulfurdiimides RN=S=NR react in donating solvents with two equivalents of lithiumalkyls to give the dimeric C,N-dilithium-methylenediimidosulfite solvent adducts [(Et2O)Li2{H2CS-(NSiMe3)(NtBu)}]2 (1) and [(thf)Li2{H8C4S(NtBu)2}]2 (2). Firstly, addition of a lithiumalkyl to sulfurdiimide gives the diimidosulfinates [RS(NR')2]- (1: R = Me, R′ = tBu, SiMe3; 2: R = nBu; R′ = tBu) while in a second step the α-carbon atom in R is metalated with one equivalent of lithiumalkyl to give the asymmetric S-ylides. The reaction of 3-bromothiophene with one equivalent of nBuLi and one of sulfurdiimide tBuN=S=NtBu resulted in the dilithium-3-thiophenylenediimidosulfite [(thf)Li2{(SC4H2)S(NtBu)2}]2 (3). It can be regardedas the first example of a dianionic S(IV)-β-ylide. This class of compounds can be rationalised as sulfite analogues, where two oxygen atoms are isoelectronically replaced by a NR group each and the remaining oxygen atom is replaced by a CR2 group. The rich coordination chemistry of the triimidosulfites is extended by the introduction of a hard carbanionic centre.

Syntheses and Electron Density Determination of Novel Polyimido Sulfur Ylides

“…[54,55] The Li-O bond distance ( The sulfur ylide 6 forms a double-cube dimer in the crystal similar to all literatureknown diimido sulfur ylides. [61][62][63][64] In contrast to those, but similar to Although, the dem molecules are fixed by coordination of the two oxygen atoms to one lithium atom each, the carbon atoms are still disordered over two positions (cf. Again, the disorder renders 6 as unsuitable for an experimental electron density study.…”

“…[230] The S-N and S-C bond lengths fit those described for the lithium diimido sulfur ylides. [62][63][64] The angles at S1 fit a slightly distorted tetrahedral environment. Thus, the sulfur atom seems to be sp 3 -hybridized like in [(thf)Li 2 {H 2 CS(N t Bu) 2 }] 2 (4).…”

“…compared to the same ligand coordinated to lithium cations (1.659 Å on av.) [63] or the ylidic fragment of [(thf)Li The third polyimido sulfur fragment of 10, the S(N t Bu) 3 2dianion in 12, has already been reported to be a versatile, highly reactive ligand. [35] 16 different metal complexes of this triimido sulfite have been characterized by X-ray crystallography.…”

“…Ten complexes of this kind have been synthesized and crystallized so far. [61][62][63][64][65] The additional carbanionic site takes part in the coordination of the metal ion. While the sulfur(IV) species prefer to form dimers for an enhanced coordination of the lithium cations, the only known sulfur(VI) species remains monomeric.…”

“…Up to now only nine complexes of this type have been prepared. [62][63][64] The general synthetic approach is the addition of an alkyl group to sulfur diimides and triimides and the subsequent deprotonation by an organo lithium base (cf. Scheme 3-1).…”