Pyrazolylborate−Zinc−Hydrosulfide Complexes and Their Reactions

Abstract

Four new hydrosulfide complexes Tp*Zn-SH of substituted pyrazolylborate ligands (Tp*) were prepared by reactions of Tp*Zn-OH with H(2)S, and three of them were structurally characterized. Unlike the Tp*Zn-OH complexes they do not react with esters, phosphates, or CO(2), e.g. for thiolytic cleavage reactions. They also cannot be deprotonated, as various bases induce precipitation of ZnS and release of anionic Tp*. Acidic organic X-OH compounds (carboxylic acids, trinitrophenol, hexafluoroacetylacetone) replace the SH groups with formation of Tp*Zn-OX. Thiols undergo an entropy-driven SH substitution to yield the Tp*Zn-SR complexes. Like the Tp*Zn-SR complexes the Tp*Zn-SH complexes are quite reactive toward alkylation with methyl iodide, yielding Tp*Zn-I and CH(3)SH. The kinetic investigation of the methylation of Tp(Ph,Me)Zn-SH has shown it to be a clean second-order reaction, thereby indicating that the SH group is alkylated in the zinc-bound state.

Zinc Thiolate Complexes [ZnLn(SR)]+ with Azamacrocyclic Ligands, Part II: Mechanism of the Reaction with CS2

“…It is worth noting that a similar reaction has not previously been reported in the literature; even the available structural models for the sulfur-analog CA, e.g. Tp Ph,Me ZnSH, [15] do not react with heterocumulenes. In the past, numerous computational studies have examined the fixation of heterocumulenes by zinc hydroxide complexes, but only one addresses zinc hydrosulfides and the mechanism of their heterocumulene reactions.…”

Zinc Thiolate Complexes [ZnLn(SR)]+ with Azamacrocyclic Ligands, Part III: The Influence of the Ligand Ln on the Reactivity of Zinc‐Bound Thiolate

“…[12][13][14][15]26,27] In this case, the methylation (as well as any other reaction) is restricted to occur at the thiolate side of the complex cation. As the coordination of the reacting molecules to Zn II implicates a steric demand, the degree of obstruction of the zinc(II) ion by the macrocycle should have a pivotal influence on the geometry of the transition state.…”

Zinc Thiolate Complexes [ZnLn(SR)]+ with Azamacrocyclic Ligands: Synthesis and Structural Properties

“…[26] Quantum mechanical calculations have revealed that a zinc hydrosulfide moiety His 3 Zn-SH is formed in the course of this interconversion. [27] A suitable structural model − the neutral hydrosulfide complex Tp Ph,Me ZnSH − has been found by Vahrenkamp et al [28,29] Our efforts to obtain an equivalent zinc hydrosulfide complex with an azamacrocyclic ligand were not successful because these compounds are not stable. Nevertheless, due to their positive overall charge, our thiolate complexes also could be regarded as suitable model systems for this species.…”