S-nitrosothiol and nitric oxide reactivity at β-diketiminato zinc thiolates

The β-diketiminato zinc halide [Me2NN]ZnCl2Li(THF)3 (1) is prepared in 51% isolated yield by addition of the lithium β-diketiminate Li[Me2NN] to ZnCl2 in THF. Reaction of 1 with 2 equiv. of the thallium thiolate TlSCy provides {[Me2NN]Zn(μ-SCy)2Tl}2 (2), a TlSCy adduct of [Me2NN]ZnSCy, as colorless crystals in 51% yield. Reaction of 1 with 1 equiv. TlSR provides the dinuclear {[Me2NN]Zn(μ-SR)}2 (R = Cy (3), tBu (4)) which possess unsymmetrically bridging thiolate ligands with pairs of dissimilar Zn–S distances in the solid state (2.350(3) and 2.417(3) Å for 3; 2.312(1) and 2.415(1) Å for 4). Reaction of 1 with LiSCPh3 results in the mononuclear zinc thiolates [Me2NN]ZnSCPh3(THF) (5) and [Me2NN]ZnSCPh3 (6) with shorter, but similar Zn–SR distances of 2.225(2) and 2.214(1) Å. Variable temperature 1H NMR studies of 3 and 4 in CDCl3 suggest that the aliphatic thiolates exist predominately as monomeric species in solution near room temperature, though at −50 °C two different β-diketiminato species are observed for 3. Thiolate exchange among 3, 4, and 6 also takes place on the NMR timescale near room temperature. Both 4 and 6 undergo transnitrosylation with CySNO in CDCl3 to give {[Me2NN]ZnSCy}2 (3) and the corresponding S-nitrosothiol tBuSNO or Ph3CSNO. Nitric oxide does not react with 4 or 6 under anaerobic conditions, but in the presence of O2, NO cleaves the zinc-thiolate bond of 4 to rapidly give tBuSNO. Similarly, anaerobic NO2 reacts with 4 to give tBuSNO providing insight into the active nitrogen oxide species capable of cleaving Zn–SR bonds.

The dinuclear β-diketiminato zinc-thiolates {[Me2NN]ZnSR}2 (R = Cy or tBu) readily dissociate in solution to form monomeric species like the three-coordinate [Me2NN]ZnSCPh3. Transnitrosylation rapidly occurs between [Me2NN]ZnStBu and CySNO favoring the formation of {[Me2NN]ZnSCy}2 and tBuSNO. While immune to anerobic NO, [Me2NN]ZnStBu is nitrosated by NO/O2 or anaerobic NO2 giving tBuSNO.Figure optionsDownload as PowerPoint slide