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

Abstract

The β-diketiminato zinc halide [Me 2NN]ZnCl 2Li(THF) 3 ( 1) is prepared in 51% isolated yield by addition of the lithium β-diketiminate Li[Me 2NN] to ZnCl 2 in THF. Reaction of 1 with 2 equiv. of the thallium thiolate TlSCy provides {[Me 2NN]Zn(μ-SCy) 2Tl} 2 ( 2), a TlSCy adduct of [Me 2NN]ZnSCy, as colorless crystals in 51% yield. Reaction of 1 with 1 equiv. TlSR provides the dinuclear {[Me 2NN]Zn(μ-SR)} 2 (R = Cy ( 3), t Bu ( 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 LiSCPh 3 results in the mononuclear zinc thiolates [Me 2NN]ZnSCPh 3(THF) ( 5) and [Me 2NN]ZnSCPh 3 ( 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 CDCl 3 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 CDCl 3 to give {[Me 2NN]ZnSCy} 2 ( 3) and the corresponding S-nitrosothiol t BuSNO or Ph 3CSNO. Nitric oxide does not react with 4 or 6 under anaerobic conditions, but in the presence of O 2, NO cleaves the zinc-thiolate bond of 4 to rapidly give t BuSNO. Similarly, anaerobic NO 2 reacts with 4 to give t BuSNO providing insight into the active nitrogen oxide species capable of cleaving Zn–SR bonds.